Nanoscale Soft Wetting Observed in Co/Sapphire during Pulsed Laser Irradiation

Abstract

Liquid drops on deformable soft substrates exhibit quite complicated wetting behavior as compared to those on rigid solid substrates. We report on a soft wetting behavior of Co nanoparticles (NPs) on a sapphire substrate during pulsed laser-induced dewetting (PLID). Co NPs produced by PLID wetted the sapphire substrate with a contact angle near 70°, which is in contrast to typical dewetting behavior of metal thin films exhibiting contact angles greater than 90°. In addition, a nanoscale γ-Al2O3 wetting ridge about 15 nm in size and a thin amorphous Al2O3 interlayer were observed around and beneath the Co NP, respectively. The observed soft wetting behavior strongly indicates that the sapphire substrate became soft and deformable during PLID. Moreover, the soft wetting was augmented under PLID in air due to the formation of a CoO shell, resulting in a smaller contact angle near 30°.

Static wetting of a barrel-shaped droplet on a soft-layer-coated fiber

“…The non-dimensional deformation of the soft layer of the fiber and the droplet profile are computed by solving the governing eqn ( 14), ( 15), ( 23) and ( 27) together with the conditions ( 16)-( 20), (22), and ( 24)-( 26) by using a finite element method (FEM). We discretize our non-dimensional variables with linear elements and solve the coupled equations using a Newton solver from the FEM library FEniCS.…”

“…1,2 The shape of deformation has been explored extensively in the last few decades; however, those studies have mainly focussed on situations of a droplet on a planar substrate. 1–25 Although there have been numerous studies of droplets on rigid fibers, 26–31 wetting on a rigid fiber coated with a soft layer has been far less investigated. 32 How this geometry modifies the deformation of the coated elastic layer remains unclear, which is the focus of this study.…”