Carbon/Molecule/Metal and Carbon/Molecule/Metal Oxide Molecular Electronic Junctions

Abstract

Molecular junctions were fabricated on the basis of a 1.7−4.5 nm thick layer of fluorene (FL) or nitroazobenzene (NAB) covalently bonded to a graphitic pyrolyzed photoresist film (PPF) substrate. The junction was completed with a top contact consisting of metallic Cu, TiO2, or aluminum(III) oxide (AlOx) and a final layer of Au. The current/voltage behavior of the junctions depended strongly both on the nature of the metal or metal oxide top layers and on the structure of the molecular layer. PPF/NAB/Cu/Au and PPF/FL/Cu/Au junctions were highly conducting, with resistances of 0.3−1.7 Ω cm2, depending on the identity and thickness of the molecular layer. Substitution of Cu with either AlOx or TiO2 caused a large increase in junction resistance by 2−4 orders of magnitude, but also yielded rectifying junctions in the case of PPF/NAB(4.5)/TiO2(3.1)/Au. For a positive bias (PPF relative to Au) above +2 V, the NAB(4.5)/TiO2(3.1) junction became highly conductive, apparently due to injection of electrons into the...