In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS. Issue 18 (4th August 2016)

• Record Type: Journal Article
• Authors: Mao, Bao-Hua; Crumlin, Ethan; Tyo, Eric C.; Pellin, Michael J.; Vajda, Stefan; Li, Yimin; Wang, Sui-Dong; Liu, Zhi
• Is Part Of: Catalysis science & technology. Volume 6:Issue 18(2016)
• Page Start: 6778
• Page End: 6783
• Publication Date: 2016-08-04
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c6cy00575f
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : APXPS was used to investigate the effect of oxygen adsorption on the band bending and electron affinity of ALD Al2 O3, ZnO and TiO2 ultrathin films. Abstract : In this work, ambient pressure X-ray photoelectron spectroscopy (APXPS) was used to investigate the effect of oxygen adsorption on the band bending and electron affinity of Al2 O3, ZnO and TiO2 ultrathin films (∼1 nm in thickness) deposited on a Si substrate by atomic layer deposition (ALD). Upon exposure to oxygen at room temperature (RT), upward band bending was observed on all three samples, and a decrease in electron affinity was observed on Al2 O3 and ZnO ultrathin films at RT. At 80 °C, the magnitude of the upward band bending decreased, and the change in the electron affinity vanished. These results indicate the existence of two surface oxygen species: a negatively charged species that is strongly adsorbed and responsible for the observed upward band bending, and a weakly adsorbed species that is polarized, lowering the electron affinity. Based on the extent of upward band bending on the three samples, the surface coverage of the strongly adsorbed species exhibits the following order: Al2 O3 > ZnO > TiO2 . This finding is in stark contrast to the trend expected on the surface of these bulk oxides, and highlights the unique surface activity of ultrathin oxide films with important implications, for example, in oxidation reactions taking place on these films or in catalyst systems where such oxides are used as a support material.