Defect-induced effects in nanomaterials

Resume : Defect engineering is the key in semiconductor device physics and technology, and it will also be the key to design memristive systems. One way to realize a memristive device is to induce a reversible soft breakdown in a dielectric material along a filamentary conduction path. In the simplest form, a digital non-volatile memory is obtained, while a highly resolved analogue resistance control is the holy grail for neuromorphic computing. Point defects provided by charge carrier doping and substitution obviously are used to tailor the electric and thermal properties of the dielectric insulator in which the soft breakdown has to be controlled on an atomistic scale. Due to the involved elevated temperatures during operation, even initially amorphous materials will develop a polycrystalline structure. It is well known from materials science, that grain boundaries interact with point defects and may have an important influence on the electronic and thermal properties of the nano-sized functional layer. Furthermore, due to the oxygen dynamics sub-stoichiometric (conducting) phases play an important role. In this paper we report the effect of oxygen vacancies on the memristive device behavior including compact modelling. One important effect is that oxygen vacancies enhance electric conductivity in the conducting filament and thermal conductivity in the surrounding dielectric matrix. We then show how grain boundaries evolve and how they can be engineered to assume a specific crystal orientation [1]. The grain boundary orientation has a dramatic effect on the forming voltages showing that they have to be taken into account for a full understanding of memristive devices. Furthermore, we investigate the occurrence of substoichiometric phases as a result of the oxygen dynamics [2]. Operando transmission electron microscopy (TEM) plays a key role in atomistic device characterization as needed for model development. Last but not least, we show how defect engineering can be applied to implement analogue depression and potentiation of the resistance in memristive devices, and how the gained knowledge serves as guideline for materials selection [3]. Last but not least, we show that high-energy irradiation triggers phase transitions in oxide based memristors [4]. [1] S. Petzold et al., Adv. Electron. Mater. 5, 1900484 (2019). [2] N. Kaiser et al., ACS Appl. Mater. Interfaces 14, 1290 (2022). [3] S. Petzold et al., Adv.Electron. Mater. 6, 2000439 (2020). [4] T. Vogel et al., IEEE Trans. Nucl. Sci. 68, 1542 (2021).

Resume : Planar defects such as stacking faults (SF) and rotational twin-planes (RT) are common occurrences during the material growth and the fabrication of III-V semiconductor devices. The nature of these defects makes it hard to mitigate their formation whereas their impact on the fabricated device?s properties are largely unknown and it is hard to quantify experimentally, due to the sheer amount of them in a single device. Hence the most cost and time efficient approach to evaluate the impact of defects on material characteristics is to execute numerical simulations. The work reported here is an attempt to reveal some light on this complicated issue using the state-of-the-art simulation software Synopsys QuantumATK. Our aim is to calculate the resistance induced by the defects as well as their impact on the current-voltage (I-V) characteristics To achieve our aims, in this paper we executed numerical first-principles simulation of the most commonly occurring types of defects in Indium Phosphide (InP). We have found that these defects have an impact on the current flow and charge distributions in the semiconductor in comparison to the pure (smooth) InP system. In particular, two types of defects, cause an increase in the resistivity of the semiconductor and a remarkable decrease in current for a small value of the drain voltages. We also observed numerically that for drain voltages above 2.0"V" , the effects of all defects on the current flow are the same and the current for all systems is equal to that of the pristine InP. Lastly, our numerical analysis reveal that a minimal width of 10 nm is required, for a crystal-phase quantum well to reach the band gap value at the centre of the well. The goal is to compare our simulations with the electrical and optical measurement and to help the improve the InP material growth process.

Resume : In this work, we report study on the impact of neutron radiation on quasi-free-standing (QFS) graphene [1]. For this purpose, we have fabricated hydrogen-intercalated QFS graphene on semiinsulating high-purity 4H-SiC (0001) [2], passivated with an Al2O3 layer [3], and exposed it to a fast-neutron fluence of ? 6.6 x 10^17 cm^-2. The results have shown that the graphene sheet is only moderately affected by the neutron radiation with the estimated defect density of ? 4 x 10^10 cm^-2. The effect was more pronounced within the SiC step edges than the terraces [4]. However, in both cases the defect density was seven orders of magnitude lower than the fluence, which indicates that graphene has a small cross-section for neutrons. The research leading to these results has received funding from the National Science Centre, Poland under Grant Agreement No. OPUS 2019/33/B/ST3/02677 for project ??Influence of the silicon carbide and the dielectric passivation defect structure on high-temperature electrical properties of epitaxial graphene?? and the National Centre for Research and Development, Poland under Grant Agreement No. LIDER 0168/L-8/2016 for project ??Graphene on silicon carbide devices for magnetic field detection in extreme temperature conditions??. [1] S. El-Ahmar, M. Szary, T. Ciuk, R. Prokopowicz, A. Dobrowolski, J. Jagiello, M. Ziemba, Applied Surface Science 590, 152992 (2022) [2] T. Ciuk, B. Stanczyk, K. Przyborowska, D. Czolak, A. Dobrowolski, J. Jagiello, W. Kaszub, M. Kozubal, R. Kozlowski, P. Kaminski, IEEE Trans. Electron Devices 66 (7), 3134-3138 (2019) [3] K. Pietak, J, Jagiello, A. Dobrowolski, R. Budzich, A. Wysmo?ek, T. Ciuk, Applied Physics Letters, 120, 063105 (2022) [4] A. Dobrowolski, J. Jagiello, D. Czolak, T. Ciuk, Physica E: Low-dimensional Systems and Nanostructures, 134, 114853 (2021)

Resume : Recent developments of photo- and sono- catalysis reconfirm their irreplaceable roles in mitigations of energy and environmental crisis. Advanced but synthetic semiconductive catalysts are materials bases hosting these catalytic activities yet requiring dedicated engineering routes to maximum functionalities. Herein, impacts of the interfaces and element deficiency on catalytic activities are presented for the bismuth semiconductors and their heterojunctional photocatalysts. Introductions of the interfaces and deficiency into the composites were realized in wet synthetic routes, namely the hydrothermal method for the Bi-oxide heterojunctions [1-4] and O-deficient BiNbO4 [5]. The catalytic activities of hydrogen evolution [1] and pollutant removal [2-5] were found substantially superior in the heterojunctional and defective catalysts over their pristine counterparts. Structural and morphological studies demonstrate the newly formed alloy regions at the interfaces are in charge of bridging hetero-sites for composite formations while keeping intrinsic redox capabilities of these sites [1-4], and mixed phases for oxygen deficiency [5]. Thanks to heterojunction constructions, bandgap energies were lowered at the interfaces and charge migrations became possible through the newly formed bands at the joint sides according to first-principles calculations [1-3]. These factors benefit catalytic activities via better visible light absorptions at wider spectral ranges and delayed recombination of photoinduced charge carriers. Following the electronic and structural properties given above, the catalytic schemes were thus proposed for both the heterojunctional [1-4] and element deficient systems [5]. [1] Qiang Z., et al., Chem. Engin. J. 403, 126327 (2021) [2] Yang C., et al., J. Mol. Cataly. A: Chem. 423, 1-11 (2016) [3] Yang C., et al., Mol. Cataly. 435, 33 (2017) [4] Qiang Z., et al., J. Inorg. Organomet. Polym. Mater. 30 (5), 182 (2020) [5] Xiong S., et al., Ceram. Internat. 46 (13), 21790 (2020)

Resume : Ligand field theory has become one of the most successful models for the description of physical properties of transition metal and lanthanoid ions in a coordinative environment. Many of these properties such as their magnetism or optical transitions can be already well understood assuming ligands to be point charges, as was originally proposed by Bethe and applied by van Vleck. Wybourne then elaborated this idea into a technical realization by expanding the ligand field potential. This Wybourne parametrization makes use of the symmetry of the coordination entity and is the foundation of what is taught as the crystal field splitting of 10Dq for d orbitals in undergraduate chemistry courses, for example. However, for low symmetric coordination entities, this approach requires several independent parameters (e.g. up to 14 for d orbitals) thus inhibiting any meaningful interpretation of their values. The alternative way of treating the ligand field is by allowance for covalent bonding, which requires a molecular orbital picture. This can be elegantly done by separating a [MLn] entity into n linear M-L bonds and considering the orbital overlap between the metal- and ligand-centered orbitals. The whole coordination entity can then be generated by using independently measurable structural information. This is the essence of the angular overlap approach. Despite its chemically very intuitive foundations, it has become an almost forgotten approach to ligand field theory. Unlike the Wybourne approach, it is independent of symmetry and always requires the same amount of independent parameters irrespective of the coordination number. Within this presentation, I will give a general overview of the foundations of the angular overlap model and demonstrate how it can help intuitively understand magnetic and optical properties of transition metal- and lanthanoid-based compounds using selected examples. With this alternative view, it is my intention to demonstrate that the angular overlap approach may offer an elegant qualitative perspective on physical properties of coordinated entities both in molecules and solids.

Resume : Recently, gallium oxide (Ga2O3) has become one of the most actively studied materials. The reason is its competitive electronic properties, such as wide bandgap, high breakdown field, simple control of carrier concentration, and high thermal stability. Due to these properties, gallium oxide is a candidate for potential applications in high-power electronic devices. Ga2O3 crystals are commonly grown by the Czochralski method, where an iridium (Ir) crucible is used. For that reason, Ir is often present in Ga2O3 crystals as an unintentional donor. In this work, the impact of Ir incorporation defects and F-centers on Ga2O3 properties in different phases is studied via density functional theory implemented in the CRYSTAL17 code. Obtained results allow us to better understand the influence of Ir on Ga2O3 properties and provide interpretation for optical transitions reported in recent experiments.

Resume : Defects are ubiquitous in solids. An insignificant number of defects in a solid can significantly alter its electrical, optical, and magnetic properties. Defect-induced ferromagnetism in a wide range of materials has become one of the most discussed issues in the recent past [1]. Some vacancy-induced room temperature ferromagnetism is achieved in non-magnetic oxides like ZnO [2], MgO [3], HfO2 [4], etc., and subsequently in GaN semiconducting nanoparticles [5]. The main reason attributed to the room temperature ferromagnetism in non-magnetic GaN is the Ga vacancies. GaN is a good candidate for various high-power electronics and optoelectronic devices because of its wide direct band gap (3.4 eV). Also, strong interatomic bonds and high thermal conductivity make it suitable for spintronic devices [6]. Defects are created by different processes in GaN to enhance ferromagnetism, such as changing deposition parameters [7], annealing temperature [8], and ion irradiation [9]. Among these, ion irradiation is a very strong tool to create defects in a controlled manner. In low-energy regions, the energy loss is mainly nuclear energy loss. In this energy regime, the energy loss is mainly governed by the collision cascade generated by elastic collision, which results in the creation of defects. Recently, our group reported irradiation studies on thick (50µm) GaN films which were irradiated with 500KeV heavy ions at different fluences. The thick GaN films show diamagnetic behaviour [10]. Now we started irradiation study on thin (GaN (100nm)/AlN (500nm)/Sapphire) GaN films. At IUAC in New Delhi, India, thin films were irradiated with different fluences of 300KeV heavy ions. All films were characterized using X-ray diffraction (XRD), Raman spectroscopy, Photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Magnetic measurements are done by a superconducting quantum interference device (SQUID) at room temperature. We were able to tune room temperature ferromagnetism in thin GaN films. The Pristine film showed saturation magnetization of 0.99 emu/g, which gradually decreased to 0.39 emu/g for higher irradiation doses. The DFT (Density Functional Theory) based calculations were also carried out, which support our experimental results. References: [1] Sarkar A, Sanyal D, Nath P, Chakrabarti M, Pal S, Chattopadhyay S, Jana D and Asokan K 2015 Defect driven ferromagnetism in SnO 2?: a combined study using density functional theory and positron annihilation spectroscopy RSC Advances 5 1148?52 [2] Singh P, Mishra V, Barman S, Balal M, Barman S R, Singh A, Kumar S, Ramachandran R, Srivastava P and Ghosh S 2021 Role of H-bond along with oxygen and zinc vacancies in the enhancement of ferromagnetic behavior of ZnO films: An experimental and first principle-based study Journal of Alloys and Compounds 889 161663 [3] Rose B H and Halliburton L E 1974 ESR hyperfine investigation of the V$\less$sup$\greater$0$\less$/sup$\greater$centre in MgO J. Phys. C: Solid State Phys. 7 3981?7 [4] Bharathi K K, Venkatesh S, Prathiba G, Kumar N H and Ramana C V 2011 Room temperature ferromagnetism in HfO2 films Journal of Applied Physics 109 07C318 [5] Madhu C, Sundaresan A and Rao C N R 2008 Room-temperature ferromagnetism in undoped $\mathrm{GaN}$ and $\mathrm{CdS}$ semiconductor nanoparticles Phys. Rev. B 77 201306 [6] Thiess A, Blügel S, Dederichs P H, Zeller R and Lambrecht W R L 2015 Systematic study of the exchange interactions in Gd-doped GaN containing N interstitials, O interstitials, or Ga vacancies Phys. Rev. B 92 104418 [7] Roul B, Rajpalke M K, Bhat T N, Kumar M, Kalghatgi A T, Krupanidhi S B, Kumar N and Sundaresan A 2011 Experimental evidence of Ga-vacancy induced room temperature ferromagnetic behavior in GaN films Appl. Phys. Lett. 99 162512 [8] Gao X, Man B, Zhang C, Leng J, Xu Y, Wang Q, Zhang M and Meng Y 2017 The important role of Ga vacancies in the ferromagnetic GaN thin films Journal of Alloys and Compounds 699 596?600 [9] Singh P, Ghosh S, Mishra V, Barman S, Roy Barman S, Singh A, Kumar S, Li Z, Kentsch U and Srivastava P 2021 Tuning of ferromagnetic behavior of GaN films by N ion implantation: An experimental and first principle-based study Journal of Magnetism and Magnetic Materials 523 167630 [10] Singh P, Ghosh S, Singh A, Kumar S, Ojha S and Srivastava P 2020 Defect mediated modification of structural, optical and magnetic properties of Xe3+ ions irradiated GaN/sapphire films Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 466 61?8

Resume : Ion implantation in wide bandgap semiconductors (WBS), such as group-III nitrides and metal oxides, is often governed by complex defect-interaction processes. High defect mobility allows, on the one hand, the annihilation of primary defects; on the other hand, it can also lead to the formation of extended defects. The complexity of defect accumulation in WBS upon ion irradiation will be discussed using three case studies. The defect accumulation in III-nitride nanowires during europium implantation will be compared to thin-film reference samples. Lower strain values are observed for the nanowires, as well as a lower density of extended defects. We also present the first red light emitting diode based on europium implanted AlN nanowires [1]. Besides doping, in some cases, ion beams can be used to tune the electrical and optical properties of materials by introducing structural defects, often referred to as defect engineering. In MoO3, ion implantation allows the electrical conductivity to be controlled over several orders of magnitude [2]. In Ga2O3, defects influence the behaviour of optical dopants such as rare earths and transition metals. An interesting example is chromium doped Ga2O3 where the typical Cr3+ emissions can be strongly enhanced by proton irradiation [3]. [1] J. P. S. Cardoso et al., ACS Appl. Nano Mater. 5 (2022) 972 [2] D.R. Pereira et al., Acta Materialia 169 (2019) 15 [3] M. Peres et al., to be published

Resume : Before realization of the p-type doping in gallium nitride by using magnesium, beryllium had been taken into account as a candidate for such doping. However, so far no one realized Be-induced p-type conductivity. Hybrid density functional calculations [1] have shown that Be is a deeper acceptor than Mg (550 vs. 260 meV ionization energy), and for this reason Be p-type doping is ineffective. The optical studies revealed two luminescence bands; one at 3.38 eV and a second near 2.2 eV which intensity increased with increasing Be content. Similar type of broadband yellow luminescence (YL) at about 2.3 eV has been observed in C-doped GaN, and related to the incorporation of C at the N site (CN) that acts as a deep acceptor with ionization energy of 0.9 eV [2]. In order to shed more light on this issue, we performed high pressure studies of Be- and C-doped GaN crystals using diamond anvil cell technique. YL in GaN:C revealed very week pressure dependence. In GaN:Be we observed a pressure-induced splitting of the YL line into two components: one strongly dependent on applied pressure and another whose pressure dependence was more modest. Basing on hybrid functional calculations, we attribute the strongly-varying component to the beryllium-oxygen complex. The second component of the YL possesses pressure behavior similar to that observed in undoped samples grown by the same method, behavior which we find consistent with the CN acceptor [3]. References: [1] Lyons, J. L.; Janotti, A.; Van de Walle, C. G.; Impact of Group-II Acceptors on the Electrical and Optical Properties of GaN, Jpn. J. Appl. Phys. 52, 2013, 08JJ04-1-5. [2] Lyons, J. L.; Janotti, A.; Van de Walle, C. G.; Carbon impurities and the yellow luminescence in GaN, Appl. Phys. Lett. 97, 2010, 152108-1-3. [3] Teisseyre, H.; Lyons, J. L.; Kaminska, A.; Jankowski, D.; Jarosz, D.; Bockowski, M.; Suchocki, A.; Van de Walle, C. G.; Identification of yellow luminescence centers in Be-doped GaN through pressure-dependent studies, J. Phys. D Appl. Phys. 50, 2017, 22LT03-1-7.

Resume : Luminophores based on ceramics pure (nominally) and doped ZrO2 are now widely used in laser technology, optoelectronic devices, luminescent dosimetery of iomising radiation [1]. To achieve an optimal combination of the working luminescent and optical characteristics of these materials, existing synthesis methods are being improved and new ones are being developed. A promising method of ceramics producing is their synthesis in the field of a powerful flux of high-energy radiation [2]. The aim of this work is to synthesize ZrO2 ceramics by the method based on the irradiation of the charge by a beam of fast electrons with 1.4 MeV energy, study their thermoluminescent (TL) properties, and calculate the kinetic parameters of TL. It was found that the dosimetric TL peak of the ceramics synthesized in this work is shifted by 40 K to the high-temperature region compared to the TL peak of compacts compressed from the same initial nanopowder used for synthesis. Kinetic TL parameters (activation energy and frequency factor) were calculated by analyzing the peak shape and variation of heating rates of two types zirconium dioxide samples: ceramics and compacts. Taking into account the different thickness of the samples, the calculation was carried out taking into account the temperature gradient between the sample and the heater. It was found that the peak shift to the high-temperature region of ZrO2 ceramics was caused by a 0.3 eV increase in the trap activation energy compared to compacted samples. [1] V Kiisk, L Puust, K Utt, A Maaroos, H Mändar, Erica Viviani, Fabio Piccinelli, Rando Saar, Urmas Joost, Ilmo Sildos. Journal of Luminescence. V. 174 (2016) 49-55. [2] V. Lisitsyn, L. Lisitsyna, A. Dauletbekova, M. Golkovskii, Zh. Karipbayev, D. Musakhanov, ?. Akilbekov, M. Zdorovets, A. Kozlovskiy, E. Polisadova. Nuclear Inst. and Methods in Physics Research B 435 (2018) 263?267

Resume : One of the urgent problems of modern optoelectronics and the chemistry of optical materials is the search for new materials with outstanding physicochemical properties. Yttrium aluminum garnet (YAG) is considered the most studied compound in the garnet class. In the development and application of "white light" LEDs, europium-doped yttrium-aluminum garnet (YAG:Eu) nanopowders are among the most important phosphors, since YAG:Eu3+ nanopowders are suitable for converting blue LED radiation into broadband yellow light. Recent times there are the cases of using YAG:Eu as the medium for radiation of cancer treatment. So, the investigation of optical properties of samples with different concentration of europium is important for the further applications. YAG:Eu samples with europium concentrations of 6%, 8%, and 10% were synthesized by solid state synthesis. From the XRD patterns we can see that all samples contain yttrium aluminate phase with garnet structure. The main peak of the cubic YAG:Eu structure is centered at 2Q = 33.4? and corresponds to the crystalline plane with Miller indices of 420. Photoluminescence characteristic of YAG:Eu were evaluated on the basis of emission (PLE) and excitation spectra (PL). Room temperature (RT) photoluminescence excitation (PLE) spectra of powder samples were measured with a FluoroMax-4P spectrofluorometer (Horiba) equipped with a 150 W xenon lamp as an excitation source and a R928 Hamamatsu photomultiplier as a detector which allows recording PL and PLE spectra in the spectral range of 250?850 nm. The PLE spectra recorded between 250 and 700 nm and contains several peaks. The first spectral domain is situated between 280 nm and 360 nm and corresponds to the Eu3+ and O2- charge transfer band. The increase in europium concentration leads to the corresponding increase of chargge transfer bands intensity. The next region in the range 375-420 nm and the main attention is paid to the maximum at 392.75 observed on 710 nm. This band is related to f-f transitions of Eu3+ ions. The intensity of the band at 392.75 decreases with the concentration. The intensity of this band on 6% sample is higher 1.15 times of 8% sample and 2.62 times than yttrium aluminum garnet doped with 10% of Eu3+ . In the photoluminescence spectra of all samples at excitation wavelength 395 nm, 6 main bands were recorded in the region of 590 nm, 595 nm, 610 nm, 630 nm, 696 nm, and 710 nm. The band intensities depend on the europium concentration. In the YAG:Eu 6% sample, the intensity of the band at 710 nm is 2650,000, while in 8% it increases to 7060,000 and reaches 7369,000 in which the europium concentration is 10%. It can be seen that with an increase in concentration from 6 to 8%, the intensity does not increase much, in contrast to the case with a low concentration. The work was carried out within the framework of the project IRN ??09057946 "Spectroscopic studies of functional materials based on perovskites and garnets doped with Ln2+, Ln3+, Ln4+".

Resume : Doping technique has been widely used for materials processing to add desired properties, such as mechanical, magnetic and optical properties, in the functional materials. Dilute amount of dopants can change such properties drastically due to an introduction of defects. It is essential to know a local environment of such dilute dopant in an atomic scale for the deep understandings of the mechanism why such property changes appear. However, it is generally difficult to determine local environments of dilute dopants experimentally in an atomic scale, since the amount of the dopants are usually very small. One of the powerful tools to overcome such difficulty is an X-ray absorption near edge structure (XANES) measurements by using a synchrotron radiation. The local environment of the ultra dilute dopants at a level of atomic ppm could be successfully analyzed by XANES with the aid of the first principles calculations [1]. The electron spin resonance (ESR) measurement is also quite efficient to analyze local environment of magnetic elements, though ESR is limited for the active valence states of the magnetic ions. On the other hand, theoretical calculations with the first principles calculations within a density functional theory level can be adopted to investigate such local environment of dilute dopants. Combining these two experimental and theoretical methods we can safely determine the local environment of the dilute dopants. In the current study, we focus upon the local environments of Mn ions in efficient red phosphor materials from both experimental and theoretical point of views. Recent results on the local environment analysis by XANES and ESR with the aid of the first principles calculations for Mn-doped CaAl12O19 [2], K2SIF6 [3] and CaMO6 will be demonstrated. [1] I. Tanaka et al., Nature Materials 2 (2003) 541. [2] M. Sagayama et al., ECS J. Solid State Sci. Tech. 10 (2021) 076004. [3] M. Subhoni et al., Opt. Mat. 115 (2021) 110986.

Resume : Halide perovskite semiconductors are attracting enormous interest for their use in high-performance optoelectronic devices. Their high-performance - in spite of crude processing - is generally attributed to most defects being shallow in nature and largely benign. Nevertheless, deep trap states do still exist, as do device instabilities, and both aspects still limit commercialisation. Here, I will present our group's work seeking to understanding the local nature of the defects and their impact on performance in halide perovskite compositions relevant for solar cells using a variety of electron and photon multimodal characterisation techniques. We show that deep trap states appear as nanoscale trap clusters appearing at some, but not all, grain boundaries (Doherty et al. Nature 2020). These trap clusters are associated with nanoscale phase impurities including hexagonal polytypes (Kosar et al. EES 2021), and trap carriers and are local sites at which degradation seeds (Macpherson et al. Nature 2022). Furthermore, we show that the in the highest performing formanidinium-rich perovskites, local octahedral tilt prevents formation of these unwanted nanoscale hexagonal phases (Doherty et al. Science 2021). Future efforts should aim at ensuring octahedral tilt is homogeneous across the sample to prevent the formation of such trap clusters and instability sites -- in turn leading to extremely efficient and stable perovskite optoelectronic devices.

Resume : Chalcopyrites in nanodevice design are perhaps best known for their application in thin film solar cells where CIGS (copper-indium-gallium-diselenide) photovoltaic elements have been an industry standard and a record holder for decades [1]. Aside from CIGS many other chalcopyritic materials have been reported to show promising photovoltaic properties [2,3]. Thus a thorough analysis of a wide class of chalcopyritic materials may prove advantageous. In our study we have considered materials with the general formula I-III-VI2 (e.g. CuGaS2, AgInSe2) and II-IV-V2(e.g. BeCN2, MgZnP2). These were investigated using first-principle calculations. We utilized different quantum-chemical computational codes such as CRYSTAL17, Quantum Espresso and Yambo and performed our computations on Latvian SuperComputer Cluster (LASC). A special care was given treating solid solutions that come up naturally in band gap tuning applications. Here we considered different atomic configurations for the crystallographic cell given element concentrations for a solid solution and the effect that these configurations have on the overall properties of the material. We simulated the optical properties utilizing the time-dependent DFT approach and obtained spectra that can serve as an indication for the application of a material in the field of photovoltaics. Lastly, the role of point defect formation was also assessed. It is known that the formation of defects can be detrimental [4] or beneficial [5] for the solar cell performance and hence we performed first-principle modelling of various point defects calculating the formation energy and estimating the possible effects on optical properties. In summary we have performed an ab initio study of a number of chalcopyritic materials aiming to accurately capture their photovoltaic properties. In the near future our goal is to widen the scope of the considered materials and organize them in a database that can then be utilized by researchers working in the field of photovoltaic cell design and manufacture. This research was funded by the Latvian Scientific Council grant LZP-2021/1-0322 [1] M.A. Contreras, B. Egaas, K. Ramanathan, J. Hiltner, A. Swartzlander, F. Hasoon, R. Noufi Prog. Photovoltaics, 7 (1999), p. 311 [2] Yan, C., Huang, J., Sun, K. et al. Nat Energy 3, 764?772 (2018). [3] Torimoto, Tsukasa, Tatsuya Kameyama, and Susumu Kuwabata. The Journal of Physical Chemistry Letters 5.2 (2014): 336-347. [4] Jeong, Woo?Lim, et al. Advanced Science 7.21 (2020): 1903085. [5] Yee, Ye Sheng, et al, Physical Review B 92.19 (2015): 195201.

Resume : Cu/W nano-multilayers are characterized by outstanding thermal, optical, electrical, and mechanical properties, which can be tailored by introducing in-plane stress controlled by deposition process parameters and post-process annealing. Using hybrid molecular dynamics/Monte Carlo simulations, we demonstrate that the segregation of Cu to W grain boundaries increases with increasing the annealing temperature and the magnitude of in-plane stress, both promoting the degradation of nano-multilayered structure in a good agreement with our experimental observations. The kinetics of such degradation is also in-plane stress-dependent and driven by atomic transport at the Cu/W interfaces, well explained in detail by our first-principles calculations for vacancy diffusion. Overall, the interplay between thermodynamics and kinetics of nano-multilayer degradation allows for tunable composite properties for a variety of applications.

Resume : In this study, we present a detailed analysis of single, double and complex vacancies formed at epitaxial graphene (EG) on SiC from He and Ne ion irradiation. From density functional theory and molecular dynamics simulations, the effect of substrate in defect production has been evaluated. The statistics on number, types and location of defects produced in each layer of EG is needed for defects engineering in graphene. The choice of ions and the energy ranges are such that the defects are produced in a controlled manner. The He focused ion beam (FIB) (operating at 30 keV) have been previously used to produce defects in EG on SiC. Here, we have considered the ion energy ranges (12.5-30 keV) within the operating range of Helium Ion Microscope (HIM).

Resume : The progress of modern electronics largely depends on the possibility of the emergence of previously unknown materials in electronic technology. The search and combination of new materials with extraordinary properties used for the production of new small-sized electronic devices, and the improvement of the properties of existing materials due to improved technology for their manufacture and processing, in general, will determine the progress of highly promising electronics. To solve the problematic tasks of miniaturization of electronic components with an increase in the level of connection of integrated circuits, new forms of electronic devices are being created using nanomaterials with controlled electrophysical characteristics. It is known that one of the unique properties of fullerene structures is to enclose one or several atoms inside their carbon framework. Such structures are usually called endohedral fullerenes. The electronic characteristics of endohedral fullerenes significantly depend on the properties of the encapsulated atom, which makes it possible to control them by choosing the encapsulated atom required by the property. Within the framework of the density functional theory in combination with the method of non-equilibrium Green's functions (DFT NEGF), the features of electron transport in fullerene nanojunctions are considered, which demonstrate "core-shell" nanoobjects, the "core" in which is an alkali halide crystal - KI, and the "shell" is an endohedral fullerene C180 located between the gold electrodes (into the nanogap). The values of the total energy and the stability diagram of a single-electron transistor based on endoetheric fullerene (KI)@C180 are determined. The dependence of the total energy of fullerene molecules on the charge state is presented. The ranges of the Coulomb blockade, as well as their areas associated with the central Coulomb diamond, are calculated. This research has been funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP09057911).

Resume : Reactive Material Structures(RMS) are a new class of materials that can release large amounts of chemical energy at the desired time by applying a strong mechanical, electrical, or thermal stimulus. RMS, which are 'energetic' materials, can be made into tough materials to act as 'structural' materials by a consolidation process such as cold isostatic pressing or cold spraying. And these materials are expected to be utilized in various military parts because they are stable in ambient environments but can react explosively in extreme environments (under strong mechanical, electrical, and thermal stimuli). In this study, we artificially introduced nano-defects and nano-interfaces into the microstructure of these reactive material structures. And the resulting changes in the reaction characteristics of the reactive material structures were closely analyzed. As a result, we found out the reaction initiation temperature of the reactive material structures could be lowered by about 350 oC by the nano-structure introduction, and we also found out the reaction intensity and reaction propagation velocity were significantly improved.

Resume : The doughnut-like porous-CdO/porous-CdS nanostructures were synthesized. The nanocomposite was formed by the electrochemical etching method on the CdS surface simultaneously with the CdO electrochemical deposition. Electrochemical etching was used to form the porous-CdS layers as well as to saturate the electrolyte with the cadmium ions. Electrochemical deposition of CdO crystallites on the surface of porous-CdS was carried out from the electrolyte solution. The obtained nanocomposite was characterized by SEM, EDX, and Raman spectroscopy. According to SEM, it was found that both the CdS surface and CdO oxide crystallites have high porosity (about 60%). The structural characteristics studied by Raman and XRD spectroscopy showed that doughnut-like crystallites consist of the cubic phase cadmium oxide. Along with this, there is a large number of amorphous CdO. The similarity of the crystal lattices and structural parameters of the CdS and CdO allows suggesting that the CdS porous structure serves as a soft substrate to avoid the tensions. In turn, the CdO layer is a reliable passivating layer for the CdS. Such coatings can often be characterized as conversion, i.e. protective. The oxide films reliably cover the semiconductor surface, thus serving as a passivating coating to protect photocorrosion and improve the photocatalytic activity and stability of the surface layer [1, 2]. The developed surface morphology of the obtained nanocomposite allows us to consider it a new material for photovoltaic devices. Furthermore, the increase in the surface area by hundreds of times and the unusual torus-shape of the crystallites can be used for photovoltaic energy converters and photocatalysts. References: 1. Sirohi, K., Kumar, S., Singh, V., & Vohra, A. ?Synthesis and characterization of CdO?SnO2 nanocomposites prepared by hydrothermal method,? Acta Metallurgica Sinica (English Letters), 2018, 31(3), 254-262. 2. Kahane, S. V., Sasikala, R., Vishwanadh, B., Sudarsan, V., Mahamuni, S. ?CdO?CdS nanocomposites with enhanced photocatalytic activity for hydrogen generation from water,? International journal of hydrogen energy, 2013, 38(35), 15012-15018.

Resume : Nowadays, special attention is paid to the aluminum-magnesium spinel MgAl2O4, which exhibits exceptional radiation resistance. It is especially important that MgAl2O4 was chosen as a matrix for transmutation of actinides by capturing neutrons in nuclear reactors, as a matrix for storing radioactive waste. Also, the intensive development of photonics and electronics requires the development of new functional materials with high radiation resistance, transparency in a wide spectral range, and thermal stability. The work presents of optical effects induced in crystals of MgAl2O4 by irradiation with high-energy heavy ions, simulating the impact of fission products of nuclear fuel. The samples were irradiated by 46 MeV Ar, 107 MeV Kr, 150 MeV Xe and 710 MeV Bi ions in the fluence range of 1010-1013 cm-2 (IC-100, U-400 cyclotrons FLNR JINR, Dubna, DC-60 Nur-Sultan). The PL measurements were performed in two experimental geometries: standard (?exc. = 355 nm) and confocal (?exc. = 355 nm, 445 nm, 473 nm and 532 nm) at RT. The PL spectra of unirradiated MgAl2O4 contain emission bands of Cr3+ (1.8 eV) and Mn2+ (2.4 and 1.6 eV) impurities. Irradiation induce a broad luminescence band at 2.48?3.1 eV (standard geometry) with a three-peak structure, which is similar to MgO crystals . The PL spectra (confocal geometry) showed an intense non-elementary bands around 1.55-3.1 eV under excitation light with wavelengths 355 nm, 445 nm, 473 nm and 532 nm. Intensities of these bands increase with the ion fluence up to 1012 cm-2. The analysis of the PL spectra obtained in standard geometry allowed us to assume that the radiation-induced defects created in the track region are surrounded predominantly by Mg and O ions. In confocal geometry, upon different energy of excitation, the PL spectra of samples have been demonstrated the similar spectral shapes (emission bands), which have been tentatively ascribed to some of impurity centers in different charge states.

Resume : The surface of pure GaAs nanocrystals is prone to oxidation, which worsens their properties. To prevent oxidation, passivation of the surface of GaAs nanocrystals is carried out. It was found that electrochemical etching of GaAs with subsequent electrochemical deposition, allows forming of the diamond-like crystallites of the arsenic trioxide on the semiconductor surface in the cubic phase of the arsenolite. Such crystallites have the shape of regular dipyramids with triangular faces (tetrahedron). Morphological and structural characteristics of the formed layers were studied by SEM, EDX, and Raman-spectroscopy methods. The light scattering spectrum of the composite shows the peaks of gallium arsenide and arsenolite. The peak shift of the Raman spectrum, which corresponds to the gallium arsenide, relative to the position of the typical peak for bulk GaAs is explained by the presence of the porous layer on the GaAs surface. This layer was formed in the first etching stage. The structural perfection of the arsenolite crystallites has been also studied. The crystallites have the shape of dipyramids with triangular faces. Some crystallites show twinning during the growth. It should be also noted that good crystallization and tight adhesion to the semiconductor substrate of the oxide layer are due to the chemical affinity of the materials (GaAs and As2O3), the similarity of the crystal parameters, and the presence of the buffer porous layer. Thus, the directed oxidation allows for the creation of the passivating oxide layer that is uniform in volume and sample area. The complication of the natural oxidation of the surfaces of the nanostructured and bulk semiconductors is the multicomponent composition of the surface layers and the formation of different types of the native oxides simultaneously [1]. The method of the directed controlled oxidation makes it possible to synthesize the oxide layer consisting of one type of oxide, namely As2O3, in the cubic phase of the arsenolite. [1]. Vishwanath, V., Demenev, E., Giubertoni, D., Vanzetti, L., Koh, A. L., Steinhauser, G., Foad, M. A. Evolution of arsenic in high fluence plasma immersion ion implanted silicon: Behavior of the as-implanted surface, Applied Surface Science, 2015, 355, 792–799. Acknowledgments: The study was supported by the Ministry of Education and Science of Ukraine, namely: • the state budget research project No. 0122U000129 The search for optimal conditions for nanostructures synthesis on the surface of A3B5, A2B6 semiconductors and silicon for photonics and solar energy • project No. 0121U10942 Theoretical and methodological bases of the system fundamentalization of the future nanomaterials experts training for productive professional activity. Ya. Suchikova thanks Goethe-Institut for supporting the House of Europe graduate emergency scholarship program. We also thank the Armed Forces of Ukraine for the safety to carry out this work. This work was only possible thanks to the resilience and courage of the Ukrainian Army.

Resume : Nanowires are generally devoid of line defects. As a result, they offer extraordinarily high mechanical strengths through deformation mechanisms, which are mainly source-controlled. As a detailed understanding of the mechanical behavior of nanowires is essential for their effective applications in nano electronic and nano-electromechanical systems, estimating the activation parameters of dislocation nucleation is a key requirement. In this study, we explore the use of a statistical method to extract the activation volume for initiation of plastic tensile deformation with aluminum nanowires as a model system. To this end, we perform molecular dynamics simulations of tensile deformation of the nanowires and record the yield stress for each simulation run. Uniaxial tensile strain is applied along the axis of the nanowire. For every structure, a large number of simulations are performed to obtain the statistical distribution of the yield stress. The statistics of incipient plasticity are shown via the cumulative distribution of shear stresses associated with the onset of the yielding event. By performing statistical analysis, we extract the activation volume corresponding to the surface nucleation of dislocations. We have also analyzed the effect of nanowire size and temperature on activation volume. The approach adopted here is not limited to dislocation nucleation but can be generalized for thermally activated driven systems.

Resume : Modern science and technology are increasingly engaged in the study of nanomaterials and the development of nanotechnologies. This primarily applies to solid-state physics. To date, various theoretical methods and research technologies are intensively used to clarify the significance of experimental results that depend on the study of the properties of defects in solids. Improvements in this area are likely due to enhancements in computer technology and the development of modern quantum chemical packages. Within the framework of density functional theory (DFT), the paper presents the results of computer simulation of the density of states and total energy of ideal NaF (Na13F14, Na4F5, Na22F23) and NaCl (Na13Cl14, Na4Cll5, Na22Cl23) nanocrystals. As well as the above characteristics with the simplest point defects in various cluster compounds (Na12F13, Na21F22, Na12Cl13, Na21Cl22). Characteristics modeling is implemented in the Atomistix ToolKit with Virtual NanoLab program in the LDA (local-density approximation) functionality. According to the spectra obtained, a certain number of energy levels are visible in the energy range from -30 eV to 20 eV. In all spectra, the first clearly pronounced narrow energy level is located in the region of -25 eV for NaF nanocrystal and -20 eV for NaCl nanocrystal. The characteristic shape of the energy levels in the density of states spectra indicates that NaF and NaCl nanocrystals in various cluster compounds at a temperature of 1 K can be attributed to quantum dots. The results obtained can be useful in the study of nanocrystals. This research has been funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP09057911).

Resume : Under certain situations, metals having fcc structures may display deformation twinning, which is an intriguing but elusive element of their deformation behavior. The phenomenon is generally understood to be caused by twinging partial dislocation activities. Multiscale modeling of crystal plasticity relies on dislocation mobility laws that inherently involve these defects' fundamental properties. However, in the context of twinning dislocations, an in-detail analysis of their properties is yet to be explored. Here, we employ the semi-discrete variational Peierls-Nabarro (SVPN) model to compute the core-structure and Peierls stress of twinning dislocation in four fcc metallic crystals of varied stacking fault energies. We have incorporated the non-local and surface corrections to the SVPN framework, which significantly affects the core properties and Peierls stress. In addition to the conventional layer-by-layer twinning model, we also investigated an alternate-shear model, where the stable stacking fault is remarkably less than the unsheared structure. This fault energy is sufficient to overcome the Peierls Barrier of the twinning dislocation. Hence, an indirect approach is formulated to compute the Peierls stress in such configurations.

Resume : In recent years, metal halide perovskites have emerged as one of the fastest growing photovoltaics technologies. By improving the quality of interfaces, carrier transport layers, and perovskite films it has achieved the 23% efficiency. Despite this tremendous progress, the organic-inorganic lead halide perovskite solar cells suffer from long-term stability, and toxicity which has fuelled the search for synthesizing lead-free perovskites. Toward this goal, one promising strategy is to substitute four Pb2+ cations with a divalent and two trivalent cations, for example, Cs4CuSb2Cl12 (CCSC). This gives rise to layered double perovskites. Theoretical and experimental studies have demonstrated that CCSC exhibits high photo- and thermal-stability, is tolerant to humidity. These properties make CCSC a suitable absorber material in solar cells. However, the excited state dynamics and nature of trap states of these microcrystals are yet to be fully explored which we address in this work. We synthesized the CCSC microcrystals (MCs) using the solution-processed method. We also synthesized the CCSC MCs using different surfactants with different concentrations to passivate the surface and study the effect of passivating agents on the shape and surface morphology of the crystals. We also studied the role of surfactant on the density of trap states near valence band maxima using ultraviolet photoemission spectroscopy. Using femtosecond to nanosecond transient absorption spectroscopy, we further studied the excited state dynamics and the effect of surfactants on charge carrier dynamics. These studies furnished valuable information on charge carrier dynamics as well as effect of surfactants on it.

Resume : In this work, the quantum chemical characteristics of alkali halide nanotubes were constructed and studied in the density functional theory (DFT). Density functional theory and bound cluster calculations imply that nanotube structures with cross sections of n=4,6,8 exhibit stability equal to or greater than the conventional cubic form of large alkali halide crystals. The characteristics of alkali halide nanotubes were studied in the range from liquid helium temperature (4 K) to human body temperature (309.75 K). Characteristics simulation was implemented in the Atomistix ToolKit with Virtual NanoLab program in the local density approximation. The presented strategy for studying clusters of alkali halide nanotubes makes it possible to predict permanent structures and can be used to derive the mechanism of cluster formation. The resulting optimized structures and their associated vibration frequencies offer a reliable information database for comparison with experiments and may be useful in further studies of alkali halide nanotubes. This research has been funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP09057911).

Resume : Gallium oxide (?-Ga2O3), well known for its unique optical and electrical properties, being semiconductor but possessing a wide band gap (4.9 -5.0 eV), has shown in recent years a constantly growing interest as a promising material in different fields of power electronics, optoelectronics and photonics. Despite a large number of es of intrinsic defects in ?-Ga2O3, information about the role of complex "donor-acceptor" defects in electronic and optical properties there is still missing. Poor theoretical data can be associated, obviously, with the difficulties of modeling complex defects in low-symmetry systems, which requires the use of large crystal cells and, consequently, makes the ab-initio calculations expensive in terms of computer resources. In this work, we present the results of the ab initio LCAO calculations of transition levels and electronic density of states of pair vacancy defects (VGa,VO) in a ?-Ga2O3 crystal in comparison with the same calculations of single vacancies and known available data. We used the pure DFT-GGA method (exchange PBE and correlation PBE functionals) as incorporated into the CRYSTAL17 computer code, using a supercell model and a linear combination of atomic orbitals (LCAO) basis set [1]. As result, we have shown that VGa-VO complexes indeed can play role as deep acceptors together with single VGa. We believe this type of defect to be more likely than a single heavily charged gallium vacancy. The formation of VGa1-VO complexes (VO=VO1, VO2, and VO3) is energetically more preferable above similar VGa2-VO complexes. [1] R. Dovesi, A. Erba, R. Orlando, C.M. Zicovich-Wilson, B. Civalleri, L. Maschio, M. R_erat, S. Casassa, J. Baima, S. Salustro, B. Kirtman, WIREs Comput. Mol. Sci., e1360 (2018)

Resume : Nanocomposite materials based on cellulose and carbon nanostructures are actively studied at present as perspective multi-functional materials [1]. Despite intensive studies, several key problems regarding the peculiarities of the interaction of the components of cellulose-carbon nanocomposites still remain unsolved. This work aims to clarify such questions using computational research methods. Chemical modification of the surface of carbon nanostructures can substantially change the physical and chemical properties of such materials and improve their performance for specific applications. Theoretical modeling of cellulose molecules adsorption on the modified surface of carbon nanostructures may allow predicting some important properties of materials perspective for practical use. The report presents results of computational studies of interaction of cellulose molecular clusters with carbon nanostructured materials - carbon nanotubes and graphene. The studies are carried out in the form of electronic structure calculations performed by the quantum chemical method in the DFT approximation [2]. Binding energies and inter-nuclear distances between adsorption components are calculated and analyzed. The calculations revealed the mechanisms of adsorption of molecular cellulose on the surface of carbon nanotubes CNT(5,5) and single-layered graphene sheets. Several kings of carbon surface modifications are also considered in calculations, in particular, doping with boron or nitrogen, functionalization by oxygen-containing surface groups and sodium dodecyl sulfate (SDS) anionic surfactants. Calculations show no covalent interatomic bonds between cellulose molecules and the surface of undoped CNTs. Interaction of cellulose molecules with graphene surface should be more pronounced if compared to the case of nanotube surface because the obtained interatomic distances between cellulose and graphene atoms are significantly shorter. These data are discussed in comparison with experimental data obtained from diffuse reflection and photoluminescence measurements performed under “nanocellulose”-graphene” nanocomposites. Calculation results were discussed in view of the possible influence of doping and surface functionalization of carbon nanostructures both on characteristics of cellulose adsorption and macroscopic properties of cellulose-carbon nanocomposite materials. [1] Nedilko, S., Barbash, V., Kleshonok T., et. al. Morphology, Optical and Electronic Characteristics of Nanocellulose Filled with Microcrystalline Cellulose and Graphene Oxide. In 2020 IEEE 10th International Conference Nanomaterials: Applications & Properties (NAP), pp. 01NP06-1, 2020. [2] M.J. Frisch, G.W. Trucks, H.B. Schlegel, et al. // Gaussian 09 (Gaussian, Inc., Wallingford, CT, 2009).

Resume : Corundum (-Al2O3) is a technologically important material considered also as a promising candidate for optical windows in future fusion reactors. Its optical and mechanical properties are controlled by presence of radiation-induced defects, including oxygen vacancy containing single and dimer centers  F-type centers in different charge states. In addition to typical absorption bands, these radiation defects are characterized by relevant luminescence bands, which could arise via either intracenter photoexcitation or secondary reactions under intense radiation (i.e. X-rays). The photoexcitation spectra for the emissions typical of various single and dimer F-type centers have been measured; they are complicated and, in some cases, demonstrate a number of secondary excitation bands related to different color centers. To analyze the recovery of radiation damage via thermal annealing, the changes in cathodoluminescence spectra of irradiated -Al2O3 crystals have been measured at 6 K after their additional preheating to certain temperatures. Both steady-state luminescence and emission measured within time-windows has been analyzed. The suppression of the exciton luminescence (7.6 eV) by irradiation has also been clearly demonstrated  this intrinsic emission undergoes stepwise enhancement with preheating temperature up to 1200 K.

Resume : The REVO4 nanoparticles are characterized by a high efficiency of excitation energy transfer from the vanadate matrix to the RE cations. At the last years attention was paid to vanadate compositions those are excited from spectral range around 400 nm. Our study has shown essential increase of luminescence efficiency of the Ca-doped REVO4 nanoparticles under excitation from 350 ? 420 nm spectral range. This increase is related with appearance of new absorption bands around 400 and 470 nm in the Ca-doped samples. Obviously, the noted bands are caused by Ca-induced defects in the vanadate crystal lattice. Up to now, origin and structure of these defects are still under discussion. In order to clarify the nature of the Ca-induced defects in the vanadate matrix, this paper presents new results of high resolution XRD investigation of the hardly doped samples and study of Ca - concentration effects on diffuse reflection spectra of the REVO4:Ca samples. Additional reflection band around 400 nm is in a good agreement with Ca ? induced wide excitation band in the 360 - 425 nm spectral range that was observed for the REVO4:Ca nanoparticles. It is supposed that this band is related with transitions in the VO43- anions distorted by the Ca2+ cation defects and oxygen vacancies those are formed in the vanadate nanoparticles with heterovalent substitutions due to requirements of charge compensation. Comparing the results of luminescent ivestigation of the La1-xEuxVO4:xCa and EuVO4:xCa nanoparticles, we found that only one additional band appeared in the reflection spectra of the REVO4 nanoparticles after Ca doping gives improvement of spectral characteristics of the EuVO4:xCa nanoparticles This is the band around 400 nm. The band around 470 nm is found to be associated with the Ca2V2O7 impurity phase and it gives only decrease of band gap value of the synthesized nanoparticles, increased absorbance of visible light and no improvement of luminescent characteristics. Thus, this band can be considered as unwanted. As this band was clearly observed only for our samples with Ca concentration y = 0.2, we should estimate maximal concentration of heterovalent dopants for the REVO4 nanoparticles those still give improvement of their luminescent characteristics as y = 0.15. This work has received funding from Ministry of Education and Science of Ukraine, Polish Academy of Sciences and from the Horizon Europe research and innovation program under grant agreement No 654360 within the framework of the NFFA-Europe Transnational Access Activity.

Resume : Wide-band-gap semiconductor gallium oxide (?-Ga2O3) has recently attracted much attention of scientists and technical specialists due to a number of unique optical and electrical properties, including high breakdown field (great advantage for power electronics), UV photodetection with high photosensitivity, etc.) [1]. Recently, metal-oxide-semiconductor field effect transistor (MOSFETs) and a Schottky barrier diode based on ?-Ga2O3 have been produced [2]. In this work, we have presented the results of the study of gallium oxide ceramics which obtained by sintering of pure (99,9999%) powder under radiation of power electronic flux, through methods of X-ray diffraction (XRD) and scanning electron microscopy (SEM) . As far as we know, gallium oxide ceramics were obtained in this way for the first time. The direct electron flow a with energy 1.4 MeV and power 15 kW/cm2 leads to the formation of ceramics in time just 1 s, without the use of any additives and precursors. After sintering, the obtained samples have typical sizes a 2-3 cm3. Synthesis of materials in the field of a powerful electronic flow is fundamentally different from synthesis in thermal fields. XRD studies were carried out on a D8 ADVANCE ECO with an X-ray tube with a Cu anode and a graphite monochromator. The surface state and elemental composition of the surface of the synthesized ceramic samples were studied using a Hitachi TM-scanning electron microscope (SEM) 3030 with a Bruker XFlash MIN SVE energy-dispersive analysis system at an accelerating voltage of 15 kV. As results, the structure of the obtained ceramics fully corresponds to the typical monoclinic structure belonging to the space group ?2/m. The crystal lattice parameters a=12.08948 Å, b=3.00727 Å, c=5.76147 Å, ?=103.651° are comparable with well-known values of high-quality crystals (a=12.21160 Å, b=3.03765 Å, c=5.80398 Å, ?=103.875°), as well as the volume of the unit cell (203.55 Å3 vs 209.00 Å3). SEM images show that, after sintering, the surface of ?-Ga2O3 is composed of homogeneous molten hard ceramic. This suggests that the crystal structure is formed successfully under the influence of the radiation flux in the process of ceramic synthesis. The elemental composition of the fabricated ?-Ga2O3 ceramics does not differ from that incorporated in the manufacture of the charge, the resulting ceramics has a stoichiometric composition. 1. Yang, J., Ren, F., Tadjer, M., Pearton, S.J., Kuramata, A. (2018). 2300V reverse breakdown voltage Ga2O3 schottky rectifiers. ECS Journal of Solid State Science and Technology, 7(5), Q92Q96. 2. Higashiwaki, M., Sasaki, K., Murakami, H., Kumagai, Y., Koukitu, A., Kuramata, A., et al. (2016). Recent progress in Ga2O3power devices. Semiconductor Science and Technology, 31(3), 034001.

Resume : The natural spinel crystal MgAl2O4 containing the Cr3+ ions was studied experimentally and theoretically. The experimental absorption and emission spectra at room and low temperatures were obtained. In addition, the crystal field calculations of the cr3+ energy levels in this host were performed. Actual trigonal D3d symmetry was used in the calculations. Low symmetry splitting of the orbital triplet states was analyzed. Good agreement between the experimental and theoretical results was demonstarted.

Resume : Defects were created in Si-doped 2D and 1D Gallium Nitride (GaN) by wet etching. The optoelectronic properties of the defects formed were characterized with super and sub-band gap surface photovoltage spectroscopy using kelvin probe, and by photoluminescence spectroscopy. A detailed picture of the electronic properties of the GaN surface is obtained, mainly the surface state type (donor or acceptor states), charge transfer mechanism (such as surface state to band or vice versa), location (deep or shallow), the chemical nature and optical (luminescent and non-luminescent) properties of these states. Opposing sheet charges at the top facet of the etched and non-etched GaN modify the local band bending at the surface and is responsible for the polarity-sensitive VCPD. These results confirm the important role of the electronic surface states in compensation of the bound surface polarity charges in GaN.

Resume : The intensive development of electronics is associated with the R&D of new advanced nanomaterials and the implementation of fundamentally new effects. Methods for obtaining nanostructures, in general, are well known, diverse, and constantly improving. The purposeful modifications of the nanomaterial properties as well as to ensure their temporal stability are the focus of the present stage of scientific and technological research. Radiation exposure methods have convincingly demonstrated their effectiveness in modifying the properties of materials. Therefore, radiation-induced effects must be taken into account when creating and operating nanostructures. The study of the radiation properties of graphene-containing nanosystems, such as oxidized porous silicon (por-Siox) – reduced graphene oxide (rGO) hybrid structures, is of particular scientific and practical interest. Radiation defects not only change the properties of the porous silicon but also cause a local electric field, which affects the electrical conductivity of graphene sheets. In this work, the por-Siox – rGO hybrid structures were created and the effect of ionizing radiation from the 226Ra source on their electrical properties was studied in the AC mode. A decrease in electrical capacitance and resistance of the porous silicon–graphene structures with increasing frequency from 25 Hz to 1 MHz was established based on the measurement of the impedance frequency dependences. We have found that the obtained hybrid structures show a decrease in resistance and an increase in capacitance due to the combined action of alpha-, beta-, and gamma-radiation. It is established that the maximum effect is exerted by alpha particles. A detailed study of the features of radiation modification of the electrical properties of the por-Siox – rGO hybrid structures opens the way to creating new types of ionizing radiation detectors.

Resume : Advanced photo-active materials have attracted attention for their potential uses in water purification. In this study, a novel and facile route was used for designing nanohybrids to be valuable sources for producing effective photocatalysts for purifying water from the colored pollutants. Hostguest interaction and intercalation reactions used long chains of hydrocarbons of n-capric acid and stearic acid to facilitate incorporation of fine particles of cobalt iron oxide nanocomposite with the internal surface of the nanolayers of Al/Zn for building nanohybrids. The thermal decomposition of the prepared nanohybrids led to formation of zinc oxide nanoparticles doped with multi-oxides of magnetic and non-magnetic dopants. These dopants created new optical centers causing a strong reduction in the band gap energy from 3.30 eV to 2.60 eV. This positive effect was confirmed by a complete removal of the dye of Naphthol green B from water after 15 min of light irradiation. Moreover, a kinetic study showed that the reaction rate of photocatalytic degradation of the pollutants was faster than that of the conventional photocatalysts. Finally, this route was effective for producing benign and fast solutions for purifying water in addition to environment-related problems.

Resume : Nanocrystalline materials based on titanium dioxide possess unique properties including photocatalytic and antibacterial activities. Therefore, the determination of the process-structure-property relationships for the nanostructured titanium dioxide synthesized by different approaches remains relevant. In this study, within the framework of the extraction-pyrolytic method (EPM), hydrothermal and sol-gel methods, we fabricated nanocrystalline TiO2-based powders with different anatase/rutile phase content. The size of nanocrystallites formed by EPM was equal to 15-52 nm, while the other techniques resulted in nanocrystallites of 30-35 nm. The hydrothermal and sol-gel methods were also utilized to grow TiO2 particles doped with Cu, Er and Er-Yb. The doping was found to decrease the TiO2 nanocrystallite size to 22-27 nm. The correlation between synthesis parameters (pyrolysis and annealing temperature) and properties of the produced materials (phase composition, photoluminescence and photocatalytic properties) was studied. To characterize the phase composition of the TiO2-based samples the X-ray diffraction (XRD) method was used. The Raman spectra of the samples formed by EPM were collected at 532 nm, by hydrothermal and sol-gel methods ? at 473 and 633 nm excitation wavelengths. The origin of the observed Raman spectra bands was analyzed and compared with available literature data. The photocatalytic activity was typical for Cu-doped TiO2 under blue light in contrast to the other samples that were active under ultraviolet light. The Er-Yb and Er-doped samples demonstrated up-conversion property upon 980 nm excitation, which provided prominent emission in the red and green ranges respectively. This research was funded in parts by the Latvian Scientific Council grant LZP-2021/1-0464 and the State Program for Scientific Research of Belarus ?Photonics and electronics for innovations? (task #2.2).

Resume : Possibility of application of diluted magnetic semiconductor oxides in spin-based electronics is actively discussed during last decades [1]. Different methods are used for synthesis of metal oxide semiconductors doped with ferromagnetic atoms. Ni-doped tin oxide films in our study were fabricated by DC magnetron sputtering of tin target with Ni inserts in argon-oxygen plasma with an oxygen content in the range of 0-6 vol. % followed by 2 stage annealing procedure in air. Variation of oxygen content in argon-oxygen plasma strongly affects structural properties of tin oxide films [2]. Raman spectral-analytical system Nanofinder HE was used for characterization of structure of Ni-doped tin oxide films. Magnetization measurements were carried out using closed-cycle Helium refrigerator CFHF Cryogenics Ltd. in the temperature range of 4 300 K and in magnetic field up to 8 T. Analysis of the Raman spectra of Ni doped tin oxide films reveal an amorphization process with increase of oxygen content in the plasma during magnetron sputtering process. S-shaped form of magnetization curves indicates superposition of dia- and ferromagnetic components in the samples. Anhysteretic form of magnetization curves of the films indicates superparamagnetic behavior of Ni-doped tin oxide films. The relative part of the ferromagnetic component gradually increases with the temperature decreasing. References [1] Gupta A, Zhang R, Kumar P, Kumar V, Kumar A, Magnetochemistry 2020;6:15. [2] Adamchuk D, Ksenevich V, Poklonski N, Navickas M, Banys J, Lithuanian Journal of Physics 2019;59:179.

Resume : Ultra-wide-band (energy band gap Eg ? 5 eV) semiconductor gallium oxide Ga2O3 has recently attracted great attention of scientists and technicians due to a number of unique optical and electrical properties, including a high breakdown field (a great advantage for power electronics), UV photodetection with extraordinary photosensitivity, etc.). MOSFETs have recently been produced-transistors and a diode with a Schottky barrier based on ?-Ga2O3. In this paper, the possibility of Radiation assisted synthesized gallium oxide ceramics is demonstrated for the first time. The effect of a direct electron flux with E = 1.4 MeV and P=15 kW /cm2 on a powder mixture of Ga2O3 gallium oxide leads to the formation of Ga2O3-based ceramics in just 1 second, without the use of any additives and precursors to facilitate synthesis conditions with a size of up to 2-3 cm3. The synthesis of materials in the field of a powerful flow of high-energy electrons is fundamentally different from the synthesis in thermal fields. X?ray diffraction studies were carried out on the D8 ADVANCE ECO with an X-ray tube with a Si - anode and a graphite monochromator. The surface condition and the elemental composition of the surface samples of synthesized ceramics were studied using a Hitachi TM-scanning electron microscope (SEM) 3030 with a Bruker XFlash MIN SVE energy dispersion analysis system at an accelerating voltage of 15 kV. The structure of the sample under study is characteristic of gallium oxide (Ga2O3) of monoclinic type with spatial C2/m(12) symmetry with crystal lattice parameters (a=12.08948 Å, b=3.00727 Å, c=5.76147 Å, ?=103.651°) from reference values (a=12.21160 Å, b=3.03765 Å, c=5.80398 Å, ?=103.875°), as well as with the volume of the crystal lattice (V=203.55 Å3) compared to the reference value (V=209.00 Å3). SEM images of the surface of the initial gallium oxide powder and the synthesized Ga2O3 ceramic sample consist of molten solid ceramics. This suggests that the crystal structure is formed under the influence of radiation flux during the synthesis of ceramics. The elemental composition of the manufactured Ga2O3 ceramics does not differ from that laid down in the manufacture of the charge, the resulting ceramics has a stoichiometric composition.

Resume : Radiation induced effects in cerium doped as well as Mg2+ codoped Gd3(Al,Ga)5:O12 (or GGAG) single crystals irradiated by swift heavy ions have been studied. A stable strong induced absorption was observed in the 200-350 nm spectral range. It is suggested that F and F+ centers as well as a stable hole center are responsible for this induced absorption in GGAG single crystals. In addition, the swift heavy ions irradiation strongly modifies the luminescence properties in GGAG namely the excitation spectra of Ce3+ emission, which have been measured over a wide spectral range including vacuum ultraviolet (VUV) diapason. In particular it was demonstrated that the formation of the stable radiation defects under swift heavy ions irradiation explains the effective transformation of Ce4+ to Ce3+ in the Mg2+ co-doped GGAG single crystals. The reasons leading to the alteration in the VUV luminescence excitation spectra of irradiated GGAG single crystals are elucidated and discussed.

Resume : YAG:Ce based phosphors are the most common light converters for LED lamps. At present, many synthesis methods have been developed: solid-phase, sol-gel, coprecipitation, laser ablation, combustion, microwave methods, etc. Work is underway to improve the synthesis and improve the light characteristics of phosphors. Methods for the radiation synthesis of refractory compounds based on YAG:Ce have been developed for the first time. In the present work, the synthesis of YAG ceramics with 1% Ce2O3, 2.5% Gd2O3, and 2.5% to 5% Ga2O3 activators was carried out to study the effect on the luminescent properties. The synthesis was carried out in powerful electron fluxes with an energy of 1.4 MeV and a power of 22 kW. Reference samples were commercial phosphors from NPO Platan (Russia) and Fultor Enterprises Co. Ltd. (China). A 450 nm LED was used as the excitation source. To evaluate the efficiency of conversion of excitation radiation into luminescence, the brightness of ceramic powders was measured using a CS-200 luminance colorimeter. The results of this study showed that the maximum brightness value of 65% of the reference phosphor is noticeable in samples with (5% Ga), (2.5% Gd, 2.5% Ga) and (1% - Ce, without Gd2O3 and Ga2O3). The maximum of the luminescence band shifts insignificantly in the region of 550?560 nm. The described patterns are in good agreement with those known for YAG:Ce materials obtained by traditionally used methods.

Resume : The glass-ceramics (GCs) are composite materials which can possess better physico-chemical properties than their starting individual components: higher mechanical strength, lower porosity, smaller thermal expansion, stability under action of humidity and high temperatures, etc. The oxide glasses and glass-ceramics have been actively elaborated as optical materials for light emitting diodes (LEDs), sealing for electronic devices, light converting covers for solar cells, etc. [1,2]. The transparency, light absorption and emission can be controlled by varying of compositions of glass host or GC. Phosphate-based vitreous and crystalline materials can be transparent in a wide optical range – from UV to infrared light. However, the phosphate glasses are hygroscopic when there is more than 50 % of P2O5 in the composition. This disadvantage can be solved by adding some amount of MoO3 oxide to phosphate-based system with obtaining of the phosphate-molybdate glasses. In this work the preparation and optical properties of the GCs made on the base of phosphate-molybdate glass host and KBi(MoO4)2:Eu micro- nanocrystals are reported. The conventional melt quenching technique was used in order to obtain homogeneous glass of 37.09K2O-31.79P2O5-25.43MoO3-5.69Bi2O3 composition. The analytically pure KH2PO4, MoO3, and Bi2O3 were used. The thoroughly grinded mixture were melted in platinum crucible at T = 900 °C and kept at this temperature during 2 hours. The obtained homogenous melt was poured on copper sheet in order to avoid crystallization. The samples of GC were obtained by adding KBi(MoO4)2:Eu micro/nanosized crystals into melt at temperature 680 °C with stirring and aging during 10 min. The samples were characterized by means of powder X-ray diffraction, differential thermal analysis, scanning electron microscopy and luminescence spectroscopy. Obtained glasses and glass-ceramics mainly consist of amorphous phase. The crystallization and melting processes take place in studied glasses and glass-ceramics at temperatures above 460 °C. The luminescence of initial glass composition is quite weak and the PL spectra consist of wide emission band related with defects in oxygen network and Bi-O binding. The glass-ceramics reveal intensive orange-red luminescence related with emission bands of 5D0→7F0-4 electronic transitions in Eu3 ions. The studied glass-ceramics have perspectives to be used as phosphor-converters for white LED applications. [1] M. He, J. Jia, J. Zhao, X. Qiao, J. Du, and X. Fan, “Glass-ceramic phosphors for solid state lighting: A review,” Ceramics International, vol. 47, pp. 2963-2980, 2021. [2] A. Chiappini, L. Zur, F. Enrichi, B. Boulard, A. Lukowiak, G. C. Righini, and M. Ferrari, “Chapter Eleven - Glass ceramics for frequency conversion,” in Solar Cells and Light Management, F. Enrichi and G. C. Righini, Eds. Amsterdam: Elsevier, 2020, pp. 391-414.

Resume : It is known that low-energy (tens and hundreds of keV) ion processing of semiconductors can lead to a remarkable variety of self-assembled nano-scale patterns whose electronic and optical properties are greatly different from those of bulk materials and find broad practical application. In this work we present the study results of the composite structures based on nanosized silver oxide inclusions in HgCdTe semiconductor matrix. (111) Hg1-xCdxTe (? ~ 0.223) layers were implanted with the silver ions (140 keV and 4.8x10^13 cm^-2) and the surface morphology of obtained structures was studied. Modification was performed using the method of oblique-incidence (? = 30°, 45°) ion bombardment. It should be noted that the implantation of the HgCdTe epilayers with Ag ions at the oblique-incidence geometry (45°) gives rise to the metal-oxide nanophase (cubic Ag2O) precipitation in the subsurface (< 100 nm) region of the host material. The methods of low-temperature photoluminescence, Raman, and surface photovoltage spectroscopy techniques were used for the sample?s investigation. The structural properties of HgCdTe-based structure were analyzed using double and triple crystal X-ray diffraction to monitor the disorder and strain of the implanted region as a function of processing conditions. We consider the ion-synthesized nanocomposite structure Ag2O/HgCdTe as a candidate for multispectral (IR and sub-THz) detection system and present a new mechanism for sub-THz radiation detection.

Resume : Technologically-modified Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics are widely used as one of the most perspective materials for application as negative temperature coefficient thermistors, precise temperature sensors, in-rush current limiters, etc. Typically, structural properties of such materials re studied using different traditional method of structural characterizations. Our previous investigations have shown that the quantity of the additional defect-related phase and its distribution in bulk and on the surface of ceramics are influenced by temperature-time sintering regimes. Also, we used positron annihilation lifetime spectroscopy to study of free volumes defects in temperature-sensitive spinel ceramics. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy within two-component fitting procedures. In addition, NiO phase results in transformation of free-volume defect-related places in the inner structure of ceramics. To study free-volume defects formed by NiO and nanopores in Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics two and three-component fitting procedures and using positron-positronium trapping algorithm was used this work.

Resume : In this work microstructure and inner free-volume defects in undoped and Ca-doped BaTiO3 ceramics were studied using combined methods. Undoped BaTiO3 ceramics and doped with 5, 10 and 15 mol% of Ca were sintered at 1250 oC. The positron annihilation lifetime measurements were performed with an ORTEC spectrometer using 22Na source placed between two sandwiched ceramic samples. The obtained data were treated with LT computer program, the best results were obtained to two-component fitting procedures. In respect to SEM investigations, typical ceramic samples show grain-porous microstructure and assemblies of fractional grains. By accepting two-state positron trapping model, for polycrystalline ceramic materials the short lifetime of 10.15 ns is generally attributed to the free annihilation of positrons. This value also correlated with theoretically calculated free positron lifetime in BaTiO3. The obtained value is closed to BaTiO3 single crystal. The second lifetime 2 arises from annihilation of positrons at defect sites. The presently observed values of 20.32 ns which is believed to come from the annihilation of positrons at vacancy complexes formed between the oxygen vacancies and the metal ion vacancies. It is shown that 2 increases with rise of Ca amount in BaTiO3 ceramics from 5 to 10 mol% and decreases in samples with 15 mol% of Ca the intensity I2 decreases from 22 to 16 % and increases to 25 % in samples with 15 mol% of Ca. This indicates that doping of Ca results in increasing of the size of free-volume defects in ceramics and decreasing of their amount. So, process of agglomeration of defects is take place at posing of BaTiO3 ceramics By Ca in amount of 5 and 10 mol%, while future increasing the Ca content to 15 mol% leads to fragmentation of free-volume defects.

Resume : Cerium doped (Lu,Y)2SiO5 single crystal is one of the most prospective scintillating material for new CMS detector currently developing in CERN. Therefore, the improvement luminescence properties of this compound is important. In current presentation we report the results of characterization of cerium doped LYSO single crystals by means of vacuum ultraviolet (VUV) excitation luminescence spectroscopy. The experiments have been carried out on the FINESTLUMI setup of FinEstBeAMS beamline of MAX IV synchrotron. A deeper understanding of the controlling physical mechanisms in the final stages of the stage of conversion of scintillation mechanisms into LYSO was obtained. A detailed study of the excitation spectra makes it possible to explain the mechanism of multiplication of electronic excitations in a LYSO single crystal upon VUV excitation.

Resume : The radiation defects in the set of relevant scintillator crystals (Gd3(Ga,Al)5O12, Y3Al5O12, Tb3Ga3O12, PbWO4, PbF2, (Lu,Y)2SiO5:Ce3+) have been produced by the irradiation of 156 MeV Xe ions to fluences 6.6·1010 of 2·1012 cm−2 at the IC-100 at FLNR JINR (Dubna, Russia). Such irradiation is capable to produce radiation defects similar to those generated by neutrons. The irradiated crystals have been studied by means of VUV optical and luminescence spectroscopy techniques. For these purposes two experimental setups have been utilized: Finestlumi endstation of the FinEstBeAMS beamline of MAX IV synchrotron and new Superlumi endstation at PETRA III storage ring of DESY synchrotron center. It was found the induced radiation defects are responsible for the non-radiative losses during the thermalization of charge carriers, which leads to the strong degradation of the excitation spectra in VUV range. Physical mechanisms of the energy absorption and the generation of electron-hole pairs in the conversion stage as well as energy transfer processes in highly irradiated crystals will be proposed.

Resume : Modern nanomaterials science are required new high-informative characterization instruments sensitive to free volumes in atomic and subatomic scales. One of such probes is positron annihilation lifetime (PAL) spectroscopy. This method can be applied to study atomistic imperfections in different solids. In application to semiconductors, this method allows identification of intrinsic free volumes owing to simple models considering competitive channels of positron trapping, where positrons trap (extended free-volume defects) and pick-off decaying of positron-electron (positronium Ps). But when dealing with nanomaterials possessing nanostructural inhomogeneities, the PAL method seems too ambiguous in view of numerous complications in the adequate interpretation of PAL spectra. In this work, we shall used modified positron-Ps trapping algorithm for analysis of PAL spectra of 80GeS2-20Ga2S3 chalcogenide glasses with different amount of CsCl, in particular, free-volume defect evolution processes caused by nanostructurization, where intrinsic inclusions can affect both positron- and Ps-trapping channels in the overall balance of annihilation events possible in a host matrix. Proposed approach allows description of nanostructurization in terms of substitutional positron-Ps trapping within the same host matrix (80GeS2-20Ga2S3), e.g. the process which occurs as a transformation of o-Ps-sites in a host matrix towards positron-trapping sites in a nanoparticle-modified material:(80GeS2-20Ga2S3)100-x-(CsCl)x, x = 0;5;10;15. By accepting a tightly connected nature of these PAL trapping sites, we can defined conditionally this approach as coupling x3-x2-decomposition algorithm to distinguish it from conventional x3-decomposition procedure, describing the PAL spectra in terms of admixed positron-Ps trapping. The quantitative characteristics of trapping-sites themselves as well as the occurring final interbalance in the PAL components are not too important. Within developed formalism grounded on coupling x3-x2-decomposition procedure, the physical characteristics of nanostructurized media can be presented to estimate interfacial void volumes responsible for positron trapping and characteristic bulk positron lifetimes in CsCl-affected inhomogeneous media.

Resume : The positron annihilation lifetime (PAL) spectroscopy method based on the fact that the unstable positron-electron system (positronium Ps) is repelled from ionic cores of atoms and tends to location in open pores. In the case of oxide water-immersed ceramics, two channels of PAL should be considered – the positron trapping and o-Ps decaying [1]. In general, these processes are independent ones. However, if trapping sites will appear in a vicinity of grain boundaries on defects neighboring with nanopores, they can become mutually interconnected resulting in a significant complication of the measured PAL spectra. In addition, adsorbed water influences on process near grain boundaries and in nanopores in the MgO-Al2O3 ceramics. To clarify this feature, we shall study the PAL characteristics of modified MgO-Al2O3 ceramics affected to water sorption treatment enhancing o-Ps decaying over positron trapping modes using positron-positronium trapping algorithm. To apply positron-positronium trapping algorithm it was shown that the chemical-adsorbed water vapor and defects modifies structural defects located at the grain boundaries in a vicinity of nanopores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying.

Resume : Nanocomposites formed by the addition of nanosized filling elements into dielectric (often polymer) matrix are known to have extraordinary mechanical, thermal and electrical properties [1]. Among such nanocomposites of significant interest are PEDOT:PSS polymer matrices reinforced with carbon nanotubes which show great potential for sensor and other applications [2]. This particular polymer is one of the most studied and a lot of works have contributed to better understanding of PEDOT/PSS tailorable properties. In this of work we experimentally analyze structural features and electrical behavior of PEDOT:PSS polymer layers with inclusions of high-purity single-walled (SWCNTs) or multi-walled carbon nanotubes (MWСNTs) before and after irradiation. All investigated samples show lowest impedance (highest conductivity) at room temperature and electrical conductivity decrease upon cooling. General trend is that Re(Z) slightly increases with frequency from 1 kHz to up to some threshold frequency and then drops rapidly. This threshold frequency for pure PEDOT:PSS and PEDOT:PSS/SWCNTs samples is about 100 kHz and is somewhat lower for composite layers with MWCNTs. Most notable temperature effect on the real part of the impedance of fabricated polymer/CNTs composite layers is that Re (Z) increases drastically starting from certain temperature, which is different for samples with different composition. For pure polymer this occurs already at 80…90 K and below 60 K Re (Z) is almost out of the measurable range. For layers reinforced with SWCNTs, increase of impedance is more gradual and even more so for MWCNTs-reinforced composites. In the latter case, reliable measurements can be performed even at temperatures as low as 40K. In samples with incorporated CNTs the conditions for residual water storage are potentially different due to structural changes introduced by specific nanofiller, so that time needed for complete water removal is different and the process is eventually finished at different temperature. This assumption is further supported by the fact that samples with MWCNTs show slower growth of real impedance with decreasing temperature and generally have higher conductivity at lowest measured temperatures. It has been demonstrated that composites reinforced with Boron, Nitrogen or Carbon elements in the form nanostructures dispersed in a matrix can provide radiation shielding for different range of energies and without the generation of harmful secondary particles. On the other hand, polymers reinforced with carbon nanotubes exhibit electrical response, strongly dependent on the absorbed dosage of radiation. The un-irradiated plate can be conductive or not, depending on the CNT doping level. If the level is above the threshold, the current is flowing across the plate, but that the conductive path can be destroyed by high enough dosage of radiation. Thus, one has a simple circuit breaker that will immediately signal about critical exposure, in case the protection layer can no longer stop the incoming rays. Experimental and theoretical studies of such structures will be discussed.

Resume : The purpose of this work is to study the processes of hydrogenation in lithium-containing ceramics under high-temperature irradiation. Irradiation was carried out with protons with an energy of 1 MeV and fluences of 1015-1017 ion/cm2 at irradiation temperatures of 300-1000 K. The choice of irradiation conditions is due to the possibility of modeling the processes of accumulation of radiation damage in the near-surface layer of Li2TiO3 ceramics, as well as establishing the dependences of changes in structural parameters during temperature heating of samples during irradiation. It has been established that at irradiation fluences of 1015-1016 ion/cm2, the formation of dislocation defects is observed, the density of which has a pronounced dependence on the irradiation temperature. At an irradiation fluence above 5x1016 ion/cm2, an increase in the deformation of the crystal structure is observed, due to swelling processes as a result of the accumulation of implanted hydrogen in the structure of the near-surface layer. In this case, an increase in the irradiation temperature leads to a decrease in the swelling value, which is due to the accelerated migration of implanted hydrogen in the near-surface layer and its release through the existing pores. The results of mechanical tests showed that the swelling of the crystal structure and its deformation leads to embrittlement and a partial decrease in the strength of the near-surface layer. The obtained research results will further allow us to evaluate the resistance of lithium ceramics to the processes of hydrogenation and destruction as a result of the formation of gas-filled cavities in the structure of the near-surface layer.

Resume : : The article considers the effect of MoO3 and SiO additives in telluride glasses on the shielding characteristics and protection of electronic microcircuits operated under conditions of increased radiation background or cosmic radiation. The choice of MoO3 and SiO dopants is due to their properties, including insulating characteristics, which make it possible to avoid breakdown processes caused by radiation damage. The relevance of the study consists in the proposed method of using protective glasses to protect the most important components of electronic circuits from the negative effects of ionizing radiation, which can cause failures or lead to destabilization of the electronics. Evaluation of the shielding efficiency of gamma and electron radiation was carried out using a standard method for determining the ∆U value of microcircuits placed behind the shield and subjected to irradiation with various doses. It has been established that an increase in the content of MoO3 and SiO in the glass structure leads to an increase in the gamma radiation shielding efficiency up to 90 %, while maintaining the stability of microcircuit performance under prolonged exposure to ionizing radiation. The results obtained allow us to conclude that the use of protective glasses based on TeO2 – WO3 – Bi2O3 – MoO3 – SiO is highly promising for creating local protection of the main components of microcircuits and semiconductor devices operating under conditions of increased background radiation or cosmic radiation.

Resume : Si(111)/Ta(150Å)Fe(t)/Nb(600Å)/Fe(t)/IrMn(60Å)/Ta(50Å) spin valves, with the thickness t of the Fe layer varying in the range from 3 - 150 Å, were produced by sputtering deposition, in the presence of an applied magnetic field of 480 Oe to set the unidirectional anisotropy axis, and studied by x-ray diffraction (XRD), magnetization measurements and ferromagnetic resonance (FMR). The FMR experiments were performed at X-Band (9.7 GHz) microwave frequency using a Bruker EleXsys E-500 electron magnetic resonance spectrometer. At room temperature, for the parallel geometry of the applied magnetic field, only the uniform (acoustic) resonance mode is excited by the microwave field and the planar angular dependence of the resonance field shows the well-known behavior of the exchange bias effect. At 4.5 K the FMR experiments do not show the uniform resonance mode observed at room temperature. This behavior may be due to a large anisotropy field at low temperatures, sufficient to allow the resonance of the sample even without an applied magnetic field, but a spatial modulation of the ferromagnetic order due to a modification of the RKKY-interaction between the Fe layers, due to the superconducting state of the Nb layers, cannot be disregarded. [1] T. Mühge et al. Physica C 296, 325 (1998). [2] I. L. Castro et al. J. Appl. Phys. 113, 203903 (2013)

Resume : This work is devoted to the study of the radiation damage kinetics and subsequent embrittlement of the near-surface layer of SiC ceramics subjected to irradiation with low-energy ?? ions. Interest in these types of ceramics is due to their great prospects for use as structural materials for nuclear power, as well as for use in the creation of protective structures for long-term storage of spent nuclear fuel. During the study, the dependences of changes in the structural, mechanical, strength, and morphological characteristics of SiC ceramics depending on irradiation fluence were obtained. It has been established that the greatest changes in the strength properties are associated with the dominance of the crystal lattice swelling effect in the structure due to an increase in the concentration of implanted helium, and its further agglomeration with the formation of vacancy complexes of the He-V type. A model for changing the structural properties of ceramics irradiated with low-energy ?? ions based on the change in the contributions of the dislocation density concentration, anisotropic distortion of the crystal lattice, and the effect of swelling as a result of implantation is proposed.

Resume : Already about 60 years ago, Levi and Dienes performed first studies of radiation damage in Al2O3 crystals caused by fast neutrons, and almost fifty years ago, Compton and Arnold measured the threshold energy to displace atoms by incident energetic electrons. At the Second International Conference on Radiation Effects in Insulators (Albuquerque, 1983), J.H. Crawford summarized in his report the work done by that time and discussed what we still did not know at all or not enough [1]. In particular, he highlighted how scanty was our knowledge of interstitial defects. Since then, many attractive ideas have been suggested, and many precise experiments have been carried out. It is impossible to list all or even the most interesting and important of them in a single presentation (see, e.g., [2,3]). Therefore, in the present talk we will try to summarize only key results related to simple electron centers (F, F+ and their dimers, colloids) with a special attention to interstitial defects: their electronic structure, role and manifestations in the processes of thermal annealing of the F-type centers in Al2O3 [4] and several other ionic oxides, such as MgO, MgAl2O4, ZnO, BeO and Y3Al5O12. We will also discuss the possible solution of the second puzzle mentioned by Crawford, namely why and how the so-called hole V-type centers could be formed under optical transformation of the electron centers F+→ F in α-Al2O3 and MgO single crystals. Finally, we will discuss the process of the intrinsic high-temperature migration/transformation of F centers in ionic oxides and demonstrate how F-type dimer centers and metallic colloids could be formed as a part of the process [5]. [1] J.H. Crawford, Nucl. Instrum. Meth. B 1 (1984) 159-165. [2] E.A. Kotomin and A.I. Popov, Nucl. Instrum. Meth. B 141 (1998) 1-15. [3] S.J. Zinkle and C. Kinoshita, J. Nucl. Mat. 251 (1997) 200-217. [4] A.I. Popov, A. Lushchik, et al. Nucl. Instrum. Meth. B 433 (2018) 93-97. [5] V.N. Kuzovkov, E.A. Kotomin, and A.I. Popov, J. Nucl. Mater., 2018, 502. 295-300.

Resume : The results of the thermostimulated luminescence measurements, performed between 300 and 720°K of the stored energy in Y3Al5O12 and Gd3Ga5O12 single crystals, irradiated by fast neutrons with fluences of 2.1 x 10^17 or 2.18 x 10^19 n/cm2 or 1.8 MeV electrons, or thermochemically reduced will be reported and compared with previously published data. A clear pronounced dose effect was found and analyzed. In particular, four TSL peaks were observed in Y3Al5O12 samples subjected 2.18 x 10^19 n/cm2, while in sample subjected to 2.16 x 10^17 , only three TSL peaks were detected. A comprehensive kinetic analysis of the glow peaks in Y3Al5O12 is performed. As usual, each TSL peak is characterized by the appropriate activation energies, in which both crystals are 0.8 ? 1.3 eV. The obtained values are compared with the appropriate activation energies for F-type center annealing. Furthermore, we have also performed a comparative analysis of the photoluminescence properties of a series of neutron-irradiated and non-irradiated Y3Al5O12 single crystals. Finally, a laser-induced F --> F+ color center photoconversion was examined and characterized as well.

Resume : Aluminium Nitride (AlN) nanostructures ? nanotubes, nanowires and nanoparticles have been successfully synthesised by using a high temperature, highly non-equilibrium DC arc plasma method and investigated with different methods, including XANES, FTIR, neutron powder diffraction and inelastic neutron scattering [1-3]. Here we report the results of the cathodoluminescence studies of the AlN nanotubes and nanoparticles, which have been measured between 80 K and room temperature (RT) under electron irradition with 10 keV energy. Low-temperature CL spectra of nanostructured AlN have been compared with those of the commercially available AlN powder. The significant difference between emission spectra of the three investigated samples has been established. Commercial AlN has been found to emit a band peaked at 3.47 eV which is commonly ascribed to oxygen impurities. Emission of the AlN nanoparticles is centered around 3.66 eV while CL spectrum of AlN nanotubes show complex character with at least three peaks at 2.2, 3.0 and 3.5 eV in the photon energy range of 1.8 ? 3.8 eV. CL intensity of the nanostructured samples has been found to decrease significantly at RT, most probably due to a combination of non-irradiative relaxations at the surface, electron-phonon interactions and the reabsorption of the emitted light. CL of AlN-nanotube/CsI-scintillator composites has been also studied. Energy transfer via luminescence emission from CsI scintillator to AlN nanotube is demonstrated. Luminescence properties AlN nanotube/polymer composites were also studied and compared with those obtained for AlN nanotubes and nanoparticles. References 1. Balasubramanian C., et al. Journal of Physics: Condensed Matter 18 (2006): S2095. 2. Bellucci S., Popov A.I. et al. Radiation Measurements 42 (2007): 708-711. 3. Bellucci S., Balasubramanian C., Ivanov A., Popov A., Schober H. J. Neutron Research, 14(2006); 287-291.

Resume : The self-trapped hole polarons (called also Vk centres) where a hole is shared by two nearest halogens, X2-) are very common color centers created in alkali halides and alkaline-earth halides under all kinds of irradiation (UV light, electrons, gamma rays, neutrons, heavy swift ions). The hole polarons start to migrate and recombine above certain critical temperatures. Their thermally induced decay has been observed by different experimental techniques (optical absorption, EPR, thermostimilated luminescence and etc) in almost all alkali halides, as well as in some halides and more complex halides, such as perovskite halides, ammonium halides, halide sodalites etc [1] . In this report, we review and analyse the self-trapped hole center migration temperatures for a series of alkali fluorides (LiF, NaF, KF, RbF, CsF), alkaline-earth fluorides (CaF2, SrF2, BaF2), MgF2, CdF2 and some fluoroperovskites such as KMgF3, RbMgF3, BaLiF3 as a function of halogen-halogen distance in a regular crystalline lattice as well as of halogen-halogen distance in isolated molecular ions. We will discuss similar situation in some other fluorides, such as CeF3 or PbF2, where Vk have not been observed. [1] A.I. Popov, E.A. Kotomin, J. Maier. Solid State Ionics, 302 (2017) 3-6.

Resume : Grain boundaries (GBs) play important role for understanding of microstructural evolution for nuclear materials, such as Fe-Cr based low activation ferritic/martensitic (RAFM) steels. Moreover, they have considerable influence on RAFM properties under neutron irradiation in future fusion plants. Subsequently therefore, it is necessary to investigate effect of radiation-induced defects on the GBs in order to a deeper understanding of the radiation damage. In the present study, we investigated characteristics of bcc-Fe and Fe-Cr based tilt GBs interacting with point defects (PDs) such as vacancy, and interstitial atoms (He impurities). Several tilt GBs with the rotation axis along [100] and [110] directions were modelled with He impurities, vacancy in Fe-Cr. Molecular dynamics (MD) simulations using the interatomic Fe-Cr-He embedded atom model potential were conducted, for twelve GBs, to investigate GBs energies, Cr and He segregation energies, and the weakening effect of He impurity as a function of Cr and He concentrations. Furthermore, spin-polarized density functional theory (DFT) calculations focused at two GBs, ?3(111) and ?5(210), allowed to deeper insights into GBs properties, especially those which are related to magnetic moments and chemical bondings. Systematic calculations of random Fe-Cr alloys, with Cr content ranging 0-20% (atomic %) in systems with and without GB, allowed us to divide the segregation energy into chemical part and elastic part. By analysing elastic dipole tensors of PDs a simple model has been proposed for evaluating segregation energy as a function of stessses caused by GBs and PDs.

Resume : In this work, we study phonon structure in thin-film titanium disulfide (TiS2) [1], which is a representative example among transition metal dichalcogenides (TMDCs) [2]. In particular, TiS2 is a widely studied compound due to its numerous applications, such as lithium?ion batteries [3], solar cells [4], and thermoelectric devices [5]. The last depicted application requires thermal and electrical conductivity tuning to provide the best possible devices? thermodynamical efficiency. Therefore, it is necessary to understand well the internal structure, phonon propagation properties, and phonon-phonon interactions caused by the anharmonicity of interatomic potentials in TiS2. However, the phonon structure in 1T-TiS2 crystals is still poorly understood. The most mysterious experimental observation involves Raman spectra measured in realistic TiS2 samples [1]. Although state-of-the-art theoretical studies predict the existence of two Raman-active phonon modes ? ?in-plane? Eg (~233 cm?1 at room temperature) and ?out-of-plane? A1g (~328 cm?1), an additional third band (called ?Sh?) is observed in the experiment at ~372 cm?1, regardless of the film thickness [6]. Surprisingly, the frequency of the extra Raman band exhibits a positive temperature coefficient ? opposite to other phonon modes in TiS2 and other TMDCs. The origin of the additional Raman band is still under debate. However, hypotheses such as local stiffening caused by excess interlayer titanium atoms and A2u phonon appearance have been reported. Here, we study the impact of defect formation in 1T-TiS2 crystals on their phonon structure using ab-initio DFT simulation. The following potential defects are considered (each with a concentration of 2-3%): excess titanium atoms, titanium Frenkel defects, titanium vacancies, substitution of titanium with sulfur, excess sulfur atoms, sulfur vacancies, and substitution of sulfur with oxygen or nitrogen. We record a splitting of phonon modes and the corresponding Raman intensities in a few defected systems, potentially explaining the experimental extra Sh band. We also study, for the first time, the anharmonicity of the phonon modes Eg and A1g in pristine TiS2 and the Sh in the defected systems - attempting to explain the experimental positive temperature trend. [1] A. Du?y?ska et al., Journal of Raman Spectroscopy 50, 1114 (2019). [2] S. Manzeli et al., Nature Rev. Materials 2, 17033 (2017). [3] J. Y. Kim et al., Energy Storage Materials 41, 289 (2021). [4] N. Alias et al., ACS Applied Materials & Interfaces 13, 3051 (2021). [5] S. Yin et al., Journal of the Ceramic Society of Japan 130, 211 (2022). [6] P. C. Sherrell et al., ACS Omega 3, 8655 (2018). [7] X. F. Tang et al., Chinese Physics B 31, 037103 (2022).

Resume : The current development of novel materials for nowadays energy production and industrial applications at extreme operating environments requires superior thermo-mechanical properties of the candidate materials [1,2]. In this work, Machine Learning (ML) based Molecular Dynamics (MD) simulations are performed to investigate the mechanical properties of irradiated polycrystalline BCC metals like: Mo and Fe being used in nuclear energy plants [1-3]. We analyze the dynamical deformation processes connected to dislocations nucleation and their evolution at 0.05 and 0.1 dpa irradiation dose and considering 2-grain cases as ?3[110]/(111) for Mo and Fe; that are obtained by performing thousands of overlap collision cascades at room temperature. The sample with grains are created by dividing the simulation box on the y-direction by two equally parts with 110 and 111 orientations. The numerical cell is then energy minimized using the conjugate gradient method and the global minimum grain boundary energy is found by a series of rigid translation and atom removal. All the obtained configurations are stored and only the sample with the lowest energy is chosen. Thus, we report dislocation density and tracking the nucleation of dislocation networks with the corresponding surface morphology by performing ML-MD simulations of spherical nanoindentation test and shear stress of irradiated samples at different dpa (displacement per atom) doses; which can be compared to experimental observations by TEM and SEM (Fig 1) [1,4]. Finally, we discuss the effects on the mechanical properties due to irradiation and grain boundary by computing the hardness and Young?s modulus as a function of indentation depth focusing in the observed mechanical annealing process. References: [1] F. Granberg et al. Phys. Rev. Lett. 116, 135504 (2016) [2] F. J. Dominguez Gutierrez et al. Mat. Sci. Eng. A, 826, 141912 (2021). [3] E. Levo et al. J. Nucl. Materials 490, 323 (2017) [4] J. Byggmästar et al. Phys. Rev. B 104, 104101 (2021)

Resume : Emerging memory classes such as oxide-based resistive, ferroelectric and phase-change random-access memory (OxRAM, FeRAM, PCRAM) are facing more and more interest in the field of memory technology and are discussed as possible successors of flash technology for highly-scaled memory cells. Thereby, radiation hardness is of particular interest, enabling applications in harsh radiation environments, e.g. space applications. Consequently, there is a scientific interest in the failure mechanisms of the stored memory induced by ion exposure, to better understand the physical background for future improvements. Additionally, investigations can be helpful to obtain a better understanding of the basic mechanisms of the different emerging memories in general. The information storage mechanisms of resistive random-access memory devices are mainly based on the movement of ions, the crystalline structure and, in contrast to flash technology, not directly on charge. In ferroelectric and phase-change memories, where the information storage mechanisms are strongly connected to the crystalline structure (including a missing long-range order) of the active layer, a possibly induced phase change by ionizing irradiation has to be considered. Therefore, we present extensive structural investigations by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) on a macroscopic and microscopic scale and correlate these results with the electrical device behavior before and after 1.635 GeV Au ion irradiation with different ion fluences. We compare the effects on properties of the different emerging memory classes: Phase Change Memory (PCM) based on GST (germanium-antimony-tellurium) and ferroelectric random-access memory (FeRAM) as well as OxRAM based on HfOx. The study reveals that the initial crystallinity, composition and microstructure of the memory materials have a crucial influence on the interaction of heavy ions with the particular material. These results clarify ion-induced failure mechanisms on a macro- and microscopic scale, especially related to oxygen-deficiency in HfOx. They also separate the effect of irradiation on the electronic circuit with its transistors as compared to the HfOx-based memory cell itself. Furthermore, we report an ion-induced ferroelectric to non-ferroelectic phase transition in HfOx-based ferroelectric devices.

Resume : This work presents the results of an experimental-theoretical analysis of radiation effects in Si3N4 ceramics with different structural responses to the high-energy heavy ion impact. Depth-resolved Raman piezo spectroscopy was used to study residual mechanical stress profiles in polycrystalline silicon nitride irradiated with 710 MeV bismuth ions to fluences of 1×1012, 2×1012, and 1×1013 cm-2. It was found that stress fields of opposite signs are formed in the irradiated Si3N4 layer, separated by a buffer zone located at a depth coinciding with the thickness of the sample layer, amorphized at high ion fluences due to multiple overlapping of track regions [1]. By a multiscale modeling is applied to investigate structural changes caused by impacts of swift heavy ions in crystalline silicon nitride matrices. The approach combines the Monte Carlo code TREKIS describing the excitation kinetics of the electronic and atomic subsystems and a classical molecular dynamic tracing subsequent relaxation of lattice atoms. Ion impacts in crystalline Si3N4 result in formation of a cylindrical amorphous region of a reduced material density, surrounded by a shell with an increased density. The track diameter inside a nanosized inclusion in crystalline or amorphous matrices has been found to be smaller than in the surrounding materials, which can be explained by a heat confinement by the grain boundaries. [1] Zhumazhanova, A.; Mutali, A.; Ibrayeva, A.; Skuratov, V.; Dauletbekova, A.; Korneeva, E.; Akilbekov, A.; Zdorovets, M. Raman Study of Polycrystalline Si3N4 Irradiated with Swift Heavy Ions. Crystals 2021, Volume 11, pp. 1313

Resume : We computed the atomic displacement magnitudes of the closest neighbouring atoms surrounding the (001) surface F-center in ABO3 perovskites [1,2]. They are considerably larger than the respective atomic displacement magnitudes of the closest neighbouring atoms surrounding the bulk F-center [1,2]. In the ABO3 perovskite matrixes, the electron charge is considerably better localized inside the bulk oxygen vacancy than inside the (001) surface oxygen vacancy. The formation energy of the oxygen vacancy on the (001) surface always is smaller than in the bulk. This microscopic energy difference stimulates the oxygen vacancy segregation from the perovskite bulk to their (001) surfaces. The ABO3 perovskite (001) surface F-center induced defect level is located closer to the (001) surface conduction band bottom than the bulk F-center induced defect level. Just opposite, the BaF2, CaF2 and SrF2 bulk and surface F-center charge is almost perfectly localized inside the fluorine vacancy [3]. The atomic displacement magnitudes of nearest atoms around the bulk and surface F-center in BaF2, CaF2 and SrF2 matrixes are very small in comparison to the case of ABO3 perovskites [1-3]. References: [1] R.I. Eglitis, J. Purans, A.I. Popov and R. Jia, Symmetry 13, 1920 (2021) [2] R.I. Eglitis and S. Piskunov, Comput. Condens. Matter 7, 1-6 (2016) [3] H. Shi, L. Chang, R. Jia and R.I. Eglitis, J. Phys. Chem. C 116, 4832-4839 (2021).

Resume : This work reports the variationally-based predictions of the lowest excited state in diamond an related materials in the unrelaxed (optical) and structurally relaxed (thermal) configurations, from direct Δ-SCF calculations based on B3LYP, PBE0, HSE06 and GGA functionals. For the B3LYP functional, which overall performs best, the energy of the optical state in diamond, 7.27 eV, is within the observed range of (7.2 - 7.4) eV. It is predicted to be insulating with indirect band gaps of (5.6 - 5.8) eV, leading to an estimate of 12.9 eV for the (Γ25՛ → X4) energy which compares with observed values of (12.4 - 12.6) eV. The thermally relaxed state is predicted to be similarly excitonic, with comparable band gaps and atomic charges. Calculations of the ground and excited state relaxations lead to a Stokes’ shift of 0.47 eV and predicted Γ-point luminescence energy of 6.89 eV. Assuming a similar shift at the band edge, an estimate of 5.29 eV is predicted for the luminescence energy, which compares with the observed value of 5.27 eV. Results on silicon and germanium will be also presented. Similar calculations of the lowest energy bi- and tri-excitons predict these to be bound states in both optical and thermal configurations and plausible precursors to exciton condensation. Estimates of bi- and triexciton luminescence energies predict red shifts with respect to the single exciton line which are compared to the recently reported values.

Resume : This seminar presents a brief summary of our research in boron related materials from boron nitride (BN). BN nanomaterials including nanotubes, nanosheets, nanowires and nanorods will be introduced from synthesis to properties and various applications. BN nanosheets (2D h-BN) will be presented in details. BN nanosheet also known as white graphene, has a similar honeycomb structure to graphene, with alternating boron and nitrogen atoms consisting of strong sp2 covalent in-plane bonding and weak van der Waal forces between layers. h-BN has unique properties; it is a lubricant due to its layered structure. BN is an electrical insulator (with a bandgap of approximately 5.9eV) at the same thermally conductive and also has high mechanical strength, large thermal conductivity and low dielectric constant. We will demonstrate our research experience and extertise in developing new target materials for fusion reaction in different structures and forms from laboratory scale to commercialisation.

Resume : A possibility of band gap engineering (BGE) in RAlO3 (R = Y, La, Gd, Yb, Lu) perovskites in the context of trap depths of intrinsic point defects was investigated comprehensively using experimental and theoretical approaches. Optical band gap of the materials, Eg was determined via both the absorption measurements in VUV spectral range and the spectra of recombination luminescence excitation by synchrotron radiation. The experimentally observed effect of Eg reduction from ~8.5 to ~5.5 eV in RAlO3 perovskites with increasing R3+ ionic radius was confirmed by the DFT electronic structure calculations performed for RMO3 crystals (R = Lu, Y, La; M = Al, Ga, In). The possibility of BGE was also proved by the analysis of thermally stimulated luminescence (TSL) measured above room temperature for the far-red emitting (Y/Gd/La)AlO3:Mn4+ phosphors that confirmed decreasing of the trap depths in the cation sequence Y ? Gd ? La. Calculations of the trap depths performed within the super cell approach for a number of intrinsic point defects and their complexes allowed to recognize specific trapping centers that tentatively can be responsible for the observed TSL. In particular, the electron traps of 1.33 and 1.43 eV (in YAlO3) were considered to be formed by the energy level of oxygen vacancy V(O) with different arrangement of neighboring Y(Al) and V(Y), while shallower electron traps of 0.9?1.0 eV were related to the energy level of Y(Al) antisite complexes with neighboring V(O) or V(O)+V(Y). The effect of lowering of electron trap depths in RAlO3 was demonstrated for the V(O)-related level of the Y(Al)+V(O)+V(Y) complex defect for the particular case of La substituting Y.

Resume : Nanostructuring approaches have remained most effective in reducing the lattice thermal conductivity closer to the amorphous limit in a polycrystal. In this work, we present the implication of nanostructuring approaches on thermoelectric transport properties of higher manganese silicides (HMS), a promising low-cost intermetallic that exhibits remarkably high-power factors and thermal stability at higher temperatures. The nanostructured alloys were synthesized by spark plasma sintering of powder obtained employing ball milling or melt-spinning at high heating rates. The characteristic evolution of defects within the microstructure of HMS alloy was presented and correlated with the thermal and electrical transport properties. A drastic reduction in the lattice thermal conductivity and suppressed MnSi striation result in a higher thermoelectric figure of merit (zT) for melt-spun alloys than their ball-milled counterpart. The study reveals the critical role of defects on physical transport properties and their evolution in nanostructured HMS alloys to provide fundamental insights into the defect-induced effects for similar transition metal silicide-based alloys.

Resume : We describe the magnetization of nanosized SFMO particles with a narrow size distribution around ca. 70 nm fabricated by the citrate-gel technique. The single-phase composition and superstructure ordering degree were proved by X-ray diffraction, the superparamagnetic behaviour by magnetization measurements using zero-field cooled and field-cooled protocols, as well as by electron magnetic resonance. Different contributions to the magnetic anisotropy constant and the temperature dependence of the magnetocrystalline anisotropy are discussed.

Resume : Magneto-ionics deals with a class of spintronic materials where the external electrical field induces ion migration and leads to a raise of magnetization as a consequence of magnetic species local segregations or increased magnetic interactions between them. Since this ion transport is activated by the voltage actuation, no large electrical currents are required and heat dissipation processes are mostly negligible. Moreover, by simply reversing the direction of the voltage bias, the generated ferromagnetic state is brought back to its original magnetic configuration, which realizes the magnetic switch concept. Using magnetometry and electron microscopy supported with positron annihilation spectroscopy techniques, oxides (Co3O4) and different nitrides (CoN and FeN) have been investigated, which are promising candidates for fast magneto-ionic switching. Positron annihilation spectroscopy provides a unique probe of open volume defects, e.g. dislocations, vacancies within crystal and at interfaces, vacancy agglomerations at grain boundaries, macro- and mesopores and it was successfully utilized to study the defect nanostructure here. We first present electrolyte-gated and defect-mediated oxygen migration in single-layer, paramagnetic Co3O4 at room temperature, which allows voltage-controlled ON-OFF magnetic switching via internal reduction/oxidation processes [1]. Here, the bias-induced motion of oxygen ions is caused by dominant vacancy clusters, with oxygen motion promoted at grain boundaries and assisted by the development of O-rich diffusion channels and Co-rich grain inner regions. In the case of nitrides, on the other hand, nitrogen transport is found to occur uniformly throughout the film, creating a plane-wave-like migration front, without assistance of diffusion channels [2,3]. Using positrons as a probe, we will show that the initial average open volume is larger compared to oxides, which likely governs the migration process and allows, moreover, for enhanced switching rates and cyclability as well as lower threshold voltages. [1] A. Quintana, E. Menéndez, M. O. Liedke et al., ACS Nano, Vol. 12, p. 10291 (2018); [2] J. de Rojas, A. Quintana, A. Lopeandía et al., Nature Communications, Vol. 11, p. 5871 (2020); [3] J. de Rojas, J. Salguero, F. Ibrahim et al. ACS Appl. Mater. Interfaces Vol. 13, p. 30826 (2021).

Resume : Chemical bath deposition [1] is a low-cost, low-temperature catalyst-free chemical deposition technique that enables to form a broad range of ZnO nanostructure morphologies including nanowires (NWs). The homogeneous and oriented growth of vertically aligned ZnO NWs from a polycrystalline seed layer can be deposited on a wide range of substrates. Despite those very interesting aspects, the bath reactants induce the formation of defects and defect complexes with a low formation energy coming from numerous impurities such as carbon, nitrogen, and hydrogen [2]. On the one hand, interstitial hydrogen in bond-centered sites (HBC) and 3-hydrogen paired zinc vacancy (VZn-3H) are examples of such defect complexes that operate as shallow donors with low formation energies [3] and govern the electrical behaviour of ZnO NWs. On the other hand, the zinc vacancy paired with nitrogen and hydrogen (VZn-NO-H) defect complex that also exhibits a low formation energy acts as a deep acceptor and hence as a compensating defect. By performing an annealing treatment under an oxidizing atmosphere, the hydrogen-related defect complexes follow a series of associative and dissociative processes depending on the temperature of the annealing [4], which enables to promote some purposeful defect complexes in order to improve ZnO NW electrical properties. Oxygen plasma is another efficient treatment that is known to activate the surface of the ZnO NWs and affect the formation and concentration of these defects [5-6]. Although some process parameters were revealed to be efficient to tune surface defects such as oxygen vacancy (VO), data on local plasma parameters such as ion energy near the interaction site is lacking. In this work, those parameters are measured using a retarding field energy analyzer (RFEA) and correlated to the presence of VO and hydrogen-related defects by using X-ray photoelectron spectroscopy, cathodoluminescence, and Raman spectroscopy. A comprehensive diagram relating the impact of the ion energy on the formation of defects and defect complexes is gained, opening some perspective towards the careful tuning of the physical properties of ZnO NWs. [1] L. Vayssieres et al. J. Phys. Chem. B. 105 (17), 3350?3352 (2001). [2] C. Van De Walle. Phys. Rev. Lett. 85 (5), 1012?1015 (2000). [3] J. Villafuerte et al. J. Phys. Chem. C, 124 (30), 16652?16662 (2020). [4] J. Villafuerte et al. Phys. Rev. Mater. 5 (5), 1?15 (2021). [5] H. Jiang et al. R. Soc. Chem. 51 (8), 28928 (2018). [6] D. Park et al. Korean J. Met. Mater. 59 (3), 209?216. (2021)

Resume : The mid-infrared (MIR) spectral range has shown great importance for both fundamental and practical applications such as optical communications, pollutants detection, trace chemical analysis as well as the next-generation imaging devices for remote sensing and medical contrast agents. Most small organic and inorganic molecules have their fundamental absorption features in the wavelength regions from 1.5 μm to 15 μm. Therefore, strong emitting sources in the MIR spectral range will be extremely useful in the construction of lidars allowing remote detection of gases (including hazardous ones), which is important for health and environmental protection, chemical rescue, the mining industry or military applications. Currently, the most effective ways of obtaining radiation in MIR are luminescence phenomena or CO2 laser emission by utilising non-linear-optical effects (SHG, THG). On the other hand, the high spectral transparency range of chalcogenide or halide crystals, glasses or ceramics (from about 400-700 nm to several ten micrometres) is unique and not available for oxygen-containing materials. In addition, these materials with low phonon energies are predestined at matrices for embedding active elements (RE or 3d elements) for long-wave luminescence or for the construction of lasers operating in the mid-infrared range along with limitations regarding embedding of rare earth ions in chalcogenide/halide structures, which is not an easy experimental undertaking. Next, we focus on the influence of the structural properties (composition, complexity and defects, presented in real materials) on the stability, luminescence, optical and nonlinear-optical efficiency of the group of binary, ternary and quaternary halide and chalcogenide crystals, that have found practical applications in IR optoelectronics. Especially above-mentioned defects have shown a significant impact on nonlinear-optical and luminescence properties. Finally, we present an analysis of the available experimental and computational data to establish “structure-property” and “property-property” relations, which should be helpful for searching for new, efficient materials operating in the MIR spectral range.

Resume : Energy and water related problems have attracted strong attention from scientists across the world because of deficient energy and water pollution. Following this line, new strategy depended on preparing nanolayers of Al/Zn and magnetic nanoparticles of cobalt iron oxides nanocomposite in addition to long chains of hydrocarbons of stearic acid to be used as roofs, fillers and pillars; respectively, to design optical-active nanohybrids in sunlight for removing the colored pollutants from water in few minutes. By using long chains of hydrocarbons of stearic acid, X-ray diffraction (XRD) results and TEM images showed expansion of the interlayered spacing from 0.76 nm to 2.02 nm and insertion of magnetic nanoparticles among the nanolayers of Al/Zn. The optical properties and activities showed that the nanohybrid structure based on zinc oxide led to clear reduction of the band gap energy from 3.3 eV to 2.75 eV to be effective in sunlight. Photocatalytic degradation of the dye of acid green 1 confirmed the high activity of the prepared zinc oxide nanohybrids because of a complete removal of the dye after ten minutes in sunlight. Finally, this strategy was effective for producing photo-active nanohybrids for using renewable and non-polluting energy for purifying water.

Resume : As a total amount of freshwater is limited in comparison with the seawater, it is important to consider the effect of chlorine in water?splitting applications due to the fact that Cl is the most abundant ion in seawater. In our theoretical research the real?time time?dependent density functional theory and Ehrenfest dynamics theory are utilized to study the excited?states nonadiabatic molecular dynamics (NAMD) in water splitting processes for deeper understanding of the photocatalytic reactions when the chlorine adatom is present at the rutile TiO2(110)/water interface. Two photoinduced water?splitting pathways related to the chlorine ion are demonstrated with the difference between the charge densities of the excited state and ground state to analyze formation of the photogenerated holes along the reactions. Besides that, the time?dependent relation between the localized Hirshfeld charges and bond?lengths of water molecule are studied to describe the detailed charge transferring behaviors. Our calculations predict that the chlorine at the TiO2 surface with H2O adsorbate could actually trigger the dehydrogenation of water molecule from the thermal effect and photoexcitation. The charge transfer involving the chlorine ion cause the formations of the localized positive charge value on the oxygen to transform water into hydroxyl and hydrogen by photoinduced driving force resulting in the first step of water dissociation.

Resume : All three titanium dioxide TiO2 polymorphs (anatase, rutile, brookite) have antibacterial properties, however, they are largely pronounced for anatase phase. The antibacterial properties of TiO2 can be explained by its nature -- it is a semiconductor with a band gap > 3.2 eV with prominent photocatalytic properties. Many harmful organic compounds can be destroyed by irradiating titanium dioxide with UV or sunlight. To improve photocatalytic properties toward visible light TiO2 can be doped. In this study, we consider TiO2 in its anatase phase. According to the available experimental data TiO2 anatase antibacterial properties can be improved if titania is doped by copper. The TiO2 anatase slab and bulk models with and without Cu dopant have been constructed, and a number of first-principles calculations have been carried out: the bulk phase of TiO2 anatase doped with Cu, as well as the (001) surface of the Cu-doped TiO2 anatase were modeled. Calculations of both Cu-doped TiO2 bulk phase and its surface reactivity were performed using the ab initio computer modelling approaches based on quantum chemistry and density functional theory (DFT) using CRYSTAL17 total energy computer code. Besides, the absorption spectrum was predicted by the GPAW code to understand the difference between Cu-doped TiO2 slab and pristine TiO2 slab. For the Cu-doped anatase (001) surface the energy of inclusion of Cu is evaluated, as well as the adsorption of OH- groups on a pristine and Cu-doped TiO2 surface is calculated. Moreover, based on the proposed models the impact on the band structure of the excited states was calculated for the anatase (001) surface. Gained results allow us to perform the thermodynamic analysis which leads to a deeper understanding of increased surface reactivity toward TiO2 antibacterial properties. This research was funded by the Latvian Scientific Council grant LZP-2021/1-0464.

Resume : The ionic interaction at electrolyte/material interface has a serious impact on the material?s properties encompassing structural integrity and optoelectronic structure. However, it is difficult to discriminate the roles of specific ions at the interface due to the complex interplay between the material?s properties and the electrochemical process. Therefore, in-situ Raman spectroelectrochemistry, a combination of in-situ Raman microspectroscopy with electrochemistry is an intriguing technique that can provide the valuable information about the electrochemical behavior of the layered material in an aqueous medium. There are two major goal of this research, (i) to interrogate the structural and electronic properties of monolayer graphene and related materials at the microscale, (ii) to explore the electrochemical ionic intercalation into multi layered materials for energy storage devices. To demonstrate the structural and electronic properties, the µ-droplet spectroelectrochemistry (µ-SEC) of monolayer graphene in concentrated aqueous electrolytes of different ionic type and ionic strength revealed charge transfer doping with alteration in the structural properties of graphene. The overall shift rate of the G peak of graphene was observed to be similar regardless of the ionic type and ionic strength. The structural properties of functionalized monolayer graphene were also studied by in situ µ-droplet µ-SEC in concentrated aqueous electrolyte. As ion storage is a fundamental mechanism for energy conversion and storage devices, in situ SEC was performed in a home-made classical cell at macroscale to explore the electrochemical ionic intercalation into graphite layered materials during charge/discharge process for dual ion batteries.