Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon, SK, S7 N5E2, Canada.
Chemistry and Materials Science Program, Lakehead University, 955 Oliver Road, Thunder Bay, ON, P7B5E1, Canada.
Chemphyschem. 2019 Dec 16;20(24):3328-3335. doi: 10.1002/cphc.201900726. Epub 2019 Dec 4.
We investigate how the electronic structure of amorphous lead oxide (a-PbO) films deposited on ITO substrate is changed after annealing at various temperatures. Both experimental soft X-ray spectroscopic and density functional theory (DFT) based computational techniques are used to explore the electronic structure of this material. X-ray emission, resonant X-ray inelastic scattering, and X-ray absorption spectroscopic techniques are employed to directly probe the valence and conduction bands. We discover that the films are very stable and remain amorphous when exposed to temperatures below 300 °C. An amorphous-to-polycrystalline (α-PbO phase) transformation occurs during annealing at 400 °C. At 500 °C, an alpha to beta phase change is observed. These structural modifications are accompanied by the band gap value changing from 1.4±0.2 eV to 2.0±0.2 eV upon annealing at 400 °C and to 2.6±0.2 eV upon annealing at 500 °C. A difference between surface and bulk structural properties is found for all samples annealed at 500 °C and above; these samples also exhibit an unexpected suppression of O : 2p density of states (DOS) near the bottom of the conduction band, whereas additional electronic states appear well within the valence band. This study provides a significant step forward to understanding the electronic properties of two polymorphic forms of PbO needed for optimization of this material for use in X-ray sensors.
我们研究了在不同温度下退火后，ITO 基底上沉积的非晶态氧化铅(a-PbO)薄膜的电子结构如何变化。我们使用实验软 X 射线光谱学和基于密度泛函理论（DFT）的计算技术来探索这种材料的电子结构。X 射线发射、共振 X 射线非弹性散射和 X 射线吸收光谱技术被用来直接探测价带和导带。我们发现，当温度低于 300°C 时，薄膜非常稳定且保持非晶态。在 400°C 退火时，会发生非晶态到多晶态（α-PbO 相）的转变。在 500°C 时，观察到α到β相的转变。这些结构的变化伴随着带隙值的变化，从 1.4±0.2 eV 到 400°C 退火时的 2.0±0.2 eV，再到 500°C 退火时的 2.6±0.2 eV。我们发现所有在 500°C 及以上温度退火的样品都存在表面和体相结构性质的差异；这些样品还表现出导带底部 O:2p 态密度（DOS）的意外抑制，而额外的电子态则出现在价带内。这项研究为理解两种 PbO 多晶型的电子性质提供了重要的一步，这对于优化这种材料在 X 射线传感器中的应用是必要的。
