GaSe thin films were deposited by thermal evaporation technique with and without Cd doping. X-ray analysis showed that the crystallinity increases in (1014) preferred orientation direction with annealing for doped and undoped films. The room temperature conductivity and mobility values of the samples were found to be for doped and undoped films in between 1.3&times / 101 - 3.4&times / 102 (&amp / #8486 / -cm)-1, 1.2&times / 10-6 - 1.5&times / 10-6 (&amp / #8486 / -cm)-1 and 5.9 &amp / #8211 / 20.9 (cm2/V.s) (for doped samples only), respectively. Due to the high resistivity of the undoped samples mobility measurements could not be performed. The dominant conduction mechanisms were determined to be thermionic emission in the high temperature region (250-400 K), tunneling in the range 160-250 K and between 100-150 K variable range hopping mechanism for the doped films. For the undoped films above 250 K thermionic emission was the dominant conduction mechanism. Space charge limited currents in parallel and perpendicular directions of the film surface showed two different localized energy levels with different concentrations for each case, namely, 99.8 meV with concentration 3.5&times / 1012 cm-3 and 418.3 meV with the concentration 2.2&times / 105 cm-3 for parallel direction and for perpendicular direction 58.3 meV with concentration 6.2&times / 1025 cm-3 and 486.1 meV with concentration 3.3&times / 1022 cm-3. Photocurrentillumination intensity dependences indicated that power exponent of illumination intensity with values n&gt / 1 implied two recombination centers exist in studied samples.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

O presente trabalho descreve os processos de preparação do aluminato de bário e cálcio, material emissor de elétrons, empregados nos catodos do tipo impregnado para utilização em uma válvula de microondas do tipo TWT. Os catodos investigados constituem-se de uma pastilha de tungstênio porosa impregnada com aluminato de bário e cálcio com proporção molar 5:3:2. Para a síntese do aluminato, utilizaram-se três diferentes métodos: reação em estado sólido, precipitação e cristalização. A termogravimetria auxiliou na consolidação dos procedimentos de preparação dos aluminatos de modo a definir os parâmetros de pirólise/calcinação. Verificou-se que a técnica que apresentou melhores características de síntese foi o método da cristalização, pois esta apresentou uma menor temperatura de formação do aluminato (800ºC) em atmosfera oxidante (O2), quando comparada às técnicas de reação em estado sólido e de precipitação (temperatura de 1000ºC em atmosfera redutora – H2). Utilizou-se o conceito da distribuição da função trabalho prática (PWFD) de Miram para a caracterização termiônica dos catodos impregnados. Empregando-se este método, foi possível traçar o perfil termiônico do catodo com aluminato de bário e cálcio. As curvas PWFD apresentaram a função trabalho média do catodo aluminato de, aproximadamente, 2,00 eV. / In the present work it is described the barium calcium aluminate manufacture processes employed to produce impregnated cathodes to be used in a traveling-wave tube (TWT). The cathodes were developed using a tungsten body impregnated with barium and calcium aluminate with a 5:3:2 proportion (molar). Three different processes were investigated to obtain this material: solid-state reaction, precipitation and crystallization. Thermal analysis, thermogravimetry specifically, supported to determine an adequate preparation procedure (taking into account temperature, time and pirolisys atmosphere). It was verified that the crystallization showed a better result when compared to those investigated (solid-state reaction and precipitation techniques – formation temperature is about 1000ºC in hydrogen atmosphere), whereas it presented the lower formation temperature (800ºC) in oxidizing atmosphere (O2). It was used the practical work function distribution theory (PWFD) of Miram to characterize thermionic impregnated cathode. The PWFD curves were used to characterize the barium-calcium aluminate cathode. PWFD curves shown that the aluminate cathode work function is about 2,00 eV.

abstract: In this dissertation, combined photo-induced and thermionic electron emission from low work function diamond films is studied through low energy electron spectroscopy analysis and other associated techniques. Nitrogen-doped, hydrogen-terminated diamond films prepared by the microwave plasma chemical vapor deposition method have been the most focused material. The theme of this research is represented by four interrelated issues. (1) An in-depth study describes combined photo-induced and thermionic emission from nitrogen-doped diamond films on molybdenum substrates, which were illuminated with visible light photons, and the electron emission spectra were recorded as a function of temperature. The diamond films displayed significant emissivity with a low work function of ~ 1.5 eV. The results indicate that these diamond emitters can be applied in combined solar and thermal energy conversion. (2) The nitrogen-doped diamond was further investigated to understand the physical mechanism and material-related properties that enable the combined electron emission. Through analysis of the spectroscopy, optical absorbance and photoelectron microscopy results from sample sets prepared with different configurations, it was deduced that the photo-induced electron generation involves both the ultra-nanocrystalline diamond and the interface between the diamond film and metal substrate. (3) Based on results from the first two studies, possible photon-enhanced thermionic emission was examined from nitrogen-doped diamond films deposited on silicon substrates, which could provide the basis for a novel approach for concentrated solar energy conversion. A significant increase of emission intensity was observed at elevated temperatures, which was analyzed using computer-based modeling and a combination of different emission mechanisms. (4) In addition, the electronic structure of vanadium-oxide-terminated diamond surfaces was studied through in-situ photoemission spectroscopy. Thin layers of vanadium were deposited on oxygen-terminated diamond surfaces which led to oxide formation. After thermal annealing, a negative electron affinity was found on boron-doped diamond, while a positive electron affinity was found on nitrogen-doped diamond. A model based on the barrier at the diamond-oxide interface was employed to analyze the results. Based on results of this dissertation, applications of diamond-based energy conversion devices for combined solar- and thermal energy conversion are proposed. / Dissertation/Thesis / Ph.D. Physics 2013

The thesis deals with numerical simulations of a hairpin thermionic electron gun, an electron source of the electron-beam welding machine. Simulations showed that the space charge in the electron gun has a significant influence on the beam current and electron trajectories. Simulation outputs are in a sufficient agreement with the experimental measurements.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21472号 / エネ博第377号 / 新制||エネ||74(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)准教授 増田 開, 教授 長﨑 百伸, 教授 大垣 英明 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

No description available.

<p>The computer program developed by T.B. Remple for the analysis of PiN photodiodes has been modified to handle Schottky barrier cases. The fundamental physics involved in the original model is summarized and the theories for a metal-semiconductor interface are presented. The boundary values for n, p, and ψ are then defined in such a way that ψ (x) would be in agreement with the thermionic-diffusion theory. An equivalent circuit approach is used to determine the RC response of the photodetector. While the modified version of the computer model provides very detailed analysis of the device, it is also very expensive to run. A simplified model is therefore employed for the design process. The objective is to design an Au-nGe photodiode with a risetime less than 50 psecs. The set of optimum design parameters obtained with the simplified model is then taken as the input to the modified version of Remple's program for further analysis. The theoretical risetime of the optimum design is found to be about 45 psecs.</p> / Thesis / Master of Engineering (ME)

No description available.

No description available.