Acquisition of a Variable Temperature Scanning Tunnelling Microscope

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9307734 Plummer The project is for the acquisition of a variable-temperature scanning tunneling microscopy/spectroscopy system that will operate in the range of 25K-~1500K. The essential component of this package will be the JEOL JSTM-4500VT Scanning Tunneling Microscope. This commercial STM has demonstrated atomic resolution from room temperature up to 1475K. Also, JEOL is in the process of engineering a low-temperature sample stage, compatible with JSTM- 4500VT, and capable of allowing atomic resolution imaging on samples as low as 25K. The participants in this proposal will be working with JEOL to explore the capabilities of the low- temperature stage. A broad range of materials problems will be investigated with the variable-temperature STM, utilizing its ability to do atomic scale microscopy and spectroscopy. The interplay between atomic and electronic structure in thin film nommetal-to-metal transitions will be studied. The detailed nature of Mott, Wilson, and Peierls- like transitions can be probed in atomic detail as a function of adsorbate density and substrate temperature. The low temperature STM will be used to monitor growth conditions for pulsed-laser ablation epitaxial growth of high Tc superconducting films, to directly measure the modulation of superconducting properties at isolated growth steps, and to identify flux pinning sites associated with surface morphology; to investigate the interaction of hydrogen with simple, noble, and carbon surfaces and thin films, concentrating on temperature-dependent changes in the structure and bonding; and to investigate the physical and chemical properties of alloy surfaces at elevated temperatures, combining the short-range real-space capabilities of the STM with the long-range-order capabilities of x-ray scattering. Finally, experiments will be aimed at nanofabrication, where selected organometallic complexes will be physisorbed and subsequently decomposed by the electron impact from the t unneling current to form "metal wires". ***