High-quality single crystalline 2H-NbSe2 grown by iodine-assisted chemical vapor transport

Two-dimensional materials are attractive in electronics, energy and optics due to their fascinating physical properties. Appropriate fabrication methods and optimized process parameters are critical for improving crystal quality and achieving precise control over the structure and properties of these materials. Here, 2H-NbSe 2 single crystals were synthesized via a chemical vapor transport (CVT) process using iodine as the transport agent in a dual-zone tube furnace. The structural, chemical compositions, electrical, and magneto-transport properties of the synthesized crystals were comprehensively investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that the crystals were well-crystallized in a single-phase hexagonal lattice configuration, consistent with the typical van der Waals layered characteristics. The Raman spectra displayed characteristic peaks for NbSe 2 . The atomic ratio of Nb: Se in the crystals was approximately 1:2. The residual resistivity ratio ( RRR ) value (18), transition temperature ( T C ≈ 7 K) and transition width (Δ T ) of 0.26 K obtained from temperature-dependent resistance measurements indicate good crystal quality. Magneto-transport measurements revealed a distinct anisotropy between in-plane and out-of-plane magnetic field directions, resulting in typically different upper critical fields ( H c 2 ). This work presents a straightforward and effective iodine-assisted CVT method for growing high-quality NbSe₂ crystals, offering fundamental and technological significance for the growth and application of two-dimensional materials.