College of Chemistry and Chemical Engineering , Xiamen University , Xiamen 361005 , P. R. China.
Key Laboratory of Photovoltaic Materials of Henan Province, School of Physics & Electronics , Henan University , Kaifeng 475004 , P. R. China.
ACS Appl Mater Interfaces. 2018 May 23;10(20):17480-17486. doi: 10.1021/acsami.8b03278. Epub 2018 May 9.
Changes in the structure and composition resulting from oxygen deficiency can strongly impact the physical and chemical properties of transition-metal oxides, which may lead to new functionalities for novel electronic devices. Oxygen vacancies (V) can be readily formed to accommodate the lattice mismatch during epitaxial thin film growth. In this paper, the effects of substrate strain and oxidizing power on the creation and distribution of V in WO thin films are investigated in detail. An O isotope-labeled time-of-flight secondary-ion mass spectrometry study reveals that WO films grown on SrTiO substrates display a significantly larger oxygen vacancy gradient along the growth direction compared to those grown on LaAlO substrates. This result is corroborated by scanning transmission electron microscopy imaging, which reveals a large number of defects close to the interface to accommodate interfacial tensile strain, leading to the ordering of V and the formation of semi-aligned Magnéli phases. The strain is gradually released and a tetragonal phase with much better crystallinity is observed at the film/vacuum interface. The changes in the structure resulting from oxygen defect creation are shown to have a direct impact on the electronic and optical properties of the films.
结构和组成的变化由于缺氧会强烈影响过渡金属氧化物的物理和化学性质，这可能会为新型电子设备带来新的功能。氧空位（V）可以很容易地形成，以适应外延薄膜生长过程中的晶格失配。在本文中，详细研究了衬底应变和氧化能力对 WO 薄膜中 V 的形成和分布的影响。O 同位素标记的飞行时间二次离子质谱研究表明，与在 LaAlO 衬底上生长的 WO 薄膜相比，在 SrTiO 衬底上生长的 WO 薄膜在生长方向上具有更大的氧空位梯度。扫描透射电子显微镜成像证实了这一结果，该成像揭示了大量靠近界面的缺陷，以适应界面拉伸应变，导致 V 的有序化和半对齐的 Magnéli 相的形成。应变逐渐释放，在薄膜/真空界面处观察到具有更好结晶度的四方相。氧缺陷形成引起的结构变化被证明对薄膜的电子和光学性质有直接影响。
