Structural and optical properties of single- and few-layer magnetic semiconductor CrPS4

TL;DR

This study characterizes the structural and optical properties of atomically thin CrPS4, a ternary antiferromagnetic semiconductor, revealing thickness-dependent vibrational and optical features with potential for future applications.

Contribution

First comprehensive analysis of the structural and optical properties of atomically thin CrPS4, including Raman spectroscopy and optical anisotropy, expanding understanding of ternary 2D magnetic semiconductors.

Findings

Thickness-dependent Raman vibrational modes

Strong in-plane optical birefringence

Thickness-dependent absorption and photoluminescence features

Abstract

Atomically thin binary 2-dimensional (2D) semiconductors exhibit diverse physical properties depending on their composition, structure and thickness. By adding another element in those materials, which will lead to formation of ternary 2D materials, the property and structure would greatly change and significantly expanded applications could be explored. In this work, we report structural and optical properties of atomically thin chromium thiophosphate (CrPS4), a ternary antiferromagnetic semiconductor. Its structural details were revealed by X-ray and electron diffractions. Transmission electron microscopy showed that preferentially-cleaved edges are parallel to diagonal Cr atom rows, which readily identified their crystallographic orientations. Strong in-plane optical anisotropy induced birefringence that also enabled efficient determination of crystallographic orientation using polarized microscopy. The lattice vibrations were probed by Raman spectroscopy for the first time and exhibited significant dependence on thickness of crystals exfoliated down to single layer. Optical absorption determined by reflectance contrast was dominated by d-d type transitions localized at Cr3+ ions, which was also responsible for the major photoluminescence peak at 1.31 eV. The spectral features in the absorption and emission spectra exhibited noticeable thickness-dependence and hinted a high photochemical activity for single layer CrPS4. The current structural and optical investigation will provide a firm basis for future study and application of this novel magnetic semiconductor.