Nanoscale elemental identification of metal interface using synchrotron-radiation-based STM. The dependence of elemental contrast on the X-ray intensity

Scanning tunneling microscope (STM) is a powerful tool for observing solid surfaces in real space at an atomic resolution. However, it is difficult for STM to discriminate the chemical information, except for a limited number of examples. On the other hand, we generally use synchrotron radiation (SR) for elemental identification because it can excite the core electrons of a specific element. Thus, we have long developed the elemental analysis method in real space at an atomic scale by using SR-based STM (SR-STM). The principle of the analysis to image the element contrast is to extract the tiny modulation of tunneling current caused by changes of the density of state (DOS) near the Fermi level which follows the inner-shell excitation at a specific core level. Recently, we have measured the metal interface (Co nano-island on Au(III)), and successfully obtained the elemental contrast. Furthermore, we obtained the dependence of elemental contrast on the incident photon density for the metal interface. This result gives clues to understand more about the principle of the elemental contrast. (author)