Dewetting of Co thin films in water driven by ns pulsed laser

• Published in: Japanese Journal of Applied Physics Vol. 59; no. 11; pp. 115003 - 115008
• Main Authors: Choi, Jung Won, Oh, Ho Jun, Noh, Do Young, Kang, Hyon Chol
• Format: Journal Article
• Language: English
• Published: Tokyo IOP Publishing 01.11.2020; Japanese Journal of Applied Physics
• Subjects: Co thin films; CoO nanowalls; Dissolution; Drying; Grooving model; Laser-induced dewetting; Laser-induced hydrothermal process; Lasers; Nanoparticles; Oxidation; Pulsed lasers; Reduction; Sapphire; Substrates; Thin films
• ISSN: 0021-4922; 1347-4065
• DOI: 10.35848/1347-4065/abc2e0

We report on the pulsed laser-induced dewetting (LID) process of Co/sapphire(0001) thin films in water environment. In contrast to LID in a vacuum, where only Co nanoparticles (NPs) are formed, a 12 nm thick Co film was dewetted into a mixture of crystalline CoO NPs and nanowalls (NWs). The formation of the CoO NPs can be explained by the grooving model occurring concurrent with the oxidation of Co to CoO. Possible scenarios for the formation of NWs are proposed. The dissolution of Co into water occurred near the hole area. Upon subsequent laser irradiation, Co 2 + and O2− ions abundant in water facilitate the laser-induced hydrothermal process (LIHP) producing CoO NWs. Furthermore, we found that the combination of dissolution and LIHP is energetically more favorable over dewetting in a 4.8 nm thick sample, where only CoO NWs were observed. Finally, the reduction of sapphire substrate is revealed by the formation of Al-rich NPs.