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.

Integration of molecule-capped gold nanoparticles (AuNP) into nanoelectronic devices requires detailed knowledge about the AuNP-electrode interface. Here, we report the pH-dependent adsorption of amine or carboxylic acid-terminated gold nanoparticles on platinum or gold/palladium (30% Pd) alloy, respectively. We synthesized amine-terminated AuNP, applying a new solid phase supported approach, as well as AuNP exhibiting carboxylic acid as terminal groups. The pH-induced agglomeration of the synthesized AuNP was investigated by UV-vis, DLS, and ζ-potential measurements. Depending on the pH and the ionic strength of the AuNP solution a preferential adsorption on the different metals occurred. Thereby, we demonstrate that by choosing the appropriate functional group and adjusting the pH as well as the ionic strength a directed binding can be achieved, which is an essential prerequisite for applications of these particles in nanoelectronics. These findings will pave the way for a controlled designing of the interface between molecule-capped AuNP and metallic electrodes for applications in nanoelectronics.

One concept to build up hybrid electronic devices based on molecules or nanoparticles with rectifying properties is based on nanoscale objects that are immobilized between two electrodes composed of different metals forming asymmetric contacts. Following this concept, we introduce an optimized procedure to fabricate heterometallic nanoelectrodes with a separation of only 5 nm. Gold nanoparticles (AuNPs) with a diameter of 15 nm, stabilized with 4-mercaptophenylamine, were used to form electrode1molecule/AuNP/molecule-electrode2 devices comprising at most a small number of AuNPs. Immobilization was performed by dielectrophoretic trapping. The molecular properties of 4-mercaptophenylamine are reflected in transition voltage spectroscopy features of the device. Cyclic current−voltage measurements on 20 functional devices revealed distinct differences in conductivities based on minor differences in device geometry. Analysis of the electron transport characteristics discloses that under these experimental conditions an asymmetric contact configuration alone is not sufficient for building up a molecule-based rectifier.

No abstract