The role of carbon in photodesorption

An extensive study of UV photon-induced desoprtion, which included mass-spectrometry, surface conductivity and Auger electron spectroscopy measurements, leads us to suggest that carbon reactions have a dominant role in chemisorption and photodesorption from certain semiconductor surfaces. Carbon, which is present as a containment on such surfaces, can be oxidized by gas phase oxygen capturing an electron from the conduction band of the substrate. Photogenerated holes, created by band-gap radiation, can then break this chemisorption bond and CO₂ molecules are then desorbed. Experimental data taken on surfaces of ZnO are discussed in detail. Additional results indicate that similar effects occur on other semiconductor surfaces such as TiO₂, CdS, the chrome-oxide surface of stainless steel, etc. It is interesting to note that metallic surfaces, carbon contaminated or not, show virtually no photodesorption activity. This behavior is not well understood at this time.