Highly crystalline synthesis of tellurene sheets on two-dimensional surfaces: Control over helical chain direction of tellurene

Recent results have identified two-dimensional (2D) tellurene as a potential van der Waals (vdW) material for thermoelectric and optoelectronics applications owing to their pseudo-one-dimensional (anisotropic) behavior and structure. While hydrothermal synthesis is suitable for yielding potentially crystalline materials, it is well known for its incompatibility with manufacturing and scaling. There is an urgent need for synthesis of tellurene sheets in vdW layered form with the desired crystallinity as well as controlled crystalline anisotropy using more conventional and scalable processes. Here, we report on the synthesis of tellurene sheets onto a variety of surfaces of vdW-bonded 2D layered crystals in their trigonal layered form with controlled tellurene chain (anisotropy) direction using horizontal physical vapor deposition method. Our systematic tellurene growth studies on six different vdW surfaces show that GaS and GaSe surfaces enable highly crystalline and self-oriented tellurene sheets. Detailed cross-sectional transmission electron microscopy (TEM), angle-resolved Raman spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy measurements provide fundamental insights into the growth dynamics and characteristics of tellurene. First-principles calculations and cross-sectional TEM measurements suggest that tellurene chains are well-oriented along the GaSe armchair lattice direction owing to the much-reduced total energy of the system and a stronger degree of coupling across adjacent layers. Synthesized tellurene sheets exhibit remarkable structural anisotropy, as evidenced by angle-resolved Raman measurements, and the overall results open a clear pathway for layer-by-layer growth of tellurene sheets with controlled crystalline anisotropy using conventional synthesis techniques.