Capturing Wetting States in Nanopatterned Silicon

Abstract

Spectacular progress in developing advanced Si circuits with reduced size, along the track of Moore's law, has been relying on necessary developments in wet cleaning of nanopatterned Si wafers to provide contaminant free surfaces. The most efficient cleaning is achieved when complete wetting can be realized. In this work, ordered arrays of silicon nanopillars on a hitherto unexplored small scale have been used to study the wetting behavior on nanomodulated surfaces in a substantial range of surface treatments and geometrical parameters. With the use of optical reflectance measurements, the nanoscale water imbibition depths have been measured and the transition to the superhydrophobic Cassie-Baxter state has been accurately determined. For pillars of high aspect ratio (about 15), the transition occurs even when the surface is grafted with a hydrophilic functional group. We have found a striking consistent deviation between the contact angle measurements and the straightforward application of the classical wetting models. Molecular dynamics simulations show that these deviations can be attributed to the long overlooked atomic-scale surface perturbations that are introduced during the nanofabrication process. When the transition condition is approached, transient states of partial imbibition that characterize intermediate states between the Wenzel and Cassie-Baxter states are revealed in our experiments.

Effect of Nanoparticles on Spontaneous Imbibition of Water into Ultraconfined Reservoir Capillary by Molecular Dynamics Simulation

“…Imbibition in porous media is ubiquitous and has numerous applications in many natural and industrial processes, such as groundwater remediation, oil recovery, and nanofluidic devices [1][2][3][4][5][6][7]. For the imbibition phenomena, capillary action is the main transport mechanism for the spontaneous process, which results in the diffusing motion of fluid into porous solids or the capillary [8][9][10][11].…”

Symmetric and Asymmetric Meniscus Collapse in Wetting Transition on Submerged Structured Surfaces

“…However, the liquid-gas interfaces of the air pockets are subject to instabilities induced by various factors including vibration, 12 evaporation, [13][14][15] air diffusion, [16][17][18] pressurization, 19,20 geometrical parameters, 21,22 electrowetting 23,24 and impact, 25,26 leading to the fully-wetted Wenzel (W) state 27 and the failure of superhydrophobicity. The dynamic process of wetting transition from the CB to the W state has been captured by various techniques, such as light reflection, 16,18,[28][29][30] optical diffraction, 31,32 X-ray 33 and confocal microscopy. 17,[34][35][36][37][38] Understanding this phenomenon is critical for the regulation and improvement of CB-based superhydrophobicity and conducive to the design of underwater structured surfaces with enhanced lifetime.…”

The mechanism for the motion of nanoscale water droplet induced by wetting gradient: A molecular dynamic study

“…Benefitting from the rapid development in computational power, molecular dynamics simulations have been widely used to explore the microscopic interactions at atomic level [32][33][34][35]. Koishi et al [36] studied the transition behavior between Wenzel state and Cassie state of water nanodroplet on periodic nanopillared hydrophobic surfaces, and the microscopic mechanism for the transformation of two states were investigated by computing the free-energy barrier.…”