Effects of electron irradiation on structure and bonding of SF₆ on Ru(0001)

Electron stimulated desorption ion angular distribution (ESDIAD) and temperature programmed desorption (TPD) techniques have been employed to study radiation-induced decomposition of fractional monolayer SF₆ films physisorbed on Ru(0001) at 25 K. Our focus is on the origin of F⁺ and F⁻ ions, which dominate ESD from fractional monolayers. F⁻ ions escape only in off-normal directions and originate from undissociated molecules. The origins of F⁺ ions are more complicated. The F⁺ ions from electron stimulated desorption of molecularly adsorbed SF₆ desorb in off-normal directions, in symmetric ESDIAD patterns. Electron beam exposure leads to formation of SFx (x = 0 - 5) fragments, which become the source of positive ions in normal and off-normal directions. Electron exposure > 10¹⁶ cm⁻ ² results in decomposition of the entire adsorbed SF₆ layer

Near-edge absorption fine structure and UV photoemission spectroscopy studies of aligned single-walled carbon nanotubes on Si(100) substrates

The self-assembled films of single-walled carbon nanotubes were studied. The study was carried out by using near-edge absorption fine structure (NEAFS) and UV photoemission spectroscopy (UPS). It was found that at lower angles of incidence, the intensity of π * core exciton at 284.4 eV, which attributed to the greater accessibility of the π * orbitals. The results from UPS spectra of the films showed little angular dependence and included features consistent with total density of states of graphite

LEEM investigation of the faceting of the Pt covered W(111) surface

A low energy electron microscope (LEEM) has been used to investigate the faceting of W(111) as induced by Pt. The atomically rough W(111) surface, when fully covered with a monolayer film of Pt and annealed to temperatures higher than {approximately} 750 K, experiences a significant morphological restructuring: the initially planar surface undergoes a faceting transition and forms three-sided pyramids with {211} faces. The experiments demonstrate the capability of LEEM for imaging both the fully and partially faceted surface. In addition, we have observed the formation of the facets in real time, when Pt is dosed onto the heated surface. We find that the transition from planar surface, to partially faceted surface, and to fully faceted surface proceeds through the nucleation and growth of spatially separated faceted regions

Structures of adsorbed CO on atomically smooth and on stepped sngle crystal surfaces

The structures of molecular CO adsorbed on atomically smooth surfaces and on surfaces containing monatomic steps have been studied using the electron stimulated desorption ion angular distribution (ESDIAD) method. For CO adsorbed on the close packed Ru(001) and W(110) surfaces, the dominant bonding mode is via the carbon atom, with the CO molecular axis perpendicular to the plane of the surface. For CO on atomicaly rough Pd(210), and for CO adsorbed at step sites on four different surfaces vicinal to W(110), the axis of the molecule is tilted or inclined away from the normal to the surface. The ESDIAD method, in which ion desorption angles are related to surface bond angles, provides a direct determination of the structures of adsorbed molecules and molecular complexes on surfaces