čas: 12.8.2020 16:51:09
Obnovit | RAW
Department of Physics and Measurement
List of available PhD theses
Applications of the corona discharge microbicidal effects
Non-thermal plasma seems to be a possible alternative to the common disinfection and sterilization methods. Scope of this work are the corona discharges and their possible practical applications for the decontamination of surfaces and liquids and as a therapeutic method in medicine. Moreover, this work covers also the investigation of microbicidal effects of corona discharges to the bacteria, bacterial spores, yeast, fungi and other microorganisms.
Black Metals Structures and their Optimization for Applications in Sensor Systems, Optics and Optoelectronics
The topic of the thesis is the research of structures based on black metals for applications in sensors, optics and optoelectronics. PVD techniques (vacuum evaporation, magnetron sputtering, pulsed laser deposition) are intended for fabrication of black metal layers. Appropriate metals will be selected with respect to the application, eg Au, Al, Ag, Pd,... In the preparation of black metal layers, the effect of deposition conditions and the possibilities of their control will be studied in order to achieve the desired properties. Impaired layer parameters include, in particular, thickness, roughness, micro and nanostructure, which significantly affect surface / volume ratio, plasmon behaviour, and consequently optical and electrical properties. The optical properties will be studied by spectrophotometry using the integration sphere, FTIR and spectral ellipsometry (UV-IR). Electrical properties will be characterized by conductivity measurements, Hall measurements and impedance spectroscopy. For application in the sensors, suggested utilization is in quartz crystal resonators with sensitive layers containing black metals decorated with organic receptors (phthalocyanines and porphyrins). These sensors will be used to detect gas analytes containing nitrogen in the molecule, including the explosive taggants. The values of their mechanical parameters (the shear modulus of elasticity and acoustic impedance) are close to the values for quartz - in synergy with a small amount of organic substances that fulfil the role of receptor specific for the analyte. This approach reduces the detection limit and improves on the selectivity of the quartz crystal resonator while maintaining a high value of the quality factor. For application in optics and optoelectronics, the aim is to ensure maximum absorption of electromagnetic radiation within a given wavelength range where diffuse reflectivity does not exceed 5%. It is assumed that structures will be used as absorbers for detectors, solar panels and displays. Modification of the properties of black metal structures by interaction with intense laser radiation will be also studied. The work will be realized together with the Inst. of Physics of the Czech Academy of Sciences.
Chemiresistors based on nanostructured oxides: detection of gaseous analytes with various characteristic groups
Although the first functional chemiresistors with oxidic sensitive layers were constructed in 1960's and since 1990's they are commercially produced in large series, their research and development is far from being completed. While the chemical composition of the sensitive layers has been more or less optimized, the boom of nanotechnologies in recent years brings new challenges how to improve chemiresistors by tuning morphology of their sensitive layers. The highest impact has the fact that the geometric dimensions of the oxidic nanostructures are comparable with Debye length of given material. Such circumstance enables us to approach the concept of "molecular switch", when just one molecule of the analyte switches on/off the conducting channel in the sensitive layer. This thesis will be focused on synthesis of oxidic nanostructures (preferably by hydrothermal methods) and on measurement of their response to certain "model analytes" (oxidizing gas, reducing gas, Lewis acid or base, variable molecular dipole-moment). The analytes will be selected according to such criteria, so that the obtained results can be generalized.
Computer modelling of non-thermal plasma and electrical discharges
Scope of this work is the computer modelling of non-thermal plasma in electrical discharges. It may help to clarify the plasma-chemical reactions in discharges and the spatial distribution of generated particles. Work deals with the issue of plasma physics, computer modelling, possible method for the modelling of selected problem and comparison with the experiment. It is also possible to combine this work with the investigation of bactericidal effects of plasma or the interaction with organic structures.
Disinfection effects of non-thermal plasma for application in medicine
Plasma medicine is a new and progressive topic of scientific research. Non-thermal plasma seems to be a possible alternative to the common disinfection and sterilization methods. Scope of this work are the corona discharges and their perspectives for the wound healing, paliative therapy in oncology or the infection treatment in dermatology and podiatry. Moreover, this work covers also the investigation of microbicidal effects of corona discharges to the bacteria, bacterial spores, yeast, fungi and other microorganisms.
Nanostructured semiconductors for chemical sensors
Nanostructuring is a prospective approach in the research and design of active parts for chemical sensors during the last years. Nano-morphology offers enhanced properties of the resulting sensors, particularly selectivity and sensitivity, in contrast with unstructured materials. The aim of this work is a systematic research of relations between morphology of semiconducting materials and their detection abilities in chemical gas sensors. Nanostructured semiconductors will be synthetized mainly by CVD methods (Chemical Vapour Deposition). Electrotransport properties, chemical composition and other parameters will be also studied besides the morphology
Percolation oxidic structures based on heterojunctions: application in sensing of toxic gases
During recent years there is a remarkable progress in the development of oxidic gas-sensing structures. In the terms of electric properties - instead of "conventional" homogeneous resistors based on one oxidic phase, more frequently the heterojunctions are utilized, that are formed by grains of two different oxides with different bandgaps. Thus the sensitive layer of resulting sensor has a character of two- or three- dimensional percolation structure. To ensure the proper functionality of such a structure, two critical requirements have to be fulfilled: a) total separation of both oxidic phases; b) grain dimensions in the order of units of microns. On interaction of detected gas with the above described heterostructure, the energy-barrier height on heterojunction is modified and, simultaneously, dramatic modulation of conductivity of both phases occurs. As a result, the "integral" value of electric resistance of such a sensor is changed by several orders of magnitude. This thesis is focused on: (i) preparation of oxidic heterostructures by thermal oxidation method; (ii) characterization of gas-sensing properties of these sensors.
Preparation and characterization of silicon nanoparticles using non-thermal plasma technique
Since the observation of efficient room-temperature photoluminescence (PL) of silicon nanocrystals (Si-NCs) these nanostructures have attracted significant attention. Much effort has been made to develop optimal preparation techniques and post preparation treatments of Si-NCs that would provide sufficient amounts of Si-NCs bearing properties specifically designed for a particular application (solar cells, light generation, bioimaging, biology and medicine etc.). One of the most promising preparation/termination techniques of Si-NCs proved to be the application of non-thermal plasma (NTP, radio frequency or dielectric-barrier discharge). In contrast to other techniques, the application of non-thermal plasma is capable of synthesising orderly higher amounts of Si-NCs (about 1mg/min) lacking of chemical artefacts. Student will optimize the preparation of Si-NCs by non-thermal plasma. Student will be opimiting mainly composition and flow of working and carring gas, plasma source power and studing the influence of ambient conditions on SI-NCs properties. Properties of NCs will be characterized mainly by time integrated and resolved photoluminescence spectroscopy and EDS.
The study of improvement of non-thermal discharges and their applicability for decontamination purposes
The aim of the work is to improve existing non-thermal electrical discharges and to analyze their decontamination properties. The term improvement means to increase the discharge current and power possibly to achieve qualitative change in the discharge regime without an undesirable phenomena such as the transition into the arc or spark discharge, the excessive release of heat in the discharge area etc. In general the improvement of discharges can be made in several ways, e.g. including of suitable component in to the electrical circuit of the discharge, changing of the electrode geometry, changing of the character of supply voltage or influencing of the created plasma between the discharge electrodes. The last case comprises additional supplying of flowing gas in to the area between electrodes, influencing of the plasma by electromagnetic field, ultrasound waves etc. Consecutively improved electrical discharge will be analyzed for surface or liquid decontamination purposes. There will be found out decontamination efficiency (percentage decrease of bacteria after discharge exposition) and energy yield of decontamination (the ratio of quantity of deactivated bacteria and the energy delivered into the process).
Transport of charge carriers in nanostructured and nanocomposite materials
The topic of the thesis is theoretical and practical study of charge transfer mechanisms in nano-structured and nano-composite materials prepared in the form of thin films, coatings and aerogels. The aim of the thesis is to design models describing the charge transfer in real materials used for chemical sensors. The properties of the nanostructured samples will be measured in the Quantum Design - PPMS system, depending on the temperature and intensity of the magnetic field. The work involves (i) modeling and simulating the transport of charge carriers using the finite element method, (ii) designing and implementing software for managing, collecting and processing data obtained from PPMS system; (iii) seeking an analytical model describing the real (measured) properties of the samples depending on their nanostructure.
Utilisation of nanostructured and nanoporous materials for chemical sensors
Significant development of technology of nanomaterials in the last two decades has enabled the preparation of a wide range of materials for sensoric applications with unique structure and properties. By utilization of relatively simple vacuum techniques it is possible to prepare nanoparticles, nanowires and nanotubes of defined dimensions and shapes on a variety of substrates. From the point of view of chemical sensing such nanostructured materials show unique properties (low working temperature, high sensitivity and selectivity). The goal of this work will be the design and implementation of sensors with different nanostructured active layers, nanostructured carriers of active layers and preparation of selective nanomembranes above the active layer of chemical sensors.