Crossover between Photochemical and Photothermal Oxidations of Atomically Thin Magnetic Semiconductor CrPS4

TL;DR

This study uncovers a thickness-dependent switch between photochemical and photothermal oxidation mechanisms in atomically thin CrPS4, revealing unique reaction sensitivities and proposing protective encapsulation strategies.

Contribution

It is the first to identify a crossover between photochemical and photothermal oxidation mechanisms in 2D CrPS4, with detailed mechanistic insights and protective measures.

Findings

CrPS4 exhibits a lower threshold power density than MoS2.

Distinct power dependences in reaction cross section at different regimes.

Encapsulation with Al2O3 effectively prevents oxidation.

Abstract

Many two-dimensional (2D) semiconductors represented by transition metal dichalcogenides have tunable optical bandgaps in the visible or near IR-range standing as a promising candidate for optoelectronic devices. Despite this potential, however, their photoreactions are not well understood or controversial in the mechanistic details. In this work, we report a unique thickness-dependent photoreaction sensitivity and a switchover between two competing reaction mechanisms in atomically thin chromium thiophosphate (CrPS4), a two-dimensional antiferromagnetic semiconductor. CrPS4 showed a threshold power density 2 orders of magnitude smaller than that for MoS2 obeying a photothermal reaction route. In addition, reaction cross section quantified with Raman spectroscopy revealed distinctive power dependences in the low and high power regimes. On the basis of optical in situ thermometric measurements and control experiments against O2, water, and photon energy, we proposed a photochemical oxidation mechanism involving singlet O2 in the low power regime with a photothermal route for the other. We also demonstrated a highly effective encapsulation with Al2O3 as a protection against the destructive photoinduced and ambient oxidations.