Shuxia Yin

Molecular Superlattices Induced by Alkyl Substitutions in Self-Assembled Triphenylene Monolayers

The configuration of the superlattices, formed from liquid-crystalline molecules on a graphite surface, are controllable through their alkyl substituents. This control may be attributed to the interplay of molecular steric interaction and the 2 D crystallization of alkyl chains. Two such lattices, as observed by STM, are shown in the accompanying graphic (C12- and (inset) C14-substituted molecules).

Studies of the effects of hydrogen bonding on monolayer structures of C18H37X (X=OH, SH) on HOPG

Abstract Based on Scanning tunneling microscopy (STM) observations of 1-C 18 H 37 X (X=OH, SH) adsorbed on HOPG, the hydrogen bonded complexes were studied using density functional theory (DFT) and molecular mechanics (MM). At B3LYP/6-31g and B3LYP/6-311g** levels, molecular dimers connected by hydrogen bond were obtained. The models of 1-C 18 H 37 X monolayer were optimized by consistent valence force field (CVFF), whose structures and interaction energies agree well with DFT calculations. It is noticed that due to the stronger hydrogen bond interactions between C 18 H 37 OH molecules, C 18 H 37 OH adsorbed on HOPG shows only one kind of molecular arrangement, while C 18 H 37 SH exhibits two kinds of packing induced by alkyl–alkyl and adsorbate–substrate interactions.

Characteristics of oxides formed from a Si0.5Ge0.5 alloy

Abstract X-ray photoelectron spectroscopy (XPS) combined with Auger electron spectroscopy (AES) have been used to study the oxides from a Si0.5Ge0.5 alloy grown by molecular beam epitaxy (MBE). The oxidation was performed at 1000°C wet atmosphere. The oxide consists of two layers: a mixed (Si,Ge)Ox layer near the surface and a pure SiOx layer underneath. Ge is rejected from the pure SiOx and piles up at the SiO x SiGe interface. XPS analysis demonstrates that the chemical shifts of Si 2p and Ge 3d in the oxidized Si0.5Ge0.5 are significantly larger than those in SiO2 and GeO2 formed from pure Si and Ge crystals.

Scanning tunneling microscopy image contrast variation on a copper (II) complex adlayer with tip–sample separation

Abstract Contrast variation of scanning tunneling microscopy (STM) image has been investigated as a function of tip–sample separation on a bis[1,3-di(p-n-tetradecyloxyphenyl)propane-1,3-dionato]copper(II) (abbreviated as C14O–Cu) adlayer on highly oriented pyrolytic graphite with STM. Submolecular features of the molecular core and interdigitated alkyl chain are clearly revealed. A preliminary theoretical calculation is carried out to simulate the image variation. The simulated results are in agreement with STM observation.