An Electron-Stimulated Desorption Ion Angular Distribution and Low-Energy Electron Diffraction Investigation of CF₃I on Ru(001)

Abstract

We have investigated the structures of CF3I, and its dissociation products, adsorbed on Ru(001) using lowenergy electron diffraction and electron-stimulated desorption ion angular distribution (ESDIAD). Atomic iodine forms (√3x√3)R30° islands even at very low coverages. At 70% of saturation and above, a (2X2) superstructure forms which we attribute to a p(2X2) unit cell with one CF 3 group and one iodine atom. ESDIAD images show F+ desorbing at normal emission and in three hexagonal patterns. The normal emission is attributed to a tilted configuration of CF 3 (ad) in which one C-F bond is oriented perpendicular to the surface. A small hexagon is attributed to F(ad) on step edges. A large hexagon at low coverages may arise from isolated CF 3 (ad) species possessing C 3v symmetry. And finally, an intermediate hexagon is attributed to perturbation of the CF 3 (ad) orientation by molecular fragments which result from electron irradiation of physisorbed CF 3 I. Received March 17, 1995. In Final Form: November 28, 1995 We have investigated the structures of CF3I, and its dissociation products, adsorbed on Ru(001) using low-energy electron diffraction and electron-stimulated desorption ion angular distribution (ESDIAD). Atomic iodine forms ( 3x 3)R30°islands even at very low coverages. At 70% of saturation and above, a (2×2) superstructure forms which we attribute to a p(2×2) unit cell with one CF3 group and one iodine atom. ESDIAD images show F + desorbing at normal emission and in three hexagonal patterns. The normal emission is attributed to a tilted configuration of CF3(ad) in which one C-F bond is oriented perpendicular to the surface. A small hexagon is attributed to F(ad) on step edges. A large hexagon at low coverages may arise from isolated CF3(ad) species possessing C3v symmetry. And finally, an intermediate hexagon is attributed to perturbation of the CF3(ad) orientation by molecular fragments which result from electron irradiation of physisorbed CF3I.

Reactivity and Structure of CF3I on Ru(001)

“…This assignment is reinforced by ESDIAD results presented elsewhere. 33 The lower-temperature state attributed to atomic fluorine is more complex and actually consists of two well-resolved features. Two features were also suggested in the previous TDS data for F+ (although not well-resolved).15 Figure 2 shows the HF+ signal in the 100-500 K range as a function of increasing CF3I exposure.…”

“…The results of a complete ESDIAD investigation will be published elsewhere. 33 For present purposes, Figure 10 shows the ESDIAD image produced from a multilayer exposure of CF3I (400% of saturation) heated to 500 K. The image itself is taken after recooling to 170 K. We believe that this image represents emission from the (001) terraces. Only a single normal beam is visible with no evidence for azimuthal ordering.…”

“…3 The details 0022-3654/95/2099-8736S09.00/0 © 1995 American Chemical Society of the ESDIAD experiments also will be given elsewhere. 33 TDS experiments are performed using a UTI100C quadrupole mass spectrometer (QMS) interfaced to a HP Vectra QS/20 microcomputer such that multiplexing of up to eight masses is possible. The heating rate is 5.3 K/s (100-200 K), 2.3 K/s (200-400 K), and 4.2 K/s (400-1500 K) for all TDS experiments.…”

Surface Chemistry and Radiation Chemistry of Trifluoroiodomethane (CF3I) on Mo(110)

“…26 Low energy electron diffraction (LEED) and electron-stimulated desorption ion angular distribution (ESDIAD) have been used to probe the electron-induced dissociation of CF 3 I on Ru(001). 27 Results of postirradiation temperature-programmed desorption experiments demonstrate carbon-carbon coupling in CF 3 I multilayer films on Ni(100). 19 We report the use of temperature-programmed desorption experiments to investigate the surface chemistry of CF 3 I on Mo-(110) under ultrahigh vacuum conditions.…”

“…The desorption of CF 3 and I - during photolysis of CF 3 I on Ag(111) has been attributed to hot electrons produced at the Ag(111) surface by the incident photons . Low energy electron diffraction (LEED) and electron-stimulated desorption ion angular distribution (ESDIAD) have been used to probe the electron-induced dissociation of CF 3 I on Ru(001) . Results of postirradiation temperature-programmed desorption experiments demonstrate carbon−carbon coupling in CF 3 I multilayer films on Ni(100) …”