Thesis (Ph. D.)--University of Chicago, Department of Chmistry, August 2000. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 170-176). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Hong Kong, 2005.

Thesis (Ph. D.)--University of Hong Kong, 2005. / Also available in print.

Dans le cadre de cette thèse, la conception, la construction et la mise en service de la plateforme de test LEETECH ont été réalisées. La performance de LEETECH, y compris le mode de fonctionnement à faible multiplicité a été démontrée. En fournissant des paquets d’électrons avec une énergie ajustable jusqu’à 3.5 MeV, une multiplicité ajustable à partir d’électrons simples et une durée des paquets jusqu’à 20ps, LEETECH prend sa place entre les faisceaux tests de hautes énergies et de coûts élevés d’un part et l’utilisation de sources radioactifs d’autre part. Dans la région, qui correspond à la particule d’ionisation minimale, la plateforme offre aux détecteurs de traces les conditions similaires aux celles de faisceaux des hautes énergies. Le mode de fonctionnement à faible multiplicité a été étudié en utilisant un détecteur diamant de grande surface. En plus une capacité d’un capteur diamant de résoudre des paquets à faible nombre des particules a été démontrée. Dans le cadre du développement de la chambre à projection temporelle (TPC) pour le projet ILC, une session de test a été dédiée à un détecteur Micromegas/InGrid de large surface. Pour la première fois les pertes d’énergie par un électron dans un mélange de gaz basée sur Helium ont été mesurées pour une énergie de quelques MeV. La résolution en dE/dx et un algorithme pour la reconstruction de traces ont été développés. Une caractérisation préliminaire du quartz barre lu par MCPPMT – un candidat pour le détecteur temps-de- vol (TOF) avec la mission de l’identification des hadrons chargés dans le futur usine tau-charm HIEPA – a été accomplie. La résolution temporelle de 50 ps obtenue pour le détecteur étudié met cette technologie prometteuse pour les études plus approfondies. / Within the present thesis the design, construction and commissioning of a new test beam facility LEETECH have been performed. Performance of the new facility, including low-multiplicity operation mode has been demonstrated. A number of interesting detector tests, including large-area diamond, Micromegas/InGrid and quartz bar detectors have been performed. Development of new detector technologies for future high-energy physics collider experiments calls for selection of versatile test beam facilities, permitting to choose or adjust beam parameters such as particles type, energy and beam intensity, are irreplaceable in characterization and tests of developed instruments. Major applications comprise generic detector R&D, conceptual design and choice of detector technologies, technical design, prototypes and full-scale detector construction and tests, detector calibration and commissioning. A new test beam facility LEETECH (Low Energy Electron TECHnique) was designed, constructed and commissioned in LAL (Orsay) as an extension of existing PHIL accelerator. Providing electron bunches of adjustable energy (up to 3.5 MeV), intensity (starting from a few particles per bunch) and bunch time duration (down to 20 ps), LEETECH fills the gap between high-cost high-energy test beam facilities and use of radioactive sources. Covering a minimum-ionization particles region (electrons of energy above 1.6 MeV), LEETECH provides for tracking detectors similar conditions as high-energy facilities. Using LEETECH as an electron source, several types of detectors were investigated in order to study their performance or applications, also providing a characterization of the LEETECH performance. First studies of the LEETECH facility were performed with a plastic scintillator coupled to the Micro-channel plate photomultiplier. A low-multiplicity mode was investigated using the diamond sensor, at the same time demonstrating its ability to resolve bunches consisting of a few particles. In framework of Time Projection Chamber development for the ILC project, a session dedicated to a large-area Micromegas/InGrid module was performed. For the first time the electron energy losses in Helium-based gas mixtures were measured for the energies of few MeV. The dE/dx resolution was obtained and track reconstruction algorithm was developed. Being a candidate for the time-of- flight detector of the BESIII upgrade and future HIEPA tau-charm factories, a preliminary characterization of the quartz bar performed. The time resolution of the detector module of 50 ps was obtained, giving a promising results for the further detector studies.

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

The interest in two-dimensional materials and materials physics has grown dramatically over the past decade. The family of two-dimensional materials, which includes graphene, transition metal dichalcogenides, phosphorene, hexagonal boron nitride, etc., can be fabricated into atomically thin films since the intralayer bonding arises from their strong covalent character, while the interlayer interaction is mediated by weak van der Waals forces. Among them, molybdenum disulfide (MoS₂) has attracted much interest for its potential applications in opto-electronic and valleytronics devices. Previously, much of the experimental studies have concentrated on optical and transport measurements while neglecting direct experimental determination of the electronic structure of MoS₂, which is crucial to the full understanding of its distinctive properties. In particular, like other atomically thin materials, the interactions with substrate impact the surface structure and morphology of MoS₂, and as a result, its structural and physical properties can be affected. In this dissertation, the electronic structure and surface structure of MoS₂ are directly investigated using angle-resolved photoemission spectroscopy and cathode lens microscopy. Local-probe angle-resolved photoemission spectroscopy measurements of monolayer, bilayer, trilayer, and bulk MoS₂ directly demonstrate the indirect-to-direct bandgap transition due to quantum confinement as the MoS₂ thickness is decreased from multilayer to monolayer. The evolution of the interlayer coupling in this transition is also investigated using density functional theory calculations. Also, the thickness-dependent surface roughness is characterized using selected-area low energy electron diffraction (LEED) and the surface structural relaxation is investigated using LEED I-V measurements combined with dynamical LEED calculations. Finally, bandgap engineering is demonstrated via tuning of the interlayer interactions in van der Waals interfaces by twisting the relative orientation in bilayer-MoS₂ and graphene-MoS₂-heterostructure systems.

"May 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / 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.

by So King Lung, Benny. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 102-109). / ABSTRACT --- p.v / ACKNOWLEDGEMENTS --- p.vii / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.xiii / Chapter Chapter 1 --- Background of the study --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Surface passivation techniques --- p.3 / Chapter 1.2.1 --- Sulfide solution passivation --- p.3 / Chapter 1.2.2 --- Gas-phase sulfide passivation --- p.4 / Chapter 1.3 --- Surface structure of sulfide-passivated surface --- p.5 / Chapter 1.4 --- Objectives of the present study --- p.7 / Chapter Chapter 2 --- Instrumentation --- p.9 / Chapter 2.1 --- Introduction --- p.9 / Chapter 2.2 --- X-ray photoelectron spectroscopy (XPS) --- p.9 / Chapter 2.2.1 --- The development of XPS --- p.9 / Chapter 2.2.2 --- Basic principle of XPS --- p.9 / Chapter 2.2.3 --- Quantitative analysis of XPS --- p.14 / Chapter 2.2.3.1 --- Atomic concentration of a homogenous material --- p.14 / Chapter 2.2.3.2 --- Layer structure --- p.15 / Chapter 2.2.3.3 --- Simulation of XPS atomic concentration ratios from proposed surface structural models --- p.17 / Chapter 2.2.4 --- XPS experiment --- p.19 / Chapter 2.3 --- Low energy electron diffraction (LEED) --- p.21 / Chapter 2.3.1 --- The development of LEED --- p.21 / Chapter 2.3.2 --- Basic principle of LEED --- p.23 / Chapter 2.3.3 --- LEED experiment --- p.28 / Chapter 2.3.3.1 --- The ultra high vacuum chamber (UHV) --- p.28 / Chapter 2.3.3.2 --- The electron gun --- p.28 / Chapter 2.3.3.3 --- The sample --- p.30 / Chapter 2.3.3.4 --- The detector system --- p.30 / Chapter Chapter 3 --- Surface treatments --- p.31 / Chapter 3.1 --- Semiconductor wafers --- p.31 / Chapter 3.2 --- Cleaning procedure --- p.31 / Chapter 3.3 --- Polysulfide passivation --- p.33 / Chapter Chapter 4 --- Gas-phase polysulfide passivation of the InP(100) surface --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Sulfide-assisted reordering at the InP(100) surface --- p.38 / Chapter 4.2.1 --- Gas-phase polysulfide-treated InP( 100) surface --- p.38 / Chapter 4.2.2 --- Further annealing of the gas-phase polysulfide-treated surface --- p.47 / Chapter 4.2.3 --- Comparison with the UV/O3-HF treatment --- p.48 / Chapter 4.2.4 --- Sulfide at the interface of SiNx/InP --- p.49 / Chapter 4.3 --- Conclusions --- p.53 / Chapter Chapter 5 --- Gas-phase polysulfide passivation of the GaAs(lOO) surface --- p.55 / Chapter 5.1 --- Introduction --- p.55 / Chapter 5.2 --- Gas-phase poly sulfide-passivated GaAs( 100) surface --- p.56 / Chapter 5.2.1 --- Surface structure of the as-treated surface --- p.56 / Chapter 5.2.2 --- Surface structure after further annealing --- p.64 / Chapter 5.2.3 --- Mechanism of the gas-phase polysulfide passivation --- p.67 / Chapter 5.3 --- Conclusions --- p.68 / Chapter Chapter 6 --- Gas-phase polysulfide passivation of the GaAs(100) surface --- p.69 / Chapter 6.1 --- Introduction --- p.69 / Chapter 6.2 --- Reordering at the gas-phase polysulfide-passivated GaAs(100) surface --- p.70 / Chapter 6.2.1 --- Adsorption of polysulfide on the GaAs(100) surface --- p.70 / Chapter 6.2.2 --- Ordered sulfide at the GaAs(l 10) surface --- p.73 / Chapter 6.2.3 --- Further analysis of the LEED pattern --- p.80 / Chapter 6.3 --- Conclusions --- p.83 / Chapter Chapter 7 --- Sulfide Solution passivation of the GaAs(100) surface --- p.84 / Chapter 7.1 --- Introduction --- p.84 / Chapter 7.2 --- Sulfide solution passivation on the GaAs(l 10) surface --- p.85 / Chapter 7.2.1 --- Etching of sulfide solution on the GaAs(l 10) surface --- p.85 / Chapter 7.2.2 --- Annealing of sulfide solution-passivated GaAs( 110) surface --- p.88 / Chapter 7.2.3 --- Further analysis of the LEED pattern --- p.92 / Chapter 7.2.4 --- Shift of XPS peak position during annealing --- p.95 / Chapter 7.3 --- Conclusions --- p.97 / Chapter Chapter 8 --- Conclusions and further work --- p.99 / Chapter 8.1 --- Conclusions --- p.99 / Chapter 8.2 --- Further work --- p.100 / References --- p.102