| Room temperature scanning tunneling microscopy has been used to study the behavior and properties of organic molecules on copper single crystals in an ultra high vacuum environment. The background and theory of scanning tunneling microscopy are briefly described. All the data and images presented in this dissertation were measured with a home built scanning tunneling microscope, the methods and procedures of which are outlined. The bare copper surfaces of Cu(111) and Cu(100) are imaged in order to better understand the substrate on which molecules are deposited. Various features of the single crystal surfaces are shown in images, including monatomic steps, frizzy steps, and screw dislocations. The adsorption behavior of C60 and hexa- t-butylhexaphenylbenzene (HB-HBC) have been studied on the Cu(111) surface and the adsorption behavior of hexa-t-butyldecacylene (HBDC) has been studied on the Cu(100) surface. C60 has been seen growing epitaxially from copper step edges, in a 4x4 overlayer of the Cu(111) surface. Internal structure of C60 has been observed as well. Ordered islands of HB-HBC have been observed to grow on terraces, as opposed to step edges. Brighter features in the ordered islands suggest the possible formation of dimers of HB-HBC, which is known to form dimers in the solid state. HBDC has been studied on the Cu(100) surface. At low coverage, HBDC behaves as a two-dimensional molecular gas on the surface at room temperature, with molecules resolved only along step edges and near surface defects. At monolayer coverage, HBDC forms ordered arrays, with a high level of intermolecular interactions. At lower coverage, HBDC has been pinned out of the gas phase by several different high voltage tunneling methods. At biases greater than 2 V, molecules are pinned into a semi-stable immobile trapped state by vertical manipulation, lateral manipulation and high voltage image. We believe the pinning occurs primarily through an inelastic tunneling mechanism, though the electric field and mechanical contact of the tip could contribute to the pinning. |
