The fabrication and characterization of metallic nanometer–
sized(nm) gaps suitable for conductivity measurements of single
molecules has been investigated systematically. First results of
conductivity measurements of single molecules and of their direct
observation by STM are presented. Epitaxially grown Ag structures
with a thickness down to 10 monolayers on Si(100) were used for a
controlled gap formation by electromigration (EM). The gaps obtained
range from several nm down to sub–nm, as revealed by lateral
conductivity measurements and by scanning tunneling microscopy
done under ultra high vacuum conditions. Annealing to 300 K closes
the gap by surface diffusion of Ag and a new cycle of opening by
EM at low temperature(77K) can be performed [1]. The functionality of
the contacts is demonstrated by adsorption of single ferrocenedithiol
molecules. The zero bias resistance is around 40kOhm. In addition,
the dI/dV curve shows clearly molecular contributions in the range
of 50meV and 150meV, which can be attributed to ferrocene induced
states near the Fermi edge, as revealed by DFT calculations[2].
[1]G. Gardinowski, J. Schmeidel, H. Pfnür, T. Block, and C. Tegenkamp
Switchable nanometer contacts: Ultrathin Ag nanostructures on Si(100), APL 89 (2006) 063120.
[2]J. Meyer, T. Bredow, C. Tegenkamp and H. Pfnür
Thiol and thiolate bond formation of ferrocene-1,1-dithiol to a Ag(111) surface, Journal of Chemical Physics 125 (2006) 194705. |