Rational control of WSe layer number via hydrogen-controlled chemical vapor deposition.

Tranistion metal dichalcogenides are a promising family of materials for electronics and optoelectronics, in part due to their range of bandgaps that can be modulated by layer number. Here, we show that WSe can be selectively grown with one, two, or three layers, as regulated by a one-step hydrogen-controlled chemical vapor deposition (H-CVD) process involving cyclical pulses of H flow. The physical and vibrational properties of the resulting mono-, bi-, and tri-layer WSe films are characterized by atomic force microscopy and Raman spectroscopy.

MoTe Lateral Homojunction Field-Effect Transistors Fabricated using Flux-Controlled Phase Engineering.

The coexistence of metallic and semiconducting polymorphs in transition-metal dichalcogenides (TMDCs) can be utilized to solve the large contact resistance issue in TMDC-based field effect transistors (FETs). A semiconducting hexagonal (2H) molybdenum ditelluride (MoTe) phase, metallic monoclinic (1T') MoTe phase, and their lateral homojunctions can be selectively synthesized by chemical vapor deposition due to the small free energy difference between the two phases. Here, we have investigated, in detail, the structural and electrical properties of -grown lateral 2H/1T' MoTe homojunctions grown using flux-controlled phase engineering.

Aligned MoO/MoS and MoO/MoTe Freestanding Core/Shell Nanoplates Driven by Surface Interactions.

Controlling the growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is an important step toward utilizing these materials for either electronics or catalysis. Here, we report a new surface-templated growth method that enables the fabrication of MoO/MoS and MoO/MoTe core/shell nanoplates epitaxially aligned on (0001)-oriented 4H-silicon carbide and sapphire substrates. These heterostructures are characterized by a variety of techniques to identify the chemical and structural nature of the interface.

In-Plane 2H-1T' MoTe Homojunctions Synthesized by Flux-Controlled Phase Engineering.

The fabrication of in-plane 2H-1T' MoTe homojunctions by the flux-controlled, phase-engineering of few-layer MoTe from Mo nanoislands is reported. The phase of few-layer MoTe is controlled by simply changing Te atomic flux controlled by the temperature of the reaction vessel. Few-layer 2H MoTe is formed with high Te flux, while few-layer 1T' MoTe is obtained with low Te flux.

Seed Crystal Homogeneity Controls Lateral and Vertical Heteroepitaxy of Monolayer MoS2 and WS2.

Heteroepitaxy between transition-metal dichalcogenide (TMDC) monolayers can fabricate atomically thin semiconductor heterojunctions without interfacial contamination, which are essential for next-generation electronics and optoelectronics. Here we report a controllable two-step chemical vapor deposition (CVD) process for lateral and vertical heteroepitaxy between monolayer WS2 and MoS2 on a c-cut sapphire substrate. Lateral and vertical heteroepitaxy can be selectively achieved by carefully controlling the growth of MoS2 monolayers that are used as two-dimensional (2D) seed crystals.