Space‐Confined Chemical Vapor Deposition Synthesis of Ultrathin HfS₂ Flakes for Optoelectronic Application

Abstract

Due to the predicted excellent electronic properties superior to group VIB (Mo and W) transition metal dichalcogenides (TMDs), group IVB TMDs have enormous potential in nanoelectronics. Here, the synthesis of ultrathin HfS 2 flakes via space-confined chemical vapor deposition, realized by an inner quartz tube, is demonstrated. Moreover, the effect of key growth parameters including the dimensions of confined space and deposition temperature on the growth behavior of products is systematically studied. Typical as-synthesized HfS 2 is a hexagonal-like flake with a smallest thickness of ≈1.2 nm (bilayer) and an edge size of ≈5 µm. The photodetector based on as-synthesized HfS 2 flakes demonstrates excellent optoelectronic performance with a fast photoresponse time (55 ms), which is attributed to the high-quality crystal structure obtained at a high deposition temperature and the ultraclean interface between HfS 2 and the mica substrate. With such properties HfS 2 holds great potential for optoelectronics applications.

Emerging in‐plane anisotropic two‐dimensional materials

“…Two‐dimensional (2D) materials are a category of materials artificially derived from layered crystals . In the in‐plane directions, the atoms are strongly bonded by covalent or ionic bonds to form atomic layers, while along the out‐of‐plane direction, these atomic layers are weakly held by van der Waals force.…”

Two‐dimensional heterostructure promoted infrared photodetection devices

“…The pristine single 2D materials are usually limited for real optoelectronics by the natural limitation such as low optical adsorption, inherent band structure, and density of states. Due to the nature of atomically thickness and weak van der Waals (vdW) force bonded intralayer, 2D materials provide the chance to design the dangling‐free interlayer architecture, or the 2D heterostructure (2DH) to solve short comings of pristine materials . The fabricated 2DHs are showing fascinating behaviors in the following aspects: (a) atomically thin thickness and no‐dangling surface give rise to the controllable generation, confinement, and transportion of photocarriers, (b) easily tunable band alignment, (c) ability to modulate the density of states, and (d) strength to leverage the merit from different materials.…”

Phase‐Engineered Growth of Ultrathin InSe Flakes by Chemical Vapor Deposition for High‐Efficiency Second Harmonic Generation

“…To date, the employment of a local environment within a confined space has become a common method, facilitating stable mass‐transfer in CVD processes . Within the space‐confined configuration constructed by two stacked mica substrates, the formation of stable laminar mass‐transport could be related to Reynolds number, defined as Re= ρνD / γ , in which ρ is the gas density, ν is the gas flow rate, D is the gap size, and γ is the coefficient of viscosity . Generally, the reactant concentrations and feeding rate are anticipated to decrease with the decrease of gap size, resulting in a small Re.…”