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

• Main Authors: Jung Won Choi, Daseul Ham, Seonghyun Han, Do Young Noh, Hyon Chol Kang
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Nanomaterials
• Subjects: soft wetting; deformation of substrate surface; pulsed laser-induced dewetting; wetting ridge; Co thin films
• Online Access: https://www.mdpi.com/2079-4991/11/2/268

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°.