Forming reliable and reproducible molecule−nanoelectrode contacts is one of the key issues for the implementation of nanoparticles as functional units into nanoscale devices. Utilizing heterometallic electrodes and Janus-type nanoparticles equipped with molecules allowing selective binding to a distinct electrode material represents a promising approach to achieve this goal. Here, the directed immobilization of individual Janus-type gold nanoparticles (AuNP) between heterometallic electrodes leading to the formation of asymmetric contacts in a highly controllable way is presented. The Janus-AuNP are stabilized by two types of ligands with different terminal groups on opposite hemispheres. The heterometallic nanoelectrode gaps are formed by electron beam lithography in combination with a self-alignment procedure and are adjusted to the size of the Janus-AuNP. Thus, by choosing adequate molecular end group/metal combinations, the immobilization direction of the Janus-AuNP is highly controllable. These results demonstrate the striking potential of this approach for the building-up of novel nanoscale organic/inorganic hybrid architectures.

Transition metal complexes are electrofunctional molecules due to their high conductivity and their intrinsic switching ability involving a metal-to-ligand charge transfer. Here, a method is presented to contact reliably a few to single redox-active Ru-terpyridine complexes in a CMOS compatible nanodevice and preserve their electrical functionality. Using hybrid materials from 14 nm gold nanoparticles (AuNP) and bis-{4′-[4-(mercaptophenyl)-2,2′:6′,2″-terpyridine]}-ruthenium­(II) complexes a device size of 302 nm2 inclusive nanoelectrodes is achieved. Moreover, this method bears the opportunity for further downscaling. The Ru-complex AuNP devices show symmetric and asymmetric current versus voltage curves with a hysteretic characteristic in two well separated conductance ranges. By theoretical approximations based on the single-channel Landauer model, the charge transport through the formed double-barrier tunnel junction is thoroughly analyzed and its sensibility to the molecule/metal contact is revealed. It can be verified that tunneling transport through the HOMO is the main transport mechanism while decoherent hopping transport is present to a minor extent.

Terpyridine derivatives reveal rich coordination chemistry and are frequently used to construct reliable metallo-supramolecular wires, which are promising candidates for optoelectronic or nanoelectronic devices. Here, we examine especially the terpyridine/electrode interface, which is a critical point in these organic/inorganic hybrid architectures and of utmost importance with respect to the device performance. We use the approach to assemble nanodevices by immobilization of single terpyridine-functionalized gold nanoparticles with a diameter of 13 nm in between nanoelectrodes with a separation of about 10 nm. Conductance measurements on the formed double-barrier tunnel junctions reveal several discrete conductance values in the range of 10–9–10–7 S. They can be attributed to distinct terpyridine/electrode contact geometries by comparison with conductance values estimated based on the Landauer formula. We could clearly deduce that the respective terpyridine/metal contact determines the length of the tunneling path through the molecule and thus the measured device conductance. Furthermore, the formation of a distinct terpyridine/electrode contact geometry correlates with the chemical pretreatment of the terpyridine ligand shell of the gold nanoparticles with an alkaline solution. By applying infrared reflection absorption spectroscopy, we found that only a chemical treatment with a concentrated ammonia solution results in effective deprotonation of the terpyridine anchor group. This enables the electrical contact to the middle pyridyl ring and thus a short tunneling path through the molecule corresponding to a high conductance value. These findings indicate a way to control the contact geometry at the terpyridine/metal interface, which is a prerequisite for reliable nanodevices based on this class of molecules.