How far can we go with laser combined STM?
Hidemi Shigekawa
Institute of Applied Physics, CREST-JST, University of Tsukuba, Tsukuba, Japan 305-8573
http://dora.bk.tsukuba.ac.jp“Smaller” and “Faster” are the main concepts in nanoscale science and technology. Indeed,
important and interesting phenomena in various systems, such as functional materials, electronicdevices, signal transfer in biosystems, and chemical reactions, are observed from the several tensof nanometers to the single-molecule range in space and from the several tens of picoseconds tosubpicosecond range in time. With the size reduction in structures, the difference in the electronicproperties, for example, caused by the structural nonuniformity in each element, has an ever morecrucial influence on macroscopic functions. And the direct observation of the characteristics,
which provides us with the basis for the macroscopic analysis of the results, is of greatimportance. Thus, for further advances, a method of exploring the transient dynamics of the local
quantum functions in organized small structures is eagerly desired. However, it is extremely
difficult to obtain spatial and temporal resolutions simultaneously on this scale. Therefore, it isnecessary to develop a new method, namely, new microscopy.
STM has an excellent spatial resolution on the subangstrom scale, which has satisfied
requirements in various fields. However, since its temporal resolution is limited by the circuit
bandwidth (~100 kHz), increasing its potential by, for example, combining its characteristics withthose of other techniques has been desired. One of the promising approaches is to control thematerial conditions, in STM measurement, using the techniques of quantum optics. Ultrashort
optical pulse technology has enabled us to observe transient phenomena in the femtosecond range,
the optical-monocycle region, which, however, has a drawback of a relatively low spatial
resolution due to the electromagnetic wavelength. Therefore, realizing the time-resolved
tunneling current measurement in the subpicosecond range by developing STM combined with
an ultrashort-pulse laser has been a challenging subject for obtaining the ultimate spatial andtemporal resolutions simultaneously.
I would like to review our researches and efforts on the laser-combined STM and related
techniques recently we have developed, with some latest results obtained based on them.
[1] O. Takeuchi, M. Aoyama, R. Oshima, Y. Okada, H. Oigawa, N. Sano, R. Morita, M. Yamashita, andH. Shigekawa, Appl. Phys. Lett. 85(15), 3268 (2004).
[2] O. Takeuchi, S. Yoshida and H. Shigekawa, Appl. Phys. Lett. 84(18), 3645 (2004).
[3] H. Shigekawa, O. Takeuchi and M. Aoyama, Sci. & Technol. of Advanced Materials, 6, 582 (2005).
[4] Mono-Cycle Photonics and Optical Scanning Tunneling Microscopy -Route to Femtosecond Angstrom
Technology-, Springer (2005), e d. by M. Yamashita, H. Shigekawa and R. Morita.
[5]  Y. Terada, M Aoyama, H. Kondo, A. Taninaka, O. Takeuchi, H. Shigekawa Nanotechnology 18, 044028 (2006).
[6] S. Yoshida, Y. Kanitani, R. Oshima, Y. Okada, O. Takeuchi, H. Shigekawa, Phys. Rev. Lett. 98, 026802 (2007).
[7] S. Yoshida, Y. Kanitani, O. Takeuchi, and H. Shigekawa, Hyomen Kagaku, 28, 2, 111 (2007), in Japanese.
[8] H. Shigekawa, S. Yoshida, O. Takeuchi, M. Aoyama,Y. Terada, H. Kondo, H. Oigawa, Thin Solid Film, in print.
[9] S. Yasuda, T. Nakamura, M. Matsumoto and H. Shigekawa, J. Am. Chem. Soc., 125, 16430 (2003).