MICROSCOPY Vol.47▶No.1 2012
■Feature Articles: Frontier of Advanced Scanning Probe Microscopy for Materials Research

Development of Femtosecond Time-Resolved STM
—a Method Visualizing Ultrafast Phenomena

Shoji Yoshida, Osamu Takeuchi and Hidemi Shigekawa

Institute of Applied Physics, University of Tsukuba

Abstract: With the size reduction in structures, the difference in the electronic properties, for example, caused by the structural nonuniformity in each element, has an ever more crucial influence on macroscopic functions of materials and current devices. Thus, for further advances of nanoscale science and technology, the direct observation of the local quantum properties, which provides us with the basis for the characteriscics of macroscopic functions, is of great importance. We have developed a new microscopy technique that enables the visualization of femtosecond carrier dynamics in nanometer-scale structures. The ultimate temporal and spatial resolutions were simultaneously realized by combining an advanced quantum optical technology with scanning tunneling microscopy. The optical pulses used for pump-probe method are selectively transmitted using a pulse picker, and the delay time is controlled digitally, which, for the first time, has allowed the probing of carrier dynamics in nanometer-scale organized structures over a wide range of time scales. Furthermore, this method reduces the measurement time and hence enables the spatial mapping of time-resolved signals, which has been desired for a long time.

Key words: STM, Ultrashort-pulse laser, pump-probe method, time-resolved STM