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Three-dimensional nanocomposite networks consisting of percolated Si nanowires in a SiOx matrix, Si:SiO2, were studied. The structures were obtained by reactive ion beam sputter deposition of SiOx (x~0.6) thin films at 450 °C and subsequent crystallization using conventional oven as well as millisecond line focus laser annealing. Rutherford backscattering spectrometry, Raman spectroscopy, X-ray diffraction, cross-sectional and energy-filtered transmission electron microscopy were applied for sample characterization. While oven annealing resulted in a mean Si wire diameter of 10 nm and a crystallinity of 72 % within the Si volume, almost single-domain Si structures with 30 nm in diameter and almost free of amorphous Si were obtained by millisecond laser application. The structural differences are attributed to the different crystallization processes: Conventional oven tempering proceeds via solid state, millisecond laser application via liquid phase crystallization of Si. The 5 orders of magnitude larger diffusion constant in the liquid phase is responsible for the three times larger Si nanostructure diameter. In conclusion, laser annealing offers not only significantly shorter process times but moreover a superior structural order of nano-Si compared to conventional heating.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18590号 / 工博第3951号 / 新制||工||1607(附属図書館) / 31490 / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 中部 主敬, 准教授 横峯 健彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18951号 / 工博第3993号 / 新制||工||1615(附属図書館) / 31902 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 北川 進, 教授 松田 建児, 教授 安部 武志 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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Piezoelectric materials are well known for their applications in surface (SAW) and bulk acoustic wave (BAW) devices such as oscillators, resonators and sensors. Quartz has been the main material used in such applications. Ternary calcium gallium germanate (CGG) structure-type materials, so-called langasites, recently emerged as very promising because of their piezoelectric properties superior to quartz. This thesis discusses the growth of langasite-type La3Ga5.5Ta0.5O14 (LGT) films by liquid phase epitaxy (LPE) technique and their chemical and structural characterization. In addition, the different techniques suitable for the growth of LGT are discussed and compared. To adjust the materials properties for given applications, doping by selected ions can be used. However, the dopants must be homogeneously distributed. In the current study, Al, Ti, Cr and Ca were investigated as dopants. In an earlier study, Al and Ti had been chosen because of their ability to substitute the octahedral site of LGT, normally occupied by Ga (CN=VI) with a segregation coefficient near unity in Czochralski growth. Doping with Ca and Cr has never been reported before, and therefore, the segregation behavior was unknown. In this study, Al, Ti and co-doping with Cr and Ca has been investigated for both X and Y-oriented films. The dopant distribution in the films was quantitatively evaluated by Secondary Ion Mass Spectroscopy (SIMS), using ion-implanted LGT substrates as standards. The drop of dopant concentration, in the SIMS profile, allows for the identification of the film-substrate interface and to accurately measure the thickness of the films. The film thickness is found to be typically of the order 0.5 to 2µm, depending on growth conditions. The solvent was found a reliable choice, as solvent ions were not incorporated in the films above the detection limits of the characterization techniques. A lead oxide solvent system is used as a solvent for the growth of LGT LPE films with different orientations. Extensive structural characterization was performed. The crystallinity of substrates and films grown with different orientations was compared by X-ray diffraction (XRD). The films show a very high structural perfection, with typically FWHM values of 0.035 for the (004) reflection of the XRD rocking curve. The films were also characterized by TEM. The optical transmittance of the films was characterized by Varian optical spectrophotometer, and the value obtained of approximately 80% is comparable with the transmittance value of the Czochralski grown polished substrate.

Liquid-liquid phase separation (LLPS) is an important phenomenon in soft condensed matter that explains many properties of membraneless organelles in living cells. The research on this topic is, therefore, a field with a wide range of applications such as biopharmacy and biomaterials. In this project, we investigate the LLPS of the antibody protein Immunoglobulin G (IgG) by analyzing the liquid dynamics of IgG solutions at a wide range of temperatures with dynamic light scattering (DLS). It was found that the slow component of the autocorrelation function increases with decreasing temperature below 0 °C. This can be attributed to either the number of protein clusters increasing as the sample approaches phase separation or LLPS droplets forming in the solution. LLPS was detected through optical microscopy, visualising the droplet formation in the IgG solution. This work confirms that LLPS can be detected for bovine IgG solutions without the presence of cosolvents and without water freezing in the sample.

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