Thickness-Dependent Optical Properties and In-Plane Anisotropic Raman Response of the 2D β-In2S3

Recent years have witnessed major advances in development of massive nonlayer structured ultrathin materials, providing great enrichment to the 2D nanomaterial family. The intriguing physical and chemical properties brought by nonlayered nanomaterials have attracted tremendous research interest. In this work, a systematica study of the optical properties of 2D nonlayered beta-diindium trisulfide (beta-In2S3) is reported. The thickness-dependent photoluminescence (PL), Raman spectra, and absorption property are measured for ultrathin beta-In2S3 flakes and found distinguished from its bulk counterpart. These peculiar features originate from the superficial indium oxide in ultrathin beta-In2S3, as revealed by low-temperature PL and X-ray photoelectron spectroscopy measurement. The Raman vibration modes are identified by Raman spectra measurements combined with calculations using density functional theory. Importantly, the tetragonal beta-In2S3 flakes exhibit strong in-plane anisotropic Raman response under the angle-resolved polarized Raman spectroscopy measurements. The results in this paper provide an in-depth understanding of the emerging 2D nonlayered material In2S3 and pave a fundamental step for its potential applications in future electronics and optoelectronics.