Tunable Charge Transport in Single-Molecule Junctions via Electrolytic Gating

Capozzi, Brian; Chen, Qishui; Darancet, Pierre; Kotiuga, Michele; Buzzeo, Marisa C.; Neaton, Jeffrey B.; Nuckolls, Colin; Venkataraman, Latha

doi:10.1021/nl404459q

Cited by 116 publications

(120 citation statements)

References 36 publications

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“…We further introduce a model that, in combination with first- principles calculations, explains the experiments quantitatively for arbitrary surface concentrations of solvent and conducting molecules and predicts that the conductance of HOMO-and LUMO-conducting molecular junctions exhibits an opposite trend in solvent-dependence, demonstrating the potential for different solvents to discriminate between hole or electron transport, much like a thermopower measurement. The magnitude of these effects is comparable to the one induced by ionic gating [31], establishing liquid neutral solvents as a potential route to realize three-terminal device physics in singlemolecular junctions.…”

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confidence: 98%

Adsorption-Induced Solvent-Based Electrostatic Gating of Charge Transport through Molecular Junctions

et al. 2015

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Recent experiments have shown that transport properties of molecular-scale devices can be reversibly altered by the surrounding solvent. Here, we use a combination of first-principles calculations and experiment to explain this change in transport properties through a shift in the local electrostatic potential at the junction caused by nearby conducting and solvent molecules chemically bound to the electrodes. This effect is found to alter the conductance of 4,4'-bipyridine-gold junctions by more than 50%. Moreover, we develop a general electrostatic model that quantitatively predicts the relationship between conductance and the binding energies and dipoles of the solvent and conducting molecules. Our work shows that solvent-induced effects are a viable route for controlling charge and energy transport at molecular-scale interfaces.PACS numbers: 31.15. A-,73.30.+y,73.63.-b,85.65.+h Single-molecule junctions, individual molecules contacted with macroscopic electrodes, provide unique insight into the nanoscale physics of charge, spin, and energy transport [1][2][3][4]. To date, the most robust and reproducible approach to assemble single-molecule junctions is the scanning tunneling microscope-based break junction (STM-BJ) technique [5,6], allowing statistically significant measurements of molecular junction conductance [5-9], thermopower [10][11][12], mechanical properties [13][14][15], and binding mechanisms [15]. Previouslydeveloped theoretical approaches have led to quantitative agreement with experiment for molecular junctions, given a good approximation to the junction geometry and a good estimate of the differences in energy ∆E between the junction Fermi energy, E F and the orbital energy of the frontier orbital, either the highest occupied or lowest unoccupied molecular orbital (HOMO or LUMO, respectively) [16]. Theoretical works focusing on this level alignment [17,18] have led to increased understanding and control of molecular junction conductance and thermopower in terms of junction level alignment, with significant impact on experiments [10][11][12]19].Commonly, these experiments take place at room temperature in a non-conductive solvent [5][6][7][8], which has recently been shown to influence both junction formation probability and, in some cases, to alter the conductance [20]. Despite its practical importance, the impact of these solvents on conductance has not yet been fully understood or explained by theory, in part due to the large computation cost [21], and, therefore, continues to be elusive to control. Previous theoretical works have focused on the effect of solvent on the average [22,23] and dynamical [24] molecular junction geometries, and how they affect level alignment and modify the conductance [25]. Another focus has been the coupling of transmission channels due to intermolecular hopping between conducting molecules [26], in the case solvent would influence the formation of multiple simultaneous junctions. However a detailed physical picture and quantitative framework for understandin...

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Adsorption-Induced Solvent-Based Electrostatic Gating of Charge Transport through Molecular Junctions

et al. 2015

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“…and subsequently by Capozzi et al 6 Non-redox gating relies directly on the modulation of the electronic energy levels of the molecule and the contacts, and closely resembles the operation of the traditional field-effect transistor.…”

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Single-Molecule Electrochemical Transistor Utilizing a Nickel-Pyridyl Spinterface

et al. 2014

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Using a scanning tunnelling microscope break-junction technique, we produce 4,4'-bipyridine (44BP) single-molecule junctions with Ni and Au contacts. Electrochemical control is used to prevent Ni oxidation, and to modulate the conductance of the devices via non-redox gating -the first time this has been shown using non-Au contacts. Remarkably the conductance and gain of the resulting Ni-44BP-Ni electrochemical transistors is significantly higher than analogous Au-based devices. Ab-initio calculations reveal that this behaviour arises because charge transport is mediated by spin-polarized Ni d -electrons, which hybridize strongly with molecular orbitals to form a 'spinterface'.Our results highlight the important role of the contact material for single-molecule devices, and show that it can be varied to provide control of charge and spin transport. KeywordsSingle-molecule, Break-junction, Electrochemical gating, Spintronics, Density functional theory, Metal-molecule interface Main TextSingle-molecule transistor behaviour can be achieved using a gate electrode to control the energy levels of a molecule bridging two metallic electrodes. 1 This gate can be provided electrochemically using the double layer potential existing at the metal-electrolyte interface (Fig. 1a). An electrochemical gate avoids the complex fabrication of solid-state threeterminal molecular devices, can operate in room temperature liquid environments, and can produce high gate efficiencies thanks to the large electric fields which are achievable. There has been significant interest in redox active molecules such as viologens as candidates for electrochemical transistors, 2-4 however the gating of non-redox molecules has only recently been demonstrated using Au electrodes by Li et al. 5 with 4,4'-bipyridine (44BP) molecules,

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“…6,7 The concept of "electrochemical gating" which provides the opportunity to overcome the technical challenges of incorporating a gate electrode in a solid-state molecular device, has been employed in electrochemically active molecular systems, including viologens, [8][9][10] oligoaniline, 11 ferrocene, [12][13][14] transition metal complexes, 7,15,16 perylenebisimides, [17][18][19] redox-active proteins, 20,21 quinones 22,23 and tetrathiafulvalene, 24 as well as redox-inactive molecules. 25 In the case of redox-inactive molecules, or more generally when the electrode potential does not overlap with the molecule's redox potential, the effect of the gate is simply to shift the molecular levels up or down in energy relative to the Fermi level. In a simple picture where tunneling through the molecule is described by "Lorentzian" transmission peaks centered at the discrete energy levels of the molecule, a large on/off conductance ratio can be achieved by moving the frontier molecular level in and out of resonance with the Fermi level E F .…”

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Electrochemical Control of Single-Molecule Conductance by Fermi-Level Tuning and Conjugation Switching

et al. 2014

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Controlling charge transport through a single molecule connected to metallic electrodes remains one of the most fundamental challenges of nanoelectronics. Here we use electrochemical gating to reversibly tune the conductance of two different organic molecules, both containing anthraquinone (AQ) centers, over >1 order of magnitude. For electrode potentials outside the redox-active region, the effect of the gate is simply to shift the molecular energy levels relative to the metal Fermi level. At the redox potential, the conductance changes abruptly as the AQ unit is oxidized/reduced with an accompanying change in the conjugation pattern between linear and cross conjugation. The most significant change in conductance is observed when the electron pathway connecting the two electrodes is via the AQ unit. This is consistent with the expected occurrence of destructive quantum interference in that case. The experimental results are supported by an excellent agreement with ab initio transport calculations.

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Tunable Charge Transport in Single-Molecule Junctions via Electrolytic Gating

Cited by 116 publications

References 36 publications

Adsorption-Induced Solvent-Based Electrostatic Gating of Charge Transport through Molecular Junctions

Adsorption-Induced Solvent-Based Electrostatic Gating of Charge Transport through Molecular Junctions

Single-Molecule Electrochemical Transistor Utilizing a Nickel-Pyridyl Spinterface

Electrochemical Control of Single-Molecule Conductance by Fermi-Level Tuning and Conjugation Switching

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