Made available in DSpace on 2014-10-09T12:28:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:23Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:28:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:23Z (GMT). No. of bitstreams: 0 / A usinagem de estruturas micrométricas pode ser feita com pulsos laser de nano, pico ou fentossegundos. Destes, porém, somente os mais curtos podem resultar em uma interação não térmica com a matéria, o que evita a fusão, formação de rebarba e zona afetada pelo calor. Devido à sua baixa potência média, contudo, a sua utilização na produção em massa somente pode ser considerada em casos muito especiais, isto é, quando o processamento não-térmico é essencial. Este é o caso da usinagem de semicondutores, aços elétricos, produção de MEMS (sistemas micro eletro-mecânicos), de micro canais e diversos dispositivos médicos e biológicos. Assim, visando a produção destes tipos de estruturas, uma estação de trabalho foi construída com capacidade de controlar os principais parâmetros de processo necessários para uma usinagem micrométrica com laser de pulsos ultracurtos. Os principais problemas deste tipo de estação são o controle da fluência e do posicionamento do ponto focal. Assim, o controle do diâmetro do feixe (no foco) e da energia devem ser feitos com grande precisão. Além disso, o posicionamento do ponto focal com precisão micrométrica nos três eixos, também é de fundamental importância. O sistema construído neste trabalho apresenta soluções para estes problemas, utilizando diversos sensores e posicionadores controlados simultaneamente por um único programa. A estação de trabalho recebe um feixe vindo de um laser de pulsos ultracurtos localizado em outro laboratório, e manipula este feixe de maneira a focalizá-lo com precisão na superfície da amostra a ser usinada. Os principais parâmetros controlados dinamicamente são a energia, o número de pulsos e o posicionamento individual de cada um deles. A distribuição espacial da intensidade, a polarização e as vibrações também foram medidas e otimizadas. O sistema foi testado e aferido com medidas de limiar de ablação do silício, que é um material bastante estudado neste regime de operação laser. Os resultados, quando confrontados com a literatura, mostram a confiabilidade e a precisão do sistema. A automatização, além de aumentar esta precisão, também aumentou a rapidez na obtenção dos resultados. Medidas de limiar de ablação também foram realizadas para o metal molibdênio, levando a resultados ainda não vistos na literatura. Assim, de acordo com o objetivo inicial, o sistema foi desenvolvido e está pronto para utilização em estudos que levem à produção de estruturas micrométricas. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The necessity of elemental analysis techniques to solve forensic problems continues to expand as the samples collected from crime scenes grow in complexity. Laser ablation ICP-MS (LA-ICP-MS) has been shown to provide a high degree of discrimination between samples that originate from different sources. In the first part of this research, two laser ablation ICP-MS systems were compared, one using a nanosecond laser and another a femtosecond laser source for the forensic analysis of glass. The results showed that femtosecond LA-ICP-MS did not provide significant improvements in terms of accuracy, precision and discrimination, however femtosecond LA-ICP-MS did provide lower detection limits. In addition, it was determined that even for femtosecond LA-ICP-MS an internal standard should be utilized to obtain accurate analytical results for glass analyses. In the second part, a method using laser induced breakdown spectroscopy (LIBS) for the forensic analysis of glass was shown to provide excellent discrimination for a glass set consisting of 41 automotive fragments. The discrimination power was compared to two of the leading elemental analysis techniques, µXRF and LA-ICP-MS, and the results were similar; all methods generated >99% discrimination and the pairs found indistinguishable were similar. An extensive data analysis approach for LIBS glass analyses was developed to minimize Type I and II errors en route to a recommendation of 10 ratios to be used for glass comparisons. Finally, a LA-ICP-MS method for the qualitative analysis and discrimination of gel ink sources was developed and tested for a set of ink samples. In the first discrimination study, qualitative analysis was used to obtain 95.6% discrimination for a blind study consisting of 45 black gel ink samples provided by the United States Secret Service. A 0.4% false exclusion (Type I) error rate and a 3.9% false inclusion (Type II) error rate was obtained for this discrimination study. In the second discrimination study, 99% discrimination power was achieved for a black gel ink pen set consisting of 24 self collected samples. The two pairs found to be indistinguishable came from the same source of origin (the same manufacturer and type of pen purchased in different locations). It was also found that gel ink from the same pen, regardless of the age, was indistinguishable as were gel ink pens (four pens) originating from the same pack.

The use of thin-film techniques for the fabrication of microfluidic devices has gained attention over the last decade, particularly for three-dimensional channel structures. The reasons for this include effective use of chip volume, mechanical flexibility, dead volume reduction, enhanced design capabilities, integration of passive elements, and scalability. Several fabrication techniques have been adapted for use on thin films: laser ablation and hot embossing are popular for channel fabrication, and lamination is widely used for channel enclosure. However, none of the previous studies have been able to achieve a strong bond that is reliable under moderate positive pressures. The present work aims to develop a thin-film process that provides design versatility, speed, channel profile homogeneity, and the reliability that others fail to achieve. The three building blocks of the proposed baseline were fifty-micron poly(methyl methacrylate) thin films as substrates, channel patterning by laser ablation, and device assembly by thermal-fusion bonding. Channel fabrication was characterized and tuned to produce the desired dimensions and surface roughness. Thermal bonding was performed using an adapted mechanical testing device and optimized to produce the maximum bonding strength without significant channel deformation. Bonding multilayered devices, incorporating conduction lines, and integrating various types of membranes as passive elements demonstrated the versatility of the process. Finally, this baseline was used to fabricate a droplet generator and a DNA detection chip based on micro-bead agglomeration. It was found that a combination of low laser power and scanning speed produced channel surfaces with better uniformity than those obtained with higher values. In addition, the implemented bonding technique provided the process with the most reliable bond strength reported, so far, for thin-film microfluidics. Overall, the present work proved to be versatile, reliable, and fast, making it a good candidate to reproduce several on-chip functions. Future work includes implementing thick-substrate bonding techniques to further improve the process and decrease energy requirements.

Title: Characterization and focusing of capillary-discharge XUV-laser beam for purposes of thin-film deposition Author: Peter Pira Department: Department of Surface and Plasma Science Supervisor: doc. RNDr. Jan Wild, CSc., Department of Surface and Plasma Science Abstract: The paper deals with the first results of the interaction of a desk-top high repetition rate XUV laser (wavelength of 46.9 nm) radiation with materials suitable for optoelectronics, in particular the ionic crystals CsI, LiF, etc. Using surface physics methods (AFM, DIC Normanski microscopy) pulse laser imprints were investigated. Based on the results obtained, general information on the nature of ablation and desorption was obtained, which were compared with the results of the XUV-ABLATOR modified code modeling. Plasma arising from ablation was examined by a modified Langmuir probe system. The main result is the pulse laser deposition of thin films of Bi and CsI. Keywords: ablation, Pulsed Laser Deposition, XUV laser

We investigate the conditions under which electron irradiation of single-walled carbon nanotube (SWCNT) bundles with 2 keV electrons produces an increase in the Raman D peak. We find that an increase in the D peak does not occur when SWCNTs are preheated in situ at 600 C for 1 h in ultrahigh vacuum (UHV) before irradiation is performed. Exposing SWCNTs to air or other gases after preheating in UHV and before irradiation results in an increase in the D peak. Small diameter SWCNTs that are not preheated or preheated and exposed to air show a significant increase in the D and G bands after irradiation. X-ray photoelectron spectroscopy shows no chemical shifts in the C1s peak of SWCNTs that have been irradiated versus SWCNTs that have not been irradiated, suggesting that the increase in the D peak is not due to chemisorption of adsorbates on the nanotubes.

The goal of this thesis is to propose and investigate a method of predicting depth of a laser dissection pulse in soft tissue without acquiring material properties of the tissue target or measuring the laser output. The method proposed is similar to what is used by laser surgical operators today, but uses regression learning to perform on-the fly predictions in place of a skilled laser surgeon. Power of the laser and the ablation depth were recorded for 57 samples and fed into the regression algorithm. Data exclusion was performed using Temperature before laser action as criteria. A linear and logarithmic model was explored using random points from the data post-exclusion, validation RMSE ranged from 135-200 micrometer. A linear and logarithmic model was explored using data points below a moving power threshold and validated with data points above said threshold, validation RMSE ranged from 108-170 micrometer. The t.test performed showed there was not a significant difference between the linear and the logarithmic models' goodness of fit metrics, but it did show there was a significant difference between the model building methods (randomly selected data points, moving power threshold). The method of building a model using lower power levels to predict larger power levels had better goodness of fit metrics than the method of selecting data points at random. In the future, this method could be used to help approximate the laser settings for surgery on a procedural basis, and allow for surgeons to perform at a higher skill level with less training.

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

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has risen to among the top tier techniques for the direct analysis of solid samples. However, significant problems remain that must be solved to achieve the full analytical potential of LA-ICP-MS. Inefficient conversion of aerosol to ions within the ICP or transmission through the MS interface may decrease precision, sensitivity, and/or accuracy. Although fundamental mechanisms that govern ion production and transmission have been studied extensively in solution-nebulization (SN) ICP-MS instruments, significant gaps in our understanding remain. Furthermore, it is unclear to what extent differences between the aerosols generated during SN and LA influence either ion production or transmission. In this work, I initially investigated differences in the spatial distributions of Ca, Ba, and Sc ions generated by LA and SN using high-resolution LIF imaging. Ions formed from aerosol generated by LA at low fluence were distributed over much greater axial and narrower radial distances than SN aerosol. Additionally, I investigated the effects of solvent, laser fluence, and ablation atmosphere (He vs Ar) on ion distributions in the ICP. Unlike solvent, changing laser fluence and ablation atmosphere produced considerable changes in the ion signal intensity and spatial distribution during LA. At greater laser fluence, the radial distance over which ions were distributed dramatically increased. Surprisingly, when helium was mixed with argon as carrier gas, ion signals decreased. Many of these effects were assumed to be related to changes in the number and size of particles generated during LA. In a follow-up study, relative contributions to ion densities in the ICP from particles of different sizes were investigated. LIF images were recorded while filtering particles above a threshold size on-line. Micron-sized particles contributed the majority of ions formed in the ICP. For Ba, Ca, and Sc, differences in the axial position where nanometer- and micron-sized particles vaporized were 2, 1, and less than 1 mm, respectively. I also performed experiments to identify changes in the ion signal related to changing ablation conditions vs. changing ICP conditions associated with helium additions to the carrier gas. LIF images were recorded during different combinations of He/Ar added upstream and/or downstream of the ablation cell. Changes in the ion signal during ablation in helium vs argon did not always match expectations based on changes in particle numbers and sizes measured with SEM. The results force re-examination of some of the fundamental assumptions about the effect of carrier gas composition on the performance of LA-ICP-MS. The research described in this dissertation provides valuable insight into fundamental aspects of key ICP processes related to LA generated aerosol.

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.