In this review, possibilities to modify intentionally the electronic transport properties of metal/molecule/metal devices (MMM devices) are discussed. Here especially the influence of the metal work function, the metal-molecule interface, the molecule dipole and different tunneling mechanisms are considered. A route to evaluate the effective surface work function of metal-molecule systems is given and, based on experimental results, an exemplary estimation is performed. The electron transport across different metal-molecule interfaces is characterized by relating transmission coefficients extracted from experimentally derived molecular conductances, decay constants or tunneling barrier heights. Based on the reported results the tunneling decay constant can be assumed to be suitable to characterize intrinsic molecular electron transport properties, while the nature of the metal-molecule contacts is properly described by the transmission coefficient. A clear gradation of transmission efficiencies of metal-anchoring group combinations can be given.

Thin films of 1,3-diethylbenzimidazol-2-ylidene (BIEt) were fabricated from THF solution on solid gold substrates and characterised by high-resolution X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. The surface-analytical data are in accord with the formation of self-assembled monolayers of BIEt molecules exhibiting an approximately vertical orientation on the substrate. The crystal structure of (BIEt)2 was also determined.

A self-assembled monolayer of dodecanethiol is grown onto (111) oriented gold by vacuum phase deposition and studied by ultrahigh vacuum scanning tunneling microscopy (STM). The films consist of domains that exhibit the c(4 x 2) over-structure of the hexagonal (square root of 3 x square root of 3)R30 of alkanethiols on gold. The domain size is only limited by the terrace size of the underlying gold. By higher resolution scans a new phase of the c(4 x 2) structure consisting of four inequivalent molecules that display different heights in the STM images is discovered.

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.

We report on resistive switching of capacitor-like SrRuO 3 /Ba 0.7 Sr 0.3 TiO 3 / Pt thin films epitaxially grown on SrTiO 3 substrates. We observe a weak but stable hysteresis in the current-voltage curve. By applying short voltage pulses, a high or low resistive state as well as intermediate states can be addressed even at room temperature. We demonstrate a multiple-branch hysteresis curve corresponding to multilevel switching modus revealing different subloops for different write voltages. Furthermore reliability issues such as cycling endurance and data retention are presented. 10 Here, different resistance levels could be addressed by a variation of length and amplitude of the programming voltage pulse. There is still some debate about the physical mechanisms of the resistance change and about the key experimental parameters. Mechanisms under discussion are ͑i͒ trapping/detrapping effects and charge transfer processes via donor and acceptor levels ͑Cr 3+ /Cr 4+ ͒, 10,13 ͑ii͒ a Mott metal-insulator transition, 14 ͑iii͒ formation of local current domains, 12 ͑iv͒ redox processes of extended defects, 15 and ͑v͒ conductivity changes due to a reversal of a local spontaneous polarization. 16 Polarization changes might not be stringently of ferroelectric nature, but might also be due to defect dipoles, e.g., formed by acceptor/oxygen vacancy defect associates. 17 In our present work, we investigate resistive switching of 0.2% chromium-doped Ba 0.7 Sr 0.3 TiO 3 ͑BST͒ capacitorlike thin films of around 40 nm thickness at RT. We investigate in detail multibranch type I͑V͒ curves, which have not been reported for perovskites dielectrics so far. We will present detailed measurements of the multilevel switching and focus on reliability issues such as cycling endurance and data retention.SrRuO 3 ͑SRO͒ bottom electrodes of 100 nm thickness and BST layer of 40 nm thickness are grown in situ epitaxially on single crystalline ͑100͒ oriented SrTiO 3 ͑STO͒ substrates. The films are deposited by pulsed laser ablation while maintaining a substrate temperatur of 700°C and an oxygen base pressure of 0.25 mbar. The epitaxial growth of the bilayers is confirmed by x-ray diffraction measurements ͓Phil-ips PW 3020 ͑Cu K␣͔͒. Pt top electrodes are deposited by sputtering and patterned by optical lithography and a lift-off process to areas of 0.09 mm 2 down to 100 m 2 . The bottom electrode is contacted after removing the BST film from the sample edge by wet chemical etching. A postannealing step in oxygen is performed at 700°C for 5 min. The currentvoltage characteristics are measured with a Keithley 2410 source meter. To protect samples from damages due to high currents a current compliance is used. All samples reveal low initial resistances so that a high voltage treatment prior to quasistatic I͑V͒ characterization or pulse measurements to convert the sample from an insulating state into a low conductive state as described in Ref. 11 for SrTiO 3 single crystals ͑"forming process"͒ is not required here. The stable switching behavior r...

A method is presented for depositing mixed self-assembled monolayers (SAMs) of dodecanethiol (C12) and 4'-methyl-1,1'-biphenyl-4-butane (H3C-C6H4-C6H4-(CH2)4-SH, BP4) by insertion of BP4 into a closely packed SAM of dodecanethiol on Au(111). Insertion takes place at defect sites such as domain boundaries or etch pits in the gold surface that are characteristic of C12 monolayers on gold. With a lower probability, insertion also occurs beside defect sites inside dodecanethiol domains. Insertion at defect sites results in domains of BP4, whereas insertion into C12 domains leads to isolated BP4 molecules. The isolated BP4 molecules are shown not to move at room temperature. By comparing the apparent height of the isolated BP4 molecules and BP4 domains, it is proposed that the isolated molecules have the same conformation as in the full-coverage phase. A simple two-layer model is proposed to characterize the current transport through BP4. The decay constant beta for the phenylene groups is deduced from the apparent STM heights of the inserted BP4 islands compared to the STM heights of the C12 closely packed monolayers.

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Using UHV-STM investigations and density-functional theory calculations we prove the contribution of Cu-adatoms to the stabilization of a new high-density phase of benzoate molecules on a Cu(110) substrate. We show that two different chemical species, benzoate and benzoate Cu-adatoms molecules, build the new close-packed structure. Although both species bind strongly to the copper surface, we identify the benzoate Cu-adatoms molecules as the more mobile species on the surface due to their reduced dipole moment and their lower binding energy compared to benzoate molecules. Therefore, the self-assembly process is supposed to be mediated by benzoate Cu-adatom species, which is analogous to the gold-thiolate species on Au(111) surfaces.