Analysis of self-trapped hole mobility in alkali halides and metal halides

Support from Latvian National Research Program IMIS2 (2014–2017) and LZP Grant No. 237/2012 (2013–2016) is greatly appreciated.The small radius hole polarons (self-trapped holes (STH) known also as the Vk centers) are very common color centers observed in numerous alkali halides and alkaline-earth halides. Their mobility controls the rate of secondary reactions between electron and hole defects and thus radiation stability/sensitivity of materials. We have analysed here the correlation between the temperatures at which hole polarons start migration in a series of alkali halides (fluorites, chlorides, bromides, iodides) and the lattice displacement around quasi-molecule. These results are especially important for identification of the self-trapped holes, for example, in novel scintillating materials such as SrI2, as well as in a large family of perovskite halides and more complex halide materials.IMIS2; LZP Grant No. 237/2012; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Nanoporous characterization of modified humidity-sensitive MgO-Al2O3 ceramics by positron annihilation lifetime spectroscopy method

The work was supported by the Ukrainian Ministry of Education and Science. H. Klym thanks Prof. O. Shpotyuk for the fruitful discussion.Investigation of nanopores in the humidity-sensitive MgO-Al2O3 ceramics modified at 1100°C for 2 hours was performed using positron annihilation lifetime spectroscopy method. Lifetimes of the third and fourth components of positron annihilation lifetime spectra obtained by four-component fitting procedure were used for calculation of nanopores radii. Transformation in free volumes was studied in ceramics after drying and exposure to water vapor. It is established that the lifetime of the third component decreases and the intensity of this component increases in ceramics exposed to water vapor reflecting ortho-positronium decay in nanopores simultaneously with annihilation in water bubbles. The characteristics of the fourth component (lifetime and intensity) decrease in ceramics exposed to water vapor reflecting ortho-positronium trapping in free-water volume of nanopores. Final drying of the MgO-Al2O3 ceramics results in returning of ortho-positronium lifetimes and intensities to the initial values confirming good desorption of water from nanopores of ceramics.Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Influence of "productive" Impurities (Cd, Na, O) on the Properties of the Cu2ZnSnS4Absorber of Model Solar Cells

The research has been supported by grant of the Ministry of Education and Science of the Republic of Kazakhstan AP09562784. The authors (D. Sergeyev) acknowledges the provision of SCAPS-1D software by Prof. Marc Burgelman. The research of A.I. Popov has been supported by the Institute of Solid State Physics (ISSP), University of Latvia (UL). ISSP UL as the Centre of Excellence is supported through the Framework Program for Euro-pean Universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project.Abstract The study focuses on the optical properties of the CZTS multicomponent semiconductor absorber with 3 % "production"impurities of Cd, Na, O within the framework of the density functional theory using the generalized gradient approximation and the SCAPS program, as well as investigates their influence on the performance and efficiency of CZTS-solar cells. The results showed that the introduction of Cd, Na, O impurities would lead to a decrease in the intensity of the absorption bands at 2.06 eV and 2.55 eV. The density of states CZTS: (Cd, Na, O) was determined from first principles, and it was revealed that impurities of Cd and O atoms would lead to a decrease in the band gap (to 0.9 eV and 0.79 eV), and an increase in Na impurity absorption (1.2 eV). It was also found that a decrease in the band gap led to a decrease in the open circuit voltage, and it was also shown that "industrial"impurities led to a decrease in the efficiency of energy conversion of solar cells to 2.34 %. © 2021 D. Sergeyev et al., published by Sciendo. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.Ministry of Education and Science of the Republic of Kazakhstan AP09562784; ISSP UL as the Centre of Excellence is supported through the Framework Program for Euro-pean Universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project

Luminescence characteristics of magnesium aluminate spinel crystals of different stoichiometry

We are grateful to Drs E. Vasil’chenko and A. Maaroos for the help with experiments and useful discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. In addition, the research leading to these results has received funding from the Estonian Research Council Institutional Research Funding IUT02-26.Magnesium aluminate spinel single crystals with different stoichiometry, MgAl2O4 (1:1 spinel) and MgO 2.5Al2O3 (1:2.5) were investigated using different optical methods (cathode-, photo- and thermally stimulated luminescence (TSL), optical absorption, "creation spectra" of TSL peaks and phosphorescence by VUV radiation). Low-temperature charge carrier traps and the position of intrinsic UV emission bands depend on the degree of stoichiometry. Antisite defects (ADs), Mg2+ or Al3+ located in a "wrong" cation site (Mg|A1 or Al|Mg) are the main as-grown structural defects, which serve also as efficient traps for electrons and holes as well as seeds for bound excitons. AD concentration is especially high in 1:2.5 spinel. There are several manifestations of ADs (electronic excitations near ADs) in the spectral region of 7-7.5 eV, slightly below the energy gap.Eesti Teadusagentuur IUT02-26; H2020 Euratom 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Neutron characterization of aluminium nitride nanotubes

The results of experiments carried out at the ILL neutron facilities in Grenoble on nanotubes of aluminum nitride synthesized through a DC arc plasma process are presented. We discuss the phonon generalized density of states G(ω) of the nanotubes in comparison with bulk AlN. G(ω) for the bulk features two main bands at low (about 30 meV) and high (about 80 meV) frequencies. Both bands are completely smeared out in the nanomaterial indicating a broad distribution of force constants induced by structural disorder. Apart from the smearing out of the vibrational bands, we observe enhanced intensities at low frequencies (ω < 10 meV) as usually found in disordered systems. Two additional bands at 12 and 17 meV hint at pure aluminium regions within the nanomaterial. The observed changes in the microscopic dynamics must lead to appreciable differences in the thermal and transport properties of the nanotubes with respect to the bulk material. Powder diffraction experiments show sharp lines from crystalline regions..

Peculiarities of the diffusion-controlled radiation defect accumulation kinetics under high fluencies

We are grateful to A. Lushchik and E. Shablonin for numerous and valuable discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.Theory is developed for kinetics of the diffusion-controlled radiation defect accumulation in crystalline solids under high fluencies taking into account recently observed correlation between the defect diffusion energy and pre-exponential (known as the Meyer-Neldel rule in chemical kinetics) and their dependence on the radiation fluence (Kotomin et al., J Phys Chem A 122 (2018) 28). The predicted accumulation kinetics could be applied to all kinds of solids. It considerably differs from the commonly used, in particular, suggesting that concentration growth at high fluencies could be nonmonotonous and the saturation defect concentrations independent on the temperature.EUROfusion Consortium Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Computer Simulation of the Electric Transport Properties of the FeSe Monolayer

The research has been supported by the grant of the Ministry of Education and Science of the Republic of Kazakhstan AP08052562. In addition, the research of AIP has been supported by the Latvian- Ukrainian Grant LV-UA/2018/2.The paper deals with the model research of electric transport characteristics of stressed and non-stressed FeSe monolayers. Transmission spectra, current-voltage characteristic (CVC) and differential conductivity spectra of two-dimensional FeSe nanostructure have been calculated within the framework of the density functional theory and non-equilibrium Green's functions (DFT + NEGF). It has been shown that the electrophysical properties depend on the geometry of the sample, the substrate, and the lattice constant. On CVC of non-stressed sample in the range from -1.2 V to -1 and from 1.2 V to 1.4 V, a region of negative differential resistance (NDR) has been observed. NDR is at both signs of the applied voltage due to the symmetry of the nanostructure. d2I/dV2 is used to determine the nature of the electron-phonon interaction and the features of quasiparticle tunnelling in stressed and non-stressed samples. The results obtained can be useful for calculating new elements of 2D nanoelectronics. © 2020 D. Sergeyev et al., published by Sciendo 2020. --//-- Published under the CC BY 4.0 license.Ministry of Education and Science of the Republic of Kazakhstan AP08052562, LV-UA/2018/2; The Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Thermal annealing and transformation of dimer F centers in neutron-irradiated Al2O3 single crystals

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. In addition, the research leading to these results has received funding from the Estonian Research Council grant (PUT PRG619).The precise study of the thermal annealing of the F2-type dimer defects, being under discussion in the literature for a long time and responsible for the number of absorption bands below 4.5 eV, has been performed in corundum single crystals irradiated by fast neutrons with a fluence of 6.9 × 1018 n/cm2. The Gaussian components of the radiation-induced optical absorption with the maxima at 4.08, 3.45 and 2.75 eV have been considered as a measure of the F2, F2+and F22+centers, respectively. In contrast to the Fand F+ centers, the concentration of which continuously decreases at the sample heating up to 1100 K, the concentration of dimer defects with different charge states passes the increasing stages above 500 K starting from the F22+centers. The tentative mechanisms of such rise of the F22+centers as well as of the subsequent transformation/rise of dimer centers, F22+→F2+→F2at 650-800 K are considered. The possible sources of carriers needed for the recharging of dimer centers are also analysed on the basis of thermally stimulated luminescence measurements up to ~850 K.EUROfusion Consortium, Euratom research and training programme 2014-2018 and 2019-2020, grant agreement No 633053; Estonian Research Council grant (PUT PRG619); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Chlorine Adsorption on TiO2(110)/Water Interface: Nonadiabatic Molecular Dynamics Simulations for Photocatalytic Water Splitting

This study was financially supported M-ERA.NET project CatWatSplit. Institute of Solid State Physics, University of Latvia, as the Center of Excellence, has received funding from the European Union’s Horizon 2020 Framework Program H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under Grant Agreement No. 739508, project CAMART2. The calculations were performed at the Latvian SuperCluster (LASC) located in Institute of Solid State Physics, University of Latvia.Chloride is one of the most abundant ions in sea water, which is more available than fresh water. Due to lack of H2O adsorbate states near the valence band maximum (VBM) edge, the difficulty of water dissociation incidents has been reported on the rutile TiO2 surface as the excitation energy is around the band gap energy of TiO2. It is interesting whether the extra chloride can be a benefit to the water dissociation or not. In this study, the models of chlorine adatoms placed on the rutile TiO2 (110)/water interface are constructed using ab initio methods. The time-dependent spatial charges, bond-lengths of water molecules, and Hirshfeld charges are calculated by real-time time-dependent density functional theory and the Ehrenfest dynamics theory for investigating the excited state nonadiabatic dynamics of water dissociation. This study presents two photoinduced water-splitting pathways related to chlorine and analyzes the photogenerated hole along the reactions. The first step of water dissociation relies on the localized competition of oxygen charges between the dissociated water and the bridge site of TiO2 for transforming the water into hydroxyl and hydrogen by photoinduced driving force. --//-- This is an open access article Y.-P. Lin, D. Bocharov, I. Isakoviča, V. Pankratov, A.A. Popov, A.I. Popov, S. Piskunov; Chlorine adsorption on TiO2(110)/water interface: Nonadiabatic molecular dynamics simulations for potocatalytic water splitting; Electron. Mater., 2023, 4, pp. 33-48; DOI: 10.3390/electronicmat4010004; https://www.mdpi.com/2673-3978/4/1/4 published under the CC BY 4.0 licence.M-ERA.NET project CatWatSplit; Institute of Solid State Physics, University of Latvia, as the Center of Excellence, has received funding from the European Union’s Horizon 2020 Framework Program H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under Grant Agreement No. 739508, project CAMART2

Electrochemical Growth and Structural Study of the AlxGa1−xAs Nanowhisker Layer on the GaAs Surface

The study was supported by the Ministry of Education and Science of Ukraine via Project No. 0122U000129 “The search for optimal conditions for nanostructure synthesis on the surface of A3B5, A2B6 semiconductors and silicon for photonics and solar energy”, Project No. 0121U10942 “Theoretical and methodological bases of system fundamentalization of the future nanomaterials experts training for productive professional activity”, and Project No. 0123U100110 “System of remote and mixed specialized training of future nanoengineers for the development of new dual-purpose nanomaterials”. In addition, the research of A.I.P. and Y.S. was partly supported by COST Action CA20129 “Multiscale irradiation and chemistry driven processes and related technologies” (MultiChem). Y.S. was partly supported by COST Action CA20126—Network for research, innovation, and product development on porous semiconductors and oxides (NETPORE). A.I.P., thanks to the Institute of Solid State Physics, University of Latvia, ISSP UL as the Center of Excellence, is supported through the Framework Program for European Universities, Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2, under Grant Agreement No. 739508, CAMART2 project.This work presents a novel, cost-effective method for synthesizing AlxGa1−xAs nanowhiskers on a GaAs surface by electrochemical deposition. The process begins with structuring the GaAs surface by electrochemical etching, forming a branched nanowhisker system. Despite the close resemblance of the crystal lattices of AlAs, GaAs, and AlxGa1−xAs, our study highlights the formation of nanowhiskers instead of layer-by-layer film growth. X-ray diffraction analysis and photoluminescence spectrum evaluations confirm the synthesized structure’s crystallinity, uniformity, and bandgap characteristics. The unique morphology of the nanowhiskers offers promising implications for solar cell applications because of the increased light absorption potential and reduced surface recombination energy losses. We conclude by emphasizing the need for further studies on the growth mechanisms of AlxGa1−xAs nanowhiskers, adjustments of the “x” parameter during electrochemical deposition, and detailed light absorption properties of the formed compounds. This research contributes to the field of wideband materials, particularly for solar energy applications, highlighting the potential of electrochemical deposition as a flexible and economical fabrication method. --//-- This is an open access article: Suchikova, Y.; Kovachov, S.; Bohdanov, I.; Abdikadirova, A.A.; Kenzhina, I.; Popov, A.I. Electrochemical Growth and Structural Study of the AlxGa1−xAs Nanowhisker Layer on the GaAs Surface. J. Manuf. Mater. Process. 2023, 7, 153. https://doi.org/10.3390/jmmp7050153 published under the CC BY 4.0 licence.Ministry of Education and Science of Ukraine via Project No. 0122U000129, Project No. 0121U10942, Project No. 0123U100110; COST Action CA20129 MultiChem; COST Action CA20126 NETPORE; the Institute of Solid State Physics, University of Latvia, ISSP UL as the Center of Excellence, is supported through the Framework Program for European Universities, Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2, under Grant Agreement No. 739508, CAMART2 project