čas: 23.4.2021 01:57:05
Obnovit | RAW
Department of Physics and Measurement
List of available PhD theses
Application of non-thermal plasma in agriculture
The application of non-thermal plasma in agriculture, especially for the treatment of seeds and young plants, is a new and developing area of scientific research. Plasma has beneficial effects on plant germination, their initial growth as well as the overall yield of production. The work is focused mainly on corona discharges and their perspective for breaking the dormancy of seeds of selected plants and the study of influencing their germination and growth. There is a place also for the study of the effect of the bactericidal agent of plasma on various types of bacteria, their spores, yeasts, fungi and other microorganisms found on the surface of seeds or other plant products.
Applications of the non-thermal plasma 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 as active layers of chemiresistors
Metals of highly porous surface are called black metals (BM). Their chemical (oxidizability), mechanical (low density), electrical (higher resistivity) and optical (low reflectivity) properties originate from a unique combination of nanostructural and microstructural features of metalic materials. Regarding the applicability of BMs in chemiresistors, following properties are beneficial: (i) there is a large portion of surface atoms, which promotes interaction of BMs with gaseous species; (ii) the surface of BMs exhibits catalytic activity - it enables decomposition of larger analyte molecules into easily detectable reactive fragments; (iii) the surface of BMs is easily oxidizable to form core-shell metal-metal oxide structures with Schottky junction; (iv) the active layers based on BMs provide possibility to measure the response with high-frequency ac-signal leading to the so-called skin-effect, which is an effective tool to investigate only "surface" detection and compare the results with "volume" detection obtained with dc-signal.
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.
Hybrid nanosctructured lithium - ion batteries
Current rapid developments in wearable electronics, production of electric energy from renewable sources, electric vehicles and other applications emphasizes increasing demands on the energy storage. While the standard lithium-ion batteries (LIB) seem to reach their maximum, new structural solutions are needed. As one of the most promising anode material for LIB technology is considered to be silicon. Silicon based anode has potential to increase storage capacity of the batteries about ten times in contrast to commonly used graphite. Unfortunately the silicon expands its volume by more than 300% during lithium charging that cause significant structural fractures and thus limits application of bulk silicon in LIB technology. The goal of this work is to study the applicability of nanostructured silicon as a part of LIB anodes and advanced flexible organic materials as electrode scaffold materials that would be electrochemically stable, highly conductive and strong and elastic enough to withstand the nanocrystal expansion.
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.
Processing of chemical sensor signals using artificial intelligence algorithms
One way to improve the selectivity and detection properties of modern chemical sensors is to use artificial intelligence algorithms. The topic of the thesis is to design, prepare and test new approaches for processing and extracting data from multi-component sources such as GC / IMS spectrometer, sensors and sensor arrays with response in the visual, infrared and radio-frequency fields of the electromagnetic spectrum. The solution assumes usage of hardware acceleration of data processing and software-defined radio.
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 aerogels for gas 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. Relatively simple supercritical drying technique, can be used to prepare active layers from the materials used for gas sensors in the form of aerogels. From the point of view of chemical sensors, such nanostructured materials show unique properties in many ways (high sensitivity and selectivity, large active surface). The aim of the work will be the design and implementation of sensors based on aerogels formed by inorganic oxides and their possible chemical (selective organic receptors, surface tension modifiers) and physical modification (laser annealing, incorporation of catalytically active nanoparticles). Impedance spectroscopy and UV-VIS-NIR spectrometry will be used to evaluate the sensor response.