Reactive sputtered ZnO thin films: Influence of the O2/Ar flow ratio on the oxygen vacancies and paramagnetic active sites
Reactive sputtered ZnO thin films: Influence of the O2/Ar flow ratio on the oxygen vacancies and paramagnetic active sites
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DOI：
10.1016/j.tsf.2019.137641
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发表时间：
2019-12-31
期刊：
影响因子：
2.1
通讯作者：
Otano, Wilfredo
中科院分区：
文献类型：
--
作者：
Camacho-Berrios, Adrian A.;Pantojas, Victor M.;Otano, Wilfredo
在反应溅射沉积过程中，通过改变氧氩比（O-2/Ar），在贫氧和富氧条件下制备了氧化锌薄膜。利用x射线衍射、x射线光电子能谱（XPS）、拉曼散射和电子顺磁共振（EPR）研究了溅射气体中氧气分压从20%增加到70%对薄膜组成、结晶度和可作为气体反应活性位点的缺陷的影响。所有的薄膜都呈现出有纹理的（0002）纤锌矿相，并且随着溅射气体中氧气分压的增加，晶体尺寸也随之增加。XPS分析表明，随着溅射气体中氧含量的增加，氧空位的数量减少。样品的拉曼光谱除了与纤锌矿结构相关的振动模式外，还包含与氢氧化物（OH）键相关的能带。在所有薄膜中都检测到强的EPR信号，与OH作为顺磁中心一致。在20% O-2/Ar下生长的薄膜中观察到一个额外的，但非常弱的EPR峰，该峰被分配到位于晶体晶格中的单电离氧空位。这些顺磁中心由于其未成对电子而具有很强的反应性，它们的形成对薄膜的物理和化学性质有重要影响。
Zinc oxide thin films were prepared under oxygen-deficient and oxygen-rich conditions by changing the oxygen to argon ratio (O-2/Ar) during the reactive sputtering deposition at room temperature. The effects of increasing the partial pressure of oxygen in the sputtering gas from 20 to 70% O-2/Ar on the thin film composition, crystallinity and defects that can act as active sites for gas reactions were studied using X-rays diffraction, X-rays photoelectron spectroscopy (XPS), Raman scattering and electron paramagnetic resonance (EPR). All the films exhibited a textured (0002) wurtzite phase and a crystallite size that increases as the partial pressure of oxygen in the sputtering gas increases. The XPS analysis showed that the number of oxygen vacancies decreases as the oxygen percent in the sputtering gas increases. The Raman spectra of the samples contained a band related to a hydroxide, OH, bond in addition to the vibrational modes associated with the wurtzite structure. A strong EPR signal, consistent with the OH acting as a paramagnetic center, was detected in all the films. An additional, but very weak EPR peak, was observed in the film grown at 20% O-2/Ar, which was assigned to singly ionized oxygen vacancies located in the crystallite lattice. These paramagnetic centers are highly reactive because of their unpaired electrons and their formation will have important effects on the physical and chemical properties of the thin films.