Raman Spectroscopy, Photocatalytic Degradation, and Stabilization of Atomically Thin Chromium Tri-iodide.

As a 2D ferromagnetic semiconductor with magnetic ordering, atomically thin chromium tri-iodide is the latest addition to the family of two-dimensional (2D) materials. However, realistic exploration of CrI-based devices and heterostructures is challenging due to its extreme instability under ambient conditions. Here, we present Raman characterization of CrI and demonstrate that the main degradation pathway of CrI is the photocatalytic substitution of iodine by water. While simple encapsulation by AlO, PMMA, and hexagonal BN (hBN) only leads to modest reduction in degradation rate, minimizing light exposure markedly improves stability, and CrI sheets sandwiched between hBN layers are air-stable for >10 days. By monitoring the transfer characteristics of the CrI/graphene heterostructure over the course of degradation, we show that the aquachromium solution hole-dopes graphene.