Single-molecule chemistry and spectroscopy on the ultrathin insulating films
Surface and Interface Science Laboratory, RIKEN, Japan
The study of single molecules provides deep insights into bonding nature and underlying quantum mechanics concerning about controlling chemical reaction. The scanning tunneling microscope (STM) is a versatile and powerful tool for investigating and controlling chemistry of individual molecules on the solid surfaces. The coupling of tunneling electrons to the electronic and vibrational states of the target molecule allows us to realize mode-selective and state-selective chemistry of the individual molecules as well as to understand how the electron energy can transport leading to carious surface processes.
Ultrathin insulating films grown on metal substrate has been a subject of great interest for investigation of individual adsorbate atoms and molecules by the STM, because of electronic decoupling between the adsorbate and supporting metal surface under an STM junction. In this talk, I will address two main issues with our experimental and theoretical efforts on investigating interaction of electrons with a single molecule on the ultrathin insulating films. The first part is assigned to the control of chemical reactivity by tuning interface between the insulating film and metal substrate. The chemical reactivity of a water molecule on an ultrathin MgO film supported by the Ag(100) substrate depends greatly on film thickness and be enhanced compared to that achieved with their bulk counterpart . The change of chemical reactivity of ultrathin MgO film depending on the film thickness can be explained by the strengthening of the interaction between the oxide and metal interface layers . Our results clearly show that such structural imperfections at the interface can improve the chemical reactivity of the MgO film supported by an Ag substrate . The second part focuses on the single-molecule luminescence with an STM . Optical properties of a single metal-free phthalocyanine (H2Pc) molecule on the 2-ML thick NaCl film supported by Ag(111) have been also studied by scanning tunneling luminescence spectroscopy. I will discuss about the single molecule reaction of an H2Pc molecule with tunneling electrons and accompanied optical property changes in a single-molecule luminescence spectra.
 H.-J. Shin, J. Jung, K. Motobayashi, S. Yanagisawa, Y. Morikawa, Y. Kim, and M. Kawai, Nat. Mater. 9, 442 (2010)
 J. Jung, H.-J. Shin, Y. Kim, and M. Kawai, Phys. Rev. B 82, 085413 (2010)
 J. Jung, H.-J. Shin, Y. Kim, and M. Kawai, J. Am. Chem. Soc. 133, 6142 (2011); J. Am. Chem. Soc. 134, 10554 (2012)
 H. Imada, K. Miwa, J. Jung, T. K. Tomoko, and Y. Kim, to be submitted