Synthesis of Atomically Thin <inline-formula><tex-math>${\bf MoS}_{\bf 2}$</tex-math></inline-formula> Triangles and Hexagrams and Their Electrical Transport Properties

Abstract

Atomically thin molybdenum disulfide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>$({\rm MoS}_{2})$</tex-math></inline-formula> triangles and hexagrams were prepared by a two-step growth ambient pressure chemical vapor deposition (APCVD) process. Molybdenum Trioxide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>$({\rm MoO}_{3})$</tex-math></inline-formula> nanobelts, a few microns in length and width, were prepared using a hydrothermal technique and utilized as the starting material. High temperature treatment of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>${\rm MoO}_{3}$</tex-math></inline-formula> nanobelts followed by a rigorous sulfurization via APCVD processing provided different morphologies of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>${\rm MoS}_{2}$</tex-math></inline-formula> monolayers and bilayer (BL) sheets. Triangle and hexagram morphologies were characterized using Raman spectroscopy, photoluminescence (PL) measurements, scanning electron microscopy and atomic force microscopy (AFM). The regrowth step in the CVD process was proven to be ideal in enlarging the grain size. PL and Raman spectroscopy and AFM results confirmed the presence of monolayer and BL regions in the regrowth growth process. Triangle and hexagram domains are observed to be cooperatively nucleating and coalescing together to form large-area layers. Furthermore, the electrical transport properties of the synthesized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>${\rm MoS}_{2}$</tex-math></inline-formula> layers were studied. Electron mobility based on back gated field effect transistors was measured to be approximately 0.02 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>${\rm cm}^{2}$</tex-math></inline-formula> /V. S.