X-ray Photoelectron Spectroscopy Analysis of Nitrogen-Doped TiO2 Films Prepared by Reactive-Ion-Beam Sputtering with Various NH3/O2 Gas Mixture Ratios

Jin-Cherng Hsu,Paul W Wang,Yung-Hsin Lin

doi:10.3390/coatings10010047

Jin-Cherng Hsu, Paul W Wang + Show 1 more

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https://doi.org/10.3390/coatings10010047

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Journal: Coatings	Publication Date: Jan 4, 2020
Citations: 34	License type: CC BY 4.0

Affiliation: Fu Jen Catholic University, Bradley University

Abstract

Nitrogen-doped TiO2 films were prepared by reactive ion-beam sputtering deposition (IBSD) in a mixed atmosphere of NH3 and O2 at a substrate temperature of 400 °C. X-ray photoelectron spectra revealed the presence of six ions, i.e., N3−, N2−, N1−, N+, N2+, and N3+, respectively, in the films. The amorphous films had complex, randomly oriented chemical bonds. The Tauc–Lorentz model was employed to determine the bandgap energy of the amorphous films prepared using different NH3/O2 gas mixing ratios by ellipsometry. In addition, the optical constants of the films were measured. With the increase in the NH3/O2 gas mixture ratio to 3.0, the bandgap of N-doped TiO2 narrowed to ~2.54 eV.

Highlights

TiO2 films doped with metal and non-metal species are extremely interesting materials due to their potential for use in heterogeneous photocatalysis
Among all nonmetal-doped TiO2 materials, N-doped TiO2 is the most investigated material due to the fact that its nanomaterials exhibit superior photocatalytic activity with respect to pure TiO2 due to band-gap narrowing under visible-light irradiation
As N atoms replace O sites of TiO2, isolated impurity levels above the valence band (VB) are formed as shallow acceptor states, with visible-light illumination leading to electron excitation [3,4]

Summary

Introduction

TiO2 films doped with metal and non-metal species are extremely interesting materials due to their potential for use in heterogeneous photocatalysis. There are three major views with respect to the modification mechanism of N-doped TiO2 , namely, bandgap narrowing, impurity energy level, and oxygen vacancies [1]. The N2p state undergoes hybridization with the O2p states in N-doped TiO2 due to their similar energies. As N atoms replace O sites of TiO2 , isolated impurity levels above the valence band (VB) are formed as shallow acceptor states, with visible-light illumination leading to electron excitation [3,4]. Oxygen-deficient sites that form in the grain boundaries of N-doped TiO2 films are key to the emerging visible-light activity. The N-doped part of an oxygen-deficient site is crucial to block reoxidation [5]

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