Surface Energy Engineering for Tunable Wettability through Controlled Synthesis of MoS₂

TLDR

MoS₂, a transition‑metal dichalcogenide, is emerging as a 2D material for low‑power electronics and optoelectronics, yet how its nanoscale surface energy and wettability depend on crystallinity and orientation remains unclear. This study synthesizes large‑area MoS₂ thin films on insulating substrates with controlled surface morphology by varying growth temperatures to investigate their wettability. The films were characterized by TEM, Raman spectroscopy, and contact‑angle measurements, linking nanoscale crystallinity to wettability. The few‑layer MoS₂ surface energy is ~46.5 mJ m⁻², and thinner layers exhibit higher contact angles, providing insight into MoS₂–water interactions for microfluidic device design.

Abstract

MoS2 is an important member of the transition metal dichalcogenides that is emerging as a potential 2D atomically thin layered material for low power electronic and optoelectronic applications. However, for MoS2 a critical fundamental question of significant importance is how the surface energy and hence the wettability is altered at the nanoscale in particular, the role of crystallinity and orientation. This work reports on the synthesis of large area MoS2 thin films on insulating substrates (SiO2/Si and Al2O3) with different surface morphology via vapor phase deposition by varying the growth temperatures. The samples were examined using transmission electron microscopy and Raman spectroscopy. From contact angle measurements, it is possible to correlate the wettability with crystallinity at the nanoscale. The specific surface energy for few layers MoS2 is estimated to be about 46.5 mJ/m2. Moreover a layer thickness-dependent wettability study suggests that the lower the thickness is, the higher the contact angle will be. Our results shed light on the MoS2–water interaction that is important for the development of devices based on MoS2 coated surfaces for microfluidic applications.