Electronic Development in Self-assembled Co Nanoparticles on Al2O3/NiAl(100)
Cheng-Hao Chuang (莊程豪)1, Chia-Hao Chen (陳家浩)2, Wen-Chin Lin (林文欽)1,
Shen-Shing Wong (翁聖勛)1, Chih-Wei Peng (彭治維) 1,2, and Minn-Tsong Lin (林敏聰)1,3
1
Department of Physics, National Taiwan University, Taipei, Taiwan
National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
2
Self-assembled magnetic Co nanoparticles can be formed on an isolated Al2O3 surface on
NiAl(100) single crystal. Based on the statistic study of different coverage, which showed that up to
2 monolayers (ML), the size distribution of Co nanoparticles is rather narrow and the nanoparticles
are well-aligned on the Al2O3 surface. The XPS data showed that the Co nano-dots do not directly
affect the NiAl(100) through the AlOisolation layers. However, the Co 3p and Al 2p of Al2O3
component shift toward the lower binding energy with increasing Co coverage up to 20 ML. This
may due to the charge redistribution or screening effect in the nanoparticle system. Moreover, we
exposed oxygen to 20 ML and 0.5ML Co of coverage. The Co 3p peak and the valence band in 20
ML Co are significantly modified by oxidation, as compared with the clean 20 ML
Co/Al2O3/NiAl(100). In the case of 0.5 ML Co nano-dots, the spectra of valence band before and
after oxidation hold similar features. But the Co 3p peak shifts to the higher binding energy after
oxidation, similar to the case in 20 ML Co. The different phenomena between 0.5 ML nano-dots
and 20ML thick layers after exposing to oxygen may come from the different size of Co
nanoparticles or the amount of oxygen exposure.