Our main research subject is development of the new deposition methods and procedures utilised for the preparation of prospective nanostructured thin films. Physical vapour deposition techniques, especially the magnetron sputtering method, are employed for thin film deposition. The principle of sputtering goes as follows; ions generated in the low-pressure plasma are accelerated by the electric field towards the surface of the target, here the target atoms are being sputtered, afterwards the atoms condense on a substrate where the thin layer is formed. By setting the parameters of the deposition process, we are able to control the composition and structure of the growing coating and hence its physical and chemical properties.
Thin films deposited in this manner have wide range of applications in modern industry such as flexible electronics, microelectronics, optoelectronics, aerospace, automotive, engineering etc. Deposited films are subsequently analysed in detail utilising modern techniques, often in cooperation with foreign partners. Both macroscopic properties and internal arrangement up to the atomic scape are studied.
Our research deals with multidisciplinary tasks; for their accomplishment the field of plasma and electrical physics have to be interlaid with plasma chemistry, thin-film physics, solid state physics and material chemistry. For a basic research, we focus on fundamental study of the thin-film deposition process and on detailed understanding of the relationship between structure and properties of deposited materials. In the applied research, we aim to prepare the layers with the required composition and internal structure, exhibiting a unique combination of desired properties. Together with our industrial partners we are developing thin layers tailored to specific applications or we transfer laboratory-developed technologies into practice, often also under the confidentiality agreement.
Deposition and analysis of new materials in the form of thin films
Our research in the field of thin films focuses on both fundamental and applied research in the area of materials prepared by magnetron sputtering. We address a wide range of coatings that can advance the current state of knowledge, primarily in material machining and sustainable renewable energy production and storage. Among industrial topics, we are working, for example, on hard oxynitride-based coatings or high-entropy stabilised ceramics that are also very thermally stable. This will lead to better quality workpieces, faster production, and the elimination of cooling lubricants, which will also help the environment. A possible application of such layers is also in the aerospace sector as protective layers. Another of our machining topics is the development of new materials that combine the seemingly incompatible properties of metals and ceramics - resistance to crack propagation and high hardness. These properties combine recently theoretically predicted nanolaminate materials containing metal, boron, and carbon in a crystal lattice similar to the so-called MAX phases, characterised by alternating strongly ionic and covalently bonded planes with weaker metal-bonded planes. We are involved in preparing high-quality dielectric oxide layers for industrial sensors. In the field of green energy, we are working on high entropy stabilised oxide-based coatings that will increase the capacity of current lithium-ion batteries due to their structure while increasing their lifetime due to their chemical and mechanical stability. We are working on ceramic electrode coatings and thin-film intermetallic catalysts for water electrolysers producing oxygen and especially hydrogen, which addresses one of the most significant weaknesses of green energy to date - storage of the produced energy. Last but not least, we are addressing the preparation of materials to harness the mechanical energy otherwise lost in the vibrations of everything around us. Thanks to the piezoelectric effect and new piezoelectric materials, we will be able to convert this energy directly into electrical energy.
HiPIMS plasma diagnostics
Thorough characterization of the deposition plasma followed by understanding of the deposition process mechanisms has a considerable impact on the development of the sputtering techniques and their further applications in industry. Fundamental task of the deposition plasma diagnostics is spatially resolved measurement of the sputtered species number density, in case of HiPIMS also temporally resolved measurement. Several diagnostics methods such as resonant optical absorption spectroscopy (ROAS) or laser inducted fluorescence (LIF) are capable to obtain space and time evolutions of the sputtered species number densities. The most common qualitative diagnostic technique is optical-emission spectroscopy (OES).
OES is a simple technique, which requires only a spectrometer and a window or a vacuum feed-through for the optical fibre. It is possible to determine particle number density just from the relative intensities of optical-emission signal by the method based on effective branching fractions (EBF method). The EBF method, originally used for determination of rare gases number densities was further extended by us to determine the absolute ground energetic state number densities of the sputtered species. Deposition process can be further studied by probe measurements, measurements of the ion flux towards the substrate or measurements of the deposition rate.
HiPIMS ionization centers study
It was recently (in 2011) discovered that the plasma in HiPIMS discharge isn’t always homogeneously distributed above the target racetrack, but under certain conditions, the plasma is organized into localized ionization zones, the so-called spokes. A higher probability of ionization in the spokes could furthermore influence the deposition of thin films. It has found out that spokes rotate in the E×B direction with the velocity of about 10 km·s-1. The spoke properties, such as the shape, their number and velocity are highly dependent on the experimental conditions including the chamber geometry and the magnetic field.
The spokes were study mainly in nonreactive HiPIMS discharge. In the last year, scientific groups focused on research spokes and their properties in reactive HiPIMS discharges. The spokes were examined by various methods, e. g. combination of diagnostic methods such as some kind of probes (Langmuir probes, strip probes, emissive probes or flat probes) and optical fibers with the simultaneous usage of a CCD/ICCD camera, MS or OES. Furthermore, measurements were made using different target materials (Al, Cr, Cu, Nb, Ti, W) and under various deposition conditions (working gas, pressure, discharge current, etc.).
Theoretical modelling of material properties
In our laboratory, we are not only committed to the experimental preparation and analysis of thin films, but a part of the group is involved in modelling material properties using quantum mechanical, so-called ab initio, methods. Theoretical and experimental methods complement each other. For example, ab initio calculations can be used to efficiently test a large number of different materials to select the most suitable candidates for subsequent detailed investigation, thus saving researchers time. Moreover, a theoretical model can be used to explain the surprising properties of the deposited thin films. The most commonly used method is density functional theory, which can be utilized to effectively predict, for example, the phase stability of materials and their mechanical properties. Recently, we have also started to apply machine learning methods, for instance, in the development of inter-atomic potentials. These methods are utilized to increase several orders of magnitude in the size of the modelled system with the same computational requirements, thus further refining and accelerating the prediction of material properties.