Methanol adsorption and dissociation on GaP(110) studied by ambient pressure X-ray photoelectron spectroscopy

• Ambient pressure X-ray photoelectron spectroscopy of GaP in CH 3 OH atmosphere. • DFT enables identification of CH 3 OH dehydrogenation products on GaP surface. • At room temperature, CH 3 O, CH 2 O, and hydrogen bonded CH 3 OH-CH 3 O are present. • Availability of surface phosphorus sites limits the formation of adsorbed CH 2 O. • Above 400 K, concentration of CH x species increases, suggesting C-O bond cleavage. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was used to investigate methanol (CH 3 OH) adsorption and reaction on the GaP(110) surface. Exposure of CH 3 OH to GaP(110) at room temperature led to the formation of at least four different surface species as indicated by analysis of C 1s and O 1s XPS features. By combining AP-XPS data with density functional theory calculations, the surface species were identified as methoxy (CH 3 O*), formaldehyde (CH 2 O*), and paired methanol (p-CH 3 O*H) and methoxy (p-CH 3 O*) species, where “paired” means that they belong to a hydrogen-bonded methoxy-methanol complex. Asterisk * here indicates an adsite. The formation of CH 2 O* via the dehydrogenation of CH 3 O* was shown to be limited by the availability of vacant phosphorus (P) sites on GaP(110). With an increase in CH 3 OH pressure, the fractional coverage of CH 3 O* species reached 0.55, and the surface P sites were completely saturated with hydrogen. Under a constant CH 3 OH pressure of 0.5 Torr, the surface concentration of the paired species and of CH 2 O* remained constant until 400 K. At higher temperatures, thermally driven reactions led to a significant increase in the concentration of surface CH x * species, which suggests that C-O bond cleavage of the CH 3 O group is the dominant decomposition mechanism on GaP(110). Based on the reactivity of GaP(110) toward CH 3 OH dehydrogenation, elevated temperatures and CH 3 OH pressures may be used to functionalize this surface.