Scanning tunneling microscopy and spectroscopy of nanometer scale metallic features on silicon surfaces

Nanometer scale metals are of great interest due to their potential applications in the future of molecular/atomic scale devices. For example, nanometer scale metal contacts on semiconducting single-walled carbon nanotubes (SWNTs) can determine the transport performance of SWNT based field effect transistors (FETs). In this thesis, I have used an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) to fabricate nanometer scale metallic features on the Si(100)-2×1:H surface and form nanoscale metal contacts on the SWNTs. Scanning tunneling spectroscopy (STS) is used to study the electronic properties of the metallic features and the nano-contacts. Two kinds of metallic features are studied. First, an unpaired dangling bond (DB) can be formed on Si(100)-2×1:H surface using an STM nanolithography method. The unpaired DB, which shows metallic behavior, can perturb its surroundings electronically up to ~1.9 nm by introducing a near-midgap state in the local density of states (LDOS) of neighboring Si atoms. The decay length of the DB-states of an unpaired DB wire can be ~2.5 nm along the dimer row direction. The perturbation of an unpaired DB to an adjacent paired DB is also demonstrated. Second, sub-5 nm HfB2 metals can be direct written on the Si surface using STM electron beam induced deposition (STM-EBID). Nanoscale contacts between HfB2 metal and semiconducting SWNTs can be formed by direct writing HfB2 onto a SWNT or by manipulating a SWNT with the STM tip onto HfB2. STS studies indicate a strong Schottky barrier formed at the HfB2/SWNT interface, which induces metallicity in the SWNT. Metal induced gap states (MIGS) are also observed adjacent to the contact