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Molecular Junctions (molecular + junction)
Selected AbstractsChemical Interactions at Metal/Molecule Interfaces in Molecular Junctions,A Pathway Towards Molecular Recognition,ADVANCED MATERIALS, Issue 3 2009Mila Manolova A 4-aminothiophenol self-assembled monolayer (see image) is prepared on top of a Au(111) crystal, which is subsequently metallized by a nearly closed Pd overlayer of monoatomic height. Analysis of its structural setup and electronic properties reveals that the monolayer consists of a minimum of two molecular layers, and strong chemical interactions between the metal overlayer and the amino groups are found to play a decisive role in determining the overall electronic, and thus the transport properties, of the layer/metal contact. [source] Response of Molecular Junctions to Surface Plasmon Polaritons,ANGEWANDTE CHEMIE, Issue 33 2010Gilad Noy Tunnel in die Freiheit: Durch Laserbestrahlung erzeugte Plasmonen beeinflussen die Leitfähigkeit an einem molekularen Übergang mit ,schwebendem Draht" (siehe Bild). Die Stromzunahme, die von Wellenlänge und Laserleistung abzuhängen scheint, ist in halbquantitativer Übereinstimmung mit theoretischen Modellen auf der Grundlage eines photonenvermittelten Tunnelmechanismus. [source] Innentitelbild: Controlled Stability of Molecular Junctions (Angew. Chem.ANGEWANDTE CHEMIE, Issue 44 200944/2009) Die Schlüsselrolle der Grenzflächen in Elektroden-Molekül-Kontakten kann anhand des zeitlichen Verlaufs der elektrischen Leitfähigkeit durch sie untersucht werden. In der Zuschrift auf S.,8423,ff. zeigen A. Filoramo et,al., dass das ,Blinken" der Thiol-Gold-Bindung durch geeignete Wahl des Moleküls unterdrückt werden kann: Bei Kontakten mit dem Terphenylenmolekül variiert die Leitfähigkeit stochastisch, dagegen sind die mit dem Terthiophenmolekül über mehrere Wochen äußerst stabil (Illustration: D. Nozaki). [source] Controlled Stability of Molecular Junctions,ANGEWANDTE CHEMIE, Issue 44 2009Diana Duli Der Einfluss der Grenzflächen auf Moleküldrähte mit Thiol-Endgruppen, die aus drei Phenyl- (P3) oder drei Thiophenringen (T3) bestehen, wurde mit der Bruchkontakt-Methode analysiert. Dabei wird die Leitfähigkeit G eines molekularen Kontakts gemessen (siehe REM-Bild des Kontakts und Schema der Molekülanordnung). Anders als beim T3-Molekül variiert G beim P3-Molekül stochastisch (siehe Diagramm). [source] Molecular Junctions Composed of Oligothiophene Dithiol-Bridged Gold Nanoparticles Exhibiting Photoresponsive PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Wei Huang Dr. Abstract Three oligothiophene dithiols with different numbers of thiophene rings (3, 6 or 9) have been synthesized and characterized. The X-ray single crystal structures of terthiophene 2 and sexithiophene 5 are reported herein to show the exact molecular lengths, and to explain the difference between their UV-visible spectra arising from the different packing modes. These dithiols with different chain lengths were then treated with 2-dodecanethiol-protected active gold nanoparticles (Au-NPs) by means of in situ thiol-to-thiol ligand exchange in the presence of 1,,m gap Au electrodes. Thus the molecular junctions composed of self-assembled films were prepared, in which oligothiophene dithiol-bridged Au-NPs were attached to two electrodes by means of AuS bonded contacts. The morphologies and current,voltage (I,V) characteristics of these films were studied by SEM and AFM approaches, which suggested that the thickness of the films (3,4 layers) varied within the size of one isolated Au-NP and typical distance-dependent semiconductor properties could be observed. Temperature dependent I,V measurements for these molecular junctions were performed in which the films served as active elements in the temperature range 6,300 K; classical Arrhenius plots and subsequent linear fits were carried out to give the activation energies (,E) of devices. Furthermore, preliminary studies on the photoresponsive properties of these devices were explored at 80, 160, and 300 K, respectively. Physical and photochemical mechanisms were used to explain the possible photocurrent generation processes. To the best of our knowledge, this is the first report in which oligothiophene dithiols act as bridging units to link Au-NPs, and also the first report about functionalized Au-NPs exhibiting photoresponse properties in the solid state. [source] Electrochemically Assisted Fabrication of Metal Atomic Wires and Molecular Junctions by MCBJ and STM-BJ Methods,CHEMPHYSCHEM, Issue 13 2010Dr. Jing-Hua Tian Abstract Atomic wires (point contacts) and molecular junctions are two fundamental units in the fields of nanoelectronics and devices. This Minireview introduces our recent approaches aiming to develop versatile methods to fabricate and characterize these unique metallic and molecular structures reliably. Electrochemical methods are coupled with mechanically controllable break junction (EC-MCBJ) or scanning tunneling microscopy (STM) break junction (EC-STMBJ) methods to fabricate metallic point contacts and metal/molecule/metal junctions. With the designed electrodeposition method, the metal of interest (e.g. Au, Cu, Fe or Pd) is deposited in a controlled way on the original electrode pair, on a chip for MCBJ or on the STM tip, to make the metallic contact. Then, various metal atomic wires and molecular junctions can be fabricated and characterized systematically. Herein, we measured the quantized conductance through the construction of histograms of these metal atomic point contacts and of single molecules including benzene-1,4-dithiol (BDT), ferrocene-bisvinylphenylmethyl dithiol (Fc-VPM), 4,4,-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA). Finally, we briefly discussed the future of EC-MCBJ and EC-STM for nanoelectronics and devices, for example, for the formation of heterogeneous metal-based atomic point contacts and molecular junctions. [source] Redox-induced configuration conversion for thioacetamide dimer can function as a molecular switchJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2010Haiying Liu Abstract The electronic switching properties of thioacetamide dimer (TAD) were investigated using the nonequilibrium Green's function method combined with density functional theory for design of a novel molecular switch. The H-bonded TAD can be converted upon hole-trapping to a three-electron (3e)-bonded configuration with a S,S linkage which could provide a more favorable channel for charge transfer than the before. The redox-induced configuration conversion between the H-bonded and the 3e-bonded TADs could govern the charge migration through the molecular junction with a considerable difference in conduction currents. The calculated I,V characteristic curves of two configurations exhibit a switching behavior with an On-Off ratio in a range of about 4.3,7.6 within the applied voltages. Clearly, this hypothetical scheme provides a potential way to explore the novel conformation-dependent molecular switch. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Study of the transport properties of a molecular junction as a function of the distance between the leadsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007Víctor M. García-Suárez Abstract We consider a model of a molecular junction made of BDT (benzene dithiol) molecule trapped between two Au(100) leads. Using the ab initio approach implemented in the SIESTA package we look for the optimal configurations of the molecule as a function of the distance between the leads. We find that for distances long enough the energy of the system is minimized when the molecule is bonded asymmetrically, i.e. chemisorbed to one of the leads, whereas for distances shorter than 12 Å the energy is minimized when the molecule sits in the middle between the leads. We discuss possible consequences of the above findings for the transport properties of the junction. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and FabricationADVANCED MATERIALS, Issue 43 2009Richard L. McCreery Abstract Molecular electronics seeks to incorporate molecular components as functional elements in electronic devices. There are numerous strategies reported to date for the fabrication, design, and characterization of such devices, but a broadly accepted example showing structure-dependent conductance behavior has not yet emerged. This progress report focuses on experimental methods for making both single-molecule and ensemble molecular junctions, and highlights key results from these efforts. Based on some general objectives of the field, particular experiments are presented to show progress in several important areas, and also to define those areas that still need attention. Some of the variable behavior of ostensibly similar junctions reported in the literature is attributable to differences in the way the junctions are fabricated. These differences are due, in part, to the multitude of methods for supporting the molecular layer on the substrate, including methods that utilize physical adsorption and covalent bonds, and to the numerous strategies for making top contacts. After discussing recent experimental progress in molecular electronics, an assessment of the current state of the field is presented, along with a proposed road map that can be used to assess progress in the future. [source] Molecular Transport Junctions: Clearing Mists,ADVANCED MATERIALS, Issue 1 2007M. Lindsay Abstract Recent progress in the measurement and modeling of transport in molecular junctions has been very significant. Tunnel transport in the Landauer,Imry regime is now broadly understood for several systems, although a detailed understanding of the role of contact geometry is still required. We overview some clear indications from recent research and note the quite reasonable agreement between measured and calculated conductance in metal,molecule,metal junctions. The next challenge lies in obtaining a microscopic understanding of charge transport that involves reduction or oxidation of molecules. [source] The Role of Charge Localization in Current-Driven DynamicsISRAEL JOURNAL OF CHEMISTRY, Issue 1 2007Ryan Jorn We explore the role of charge localization in current-triggered, resonance-mediated, dynamical events in molecular junctions. To that end we use a simple model for a molecular rattle, a Li+C9H,9 zwitterion attached between two metal clusters. By varying the size of the metal clusters we systematically vary the degree of delocalization of the electronic orbitals underlying the resonant current, and thus can draw general conclusions regarding the effect of delocalization on dynamical processes induced by resonance inelastic current in molecular electronics. In the small cluster limit, we find interesting quantum dynamics in the nuclear subspace, corresponding to coherent tunneling of the wave packet through the barrier of an asymmetric double-well potential. These dynamics are rapidly damped with increasing charge delocalization in extended systems. [source] Molecular Junctions Composed of Oligothiophene Dithiol-Bridged Gold Nanoparticles Exhibiting Photoresponsive PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Wei Huang Dr. Abstract Three oligothiophene dithiols with different numbers of thiophene rings (3, 6 or 9) have been synthesized and characterized. The X-ray single crystal structures of terthiophene 2 and sexithiophene 5 are reported herein to show the exact molecular lengths, and to explain the difference between their UV-visible spectra arising from the different packing modes. These dithiols with different chain lengths were then treated with 2-dodecanethiol-protected active gold nanoparticles (Au-NPs) by means of in situ thiol-to-thiol ligand exchange in the presence of 1,,m gap Au electrodes. Thus the molecular junctions composed of self-assembled films were prepared, in which oligothiophene dithiol-bridged Au-NPs were attached to two electrodes by means of AuS bonded contacts. The morphologies and current,voltage (I,V) characteristics of these films were studied by SEM and AFM approaches, which suggested that the thickness of the films (3,4 layers) varied within the size of one isolated Au-NP and typical distance-dependent semiconductor properties could be observed. Temperature dependent I,V measurements for these molecular junctions were performed in which the films served as active elements in the temperature range 6,300 K; classical Arrhenius plots and subsequent linear fits were carried out to give the activation energies (,E) of devices. Furthermore, preliminary studies on the photoresponsive properties of these devices were explored at 80, 160, and 300 K, respectively. Physical and photochemical mechanisms were used to explain the possible photocurrent generation processes. To the best of our knowledge, this is the first report in which oligothiophene dithiols act as bridging units to link Au-NPs, and also the first report about functionalized Au-NPs exhibiting photoresponse properties in the solid state. [source] Electrochemically Assisted Fabrication of Metal Atomic Wires and Molecular Junctions by MCBJ and STM-BJ Methods,CHEMPHYSCHEM, Issue 13 2010Dr. Jing-Hua Tian Abstract Atomic wires (point contacts) and molecular junctions are two fundamental units in the fields of nanoelectronics and devices. This Minireview introduces our recent approaches aiming to develop versatile methods to fabricate and characterize these unique metallic and molecular structures reliably. Electrochemical methods are coupled with mechanically controllable break junction (EC-MCBJ) or scanning tunneling microscopy (STM) break junction (EC-STMBJ) methods to fabricate metallic point contacts and metal/molecule/metal junctions. With the designed electrodeposition method, the metal of interest (e.g. Au, Cu, Fe or Pd) is deposited in a controlled way on the original electrode pair, on a chip for MCBJ or on the STM tip, to make the metallic contact. Then, various metal atomic wires and molecular junctions can be fabricated and characterized systematically. Herein, we measured the quantized conductance through the construction of histograms of these metal atomic point contacts and of single molecules including benzene-1,4-dithiol (BDT), ferrocene-bisvinylphenylmethyl dithiol (Fc-VPM), 4,4,-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA). Finally, we briefly discussed the future of EC-MCBJ and EC-STM for nanoelectronics and devices, for example, for the formation of heterogeneous metal-based atomic point contacts and molecular junctions. [source] | ||||||||||