Jae-Gook Lee

The adsorption conformation of chemisorbed pyridine on the Cu(110) surface

The adsorption conformation of pyridine on the Cu(110) surface has been studied using temperature programmed desorption, low energy electron diffraction, and electron stimulated desorption ion angular distribution techniques. Pyridine adsorbs on Cu(110) via the nitrogen lone pair orbital. The molecular symmetry axis is perpendicular to the surface. At low coverage, the aromatic ring plane of adsorbed pyridine is oriented parallel to the 〈001〉 plane, which is perpendicular to the close-packed copper atom rows on Cu(110). At high coverage, the aromatic ring plane of pyridine is azimuthally rotated by 25 (±5)° away from the 〈001〉 direction as a result of an attractive contribution from nonparallel aromatic ring–aromatic ring interactions superimposed on the overall repulsive adsorbate–adsorbate interactions. The zero coverage desorption activation energy of pyridine on Cu(110) is 0.97 eV and the repulsive adsorbate–adsorbate interaction energy is 0.16 eV/monolayer. At near saturation coverage, (5×3) and (4×3...

Thermal excitation of rotation of the methyl group in chemisorbed acetate on Cu(110)

The adsorption of acetic acid on the Cu(110) surface has been investigated by the time-of-flight electron stimulated desorption ion angular distribution technique by observing H+(D+) ions from the methyl groups. The activated conversion of acetic acid to acetate has been witnessed by observing the formation of oriented acetate species. It has been found that the activation energy for acetate formation varies from 0.39±0.06 eV at low coverage to 1.1±0.1 eV at high coverage, possibly because of acetic acid stabilization at high coverage by hydrogen bonding. Methyl groups are oriented with one C–H bond azimuthally directed in the 〈110〉 direction. At high coverage, the methyl groups are tilted slightly in the 〈110〉 direction due to repulsive acetate–acetate interactions. The activated rotation of the methyl groups on adsorbed acetate is clearly observed by the electron stimulated desorption ion angular distribution method and the barrier height for CH3 rotation is estimated to be 12±6 meV, and for CD3 group...

Molecular triangulation : finding the conformation of adsorbed self-assembled organic monolayers

Abstract We have developed a method that images two or more C–H bond directions within a complex adsorbed molecule on a single-crystal substrate. Since most surface-science methods are insensitive to H atoms in adsorbed molecules, this method offers unique capabilities for determining molecular conformations of relatively complex molecules at surfaces, permitting studies of structural changes over a wide range of coverage. This procedure, called molecular triangulation, is a new development based on the electron stimulated desorption ion angular distribution (ESDIAD) phenomenon used to measure individual bond directions in simple adsorbed molecules. The new ESD-molecular triangulation (ESD-MT) method provides incisive conformational information for large adsorbed organic species.

Dynamics of the striped nanostructure of the oxidized Cu(110) surface: A momentum-resolved electron stimulated desorption ion angular distribution study

The striped structure of the partially oxidized Cu(110) surface has been studied using a novel technique, momentum-resolved electron stimulated desorption ion angular distribution (ESDIAD) Long …O–Cu–O… strings oriented in the 〈001〉 direction and exhibiting attractive interactions with each other form periodically arranged stripes with widths in the nanometer range [D. J. Coulman et al., Phys. Rev. Lett. 64, 1761 (1990); K. Kern et al., ibid. 67, 855 (1991)]. Two different oxygen sites were detected, leading to a twofold symmetrical four-beam O+ ESDIAD pattern with 22° tilting of the beams in the 〈110〉 azimuth (A) direction and 8° in the 〈001〉 azimuth (B) direction. The relative intensities of the four beams have been compared for a wide range of oxygen coverages leading to a model in which the A beams correspond to O+ ions desorbing from the edges of the stripes and the B beams from the internal regions of the stripes. This model is confirmed by studying the effect of the coadsorption of Ar at 32 K on t...

Construction and performance of an ultrahigh vacuum-compatible high temperature vapor dosing system for low vapor pressure compounds

A gas dosing system for the quantitative deposition of low vapor pressure compounds onto surfaces in an ultrahigh vacuum system is reported. The dosing system is maintained at elevated temperature to achieve sufficiently high gas pressure for rapid transfer to the surface. Dosing is achieved through a heated calibrated leak valve which connects the high temperature source system to an internal tubular doser. The leak valve and the internal doser head are heated to a higher temperature than the source system to prevent condensation of the compound. The quantitative behavior of this doser is demonstrated for two low vapor pressure compounds.