RNDr. Petr Hruška, Ph.D.
The Multi-Principal Element Films (MPEF) group focuses on high-entropy materials (HEMs), their preparation in thin-film form, and the analysis of their microstructure and functional properties. The versatility of HEMs makes them one of the most rapidly developing areas in contemporary materials research. We specialize in scaling these materials down to the nanometer level, where enhanced compositional and structural variability unlocks further functionalities that are challenging to access in bulk form.
Multi-Pricipal Element Films
For thin films preparation, we employ two physical vapor deposition (PVD) techniques: magnetron sputtering (MS) and pulsed laser deposition (PLD). Magnetron sputtering enables homogeneous coating of large-area substrates and is therefore closer to industrial applications. In contrast, pulsed laser deposition is a highly versatile method capable of producing both metallic and semiconducting materials with precise control over film growth and composition, making it particularly suitable for fundamental research. A conceptual bridge between these approaches is plasma diagnostics (optical emission spectroscopy, Langmuir probe, and mass spectrometry), which we employ within our department.
Ultra-high vacuum system for thin film deposition by magnetron sputtering at the Department of Analysis of Functional Materials
Vacuum chamber for pulsed laser deposition of thin films at the Department of Analysis of Functional Materials
By controlling deposition parameters, we tailor the film structure (ranging from amorphous to single-phase nanocrystalline and multiphase polycrystalline), as well as the type and concentration of defects (from vacancies and vacancy-like defects to vacancy clusters), and we also tune their chemical behavior (oxidation affinity, transitions from metallic films to oxides and nitrides). This capability for controlled property modification has been successfully demonstrated in multicomponent films based on Ti–V–Zr–Nb–Hf–Ta.
From an application perspective, our research focuses on selected functional properties of multi-principal element thin films, particularly their use in photocatalysis and as microwave absorbers. In addition, we explore their potential for hydrogen technologies, enhanced radiation resistance, superconductivity, and memristors.
High-Entropy Materials
High-entropy materials (HEMs), also known as Multi-Principal Element Materials (MPEMs), represent a new paradigm in materials science. While the field originated with High-Entropy Alloys (HEAs) – metallic systems composed of five or more elements in near-equiatomic proportions – the concept has since expanded into high-entropy oxides, nitrides, and carbides. Unlike traditional materials based on a single primary element, these systems utilize multiple principal elements to unlock unique properties driven by four core effects:
High Entropy: The high configurational entropy of mixing stabilizes random solid-solution phases over intermetallic compounds.
Lattice Distortions: Variations in atomic sizes and bonding characteristics significantly strain and distort the crystal lattice.
Sluggish Diffusion: Atomic movement is restricted in these complex environments due to local fluctuations in atomic potential.
Cocktail Effect: Synergistic interactions between different elements produce properties that are not simply an average of the constituents, often resulting in unexpected, non-linear behavior.
These four core effects allow for chemically complex yet structurally simple materials, facilitating the “magic” of the mixture, where the whole becomes greater than the sum of its parts.
The compositional space of high-entropy materials is virtually infinite, allowing us – in principle – to tune their properties for nearly any application, providing a versatile toolkit for 21st-century material design. However, exploring this vast combinatorial landscape through traditional trial-and-error approach would figuratively take centuries. By leveraging machine learning (ML) algorithms, high-performance compositions and their preparation recipes can now be effectively predicted. Interestingly, it was the theoretical ML postulation of these complex interactions that initially predicted the very existence of stable high-entropy phases.