Many deductions made about STM images are based upon the model of Tersoff and Hamann, in which images are given in principal by a combination of surface atomic positions and local charge density. There is a now a need for a fuller understanding of this technique in order to explain experimental evidence which indicates that the tip and sample can interact strongly during normal imaging. In order to investigate the fundamental STM imaging process, a method for deducing the tunnel barrier height has been developed which is based on corrugation height measurements of constant current topographs. From experiments on clean Cu(100), values of the tunnel barrier height have been shown to be somewhat below the workfunction (~ 1-2.5eV) but are in good agreement with other reports of atomically resolved barrier height data. At large values of the tunnel conductance (~ 1μS), a fall-off (based upon extrapolation of large separation data) in the corrugation heights is observed with increasing conductance. This effect is quantitatively explained using a Molecular Dynamics simulation of the tip approaching the sample. The simulation gives a good estimate of both the absolute tip-sample separation and site-dependent tip-surface forces. Distributions of corrugation heights indicate that variations in both tip geometry and chemistry are likely to occur in practice and strongly influence the phenomena described above. Similarly, it is found that increased local tunnel barrier heights are measured when the Cu(100) surface is modified with small numbers of single halogen atoms. This data has been used to estimate the contributions to the increase in local barrier height of both adsorbate induced dipoles and geometric topography. Values for the charge transfer between the surface and adsorbate have been established. The process of tip-induced adsorbate manipulation has also been demonstrated at room temperature.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Frequency-based ocean synthesis is a class of methods for generating ocean waves in deep water using physically based ocean spectra provided by oceanographic research. The output of these methods is a heightfield which is periodic and can be used to tile a larger area. However, when using a larger number of tiles, a repetition pattern becomes apparent. Wang tiling is a method of tiling the plane non- periodically by using only a small set of input tiles with given constraints. The aim of this thesis is to create a set of Wang Tiles, each of which represents an ocean heightfield synthesised by a frequency- based method, so one can create large ocean scenes without apparent periodicity in the tiling pattern. Powered by TCPDF (www.tcpdf.org)

Dans ce travail, nous étudions les surfaces dont les composantes irréductibles sont des surfaces toriques. En particulier, nous donnons une formule pour calculer l'obstruction d'Euler locale de ces surfaces. Comme application de cette formule, nous calculons l'obstruction d'Euler locale pour certaines familles de surfaces déterminantales. De plus, nous définissons et donnons une formule pour calculer la caractéristique d'Euler évanescente d'une surface torique normale $X_{sigma}$. Nous montrons que ce nombre est relié à la seconde multiplicité polaire de $X_{sigma}$. Nous présentons aussi une formule pour l'obstruction d'Euler d'une fonction $f: X_{sigma} to mathbb{C}$ et pour le nombre de Brasselet d'une telle fonction. Comme application de ce résultat nous calculons l'obstruction d'Euler d'un type de polynôme sur une famille de surfaces déterminantales. / In this work we study surfaces with the property that their irreducible components are toric surfaces. In particular, we present a formula to compute the local Euler obstruction of such surfaces. As an application of this formula we compute the local Euler obstruction for some families of determinantal surfaces. Furthermore, we define the vanishing Euler characteristic of a normal toric surface $X_{sigma}$, we give a formula to compute it, and we relate this number with the second polar multiplicity of $X_{sigma}$. We also present a formula for the Euler obstruction of a function $f: X_{sigma} to mathbb{C}$ and for the Brasselet number of it. As an application of this result we compute the Euler obstruction of a type of polynomial on a family of determinantal surfaces.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, October 2016. / The adsorption of molecules on a metal surface is core in heterogeneous catalysis. Surface sensitive techniques such as low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) are key tools to study adsorption geometries and structures of molecules and atoms on a metal surface. As our first model system we investigated the dissociation of NO on Ir{100}. The LEED experimental results showed a p(2 X 2) diffraction pattern at 300 K using. In this study two options were explored: phase mixing where dissociated nitrogen and oxygen are on the same unit cell, as well as phase separation where both nitrogen and oxygen form their own separate unit cell which results in a p(2 x 2) unit cell. Calculations were done on atop, bridge and hollow sites, with only perpendicular parameters and vibrational amplitude being varied initially. Results for phase mixing calculations gave the lowest R-factor of 0.70 ± 0.11 for atop site. We further considered phase separation for hollow and bridge sites for nitrogen and oxygen respectively because these two sites were found to be the most stable sites using DFT from previous studies. The lowest R-factors were 0.37 ± 0.06 for nitrogen c(2x2) and 0.24 ± 0.13 for oxygen p(2 X 1) For oxygen significant row pairing of iridium atoms stabilized the structure as mentioned in previous studies. Therefore from our results it is evident that phase separation models the experimental data better than phase mixing. Nitrogen and oxygen form c(2 X 2) and p(2 X 1) overlayer structures respectively which in combination result in a p(2 X 2) pattern that is in agreement with experimental results. The second system involves enantio-selectivity and chiral resolution at the organic-inorganic interfaces. The d-serine molecule was adsorbed on the Cu{110} surface. Density functional theory (DFT) calculations were used as a benchmark for our CLEED calculations. LEED experiments showed a (- 1 + 2: 40) overlayer pattern for d-serine adsorbed on Cu{110} surface. Three structures from DFT calculations with the lowest energy were used for CLEED calculations. These structures differed by the way they bond to the surface and molecular interactions. Calculations were carried out on these three structures and the structure with intra-dimer bonding was the best structure. The searches for this structure were further optimized by introducing pairing of the atoms in the row reconstruction on the copper surface and angle search. The lowest value obtained was 0.37 ± 0.09, which suggests that further understanding of this system is needed. The ultra-high vacuum (UHV) chamber was fully commissioned and is now ready for TPD and XPS studies. / LG2017

Our goal was to assess regional differences in denticle density and skin tensile properties in four coastal species of shark. We hypothesized that the denticle density, tensile strength (MPa), stiffness (MPa), and toughness of skin (MJ·m^-3) would vary regionally along the body of an individual and among species. An hourglass-shaped punch was used to extract the skin samples at 10 anatomical landmarks and denticle density was quantified. Denticle density varied significantly among both regions and species, and showed a significant species by region interaction. Skin samples were tested in tension at a strain rate of 2 mm-s until failure. We found significant species and region effects for all tensile and denticle density properties. Also, denticle density increases with skin stiffness but decreases with toughness. Shark skin toughness is similar to that of mammalian tendons. These data show shark skin functions as an exotendon, able to conserve energy during swimming. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Neste trabalho será demonstrada uma versão dos teoremas de Hilbert Liebmann para superfícies em S² x R e H² x R, que são teoremas de existência e unicidade de superfícies completas com curvatura Gaussiana constante nesses ambientes. Como parte da demonstração, a saber a existência, será apresentada uma classificação das superfícies de revolução completas com curvatura Gaussiana constante em torno de um eixo qualquer, em S² x R e em torno de um eixo lorentziano, em H² x R. / In this work it will be proved a version of Hilbert and Liebmann theorems for surfaces in S² X R and H² X R, wich are theorems about existence and uniqueness of complete surfaces with constant Gaussian curvature in those ambients. As part of the proof, namely the existence, it will be presented a classication of complete revolution surfaces with constant Gaussian curvature around any axis in S² X R and around a Lorentzian axis in H² X R.

Zhang, Zhongxiang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

by Chu Hon Yue. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1990. / Bibliography: leaves 91-93. / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / Chapter I. --- INTRODUCTION --- p.1 / Chapter II. --- LOW ENERGY ELECTRON DIFFRACTION --- p.4 / Chapter 2.1. --- LEED EXPERIMENT --- p.4 / Chapter 2.2. --- LEED CRYSTALLOGRAPHY：I(E) CURVE --- p.7 / Chapter 2.3. --- AN OUTLINE OF THE PHYSICS OF LEED --- p.8 / Chapter 2.3.1. --- LEED Process In One-Dimensional Surface --- p.8 / Chapter 2.3.2. --- LEED Process In Three-Dimensional Surface --- p.11 / Chapter 2.3.3. --- Surface With An Overlayer --- p.12 / Chapter 2.3.4. --- The Muffin-Tin Model And The Inner Potential --- p.13 / Chapter 2.3.5. --- The Phase Shift --- p.17 / Chapter 2.3.6. --- Thermal Effects --- p.19 / Chapter III. --- DYNAMICAL LEED CALCULATION： THE RENORMALIZED FORWARD SCATTERING PERTURBATION METHOD --- p.22 / Chapter IV. --- THE ZANAZZI-JONA RELIABILITY FACTOR --- p.30 / Chapter V. --- CALCULATIONS AND RESULTS --- p.33 / Chapter 5.1. --- EXPERIMENTAL I(E) CURVES --- p.33 / Chapter 5.2. --- CALCULATED I(E) CURVES --- p.36 / Chapter 5.2.1. --- Top Site --- p.4o / Chapter 5.2.2. --- Bridge Site --- p.41 / Chapter 5.2.3. --- Hollow Site --- p.42 / Chapter VI. --- DISCUSSIONS AND CONCLUSIONS --- p.44 / APPENDIX I --- p.51 / TABLES --- p.52 / I(E) CURVES AND CONTOUR MAPS --- p.61 / APPENDIX II --- p.79 / MAIN PROGRAMME FOR Rh(100)-c(2x2) -S --- p.80 / INPUT PARAMETERS FOR TOP SITE --- p.85 / INPUT PARAMETERS FOR BRIDGE SITE --- p.87 / INPUT PARAMETERS FOR HOLLOW SITE --- p.89 / REFERENCES --- p.91

by Kwok-fung Kan = 低能量氬離子濺射於表面淸潔及高解像深度剖析時所產生的損傷及離子混合的硏究 / 簡國豐. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Kwok-fung Kan = Di neng liang ya li zi jian she yu biao mian qing jie ji gao jie xiang shen du pou xi shi suo chan sheng de sun shang ji li zi hun he de yan jiu / Jian Guofeng. / Abstract --- p.ii / 論文摘要 --- p.iii / Acknowledgement --- p.iv / Table of Contents --- p.v / List of Figures --- p.ix / List of Tables --- p.xi / Chapter Chapter 1 --- Background and Goals of the Thesis Work --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.1.1 --- Surface contamination of semiconductors --- p.1 / Chapter 1.1.2 --- Common surface cleaning methods --- p.2 / Chapter 1.1.3 --- Quality control in ultrathin gate dielectrics --- p.3 / Chapter 1.1.4 --- High-resolution depth profiling --- p.5 / Chapter 1.2 --- Energy range limitation in sputtering --- p.5 / Chapter 1.3 --- Goals of this thesis study --- p.6 / References for Chapter1 --- p.7 / Chapter Chapter 2 --- Theoretical Background and Instrumentation --- p.9 / Chapter 2.1 --- Ion Bombardment --- p.9 / Chapter 2.1.1 --- Bombardment mechanism --- p.9 / Chapter 2.1.2 --- Ion beam induced damage --- p.10 / Chapter 2.1.2.1 --- Region of damage --- p.10 / Chapter 2.1.2.2 --- Structural changes --- p.11 / Chapter 2.1.3 --- Assessment methods on ion beam damage and ion mixing --- p.12 / Chapter 2.1.3.1 --- Assessment methods on ion beam damage --- p.12 / Chapter 2.1.3.2 --- Assessment of ion mixing in the sample --- p.13 / Chapter 2.1.4 --- Minimizing the sputtered damage and ion mixing --- p.14 / Chapter 2.1.5 --- Ion gun --- p.15 / Chapter 2.1.5.1 --- Mechanism of the generation of an argon ion beam --- p.15 / Chapter 2.1.5.2 --- Description of ion gun --- p.16 / Chapter 2.1.5.3 --- Calibration of current density provided by the ion gun --- p.16 / Chapter 2.1.5.4 --- Sputtering time --- p.16 / Chapter 2.2 --- X-ray photoelectron spectroscopy(XPS) --- p.18 / Chapter 2.2.1 --- Principle of XPS --- p.18 / Chapter 2.2.1.1 --- Qualitative analysis of XPS --- p.18 / Chapter 2.2.1.2 --- Quantitative analysis of XPS --- p.20 / Chapter 2.2.2 --- Angle-resolved XPS --- p.24 / Chapter 2.2.3 --- Set-up --- p.25 / Chapter 2.2.3.1 --- UHV system --- p.27 / Chapter 2.2.3.2 --- X-ray source --- p.27 / Chapter 2.2.3.3 --- Electron energy analyser --- p.27 / Chapter 2.2.3.4 --- Detector --- p.28 / Chapter 2.2.4 --- Calibration of XPS --- p.28 / References for Chapter2 --- p.29 / Chapter Chapter 3 --- Damages induced by ion sputtering --- p.31 / Chapter 3.1 --- Introduction --- p.31 / Chapter 3.2 --- Experimental --- p.31 / Chapter 3.2.1 --- Sample preparation --- p.31 / Chapter a. --- Surface cleaning and oxidization --- p.31 / Chapter b. --- HF etching --- p.32 / Chapter c. --- Indium back contact --- p.32 / Chapter 3.2.2 --- XPS analysis --- p.33 / Chapter 3.2.2.1 --- Data acquisition --- p.33 / Chapter 3.2.2.2 --- Peak deconvolution --- p.33 / Chapter 3.2.3 --- Ion sputtering --- p.34 / Chapter 3.3 --- Results and discussion --- p.34 / Chapter 3.3.1 --- Spectral width of In3d and P2p peak --- p.34 / Chapter 3.3.2 --- Deconvolution of In3d signal at take-off angle of 90° --- p.37 / Chapter 3.3.2.1 --- In in bulk InP --- p.37 / Chapter 3.3.2.2 --- In metal --- p.37 / Chapter 3.3.2.3 --- In in damaged InP region --- p.37 / Chapter 3.3.3 --- Deconvolution of P2p signal at take off angle of 45° --- p.37 / Chapter 3.3.3.1 --- P in bulk InP --- p.37 / Chapter 3.3.3.2 --- P in damaged InP region --- p.37 / Chapter 3.3.4 --- Relative composition of deconvoluted components --- p.38 / Chapter 3.3.5 --- Fermi level shift --- p.39 / Chapter 3.3.6 --- Analysis at take-off angle of 45° --- p.40 / Chapter 3.3.7 --- Stoichiometry in sputtered InP --- p.43 / Chapter 3.4 --- Conclusions --- p.45 / References for Chapter3 --- p.46 / Chapter Chapter 4 --- Ion mixing in sputtered depth profiling --- p.47 / Chapter 4.1 --- Introduction --- p.47 / Chapter 4.2 --- Experimental --- p.47 / Chapter 4.2.1 --- Sample description --- p.47 / Chapter 4.2.2 --- Acquisition conditions --- p.47 / Chapter 4.2.3 --- Raw data --- p.48 / Chapter 4.2.4 --- Data treatments --- p.48 / Chapter 4.2.4.1 --- Depth calibration --- p.48 / Chapter 4.2.4.2 --- Calibration procedure --- p.55 / Chapter A. --- Overlayer region --- p.55 / Chapter B. --- Substrate region --- p.56 / Chapter 4.3 --- Results and discussions --- p.57 / Chapter 4.3.1 --- Study of ion mixing using depth profile --- p.57 / Chapter A. --- Comparing the carbon profiles at two ion sputtering energies --- p.59 / Chapter B. --- Comparing the nitrogen profiles at two ion sputtering energies --- p.59 / Chapter C. --- Comparing the oxygen profiles at two ion sputtering energies --- p.59 / Chapter 4.3.2 --- Study of ion mixing from a change in sputtering rate --- p.60 / Chapter 4.3.3 --- Approximation on ion mixing --- p.64 / Chapter 4.3.4 --- Conclusions --- p.66 / References for Chapter4 --- p.67 / Chapter Chapter 5 --- Conclusions --- p.68