Chemically modified scanning tunneling microscopy tips for molecular imaging

A new approach to chemical imaging was reported by the group of Umezawa in 1998, utilizing scanning tunneling microscopy (STM) with chemically modified tips. Just as in electrochemistry, electron transfer through the overlap of electronic wave functions of tip and sample surfaces plays a central role in STM, which relies on the tunneling effect as operating principle. This similarity and the success of chemically modified electrodes suggested us that "tailored" chemical modification of STM tips should allow the control of electron tunneling through rational use of chemical interactions. The chemical imaging was obtained from a distinctive chemical affinity between the imaging tip and the substrate, such as hydrogen bond and metal coordination interactions that enhanced the electron tunneling. This technique allows imaging of specific surface species at atomic/molecular resolution and will become a powerful method for fundamental chemical studies at molecular level.