Chemical Vapor Transport Synthesis and Ambient Stability of 1D WTe₂ van der Waals Crystals

The recent development of 1D van der Waals (vdW) crystals enables the exploration of new physics and new designs in photonic and electronic devices. However, because of the large variation in the material library, synthesizing and understanding these 1D vdW crystals are still in an early stage compared to their 2D counterparts. Here, a chemical vapor transport (CVT) synthesis route is proposed to produce 1D WTe₂ vdW crystals with controlled small diameters ranging from 2 to 20 nm. These 1D crystals exhibit high crystallinity, high phase purity and strong anisotropic optical responses. We also systematically studied the stability of these materials in the ambient environment and observed that 1D WTe₂ vdW crystals undergo rapid oxidation within 10 min. The ambient-generated oxide layer on a 1D WTe₂ formed a natural WTe₂/O-WTe₂ heterojunction, which gave rise to a negative photoconductive effect, resulting in two different transport properties in the temperature range of 40-300K. These findings shed light on the suppression of photoexcitation conductivity and offered a framework for studying other 1D vdW materials, particularly these interesting but less explored Te-group crystals.