Complex roughening dynamics and wettability mechanism in MoS2 thin films — A system theoretic approach

We utilized fractal geometry to advance insights into the complex roughening and its facilitated wettability mechanism of sputtered MoS2 film surfaces with varying thickness are studied. Fractal parameters indicate the dominance of shadowing at lower thickness while enhancement in vertical growth rate and variation in local irregularities are observed at higher thicknesses along with anomalous roughening up to thickness of 200 nm. In addition, anti-persistent trend of surface heights was observed to be independent of thickness. Multifractal analysis exposed the non-linear variation in multifractality strength and vertical complexities of surface heights. The results corroborates the stereometric analysis revealing the 3D surface topography of analyzed films. The wettability was observed to increase with thickness. In consideration, the roughening expedited wetting trend is defined in light of stereometric parameters and multifractility strength suggesting increases the penetration of water droplets into the surface voids with decline in the surface complexities. The mechanism for increase in contact angle is realized from the augmentation in curvature pressure indicating the existence of large air pressure within the void lying lower than the water droplets as compared to the pressure from the meniscus sides of the droplets. In addition, principal component analysis is utilized to reveal the significance of fractal parameters in probing the surface roughening. The results hold prospects in surface engineering of MoS2 thin films as a function of thickness for enhanced catalytic activity in electrochemical splitting of water for hydrogen evolution reactions.