Diamond is a semiconductor with many superior material properties such as high breakdown field, high saturation velocity, high carrier mobilities and the highest thermal conductivity of all materials. These extreme properties, as compared to other (wide bandgap) semiconductors, make it desirable to develop single-crystalline epitaxial diamond films for electronic device and detector applications. Future diamond devices, such as power diodes, photoconductive switches and high-frequency field effect transistors, could in principle deliver outstanding performance due to diamond's excellent intrinsic properties. However, such electronic applications put severe demands on the crystalline quality of the material. Many fundamental electronic properties of diamond are still poorly understood, which severely holds back diamond-based electronic device and detector development. This problem is largely due to incomplete knowledge of the defects in the material and due to a lack of understanding of how these defects influence transport properties. Since diamond lacks a shallow dopant that is fully thermally activated at room temperature, the conventional silicon semiconductor technology cannot be transferred to diamond devices; instead, new concepts have to be developed. Some of the more promising device concepts contain thin delta-doped layers with a very high dopant concentration, which are fully activated in conjunction with undoped (intrinsic) layers where charges are transported. Thus, it is crucial to better understand transport in high-quality undoped layers with high carrier mobilities. The focus of this doctoral thesis is therefore the study of charge transport and related electronic properties of single-crystalline plasma-deposited (SC-CVD) diamond samples, in order to improve knowledge on charge creation and transport mechanisms. Fundamental characteristics such as drift mobilities, compensation ratios and average pair-creation energy were measured. Comparing them with theoretical predictions from simulations allows for verification of these models and improvement of the diamond deposition process.

The development and characterization of experimental setups for angle-resolved photoelectron spectroscopy (ARPES) and spin- and angle-resolved photoelectron spectroscopy (SARPES) is described. Subsequently, the two techniques are applied to studies of the electronic band structure in topologically non-trivial materials. The laser-based ARPES setup works at a photon energy of 10.5 eV and a typical repetition rate in the range 200 kHz to 800 kHz. By using a time-of-flight electron energy analyzer electrons emitted from the sample within a solid angle of up to ±15 degrees can be collected and analyzed simultaneously. The SARPES setup is equipped with a traditional hemispherical electron energy analyzer in combination with a mini-Mott electron polarimeter. The system enables software-controlled switching between angle-resolved spin-integrated and spin-resolved measurements, thus providing the possibility to orient the sample by mapping out the electronic band structure using ARPES before performing spin-resolved measurements at selected points in the Brillouin zone. Thin films of the topological insulators (TIs) Bi2Se3, Bi2Te3 and Sb2Te3 are grown using e-beam evaporation and their surface states are observed by means of ARPES. By using a combination of low photon energies and cryogenic sample temperatures the topological states originating from both the vacuum interface (surface) and the substrate interface are observed in Bi2Se3 films and Bi2Se3/Bi2Te3 heterostructures, with total thicknesses in the ultra-thin limit (six to eight quintuple layers), grown on Bi-terminated Si(111) substrates. Band alignment between Si and Bi2Se3 at the interface creates a band bending through the films. The band bending is found to be independent of the Fermi level (EF) position in the bulk of the substrate, suggesting that the surface pinning of EF in the Si(111) substrate remains unaltered after deposition of the TI films. Therefore, the type and level of doping of the substrate does not show any large influence on the size of the band bending. Further, we provide experimental evidence for the realization of a topological crystalline insulator (TCI) phase in the narrow-band semiconductor Pb1−xSnxSe. The TCI phase exists for temperatures below the transition temperature Tc and is characterized by an inverted bulk band gap accompanied by the existence of non-gapped surface states crossing the band gap. Above Tc the material is in a topologically trivial phase where the surface states are gapped. Thus, when lowering the sample temperature across Tc a topological phase transition from a trivial insulator to a TCI is observed. SARPES studies indicate a helical spin structure of the surface states both in the topologically trivial and the TCI phase. / <p>QC 20130507</p>

名古屋大学年代測定総合研究センターシンポジウム報告

Numerous glacial advances over the past 2 million years have covered the entire Canadian and Fennoscandian Shield outcrop. During glacial advance and retreat, permafrost is expected to form in front of the glacier. The question of how permafrost and freezing impact the formation and evolution of brines in natural systems may be vital to understanding the chemistry of groundwater in crystalline rocks. Investigations of groundwater conditions beneath thick permafrost can provide valuable information that can be applied to assessing safety of deep, underground nuclear waste repositories and understanding analogues to potential life-bearing zones on Mars. However, very little scientific investigation of cryogenic processes and hydrogeology deep within crystalline systems has been published. The purpose of this research is to evaluate the impacts of thick permafrost (>300m) formation on groundwater chemical and flow system evolution in the crystalline rock environment over geologic timescales. A field investigation was conducted at the Lupin Mine in Nunavut, Canada, to characterize the physical and hydrogeochemical conditions within and beneath a thick permafrost layer. Taliks, or unfrozen channels within the permafrost, are found beneath large lakes in the field area, and provide potential hydraulic connections through the permafrost. Rock matrix waters are dilute and do not appear to affect groundwater salinity. Permafrost waters are Na-Cl and Na-Cl-SO4 type, and have been contaminated with chloride and nitrate by mining activities. Sulfide oxidation in the permafrost may be naturally occurring or is enhanced by mining activities. Basal permafrost waters (550 to 570 mbgs) are variably affected by mining. The less contaminated basal waters have medium sulfate concentrations and are Ca-Na dominated. This is similar to deeper, uncontaminated subpermafrost waters, which are Ca-Na-Cl or Na-Ca-Cl type with a wide range of salinities (2.6 to 40 g•L-1). The lower salinity subpermafrost waters are attributed to dissociation of methane hydrate and drawdown of dilute talik waters by the hydraulic gradient created by mine dewatering. This investigation was unable to determine the influence of talik waters to the subpermafrost zone in undisturbed conditions. Pressures are also highly variable, and do not correlate with salinity. Fracture infillings are scarce and calcite δ18O and δ13C values have a large range. Microthermometry indicates a large range in salinities and homogenization temperatures as well, indicative of a boiling system. In situ freezing of fluids and methane hydrate formation may have concentrated the remaining fluids. Field activities at the Lupin mine also provided an opportunity to study the nature of gases within crystalline rocks in a permafrost environment. Gases were generally methane-dominated (64 to 87), with methane δ13C and δ2H values varying between -56 and -42‰ VPDB and -349 to -181 ‰ VSMOW, respectively. The gases sampled within the Lupin mine have unique ranges of chemical and isotopic compositions compared with other Canadian and Fennoscandian Shield gases. The gases may be of thermogenic origin, mixed with some bacteriogenic gas. The generally low δ2H-CH4 ratios are somewhat problematic to this interpretation, but the geologic history of the site, a metaturbidite sequence, supports a thermogenic gas origin. The presence of gas hydrate in the rock surrounding Lupin was inferred, based on temperature measurements and hydrostatic pressures. Evidence also suggests fractures near the mine have been depressurized, likely due to mine de-watering, resulting in dissipation of methane hydrate near the mine. Modeling results indicate methane hydrates were stable throughout the Quaternary glacial-interglacial cycles, potentially limiting subglacial recharge. The effects of deep permafrost formation and dissipation during the Pleistocene glacial/interglacial cycle to deep groundwaters in the Canadian Shield were also investigated by compiling data from thirty-nine sites at twenty-four locations across the Canadian Shield. Impacts due to glacial meltwater recharge and surficial cryogenic concentration of fluids, which had been previously considered by others, and in situ freeze-out effects due to ice and/or methane hydrate formation were considered. At some Canadian Shield sites, there are indications that fresh, brackish, and saline groundwaters have been affected by one of these processes, but the data were not sufficient to differentiate between mixed, intruded glacial meltwaters, or residual waters resulting from either permafrost or methane hydrate formation. Physical and geochemical data do not support the cryogenic formation of Canadian Shield brines from seawater in glacial marginal troughs. The origin and evolution of Canadian and Fennoscandian Shield brines was explored with a survey of chlorine and bromine stable isotope ratios. The δ37Cl and δ81Br isotopic ratios varied between -0.78 ‰ and 1.52 ‰ (SMOC) and 0.01 ‰ and 1.52 ‰ (SMOB), respectively. Variability of chlorine and bromine isotope ratios decreases with increasing depth. Fennoscandian Shield groundwaters tend to be more enriched than Canadian Shield groundwaters for both 37Cl and 81Br. Other sources and processes which may affect δ37Cl and δ81Br composition are also explored. Primary processes such as magmatic and/or hydrothermal activity are thought to be responsible for the isotopic composition of the most concentrated fluids at each site. Positive correlations between δ81Br, and δ37Cl with δ2H-CH4 and δ13C-CH4 were noted. At this time the cause of the relationship is unclear, and may be a result of changing redox, pH, temperature, and/or pressure conditions during hydrothermal, metamorphic, or volcanogenic processes. The data suggest solute sources and fluid evolution at individual sites would be better constrained utilizing a multi-tracer investigation of δ37Cl, δ81Br, and 87Sr/86Sr ratios comparing fluids, rocks, and fracture filling minerals (including fluid inclusions).

No description available.

Numerous glacial advances over the past 2 million years have covered the entire Canadian and Fennoscandian Shield outcrop. During glacial advance and retreat, permafrost is expected to form in front of the glacier. The question of how permafrost and freezing impact the formation and evolution of brines in natural systems may be vital to understanding the chemistry of groundwater in crystalline rocks. Investigations of groundwater conditions beneath thick permafrost can provide valuable information that can be applied to assessing safety of deep, underground nuclear waste repositories and understanding analogues to potential life-bearing zones on Mars. However, very little scientific investigation of cryogenic processes and hydrogeology deep within crystalline systems has been published. The purpose of this research is to evaluate the impacts of thick permafrost (>300m) formation on groundwater chemical and flow system evolution in the crystalline rock environment over geologic timescales. A field investigation was conducted at the Lupin Mine in Nunavut, Canada, to characterize the physical and hydrogeochemical conditions within and beneath a thick permafrost layer. Taliks, or unfrozen channels within the permafrost, are found beneath large lakes in the field area, and provide potential hydraulic connections through the permafrost. Rock matrix waters are dilute and do not appear to affect groundwater salinity. Permafrost waters are Na-Cl and Na-Cl-SO4 type, and have been contaminated with chloride and nitrate by mining activities. Sulfide oxidation in the permafrost may be naturally occurring or is enhanced by mining activities. Basal permafrost waters (550 to 570 mbgs) are variably affected by mining. The less contaminated basal waters have medium sulfate concentrations and are Ca-Na dominated. This is similar to deeper, uncontaminated subpermafrost waters, which are Ca-Na-Cl or Na-Ca-Cl type with a wide range of salinities (2.6 to 40 g•L-1). The lower salinity subpermafrost waters are attributed to dissociation of methane hydrate and drawdown of dilute talik waters by the hydraulic gradient created by mine dewatering. This investigation was unable to determine the influence of talik waters to the subpermafrost zone in undisturbed conditions. Pressures are also highly variable, and do not correlate with salinity. Fracture infillings are scarce and calcite δ18O and δ13C values have a large range. Microthermometry indicates a large range in salinities and homogenization temperatures as well, indicative of a boiling system. In situ freezing of fluids and methane hydrate formation may have concentrated the remaining fluids. Field activities at the Lupin mine also provided an opportunity to study the nature of gases within crystalline rocks in a permafrost environment. Gases were generally methane-dominated (64 to 87), with methane δ13C and δ2H values varying between -56 and -42‰ VPDB and -349 to -181 ‰ VSMOW, respectively. The gases sampled within the Lupin mine have unique ranges of chemical and isotopic compositions compared with other Canadian and Fennoscandian Shield gases. The gases may be of thermogenic origin, mixed with some bacteriogenic gas. The generally low δ2H-CH4 ratios are somewhat problematic to this interpretation, but the geologic history of the site, a metaturbidite sequence, supports a thermogenic gas origin. The presence of gas hydrate in the rock surrounding Lupin was inferred, based on temperature measurements and hydrostatic pressures. Evidence also suggests fractures near the mine have been depressurized, likely due to mine de-watering, resulting in dissipation of methane hydrate near the mine. Modeling results indicate methane hydrates were stable throughout the Quaternary glacial-interglacial cycles, potentially limiting subglacial recharge. The effects of deep permafrost formation and dissipation during the Pleistocene glacial/interglacial cycle to deep groundwaters in the Canadian Shield were also investigated by compiling data from thirty-nine sites at twenty-four locations across the Canadian Shield. Impacts due to glacial meltwater recharge and surficial cryogenic concentration of fluids, which had been previously considered by others, and in situ freeze-out effects due to ice and/or methane hydrate formation were considered. At some Canadian Shield sites, there are indications that fresh, brackish, and saline groundwaters have been affected by one of these processes, but the data were not sufficient to differentiate between mixed, intruded glacial meltwaters, or residual waters resulting from either permafrost or methane hydrate formation. Physical and geochemical data do not support the cryogenic formation of Canadian Shield brines from seawater in glacial marginal troughs. The origin and evolution of Canadian and Fennoscandian Shield brines was explored with a survey of chlorine and bromine stable isotope ratios. The δ37Cl and δ81Br isotopic ratios varied between -0.78 ‰ and 1.52 ‰ (SMOC) and 0.01 ‰ and 1.52 ‰ (SMOB), respectively. Variability of chlorine and bromine isotope ratios decreases with increasing depth. Fennoscandian Shield groundwaters tend to be more enriched than Canadian Shield groundwaters for both 37Cl and 81Br. Other sources and processes which may affect δ37Cl and δ81Br composition are also explored. Primary processes such as magmatic and/or hydrothermal activity are thought to be responsible for the isotopic composition of the most concentrated fluids at each site. Positive correlations between δ81Br, and δ37Cl with δ2H-CH4 and δ13C-CH4 were noted. At this time the cause of the relationship is unclear, and may be a result of changing redox, pH, temperature, and/or pressure conditions during hydrothermal, metamorphic, or volcanogenic processes. The data suggest solute sources and fluid evolution at individual sites would be better constrained utilizing a multi-tracer investigation of δ37Cl, δ81Br, and 87Sr/86Sr ratios comparing fluids, rocks, and fracture filling minerals (including fluid inclusions).

The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation.

The emergence of multi-band communications standards, and the fast pace of the consumer electronics markets for wireless/cellular applications emphasize the need for fast design closure. In addition, there is a need for electronic product designers to collaborate with manufacturers, gain essential knowledge regarding the manufacturing facilities and the processes, and apply this knowledge during the design process. In this dissertation, efficient layout-level circuit sizing techniques, and methodologies for design-for-manufacturability have been investigated. For cost-effective fabrication of RF modules on emerging technologies, there is a clear need for design cycle time reduction of passive and active RF modules. This is important since new technologies lack extensive design libraries and layout-level electromagnetic (EM) optimization of RF circuits become the major bottleneck for reduced design time. In addition, the design of multi-band RF circuits requires precise control of design specifications that are partially satisfied due to manufacturing variations, resulting in yield loss. In this work, a broadband modeling and a layout-level sizing technique for embedded inductors/capacitors in multilayer substrate has been presented. The methodology employs artificial neural networks to develop a neuro-model for the embedded passives. Secondly, a layout-level sizing technique for RF passive circuits with quasi-lumped embedded inductors and capacitors has been demonstrated. The sizing technique is based on the circuit augmentation technique and a linear optimization framework. In addition, this dissertation presents a layout-level, multi-domain DFM methodology and yield optimization technique for RF circuits for SOP-based wireless applications. The proposed statistical analysis framework is based on layout segmentation, lumped element modeling, sensitivity analysis, and extraction of probability density functions using convolution methods. The statistical analysis takes into account the effect of thermo-mechanical stress and process variations that are incurred in batch fabrication. Yield enhancement and optimization methods based on joint probability functions and constraint-based convex programming has also been presented. The results in this work have been demonstrated to show good correlation with measurement data.

&Ccedil / i&ccedil / ekdagi basin developed on the Central Anatolian Crystalline Complex (CACC) is a foreland basin developed as the southern integral part of the &Ccedil / ankiri Basin during the Late Paleocene to middle Oligocene. The basin has two compartments separated by the &Ccedil / i&ccedil / ekdagi High comprises two sedimentary cycles. The oldest cycle comprises Barakli, Koca&ccedil / ay and Bogazk&ouml / y formationsa and is exposed both in the northern and the southern sectors. They were deposited in marine conditions. The second cycle comprises incik and G&uuml / vendik formations and was deposited in continental settings. The first cycle comprises uniformly south-directed paleocurrent directions in both the northern and southern sectors whereas the second cycle deposits are represented by south-directed directions in the southern sector, and bimodal directions in the northern sector. In addition, the second cycle formations contain progressive unconformities and coarsening upwards sequences indicative of thrusting. Internal structures of the units and paleostress data indicate that the basin experienced over-all compression and local extension due to flexural bending. This gave way to inversion of some of the normal faults and uplift of the &Ccedil / i&ccedil / ekdagi High during the deposition of second cycle in the Late Eocene to middle Oligocene time which subsequently resulted in compartmentalization of the basin.

ABSTRACT HYDROGEN STORAGE IN MAGNESIUM BASED THIN FILMS Akyildiz, Hasan Ph.D., Department of Metallurgical and Materials Engineering Supervisor : Prof. Dr. Tayfur &Ouml / zt&uuml / rk Co-Supervisor : Prof. Dr. Macit &Ouml / zenbas October 2010, 146 pages A study was carried out for the production of Mg-based thin films which can absorb and desorb hydrogen near ambient conditions, with fast kinetics. For this purpose, two deposition units were constructed / one high vacuum (HV) and the other ultra high vacuum (UHV) deposition system. The HV system was based on a pyrex bell jar and had two independent evaporation sources. The unit was used to deposit films of Mg, Mg capped with Pd and Au-Pd as well as Mg-Cu both in co-deposited and multilayered form within a thickness range of 0.4 to 1.5 &mu / m. The films were crystalline with columnar grains having some degree of preferred orientation. In terms of hydrogen storage properties, Mg/Pd system yielded the most favorable results. These films could desorb hydrogen at temperatures not greater than 473 K. The study on crystalline thin films has further shown that there is a narrow temperature window for useful hydrogenation of thin films, the upper limit of which is determined by the intermetallic formation. The UHV deposition system had four independent evaporation sources and incorporated substrate cooling by circulating cooled nitrogen gas through the substrate holder. Thin films of Mg-Cu were produced in this unit via co-evaporation technique to provide concentrations of 5, 10 and 15 at. % Cu. The films were 250-300 nm thick, capped with a thin layer of Pd, i.e. 5-25 nm. The deposition was yielded nanocrystalline or amorphous Mg-Cu thin films depending on the substrate temperature. At 298 K, the films were crystalline, the structure being refined with the increase in Cu content. At 223 K, the films were amorphous, except for Mg:Cu=95:5. The hydrogen sorption of the films was followed by resistance measurements, with the samples heated isochronally, initially under hydrogen and then under vacuum. The resistance data have shown that hydrogen sorption behaviour of thin films was improved by size refinement, and further by amorphization. Among the films deposited, amorphous Mg:Cu=85:15 alloy could absorb hydrogen at room temperature and could desorb it at 223 K (50 &ordm / C), with fast kinetics.