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Articles 91  107 of 107
FullText Articles in Physics
Rheed Studies Of The Nucleation, Growth, And Mobility Of Ag Atoms On The Si(111)7x7 Surface , Kelly Ryan Roos
Rheed Studies Of The Nucleation, Growth, And Mobility Of Ag Atoms On The Si(111)7x7 Surface , Kelly Ryan Roos
Retrospective Theses and Dissertations
The low temperature and flux dependent growth of ultrathin Ag films on the Si(111)7 x 7 surface is studied with Reflection HighEnergy Electron Diffraction (RHEED). The grazing incidence geometry of RHEED allows for an incident molecular beam normal to the surface, and makes it an ideal surface probe for studying ultrathin film growth in real time. Shortlived oscillations in the diffracted intensity are observed during Ag deposition at 150 K, indicating quasilayerbylayer growth mediated by adatom mobility. When the 150 K growth is performed over a wide range of deposition rates F, the peak intensity is observed to ...
Growth And Characterization Of Polysilicon Films Deposited By Reactive Plasma Beam Epitaxy , Behnam Moradi
Growth And Characterization Of Polysilicon Films Deposited By Reactive Plasma Beam Epitaxy , Behnam Moradi
Retrospective Theses and Dissertations
Polycrystalline silicon was deposited at low temperatures (400550°C) by using a new technique, reactive plasma beam epitaxy. The technique consists of using an intense flux of hydrogen radicals, generated by an electron cyclotron resonance (ECR) source to promote nucleation and crystallinity at low temperatures. The film structure could be smoothly changed from polysilicon to amorphous by changing the flux of incoming H radicals on the surface of the sample. The flux of hydrogen radicals can be controlled by changing the deposition pressure, with lower pressures leading to a higher H radical flux and greater degree of crystallinity. The effect ...
Density Functional Studies: First Principles And SemiEmpirical Calculations Of Clusters And Surfaces , Susan Buthaina Sinnott
Density Functional Studies: First Principles And SemiEmpirical Calculations Of Clusters And Surfaces , Susan Buthaina Sinnott
Retrospective Theses and Dissertations
In the research presented here, various theoretical electronic structure techniques are utilized to analyze widely different systems from silicon clusters to transition metal solids and surfaces. For the silicon clusters, first principles density functional methods are used to investigate Si[subscript] N for N = 28. The goal is to understand the different types of bonding that can occur in such small clusters where the coordination of the atoms differs substantially from that of the stable bulk tetrahedral bonding. Such uncoordinated structures can provide a good test of more approximate theories that can be used eventually to model silicon surfaces, of ...
HighSpin [Gamma]Ray Spectroscopy In 198bi, Superdeformation In 191au, And MultiPhoton Resonances In Low Energy E+E Scattering , Duc Ta Vo
Retrospective Theses and Dissertations
The properties of lowand highspin levels in [superscript]198Bi have been studied with the [superscript]181Ta([superscript]22Ne,5n)[superscript]198Bi reaction at 116 MeV and 120 MeV bombarding energies. Levels along and near the yrast lines, including one isomer, were established up to spin J ≈ 30\hbar. The main configurations of these states are suggested to be [pi] h[subscript]9/2 coupled to the known excited states in [superscript]197Pb. A sequence of states built on the excitation of the odd proton (coupled to one, two, or three quasi neutronholes) was observed. In addition, at least two collective ...
Relativistic TwoBody Wave Equations , Alan James Sommerer
Relativistic TwoBody Wave Equations , Alan James Sommerer
Retrospective Theses and Dissertations
The history and conceptual development of relativistic twobody formalisms leading up to the BetheSalpeter equation are reviewed. The various three dimensional reductions of the BetheSalpeter equation, in particular the quasipotential equations, and methods for solving them are discussed. Previous studies which attempted to assess the relative merits of the various equations are examined, and a new criterion for judging the equations is proposed. The bound state energy predictions of the traditional quasipotential equations are compared with the predictions of fourth order perturbation theory at small coupling. The equations are ranked according to how well they reproduce perturbation theory at low ...
An Axial Approach To Detection In Capillary Electrophoresis , John Aaron Taylor
An Axial Approach To Detection In Capillary Electrophoresis , John Aaron Taylor
Retrospective Theses and Dissertations
The purpose of this research has been to develop and demonstrate visualization schemes which further the capabilities of capillary electrophoresis instrumentation. Our approach involves onaxis illumination of the compounds inside the capillary detection region and is applied to absorbance and fluorescence detection;Absorbance measurements were accomplished by focussing an incident beam of laser light into one end of the separation capillary. By utilizing signals collected over the entire length of the analyte band, this technique enhances the analytical path length of conventional absorbance detection sixty fold. The demonstrated instrument offers a fifteenfold improvement in concentration limits of detection;Three fluorescence ...
Effects Of Randomly Rough Surfaces On Ultrasonic Inspection , Mehmet Bilgen
Effects Of Randomly Rough Surfaces On Ultrasonic Inspection , Mehmet Bilgen
Retrospective Theses and Dissertations
Surface finish of an industrial part affects its ultrasonic inspection and consequently the surfaces are often machined smooth before the evaluation. Ultrasonic inspection through smooth surfaces has been well studied and understood. A theoretical basis has been established for the characterization of interior cracks, voids and inclusions, and vast amount of literature exists. However, much less is known about quantitative ultrasonic inspection of such flaws in parts with rough surfaces, e.g. machine marks or "ascast" surfaces. A question arises "When can an industrial part with randomly rough surfaces be inspected robustly using ultrasound?" This dissertation is aimed at answering ...
Topics In Electroweak Baryogenesis: The Sphaleron And TViolation , Seungkoog Lee
Topics In Electroweak Baryogenesis: The Sphaleron And TViolation , Seungkoog Lee
Retrospective Theses and Dissertations
Assuming that beyond the standard model physics can be parametrized in terms of high dimensional operators, we examine their effects on the energy of the sphaleron and the classical solution of the gauge and Higgs fields. In the absence of fermions, all of the six dimension 6 operators which are SU(2) symmetric have a small effect when calculated perturbatively. However, calculated nonperturbatively, one of the operators alters the boundary conditions of the equations of motion of the Higgs and gauge fields involved, and another operator gives rise to an abrupt change in the sphaleron energy at a small but ...
Random And Cooperative Sequential Adsorption, James W. Evans
Random And Cooperative Sequential Adsorption, James W. Evans
Physics and Astronomy Publications
Irreversible random sequential adsorption (RSA) on lattices, and continuum "car parking" analogues, have long received attention as models for reactions on polymer chains, chemisorption on singlecrystal surfaces, adsorption in colloidal systems, and solid state transformations. Cooperative generalizations of these models (CSA) are sometimes more appropriate, and can exhibit richer kinetics and spatial structure, e.g., autocatalysis and clustering. The distribution of filled or transformed sites in RSA and CSA is not described by an equilibrium Gibbs measure. This is the case even for the saturation "jammed" state of models where the lattice or space cannot fill completely. However exact analysis ...
Transitions In The Kinetics And Steady States Of Irreversible A+Bc SurfaceReaction Models, B. Weng, W. H. Weinberg, James W. Evans
Transitions In The Kinetics And Steady States Of Irreversible A+Bc SurfaceReaction Models, B. Weng, W. H. Weinberg, James W. Evans
Physics and Astronomy Publications
The threecomponent irreversible surfacereaction model A+BC→AC+1/2B2 with infinite reaction rates between nearestneighbor adspecies is studied by Monte Carlo simulations. For a square lattice the system evolves to a degenerate poisoned state exponentially in time, except for a narrow range of pressures in which a reactive quasisteadystate exists. The latter poisons very slowly in time. For a hexagonal lattice a true reactive steady state occurs for a range of pressures bordered by continuous and discontinuous transitions to poisoned states. The latter behavior is observed by adding the reaction channel A+B→AB on a square lattice. Some ...
The Car‐Parking Limit Of Random Sequential Adsorption: Expansions In One Dimension, M. C. Bartelt, James W. Evans, M. L. Glasser
The Car‐Parking Limit Of Random Sequential Adsorption: Expansions In One Dimension, M. C. Bartelt, James W. Evans, M. L. Glasser
Physics and Astronomy Publications
We consider the irreversible random sequential adsorption of particles taking ksites at a time, on a one‐dimensional lattice. We present an exact expansion for the coverage, θ(t,k)=A0(t)+A1(t)k−1+A2(t)k−2+..., for times, 0≤t≤O(k), and at saturation t=∞. The former is new and the latter extends Mackenzie’s results [J. Chem. Phys. 37, 723 (1962)]. For these expansions, we note that the coefficients Ai≥1(∞) are not obtained as large‐t limits of the Ai≥1(t). Finally, we comment on the ...
IslandSize Scaling In Surface Deposition Processes, M. C. Bartelt, Michael C. Tringides, James W. Evans
IslandSize Scaling In Surface Deposition Processes, M. C. Bartelt, Michael C. Tringides, James W. Evans
Physics and Astronomy Publications
Diffusionmediated nucleation and growth of islands during deposition occurs essentially irreversibly in a variety of systems. We provide a scaling theory for the full islandsize distribution, both with the ratio of surface diffusion to deposition rates and with time. Scaling functions and exponents are determined by simulation and explained analytically by an unconventional rateequation analysis. Experimental tests for theoretical predictions are discussed, including the scaling of superlattice beam profiles for diffraction studies of heteroepitaxial systems.
Zgb Surface Reaction Model With High Diffusion Rates, James W. Evans
Zgb Surface Reaction Model With High Diffusion Rates, James W. Evans
Physics and Astronomy Publications
The diffusionless ZGB (monomer–dimer) surface reaction model exhibits a discontinuous transition to a monomer‐poisoned state when the fraction of monomer adsorption attempts exceeds 0.525. It has been claimed that this transition shifts to 2/3 with introduction of rapid diffusion of the monomerspecies, or of both species. We show this is not the case, 2/3 representing the spinodal rather than the transition point. For equal diffusion rates of both species, we find that the transition only shifts to 0.5951±0.0002.
Kinetics Of The MonomerMonomer Surface Reaction Model, James W. Evans, T. R. Ray
Kinetics Of The MonomerMonomer Surface Reaction Model, James W. Evans, T. R. Ray
Physics and Astronomy Publications
The twodimensional monomermonomer (AB) surface reaction model without diffusion is considered for infinitesimal, finite, and infinite reaction rates k. For equal reactant adsorption rates, in all cases, simulations reveal the same form of slow poisoning, associated with clustering of reactants. This behavior is also the same as that found in simulations of the twodimensional voter model studied in interactingparticle systems theory. The voter model can also be obtained from the dimerdimer or monomerdimer surface reaction models with infinitesimal reaction rate. We provide a detailed elucidation of the slow poisoning kinetics via an analytic treatment for the k=0+ AB reaction ...
Support Minimized Inversion Of Acoustic And Elastic Wave Scattering , Ali Safaeinili
Support Minimized Inversion Of Acoustic And Elastic Wave Scattering , Ali Safaeinili
Retrospective Theses and Dissertations
Inversion of limited data is common in many areas of NDE such as Xray Computed Tomography (CT), Ultrasonic and eddy current flaw characterization and imaging;In many applications, it is common to have a bias toward a solution with minimum (L[superscript]2)[superscript]2 norm without any physical justification. When it is a priori known that objects are compact as, say, with cracks and voids, by choosing "Minimum Support" functional instead of the minimum (L[superscript]2)[superscript]2 norm, an image can be obtained that is equally in agreement with the available data, while it is more consistent ...
Acoustically Driven Integrated Microstrip Antennas And Electromagnetic Radiation From Piezoelectric Devices , Charles Forrest Campbell
Acoustically Driven Integrated Microstrip Antennas And Electromagnetic Radiation From Piezoelectric Devices , Charles Forrest Campbell
Retrospective Theses and Dissertations
For a receiver system to be considered integrated, the antenna and electronics need to be fabricated on a single semiconductor wafer. To avoid EMI problems, the circuitry must somehow be shielded from the environment where the antenna resides. The required shielding may be accomplished by separating the antenna on one side of the wafer from the electronics on the other side with a conducting ground plane. Energy may be acoustically coupled from the antenna to the circuitry through the ground plane via thin film piezoelectric transducers on either side of the wafer. The radiating side of the wafer would then ...
Frequency Conversion Analysis Of Noise In Heterojunction Bipolar Transistor Oscillators Including Periodically Modulated Noise Sources , Bradley Allen Kramer
Frequency Conversion Analysis Of Noise In Heterojunction Bipolar Transistor Oscillators Including Periodically Modulated Noise Sources , Bradley Allen Kramer
Retrospective Theses and Dissertations
A procedure which may be used to analyze the noise characteristics of HBT oscillators is presented. A large signal model of a HBT is developed based largely on the GummelPoon transistor model. A new baseemitter diffusion capacitance model is also generated which shows improved accuracy over conventional bipolar transistor models in characterizing HBTs. The large signal characteristics of the oscillator are then established using a time domain simulator. Conversion matrix theory is applied to the large signal model to generate an equivalent linear oscillator model which accounts for all of the frequency conversion effects which occur due to circuit nonlinearities ...