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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.


 

ABSTRACT: One-dimensional (1D) nanostructures – nanowires (NWs) – exhibit attractive properties for integration in different types of functional devices. Their properties can be enhanced even further or tuned for a specific application by combining different promising materials, such as layered van der Waals materials and conventional semiconductors, into 1D-1D core–shell heterostructures. In this work, we demonstrated growth of GaN-MoS2 and GaN-WS2 core–shell NWs via two different methods: (1) two-step process of sputter-deposition of a sacrificial transition metal oxide coating on GaN NWs followed by sulfurization; (2) pulsed laser deposition of few-layer MoS2 or WS2 on GaN NWs from the respective material targets. As-prepared nanostructures were characterized via scanning and transmission electron microscopies, X-ray diffraction, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. High crystalline quality core–shell NW heterostructures with few-layer MoS2 and WS2 shells can be prepared via both routes. The experimental results were supported by theoretical electronic structure calculations, which demonstrated the potential of the synthesised core–shell NW heterostructures as photocatalysts for efficient hydrogen production from water.


Appl. Surf. Sci. 590, 153106 (2022)
DOI: 10.1016/j.apsusc.2022.153106
Download preprint



ABSTRACT: During the synthesis of heterostructured nanomaterials, unwanted structural and morphological changes in nanostructures may occur, especially when multiple sequential growth steps are involved. In this study, we describe a synthesis strategy of heterostructured ZnS/Al2O3/MoS2 core-shell nanowires (NWs), and explore the role of the Al2O3 interlayer during synthesis. Core-shell NWs were produced via a four-step route: (1) synthesis of ZnO NWs on a silicon wafer, (2) deposition of thin Al2O3 layer by ALD, (3) magnetron deposition of MoO3 layer, and (4) annealing of the sample in the sulphur atmosphere. During sulphurization, ZnO is converted into ZnS, and MoO3 into MoS2 , while the Al2O3 interlayer preserves the smooth surface of an NW required for the growth of a continuous MoS2 shell. The resulting ZnS/Al2O3/MoS2 core-shell NWs were characterized by transmission electron microscopy, X-ray diffraction and photoelectron spectroscopy, Raman spectroscopy, and optical photoluminescence spectroscopy. A reported strategy can be used for the synthesis of other core-shell NWs with a transition metal dichalcogenides (TMDs) shell to protect the NW core material that may otherwise be altered or damaged by the reactive chalcogenides at high temperatures.


Journal of Alloys and Compounds (in press), Volume 918, 15 October 2022, 165648
DOI: 10.1016/j.jallcom.2022.165648
Download preprint




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.

 

 

Conferences:

CSW-2021, Multilayer Structures With Spectral Darkness For Biomedical Sensor Applications, abstract (download), poster (download).

E-MRS 2021 Fall meeting, Magnetron sputtered YHO thin film oxydation dynamics and optical properties, abstract (download), presentation (download).

E-MRS 2021 Fall meeting, Optical band gap determination issues for amorphous and crystalline metal-oxide thin films, abstract (download), presentation (download).

 

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:
Oxidation dynamics and optical properties of oxygen-containing yttrium hydride thin films”, M. Zubkins, I. Aulika, E. Strods, V. Vibornijs, L. Bikse, A. Sarakovskis, H. Arslan, J. Purans.
 

 

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;
  • Nanocrystalline/Amorphous semiconducting yttrium monoxide.

An article has been published within this project:

I. Aulika, M. Zubkins, J. Butikova & J. Purans,
Enhanced Reflectivity Change and Phase Shift of Polarized Light: Double Parameter Multilayer Sensor,
Phys. Status Solidi A 2021, 2100424.
(Fig. 2).
(a)
 
 (b) 
 
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.


Phys. Status Solidi A 2021, 2100424.
DOI: 10.1002/pssa.202100424
Download preprint


 
 
European Regional Development Fund projects

 

Total funding: The total budget is 500 000 EUR with ERAF contribution of 425 000 EUR.

Duration: 01.01.2022 - 30.11.2023
 
Identification number: Nr.1.1.1.1/21/A/050
 
Project aim:

The aim of this industrial research project is to develop advanced roll-to-roll (hereinafter R2R) physical vapour deposition (PVD) technology for large scale production of a new type of multifunctional antibacterial and antiviral (MABAV) coatings. We propose to produce and investigate MABAV materials in the form of thin films and multilayers with photochromic and transparent conducting multifunctionalities based on rare-earth oxy-hydrides (REHO) and metal oxides (MO) in combination with the metal and other dopants.

Project summary:

COVID-19 pandemic calls for new ways to combat pathogen resistance. The pathogens can persist on several types of surfaces long enough causing transmission of various infectious diseases [1], which are a continuous threat to human health and have a negative impact on the economy. The hospital environment is the epicentre of most antibiotic-resistant infections, especially respiratory pathogens, and where outbreaks occur. According to the European Centre for Disease Prevention and Control, more than four million people are estimated to acquire a healthcare-associated infection (HCAI) every year in Europe [2]. In addition, antimicrobial resistance towards antibiotics is growing everyday due to environmental changes and microbial adaptation abilities. For these reasons, the development of advanced solutions is urgently needed today. The knowledge on the survival of bacteria, fungi, viruses, and protozoa on surfaces, and hence, in a broader sense, in the human environment, is important for planning and implementing tactics for prevention of HCAI [3].

Within the framework of this industrial research project an advanced roll-to-roll (hereinafter R2R) physical vapour deposition (PVD) technology for large scale production of a new type of multifunctional antibacterial and antiviral (MABAV) coatings will be developed. MABAV materials in the form of thin films and multilayers with photochromic and transparent conducting multifunctionalities based on rare-earth oxy-hydrides (REHO) and metal oxides (MO) in combination with the metal and other dopants will be produced and investigated.

Applications: smart windows/glass, smart foils/sheets (as partitions and barriers in public places) and transparent electronics applications, including medical devices, with the aim to prevent the diseases in terms of reduction of bacteria and virus prevalence with attention to the SARS-CoV-2 to limit and reduce the spread of this virus and consequently caused illness COVID-19.

This project will be implemented by the Institute of Solid State Physics of University of Latvia (ISSP UL), a vacuum coating SME company SIDRABE Vacuum Ltd (SIDRABE) and Latvian Biomedical Research and Study Centre (LBMC). This interdisciplinary project consists of the research activities in Physical (1.3), Chemical (1.4) and Biological (1.6) sciences, and Materials engineering (2.5).

[1] Journal of Hospital Infection 99 (2018) 239-249.
[2] European Centre for Disease Prevention and Control. Point prevalence survey of healthcare-associated infections and antimicrobial use in European acute care hospitals 2011–2012. Stockholm: ECDC; 2013.
[3] Coatings 9 (2019) 654.

Expected scientific results:

Novel R2R deposition technology of MABAV coatings on flexible substrate (results: new technology, patent);
Novel REHO and MO thin films and multilayers with advanced MABAV properties (results: scientific articles, new product prototype, patent).
 

 

PROJECT PROGRESS INFORMATION

Period: 01.07.2022 – 30.09.2022 | September 30, 2022

Performed activities.

ISSP:
Deposition of new WO3/Cu/WO3 samples continued (still ongoing) with the main goal of studying the stability of the coatings. The coatings are deposited on previously specially prepared glass substrates with electrical contacts, in order to be able to measure the electrical conductivity over a longer period of time and to determine the effect of deposition parameters. In addition, the optical properties of these samples are regularly measured by spectral ellipsometry. Both electrical and optical properties are observed to vary with time and correlate with deposition parameters. Manufacturing parameters have been found that guarantee stable films whose physical properties do not change over time. The next steps in the research include determining the physical processes that cause the instability of the described properties. X-ray diffraction, deep modeling of ellipsometry data, Raman and infrared spectroscopy and other techniques will be used for this purpose. The results will provide additional knowledge for the interpretation of antimicrobial activity and for fabricating stable coatings.

SIDRABE:

 

During the past research period the functionality of the roll-to-roll (R2R) equipment was expanded and large-area PET/WO3/Cu/WO3 samples production has been started.
  • A linear actuator with a movable screen was designed, manufactured and placed in the sample production plant to ensure the creation of metallic Cu contacts on the sides of the samples.
  • Calibration of the equipment was carried out, determining the thickness of the WO3 layer depending on the oxygen flow, for the production of a new series of PET/WO3/Cu/WO3 large-size samples according to the specification submitted by the partners. 
  • The production of the new series of samples has been started.

LBMC:

 

Testing activities for anti-bacterial and anti-viral effects include a wide range of testing methodologies and techniques. Performed activity is not limited to the implementation of traditionally used testing methodologies. The methodologies described in the testing standards were adapted to the optimal number of tested samples in their more suitable sizes. Optimizations led to more effective usage of samples and increased overall accuracy of the experiments. The optimized methodology has been approved on several bacterial species and supplemented with methods for determining anti-viral effects. Molecular testing methodologies are used in order to better understand the mechanisms of action of the tested anti-microbial coatings on microorganisms. Changes in the enzymatic activity of bacteria and the production of reactive oxygen species compounds in contact with the coating surface are determined. The experimental work with a wild-type SARS-CoV2 virus (lineage B1.1.7) has been started at BSL3 biosafety laboratory. The methodology for virus cultivation and testing on the PET surface will be developed.


 

PROJECT PROGRESS INFORMATION

Period: 01.04.2022 – 30.06.2022 | June 30, 2022

Performed activities at ISSP:
1. A new set of multilayer (WO3 /Cu, WO3/Cu/WO3, WO3/Cu/W/WO3, ZnO/Cu/ZnO) coatings was prepared on glass substrate with the goal to improve electrical conductivity, optical transparency and antiviral and antibacterial properties by varying the thickness of individual layers.
2. Spectroscopic ellipsometry measurements revealed:
  • Glass/Cu and Glass/WO3 films are homogeneous
    • Optical properties of Cu and WO3 are comparable with the data base, however resistivity of Cu is of one order lower (3.1·10-5 Ω cm) respect to the reference data (5.4·10-6 Ω cm);
    • No variation of refractive index and extinction coefficient was observed within the depth of the films;
    • Obtained thickness of the Cu and WO3 films coincide with the planned values during deposition.
  • Glass/WO3/Cu and Glass/WO3/Cu/WO3 films are inhomogeneous:
    • Variation of refractive index and extinction coefficient was observed within the depth of the films due to the Cu diffusion in both WO3 layers;
    • The second layer of WO3 (on Cu) is thinner compared to single WO3 on glass: it is possible that the growth of WO3 on Cu is slower.
3. Electrical resistance of Cu was measured during the deposition of the Glass/Cu/WO3 sample. The value obtained indicates the formation of metallic Cu and is constant during the deposition of the WO3 film. We conclude that no significant oxidation of Cu occurs during the sample preparation process.

In parallel, SIDRABE continued the preparation of R2R equipment for the application of large-area antiviral and antibacterial coatings on PET substrates:
1. Drying of PET substrate has been realized in the R2R device.
2. The supply of gases required for magnetron sputtering processes has been realized.
3. The operation of the R2R device in the:

  • Metallic mode of Cu and W coatings (Ar atmosphere) has been established.
  • Tungsten oxide (WO3 ) sputtering mode (Ar and O2 atmosphere) has been established.

4. The R2R equipment was calibrated for the thicknesses of the metallic and oxide layers depending on the amount of oxygen supplied to the process, the power of the magnetrons and the pressure in the chamber.
5. The first series of 8 pilot samples has been produced and submitted to the project partners for characterization to further optimize the parameters of coating production.
LBMC analysed antimicrobial properties for a set of ZnO and Cu nanocoatings using two types of bacteria, including Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus:
1. ZnO and ZnOCuZnO coatings did not show a significant antibacterial effect.
2. Cu coated PET samples showed antibacterial activity:
  • When analyzing the viability properties of bacterial cells (MTT test), it was found that copper coatings reduce the viability of cells in both cultures.
  • The amount of reactive oxygen species (ROS) was measured by cultivating cells on different coatings. As a result, only copper showed an active type of oxygen on the surface, causing a significant antibacterial effect.
  • Similar results were obtained in virus experiments using MS2 bacteriophage and replication defective human SFV virus, where only Cu-coated PET samples showed statistically significant antiviral effects. 
3. When comparing two bacterial cultures, S. aureus showed a much higher degree of inhibition than E. coli, respectively.
4. Innovative digital PCR quantification method was used to determine the SFV virus titre, which was presented at FEBS3+ conference, 16.06 - 18.06.2022, Tallinn, Estonia. The title of the poster presented was “Quantification of alphaviral vectors using droplet digital PCR”, autors: Ksenija Korotkaja and Anna Zajakina. 

 

PROJECT PROGRESS INFORMATION

Period: 01.01.2022.- 31.03.2022. | March 31, 2022

At the beginning of the project, ISSP prepared the thin-film magnetron sputtering equipment, compiled the procurement list of the required metallic and alloyed targets, and did first characterization of the fabricated coatings:

Optimization of magnetron sputtering process, preparation of first single-layer (Cu, ZnO, WO) and multilayer (WO3/ Cu/WO3, WO3/Cu/W/WO3, ZnO/W ZnO) coatings.

  1. A list of targets to be obtained for the development of innovative single-layer and multi-layer MABAV coatings on glass and plastic sheets has been established:
    • Gold (Au) wire, 1 gram, 99.99% purity, 1.0 mm diameter
    • Silver (Ag) wire, 1 foot, 99.99% purity, 1.5 mm diameter
  2. UV-VIS-IR spectroscopic measurements of transparent conductive thin films to determine the reflectance, transmission and absorption spectra of the films.
  3. Spectroscopic ellipsometry measurements of transparent conductive thin films to evaluate film thickness and quality (dispersion curves of optical constants, band gap, optical gradient, surface roughness).

SIDRABE has adapted the roll-to-roll (R2R) equipment for the sputtering of the thin films required in the project:

  1. Tightness and necessary high vacuum condition of the sputtering chamber have been checked, and found shortcomings have been rectified.
  2. Magnetron cooling system was cleaned and checked for leaks.
  3. Conditioning of the film winding system has been made and stability improved.
  4. W and Cu magnetrons have been installed to allow the first coatings to be formed in the pilot mode.

To evaluate the antiviral and antibacterial properties of novel nanocoatings  the testing methodology was established according to EN ISO 1276 and EN ISO 16615 and approved by LBMC on the first samples obtained from ISSP:

  1. Currently, the protocol is optimised for gram-negative and gram-positive bacteria cultivation: Escherichia coli, Staphylococcus aureus.
  2. Preliminary data on biocidal activity of tungsten oxide containing nanocoatings have been obtained.
  3. Furthermore, to evaluate the antiviral activity of nanocoatings, several model viruses have been selected: Semliki forest virus (mammalian enveloped RNA virus), MS2 bacteriophage (RNA non-enveloped virus), Pf1 bacteriophage (circular single-stranded DNA filamentous virus). The respective viruses were produced and quantified.

 



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 01.04.2022.- 30.06.2022.)

June 30 2022

The development of the high-speed deposition technology of ZnGa2O3 thin films was continued, by simultaneously sputtering a liquid gallium target and a zinc target in reactive DC mode. The process parameters were varied to develop the technology for obtaining highly transparent films with different Zn:Ga ratios and different degrees of crystallinity. The obtained layer manufacturing speed significantly exceeds the speeds obtained in the literature and also in this project, when the layers are manufactured in the RF mode. Tuning of the film production process was also continued by sputtering the ZnGa2O3 target in the RF mode. Preparation of a publication on the preparation and properties of Ga2O3 films was completed. (Activity 1).

Experimental work was initiated to find out the growth parameters of ZnGa2O3 for the existing MOCVD facility. Several experiments were conducted to determine the ratio of Zn and Ga precursors, and several experiments were conducted to determine the growth temperature of the ZnGa2O3 thin film. (Activity 2).

Characterization of the ZnGaxO3 films produced under different conditions was performed using optical spectroscopy, X-ray diffraction, ellipsometry, X-ray photoelectron spectroscopy, optical microscopy and Raman spectroscopy. Data collection was carried out, the results were used as feedback for adjusting the production process in Activity 1. Atomic force microscopy (AFM) measurements of Ga2O3 thin films were performed during the mission in the equipment available at the University of Tartu. AFM measurements were necessary to understand the surface morphology of the resulting thin films and to adjust their deposition parameters to obtain the smoothest possible surface. (Activity 4).

 

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.01.2022. - 31.03.2022.)

April 04 2022

The production of Ga2O3 thin films was continued, sputtering the liquid gallium target in the reactive DC mode and the Ga2O3 target in the RF mode. It was found that in order to ensure the necessary stoichiometry of the films, the sputtering of the Ga2O3 target must also be performed in a reactive process. The development of a high-speed deposition technology for ZnGa2O3 thin films was initiated, simultaneously sputtering the liquid gallium target and the zinc target in the reactive DC mode. A set of process parameters for the production of highly transparent films was found. The production of films by sputtering the ZnGa2O3 target in RF mode was also started (Activity 1). A patent application with no. LVP2021000105 for A method for reactive magnetron sputter deposition of gallium oxide thin films has been submitted. (Activity 1)

The optimization of the growth of Ga2O3 thin films in the MOCVD plant was continued. The process for obtaining a high-temperature buffer layer was continued in order to obtain a higher degree of crystallization of Ga2O3 thin films. The growth of Ga2O3 and ZnGa2O4 thin films with MOCVD on sapphire substrates of different orientations was continued and the sputtering of Ga2O3 and ZnGa2O4 thin films on c-plane sapphire substrates was continued. Ga2O3 and ZnGa2O4 thin films were grown with PLD on sapphire substrates of different orientations and in-depth study of the structure and morphology of the grown thin films was performed. (Activity 2)

Ab-initio DFT calculations were performed for ZnO2 materials. DFT functionals and basis sets of gaussiantype functions within the linear combination of atomic orbitals (LCAO) approximation were examined and these results were compared with the experimental data and planewave calculations. According to the performed calculations and the obtained results, the scientific article "Zinc peroxide from the first principles" has been prepared. (Activity 3)

Characterization of Ga2O3 and ZnGa2O3 films prepared under different conditions was performed by optical spectroscopy, X-ray diffraction and Raman spectroscopy. High-resolution X-ray diffraction analysis (performed in collaboration with partners from Angström Laboratory, Uppsala, Sweden) showed that the high-temperature Ga2O3 films on the sapphire substrate are epitaxial. Analysis of the composition of Ga2O3 films by ERDA (in collaboration with KTH, Stockholm, Sweden) and XPS showed that the films are free of impurities. The morphology of the films was analyzed by electron microscopy (Activity 4).
A publication on the preparation and properties of Ga2O3 films was started.

In-depth high-resolution X-ray diffraction measurements of crystalline Ga2O3 thin films were initiated to determine their degree of monocrystallinity and epitaxial orientation to sapphire substrates. (Activity 4)

 

 

ON THE IMPLEMENTATION OF THE PROJECT (PERIOD 01.10.2021. - 31.12.2021.)

January 11 2021

The development of high-speed application technology of Ga2O3 thin films was continued, and the parameters of the sample preparation process were optimized by sputtering the liquid gallium target in the reactive direct current mode. A series of amorphous and crystalline samples were prepared on quartz and sapphire substrates in the temperature range from room temperature to 800°C. Ga2O3 thin films were created by sputtering the Ga2O3 target in RF mode. A LV patent application for Ga2O3 thin film deposition technology for sputtering a liquid gallium target in reactive direct current mode was prepared and filed. (Activity 1)

The growth of Ga2O3 thin films in the MOCVD plant is further optimized by simultaneously combining H2O and O2 precursor gases. In order to obtain a higher degree of crystallization, a process for obtaining a high-temperature buffer layer is being developed. An in-depth study of the structure and morphology of the grown thin films is being carried out. (Activity 2)

Ab-initio DFT calculations were employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk β-Ga2O3 crystals. Hybrid exchange–correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in β-Ga2O3. The calculations predict that an oxygen vacancy in β-Ga2O3 is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in β-Ga2O3. All types of charge states of gallium vacancies are sufficiently deep acceptors, however, due to high formation energy, they cannot be considered as a source of p-type conductivity in β-Ga2O3. As a result, a scientific publication " Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure" was prepared and published in Materials. (Activity 3)

Optical transmittance, reflection and absorption spectra, X-ray diffraction and Raman spectroscopy data of Ga2O3 coatings prepared under different conditions were studied and collected. (Activity 4)
Publication:
Usseinov, Abay; Koishybayeva, Zhanymgul; Platonenko, Alexander; Pankratov, Vladimir; Suchikova, Yana; Akilbekov, Abdirash; Zdorovets, Maxim; Purans, Juris; Popov, Anatoli.
Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure.
Materials. 14, 7384 (2021);
DOI:10.3390/ma14237384
 

 

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 01.01.2022.- 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.


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