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Thin Films Laboratory website » Projects » Ongoing projects
 
Ongoing projects  
 
 
 
Latvian Council of Science Projects

  

Total budget: 299 991 EUR

Duration (years): 2021 - 2023

Agreement No: LZP-2020/1-0026

In this project, we plan to develop and to investigate new charge density wave (CDW) material hybrid nanowire heterostructures suitable for photodetection in a wide wavelength range. The project idea is based on the combination of CDW material shell and semiconductor nanowire core, resulting in hybrid core-shell nanowires. We plan to investigate layered CDW hybrid systems growth on substrates with a hexagonal crystal structure that are stable in a corrosive sulfur atmosphere, such as GaN, InN, and ZnS, and on materials that can be converted to sulfides, such as ZnO (ZnS). The layered CDW materials to be studied are mainly transition metal chalcogenides (TaS2, VS2, VSe2, TiSe2, etc.). Several synthesis methods will be used and compared to grow the shell of the CDW material (eg pulsating layer deposition, magnetron sputtering, etc.). The electronic and optoelectronic properties of the core-shell nanowires will be studied by integrating them into a single nanowire device, such as a field effect transistor and a phototransistor. The project includes theoretical calculations aimed at studying the structure and properties of the core-shell interface.



Total budget: 281 478 EUR

Duration: 01.01.2021 – 31.12.2023.

Agreement No: lzp-2020/1-0345

Motivated by the high demand for transparent electrical conductors, in this fundamental project we will investigate the topological-like electrical conductivity in Ga2O3 thin films grown via MOCVD on different orientation (including off-axis) sapphire substrates that could be applied in Ga2O3 -based transparent electrodes in ultraviolet optoelectronic devices. The key result will be deeper physical understanding of sapphire substrate crystallographic orientation impact on topological-like metallic conductivity in β– Ga2O3 thin films. Information about epitaxial relations between the film and the substrate together with advanced in-depth film characterization methods might elucidate the surface conductivity mechanism. The origin of a such exceptionally robust conduction merits to be investigated more deeply, because it challenges our current understanding and ways to achieve solar-transparent conducting electrodes in a wide bandgap insulator.
The planned activities include establishment of the MOCVD process for growing epitaxial monocrystalline β–Ga2O3 thin films, investigation of as-grown thin film electrical properties together with detailed structural, compositional and optical characterization of the films by traditional laboratory and advanced synchrotron radiation methods with focus on surface properties and possible donor doping, and large-scale theoretical calculations to elucidate the possible surface conductivity mechanisms.



Total cost: 100 389.00 EUR

Duration (years): 2020-2021

LZP FLPP Nr. lzp-2020/2-0291

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.


 

 
 
 
European Regional Development Fund projects

 

Total budget: 539 594.38 EUR

ISSP UL budget: 309 397.25 EUR

Duration: 01.04.2021 - 30.09.2023.

Agreement No: 1.1.1.1/20/A/060

Functional ink-jet printing is a promising new technology, cheap and environmentally friendly, and creates a new paradigm in digital manufacturing where electronic devices and circuits can be printed on demand.
The main goalof this project is a development and demonstration of the ink-jet technology that will be able to print wearable and flexible functional electronic devices, including the inductive antenna, capable of capturing electrical energy in the kilohertz range and feeding printed electroluminescent light-emitting devices implemented as 2D drawings.
The main result of the project is the development of the ink-jet printed prototype of a light-emitting device coupled with a wireless energy-receiving antenna.
The proposed Industrial research project is implemented by the Institute of Solid State Physics, University of Latvia (ISSP UL) and LESLA LATVIA company. This interdisciplinary project consists of the research activities in Physical (1.3) and Chemical (1.4) sciences, Electrical engineering, electronics, information and communication technologies (2.2), Materials science (2.5) and Nanotechnology (2.10), according to the OECD Frascati Manual.




Total budget: 537 004 EUR

Duration: 01.01.2021 - 30.06.2023.

Agreement No: 1.1.1.1/20/A/057

Gallium oxide Ga2O3 has become one of the most investigated materials of today. Nearly every issue of material-related scientific journals contains articles on growth, material properties, or device applications of gallium oxide. The reason for this large interest is the extremely promising properties for electronic and optical applications of this wide bandgap material, together with the relatively un-expensive substrate wafers. Very recently, ultrawide-bandgap spinel zinc gallate ZnGa2O4 has been demonstrated to exhibit several benefits over gallium oxide that merits to be investigated more deeply.
The aim of this industrial research project is to develop advanced high rate PVD magnetron sputtering and MOCVD technologies for deposition of functional ultrawide-bandgap gallium oxide Ga2O3 and zinc gallate ZnGa2O4 thin films for optoelectronics and electronics applications.
The main goals are:
• To develop high rate PVD magnetron sputtering technology for deposition of pure and doped (p-type dopants and RE) amorphous and crystalline gallium oxide Ga2O3 thin films and ZnGa2O4 thin films. The applications in focus are (1) deep UV TCOs/TSOs and (2) efficient inorganic luminescence devices (a-Ga2Ox:RE).
• To develop MOCVD technology of Ga2O3 and ZnGa2O4 thin films deposition and to establish epitaxial n- and p-type Ga2O3 and ZnGa2O4 thin film growth processes for deep UV optoelectronics and electronics applications.
The proposed Industrial research project will be implemented by ISSP LU, SIA AGL Technologies and SIA BC Corporation Limited. This Interdisciplinary Project consists of the research activities in Physical and Chemical sciences (1.3, 1.4) and Materials engineering (2.5).

 

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.07.2021.- 30.09.2021.)

October 7 2021

Within the framework of the project, the development of high-speed Ga2O3 thin films deposition technology has been started and the production and characterization of a series of samples has been performed. The optical transmittance, reflection and absorption spectra, X-ray diffraction data and properties of Ga2O3 coating at different temperatures were studied and collected. (Activity 1).

A price survey was conducted and the purchase of sputtering targets was made (Activity 1).

The preparation of the Aixtron (AIX-200RF) MOCVD system for the growth of Ga2O3 and ZnGa2O4 films was completed and the preparation of the technical report has been started. Work has begun on growing Ga2O3 thin films on c-plane sapphire using H2O as the oxygen source. The development and drawing of a new reactor design is continued in cooperation with SIA BC Corporation Limited - the drawing of the chamber's cooling body, substrate heater and rotation mechanism is being performed. The MOCVD is now equipped with an O2 gas precursor, which is used in parallel with H2for Ga2O3 thin film synthesis experiments. An in-depth study of the structure and composition of the grown thin films is performed. (Activity 2).

Nanocrystalline zinc peroxide (nano-ZnO2) was synthesized through a hydrothermal process and comprehensively studied using several experimental techniques. Its crystal structure was characterized by X-ray diffraction. The temperature-dependent local environment around zinc atoms was reconstructed using reverse Monte Carlo (RMC) analysis. Lattice dynamics of nano-ZnO2 was studied by infrared and Raman spectroscopy. The obtained experimental results were supported by first-principles density functional theory (DFT) calculations. As result scientific publication "A comprehensive study of structure and properties of nanocrystalline zinc peroxide" was prepared and published in Journal of Physics and Chemistry of Solids. (Activity 3).

The preparation and testing of structural and morphological methods (XRD, XPS, SEM, TEM) for the characterization of Ga2O3 and ZnGa2O4 thin films were completed and the preparation of a technical report has been started. The characterization of Ga2O3 thin films obtained by magnetron sputtering and MOCVD was started in order to understand and optimize deposition processes. (Activity 4).

The project results were presented at the 2021 Fall Meeting conference of the European Materials Research Society (E-MRS) with a poster presentation "Growth of gallium oxide based core-shell nanowire heterostructures". (Activity 4).

 

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.04.2021.-30.06.2021.)

July 23 2021

Preparation of the sputtering system for use in two-magnetron DC, RF and HiPIMS sputtering configuration was continued. The design and installation of target containers for metallic Ga targets suitable for reactive sputtering from a liquid metal target and arrangement of the chamber interior geometry for sputtering in upward direction was completed. Testing of the installed target has been started. Practical knowledge related to the growth of Ga2O3 and ZnGa2O4 thin films on their structure, electrical and optical physical properties has been acquired. As a result of the research, a scientific article “A comprehensive study of the structure and properties of nanocrystalline zinc peroxide” was prepared and submitted (activity 1).

Plasma Optical Emission spectroscopy line has been installed and tuned, Gallium spectral lines have been identified for process control (activity 1).

Aixtron (AIX-200RF) MOCVD system preparation for Ga2O3 and ZnGa2O4 thin film deposition has been performed: fabrication and testing of a new silicon carbide heating element in an oxidative atmosphere; growing Ga2O3 and ZnGa2O4 thin films with MOCVD on sapphire substrates of different orientations; engineering and drawing of a new reactor design in collaboration with SIA BC Corporation Limited (activity 2).

Ab-initio calculations of doped Ga2O3 was conducted. Analysis of material atoms, electronic and oscillation properties, analysis of formation energies of various configurations were performed. The article “Ab-initio calculations of oxygen vacancy in Ga2O3 crystals” was published in an internationally cited journal: LATVIAN JOURNAL OF PHYSICS AND TECHNICAL SCIENCES, Vol. 58, N 2 (2021), 3-11 (activity 3).

An open procurement was announced for the purchase of substrates, chemicals and other laboratory equipment necessary for the implementation of the project. Preparation and testing of structural and morphology characterization methods (XRD, XPS, SEM, TEM) for Ga2O3 and ZnGa2O4 thin films has been continued (activity 4).

 

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.01.2021. - 31.03.2021.)

April 2 2021

As part of Project No 1.1.1.1/20/A/057 preparation and testing of the vacuum system, gas inlet system, substrate heating system, target cooling and heating system and connection of the necessary (DC, RF, HiPIMS) power supplies for use in two-magnetron sputtering configuration has been started. Development of design of target containers for metallic Ga targets suitable for reactive sputtering from a liquid metal target and arrangement of the chamber interior geometry for sputtering in upward direction also is started (activity 1).

Magnetron sputtering targets purchase order placed (activity 1).

Aixtron (AIX-200RF) MOCVD system preparation for Ga2O3 and ZnGa2O4 thin film deposition has been done: testing of reactor stability at high temperature while using oxidative precursor; engineering and drawing of a new reactor design in collaboration with SIA BC Corporation Limited; replacement of malfunctioning parts (activity 2).

Study was conducted and the formation energy and transition levels of oxygen vacan­cies in β-Ga2O3 crystal using the B3LYP hybrid exchange-correlation functional within the LCAO-DFT approach was calculated. As result information for article “Ab-initio calculations of oxygen vacancy in Ga2O3 crystals” was prepared (activity 3).

Preparation and testing of structural and morphology characterization methods (XRD, XPS, SEM, TEM) for Ga2O3 and ZnGa2O4 thin films has been done (activity 4).



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 01.07.2021.- 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.


Crystals 2021, 11(4), 455.
DOI: 10.3390/cryst11040455
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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.



Journal of Materials Chemistry C, 2021, Accepted Manuscript.
DOI: 10.1039/D1TC00223F
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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.

DOI: 10.1016/j.apsusc.2020.147841
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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

DOI: 10.1016/j.surfcoat.2020.126269
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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.


Journal of Materials Science, volume 55, pages 203–217 (2020)
DOI: 10.1007/s10853-019-04016-3
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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.


Crystals 2020, 10(9), 745.
DOI: 10.3390/cryst10090745
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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.


Nucl. Instrum. Methods Phys. Res. B, 2020, 481, pp. 30–34.
DOI: 10.1016/j.nimb.2020.08.009
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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.


Cryst. Growth Des. 2020, 20, 9, 6147–6156
DOI: 10.1021/acs.cgd.0c00848
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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.


International Journal of Modern Physics B, Vol. 33, No. 32, 1950390 (2019)
DOI: 10.1142/S0217979219503909
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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.


AIP Conference Proceedings 2174, 020181 (2019)
DOI: 10.1063/1.5134332


 
 
Postdoctoral projects

  


Total budget: 111 504.90 EUR

Duration: 01.01.2021 - 30.06.2023.

Agreement No: 1.1.1.2/16/I/001

Within the framework of this project, various 2D materials will be studied to find the best combinations between: sulfide materials - MoS2, WS2, ReS2, TaS2, VS2, TiS2, SnS2, CuS; and oxide materials - MoO3, WO3, V2O5, MnO2, etc., with the aim of developing sensor elements in the form of a field effect transistor (FET). In addition to the FET configuration, a p-n transition will be created instead of a simple S-D channel based on 2D materials, which can significantly expand the functionality of this type of element. In order to achieve a certain level of sensor selectivity, it is necessary to functionalize the working surface of the obtained elements with certain types of organic and inorganic chemicals (linkers), the level of response of such elements to the chemical reaction on their surfaces will be studied. The elements will be combined in an array, each sensitive element must respond uniquely to each substance of interest. However, instead of seeking to increase the sensitivity and selectivity of an array of individual sensor elements, which may be difficult to achieve, an option with less selective components is possible by creating a so-called 'cross-reactive' sensor array. This type of response processing of individual sensor elements will be performed using machine learning algorithms, obtaining a unique response pattern or "fingerprint". This challenging task will be solved using modern experimental methods, incl. also pulsed laser sputtering (PLD), atomic force microscopy (AFM), scanning electron microscopy (SEM). The multidisciplinary aspects of the project reflect its complex nature, which includes various chemical and physical methods of sensor fabrication, the use of a wide range of experimental methods for sensor testing, and the use of electronics and computer programming for sensor performance analysis.



 
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Institute of Solid State Physics, University of Latvia, Thin Films Laboratory