Using scanning tunneling microscope (STM) and atomic force microscope (AFM), we investigate the properties of atoms and electrons on surfaces with an aim of finding new physics in nanometer scales. Eliminating thermal fluctuations and disturbances, low-temperature STMs allow us to measure surface electronic states locally with very high energy and spatial resolutions and to control them precisely by arranging individual atoms on surfaces with the probe tip. Using the setups, we have observed electron standing waves, screened potential and the Friedel oscillation, and the superconducting gap of individual nano-size particles. By improving a force sensitivity of the AFM probe to the ultimate level, we achieved the world-best high resolution AFM imaging, and now use it for measuring surface electrostatic potential accurately in a nanometer scale spatial resolution. We are also engaged in developments of probe microscopes under various extreme conditions, such as, ultralow temperature, high magnetic field, or under an irradiation of synchrotron radiation light, and new functional and analytical methods with probes such as AFM lithography.
An STM image of Cu(111) surface. Electron standing waves, which are formed as a result of scattering and interference of surface electronic states by steps and surface defects, are observed. The wave length of the oscillatory structure is 1.4 nm.
Low temperature STM image of nano-size Pb island structure, and an real-space image of quantized magnetic flux (vortex) obtained from tunneling spectra showing a superconducting gap under magnetic field
Observation of Vortex Clustering in Nano-Size Superconducting Pb Island Structures by Low-Temperature Scanning Tunneling Microscopy/ Spectroscopy: T. Tominaga, T. Sakamoto, T. Nishio, T. An, T. Eguchi, Y. Yoshida and Y. Hasegawa, J. Supercond. Nov. Magn.- (2012) -.