In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS

Bao-Hua Mao; Ethan Crumlin; Eric C. Tyo; Michael J. Pellin; Stefan Vajda; Yimin Li; Sui-Dong Wang; Zhi Liu

doi:10.1039/C6CY00575F

In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS†

Bao-Hua Mao,^abc Ethan Crumlin,^c Eric C. Tyo,^d Michael J. Pellin,^d Stefan Vajda,^defg Yimin Li,*^bh Sui-Dong Wang*^a and Zhi Liu*^bch

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* Corresponding authors

^a Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, People's Republic of China
E-mail: wangsd@suda.edu.cn

^b State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, People's Republic of China
E-mail: zliu2@mail.sim.ac.cn, yml@mail.sim.ac

^c Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^d Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

^e Nanoscience & Technology Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

^f Department of Chemical and Environmental Engineering, School of Engineering & Applied Science, Yale University, New Haven, Connecticut 06520, USA

^g Institute of Molecular Engineering, The University of Chicago, 5747 South Ellis Avenue, Chicago, IL, USA

^h School of Physical Science and Technology, ShanghaiTech University, Shanghai 200031, China

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 Al₂O₃, 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 Al₂O₃ 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: Al₂O₃ > 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.

This article is part of the themed collection: Nanocatalysis

Catalysis Science & Technology

In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS†

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In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS

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