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

Suhyeon Kim, Jinhwan Lee, Gangtae Jin, Moon-Ho Jo, Changgu Lee, and Sunmin Ryu*

 

저차원 물질의 광산화 반응 메커니즘을 규명하는 것은 기초 과학 연구로서 의미가 있을 뿐만 아니라 응용 장치 개발을 위해서도 필수적인 실정이다. 본 연구에서는 라만 분광법 (Raman spectroscopy) 및 AFM imaging을 이용하여 이차원 자성 반도체 결정인 CrPS₄의 광산화 반응을 고찰하였다. 라만 분광법을 이용해 광산화 반응을 일으킴과 동시에 다양한 기체 환경에서 광산화 속도를 정량함으로서 그 반응 메커니즘에 대해 최초로 보고 할 수 있었다. 광자를 받고 들뜬 CrPS₄가 바닥상태의 산소 (³O₂)로 에너지 전달을 통해 반응성이 큰 일중항 산소 (¹O₂)를 생성하게 되고 이로 인해 CrPS₄가 광산화 될 것이라 제안하였다. 본 결과는 2019년 5월 10일 Nano Letters에 게재되었다.

 

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.

 

https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b01417