Pulsed Carrier Gas Assisted High-Quality Synthetic 3<i>R</i>-Phase Sword-like MoS₂: A Versatile Optoelectronic Material.

Abstract

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<i>R</i>)-phase MoS₂ 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<i>R</i>-phase of the material. A high value (∼844 pm/V) of second-order susceptibility for few-layer-thick MoS₂ swords signifies the potential of MoS₂ to serve as an atomically thin nonlinear medium. A field effect mobility of 40 cm²/V-s and <i>I</i>_on/<i>I</i>_off ratio of ∼10⁶ further confirm the electronic-grade standard of this 3<i>R</i>-phase MoS₂. These findings are significant for the development of emerging quantum electronic devices utilizing valley-based physics and nonlinear optical phenomena in layered materials.