Model reaction studies on vanadium oxide nanostructures on Pd(111)

摘要

Deuterium desorption and reaction between deuterium and oxygen to water has been studied on ultrathin vanadium oxide structures prepared on Pd(111).The palladium sample was part of a permeation source,thus enabling the supply of atomic deuterium to the sample surface via the bulk.Different vanadium oxide films have been prepared by e-beam evaporation in UHV under oxygen atmosphere.The structure of these films was determined using low energy electron diffraction and scanning tunneling microscopy.The mean translational energy of the desorption and reaction products has been measured with a time-of-flight spectrometer.The most stable phases for monolayer and submonolayer VO_x are particular surface-V_2O_3 and VO phases at 523 and 700 K,respectively.Thicker films grow in the form of bulk V_2O_3.The mean translational energy of the lesorbing deuterium species corresponds in all cases to the thermalized value.Apparent deviations from this energy distribution could be attributed to different adsorption/desorption and/or accommodation behaviors of molecular deuterium from the gas phase on the individual vanadium oxide films.The water reaction product shows a slightly hyperthermal mean translational energy,suggesting that higher energetic permeating deuterium contributes with higher probability to the water formation.