Surface and Interface Science Laboratory

Outline

Our research focuses on describing details of the energy transport and conversion at solid surfaces and interfaces in the nanoscale regime. In order to understand their basic mechanisms at the individual molecule/atom level, we carry out combined study of density functional theory calculation and scanning probe microscopy/spectroscopy on the well-defined solid surfaces under ultra-high vacuum conditions. Part of our research is directed toward investigation of single-molecule chemistry by the use of vibrational and electronic quantum states on metal or metal oxide thin-film surfaces. Another important part of our research focuses on self-assembled organic thin films aiming at understanding their microscopic structure and electronic properties, and their use as templates for the development of molecular-based functional materials. In addition, we have investigated local electronic structures of carbon nanotubes and nano graphenes on metal electrode surfaces and tuning their electronic properties by chemical modification. Recently, we have also started working on photon detection from a single molecule and on atomic scale investigation of energy conversion between electrons and photons of nanometer scale materials.

Recent Research Topic

Local electronic properties of a single molecule

Fig. 1 STM and STS on the various superstructures of meta-aminobenzoate monolayers on Cu(110)

One of the objectives of our research is to elucidate electron transport through a single-molecule junction at the atomic scale using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS).

We have studied the effect of modification of a benzoate (C6H5COO-) molecule with various functional groups on local conductivity and the electronic structure of the contact point between molecule and Cu(110) electrode. The electronic structures of cyanobenzoate derivatives (NCC6H5COO-) have been investigated by combining STM/STS measurement with X-ray core-level spectroscopy at SPring-8 [Langmuir 2009, 25, 5504].

In addition, we have investigated the tripod-shaped bromo adamantane trithiol (BATT) molecule on Au(111) using STM at 4.7 K. Adsorption of BATT leads to the formation of highly ordered self-assembled monolayers (SAMs) with three-point contacts on Au(111). The structure of these SAMs has been found to have a two-tiered hierarchical chiral organization. The self-assembly of achiral monomers produces chiral trimers, which then act as the building blocks for chiral hexagonal supermolecules. STS spectra measured on the BATT layers show that the intrinsic surface state of an Au(111) surface is blocked by the BATT molecule, suggesting the possibility of application as an organic insulating layer [J. Am. Chem. Soc. 2007, 129, 2511].

The exceptional cleanliness of the UHV deposition method has allowed us to investigated the effects of the interaction between SWCNT and metal surface. We have succeeded in deposition of SWCNT on various metal (Au(111), Cu(111), Cu(100) and Ag(100)) and insulating (NaCl or MgO on Ag(100)) surfaces and performed STM/STS on the single SWCNT. We showed that the charge transfer which naturally occurs between the SWCNT and the surface is related to the difference in the work function of the two materials [Nature Nanotech. 2009, 4, 567].

Fig. 2 1-D array of quantum dots on a SWCNT on Ag(100) surface

Fig. 3 Views of the hierarchical chiral assembly of the adamantane derivative on a gold surface — from molecule to microscopy