The electronic structure at interface between two insulators LaAlO3 and SrTiO3 has been investigated by using scanning tunneling microscopy and spectroscopy. The atomic-scale interfacial band structure is also demonstrated in the work with the consideration of the tip-induced band bending effect. Experimental results indicate that the magnitude of the built-in field across LaAlO3 is 0.075¡Ó0.005 V/Å. The band bending on SrTiO3 side at the heterointerface is observed. The band downshift of SrTiO3 side at the interface is 0.1 eV with ~1 nm decay length.

In this work, the interfacial electronic property between N-type LaAlO3/TiO2-SrTiO3 has been investigated by using scanning tunneling microscopy and spectroscopy (STM/S). With the consideration of the tip-induced band bending effect during STM measurements and in conjunction with the three-dimensional theoretically analysis, the schematic band structure of the hetero-structured SrTiO3/LaAlO3 is also revealed. Results indicate that the magnitude of the built-in field on the LaAlO3 is (30¡Ó5) mV/Å. The band bending on SrTiO3 side at the heterointerface is also observed. The band downshift of SrTiO3 side at the interface is 0.31 eV with about 0.8 nm decay length.

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Thesis (Ph.D.)--Michigan State University. Dept. of Physics and Astronomy, 2008. / Title from PDF t.p. (viewed on Mar. 27, 2009) Includes bibliographical references (p. 95-102). Also issued in print.

An experiment has been completed which demonstrated quantum mechanical tunneling of electrons between two gold electrodes separated in vacuum. The tunneling current between the gold electrodes has been measured, for fixed voltages of 0.1 and 0.01 volts, as the electrode spacing was varied from a distance of approximately 2.0 nm down to a point where the electrodes touched. Current-voltage characteristics for fixed electrode spacing in the direct tunneling region have also been measured. Numerical calculations of the tunneling current based on the free-electron model of the electrodes and the barrier, an image-potential reduced barrier, and a WKB approximation for the tunneling probability have been performed and compared with Simmons' theory and with the experimental results. Within experimental error the results indicate that an image potential reduced barrier with the modifications suggested by Lang and Kohn gives a close approximation to the true barrier for metal-vacuum-metal tunneling. For the first time, the work function of the electrodes in a tunneling experiment has been deduced from experimental parameters independent of the tunneling device.

This thesis presents the study for the temperature-driven and current-driven metal-insulator phase transition (MIT) in Ca₂RuO₄ via home-built variable temperature Scanning Tunneling Microscope. Atomically resolved topography images along with temperature dependence of resistivity are taken verifying the quality of the single crystals used in this experiment. Tunneling spectra are measured under various temperatures across the Tmi = 357K, which clearly shows spectra evolution with temperature and the difference between the room- temperature insulator phase and the high-temprature metal phase. Compared with DMFT calculation, the STS indicates lattice structure plays a vital role in the phase transition. Same measurement is conducted on the crystals under a DC current, thanks to a custom designed sample holder. The evolution of the tunneling spectra with source current demon- strates similarity with the one of temperature-driven MIT. The comparison between the spectra taken at high-temperature metalic state and the high-current metalic state high- lights the similarity of these 2 phases, with both showing a DOS transfer from 1eV to lower energy, when compared with the ground state. Combined with a variety of other studies via transport, scattering technique and infrared thermal imaging, it is found that the local temperature dominates both temperature-driven and current-driven MIT. It is very likely that the current-driven is caused by the inevitable Joule heating generated by the current, indicating the high-current metallic phase might be the same with high-current metallic phase. Finally, surface roughness and autocorrelation length analysis suggests an inhomo- geneous surface topography stemmed from the coexistence of the insulating S* phase and conducting L* phase under current.

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More that just magnificent views of atoms and molecules, Scanning Tunneling Microscopy, STM, images have the potential to answer some fundamental questions relating to surface molecular dynamics and bonding characteristics of localized species versus more common analytical tools that provide average of bulk sample information. A special feature of the STM is utilized in this study which is the ability to image organic monolayers at liquid-solid interface at ambient conditions. For STM analysis of organic fluids, the choice of a substrate is critical to the success of the images. The substrate must meet three criteria, the ability to sustain a tunneling current, retain an atomically flat surface over the area scanned, and immobilize a monolayer of the sample. The adsorption geometry created by the liquid crystalline materials analyzed in this study provided magnificent detailed features of the sample monolayer on a graphite substrate. These data provide information about the balance of intermolecular forces at the interface. It is illustrated that the quality or amount of information available from any fluid-solid interfacial image is dependent upon the existence of molecular symmetry within the monolayer of the substrate surface. / Graduation date: 1995

Thesis (Ph.D.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 181-189).