Residual-Strain-Induced Transport Anisotropy in Chemical Vapor Deposition-Grown Monolayer Molybdenum Disulfide.

Abstract

Chemical vapor deposition (CVD) is a leading route for scalable integration of two-dimensional semiconductors, but growth can also introduce hidden symmetry-breaking fields absent in ideal crystals. Here, we show that CVD-grown monolayer MoS₂, a material expected to exhibit isotropic in-plane transport, develops a pronounced directional charge-transport response due to the built-in residual strain. Angle-resolved electrical measurements reveal an electron-current anisotropy approaching a factor of 2. Comparative studies using as-grown triangular flakes, lithographically reshaped circular channels, and transferred flakes indicate that asymmetric contact geometry is not the dominant origin and instead identify the as-grown interfacial mechanical state as the key source of the anisotropy. Optical and spectroscopic analyses, including self-assembled nanoscroll formation, second-harmonic generation, and polarization-dependent Raman spectroscopy, consistently indicate a built-in in-plane strain field and show that the tensile-loading direction aligns with the transport-enhanced axis. A thermal expansion mismatch estimate supports a residual tensile strain of about 0.5% after growth and cooldown on SiO₂/Si. First-principles calculations further show that tensile loading breaks the in-plane symmetry of monolayer MoS₂ and produces a modest intrinsic conductivity anisotropy. These results identify residual strain as an underappreciated origin of transport anisotropy in CVD monolayer MoS₂.