Plasma Technologies
Research group

Diamond is a material that hosts point defects, colour centres, which can serve as spin quantum bits. An example is the nitrogen-vacancy (NV) centre, widely applicable in quantum sensing. An essential component of spin physics and spin-state readout is the suppression of the spin bath in the NV centre environment. For NV centres fabricated only a few nanometres from the surface, surface defects, dangling bonds, or functional groups play a critical role. Therefore, control of the diamond surface is of utmost importance for engineering highly performant shallow NV qubits. In this PhD work, the student will become acquainted with the quantum properties of NV centres and other colour centres. Plasma and ion-beam processing methods, such as reactive ion etching (RIE) using inductively coupled plasma (ICP), and focused ion beam (FIB) processing, will be applied to diamond to control surface properties, including functional groups and spin/charge defects. The surface properties will be studied using advanced surface science methods (XPS, ARPES, AFM/STM, electron microscopy, etc.) and compared with nanoscale double electron–electron resonance to understand the interactions between spin qubits and surface states. The ultimate goal of this project is to develop a functional quantum chip. High-impact publications are expected from this work. The student must demonstrate a relevant background in physics.

SiC provides several advantages over silicon in semiconductor applications: 10× higher dielectric breakdown field strength, 2× higher electron saturation velocity, 3× higher energy band gap, and 3× higher thermal conductivity. The drawbacks are the SiC wafer cost and availability. Thus, key improvements and innovations are needed in SiC surface polishing, which is extremely difficult due to its high hardness and chemical and thermal stability. One of the promising techniques used in the development of SiC polishing is plasma etching. This thesis aims to deepen the understanding of how various plasma discharges interact with the SiC surface to propose optimized processes for industrial applications. Thus, the Ph.D. candidate will collaborate closely with the Czech branch of ONSEMI in Rožnov. The SiC reactive ion etching (RIE) will be investigated in a radio frequency (RF) inductively coupled plasma (ICP) in which the processed wafer can be biased by RF or LF (low frequency) voltage. The etching and polishing processes will be influenced by the choice of working gases (e.g., Ar, oxygen, SF₆) and the variations of the ion energy distribution function. Basic research on the ion interaction with the SiC surface will also use reactive ion beam etching (RIBE), in which the ion energy is precisely defined by its accelerating voltage, and it is also possible to vary the angle of incidence of the ions by tilting the substrate. Surface conditions will be analyzed regarding roughness and depth of the damaged layer by, e.g., atomic force microscopy (AFM), ellipsometry, optical Raman or fluorescence microscopy, surface composition, and crystallinity analyses. The epitaxial growth of SiC will test surface quality.

Plasma treatment and plasma enhanced chemical vapor deposition are highly efficient technologies for the modification of polymer surfaces because the processes take advantage of a highly reactive plasma environment, enabling low processing temperatures. The technologies are dry and, therefore, belong to ecological alternatives to chemical modification of surfaces that require large amounts of liquid chemicals. However, the complexity of plasma-surface interactions hinders the entire understanding and optimization of the processes. The thesis aims to improve the knowledge base for the plasma treatment of polymers by atmospheric pressure plasma jets. One of the tasks will be to understand the factors influencing the strength of the adhesive joints of plasma-treated polymers, such as polypropylene, by combining several surface characterization methods. Other tasks are related to the plasma activation of hybrid polymer composites and hydrogels.

Plasma enhanced chemical vapor deposition (PECVD) is gaining momentum in many areas, spanning from microelectronics (thin films in integrated circuits and memories) to biomedical applications (surface finishes for biosensors or implants). Higher integration in the case of microelectronics and sensing devices, as well as complex porous structures of implanted materials, pushes the technologies towards higher deposition conformality, enabling uniform coatings on 3D microstructures. PECVD cannot offer as high deposition uniformity as atomic layer deposition (ALD), but understanding the deposition mechanisms and using precursors that produce depositing species with low sticking coefficients can push the process towards high conformality. On the contrary, the knowledge gained about the processes can tune the deposition towards defined gradients in the film properties, an attractive approach for bottom-up structuring. The project will involve dedicated experiments with well-defined 3D microstructures to obtain information about the sticking coefficient of deposition species and the role of ions, as well as parallel tests of ALD conformality. The experiments should be supported by calculations, e.g., Monte Carlo or molecular dynamics simulations.

Inspired by covalent bonds in proteins, in which the carboxyl group (-COOH) of one amino acid links with the amino group (-NH2) of another amino acid, surfaces aimed at the immobilization of biomolecules, as well as adhesive surfaces in general, are prepared with these functional groups. Besides through covalent bonds, immobilization can also proceed through electrostatic interactions, which can be strong for micro- and nanostructured surfaces. The polarity of amino and carboxyl groups plays opposite roles in this process. In another approach, the radicals trapped in thin films prepared by plasma processing methods are efficiently utilized for the covalent immobilization of biomolecules. The presence of unsaturated bonds, reactive in aqueous environments, raises questions about their significance. Thus, the multifunctionality of plasma-prepared materials can be leveraged to advantage by tuning their surface bioactivity. Moreover, understanding the role of various functionalities in plasma-prepared films can serve as an inspiration for understanding the bioactivity of carbon dots, which are prepared by plasma or wet chemical processes, and whose structures can contain molecular fluorophores.