CHARACTERIZATION OF THE CONDUCTIVITY OF ORGANIC THIOLS BY FIELD-EMISSION MICROSCOPY AND FIELD-EMISSION SPECTROSCOPY

The conducting properties of two organic thiols (5-mercapto-2,2'-bithiophene and 4-mercaptobiphenyl) deposited by the self-assembly method on Pt tips have been characterized in ultrahigh vacuum by field emission microscopy and spectroscopy. It was shown that these two molecular species can be successfully adsorbed from solution on the Pt tip. The presence of the molecules causes a large decrease in the required field emission voltages by a factor of similar to 3-5. Measurement of the total energy distributions of the emitted electrons showed that the electrons are emitted from a narrow band which is not pinned at the Fermi level but which shifts to lower energy with increased applied field. The molecules thus appear more like an insulator than a conductor. Significant current-induced heating of the molecules was found: for example, Delta T approximate to 80 K for 0.3 nA. Taken together these properties pose problems for the use of these and similar one-dimensional molecules as current-carrying connections in proposed nanoscale electronic applications. However, when used in the subpicoampere range, the current through the wire may be sustainable and dissipation small. In general, these experiments open a door to exploring other molecules.