Self-Assembled Surface Oxidation Nanostructure on CoPd Thin Film: Magnetism and Morphology Evolution
Chuan-Che Hsu1*, Po-Chun Chang1, Yu-Chan Chen1, Hsiang-Chih Chiu1, Wen-Chin Lin1
1Department of Physics, National Taiwan Normal University, Taipei, Taiwan
* presenting author:Chuan-Che Hsu,
Self-assembled nano-dot arrays were observed by atomic force microscope (AFM) in 10-20 nm CoPd/Al2O3 (0001) thin films. The height and lateral size of the nano-dots ranged 10-20 nm and 200-400 nm respectively. Due to the non-uniform stiffness distribution, the phase image indicated the appearance of fine structures on the nano-dot surface. When the AFM tip was applied with a bias voltage, The dark color area in current image resembled the nano-dots distributions, indicating the insulating property of the nano-dots while the flat area was still conductive. This self-assembled nano-dot array evolved with the waiting time period between the thin film deposition and AFM characterization. The corresponding magnetic behavior was investigated by magneto-optical Kerr effect (MOKE) with the variation of measurement temperature and hydrogen pressure in the environment, as the possible effects from antiferromagnetic Co-oxide and Pd-catalyzed hydrogen absorption were considered. In order to analyze the composition of the nano-dots, further microscopic characterization was carried out by Auger mapping microscopy, transmission electron microscopy (TEM) and scanning photoemission electron microscopy (SPEM). Similar self-assembled nanostructures are supposed to appear on other metallic thin films, which might be the origin of the reported time-dependent evolution of magnetism or other physical properties.

Keywords: Self-assembled nano-dot, atomic force microscope , magneto-optical Kerr effect, Co-oxide