Investigations of Novel Materials via Scanning Tunneling Microscopy and Conventional Tunneling Techniques.

In this dissertation, a new, simple and economical design for a Scanning Tunneling Microscope (STM) is described. This STM has been found to work well at room temperature in air, and also at liquid nitrogen temperature. The topographic images of metal films, layer compounds, and CDW materials are presented with resolution of 10nm down to 0.1nm. The present theories of STM are also discussed. The tunneling current between probe tip and sample surface, in a three dimensional model, is found to be proportional to the local electronic density of states at E_{ rm fermi}. This leads to many interesting applications. The STM study of Bi_2S _3 clusters is reported. Disk-like structure of the clusters was observed for the first time, indicating highly anisotropic growth in the nucleation of Bi_2S_3 crystal. The STM imaging of NbSe_3 and Blue Bronze is also presented, the chain-structure of Blue Bronze crystal is observed for the first time in the helium gas environment. Tunneling spectroscopy measurements on the high-temperature superconductor YBa_2 Cu_3O_{7 -rm x}, which used a simplified version of an STM as well as some conventional techniques, are also reported. Here a spectrum very different from the BCS form was observed, suggesting the existence of new mechanisms of superconductivity. (Copies available exclusively from Micrographics Department, Doheny Library, USC, Los Angeles, CA 90089-0182.).