9306684 Lieber The relationship between local atomic structure, microstructure, electronic states and physical properties in complex low- dimensional solids will be investigated with an emphasis on high- temperature copper oxide superconductors and transition metal chalcogenide conductors. Detailed physical measurements of the structure, electronic states and transport properties will be made using scanning tunneling microscopy (STM) and other techniques. Measurements will be made as a function of systematic variations in composition and processing to develop an understanding of fundamental material properties and how these properties can be rationally changed. Investigations of the copper oxide superconductors will focus on two general areas. First, the structural and electronic effects of metal-substitution and oxygen doping in BiSrCaCuO single crystals will be characterized at the atomic to nanometer scale using STM and scanning tunneling spectroscopy (STS) and on a macroscopic scale using diffraction and transport measurements. These studies will provide data needed to eleucidate the relationship between atomic structure, microstructure, electronic states, and the observable parameters such as Tc and the critical current density. Secondly, the low- energy excitations in the superconducting state of Bi2Sr2CaCu2O8 single crystals will be characterized using high-resolution electron energy loss spectroscopy (HREELS) and STS. HREELS and STS will be used to characterize the magnitude of the energy gap as a function of temperature and sample Tc in oxygen doped BiSrCaCuO single crystals. These HREELS and STS investigations will provide new data essential for probing the mechanism of superconductivity. In addition, STM and STS also will be used to characterize the local atomic structure and electronic states in metal dichalcogenide materials. Results from these studies will address systematically the problem of pining and disorder in two- dimensional mate rials. Overall, these investigations will provide general insights into the relationship between atomic level properties and macroscopic phenomena, and will develop further STM and STS for probing complex materials problems. ***
