Considerable efforts have been made to realize nanoscale diodes based on single molecules or molecular ensembles for implementing the concept of molecular electronics. However, so far, functional molecular diodes have only been demonstrated in the very low alternating current frequency regime, which is partially due to their extremely low conductance and the poor degree of device integration. Here, we report about fully integrated rectifiers with microtubular soft-contacts, which are based on a molecularly thin organic heterojunction and are able to convert alternating current with a frequency of up to 10 MHz. The unidirectional current behavior of our devices originates mainly from the intrinsically different surfaces of the bottom planar and top microtubular Au electrodes while the excellent high frequency response benefits from the charge accumulation in the phthalocyanine molecular heterojunction, which not only improves the charge injection but also increases the carrier density.

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The metal-organic interface between polycrystalline gold and hexafluorotetracyanonaphthoquinodimethane (F 6 TCNNQ) was investigated by photoelectron spectroscopy with the focus on the charge transfer characteristics from the metal to the molecule. The valence levels, as well as the core levels of the heterojunction, indicate a full electron transfer and a change in the chemical environment. The changes are observed in the first F 6 TCNNQ layers, whereas for further film growth, only neutral F 6 TCNNQ molecules could be detected. New occupied states below the Fermi level were observed in the valence levels, indicating a lowest unoccupied molecular orbital (LUMO) occupation due to the charge transfer. A fitting of the spectra reveals the presence of a neutral and a charged F 6 TCNNQ molecules, but no further species were present.

The electronic properties of organic semiconductors can be modified by a charge transfer to electron accepting molecules. In this study, the charge transfer reactions between BEDT-TTF (ET) and the two molecular acceptors F2TCNQ and F6TCNNQ were investigated by photoemission spectroscopy. The materials were evaporated under vacuum conditions on top of each other, and changes in the core levels as well as the valence orbitals were probed after each deposition step. The core level spectra showed charge transfer for both interfaces, which was higher for the ET/F6TCNNQ interface according to different intensity ratios as well as different BE shifts of neutral and cationic spectra. The unequal contribution of the sulfur atoms to the HOMO of ET translated to an additional contribution to the S 2p core level spectra of oxidized ET. The valence spectra showed the occupation of the acceptor’s LUMO. Both interfaces did not show signs of occupied density of states at the Fermi level. The progression of the work function suggested that ET and F6TCNNQ form relatively sharp interfaces while signs for interdiffusion were observed for the ET/F2TCNQ combination.

A newly synthesised ruthenium–acetylide complex is characterised by various methods and its charge transfer to the acceptor F6TCNNQ is studied by optical and photoelectron spectroscopy.