Electron Transfer through Organic Molecules

Bumm, Lloyd A.; Arnold, Jamie J.; Dunbar, T. D.; Allara, David L.; Weiss, Paul S.

doi:10.1021/jp9921699

Cited by 383 publications

(501 citation statements)

References 52 publications

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“…However, Weiss et al proposed a model for the influence of the chain on electron tunneling in an explanation of the STM image contrast of SAM samples with mixed compositions. 28 In their model, the conductance of the SAM films decreased much more slowly as the alkyl chain length increased than it did for an increase in air gap thickness. The decay constant of the air was larger (0.23 nm…”

Section: Molecular Scale Images Reveal That Alkanethiol Sams Form a (mentioning

confidence: 95%

Effects of Tunneling Current on STM Imaging Mechanism for Alkanethiol Self-assembled Monolayers on Au(111)

Mamun¹,

Bae²,

Hahn³

2011

Bulletin of the Korean Chemical Society

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We investigated the effects of tunneling current on scanning tunneling microscopy (STM) images of 1-octanethiol (OT) and 1-decanethiol (DT) self-assembled monolayers (SAMs). At a low tunneling current, the domain boundaries and ordered alkanethiol molecules were clearly resolved. As the tunneling current was increased at a constant bias voltage, however, the STM images showed disordered structures of the OT and DT SAMs. As the tunneling current was reduced back to low values, the ordered structures of the alkanethiol molecules reappeared. The reversibility of the process suggests that the sulfur head groups did not rearrange under any of the tunneling current conditions. On the basis of our observations, which are inconsistent with the standard model for STM imaging of molecules on metal surfaces, we consider the STM imaging mechanism in terms of a two-region tunneling junction model.

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Section: Molecular Scale Images Reveal That Alkanethiol Sams Form a (mentioning

confidence: 95%

Effects of Tunneling Current on STM Imaging Mechanism for Alkanethiol Self-assembled Monolayers on Au(111)

Mamun¹,

Bae²,

Hahn³

2011

Bulletin of the Korean Chemical Society

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“…The most difficult challenge in molecularbased electronics is without doubt the necessity of demonstrating that the data obtained in using molecular bridges between electrodes do not result from artifacts (32). The techniques available for measuring individual molecules [e.g., STM (33)(34)(35)(36), mechanically controlled break junction (MCBJ) (37)(38)(39), and more recently the nanosquid (40)] require the design of suitable molecular candidates for switch devices to help resolve these fundamental issues.…”

Section: Wwwannualreviewsorg • Light Switching Of Molecules On Surfmentioning

confidence: 99%

Light Switching of Molecules on Surfaces

Browne

Feringa

2009

Annu. Rev. Phys. Chem.

274

254

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Smart surfaces, surfaces that respond to an external stimulus in a defined manner, hold considerable potential as components in molecular-based devices, not least as discrete switching elements. Many stimuli can be used to switch surfaces between different states, including redox, light, pH, and ion triggers. The present review focuses on molecular switching through the electronic excitation of molecules on surfaces with light. In developing light-responsive surfaces, investigators face several challenges, not only in achieving high photostationary states and fully reversible switching, but also in dealing with fatigue resistance and the effect of immobilization itself on molecular properties. The immobilization of light-responsive molecules requires the design and synthesis of functional molecular components both to achieve light switching and to anchor the molecular entity onto a surface. This review discusses several demonstrative examples of photoswitchable molecular systems in which the photochemistry has been explored in the immobilized state under ambient conditions and especially on electroactive surfaces, including self-assembled monolayers, bilayers, and polymer films.

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“…Alkane chains are standard molecules in which electron transport has been studied extensively. [15][16][17][18][19][20][21][22] The main result of those prior studies is that the current decays exponentially with chain length with a decay constant β ∼ 1.0 per CH 2 unit, with some variation across different experiments. [15][16][17][18][19]23 This dependence has been also successfully addressed computationally using Density Functional Theory (DFT) combined with non-equilibrium Green's function (NEGF) studies.…”

Section: Introductionmentioning

confidence: 99%

Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure

et al. 2014

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This paper examines charge transport by tunneling across a series of electrically (insulating molecules with the structure HS(CH 2 ) 4 CONH(CH 2 ) 2 R) in the form of selfassembled monolayers (SAMs), supported on silver. The molecules examined were studied experimentally by Yoon et al. (Angew. Chem. Int. Ed., 51, 4658−4661, 2012), using junctions of the structure AgS(CH 2 ) 4 CONH(CH 2 ) 2 R//Ga 2 O 3 /EGaIn. The tail group R had approximately the same length for all molecules, but a range of different structures. Changing the R entity over a range of different structures (aliphatic to aromatic) does not influence the conductance significantly. To rationalize this surprising result, we investigate transport through these SAMs theoretically, using both full quantum methods and a generic, independent-electron tight-binding toy model. We find that the frontier orbitals HOMO, HOMO-1, HOMO-2 and HOMO-3, have similar structures for all of the different R-groups, and that the HOMO, which is largely responsible for the transport in these molecules, is always strongly localized on the thiol group. The relative insensitivity of the current density to the structure of the R group is due not only to these similar frontier orbitals but also to a combination of energy levels (ε) and tunneling amplitudes (t), which lead to similar conductance for different tail groups, i.e. the large difference between ε's in conjugated and saturated groups is compensated by tunneling amplitudes inside the tail group. In addition, the coupling of the tail group to the alkane chain is much weaker for conjugated groups than for saturated ones. Conductance change in these molecules is not influenced by the broadening of the molecular levels connected to the left and right electrodes, since in all these molecules the effective coupling to the silver substrate is the same, whereas the other effective couplings are determined by the weak connection to the oxide Ga 2 O 3 layer. All these factors combine to produce currents largely insensitive to the R group.An estimation of the attenuation constant, β, of the simplified Simmons equation obtained using these methods is β = 1.1 per CH 2 group, in good agreement with observed results. Our analysis sketches the potential landscapes across which tunneling occurs, and suggests that it will be difficult to change rates of tunneling by simple changes 2 in molecular structure. This work indicates that significant control over SAMs largely composed of nominally insulating groups may be possible when tail groups are used that are significantly larger than those used in the experiments of Yoon et al. 13

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Electron Transfer through Organic Molecules

Cited by 383 publications

References 52 publications

Effects of Tunneling Current on STM Imaging Mechanism for Alkanethiol Self-assembled Monolayers on Au(111)

Effects of Tunneling Current on STM Imaging Mechanism for Alkanethiol Self-assembled Monolayers on Au(111)

Light Switching of Molecules on Surfaces

Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure

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