Controlling the Electronic Contact at the Terpyridine/Metal Interface

Abstract

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.

Impact of device design on the electronic and optoelectronic properties of integrated Ru-terpyridine complexes

“…The fabrication of nanoelectrode samples, each equipped with 12 nanoelectrode pairs (consisting of an AuPd and a Pt electrode with a nanometer sized gap in between), was performed according to a process described recently using electron beam lithography and lift-off [21]. These nanoelectrode samples with gap sizes of 8 nm to 20 nm in between the electrodes were used in order to fabricate Ru(TP)2-complex wire devices.…”

“…The electronic characterization of the Ru(TP)2-complex wire devices as well as the Ru(MPTP)2-AuNP devices was conducted with a Keithley 6430 sub-femtoamp remote source meter as described recently [21]. Current-voltage (I/U) characteristics were taken in the temperature range from 300 K to 360 K at 1 bar pressure under helium atmosphere in an optical continuous flow cryostat (Oxford Optistat CF).…”

“…Here, our approach is to employ nanodevices equipped with nanoelectrodes separated by gaps of 8 nm to 20 nm. They are fabricated by electron beam lithography (EBL) in a lift-off process and the use of a self-aligned Al2O3 hard mask to define the nanogap size [20,21]. The resulting nanoelectrode pairs are used for the on-chip preparation of Ru(TP)2-complex wires according to the wire-growth protocol developed recently and thus, to assemble Ru(TP)2-complex wire nanodevices [19].…”

“…Additionally, we will use our already successfully applied approach to fabricate nanodevices from ligand-stabilized gold nanoparticles (AuNP) immobilized between nanoelectrodes [21][22][23][24]. Very recently, we have assembled nanodevices based on single AuNP with a diameter of 14 nm and stabilized by the twofold positively charged bis-{4'-[4-(mercaptophenyl)-2,2';6',2''-terpyridine]}ruthenium complexes (Ru(MPTP)2).…”

Impact of device design on the electronic and optoelectronic properties of integrated Ru-terpyridine complexes

“…Additionally, we will use our already successfully applied approach to fabricate nanodevices from ligand-stabilized gold nanoparticles (AuNPs) immobilized between nanoelectrodes [21][22][23][24]. Very recently, we have assembled nanodevices based on single AuNPs with a diameter of 14 nm and stabilized by twofold positively charged bis{4′-[4-(mercaptophenyl)-2,2′;6′,2″-terpyridine]}ruthenium complexes (Ru(MPTP) 2 ).…”