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Piezoelectric nanofiber materials for wearable electronics
Frolíková, Štěpánka ; Škarvada, Pavel (referee) ; Macků, Robert (advisor)
This thesis deals with the influence of production parameters on the morphology of PVDF nanofibers produced by electrospinning. Nanofibers are generally a widely used material, nanofibers are generally a widely used material, they can also have piezoelectric properties, which gives them a specific spectrum of use, eg in biosensors. The production of nanofibers was realized by electrospinning. A scanning electron microscope was used to examine the morphology and surface properties. The aim of this thesis is to compare the properties of PVDF nanofibers produced under different settings of production parameters.
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Controlled light source
Pazderský, Tomáš ; Macků, Robert (referee) ; Škarvada, Pavel (advisor)
The aim of the Master´s thesis is proposing and implementation of computer controlled optical radiation source. The theoretical part describes the photometric, the radiometric quantities, applied components such as LED, the microcontroller and possible methods for the LED brightness control. The development of the device is described from the selection of the individual LEDs to the end of the device assembling and programing. On the several LEDs were made properties measurement. A circuit with microcontroller was designed and then was fabricated. The device was programmed for communication and control from the PC. The entire electronic is fitted in the metal frame of the construction box and finally the device functionality is tested.
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Solar cell non-destructive analysis
Černý, Michal ; Škarvada, Pavel (referee) ; Macků, Robert (advisor)
This thesis briefly analyse contemporary situation of photovoltaic systems and their actual developemenet. It shows a typical properties of most produced up-to-date types. Decision point of this thesis consist in nondestructive analyse of monocristalic unijunction solar cells. It describes two main diagnostic aproaches. First – through the use of measuring of VA characteristics, second – through the use of measuring noise characteristics. With selected samples are performed experimental measurements and estabilished basic parameters. In case of drone analysis considerably attention is devoted to experimental equipment for automatized measuring of spectral power density. This experimental equipment is consequently used for measuring some samples where we can observe microplazmatic noise.
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Design of thermal system for accurate temperature stabilization using Peltier thermoelectric modules
Motl, Jakub ; Trčka, Tomáš (referee) ; Macků, Robert (advisor)
This master’s thesis describes design procedure of a heat-regulating system to stabilize its temperature using a Peltier module. The implementation uses eight-bit microcontroller ATmega16 made by company ATMEL for the local and remote control system. The temperature sensors communicate with the microcontroller by serial SPI interface. To display user data, it has a DEM16217SYH type character LCD display with HD44780 control circuit. To collect data from the cooling areas of Peltier module, accurate ADT7320 temperature sensors are used, made by company Analog Devices. The Control of the Peltier module happens in two points of the electrode system and a bistable hysteresis software regulator is used. The first part summarizes the theory, which concerns with the design. Next part concerned with issues of the Peltier module, overview of temperature sensors, description of the microcontroller, the display unit and the used regulator. Last part describes the hardware and software implementation.
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Noise diagnostics of rectifier diodes PN junctions
Klimíček, Jaromír ; Macků, Robert (referee) ; Raška, Michal (advisor)
The thesis deals with the design of the measurement installation, which is intended for the microplasma noise measurements. This noise is being generated in the defective parts of the PN junction. The goal of this work is to design the measurement installation and to realize the fully functional workbench for the analogical noise related measurements and to determine the transfer function of the measurement installation. Main part of the work is to choose proper parameters for the measuring devices and to design the software intended for the automated measurements. Consequently, we have to process the measured waveforms of the microplasma noise, to determine the dependency of the noise on the signal magnitude and to calculate the power spectral noise density. Finally, we have to determine the transfer function of the measurement installation and to design the inversion filter.
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Thin-Film Solar Cells Characterization and Microstructure Defect Analysis
Škvarenina, Ľubomír ; Šály,, Vladimír (referee) ; Fejfar, Antonín (referee) ; Macků, Robert (advisor)
Thin-film solar cells based on an absorber layer of chalcogenide compounds (CIGS, CdTe) are today among the most promising photovoltaic technologies due to their long-term ability to gain a foothold in mass commercial production as an alternative to conventional Si solar cells. Despite this success, the physical origin of the defects present in the thin films are still insufficiently elucidated, especially in the compounds of the chalcopyrite family Cu(In_{1x},Ga_{x})(S_{y},Se_{1y})_{2}. The research focuses on the identification and analysis of microstructural defects responsible for the electrical instability of chalcopyrite-based thin-film solar cells with a typical heterostructure arrangement ZnO:Al/i-ZnO/CdS/Cu(In,Ga)Se_{2}/Mo. The non-uniform polycrystalline nature of semiconductor materials in this complex multilayer structure requires a comprehensive analysis of electro-optical, structural and compositional properties associated with the actual morphology at the macroscopic, microscopic or even nanoscopic level. The observed predominant ohmic or non-ohmic current conduction in the dark transport characteristics was also reflected in the slope deviations of the excessive noise fluctuations, which were in the spectral domain exclusively in the form of flicker noise with dependency S_{i} ~ f^{1}. Spatially resolved electroluminescence based on stimulated photon emission by charge carriers injecting into the depletion region, not only showed a significantly inhomogeneous distribution of intensity in planar heterojunction under forward bias, but also revealed light emitting local spots in reverse bias due to a trap-assisted radiative recombination through the high density of defect states. Microscopic examination of the defect-related light emitting spots revealed rather extensive defective complexes with many interruptions through the layers, especially at the heterojunction CdS/Cu(In,Ga)Se_{2} interface. Besides, the high leakage current via these defective complexes subsequently led to a considerable local overheating, which caused a clearly observable structural and morphological changes, such as deviations in absorber layer stoichiometry due to Cu–In–Ga–Se segregation, Cu-rich and Ga-rich grains formation with an occurrence of Se-poor or Cu_{x}Se_{y} secondary phases regions, material redeposition accompanied by evaporation of ZnO:Al/i-ZnO/CdS layers together with the formation of Se structures on the surface around the defects. Within the research, analytical modelling of transport characteristics was implemented with parameters extraction of individual transport mechanisms to understand the non-ohmic shunt behaviour due to leakage current. In addition to the proper current path along the main heterojunction, the proposed model contains parasitic current pathways as a consequence of recombination-dominated charge transport or current conduction facilitated by multi-step tunnelling via high density of mid-gap defect states in the depletion region, ohmic leakage current caused by pinholes or low-resistance paths along grain boundaries in Cu(In,Ga)Se_{2}, or space-charge limited current due to metals diffusion from the ZnO:Al layer and grid Ag contacts through disruptions in i-ZnO/CdS layers.
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Characterization and preparation of PVDF nanofiber matrices for wearable electronics
Zajacová, Lucia ; Papež, Nikola (referee) ; Macků, Robert (advisor)
The presented bachelor thesis deals with the process of production PVDF nanofiber matrices uising electrospinning and subsequent electrical characterization of the produced material. At the beginning, it introduces nanotechnologies and their undeniable importance in medical applications. It focuses on the influence of process parameters, production enviroment and the very properties of the spinning solution itself, leading to final character of the spun fiber. Various morphological differences obtained by individual process settings then continue to influence their piezoelectric properties, which are the subject of the reaserch in the experimental part of this thesis. The obtained results are applied to devices uising the piezoelectric effect with the potential for application in the biotechnological fields.
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Application of radiation emitted from local areas of PN junction for solar cell diagnostics
Krčál, Ondřej ; Raška, Michal (referee) ; Macků, Robert (advisor)
The microplasma discharges in the PN junction local defect micro-regions are as a rule, accompanied by the emission of light. This radiation from solar cell PN junctions was measured by means of a optical fibre connected to the optical input of a photomultiplier. By inching the fibre by means of computercontrolled X-Y plotter above the cell surface a 2-D image of the irradiation local regions has been created. It is seen that a cell of a superficial area of 100 square cm contains a large number of defects, which depends on applied reverse voltage. This method can be a convenient tool for study and diagnostics of optoelectronic devices.
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Electrical characteristics of graphene layers and their use as gas sensors
Kučera, Štěpán ; Kaspar, Pavel (referee) ; Macků, Robert (advisor)
This bachelor thesis focuses on the general characterization and description of graphene and related nanostructures. It involves production by the most used methods, including their advantages and disadvantages. Due to the impossibility of connection in the usual way, the graphene sample had to be contacted under visual inspection with a microscope with the tip contacts in the shielded area. Subsequently, it was subjected to current-voltage characterization with normal conditions on a Keithley 4200-CSC instrument. The next step was to measure the same sample under a different gas atmosphere. The result is a comparison of the specific responses to the change in gas atmosphere in which the graphene monolayer was exposed.
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Analysis of solar cell surface features
Lipr, Tomáš ; Macků, Robert (referee) ; Škarvada, Pavel (advisor)
This thesis is focused on the study of electrical and optical properties of solar cell samples using the near field optical microscope. Process of the image formation is described. Artefacts which are presented on some of topography images are described, too. There are some timing problems with measuring of the sample local electric response. If the measuring and scanning devices are not in the time synchronization there will be some difficulties with measured data representation and 2D image offline formation. Created electronic for SNOM and measuring devices synchronization is presented.
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