LEED STRUCTURES DUE TO INTERACTION OF CO AND O2 WITH (0001) RE

Exposures to CO in the range 1 × 10-8 to 1 × 10-2 Torr-min at 20°C produced an adsorbed surface structure with fractional-order beams in the diffraction pattern, thus indicating a multiple-spaced adsorbed structure. The pattern was enhanced by mild heating at 425°C for 10 min but was weakened by further heating at 615°C for 30 min. Exposures of 1 × 10-4 Torr-min at temperatures of 615°C and 780°C resulted in more intense fractional-order patterns with some changes in the I-vs.-V curve for the (01) beam. Oxygen exposures at 20°C produced similar half-order patterns and after mild heating at 425°C the I-vs.-V curve for the (0 1 2) beam was identical with that of the corresponding beam from the CO-exposed surface. However, the fractional-order patterns from the oxygen structure continued to increase with the temperature of previous vacuum heating to at least 1130°C, after which they decreased with increasing temperature of preceding heat treatment. Thus the oxygen structure was more tightly bound than the CO structure. The similar shapes of the I-vs.-V curves for the fractional order patterns suggest that in both cases the adsorbed atoms remain on the surface and result in similar double scattering. Oxygen exposures of 1 × 10-4 Torr-min at 780°C and 920°C resulted in a diffraction pattern containing integral-order beams only, whose intensities were more than three times those of the corresponding beams from the clean surface. This pattern indicates a ReO surface structure. CO exposures at 20°C caused a maximum increase in work function of 0.35 eV. A maximum increase in work function of about 0.55 eV was caused by O2 exposures at 20°C while exposures at 600°C to 900°C caused increases as great as 1.5 eV. © 1969.