京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18086号 / 理博第3964号 / 新制||理||1571(附属図書館) / 30944 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 平田 岳史, 教授 田上 高広, 准教授 三宅 亮 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

We present a model of laser-solid interactions in silicon based on an empirical potential developed under conditions of strong electronic excitations. The parameters of the interatomic potential depends on the temperature of the electronic subsystem Te, which is directly related to the density of the electron-hole pairs and hence the number of broken bonds. We analyze the dynamics of this potential as a function of electronic temperature Te and lattice temperature Tion. The potential predicts phonon spectra in good agreement with finite-temperature densityfunctional theory, including the lattice instability induced by the high electronic excitations. For 25fs pulse, a wide range of fluence values is simulated resulting in heterogeneous melting, homogenous melting, and ablation. The results presented demonstrate that phase transitions can usually be described by ordinary thermal processes even when the electronic temperature Te is much greater than the lattice temperature TL during the transition. However, the evolution of the system and details of the phase transitions depend strongly on Te and corresponding density of broken bonds. For high enough laser fluence, homogeneous melting is followed by rapid expansion of the superheated liquid and ablation. Rapid expansion of the superheated liquid occurs partly due to the high pressures generated by a high density of broken bonds. As a result, the system is readily driven into the liquid-vapor coexistence region, which initiates phase explosion. These results strongly indicates that phase explosion, generally thought of as an ordinary thermal process, can occur even under strong non-equilibrium conditions when Te > > TL. In summary, we present a detailed investigation of laser-solid interactions for femtosecond laser pulses that yield strong far-from-equilibrium conditions.

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is now a well established analytical technique used to sample solid materials and determine their elemental composition. Two areas that are becoming increasingly important, and for which LA-ICP-MS is a key tool, are bio-imaging and the analysis of micro-particulates. However, current instrumental designs limit the practicality of the technique for these applications. This study investigates the development of a high speed, high efficiency LA-ICP-MS interface through modelling of the flow dynamics of a newly designed laser ablation cell and experimental investigation of single laser pulse response. Through this work the Sniffer-Dual Concentric Injector interface was realised. This interface reduced particle residence times within the laser cell and transport tubing. The interface was also used to investigate turbulence related aerosol dispersion within the ICP and potential designs to overcome this. The resulting design yields an interface with improved sensitivity and reduced aerosol dispersion such that a lower limit of detection is achieved, important when considering the mass of analyte in a single cell or micro-particulate, compared to existing designs. Thus the interface can be used to improve image spatial resolution as the ablation spot size, and thus pixel information, can be reduced; and also reduces total analysis time. The calibration technique Laser Ablation of a Sample In Liquid (LASIL) was also investigated as a means of calibration for solid samples. The investigation lead to the development of LASIL in a droplet, a technique that can be used to calibrate solid samples when a matrix matched standard is unavailable. The mechanism of the technique resulted in an improved laser-energy sample coupling efficiency and a reduction in the liquid to ablated mass ratio, thus decreasing sampling time. As the technique captures the ablated particulate in solution, post chemistry techniques can be used to remove analyte interferences.

Ag thin and thick films have been experimentally deposited using a technique called Laser Ablation of a Microparticle Aerosol (LAMA). This technique is based on a supersonic jet accelerating NPs of a few nm diameter up to 1000 m/s and operating at room temperature. The deposited films have experimentally demonstrated interesting properties such as dense growth with good adherence on the substrate. Aerosol feed rates have been fixed to 10 mg/h which corresponds to rate depositions of 10¹⁰ to 10¹¹ NPs/s/cm². In order to model this deposition technique and possibly be able to predict the morphology and structure of deposited films using computational methods, we have designed MD programs simulating the depositions of several Ag nanoclusters onto a substrate at a fixed temperature (300 K). The variation of parameters such as cluster size, cluster impact energy, and deposition rate has influenced the morphology and structure of the deposited films. Cluster diameters have been set to 3 nm or 5 nm, cluster velocities set to 200 m/s (0.022 eV/atom), 400 m/s (0.069 eV/ atom), or 800 m/s (0.358 eV/atom), and the deposition rate adjusted to ensure relaxation times between impactions of 5 ps to 20 ps. The evolution of deposited film density, adherence, and crystal arrangement has been analyzed with the variation of the aforementioned parameters. The highest cluster velocities have enabled the deposition of smoother, denser, and more adherent films. NCs with an initial velocity of 200 m/s have shown ratios of flattening equal to 50 % as opposed to 85% flattening for NCs deposited at 800 m/s. These observations have enabled us to draw qualitative conclusions on the film density The deposited films are less porous when the cluster impaction velocity increases. Atomic mixing between substrate and impacted NC atoms increased with increasing deposition velocity, which can perhaps be correlated to an increase of adherence, assuming that more mixing will create stronger molecular binding in the cluster-substrate interaction. Finally, complete epitaxial growth was observed for the highest impaction velocities only, which indicates that recrystalization can occur for this range of impact energies (0.3 eV/atom - 0.5 eV/atom). Although experimental results have given more quantitative data on film density and sticking ratios, they agree with our modeling, and this comparison allows us to validate our MD simulations. However, some limitations have been faced, mainly because of long computing time requirements that a single laptop computer has not been able to support. / text

A common analytical problem in applying LA sampling concerns dealing with large planar samples, e.g. gel plates, Si wafers, tissue sections or geological samples. As the current state of the art stands, there are two solutions to this problem: either sub-sample the substrate or build a custom cell. Both have their inherent drawbacks. With sub-sampling, the main issue is to ensure that a representative is sample taken to correctly determine the analytes of interest. Constructing custom cells can be time consuming, even for research groups that are experienced or skilled, as they have to be validated before data can be published. There are various published designs and ideas that attempt to deal with the issue of large samples, all of which ultimately enclose the sample in a box. The work presented in this thesis shows a viable alternative to enclosed sampling chambers. The non-contact cell is an open cell that uses novel gas dynamics to remove the necessity for an enclosed box and, therefore, enables samples of any arbitrary size to be sampled. The upper size limit of a sample is set by the travel of the XY stages on the laser ablation system, not the dimensions of the ablation cell.

The rotational spectrum of ScO (X-2 Sigma(+)) has been measured in the gas phase in the frequency range 30-493 GHz using a combination of Fourier transform microwave/millimeter-wave (FTM/mmW) and submillimeter direct absorption methods. This work is the first pure rotational study of this radical. Both the ground vibrational and v=1 states were observed. ScO was created from the reaction of metal vapor, produced either by a laser ablation source or a Broida-type oven, and N2O, in the former case heavily diluted in argon. Extensive hyperfine structure was observed in the FTM/mmW data, although the spin-rotation splitting was found to be small (similar to 3 MHz). In the mm-wave spectra, however, the fine and hyperfine structure was blended together, resulting in broad, single lines for a given transition N + 1 <- N. The data were analyzed in a combined fit using the very accurate hyperfine measurements of Childs and Steimle (1988), employing a Hund's case b Hamiltonian, and an improved set of rotational and centrifugal distortion constants were determined. These measurements improve the accuracy of predicted frequencies for astronomical searches by 14-18 MHz, or 16-20 km/s, in the 1 mm region - a difference of half to a full linewidth for certain interstellar sources. This work also demonstrates the capabilities of the FTM/mmW spectrometer at 61 GHz.

15 samples of gem opals were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). For this study were selected the most representative samples from Slovakia, Australia, Peru, Ethiopia, Mexico, USA and the Czech Republic. These samples were obtained from private collections. The study focuses on the geochemical relationships between various forms of opal originating from igneous and sedimentary environments based on the results from LA ICP-MS and ICP-MS. The major and trace element compositions are unique for each studied opal locality and important for understanding numerous aspects of opal formation. Major element analysis shows that opals are essentially pure SiO2 (77 - 92 wt. %). Al, Fe, Ca, K, Na and Mg are the main elemental impurities. The concentrations of the trace elements vary strongly depending on the opal locality. Differences were found, e.g., in the concentrations of REE and some refractory elements, which might be indicative for determining the provenance of opals. Many studies have been published explaining the origin of luminescence, microstructures and the thermal properties of opals. However, there are very few comprehensive studies comparing gem opals from the most important historical and...

ABSTRACT The focus of this work was the study possible ways to improve the efficiency of solar cells. To this end, the main aim was to investigate the deposition process of Indium Tin Oxide (ITO), Titanium Dioxide (TiO2), multi-layers ITO/TiO2 on quartz SiO2 substrates under different conditions (oxygen pressure, laser fluence and wavelength, and temperature) and later gold nanoparticles by the Reactive Pulsed Laser Ablation Deposition (RPLAD) technique. It was intended to investigate their electrical structural and optical properties under selected conditions for possible application to Dye Sensitised Solar Cells (DSSC). Under optimised conditions, maximum deposition rates of 12nm/min for ITO and 21nm/min for TiO2 thin films were achieved. Rutherford Backscattering Spectrometry (RBS) with 2MeV He+ ions was used to measure the films thickness. Uniform thicknesses over a large area were found to be about 400nm and 800nm for ITO and TiO2 films, respectively. Crystalline properties were studied via x-ray diffraction and Raman spectroscopy. X-ray Diffraction (XRD) analysis revealed that the ITO films are highly orientated nanocrystals with their a-axis normal to the glass substrate surface. The average particle size of the precipitated nanocrystals was calculated to be 10-15nm. The structure of the films was characterised via Atomic Force Microscopy (AFM) imaging of the top surface of the film. The films have a rough surface with average roughness of 26-30nm. Pores were observed with a density of 144 and 125 pores/mm2 and average size of 150 and 110nm for ITO films deposited at 200 and 400°C, respectively. TiO2 films deposited on the prepared ITO films were less crystalline. Annealing was performed at 300 and 500°C for 3 consecutive hours and the XRD results show that the transformation of TiO2 film into anatase phase was almost complete with a crystal size of ~ 6-7nm. Scanning Transmission Electron Microscopy (STEM) of the surfaces was also performed. The TiO2 films deposited onto the prepared ITO films present a relatively high pore size with an average pore diameter of ~ 40nm and excellent uniformity. It is interesting to note that the pores are randomly arranged. The random arrangement of the pores network may actually be beneficial for producing a uniform electrode. In addition, STEM cross-sectional analysis of the films showed a columnar structure but no evidence of voids in the structure. The large surface area produced suggests applications in DSSC. The electrical properties of the films were investigated and an estimation of resistivity and Hall mobility was made. Low values of resistivity and high values of mobility were observed for ITO films. The resistivity of the film increases with increasing thickness while it decreases when increasing the deposition temperature. The lowest value was found to be 1.5x10-6Ωm for ITO films deposited at 400°C. Hall mobility was found to increase with substrate temperature. In this investigation, the highest Hall mobility at room temperature was estimated to be 22.3cm2/Vs under ambient O2 pressure (PO2) of 1Pa and 52.1 and 51.3cm2/Vs for films deposited at 200 and 400°C, respectively. But the best ITO film was deposited at 200°C, since this film combines good resistivity, good Hall mobility and good transmittance. UV-VIS-IR transmission spectra were recorded on a Perkin Elmer Lambda 900. From the transmission data, the energy gap as well as the optical constant was estimated. A high transmission for ITO films in the visible (Vis) range was observed which was above 88% for films produced at room temperature and above 95% for those deposited at 200°C. The transmission for the films produced in oxygen was about 90% above 400nm, whereas it lies between 70 and 80% for films produced in rare gases. An increase in the band gap was observed by increasing the oxygen pressure and substrate temperature for ITO films. Increasing the quartz SiO2 substrate temperature from room temperature to 400 °C resulted in an increase of the transmission of TiO2 films, mostly in the Visible Near Infrared (Vis-NIR) from about 70% to 92%. After annealing at 500°C for 3 consecutive hours, the transmission of TiO2 film further sharply decreases toward shorter wavelengths. Analysis of the transmittance curve of TiO2/Au shows a decrease of about 6% of the transmission in the Ultraviolet Visible (UV-Vis) range. Optical absorption edge analysis showed that the optical density could be used to detect the film growth conditions and to correlate the film structure and the absorption edge. The TiO2 films deposited present a direct band gap at 3.51eV and 3.37eV for TiO2 as deposited and after annealing, respectively, while the indirect band gap was found to be 3.55eV and 3.26eV for TiO2 films as deposited and after annealing, respectively. There was a shift of about 0.1eV between as deposited ITO monolayer films and ITO/TiO2 bilayers deposited at 200°C. A small shift towards shorter wavelengths has been observed for multilayer ITO/TiO2/Au. In this case, the increase of Eg was ascribed to a reduction of the oxygen vacancies with increasing substrate temperature at which the ITO film was deposited. The change in the shape of the fundamental absorption edge is considered to reflect the variation of density and the short range structural modifications undetected by structural characterisations. Enlargement of band-gap energies of semiconductors may be advantageous when used in DSSC to suppress the charge recombination between the reduced electrolytes and the photo-excited holes in the valence band of TiO2 substrates and enhance the open-circuit potential of the cell. When ITO/TiO2 bilayers were annealed before depositing Au, the gap energy remained constant.

The primary aim of this thesis is to develop image processing algorithms to quantitatively determine the link between traumatic brain injury (TBI) severity and chronic traumatic encephalopathy (CTE) neuropathology, specifically looking into the role of blood-brain barrier disruption following TBI. In order to causally investigate the relationship between the tau protein neurodegenerative disease CTE and TBI, mouse models of blast neurotrauma (BNT) and impact neurotrauma (INT) are investigated. First, a high-speed video tracking algorithm is developed based on K-means clustering, active contours and Kalman filtering to comparatively study the head kinematics in blast and impact experiments. Then, to compare BNT and INT neuropathology, methods for quantitative analysis of macroscopic optical images and fluorescent images are described. The secondary aim of this thesis focuses on developing methods for a novel application of metallomic imaging mass spectrometry (MIMS) to biological tissue. Unlike traditional modalities used to assess neuropathology, that suffer from limited sensitivity and analytical capacity, MIMS uses a mass spectrometer -- an analytical instrument for measuring elements and isotopes with high dynamic range, sensitivity and specificity -- as the imaging sensor to generate spatial maps with spectral (vector-valued) data per pixel. Given the vector nature of MIMS data, a unique end-to-end processing pipeline is designed to support data acquisition, visualization and interpretation. A novel multi-modal and multi-channel image registration (MMMCIR) method using multi-variate mutual information as a similarity metric is developed in order to establish correspondence between two images of arbitrary modality. The MMMCIR method is then used to automatically segment MIMS images of the mouse brain and systematically evaluate the levels of relevant elements and isotopes after experimental closed-head impact injury on the impact side (ipsilateral) and opposing side (contralateral) of the brain. This method quantifiably confirms observed differences in gadolinium levels for a cohort of images. Finally, MIMS images of human lacrimal sac biopsy samples are used for preliminary clinicopathological assessments, supporting the utility of the unique insights MIMS provides by correlating areas of inflammation to areas of elevated toxic metals. The image processing methods developed in this work demonstrate the significant capabilities of MIMS and its role in enhancing our understanding of the underlying pathological mechanisms of TBI and other medical conditions. / 2019-07-09T00:00:00Z

O desenvolvimento de sistemas laser com pulsos ultracurtos trouxe a possibilidade de usinagem de estruturas muito pequenas em praticamente qualquer tipo de material. Neste trabalho foi dada continuidade a estudos já iniciados no Centro de Lasers e Aplicações (CLA) com os materiais dielétricos, introduzindo a largura temporal dos pulsos laser como mais uma variável e utilizando os conhecimentos adquiridos para a determinação de limiares de ablação e parâmetros de incubação em alguns metais como: aço AISI 1045, aço inoxidável VI138, cobre eletrolítico e molibdênio. A ausência de calor no processo de ablação dos metais torna-se muito difícil, pois a criação de uma camada de íons é muito prejudicada pela mobilidade eletrônica ao seu redor. Assim a ablação de metais com pulsos ultracurtos, tem como principal mecanismo a explosão de fase associada a outros processos que também contribuem na ablação, porém em menor escala, como a explosão coulombiana e a fusão ultrarrápida. Além disso, propriedades como a constante de acoplamento elétron-fônon e a condutividade térmica assumem um papel importante e devem ser levadas em conta na investigação do processo de ablação dos metais. Este trabalho possibilitou a obtenção de parâmetros de operação nos quais o calor transferido para a rede é minimizado, possibilitando a microusinagem de precisão e alterações controladas na morfologia da superfície de diversos metais. Os resultados propiciaram assim condições para novos desenvolvimentos e aplicações práticas de usinagem com pulsos ultracurtos. / The development of laser systems with ultrashort pulses brought the possibility of machining very small structures in virtually any type of material. In this work was continued the studies already started in Lasers and Applications Center (CLA), with dielectric materials, introducing temporal width of the laser pulses as another variable, and using the knowledge acquired to determine ablation threshold and incubation parameters of some metals such as AISI 1045 steel, VI 138 stainless steel, electrolytic copper and molybdenum. The absence of heat in the ablation process of metals is much more difficult since the creation of a layer of ions is greatly impaired by electronic mobility in its vicinity. Hence, the ablation process for metals with ultrashort pulses, has, as main mechanism, the phase explosion associated with other processes that also contribute in the process, but on a smaller scale, such as Coulomb explosion and ultrafast fusion. Moreover, properties such as electron-phonon coupling constant and thermal conductivity play an important role and should be taken into account in investigating the process of ablation of metals. This study made it possible to obtain operation parameter where the heat transferred to the lattice is minimized, enabling precision micromachining and controlled changes in the morphology of the surface of metals. The results provided conditions for new developments and real machining applications with ultrashort pulses.