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Studies of oxide desoption from GaAs by diffuse electron scattering and optical reflectivityVan Buuren, Anthony W.H. January 1991 (has links)
We have determined that the temperature for desorption of gallium oxide from GaAs increases linearly with oxide thickness, for oxide layers between about 6Å and 26Å thick. The temperature for the oxide desorption ranged from 580°C to 630°C. The wafer temperature was determined from the optical band-gap measured from the diffuse reflectivity of the sample, which was polished on the front surface and textured on the back surface. Different thicknesses of oxide layers were created by varying the exposure time of the GaAs wafers to a low pressure oxygen plasma. The oxide thicknesses were determined by XPS analysis. Desorption experiments were carried out in a VG V80H MBE system under a As4 beam equivalent pressure of 1.5 x 10⁻⁵ ton.
Measurement of diffuse light scattering using a HeNe laser shows an abrupt and non-reversible increase in the scattered light intensity during the oxide desorption. This suggests the surface is macroscopically roughened due to inhomogeneous desorption of the oxide.
The oxide desorption was also studied by monitoring the secondary electrons produced by the high energy electrons from the RHEED gun. After the gallium oxide desorption there is a reversible, order of magnitude, increase in the number of scattered electrons produced by the incoming primary beam. We interpret this result as evidence for some form of microscopic roughening. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
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Study on the ion formation process(es) in matrix-assisted laser desorption/ionization mass spectrometry.January 1997 (has links)
by King Lai Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 86-93). / Title Page --- p.i / Table of Contents --- p.ii / List of Tables --- p.iv / List of Figures --- p.v / Abbreviations --- p.viii / Acknowledgements --- p.ix / Abstract --- p.x / Chapter CHAPTER ONE --- INTRODUCTION / Chapter 1.1. --- Mass Spectrometry for Macromolecular Analysis --- p.1 / Chapter 1.2. --- Laser Desorption --- p.3 / Chapter 1.3. --- Development of Matrix-assisted Laser Desorption/Ionization (MALDI) --- p.4 / Chapter 1.4. --- Matrix-assisted Laser Desorption/Ionization --- p.5 / Chapter 1.4.1. --- Laser --- p.6 / Chapter 1.4.2. --- Matrix Selection --- p.6 / Chapter 1.4.3. --- Sample Preparation Methodology --- p.7 / Chapter 1.4.4. --- Ion Formation Process(es) --- p.7 / Chapter 1.4.4.1. --- Desorption --- p.8 / Chapter 1.4.4.2. --- Ionization --- p.9 / Chapter 1.5. --- Time-of-Flight Mass Spectrometry --- p.12 / Chapter 1.6. --- Outline of the Present Work --- p.16 / Chapter CHAPTER TWO --- INSTRUMENTATION AND EXPERIMENTAL / Chapter 2.1. --- Instrumentation --- p.17 / Chapter 2.1.1. --- Laser System --- p.17 / Chapter 2.1.2. --- Ion Source --- p.19 / Chapter 2.1.3. --- Reflector --- p.20 / Chapter 2.1.4. --- Detector --- p.20 / Chapter 2.2. --- Experimental --- p.21 / Chapter 2.2.1. --- Synthesis of nitroanthracene-d9 --- p.21 / Chapter 2.2.2. --- Sample Preparation --- p.22 / Chapter CHAPTER THREE --- STUDIES OF THE EFFECTS OF SOLUTION pH / Chapter 3.1. --- Introduction --- p.25 / Chapter 3.2. --- Sample Preparation --- p.26 / Chapter 3.3. --- Results and Discussion --- p.28 / Chapter 3.3.1. --- Effect of Bronsted Base (NaOH) --- p.28 / Chapter 3.3.2. --- Effect of Lewis Base (Imidazole) --- p.33 / Chapter 3.3.3. --- Effect of Salt Concentration --- p.40 / Chapter 3.4. --- Conclusions --- p.44 / Chapter CHAPTER FOUR --- PROTON SOURCES FOR ION GENERATION IN MALDI-MS / Chapter 4.1. --- Introduction --- p.46 / Chapter 4.2. --- Sample Preparation --- p.47 / Chapter 4.3. --- Results and Discussion --- p.49 / Chapter 4.4. --- Conclusions --- p.55 / Chapter CHAPTER FIVE --- CATIONIZATION PROCESSES IN MALDI-MS : ATTACHMENT OF DIVALENT AND TRIVALENT METAL IONS / Chapter 5.1. --- Introduction --- p.57 / Chapter 5.2. --- Sample Preparation --- p.58 / Chapter 5.3. --- Results and Discussion --- p.60 / Chapter 5.3.1. --- Protonation versus Cationization --- p.60 / Chapter 5.3.2. --- Attachment of Divalent and Trivalent Metal Ions --- p.63 / Chapter 5.4. --- Conclusions --- p.80 / Chapter CHAPTER SIX --- CONCLUDING REMARKS --- p.82 / REFERENCES --- p.86
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Laser-induced desorption and damage of water- and heavy water-dosed optical thin films.Franck, Jerome Bruce. January 1989 (has links)
Previous work has shown that laser-induced desorption (LID) can prove useful for the determination of surface contamination. However, because of the nature of small-spot sampling utilized in the previous work, it proved rather difficult to gather statistically significant data. A solution to this problem that still allowed sampling the surface with small focused laser spots was to automate the sample manipulation, laser control, and data acquisition of the system. With the automation of the LID facility in place, a detailed study of the LID of water/heavy water (H₂O/D₂O) was undertaken. As in the earlier work, samples were irradiated with a hydrogen fluoride/deuterium fluoride (HF/DF) laser beam focused inside an ultrahigh vacuum (UHV) chamber. The molecules desorbed from the sample surface were partially contained in a glass envelope that also contained a quadrupole mass analyzer. Samples consisted of bulk-etched CaF₂ and optical thin-film coatings of CaF₂--undosed or H₂O/D₂O dosed--on a variety of substrates. Some analysis was performed on cleaved, single-crystal alkali halides. The focused laser spot size was 155 μm (l/e² diameter) for the HF laser and 138 μm (l/e² diameter) for the DF laser. Between 400 and 800 sites per sample were tested for each desorption onset analysis. A study was also performed to test the possibility of correlation between (1) laser-induced damage and defects and (2) laser-induced desorption and adsorption sites for some of the samples listed above. Attempts to deuterate and hydrate CaF₂ thin films met with limited success as laser-induced desorption samples. Other analysis techniques showed that dosing during the coating process produced a more ordered coating; in fact, dosing with H₂O reduced the optical absorption in the "H₂O" band, modified the damage morphology, and, along with a low temperature bakeout, raised the laser-damage threshold.
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Analysis of oligonucleotides by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF-MS). / CUHK electronic theses & dissertations collectionJanuary 2001 (has links)
Li Yiu-Ching. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (p. 123-132). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.
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Development of new methods to perform matrix-assisted laser desorption/ionization (MALDI) experiments in fourier-transform ion-cyclotron-resonance mass spectrometer (FTICR-MS). / CUHK electronic theses & dissertations collectionJanuary 2000 (has links)
Sze Tung Po Eric. / "Mar 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.
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Effects of ammonium salts as co-matrices for the analysis of oligonucleotides by matrix-assisted laser desorption/ionization mass spectrometry.January 1996 (has links)
by Cheng Sau Wan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves [72]-[76]). / TABLE OF CONTENTS --- p.i / ABSTRACT --- p.iv / LIST OF FIGURES --- p.vi / LIST OF TABLES --- p.x / Chapter CHAPTER ONE --- RESEARCH BACKGROUND --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Matrix-assisted laser desorption / ionization mass spectrometry (MALDI) --- p.2 / Chapter 1.2.1 --- Laser desorption methods --- p.2 / Chapter 1.2.2 --- The matrix --- p.3 / Chapter 1.2.2.1 --- Role of the matrix --- p.3 / Chapter 1.2.2.2 --- Features of the matrix --- p.4 / Chapter 1.2.3 --- Mechanisms of ion formation --- p.6 / Chapter 1.2.3.1 --- Desorption process(es) --- p.6 / Chapter 1.2.3.2 --- Ionization process(es) --- p.7 / Chapter 1.3 --- Sequencing of DNA --- p.8 / Chapter 1.3.1 --- DNA sequencing procedure --- p.10 / Chapter 1.3.1.1 --- Generation of the nested set of DNA molecules --- p.11 / Chapter 1.3.1.2 --- Sequence analysis --- p.11 / Chapter 1.3.2 --- MALDI-TOF-MS as a DNA sequencing tool --- p.12 / Chapter 1.3.3 --- MALDI analysis of oligonucleotides --- p.14 / Chapter 1.4 --- Outline of the present work --- p.16 / Chapter CHAPTER TWO --- INSTRUMENTATION AND EXPERIMENTAL --- p.18 / Chapter 2.1 --- Time-of-flight mass spectrometry (TOF-MS) --- p.18 / Chapter 2.1.1 --- Linear time-of-flight mass spectrometry --- p.18 / Chapter 2.1.2 --- Reflectron time-of-flight mass spectrometry --- p.21 / Chapter 2.1.3 --- Ion detection --- p.22 / Chapter 2.1.4 --- Vacuum system --- p.22 / Chapter 2.2 --- Instrumentation --- p.24 / Chapter 2.2.1 --- The laser system --- p.24 / Chapter 2.2.2 --- Ion source and vacuum system --- p.24 / Chapter 2.2.3 --- Flight tube and reflector --- p.27 / Chapter 2.2.4 --- The detector --- p.28 / Chapter 2.2.5 --- Data acquisition and computer control --- p.28 / Chapter 2.3 --- Experimental --- p.29 / Chapter 2.3.1 --- Sample preparation --- p.29 / Chapter 2.3.2 --- Mass spectrometric analysis --- p.30 / Chapter CHAPTER THREE --- USE OF AMMONIUM SALTS AS CO-MATRICES --- p.32 / Chapter 3.1 --- Introduction --- p.32 / Chapter 3.2 --- Experimental --- p.35 / Chapter 3.3 --- Results and Discussion --- p.36 / Chapter 3.3.1 --- Effects of counter-anions --- p.36 / Chapter 3.3.2 --- Effects of matrix materials --- p.40 / Chapter 3.4 --- Conclusions --- p.43 / Chapter CHAPTER FOUR --- USE OF POTASSIUM SALTS AS CO-MATRICES --- p.44 / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- Experimental --- p.44 / Chapter 4.3 --- Results and Discussion --- p.44 / Chapter 4.3.1 --- Adduct formation --- p.49 / Chapter 4.3.2 --- Signal enhancement --- p.50 / Chapter 4.4 --- Conclusions --- p.52 / Chapter CHAPTER FIVE --- ANALYSIS OF HIGH MASS OLIGONUCLEOTIDES --- p.53 / Chapter 5.1 --- Introduction --- p.53 / Chapter 5.2 --- Experimental --- p.53 / Chapter 5.3 --- Results and Discussion --- p.54 / Chapter 5.4 --- Conclusions --- p.67 / Chapter CHAPTER SIX --- CONCLUSIONS AND FURTHER WORK --- p.68 / Chapter 6.1 --- Conclusions --- p.68 / Chapter 6.2 --- Further work --- p.70 / ACKNOWLEDGMENT --- p.A1 / REFERENCES --- p.R1 - R5
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Non-thermal Interactions on Low Temperature Ice and Aqueous InterfacesCaptain, Janine Elizabeth 06 April 2005 (has links)
Electron-impact ionization of low-temperature water ice leads to H+, H2+,
and H+(H2O)n=1-8 desorption. The threshold energy for ESD of H2+ from CI and H3O+ from PASW and ASW is 22 ± 3 eV. There is also a H2+ yield increase at 40 ± 3 eV and a 70 ± 3 eV threshold for ESD of H+(H2O)n=2-8
from PASW and ASW. H2+
production and desorption involves direct molecular elimination and reactive
scattering of an energetic proton. Both
of these channels likely involve localized two-hole one-electron and/or
two-hole final states containing 4a1, 3a1 and/or 2a1
character. The 70 eV
cluster ion threshold implicates either an initial (2a1-2)
state localized on a monomer or the presence of at least two neighboring water
molecules each containing a single hole.
The resulting correlated two-hole or two-hole, one-electron
configurations are localized within a complex and result in an intermolecular
Coulomb repulsion and cluster ion ejection.
The changes in the yields with
phase and temperature are associated with structural and physical changes in
the adsorbed water and longer lifetimes of excited state configurations
containing a1 character. The dependence
of the ESD cation yields on the local potential has
been utilized to examine the details of HCl
interactions on low temperature ice surfaces.
The addition of HCl increases cluster ion
yields from pure ice while decreasing H+ and H2+
yields. These changes reflect the
changes in the local electronic potential due to the changing bond lengths at
the surface of the ice as HCl ionizes and the
surrounding water molecules reorient to solvate the ions.
This work has been extended to
ionic solutions at higher temperatures using a liquid jet and ultraviolet
photoionization to interrogate the surface of aqueous ionic
interfaces. Desorption of protonated
water clusters and solvated sodium ion clusters were measured over a range of
concentrations from NaCl, NaBr,
and NaI solutions.
The flux dependence indicated a multiple photon process and the proposed
mechanism involves a Coulomb explosion resulting from the repulsion of nearby
ions. The surface is investigated with
regard to its importance in heterogeneous atmospheric chemistry.
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Doping and electron stimulated desorption of zinc selenide grown by molecular beam epitaxyVanMil, Brenda. January 1900 (has links)
Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 105 p. : ill. Includes abstract. Includes bibliographical references (p. 100-105).
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A kinetic study of the electron stimulated adsorption of ammonia on tungsten single crystal surfaces /Kong, Fu wing. Dawson, P.T. January 1900 (has links)
Thesis (Ph.D.)--McMaster University, 2004. / Includes bibliographical references (leaves193-201). Also available via World Wide Web.
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Xenon and krypton adsorption on palladium (100) and electron stimulated desorption of xenon, krypton, and argonMoog, Elizabeth Rahm. January 1984 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 211-215).
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