Temperature-Dependent Electronic Structure of TiO<sub>2</sub> Thin Film Deposited by the Radio Frequency Reactive Magnetron Sputtering Technique: X ray Absorption Near-Edge Structure and X ray Photoelectron Spectroscopy
Sekhar C. Ray, Dilip Kumar Mishra, Atala Bihari Panda, Hsiao‐Tsu Wang, Sriparna Bhattacharya, W. F. Pong
Abstract
TiO2 thin films were prepared by the reactive magnetron cosputtering technique on the n-type silicon substrates and annealed at different temperatures ranging from 110 to 250 °C. The X-ray diffraction, transmission electron microscopy, and Raman spectroscopy measurements show the formation of TiO2 thin films at 250 °C in the anatase phase (101) with a tetragonal structure. The modification in the electronic structure with the increase of annealing temperatures is studied by the X-ray absorption near-edge structure (XANES) at O K- and Ti L3,2-edges showing the splitting of pre-edge spectral features into t2g (Ti 3d + O 2pπ) and eg (Ti 3d + O 2pσ) symmetry bands in the structural matrix. The intensities of the O K-edge and Ti L3,2-edge increase with the annealing temperature because of induced structural disorder/distortion which could be correlated to the modification in unoccupancies that are associated with the hybridization of O-2p and Ti-3d states. The doublet Ti 2p3/2 and Ti 2p1/2 in Ti 2p X-ray photoelectron spectroscopy (XPS) are revealed with the t2g and eg symmetry bands along with the formation of Ti–O/Ti–OH and/or Ti–O–C bonds observed in O 1s XPS spectra. The estimated work functions (ionization potential) obtained from ultraviolet photoelectron spectroscopy were significantly reduced from ≈4.21 eV (≈7.69 eV) to ≈3.64 eV (≈7.01 eV) when the annealing temperature of the prepared TiO2 thin films is increased from 110 to 250 °C.