<p>The purpose of this research has been to use off-line characterization techniques to establish material-specific properties of gate-stack constituents (i.e., high-k dielectric stacks and electrodes) and complete gate-stack structures. Hence, the characterization methodologies were established to evaluate high-k dielectrics at various processing levels, which, in part, determine the final characteristics of an advanced gate-stack device. Material systems that were investigated include: Al-O, Hf-Si-O, Zr-Si-O, Ti-O, Ta-O and Sr-Ti-O. Various physical and electrical characterization techniques were used to establish fundamental understandings of the materials selected, thin-film growth/deposition processes, and gate-stack structures. General conclusions for stable and unstable gate-dielectric materials have been establishedregarding the presence of a problematic interfacial layer at the Si/dielectric interface, graded dielectric layers, and the stability of gate electrodes on high-k dielectrics.The nanometer-scale chemistry of a gate-stack capacitor whose expected structure is Si/SiOxNy/Ta2O5/TiN/Al was studied by high-resolution electron-energy-loss spectroscopy in a scanning transmission electron microscope. Elemental profiles with near-atomic-level resolution for Si, Ti, N, Al, and O demonstrate that the device structure deviates drastically from the expectation and is chemically complex.It is concluded that the graded distribution of certain elements across the gate-stack capacitor completely precludes a band-structure model that assumes abrupt interfaces and chemically discrete layers. This study impacted on subsequent interpretations of flatband voltage extractions and electrical degradation following backside metallization/postmetallization annealing for capacitors whose dielectric-stack was based on Ta-O.Detailed and extensive electrical characterizations of Pt/SiOx/Sr-Ti-O/Si MOS capacitors were carried out to investigate reliability issues in a bi-layer gate dielectric. Based on these studies, models are proposed to describe the carrier transport and dielectric degradation for a Sr-Ti-O capacitor. It is concluded that conduction is dominated by Frenkel-Poole emission from mid-gap trap levels. The trap barrier height is estimated to be 1.51eV. A model based on the atomic and electronic structure of oxygen vacancies can account for the reported leakage-current characteristics. In addition, it is tentatively proposed that anode-hole injection and hole trapping control the dielectric degradation under gate injection.<P>

<p>Characterization of nitride films on 6H-SiC (0001) wafers via x-ray, TEM, and AFM was accomplished on standard GaN thin films with AlN or AlGaN buffer layers. TEM sample thinning capability was improved through the use of Nomarski in an optical microscope to gauge the thickness of the sample during preparation. TEM analysis was then completed of Au and Pt films deposited on chemical vapor cleaned GaN with annealed up to 800°C. Chemical reactions were detected in x-ray measurements of the 800°C Pt samples and GaN/metal interface roughening were confirmed by TEM images in both metals. Interface roughening is attributed to the chemical reactions and interfacial stresses greater than the yield stress of the metal created during heat treatments by the difference in the thermal expansion coefficients of the GaN and the metals. The GaN rocking curves were found to track very closely to the values of the underlying substrate and changes in buffer layer growth temperatures were found to change the screw and edge dislocation populations of subsequent GaN layers. GaN grown on 1030°C AlN buffer layers showed the lowest edge dislocation populations when compared against buffers grown in the range of 1010-1220°C, even though the 1220°C AlN was much smoother. AlGaN buffer layers provided more edge dislocation reduction, with a 1090°C Al0.2Ga0.8N layer yielding the best GaN rocking curve values found in this work. GaN films with AlN buffer layers grown on hydrogen etched SiC substrates did not show rocking curve improvement when compared against samples with unetched substrates. The AlN layers showed extremely narrow, substrate limited, on-axis rocking curve values, but it is not clear as to whether additional defects are present that may broaden the off-axis rocking curves, causing the poorer results seen in the GaN films. Reciprocal space maps of uncoalesced, maskless pendeo epitaxy samples revealed that the wing regions are shielded from poor substrate material when compared against the seed material. The wing regions also have lower strain and rocking curve widths than the corresponding seed material.<P>

<p>LOESING, RAINER, Development of High Resolution Depth Profiling Of Ultra Shallow Dopant Implants with SIMS (under the direction of Phillip E. Russell. Secondary Ion Mass Spectrometry (SIMS) is considered a reliable technique for precise and accurate dopant depth profiling in Si with respect to junction depth and implanted dose. The junction depths of source drain extension structures are predicted to be between 19-33nm for the 0.1µm MOSFET generation. Accurate high depth resolution analysis of these ultra-shallow junctions by SIMS can only be provided if atomic mixing caused by energetic primary ion bombardment is minimized and extensive beam induced crater bottom roughening is avoided. For quantitative measurements, the influence of primary ion implantation, sputter rate changes and beam induced crater bottom roughness on secondary ion intensities has to be known. In this work SIMS was used to develop techniques for the accurate analysis of ultra shallow B, P and As implants in Si.Low energy O2+ primary ion bombardment was found to give the highest depth resolution for the analysis of B and P in Si, while low energy Cs+ and CsC6- primary ion bombardment resulted in the highest depth resolution for the analysis of As in Si. To obtain a more accurate profile shape and depth scale it was found to be essential to limit beam induced crater bottom roughness by means of sample rotation, variations of primary ion angle of incidence or change in sample chamber vacuum conditions. Beam induced crater bottom roughness was investigated for low energy O2+, Cs+ and CsC6- ion bombardment using atomic force microscopy (AFM) and optical profilometer (OP) measurements. OP was found to be a valuable tool for investigating small changes in sputter rate in the initial stages of a SIMS depth profile. It was shown that dose measurements of ultra shallow implants can be improved by using a correction procedure based on bulk doped standards. SIMS was proven to be a valuable tool for the characterization of ultra shallow implants in Si, but careful consideration of analysis conditions and SIMS artifacts is required for accurate analysis.<P>

<p>Free-standing single crystals of bulk GaN were grown via unseeded vapor phase transport at 1130C on hexagonal BN surfaces via direct reaction of Ga with ammonia. The temperature and stability of the Ga source were critical in terms of uniform nucleation and growth. The source temperature was maintained at 1260C to minimize a rapid reaction leading to the formation of GaN and the subsequent decomposition beneath the surface and consequent spattering of Ga. A maximum crystal growth temperature of 1130C was determined in which the GaN growth kinetics were much greater than decomposition. The number of nucleation events was reduced and the crystal size increased by a novel nucleation technique wherein ammonia was introduced at high temperatures. The resulting crystals were either needles or platelets depending on the process variables employed. Low V/III ratios achieved via ammonia flow rates 75sccm and/or ammonia total pressures 430Torr favored lateral growth. The average lateral growth rate for the platelets was ~50micron/hr; the average vertical growth rate for the needles was ~500micron/hr. Growth rates in all other directions for each of these two morphologies were very low. Seeded growth of both needle and platelet crystals was also achieved; however, the growth rate decreased at longer times and higher pressures due to reaction with hydrogen from the increased decomposition of ammonia. Nitrogen dilution of ammonia reduced the amount of hydrogen generated as a result of ammonia decomposition and increased the kinetic barrier to desorption of reactants from the GaN surface and then alleviated the enhanced decomposition of GaN crystals. A 2mm x 1.5mm needle and a 2.3mm x 1.8mm x 0.3mm platelet of GaN were grown with minimal decomposition in a 66.7% ammonia + 33.3% nitrogen gas mixture. Excellent crystalline quality was confirmed by Raman spectroscopy and Photoluminescence.Crystal growth using a Ga- 5at%Al source was conducted in an attempt to increase growth rate and inhibit decomposition. No notable change in growth rate was observed and hollow crystals were formed, indicating that Al promotes vertical growth under otherwise similar conditions for GaN growth. In addition, fine-grained AlN was formed within the binary Ga-Al source, thus, the supply of Al was progressively reduced. Nucleation control via addition of Si resulted in a slightly reduced number of larger crystals. X-ray Photoelectron Spectroscopy suggested that amorphous silicon nitride was formed on the BN substrate and nucleation rate was slightly reduced. Silicon was not detected within the sensitivity of Energy Dispersive Spectroscopy. Raman spectroscopy revealed insignificant amount of Si present in the crystal. Smoother surface morphology of the crystals grown in the presence of Si was observed by Scanning Electron Microscopy.<P>

<p>The purpose of the research presented herein has been to determine the underlyingmechanisms of and to optimize the growth parameters for the growth of smooth surfaceson InGaN and GaN thin films via metalorganic vapor phase epitaxy. Relationshipsamong dislocation density, film thickness, flow rates of the reactants, kinetic growthregime, and thermodynamic growth mode with the surface morphology and surfaceroughness were determined. The two chief parameters affecting template surface roughness in both growth ofGaN above 1000ºC were determined to be temperature and layer thickness. An optimumtemperature of 1020ºC was found for the former process, below which the islands formedin the growth on AlN buffer layers did not coalesce properly, and above which a hillockgrowth instability was pervasive on the surface. Increasing the GaN film depositiontemperature to 1100°C for GaN film deposition via PE enhanced sidewall growth;however, surface roughness was increased on the (0001) growth plane through theformation of hillocks. Template thickness above 2.5 microns had the lowest root mean squaresurface roughness of 0.48nm over 100 square microns. This was attributed to reductions indislocation density, as measured by corresponding 50% reductions in symmetric andasymmetric full width half maximum values of X-ray rocking curves. GaN films were grown at 780ºC to remove the influence of indium incorporationon the surface roughness. V-defects covered the surface at a density of 2E9 per square centimeter andwere linked with a boundary dragging effect. Growth parameters that affect Inincorporation into the InGaN films were investigated and measured using roomtemperature photoluminescence, x-ray diffraction, and x-ray photoelectron spectroscopy.Temperature and growth rate had the greatest effect on incorporation over the range of760 to 820ºC and 25 and 180nm/hr, respectively, through kinetically limiting InNdecomposition. Additions of In into the GaN film produced hillock islands that wereattributed to a strain relief mechanism. The V-defects were also observed in InGaN films;however, their formation was suppressed below a nominal thickness of 25nm<P>

<p>JONSEN, DANIEL EVERETT. Experimental and Computational Studies of Carbon Sputtering with Application to Deposition of Tetrahedrally Bonded Amorphous Carbon Films. (Under the direction of Dr. Jerome J. Cuomo.) <p>In this work, amorphous carbon films are deposited on various substrates by ion beam sputtering of a graphite target. In addition, computational studies of the carbon sputtering process are performed using a molecular dynamics simulation program. In both cases, several process parameters are varied with the intent to find the optimum conditions for the sputter deposition of amorphous carbon films of high sp content amorphous carbon films.<P>

<p>The goals of this thesis were to synthesize nanocrystalline Zn, to study the mechanical properties of bulk nanocrystalline Zn and try to reveal the deformation mechanisms in nanocrystalline materials. Nanocrystalline Zn powder has been synthesized by a cryomilling method. The average grain size decreased exponentially with the cryomilling time and reached a minimum average grain size of around 17nm. Large numbers of small grains (2~6nm) have been found in the very early stages of cryomilling. Dynamic recrystallization (DRX) was used to explain the observed phenomena. Differential scanning calorimetry (DSC), x-ray diffraction and transmission electron microscopy (TEM) were used to study the structural changes and grain size distribution with milling time and subsequent annealing. Maxima in both stored enthalpy (for the low temperature DSC peak) and lattice strain on the Zn basal planes were observed at the same milling time. Dislocation density on the basal planes is proposed as a major source for lattice strain and the measured stored enthalpy. The released enthalpy that might be due to grain growth is very small. These cryomilled nanocrystalline Zn powders were consolidated into disks with a density of nearly theoretical density by uniaxial compression at room temperature. Cyclic variation of microhardness with milling time has been observed in cryomilled nanocrystalline Zn. Evidence from transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) suggests that the variation of dislocation density and grain size distributions determine the hardness behavior. A model, based on a kinetic reaction-rate model for cyclic amorphous-to-crystalline phase transformations observed during ball milling, simulates the experimental results very well. The model confirms the effect of DRX on modulated cyclic variation of microhardness. Dislocation strain hardening and recrystallization effects are superposed linearly with the intrinsic grain boundary hardening during the simulation. A dislocation density on the order of 10/sup 16/m /sup -2/ is predicted to be necessary to trigger DRX from the model. This prediction is evidenced by HRTEM observation of dislocation density on the same order and consistent with the estimation from thermodynamic calculation. The activation energy for rate controlling step in DRX estimated from the model is around 50 kJ/mol. This estimation indicates that a grain boundary diffusion controlled mechanism could dominate in DRX. Ductility of cryomilled nanocrystalline Zn has been studied by MDBT. The yield strength obtained from MDBT shows modulated cyclic variations with cryomilling time. Three times yield strength is consistent with the microhardness values for the same Zn samples. Ductility of CM2h and CM4h samples are much better than other cryomilled samples as indicated by a much larger ratio of normalized displacement than other cryomilled nanocrystalline Zn samples. However, the ductility of all cryomilled Zn samples is poor or very limited. The poor ductility of cryomilled Zn is presumably due to the remaining flaws as a result of incomplete bonding between particles. The Young?s modulus measured from MDBT barely changes for all tested samples. Bulk (spherical balls) ultra-fine-grained (UFG) or nanostructured Zn via in situ consolidation of powders are produced by mechanical attrition at room temperature. The size of these spherical balls increased with the increase of ball milling time. The grain size decreased rapidly to around 80nm after 1h of ball milling and then increased to around 240nm at 3h. The grain size decreased gradually thereafter with the increase of milling time. An average gain size of around 23nm was achieved for Zn bulk samples ball milled for 25h. In situ consolidation of metal powders during mechanical attrition may be a promising method to produce bulk UFG or nanostructured materials with full density and less contamination. The hardness, yield stress measured from MDBT, and tensile tests are consistent with one another. The hardness increased almost linearly with the decrease of grain size. The positive Hall-Petch slope is much smaller compared to the slope for coarse-grained Zn. Except for BM1h Zn sample, all other samples possess good ductility as evidenced from miniaturized disk bend test (MDBT) results and from the observations of fracture surfaces studied by FESEM. A bulged hat shape sample is usually obtained after MDBT test. The Young?s modulus almost keeps the same as for conventional coarse-grained Zn. The low temperature ball milling proves to be more efficient in reducing the grain size. A maximum elongation of around 110% is achieved for UFG Zn (around 240nm) under uniaxial tension test, which discloses a superplastic deformation in UFG Zn at room temperature. The elongation of room temperature ball milled Zn decreases with the decrease of grain size. Around 20% elongation is observed for Zn with an average grain size of around 23nm. Tension tests at elevated temperature result in a reduction of yield stress. The significant drop of yield stress at 200 centigrade degree or above may be due to recovery or recrystallization as evidenced from FESEM images. A strain rate sensitivity value of around 0.14 is usually found for Zn tested at 20 centigrade degree - 40 centigrade degree. <P>

<p>High-density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE) and blends thereof are used to produce ternary and quaternary conductive polymer composites (CPCs) containing carbon black (CB), graphite (G), carbon fiber (CF) and selected mixtures thereof to discern if polymer blends and mixed fillers yield appreciable advantages over CPCs composed of single polymers and/or single fillers. The effects of polymer blend composition and filler type, concentration and composition on electrical conductivity, composite morphology, mechanical properties and thermal behavior have been examined and correlated to establish meaningful structure-property relationships that can facilitate the rational design of efficient CPCs. Enhanced conductivity due to double-percolation is observed in ternary CPCs containing CB or G, whereas the concept of bridged double percolation is proposed to explain substantial conductivity increases in quaternary composites.<P>

<p>&#09The energy distribution of electrons transported through intrinsic AlN films was directly measured as a function of the applied field and film thickness. The electron energy distribution featured kinetic energies higher than that of completely thermalized electrons. Transport through films thicker than 95 nm and applied field between 200 kV/cm - 350 kV/cm occurred as steady-state hot electron transport represented by a Fermi-Dirac/ Maxwellian energy distribution. At higher fields (470 kV/cm), intervalley scattering was evidenced by a second peak corresponding to the first satellite valley in AlN. Transport through 80 nm thick layers revealed the onset of quasi-ballistic transport.&#13 &#09 From these measurements, saturation velocities between 1.2 and 1.5x10 cm/s and a mean free path of 5.1 nm were determined under steady state conditions. Overshoots as high as five times the saturation velocity were observed and a transient length of less than 80 nm was deduced.&#13 &#09 Two field-emission states of single-walled carbon nanotubes were identified. The state yielding 10 times increased emission current was attributed to the presence of adsorbates on the nanotubes as confirmed by electron emission measurements at different background pressures. In the high current state, field-emitted electrons originated from states located up to 1 eV below the Fermi level, as determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface which enhanced the tunneling probability of electrons. The adsorbed states were removed at high applied electric fields, presumably due to ohmic heating caused by large emission currents. This adsorption/desorption process was completely reversible.&#13 &#09 Using the Duke and Alferieff model, and a one-dimensional Fowler-Nordheim scheme, we demonstrated that adsorption enhances the field emission from single-walled carbon nanotubes through elastic resonance tunneling. As anticipated from this model, we observed FEED peak shifts towards lower energies and a symmetric peak shape in the energy distribution. The difference between the work function and the electronic binding energy of the non-perturbed state involved in the resonance was 0.3 eV ?± 0.2 eV, thus the state lied close to the Fermi level of the carbon nanotubes. <P>

This dissertation investigates how collectibles are made meaningful within collecting communities in order to better understand the intricate processes by which lead soldiers, toy trains, dolls, Dinkie cars, Star Wars figurines, and teddy bears come to be so enchanting for their collectors. An ethnography of toy collecting, including interviews with toy collectors, and observations at toy fairs and gatherings, this project contributes to debates on the use and role of material goods in practices of meaning making and social reproduction. In contrast to theories of material culture, this project aligns itself with consumer theories of the cultural constitution of objects. Emphasizing that object-centered analyses provide little insight on the value of collectibles, it advocates, instead, the centrality of perception and imaginative practice in the hold collectibles come to have over collectors. Drawing from consumer culturalists work on processes of identification; Bourdieus theory of consumption; Foucault on the archive; as well as Marxist inspired theories of the fetish, this project engages with nostalgic practice, the collectible market, judgments of authenticity, practices of ordering, as well as the complicated rules governing collecting. Working from collectors own stories, debates, contradictions, discussions and imaginative engagements this study uncovers that the mutability of the meanings assigned to collectibles is at the heart of collectors enchantment with their collectibles, and a central factor in how collecting becomes an eminently political activity. Collectors are not free to construct meanings for their collectibles at will but subject to community constraints, markets and battles of legitimacy. The various mystifications and social maneuverings present in their collecting practices imply that an objects value is the outcome of a careful mediation of both personal and wider cultural meanings. Mobilized to particular ends however tenuously held their meanings may be, material goods become powerful components to the wider cultural, social and economic fields in which they circulate. / Sociology