X射线光电子能谱
分析化学(期刊)
材料科学
溅射
钼
退火(玻璃)
薄膜
无定形固体
溅射沉积
分压
单斜晶系
氧气
化学
结晶学
冶金
核磁共振
纳米技术
晶体结构
有机化学
色谱法
物理
作者
Hamed Simchi,Brian E. McCandless,Tao Meng,J. H. Boyle,William N. Shafarman
摘要
Molybdenum oxide (MoO3) thin films were prepared via Radio Frequency (RF) sputtering at different ambient composition and post-deposition annealing. The effects on the structural, optical, and surface properties of the deposited films were investigated. The ambient oxygen concentration O2/(O2 + Ar) was varied from 10% to 100% at 10 mTorr. Post deposition anneals were performed in Ar at 300–500 °C. The films were analyzed using glancing incidence x-ray diffraction (GIXRD), UV/Vis/NIR spectrophotometry, and x-ray photoelectron spectroscopy (XPS). As-deposited films have amorphous structures, independent of the oxygen partial pressure. Annealing at 300 °C in air resulted in crystallization of the molybdenum oxide films to the monoclinic β-MoO3 phase. Samples annealed at 400 and 500 °C were identified as pure orthorhombic α-MoO3 phase with (020) preferred orientation. High resolution XPS studies showed the presence of Mo6+ (MoO3) and Mo5+ (Mo4O11) oxidation states at the surface of as deposited and low temperature (300 °C) annealed films, and the Mo6+ to Mo5+ did not change much with deposition oxygen partial pressure. Annealing at 400–500 °C suppressed the oxygen deficiency at the surface, resulting in films with composition close to stoichiometric phases. UV/Vis/NIR spectrophotometry revealed that all films have a high optical transmittance (>80%) in the visible range, followed by a steep drop at λ ≈ 400 nm indicating a strong absorption due to band-to-band transition. Increasing the oxygen partial pressure had no significant effect on optical transmittance of the films, and the bandgaps in the range of 2.6 eV to 2.9 eV were obtained. Annealing at 300 °C had a negligible effect on the optical properties of the MoO3 films, but samples annealed at 400 °C and 500 °C exhibited wider bandgaps within the range of 3.1–3.4 eV.
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