Li Qiu, Wang Yong, Li Tiantian, Li Wei, Wang Feifan, Janotti Anderson, Law Stephanie, Gu Tingyi
Tianjin Key Laboratory of High Speed Cutting and Precision Machining, Tianjin University of Technology and Education, Tianjin 300222, China.
Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware 19716, United States.
ACS Omega. 2020 Mar 31;5(14):8090-8096. doi: 10.1021/acsomega.0c00224. eCollection 2020 Apr 14.
We developed an experimental metrology for measuring local strain in molecular beam epitaxially (MBE) grown crystalline chalcogenide thin films through micro-Raman spectroscopy. For InSe and BiSe on c-plane sapphire substrates, the transverse-optical vibrational mode (A phonon) is most sensitive to strain. We first calibrated the phonon frequency-strain relationship in each material by introducing strain in flexible substrates. The Raman shift-strain coefficient is -1.97 cm/% for the InSe A(LO + TO) mode and -1.68 cm/% for the BiSe A mode. InSe and BiSe samples exhibit compressive strain and tensile strain, respectively. The observations are compliant with predictions from the opposite relative thermal expansion coefficient between the sample and the substrate. We also map strain cartography near the edge of as-grown MBE samples. In InSe, the strain accumulates with increasing film thickness, while a low strain is observed in thicker BiSe films.
我们开发了一种实验计量方法，通过显微拉曼光谱测量分子束外延（MBE）生长的晶体硫族化物薄膜中的局部应变。对于在c面蓝宝石衬底上的InSe和BiSe，横向光学振动模式（A声子）对应变最为敏感。我们首先通过在柔性衬底中引入应变来校准每种材料中的声子频率-应变关系。InSe的A(LO + TO)模式的拉曼位移-应变系数为-1.97 cm/%，BiSe的A模式的拉曼位移-应变系数为-1.68 cm/%。InSe和BiSe样品分别表现出压缩应变和拉伸应变。这些观察结果与样品和衬底之间相反的相对热膨胀系数的预测相符。我们还绘制了生长态MBE样品边缘附近的应变分布图。在InSe中，应变随着膜厚度的增加而累积，而在较厚的BiSe薄膜中观察到低应变。
