Thesis (Ph. D.)--Princeton University. / From the Philosophical magazine for August 1910 and December 1911.

In this work, the theory of internal photoemission is reviewed and extended for the special case of platinum silicide Schottky barrier infrared photodiodes. Vickers' model of hot-electron-mode photodetection is recast in terms of hot-holes, and the effects of carrier energy loss due to phonon collisions, as well as the depletion of the occupation of the emitting states due to emission are included. The optical absorption of the Schottky diodes is measured and used to relate the quantum efficiency of the diodes to the internal yield as calculated from the model. By including the effects of the carrier energy loss due to phonon collisions and the depletion of the occupation of the emitting states in the model, one can resolve previously unexplained anomalies in the photoresponse data (the shape of the Fowler plots, the absolute magnitude of the yield, and the difference between the optical and thermal barriers). Independent estimates are obtained for the mean-free-path between hot-hole/phonon, hot-hole/cold-electron, and hot-hole/imperfection collisions as well as the mean phonon energy, mean transmission coefficient across the Schottky barrier, and the Fermi energy. The model is found to be in excellent agreement with the experimental data for parameter values consistent with those reported in the literature. Some degree of correlation is found to exist between the one free variable for each diode and the processing used for that diode. Namely, the temperature of the substrate during deposition is correlated with the value of the mean-free-path between imperfection scattering events.

No description available.

This thesis consists of photoemission studies of the rutile and anatase polymorphs of TiO2. It is split into two sections. In the first part, studies of the functionalisation of the rutile TiO2 (110) and the anatase TiO2 (101) surfaces with small organic molecules are presented. In the second part, studies of defects at the anatase TiO2 (101) surface are presented. Four organic molecules are investigated, p-aminobenzoic acid (pABA) and 3-fluoroaniline (3-FA) on anatase TiO2 (101), and dopamine and malonic acid (MA) on rutile TiO2 (110). The four adsorbates studied all have potential as dyes for dye-sensitised solar cells (DSSCS), and dopamine and pABA have the potential to be used as linkers for light sensitisers for photocatalytic applications such as DSSCs. Near-edge X-ray fine structure (NEXAFS) spectroscopy was used to determine the orientation of the molecules on the surface, and X-ray photoemission (XPS) spectroscopy was used to determine the chemical environment of the molecule on the surface. On the anatase TiO2 (101) surface, for pABA, the plane of the ring sits upright, normal to the surface, bonding through the carboxylic acid group after deprotonation. 3-FA also bonds upright, normal to the surface. It bonds through the amine group to the surface. It is unclear whether the molecule bonds dissociatively (the amine group deprotonating). On the rutile TiO2 (110) surface, dopamine is found to sit just off normal at ~ 78 º. It bonds through the catechol moiety after dissociation of the hydrogens. Both of the MA carboxylic acid protons dissociate and both moieties bond to the surface. MA is unstable under irradiation from insertion device beamlines. The defects in the anatase TiO2 (101) surface layers are investigated by XPS. Defects in the form of oxygen vacancies are observed in the band gap region of the photoelectron spectrum at around 1 eV binding energy (BE). Understanding the nature of these defects, intrinsic dopants in n-type TiO2 is imperative for photocatalytic applications. The effect of water adsorption on the stoichiometric and Ar cluster-ion-source-sputtered anatase TiO2 (101) surface is investigated at near-ambient pressures (NAP) and high vacuum. High vacuum studies show the anatase surface oxygen vacancies migrate to the subsurface region over time, as has been postulated with scanning tunnelling microscopy and density functional theory analysis. NAP-XPS is a developing technology allowing the analysis of surfaces and interfaces in "real-life" conditions. Results show water adsorbs in a similar fashion on both surfaces and reaches a saturation point between 0.6 and 1.8 mbar at room temperature, meaning there is little difference in reactivity between the stoichiometric and reduced surfaces. Oxygen vacancies are created at the TiO2 surface by insertion-device synchrotron radiation beamlines and the creation of these defects is monitored in situ with XPS. The bandgap state is made up of three components, relating to oxygen vacancies at 1.0 eV BE and two related components at 0.2 and 1.7 eV BE that are due to a surface 2D electron gas, created by electron doping via Nb impurities and synchrotron radiation-induced oxygen vacancies.

Thesis (Ph. D.)--Oregon Graduate Center, 1980.

M.Sc. / This dissertation presents experimental data on the near Fermi-level electronic structure of Sr₄Ru₃O₁₀. This summary gives a review of the facts that have been observed in the analysis of the data taken, and directions for future work are suggested. The first part of this dissertation (from chapter 1 to chapter 3) is dedicated to a review on the studied system and the experimental technique exploited in this study. In fact, chapter 1 gives a review of the general physical properties of different members of the Ruddlesden Popper strontium ruthenate family Srn+1RunO3n+1, focusing on the trilayered Sr4Ru3O10 in particular. Furthermore, chapters 2 and 3 discuss some essential features of the theoretical and experimental aspects of angle resolved photoemission spectroscopy (ARPES), respectively. In the second part of the dissertation (chapter 4), the fi rst experimental ARPES data on band dispersions and Fermi surface maps of Sr4Ru3O10, are presented and discussed. The experiment was performed at the beamline Cassiopee of the Soleil synchrotron radiation facility in Paris (France). The study has provided the first information on the near Fermi-level band dispersions and Fermi surface of Sr4Ru3O10, the effect of changing different matrix elements on electronic band dispersions and Fermi surface maps of Sr4Ru3O10, and electronic correlations effects present in this compound. Remarkably, low temperature ( 5 K) ARPES data presented in this study suggest that there is only a 45 rotation of the square unit cell of Sr4Ru3O10, due to correlated rotations about the c-axis of the RuO6 octahedra, but no elongation of the sides of this unit cell; and consequently in reciprocal space the square BZ, determined by considering the symmetry of the Fermi surface sheets, is only rotated by 45 but its size is unchanged with respect to the non-distorted situation. However, this is not what is expected. Using room temperature lattice parameters from ref. [17], the BZ of this compound would be 45 rotated and reconstructed into a square twice smaller, a situation that was also previously observed in band structure calculations and ARPES data of Sr3Ru2O7 from ref. [4]. This behaviour was ascribed to the fact that the structure of this system is possibly not the same at room temperature as at low temperatures (down to 5 K), where the ARPES data of this work were acquired. Therefore low temperature (<100 K) X-ray diffraction data of Sr4Ru3O10 are needed in order to determine low temperature lattice parameters and compare them with room temperature ones so as to verify whether the structure of Sr4Ru3O10 is not the same at room and low temperatures.

published_or_final_version / Physics / Master / Master of Philosophy

No description available.

Rosetta is a European spacecraft that will rendevouz with andfollow the comet 67P/Churyumov-Gerasimenko from 2014 to 2015. Among other instruments are two Langmuir probes that measure certain plasma parameters. This study aims to describe the photoemssionon Rosetta and in particular on the Langmuir probes. More than 7800 bias voltage sweeps were analyzed and parameters such as photosaturationcurrent, spacecraft potential, photoelectron temperature and offset current were calculated from these sweeps. It is found that the photoemission is stronger on Probe 1 than Probe 2. The photosaturation currents for dierent mission phases align rather well when normalized to distance to the Sun and the solar activity, when correcting for the offset currents found on the probes the alignment became even better. The typical electron density in the photoelectron cloud is 25 cm^-3 at 1 AU and the electron temperature varies from 1 - 2 eV.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Apr. 9, 2009). PDF text:ix, 101 p. : ill. (some col.) ; 20 Mb. UMI publication number: AAT 3338833. Includes bibliographical references. Also available in microfilm and microfiche formats.