NMP 2008
 |
BongSoo Kim |
ADVISOR:
Dan Frisbie |
Measuring the Electrical Resistance of Molecules
BongSoo Kim, Seongho Choi, Moon Sung Kang, C. Daniel Frisbie
Understanding of charge transport at the interface of metal/organic molecules is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity include the nature of metal-molecule contacts and the electronic structure of the molecular backbone as well as the type of metal. We have studied the electronic properties of self-assembled monolayers (SAMs) of aromatic acenes (benzene, naphthalene, anthracene, tetracene) monothiols and dithiols by conducting probe atomic force microscopy (CP-AFM). Nanoscopic tunnel junctions were formed by contacting Au-, Pt-, or Ag-coated AFM tips to SAMs of the molecules on Au, Pt, or Ag substrates. Resistance (R) in a low bias regime increased exponentially with molecular length (s) in both cases according to the expected relationship, R = R0 exp (ß•s). The attenuation factor (ß) is 0.4~0.6/Å for both aromatic series, while contact resistance (R0) of aromatic dithiols on gold is less than that of aromatic monothiols. The resistance versus length data was also used to calculate transmission values for each type of contact and the transmission per ring. Ultraviolet photoelectron spectroscopy measurements were used to determine the electronic structure of these interfaces.
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