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.

Synthesis and analysis of nanostructured coatings

The research of nanostructured coatings is currently ongoing in two branches. The first is focused on the preparation, analysis and optimization of nanocomposites based on nanocrystalline titanium carbide grains embedded in an amorphous hydrogenated carbon matrix (nc-TiC/a-C:H). These coatings are prepared by a hybrid PVD-PECVD process and, depending on their composition, can reach superhardness or a very low coefficient of friction. Such properties predetermine these coatings for application as protective coatings for e.g. machining of non-ferrous materials. The deposition process was up-scaled in collaboration with PLATIT a.s. for their deposition machines. Therefore, it is possible to find industrially prepared nc-TiC/a-C:H coated tools as well as machines capable of producing them on the market.

The second branch is focused on materials based on a nanolaminated design. Specific focus is given on recently theoretically predicted materials containing metal, boron and carbon in a unit cell with a high aspect ratio similar to the so-called MAX phases. Such a unit cell consists of alternating strongly bonded planes with ionic and covalent bonds together with comparatively more weakly bonded planes with metallic bonds. This structure allows for simultaneous high hardness and enhanced ductility of the prepared material. The combination of high hardness and enhanced ductility is very rare in the currently used protective coatings. Typical present protective coatings are often ceramics. They are very hard, but also brittle. This can lead to premature failure of the coating as well as the whole coated tool due to fast crack propagation. Nanolaminates combining hardness with enhanced ductility are, therefore, prospective candidates for the next generation of protective coatings custom tailored for applications where the coated tool undergoes significant deformation such as forming.

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.