Modelling and characterization of novel functional materials for green energy, sensing, and catalysis applications

Resume : Molecular Doping (MD) represents an efficient, low-cost alternative way to dope silicon. MD is based on the use of dopant containing molecules – typically ester molecules - dissolved in mesitylene. The solution forms a layer of molecules over the substrate to be doped through an immersion process in the liquid. After a successive annealing process, the dopant atoms are released from the molecular layer and diffuse inside Si where they are electrically active [Nanomaterials 2021, 11, 1899. https:// doi.org/10.3390/nano11081899]. Both the solute and the solvent contain carbon atoms, which during the annealing are released too, making MD not feasible for some technological applications because C can act as a charge carriers trap. Recently a new MD technique has been proposed for solution-based n-type doping, where the solution components are carbon-free. The technique is based on the use of phosphoric acid as a precursor of the dopant and water as solvent. The acid chosen is smaller than the ester molecules allowing for an improved molecules packing. The data demonstrate concentrations of about 1×1020 cm-3 carriers [Nanomaterials 2021,11, 2006. https://doi.org/10.3390/nano11082006]. In this talk I will present an overview of the recent experimental and theoretical study on MD and on the C free n-type MD, showing also preliminary data on a different molecule providing p-type doping with concentrations as high as 6×1020 cm-3.

Resume : Water-in-salt electrolytes (WiSEs) are high-concentration aqueous electrolyte with a thermodynamic voltage limit of about 3 V.1,2 A representative WiSE comprises a ~20 m aqueous solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. It has been observed that the addition of ionic liquids (ILs) improves the safety of WiSEs.3 In this talk, I shall outline the results of our molecular dynamics (MD) study4 on the structural arrangement in LiTFSI-based WiSE. I shall discuss how the addition of an IL (EmimTFSI) influences the microscopic structure of WiSE.4 Also, what is the influence of further addition of LiTFSI salt on the WiS-IL hybrid electrolyte structure? 1. Suo, L.; Borodin, O.; Gao, T.; Olguin, M.; Ho, J.; Fan, X.; Luo, C.; Wang, C.; Xu, K. Science 2015, 350, 938. 2. Tian, X.; Zhu, Q.; Xu, B. ChemSusChem 2021, 14, 2501. 3. Becker, M.; Rentsch, D.; Reber, D.; Aribia, A.; Battaglia, C.; Kühnel, R.-S. Angew. Chem., Int. Ed. 2021, 60, 14100. 4. Dhattarwal, H. S; Kashyap, H. K. J. Phys. Chem. B 2015, 126, 5291.

Resume : In biological systems, transmembrane proteins and ion channels contribute to most of the communications between cells and their environments. Ion channels either passively allow or actively control the flow of ions, typically Na+, K+, Ca2+, Cl-, and small molecules across the cell membrane. Although protons are not directly involved in neuronal action potential generation and propagation, proton (H+) transport is essential in many natural processes. One of the important examples is oxidative phosphorylation in mitochondria, in which proton gradients serve as a means to translate energy from the oxidation of glucose during the Kerb’s cycle into ATP, the biological energy currency. Other examples include the light-activated H+ pumping by archaeal bacteriorhodopsins, the activation of bioluminescence from H+ dinoflagellates, the bacterial flagellar motor activation, and the activity of antibiotic Gramicidin, etc. Artificial electronic platforms, which use electronic currents to carry charges, have an intrinsic difficulty connecting to the biological systems that rely primarily on ionic currents. We have developed an air-stable bio-protonic device to mimic the proton channel structure present in the cell membrane for studying proton transport through the ion channels. We fabricated a two-terminal device with the gelatin-SLB-gelatin structure to mimic the proton channel structure in the cell membrane. The used contacts materials are Al and Cu. Gelatin absorbs water molecules and creates protons (H+) through self-ionization. We have measured the current flow with increasing humidity conditions. The number of protons increases with the increase in relative humidity. As the number of protons increases, that will increase the current of the bio-protonic device. The I-V curves show H+ flow through the ion channels increases as we increase the relative humidity around the device.

Resume : Green and sustainable production of hydrogen by water electrolysers is expected as one of the most promising ways for the industrial decarbonisation and to satisfy the ever-growing demand of renewable energy production and storage. Hydrogen evolution reaction in alkaline electrolyte is preferable as an industrial point of view, as it does not require the more expensive proton exchange membranes required in an acid environment. Unfortunately, hydrogen evolution reaction in alkaline electrolyte is still challenging, due to its slow kinetic. In this work we propose new nanoelectrode arrays for high Faradaic efficiency of the electro-sorption reaction of hydrogen in alkaline electrolyte. Platinum or palladium or bimetallic Pt80Pd20 (wt.%) nanoparticles (NPs) were fabricated by nanosecond pulsed laser ablation in aqueous environment. Nanoelectrode arrays were obtained by casting onto graphene paper the water based suspension of NPs. Moreover, this work comparatively describes the effects of 0.7 ?m thin films of perfluoro-sulfonic ionomer surrounding the NPs. The thin film of ionomer acts as inexpensive membrane between metal electro-catalyst and the electrolyte. Thin film of ionomer produces a significant modification in the material morphology, as well as in the nanoparticles dispersion and electrochemical performance. The NPs-GP systems have been characterized by field emission scanning electron microscopy, Rutherford backscattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge cycles. State of the art competitive Faradaic efficiency up to 86.6% and hydrogen storage capacity up to 6 wt.% have been obtained by the Pt80Pd20 system.

Resume : In the last decades, the anthropogenic emission of carbon dioxide (CO2), one of the gases mainly responsible for greenhouse effects, has progressively increased to a level that has raised the worries of the international community due to its catastrophic environmental impact [1]. The scientific communities are focusing their attention on this problematic scenario, and new technologies for CO2 capture and reuse are currently at an explorative research level [2]. The electrochemical CO2 reduction is a promising strategy towards carbon recycling by CO2 dissolution in electrolytic solution, in which CO2 adsorbs and gets reduced at the cathode under the application of an external voltage [3]. However, several challenges must be overcome such as poor selectivity, considerable reaction barriers, sluggish kinetics and the high thermodynamic stability of the CO2 molecule. Tin dioxide (SnO2) is an efficient catalyst for the CO2 reduction reaction (CO2RR) to formic acid (HCOOH), since SnO2 samples typically present higher specific area and roughness. However, the comprehension of the SnO2 surface structure at working electrocatalytic conditions and the nature of catalytic active site is a current matter of debate. Operando Raman spectroscopic characterizations show that the highest selectivity towards HCOOH occurred at potentials where SnO2 should get completely reduced to metallic tin according to Pourbaix analysis [4, 5]. In this study, ab initio calculations have been performed to investigate how the selectivity and activity of SnO2 surfaces towards CO2RR changes at varying surface stoichiometry and increasing reduction degree. The employment of Density Functional Theory (DFT) combined with the theoretical electrochemistry approach [6] has been carried out with the Quantum ESPRESSO (QE) suite [7]. The free energy profiles for CO2RR to chemicals with a single carbon atom (C1), such as formic acid and carbon monoxide, has been compared with the competitive hydrogen evolution reaction (HER) and SnO2 self-reduction processes. The studied mechanisms involve two proton-electron transfers and a single intermediate step. The results reveal that the stoichiometric SnO2 surface is not intrinsically catalytically active at low applied potential and spontaneously loses oxygen species leading to tin rich metallic surfaces. The electrocatalyst becomes selective towards HCOOH product when at least a Sn bilayer is formed at the catalyst surface, while when SnO2 is completely reduced to metal the HER becomes competitive. [1] BP Statistical Review of World Energy, 2018. [2] J. Chem. Technol. Biotechnol. 2014, 89, 334–353. [3] Chem. Soc. Rev. 2013, 42, 6, 2423–2436. [4] K. Wandelt (Ed.), Encyclopedia of Interfacial Chemistry, Surface Science and Electrochemistry, Elsevier, 2018, 217-226. [5] ACS Catal. 2015, 5, 7498–7502. [6] J. Phys. Chem. B, 2004, 108 (46), 17886-17892. [7] J. Phys. Condens. Matter 2009, 21

Resume : WO3-based nanostructures have emerged as one of the most promising candidates for electrocatalytic hydrogen evolution reaction (HER) due to their low cost, electrochemical durability, and high stability in acidic environment. A powder of WO3 nanorods (400 nm long, 5 nm large) is produced by hydrothermal synthesis and thermal annealed. In depth investigation is performed involving transmission elector microscopy and electrochemical analysis with linear sweep voltammetry (LSV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The catalytic activity for hydrogen evolution reaction (HER) is investigated both for as-prepared and annealed WO3 nanorods demonstrating the peculiar HER dependence on crystalline phase, energy gap and oxygen vacancy density. The annealed nanostructures show the best performance in terms of overpotential (173 mV), Tafel slope (140 mV/dec) and turn-over frequency (TOF).

Resume : With the fast depletion of fossil fuels and the increase of the environmental pollution, achieving a sustainable and non-effective energy supply has become crucial in material science field. Electrochemical transformation reactions, including water splitting, are suitable candidates to achieve such a goal, and are now one of the research focuses in renewable energy storage and conversion. Transition metal oxides (TMO) lead to an innovative direction for the development of materials for Hydrogen Evolution Reaction (HER) due to their low cost and excellent stability. Zinc oxide (ZnO), a primary TMO, represents a green choice due to its abundance and biocompatibility. Here we focus on a cost-efficient mass production of nanostars by means of Chemical Bath Deposition (CBD) in aqueous solution. Nanostars appear as 2D self-assembled bunch of crystalline ZnO nanorods (sized 1oo up to 1000 nm), with clear hexagonal symmetry on the assembly plane (building 6-point stars). These novel nanostructures are deeply characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), Photoluminescence spectroscopy (PL) and electrochemical measurements in order to evidence their structural, morphological, optical and electrical properties. Zinc oxide nanostars annealead and as prepared, with and without a Pt nanoparticles decoration, have been evaluated as electrodes for HER in alkaline media. Battiato, S., Bruno, L., Terrasi, A. and Mirabella, S., ACS Applied Energy Materials, 2022. DOI: 10.1021/acsaem.1c03880

Resume : Graphitic carbon nitride (g-C3N4) has been investigated in the past years as an organic photocatalyst for potential application such as remediation (organics degradation), CO2 artificial photosynthesis and for water splitting under light irradiation (Ge et al., 2011). However, its applications are limited due to low utilization of the visible solar energy, low specific surface area and high recombination of photogenerated electron-hole pairs (Wang et al., 2015). Therefore, carbonitride-based nanocomposites with engineered heterojunction and/or doping of g-C3N4 with elements such as B, C, N, O and F have been investigated. Few studies focused on the fluorination of g-C3N4 and with limited doping using mainly hydrothermal methods with F- (via NH4F or analogues) (Wang et al., 2010). Recently, L. Sun et al have explored the F2 (diluted) gas approach to prepare fluorinated g-C3N4 (F/concentration of 7.05 at. %) with drastic structural distortion due to transformation of sp2 hybridization to sp3carbon atoms and enrichment of nitrogen defects (Sun et al., 2021). It results with the improvement of absorption in the visible range and of the photocatalytic performance. In order to extend the fluorination content and to investigate the resulting photocatalytic properties, carbonitride-base materials were fluorinated with pure F2 gas at room temperature. The pristine materials were defective carbonitrides (CN and CNO) prepared from melamine decomposition and a g-C3N4 nanocomposites embedding carbon nanodomains (CCN) derived from the melamine/carboxylic adduct route [(Gashi et al., 2022)]. The resulting highly fluorinated materials (F/C at ratio up to 0.96), after stabilization due to their explosive character, were characterized by a large panel of techniques such as X-Ray Diffraction, FTIR, XPS, diffuse reflectance spectroscopy (DRS), EPR in dark and visible mode and thermogravimetry analysis coupled with mass-spectroscopy (TG-MS). The photocatalytic properties of fluorinated materials were explored by studying the photodegradation kinetics of methyl orange using a Xe lamp. After a blue shift of the dye absorption band in the dark, probably related to an acidification of the media, a significantly higher kinetics of degradation was observed for all fluorinated materials compared to their pristine counterpart. refs: Gashi, A., Parmentier, J., Fioux, P., Marsalek, R., 2022. Tuning the C/N Ratio of C-Rich Graphitic Carbon Nitride (g-C3N4) Materials by the Melamine/Carboxylic Acid Adduct Route. Chem. – Eur. J. n/a, e202103605. Ge, L., Han, C., Liu, J., 2011. Novel visible light-induced g-C3N4/Bi2WO6 composite photocatalysts for efficient degradation of methyl orange. Appl. Catal. B Environ. 108–109, 100–107. Sun, L., Li, Y., Feng, W., 2021. Gas-Phase Fluorination of g-C3N4 for Enhanced Photocatalytic Hydrogen Evolution. Nanomaterials 12, 37. Wang, H., Zhang, X., Xie, J., Zhang, J., Ma, P., Pan, B., Xie, Y., 2015. Structural distortion in graphitic-C 3 N 4 realizing an efficient photoreactivity. Nanoscale 7, 5152–5156. https://doi.org/10.1039/C4NR07645A Wang Y, Di Y, Antonietti M, Li H., Chen X, Wang X, 2010. Excellent Visible-Light Photocatalysis of Fluorinated Polymeric Carbon Nitride Solid. Chem. Mater., 22, 5119–5121

Resume : Most of the current knowledge in enantioselective heterogeneous catalysis refers to the hydrogenation of β-ketoester over Ni-based catalysts and the hydrogenation of α-ketoester on Pd-based systems. These reactions require a crucial step in the catalyst preparation: the adsorption of chiral modifiers onto the metal nanoparticles of the catalyst. In the case of the simplest β-ketoester, methyl acetoacetate (MAA), the hydrogenation results in a racemic mixture R- and S-methyl-3-hydroxybutyrate (MHB) when performed over an unmodified Raney Ni catalyst. The reaction, however, can be directed to a high enantiomeric excess if the Ni surface is modified with chiral α-amino acids or α-hydroxy acids. Even though the process is well-characterized in terms of macroscopic quantities, [1–4] information at molecular scale regarding the influence of chiral modifiers have on adsorption complex of MAA is missing. The understanding of this mechanism would help to achieve and optimize enantioselective behavior of Ni-based catalysts. By combining X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) with Density Functional Theory (DFT) modelling, we have been studying the adsorption complex of reactant MAA and typical chiral modifiers (e.g., alanine, aspartic acid, and tartaric acid) over Ni{111} and Ni{100} surfaces. [5–7] We have found MAA adsorbs on flat surfaces forming deprotonated enolate species with bidentate coordination, and the molecular plane of the adsorbate leans towards one side. These findings suggest that the role of modifiers in the enantioselective hydrogenation of MAA is to stabilize only one of two possible tilt directions, which would lead to the chiral product formation. REFERENCES 1 Y. Izumi, Adv. Catal., 1983, 32, 215–271. 2 M. A. Keane, Langmuir, 1994, 10, 4560–4565. 3 M. A. Keane, Langmuir, 1997, 13, 41–50. 4 T. E. Jones, A. E. Rekatas and C. J. Baddeley, J. Phys. Chem. C, 2007, 111, 5500–5505. 5 J. Ontaneda, R. E. J. Nicklin, A. Cornish, A. Roldan, R. Grau-Crespo and G. Held, J. Phys. Chem. C, 2016, 120, 27490–27499. 6 P. Tsaousis, J. Ontaneda, L. Bignardi, R. A. Bennett, R. Grau-Crespo and G. Held, J. Phys. Chem. C, 2018, 122, 6186–6194. 7 W. Quevedo, J. Ontaneda, A. Large, J. M. Seymour, R. A. Bennett, R. Grau-Crespo and G. Held, Langmuir, 2020, 36, 9399–9411.

Resume : Two urgent, interconnected problems of our times are the exhaust of conventional energy resources and the need to reduce CO2 emissions and move towards a sustainable carbon emission free economy. Environmentally-friendly reduction of CO2 to fuels might serve as a solution to both problems. The use of electrocatalysis or photocatalysis for this reaction will result in green fuel production that could rely on renewable energy sources alone. Up to now, CO2 reduction is at the forefront of catalysis science and is challenged by selectivity and stability issues in the existing catalytic materials and processes. Aiming to design optimized anode materials for electrochemical CO2 reduction to fuels, our quest on electrocatalytic CO2 reduction is twofold; we explore the catalytic properties of two classes of materials, transition metals and perovskite semiconductors, by means of first principles calculations. Our starting point is the best-known catalyst for CO oxidation towards CO2, which is gold nanoparticles. We employ Density Functional Theory (DFT) calculations and the Nudged-Elastic Band (NEB) method to locate reaction transition states and identify minimum-energy paths (MEPs) for chemical reactions on 10-atom gold nanoclusters. We discuss energetics of the reactions and provide insight into the conditions that favor one reaction over the other, thus helping improving catalyst selectivity. We compare to standard CO2 reduction catalysts such as single-crystal Cu. For the second family of materials, metal halide perovskites and their 2D structures and nanostructures have emerged in the last decade as superb semiconducting materials, mainly driven by their high output in photovoltaics. Many side applications have already branched out, with one being their applications in electrocatalytic and photocatalytic fuel cells. Due to their superior optical absorption and their ability to operate for a wide range of bandgaps depending on how one varies their chemical composition, metal halide perovskites can be tailored to the needs of each specific photoelectrocatalytic process. We mainly focus on 2D perovskites with bulky hydrophobic cations between the sheets of corner-connected octahedra. We perform DFT electronic-structure calculations for such systems and comment on their potential uses in environmentally-friendly catalytic processes. This research work was supported by the Hellenic Foundation for Research and Innovation (HFRI) under the project "MULTIGOLD" (HFRI-FM17-1303, KA 10480)

Resume : Interest in the optoelectronic properties of 2D materials has increased due to the discovery of the coupling between spin and valley degrees of freedom in transition metal dichalcogenides (TMDs), which can be manipulated experimentally using a circularly polarized laser. After excitation the newly formed carrier populations move towards the other valley until balance is reached. However, this relaxation process is not entirely understood in the literature, where the relative importance of the electron-electron and electron-phonon interactions is still a subject of debate. Using a fully ab-initio framework [1] we study the influence of the e-p interaction on MoSe2 after its excitation by a laser field. We show how phonons allow carrier relaxation and how the Kerr signal and total magnetization are affected at different temperatures, with the latter exhibiting a non-monotonic behaviour as the temperature increases [2]. By cross-correlating information from electronic transport and spectroscopy, we have shown that it is possible to recover previously inaccessible details of the valley structure[3]. An important conclusion was that long lived spin states probably reside within defects, which pushed us to consider the spectral signatures of different types of point defects in TMDs (figure). We find two main classes based on the presence of in-gap states, and estimate the experimental resolution needed to provide quantification of the defect concentration [4]. In hexagonal BN the negatively charged boron vacancy (V_B-) has been proposed as a qubit candidate for solid state quantum computing. Its photoluminescence dynamics is central to the preparation and readout of qubits, but is not well understood. Here we combine the approaches used above for electron phonon dynamics with those for defects: we use many body quantum dynamics within the Bethe Salpeter equation, and incorporate the coupling with phonons to analyse the deceptively simple photoluminescence spectrum of V_B-[5]. The localization of excitonic states around defects provides a benchmark for scanning probe characterization and sample quality control, and opens vistas for quantum computing platforms based on 2D materials. [1] P de Melo and A. Marini, Phys. Rev. B 93, 155102 (2016) [2] M Ersfeld et al. Nano Letters 19, 4083 (2019) [3] T Sohier et al. arXiv:2207.00452 (2022) [4] P de Melo et al. Adv Quant Mater 4, 2000118 (2021) [5] F Libbi et al. Physical Review Letters 128, 167401 (2022)

Resume : The rapid advancement in technologies and a surge in the global population with the swift Industrialization leads to severe challenges in fulfilling global energy demand. In the last few decades, researchers have been fiercely looking for the development of sustainable energy sources to achieve the goal of carbon neutrality and green energy generation. Among the various approaches to green energy generations, solar and thermoelectric conversions are the most lucrative. In both solar and thermoelectric means of energy generation, there is a direct conversion of sunlight and temperature gradient into useful electricity is possible without involving heavy mechanical instruments or hazardous gases, which makes it more robust and prone to environmental degradation. Despite the several advantages, solar cell and thermoelectric power generation are still suffering from the challenge of low power conversion efficiency and long-term stability. After the discovery of graphene in 2004, a new era of 2D materials are explored. Owing to their unique material properties, the family of two-dimensional materials immersed the research interest and vigorously investigated in recent years as robust and effective alternative materials for various components of solar cells, and thermoelectric power conversion applications. The electronic properties of 2D layered nanomaterials are very sensitive to structural perfection, and geometric symmetry plays a significant role in defining them. Recently, a new class of 2D families emerges called the Janus monolayers. In Janus formations, breaking mirror symmetry can lead to an agglomeration of new features. The Janus structures have been recently interested because they are expected to exhibit an ultra-low lattice thermal conductivity and an excellent visible-light photocatalyst with strong evidence of Rashba splitting. In this work, we have done an in-depth analysis of group-IV based Janus monolayers (Ge2XY, where X/Y=S/Se/Te), for their electronic, optical, and thermoelectric behaviors. The presence of tracking bands and multi-valleys in the E-k dispersion curve motivated to investigate the transport parameters with the other relevant characteristics. The key thermoelectric parameters such as power factor, Seebeck coefficient, and conductivity has calculated using the combined approach of density functional theory and semiclassical Boltzmann transport equations. Furthermore, the optical characteristics including Absorption coefficient, Dielectric-constant, refractive index, and extinction coefficients are calculated using the Kubo-Greenwood formalism. The impressive thermoelectric Figure-of-Merit and excellent optical characteristics advocate for the strong candidature of these materials for photovoltaic and thermoelectric devices, and hence a useful toolset to achieve the goal of carbon-neutrality with sustainable sources of energy.

Resume : The unique sandwiched structure and favorable crystallization kinetics have endowed two-dimensional (2D) halide perovskites with excellent ambient stability and facile film formation compared to their three-dimensional counterparts. However, the heterogeneous crystallization of multiple n-value phases during solution-casting of 2D perovskite thin films, resulting in the random and disordered crystalline alignment in conjunction with numerous lattice defects, all of which ultimately impair device performance. Herein we demonstrate that the highly ordered lattice arrangements in 2D lead halide perovskites, exemplified as a paradigm phenylethylamine (PEA) spacer, can be achieved by 4,5-dicyanoimidazole (DCI) additive without any post-treatment. Electrostatic potential distribution mapping and X-ray photoelectron spectroscopy collectively confirm the Lewis acid-base interaction between -CN- units in DCI and Pb2+, which is conducive to homogeneous nucleation during perovskite crystallization. A sequence of in-situ grazing-incident wide-angle X-ray scattering and high-resolution transmission electron microscopy characterization unravel the epitaxial growth of multi-phases that gradually buffer internal lattice strain and consequently regulate lattice orientation, which markedly leads to a reduction of trap density and a prolongation of carrier lifetime. The resulting planar solar cells based on 2D PEA2MA3Pb4I13 (n = 4) deliver an outstanding efficiency of ~17.0% along with excellent operational stability.

Resume : In recent years, the interest in nanotechnology has moved from equilibrium self-assembly toward dynamic self-assembly (DySA). Materials active in the presence of an external stimulus or requiring a constant energy supply are going to be the future of new complex nanotechnological systems. Such an approach needs the rational design of the building blocks of a nanocomposite. Our research focuses on the formulation of the interfacial (pseudo-2D) colloidal DySA systems with potential application to fabricate adjustable membranes or active and reconfigurable coatings. FexOy@SiO2 nanoparticles capped with thermo-responsive PNIPAM were synthesized and used as a building block with almost binary properties due to the two temperature regimes. We established the procedure of successful deposition of hydrophilic nanoparticles at the air/water interface (Langmuir film) and examined the behavior of the system upon temperature change, compression, and the ionic force of the subphase. The surface pressure and surface potential measurements were supported by SEM, BAM, DLS, profilometry, and theoretical calculations. We discussed the design of the nanoparticles in the context of possible interfacial phenomena. The different, controlled aggregation was observed due to certain stimuli, especially the temperature regime. The nanoparticles performed reversible self-assembly between a uniform state (high temperature) and a non-uniform state (low temperature). Short oligomer chains (ca. 5 nm) were able to control nanoparticles (65 nm or 90 nm) by “closing” and “opening” above and below the critical temperature (around 32 °C). As expected, the area occupied by a single nanoparticle on the ultra-pure water surface was decreased above 32 °C. However, the system changes its behavior significantly by increasing the concentration of KCl dissolved in the subphase. We discuss the interactions within the system to allow further development of 2D DySA designs. The research was financed by the National Science Centre within the OPUS grant according to decision number 2019/35/B/ST5/03229.

Resume : Permanent magnets based on ferrites are a possible alternative, in several application areas, to rare-earth-based magnets. Their attractiveness lies in the large crystalline anisotropy, but the often used measure of performance, (BH)$_\textrm{max}$, is roughly 10x lower than that of high performance rare-earth magnets. There is thus a need to increase the performance of the ferrites, in order to bridge the gap to rare-earth magnets. This talk investigates strontium hexaferrite magnets using micromagnetic finite-element calculations, implemented using FEniCS in an Open Source python code. Scalable solvers enables calculations with realistic microstructure, up to the micro-meter scale, which is needed to understand and ultimately enhance the coercivity of the materials. Different microstructures are investigated and the exchange-spring mechanism is considered to enhance the (BH)$_\textrm{max}$ value.

Resume : Due to the advanced technological applications that fulfill human daily life needs, the importance of interdisciplinary research is extensively growing. In material science and engineering, employing a material possessing outstanding properties in various fields is of great interest. Among these materials, zinc oxide (ZnO) has the potential for having interesting optical, piezoelectric, and mechanical features. Despite the massive research to show the capabilities of ZnO, some of its derivatives lack investigations regarding their multi-physical properties. One of these compounds is Al-doped ZnO (AZO), well-known for its unique optical properties [1] but still unknown for mechanical features. In this work, we aim to seek the Opto-electro-mechanical properties of AZO by utilizing the ab-initio density functional theory technique. Specifically, we provide a theoretical method for calculating the elastic constant of any hexagonal crystal structure from atomic-scale simulations, including ZnO. To this end, we perform DFT energy calculations, including structural relaxation of pure and different Al atomic percentages of AZO, to find the crystal structure with minimum energy for LDA exchange-correlation functional. To calculate the elastic and mechanical characteristics, we apply a set of different strain matrices to the lattice vectors of ZnO (AZO) crystal structures. The extracted optical, electronic, and mechanical properties are compared with other experimental and theoretical works in the literature to verify the methodology used in this research. The generated optomechanical data, including optical dispersion functions and elastic constant matrices of pure and Al-doped ZnO, are suitable for larger-scale differential equation solvers such as the finite-element method for device modeling of any optomechanical system made of ZnO (AZO). In this way, we can readily predict the proposed compounds’ optomechanical functionality while avoiding existing limitations in experimental works. Keywords: DFT simulation, ZnO, Mechanical properties, Elastic constant [1] Shabani, A., Khazaei Nezhad, M., Rahmani, N., Mishra, Y.K., Sanyal, B., & Adam, J. (2021). Revisiting the optical dispersion of aluminum‐doped zinc oxide: new perspectives for plasmonics and metamaterials. Advanced Photonics Research, 2(4), [2000086]. https://doi.org/10.1002/adpr.202000086

Resume : There is a huge surge towards development of flexible thermoelectric thin films for powering wearable electronic devices. Herein, we report the fabrication of novel tilted structured silver selenide (Ag2Se) thin films by a two-step thermal evaporation method. We adopt a strategy of interface engineering at nanoscale regime to grow well oriented Ag2Se nanorod arrays. Firstly, silver nanorods were fabricated via Glancing angle deposition (GLAD) method followed by a facile selenization process to obtain Ag2Se nanocolumnar arrays. Further, by controlling the tilt angle, Ag2Se planar films were also fabricated. The thermoelectric performance of the obtained Ag2Se films was studied by varying their thickness. The tilted Ag2Se nanocolumnar arrays exhibits a high thermoelectric dimensionless figure-of-merit zT= 1.28 at room temperature. Meanwhile, a corresponding maximum power factor of ~3200 µW/m-K2 was attained at room temperature. The as-prepared Ag2Se nanorod arrays exhibits superior thermoelectric performance compared to planar Ag2Se thin films. The excellent thermoelectric properties could be attributed to the nanocolumnar design of Ag2Se that not only provides a pathway for electron transport but also enhances the phonon scattering at the interfaces, leading to reduced thermal conductivity. Besides, the elasticity of the Ag2Se nanorod arrays can be ascertained by their lower values of hardness (49.2 ± 5 MPa) and elastic modulus (1896.2 ± 20 MPa), which is several times smaller than their planar counterpart. This work opens a new path to design and optimize nanostructured thin films for next-generation flexible thermoelectric materials and devices.

Resume : In a continuous magnetization-demagnetization cycling at audio frequencies, a mechanically vibrating magnetostrictive material produces acoustic (sound) waves that can be annoying to a human ear. A zero-magnetostriction material, the opposite of the high-magnetostriction materials used for the actuators and sensors, in combination with magnetic softness could find its niche application for the production of “supersilent” (inaudible to a human ear) transformers, magnetocaloric refrigerators and other “humming” electromagnetic machinery in audio-frequency applications. Recent research of multi-component alloys composed of five or more chemical elements in near-equiatomic concentrations, termed high-entropy alloys (HEAs), has shown that ferromagnetic HEAs based on the magnetic 3d transition elements Fe, Co and Ni generally exhibit a tendency towards magnetic softness [1]. The number of magnetically soft materials that also show vanishing magnetostriction is currently small. Near-zero magnetostriction is present in permalloys with composition close to Ni80Fe20, sendust (Fe85Si10Al5) and Co-rich alloys near the glass-forming compositions M80T20 in the system T = Fe, Co, Ni and M = B, Si (an example is the amorphous a-Fe5Co70Si15B10). Vanishing small magnetostriction is also present in finmet alloys, prepared as two-phase nanocomposites of crystalline Fe–Si grains in an amorphous matrix. Here we present a study of the HEA system AlFeCoNiCux (x = 0.6 – 3.0) where the Cu-rich compositions in the range x = 2.0 – 3.0 possess a combination of good magnetic softness and vanishing magnetostriction, classifying as magnetically soft and supersilent materials for the audio-frequency AC applications. Magnetic softness and vanishing magnetostriction are both a consequence of the specific multi-phase micro- and nanostructure structure that develops in this HEA system. References [1] P. Ko¸elj, S. Vrtnik, A. Jelen, M. Krnel, D. Gačnik, G. Dra¸ić, A. Meden, M. Wencka, D. Jezer¨ek, J. Leskovec, S. Maiti, W. Steuer, J. Dolin¨ek: Discovery of a FaCoNiPdCu High-Entropy Alloy with Excellent Magnetic Softness, Adv. Eng. Mater. (2019) 1801055

Resume : In this study, the mechanical characteristic of MoS2 on nickel substrate under nanoindentation and nanoscratch process by molecular dynamics (MD) simulation. The influences of the temperature, sliding depth, sliding speed, and indentation depth, on the deformation behavior and wear mechanism are surveyed. The results indicate that the higher sliding speed, larger sliding and indentation depth lead to a higher friction and normal force. The deformation of the MoS2 layer are affected by competing tip-to- layer and layer- to-substrate interactions.

Resume : Si as anode material for lithium-ion batteries promises 10x the capacity of state-of-the-art graphite. However, Si anodes suffer from pulverization and electrode collapse due to large volume increase during lithiation. It has been shown that Si structures with sizes below about 200 nm remain stable [1]. Therefore, we try to understand the formation of Si nanosponge in µ-sized particles during quenching of AlSi droplets. Subsequently Al is removed from the as-produced particles by etching. Phase separation of Si and Al upon solidification of the molten AlSi alloy occurs in two stages: First nucleation and growth of primary Si grains and second formation of eutectic sponge in the Si depleted melt, with faster cooling leading to finer structures. Through modelling and simulation, the reaction pathway can be understood, allowing to optimize process parameters. For this, a model was developed, which has as initial state a fully liquid, spherical droplet with random distribution of atom species Al, Si, vacancies and oxygen impurities. A many body angular-dependent potential (ADP) has been employed which reproduces the Al-Si phase diagram quite reasonable. As the melt cools below the liquidus temperature, precipitation of primary Si takes place, followed by spinodal demixing of the melt upon reaching the eutectic. Nucleation is influenced by trace oxygen which modifies surface energies and leads to formation of sites for heteronucleation. The diffusion-reaction behavior of the species, including nucleation and/or spinodal decomposition are simulated with a 3D kinetic lattice Monte Carlo program [2] using the ADP-potential for the Al-Si system [3] with modifications added to model surface oxidation. This program enables large scale calculations by a bit-encoded lattice and lattice jumps via bit-manipulation. Our simulations qualitatively reproduce the Al-Si phase diagram, as well as composition dependent interface energies of solid Si to Al-Si melt and the nucleation behavior. The simulation results agree with the experimentally found Si nanostructures and highlight the relevance of oxygen impurities for their formation. This work is supported by the German federal ministry for economic affairs and climate protection under grant number 01221755/1. [1] Su et al., Adv. En. Mat. 4 (2014) 1300882 [2] Strobel et al., Phys. Rev. B 64 (2001) 245422 [3] Starikov et al., Comp. Mat. Sc. 184 (2020) 109891

Resume : Deep eutectic solvents (DESs) have found their application as a potential class of solvents for nanotechnology, notably in developing novel carbon-based functional nanomaterials. Here, we have used molecular dynamics simulations to understand the structure of reline (choline chloride:urea in molar ratio 1:2) nanodroplets on carbon sheets with different strengths of DES–sheet interaction potentials. The simulated contact angle formed by the reline nanodroplet on the carbon surface is found to be greater than 150° at the lowest DES–sheet interaction strength, showing that the surface is supersolvophobic. The DES nanodroplet, on the other hand, wets the surface of the sheets at higher interaction potentials, generating an adlayer predominantly composed of urea molecules. When compared to chloride anions, the choline cation and urea molecules demonstrate stronger interactions with the carbon surface. The urea molecules have a larger density in the bulk of the nanodroplet at the supersolvophobic carbon surface, while the choline cation and chloride significantly contribute to the droplet's outer layers. Furthermore, urea molecules are found in the adlayer as well as the bulk of the droplets at solvophilic surfaces, whereas the reline–vapor interface is primarily composed of choline and chloride ions.

Resume : In this era, where nanoscale devices have made their way to industry, the problem of heat management still hinders their performances and is a limiting factor. To achieve the ultimate control over heat flow and cool down closely packed systems in current microchips, a thermal diode must be realized. A thermal diode is a device that allows heat to flow preferentially in one direction, thus, giving rectification. Efforts have been made as early as the 1930s to study heat rectification theoretically and experimentally by exploring several mechanisms including temperature dependence of thermal conductivity. Nanostructuring further helps in tuning the thermal conductivity due to phonon scattering effects, which was explored in nanowires for thermal rectification effects through molecular dynamic simulations in 2015. In this work, we have exploited the size and temperature dependence of thermal conductivity to manipulate heat flux and study thermal rectification experimentally. For this purpose, we investigate the thermal properties of nanowires with an abrupt change in diameter, also called telescopic nanowires. To perform precisely controlled thermal transport measurements on these nanowires, suspended Silicon nitride platforms with Joule heaters are used to apply thermal gradients and measure thermal conductivity. Further, to obtain a temperature profile along the axis of the nanowire, Raman thermometry is performed upon the application of a thermal gradient. Mapping the temperature of the heat channel also allows for extracting the thermal conductivity of each section of the nanowire, as well as the interface resistance. These are the first measurements to be performed on this kind of material system. So far, we have been able to measure rectification values ranging from 2 to 7% at different system temperatures with an average value of rectification increasing with an increasing temperature gradient. This is the first experimental indication of rectification in this material system. This research takes us a step closer in the direction of efficient thermal management and the development of thermal circuit elements.

Resume : Transition to sustainable and clean energy requires design of cost and performance effective, novel materials for energy conversion and storage. Computer-aided materials design can play a crucial role in development of energy technologies of the future. In particular, rapid increase in the supercomputers computing power allows for molecular level exploration of electrochemical phenomena with the first principles methods. Various materials features such as ionic and electronic structures, interface phenomena or electrocatalytic properties, to name but a few, can nowadays be effectively studied with the aid of density functional theory (DFT) calculations. However, the materials considered for energy transition contain elements with strongly correlated electrons (e.g. transition metals) and thus represent a computational challenge to quantum chemical methods. At IEK-13 we apply world-class high performance computing resources and state-of-the-art computational methodologies to enhance the fundamental understanding of energy materials and provide support for interpretation of the experimental data. A key to successful research in this field is a reliable and feasible computational approach. We discuss application of the parameter-free DFT+U method to various classes of energy materials [1-4]. We will demonstrate that the proper derivation of the Hubbard U parameter is crucial for the reliable computation of electrochemical phenomena. In this context we will discuss performance of the linear response method [5] for derivation of the Hubbard U parameter for d cations in different oxidation states and demonstrate the improvement in the method’s performance by selecting realistic projectors for the estimation of d orbitals occupations (e.g. Wannier-type orbitals) [1-3]. Last, but not least, we will discuss associated challenges encountered when computing mixed metal/metal-oxide systems [6]. Our key findings and methodology advancements were enabled through close cooperation with experimental partners and access to excellent data on the atomic scale properties of investigated materials [2-4]. [1] Kowalski, He & Cheong, Frontiers in Energy Research 9, 653542 (2021) [2] Murphy et al. Inorganic Chemistry 60, 2246 (2021) [3] Kvashnina et al. Chemical Communications 54, 9757 (2018) [4] Connor et al. Frontiers in Chemistry 9, 733321 (2021) [5] Cococcioni & de Gironcoli, Physical Review B 71, 035105 (2005) [6] Tesch & Kowalski, Physical Review B 105, 194153 (2022)

Resume : It is well known that microorganisms can produce fuels, such as ethanol, methane, and hydrogen, from organic matter. It is less well known that microorganisms can also convert organic matter into electricity in devices known as microbial fuel cells. However, interest in microbial fuel cells is increasing. Microbial fuel cells offer the possibility of harvesting electricity from organic waste and renewable biomass. Here we have used the Bacteria Escherichia Coli in our device to generate electrical energy. The important fact is that in our device without any applied voltage, we are getting a vast current(µA) concerning device current(nA). From Scanning Electron Microscopy(SEM), we can confirm that E. Coli has been trapped on the positively biased gold electrode due to the surface charge of E. Coli. And the novelty of this work is that it is not an Antigen-Antibody reaction as we haven’t used any antibody here. So we have also experimentally verified the Charge Transfer between E. Coli bacterial cell and electrode. So our device also can be used for water cleaning purposes.

Resume : Because of excessive anthropogenic emissions, the increasing concentration of carbon dioxide (CO2) in the atmosphere has led to an energy crisis and various disastrous environmental impacts [1]. This problematic scenario has received great attention by the scientific communities, which are committed to develop new technologies for CO2 capture and conversion into renewable fuels through clean and low-cost chemical processes [2]. Among possible strategies is the electrochemical reduction of CO2 as a step towards carbon recycling. There, CO2 is dissolved in an electrolytic solution and is reduced at the cathode under the application of an external voltage [3]. However, several challenges, such as high thermodynamic stability of the CO2 molecule, substantial reaction barriers, slow kinetics and poor selectivity, need to be overcome. The main single carbon atom products (C1) from CO2 conversion are carbon monoxide (CO) and formic acid (HCOOH). Open questions remain regarding the first step of CO2 electroreduction, which leads either to *COOH or HCOO-, which then evolve in subsequent step to CO or HCOOH, respectively. The challenge is to obtain an understanding of the structure-activity-selectivity relations in CO2 reduction at the various metal cathode surfaces. In this study, theoretical calculations aimed at gaining a better understanding of Ag, Pb and Zn low-index surface selectivity towards HCOOH and CO have been performed, analogous to the work of Van den Bossche et al. for Cu surfaces [4]. The calculations are carried out using electron density functional theory (DFT) with the Vienna Ab initio Simulation Package (VASP) [5]. The effect of the surrounding aqueous electrolyte is described by implicit solvent model in VASPsol [6, 7]. Tafel and Heyrovsky mechanisms have been considered: the reduction of CO2 occurs by transfer of an electron from the electrode and addition of adsorbed hydrogen atom or proton transfer from a H2O cluster, respectively. The activation energy barrier is found for a given applied voltage by identifying the saddle point on the corresponding energy surface representing the transition state for the reaction. While thermodynamic computational approaches can be used to estimate the free energy landscape of electrochemical processes by providing estimates of thermodynamic stabilities of CO2 reaction intermediates, it is important to address the kinetics as they can drastically affect the reaction progression. The calculations presented here show how the activation energy for the various reduction steps are lowered by the applied potential and provide insight on the different catalytic activity of the Pb, Ag and Zn electrodes. For all three electrode materials, the results show that the Tafel mechanism involves higher energy barrier than the Heyrovsky mechanism. [1] BP Statistical Review of World Energy, 2018. [2] J. Chem. Technol. Biotechnol. 2014, 89, 334–353. [3] Chem. Soc. Rev. 2013, 42, 6, 2423–2436. [4] J. Phys. Chem. C 2021, 125, 13802−13808 [5] Phys. Rev. B: Condens. Matter Mater. Phys. 1993, 47, 558− 0561 [6] J. Chem. Phys. 2014, 140, 084106. [7] J. Chem. Phys. 2019, 151, 234101.

Resume : Over the last decade, the halide perovskites have emerged in the photovoltaic field as third generation of absorber materials for high-efficiency and low-cost solar cells. Today, the amazing progression of the power conversion efficiency is pushed back to 25.7% for single cells and to 29.8% for tandem cells of Perovskite/Si. Additionally, halide perovskites show interesting potentials for various applications such as Lasers, LEDs, Photodetectors, Photocatalysis. Actually, the toxicity of halide perovskites, the stability and upscaling of the related devices are still under debate even though low manufacturing costs, short payback time and abundant material resources for eventual industrialization are promising. Researchers are therefore still working on finding alternative materials1,2 based on lead-free perovskites and compatible with inkjet-printing based technologies to tackle simultaneously these 3 issues. Recent theoretical3 studies based on the Density Functional Theory focused on understanding and controlling the surface and interface functionalizations after the assembly with charge transport layer (CTL) which are the most critical parts of the device architectures4,5. Thus, the influence of the material surface termination on the properties of the interfaces with CTL, including intermediate work function calculations on free-standing slabs, has been thoroughly investigated. This clarifies "where and how" optimizing interfacial charge transport can be possible for instance by surface dipole tuning. This DROP-IT project6 has received funding from the European Union’s Horizon 2020 research and innovation Program under the grant agreement No 862656. The information and views set out in the abstracts and presentations are those of the authors and do not necessarily reflect the official opinion of the European Union. Neither the European Union institutions and bodies nor any person acting on their behalf may be held responsible for the use which may be made of the information contained herein. References: 1. Li, J. et al. Review on recent progress of lead-free halide perovskites in optoelectronic applications. Nano Energy 80, 105526 (2021). 2. Dong, Q. et al. Electron-hole diffusion lengths>175 μm in solution-grown CH3NH3PbI3 single crystals. Science 347, 967–970 (2015). 3. Traoré, B. et al. A Theoretical Framework for Microscopic Surface and Interface Dipoles, Work Functions, and Valence Band Alignments in 2D and 3D Halide Perovskite Heterostructures. ACS Energy Lett. 7, 349–357 (2022). 4. Shao, S. & Loi, M. A. The role of the interfaces in perovskite solar cells. Adv. Mater. Interfaces 7, 1901469 (2020). 5. Lin, R. et al. All-perovskite tandem solar cells with improved grain surface passivation. Nature (2022) doi:10.1038/s41586-021-04372-8. 6. DROPIT. https://www.uv.es/dropit/.

Resume : Searching for novel functional materials has attracted significant interest for the breakthrough in photovoltaics to tackle the prevalent energy crisis. Through density functional calculations, we evaluate the structural, electronic, magnetic, and optical properties of new double perovskites Sn2MnTaO6 and Sn2FeTaO6 for potential photovoltaic applications. Our structural optimizations reveal a non-centrosymmetric distorted triclinic structure for the compounds. Using total energy calculations, antiferromagnetic and ferromagnetic orderings are predicted as the magnetic ground states for Sn2MnTaO6 and Sn2FeTaO6, respectively. The empty d orbitals of Ta5+-3d0 and partially filled d orbitals of Mn/Fe are the origins of ferroelectricity and magnetism in these double perovskites resulting in the potential multiferroicity. The studied double perovskites have semiconducting nature and possess narrow band gaps of approximately 1.00 eV. The absorption coefficient (α) calculations showed that the value of α in the visible region is in the order of 10^5 cm-1. The structural stability, suitable band gap, and high absorption coefficient values of proposed compounds suggest they could be good candidates for photovoltaic applications. Keywords: Density functional calculations, Double perovskites, Multiferroicity, Photovoltaic applications

Resume : Detection of minor gas leaks in a hazardous work environment has been a challenging research problem for many decades as it involves health, safety and environmental risks. The past decade has shown enormous research contribution in terms of publication to achieve high quality sensor. A report of the World Health Organisation has revealed Gwalior is the most polluted city in India in terms of air pollution along with other 12 cities of India. The report also suggests that the Indian population living outside Kashmir and the Himalayan belt are exposed to air pollution beyond the WHO safe limits. Meanwhile, Delhi, touted as the most polluted city in the world, doesn’t feature in the list of cities with highest air pollution levels. Also, no other metro city features in the notorious list. Both experimentalists as well as theoreticians have attempted their level best to design and miniaturize sensor materials. Some of them got well recognition but still the goal to achieve quality sensor is far apart. Conventional sensors based on semiconducting metal oxide thin films, organic polymeric materials, silicon and carbon black-polymer composites have been preceded by nanostructure sensor for past decade. In this race, carbon nanostructures have been evolved as prominent candidate due to its extraordinary chemical and physical properties. 2D-nanostructures served fascinating research prospects for scientific community in past few decades. Starting with carbon nanotube (CNT) and graphene different new 1D and 2D nanostructures have been introduced with novel chemical and physical characteristic. These nanostructures are expected as quality sensor materials and are essential for miniaturizing electronic devices. The present talk will include our group’s recent computational work on 2D nanostructures for their sensor application for Air and water pollution, using density functional theory approach. Analysis has been made in terms of electronic and transport properties.

Resume : Due to increasing levels of pollution in water, the need for rapid and accurate detection of life-threatening substances is becoming urgent. This work dealt with aromatic hydrocarbons due to their highly damaging carcinogenic and genotoxic properties. While a number of chemical sensors are commercially available for field measurements, they still have shortcomings due to cost, multiple detection failures, actual portability, and/or reliability. Creating a sensor that would improve on these characteristics is the main objective of this paper. Various water solutions containing pollutants were prepared, with concentrations ranging from 50 ppb to 100 ppm. The samples were measured in first approach using attenuated total reflectance, allowing a direct flow measurement of aromatic hydrocarbons in water. Two polymers were tested as possible membranes, responsible for extracting molecules from water – polyisobutylene and polyhydroxybutyrate-co-hydroxyvalerate from a family of polyhydroxyalkanoates (PHAs). The former was chosen for its hydrophobicity, easy preparation and compatibility with chalcogenide thin films and the latter for its hydrophobicity and biodegrability. Both polymer layers were prepared by spin-coating and knife-coating in different thicknesses and then tested for fabrication reproducibility, analysis time, limit of detection, long-term cycle repeatability and regeneration. For polyisobutylene, the method for reproducible fabrication was relatively quickly established. The polymer was dissolved in mixture of xylenes, followed by deposition via spin-coating. The thickness of 5 µm was chosen as a compromise between the ability to extract water and the time required to reach saturation of the membrane. The peak areas as a function of concentration showed mostly a linear increase, with a step between 30 and 50 ppm. The polymer proved its ability to measure samples repeatedly after regenerating via water cycle, reaching the same values of peak areas as on the first measurement. In addition, the detection limit was reduced to 150 ppb, which promises good results in this detection range. The next step is the transposition of pollutants detection on chalcogenide waveguide with an integrated microfluidic system. The fabrication of the microfluidic cell on the polyisobutylene coating of the chalcogenide planar waveguide has been successfully performed. PHAs films in the range of 5-10 µm was for the first time prepared via spin-coating. As the preferred solvent is chloroform, with a high evaporation rate, the obtained membrane contains air bubbles, causing an imperfect contact between the polymer and the ZnSe prism or chalcogenide waveguide surface, negatively affecting the hydrocarbon extraction capacity from water. To conclude, the polyisobutylene proved to be an appropriate material for detecting aromatic hydrocarbons in water, which is compatible with chalcogenide planar waveguide. It showed low limit of detection along with capability to regenerate and possibility to integrate microfluidic cell on its surface. While PHAs seem to be a good choice as hydrophobic membranes since they are already used for filtration and have the great advantage of being biodegradable, the problem still lies in the optimization of their deposition in 5-10 µm layers and needs further improvements.

Resume : Sensing gases find a vital role in applications and industries varying from food to production, environmental to space, and medical to material synthesis. Gas sensing chambers are very vital when developing gas sensors and studying their sensing characteristics including sensitivity, selectivity, temperature dependence studies, accuracy, repeatability, responsivity, time of response etc. To accurately characterize the behaviour of the gas sensor, it is vital to analyse the behaviour of the gas sensing chamber. Most often, the design and behavioural or operating characteristics of the sensing chamber are ignored or taken for granted by the researchers. It’s imperative to design an optimised, efficient gas sensing chamber with stable and reliable operating characteristics, which this paper aims at. A portable gas sensing chamber with a low sample requirement, optimised flow characteristics over the sensing layer to enhance the surface reaction and hence the sensitivity of the gas sensor was designed using COMSOL Multiphysics software. The chamber was designed with three inlet ports to allow three different gases to be passed into the chamber for sensing. The gas flow through these inlet ports can be individually controlled to change the mixing ratio of the gases. These gases would be mixed by passing them through baffles placed at an optimised angle in the flow path creating localised vertices and hence mixing of gases. This helps in determining the gas selectivity response of the sensor. A turbulent to laminar transition zone follows the baffles to allow the mixed gas flow to transform into a laminar flow since gas sensors have higher sensitivity toward laminar gas flow over the surface than compared to turbulent flows. The optimal placement of the substrate is very critical to achieving effective laminar flow over the substrate. The sensor mounting platform was angled at 11 degrees facing the gas flow to facilitate smooth flow over the gas sensor surface and avert the formation of a boundary layer at the sensor leading edge. The sensor mounting platform is placed on an integrated heater with a Nichrome heater coil inside a stainless-steel sheath. The heater provides a quick and localised heating zone directly below the sensor. This reduces the error in the set temperature and actual temperature at the substrate. Moreover, this also facilitates a preheating zone around the sensor heating up the gas as they flow towards the sensor. The gas inlet ports, mixing baffles, the flow chamber, sensing zone and the exhaust port are aligned along the horizontal axis to prevent the formation of turbulences or flow bottlenecks in the gas sensing chamber. The paper focuses on the complete modelling of the portable gas sensing chamber, fluid dynamic studies of the gas flow inside the chamber, optimal placement of substrate, and optimal angling of the substrate facing the gas flow.

Resume : Tons of unexpired food are thrown away by the supermarkets every year. According to the FUSIONS report (2016), wholesale and retail food waste takes up 5% of the overall amount of waste in the European Union (EU), which corresponds to 4.6 billion tons per year. From which 4.74% is an avoidable amount of meat food waste. One of the key causes of such waste is the problem associated with the expiration dates shown on the packaging, which were presented as a crucial safety measure to prevent the consumption by customers of products that might be unsafe. Labels on food products do not reflect the different storage conditions of the product when it is transported to the store and, eventually, to the customer's residence. The general idea is to install a cellulose-based gas sensor in the food package, which will trace food quality during spoilage. Microbiological tests were employed for benchmarking. The sensor itself is made by the pure cellulose substrate with interdigitated contacts that changes its electrical parameters when it is exposed to a humid environment like in a food packaging/container. As a result, activated by water content, cellulose fibres act as the sensor for water-soluble gases released during the degradation of protein foods. We designed a setup that harvested the data from an array of six cellulose-based gas sensors simultaneously. These six sensors coupled with humidity/temperature sensors were placed in two sealed containers kept in the climatic chamber at 25°C: one container included a fresh sample of codfish’s fillet, and another test container was filled with distilled water. The resistance signals and ambient parameters were plotted on a read-out unit like a PC. After 3-4 hours from launching the experiment, sensors in both boxes reached 100% humidification. Deterioration of the fish fillets at 25°C indicated by the cellulose sensor was in line with the one obtained by the microbiological test. The control test with pure water showed that after 4 hours the sensors’ resistance reached a steady-state, while the sensors’ resistance in the container with fish fillets continued to decrease. After stabilization, the relative difference in the resistance of the sensors in the two containers was 40 %. Therefore, the designed data acquisition system can trace food spoilage.

Resume : Owing to fiber-optic pH sensing, phenolphthalein immobilized SiO2 nanoparticles (P-SNPs) and phenolphthalein immobilized SiO2–TiO2 nanoparticles (P-STNPs) are synthesized by low-temperature sol-gel route. The P-SNPs revealed hierarchical structure, surface roughness (Ra) 7 nm, surface area ~442 m2 /g, n (refractive index) 1.37 at 550 nm which is significant for pH sensing. The P-STNPs exhibited granular structure, low Ra 3 nm, surface area ~219 m2 /g, n around 1.52 at 550 nm. Both matrices are thermally stable around 250 ◦C. The P-SNPs and PSTNPs sensitivity is calculated ~22 counts/pH and 19 counts/pH with the determination coefficient (R2 ) ~ 0.99. The pka value of P-SNPs is measured ~9.5 and time response 0.11s within pH 12 without leaching which is higher than P-STNPs (9.1) and 3.9 s with leaching. Experimental findings suggested P-SNPs have the potential for practical usage in intense basic media.

Resume : In the context of solar energy exploitation, dye- sensitized solar cells (DSCs) and dye-sensitized photoelectrosynthetic cells (DSPECs) offer the promise of cost effective sunlight conversion and storage, respectively. Dye-functionalization of bot n- and p-type semiconductors (like TiO2 and NiO) can be either exploited to build active DS photoelectrodes or tandem DSC and DSPECs devices. Computational modelling has played a prominent role in the development of the DSC technology. Here I will discuss the recent advances concerning first principles modeling of materials, interfaces and processes of n- and p-type photoelectrodes. On the photoanode side, we will discuss the recent advances toward the development of more efficient Iron-based DSCs, addressing both the dye design and the electrolyte optimization. On the photocathode side, particular emphasis will be put on the discussion of the electronic and structural properties of the complex NiO/solvent/dye/interface, whose characterization is still poor when compared to the level of understanding reached for TiO2 sensitized photoanodes, from both the experimental and computational point of view We will discuss the problem of accurately predict the energy level alignment across the dye/semiconductor interface by state of the art DFT and large scale GW calculations and the challenging definition of a proper structural model needed to reliably capture the interface complexity.

Resume : Nanostructures that can be used in environmental applications, especially related to renewable energy, its conversion and storage, are at the heart of nowadays research world. As most of the works are focused on the solar energy, the possibility of manipulation the passage of light through material is essential. One of the nanostructures that allow to control light guiding are photonic crystals – due to their periodical architecture. Herein, the closed nanopillars from titania nanotube arrays modified by pulsed-laser treatment are proposed as an exemplary electrode material. Titanium oxide nanotubes (NTs) can be grown via electrochemical process carried out in two-electrode arrangement where Ti substrate acts as an anode. Such a fabrication approach ensures growth of highly ordered architecture of titanium oxide NTs already onto the conductive substrate. After calcination at 450 deg. C oxide NTs are treated over any area and shape by laser beam precisely guided owing to the usage of motorized X-Y stage. For the optimized geometry of nanotubes and laser working parameters, the side selective plugging of nanocylinders can be reached offering unique structure. In the exception of closing of NTs tops, the remaining architecture of oxide support remains intact providing the straight percolation path. This is supported both by the scanning and transmission electron microscopies inspection. The appearance of the interference fringes in the reflectance spectra of the proposed material can be an indicator of the photonic crystal behavior [1]. Additional modification of the titania based platform with Fe, Co, Ni and Cu magnetron deposited layers prior to the laser treatment leads to the further altering of optical properties as the metal species are accumulated at the top part of capped NTs [2]. The electrochemical investigations of prepared materials show that the intense light-matter interaction results in improved photocatalytic activity toward oxygen evolution reaction. Moreover, precise laser sealing can be also used for the selective closing of nanotubes filled in with the nanoparticles, e.g. luminescent ones and then used for unique labelling. Thus, proposed electrodes could be further utilized in photonics or electrochemical applications. Furthermore, easy upscaling can be reached since both anodization and laser treatment are well-mastered processes onto the technological scale. This work received financial support from the Polish National Science Centre: grants no 2017/26/E/ST5/00416, 2020/02/Y/ST8/00030 and 2021/41/B/ST8/01849. [1] J. Wawrzyniak, J. Karczewski, P. Kupracz, K. Grochowska, E. Coy, A. mazikowski, J. Ryl, K. Siuzdak, Scientific Reports 10 (2020) 20235 [2] J. Wawrzyniak, J. Karczewski, E. Coy, J. Ryl, K. Grochowska, K. Siuzdak, Nanotechnology 33 (2022) 205401

Resume : Hydrogen by photoelectrochemical (PEC) water splitting can play a key role in future energy storage systems. In the last decade, water splitting multijunction devices could reach solar-to-hydrogen efficiencies of up to 19%. However, the fundamental loss mechanisms along the device interfaces are still not fully understood and impede further efficiency improvement. In order to address the charge transfer losses at the electrochemical interface, we focus on the electronic passivation of the photoabsorber system and its interaction with molecular water. For that purpose, we investigate the surface reconstructions of p-InP(100) by low energy electron diffraction (LEED) and their electronic structure using X-ray photoemission spectroscopy (XPS) as well as monochromatic ultraviolet photoelectron spectroscopy (UPS). Subsequently, water from the gas phase is stepwise adsorbed on the surfaces at cryogenic temperatures and the evolution of the electronic structure is examined with respect to chemical composition, hydroxylation and charge transfer. Experimentally, we found a strong Fermi level pinning at the clean surface. According to our theoretical DFT calculations, Phosphorous dangling bonds lead to partially occupied mid-gap states at the surface causing the pinning level. In this study, the impact of these Phosphorous dangling bonds on the water adsorption behavior of P-rich InP is investigated. We present our model experiment of the semiconductor/electrolyte interface and compare our experimental findings to our DFT calculations.

Resume : The Long exciton diffusion length (Ld) is revealed to be a desirable feature of nonfullerene electron acceptors (NFA) utilized in organic solar cells by exciton-exciton annihilation measurements. In order to verify and explain the experimental Ld values, we employed Kinetic Monte Carlo (KMC) method to simulate the transient absorption (TA) spectroscopy kinetics in pristine NFA materials such as ITIC, IT4F and ITM. The photogenerated singlet excitons were assumed to transport through hopping in a cubic lattice with Gaussian energetic disorder, and the hopping rates given by the Forster resonant transfer mechanism. Through reproduction of the experimental TA kinetics, the hopping prefactor and the energetic disorder were determined, with which the exciton diffusion lengths were further calculated using the KMC method, and the results turn out to be able to approximate the experimental values well. It is found that the energetic disorder in all the simulated NFA materials are ubiquitously around or below 50 meV, which contributes to the long exciton diffusion length in NFA. This work also establishes a theoretical framework for predicting exciton diffusion lengths and estimating the exciton transport parameters which are difficult to determine via experimental measurements.

Resume : Bi2MoO6 is the simplest member of the Aurivillius group and has been lately studied for its photocatalytic activity. An anionic discoidal nanoclay was organically modified and used to template the growth of Bi2MoO6. The organically-modified clay interface templated Bi2MoO6 crystal growth along the [010] direction, resulting in the formation of clay-Bi2MoO6 hybrids terminating in {100}-facets of Bi2MoO6. These {100}-faceted Bi2MoO6-clay hybrids exhibited enhanced and instantaneous adsorption of both cationic and anionic dyes from their aqueous solutions, compared to pristine Bi2MoO6 nanoparticles and other clay-based composites. These dye-laden composite particles sediment, rendering their recovery trivial. Moreover, their reuse over multiple cycles can be achieved by photocatalytically degrading the adsorbed dye. [1] Furthermore, templating growth using a cationic clay-like template, such as layered double hydroxides, provided a similar composite which selectively sequestered anionic dyes from aqueous solution. [2] Further improvements to the adsorption performance of clay-Bi2MoO6 hybrids could also be accomplished by encapsulating them with a thin shell of crosslinked polymers, in which crosslinker amount and polymer blend were optimized for ideal adsorption. The removal of dissolved molecular species under flow conditions was attained by depositing these polymer-particle composites on filtration membranes. The repeated reuse of these membranes was also rendered possible by photocatalytically degrading the adsorbed dye, showing that such materials have great promise in anti-fouling water filtration membranes. [3] In summary, surface modification and choice of template particles provided a means to tune the adsorptivity and selectivity of Bi2MoO6 composites. References [1] S. Jatav, J. Liu, M. Herber and E. H. Hill, ACS Appl. Mater. Interfaces, 2021, 13, 16, 18713-18723. [2] S. Jatav, et al., unpublished work. [3] S. Jatav, M. Herber, H. Xiang and E. H. Hill, ACS Appl. Mater. Interfaces, 2022.

Resume : Manganese oxides can adopt several stochiometries thanks to the relative stability of the Mn ion in oxidation states +2, +3 and +4, and accommodate cations of different sizes, leading to a range of different layered and tunneled crystal structures. [1, 2] On top of that, structural defects such as De Wolff disorder and micro twinning can lead to the formation of defect-driven phases such as γ-MnO2 [3] which is an intergrowth of pyrolusite β-MnO2 and ramsdellite R-MnO2. Each of these phases have distinct properties, and synthetic control of polymorph formation is crucial. Here, we use in situ X-ray total scattering and PDF analysis supported by in situ XANES to study the formation mechanism leading to different manganese oxide polymorphs during hydrothermal synthesis. PDF analysis allows to follow structural changes all the way from the precursors in solution to the final product. We show that by changing the ratio between manganese(II) salt and oxidizer, it is possible to not only select between R, γ-, β- and α-MnO2, but more importantly the formation mechanism differs as well. Furthermore, we show that these processes involve intermediate manganese oxido-clusters, structurally similar to those found in nature or in molecular magnets,[4, 5] which act as building blocks in the formation of the crystalline nanoparticles. 1. Fortunato, J., et al., Surveying manganese oxides as electrode materials for harnessing salinity gradient energy. 2020. 54(9): p. 5746-5754. 2. Robinson, D.M., et al., Photochemical water oxidation by crystalline polymorphs of manganese oxides: structural requirements for catalysis. J Am Chem Soc, 2013. 135(9): p. 3494-501. 3. Hill, L.I. and A. Verbaere, On the structural defects in synthetic γ-MnO2s. Journal of Solid State Chemistry, 2004. 177(12): p. 4706-4723. 4. Yano, J. and V.J.C.r. Yachandra, Mn4Ca cluster in photosynthesis: where and how water is oxidized to dioxygen. 2014. 114(8): p. 4175-4205. 5. Charalambous, M., et al., [Mn14] “Structural Analogues” of Well-Known [Mn12] Single-Molecule Magnets. 2018. 2018(35): p. 3905-3912.

Resume : Titanium dioxide (TiO2) is considered a reference standard material for photocatalysis: it is widely used in environmental as well as green energy field. The most important applications span from hydrogen evolution, self-cleaning surface and water/air purification. TiO2 takes also advantage of earth-abundance and low cost which make it easily available and industrially attractive. A plethora of structures or film morphologies were studied in literature running from nanotubes, nanofibers, nanoparticles and nanowires (NWs) depending on the targeted application. Anyhow, all these structures display a high surface/volume ratio, favouring the interaction with the external environment. An interesting structure to be used in the catalysis is represented by NWs because they show high activity in the decontamination of organic pollutants in water and they can be firmly anchored to a surface. In recent years, we developed a seed-assisted thermal-oxidative synthesis of TiO2-NW, in presence of Au as a co-catalyst. This technique is robust, easy, scalable and allows to realise high-quality NWs with low external contamination, as well as, easy control of film growth. The further step in tailoring the properties of the grown nanowires is the doping. In the present paper, we investigate the doping of the NWs by Fe and Cr obtained by ion implantation. Some samples were implanted with Fe and Cr ions to investigate the effect of co-doping. Due to the ionic nature of the Ti and O bound, the doping of the TiO2 is a complex process heavily influenced by the presence of vacancies, as well as temperature and environment. In our case, dopant ions were implanted into Ti layer before the oxidation process and thus before the growth of the NWs. We implanted with Fe or Cr ions and thus we also realised samples co-doped with Fe and Cr ions. The crystalline phase, surface morphology, structural and photo-electro-chemical properties of doped TiO2 NWs grown with thermal-oxidative synthesis are investigated. We paid particular attention to the wetting properties of the surface and photocatalytic activity in the oxidation of contaminants in water.

Resume : The design of robust and cost-effective smart materials requires a rational chemical nanoengineering to afford an efficient final device covering a wild range of possible applications in electronics, medicine, catalysis, photovoltaic, etc. While different strategies have been used depending on the targeted architecture, a common important factor is the development of viable and reproducible nanodevices that are easily manufactured and carry a high potential for industrial application. Recently, a powerful methodology based on the electrografting of diazonium salts has attracted a great deal of attention due to its numerous advantages, such as a rapid and efficient functionalization process, a universal approach for various materials and proven enhanced stability of the covalent bonding. Additionally, several studies on graphene-based materials reveal that the covalent attachment of aryl groups via the above approach could lead to additional beneficial properties of this versatile material including improved conductivity, asymmetric conductance and magnetism. In this context, we report in this work the development of covalently linked metalorganic wires on two transparent, cheap, and conductive materials: fluorine-doped tin oxide (FTO) and FTO/single-layer graphene (FTO/SLG). The wires are terminated with nitrilotriacetic acid (NTA) metal complexes which are universal molecular anchors to immobilize His6-tagged proteins, such as biophotocatalysts and other types of redox-active proteins of great interest in biotechnology, optoelectronics and artificial photosynthesis. We show for the first time that the covalent grafting of diazonium salt precursor on two different electron-rich surfaces leads to the formation of the molecular wires that promote the p-doping resulting in a significantly enhanced unidirectional cathodic photocurrent up to 1 µA·cm-2. Density functional theory modeling reveals that the exceptionally high photocurrent values are due to two distinct mechanisms of electron transfer originating from different orbitals/bands of the diazonium-derived wires depending on the nature of the chelating metal redox center (Co2+ or Ni2+). Importantly, the novel metalorganic interfaces reported here offer an effective means of minimizing back electron transfer, which is essential for the maximization of solar conversion efficiency.

Resume : Localised surface plasmon resonance (LSPR) presented by gold nanorods (AuNRs) has been proved to be used in different applications such as photoredox catalysis, plasmon-enhanced spectroscopy, biomedical technologies, and optoelectronic devices. Here, a hybrid nanoplatform has been synthesized by combining AuNRs and polydopamine (PDA). The synthesis process is divided in three main steps, starting from a seed-mediated growth followed by the substitution of the capping agent with poly(ethylene glycol) methyl ether thiol (PEG), and finally, by adding the PDA precursor, creation of the final PDA cover.. Several AuNRs/PDA were synthesized with average shell thicknesses going from ≈ 4 nm to ≈ 30 nm showing LSPR values in the range between 920 nm and 800 nm. The photocatalytic study was carried out for three different samples (AuNRs/PDA1, AuNRs/PDA2, and AuNRs/PDA3) towards Rhodamine 6G (Rh6G) degradation showing for all situations better performance than bare AuNRs and bare PDA nanoparticles. Within the three samples, the highest performance was achieved by AuNRs/PDA1 which presented the thicker PDA shell (30.45 ± 4.9 nm) with almost 35% of Rh6G initial concentration depleted in 1h for a relatively small concentration of the catalyst ([AuNRs] = 9815.60 µg/L). As final conclusion, different shell thickness AuNRs/PDA have been synthesized and could be used as a model for enhanced organic dye photocatalysis.

Resume : The Molecular Doping process is based on the deposition of a self-assembled layer of dopant-containing molecules over the surface of a semiconductor substrate. The dopant atoms are released inside the substrate during the successive drive-in annealing step. In the typical deposition conditions, the formation of the layer is in the order of the tens of minutes, allowing for a fast dopant source layer formation. Even if the process is well controlled and its doping efficiency already demonstrated [Nanomaterials 2021, 11, 1899. https:// doi.org/10.3390/nano11081899], however the early stages are very interesting to study because they reveal the micro- and nano- features of the final self-assembled layer, not known so far. Our previous works suggest that molecular clusters form during the early nucleation phase, and they successively grow into self-assembled layers on the substrate. Little is known about the nucleation kinetics influence on the molecular clusters’ morphology and the final morphological properties of the layers. In this work, we monitor the nucleation and coalescence process, in terms of molecular clusters density, size and shape, of diethyl-propyl phosphonate on silicon at different deposition conditions through a high-resolution morphological characterization. We correlate the results to the electrical characteristics of the final doped samples identifying the role of the clusters characteristics, and how these impact the electrical properties.

Resume : SERS is more applied to study solid-state materials or liquid, i.e. solution. However, using SERS to detect molecules in the gas phase is fewest. Indeed, handling and preparing gas samples are difficult, in addition, the gas medium is more diluted even at high concentrations. The latter leads to a small cross section of collected signal. Despite these difficulties, there is more need for new sensors based on SERS to study the gas adsorption properties onto the interface gas/solid, e.g., to study the toxicity degree of some gases such NO2. NO2 is an irritant gas that will cause lachrymation, coughing, respiratory distress, increases in methemoglobin (MetHb) levels, and lung edema.16 In fact, understanding the mechanism of adsorption of NO2 will provide more insights and information on the interaction properties of NO2. That’s why a development of a new method of detection such as SERS is very important. In early studies, SERS has shown its capability to monitor the photochemical reaction of N2O gas driven by hot electron of localized surface plasmon resonances (LSPRs) on the surface of metallic nanostructures. In this work, we report for the first time a steady-state detection method of 50 ppm of nitrogen dioxide (NO2) gas in a polyethylene (PET) bag using surface-enhanced Raman spectroscopy (SERS). SERS was performed on different shapes of gold nanostructures; gold nanostars (GNS) and nanoporous gold film (NPG). In both, we detected the vibrational modes assigned to the adsorbents of NO2 molecules such as NO2, NO, NO3-, N2O3, and N2O5. The generation of the adsorbents is due to the photo-chemical reaction driven by the hot electron generated at the surface of gold nanostructures. Our funding is supported by a finite element simulation excluding the plasmon induced photo-thermal process due to the long duration of excitation compared to the duration of SERS measurement. The mechanism of NO2 photochemical reactions is explained, confirming the adsorbtion of NO2 molecules on the gold surface towards their oxygen atoms.

Resume : Photovoltaics is an important and strategic topic in the field of renewable and sustainable energy. The light harvesting performance of a solar cell is a crucial factor which heavily affects its efficiency [1,2]. In this context, metal nanostructures, thanks to their unique properties related to their small physical dimension, large surface/volume ratio and surface properties, have gained increasing attention as one of the best solution to ensure sunlight absorption enhancement by surface plasmon resonance (SPR) [3]. Although many studies and scientific researches have been done in this fields, mainly with gold and silver nanostructures, one of the challenges is to integrate Cu nanostructures in solar cells in order to enhance the solar cell efficiency over NUV-visible-NIR spectrum. Herein Cu Nanostructures are obtained by solid-state dewetting of 9 nm Copper layer (dry) or by ablating Copper target, using a nanosecond pulsed laser at 1064 nm, in acetone and Isopropyl alcohol (wet). Once the Cu nanostructures were realized, they were embedded in Aluminum-doped Zinc Oxide (AZO) layer or Zirconium-doped Indium Oxide (IZrO) layer. The TCO/Cu nanostructures/TCO system were synthetized with all combinations of AZO and IZrO as top and bottom layers. Cu nanostructures morphology (shape and size) were investigated as a function of the involved method of synthesis and key parameters: In SSD process the morphology was studied as a function of the annealing temperature, ranging from 300 to 500°C in N2, while in laser ablation as a function of the used liquid environment. The electrical, optical and morphological properties of the systems were investigated by SEM, Rutherford backscattering spectrometry, image analysis processing, four-point collinear probe method, UV-Vis-NIR spectrophotometer. The aim is to compare the two fabrication methods of Cu nanostructures and select the best sequence of TCOs in order to achieve a system working in solar cell as a plasmonic and conductive interface. The main differences exhibited by wet and dry processes were in shape and size of the Cu nanostructures, dewetting in nitrogen produces faceted nanoparticles with an average size below 150 nm, while laser ablation originates spherical and smaller nanoparticles, below 50 nm. Dry system, made of only AZO, underwent to thermal annealing improves the electrical properties compared to wet system, sheet resistance of 103 vs 106 Ω/sq respectively; while dry system shows a maximum transmittance of 89,7% at 697 nm compared to wet system in acetone, 88.4% at 647 nm, and in Isopropyl alcohol, 86.9% at 686 nm. Moreover, wet systems show higher trasmittance in NUV. Dry and wet systems made of only IZrO, thanks to this TCO, improves the electrical properties until to sheet resistance lower than 200 Ω/sq; while the optical properties suffered of low transmittance in VIS range with a maximum of 70% at 800 nm. Finally, hybrid system with AZO and IZrO, showed a conductivity dominated by IZrO, with a sheet resistance of 200-400 Ω/sq, while the optical properties showed a dependence on the sequence of the top and bottom TCOs. We believe that these results, with low-cost and simple-fabricated method, supply pratical data for a better utilization of cost-effective Cu nanostructures to improve the light harvesting performance of photovoltaic devices. References 1. De Aberasturi, D. J.; Serrano-Montes, A.B.; Liz-Marzán, L.M. Modern Applications of Plasmonic Nanoparticles: From Energy to Health. Adv. Optical Mater. 2015, 3, 602-617. https://doi.org/10.1002/adom.201500053. 2. Parveen, F.; Sannakki, B.; Mandke,M.V.; Pathan, H.M. Copper nanoparticles: Synthesis methods and its light harvesting performance. Solar Energy Materials and Solar Cells 2016, 144, 2016, Pages 371-382. https://doi.org/10.1016/j.solmat.2015.08.033. 3. Liu, J.; He, H.; Xiao, D.; Yin, S.; Ji, W.; Jiang, S.; Luo, D.; Wang, B.; Liu, Y. Recent Advances of Plasmonic Nanoparticles and their Applications. Materials 2018, 11, 1833. https://doi.org/10.3390/ma11101833.

Resume : Singlet fission is an internal conversion process in which a high-energy photoexcited singlet can degenerate into two low-energy triplets forming a triplet pair. Investigating the energy transfer pathways of the excited states during the singlet fission is important for the design of efficient fission-based solar cells. Two typical mechanisms have been proposed in the literature to describe singlet fission. One mechanism suggests a direct transition from singlet to triplet pair, while the other mechanism suggests that there is an intermediate multiexciton bounded T..T state during the transition[1]. However, multiexcitonic T..T states are considered optically dark and difficult to be directly verified by conventional spectroscopy. Here we use two-dimensional coherent electronic spectroscopy (2DES) to study singlet fission dynamics in two pentacene dimer derivatives (DP-TIPS and DP-MES). In both molecules, the population dynamics suggest the presence of the intermediate triplet pair (T..T) during the intramolecular singlet fission which happens on the timescale ~200 fs. Due to the mixing of singlet exciton and multiexcitonic T..T state[2], we can further locate the energy of the T..T state through beating maps of selected vibrational mode, and we provide Liouville pathway analysis to all beating peaks which relate to the transition from singlet to T..T pair. Our experiment demonstrates the prevalence of bound triplet pair states as an intermediate in the intramolecular singlet fission system. The result reveals a connection between the presence of multiexciton intermediate states near resonant with S and a more rapid fission rate. [1] Lukman, S. et al. Nat. Commun. 2016,7, 13622 [2] Bakulin, A. et al. Nat. Chem 2016, 8, 16?23

Resume : Liquid Crystal Elastomers (LCEs) are lightly crosslinked polymers incorporated with rigid and anisotropic liquid crystal molecules (mesogens). The liquid-crystalline ordering of such mesogen in nematic monodomain LCEs brings about reversible shape memory performance by the isotropic-nematic transition. Due to this reversible shape memory behavior, LCEs are used in various applications, e.g., smart fibers, 4D printing, soft robotics, biomedical engineering, smart coatings, etc. There are two main parameters that affect the anisotropic ordering of mesogens: temperature and mechanical strain. This research was aimed to investigate degree of orientation of main-chain in LCE under both varying temperature and mechanical strain via wide angle X-ray scatterings (WAXS) analysis. LCE was synthesized by two-stage thiol-acrylate Michael addition. Mesogenic acrylate monomers (RM257, excessive acrylate 2 mol%), flexible polymer chain of 1,3-propanedithiol, and PETMP crosslinker were used. WAXS analysis was carried out to observe the anisotropic orientational behavior of mesogens in prepared LCE when various temperature and mechanical force were given. WAXS analysis revealed that as the temperature approaches Ti, isotropic-nematic phase transition temperature, the change of degree of orientation becomes more influenced by thermal energy than the mechanical strain. Dynamic mechanical analysis was also carried out to identify this inflection temperature at various temperatures, finding about 70 Celsius temperature through relaxation test. Finally, the orientational behavior of mesogens in LCE was quantitatively established as a function of temperature and mechanical strain, enabling to simulate the deformation behavior of LCE considering its microstructure.

Resume : Fast, selective and low-cost nitric oxide (NO) sensors are highly needed due to the harmful effects of this gas. Low temperature NO detection is as requested as challenging, requiring selective and effective catalytic processes. Metal oxides (MOx) are most widely used materials for gas sensor applications [1]. Usually, n-type semiconductors require high operating temperature (>300°C) and have low sensitivities [2]. For this reason, p-type semiconductors have been extensively studied for gas sensors. Here, we present an experimentally based CuO-NO interaction model in the 50-400 °C temperature range and a promising NO detector working at 50°C based on CuO nanoparticles (NPs) realized by pulsed laser ablation in liquid environment (PLAL) technique. Ligand-free Cu/Cu2O nanostructures produced by PLAL in deionized water and were converted into CuO NPs by 400°C annealing, and analysed by X-Ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray techniques. A chemoresistive sensor is produced by drop-casting 0.1 mL of CuO NPs suspension onto an interdigitated electrode of Pt/Al2O3 and tested in a flow-controlled test chamber. Studying the sensor response toward several gas, the highest and fastest response toward NO is obtained at 50°C. It was observed that the resistance had an opposite behaviour fluxing NO at different temperatures. Below 250°C an oxidation behaviour is recorded while above 350°C reduction takes place, with a peculiar transient regime observed at 300°C. Hence, a full model of CuO-NO interaction based on Langmuir adsorption theory is proposed and kinetics barriers has been extracted by analysing the response curves in the 50-400 °C temperature range [3]. A peculiar catalytic activity of CuO NPs emerges in combination with oxygen species absorbed at different temperature, leading to effective NO detection. The ease and scalability of CuO NPs production by PLAL and the reported fast and selective NO sensor working at 50°C open promising routes towards exploitation for massive and affordable harmful gas detection. [1] R. Malik, V. K. Tomer, Y. K. Mishra and L. Lin, Functional gas sensing nanomaterials: A panoramic view, Applied Physics Reviews 2020, 7, 021301. https://doi.org/10.1063/1.5123479 [2] Hou, C. Zhang, L. Li, C. Du, X. Li, X. F. Kang, W. Chen, CO gas sensors based on p-type CuO nanotubes and CuO nanocubes: Morphology and surface structure effects on the sensing performance, Talanta 2018, 188, 41-49. https://doi.org/10.1016/j.talanta.2018.05.059 [3] M. Censabella, V. Iacono, A. Scandurra, K. Moulaee, G. Neri, F. Ruffino, S. Mirabella, Low temperature detection of nitric oxide by CuO nanoparticles synthesized by pulsed laser ablation. Sensors and Actuators B: Chemical, 2022, 358, 131489. https://doi.org/10.1016/j.snb.2022.131489

Resume : In the field of lighting, white light-emitting-diodes (WLEDs) are increasingly regarded as a replacement for inefficient incandescent light bulbs and environmentally damaging fluorescent lamps[1]. Recently, important research efforts have been devoted to the development of inorganic LEDs, in both the design of new materials exhibiting a broadband emission[2] and the implementation of devices with architectures based on the down-conversion concept[3,4]. Both approaches, however, have shown serious limitations due to toxicity and/or unavailability of either the fluorophore or the down-converting filters, which often contain heavy metals or rare-earth elements[5]. The rising costs and ecological impact (mining/refining/toxicity) put a heavy burden on the long-term sustainability of inorganic WLEDs. An innovative, sustainable and cheap alternative is offered by the bio-LED concept[6], in which the downconverting filter is made of a fluorescent protein embedded in a polymeric matrix. In this regard , we propose a fully theoretical design of a fluorophore-protein system for applications in bio-LEDs in the low energy range of the visible spectrum, using a modified NDI chromophore and a nitrobinding type protein. The study required a quantum mechanical approach for the characterisation of the excited states of the proposed chromophore and protein docking simulations for the evaluation of the possible protein-chromophore assemblies. Subsequently, quantum mechanics/molecular dynamics calculations were performed to study the stability of the system and obtain insights in to the effects of relative ortientations of the chromophore within the protein , environment and hydrogen bonds on the spectroscopic behaviour of the system. The obtained results have been compared with and corroborated by experimental spectroscopic analysis and the applicability of the designed system has been proven by a prototype device performance and stability. Bibliography 1. Cho, J. et al., Laser and Photonics Rev., 11, 1600147 (2017). 2. a) Smith, M. D. et al., Chem. Sci., 8, 6, 4497 (2017); b) Febriansyah, B. et al., J. Mater. Chem , 8, 3, 889 (2020); c) Wu, Z. et al., J. Mater. Chem. C, 6, 1171 (2018); d) Li, D. et al., Adv. Opt. Mater., 6, 1800273 (2018). 3. Mukherjee, S. and Thilagar, P. Dyes Pigm., 110, 2 (2014). 4. Fernández-Luna, V. et al., Angew. Chemie - Int. Ed. 57, 8826 (2018). 5. a) Wei, Y., et al., Chem. Soc. Rev., 48, 310 (2019); b) Xia, Z. et al., Dalton Trans., 45, 11214 (2016); c) Qin, X. et al., Chem. Rev., 117, 4488 (2017); d) Xia, Z. and Meijerink, A.., Chem. Soc. Rev., 46, 275 (2017). 6. a) Espasa, A. et al., Nat. Commun., 11, 1 (2020); b) Weber, M. D. et al., Adv. Mater., 27, 5493 (2015); c) Fernández-Luna, V. et al., Adv. Funct. Mater., 29, 1 (2019); d) Niklaus, L. et al., Mater. Horizons, 3, 340 (2016); e) Niklaus, L. et al., Adv. Funct. Mater. 27, 1601792 (2017); f) Fresta, E. et al., Adv. Funct. Mater., 28, 1 (2018).

Resume : Nature presents collective behavior of living organisms aiming to accomplish complex tasks, inspiring the development of cooperative micro/nanorobots. Herein, the spontaneous assembly of hematite-based microrobots with different shapes is presented. Autonomous motile light-driven hematite/Pt microrobots with cubic and walnut-like shapes are prepared by hydrothermal synthesis. We characterizied the structure and composition of the microrobots. Both microrobots show a fuel-free motion ability on the basic of photocatalysis. Because of the asymmetric orientation of the dipolar moment in the crystal, cubic hematite/Pt microrobots can self-assemble into ordered microchains. The microchains exhibit different synchronized motions under light irradiation depending on the mutual orientation of the individual microrobots during the assembly, which allow them to accomplish multiple tasks, including capturing, picking up and transporting microscale objects, microplastics in water, as well as degrading polymeric materials for environmental remediation. Such novel light-powered self-assembled microchains hold great potential toward cargo capture, transport and delivery, and wastewater remediation, which may make contribute to green energy in the future.

Resume : Organic upconversion devices (OUCs) consist of an organic infrared photodetector and an organic visible light-emitting diode (OLED), connected in series. OUCs directly convert photons from the infrared to the visible and are of use in applications such as process control or imaging. Many applications require a fast OUC response speed, namely the ability to accurately detect in the visible a rapidly changing infrared signal. Here, high image-contrast, solution-processed, narrowband OUCs are reported that convert near-infrared (NIR) light at close to 1000 nm with a full-width at half maximum of 130 nm into visible light. Transient photocurrent measurements show that the response speed decreases when lowering the NIR light intensity. This is contrary to conventional organic photodetectors that show the opposite speed versus light trend. It is further found that the response speed can even decrease when increasing the driving voltage. Again, this is an unexpected result because the charge drift velocity gets faster by an enhanced electric field. To understand this surprising response speed behavior, an analysis by numerical simulation is conducted. Results show that the response speed is primarily determined by the (low) electron mobility value in the OLED. Simulations confirm that the speed indeed decreases when lowering the NIR light intensity, and an increase of the applied voltage does not necessarily increase the response speed, as would intuitively be taken for granted. Our work is the first systematic study on the response speed of OUCs. A few reported single-parameter measurements show that the response speed of OUCs so far is limited to around 10 kHz. This is much lower than the speed of organic photodetectors, for which typical cut-off frequencies are above 100 kHz. We think that the main reason for this discrepancy is the low electric field in the OUC emitter layer, which results in a low charge drift velocity, and in a lower effective electron mobility value because the mobility is electric field dependent. It thus seems that the specific device architecture sets a fundamental limit to the response speed of OUCs. Reference: Wei Hsu et al., On the response speed of narrowband organic optical upconversion devices, Adv. Optical Mater. 2022, doi:10.1002/adom.202200695.

Resume : Zinc oxide (zincite) decorated silica-titania nanocomposite (ZST-NC) is synthesized by sol-gel method. For dynamic pH range and fast-response fibre-optic pH sensing characteristics, a blend of phenol red, bromophenol blue, phenolphthalein, and cresol red is immobilised in ZST-NC (D/ZST-NC). A fundamental analysis revealed that ZST-NC and D/ZST-NC had crack-free morphology and thermal stability at 560 ◦C. The ZST-NC exhibited a surface roughness (Ra) 0.4 nm, a crystallite size 5 nm, and a refractive index 1.48. The D/ZST-NC revealed a Ra 0.8 nm, a crystallite size 2 nm, and a refractive index 1.49. The sensitivity of the D/ZST-NC coated optic fibre is estimated to be 15.67 counts/pH at 440 nm, with a determination coefficient (R2 ) ~99%. A high pKa ~8 and a rapid response time 0.13 s at pH 12 are observed. The prepared pH sensor displays a reversible and non-leaching behaviour, which is advantageous for applied opto-chemical pH sensing purposes.