Time-resolved electrostatic force detection using scanning probe microscope
Institute of Scientific and Industrial Research, Osaka University
Abstract: Photo-induced charge transfer is essential process in the wide range of scientific and technological issues including optoelectronic devices, light harvest, photocatalysis, and electrophotography. Although the dynamics of photoexcited charge are seriously influenced by local structure and electronic properties with nanometer scale, there is no effective method to observe the dynamics with nanometer scale resolution. This paper describes a development of time-resolved electrostatic force detection based on dynamic mode atomic force microscopy. In the dynamic-mode operation, the tip interacts with the surface only at the moment when the tip closes to the sample surface. The interactive duration can be estimated 1μs or less. Taking advantage of this short duration, submicrosecond-class time-resolved force detection has been achieved by the coincidence between photo-irradiation and cantilever motion. The oscillation amplitude is changed clearly as a function of bias voltage indicating the polarity of photo-excited charges. These results suggest that the transient charges generated by pulsed laser irradiation can be detected with μs-class resolution.
Key words: Time resolution, Electrostatic force, Scanning probe microscopy, Frequency shift mode, Surface photovoltage