title: Optical Constants and Band Gap Evolution with Phase Transition in Sub-20-nm-Thick TiO2Films Prepared by ALD.
abstract: Titanium dioxide (TiO2) ultrathin films with different thicknesses below 20 nm were grown by atomic layer deposition (ALD) on silicon substrates at 300 °C. Spectroscopic ellipsometry (SE) measurements were operated to investigate the effect of thickness on the optical properties of ultrathin films in the spectra range from 200 to 1000 nm with Forouhi-Bloomer (F-B) dispersion relation. It has been found that the refractive index and extinction coefficient of the investigated TiO2ultrathin film increase while the band gap of TiO2ultrathin film decreases monotonically with an increase in film thickness. Furthermore, with the purpose of studying the temperature dependence of optical properties of TiO2ultrathin film, the samples were annealed at temperature from 400 to 900 °C in N2atmosphere. The crystalline structure of deposited and annealed films was deduced by SE and supported by X-ray diffraction (XRD). It was revealed that the anatase TiO2film started to transform into rutile phase when the annealing temperature was up to 800 °C. In this paper, a constructive and effective method of monitoring the phase transition in ultrathin films by SE has been proposed when the phase transition is not so obvious analyzed by XRD.
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Yue-Jie
authors.initials: YJ
authors.lastname: Shi
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China. rjzhang@fudan.edu.cn.
authors.forename: Rong-Jun
authors.initials: RJ
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Da-Hai
authors.initials: DH
authors.lastname: Li
authors.affiliation: National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, 200083, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.affiliation: National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, 200083, China. xinchen@mail.sitp.ac.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.affiliation: National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, 200083, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Sun
authors.affiliation: National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, 200083, China.
authors.forename: Yan-Feng
authors.initials: YF
authors.lastname: Wei
authors.affiliation: State Key Laboratory of ASIC & System, Fudan University, Shanghai, 200433, China.
authors.forename: Hong-Liang
authors.initials: HL
authors.lastname: Lu
authors.affiliation: National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, 200083, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Dai
authors.affiliation: Key Laboratory of Micro and Nano Photonic Structures, Ministry of Education, Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Liang-Yao
authors.initials: LY
authors.lastname: Chen
keywords: Atomic layer deposition; Phase transition; Rapid thermal annealing; Spectroscopic ellipsometry; TiO2 ultrathin film