Chemisorption, photodesorption and conductivity measurements on ZnO surfaces

Y. Shapira, S. M. Cox, David Lichtman

Research output: Contribution to journalArticlepeer-review

Abstract

Experimental results of a mass-spectro metric analysis of photodesorption from ZnO single crystals at different temperatures are reported. They provide direct evidence that CO2 is the only photodesorbed species from both the single crystal and powder samples studied. The CO2 photodesorption occurs only when the incident photon energy exceeds the ZnO band gap energy. Excellent agreement between the illumination time dependence of the CO2 photodesorption and surface conductivity data in both single crystals and powder samples strongly suggests a substrate dependent mechanism in which photodesorption occurs by the neutralization of chemisorbed CO2- "ion-molecules" by photogenerated holes. In addition, measurements of the chemisorption kinetics of oxygen on ZnO single crystal and powder surfaces are reported. The results are compared with CO2 and CO chemisorptiun experiments to show that, of these gases, only oxygen chemisorbs from the gas phase. Auger analysis of oxygen saturated and photodesorbed surfaces of ZnO show a significant relation between the carbon content and the photo-desorptive and conductive activities of those surfaces. These observations indicate that impurity carbon atoms on ZnO surfaces can be oxidized by electron capture to produce chemisorbed CO2- "ion-molecules' which will then readily photodesorb by bandgap radiation. This proposed process is discussed together with further supporting evidence.

Original languageEnglish
Pages (from-to)43-59
Number of pages17
JournalSurface Science
Volume54
Issue number1
DOIs
StatePublished - Jan 1976
Externally publishedYes

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