via Organic-Inorganic Encapsulation*

2D transition metal halides have recently attracted significant attention due to their thickness dependent magnetism and electrical control of magnetic order. However, this class of materials is extremely reactive chemically, leading to rapid irreversible degradation upon ambient exposure. Here we demonstrate long-term encapsulation of the prototypical 2D transition metal halide CrI₃ by using atomic layer deposition (ALD) of alumina that is seeded with an organic buffer layer of perylenetetracarboxylic dianhydride (PTCDA). We show that this protocol allows for long-term encapsulation of CrI₃ and preserves the structure and magnetic order down to monolayer thickness. In the absence of the PTCDA buffer layer, the ALD precursors damage the CrI₃ top layer as revealed by X-ray photoelectron spectroscopy and thickness dependent magneto-optical Kerr-effect measurements. With this hybrid organic-inorganic encapsulation protocol, we demonstrate field-effect transistors, photodetectors, and optothermal measurements of CrI₃ thermal conductivity in ambient conditions. Ongoing efforts to extend this methodology to charge transport measurements of additional 2D transition metal halides will also be discussed.