Understanding the Intrinsic Water Wettability of Molybdenum Disulfide (MoS₂)

Abstract

2D semiconductors allow for unique and ultrasensitive devices to be fabricated for applications ranging from clinical diagnosis instruments to low-energy light-emitting diodes (LEDs). Graphene has championed research in this field since it was first fabricated; however, its zero bandgap creates many challenges. Transition metal dichalcogenides (TMDCs), e.g., MoS2, have a direct bandgap which alleviates the challenge of creating a bandgap in graphene-based devices. Water wettability of MoS2 is critical to device fabrication/performance and MoS2 has been believed to be hydrophobic. Herein, we report that water contact angle (WCA) of freshly exfoliated MoS2 shows temporal evolution with an intrinsic WCA of 69.0 ± 3.8° that increases to 89.0 ± 3.1° after 1 day exposure to ambient air. ATR-FTIR and ellipsometry show that the fresh, intrinsically mildly hydrophilic MoS2 surface adsorbs hydrocarbons from ambient air and thus becomes hydrophobic.

Understanding the intrinsic water wettability of graphite

“…It is important to note that all experiments conducted by myself and my co-workers were taken on samples that were purchased new and once the sample got substantially thin it was replaced and no longer used for experiments. 62,70,[75][76][77] ZYA is the highest quality of HOPG and exfoliates nearly perfectly. Visually, there were no flakes or exfoliation-induced defects noticeable and all experimental testing was performed only on the visually pristine basal surface.…”

“…Using the data from MoS 2 (Section 6.5 on page 128), 70 r would have to be 20.5 for the WCA on fresh MoS 2 to be 89° (its generally accepted value). The projected surface area of the image was 2500 µm 2 (50x50 µm AFM scan).…”

“…determined using the b-spline model. 70,76 See Appendix A for details pertaining to the ellipsometry measurements.…”

Molecular Structure and Dynamics of Water on Pristine and Strained Phosphorene: Wetting and Diffusion at Nanoscale

“…The structure of water is perturbed heavily near the surfaces which have the potential to affect water diffusion1314 and proteins’ adsorption15. During recent years, the wetting and diffusive properties of water in contact with two-dimensional (2D) nanomaterials, such as graphene1617181920, boron-nitride sheets162122, WS 2 and MoS 2  2324, have attracted great attention. These studies have helped the promotion of potential applications of these 2D nanomaterials in both biomedicine and nanofluidics.…”

Tunable Wetting Property in Growth Mode-Controlled WS2 Thin Films

“…Furthermore, to understand the influence of airborne contaminants [32, 34], we repeated the CA measurements after keeping the samples in ambient conditions for 20 days, to exceed the air exposure saturation period of 1 week in the previous study [22]. As shown in the right-hand graphs of Fig.…”