501
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Jiang J, Kula M, Lu W, Luo Y. First-principles simulations of inelastic electron tunneling spectroscopy of molecular electronic devices. NANO LETTERS 2005; 5:1551-5. [PMID: 16089487 DOI: 10.1021/nl050789h] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Inelastic electron tunneling spectroscopy (IETS) is a powerful experimental tool for studying the molecular and metal contact geometries in molecular electronic devices. A first-principles computational method based on the hybrid density functional theory is developed to simulate the IETS of realistic molecular electronic devices. The calculated spectra of a real device with an octanedithiolate embedded between two gold contacts are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intramolecular conformation and the molecule-metal contact geometry changes. With the help of theoretical calculations, it has finally become possible to fully understand and assign the complicated experimental IETS and, more importantly, provide the structural information of the molecular electronic devices.
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Affiliation(s)
- Jun Jiang
- Theoretical Chemistry, Royal Institute of Technology, AlbaNova, S-106 91 Stockholm, Sweden, and National Lab for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, China
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502
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Blum AS, Soto CM, Wilson CD, Brower TL, Pollack SK, Schull TL, Chatterji A, Lin T, Johnson JE, Amsinck C, Franzon P, Shashidhar R, Ratna BR. An engineered virus as a scaffold for three-dimensional self-assembly on the nanoscale. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2005; 1:702-6. [PMID: 17193509 DOI: 10.1002/smll.200500021] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Affiliation(s)
- Amy Szuchmacher Blum
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA.
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503
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Blum AS, Ren T, Parish DA, Trammell SA, Moore MH, Kushmerick JG, Xu GL, Deschamps JR, Pollack SK, Shashidhar R. Ru2(ap)4(σ-oligo(phenyleneethynyl)) Molecular Wires: Synthesis and Electronic Characterization. J Am Chem Soc 2005; 127:10010-1. [PMID: 16011359 DOI: 10.1021/ja052604e] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone.
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504
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Leng Y, Krstić PS, Wells JC, Cummings PT, Dean DJ. Interaction between benzenedithiolate and gold: Classical force field for chemical bonding. J Chem Phys 2005; 122:244721. [PMID: 16035807 DOI: 10.1063/1.1942468] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have constructed a group of classical potentials based on ab initio density-functional theory (DFT) calculations to describe the chemical bonding between benzenedithiolate (BDT) molecule and gold atoms, including bond stretching, bond angle bending, and dihedral angle torsion involved at the interface between the molecule and gold clusters. Three DFT functionals, local-density approximation (LDA), PBE0, and X3LYP, have been implemented to calculate single point energies (SPE) for a large number of molecular configurations of BDT-1, 2 Au complexes. The three DFT methods yield similar bonding curves. The variations of atomic charges from Mulliken population analysis within the molecule/metal complex versus different molecular configurations have been investigated in detail. We found that, except for bonded atoms in BDT-1, 2 Au complexes, the Mulliken partial charges of other atoms in BDT are quite stable, which significantly reduces the uncertainty in partial charge selections in classical molecular simulations. Molecular-dynamics (MD) simulations are performed to investigate the structure of BDT self-assembled monolayer (SAM) and the adsorption geometry of S adatoms on Au (111) surface. We found that the bond-stretching potential is the most dominant part in chemical bonding. Whereas the local bonding geometry of BDT molecular configuration may depend on the DFT functional used, the global packing structure of BDT SAM is quite independent of DFT functional, even though the uncertainty of some force-field parameters for chemical bonding can be as large as approximately 100%. This indicates that the intermolecular interactions play a dominant role in determining the BDT SAMs global packing structure.
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Affiliation(s)
- Yongsheng Leng
- Department of Chemical Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA.
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505
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Seferos DS, Trammell SA, Bazan GC, Kushmerick JG. Probing pi-coupling in molecular junctions. Proc Natl Acad Sci U S A 2005; 102:8821-5. [PMID: 15956193 PMCID: PMC1157018 DOI: 10.1073/pnas.0500002102] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2005] [Indexed: 11/18/2022] Open
Abstract
Charge transport characteristics for metal-molecule-metal junctions containing two structurally related pi-conjugated systems were studied to probe pi-pi interactions in molecular junctions. The first molecule contains a typical pi-conjugated framework derived from phenylene vinylene units, whereas the second has the phenylene vinylene structure interrupted by a [2.2]paracyclophane (pCp) core. Electrochemical investigations were used to characterize the defects and packing density of self-assembled monolayers of the two molecules on gold surfaces and to enable quantitative comparison of their transport characteristics. Current-voltage measurements across molecular junctions containing the two species demonstrate that the pCp moiety yields a highly conductive break in through-bond pi-conjugation. The observed high conductivity is consistent with density functional theory calculations, which demonstrate strong through-space pi-pi coupling across the pCp moiety.
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Affiliation(s)
- Dwight S Seferos
- Department of Chemistry, Institute for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USA
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506
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Lee HJ, Park SM. Electrochemistry of Conductive Polymers 37. Nanoscale Monitoring of Electrical Properties during Electrochemical Growth of Polypyrrole and Its Aging. J Phys Chem B 2005; 109:13247-54. [PMID: 16852652 DOI: 10.1021/jp050741s] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electrical and morphological properties of polypyrrole (PPy) films were studied during and after their electrochemical growth under various experimental conditions on a nanometer scale using a current-sensing atomic force microscope (CS-AFM). Of acetonitrile (ACN) solutions containing various amounts of water, one that contained 1.0% water produced the best quality films in their electrical and morphological properties in terms of homogeneities. The degree of doping, as well as time evolution of the film structure and its conductivity, of the PPy films was investigated during their growth in water and ACN with 1.0% water by obtaining the current images at a few designated growing stages, and the results were compared. Well-doped, conductive films were obtained from the very early stage during the electrodeposition of PPy in the ACN solution, while the films were poorly doped in water. As the film deposition progressed further in both aqueous and nonaqueous media, the doped areas spread over the whole surface leading to a more homogeneously conducting film. The current-voltage traces were obtained at each growing stage, which showed that the conductivity increases in both media as the PPy grows; the conductivity of the film grown in ACN is much higher than that of the film grown in water at all growing stages. The electrical properties of the PPy film deteriorated gradually upon exposure to air.
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Affiliation(s)
- Hyo Joong Lee
- Department of Chemistry and Center for Integrated Molecular Systems, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang, Gyeongbuk 790-784, Korea (Republic of Korea)
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507
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Nazin GV, Wu SW, Ho W. Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope. Proc Natl Acad Sci U S A 2005; 102:8832-7. [PMID: 15956189 PMCID: PMC1157031 DOI: 10.1073/pnas.0501171102] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.
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Affiliation(s)
- G V Nazin
- Department of Physics & Astronomy, University of California, Irvine, CA 92697-4575, USA
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508
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Tada T, Hamayama S, Kondo M, Yoshizawa K. Quantum Transport Effects in Copper(II) Phthalocyanine Sandwiched between Gold Nanoelectrodes. J Phys Chem B 2005; 109:12443-8. [PMID: 16852539 DOI: 10.1021/jp0442596] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electrical transmission of copper(II) phthalocyanine (CuPc) sandwiched between gold nanoelectrodes is studied on the basis of the Green function formalism coupled with the Gaussian-broadening technique. In the Au-CuPc-Au junction, broadened density of states (DOS) of the Au chains is defined as continuous DOS of electrodes to calculate the Green function of the electrodes. Two peaks of the transmission function found in the vicinity of the Fermi level are analyzed in terms of molecular orbitals (MOs). A convenient procedure to analyze MO contribution to a transmission peak is proposed. It is found that (I) symmetry-matched interactions between CuPc and the gold nanoelectrodes are important to the enhancement of the transmission function and (II) the nanoelectrodes have almost no effect on the electronic states of CuPc.
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Affiliation(s)
- Tomofumi Tada
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan
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509
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Geng H, Yin S, Chen KQ, Shuai Z. Effects of Intermolecular Interaction and Molecule−Electrode Couplings on Molecular Electronic Conductance. J Phys Chem B 2005; 109:12304-8. [PMID: 16852518 DOI: 10.1021/jp050650v] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
By applying nonequilibrium Green's function and first-principle calculation, we investigate the transport behavior of a prototype of a molecular device. The intermolecular interaction and molecule-electrode coupling effects are analyzed in detail, through which we can gain insight into the complexities within a molecular device such as intermolecular charge transport contributions and the imperfect molecule-electrode contact. The existing discrepancy between theory and experiment is discussed.
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Affiliation(s)
- Hua Geng
- Laboratory of Organic Solids, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, 100080 Beijing, PRC
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510
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Piva PG, DiLabio GA, Pitters JL, Zikovsky J, Rezeq M, Dogel S, Hofer WA, Wolkow RA. Field regulation of single-molecule conductivity by a charged surface atom. Nature 2005; 435:658-61. [PMID: 15931218 DOI: 10.1038/nature03563] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2005] [Accepted: 03/17/2005] [Indexed: 11/08/2022]
Abstract
Electrical transport through molecules has been much studied since it was proposed that individual molecules might behave like basic electronic devices, and intriguing single-molecule electronic effects have been demonstrated. But because transport properties are sensitive to structural variations on the atomic scale, further progress calls for detailed knowledge of how the functional properties of molecules depend on structural features. The characterization of two-terminal structures has become increasingly robust and reproducible, and for some systems detailed structural characterization of molecules on electrodes or insulators is available. Here we present scanning tunnelling microscopy observations and classical electrostatic and quantum mechanical modelling results that show that the electrostatic field emanating from a fixed point charge regulates the conductivity of nearby substrate-bound molecules. We find that the onset of molecular conduction is shifted by changing the charge state of a silicon surface atom, or by varying the spatial relationship between the molecule and that charged centre. Because the shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature.
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Affiliation(s)
- Paul G Piva
- Department of Physics, 534 Avadh Bhatia Physics Lab, University of Alberta, Edmonton, Alberta T6G 2J1, Canada
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511
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Wanunu M, Vaskevich A, Rubinstein I. Improved blocking properties of short-chain alkanethiol monolayers self-assembled on gold. Isr J Chem 2005. [DOI: 10.1560/2pr6-dw83-9dg9-9g2y] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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512
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513
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Sai N, Zwolak M, Vignale G, Di Ventra M. Dynamical corrections to the DFT-LDA electron conductance in nanoscale systems. PHYSICAL REVIEW LETTERS 2005; 94:186810. [PMID: 15904400 DOI: 10.1103/physrevlett.94.186810] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2004] [Indexed: 05/02/2023]
Abstract
Using time-dependent current-density functional theory, we derive analytically the dynamical exchange-correlation correction to the dc conductance of nanoscale junctions. The correction pertains to the conductance calculated in the zero-frequency limit of time-dependent density functional theory within the adiabatic local-density approximation. In particular, we show that in linear response, the correction depends nonlinearly on the gradient of the electron density; thus, it is more pronounced for molecular junctions than for quantum point contacts. We provide specific numerical examples to illustrate these findings.
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Affiliation(s)
- Na Sai
- Department of Physics, University of California-San Diego, La Jolla, CA 92093-0319, USA
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514
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Anariba F, Steach JK, McCreery RL. Strong Effects of Molecular Structure on Electron Transport in Carbon/Molecule/Copper Electronic Junctions. J Phys Chem B 2005; 109:11163-72. [PMID: 16852362 DOI: 10.1021/jp051093f] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Carbon/molecule/copper molecular electronic junctions were fabricated by metal deposition of copper onto films of various thicknesses of fluorene (FL), biphenyl (BP), and nitrobiphenyl (NBP) covalently bonded to flat, graphitic carbon. A "crossed-wire" junction configuration provided high device yield and good junction reproducibility. Current/voltage characteristics were investigated for 69 junctions with various molecular structures and thicknesses and at several temperatures. The current/voltage curves for all cases studied were nearly symmetric, scan rate independent, repeatable at least thousands of cycles and exhibited negligible hysteresis. Junction conductance was strongly dependent on the dihedral angle between phenyl rings and on the nature of the molecule/copper "contact". Junctions made with NBP showed a decrease in conductivity of a factor of 1300 when the molecular layer thickness increased from 1.6 to 4.5 nm. The slope of ln(i) vs layer thickness for both BP and NBP was weakly dependent on applied voltage and ranged from 0.16 to 0.24 A(-1). These attenuation factors are similar to those observed for similar molecular layers on modified electrodes used to study electrochemical kinetics. All junctions studied showed weak temperature dependence in the range of approximately 325 to 214 K, implying activation barriers in the range of 0.06 to 0.15 eV. The carbon/molecule/copper junction structure provides a robust, reproducible platform for investigations of the dependence of electron transport in molecular junctions on both molecular structure and temperature. Furthermore, the results indicate that junction conductance is a strong function of molecular structure, rather than some artifact resulting from junction fabrication.
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Affiliation(s)
- Franklin Anariba
- Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA
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515
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Han DH, Lee HJ, Park SM. Electrochemistry of conductive polymers XXXV: Electrical and morphological characteristics of polypyrrole films prepared in aqueous media studied by current sensing atomic force microscopy. Electrochim Acta 2005. [DOI: 10.1016/j.electacta.2004.10.085] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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516
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Zhang J, Chi Q, Albrecht T, Kuznetsov AM, Grubb M, Hansen AG, Wackerbarth H, Welinder AC, Ulstrup J. Electrochemistry and bioelectrochemistry towards the single-molecule level: Theoretical notions and systems. Electrochim Acta 2005. [DOI: 10.1016/j.electacta.2004.12.044] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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517
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Speets EA, Dordi B, Ravoo BJ, Oncel N, Hallbäck AS, Zandvliet HJW, Poelsema B, Rijnders G, Blank DHA, Reinhoudt DN. Noble metal nanoparticles deposited on self-assembled monolayers by pulsed laser deposition show coulomb blockade at room temperature. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2005; 1:395-8. [PMID: 17193461 DOI: 10.1002/smll.200400126] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Nanometer-sized noble-metal clusters are fabricated on top of alkylthiolate self-assembled monolayers (SAMs) on annealed gold by pulsed laser deposition at elevated pressures. The size distribution of the clusters depends on the metal and on the pressure during the deposition. Scanning tunneling microscopy (STM) and conductive probe atomic force microscopy (CP-AFM) showed that the metal clusters are insulated from the substrate on top of the SAM. Coulomb blockades could be measured at room temperature by STM for palladium clusters on decanethiol SAMs.
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Affiliation(s)
- Emiel A Speets
- Laboratory of Supramolecular Chemistry and Technology, MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
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518
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Chen YC, Zwolak M, Di Ventra M. Inelastic effects on the transport properties of alkanethiols. NANO LETTERS 2005; 5:621-624. [PMID: 15826097 DOI: 10.1021/nl047899t] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Using first-principles approaches, we investigate local heating and the inelastic contribution to the current for various alkanethiols sandwiched between metal electrodes. In the absence of good heat dissipation into the bulk electrodes, we find that the local temperature of the alkanethiols is relatively insensitive to their length. This is due to the rates of heating and cooling processes scaling similarly with length. On the other hand, when considering heat dissipation into the bulk electrodes, the local temperature of alkanethiols decreases as their length increases. We also find that the inelastic scattering profile displays an odd-even effect with length which compares well with experimental results. This effect is due to the alternating direction of the CH(3) group motion with respect to current flow with increasing C atoms in the chain and is very sensitive to the structure of the carbon-sulfur-gold bond. Inelastic scattering profiles can therefore help illuminate the bonding configuration of molecules to metallic surfaces.
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Affiliation(s)
- Yu-Chang Chen
- Department of Physics, University of California, San Diego, La Jolla, California 92093-0319, USA
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519
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Bilić A, Reimers JR, Hush NS. The structure, energetics, and nature of the chemical bonding of phenylthiol adsorbed on the Au(111) surface: Implications for density-functional calculations of molecular-electronic conduction. J Chem Phys 2005; 122:094708. [PMID: 15836163 DOI: 10.1063/1.1850455] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The adsorption of phenylthiol on the Au(111) surface is modeled using Perdew and Wang density-functional calculations. Both direct molecular physisorption and dissociative chemisorption via S-H bond cleavage are considered as well as dimerization to form disulfides. For the major observed product, the chemisorbed thiol, an extensive potential-energy surface is produced as a function of both the azimuthal orientation of the adsorbate and the linear translation of the adsorbate through the key fcc, hcp, bridge, and top binding sites. Key structures are characterized, the lowest-energy one being a broad minimum of tilted orientation ranging from the bridge structure halfway towards the fcc one. The vertically oriented threefold binding sites, often assumed to dominate molecular electronics measurements, are identified as transition states at low coverage but become favored in dense monolayers. A similar surface is also produced for chemisorption of phenylthiol on Ag(111); this displays significant qualitative differences, consistent with the qualitatively different observed structures for thiol chemisorption on Ag and Au. Full contours of the minimum potential energy as a function of sulfur translation over the crystal face are described, from which the barrier to diffusion is deduced to be 5.8 kcal mol(-1), indicating that the potential-energy surface has low corrugation. The calculated bond lengths, adsorbate charge and spin density, and the density of electronic states all indicate that, at all sulfur locations, the adsorbate can be regarded as a thiyl species that forms a net single covalent bond to the surface of strength 31 kcal mol(-1). No detectable thiolate character is predicted, however, contrary to experimental results for alkyl thiols that indicate up to 20%-30% thiolate involvement. This effect is attributed to the asymptotic-potential error of all modern density functionals that becomes manifest through a 3-4 eV error in the lineup of the adsorbate and substrate bands. Significant implications are described for density-functional calculations of through-molecule electron transport in molecular electronics.
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Affiliation(s)
- Ante Bilić
- School of Chemistry, University of Sydney, New South Wales 2006, Australia
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520
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Walker AV. Structure and energetics of small gold nanoclusters and their positive ions. J Chem Phys 2005; 122:094310. [PMID: 15836131 DOI: 10.1063/1.1857478] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We performed density functional theory calculations at the PW91PW91/LANL2DZ, PW91PW91/Stuttgart 1997, PW91PW91/CRENBL, B3LYP/LANL2DZ, and SVWN5/LANL2DZ levels of theory to attain the minimum-energy structures of neutral and cationic gold clusters of up to nine gold atoms. We locate the 2D-to-3D (two-dimensional to three-dimensional) transition in cationic clusters as occurring between Au(8) (+) and Au(9) (+). We also demonstrate that we can correlate the 2D-to-3D transition in cationic clusters with a linear extrapolation of the energy differences of the lowest-lying 2D and 3D structures of cluster sizes below the transition. We then use the same approach to predict that the 2D-to-3D transition occurs in neutral clusters at Au(11); this is confirmed by locating 3D Au(11) structures that are lower in energy than the best 2D structures reported to date. We examine the effects of choice of basis sets and exchange-correlation functionals on the relative stabilities and other properties of the calculated structures. Finally we find that there is good agreement between calculated and experimental data for clusters with up to six constituent atoms. For clusters with more than seven atoms, there are significant differences observed between the calculated and experimental properties using SVWN5/LANL2DZ, but there is still good agreement for the other levels of theory used.
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Affiliation(s)
- A V Walker
- Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA
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521
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Zhao J, Davis JJ. Molecular electron transfer of protein junctions characterised by conducting atomic force microscopy. Colloids Surf B Biointerfaces 2005; 40:189-94. [PMID: 15708512 DOI: 10.1016/j.colsurfb.2004.10.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The transport characteristics of the blue copper metalloprotein, azurin, have been characterised by conducting atomic force microscopy (C-AFM) at molecular level. Tunnel junctions have been constructed by sandwiching chemisorbed protein molecules between a conducting AFM tip and a planar conducting substrate. Asymmetric current curves with respect to the polarity of the bias (I-V) have been observed. The modulation of I-V behaviour with compressional force has been examined and is described by a modified Simmons model within which both tunnel distance (protein dimensions) and tunnel barrier are modulated. The modified Simmons formula, which considered unequal Fermi level shifts on two electrodes as being responsible for the asymmetric I-V curves, accurately describes the behaviour observed.
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Affiliation(s)
- Jianwei Zhao
- Inorganic Chemistry Laboratory, Department of Chemistry, South Parks Road, Oxford OX1 3QR, UK
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522
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Champagne AR, Pasupathy AN, Ralph DC. Mechanically adjustable and electrically gated single-molecule transistors. NANO LETTERS 2005; 5:305-8. [PMID: 15794616 DOI: 10.1021/nl0480619] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
We demonstrate a device geometry for single-molecule electronics experiments that combines both the ability to adjust the spacing between the electrodes mechanically and the ability to shift the energy levels in the molecule using a gate electrode. With the independent in-situ variations of molecular properties provided by these two experimental "knobs", we are able to achieve a much more detailed characterization of electron transport through the molecule than is possible with either technique separately. We illustrate the performance of the device using C(60) molecules.
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Affiliation(s)
- Alexandre R Champagne
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
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523
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Liu R, Ke SH, Baranger HU, Yang W. Intermolecular effect in molecular electronics. J Chem Phys 2005; 122:44703. [PMID: 15740279 DOI: 10.1063/1.1825377] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We investigate the effects of lateral interactions on the conductance of two molecules connected in parallel to semi-infinite leads. The method we use combines a Green function approach to quantum transport with density functional theory for the electronic properties. The system, modeled after a self-assembled monolayer, consists of benzylmercaptane molecules sandwiched between gold electrodes. We find that the conductance increases when intermolecular interaction comes into play. The source of this increase is the indirect interaction through the gold substrate rather than direct molecule-molecule interaction. A striking resonance is produced only 0.3 eV above the Fermi energy.
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Affiliation(s)
- Rui Liu
- Department of Chemistry, Duke University, Durham, NC 27708-0354, USA
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524
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Combellas C, Kanoufi F, Pinson J, Podvorica FI. Time-of-flight secondary ion mass spectroscopy characterization of the covalent bonding between a carbon surface and aryl groups. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:280-286. [PMID: 15620315 DOI: 10.1021/la048106l] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Grafting of aryl layers derived from aryl diazonium salts onto glassy carbon electrodes is observed by time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The grafting occurs spontaneously when a glassy carbon plate is immersed into a solution of aryl diazonium salt and can be enhanced by biasing the carbon plate at a potential a little more negative than the diazonium salt reduction. C-C and C-O covalent bonding are believed to be responsible for the strong attachment of these layers onto the carbon substrate. Fragments containing aryl dimers, trimers, or tetramers are also observed. A mechanism is proposed to account for the formation of these polymeric chains.
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Affiliation(s)
- Catherine Combellas
- Laboratoire Environnement et Chimie Analytique, CNRS-ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France.
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525
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Morales RGE, González-Rojas C. Dipole moments of polyenic oligomeric systems. Part II—molecular organic wire resistivities: polyacetylenes, allenes and polyynes. J PHYS ORG CHEM 2005. [DOI: 10.1002/poc.931] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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526
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527
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Selzer Y, Cai L, Cabassi MA, Yao Y, Tour JM, Mayer TS, Allara DL. Effect of local environment on molecular conduction: isolated molecule versus self-assembled monolayer. NANO LETTERS 2005; 5:61-65. [PMID: 15792413 DOI: 10.1021/nl048372j] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Developing a fundamental understanding of molecular conduction in different device environments is essential to the advance of molecular electronics. We show through a quantitative comparison of two types of junctions with the same molecule - one based on an isolated individual molecule and the other on a self-assembled monolayer - that intrinsic differences in the conduction per molecule as large as several orders of magnitude can exist simply as a function of the presence or absence of neighboring molecules. This behavior can be understood on the basis of thermal and electrostatic effects that depend critically on the local molecular environment. These results will help to unify data obtained from disparate device structures and to provide an improved basis for designing future molecular electronic devices.
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Affiliation(s)
- Yoram Selzer
- Department of Chemistry and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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528
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529
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Galperin M, Ratner MA, Nitzan A. Hysteresis, switching, and negative differential resistance in molecular junctions: a polaron model. NANO LETTERS 2005; 5:125-130. [PMID: 15792425 DOI: 10.1021/nl048216c] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Within a simple mean-field model (self-consistent Hartree approximation) we discuss the possibility of polaron formation on a molecular wire as a mechanism for negative differential resistance (NDR), switching, and/or hysteresis in the I-V characteristic of molecular junctions. This mechanism differs from earlier proposed mechanisms of charging and conformational change. The polaron model captures the essential physics and provides qualitative correspondence with experimental data. The importance of active redox centers in the molecule is indicated.
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Affiliation(s)
- Michael Galperin
- Department of Chemistry and Nanotechnology Center, Northwestern University, Evanston, Illinois 60208, USA
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530
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Samorì P. Exploring supramolecular interactions and architectures by scanning force microscopies. Chem Soc Rev 2005; 34:551-61. [PMID: 15965537 DOI: 10.1039/b404021j] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The development of new methodologies based on scanning force microscopy (SFM) has made it possible to map topographies, chemical functionalities, and numerous other physicochemical properties of complex assemblies, to unravel dynamic processes, to measure forces generated along a reaction coordinate, to nanopattern surfaces and to nanomanipulate objects. This tutorial review highlights the most recent applications of these SFM-based capabilities, on and beyond imaging, to the exploration of supramolecular interactions and architectures, to the fabrication of smart materials and to the optimization of (nano)devices.
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Affiliation(s)
- Paolo Samorì
- Istituto per la Sintesi Organica e la Fotoreattività--Consiglio Nazionale delle Ricerche, via Gobetti 101, I-40129 Bologna, Italy.
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531
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Chung SW, Ginger DS, Morales MW, Zhang Z, Chandrasekhar V, Ratner MA, Mirkin CA. Top-down meets bottom-up: dip-pen nanolithography and DNA-directed assembly of nanoscale electrical circuits. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2005; 1:64-9. [PMID: 17193349 DOI: 10.1002/smll.200400005] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Affiliation(s)
- Sung-Wook Chung
- Department of Chemistry & Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA
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532
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Cao Z, Zhang Q. Computational analyses of singlet-singlet and singlet-triplet transitions in mononuclear gold-capped carbon-rich conjugated complexes. J Comput Chem 2005; 26:1214-21. [PMID: 15957180 DOI: 10.1002/jcc.20258] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Density functional theory and CASSCF calculations have been used to determine equilibrium geometries and vibrational frequencies of metal-capped one-dimensional pi-conjugated complexes (H3P)Au(C[triple chemical bond]C)(n)(Ph) (n = 1-6), (H3P)Au(C[triple chemical bond]CC6H4)(C[triple chemical bond]CPh), and H3P--Au(C[triple chemical bond]CC6H4)C[triple chemical bond]CAu--PH3 in their ground states and selected low-lying pi(pi)* excited states. Vertical excitation energies for spin-allowed singlet-singlet and spin-forbidden singlet-triplet transitions determined by the time-dependent density functional theory show good agreement with available experimental observations. Calculations indicate that the lowest energy 3(pi(pi)*) excited state is unlikely populated by the direct electronic excitation, while the low-lying singlet and triplet states, slightly higher in energy than the lowest triplet state, are easily accessible by the excitation light used in experiments. A series of radiationless transitions among related excited states yield the lowest 3(pi(pi)*) state, which has enough long lifetimes to exhibit its photochemical reactivities.
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Affiliation(s)
- Zexing Cao
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China.
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533
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Davis JJ, Morgan DA, Wrathmell CL, Axford DN, Zhao J, Wang N. Molecular bioelectronics. ACTA ACUST UNITED AC 2005. [DOI: 10.1039/b417712f] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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534
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Photoinduced Electron/Energy Transfer Across Molecular Bridges in Binuclear Metal Complexes. MOLECULAR WIRES AND ELECTRONICS 2005; 257:63-102. [DOI: 10.1007/b136067] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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535
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Holman MW, Adams DM. Using Single-Molecule Fluorescence Spectroscopy to Study Electron Transfer. Chemphyschem 2004; 5:1831-6. [PMID: 15648130 DOI: 10.1002/cphc.200400123] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Techniques in single-molecule fluorescence spectroscopy now allow sophisticated studies of photophysical processes in single molecules. As interest grows in the possibilities of molecular electronics, researchers have begun to turn these techniques to the study of electron transfer. Electron-transfer reactions have now been detected and measured at the single-molecule level in a variety of systems and on a variety of timescales by adapting techniques from previous single-molecule fluorescence studies.
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Affiliation(s)
- Michael W Holman
- Department of Chemistry, Columbia University, New York, NY 10027, USA
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536
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Wu SW, Nazin GV, Chen X, Qiu XH, Ho W. Control of relative tunneling rates in single molecule bipolar electron transport. PHYSICAL REVIEW LETTERS 2004; 93:236802. [PMID: 15601185 DOI: 10.1103/physrevlett.93.236802] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2004] [Indexed: 05/24/2023]
Abstract
The influence of relative electron tunneling rates on electron transport in a double-barrier single-molecule junction is studied. The junction is defined by positioning a scanning tunneling microscope tip above a copper phthalocyanine molecule adsorbed on a thin oxide film grown on the NiAl(110) surface. By tuning the tip-molecule separation, the ratio of tunneling rates through the two barriers, vacuum and oxide, is controlled. This results in dramatic changes in the relative intensities of individual conduction channels, associated with different vibronic states of the molecule.
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Affiliation(s)
- S W Wu
- Department of Physics and Astronomy, University of California, Irvine, CA 92697-4575, USA
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537
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Jiang J, Lu W, Luo Y. Length dependence of coherent electron transportation in metal–alkanedithiol–metal and metal–alkanemonothiol–metal junctions. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2004.10.136] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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538
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Nowak AM, McCreery RL. In Situ Raman Spectroscopy of Bias-Induced Structural Changes in Nitroazobenzene Molecular Electronic Junctions. J Am Chem Soc 2004; 126:16621-31. [PMID: 15600368 DOI: 10.1021/ja045763r] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Carbon/nitroazobenzene (NAB)/titanium/gold molecular electronic junctions with active thicknesses of 7-8 nm were constructed having partially transparent Ti/Au top contacts, which permitted in situ monitoring of molecular structure with Raman spectroscopy for applied biases between +3 and -3 V. Deposition of the Ti/Au top contacts resulted in spectral changes similar to those accompanying NAB reduction in a conventional spectroelectrochemical experiment. Upon application of +3 V (carbon relative to Ti), the spectrum indicated reoxidation of the NAB reduction product, and this redox cycle could be repeated at least three times. When a voltage excursion to -2 or -3 V occurred, the spectra indicated irreversible loss of the nitro group, and a dramatic but reversible decrease in Raman intensity over the entire shift range examined. Negative applied voltage causes formation of reduced NAB and a high oxidation state of titanium, while positive voltage forms oxidized NAB and injects electrons into the titanium oxide layer. The spectral changes were correlated with current/voltage curves in order to probe the mechanism of rectification and conductance switching reported previously. Overall, the combination of spectroscopic and voltammetric results implies a conduction mechanism involving both NAB and titanium oxide, possibly mediated by the injection of carriers into the semiconducting titanium oxide, or by reduction of an insulating titanium oxide to a more conductive form.
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Affiliation(s)
- Aletha M Nowak
- Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA
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539
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Blum AS, Kushmerick JG, Pollack SK, Yang JC, Moore M, Naciri J, Shashidhar R, Ratna BR. Charge Transport and Scaling in Molecular Wires. J Phys Chem B 2004. [DOI: 10.1021/jp0480854] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Amy Szuchmacher Blum
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - James G. Kushmerick
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - Steven K. Pollack
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - John C. Yang
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - Martin Moore
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - Jawad Naciri
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - Ranganathan Shashidhar
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
| | - Banahalli R. Ratna
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375
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540
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Zhao J, Uosaki K. Electron Transfer through Organic Monolayers Directly Bonded to Silicon Probed by Current Sensing Atomic Force Microscopy: Effect of Chain Length and Applied Force. J Phys Chem B 2004. [DOI: 10.1021/jp049719+] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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541
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Alliata D, Andolfi L, Cannistraro S. Tip to substrate distances in STM imaging of biomolecules. Ultramicroscopy 2004; 101:231-40. [PMID: 15450668 DOI: 10.1016/j.ultramic.2004.06.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2003] [Revised: 06/03/2004] [Accepted: 06/21/2004] [Indexed: 10/26/2022]
Abstract
STM images of single biomolecules adsorbed on conductive substrates do not reproduce the expected physical height, which generally appears underestimated. This may cause the tip to interfere with the soft biological sample during the imaging scans. Therefore, a key requirement to avoid invasive STM imaging is the knowledge, and the control, of the initial tip to substrate distance. This is connected to the setting of the tunnelling current and applied voltage, which define a tunnelling resistance. The height of the STM tip was measured by calibrating the tunnelling resistance, as a function of its vertical displacement until establishing a mechanical contact. At a tunnelling resistance of 4 x 10(9)Omega, distances of about 3 and 6 nm are estimated when flat Au substrates are imaged in water and in air, respectively. On such a ground, the relevance of the starting tip-substrate distance in determining a non-invasive imaging has been investigated for a plastocyanin mutant chemisorbed on Au(111) electrodes. At tunnelling distances sufficient to overcome the physical height of the imaged biomolecules, their lateral dimensions are found to be consistent with the crystallography, whereas they are significantly broadened for smaller distances.
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Affiliation(s)
- Dario Alliata
- Biophysics & Nanoscience Centre, INFM, Dipartimento di Scienze Ambientali, Università della Tuscia, I-01100 Viterbo, Italy
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542
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Tada T, Nozaki D, Kondo M, Hamayama S, Yoshizawa K. Oscillation of Conductance in Molecular Junctions of Carbon Ladder Compounds. J Am Chem Soc 2004; 126:14182-9. [PMID: 15506784 DOI: 10.1021/ja031736+] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electrical conductances of dithiolates of polyacene (PA(n)DTs) and polyphenanthrene (PPh(n)DTs), which are typical carbon ladder compounds, are calculated by means of the Landauer formulation combined with density functional theory, where n is the number of benzene rings involved. Surface Green function used in the Landauer formulation is calculated with the Slater-Koster parameters. Attention is turned to the wire-length dependence of the conductances of PA(n)DTs and PPh(n)DTs. The damping of conductance of PA(n)DTs is much smaller than that of PPh(n)DTs because of the small HOMO-LUMO gaps of PA(n)DTs. PA(n)DTs are thus good molecular wires for nanosized electronic devices. Conductance oscillation is found for both molecular wires when n is less than 7. The electrical conductance is enhanced in PA(n)DTs with even-numbered benzene rings, whereas it is enhanced in PPh(n)DTs with odd-numbered benzene rings. The observed conductance oscillation of PA(n)DTs and PPh(n)DTs is due to the oscillation of orbital energy and electron population. Other pi-conjugated oligomers (polyacetylene-DT, oligo(thiophene)-DT, oligo(meso-meso-linked zinc(II) porphyrin-butadiynylene)-DT, oligo(p-phenylethynylene)-DT, and oligo(p-phenylene)-DT) are also studied. In contrast to PA(n)DTs and PPh(n)DTs, the five molecular wires show ordinary exponential decays of conductance.
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Affiliation(s)
- Tomofumi Tada
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan
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543
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544
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Lee HJ, Park SM. Electrochemistry of Conductive Polymers. 33. Electrical and Optical Properties of Electrochemically Deposited Poly(3-methylthiophene) Films Employing Current-Sensing Atomic Force Microscopy and Reflectance Spectroscopy. J Phys Chem B 2004. [DOI: 10.1021/jp0472764] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hyo Joong Lee
- Department of Chemistry and Center for Integrated Molecular Systems, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, Korea
| | - Su-Moon Park
- Department of Chemistry and Center for Integrated Molecular Systems, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, Korea
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545
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Kondo M, Tada T, Yoshizawa K. Wire-Length Dependence of the Conductance of Oligo(p-phenylene) Dithiolate Wires: A Consideration from Molecular Orbitals. J Phys Chem A 2004. [DOI: 10.1021/jp038018u] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Masakazu Kondo
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan
| | - Tomofumi Tada
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan
| | - Kazunari Yoshizawa
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan
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546
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Haiss W, van Zalinge H, Höbenreich H, Bethell D, Schiffrin DJ, Higgins SJ, Nichols RJ. Molecular wire formation from viologen assemblies. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:7694-7702. [PMID: 15323521 DOI: 10.1021/la049183j] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The adsorption behavior of viologen alpha,omega-dithiols (viologen dithiols) on gold has been investigated. At short exposures, a low-coverage phase consisting of flat-lying molecules has been determined by STM and IR spectroscopy. In contrast, multilayer films are formed after long adsorption times. Single molecular wires could be formed between a gold STM tip and a surface with a low coverage of the adsorbed dithiols, and their electrical behavior was investigated. Molecular conductivity was determined either by the repeated measurement of I(s) curves or by recording I-V curves for different tip-sample separations. These methods concurred in producing a value of (0.5 +/- 0.1) nS for the single-molecule conductivity of the alpha,omega-viologen dithiol molecule HS-6V6-SH. The high conductivity of HS-6V6-SH, as compared to that of HS-C12-SH, may be related to the low-lying LUMO, which provides a barrier indentation for electron transport in a two-step electron-transfer mechanism.
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Affiliation(s)
- Wolfgang Haiss
- Centre for Nanoscale Science, Chemistry Department, University of Liverpool, Liverpool L69 7ZD, UK
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547
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Han DH, Park SM. Electrochemistry of Conductive Polymers. 32. Nanoscopic Examination of Conductivities of Polyaniline Films. J Phys Chem B 2004. [DOI: 10.1021/jp0494279] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dong-Hun Han
- Department of Chemistry and Center for Integrated Molecular Systems, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, Korea
| | - Su-Moon Park
- Department of Chemistry and Center for Integrated Molecular Systems, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, Korea
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548
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Nobusada K. Electronic Structure and Photochemical Properties of a Monolayer-Protected Gold Cluster. J Phys Chem B 2004. [DOI: 10.1021/jp049879l] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Katsuyuki Nobusada
- Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, 060-0810 Japan
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549
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Anderson NA, Lian T. Ultrafast electron injection from metal polypyridyl complexes to metal-oxide nanocrystalline thin films. Coord Chem Rev 2004. [DOI: 10.1016/j.ccr.2004.03.029] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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550
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Wang B, Luo J, Wang X, Wang H, Hou JG. Dielectric properties and frequency response of self-assembled monolayers of alkanethiols. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:5007-12. [PMID: 15984261 DOI: 10.1021/la036295m] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
This paper presents dielectric properties of alkanethiol self-assembled monolayers (SAMs) under an ac electric field. Using a Hg-SAM/SAM-Hg junction, we measured the ac impedance of alkanethiol SAMs using a sinusoidal perturbation of 30 mV (peak-to-peak) with frequency ranging from 1 Hz to 1 MHz at zero bias. Semicircles at higher frequencies and at middle frequencies along with Warburg lines at lower frequencies were observed in complex plane impedance plots, that is, Nyquist plots. The frequency response of SAMs was analyzed by modeling the junction using an equivalent circuit and fitting the Nyquist plots. The semicircles at higher frequencies are attributed to the effect of the SAM/SAM interfaces, and the ones at middle frequencies are attributed to the effect of alkanethiol SAMs. The comparison in the plots of the imaginary part of the impedance Z against frequency for the bare Hg electrodes (in pure ethanal) and the SAM-covered Hg electrodes (in alkanethiol solution) supports the analysis. The Warburg lines are attributed to a certain ionic impurity. The dielectric loss spectra are further analyzed. Chain-length-dependent peaks, which correspond to different relaxation mechanisms, at higher frequencies and middle frequencies were observed in the spectra of the dissipation factor (tan delta vs frequency). The peaks move to small frequency with the increase of chain length of alkanethiols. Using a correlation of peak position with the chain length, we then derived active energies of 39-99 meV for alkanethiol SAMs of C7-C18 under an ac electric field.
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Affiliation(s)
- Bing Wang
- Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
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