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 μm and thickness down to monolayer (∼0.59 nm) and bilayer (∼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.