Two-dimensional transitional metal halides have recently attracted significant attention due to their thickness-dependent and electrostatically tunable magnetic properties. However, this class of materials is highly reactive chemically, which leads to irreversible degradation and catastrophic dissolution within seconds in ambient conditions, severely limiting subsequent characterization, processing, and applications. Here, we impart long-term ambient stability to the prototypical transition metal halide CrI3 by assembling a noncovalent organic buffer layer, perylenetetracarboxylic dianhydride (PTCDA), which templates subsequent atomic layer deposition (ALD) of alumina. X-ray photoelectron spectroscopy demonstrates the necessity of the noncovalent organic buffer layer since the CrI3 undergoes deleterious surface reactions with the ALD precursors in the absence of PTCDA. This organic-inorganic encapsulation scheme preserves the long-range magnetic ordering in CrI3 down to the monolayer limit as confirmed by magneto-optical Kerr effect measurements. Furthermore, we demonstrate field-effect transistors, photodetectors, and optothermal measurements of CrI3 thermal conductivity in ambient conditions.

2D magnetic materials hold promise for quantum and spintronic applications. 2D antiferromagnetic materials are of particular interest due to their relative insensitivity to external magnetic fields and higher switching speeds compared to 2D ferromagnets. However, their lack of macroscopic magnetization impedes detection and control of antiferromagnetic order, thus motivating magneto‐electrical measurements for these purposes. Additionally, many 2D magnetic materials are ambient‐reactive and electrically insulating or highly resistive below their magnetic ordering temperatures, which imposes severe constraints on electronic device fabrication and characterization. Herein, these issues are overcome via a fabrication protocol that achieves electrically conductive devices from the ambient‐reactive 2D antiferromagnetic semiconductor NiI2. The resulting gate‐tunable transistors show band‐like electronic transport below the antiferromagnetic and multiferroic transition temperatures of NiI2, revealing a Hall mobility of 15 cm2 V−1 s−1 at 1.7 K. These devices also allow direct electrical probing of the thickness‐dependent multiferroic phase transition temperature of NiI2 from 59 K (bulk) to 28 K (monolayer).

Transition metal dichalcogenides (TMDs) are a promising solid-state platform for single photon emission. The versatile fabrication methods afforded by their two-dimensional nature facilitate the integration of TMDs into optoelectronic devices where localized exciton states can be electrically pumped. While this functionality is highly desirable for applications in quantum nanophotonics, enabling more compact and scalable devices, the lack of control of emitter spatial positions and energies has impeded the integration of TMDs into quantum optical systems. Here we demonstrate single photon electroluminescence from monolayer WSe 2 in a lateral gate-defined junction that allows the electrostatic environment to be tuned in situ. By utilizing local strain engineering, we reliably position bright localized exciton states in the optically active region of the gate-defined junction, enabling the deterministic creation of devices that predominantly produce single photon emission. Modulation of the gate voltages tunes the emission between different electrostatic regimes, revealing a new localized exciton state that exhibits a gate-dependent redshift. A spectral shift of the electroluminescence of over 10 meV is achieved, demonstrating the capability for simultaneous electrical pumping and tuning of localized exciton emission in TMD devices.