Current trends in optical and X-ray metrology of advanced materials for nanoscale devices VI

Resume : The surfaces of topological insulators contain two dimensional massless Dirac electrons. Plasmon can be excited using coupled electrons of top and bottom surfaces and shows resonance in the terahertz frequency rage with exceptionally large mode indices and long lifetimes. In the range of terahertz wave length, there are a number of important resonance absorption modes caused by intermolecular coupling and it enables us to directly observe the specific binding state of a bio-related molecular system without modifying fluorescent molecules. However, in general, it is necessary to amplify the signal intensity by some techniques. Two-dimensional Dirac plasmons can be excited from these surface electrons. These plasmons are expected to exhibit resonances in the terahertz (THz), a frequency range of interest for bio-medical sensing and chemical identification. Topological insulators (TIs) are materials having a bulk bandgap crossed by linearly-dispersing two-dimensional surface states and are expected to show surface plasmon in the THz wave length range. In addition, TI plasmons should also exhibit spin-momentum locking, leading to a reduction in scattering and an increased plasmon lifetime. In this study, we have focused on TIs of Bi2(Te,Se)3 as topological insulators those generate surface plasmon resonance in the terahertz range, and fabricated thin films on sapphire substrates by a pulsed laser deposition (PLD). Crystallographic, nano-micro structural properties are discussed. And their physical, electrical and optical properties are also presented in a view point of the terahertz plasmonics.

Resume : We study the plasmonic response of free charge carriers in GaAs/InGaAs core/shell nanowires by means of THz spectroscopy. In the first set of experiments, we generate an electron-hole plasma in an ensemble of nanowires using photoexcitation by a femtosecond optical pump pulse. Fitting the plasmon peak measured in the linear low-field regime allows us to deduce room-temperature mobilities around 4000 cm2/Vs. Besides that, we drive the plasmon in nanowires with intense THz pulses generated in an organic DSTMS crystal. In a THz field of >MV/cm the plasmon peak is red shifted, indicating intervalley transfer of the electrons. In the second experiment, we investigate a single, highly electron doped nanowire by scattering infrared near-field infrared microscopy (s-SNIM). Here we observe a red shift of the mid-infrared plasma resonance from 125 meV to 95 meV at a peak power of 0.5-1 kW (pulse energy of 2-3.5 nJ) from our free-electron laser, which can be explained by heating the electron system in the nonparabolic conducting band. We gratefully acknowledge contributions from S. Shan, J. Schmidt, R. Hübner, S. C. Kehr, and L. M. Eng

Resume : Carcinogenesis involves DNA methylation which is a primary alteration in DNA in the development of cancer before genetic mutation. Because the abnormal DNA methylation is found in the most of cancer cells, assessment of DNA methylation using terahertz radiation can be a novel optical method to detect and control cancer. The methylation has been directly observed by terahertz spectroscopy at around 1.6-1.7 THz and this epigenetic chemical change could be manipulated to the state of demethylation using high-power terahertz radiation. Demethylation of cancer DNA is a key issue in epigenetic cancer therapy and our results may lead to the treatment of cancer using electromagnetic waves. In the presentation, the manipulation of biological molecules and cells toward cancer treatment using intense terahertz radiation will be explained in detail.

Resume : Our recent experimental research on THz irradiation experiment by two different THz sources, a THz-FEL and a gyrotron, targeting actin filaments, which serve as representative biopolymer materials, will be presented. The THz-FEL produces pulsed THz waves in the 3–6 THz frequency range with a duration of 2 ps. In early studies, morphological changes were observed in the macromolecules after THz irradiation, and these phenomena were believed to be the result of the THz photons acting on the molecular dynamics. However, our recent study revealed that the pulsed THz waves with energy density of ~10−4 J/cm2 (~108 W/cm2 at the peak) generate acoustic waves efficiently in the aqueous media. These acoustic waves propagated deeply into the water and demolished the actin filaments in living HeLa cells that were submerged into the cell culture medium. The results implied that THz pulsed irradiation affects the biomolecules in the tissues, even if these molecules are located a few millimeters away from the body surface. These results must be considered when the safety guidelines for use of THz radiation are determined in the future. In contrast, irradiation experiment using a gyrotron with lower peak power of the order of ~W/cm2 induces the elongation of the actin biopolymer without thermal or acoustic effects. The polymerization of monomeric actin into filaments plays pivotal roles in cell motility, growth, differentiation and gene expression. Therefore, techniques for manipulation of actin polymerization have been developed to aid in understanding and regulation of multiple biological functions. THz irradiation technology, instead of actin-binding chemicals, should provide a safe and novel approach for regulation of the dynamics of actin polymerization and depolymerization in living cells. Our findings indicate the possibility of use of THz waves for artificial manipulation of biological phenomena through modulation of the functions and dynamics of various biomolecules.

Resume : The HfO2-based ferroelectric materials have gathered much attention due to their excellent compatibility with state-of-the-art semiconductor technology because the HfO2-based materials are employed as alternate gate dielectrics for field-effect transistors. The ferroelectricity in HfO2 is considered to originate from the metastable orthorhombic structure. On the other hand, it has been scarcely reported that the ferroelectric phase transition of HfO2 ferroelectric materials because most polycrystalline HfO2-based ferroelectric film transforms into the most stable monoclinic phase upon heating. We have developed the epitaxial film of HfO2 ferroelectric materials by substituting Y and investigated the fundamental properties of the materials. In this study, we investigate the phase transition of HfO2-based ferroelectric materials with epitaxial film by means of X-ray diffraction including synchrotron X-ray source. In addition, we also study the phase formation of the orthorhombic ferroelectric phase in epitaxial film. As a result, the tetragonal phase stabilized at high temperature transition to the orthorhombic phase during the cooling process.

Resume : Piezoelectric microelectromechanical-systems (MEMS) are widely used for actuators, sensors and other devices. Pb-contained piezoelectric materials such as Pb(Zr,Ti)O3 [PZT] and Pb(Mg,Nb)O3-PbTiO3 [PMN-PT] with superior piezoresponse and electromechanical properties are commonly used in piezo-MEMS. However, Pb-based materials are toxic, and there is an urgent need to replace those materials. In this work, we propose Pb-free (Bi,Sm)FeO3 [BSFO] which has a perovskite structure. Epitaxial BSFO films prepared on (100)cSrRuO3//(100)SrTiO3 substrates by pulsed laser deposition display robust piezoresponse at the morphotropic phase boundary composition. The origin of piezoelectricity is investigated by in-situ synchrotron-high resolution x-ray diffraction under pulsed applied electric field. We find that the large piezoresponse in BSFO at this composition originates from an extrinsic effect of field-induced phase transition from an antiferroelectric phase to a ferroelectric phase. Maximum longitudinal piezoresponse (d33) of approximately 240 pm/V was detected based on displacement of diffraction peaks measured under electric field.

Resume : The frequency response of the complex permittivity in oxides is described by the dielectric dispersion of four contributions: the interfacial, dipole, ionic, and electronic polarizations. Two methods, i.e., the micro-sized planar electrode and ring resonator techniques, were developed to measure the microwave dielectric properties of specimens having a large permittivity. The modified Kohlrausch–Williams–Watts (KWW) model was used for the dipole relaxation function. Using mentioned technique, the complex permittivities of various dielectric oxides were determined up to a few GHz. For instance, the dipole polarization contribution to the dielectric response under a DC electric field in BaTiO3 based ferroelectrics was investigated [1, 2]. The apparent tunability of BST was determined by the domain wall density; a higher domain wall density resulted in a larger dipole polarization. The origin of colossal polarization of doped TiO2 based compounds were also discussed via microwave dielectric spectroscopy [3]. Ionic polarization in THz was analyzed by the four-parameter semi-quantum (FPSQ) phonon dispersion model. Broadband dielectric spectroscopy from low to THz was consequently determined via combining dielectric relaxation function and mentioned FPSQ relation. The dipole and ionic polarizations and electronic contributions were simultaneously quantified for various perovskite ferroelectrics, in attempt to analyze the microscopic behavior in dipole polarizations [4-8]. The broadband conductivity spectrum of 8 mol% yttria-stabilized zirconia (8YSZ), a fast oxygen-ion conductor, was also acquired to quantify all conduction contributions, i.e., interfacial, grain boundary, and bulk contributions [9]. [1] T. Teranishi et al., Jpn. J. Appl. Phys. 52, 09KF06 (2013). [2] T. Teranishi et al., Jpn. J. Appl. Phys. 58, SLLC03 (2019). [3] N. Delegan, T. Teranishi et al., J. Appl. Phys. 125, 205103 (2019). [4] T. Tsurumi et al., Appl. Phys. Lett. 91, 182905 (2007). [5] T. Teranishi et al., J. Appl. Phys. 105, 054111 (2009). [6] T. Teranishi et al., Appl. Phys. Lett. 100, 242903 (2012). [7] T. Teranishi et al., IEEE Trans. Ultrason. Ferroelectr. Freq. Contr. 57, 2118 (2010). [8] K. Miyata, T. Teranishi et al., J. Chem. Phys. 152, 084704 (2020). [9] T. Teranishi et al., Jpn J. Appl. Phys. 51, 011102 (2012).

Resume : We are developing A3B5 superlattices (SLs) grown by the molecular beam epitaxy with sharp heterointerfaces, constancy of composition, good homogeneity and a large number of periods (up to 1000) and thickness of up to 15 μm. Such semiconductor structures can be used for creation of tunable laser sources of far infrared and terahertz radiation using the formation of corresponding minibands and sequential tunneling of carriers through many periods. To synthesize such super-multiperiod (SMP) SLs with an accuracy of layer thickness at the atomic level and roughness/diffuseness of interfaces at the subatomic level, it is necessary to create new methods for precision control of composition and structural parameters: rigorous theoretical methods (Deep X-Ray Reflectometry – DXRR) and valid extended data obtained, particularly, with synchrotron radiation sources with high brilliance. A key future of the considered technique is matched investigation using DXRR, XRR, and XRD which is applicable for analysis of SMP SLs of various designs and allows one to characterize samples and determine with high reliability and accuracy the morphology and composition of layers. It was demonstrated using the laboratory equipment, the XRR results for Design I semiconductor superlattice (SL) grown by molecular-beam epitaxy (MBE) provide overestimated values of σ for several interfaces. In contrast, with Design II & III SLs, the inaccuracy of the derived results for σ = 0.35 nm is only about 1% for all the layers studied. This value of σ is close to the critical (before an overestimation) one and the usual XRR study with σ ≈ 0.3 nm provide accurate results for all correlation lengths and incidence angles under study. However, in the general case, such a value depends on the correlation length (roughness statistics), angle of incidence, and radiation wavelength and can be determined only using the rigorous theory of scattering. The range of grazing incidence angles was ~ 0–3° for Cu Kα diffractometer radiation and the thickness of SL was ~ 1 μm. To investigate with the same accuracy SLs with thicknesses of ~ 10 μm and more, like as super-multiperiod (SMP) structures, higher grazing angles, higher radiation energies and much higher source brightness are required. First, we use XRD to find the SL period and thicknesses of individual layers in the period by the envelope shape of the satellites and their positions and fitting a theoretical curve. To verify the XRD model and to determine the absolute errors for this structure, the XRR & DXRR methods were used. In the resulting model of XRR, exact values of layer thicknesses, as well as rms roughnesses can be obtained for the best agreement with the experimental data. Then, applying successively XRD after XRR we finally obtain perfectly matched XRD curves, which are also matched in the best way to XRR data. The next step in the matched procedure is to determine the proportion of some material in the solid semiconductor solution. It can be done, for example, using rocking curves obtained near specific reflexes. Such a methodology can be (and should be) applied to any design of such SMP SLs.

Resume : Functionality of thin films often depends on phase transitions, which either occur during device operation or reside nearby in the space of thermodynamic variables, thereby maximizing the essential characteristics. Characterizing the critical dynamics, associated with the transition in films was always challenging, especially the dynamics of inhomogeneous order parameters, which are described by finite wavevectors and can be probed only by short-wavelength radiation scattering. Practically important example are antiferroelectric (AFE) films, where the transition is related to inhomogeneous (staggered) dipole arrangement. We report on the first measurements of critical diffuse scattering (DS) in PbZrO3 AFE epitaxial thin films. The sample heterostructures PbZrO3 (100 nm)/SrRuO3 (20 nm)/SrTiO3 were grown by pulsed laser deposition at UC Berkeley. The measurements were performed at ID03 beamline of the ESRF. Using grazing-incidence setup we were able recording the critical DS distributions in the large regions of the Brillouin zone and tracing the temperature dependence of the signal. The results rule out the possibility of first- to second-order change of the transition character, suggested by recent studies, and point out towards near-interface structural heterogeneity as the origin of observed differences in phase transition scenarios in the film and bulk forms.

Resume : Ferroic materials possess regions (domains) with defined orientations of the order parameter (spontaneous polarization for ferroelectrics) that together form its domain configuration which influences the functional behavior of the material. Modifications in the domain configuration may be introduced through dimensional and epitaxial effects, therefore, domains of bulks will be arranged differently than films of the same material. In the case of domains outside the capability of the polarized-light optical microscopy, research in domain configurations is usually carried out using electron diffraction and piezo-response force microscopy. Those methods exhibit some limitations, such as the need for the material to be polar in the case of PFM, or the demand for high-vacuum and charge issues in electron techniques. The objective of this work is the development of an alternative non-destructive method for characterizing the domain configuration of films and its changes when external stimuli are applied, such as high temperatures or electric fields. For this purpose, we adapt the relatively new method of X-ray nanoscopy, which consists of scanning the surface of the film with an ultra-sharp-focused synchrotron X-ray beam and monitoring the diffracted intensities. We have tested a 1000-nm-thick PbZrO3 epitaxial film, grown at UC, Berkeley. The experiment was carried out at the beamline ID01 – ESRF. Measurements were made at room temperature, where the material resides in the antiferroelectric phase. Aiming to interpret the data, a statistical analysis was developed based on the calculation of the covariance and variance between intensity distributions coming from different domain orientational states. Four 3D-maps (Z–domain intensity distribution, X-Y–translational shifts of the sample) corresponding to a different domain orientational state were obtained. Distributions do not have regular patterns, contrasted to bulk samples, and have a rather chaotic spatial domain distribution, with no visible traces of domain walls oriented in usual high-symmetry directions. Domains, apparently, often have sizes smaller than the spot size (about 100 nm), due to spatial overlapping of different domains under the spot, smearing of the intensity distribution takes place. To find the reason behind the smearing of intensity distributions, mutual covariances were calculated and compared against an ideal case with no domain overlap and absolutely sharp contrast. The experimental covariance was close to 50% of the ideal case, which we attribute to the large sample thickness, finite spot size and non-perpendicular angle of incidence. X-ray nanoscopy showed its capability to study the domain configuration of antiferroelectric thin films. We assume that if thinner samples are used, results will be more deterministic, thus allowing the exact determination of the domain configuration and the consequent characterization of its changes when external stimuli are applied.

Resume : It is well known that the materials to be used for electrochromic applications must fulfill many of the same criteria as battery electrodes and they must be able to react very fast with small cations such as hydrogen or lithium and totally reversibly. Vanadium oxides have gained a constantly growing interest in this field, because of their varying material properties according to oxidation state. For example, vanadium pentoxide V2O5 exhibits both anodic and cathodic coloration, and thus the reversible lithium-ion insertion/extraction processes in V2O5 lead to not only reversible changes in optical parameters but also multicolor changes for esthetics in the voltage range of ± 1 V [1,2]. Herein, orthorhombic α-V2O5 nanostructured thin films grown by spray deposition technique were investigated. Further details can be found in our previous work [3,4]. In particular, the focus of interest is the strain and the associated relaxation processes, that lead to the occurrence of the structural defects. X-ray diffraction investigations showed that the thin films are highly oriented along the (001) preferential plane perpendicular to c-axis, which is very useful for intercalation of hosts for Li-ions, as happens in rechargeable batteries and electrochromic devices. To have a quantitative evaluation of the strain processes, Rietveld refinement and Williamson-Hall plot were employed in XRD data analysis. The presence of dislocations can be also observed from Raman spectroscopy, where a broadening of the main Raman peak A1g was happening accompanied by an asymmetricity of the shape. In addition, the relationship between the structural defects and electrochromic/storage performances was studied. Using cyclic voltammetry measurements results in correlation with the XRD and Raman studies one can conclude that the dislocations seem to govern both Li-diffusion in our samples and redox reactions. The results clearly prove a strong dependence between the strain/dislocations and the device performances; thus, the strain engineering approach may be considered a valuable method for a further development of energy storage electrodes applications. Acknowledgments: This research was partially co-financed by Romania through PN-III-P4-ID-PCE-2020-1712 project within PNCDI III, Greece and the EU (European Social Fund—ESF) through the Operational Program “Human Resources Development, Education and Lifelong Learning” in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research—2nd Cycle” (MIS-5000432), implemented by the State Scholarships Foundation (IKΥ). [1] Tong, Z., Lv, H., Zhang, X., Yang, H., Tian, Y. & Li, N. (2015). Sci. Rep. 5, 16864. [2] Chernova, N. A., Roppolo, M., Dillon, C. & Whittingham, M. S. (2009). J. Mater. Chem. 19, 2526–2552. [3] Mouratis, K., Tudose, I. V., Bouranta, A., Pachiu, C., Romanitan, C., Tutunaru, O., Couris, S. & Koudoumas, E. (2020). Nanomaterials. 10, 2397. [4] Mouratis, K., Tudose, V., Romanitan, C., Pachiu, C., Tutunaru, O., Suchea, M., Couris, S. & Vernardou, D. (2020). Materials (Basel). 13, 3859.

Resume : Rayleigh and Abbe derived formula for the diffraction limit, which is due to the finite width of each imaging system, because the optical near fields cannot be transmitted through it. The intensity overlaps on the screen and it cannot be any more unambiguously decided if the image stems from one or from two distinct points or areas. With the appearance of spectroscopic imaging ellipsometers (SIE) especially applied to structured samples, and capable of imaging the ellipsometric angles or Mueller Matrix elements the problem above cannot be solved in direct way, i.e. the angular resolution cannot be changed. However, with a slight reformulation the number (and size) of the contributing points or areas can be determined with an imaging ellipsometer on a field of view of e.g. 50 x 50 µm area with resolution of a few µm by a few µm (for numerical purposes we assume 2 x 2 µm). In our contribution we will first discuss, how ellipsometric measurements with an imaging ellipsometer shall be interpreted in the case of no depolarisation and with depolarisation. Then it is shown with numerical techniques based on finite element methods or rigorous coupled wave analysis. 1) that the presence of subwavelength defects or structures (Au) of an areal size of e.g. 50 x 50 nm and 10 nm height on Si can be easily detected by SIE, provided the two ellipsometric angles and are measured with an accuracy of 0.01°. This result proves that the well known sensitivity of ellipsometry on the thickness of vertical overlayers can be extended also to the horizontal dimensions. 2) Knowing that there is more than one structure with the given size in the real plane even closer than the Abbe formula can resolve in the image plane, SIE will immediately determine this number by measuring  and 3) In addition we show that extremely high precision SIEs will allow to estimate the approximate distance between the different structures. The ellipsometric response depends, due to the existence of evanescent fields in plane [5], on the distance between the single structures. A matrix of in total 9 structures (i.e. a field of 3 x 3) of 20 nm x 20 nm structures a distance p apart will yield different SEI responses depending on the distance.

Resume : Structural templating is one of the strategies for controlling the orientation of small molecule absorbers in the photoactive layer of an organic solar cell to increase its power conversion efficiency. A pi-stacked crystalline template layer is deposited below the photoactive layer to induce flat-lying (“face-on”) growth in the absorber phase by pi-pi-interactions. For improvement of the solar cell efficiency template molecules with suitable HOMO level alignment have to be found. We report on the template molecule ellagic acid, a polyphenol present in numerous fruits, and its effect on the morphology of thin films of the oligothiophene DCV4T-Et2. By differential reflection spectroscopy and photoluminescence spectroscopy we find J-aggregation in the monolayer regime. In “bulk” films of 30 nm we confirm the change from “edge-on” to “face-on” orientation of the DCV4T-Et2 phase by grazing-incidence wide angle X-ray scattering (GIWAXS) and spectroscopic ellipsometry. Finally, we show that the short circuit current density and the fill factor of corresponding organic solar cells with a templated photoactive layer are significantly improved.

Resume : Terahertz Mueller matrix ellipsometry is a powerful technique for materials characterization, which has been used to determine the complex dielectric tensor of thin films and substrates in the spectral range of 0.1 THz to 1 THz[1,2]. Its sensitivity can be greatly enhanced by utilizing Fabry-Pérot interferences that occur between multiple reflections off of the sample's interfaces for samples containing THz-transparent substrates. Further enhancement is possible by creating an external Fabry-Pérot cavity via adding a reflective metal surface behind such samples[3]. These techniques, for example, have enabled the detection of optical Hall effect signatures in two-dimensional electron gases, and recently, were used to detect the electron paramagnetic resonance (EPR) signal in Ce-doped lutetium oxyorthosilicate. [1] Philipp Kühne, et al., ‎IEEE Trans. Terahertz Sci. Technol 8, 257 (2018). [2] Sean Knight et al., Sci. Rep. 9, 1353 (2019) [3] Sean Knight et al., Opt. Lett. 40, 2688 (2015).

Resume : Opto-electronic devices like photovoltaics (PV) depend on both optical response of component materials to control how incident light is collected as well as material electronic transport properties to utilize that absorbed light. Millimeter (THz) to ultraviolet range spectroscopic ellipsometry measures the complex optical response of materials for and within solar cells. Layer thickness, interfacial formation, structure, electronic transitions, bandgap, Urbach tails, and relative defect density are identified optically for components of silicon wafer, polycrystalline organic-inorganic lead halide perovskite, and other thin film PV technologies. THz optical Hall effect measures majority and minority carrier transport properties of semiconductors within solar cells. Open circuit voltage and fill factor simulated using those transport properties agree with direct measurement. Spectroscopic ellipsometry measurements of complete single and tandem junction PV generate structure and optical property input parameters for simulations of external quantum efficiency (EQE) and short circuit current density. Sources of optical and electronic losses are identified through quantification of parasitic absorption in non-current generating layers and carrier collection profiles of PV devices. Non-contacting optical measurements provide a means of full PV device property prediction and loss diagnosis.

Resume : Wide-bandgap materials, which are interesting for opto-electronic devices, like Ga2O3, exhibit often a low crystal symmetry. Here, we present the determination of the optical properties of such materials by spectroscopic ellipsometry. For the investigation of the nature of the underlying excitations, we present a general approach for the decomposition of the dielectric function by taking into account the dipole orientation distribution of each excitation into account. The application of this approach is demonstrated exemplary on an orthorhombic KTiOPO4, monoclininc Ga2O3 and triclinic K2Cr2O7. Without making any assumptions, we show that the tensor elements of the dielectric function in general are not independent of each other. The dielectric function can be described by a superposition of electronic transitions. For each transition an eigensystem exists in which the contribution to the dielectric function is given by a diagonal susceptibility tensor. The relative magnitude of these tensor elements is given by the dipole orientation distribution of the corresponding transition. In the limiting case, the oriented dipole approach is obtained as well as the tensor for uniaxial and isotropic materials. It is also shown that the imaginary part of the non-diagonal tensor elements can become negative, which is forbidden in scalar systems.

Resume : Several bulk and thin-film crystals of SnO2 were grown and examined using generalized ellipsometry techniques. The bulk samples were grown using the chemical vapor transport technique and resulted in two different habits of the crystals, depending on the processing parameters: 1) Needles of SnO2 crystals were obtained that were 1-2 cm long, less than 1 mm wide and oriented with the optic axis (OA) along the long crystal axes. 2) Using a different set of growth parameters, larger crystals were obtained, but the crystals were twinned to adjoining crystals. Thin films of SnO2 were grown using the pulsed laser deposition technique - one set on sapphire and another on rutile. Two different generalized ellipsometry techniques were employed to examine these samples. The normal-incidence two-modulator generalized ellipsometry microscope (2-MGEM) operating at 577 nm measures the diattenuation N = (Ra - Rb)/(Ra + Rb) where Ra and Rb are the reflectivities for light polarized along two mutually perpendicular directions - where Ra is the maximum reflectivity. The 2-MGEM also measures the direction of the principal axis. Spectroscopic generalized ellipsometry measurements were also preformed using the two-modulator generalized ellipsometer (2-MGE) which measures the standard ellipsometric parameters including cross-polarization terms. The 2-MGEM measurements on the bulk needle-like samples determined that the maximum diattenuation was 0.0611 ± 0.0008, which is related to the birefringence at 577 nm. Similar measurements on the bulk sample showed that the OA was at an angle of ~75° with respect to the normal to the sample surface. The 2-MGE measurements of the larger bulk SnO2 sample were used to determine the ordinary and extraordinary complex dielectric functions of the SnO2 crystal. The 2-MGE measurements of the two thin-film samples showed no cross polarization, which indicates that the samples were either isotropic or that the OA was perpendicular to the sample surface. The films grown on sapphire were fit best using a Tauc-Lorentz model for the thin film. This is consistent with X-ray measurements that showed that the film consisted of very small crystallites aligned with the OA in the plane of the sample surface but otherwise randomly oriented. According to X-ray measurements, the films grown on rutile had the OA perpendicular to the sample surface. The model of the 2-MGE data that fit best consisted of the structure: air/roughness/SnO2/interface/rutile, where the roughness and interface layers were modeled using the incomplete Beta function, and the optical functions of the SnO2 layer were determined from the bulk measurements.

Resume : The talk will focus on the emerging area of metasurfaces, which are increasingly replacing conventional optical components in optics and optoelectronics applications due to their miniature size and flexibility in design. In particular, the talk will concentrate on the design of metasurfaces for imaging applications in the infrared spectral region. Different configurations of all-dielectric metasurfaces will be presented, the emphasis being on providing solutions for imaging/focusing devices with variable focus and reduced aberrations and/or for handling partially coherent light fields. Limitations imposed by implementations of the designed metasurfaces will be also addressed. The research leading to these results has received funding from the EEA Grants 2014-2021, under project no. EEA-RO-NO-2018-0438 - ElastoMETA

Resume : Static (SLS) and Dynamic (DLS) Light Scattering are among the most powerful techniques to study nanostructures. These technologies have been widely employed for more than 30 years, and are still undergoing constant improvement. While SLS and DLS are well-established characterization techniques, several completely new light scattering methods have gained significant traction among material scientists over the past decade. Among these, Diffusing Wave Spectroscopy (DWS) can be used to characterize the viscoelasticity of materials on a wide frequency range using low sample volumes if compared to classical mechanical rheometers. This presentation will feature a review of the scientific fundamentals of the techniques mentioned above, and take a closer look at some of the recent advancements, including Depolarized Dynamic Light Scattering (DDLS) and Modulated 3D Cross-Correlation. [1] Weitz & Pine, Diffusing-Wave Spectroscopy. In Dynamic Light Scattering; Brown, W., Ed.; Oxford University Press: New York, 652-720 (1993). [2] Balog & al., Characterizing nanoparticles in complex biological media and physiological fluids with depolarized dynamic light scattering, Nanoscale, 2015, 7, 5991-5997 [3] Block & Scheffold, “Modulated 3D cross-correlation light scattering: Improving turbid sample characterization”, Rev. Sci. Instrum. 81, 123107 (2010).

Resume : Conventional optical techniques applied in the fingerprint region of the mid-infrared (MIR) spectral range typically rely on thermal emitters. Such sources are characterized by low brightness, which finds expression in poor signal-to-noise ratios (SNR), long acquisition times and insufficient spatial resolution. By exploiting high-brightness broadband MIR laser sources, however, the limits of conventional instruments can be exceeded by orders of magnitude. The application of a spectrally tunable MIR quantum cascade laser (QCL) for spectroscopic ellipsometry is presented. The QCL based ellipsometer is outperforming state-of-the-art FTIR ellipsometers in terms of SNR by a factor of 290. This exceptional noise performance allows to acquire high-resolution (1 1/cm) broadband (900 1/cm – 1204 1/cm) ellipsometry spectra in less than a second (887 ms), which designates a reduction in acquisition time by a factor of 66,000 compared to reference measurements performed with a state-of-the-art instrument. The great benefit of this approach is illustrated by monitoring molecular reorientation during the stretching of a 6 µm Polypropylene film at sub-second temporal resolution. In addition, we demonstrate the advanced investigation of semiconductor materials by means of spectroscopic transmission ellipsometry measurements at continuously varying angle of incidence and sample orientation – likewise enabled by the available brightness of the applied QCL.

Resume : In recent years, correlated transition metal oxides (TMOs) have attracted significant attention due to their remarkable structural, electronic, magnetic, and optical properties that provide many ways to finely tune their functionalities. An example is the rare-earth nickelates (RNiO3), which are unusual among other TMOs due to their negative charge-transfer behaviour with an electronic configuration of Ni 3d8L (L = oxygen ligand hole) in their paramagnetic metallic state. Most RNiO3 (except for R = La) undergo metal-insulating (MIT) and antiferromagnetic (AFM) transitions at low temperatures accompanied by a breathing distortion in their crystal structure. This breathing motion leads to a bond disproportionation where expanded NiO6 octahedra (Ni 3d8 configuration, no holes on oxygen, and high spin) alternate with collapsed NiO6 octahedra (Ni 3d8L2 configuration, average of two holes on oxygen, and low spin), resulting in an AFM ordering vector of Q = (1/4 1/4 1/4)pc (pc = pseudocubic). This close relationship between breathing distortion and electronic configurations suggests that electron-phonon couplings (EPC) lie at the heart of the MIT in RNiO3. Recent progresses in both theory and instrumentation have allowed the use of high-resolution resonant inelastic x-ray scattering (RIXS) to probe this EPC. Here, we use high-resolution RIXS to track the momentum- and temperature-dependent evolution of the EPC across the phase transitions of RNiO3 thin films for R = La, Nd, and Sm. We find that the EPC of the phonon mode related to the breathing distortion of NdNiO3 reduces significantly by ~20% at the onset of its MIT just below 180 K. This drastic change of EPC is consistent with the polaronic condensation scenario, which proposes that the MIT of RNiO3 is caused by the condensation (melting) of polaronic carriers at low (high) temperatures. Furthermore, we also find that the momentum-dependent EPC of insulating NdNiO3 becomes maximum at half of the AFM ordering vector, signifying a strong magneto-elastic coupling in this material. These results reveal the intimate connection between electronic, lattice, and spin degrees of freedom in RNiO3 that can be exploited for future advanced functional devices, and demonstrate the capability of high-resolution RIXS in probing and even quantifying the electron-phonon interactions in advanced materials.

Resume : Spectroscopic Ellipsometry (SE) is the primary metrology tool for determining the optical constants of materials, and therefore gaining knowledge of which materials and in which cases we can extract precise information from SE is of great importance. The implementation of semiconductors and Transparent Conductive Oxides (TCO) has enabled the unlocking of the near-infrared and infrared window for plasmonics. As materials with lower carrier concentration (N) become of utmost importance for this regime, so do the optical characterisation techniques that have the capability to deliver the exact optical constants of such materials. In this work, we combine an experimental and theoretical approach to find the precise limits (in terms of N) of SE in the different spectral regimes (from IR to UV: 0.03 - 6.5 eV) for which one can, with confidence, extract the explicit optical constants of materials. We focus our attention to the most common TCO candidates for IR plasmonics: tin-doped indium oxide (ITO), aluminium-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO). We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behaviour, grain size, presence of a substrate, film thickness, and measurement noise. This work is hugely timely to the discipline of photonics as we are on the onset of employing alternative, low-N materials to ensure practical applications for plasmonics. Vitally, the methodology we outline can be readily applied to other materials on a case-by-case basis.

Resume : Phononic crystals are periodic arrays embedded in an elastic medium, arranged in a specific lattice symmetry that represent a very promising route for tuning the properties of next-generation nanoelectronics, thermoelectrics, and ultralight materials. Nanofabrication techniques can now produce metalattices, i.e., nanoscale phononic crystals with dimensions <<100 nm, that make it possible to engineer new physical properties [1]. To synthesize these nanostructures, nanospheres are first assembled into a colloidal crystal with face centered cubic order. The interstitial space between the nanospheres is then infiltrated with another material, finally forming the metalattice structure. Measurement of the mechanical properties of such nanostructures to date have focused only on one component of the metalattice—either the template or the etched-out structures, and always for periodicities >100 nm. In this work, we present a nondestructive method to accurately extract, for the first time, the mechanical and structural properties of metalattices with much smaller feature sizes. In particular, we probe silicon metalattices fabricated from sphere diameters of 14 nm and 30 nm that contain feature sizes that are an order of magnitude smaller than opals that have been characterized to date. To investigate their mechanical and structural properties, we deposited a set of metallic gratings with linewidths as small as 50nm on top of the metalattice surface. In a pump-probe experimental setup, we use a 25-femtosecond infrared pump pulse to heat the gratings, which impulsively launch surface acoustic waves (SAW) in the metalattice. The wavelength of the SAW can be tuned by varying the grating periodicity, which also changes the SAW penetration depth into the metalattice and the silicon substrate. We then monitor the SAW frequency from the time-dependent change in diffraction of extreme ultraviolet ultrashort (<20fs) probe pulses, created by high-order harmonic generation [2], as a function of pump-probe delay time. This method allows us to simultaneously extract the acoustic dispersion, the Young’s modulus, thickness and filling fraction of the metalattice [3]. Interestingly, these measured properties agree well with macroscopic predictions, while the transport properties of the same metalattices do not agree with bulk models. Additionally, the measured metalattice thicknesses agree with scanning electron microscopy images and the extracted Young’s moduli agree with nanoindentation measurements. This technique represents the only approach to date to nondestructively validate the filling fraction of deep-nanoscale metalattices. These results can enable precise fabrication, characterization and understanding of materials with tailored mechanical and transport properties. [1] Chen, W, et al. ACS Nano 14, 4, 4235-4243 (2020). [2] A. Rundquist et al., Science 280(5368), 1412–1415 (1998) [3] Abad, B., et al. Nano Lett. 20, 3306-3312, (2020)

Resume : Hyperbolic metamaterials (HMMs) show exotic optical properties unattainable in bulk materials, enabling the opportunity for confinement and propagation of light at the nanoscale. To date, most of the HHMs are fabricated by sequential deposition and growth of alternating metal/dielectric layers. The optical axis of the so-obtained HMMs lies in the out-of-plane direction, thus preventing their exploitation into more complex photonic devices and circuitries. In-plane orientation of the optical axis, in the direction coinciding with the anisotropy of the HMMs, is desirable for a variety of novel applications in nanophotonics and imaging. Here, we introduce a method for creating localized HMMs with in-plane optical axis based on the dewetting of block copolymer (BCP)/homopolymer blend thin films. By exploiting the blend film instability over topographically defined substrates, droplets composed of highly ordered lamellar nanostructures in hierarchical configuration were obtained. The pattern transfer process onto a transparent and flexible substrate, generates a hybrid Au/air HMM with hyperbolic dispersion in broad wavelength range in the visible spectrum, crucial for the realization of novel smart nanostructured materials for future stretchable and wearable devices. A strong reduction in the fluorescence lifetime of defects in nanodiamonds placed on top of the HMM is supported by computed Purcell factor as high as 32 at 580 nm. This fast and low-cost method allows to obtain hybrid metal/dielectric nanopatterned substrates with in-plane optical axis whose orientation can be further tuned through the control of the dewetting process, suitable for on-chip integration.

Resume : The ferroelectric crystalline phase Bi2GeO5 has spontaneous polarization value comparable to BaTiO3 ceramics. To date, most researchers consider this phase to be metastable so it can be hardly synthesized by conventional crystal growth methods. We offer a new look at the phase formation in the Bi-Ge-O system, which considers Bi2GeO5 as an oxygen-deficient phase and makes it easy to synthesize from non-stoichiometric compositions. The Bi2GeO5 single phase has been successfully synthesized from Bi2O3-Bi-GeO2 batch when Bi oxide has been partially replaced by metallic Bi to form an oxygen deficiency. The crystallization was made both in solid phase and from melts at different temperatures. The structure of the formed crystal phases have been investigated by XRD. It was found that both the melt temperature rise and metallic Bi amount increase led to the formation of Bi2GeO5 single phase. The optimal initial batch compositions and crystallization conditions to produce a single Bi2GeO5 crystal phase has also been found. The research was supported by the Ministry of Science and High Education of the Russian Federation by the project FSSM-2020-0003.

Resume : A typical strategy for MCM-41 synthesis consists of acid/base catalyzed sol-gel condensation of silica precursor that takes place in solvent in the presence of template as structure-directing agent. So, variation of synthesis conditions (temperature, stirring rate, aging time, microwave irradiation, hydrothermal treatment etc.) as well as chemical composition of reaction mixture gives great opportunities for regulation of morphology and structural parameters of mesoporous silica nanoparticles. As condensation of structure-forming silanes proceeds around supramolecular surfactant assemblies, template plays extremely important role in directing the formation of arranged mesoporous silica framework. Long-chain quaternary ammonium salts belong to the most widely used structure-directing agents in sol-gel synthesis of MCM-41 type silicas. Incorporation of auxiliary organic compounds into the surfactant aggregates, consisting of hydrophobic core and hydrophilic external surface lined with positively charged quaternary ammonium groups, causes changes in critical micelle concentration and configuration of mixed micelles in comparison with individual surfactant and, as a result, has substantial influence on mesoporous structure of silica materials prepared by template-assisted sol-gel synthesis. Taking into account the ability of organic additives to incorporate into the long-chain cationic surfactant micelles, we focused our attention on the effect of amphiphilic organic compounds (azo dyes, bile acids, cyclic oligosaccharides) as cosurfactants and their alkoxysilane derivatives as structure-forming silanes on mesoporous structure of silica materials obtained by template-assisted sol-gel synthesis. The effect of auxiliary agents on mesoporous structure of resulting silicas was estimated by low-temperature nitrogen adsorption-desorption and x-ray diffraction analysis. It was found that introduction of moderate amounts of amphiphilic organic additives or their alkoxysilane derivatives into sol-gel reaction mixture causes formation of silica materials with higher surface area and more distinct long-range ordering of mesopores. Observed pronounced effect on mesoporous structure of silica materials was explained by tight interactions arising between hydrophobic parts of amphiphilic organic compounds and long alkyl chains of cationic surfactant on the one side and between hydrophilic groups of additives and growing anionic oligomers of orthosilicic acid on the other side. Obtained results open up new opportunities for synthesis of MCM-41-type silica materials with improved structural characteristics.

Resume : The coupling of quantum dots (QDs) heterostructures with regular metal subwavelength gratings on the semiconductor surface was demonstrated to be powerful tool of photocurrent enhancement in mid-IR InAs/(In)GaAs and Ge/Si QDs photodetectors (QDIPs). Besides surface plasmon waves the Rayleigh anomaly are characteristic optical phenomena exhibited by periodic subwavelength grating structures. At present work a hybrid metal-dielectric metasurface is developed to improve the photoresponse of Ge/Si QDIPs. The structure consists of a regular array of silicon pillars protruding through subwavelength holes in a periodically perforated gold film on detector top. Compared with a bare QDIP, the peak responsivity of the hybrid detector at a wavelength of 4.4 µm is increased by a factor of 15. The enhanced sensitivity is supposed to arise from coupling of the surface plasmon resonance and diffractive effect of Rayleigh anomaly. The hybrid structures containing Ag nanoparticles over SiGe QDs layer were developed using self-organization of metal nanoislands on the surface of a strained semiconductor structure. Enhanced photoluminescence from SiGe QDs coupled with Ag nanoislands was found. Ag nanoislands grown on the top of the multilayered structures with SiGe QDs support a surface plasmon resonance that can be tuned to the QDs emission wavelength by changing of Ag nanoparticle parameters. Modeling of surface plasmon resonance allows attributing this effect to the increase of the recombination rate due to electromagnetic field enhancement in QDs layer. This work is funded by Russian Science Foundation, grant No.19-12-00070.

Resume : Oxyhalide glasses are used both as luminescent and laser materials and as precursors to obtain glass-ceramics with a halide crystalline phase. The addition of fluorides or chlorides into the composition of glasses makes it possible to change the properties of glasses over a wide range - to expand the transparency range of glasses, to change the mechanical properties and viscosity of melts. Optical halide materials with a low-frequency phonon spectrum, doped with ions of rare-earth elements, are of great interest for IR applications. The transfer from oxofluoride glasses to oxochloride glasses should a decrease in the phonon energy, an expansion of the transparency range, and the production of luminescence in regions of spectra where this is impossible in oxide and oxofluoride systems. Doping with neodymium makes it possible to obtain luminescence both in the near infrared region and in the middle - at 2.6 and 5.2 microns. Moreover, the last band appears only in media with low-energy phonons, for example, in PbCl2. Lead oxochloride glasses, in contrast to oxofluoride glasses, has been much less studied. Based on a very wide field of vitrification in lead oxofluoride systems, in our work we decided to synthesize glasses based on PbF2-PbO-B2O3 (SiO2) systems by partially replacing PbF2 with PbCl2. Synthesized high-quality glass with a maximum PbCl2 content of 50 mol% in both chloroborate and chlorosilicate systems. In experiments with a higher concentration of PbCl2 in the charge, polycrystalline castings were obtained containing the crystalline phases PbCl2, Pb2OCl2, PbFCl. The absorption spectra of glasses doped with neodymium have all absorption bands typical of Nd. A detailed examination of individual transitions showed that for them the wavelength of the maximum shifts to longer wavelengths with the replacement of fluorine by chlorine. The luminescence spectra also show a shift in the maximum of the transition to longer wavelengths by more than 7 nm. In this case, as the chlorine content increases, the intensity of the long-wavelength components associated with transitions to excited sublevels increases. The shift to longer wavelengths depends on the ratio of the concentrations of lead chloride and fluoride; the larger the proportion of PbCl2, the greater the shift to longer wavelengths. The properties of the glasses were modified by heat treatment above the glass transition temperature and by exposure to laser radiation. During the modification, partial crystallization of the glasses is observed. This work was financially supported by the Ministry of Science and Higher Education of the Russian Federation within the FSSM-2020-0005 project.

Resume : FePt thin films are of high interest as a promising material for ultrahigh density magnetic recording media in data storage and HAMR application due to a high magnetocrystalline anisotropy, high values of saturation magnetization and corrosion resistance of ordered L1₀-FePt phase. The aim of the present work is an investigation of the effect of the additional Au(7.5 nm) layer which located as top, intermediate or bottom of FePt(15 nm) layer on phase formation, A1-FePt→L1₀-FePt transformation and structure in FePt-Au thin films during annealing in situ in the temperature range of 20 °C-700 °C Au/FePt, FePt/Au/FePt and FePt/Au thin films, as well as the reference FePt(15 nm) sample, were deposited by magnetron sputtering (Ar pressure 3.5×10^(-3) mbar) from individual Fe, Au and Pt targets onto Si(001)/SiO₂(100 nm) substrates kept at a room temperature. After deposition films with different location of Au layers, were separated from Si(001)/SiO₂(100 nm) substrates by etching in a mixture of HNO₃ and HF acids. Free films were placed onto Cu grids for TEM and then investigated by HEED method during annealing inside electron diffraction camera. The phase composition and structure of as-deposited and annealed in situ films were investigated by TEM as well. It was established that the location of the Au layer in the as-deposited film composition affects the stress in the FePt layer, parameters of its grain structure and ordering temperature of L1₀-FePt phase formation. In the separated from substrate films, the compressive stresses arise in FePt grains only due to the diffusion of gold along the FePt grain boundaries during annealing in situ. Compressive stresses contribute to the formation of the L1₀-FePt phase in accordance with the Le Chatelier rule, since the unit cell volume of this phase is less than that of disordered A1 – FePt. The lowest temperature (300 °C) of the beginning of L1₀ phase formation is observed in FePt/Au/FePt films with an intermediate Au layer.

Resume : The projective two-valued representations of spinor states for different points of Brollouin zones of crystalline graphite and single-layered graphene as well as of boron nitride (BN) and nitroborene have been constructed for the first time. Projective classes, which transform spin-dependent electronic wave functions at the points of high symmetry of the Brillouin zone have been determined for the above-mentioned structures. For the establishment of projective classes we found the method of constructing of factor systems, in particular, the correct factor system for spinor representations; the form of standard factor systems and the phase factors for their conversion to standard factor systems for each projective class have been found. The dispersion of the electronic states of these structures has been investigated by using the symmetric theoretical group methods. It is shown that the results of the developed methods of theoretical-group analysis are consistent with the data of experimental and computational studies of energy spectra and multiplicities of degeneration of quantum states of pi-electron zones.

Resume : Our research is based on two major scientific and technical problems: 1) the use of unique physicochemical properties of two-dimensional (2D) structures of graphene, BN and transition metals dichalcogenides of (TMD) MeX2, where Me - metals of IV, V and VI groups (Ti- Hf, V-Ta, Mo, W), and X = S, Se, Te, as well as 2) enhancing their capabilities during intercalation by impurity atoms and molecules. The results of a detailed study of the Raman spectra of natural MoS2 microcrystal (MC) powder and synthesized graphene-like 2H-MoS2 nanoparticles (NP) with additives 0.5 and 1 wt% of carbon excited by 488 nm and 632.8 nm laser radiation are highlighted here. A detailed numerical analysis of the shape of the observed D and G Raman bands, including their decomposition into spectral components, as well as comparison with the reference spectra of the detonation nanodiamonds of ~ 5 nm, is carried out. This revealed the formation of graphite and diamond-like nanostructures in MoS2 NC and their existence in molybdenite MC. Significant effect of 632.8 nm laser radiation that is in resonance with 2H-MoS2 excitons on synthesis and ordering of diamond and graphite-like structures was established for the first time

Resume : Among Chemical Vapor Depositions techniques, Vapour-Liquid-Solid (VLS) Gold-catalysed processes have been widely used to fabricate bottom-up Si nanowires (NWs). These 1D nanostructures improve the intrinsic thermoelectric (TE) properties of bulk Si and can be integrated into micromachined TE generators (μTEGs) [1]. However, NWs of SiGe alloys have always been more desirable thanks to their reduced thermal conductivity and, consequently, better TE Figure-of-Merit. Nevertheless, so far, these grow processes require relatively low growth temperatures (over 650 K); thus, they are slow and not suitable for integrating NWs into μTEGs. The correct doping of such NWs has resulted in being problematic too. Here we present a novel VLS methodology to grow in-situ heavily boron-doped SiGe NWs up to 15 μm long at a rate higher than 100 nm/min. This is the result of a combination of flows that include the use of borane, chloride acid, relatively low pressures (~ 300 Pa), and temperatures above 900 K. These NWs are easily integrated into μTEGs, and the improvement in the device's performance from Si NWs to SiGe ones have been evaluated. Moreover, the effect of boron impurities in the growth process has been assessed. X-ray fluorescence mapping of these NWs has revealed trends in the compositional properties, likely related to the morphological changes observed. Among those, maximum thresholds in the boron content for this VLS process can be highlighted. Beyond them, the catalyst gold amount trapped into the SiGe lattice dramatically increases, degrading the electrical conductivity and, thus, the TE properties. Additionally, hydrochloric acid's increased presence has shown to have positive effects in avoiding this phenomenon. Understanding this phenomenon is essential to overcome this limit and further improve the already encouraging results showed by this material [2]. References: [1] G. Gadea et al., "Towards a full integration of vertically aligned silicon nanowires in MEMS using silane as a precursor," Nanotechnology, vol. 26, no. 19, p. 195302, May 2015. [2] I. Donmez Noyan et al., "SiGe nanowire arrays based thermoelectric microgenerator," Nano Energy, vol. 57, pp. 492–499, Mar. 2019.

Resume : We study of the nonlinear optical and electronic properties in cylindrical core/shell quantum dots AlAs/GaAs in the presence of a donor impurity under a magnetic field. Our computations were carried out within the effective mass approximations. For the numerical solution of the resulting 3D partial differential equation (PDE) via finite element method. A detailed study of the donor binding energies as a function of the magnetic fields and impurity position is determined. Dipole matrix elements related inter-level optical transitions is investigated in order to analyze the absorption coefficient, second and third harmonic generation. Our results show that the magnetic fields have significant influences on the binding energy and on the linear and nonlinear optical properties.

Resume : The Zr0.8Sn0.2TiO4 (ZST) ceramics are very attractive for microwave (MW) applications, being successfully employed in dielectric resonator (DR) based devices. However, the use of ZST materials can be limited due to their extrinsic dielectric loss. Therefore, determination of the extrinsic and intrinsic losses is essential to decide when a synthesis cycle should be stopped. In this work, we present and discuss the THz and MW properties of the ZST ceramics obtained by conventional ceramic technology (CCT) and spark plasma sintering (SPS). The ZST-DRs obtained by CCT and SPS have shown relative densities of 96.5 % and 99.5 %, respectively. Structural, morphological, and dielectric characterizations of the samples were performed by X-ray Diffraction, Scanning Electron Microscopy, MW spectroscopy, and Terahertz Time-Domain Spectroscopy (THz-TDS). The ZST samples present no secondary phases and their lattice exhibit an orthorhombic unit cell. The SEM micrographs show that a segregation of pores occurs in the samples when the sintering time increases. The dielectric measurements show a change between extrinsic and intrinsic losses depending on the frequency band: in MWs, a substantial contribution is given by the extrinsic losses, while the THz measurements actually provide mainly information on the intrinsic losses. The intrinsic losses (Q × f ~ 60 THz) of the ZST DRs have been derived from THz data. The THz-TDS is shown to be a very useful technique for estimation of intrinsic losses of MW dielectrics, ensuring a fast screening of new materials. Acknowledgments: This work was supported by a grant of the Romanian Ministry of Education and Research, CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED-2019-3351, within PNCDI III.