1
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Alvertis AM, Williams-Young DB, Bruneval F, Neaton JB. Influence of Electronic Correlations on Electron-Phonon Interactions of Molecular Systems with the GW and Coupled Cluster Methods. J Chem Theory Comput 2024; 20:6175-6183. [PMID: 38954597 DOI: 10.1021/acs.jctc.4c00327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/04/2024]
Abstract
Electron-phonon interactions are of great importance to a variety of physical phenomena, and their accurate description is an important goal for first-principles calculations. Isolated examples of materials and molecular systems have emerged where electron-phonon coupling is enhanced over density functional theory (DFT) when using the Green's-function-based ab initio GW method, which provides a more accurate description of electronic correlations. It is, however, unclear how general this enhancement is and how employing high-end quantum chemistry methods, which further improve the description of electronic correlations, might further alter electron-phonon interactions over GW or DFT. Here, we address these questions by computing the renormalization of the highest occupied molecular orbital energies of Thiel's set of organic molecules by harmonic vibrations using DFT, GW, and equation-of-motion coupled-cluster calculations. We find that, depending on the amount of exact exchange included in the DFT starting point, GW can increase the magnitude of the electron-phonon coupling across Thiel's set of molecules by an average factor of 1.1-1.8 compared to the underlying DFT, while equation-of-motion coupled-cluster leads to an increase of 1.4-2. The electron-phonon coupling predicted with the ab initio GW method is generally in much closer agreement to coupled cluster values compared to DFT, establishing GW as a promising route for accurately computing electron-phonon phenomena in molecules and beyond at a much lower computational cost than higher-end quantum chemistry techniques.
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Affiliation(s)
- Antonios M Alvertis
- KBR, Inc., NASA Ames Research Center, Moffett Field, California 94035, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - David B Williams-Young
- Applied Mathematics and Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Fabien Bruneval
- Université Paris-Saclay, CEA, Service de Corrosion et de Comportement des Matériaux, SRMP, 91191 Gif-sur-Yvette, France
| | - Jeffrey B Neaton
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Physics, University of California Berkeley, Berkeley, California 94720, United States
- Kavli Energy NanoScience Institute at Berkeley, Berkeley, California 94720, United States
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2
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Wang Z, Yin R, Tang Z, Du H, Liang Y, Wang X, Deng QS, Tan YZ, Zhang Y, Ma C, Tan S, Wang B. Topologically Localized Vibronic Excitations in Second-Layer Graphene Nanoribbons. PHYSICAL REVIEW LETTERS 2024; 133:036401. [PMID: 39094172 DOI: 10.1103/physrevlett.133.036401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2023] [Accepted: 06/06/2024] [Indexed: 08/04/2024]
Abstract
It is of fundamental importance to characterize the intrinsic properties, like the topological end states, in the on-surface synthesized graphene nanoribbons (GNRs), but the strong electronic interaction with the metal substrate usually smears out their characteristic features. Here, we report our approach to investigate the vibronic excitations of the topological end states in self-decoupled second-layer GNRs, which are grown using an on-surface squeezing-induced spillover strategy. The vibronic progressions show highly spatially localized distributions at the second-layer GNR ends, which can be ascribed to the decoupling-extended lifetime of charging through resonant electron tunneling at the topological end states. In combination with theoretical calculations, we assign the vibronic progressions to specific vibrational modes that mediate the vibronic excitations. The spatial distribution of each resolved excitation shows evident characteristics beyond the conventional Franck-Condon picture. Our work by direct growth of second-layer GNRs provides an effective way to explore the interplay between the intrinsic electronic, vibrational, and topological properties.
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Affiliation(s)
| | | | | | | | | | | | - Qing-Song Deng
- Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory for Physical Chemistry of Solid Surfaces, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, 361005 Xiamen, China
| | - Yuan-Zhi Tan
- Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory for Physical Chemistry of Solid Surfaces, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, 361005 Xiamen, China
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3
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Tang X, Wang W, Tang H, Wang M, Ye X, Hao D, Zhang J, Shan X, Lu X. Large negative differential conductance and its transformation in a single radical molecule. Chem Sci 2024; 15:10989-10996. [PMID: 39027270 PMCID: PMC11253162 DOI: 10.1039/d4sc01782j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2024] [Accepted: 06/02/2024] [Indexed: 07/20/2024] Open
Abstract
The discovery of negative differential conductance (NDC) in a single molecule and mechanism controlling this phenomenon are important for molecular electronics. We investigated the electronic properties of a typical radical molecule 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (CTPO) on an Au(111) surface using low-temperature scanning tunneling microscopy (STM) and inelastic electron tunneling spectroscopy. Large NDC was observed in single CTPO molecules at the boundary of the crystal monolayer. The origin of observed NDC is revealed as the inelastic electron-phonon scattering during tunneling, and the strong spatial variation of the NDC over the single molecule illustrates the nature of the localized radical group. In addition, the NDC can be transformed into a positive differential conductance peak by tuning coupling strengths between different tunneling channels. An empirical multi-channel model has been developed to describe the competition between the valley-shaped NDC and peak-shaped positive differential conductance. The unique electronic property and giant conductance change observed in this radical molecule is valuable for designing novel molecular devices in the future.
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Affiliation(s)
- Xiangqian Tang
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
| | - Wenyu Wang
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
| | - Haitao Tang
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
| | - Muyu Wang
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
| | - Xia Ye
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
| | - Dong Hao
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physics and Electronic Engineering, Jiangsu University Zhenjiang Jiangsu 212013 China
| | - Jinyu Zhang
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
| | - Xinyan Shan
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
- Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China
| | - Xinghua Lu
- Beijing National Laboratory for Condensed-Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190 China
- School of Physical Sciences, University of Chinese Academy of Sciences Beijing 100049 China
- Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China
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4
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Friedrich N, Li J, Pozo I, Peña D, Pascual JI. Tuneable Current Rectification Through a Designer Graphene Nanoribbon. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2401955. [PMID: 38613435 DOI: 10.1002/adma.202401955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Revised: 03/31/2024] [Indexed: 04/15/2024]
Abstract
Unimolecular current rectifiers are fundamental building blocks in organic electronics. Rectifying behavior has been identified in numerous organic systems due to electron-hole asymmetries of orbital levels interfaced by a metal electrode. As a consequence, the rectifying ratio (RR) determining the diode efficiency remains fixed for a chosen molecule-metal interface. Here, a mechanically tunable molecular diode exhibiting an exceptionally large rectification ratio (>105) and reversible direction is presented. The molecular system comprises a seven-armchair graphene nanoribbon (GNR) doped with a single unit of substitutional diboron within its structure, synthesized with atomic precision on a gold substrate by on-surface synthesis. The diboron unit creates half-populated in-gap bound states and splits the GNR frontier bands into two segments, localizing the bound state in a double barrier configuration. By suspending these GNRs freely between the tip of a low-temperature scanning tunneling microscope and the substrate, unipolar hole transport is demonstrated through the boron in-gap state's resonance. Strong current rectification is observed, associated with the varying widths of the two barriers, which can be tuned by altering the distance between tip and substrate. This study introduces an innovative approach for the precise manipulation of molecular electronic functionalities, opening new avenues for advanced applications in organic electronics.
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Affiliation(s)
| | - Jingcheng Li
- CIC nanoGUNE-BRTA, Donostia-San Sebastián, 20018, Spain
- School of Physics, Sun Yat-sen University, Guangzhou, 510275, China
| | - Iago Pozo
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica Universidade de Santiago de Compostela, Santiago de Compostela, 15782, Spain
| | - Diego Peña
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica Universidade de Santiago de Compostela, Santiago de Compostela, 15782, Spain
| | - José Ignacio Pascual
- CIC nanoGUNE-BRTA, Donostia-San Sebastián, 20018, Spain
- Ikerbasque, Basque Foundation for Science, Bilbao, 48013, Spain
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5
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Alkorta M, Cizek R, Néel N, Frederiksen T, Kröger J. Impact of Single-Melamine Tautomerization on the Excitation of Molecular Vibrations in Inelastic Electron Tunneling Spectroscopy. NANO LETTERS 2024; 24:7195-7201. [PMID: 38748446 PMCID: PMC11194823 DOI: 10.1021/acs.nanolett.4c00904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2024] [Revised: 05/10/2024] [Accepted: 05/10/2024] [Indexed: 06/26/2024]
Abstract
Vibrational quanta of melamine and its tautomer are analyzed at the single-molecule level on Cu(100) with inelastic electron tunneling spectroscopy. The on-surface tautomerization gives rise to markedly different low-energy vibrational spectra of the isomers, as evidenced by a shift in mode energies and a variation in inelastic cross sections. Spatially resolved spectroscopy reveals the maximum signal strength on an orbital nodal plane, excluding resonant inelastic tunneling as the mechanism underlying the quantum excitations. Decreasing the probe-molecule separation down to the formation of a chemical bond between the melamine amino group and the Cu apex atom of the tip leads to a quenched vibrational spectrum with different excitation energies. Density functional and electron transport calculations reproduce the experimental findings and show that the shift in the quantum energies applies to internal molecular bending modes. The simulations moreover suggest that the bond formation represents an efficient manner of tautomerizing the molecule.
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Affiliation(s)
- Manex Alkorta
- Donostia
International Physics Center (DIPC), E-20018 Donostia-San Sebastián, Spain
- Centro
de Física de Materiales (CFM) CSIC-UPV/EHU, E-20018 Donostia-San Sebastián, Spain
| | - Rebecca Cizek
- Institut
für Physik, Technische Universität
Ilmenau, D-98693 Ilmenau, Germany
| | - Nicolas Néel
- Institut
für Physik, Technische Universität
Ilmenau, D-98693 Ilmenau, Germany
| | - Thomas Frederiksen
- Donostia
International Physics Center (DIPC), E-20018 Donostia-San Sebastián, Spain
- IKERBASQUE,
Basque Foundation for Science, E-48011 Bilbao, Spain
| | - Jörg Kröger
- Institut
für Physik, Technische Universität
Ilmenau, D-98693 Ilmenau, Germany
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6
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Meng Q, Zhang J, Zhang Y, Chu W, Mao W, Zhang Y, Yang J, Luo Y, Dong Z, Hou JG. Local heating and Raman thermometry in a single molecule. SCIENCE ADVANCES 2024; 10:eadl1015. [PMID: 38232173 DOI: 10.1126/sciadv.adl1015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Accepted: 12/15/2023] [Indexed: 01/19/2024]
Abstract
Because of the nonequilibrium nature of thermal effects at the nanoscale, the characterization of local thermal effects within a single molecule is highly challenging. Here, we demonstrate a way to characterize the local thermal properties of a single fullerene (C60) molecule during current-induced heating processes through tip-enhanced anti-Stokes Raman spectroscopy. Although the measured vibron populations are far from equilibrium with the environment, we can still define an "effective temperature (Teff)" statistically via a Bose-Einstein distribution, suggesting a local equilibrium within the molecule. With increased current heating, Teff is found to rise up to about 1150 K until the C60 cage is decomposed. Such a decomposition temperature is similar to that reported for ensemble C60 samples, thus justifying the validity of our methodology. Moreover, the possible reaction pathway and product can be identified because of the chemical sensitivity of Raman spectroscopy. Our findings provide a practical method for noninvasively detecting the local heating effect inside a single molecule under nonequilibrium conditions.
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Affiliation(s)
- Qiushi Meng
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Junxian Zhang
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Yao Zhang
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
- School of Physics and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Weizhe Chu
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Wenjie Mao
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Yang Zhang
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
- School of Physics and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Jinlong Yang
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
- School of Physics and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Yi Luo
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
- School of Physics and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Zhenchao Dong
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
- School of Physics and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - J G Hou
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
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7
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Wu X, Néel N, Brandbyge M, Kröger J. Enhancement of Graphene Phonon Excitation by a Chemically Engineered Molecular Resonance. PHYSICAL REVIEW LETTERS 2023; 130:116201. [PMID: 37001107 DOI: 10.1103/physrevlett.130.116201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 02/21/2023] [Indexed: 06/19/2023]
Abstract
The abstraction of pyrrolic hydrogen from a single phthalocyanine on graphene turns the molecule into a sensitive probe for graphene phonons. The inelastic electron transport measured with a scanning tunneling microscope across the molecular adsorbate and graphene becomes strongly enhanced for a graphene out-of-plane acoustic phonon mode. Supporting density functional and transport calculations elucidate the underlying physical mechanism. A molecular orbital resonance close to the Fermi energy controls the inelastic current while specific phonon modes of graphene are magnified due to their coupling to symmetry-equivalent vibrational quanta of the molecule.
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Affiliation(s)
- Xiaocui Wu
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
| | - Nicolas Néel
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
| | - Mads Brandbyge
- Center of Nanostructured Graphene, Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Jörg Kröger
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
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8
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Bian X, Chen Z, Sowa JK, Evangeli C, Limburg B, Swett JL, Baugh J, Briggs GAD, Anderson HL, Mol JA, Thomas JO. Charge-State Dependent Vibrational Relaxation in a Single-Molecule Junction. PHYSICAL REVIEW LETTERS 2022; 129:207702. [PMID: 36462006 DOI: 10.1103/physrevlett.129.207702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 10/20/2022] [Indexed: 06/17/2023]
Abstract
The outcome of an electron-transfer process is determined by the quantum-mechanical interplay between electronic and vibrational degrees of freedom. Nonequilibrium vibrational dynamics are known to direct electron-transfer mechanisms in molecular systems; however, the structural features of a molecule that lead to certain modes being pushed out of equilibrium are not well understood. Herein, we report on electron transport through a porphyrin dimer molecule, weakly coupled to graphene electrodes, that displays sequential tunneling within the Coulomb-blockade regime. The sequential transport is initiated by current-induced phonon absorption and proceeds by rapid sequential transport via a nonequilibrium vibrational distribution of low-energy modes, likely related to torsional molecular motions. We demonstrate that this is an experimental signature of slow vibrational dissipation, and obtain a lower bound for the vibrational relaxation time of 8 ns, a value dependent on the molecular charge state.
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Affiliation(s)
- Xinya Bian
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Zhixin Chen
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Jakub K Sowa
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
| | | | - Bart Limburg
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Jacob L Swett
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Jonathan Baugh
- Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - G Andrew D Briggs
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
| | - Harry L Anderson
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Jan A Mol
- School of Physical and Chemical Sciences, Queen Mary University, London E1 4NS, United Kingdom
| | - James O Thomas
- Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
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9
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Cirera B, Wolf M, Kumagai T. Joule Heating in Single-Molecule Point Contacts Studied by Tip-Enhanced Raman Spectroscopy. ACS NANO 2022; 16:16443-16451. [PMID: 36197071 DOI: 10.1021/acsnano.2c05642] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Heating and cooling in current-carrying molecular junctions is a crucial issue in molecular electronics. The microscopic mechanism involves complex factors such as energy inputs, molecular properties, electrode materials, and molecule-electrode coupling. To gain an in-depth understanding, it is a desired experiment to assess vibrational population that represents the energy distribution stored within the molecule. Here, we demonstrate the direct observation of vibrational heating in a single C60 molecule by means of tip-enhanced Raman spectroscopy (TERS). The heating of respective vibrational modes is monitored by anti-Stokes Raman scattering in the TERS spectra. The precise control of the gap distance in the single-molecule junction allows us to reveal a qualitatively different heating mechanism in distinct electron transport regimes, namely, the tunneling and single-molecule point contact (SMPC) regimes. Strong Joule heating via inelastic electron-vibration scattering occurs in the SMPC regime, whereas optical heating is predominant in the tunneling regime. The strong Joule heating at the SMPC also leads to a pronounced red shift of the Raman peak position and line width broadening. Furthermore, by examining the SMPC with several types of contact surfaces, we show that the heating efficiency is related to the current density at the SMPC and the vibrational dissipation channels into the electrode.
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Affiliation(s)
- Borja Cirera
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195Berlin, Germany
| | - Martin Wolf
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195Berlin, Germany
| | - Takashi Kumagai
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195Berlin, Germany
- Center for Mesoscopic Sciences, Institute for Molecular Science, Okazaki444-8585, Japan
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10
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Homberg J, Weismann A, Markussen T, Berndt R. Resonance-Enhanced Vibrational Spectroscopy of Molecules on a Superconductor. PHYSICAL REVIEW LETTERS 2022; 129:116801. [PMID: 36154405 DOI: 10.1103/physrevlett.129.116801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 04/13/2022] [Accepted: 07/13/2022] [Indexed: 06/16/2023]
Abstract
Molecular vibrational spectroscopy with the scanning tunneling microscope is feasible but usually detects few vibrational modes. We harness sharp Yu-Shiba-Rusinov states observed from molecules on a superconductor to significantly enhance the vibrational signal. From a lead phthalocyanine molecule 46 vibrational peaks are resolved enabling a comparison with calculated modes. The energy resolution is improved beyond the thermal broadening limit and shifts induced by neighbor molecules or the position of the microscope tip are determined. Vice versa, spectra of vibrational modes are used to measure the effect of an electrical field on the energy of Yu-Shiba-Rusinov states. The method may help to further probe the interaction of molecules with their environment and to better understand selection rules for vibrational excitations.
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Affiliation(s)
- Jan Homberg
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| | - Alexander Weismann
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
| | - Troels Markussen
- Synopsys Denmark, Fruebjergvej 3, Postbox 4, DK-2100 Copenhagen, Denmark
| | - Richard Berndt
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel, Germany
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11
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Wit B, Vranik R, Müllegger S. Enhanced conductance response in radio frequency scanning tunnelling microscopy. Sci Rep 2022; 12:6183. [PMID: 35418594 PMCID: PMC9007990 DOI: 10.1038/s41598-022-09820-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 03/23/2022] [Indexed: 11/13/2022] Open
Abstract
Diverse spectroscopic methods operating at radio frequency depend on a reliable calibration to compensate for the frequency dependent damping of the transmission lines. Calibration may be impeded by the existence of a sensitive interdependence of two or more experimental parameters. Here, we show by combined scanning tunnelling microscopy measurements and numerical simulations how a frequency-dependent conductance response is affected by different DC conductance behaviours of the tunnel junction. Distinct and well-defined DC-conductance behaviour is provided by our experimental model systems, which include C60 molecules on Au(111), exhibiting electronic configurations distinct from the well-known dim and bright C60's reported so far. We investigate specific combinations of experimental parameters. Variations of the modulation amplitude as small as only a few percent may result in systematic conductance deviations as large as one order of magnitude. We provide practical guidelines for calibrating respective measurements, which are relevant to RF spectroscopic measurements.
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Affiliation(s)
- Bareld Wit
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040, Linz, Austria.
| | - Radovan Vranik
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040, Linz, Austria
| | - Stefan Müllegger
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040, Linz, Austria
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12
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Cirera B, Litman Y, Lin C, Akkoush A, Hammud A, Wolf M, Rossi M, Kumagai T. Charge Transfer-Mediated Dramatic Enhancement of Raman Scattering upon Molecular Point Contact Formation. NANO LETTERS 2022; 22:2170-2176. [PMID: 35188400 PMCID: PMC8949761 DOI: 10.1021/acs.nanolett.1c02626] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Revised: 02/11/2022] [Indexed: 06/14/2023]
Abstract
Charge-transfer enhancement of Raman scattering plays a crucial role in current-carrying molecular junctions. However, the microscopic mechanism of light scattering in such nonequilibrium systems is still imperfectly understood. Here, using low-temperature tip-enhanced Raman spectroscopy (TERS), we investigate how Raman scattering evolves as a function of the gap distance in the single C60-molecule junction consisting of an Ag tip and various metal surfaces. Precise gap-distance control allows the examination of two distinct transport regimes, namely tunneling regime and molecular point contact (MPC). Simultaneous measurement of TERS and the electric current in scanning tunneling microscopy shows that the MPC formation results in dramatic Raman enhancement that enables one to observe the vibrations undetectable in the tunneling regime. This enhancement is found to commonly occur not only for coinage but also transition metal substrates. We suggest that the characteristic enhancement upon the MPC formation is rationalized by charge-transfer excitation.
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Affiliation(s)
- Borja Cirera
- Department
of Physical Chemistry, Fritz-Haber Institute
of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Yair Litman
- MPI
for Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Chenfang Lin
- Department
of Physical Chemistry, Fritz-Haber Institute
of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Alaa Akkoush
- MPI
for Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Adnan Hammud
- Department
of Inorganic Chemistry, Fritz-Haber Institute
of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Martin Wolf
- Department
of Physical Chemistry, Fritz-Haber Institute
of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
| | - Mariana Rossi
- MPI
for Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Takashi Kumagai
- Department
of Physical Chemistry, Fritz-Haber Institute
of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
- Center
for Mesoscopic Sciences, Institute for Molecular
Science, Okazaki 444-8585, Japan
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13
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Cochrane KA, Lee JH, Kastl C, Haber JB, Zhang T, Kozhakhmetov A, Robinson JA, Terrones M, Repp J, Neaton JB, Weber-Bargioni A, Schuler B. Spin-dependent vibronic response of a carbon radical ion in two-dimensional WS 2. Nat Commun 2021; 12:7287. [PMID: 34911952 PMCID: PMC8674275 DOI: 10.1038/s41467-021-27585-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 11/22/2021] [Indexed: 11/29/2022] Open
Abstract
Atomic spin centers in 2D materials are a highly anticipated building block for quantum technologies. Here, we demonstrate the creation of an effective spin-1/2 system via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip. In its anionic state, the carbon impurity is computed to have a magnetic moment of 1 μB resulting from an unpaired electron populating a spin-polarized in-gap orbital. We show that the CRI defect states couple to a small number of local vibrational modes. The vibronic coupling strength critically depends on the spin state and differs for monolayer and bilayer WS2. The carbon radical ion is a surface-bound atomic defect that can be selectively introduced, features a well-understood vibronic spectrum, and is charge state controlled. Spin-polarized defects in 2D materials are attracting attention for future quantum technology applications, but their controlled fabrication is still challenging. Here, the authors report the creation and characterization of effective spin 1/2 defects via the atomically-precise generation of magnetic carbon radical ions in 2D WS2.
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Affiliation(s)
- Katherine A Cochrane
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Jun-Ho Lee
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.,Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA
| | - Christoph Kastl
- Walter-Schottky-Institut and Physik-Department, Technical University of Munich, Garching, 85748, Germany
| | - Jonah B Haber
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.,Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA
| | - Tianyi Zhang
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16082, USA.,Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Azimkhan Kozhakhmetov
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16082, USA
| | - Joshua A Robinson
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16082, USA.,Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Mauricio Terrones
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, 16082, USA.,Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA, 16802, USA.,Department of Physics and Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Jascha Repp
- Institute of Experimental and Applied Physics, University of Regensburg, Regensburg, 93040, Germany
| | - Jeffrey B Neaton
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. .,Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA. .,Kavli Energy Nanosciences Institute at Berkeley, Berkeley, CA, 94720, USA.
| | | | - Bruno Schuler
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. .,nanotech@surfaces Laboratory, Empa-Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, 8600, Switzerland.
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14
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Choi JW, Lee C, Osawa E, Lee JY, Sur JC, Lee KH. Electromechanical Characteristics by a Vertical Flip of C 70 Fullerene Prolate Spheroid in a Single-Electron Transistor: Hybrid Density Functional Methods. NANOMATERIALS (BASEL, SWITZERLAND) 2021; 11:2995. [PMID: 34835759 PMCID: PMC8623830 DOI: 10.3390/nano11112995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Revised: 10/29/2021] [Accepted: 11/04/2021] [Indexed: 11/29/2022]
Abstract
In this study, the B3LYP hybrid density functional theory was used to investigate the electromechanical characteristics of C70 fullerene with and without point charges to model the effect of the surface of the gate electrode in a C70 single-electron transistor (SET). To understand electron tunneling through C70 fullerene species in a single-C70 transistor, descriptors of geometrical atomic structures and frontier molecular orbitals were analyzed. The findings regarding the node planes of the lowest unoccupied molecular orbitals (LUMOs) of C70 and both the highest occupied molecular orbitals (HOMOs) and the LUMO of the C70 anion suggest that electron tunneling of pristine C70 prolate spheroidal fullerene could be better in the major axis orientation when facing the gate electrode than in the major (longer) axis orientation when facing the Au source and drain electrodes. In addition, we explored the effect on the geometrical atomic structure of C70 by a single-electron addition, in which the maximum change for the distance between two carbon sites of C70 is 0.02 Å.
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Affiliation(s)
- Jong Woan Choi
- Department of Semiconductor and Display, Wonkwang University, Iksan 54538, Korea;
| | - Changhoon Lee
- Max Planck POSTECH Center for Complex Phase of Materials, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Eiji Osawa
- NanoCarbon Research Institute, AREC, Shinshu University, Ueda, Nagano 386-8567, Japan;
| | - Ji Young Lee
- Department of Chemistry, Nanoscale Sciences and Technology Institute, Nanocarbon R&D Institute, Wonkwang University, Iksan 54538, Korea
| | - Jung Chul Sur
- Department of Semiconductor and Display, Wonkwang University, Iksan 54538, Korea;
| | - Kee Hag Lee
- Department of Chemistry, Nanoscale Sciences and Technology Institute, Nanocarbon R&D Institute, Wonkwang University, Iksan 54538, Korea
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15
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Han Y, Nijhuis CA. Functional Redox-Active Molecular Tunnel Junctions. Chem Asian J 2020; 15:3752-3770. [PMID: 33015998 PMCID: PMC7756406 DOI: 10.1002/asia.202000932] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 09/29/2020] [Indexed: 01/10/2023]
Abstract
Redox-active molecular junctions have attracted considerable attention because redox-active molecules provide accessible energy levels enabling electronic function at the molecular length scales, such as, rectification, conductance switching, or molecular transistors. Unlike charge transfer in wet electrochemical environments, it is still challenging to understand how redox-processes proceed in solid-state molecular junctions which lack counterions and solvent molecules to stabilize the charge on the molecules. In this minireview, we first introduce molecular junctions based on redox-active molecules and discuss their properties from both a chemistry and nanoelectronics point of view, and then discuss briefly the mechanisms of charge transport in solid-state redox-junctions followed by examples where redox-molecules generate new electronic function. We conclude with challenges that need to be addressed and interesting future directions from a chemical engineering and molecular design perspectives.
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Affiliation(s)
- Yingmei Han
- Department of ChemistryNational University of Singapore3 Science Drive 3Singapore117543Singapore
| | - Christian A. Nijhuis
- Department of ChemistryNational University of Singapore3 Science Drive 3Singapore117543Singapore
- Centre for Advanced 2D Materials and Graphene Research CentreNational University of Singapore6 Science Drive 2Singapore117546Singapore
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16
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Reecht G, Krane N, Lotze C, Zhang L, Briseno AL, Franke KJ. Vibrational Excitation Mechanism in Tunneling Spectroscopy beyond the Franck-Condon Model. PHYSICAL REVIEW LETTERS 2020; 124:116804. [PMID: 32242680 DOI: 10.1103/physrevlett.124.116804] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 01/22/2020] [Accepted: 02/21/2020] [Indexed: 06/11/2023]
Abstract
Vibronic spectra of molecules are typically described within the Franck-Condon model. Here, we show that highly resolved vibronic spectra of large organic molecules on a single layer of MoS_{2} on Au(111) show spatial variations in their intensities, which cannot be captured within this picture. We explain that vibrationally mediated perturbations of the molecular wave functions need to be included into the Franck-Condon model. Our simple model calculations reproduce the experimental spectra at arbitrary position of the scanning tunneling microscope's tip over the molecule in great detail.
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Affiliation(s)
- Gaël Reecht
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Nils Krane
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Christian Lotze
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Lei Zhang
- Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA
| | - Alejandro L Briseno
- Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA
| | - Katharina J Franke
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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17
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Dodin A, Aull B, Kunz RR, Willard AP. Theoretical Bounds on Electron Energy Filtering in Disordered Nanomaterials. NANO LETTERS 2019; 19:8441-8446. [PMID: 31670966 DOI: 10.1021/acs.nanolett.9b02701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Electron energy filters have recently been proposed as a method of reducing the effects of thermal broadening in device and sensing applications, enabling substantial improvements in their room temperature performance. Nanostructured materials can act as electron energy filters by funneling thermally broadened electrons through discrete energy levels. In this study, we develop a theoretical model of the electron filtering properties of nanostructured materials that explicitly includes the effects of thermal broadening and size heterogeneity on the heterogeneity of nanostructure energy levels. We find that under certain conditions quantum dot solids can perform as effective electronic energy filters. We identify a material-specific length scale parameter, Lcrit, that specifies the maximum mean quantum dot size that can yield effective energy filtering. Moreover, we show that energy filtering materials composed of quantum dots with size near Lcrit are maximally robust to heterogeneity in quantum dot size, tolerating variations ∼10% of the mean size. The length scale Lcrit can be estimated directly from the widely tabulated density of states effective mass and shows that semiconductors with light conduction band electrons, such as III-V type materials InSb and GaAs, are the most forgiving for energy filtering applications. Taken together, these results provide a practical set of quantitative design principles for semiconductor electron filters.
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Affiliation(s)
- Amro Dodin
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Brian Aull
- Lincoln Laboratory , Massachusetts Institute of Technology , Lexington , Massachusetts 02421 , United States
| | - Roderick R Kunz
- Lincoln Laboratory , Massachusetts Institute of Technology , Lexington , Massachusetts 02421 , United States
| | - Adam P Willard
- Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
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18
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Mehler A, Néel N, Bocquet ML, Kröger J. Exciting vibrons in both frontier orbitals of a single hydrocarbon molecule on graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:065001. [PMID: 30523960 DOI: 10.1088/1361-648x/aaf54c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Vibronic excitations in molecules are key to the fundamental understanding of the interaction between vibrational and electronic degrees of freedom. In order to probe the genuine vibronic properties of a molecule even after its adsorption on a surface appropriate buffer layers are of paramount importance. Here, vibrational progression in both molecular frontier orbitals is observed with submolecular resolution on a graphene-covered metal surface using scanning tunnelling spectroscopy. Accompanying calculations demonstrate that the vibrational modes that cause the orbital replica in the progression share the same symmetry as the electronic states they couple to. In addition, the vibrational progression is more pronounced for separated molecules than for molecules embedded in molecular assemblies. The entire vibronic spectra of these molecular species are moreover rigidly shifted with respect to each other. This work unravels intramolecular changes in the vibronic and electronic structure owing to the efficient reduction of the molecule-metal hybridization by graphene.
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Affiliation(s)
- A Mehler
- Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
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19
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Krane N, Lotze C, Reecht G, Zhang L, Briseno AL, Franke KJ. High-Resolution Vibronic Spectra of Molecules on Molybdenum Disulfide Allow for Rotamer Identification. ACS NANO 2018; 12:11698-11703. [PMID: 30380829 DOI: 10.1021/acsnano.8b07414] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Tunneling spectroscopy is an important tool for the chemical identification of single molecules on surfaces. Here, we show that oligothiophene-based large organic molecules which only differ by single bond orientations can be distinguished by their vibronic fingerprint. These molecules were deposited on a monolayer of the transition metal dichalcogenide molybdenum disulfide (MoS2) on top of a Au(111) substrate. MoS2 features an electronic band gap for efficient decoupling of the molecular states. Furthermore, it exhibits a small electron-phonon coupling strength. Both of these material properties allow for the resolution of vibronic states in the range of the limit set by temperature broadening in our scanning tunneling microscope at 4.6 K. Using DFT calculations of the molecule in gas phase provides all details for an accurate simulation of the vibronic spectra of both rotamers.
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Affiliation(s)
- Nils Krane
- Fachbereich Physik , Freie Universität Berlin , Arnimallee 14 , 14195 Berlin , Germany
| | - Christian Lotze
- Fachbereich Physik , Freie Universität Berlin , Arnimallee 14 , 14195 Berlin , Germany
| | - Gaël Reecht
- Fachbereich Physik , Freie Universität Berlin , Arnimallee 14 , 14195 Berlin , Germany
| | - Lei Zhang
- Department of Polymer Science and Engineering , University of Massachusetts , Amherst , Massachusetts 01003 , United States
| | - Alejandro L Briseno
- Department of Polymer Science and Engineering , University of Massachusetts , Amherst , Massachusetts 01003 , United States
| | - Katharina J Franke
- Fachbereich Physik , Freie Universität Berlin , Arnimallee 14 , 14195 Berlin , Germany
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20
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Zhang W, Song Y, Liu X, Yan L, Wang Z, Yang Y. Tracking intra-molecular electron and vibrational energy redistribution by time and frequency resolved transient grating spectroscopy. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2018.07.063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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21
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Foti G, Vázquez H. Origin of Vibrational Instabilities in Molecular Wires with Separated Electronic States. J Phys Chem Lett 2018; 9:2791-2796. [PMID: 29741892 DOI: 10.1021/acs.jpclett.8b00940] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Current-induced heating in molecular junctions stems from the interaction between tunneling electrons and localized molecular vibrations. If the electronic excitation of a given vibrational mode exceeds heat dissipation, a situation known as vibrational instability is established, which can seriously compromise the integrity of the junction. Using out of equilibrium first-principles calculations, we demonstrate that vibrational instabilities can take place in the general case of molecular wires with separated unoccupied electronic states. From the ab initio results, we derive a model to characterize unstable vibrational modes and construct a diagram that maps mode stability. These results generalize previous theoretical work and predict vibrational instabilities in a new regime.
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Affiliation(s)
- Giuseppe Foti
- Institute of Physics , Academy of Sciences of the Czech Republic , Cukrovarnicka 10 , Prague , Czech Republic
| | - Héctor Vázquez
- Institute of Physics , Academy of Sciences of the Czech Republic , Cukrovarnicka 10 , Prague , Czech Republic
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22
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Foti G, Vázquez H. Adsorbate-driven cooling of carbene-based molecular junctions. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2017; 8:2060-2068. [PMID: 29090108 PMCID: PMC5647705 DOI: 10.3762/bjnano.8.206] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 09/07/2017] [Indexed: 06/07/2023]
Abstract
We study the role of an NH2 adsorbate on the current-induced heating and cooling of a neighboring carbene-based molecular circuit. We use first-principles methods of inelastic tunneling transport based on density functional theory and non-equilibrium Green's functions to calculate the rates of emission and absorbtion of vibrations by tunneling electrons, the population of vibrational modes and the energy stored in them. We find that the charge rearrangement resulting from the adsorbate gates the carbene electronic structure and reduces the density of carbene states near the Fermi level as a function of bias. These effects result in the cooling of carbene modes at all voltages compared to the "clean" carbene-based junction. We also find that the direct influence of adsorbate states is significantly smaller and tends to heat adsorbate vibrations. Our results highlight the important role of molecular adsorbates not only on the electronic and elastic transport properties but also on the current-induced energy exchange and stability under bias of single-molecule circuits.
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Affiliation(s)
- Giuseppe Foti
- Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, Prague, Czech Republic
| | - Héctor Vázquez
- Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, Prague, Czech Republic
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23
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Ienaga K, Iimori T, Yaji K, Miyamachi T, Nakashima S, Takahashi Y, Fukuma K, Hayashi S, Kajiwara T, Visikovskiy A, Mase K, Nakatsuji K, Tanaka S, Komori F. Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC. NANO LETTERS 2017; 17:3527-3532. [PMID: 28520435 DOI: 10.1021/acs.nanolett.7b00606] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Local electron-phonon coupling of a one-dimensionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron-phonon coupling to the out-of-plane phonon at the K̅ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron-phonon coupling in the surface graphene.
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Affiliation(s)
- Koichiro Ienaga
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Takushi Iimori
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Koichiro Yaji
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Toshio Miyamachi
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Shuhei Nakashima
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Yukio Takahashi
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Kohei Fukuma
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Shingo Hayashi
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Takashi Kajiwara
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Anton Visikovskiy
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Kazuhiko Mase
- Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK) , Tsukuba 305-0801, Japan
- Department of Materials Structure Science, SOKENDAI (The Graduate University for Advanced Studies) , 1-1 Oho, Tsukuba 305-0801, Japan
| | - Kan Nakatsuji
- Department of Materials Science and Engineering, Tokyo Institute of Technology , Yokohama 226-8502, Japan
| | - Satoru Tanaka
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Fumio Komori
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
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24
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Gaudenzi R, Misiorny M, Burzurí E, Wegewijs MR, van der Zant HSJ. Transport mirages in single-molecule devices. J Chem Phys 2017. [DOI: 10.1063/1.4975767] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Affiliation(s)
- R. Gaudenzi
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
| | - M. Misiorny
- Department of Microtechnology and Nanoscience MC2, Chalmers University of Technology, 412 96 Göteborg, Sweden
- Faculty of Physics, Adam Mickiewicz University, 61-614 Poznań, Poland
| | - E. Burzurí
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
| | - M. R. Wegewijs
- Peter Grünberg Institut, Forschungszentrum Jülich, 52425 Jülich, Germany
- JARA-FIT, 52056 Aachen, Germany
- Institute for Theory of Statistical Physics, RWTH Aachen, 52056 Aachen, Germany
| | - H. S. J. van der Zant
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
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25
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Monazami E, McClimon JB, Rondinelli J, Reinke P. Electronic Structure and Band Gap of Fullerenes on Tungsten Surfaces: Transition from a Semiconductor to a Metal Triggered by Annealing. ACS APPLIED MATERIALS & INTERFACES 2016; 8:34854-34862. [PMID: 27998144 DOI: 10.1021/acsami.6b10813] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The understanding and control of molecule-metal interfaces is critical to the performance of molecular electronics and photovoltaics devices. We present a study of the interface between C60 and W, which is a carbide-forming transition metal. The complex solid-state reaction at the interface can be exploited to adjust the electronic properties of the molecule layer. Scanning tunneling microscopy/spectroscopy measurements demonstrate the progression of this reaction from wide band gap (>2.5 eV) to metallic molecular surface during annealing from 300 to 800 K. Differential conduction maps with 104 scanning tunneling spectra are used to quantify the transition in the density of states and the reduction of the band gap during annealing with nanometer spatial resolution. The electronic transition is spatially homogeneous, and the surface band gap can therefore be adjusted by a targeted annealing step. The modified molecules, which we call nanospheres, are quite resistant to ripening and coalescence, unlike any other metallic nanoparticle of the same size. Densely packed C60 and isolated C60 molecules show the same transition in electronic structure, which confirms that the transformation is controlled by the reaction at the C60-W interface. Density functional theory calculations are used to develop possible reaction pathways in agreement with experimentally observed electronic structure modulation. Control of the band gap by the choice of annealing temperature is a unique route to tailoring molecular-layer electronic properties.
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Affiliation(s)
- Ehsan Monazami
- Department of Materials Science and Engineering, University of Virginia , Charlottesville, Virginia 22901, United States
| | - John B McClimon
- Department of Materials Science and Engineering, University of Virginia , Charlottesville, Virginia 22901, United States
- Department of Materials Science and Engineering, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - James Rondinelli
- Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States
| | - Petra Reinke
- Department of Materials Science and Engineering, University of Virginia , Charlottesville, Virginia 22901, United States
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26
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Frisenda R, van der Zant HSJ. Transition from Strong to Weak Electronic Coupling in a Single-Molecule Junction. PHYSICAL REVIEW LETTERS 2016; 117:126804. [PMID: 27689291 DOI: 10.1103/physrevlett.117.126804] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Indexed: 06/06/2023]
Abstract
We have investigated charge transport in single-molecule junctions using gold nanoelectrodes at room and cryogenic (10 K) temperatures. A statistical analysis of the low-bias conductance, measured during the stretching of the molecular junctions, shows that the most probable single-molecule conductance is insensitive to the temperature as expected for off-resonant coherent transport. Low-temperature current-voltage measurements show that these junction conformations have a smooth tunnelinglike shape. While separating the electrodes further we find that, in about one-fourth of the cases, the junction switches in an abrupt way to a configuration with I-V characteristics exhibiting a gap around zero bias and resonances at finite bias. The analysis of the I-V shape and of the conductance distance dependence suggests a stretching-induced transition from the strong to the weak electronic coupling regime. The transition involves a large renormalization of the injection barrier and of the electronic coupling between the molecule and the electrodes.
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Affiliation(s)
- R Frisenda
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, The Netherlands
| | - H S J van der Zant
- Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA, The Netherlands
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27
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Zimbovskaya NA. Nonlinear thermoelectric transport in single-molecule junctions: the effect of electron-phonon interactions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:295301. [PMID: 27248442 DOI: 10.1088/0953-8984/28/29/295301] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In this paper, we theoretically analyze steady-state thermoelectric transport through a single-molecule junction with a vibrating bridge. The thermally induced charge current in the system is explored using a nonequilibrium Green function formalism. We study the combined effects of Coulomb interactions between charge carriers on the bridge and electron-phonon interactions on the thermocurrent beyond the linear response regime. It is shown that electron-vibron interactions may significantly affect both the magnitude and the direction of the thermocurrent, and vibrational signatures may appear.
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Affiliation(s)
- Natalya A Zimbovskaya
- Department of Physics and Electronics, University of Puerto Rico-Humacao, CUH Station, Humacao, PR 00791, USA
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28
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Meierott S, Néel N, Kröger J. Spectroscopic Line Shapes of Vibrational Quanta in the Presence of Molecular Resonances. J Phys Chem Lett 2016; 7:2388-2393. [PMID: 27280313 DOI: 10.1021/acs.jpclett.6b00923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Line shapes of molecular vibrational quanta in inelastic electron tunneling spectroscopy may indicate the strength of electron-vibration coupling, the hybridization of the molecule with its environment, and the degree of vibrational damping by electron-hole pair excitation. Bare as well as C60-terminated Pb tips of a scanning tunneling microscope and clean as well as C60-covered Pb(111) surfaces were used in low-temperature experiments. Depending on the overlap of orbital and vibrational spectral ranges different spectroscopic line shapes of molecular vibrational quanta were observed. The energy range covered by the molecular resonance was altered by modifying the adsorption configuration of the molecule terminating the tip apex. Concomitantly, the line shapes of different vibrational modes were affected. The reported observations represent an experimental proof to theoretical predictions on the contribution from resonant processes to inelastic electron tunneling.
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Affiliation(s)
- Stefan Meierott
- Institut für Physik, Technische Universität Ilmenau , D-98693 Ilmenau, Germany
| | - Nicolas Néel
- Institut für Physik, Technische Universität Ilmenau , D-98693 Ilmenau, Germany
| | - Jörg Kröger
- Institut für Physik, Technische Universität Ilmenau , D-98693 Ilmenau, Germany
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29
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Lau CS, Sadeghi H, Rogers G, Sangtarash S, Dallas P, Porfyrakis K, Warner J, Lambert CJ, Briggs GAD, Mol JA. Redox-Dependent Franck-Condon Blockade and Avalanche Transport in a Graphene-Fullerene Single-Molecule Transistor. NANO LETTERS 2016; 16:170-176. [PMID: 26633125 DOI: 10.1021/acs.nanolett.5b03434] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report transport measurements on a graphene-fullerene single-molecule transistor. The device architecture where a functionalized C60 binds to graphene nanoelectrodes results in strong electron-vibron coupling and weak vibron relaxation. Using a combined approach of transport spectroscopy, Raman spectroscopy, and DFT calculations, we demonstrate center-of-mass oscillations, redox-dependent Franck-Condon blockade, and a transport regime characterized by avalanche tunnelling in a single-molecule transistor.
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Affiliation(s)
- Chit Siong Lau
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Hatef Sadeghi
- Quantum Technology Center, Physics Department, Lancaster University , Lancaster LA1 4YB, United Kingdom
| | - Gregory Rogers
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Sara Sangtarash
- Quantum Technology Center, Physics Department, Lancaster University , Lancaster LA1 4YB, United Kingdom
| | - Panagiotis Dallas
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Kyriakos Porfyrakis
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Jamie Warner
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Colin J Lambert
- Quantum Technology Center, Physics Department, Lancaster University , Lancaster LA1 4YB, United Kingdom
| | - G Andrew D Briggs
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
| | - Jan A Mol
- Department of Materials, University of Oxford , 16 Parks Road, Oxford OX1 3PH, United Kingdom
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30
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Frisenda R, Perrin ML, van der Zant HSJ. Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2015; 6:2477-2484. [PMID: 26885460 PMCID: PMC4734430 DOI: 10.3762/bjnano.6.257] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Accepted: 12/09/2015] [Indexed: 06/05/2023]
Abstract
We study single-molecule oligo(phenylene ethynylene)dithiol junctions by means of inelastic electron tunneling spectroscopy (IETS). The molecule is contacted with gold nano-electrodes formed with the mechanically controllable break junction technique. We record the IETS spectrum of the molecule from direct current measurements, both as a function of time and electrode separation. We find that for fixed electrode separation the molecule switches between various configurations, which are characterized by different IETS spectra. Similar variations in the IETS signal are observed during atomic rearrangements upon stretching of the molecular junction. Using quantum chemistry calculations, we identity some of the vibrational modes which constitute a chemical fingerprint of the molecule. In addition, changes can be attributed to rearrangements of the local molecular environment, in particular at the molecule-electrode interface. This study shows the importance of taking into account the interaction with the electrodes when describing inelastic contributions to transport through single-molecule junctions.
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Affiliation(s)
- Riccardo Frisenda
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands
| | - Mickael L Perrin
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands
| | - Herre S J van der Zant
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands
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31
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Paßens M, Waser R, Karthäuser S. Enhanced fullerene-Au(111) coupling in (2√3 × 2√3)R30° superstructures with intermolecular interactions. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2015; 6:1421-1431. [PMID: 26199846 PMCID: PMC4505183 DOI: 10.3762/bjnano.6.147] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 06/01/2015] [Indexed: 06/07/2023]
Abstract
Disordered and uniform (2√3 × 2√3)R30° superstructures of fullerenes on the Au(111) surface have been studied using scanning tunneling microscopy and spectroscopy. It is shown that the deposition and growth process of a fullerene monolayer on the Au(111) surface determine the resulting superstructure. The supply of thermal energy is of importance for the activation of a Au vacancy forming process and thus, one criterion for the selection of the respective superstructure. However, here it is depicted that a vacancy-adatom pair can be formed even at room temperature. This latter process results in C60 molecules that appear slightly more bright in scanning tunnelling microscopy images and are identified in disordered (2√3 x 2√3)R30° superstructures based on a detailed structure analysis. In addition, these slightly more bright C60 molecules form uniform (2√3 x 2√3)R30° superstructures, which exhibit intermolecular interactions, likely mediated by Au adatoms. Thus, vacancy-adatom pairs forming at room temperature directly affect the resulting C60 superstructure. Differential conductivity spectra reveal a lifting of the degeneracy of the LUMO and LUMO+1 orbitals in the uniform (2√3 x 2√3)R30° superstructure and in addition, hybrid fullerene-Au(111) surface states suggest partly covalent interactions.
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Affiliation(s)
- Michael Paßens
- Peter Grünberg Institut (PGI-7) and JARA-FIT, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
| | - Rainer Waser
- Peter Grünberg Institut (PGI-7) and JARA-FIT, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
- IWE 2 and JARA-FIT, RWTH Aachen University, Sommerfeldstraße 24, 52056 Aachen, Germany
| | - Silvia Karthäuser
- Peter Grünberg Institut (PGI-7) and JARA-FIT, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
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32
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Krause T, Brandes T, Esposito M, Schaller G. Thermodynamics of the polaron master equation at finite bias. J Chem Phys 2015; 142:134106. [DOI: 10.1063/1.4916359] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Thilo Krause
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany
| | - Tobias Brandes
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany
| | - Massimiliano Esposito
- Complex Systems and Statistical Mechanics, University of Luxembourg, L-1511 Luxembourg, Luxembourg
| | - Gernot Schaller
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany
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33
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Nirmalraj P, Thompson D, Molina-Ontoria A, Sousa M, Martín N, Gotsmann B, Riel H. Nanoelectrical analysis of single molecules and atomic-scale materials at the solid/liquid interface. NATURE MATERIALS 2014; 13:947-953. [PMID: 25129620 DOI: 10.1038/nmat4060] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Accepted: 07/15/2014] [Indexed: 06/03/2023]
Abstract
Evaluating the built-in functionality of nanomaterials under practical conditions is central for their proposed integration as active components in next-generation electronics. Low-dimensional materials from single atoms to molecules have been consistently resolved and manipulated under ultrahigh vacuum at low temperatures. At room temperature, atomic-scale imaging has also been performed by probing materials at the solid/liquid interface. We exploit this electrical interface to develop a robust electronic decoupling platform that provides precise information on molecular energy levels recorded using in situ scanning tunnelling microscopy/spectroscopy with high spatial and energy resolution in a high-density liquid environment. Our experimental findings, supported by ab initio electronic structure calculations and atomic-scale molecular dynamics simulations, reveal direct mapping of single-molecule structure and resonance states at the solid/liquid interface. We further extend this approach to resolve the electronic structure of graphene monolayers at atomic length scales under standard room-temperature operating conditions.
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Affiliation(s)
- Peter Nirmalraj
- IBM Research-Zurich, Säumerstrasse 4 8803 Rüschlikon, Switzerland
| | - Damien Thompson
- 1] Department of Physics and Energy, University of Limerick, Ireland [2] Materials and Surface Science Institute, University of Limerick, Ireland
| | - Agustín Molina-Ontoria
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain
| | - Marilyne Sousa
- IBM Research-Zurich, Säumerstrasse 4 8803 Rüschlikon, Switzerland
| | - Nazario Martín
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain
| | - Bernd Gotsmann
- IBM Research-Zurich, Säumerstrasse 4 8803 Rüschlikon, Switzerland
| | - Heike Riel
- IBM Research-Zurich, Säumerstrasse 4 8803 Rüschlikon, Switzerland
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34
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Tahir M, MacKinnon A, Schwingenschlögl U. Novel spectral features of nanoelectromechanical systems. Sci Rep 2014; 4:4035. [PMID: 24531805 PMCID: PMC3925967 DOI: 10.1038/srep04035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 01/24/2014] [Indexed: 12/03/2022] Open
Abstract
Electron transport through a quantum dot or single molecule coupled to a quantum oscillator is studied by the Keldysh nonequilibrium Green's function formalism to obtain insight into the quantum dynamics of the electronic and oscillator degrees of freedom. We tune the electronic level of the quantum dot by a gate voltage, where the leads are kept at zero temperature. Due to the nonequilibrium distribution of the electrons in the quantum dot, the spectral function becomes a function of the gate voltage. Novel spectral features are identified for the ground and excited states of nanomechanical oscillators that can be used to enhance the measurement sensitivity.
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Affiliation(s)
- M. Tahir
- PSE Division, KAUST, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - A. MacKinnon
- Department of Physics, The Blackett Laboratory, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
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