Introduction The internal pressure experienced by a gas tar-get during irradiation is dependent on the beam energy deposited in the target, the beam cur-rent, and the thermal behaviour of the target. [1] The maximum beam energy deposited is a function of the cyclotron capabilities and the gas inventory within the target. The maximum beam current is limited by the pressure produced in the target and the ability of the target assembly to remain intact. This is also a function of the thermal behaviour of the target, which is difficult to predict a priori since it is dependent on such things as convection currents that occur during irradiation. We conducted bench tests with model gas targets with and without forced convection currents to observe the effect on thermal behaviour. Based on those results we constructed a prototype gas target, suitable for irradiation, with an internal fan assembly that is rotated via external magnets. Material and Methods Bench tests were conducted with cylindrical and conical target bodies of aluminum. A nickel-chromium heater wire was inserted into the gas volume through the normal beam entrance port (FIGURE 1) to heat the gas while water cooling was applied to the target body. The voltage and current of the heater coil was monitored along with the pressure inside the target and the water inlet and outlet temperature. In the case of tests with a driven fan blade either the voltage applied to the electric motor was monitored or the fan speed itself was recorded. By assuming the ideal gas law, the pressure gives the average bulk temperature and a global heat transfer coefficient can be calculated between the target gas and the cooling water. [2] A cylindrical target body was constructed that incorporated a fan blade driven by an external motor. This assembly used a simple o-ring seal on the rotating shaft. This seal was not robust enough for any tests under beam conditions. A prototype design suitable for in-beam operation employs a propeller mounted on a rotating disc housing two samarium cobalt magnets and spinning on two micro-bearings which are constructed to operate in high temperature environments. The micro-bearings are mounted on a pin projecting from a plate welded to the back of the gas target to allow assembly of the fan mechanism prior to attachment to the body (FIGURE 2).

Introduction Batch-style water targets used for F-18 production are known to operate under boiling conditions in the target irradiation chamber, but the distribution of vapor under steady-state conditions was previously unknown. Thermal performance of batch targets has been correlated to average void in the target [1], but the simplified assumptions of such models do not represent the true non-uniform boiling behavior. Visualization targets can be used to observe boiling inside of a target during operation [2–5]. Commercial BTI targets operate at 28–35 bar (400–500 psi) with heat inputs of 0.5 to 3 kW and fill volumes of 1 to 4 mL. Recently, a visualization target featuring two transparent viewing windows was used to observe boiling conditions for realistic operating beam power, target pressure, and fill volume [4]. The same methodology has been applied to three additional visualization targets to examine the effect of target geometry on observed boiling phenomena. Material and Methods The original visualization target featured an aluminum body with a 0.127 mm (0.005 inch) integral aluminum beam window and two viewing windows made of optically clear sapphire (Al2O3). It was operated on an IBA 18/9 cyclotron with 18 MeV protons at beam power up to 1.1 kW, for pressures of 5 to 21 bar (70 to 300 psi), and a fill volume of 2.5 mL. All of the new designs featured a wider chamber to allow for higher beam transmission and an increased chamber height, consistent with cur-rent trends in high power targets. One target featured a reduced chamber depth, and another had a ramp in the back of the chamber to reduce fill volume. Target pressure was limited to a maximum of 14 bar (200 psi) due to the larger diameter beam window. A video camera was used to record the boiling conditions observed for each target under several lighting conditions. During irradiation, the proton beam excites the water molecules, producing visible blue light emissions during de-excitation. These light emissions provide a good indication of beam distribution and penetration depth. A strong backlight can be used to produce clearer images of bubbles generated during boiling. Results and Conclusion Proton range and visible blue light emissions were recorded in dark ambient conditions. The width of the Bragg peak and natural circulation in the bulk fluid were visible with good ambient lighting. Size and distribution of vapor bubbles could be observed by using a strong backlight. The beam current was increased gradually to determine the thermal limit for each target for several fill volumes and pressures. Two thermal limits were observed which resulted in some beam penetration in the top region of the beam. For lower fill volumes, steam ac-cumulates in or around the helium overpressure bubble, causing the helium bubble to move into the upper region of the beam. For higher fill volumes, beam penetration occurs due to excessive voiding, when bubbles produced in the beam region cannot rise quickly enough out of the path of the beam.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18055号 / 理博第3933号 / 新制||理||1567(附属図書館) / 30913 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 芝内 孝禎, 教授 石田 憲二, 教授 松田 祐司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21070号 / 工博第4434号 / 新制||工||1689(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 大村 善治, 教授 松尾 哲司, 准教授 小嶋 浩嗣 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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<p> Thin silicon based films were produced using low temperature (less than 60° C) electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR PECVD). These films were examined for suitability in flat panel display applications. SiOxNy films were tested for use as insulating films in thin film electroluminescent (TFEL) devices. The ECR PECVD method was found to be suitable when the plasma was created using pure nitrogen (as opposed to argon) in high ratios to the silane precursor.</p> <p> Hydrogenated silicon films were also produced and evaluated for their suitability as semiconductor layers in thin film transistors (TFTs). The silicon films were subject to nickel induced crystallization. The silicon films were found to crystallize at low temperatures, (<950° C) in the presence of nickel. These films were used to produce prototype metal insulator semiconductor (MIS) capacitors and TFTs.</p> / Thesis / Master of Applied Science (MASc)

Ce manuscrit présente l'étude de la fabrication de couches minces de silicium basée sur des différents types de dépôt chimique en phase vapeur assisté par plasma (PECVD) pour des applications dans le photovoltaïque. Tout d'abord, nous avons combiné une chimie du plasma halogéné en utilisant un mélange de SiF4/H2 et la technique plasmas distributés matriciellement à résonance cyclotronique électronique (MDECR) PECVD pour le dépôt de μc-Si:H à grande vitesse. Nous trouvons que les conditions d'énergie ionique modérée sont bénéfiques pour obtenir une diminution significative de la densité des nano-vides, et ainis nous pouvons obtenir un matériaux de meilleure qualité avec une meilleure stabilité. Une méthode de dépôt en deux étapes a été introduite comme moyen alternatif d'éliminer la formation d'une couche d'incubation amorphe pendant la croissance du film. Ensuite, nous avons exploré la technique d'excitation Tailored Voltage Waveform (TVW) pour les processus plasma radiofréquence capacitivement couplé (RF-CCP). Grâce à l'utilisation de TVW, il est possible d'étudier indépendamment l'influence de l'énergie ionique sur le dépôt de matériaux à une pression de processus relativement élevée. Basé sur ce point, nous avons étudié le dépôt de μc-Si:H et a-Si:H à partir des plasma de SiF4/H2/Ar et de SiH4/H2, respectivement. A partir d'une analyse des propriétés structurelles et électroniques, nous constatons que la variation de l'énergie ionique peut directement traduite dans la qualité du matériaux. Les résultats se sont appliqués aux dispositifs photovoltaïques et ont établi des liens complets entre les paramètres de plasma contrôlables par TVW et les propriétés de matériaux déposé, et finalement, les performances du dispositif photovoltaïque correspondant. Enfin, nous avons trouvé que dans le cas du dépôt de couches minces de silicium à partir du plasma de SiF4/H2/Ar à l'aide de sawtooth TVW, on peut réaliser un processus de dépôt sur une électrode, sans aucun dépôt ou gravure. contre-électrode. Ceci est dû à deux effets: la nature multi-précurseur du processus de surface résultant et la réponse de plasma spatiale asymétrique par l'effet d'asymétrie de pente de la sawtooth TVW. La découverte de tels procédés “electrode-selective” encourage la perspective que l'on puisse choisir un ensemble de conditions de traitement pour obtenir une grande variété de dépôts désirés sur une électrode, tout en laissant l'autre vierge. / This thesis describes the study of silicon thin film materials deposition and the resulting photovoltaic devices fabrication using different types of plasma-enhanced chemical vapour deposition (PECVD) techniques.In the first part, we combine a SiF4/H2 plasma chemistry with the matrix-distributed electron cyclotron resonance (MDECR) PECVD to obtain high growth rate microcrystalline silicon (µc-Si:H). Due to the special design of MDECR system, careful investigation of the impact energy of impinging ions to material deposition can be accessible. We find that moderate ion energy conditions is beneficial to achieve a significant drop in the density of nano-voids, thus a higher quality material with better stability can be obtained. A two-step deposition method is introduced as an alternative way to eliminate the existence of amorphous incubation layer during film growth.The second part of work is dedicate to the exploration of the Tailored Voltage Waveforms (TVWs) excitation technique for capacitively coupled plasmas (CCP) processes. As an advantage over the conventional sinusoidal excitations, TVWs technique provide an elegant solution for the ion flux-energy decoupling in CCP discharges through the electrical asymmetry effect, which makes the independent study of the impact of ion energy for material deposition at relatively high process pressure possible. Based on this insight, we have studied the deposition of µc-Si:H and amorphous silicon (a-Si:H) from the SiF4/H2/Ar and SiH4/H2 plasma chemistry, respectively. From the structural and electronic properties analysis, we find that the variation of ion energy can be directly translated into the material quality. We have further applied these results to photovoltaic applications and established bottom-up links from the controllable plasma parameters via TVWs to the deposited material properties, and eventually to the resulting device quality.In the last part, as a further application of TVWs, an “electrode-selective” effect has been discovered in the CCP processes. In the case of silicon thin film deposition from the SiF4/H2/Ar plasma chemistry, one can achieve a deposition process on one electrode, while at the same time either no deposition or an etching process on the counter electrode. This is due to two effects: the multi-precursor nature of the resulting surface process and the asymmetric plasma response through the utilization of TVWs. Moreover, such deposition/etching balance can be directly controlled through H2 flow rate. From a temporal asymmetry point of view, we have further studied the impact of process pressure and reactor geometry to the asymmetric plasma response for both the single-gas and multi-gas plasmas using the sawtooth waveforms. The product of pressure and inter-electrode distance P·di is deduced to be a crucial parameter in determine the plasma heating mode, so that a more flexible control over the discharge asymmetry as well as the relating “electrode-selective” surface process can be expected.

Dans un semiconducteur polaire, la propagation d'un phonon optique longitudinal s'accompagne d'un champ électrique macroscopique qui se couple aux porteurs libres pour donner naissance à l'effet magnéto-polaron résonant. Cet effet est une des manifestations les plus spectaculaires de l'interaction électron-phonon dans un milieu polaire et devrait se manifester par un comportement d'anti croisement entre les niveaux de Landau. Du point de vue expérimental, les résultats sont souvent masqués par la forte absorption du substrat et cette interaction n'a jamais été clairement observée. Nous avons pu résoudre ce problème en décollant les structures de leur substrat originel de GaAs pour les recoller sur un substrat de silicium qui est transparent dans l'infrarouge lointain. Ces structures décollées nous permettent de mesurer, de manière absolue, la transmission dans la région énergétique des phonons optiques de GaAs. Je présenterai des expériences de transmission infra rouge effectuées sur une série de puits quantiques de GaAs de haute mobilité et fortement dopées en configuration de Faraday perpendiculaire et de Faraday oblique. Les résultats seront interprétés dans le formalisme de la fonction diélectrique.