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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Development of Be(x)Zn(1−x)O Nanowires for Radiation Detection

Xu, Xiaofeng 28 November 2012 (has links)
Scanning electron microscope, X-ray diffraction and photoluminescence measurements were conducted on Be(x)Zn(1−x)O nanowires prepared by electrochemical and hydrothermal deposition to study their morphology, structure and optical properties. The bowing parameter for nanowires prepared by electrochemical and hydrothermal deposition was found to be 4.8 eV and 3.6 eV, respectively. It was observed that for electrochemical deposition, it is more difficult for Be(2+) to incorporate in the crystal lattice than Zn(2+). The electrochemical deposited samples exhibited stronger deep level emissions, indicating a higher density of deep level states. A home-made Optically Stimulated Luminescence (OSL) system was successfully constructed and calibrated with Al2O3:C and BeO. The OSL lifetime measurements on electrochemical deposited samples showed there were measurable OSL signals even on 500 nm long Be(x)Zn(1−x)O nanowires. The lifetimes of these OSL signals were found to decrease with increasing Be concentration. Be(x)Zn(1−x)O nanowires show considerable promise as new OSL materials.
2

Development of Be(x)Zn(1−x)O Nanowires for Radiation Detection

Xu, Xiaofeng 28 November 2012 (has links)
Scanning electron microscope, X-ray diffraction and photoluminescence measurements were conducted on Be(x)Zn(1−x)O nanowires prepared by electrochemical and hydrothermal deposition to study their morphology, structure and optical properties. The bowing parameter for nanowires prepared by electrochemical and hydrothermal deposition was found to be 4.8 eV and 3.6 eV, respectively. It was observed that for electrochemical deposition, it is more difficult for Be(2+) to incorporate in the crystal lattice than Zn(2+). The electrochemical deposited samples exhibited stronger deep level emissions, indicating a higher density of deep level states. A home-made Optically Stimulated Luminescence (OSL) system was successfully constructed and calibrated with Al2O3:C and BeO. The OSL lifetime measurements on electrochemical deposited samples showed there were measurable OSL signals even on 500 nm long Be(x)Zn(1−x)O nanowires. The lifetimes of these OSL signals were found to decrease with increasing Be concentration. Be(x)Zn(1−x)O nanowires show considerable promise as new OSL materials.
3

Hrabě František Josef Pachta v roli stavebníka i stavitele. Architektonická proměna rodových statků Františka Josefa Pachty v pozdním baroku. / Count František Josef Pachta in the role of the builder and architect. The architectonic transformation of the ancestral estates of František Josef Pachta in the late baroque period.

Chrástecká, Marie January 2017 (has links)
The thesis was named "Count František Josef Pachta in the role of the builder and architect. The architectonic transformation of the ancestral estates of František Josef Pachta in the late baroque period". Count František Josef Pachta was quite a notable person of Czech baroque and he held many significant political posts. Especially during the baroque period, members of Pachta family were involved in building activities at their ancestral residences, and František Josef Pachta was no exception. The thesis is primary focused on summarising Pachta's building activities and the architectural description of individual buildings such as for example mansion and church of St. Peter and Paul in Bezno, mansion Nový Falkenburg and Virgin Mary's Birth church in Jablonné v Podještědí or Pachta's townhouses in Prague. The thesis also deals with question, if count Pachta was also an "architect-dilettante", which in this case means a person, who deals with designing buildings even though he is not trained to do it. Keywords František Josef Pachta, architecture, baroque, Bezno, Jablonné v Podještědí, Pachta's townhouses in Prague
4

Growth and Characterization of Wide Bandgap Quaternary BeMgZnO Thin Films and BeMgZnO/ZnO Heterostructures

Toporkov, Mykyta 01 January 2016 (has links)
This thesis reports a comprehensive study of quaternary BeMgZnO alloy and BeMgZnO/ZnO heterostructures for UV-optoelectronics electronic applications. It was shown that by tuning Be and Mg contents in the heterostructures, high carrier densities of two-dimensional electron gas (2DEG) are achievable and makes its use possible for high power RF applications. Additionally, optical bandgaps as high as 5.1 eV were achieved for single crystal wurtzite material which allows the use of the alloy for solar blind optoelectronics (Eg>4.5eV) or intersubband devices. A systematic experimental and theoretical study of lattice parameters and bandgaps of quaternary BeMgZnO alloy was performed for the whole range of compositions. Composition independent bowing parameters were determined which allows accurate predictions of experimentally measured values. The BeMgZnO thin films were grown by plasma assisted molecular beam epitaxy (P-MBE) in a wide range of compositions. The optimization of the growth conditions and its effects on the material properties were explored. The surface morphology and electrical characteristics of the films grown on (0001) sapphire were found to critically depend on the metal-to-oxygen ratio. Samples grown under slightly oxygen-rich conditions exhibited the lowest RMS surface roughness (as low as 0.5 nm). Additionally, the films grown under oxygen-rich conditions were semi-insulating (>105 Ω∙cm), while the films grown under metal-rich conditions were semiconducting (~102 Ω∙cm). Additionally, with increasing bandgap Stokes shift increases, reaching ~0.5 eV for the films with 4.6 eV absorption edge suggests the presence of band tail states introduced by potential fluctuations and alloying. From spectrally resolved PL transients, BeMgZnO films grown on a GaN/sapphire template having higher Mg/Be content ratio exhibit smaller localization depth and brighter photoluminescence at low temperatures. The optimum content ratio for better room temperature optical performance was found to be ~2.5. The BeMgZnO material system and heterostructures are promising candidates for the device fabrication. 2DEG densities of MgZnO/ZnO heterostructures were shown to improve significantly (above 1013 cm-2) by adding even a small amount of Be (1-5%). As an essential step toward device fabrication, reliable ohmic contacts to ZnO were established with remarkably low specific contact resistivities below 10-6 Ohm-cm2 for films with 1018 cm-3 carrier density.

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