Thin films of rare-earth metal oxy-hydrides (REHO) are a new class of inorganic mixed-anion materials, which exhibit a photochromic effect and a light-induced resistivity change at room temperature and ambient pressure. This switchable optical and electrical property enables their utilization in a multitude of technological applications, such as energy-saving smart windows, sensors, ophthalmic lenses, and medical devices. In order to tune and fully exploit REHOs in these applications, complete knowledge of the dependence of physical properties on the composition and the structure is crucial. The proposed project is based on the very recent discovery of the photochromism in REHOs and aims to study the relationship between the thin film deposition parameters, chemical composition, and structure of existing REHOs with the focus on the photochromic effect and discover new photochromic REHOs. The project proposes to produce REHOs in the thin film form and do in-depth characterisation by advanced in-lab techniques both ex-situ and in-operando. Magnetron sputtering has been chosen as the deposition technique since it is among the most widely used types of deposition by the glazing industry because it can be scaled up to large-area substrates together with a high growth rate, which is highly important for the large-scale production.
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.09.2021. - 31.12.2021.)
Work package 1. Deposition of REHO thin films.
Vibration spectroscopy techniques (Raman and FTIR) were exploited to study the structure of YHxOy in more detail, as it is still not fully understood. The YHxOy films were deposited on silicon and metal substrates to be able to measure high quality FTIR and Raman spectra, respectively, without a disturbing signal from the substrate. To supress the interaction between YHxOy and air, the part of samples was covered by a thick metal film in the same deposition chamber before breaking the vacuum. In this case, for the Raman measurements, the metal substrates were replaced with substrates that have high visible light transmittance but low Raman signal. Isotopically exchanged films were synthesised to identify hydrogen related vibrations in the measured spectra.
In the search for a new photochromic REHO material, Eu of the rare-earth elements was selected. Since the surface oxide layer does not stop further oxidation of Eu, as in the case of Y, the work with Eu is more complicated. Process parameters for a stable discharge in the reactive pulsed-DC magnetron sputtering from metallic Eu target were found. Total sputtering pressure was the main parameter that was varied during the development of Eu hydride and oxy-hydride films deposition. Pressure is an effective parameter to control the hydrogen concentration in the Eu films, see Fig. 1(a). Oxy-hydride phase was produced by the introduction of oxygen in the deposition chamber after the deposition. The samples of EuHx, EuH2-x, and EuHxOy were directly transferred (without breaking the vacuum) and stored in an Ar atmosphere glove-box connected to the vacuum system to protect the films from the interaction with air. A thin (15 nm) capping layer of aluminium (Al) deposited by thermal evaporation was tested to protect the films from the oxidation in the ambient conditions. A photochromic effect in EuHxOy was not discovered after irradiation with UV/blue light.
Work package 2. Thin film characterisation.
Several measurement techniques/geometries and samples/structures were used to obtain the vibration spectra of YHxOy samples. In the beginning, the samples were irradiated from the film surface side. The FTIR spectra were measured in transmittance mode, and the Raman signal was collected from the scattered light. The films, which were covered by a metal layer, were irradiated through the substrate during the measurements. In this case, the FTIR spectra were measured in reflectance mode.
The detected vibration bands are relatively wide due to the small crystallite size of approximately 10 nm according to XRD data. Vibration data of YHO are almost non-existent to the best of our knowledge, so no reference can be used to identify the structure. Both experiment and theory were used to interpret the spectra. Based on the theoretically stable YHxOy structures found in literature and our XRD data, YHxOy was modelled using the crystallographic structure belonging to different space groups. YHxOy was modelled using linear combination of atomic orbitals (LCAO) method within the framework of the hybrid density functional approach. LCAO calculations, including analyses of phonon frequencies and vibration intensities, were performed using algorithms as implemented in CRYSTAL17 code. The activities on the vibration properties of YHxOy and interpretation will continue after the project to complete the results for publication in a scientific journal.
EuHxOy and alloyed Y-Eu hydride films were produced in accordance with the project objectives. The films were characterised by XRD, SEM (Fig. 1(b)), ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy, and spectroscopic ellipsometry. Due to the lack of information on the deposition of this type of materials, the results obtained appear to be suitable for a short communication paper.
(a)
In Ar atmosphere
3 hours in air
(b)
Figure 1. EuHx thin films on glass substrates synthesised at different H2 pressures (a), and surface morphology of the EuH<sub>x</sub>O<sub>y</sub> film imaged by an electron scanning microscope at high magnification (b).
An article has been submitted in international scientific journal within the framework of this project:
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.06.2021. - 31.08.2021.)
Work package 1. Deposition of REHO thin films.
During this period, a set of YHO samples for X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy measurements at different film deposition pressures were prepared on titanium substrates. Samples were stored under an inert gas (argon) atmosphere to evaluate their stability to samples stored at ambient conditions.
Work package 2. Thin film characterisation.
The XPS results confirm that the previously observed gradient of optical properties perpendicular to the film substrate is related to changes in chemical composition (Fig. 1). The ratio of oxygen to yttrium concentration decreases from the surface of the films to the substrate.
Figure 1. YHO film on Ti substrate XPS depth profile measurement. Y signal - blue line, O signal - green line, Ti signal - red line.
The results of this project are presented in several reports at the international conference E-MRS Fall meeting 2021:
Magnetron sputtered YHO thin film oxydation dynamics and optical properties;
Optical band gap determination issues for amorphous and crystalline metal-oxide thin films;
Figure 2. Schematic illustration of the sensory device based on reflectivity measurement setup with the capability to measure both the ratio of the amplitude and the phase shift (a). Main ellipsometric angles (Δ, Ψ) as a function of photon energy with 0.02 eV step for the structure Si/Au(29 nm)/YHO(12 nm)/SiO2(35 nm)/YHO(15 nm)/Au(6 nm) (b).
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.03.2021. - 31.05.2021.)
Work package 1. Deposition of REHO thin films.
During the appropriate time period, a vacuum device was prepared for film deposition in plasma at elevated substrate temperature – 300 °C, and a short set of YHO samples were prepared to evaluate the effect of substrate temperature on film oxidation both during the process and after in the oxygen-containing atmosphere. The vacum coater is being equipped with an additional gas supply to vary the composition of the films and to decipher the vibration spectra of the films in detail.
Work package 2. Thin film characterisation.
Surface morphology studies of the prepared YHO films were performed by scanning electron microscopy (Fig. 1) and its change depending on the deposition pressure was observed. SE studies of new sample series show an increase in the refractive index n and the fundamental optical bandwidth Eg and a decrease in the extinction coefficient k, increasing the pressure from 3 to ~6.5 mTorr. As the pressure increases above 6.5 mTorr, the (n, k) decrease. Semiconductor films have a pronounced optical gradient: n decreases from the bottom to the top of the film. With an increase of sputtering pressure, the gradient decreases.
Figure 1. Surface morphology of an YHO film imaged by an electron scanning microscope at high magnification.
A scientific paper is currently being prepared that includes all the results obtained from the deposition of the YHO thin films and their characterization. The paper describes in detail the oxidation dynamics of the films depending on the deposition parameters. In addition, a comprehensive description of the structure, surface morphology, and optical properties of the films is provided. At the international conference CSW2021, a poster presentation entitled “Multilayer Structures With Spectral Darkness For Biomedical Sensor Applications” was presented, which included the results of the respective project. In addition, two abstracts have been submitted for the international conference E-MRS Fall meeting 2021.
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.12.2020. - 28.02.2020.)
Work package 1. Deposition of REHO thin films.
During the appropriate time period, a reactive magnetron sputtering vacuum system for the deposition of YHO thin films was successfully prepared and several sets of YHO samples were prepared on different types of substrates – glass, silicon and titanium. In a narrow range of process parameters (sputtering pressure), photosensitive films were obtained (see Figure 1). For the first time in the study of this material, the oxidation dynamics was determined both during the deposition process and during the introduction of oxygen gas after the process by measuring the visible light transmittance spectra while the sample is still in the vacuum chamber.
Figure 1. Photochromic effect of YHO thin film using UVA and blue light.
Work package 2. Thin film characterisation.
The following measurements were performed on the prepared samples – X-ray diffraction (XRD), light (UV-Vis-NIR) transmittance and reflectance, spectral ellipsometry (SE) and analysis, optical microscopy, and profilometry measurements. An experimental system was prepared and the first measurments were performed to determine the change in light absorption during illumination, and a photochromic effect was observed. The films are polycrystalline and the transmitance of visible light is controlled by the deposition pressure. SE studies show a significant decrease in the refractive index n and the fundamental optical bandwidth Eg and a decrease in the extinction coefficient k, increasing the pressure from 3 to ~8.0 mTorr. As the pressure increases above 8 mTorr, the optical constants decrease. Semiconductor films have a pronounced optical gradient: n decreases from the bottom to the top of the film. During the photochromic effect, the k increase and the Eg decreases.
As a result of the experiments, the milestone 1 provided in the project plan has been achieved - definition of optimal process parameters for the stable/reproducible synthesis of YHO films.
PROJECT'S PUBLICATIONS:
ABSTRACT: Herein, the concept of point of darkness based on polarized light phase difference and absorption of light is demonstrated by simulations using low refractive index and extinction coefficient semiconductor and dielectric, and high refractive index nonoxidizing metal multilayer thin film structures. Several multilayer sensor configurations show great sensitivity to thickness and refractive index variation of the detectable material by measuring the reflectivity ratio Ψ and phase shift Δ. Focus is on such multilayers, which have sensitivity to both parameters (Ψ, Δ) in the visible spectral range, thus opening the possibility for further research on a new biomedical sensor development with enhanced double parameter sensing.
VPP-COVID-2020/1-0004
The Institute of Solid State Physics, together with other institutions, participates in the implementation of the project, which is related to the solution of problems related to COVID-19. The overall goal of the project is to provide medical institutions with up-to-date information and technologies that will help reduce the risk of infection and reduce the workload of medical staff.
Within the framework of the project, the Institute of Solid State Physics study the anti-microbial effect of different types of WO3-x, WO3-x:Cu, Cu, WO3-x/Cu/WO3-x thin coatings, as well as the possibilities of improving the chemical and mechanical strength of these coatings.
Magnetron sputtering technology is used to obtain coatings. Variation of process parameters provides an opportunity to obtain coatings with different physical-chemical properties, and to variate chemical composition.
Obtained coatings ability to transmit visible light provides the possibility to use coatings on protective screens, contact surfaces, and in protective suits visors. The possibilities of practical application of the developing prototype correspond to the project goals.
Project implementation process:
At the beginning of 09.2020, the first batch of samples was tested, anti-microbial activity was observed for several coating types, also physical-chemical properties were tested.
Based on the previously collected data, a second batch of test samples was prepared.
Total cost: 200 000 EUR
Duration (years): 2018-2020
LZP FLPP No.LZP-2018/2-0353
Searching for new high temperature superconductors which could be used in everyday applications is nowadays one of the most important and challenging problems in physics and materials science. A huge step forwad has been made in 2015, when superconductivity has been discovered in hydrogen sulfide with the record-hight critical temperature Tc = 203K. Although the physical mechanisms responsible for superconductivity are known, more detailed experimental information about behaviour of the electrons and their coupling with the phonons is requied. In this project we aim to obtain new information about the evolution of the electronic and the local atomic structures in hydrogen rich metal hydrides as temperature and pressure (200 GPa) are varied. We will apply the novel microbeam synchrotron-radiation based X-ray absorption fine structure (XAFS) technique at extreme pressure. The Y-H and La-H systems, will be examined where new hydrogen-rich phases are predicted to be formed with the Tc higher than in supfur hydride. The structural information obtained by advanced ab-initio XAFS analysis including including Reverse Monte Carlo will be compared with the theoretically predicted superconducting phases. The project is multidisciplinary and combines materials science, synchrotron radiation technique at extreme pressure, solid state chemistry, physics and computer science.
Total cost: 199 508 EUR
Duration (years): 2018-2020
LZP FLPP Nr. lzp-2018/2-0083
The utilization of solar energy to convert water into hydrogen via efficient photocatalysis is an ultimate goal of clean energy society. The current understanding of processes taking place at nanostructured photoelectrode surfaces is insufficient to rationally design the efficient photochemical reactor for visible-light-driven water splitting. Engineering the electronic energy band structure of hybrid nanostructured semiconductor materials through judicious control of their atomic composition is a promising route to increase visible light photoresponse. In this respect, before time-consuming and expensive experimental synthesis of nanophotocatalyst combined with spectroscopy and electrochemical measurements, it is reasonable to perform thorough theoretical modelling of the mid-gap states and band edge positions of promising photoelectrodes. The main goal of our project is to develop a reliable theoretical approach based on multi-scale computer modelling for fundamental understanding of such factors as composition, atomic and electronic structure, and charge transfer processes at hybrid nanostructured photocatalysts vital for their further synthesis and experimental characterization. The project results in improvements in efficiency, durability, and, consequently, the cost of photochemical reactors allowing efficient hydrogen production from water.
Horizon 2020
Duration (years): 2018-2020
Grant agreement No 768789.
The CO2EXIDE project aims at the development of a combined electrochemical-chemical technology for the production of ethylene oxide from biobased CO2. Initially, the electrochemical step pursues the simultaneous conversion of CO2 to ethylene at the cathode and water oxidation to hydrogen peroxide at the anode. A subsequent chemical conversion of both intermediates to ethylene oxide will deliver e.g. oligo-/polyethylene glycol in a chemical cascade reaction. The CO2EXIDE technology combines a modular nature for the feasibility of a decentralised application, a high energy and material efficiency/yield and the substitution of fossil based production of ethylene oxide. In line with the energy turnaround, the CO2EXIDE technology will be combinable with renewables and allows for the direct creation of products, which can be integrated into the existing supply chain. The reactions will be operated at low temperatures and pressures and forecast significant improvements in energy and resource efficiency combined with an enormous reduction of GHG emissions. All improvements will be quantitated using life cycle assessment.
The role of the Institute of Solid State Physics, University of Latvia (ISSP UL) in the project is to create an alternative structure of the cathode for electrocatalytic reduction of CO2 to ethylene, based on modified multi-layer graphene stacks obtained from recycled graphite. In addition, the ISSP UL will perform theoretical calculations from the first principles of the graphene sheet modified with copper atom clusters, and will construct innovative electrochemical half-cell to monitor with FTIR spectroscopy the gases in CO2 reduction process. SPEEK polymer composites with zirconium oxide nanoparticles and ionic liquid derived from imidazole compounds will be developed to form a membrane that is compatible with the catalyst materials and stimulates the adsorption of the CO2 on the electrode.
EUROfusion
XAS studies on a 14%Cr ODS alloy and on ion-irradiated RAFM steels (2018 - 2020)
European Regional Development Fund projects
Total budget: 25 000 EUR
Duration: 1.04.2020.-30.09.2020.
Project number: KC-PI-2020/45
The aim of the project is to develop and commercialize cheap nanowire-based photodetectors for the UV-VIS-IR range and nanowire photodetectors for the X-ray range. Inexpensive small photodetectors may be in high demand for the implementation of the Internet of Things concept. Within the first stage of the project, it is planned to carry out a technical and economic feasibility study of the technology transfer project and to develop a commercialization strategy.
Total budget: 648 750 EUR
Duration of the project: 01.03.2019. – 28.02.2022.
Project number: 1.1.1.1/18/A/073
The aim of this industrial research project is to develop advanced Reactive High Power Impulse Magnetron Sputtering (HiPIMS) technologies for deposition of functional transition metal oxide (TMO) multilayers for electrochromic and transparent electronics applications to produce and investigate functional TMO multilayers on the basis of ReO3-WO3 and their combination with transparent conducting oxides as novel bifunctional coatings and to develop roll-to-roll reactive R-HiPIMS technologies.
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.01.2022.- 28.02.2022.)
March 17 2022
The project No. 1.1.1.1/18/A/073 has been implemented in collaboration between the Institute of Solid State Physics University of Latvia (ISSP UL, in Thin Films Laboratory (TFL)) and the vacuum coating SME company Sidrabe Vacuum, Ltd. The project is related to non-economic activity and combines fundamental and industrial research. The total cost is 648750 EUR with 600000 EUR (92.5%) EU contribution. The duration of the project is 36 months (01.03.2020-28.02.2022).
The aim of this industrial research project was to develop advanced Reactive High Power Impulse Magnetron Sputtering (R-HiPIMS) technologies for deposition of functional transition metal oxide (TMO) multilayers for electrochromic and transparent electronics applications. We proposed to produce and investigate functional TMO multilayers and their combination with transparent conducting oxides as novel bifunctional coatings. This Interdisciplinary Project consists of the research activities in Physical and Chemical sciences (1.3, 1.4) and Materials engineering (2.5).
The products of the project:
Novel R-HiPIMS technology of deposition of functional TMO thin films and multilayers on flexible substrate, and upscale the process (4 patents are submitted: (EU) - EP20020352.9, (LV) - LVP2020000040, (EU) - EP21208104.6, (LV) - LVP2021000084, and description of the roll-to-roll process technology is prepared);
Novel thin films of ReO3, ReO3-WO3, ReO3/WO3, WO3/Cu/WO3, and Zn-Ir-O with advanced electric and optical properties. The description of local electronic and atomic structures in conjunction with their phys-chem. properties using the state-of-art XAFS. Atomic structures of the TMO using first-principles computer modelling. Original scientific articles published in magazines or conference proceedings included in the Web of Science or SCOPUS (A or B) database) – 15 (14 published and 1 submitted) scientific papers.
The project greatly contribute to advanced materials research on oxide-based optoelectronics devices, which according to the International Technology Roadmap for Semiconductors (ITRS2.0), have global impact ensuring the competitiveness of Latvian science and Industry at the international level. In addition to the impact on the market, there are scientific benefits resulting from the use of interdisciplinary approach combining advanced plasma technologies of R-HiPIMS technology (2.5. Materials engineering) with a theoretical quantum chemical approach along with samples experimental characterisation by phys-chem. methods (1.3. Phys. sciences; 1.4. Chem. sciences) with a focus on the first-principles computer modelling of TMO and heterostructures as well as the state-of-the-art synchrotron-based techniques.
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.10.2021.- 31.12.2021.)
January 11 2022
An article entitled Reactive HiPIMS deposition process of ReOx (x = 1.6–2.9) thin films is submitted in journal Materials Chemistry and Physics (IF=4.1). Repeated XRD measurements were performed to determine the stability of the coatings under ambient conditions. Prior to the publication of the article, in-depth XPS measurements and analysis were performed, revealing Re ions of different oxidation states on the film surface (activity 1).
Bulk and (001) surface F-center ab initio computations in ABO3 perovskites in their high-symmetry cubic phase were performed for SrZrO3, PbTiO3, BaTiO3 and SrTiO3 perovskites, as well as SrF2, BaF2 and CaF2 fluorites, by means of the CRYSTAL computer program package. Results allow to report comprehensive ab initio computation results dealing with F-centers in SrZrO3, PbTiO3, BaTiO3 and SrTiO3 matrixes, as well as SrF2, BaF2 and CaF2 fluorites. As result the publication "Tendencies in ABO3 perovskite as well as SrF2, BaF2 and CaF2 bulk and surface F-center ab initio computations at high symmetry cubic structure", Roberts I. Eglitis, Juris Purans, Anatoli I. Popov, Ran Jia has been prepared and submitted to a scientific journal Symmetry (activity 3).
Article “Unraveling the Structure and Properties of Layered and Mixed ReO3-WO3 Thin Films Deposited by Reactive DC Magnetron Sputtering” written by Boris Polyakov, Edgars Butanovs, Andrejs Ogurcovs, Anatolijs Sarakovskis, Martins Zubkins, Liga Bikse, Jevgenijs Gabrusenoks, Sergei Vlassov, Alexei Kuzmin, and Juris Purans was accepted for publication in ACS Omega journal (IF= 3.5, Q1, 70th Percentile in Chemical Engineering) (activity 4).
In this study, we developed a novel method to produce layered ReO3/WO3 and mixed ReO3-WO3 thin films by reactive DC magnetron sputtering and subsequent film annealing in air. The crystalline structure of obtained films, their optical and electrical properties were studied by several methods, and the formation of ReO3-WO3 solid solutions was proposed. Additionally, first-principles density functional theory (DFT) calculations were performed for selected compositions of solid solutions to model their structural and electronic properties. Our work significantly complements the previous research performed on ReO3-WO3 solid solution thin films and will stimulate future studies on practical applications of the films, such as electro- and photo-catalysis (activity 4).
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.07.2021.- 30.09.2021.)
October 7 2021
During the appropriate time period, the results on the deposition of ReOx thin films by reactive HiPIMS were presented at the international conference “11th International Conference on HIPIMS” and a publication entitled “Reactive HiPIMS deposition process of ReOx thin films” has been prepared for submission to a scientific journal (Activity 1).
Taking into account the analysis of systematic trends of different surfaces, the scientific article “Comparative hybrid Hartree-Fock-DFT calculations 2 of WO2-terminated cubic WO3 as well as SrTiO3, 3 BaTiO3, PbTiO3 and CaTiO3 (001) surfaces” was published (activity 3) in a journal Crystals whose citation index reaches at least 50 per cent of the industry average citation index.
The calculations with Hybrid Density Functional Theory (DFT) and experiments with X-ray absorption spectroscopy (XAS) were performed to conduct the studies of of the local atomic structure around Ir ions in ZnO thin films. The results were used in the analysis of the first principles of thermoelectric properties of materials. A scientific article “The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiments” was published (activity 3) in a journal žurnālā Journal of Materials Chemistry C and access to the article in the form of Open Access is being prepared.
A study was conducted, and a novel method was developed to produce layered ReO3/WO3 and mixed ReO3-WO3 thin films by reactive DC magnetron sputtering and subsequent film annealing in air. The crystalline structure of obtained films, their optical and electrical properties were studied by several methods, and the formation of ReO3-WO3 solid solutions was proposed. Additionally, first-principles density functional theory (DFT) calculations were performed for selected compositions of solid solutions to model their structural and electronic properties. Our theoretical predictions qualitatively agree with the experimental results. The publication entitled "Unraveling the Structure and Properties of Layered and Mixed ReO3-WO3 Thin Films Deposited by Reactive DC Magnetron Sputtering" has been prepared for submission to a scientific journal ACS Omega (Activity 4).
The preparation and characterization of ReO3-WO3 thin film samples on quartz was continued.
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.04.2021. - 30.06.2021.)
July 23 2021
As part of Project production of new TMO/Me/TMO samples and optimization of parameters were carried out (activity 1).
A scientific publication entitled "Reactive HiPIMS deposition process of ReOx thin films" is in preparation process (activity 1), which includes all the results obtained from the study of the reactive HiPIMS process using the Re target and the characterization of ReOx thin films. The publication describes in detail the changes in pulse current profiles and plasma optical emission spectra (OES) depending on the process parameters. In addition, a comprehensive description of the structure, composition and physical properties of the films is provided.
The first first-principles calculations were performed for the WO2-terminated cubic WO3 (001) surface and analyzed the systematic trends for different surfaces. As result the article “Comparative hybrid Hartree-Fock-DFT calculations 2 of WO2-terminated cubic WO3 as well as SrTiO3, 3 BaTiO3, PbTiO3 and CaTiO3 (001) surfaces” were published (activity 3).
The study of the local atomic structure around Ir ions in ZnO thin films with different iridium content was conducted and combined with the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments. Results was then used in the first principles analysis of the thermoelectric properties of material. The research allowed to look at the sensitivity of calculated Seebeck coefficient dependences to the atomic and electronic structure. As result scientific publication "The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiments" was prepared and published (activity 3).
The ReO3 and WO3 thin films deposition technology using magnetron sputtering and thermal anneling methods was developed and improved.
The preparation and characterization of ReO3-WO3 thin film samples on quartz was continued.
An article related to experiments with Zinc-Iridium Oxide (Zn-Ir-O) thin films as a p-type conducting material in different conditions is in the process of preparation (Activity 4).
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.01.2021. - 31.03.2021.)
April 10 2021
A scientific publication entitled "Reactive HiPIMS deposition process of ReOx thin films" is currently being prepared (activity 1), which includes all the results obtained from the study of the reactive HiPIMS process using the Re target and the characterization of ReOx thin films. The publication describes in detail the changes in pulse current profiles and plasma optical emission spectra (OES) depending on the process parameters. In addition, a comprehensive description of the structure, composition and physical properties of the films is provided.
The formation of CdTe and CdO nanocrystals in a-SiO2/n-Si ion track templates were synthesized by electrochemical and chemical deposition as well as the results of a study of the electrical properties of such new systems were studied. As result the scientific study “Ion track template technology for fabrication of CdTe and CdO nanocrystals” were published.
A study was conducted in which the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments with different parameters were combined and used in the first principles analysis of thermoelectric properties of ZnO material. As result scientific publication "The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiments" was submitted and positively reviewed (activity 3). The final version is being prepared (activity 3).
The article “Comparative hybrid Hartree-Fock-DFT calculations 2 of WO2-terminated cubic WO3 as well as SrTiO3, 3 BaTiO3, PbTiO3 and CaTiO3 (001) surfaces” (DOI: 10.1016/j.nimb.2020.08.009), which is based on the first principle calculations for different surfaces has been submitted and accepted for publication.
EXAFS experiments were also held on amorphous ReO3 and preparation of publication is in progress (activity 4). Two more articles are prepared. One related to experiments with Zinc-Iridium Oxide (Zn-Ir-O) thin films as a p-type conducting material in different conditions with focusing on the structure and the electrical properties of Zn-Ir-O films in the large Ir concentration range (activity 4). Additionally, two different substrate temperatures were used – without intentional heating and at 300 °C. Second article is related to research held with nanocrystalline zinc peroxide (nano-ZnO2), its structure, optical and vibrational properties (activity 4). Nanocrystalline zinc peroxide was synthesized through a hydrothermal process and comprehensively studied using several experimental techniques.
PUBLICATIONS:
1. A. Chesnokov, D. Gryaznov, N. V. Skorodumova, E. A. Kotomin, A. Zitolo, M. Zubkins, A. Kuzmin, A. Anspoks, J. Purans.
The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiments.
2. A. Akilbekov, R. Balakhayeva, M. Zdorovets, Z. Baymukhanov, F.F. Komarov, K. Karim, A.I. Popov, A. Dauletbekova.
Ion track template technology for fabrication of CdTe and CdO nanocrystals.
Nucl. Instrum. Methods Phys. Res. B, 2020, 481, pp. 30–34.
DOI: 10.1016/j.nimb.2020.08.009
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.10.2020. - 31.12.2020.)
January 10 2021
As part of Project No 1.1.1.1/18/A/073 “Smart Metal Oxide Nanocoatings and HIPIMS Technology” Thin films of rhenium oxide on quartz substrates were deposited by reactive high power impulse magnetron sputtering (R-HiPIMS) (activity 1). They were made by varying the synthesis parameters - substrate temperature and gas composition during deposition. The surface morphology of the films was studied by high-resolution electron microscopy and demonstrated at different substrate temperatures and post-treatment (annealing). Depending on the manufacturing conditions, both crystalline and amorphous structures were detected. In addition, film composition (XPS), visible and near infrared absorption, and electrical conductivity were measured (activity 4).
Comparative first principles calculations (activity 3) for the ReO2-terminated ReO3 as well as TiO2-terminated SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces were carried out. The first principles calculations showed systematic trend for the ReO2-terminated ReO3 as well as for TiO2-terminated SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces is inward relaxation of all upper layer and outward relaxation of all second layer atoms. The only two exceptions from this systematic trend is outward relaxation of the first layer O atom on the TiO2-terminated PbTiO3 (001) surface as well as inward relaxation of the ReO2-terminated ReO3 (001) surface second layer O atom.
Our calculated band gaps at the G-G point for the ReO2-terminated ReO3 as well as TiO2-terminated SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces in all cases are decreased regarding to the respective bulk values. Just opposite to the TiO2-terminated SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces, where the Ti-O chemical bond population are larger than in the bulk, near the ReO2-terminated ReO3 (001) surface, the Re-O chemical bond population is reduced in comparison to the bulk value.
The publication “Comparative hybrid Hartree-Fock-DFT calculations of ReO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surfaces” were prepared (activity 3) within the project.
ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.05.2020. – 31.07.2020.)
July 31 2020
Research activities (activity 1) on the production of ReO3 and WO3 thin films and their heterostructures were continued within the project activities “Development of the reactive R-HiPIMS sputtering TMO thin film deposition technology” and “Characterization of the obtained TMO and EC samples”. Successfully developed ReO3 and WO3 thin film deposition technology using reactive high power impulse magnetron sputtering (R-HiPIMS) mode and thermal annealing. The R-HiPIMS mode at different pulse configurations and oxygen flows has been studied using I-V-t curves and plasma optical emission spectroscopy. In total, 10 ReO3-WO3 thin film samples on quartz and 18 ReOx samples on capton, glass and quartz were prepared and characterized. International patent (EU) - EP20020352.9 submitted 04.09.2020.
Development (activity 2) of the roll-to-roll reactive R-HiPIMS sputtering TMO thin film deposition technology (activity 2). One patent (LV) - LVP2020000040 already submitted and roll-to-roll R-HIPIMS process technology is described (2 reports). 10 samples synthesized (planned 10), deposition reports are delivered by Ltd.Sidrabe Vacuum. Samples are used for activity N.4. Connecting R-HIPIMS power supply to the chamber with two magnetrons installed Ltd.Sidrabe Vacuum. Choosing optimal hardware for in situ plasma spectroscopy and installing it in the chamber using optical fiber in the way that it gives trustworthy results with stationary installments. Choosing necessary targets and substrates for the experiment.
Four articles have been published (ativity3) in internationally cited journals. We performed, for first time, ab initio calculations for the ReO2-terminated ReO3 (001) surface and analyzed systematic trends in the ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surfaces using first-principles calculations. According to the ab initio calculation results, all ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, all second-layer atoms relax upwards and all third-layer atoms, again, relax inwards.
The ReO2-terminated ReO3 and ZrO2-terminated SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface band gaps at the G–G point are always reduced in comparison to their bulk band gap values. The Zr–O chemical bond populations in the SrZrO3, BaZrO3, PbZrO3 and CaZrO3 perovskite bulk are always smaller than those near the ZrO2-terminated (001) surfaces. In contrast, the Re–O chemical bond population in the ReO3 bulk (0.212e) is larger than that near the ReO2-terminated ReO3 (001) surface (0.170e). Nevertheless, the Re–O chemical bond population between the Re atom located on the ReO2-terminated ReO3 (001) surface upper layer and the O atom located on the ReO2-terminated
ReO3 (001) surface second layer (0.262e) is the largest.
Research activities (activity 4). Two articles have been published in internationally cited journals on ReOx, ReO3 and ReS2: 1) "Understanding the Conversion Process of Magnetron-Deposited Thin Films of Amorphous ReOx to Crystalline ReO3 upon Thermal Annealing", Polyakov et al, Cryst. Growth Des. 2020, 20, 6147−6156 ; 2) "Synthesis and characterization of GaN/ReS2, ZnS/ReS2 and ZnO/ReS2 core/ shell nanowire heterostructures", Butanovs et al, Applied Surface Science 536 (2021) 147841.
ABSTRACT: We performed, to the best of our knowledge, the world’s first first-principles calculations for the WO2-terminated cubic WO3 (001) surface and analyzed the systematic trends in the WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface ab initio calculations. According to our first principles calculations, all WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, while all second-layer atoms relax upwards. The only two exceptions are outward relaxations of first layer WO2 and TiO2-terminated WO3 and PbTiO3 (001) surface O atoms. The WO2 or TiO2-terminated WO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (001) surface-band gaps at the Γ–Γ point are smaller than their respective bulk-band gaps. The Ti–O chemical bond populations in the SrTiO3, BaTiO3, PbTiO3 and CaTiO3 bulk are smaller than those near the TiO2-terminated (001) surfaces. Conversely, the W–O chemical bond population in the WO3 bulk is larger than near the WO2-terminated WO3 (001) surface.
ABSTRACT: We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content. This was then used in the first principles analysis of the thermoelectric properties of material. The emphasis has been put on the conditions for a positive Seebeck coefficient and p-type electrical conductivity as the functions of the Fermi level. We studied both computationally and experimentally several possible IrOx polyhedra (complexes) with a different number of surrounding oxygens and Ir oxidation states, including those with the formation of peroxide ions (O22−). In particular, octahedral coordination of iridium ions was identified by reverse Monte Carlo (RMC) simulations of the Ir L3-edge EXAFS spectra of ZnO:Ir thin films as the predominant complex, which is supported by the calculated lowest interstitial oxygen incorporation energies. All the calculated IrOx (x = 4, 5, 6) complexes, regardless of Ir the oxidation state, demonstrate potential for p-type conduction if the Fermi level (μF) falls in the range of 0–0.8 eV from the valence band maximum (VBM) and the Ir concentration is high enough (12.5% in the present DFT calculations). Even though the corresponding calculated Seebeck coefficient (S) around 80–89 μV K−1 slightly exceeds the experimental values, we emphasise the presence of an important plateau in the dependence of S on μF in this range for two complexes with the formation of peroxide ions (O22−). We predicted also that peroxide ions O22− are characterized by the calculated phonon frequencies of 810–942 cm−1 in agreement with our previous Raman experimental results. In this light, we discuss the high sensitivity of calculated S(μF) dependences to the atomic and electronic structure.
ABSTRACT: Layered 2D van der Waals (vdW) materials such as graphene and transition metal dichalcogenides have recently gained a great deal of scientific attention due to their unique properties and prospective applications in various fields such as electronics and optoelectronics, sensors and energy. As a direct bandgap semiconductor in both bulk and monolayer forms, ReS2 stands out for its unique distorted octahedral structure that results in distinctive anisotropic physical properties; however, only a few scalable synthesis methods for few-layer ReS2 have been proposed thus far. Here, the growth of high-quality few-layer ReS2 is demonstrated via sulfurization of a pre-deposited rhenium oxide coating on different semiconductor material nanowires (GaN, ZnS, ZnO). As-produced core-shell heterostructures were characterized by X-ray diffraction, scanning and transmission electron microscopy, micro-Raman spectroscopy and X-ray absorption spectroscopy. Experimental characterizations were supported by total energy calculations of the electronic structure of ReS2 nanosheets and GaN, ZnS, and ZnO substrates. Our results demonstrate the potential of using nanowires as a template for the growth of layered vdW materials to create novel core-shell heterostructures for energy applications involving photocatalytic and electrocatalytic hydrogen evolution.
Applied Surface Science, Volume 536, 15 January 2021, 147841.
ABSTRACT: The synthesis of CdTe nanocrystals was studied by electrochemical (ECD) and chemical (CD) deposition in SiO2/Si-n structures irradiated with 200 MeV 132Xe ions. Both types of electrolyte (sulfate and chloride) used in ECD led to the formation of CdTe nanocrystals in single wurtzite phase. On the other hand, in the case of CD in a sulfate solution, CdTe nanocrystals with a zinc blende structure (ZBS) are formed that coexist with CdO nanocrystals in the hexagonal structure. Furthermore, an increase in the temperature of the CD solution led only to the formation of hexagonal phase of CdO nanocrystals. A model is proposed for the formation of a CdTe nanocrystal inside the ion track, taking into account the influence of a weak external electric field on the region of the inner surface of the ion tracks.
Surface and Coatings Technology, Volume 401, 15 November 2020, 126269
ABSTRACT: By means of the CRYSTAL computer program package, first-principles calculations of polar ZrO-, Ca- and O-terminated CaZrO3 (011) surfaces were performed. Our calculation results for polar CaZrO3 (011) surfaces are compared with the previous ab initio calculation results for ABO3 perovskite (011) and (001) surfaces. From the results of our hybrid B3LYP calculations, all upper-layer atoms on the ZrO-, Ca- and O-terminated CaZrO3 (011) surfaces relax inwards. The only exception from this systematic trend is outward relaxation of the oxygen atom on the ZrO-terminated CaZrO3 (011) surface. Different ZrO, Ca and O terminations of the CaZrO3 (011) surface lead to a quite different surface energies of 3.46, 1.49, and 2.08 eV. Our calculations predict a considerable increase in the Zr–O chemical bond covalency near the CaZrO3 (011) surface, both in the directions perpendicular to the surface (0.240e) as well as in the plane (0.138e), as compared to the CaZrO3 (001) surface (0.102e) and to the bulk (0.086e). Such increase in the B–O chemical bond population from the bulk towards the (001) and especially (011) surfaces is a systematic trend in all our eight calculated ABO3 perovskites.
ABSTRACT: We performed, for first time, ab initio calculations for the ReO2-terminated ReO3 (001) surface and analyzed systematic trends in the ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surfaces using first-principles calculations. According to the ab initio calculation results, all ReO3, SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface upper-layer atoms relax inwards towards the crystal bulk, all second-layer atoms relax upwards and all third-layer atoms, again, relax inwards. The ReO2-terminated ReO3 and ZrO2-terminated SrZrO3, BaZrO3, PbZrO3 and CaZrO3 (001) surface band gaps at the Γ–Γ point are always reduced in comparison to their bulk band gap values. The Zr–O chemical bond populations in the SrZrO3, BaZrO3, PbZrO3 and CaZrO3 perovskite bulk are always smaller than those near the ZrO2-terminated (001) surfaces. In contrast, the Re–O chemical bond population in the ReO3 bulk (0.212e) is larger than that near the ReO2-terminated ReO3 (001) surface (0.170e). Nevertheless, the Re–O chemical bond population between the Re atom located on the ReO2-terminated ReO3 (001) surface upper layer and the O atom located on the ReO2-terminated ReO3 (001) surface second layer (0.262e) is the largest.
ABSTRACT: CdTe and CdO nanocrystals were synthesized by chemical deposition into a-SiO2/n-Si ion track template formed by 200 MeV Xe ion irradiation with the fluence of 108 ions/cm2. Depending on the temperature of the solution CdTe + CdO and single-phase CdO with a hexagonal crystal structure were obtained, respectively. The study of the current – voltage characteristics of the obtained structure with the single-phase CdO allows us to estimate the number of grain boundaries and the height of the potential barrier, as well as the n-type conductivity.
Thin films of rhenium trioxide (ReO3) were produced by reactive DC magnetron sputtering from a metallic rhenium target, followed by annealing in the air in a range of temperatures from 200 to 350 °C. Nanocrystalline single-phase ReO3 films were obtained after being annealed at about 250 °C. The thin films appeared bright red in reflected light and blue-green in transmitted light, thus showing an optical transparency window in the spectral range of 475–525 nm. The film exhibited a high conductivity as evidenced by macro- and nanoscale conductivity measurements. The long-range and local atomic structures of the films were studied in detail by structural methods, such as X-ray diffraction and X-ray absorption spectroscopy. The oxidation state (6+) of rhenium was confirmed by X-ray photoemission and X-ray absorption spectroscopy. The nanocrystalline morphology of the annealed films was evidenced by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The obtained results allowed us to propose a mechanism of rhenium oxide conversion from the initially amorphous ReOx phase to cubic ReO3.
ABSTRACT: The paper presents and discusses the results of performed calculations for YAlO3 (111) surfaces using a hybrid B3LYP description of exchange and correlation. Calculation results for SrTiO3, BaTiO3 and BaZrO3 (111) as well as YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surfaces are listed for comparison purposes in order to point out systematic trends common for these four ABO3 perovskite (001) and (111) surfaces. According to performed ab initio calculations, the displacement of (001) and (111) surface metal atoms of YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskite, upper three surface layers for both AO and BO2 (001) as well as AO3 and B (111) surface terminations, in most cases, are considerably larger than that of oxygen atoms. The YAlO3, SrTiO3, BaTiO3 and BaZrO3 (001) surface energies for both calculated terminations, in most cases, are almost equal. In contrast, the (111) surface energies for both AO3 and B-terminations are quite different. Calculated (111) surface energies always are much larger than the (001) surface energies. As follows from performed ab initio calculations for YAlO3, SrTiO3, BaTiO3 and BaZrO3 perovskites, the AO- and BO2-terminated (001) as well as AO3- and B-terminated (111) surface bandgaps are almost always reduced with respect to their bulk bandgap values.
ABSTRACT: Atomistic understanding of the interaction between defects and active surface of the sensor is necessary for the developing devices detecting bio-and gas mixtures. We performed first principles computer simulations of the carbon dioxide (CO2) molecule adsorption on a ZnO surface in various configurations and location on the surface. It is shown that the tridentate configuration is the most energetically favorable, the binding energy of the molecule weakly depends on the surface coverage. The presence of intrinsic defects on the surface, such as an oxygen vacancy, leads to a small reduction of the binding energy. The observed data from the NEXAFS experiment and hypothetical formation of a new compound H2CO on the surface are discussed in the light of our calculations.
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