When metal/single-walled carbon nanotube (SWCNT) interface is formed, charge transfer between metal and SWCNT occurs and the position of SWCNT Fermi-level is shifted by local electrostatic potential perturbation. Most STM or STS of SWCNT have been measured on Au (111) surface so far, and the Fermi-level shifts of about 0.2eV to the valence band on gold have been reported experimentally and theoretically [1, 2]. In this study, we investigated the electronic structure of SWCNT on Ag (100) surface by STM and STS at low temperature (4.7K). Ultra-clean SWCNT on silver surface were prepared by dry contact transfer (DCT) technique [3]. The STS results showed that the Fermi-level of SWCNT was shifted to the conduction band, since the work function of Ag (100) (4.3eV) is much smaller than that of Au (111) (5.3eV) and that of SWCNT (4.8 ~ 5.0eV). In addition, we observed that the periodic modulation developed on semiconducting (6, 2) SWCNT over whole length (~300nm). Interestingly, we could observe bandgap modulation of same period from spatially-resolved STS mapping. Considering the chirality and unit cell of SWCNT, the period of modulation showed a good epitaxial relationship between SWCNT and Ag (100) in this configuration. The amount of charge transfer depends on the atomic distance between carbon and silver atom. Thus, the shift of bandgap might be enhanced for the atoms having a good epitaxial relationship. At the peak positions of the height profile, the bandgap was shifted downwards (to the valence band), which implies that carbon and silver atoms have a better epitaxial configuration at these locations.
[1] J.W.G. Wildör, L.C. Venema, A.G. Rinzler, R.E. Smalley, and C. Dekker. Nature 391, 59 (1998).
[2] Y. Xue and S. Datta, Phys. Rev. Lett. 83, 4844 (1999).
[3] P.M. Albrecht and J.W. Lyding, Appl. Phys. Lett. 83, 5029 (2003). |