Hao Qiaoyan, Yi Huan, Su Huimin, Wei Bin, Wang Zhuo, Lao Zhezhu, Chai Yang, Wang Zhongchang, Jin Chuanhong, Dai Junfeng, Zhang Wenjing
International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology , Shenzhen University , Shenzhen 518060 , P. R. China.
Department of Physics , Southern University of Science and Technology , Shenzhen 518055 , P. R. China.
Nano Lett. 2019 Apr 10;19(4):2634-2640. doi: 10.1021/acs.nanolett.9b00487. Epub 2019 Mar 11.
Two-dimensional material indium selenide (InSe) has offered a new platform for fundamental research in virtue of its emerging fascinating properties. Unlike 2H-phase transition-metal dichalcogenides (TMDs), ε phase InSe with a hexagonal unit cell possesses broken inversion symmetry in all the layer numbers, and predicted to have a strong second harmonic generation (SHG) effect. In this work, we find that the as-prepared pure InSe, alloyed InSeTe and InSeS ( x = 0.1 and 0.2) are ε phase structures and exhibit excellent SHG performance from few-layer to bulk-like dimension. This high SHG efficiency is attributed to the noncentrosymmetric crystal structure of the ε-InSe system, which has been clearly verified by aberration-corrected scanning transmission electron microscopy (STEM) images. The experimental results show that the SHG intensities from multilayer pure ε-InSe and alloyed InSeTe and InSeS ( x = 0.1 and 0.2) are around 1-2 orders of magnitude higher than that of the monolayer TMD systems and even superior to that of GaSe with the same thickness. The estimated nonlinear susceptibility χ of ε-InSe is larger than that of ε-GaSe and monolayer TMDs. Our study provides first-hand information about the phase identification of ε-InSe and indicates an excellent candidate for nonlinear optical (NLO) applications as well as the possibility of engineering SHG response by alloying.
二维材料硒化铟（InSe）凭借其新出现的迷人特性为基础研究提供了一个新平台。与2H相过渡金属二硫属化物（TMDs）不同，具有六边形晶胞的ε相InSe在所有层数中都具有破缺的反演对称性，并预计具有很强的二次谐波产生（SHG）效应。在这项工作中，我们发现所制备的纯InSe、合金化的InSeTe和InSeS（x = 0.1和0.2）为ε相结构，并且从少层到块状尺寸都表现出优异的SHG性能。这种高SHG效率归因于ε-InSe体系的非中心对称晶体结构，这已通过像差校正扫描透射电子显微镜（STEM）图像得到明确验证。实验结果表明，多层纯ε-InSe以及合金化的InSeTe和InSeS（x = 0.1和0.2）的SHG强度比单层TMD体系高约1 - 2个数量级，甚至优于相同厚度的GaSe。估计的ε-InSe的非线性极化率χ大于ε-GaSe和单层TMDs的非线性极化率χ。我们的研究提供了关于ε-InSe相识别的第一手信息，并表明其是一种用于非线性光学（NLO）应用的优秀候选材料，以及通过合金化调控SHG响应的可能性。
