Stavba laserového skenovacího magneto-optického mikroskopu

Názov práce: Stavba laserového skenovacieho magneto-optického mikroskopu Autor: Marián Betušiak Katedra: Katedra chemickej fyziky a optiky Vedúci bakalárskej práce: prof. RNDr. Petr Němec, Ph.D., Katedra chemickej fyziky a optiky Abstrakt: Cieľom tejto práce bolo postaviť skenovací magneto-optický mikroskop v novo vybudovanom Magneto-optickom laboratóriu na katedre chemickej fyziky a optiky a hlavne porovnať rôzne techniky detekcie magneto-optického (MO) signálu. V rámci príprav sme najprv simulovali signál detegovaný v jednotlivých optických usporiadaniach pomocou Jonesovho maticového formalizmu. Následne sme overili funkčnosť postaveného mikroskopu na feromagnetickej vzorke YIG:Pr a experimentálne porovnali jednotlivé metódy merania MO signálu. Získané experimentálne výsledky sú vo výbornej kvalitatívnej zhode s predikciami Jonesovej teórie. Kľúčové slová: skenovací magneto-optický mikroskop, Kerrov jav, magnetické doményTitle: Construction of laser scanning magneto-optical microscope Author: Marián Betušiak Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Němec, Ph.D., Department of Chemical Physics and Optics Abstract: The main goal of this thesis was to build a scanning magneto-optical microscope in the newly established Magneto-optical laboratory at the Department of Chemical Physics and Optics and particularly to compare different techniques for detection of magneto-optical (MO) signals. During the preparation stages, we first simulated the signal detected in different optical arrangements using Jones matrix formalism. Subsequently, we verified the functionality of the constructed microscope using a ferromagnetic sample of YIG:Pr and we compared experimentally different methods of the MO signal detection. Obtained experimental results are in perfect qualitative agreement with the predictions of Jones theory. Keywords: scanning magneto-optical microscope, Kerr effect, magnetic domainsKatedra chemické fyziky a optikyDepartment of Chemical Physics and OpticsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Effect of the laser pulse illumination on charge collection efficiency in radiation detectors.

Hlavným cieľom tejto diplomovej práce je charakterizácia transport náboja v CdZnTe radiačných detektoroch a stúdia vplyvu osvetlenia detektoru na transport náboja.Transportné vlastnosti sú zmerané pomocou metódy laserom-indukovaných tranzientných prúdov a simulácia Monte Carlo bola použitá na fitovanie meraných prúdových waveform. V tejto práci boli skúmané vlastnosti detektoru pripraveného semi-izolačného monokryštálu CdZnTe s platinovými Schottkyho kontaktami za tmy v nepolarizovanom a polarizovanom stave. Vlastnosti detektoru boli tiež skúmané s kontinuálnym nadgapovým LED osvetlením anódy a katódy.The main focus of this thesis is the characterization of the charge transport in CdZnTe radiation detectors and the study of the effect of the detector illumination on charge transport. The transport properties are evaluated using Laser-induced Transient Current Technique and the Monte Carlo simulation is used for fitting the measured current waveforms. The properties of the detector prepared from semi-insulating CdZnTe single crystal with a platinum Schottky contacts were measured in the dark in the unpolarized and polarized state and under the anode and cathode continuous LED above-bandgap illumination.Institute of Physics of Charles UniversityFyzikální ústav UKFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI(3), giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes

Construction of laser scanning magneto-optical microscope

Title: Construction of laser scanning magneto-optical microscope Author: Marián Betušiak Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Němec, Ph.D., Department of Chemical Physics and Optics Abstract: The main goal of this thesis was to build a scanning magneto-optical microscope in the newly established Magneto-optical laboratory at the Department of Chemical Physics and Optics and particularly to compare different techniques for detection of magneto-optical (MO) signals. During the preparation stages, we first simulated the signal detected in different optical arrangements using Jones matrix formalism. Subsequently, we verified the functionality of the constructed microscope using a ferromagnetic sample of YIG:Pr and we compared experimentally different methods of the MO signal detection. Obtained experimental results are in perfect qualitative agreement with the predictions of Jones theory. Keywords: scanning magneto-optical microscope, Kerr effect, magnetic domain

Effect of the laser pulse illumination on charge collection efficiency in radiation detectors.

The main focus of this thesis is the characterization of the charge transport in CdZnTe radiation detectors and the study of the effect of the detector illumination on charge transport. The transport properties are evaluated using Laser-induced Transient Current Technique and the Monte Carlo simulation is used for fitting the measured current waveforms. The properties of the detector prepared from semi-insulating CdZnTe single crystal with a platinum Schottky contacts were measured in the dark in the unpolarized and polarized state and under the anode and cathode continuous LED above-bandgap illumination

Effect of the laser pulse illumination on charge collection efficiency in radiation detectors.

The main focus of this thesis is the characterization of the charge transport in CdZnTe radiation detectors and the study of the effect of the detector illumination on charge transport. The transport properties are evaluated using Laser-induced Transient Current Technique and the Monte Carlo simulation is used for fitting the measured current waveforms. The properties of the detector prepared from semi-insulating CdZnTe single crystal with a platinum Schottky contacts were measured in the dark in the unpolarized and polarized state and under the anode and cathode continuous LED above-bandgap illumination

Modelling Polarization Effects in a CdZnTe Sensor at Low Bias

Semi-insulating CdTe and CdZnTe crystals fabricated into pixelated sensors and integrated into radiation detection modules have demonstrated a remarkable ability to operate under rapidly changing X-ray irradiation environments. Such challenging conditions are required by all photon-counting-based applications, including medical computed tomography (CT), airport scanners, and non-destructive testing (NDT). Although, maximum flux rates and operating conditions differ in each case. In this paper, we investigated the possibility of using the detector under high-flux X-ray irradiation with a low electric field satisfactory for maintaining good counting operation. We numerically simulated electric field profiles visualized via Pockels effect measurement in a detector affected by high-flux polarization. Solving coupled drift–diffusion and Poisson’s equations, we defined the defect model, consistently depicting polarization. Subsequently, we simulated the charge transport and evaluated the collected charge, including the construction of an X-ray spectrum on a commercial 2-mm-thick pixelated CdZnTe detector with 330 µm pixel pitch used in spectral CT applications. We analyzed the effect of allied electronics on the quality of the spectrum and suggested setup optimization to improve the shape of the spectrum

Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport (Adv. Funct. Mater. 48/2021)

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