Chromium Trihalides CrX3 (X = Cl, Br, I): Direct Deposition of Micro‐ and Nanosheets on Substrates by Chemical Vapor Transport

다국어 초록 (Multilingual Abstract)

The experimental observation of intrinsic ferromagnetism in single layered chromium trihalides CrX3 (X = Cl, Br, I) has gained outstanding attention recently due to their possible implementation in spintronic devices. However, the reproducible preparation of highly crystalline chromium(III) halide nanolayers without stacking faults is still an experimental challenge. As chromium trihalides consist of adjacent layers with weak interlayer coupling, the preparation of ultrathin CrX3 nanosheets directly on substrates via vapor transport proves as an advantageous synthesis technique. It is demonstrated that vapor growth of ultrathin highly crystalline CrX3 micro‐ and nanosheets succeeds directly on yttrium stabilized zirconia substrates in a one‐step process via chemical vapor transport (CVT) in temperature gradients of 100 K (600 °C → 500 °C for CrCl3 and 650 °C → 550 °C for CrBr3 or CrI3) without a need for subsequent delamination. Due to simulation results, optimization of synthesis conditions is realized and phase pure CrX3 nanosheets with thicknesses ≤25 nm are obtained via short term CVT. The nanosheets morphology, crystallinity, and phase purity are analyzed by several techniques, including microscopy, diffraction, and spectroscopy. Furthermore, a potential subsequent delamination technique is demonstrated to give fast access to CrX3 monolayers using the example of CrCl3.
Preparation of highly crystalline, phase pure, and as‐grown CrX3 (X = Cl, Br, I) micro‐ and nanostructures directly on substrates by short term chemical vapor transport (CVT) is demonstrated. A rational synthesis planning by modeling of the vapor transport leads to the targeted formation of nanolayers with thicknesses less than 25 nm down to the monolayer limit.