Themes of PhD Thesis

“Physical Engineering”

  • Theme: Optical spectroscopy of 2D materials

    Supervisor: Dr. M. Hulman, PhD. ( Department of Physics and Technology at Nanoscale )
    Abstract:Two-dimensional materials now represent one of the most intensively studied classes of materials. There are many reasons for that, however, sufficient to mention are two of them: 1) that the materials can be prepared as an ultimate thin layer having a thickness of only one unit cell, 2) the electronic properties span a wide range from of insulators to superconductors.
    There is a group dealing with the growth and characterization of 2D materials at the Institute of Electrical Engineering SAS. Dissertation thesis would complement the activities of the group.
    The topic of the thesis is spectroscopic characterisation of (ultra) thin films of materials from the transition metal dichalcogenides (TMDs: MoS2, WS2, TiSe2 and others) family. The work is predominantly experimental with two main techniques explored: 1) Raman spectroscopy, and 2) optical spectroscopy from the infrared to UV frequency range. The aim of the work is characterisation of materials and investigating the effect of temperature, doping and the structure on the optical properties of 2D materials. Another aim of the work is to identify “exotic” electronic ground states in selected materials such as charge density wave, and phase transitions using spectroscopic methods.
  • Theme: Thermal stability of composite MgB2 superconductors at high current densities

    Supervisor: Ing. P. Kováč, DrSc. ( Department of Superconductor Physics )
    Abstract: Utilization of MgB2 superconductors is the most actual for the range of medium and low magnetic fields (1-5 T) and temperature around 20 K (MRI magnets, generators and engines), where the transport currents are very high and requirement of thermal stability especially needed. Therefore, thermal stability of composite MgB2 superconductors with well-conductive elements (Cu, Al) will be modelled and studied experimentally at low temperatures (4.2-20K). Current-voltage characteristics will be measured far above the level of critical current and also generated heath and critical warming of differently stabilized MgB2 wires and cables will be examined by pulse currents. Obtained results allows to optimize the design of MgB2superconductor for well stable working conditions.
  • Theme: Technology of advanced and homogeneous superconductors with ceramic fibres

    Supervisor: Ing. P. Kováč, DrSc. ( Department of Superconductor Physics )
    Abstract: High temperature superconducting materials discovered in the last decades have dominantly ceramic character (BSCCO, magnesium boride  and iron pniktides). For practical applications of these materials they have to be integrated into composite wires consisting of several metallic sheaths, which requires a special demands on the deformation process of composite components having different mechanical properties and also on the heat treatment conditions with used barriers to avoid interactions between aby filaments and sheaths.  In the frame of present topic a composite wires with superconducting and highly uniform filaments will be prepared (especially with Mg core surrounded by boron powder). The uniformity of filaments will be tested from the transversal and longitudinal sections of wire samples as well as by RTG tomography. Chemical interactions on the interfaces will be analysed by scanning electron microscopy with EDS. The measurements of current-voltage characteristics will be used for the estimation of critical currents and also for heat generation and thermal stability of composite wires at high DC currents.  Obtained results allow to optimise the architecture of composite wire having not only high current densities but also sufficient thermal stability at working conditions.
  • Theme: Superconducting conductors for fault current limiters with advanced architecture at temperatures below 77 K
    Supervisor: Ing. M. Vojenčiak, PhD.  ( Department of Superconductor Physics )
    Abstract: Superconducting fault current limiters (SCFCLs) allow further development of power distribution grid without increase of fault currents level. Principle of SCFCLs is based on steep increase of superconductor resistance when electric current exceeds critical current of the conductor. However, during limitation of fault current temperature of the conductor rises, what can lead to damage of the supercoducting material. Research in this field focuses on superconducting tapes with advanced architecture and operating temperatures < 77 K. Even small changes of operating temperature uncovered gaps in knowledge of dynamic thermal processes at these conditions.
    The thesis will include detail study of thermal and electrical processes in advanced superconducting tape at temperatures < 77 K. The most important of them are dissipation (AC loss) during normal operation, changes of electrical resistance, temperature and heat transfer during limiting and recooling period.
    The goal of the thesis is identification of differneces in thermal processes at temperature of 77 K and temperatures below this level, design of improved architecture of the conductor and/or architecture of a SCFCL and experimental verification. Preferably, there will be studied concept of advanced conductor with increased heat capacity and cryogen-free cooling.
    Thesis will be supported by H2020 project FASTGRID
  • Theme: Preparation and study of semiconductor detectors of ionizing radiation
    Supervisor: Mgr. B. Zaťko, PhD. (Department of Microelectronics and Sensors )
    Abstract: The aim of the thesis is technology preparation of ionizing detectors, study of electrical and detection properties and interpretation of obtained results. Used detection materials are semi-insulating GaAs and high quality epi-layer of 4H-SiC. At first the work will be concentrated on design and preparation of detection structures. Following the electrical characterization (current-voltage, capacity-voltage measurements) will be realized. Selected suitable detection structure can be conneted to spectrometric set-up. The optimalization in term of noise should be perfomed according to detector characteristics (reverse current in operation point, value of capacity). Finally the detection and spectrometric properties will be evaluated.

 “Electronics and photonics”

  • Theme: Growth and properties of III-N quantum structures for electronic devices
    Supervisor: Ing. J. Kuzmík, DrSc.Department of III-V Semiconductors )
    Abstract:Topic of the work deals with the growth and investigations of epitaxial III-N quantum structures prepared by metal-organic chemical-vapor deposition. GaN, as a constituting member of III-N family, is a most dynamically developed material in semiconductor industry marked by a Nobel Prize for invention of blue/white LEDs. Presently III-Ns attract a lot of interest also for applications in power, high frequency and automotive electronics.
    Compounds based on III-N (GaN, AlN, InN) and its combinations facilitate preparation of countless heterostructures showing quantum effects. In particular, 2-dimensional charge carrier gas can be created having high density and mobility, which are crucial aspects for future electronic devices.
    Work will be focused on mastering the growth at the state-of-the-art AIXTRON system. Main emphasize will be given to heterostructure quantum wells containing  In(Al)N for future ultra-fast transistors, as well as to p-doping for hole conduction in alternative GaN-based CMOS systems. Proposal of heterostructures and energetic band diagrams will be calculated using numerical simulations. Material study will include several techniques for structural, electrical and optical investigations.
  • Theme: Development and characterization of MOS gate structures for power transistors based on wide band-gap semiconductors

    Supervisor: Ing. Milan Ťapajna, PhD. ( Department of III-V Semiconductors )
    Abstract: Despite its immaturity, lateral GaN heterostructure field-effect transistor (HFET) technology can nowadays over-perform state-of-the-art Si devices, so that converters with GaN devices reach conversion efficiency as high as 99%. However, further power boost of the lateral GaN HFETs faces limitations related to maximum operating blocking voltage (~1 kV), thermal effects, frequency dispersion, and packaging. To fully exploit the excellent properties of the GaN material, it is therefore necessary to develop new concepts for vertical GaN power transistors, e.g. metal-oxide-semiconductor FETs (MOSFETs). Also, owing to its high breakdown field (8 MV/cm), b-Ga2O3 represents another promising wide band-gap material for processing of power MOSFETs. The goal of the PhD study will aim the technology development and detail characterization of MOS gate structure with 2-D and 3-D architecture for GaN and Ga2O3 based power MOSFETs. The research will focus on understanding the formation and distribution of charges in MOS gate structures, their technological control enabling adjustment of the transistor’s threshold voltage, and optimization of the oxide/semiconductor interface quality to suppress undesired device instabilities. The work will employ the state-of-the-art technologies available at IEE SAS, and combination of detail electrical and structural characterization of MOSFET structures and simulations.
  • Theme: Piezoelectric energy harvester for new generation MEMS sensors

    Supervisor: Ing. Gabriel Vanko, PhD. (Department of Microelectronics and Sensors )
    Abstract: Sensors are part of our everyday life and can be found in common electronic devices (e. g. smartphones) or in devices for health/environment monitoring. Autonomous sensors can be percieved as sensing elements capable of independent and wireless operation over a relatively long time period without need of an external power supply system that can be replaced by a battery powered by an energy harvester. The energy accumulator is currently one of the least explored application areas of microelectromechanical systems (MEMS) based on a group of nitride semiconductor materials (III-N). The concept of piezoelectric MEMS energy storage batteries based on AlGaN/GaN heterostructures is highly challenging in terms of optimizing the charge conversion efficiency. In this area, the possibilities of using materials with high values of piezoelectric coefficients (ZnO, PZT, 2D materials from the group of monochalogenesis) will be discussed. The thesis will be focused on the preparation and characterization of these layers as well as on study of the possibilities of their integration into the existing MEMS concepts.

 Physics of condensed matter and acoustics

  • Theme: Magnetic nanostructures

    Supervisor: RNDr. V. Cambel, DrSc.Department of Physics and Technology at Nanoscale )
    Co-advisor 1: Dr. Jan Fedor
    Co-advisor 2: Dr. Michal Mruczkiewicz
    Abstract: Magnetic nanostructures are presented as perspective devices for data storage, logical circuits and operations. Moreover they become promising for quantum informatics area. They have a potential to overcome constrains of semiconductor technology especially in energetic consumption, due to very low energy dissipation at writing and reading processes. Nowadays due to Dzyaloshinskii-Moriya interaction in ultrathin metallic layers brought magnetic devices with their unique physics properties (skyrmions, domains walls, etc. ) to foremost interest.
    PhD. student will be studying these objects theoretically (by numerical methods) and experimentally as well. In experimental part the student will focus on fabrication of nanomagnetic devices and he will contribute to build a low temperature scanning probe system at IEE SAS. Together with partners he will evaluate static and dynamic parameters of magnetic objects by MFM, FMR, BLS, STXM, spin polarized STM and other techniques. The aim of the thesis is to experimentally understand and evaluate the application of skyrmions as memory objects which can store quantum information.
  • Theme: Optical spectroscopy of 2D materials

    Supervisor: Dr. M. Hulman, PhD. ( Department of Physics and Technology at Nanoscale )
    Abstract:Two-dimensional materials now represent one of the most intensively studied classes of materials. There are many reasons for that, however, sufficient to mention are two of them: 1) that the materials can be prepared as an ultimate thin layer having a thickness of only one unit cell, 2) the electronic properties span a wide range from of insulators to superconductors.
    There is a group dealing with the growth and characterization of 2D materials at the Institute of Electrical Engineering SAS. Dissertation thesis would complement the activities of the group.
    The topic of the thesis is spectroscopic characterisation of (ultra) thin films of materials from the transition metal dichalcogenides (TMDs: MoS2, WS2, TiSe2 and others) family. The work is predominantly experimental with two main techniques explored: 1) Raman spectroscopy, and 2) optical spectroscopy from the infrared to UV frequency range. The aim of the work is characterisation of materials and investigating the effect of temperature, doping and the structure on the optical properties of 2D materials. Another aim of the work is to identify “exotic” electronic ground states in selected materials such as charge density wave, and phase transitions using spectroscopic methods.
  • Theme: Growth and properties of III-N quantum structures for electronic devices
    Supervisor: Ing. J. Kuzmík, DrSc.Department of III-V Semiconductors )
    Abstract:Topic of the work deals with the growth and investigations of epitaxial III-N quantum structures prepared by metal-organic chemical-vapor deposition. GaN, as a constituting member of III-N family, is a most dynamically developed material in semiconductor industry marked by a Nobel Prize for invention of blue/white LEDs. Presently III-Ns attract a lot of interest also for applications in power, high frequency and automotive electronics.
    Compounds based on III-N (GaN, AlN, InN) and its combinations facilitate preparation of countless heterostructures showing quantum effects. In particular, 2-dimensional charge carrier gas can be created having high density and mobility, which are crucial aspects for future electronic devices.
    Work will be focused on mastering the growth at the state-of-the-art AIXTRON system. Main emphasize will be given to heterostructure quantum wells containing  In(Al)N for future ultra-fast transistors, as well as to p-doping for hole conduction in alternative GaN-based CMOS systems. Proposal of heterostructures and energetic band diagrams will be calculated using numerical simulations. Material study will include several techniques for structural, electrical and optical investigations.
  • Theme: Modeling of magnetic processes on sub-micrometer scale

    Supervisor: Ing. J. Tóbik, PhD. ( Department of Physics and Technology at Nanoscale )
    Abstract: Contemporary technology allows production of electronic devices on nanometer size scale. The size reduction has dramatic effects especially on devices made of ferromagnetic materials. The magnetisation and consequently also properties of ferromagnetic devices are defined by balance of several interactions. Some of them are local – for example anisotropy or Zeeman energy, others are shot-range – for example exchange interaction and dipole-dipole interaction is long-range. The ferromagnetic device size reduction changes the proportions of the energy terms contribution. Consequently, the properties of devices changes not only quantitatively, but also qualitatively. The use of the analytical tools is usually very limited to cases of geometries with high symmetry, because usually the magnetic state is non-uniform. Therefore practical analysis is usually based on numerical simulations. The aim of this work is modelling of static and dynamic properties of magnetic devices of the sub-micron size. The extension of our software capabilities by implementing new algorithms is also expected in this work.