Large Metallic Vanadium Disulfide Ultrathin Flakes for Spintronic Circuits and Quantum Computing Devices

Atmospheric pressure chemical vapor deposition (APCVD) is employed for the synthesis of layered vanadium disulfide. By tuning several critical growth parameters, we achieve VS2 flakes with lateral dimension over 100 mu m and thickness down to monolayer (similar to 0.59 nm) and bilayer (similar to 1.17 nm), which are larger and thinner than those previously reported in the literature. Furthermore, ultrathin flakes with thicknesses of several atomic layers are directly synthesized on mica and SiO2 substrates without the use of an exfoliation method. X-ray diffraction and high-resolution transmission electron microscopy confirm the flakes' monocrystalline quality. Raman spectra are collected and are consistent with the vibrational modes for the trigonal phase of VS2 as determined by density functional theory calculations. Through electron backscatter diffraction pole figure analysis, transmission electron microscopy, and optical microscopy, a complex epitaxial relationship with nine preferred in-plane orientations is observed in some regions of the VS2/mica samples. Remarkably, this is in agreement qualitatively with a superlattice area mismatch model, providing further evidence of the interfacial interactions with mica dictating the nucleation of film atoms in van der Waals heterostructures. Finally, magnetic force microscopy measurements suggest room-temperature ferromagnetism in ultrathin VS2 flakes, in agreement with several density functional theory calculations. The discovery of an ultrathin ferromagnetic metal such as VS2 may have an impact on emerging fields such as spintronics and quantum computing.