Carbon/molecule/metal molecular electronic junctions: the importance of "contacts".

Molecular electronic junctions fabricated by covalent bonding onto a graphitic carbon substrate were examined with Raman spectroscopy and characterized electronically. The molecular layer was a 4.5 nm thick multilayer of nitroazobenzene (NAB), and the top contact material was varied to investigate its effect on junction behavior.

In situ Raman spectroscopy of bias-induced structural changes in nitroazobenzene molecular electronic junctions.

Carbon/nitroazobenzene (NAB)/titanium/gold molecular electronic junctions with active thicknesses of 7-8 nm were constructed having partially transparent Ti/Au top contacts, which permitted in situ monitoring of molecular structure with Raman spectroscopy for applied biases between +3 and -3 V. Deposition of the Ti/Au top contacts resulted in spectral changes similar to those accompanying NAB reduction in a conventional spectroelectrochemical experiment. Upon application of +3 V (carbon relative to Ti), the spectrum indicated reoxidation of the NAB reduction product, and this redox cycle could be repeated at least three times.

Ultraflat carbon film electrodes prepared by electron beam evaporation.

A facile method for the preparation of thin-film carbon electrodes by electron beam evaporation onto highly doped silicon is presented. The physical and electrochemical properties of these films both before and after postdeposition pyrolysis are investigated. Raman spectroscopy establishes the amorphous structure of the nonpyrolyzed carbon films and confirms the formation of graphitic carbon after pyrolysis at 1000 degrees C.

Characterization of carbon/nitroazobenzene/titanium molecular electronic junctions with photoelectron and Raman spectroscopy.

Molecular junctions consisting of nitroazobenzene (NAB) chemisorbed to a substrate of pyrolyzed photoresist film (PPF) and a top contact of vapor-deposited titanium were examined with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The thickness of the NAB layer varied from submonolayer to 4.5 nm, and a thin (1-3 nm) overlayer of Ti was deposited by electron beam deposition.

Molecular rectification and conductance switching in carbon-based molecular junctions by structural rearrangement accompanying electron injection.

Molecular junctions were fabricated consisting of a 3.7 nm thick layer of nitroazobenzene (NAB) molecules between a pyrolyzed photoresist substrate (PPF) and a titanium top contact which was protected from oxidation by a layer of gold. Raman spectroscopy, XPS, and AFM revealed that the NAB layer was 2-3 molecules thick and was bonded to the two conducting contacts by C-C and N-Ti covalent bonds.