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.

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

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Many low dimensional structures arise from self-assembly when depositing metals on silicon surfaces, including both quantum dots and quantum wires. One class of these objects are rare earth silicide nanowires (RENW) grown on Si(001). In this dissertation, NW thermal stability, control of NW cross section, and associated surface reconstructions are studied by Scanning Tunneling Microscopy (STM). We test thulium and find for the first time that it forms NWs and these NWs are stable against prolonged annealing. We also find that the RENWs nucleate at 2×7 reconstruction domain boundaries. These results pave the way for precise control over NW size, placement, and integration with functional nanostructures and nanodevices.Another type of self-assembled NWs on Si(001) are insulating CaF2 NWs. As an ideal model system for epitaxial growth of an insulator on a semiconductor surface, CaF2 offers unique properties such as simple structure, good lattice match to silicon and congruent evaporation. In this thesis the growth behavior of CaF2 on the Si(001) surface is investigated. At low coverages CaF2 molecules randomly locate on Si(001). Features observed at this stage are explained in terms of dissociated fragments of CaF2 terminating the dangling bonds of Si dimers. Etching is observed after surface is saturated by these features with a 2×1 periodicity. A 2×n phase, grown at 750°C, suggests the dissociation of CaF2, as proved by the simulation of LEED patterns. A c(4×4) phase is observed from 0.5ML to about 1ML with deposition temperature from 600oC to 700oC. At the highest CaF2 deposition coverages studied, a stripe phase and CaF2 NWs are observed by a combination of STM, AFM and SEM. The results provide a significant expansion in the knowledge of CaF2 on Si(001). The common thread that links all these studies is the extent to which nanostructures can be controlled by careful growth conditions, not just by substrate temperature and the amount of material deposited, but also by timing of post-deposition annealing, etc. The grown nanostructures are metastable and result from a balance of energetic considerations and kinetics.

Many low dimensional structures arise from self-assembly when depositing metals on silicon surfaces, including both quantum dots and quantum wires. One class of these objects are rare earth silicide nanowires (RENW) grown on Si(001). In this dissertation, NW thermal stability, control of NW cross section, and associated surface reconstructions are studied by Scanning Tunneling Microscopy (STM). We test thulium and find for the first time that it forms NWs and these NWs are stable against prolonged annealing. We also find that the RENWs nucleate at 2×7 reconstruction domain boundaries. These results pave the way for precise control over NW size, placement, and integration with functional nanostructures and nanodevices.Another type of self-assembled NWs on Si(001) are insulating CaF2 NWs. As an ideal model system for epitaxial growth of an insulator on a semiconductor surface, CaF2 offers unique properties such as simple structure, good lattice match to silicon and congruent evaporation. In this thesis the growth behavior of CaF2 on the Si(001) surface is investigated. At low coverages CaF2 molecules randomly locate on Si(001). Features observed at this stage are explained in terms of dissociated fragments of CaF2 terminating the dangling bonds of Si dimers. Etching is observed after surface is saturated by these features with a 2×1 periodicity. A 2×n phase, grown at 750°C, suggests the dissociation of CaF2, as proved by the simulation of LEED patterns. A c(4×4) phase is observed from 0.5ML to about 1ML with deposition temperature from 600oC to 700oC. At the highest CaF2 deposition coverages studied, a stripe phase and CaF2 NWs are observed by a combination of STM, AFM and SEM. The results provide a significant expansion in the knowledge of CaF2 on Si(001). The common thread that links all these studies is the extent to which nanostructures can be controlled by careful growth conditions, not just by substrate temperature and the amount of material deposited, but also by timing of post-deposition annealing, etc. The grown nanostructures are metastable and result from a balance of energetic considerations and kinetics.