101
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Vacek J, Chocholoušová JV, Stará IG, Starý I, Dubi Y. Mechanical tuning of conductance and thermopower in helicene molecular junctions. NANOSCALE 2015; 7:8793-8802. [PMID: 25905658 DOI: 10.1039/c5nr01297j] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Helicenes are inherently chiral polyaromatic molecules composed of all-ortho fused benzene rings possessing a spring-like structure. Here, using a combination of density functional theory and tight-binding calculations, it is demonstrated that controlling the length of the helicene molecule by mechanically stretching or compressing the molecular junction can dramatically change the electronic properties of the helicene, leading to a tunable switching behavior of the conductance and thermopower of the junction with on/off ratios of several orders of magnitude. Furthermore, control over the helicene length and number of rings is shown to lead to more than an order of magnitude increase in the thermopower and thermoelectric figure-of-merit over typical molecular junctions, presenting new possibilities of making efficient thermoelectric molecular devices. The physical origin of the strong dependence of the transport properties of the junction is investigated, and found to be related to a shift in the position of the molecular orbitals.
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Affiliation(s)
- Jaroslav Vacek
- Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610 Prague 6, Czech Republic.
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102
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Affiliation(s)
- Robert M. Metzger
- Laboratory for Molecular
Electronics, Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336, United States
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103
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Huang J, Wang W, Li Q, Yang J. Negative differential resistance devices by using N-doped graphene nanoribbons. J Chem Phys 2015; 140:164703. [PMID: 24784295 DOI: 10.1063/1.4871739] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Recently, extensive efforts have been devoted to the investigations of negative differential resistance (NDR) behavior in graphene. Here, by performing fully self-consistent density functional theory calculations combined with non-equilibrium Green's function technique, we investigate the transport properties of three molecules from conjugated molecule, one-dimension alkane chain, and single molecule magnet, which are sandwiched between two N-doped zigzag and armchair graphene nanoribbons (GNRs). We observe robust NDR effect in all examined molecular junctions including benzene, alkane, and planar four-coordinated Fe complex. Through the analyses of the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of N-doped GNRs and the bias-dependent effective coupling between the discrete frontier molecular orbitals and the subbands of N-doped GNRs are responsible for the observed NDR phenomenon. These theoretical findings imply that N-doped GNRs hold great potential for building NDR devices based on various molecules.
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Affiliation(s)
- Jing Huang
- School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei, Anhui 230601, China
| | - Weiyi Wang
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Qunxiang Li
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jinlong Yang
- Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
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104
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Ochoa MA, Selzer Y, Peskin U, Galperin M. Pump-Probe Noise Spectroscopy of Molecular Junctions. J Phys Chem Lett 2015; 6:470-476. [PMID: 26261965 DOI: 10.1021/jz502484z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The slow response of electronic components in junctions limits the direct applicability of pump-probe type spectroscopy in assessing the intramolecular dynamics. Recently the possibility of getting information on a sub-picosecond time scale from dc current measurements was proposed. We revisit the idea of picosecond resolution by pump-probe spectroscopy from dc measurements and show that any intramolecular dynamics not directly related to charge transfer in the current direction is missed by current measurements. We propose a pump-probe dc shot noise spectroscopy as a suitable alternative. Numerical examples of time-dependent and average responses of junctions are presented for generic models.
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Affiliation(s)
| | - Yoram Selzer
- ‡School of Chemistry, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Uri Peskin
- §Schulich Faculty of Chemistry and the Lise Meitner Center for Computational Quantum Chemistry, Technion - Israel Institute of Technology, Haifa 32000, Israel
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105
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Dell EJ, Capozzi B, Xia J, Venkataraman L, Campos LM. Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes. Nat Chem 2015; 7:209-14. [DOI: 10.1038/nchem.2160] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 12/12/2014] [Indexed: 12/22/2022]
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106
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Khoo KH, Chen Y, Li S, Quek SY. Length dependence of electron transport through molecular wires – a first principles perspective. Phys Chem Chem Phys 2015; 17:77-96. [DOI: 10.1039/c4cp05006a] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The length dependence of coherent electron transport through molecular wires is discussed in the context of a survey of state-of-the-art first principles calculation methods.
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Affiliation(s)
- Khoong Hong Khoo
- Department of Physics
- Faculty of Science
- National University of Singapore
- Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre
| | - Yifeng Chen
- Department of Physics
- Faculty of Science
- National University of Singapore
- Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre
| | - Suchun Li
- Department of Physics
- Faculty of Science
- National University of Singapore
- Singapore
- Institute of High Performance Computing
| | - Su Ying Quek
- Department of Physics
- Faculty of Science
- National University of Singapore
- Singapore
- Centre for Advanced 2D Materials and Graphene Research Centre
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107
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Leary E, La Rosa A, González MT, Rubio-Bollinger G, Agraït N, Martín N. Incorporating single molecules into electrical circuits. The role of the chemical anchoring group. Chem Soc Rev 2015; 44:920-42. [DOI: 10.1039/c4cs00264d] [Citation(s) in RCA: 134] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Constructing electronic circuits containing singly wired molecules is at the frontier of electrical device miniaturisation. Understanding the behaviour of different anchoring groups is key to this goal because of their significant role in determining the properties of the junction.
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Affiliation(s)
- Edmund Leary
- IMDEA Nanociencia
- C/Faraday 9
- 28049 Madrid
- Spain
- Depto. Física de la Materia Condensada Mod. 3-610 – Universidad Autónoma de Madrid
| | - Andrea La Rosa
- Departamento de Química Orgánica
- Facultad de Ciencias Quıímicas
- Universidad Complutense de Madrid
- Madrid
- Spain
| | | | - Gabino Rubio-Bollinger
- Depto. Física de la Materia Condensada Mod. 3-610 – Universidad Autónoma de Madrid
- 28049 Madrid
- Spain
| | - Nicolás Agraït
- IMDEA Nanociencia
- C/Faraday 9
- 28049 Madrid
- Spain
- Depto. Física de la Materia Condensada Mod. 3-610 – Universidad Autónoma de Madrid
| | - Nazario Martín
- IMDEA Nanociencia
- C/Faraday 9
- 28049 Madrid
- Spain
- Departamento de Química Orgánica
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108
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Chang WB, Russ B, Ho V, Urban JJ, Segalman RA. Gold nanocrystal arrays as a macroscopic platform for molecular junction thermoelectrics. Phys Chem Chem Phys 2015; 17:6207-11. [DOI: 10.1039/c4cp04465g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The thermoelectric properties of gold nanocrystal arrays with thiol-terminated ligands are compared to molecular junction experiments.
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Affiliation(s)
- W. B. Chang
- Department of Materials
- University of California
- Santa Barbara
- USA
| | - B. Russ
- Lawrence Berkeley National Laboratory
- Berkeley
- USA
- Department of Chemical and Biomolecular Engineering
- University of California
| | - V. Ho
- Department of Chemical and Biomolecular Engineering
- University of California
- Berkeley
- USA
| | - J. J. Urban
- Lawrence Berkeley National Laboratory
- Berkeley
- USA
| | - R. A. Segalman
- Department of Materials
- University of California
- Santa Barbara
- USA
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109
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Torres A, Pontes RB, da Silva AJR, Fazzio A. Tuning the thermoelectric properties of a single-molecule junction by mechanical stretching. Phys Chem Chem Phys 2015; 17:5386-92. [DOI: 10.1039/c4cp04635h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We theoretically investigate, as a function of the stretching, the behaviour of the Seebeck coefficient, the electronic heat conductance and the figure of merit of a molecule-based junction composed of a benzene-1,4-dithiolate (BDT) molecule coupled to Au(111) surfaces at room temperature.
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Affiliation(s)
- Alberto Torres
- Instituto de Física
- Universidade de São Paulo
- CP 66318
- São Paulo
- Brazil
| | - Renato B. Pontes
- Instituto de Física
- Universidade Federal de Goiás
- CP 131
- Goiânia
- Brazil
| | | | - Adalberto Fazzio
- Instituto de Física
- Universidade de São Paulo
- CP 66318
- São Paulo
- Brazil
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110
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Maksymovych P, Kelly SJ, Cerdá JI. Surface-state enhancement of tunneling thermopower on the Ag(111) surface. ACS NANO 2014; 8:12110-12119. [PMID: 25405264 DOI: 10.1021/nn506123g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Thermoelectric effects in tunnel junctions are currently being revisited for their prospects in cooling and energy harvesting applications, and as sensitive probes of electron transport. Quantitative interpretation of these effects calls for advances in both theory and experiment, particularly with respect to the electron transmission probability across a tunnel barrier which encodes the energy dependence and the magnitude of tunneling thermopower. Using noble metal surfaces as clean model systems, we demonstrate a comparatively simple and quantitative approach where the transmission probability is directly measured experimentally. Importantly, we estimate not only thermovoltage, but also its energy and temperature dependencies. We have thus resolved surface-state enhancement of thermovoltage, which manifests as 10-fold enhancement of thermopower on terraces of the Ag(111) surface compared to single-atom step sites and surface-supported nanoparticles. To corroborate experimental analysis, the methodology was applied to the transmission probability obtained from first-principles calculations for the (111) surfaces of the three noble metals, finding good agreement between overall trends. Surface-state effects themselves point to a possibility of achieving competitive performance of all-metal tunnel junctions when compared to molecular junctions. At the same time, the approach presented here opens up possibilities to investigate the properties of nominally doped or gated thermoelectric tunnel junctions as well as temperature gradient in nanometer gaps.
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Affiliation(s)
- Petro Maksymovych
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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111
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Catarelli SR, Higgins SJ, Schwarzacher W, Mao BW, Yan JW, Nichols RJ. Ionic liquid based approach for single-molecule electronics with cobalt contacts. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:14329-14336. [PMID: 25370276 DOI: 10.1021/la503077c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
An electrochemical method is presented for fabricating cobalt thin films for single-molecule electrical transport measurements. These films are electroplated in an aqueous electrolyte, but the crucial stages of electrochemical reduction to remove surface oxide and adsorption of alkane(di)thiol target molecules under electrochemical control to form self-assembled monolayers which protect the oxide-free cobalt surface are carried out in an ionic liquid. This approach yields monolayers on Co that are of comparable quality to those formed on Au by standard self-assembly protocols, as assessed by electrochemical methods and surface infrared spectroscopy. Using an adapted scanning tunneling microscopy (STM) method, we have determined the single-molecule conductance of cobalt/1,8-octanedithiol/cobalt junctions by employing a monolayer on cobalt and a cobalt STM tip in an ionic liquid environment and have compared the results with those of experiments using gold electrodes as a control. These cobalt substrates could therefore have future application in organic spintronic devices such as magnetic tunnel junctions.
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Affiliation(s)
- Samantha R Catarelli
- Chemistry Department, University of Liverpool , Liverpool L69 7ZD, United Kingdom
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112
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Schwarz F, Lörtscher E. Break-junctions for investigating transport at the molecular scale. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:474201. [PMID: 25352355 DOI: 10.1088/0953-8984/26/47/474201] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Break-junctions (BJs) enable a pair of atomic-sized electrodes to be created and the relative position between them to be controlled with sub-nanometer accuracy by mechanical means-a level of microscopic control that is not yet achievable by top-down fabrication. Locally, a BJ consists of a single-atom contact, an arrangement that is ideal not only to study various types of quantum point contacts, but also to investigate transport through an individual molecule that can bridge such a junction. In this topical review, we will provide a broad overview on the field of single-molecule electronics, in which BJs serve as the main tool of investigation. To correlate the molecular structure and transport properties to gain a fundamental understanding of the underlying transport mechanisms at the molecular scale, basic experiments that systematically cover all aspects of transport by rational chemical design and tailored experiments are needed. The variety of fascinating transport mechanisms and intrinsic molecular functionalities discovered in the past range from nonlinear transport over conductance switching to quantum interference effects observable even at room temperature. Beside discussing these results, we also look at novel directions and the most recent advances in molecular electronics investigating simultaneously electronic transport and also the mechanical and thermal properties of single-molecule junctions as well as the interaction between molecules and light. Finally, we will describe the requirements for a stepwise transition from fundamental BJ experiments towards technology-relevant architectures for future nanoelectronics applications based on ultimately-scaled molecular building blocks.
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Affiliation(s)
- Florian Schwarz
- IBM Research-Zurich, Department of Science and Technology, Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland
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113
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Bâldea I. Quantifying the relative molecular orbital alignment for molecular junctions with similar chemical linkage to electrodes. NANOTECHNOLOGY 2014; 25:455202. [PMID: 25327824 DOI: 10.1088/0957-4484/25/45/455202] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Estimating the relative alignment between the frontier molecular orbitals (MOs) that dominates the charge transport through single-molecule junctions represents a challenge for theory. This requires approaches beyond the widely employed framework provided by the density functional theory, wherein the Kohn-Sham 'orbitals' are treated as if they were real MOs, which is not the case. In this paper, we report results obtained by means of quantum chemical calculations, including the equation-of-motion coupled-cluster singles and doubles, which is the state-of-the-art of quantum chemistry for medium-size molecules like those considered here. These theoretical results are validated against data on the MO energy offset relative to the electrodes' Fermi energy extracted from experiments for junctions based on 4,4'-bipyridine and 1,4-dicyanobenzene.
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114
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Kim Y, Jeong W, Kim K, Lee W, Reddy P. Electrostatic control of thermoelectricity in molecular junctions. NATURE NANOTECHNOLOGY 2014; 9:881-5. [PMID: 25282046 DOI: 10.1038/nnano.2014.209] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 08/21/2014] [Indexed: 05/03/2023]
Abstract
Molecular junctions hold significant promise for efficient and high-power-output thermoelectric energy conversion. Recent experiments have probed the thermoelectric properties of molecular junctions. However, electrostatic control of thermoelectric properties via a gate electrode has not been possible due to technical challenges in creating temperature differentials in three-terminal devices. Here, we show that extremely large temperature gradients (exceeding 1 × 10(9) K m(-1)) can be established in nanoscale gaps bridged by molecules, while simultaneously controlling their electronic structure via a gate electrode. Using this platform, we study prototypical Au-biphenyl-4,4'-dithiol-Au and Au-fullerene-Au junctions to demonstrate that the Seebeck coefficient and the electrical conductance of molecular junctions can be simultaneously increased by electrostatic control. Moreover, from our studies of fullerene junctions, we show that thermoelectric properties can be significantly enhanced when the dominant transport orbital is located close to the chemical potential (Fermi level) of the electrodes. These results illustrate the intimate relationship between the thermoelectric properties and charge transmission characteristics of molecular junctions and should enable systematic exploration of the recent computational predictions that promise extremely efficient thermoelectric energy conversion in molecular junctions.
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Affiliation(s)
- Youngsang Kim
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Wonho Jeong
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Kyeongtae Kim
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Woochul Lee
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Pramod Reddy
- 1] Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA [2] Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
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115
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Neaton JB. Single-molecule junctions: thermoelectricity at the gate. NATURE NANOTECHNOLOGY 2014; 9:876-877. [PMID: 25370426 DOI: 10.1038/nnano.2014.256] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Affiliation(s)
- Jeffrey B Neaton
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA, the Department of Physics, University of California, Berkeley, Berkeley, California 94720, USA, and Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720, USA
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116
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Bâldea I. A quantum chemical study from a molecular transport perspective: ionization and electron attachment energies for species often used to fabricate single-molecule junctions. Faraday Discuss 2014; 174:37-56. [PMID: 25270244 DOI: 10.1039/c4fd00101j] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The accurate determination of the lowest electron attachment (EA) and ionization (IP) energies for molecules embedded in molecular junctions is important for correctly estimating, for example, the magnitude of the currents (I) or the biases (V) where an I-V curve exhibits significant non-Ohmic behavior. Benchmark calculations for the lowest electron attachment and ionization energies of several typical molecules utilized to fabricate single-molecule junctions characterized by n-type conduction (4,4'-bipyridine, 1,4-dicyanobenzene and 4,4'-dicyano-1,1'-biphenyl) and p-type conduction (benzenedithiol, biphenyldithiol, hexanemonothiol and hexanedithiol) based on the EOM-CCSD (equation-of-motion coupled-cluster singles and doubles) state-of-the-art method of quantum chemistry are presented. They indicate significant differences from the results obtained within current approaches to molecular transport. The present study emphasizes that, in addition to a reliable quantum chemical method, basis sets much better than the ubiquitous double-zeta set employed for transport calculations are needed. The latter is a particularly critical issue for correctly determining EAs, which is impossible without including sufficient diffuse basis functions. The spatial distribution of the dominant molecular orbitals (MOs) is another important issue, on which the present study draws attention, because it sensitively affects the MO energy shifts Φ due to image charges formed in electrodes. The present results cannot substantiate the common assumption of a point-like MO midway between electrodes, which substantially affects the actual Φ-values.
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Affiliation(s)
- Ioan Bâldea
- Theoretische Chemie, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
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117
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Lee SK, Ohto T, Yamada R, Tada H. Thermopower of benzenedithiol and C60 molecular junctions with Ni and Au electrodes. NANO LETTERS 2014; 14:5276-80. [PMID: 25141337 DOI: 10.1021/nl502305e] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We have performed thermoelectric measurements of benzenedithiol (BDT) and C60 molecules with Ni and Au electrodes using a home-built scanning tunneling microscope. The thermopower of C60 was negative for both Ni and Au electrodes, indicating the transport of carriers through the lowest unoccupied molecular orbital in both cases, as was expected from the work functions. On the other hand, the Ni-BDT-Ni junctions exhibited a negative thermopower, whereas the Au-BDT-Au junctions exhibited a positive thermopower. First-principle calculations revealed that the negative thermopower of Ni-BDT-Ni junctions is due to the spin-split hybridized states generated by the highest occupied molecular orbital of BDT coupled with s- and d-states of the Ni electrode.
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Affiliation(s)
- See Kei Lee
- Graduate School of Engineering Science, Osaka University , 1-3 Machikaneyama, Toyonaka, Osaka, 560-8531, Japan
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118
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Liu ZF, Wei S, Yoon H, Adak O, Ponce I, Jiang Y, Jang WD, Campos LM, Venkataraman L, Neaton JB. Control of single-molecule junction conductance of porphyrins via a transition-metal center. NANO LETTERS 2014; 14:5365-70. [PMID: 25111197 DOI: 10.1021/nl5025062] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Using scanning tunneling microscope break-junction experiments and a new first-principles approach to conductance calculations, we report and explain low-bias charge transport behavior of four types of metal-porphyrin-gold molecular junctions. A nonequilibrium Green's function approach based on self-energy corrected density functional theory and optimally tuned range-separated hybrid functionals is developed and used to understand experimental trends quantitatively. Importantly, due to the localized d states of the porphyrin molecules, hybrid functionals are essential for explaining measurements; standard semilocal functionals yield qualitatively incorrect results. Comparing directly with experiments, we show that the conductance can change by nearly a factor of 2 when different metal cations are used, counter to trends expected from gas-phase ionization energies which are relatively unchanged with the metal center. Our work explains the sensitivity of the porphyrin conductance with the metal center via a detailed and quantitative portrait of the interface electronic structure and provides a new framework for understanding transport quantitatively in complex junctions involving molecules with localized d states of relevance to light harvesting and energy conversion.
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Affiliation(s)
- Zhen-Fei Liu
- Molecular Foundry and Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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119
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Morikawa T, Arima A, Tsutsui M, Taniguchi M. Thermoelectric voltage measurements of atomic and molecular wires using microheater-embedded mechanically-controllable break junctions. NANOSCALE 2014; 6:8235-8241. [PMID: 24930503 DOI: 10.1039/c4nr00127c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We developed a method for simultaneous measurements of conductance and thermopower of atomic and molecular junctions by using a microheater-embedded mechanically-controllable break junction. We find linear increase in the thermoelectric voltage of Au atomic junctions with the voltage added to the heater. We also detect thermopower oscillations at several conductance quanta reflecting the quantum confinement effects in the atomic wire. Under high heater voltage conditions, on the other hand, we observed a peculiar behaviour in the conductance dependent thermopower, which was ascribed to a disordered contact structure under elevated temperatures.
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Affiliation(s)
- Takanori Morikawa
- The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
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120
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Géranton G, Seiler C, Bagrets A, Venkataraman L, Evers F. Transport properties of individual C60-molecules. J Chem Phys 2014; 139:234701. [PMID: 24359380 DOI: 10.1063/1.4840535] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Electrical and thermal transport properties of C60 molecules are investigated with density-functional-theory based calculations. These calculations suggest that the optimum contact geometry for an electrode terminated with a single-Au atom is through binding to one or two C-atoms of C60 with a tendency to promote the sp(2)-hybridization into an sp(3)-type one. Transport in these junctions is primarily through an unoccupied molecular orbital that is partly hybridized with the Au, which results in splitting the degeneracy of the lowest unoccupied molecular orbital triplet. The transmission through these junctions, however, cannot be modeled by a single Lorentzian resonance, as our results show evidence of quantum interference between an occupied and an unoccupied orbital. The interference results in a suppression of conductance around the Fermi energy. Our numerical findings are readily analyzed analytically within a simple two-level model.
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Affiliation(s)
- G Géranton
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe, Germany
| | - C Seiler
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe, Germany
| | - A Bagrets
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe, Germany
| | - L Venkataraman
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA
| | - F Evers
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe, Germany
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121
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Ponce J, Arroyo CR, Tatay S, Frisenda R, Gaviña P, Aravena D, Ruiz E, van der Zant HSJ, Coronado E. Effect of Metal Complexation on the Conductance of Single-Molecular Wires Measured at Room Temperature. J Am Chem Soc 2014; 136:8314-22. [DOI: 10.1021/ja5012417] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Julia Ponce
- Instituto
de Ciencia Molecular (ICMol), Universidad de Valencia, Catedrático
José Beltrán 2, 46980 Paterna, Spain
| | - Carlos R. Arroyo
- Kavli
Institute of Nanoscience, Delft University of Technology, Lorentzweg
1, 2628 CJ Delft, The Netherlands
| | - Sergio Tatay
- Instituto
de Ciencia Molecular (ICMol), Universidad de Valencia, Catedrático
José Beltrán 2, 46980 Paterna, Spain
| | - Riccardo Frisenda
- Kavli
Institute of Nanoscience, Delft University of Technology, Lorentzweg
1, 2628 CJ Delft, The Netherlands
| | - Pablo Gaviña
- Centro
de Reconocimiento Molecular y Desarrollo Tecnológico (IDM), Unidad mixta Universidad Politécnica de Valencia-Universidad de Valencia, Dr. Moliner
50, 46100 Burjassot, Spain
| | - Daniel Aravena
- Departament
de Química Inorgànica and Institut de Recerca de Química
Teòrica i Computacional, Universitat de Barcelona, Diagonal
645, 08028 Barcelona, Spain
| | - Eliseo Ruiz
- Departament
de Química Inorgànica and Institut de Recerca de Química
Teòrica i Computacional, Universitat de Barcelona, Diagonal
645, 08028 Barcelona, Spain
| | - Herre S. J. van der Zant
- Kavli
Institute of Nanoscience, Delft University of Technology, Lorentzweg
1, 2628 CJ Delft, The Netherlands
| | - Eugenio Coronado
- Instituto
de Ciencia Molecular (ICMol), Universidad de Valencia, Catedrático
José Beltrán 2, 46980 Paterna, Spain
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122
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Wu QH, Zhao P, Liu HY, Liu DS, Chen G. Odd–even dependence of rectifying behavior in carbon chains modified diphenyl–dimethyl molecule. Chem Phys Lett 2014. [DOI: 10.1016/j.cplett.2014.05.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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123
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García-Suárez VM, Lambert CJ, Manrique DZ, Wandlowski T. Redox control of thermopower and figure of merit in phase-coherent molecular wires. NANOTECHNOLOGY 2014; 25:205402. [PMID: 24784933 DOI: 10.1088/0957-4484/25/20/205402] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We demonstrate how redox control of intra-molecular quantum interference in phase-coherent molecular wires can be used to enhance the thermopower (Seebeck coefficient) S and thermoelectric figure of merit ZT of single molecules attached to nanogap electrodes. Using first principles theory, we study the thermoelectric properties of a family of nine molecules, which consist of dithiol-terminated oligo (phenylene-ethynylenes) (OPEs) containing various central units. Uniquely, one molecule of this family possesses a conjugated acene-based central backbone attached via triple bonds to terminal sulfur atoms bound to gold electrodes and incorporates a fully conjugated hydroquinonecentral unit. We demonstrate that both S and the electronic contribution Z el T to the figure of merit ZT can be dramatically enhanced by oxidizing the hydroquinone to yield a second molecule, which possesses a cross-conjugated anthraquinone central unit. This enhancement originates from the conversion of the pi-conjugation in the former to cross-conjugation in the latter, which promotes the appearance of a sharp anti-resonance at the Fermi energy. Comparison with thermoelectric properties of the remaining seven conjugated molecules demonstrates that such large values of S and Z el T are unprecedented. We also evaluate the phonon contribution to the thermal conductance, which allows us to compute the full figure of merit ZT = Z el T/(1 + κ p/κ el), where κ p is the phonon contribution to the thermal conductance and κ el is the electronic contribution. For unstructured gold electrodes, κ p/κ el ≫⃒ 1 and therefore strategies to reduce κ p are needed to realize the highest possible figure of merit.
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Affiliation(s)
- Víctor M García-Suárez
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK. Departamento de Física, Universidad de Oviedo and CINN (CSIC), ES-33007 Oviedo, Spain
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124
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Péterfalvi CG, Grace I, Manrique DZ, Lambert CJ. Thermoelectric performance of various benzo-difuran wires. J Chem Phys 2014; 140:174711. [DOI: 10.1063/1.4871801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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125
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Ness H, Dash LK. Nonequilibrium fluctuation-dissipation relations for one- and two-particle correlation functions in steady-state quantum transport. J Chem Phys 2014; 140:144106. [PMID: 24735287 DOI: 10.1063/1.4870637] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We study the non-equilibrium (NE) fluctuation-dissipation (FD) relations in the context of quantum thermoelectric transport through a two-terminal nanodevice in the steady-state. The FD relations for the one- and two-particle correlation functions are derived for a model of the central region consisting of a single electron level. Explicit expressions for the FD relations of the Green's functions (one-particle correlations) are provided. The FD relations for the current-current and charge-charge (two-particle) correlations are calculated numerically. We use self-consistent NE Green's functions calculations to treat the system in the absence and in the presence of interaction (electron-phonon) in the central region. We show that, for this model, there is no single universal FD theorem for the NE steady state. There are different FD relations for each different class of problems. We find that the FD relations for the one-particle correlation function are strongly dependent on both the NE conditions and the interactions, while the FD relations of the current-current correlation function are much less dependent on the interaction. The latter property suggests interesting applications for single-molecule and other nanoscale transport experiments.
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Affiliation(s)
- H Ness
- Department of Physics, School of Natural and Mathematical Sciences, King's College London, Strand, London WC2R 2LS, United Kingdom
| | - L K Dash
- European Theoretical Spectroscopy Facility (ETSF)
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126
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Lee ES, Cho S, Lyeo HK, Kim YH. Seebeck effect at the atomic scale. PHYSICAL REVIEW LETTERS 2014; 112:136601. [PMID: 24745445 DOI: 10.1103/physrevlett.112.136601] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Indexed: 06/03/2023]
Abstract
The atomic variations of electronic wave functions at the surface and electron scattering near a defect have been detected unprecedentedly by tracing thermoelectric voltages given a temperature bias [Cho et al., Nat. Mater. 12, 913 (2013)]. Because thermoelectricity, or the Seebeck effect, is associated with heat-induced electron diffusion, how the thermoelectric signal is related to the atomic-scale wave functions and what the role of the temperature is at such a length scale remain very unclear. Here we show that coherent electron and heat transport through a pointlike contact produces an atomic Seebeck effect, which is described by the mesoscopic Seebeck coefficient multiplied by an effective temperature drop at the interface. The mesoscopic Seebeck coefficient is approximately proportional to the logarithmic energy derivative of local density of states at the Fermi energy. We deduced that the effective temperature drop at the tip-sample junction could vary at a subangstrom scale depending on atom-to-atom interaction at the interface. A computer-based simulation method of thermoelectric images is proposed, and a point defect in graphene was identified by comparing experiment and the simulation of thermoelectric imaging.
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Affiliation(s)
- Eui-Sup Lee
- Graduate School of Nanoscience and Technology, KAIST, Daejeon 305-701, Republic of Korea
| | - Sanghee Cho
- Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea
| | - Ho-Ki Lyeo
- Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea
| | - Yong-Hyun Kim
- Graduate School of Nanoscience and Technology, KAIST, Daejeon 305-701, Republic of Korea
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127
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Capozzi B, Chen Q, Darancet P, Kotiuga M, Buzzeo M, Neaton JB, Nuckolls C, Venkataraman L. Tunable charge transport in single-molecule junctions via electrolytic gating. NANO LETTERS 2014; 14:1400-1404. [PMID: 24490721 DOI: 10.1021/nl404459q] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We modulate the conductance of electrochemically inactive molecules in single-molecule junctions using an electrolytic gate to controllably tune the energy level alignment of the system. Molecular junctions that conduct through their highest occupied molecular orbital show a decrease in conductance when applying a positive electrochemical potential, and those that conduct though their lowest unoccupied molecular orbital show the opposite trend. We fit the experimentally measured conductance data as a function of gate voltage with a Lorentzian function and find the fitting parameters to be in quantitative agreement with self-energy corrected density functional theory calculations of transmission probability across single-molecule junctions. This work shows that electrochemical gating can directly modulate the alignment of the conducting orbital relative to the metal Fermi energy, thereby changing the junction transport properties.
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Affiliation(s)
- Brian Capozzi
- Department of Applied Physics and Mathematics and ‡Department of Chemistry, Columbia University , New York, New York, United States
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128
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Kim T, Darancet P, Widawsky JR, Kotiuga M, Quek SY, Neaton JB, Venkataraman L. Determination of energy level alignment and coupling strength in 4,4'-bipyridine single-molecule junctions. NANO LETTERS 2014; 14:794-8. [PMID: 24446585 DOI: 10.1021/nl404143v] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We measure conductance and thermopower of single Au-4,4'-bipyridine-Au junctions in distinct low and high conductance binding geometries accessed by modulating the electrode separation. We use these data to determine the electronic energy level alignment and coupling strength for these junctions, which are known to conduct through the lowest unoccupied molecular orbital (LUMO). Contrary to intuition, we find that, in the high-conductance junction, the LUMO resonance energy is further away from the Au Fermi energy than in the low-conductance junction. However, the LUMO of the high-conducting junction is better coupled to the electrode. These results are in good quantitative agreement with self-energy corrected zero-bias density functional theory calculations. Our calculations show further that measurements of conductance and thermopower in amine-terminated oligophenyl-Au junctions, where conduction occurs through the highest occupied molecular orbitals, cannot be used to extract electronic parameters as their transmission functions do not follow a simple Lorentzian form.
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Affiliation(s)
- Taekyeong Kim
- Department of Applied Physics and Applied Mathematics, Columbia University , 500 W. 120th Street, New York, New York 10027, United States
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129
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Karlström O, Strange M, Solomon GC. Understanding the length dependence of molecular junction thermopower. J Chem Phys 2014; 140:044315. [DOI: 10.1063/1.4862905] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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130
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Abstract
Understanding charge transport of single molecules or a small collection of molecules sandwiched between electrodes is of fundamental importance for molecular electronics. This requires the fabrication of reliable devices, which depend on several factors including the testbed architectures used, the molecule number and defect density being tested, and the nature of the molecule-electrode interface. On the basis of significant progresses achieved in both experiments and theory over the past decade, in this tutorial review, we focus on new insights into the influence of the nature of the molecule-electrode interface, the most critical issue hindering the development of reliable devices, on the conducting properties of molecules. We summarize the strategies developed for controlling the interfacial properties and how the coupling strength between the molecules and the electrodes modulates the device properties. These analyses should be valuable for deeply understanding the relationship between the contact interface and the charge transport mechanism, which is of crucial importance for the development of molecular electronics, organic electronics, nanoelectronics, and other interface-related optoelectronic devices.
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Affiliation(s)
- Chuancheng Jia
- Center for NanoChemistry, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China
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131
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Valkenier H, Guédon CM, Markussen T, Thygesen KS, van der Molen SJ, Hummelen JC. Cross-conjugation and quantum interference: a general correlation? Phys Chem Chem Phys 2014; 16:653-62. [DOI: 10.1039/c3cp53866d] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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132
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Wang K, Hamill J, Zhou J, Guo C, Xu B. Measurement and control of detailed electronic properties in a single molecule break junction. Faraday Discuss 2014; 174:91-104. [DOI: 10.1039/c4fd00080c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The lack of detailed experimental controls has been one of the major obstacles hindering progress in molecular electronics. While large fluctuations have been occurring in the experimental data, specific details, related mechanisms, and data analysis techniques are in high demand to promote our physical understanding at the single-molecule level. A series of modulations we recently developed, based on traditional scanning probe microscopy break junctions (SPMBJs), have helped to discover significant properties in detail which are hidden in the contact interfaces of a single-molecule break junction (SMBJ). For example, in the past we have shown that the correlated force and conductance changes under the saw tooth modulation and stretch–hold mode of PZT movement revealed inherent differences in the contact geometries of a molecular junction. In this paper, using a bias-modulated SPMBJ and utilizing emerging data analysis techniques, we report on the measurement of the altered alignment of the HOMO of benzene molecules with changing the anchoring group which coupled the molecule to metal electrodes. Further calculations based on Landauer fitting and transition voltage spectroscopy (TVS) demonstrated the effects of modulated bias on the location of the frontier molecular orbitals. Understanding the alignment of the molecular orbitals with the Fermi level of the electrodes is essential for understanding the behaviour of SMBJs and for the future design of more complex devices. With these modulations and analysis techniques, fruitful information has been found about the nature of the metal–molecule junction, providing us insightful clues towards the next step for in-depth study.
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Affiliation(s)
- Kun Wang
- Single Molecule Study Laboratory
- College of Engineering and Nanoscale Science and Engineering Center
- University of Georgia
- Athens, USA
| | - Joseph Hamill
- Single Molecule Study Laboratory
- College of Engineering and Nanoscale Science and Engineering Center
- University of Georgia
- Athens, USA
| | - Jianfeng Zhou
- Single Molecule Study Laboratory
- College of Engineering and Nanoscale Science and Engineering Center
- University of Georgia
- Athens, USA
| | - Cunlan Guo
- Single Molecule Study Laboratory
- College of Engineering and Nanoscale Science and Engineering Center
- University of Georgia
- Athens, USA
| | - Bingqian Xu
- Single Molecule Study Laboratory
- College of Engineering and Nanoscale Science and Engineering Center
- University of Georgia
- Athens, USA
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133
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Thermoelectricity in atom-sized junctions at room temperatures. Sci Rep 2013; 3:3326. [PMID: 24270238 PMCID: PMC3839037 DOI: 10.1038/srep03326] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 11/08/2013] [Indexed: 11/08/2022] Open
Abstract
Atomic and molecular junctions are an emerging class of thermoelectric materials that exploit quantum confinement effects to obtain an enhanced figure of merit. An important feature in such nanoscale systems is that the electron and heat transport become highly sensitive to the atomic configurations. Here we report the characterization of geometry-sensitive thermoelectricity in atom-sized junctions at room temperatures. We measured the electrical conductance and thermoelectric power of gold nanocontacts simultaneously down to the single atom size. We found junction conductance dependent thermoelectric voltage oscillations with period 2e(2)/h. We also observed quantum suppression of thermovoltage fluctuations in fully-transparent contacts. These quantum confinement effects appeared only statistically due to the geometry-sensitive nature of thermoelectricity in the atom-sized junctions. The present method can be applied to various nanomaterials including single-molecules or nanoparticles and thus may be used as a useful platform for developing low-dimensional thermoelectric building blocks.
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134
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Demonstrating why DFT-calculations for molecular transport in solvents need scissor corrections. Electrochem commun 2013. [DOI: 10.1016/j.elecom.2013.08.027] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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135
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Nakamura H, Ohto T, Ishida T, Asai Y. Thermoelectric efficiency of organometallic complex wires via quantum resonance effect and long-range electric transport property. J Am Chem Soc 2013; 135:16545-52. [PMID: 24102142 DOI: 10.1021/ja407662m] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Superior long-range electric transport has been observed in several organometallic wires. Here, we discuss the role of the metal center in the electric transport and examine the possibility of high thermoelectric figure of merit (ZT) by controlling the quantum resonance effects. We examined a few metal center (and metal-free) terpyridine-based complexes by first-principles calculations and clarified the role of the metals in determining the transport properties. Quasi-resonant tunneling is mediated by organic compounds, and narrow overlapping resonance states are formed when d-electron metal centers are incorporated. Distinct length (L) and temperature (T) dependencies of thermopower from semiconductor materials or organic molecular junctions are presented in terms of atomistic calculations of ZT with and without considering the phonon thermal conductance. We present an alternative approach to obtain high ZT for molecular junctions by quantum effect.
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Affiliation(s)
- Hisao Nakamura
- Nanosystem Research Institute (NRI), "RICS", Advanced Industrial Science and Technology (AIST) , 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
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136
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Bâldea I. Transition voltage spectroscopy reveals significant solvent effects on molecular transport and settles an important issue in bipyridine-based junctions. NANOSCALE 2013; 5:9222-9230. [PMID: 23933675 DOI: 10.1039/c3nr51290h] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Results of a seminal study (B. Xu and N. J. Tao, Science, 2003, 301, 1221) on the single-molecule junctions based on bipyridine placed in a solvent have been challenged recently (S. Y. Quek et al., Nat. Nano, 2009, 4, 230) by implicitly assuming a negligible solvent impact on the molecular transport and by merely considering low bias conductance data. In this paper we demonstrate that solvent effects on the molecular transport are important, and to show this we focus our attention on the energy offset ε(0) of the dominant molecular orbital (LUMO) relative to the electrode Fermi level. To estimate the energy offset ε(0)(sol) from the full I-V curves presented by Xu and Tao for wet junctions, we resort to the recently proposed transition voltage spectroscopy (TVS). TVS, which plays a key role in the present analysis, emphasizes that data beyond the ohmic conductance regime are needed to reveal the solvent impact. We show that ε(0)(sol) significantly differs from the energy offset ε(0)(0)deduced for dry junctions (J. R. Widawsky et al., Nano Lett., 2012, 12, 354). The present work demonstrates that solvent effects on molecular transport are important and can be understood quantitatively. Results of ab initio calculations with and without solvent are reported that excellently explain the difference δε(0) = ε(0)(sol)-ε(0)(0). δε(0) = ΔΔG + δΦ + δW can be disentangled in contributions with a clear physical content: solvation energies (ΔΔG), image charges (δΦ), and work functions (δW). Accurate analytical formulae for ΔΔG and δΦ are reported, which provide experimentalists with a convenient framework to quantify solvent effects obviating demanding numerical efforts.
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Affiliation(s)
- Ioan Bâldea
- Theoretische Chemie, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
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137
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Guo S, Zhou G, Tao N. Single molecule conductance, thermopower, and transition voltage. NANO LETTERS 2013; 13:4326-32. [PMID: 23895464 DOI: 10.1021/nl4021073] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We have measured the thermopower as well as other important charge transport quantities, including conductance, current-voltage characteristics, and transition voltage of single molecules. The thermopower has little correlation with the conductance, but it decreases with the transition voltage, which is consistent with a theory based on Landauer's formula. Since the transition voltage reflects the molecular energy level alignment, our finding also shows that the thermopower provides valuable information about the relative alignment between the molecular energy levels and the electrodes' Fermi energy level.
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Affiliation(s)
- Shaoyin Guo
- Center for Bioelectronics and Biosensors, Biodesign Institute, and Department of Electrical Engineering, Arizona State University , Tempe, Arizona 85287, United States
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138
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Lee W, Kim K, Jeong W, Zotti LA, Pauly F, Cuevas JC, Reddy P. Heat dissipation in atomic-scale junctions. Nature 2013; 498:209-12. [PMID: 23765496 DOI: 10.1038/nature12183] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Accepted: 04/06/2013] [Indexed: 12/23/2022]
Abstract
Atomic and single-molecule junctions represent the ultimate limit to the miniaturization of electrical circuits. They are also ideal platforms for testing quantum transport theories that are required to describe charge and energy transfer in novel functional nanometre-scale devices. Recent work has successfully probed electric and thermoelectric phenomena in atomic-scale junctions. However, heat dissipation and transport in atomic-scale devices remain poorly characterized owing to experimental challenges. Here we use custom-fabricated scanning probes with integrated nanoscale thermocouples to investigate heat dissipation in the electrodes of single-molecule ('molecular') junctions. We find that if the junctions have transmission characteristics that are strongly energy dependent, this heat dissipation is asymmetric--that is, unequal between the electrodes--and also dependent on both the bias polarity and the identity of the majority charge carriers (electrons versus holes). In contrast, junctions consisting of only a few gold atoms ('atomic junctions') whose transmission characteristics show weak energy dependence do not exhibit appreciable asymmetry. Our results unambiguously relate the electronic transmission characteristics of atomic-scale junctions to their heat dissipation properties, establishing a framework for understanding heat dissipation in a range of mesoscopic systems where transport is elastic--that is, without exchange of energy in the contact region. We anticipate that the techniques established here will enable the study of Peltier effects at the atomic scale, a field that has been barely explored experimentally despite interesting theoretical predictions. Furthermore, the experimental advances described here are also expected to enable the study of heat transport in atomic and molecular junctions--an important and challenging scientific and technological goal that has remained elusive.
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Affiliation(s)
- Woochul Lee
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
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139
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Widawsky JR, Chen W, Vázquez H, Kim T, Breslow R, Hybertsen MS, Venkataraman L. Length-dependent thermopower of highly conducting Au-C bonded single molecule junctions. NANO LETTERS 2013; 13:2889-94. [PMID: 23682792 DOI: 10.1021/nl4012276] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We report the simultaneous measurement of conductance and thermopower of highly conducting single-molecule junctions using a scanning tunneling microscope-based break-junction setup. We start with molecular backbones (alkanes and oligophenyls) terminated with trimethyltin end groups that cleave off in situ to create junctions where terminal carbons are covalently bonded to the Au electrodes. We apply a thermal gradient across these junctions and measure their conductance and thermopower. Because of the electronic properties of the highly conducting Au-C links, the thermoelectric properties and power factor are very high. Our results show that the molecular thermopower increases nonlinearly with the molecular length while conductance decreases exponentially with increasing molecular length. Density functional theory calculations show that a gateway state representing the Au-C covalent bond plays a key role in the conductance. With this as input, we analyze a series of simplified models and show that a tight-binding model that explicitly includes the gateway states and the molecular backbone states accurately captures the experimentally measured conductance and thermopower trends.
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Affiliation(s)
- J R Widawsky
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, USA
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140
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Aradhya SV, Venkataraman L. Single-molecule junctions beyond electronic transport. NATURE NANOTECHNOLOGY 2013; 8:399-410. [PMID: 23736215 DOI: 10.1038/nnano.2013.91] [Citation(s) in RCA: 481] [Impact Index Per Article: 40.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Accepted: 04/22/2013] [Indexed: 05/21/2023]
Abstract
The idea of using individual molecules as active electronic components provided the impetus to develop a variety of experimental platforms to probe their electronic transport properties. Among these, single-molecule junctions in a metal-molecule-metal motif have contributed significantly to our fundamental understanding of the principles required to realize molecular-scale electronic components from resistive wires to reversible switches. The success of these techniques and the growing interest of other disciplines in single-molecule-level characterization are prompting new approaches to investigate metal-molecule-metal junctions with multiple probes. Going beyond electronic transport characterization, these new studies are highlighting both the fundamental and applied aspects of mechanical, optical and thermoelectric properties at the atomic and molecular scales. Furthermore, experimental demonstrations of quantum interference and manipulation of electronic and nuclear spins in single-molecule circuits are heralding new device concepts with no classical analogues. In this Review, we present the emerging methods being used to interrogate multiple properties in single molecule-based devices, detail how these measurements have advanced our understanding of the structure-function relationships in molecular junctions, and discuss the potential for future research and applications.
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Affiliation(s)
- Sriharsha V Aradhya
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA
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141
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Evangeli C, Gillemot K, Leary E, González MT, Rubio-Bollinger G, Lambert CJ, Agraït N. Engineering the thermopower of C60 molecular junctions. NANO LETTERS 2013; 13:2141-5. [PMID: 23544957 DOI: 10.1021/nl400579g] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We report the measurement of conductance and thermopower of C60 molecular junctions using a scanning tunneling microscope (STM). In contrast to previous measurements, we use the imaging capability of the STM to determine precisely the number of molecules in the junction and measure thermopower and conductance continuously and simultaneously during formation and breaking of the molecular junction, achieving a complete characterization at the single-molecule level. We find that the thermopower of C60 dimers formed by trapping a C60 on the tip and contacting an isolated C60 almost doubles with respect to that of a single C60 and is among the highest values measured to date for organic materials. Density functional theory calculations show that the thermopower and the figure of merit continue increasing with the number of C60 molecules, demonstrating the enhancement of thermoelectric preformance by manipulation of intermolecular interactions.
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Affiliation(s)
- Charalambos Evangeli
- Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain
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142
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Dubi Y. The effect of fluctuations, thermal and otherwise, on the temperature dependence of thermopower in aromatic chain single-molecule junctions. J Chem Phys 2013; 138:114706. [DOI: 10.1063/1.4795496] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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143
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Wen S, Yang G, Yan L, Li H, Su Z. Theoretical study on the rectifying performance of organoimido derivatives of hexamolybdates. Chemphyschem 2013; 14:610-7. [PMID: 23303530 DOI: 10.1002/cphc.201200770] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Revised: 11/29/2012] [Indexed: 11/11/2022]
Abstract
We design a new type of molecular diode, based on the organoimido derivatives of hexamolybdates, by exploring the rectifying performances using density functional theory combined with the non-equilibrium Green's function. Asymmetric current-voltage characteristics were obtained for the models with an unexpected large rectification ratio. The rectifying behavior can be understood by the asymmetrical shift of the transmission peak observed under different polarities. It is interesting to find that the preferred electron-transport direction in our studied system is different from that of the organic D-bridge-A system. The results show that the studied organic-inorganic hybrid systems have an intrinsically robust rectifying ratio, which should be taken into consideration in the design of the molecular diodes.
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Affiliation(s)
- Shizheng Wen
- Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China
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144
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Bâldea I, Köppel H, Wenzel W. (4,4′)-Bipyridinein vacuo and in solvents: a quantum chemical study of a prototypical floppy molecule from a molecular transport perspective. Phys Chem Chem Phys 2013; 15:1918-28. [DOI: 10.1039/c2cp43627b] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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145
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Darancet P, Widawsky JR, Choi HJ, Venkataraman L, Neaton JB. Quantitative current-voltage characteristics in molecular junctions from first principles. NANO LETTERS 2012; 12:6250-4. [PMID: 23167709 DOI: 10.1021/nl3033137] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Using self-energy-corrected density functional theory (DFT) and a coherent scattering-state approach, we explain current-voltage (IV) measurements of four pyridine-Au and amine-Au linked molecular junctions with quantitative accuracy. Parameter-free many-electron self-energy corrections to DFT Kohn-Sham eigenvalues are demonstrated to lead to excellent agreement with experiments at finite bias, improving upon order-of-magnitude errors in currents obtained with standard DFT approaches. We further propose an approximate route for prediction of quantitative IV characteristics for both symmetric and asymmetric molecular junctions based on linear response theory and knowledge of the Stark shifts of junction resonance energies. Our work demonstrates that a quantitative, computationally inexpensive description of coherent transport in molecular junctions is readily achievable, enabling new understanding and control of charge transport properties of molecular-scale interfaces at large bias voltages.
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Affiliation(s)
- Pierre Darancet
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States.
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146
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Egger DA, Rissner F, Zojer E, Heimel G. Polarity switching of charge transport and thermoelectricity in self-assembled monolayer devices. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:4403-4407. [PMID: 22807087 DOI: 10.1002/adma.201200872] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Revised: 05/09/2012] [Indexed: 05/28/2023]
Abstract
Self-assembled monolayer devices can exhibit drastically different charge-transport characteristics and thermoelectric properties despite being composed of isomeric molecules with essentially identical frontier-orbital energies. This is rationalized by the cooperative electrostatic action of local intramolecular dipoles in otherwise nonpolar species, thus revealing new challenges but also new opportunities for the targeted design of functional building blocks in future nanoelectronics.
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Affiliation(s)
- David A Egger
- Institut für Physik, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 6, 12489 Berlin, Germany
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147
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Tsutsui M, Taniguchi M. Single molecule electronics and devices. SENSORS (BASEL, SWITZERLAND) 2012; 12:7259-98. [PMID: 22969345 PMCID: PMC3435974 DOI: 10.3390/s120607259] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 05/15/2012] [Accepted: 05/17/2012] [Indexed: 11/21/2022]
Abstract
The manufacture of integrated circuits with single-molecule building blocks is a goal of molecular electronics. While research in the past has been limited to bulk experiments on self-assembled monolayers, advances in technology have now enabled us to fabricate single-molecule junctions. This has led to significant progress in understanding electron transport in molecular systems at the single-molecule level and the concomitant emergence of new device concepts. Here, we review recent developments in this field. We summarize the methods currently used to form metal-molecule-metal structures and some single-molecule techniques essential for characterizing molecular junctions such as inelastic electron tunnelling spectroscopy. We then highlight several important achievements, including demonstration of single-molecule diodes, transistors, and switches that make use of electrical, photo, and mechanical stimulation to control the electron transport. We also discuss intriguing issues to be addressed further in the future such as heat and thermoelectric transport in an individual molecule.
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Affiliation(s)
- Makusu Tsutsui
- The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan; E-Mail:
| | - Masateru Taniguchi
- The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan; E-Mail:
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148
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Natelson D. Mechanical break junctions: enormous information in a nanoscale package. ACS NANO 2012; 6:2871-2876. [PMID: 22483036 DOI: 10.1021/nn301323u] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Mechanical break junctions, particularly those in which a metal tip is repeatedly moved in and out of contact with a metal film, have provided many insights into electronic conduction at the atomic and molecular scale, most often by averaging over many possible junction configurations. This averaging throws away a great deal of information, and Makk et al. in this issue of ACS Nano demonstrate that, with both simulated and real experimental data, more sophisticated two-dimensional analysis methods can reveal information otherwise obscured in simple histograms. As additional measured quantities come into play in break junction experiments, including thermopower, noise, and optical response, these more sophisticated analytic approaches are likely to become even more powerful. While break junctions are not directly practical for useful electronic devices, they are incredibly valuable tools for unraveling the electronic transport physics relevant for ultrascaled nanoelectronics.
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Affiliation(s)
- Douglas Natelson
- Department of Physics and Astronomy, Rice University, 6100 Main Street, Houston, Texas 77005, United States.
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