Pulsed Carrier Gas Assisted High-Quality Synthetic 3 R -Phase Sword-like MoS 2 : A Versatile Optoelectronic Material.

Synthesizing a material with the desired polymorphic phase in a chemical vapor deposition (CVD) process requires a delicate balance among various thermodynamic variables. Here, we present a methodology to synthesize rhombohedral (3 R )-phase MoS ₂ in a well-defined sword-like geometry having lengths up to 120 μm, uniform width of 2-3 μm and thickness of 3-7 nm by controlling the carrier gas flow dynamics from continuous mode to pulsed mode during the CVD growth process. Characteristic signatures such as high degree of circular dichroism (∼58% at 100 K), distinct evolution of low-frequency Raman peaks and increasing intensity of second harmonic signals with increasing number of layers conclusively establish the 3 R -phase of the material. A high value (∼844 pm/V) of second-order susceptibility for few-layer-thick MoS ₂ swords signifies the potential of MoS ₂ to serve as an atomically thin nonlinear medium. A field effect mobility of 40 cm ² /V-s and I _on / I _off ratio of ∼10 ⁶ further confirm the electronic-grade standard of this 3 R -phase MoS ₂ . These findings are significant for the development of emerging quantum electronic devices utilizing valley-based physics and nonlinear optical phenomena in layered materials.