(Invited) Porous Silicon Studies of Prof. Yukio H. Ogata
Authors: Sakka Tetsuo , Fukami Kazuhiro 
Published: February 2020

In 1989 Prof. Yukio H. Ogata moved to Institute of Atomic Energy, Kyoto University from Nagoya Institute of Technology. Since then one of the authors (TS) worked with him in the same laboratory, and later the other author (KF) joined the group. In Kyoto University Yukio started his career as an associate professor in Prof. Iwasaki’s laboratory. Shortly later he was promoted to full professor to succeed Prof. Iwasaki after his retirement. Yukio majored electrochemistry when he was a student in Department of Industrial Chemistry, Kyoto University. Before 1989 he was working on electrolysis engineering in Prof. Hine’s laboratory in Nagoya Institute of Technology. He started porous silicon research in the Institute of Atomic Energy (later reorganized to Institute of Advanced Energy), where he spent 24 years in his carrier. The author (TS) is in honor to have spent 23 years with him in his laboratory.
To start porous silicon research, Yukio prepared a fume hood to handle HF solutions and made a potentiostat with an excellent technician Mr. Hotta. The only analytical tool we had at that time to look into porous silicon was FT-IR. Vibrational frequencies related to surface hydrogen species of porous silicon were easily detected, but the detailed assignment was not easy. In principle vibrational frequencies are calculated from the force field. Therefore, precise calculation of the vibrational frequency requires a precise calculation of the bond strength, and hence should be calculated quantum-mechanically. However, the calculation of the electronic structure of surface species is quite difficult, since they are bonded to solid and does not have a periodic boundary condition. To overcome this problem Yukio thought out a method, in which the electronic structure of a piece of truncated solid is calculated by ab initio molecular orbital method. This was successful in assigning the observed vibrational frequencies in detail [1]. Based on the FT-IR spectra long-term stability of the surface species, and hence the porous silicon layer itself, was investigated [2,3]. Later on, Yukio’s work on porous silicon extended to electrochemistry of metal deposition into porous silicon layer [4]. The deposition reaction is not simply explained by the diffusion processes of the intrusion of the metal ions into the pores and the release of the reaction products from the pores. It was found that the displacement reaction and the catalytic behavior of the deposited metal play important roles. In addition his research further extended to the clarification of the mechanism of pore formation [5], laser-assisted metal deposition [6], optimization of rugate structures [7], and many others. We would like to remember Prof. Yukio H. Ogata as a leading scientist in this field, and his diverse and informative achievements in the field of porous silicon research.
[1] Yukio Ogata, Hiroyuki Niki, Tetsuo Sakka, Matae Iwasaki, J. Electrochem. Soc., 142(1), 195-201 (1995).
[2] Yukio Ogata, Hiroyuki Niki, Tetsuo Sakka, Matae Iwasaki, J. Electrochem. Soc., 142(5), 1595-1601 (1995).
[3] Yukio H. Ogata, Fumio Kato, Takashi Tsuboi, Tetsuo Sakka, J. Electrochem. Soc., 145(7), 2439-2444 (1998).
[4] T. Tsuboi, T. Sakka, Y. H. Ogata, J. Appl. Phys. 83 (8), 4501-4506 (1998).
[5] D. Hamm, T. Sakka, Y. H. Ogata, Electrochemistry 71(10), 853-859 (2003).
[6] J. Sasano, P. Schmuki, T. Sakka, Y. H. Ogata, Electrochem. Solid State Lett. 7(5), G98-G101 (2004).
[7] M. S. Salem, M. J. Sailor, F. A. Harraz, T. Sakka, Y. H. Ogata, J. Appl. Phys. 100(8), 083520 (2006).