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Size and surface coverage density are major factors in determining thiol modified gold nanoparticles characteristics. COMPUT THEOR CHEM 2022. [DOI: 10.1016/j.comptc.2021.113581] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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2
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The Potential of X-ray Photoelectron Spectroscopy for Determining Interface Dipoles of Self-Assembled Monolayers. APPLIED SCIENCES-BASEL 2020. [DOI: 10.3390/app10175735] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the current manuscript we assess to what extent X-ray photoelectron spectroscopy (XPS) is a suitable tool for probing the dipoles formed at interfaces between self-assembled monolayers and metal substrates. To that aim, we perform dispersion-corrected, slab-type band-structure calculations on a number of biphenyl-based systems bonded to an Au(111) surface via different docking groups. In addition to changing the docking chemistry (and the associated interface dipoles), the impacts of polar tail group substituents and varying dipole densities are also investigated. We find that for densely packed monolayers the shifts of the peak positions of the simulated XP spectra are a direct measure for the interface dipoles. In the absence of polar tail group substituents they also directly correlate with adsorption-induced work function changes. At reduced dipole densities this correlation deteriorates, as work function measurements probe the difference between the Fermi level of the substrate and the electrostatic energy far above the interface, while core level shifts are determined by the local electrostatic energy in the region of the atom from which the photoelectron is excited.
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Baghbanzadeh M, Pieters PF, Yuan L, Collison D, Whitesides GM. The Rate of Charge Tunneling in EGaIn Junctions Is Not Sensitive to Halogen Substituents at the Self-Assembled Monolayer//Ga 2O 3 Interface. ACS NANO 2018; 12:10221-10230. [PMID: 30226988 DOI: 10.1021/acsnano.8b05217] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
This paper describes experiments that are designed to test the influence of terminal groups incorporating carbon-halogen bonds on the current density (by hole tunneling) across self-assembled monolayer (SAM)-based junctions of the form MTS/S(CH2)9NHCOCH nX3- n//Ga2O3/EGaIn (where M = Ag and Au and X = CH3, F, Cl, Br, I). Within the limits of statistical significance, these rates of tunneling are insensitive to the nature of the terminal group at the interface between the SAM and the Ga2O3. The results are relevant to the origin of an apparent inconsistency in the literature concerning the influence of halogen atoms at the SAM//electrode interface on the tunneling current density.
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Affiliation(s)
- Mostafa Baghbanzadeh
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
| | - Priscilla F Pieters
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
- Stratingh Institute for Chemistry , University of Groningen , Nijenborgh 4 , 9747 AG Groningen , The Netherlands
| | - Li Yuan
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
| | - Darrell Collison
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
| | - George M Whitesides
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
- Kavli Institute for Bionano Science and Technology , Harvard University 29 Oxford Street , Cambridge , Massachusetts 02138 , United States
- Wyss Institute of Biologically Inspired Engineering , 60 Oxford Street , Cambridge , Massachusetts 02138 , United States
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Yokota Y, Akiyama S, Kaneda Y, Imanishi A, Inagaki K, Morikawa Y, Fukui KI. Computational investigations of electronic structure modifications of ferrocene-terminated self-assembled monolayers: effects of electron donating/withdrawing functional groups attached on the ferrocene moiety. Phys Chem Chem Phys 2017; 19:32715-32722. [PMID: 29199295 DOI: 10.1039/c7cp07279a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The electrochemical properties of chemically modified electrodes have long been a significant focus of research. Although the electronic states are directly related to the electrochemical properties, there have been only limited systematic efforts to reveal the electronic structures of adsorbed redox molecules with respect to the local environment of the redox center. In this study, density functional theory (DFT) calculations were performed for ferrocene-terminated self-assembled monolayers with different electron-donating abilities, which can be regarded as the simplest class of chemically modified electrodes. We revealed that the local electrostatic potentials, which are changed by the electron donating/withdrawing functional groups at the ferrocene moiety and the dipole field of coadsorbed inert molecules, practically determine the density of states derived from the highest occupied molecular orbital (HOMO) and its vicinities (HOMO-1 and HOMO-2) with respect to the electrode Fermi level. Therefore, to design new, sophisticated electrodes with chemical modification, one should consider not only the electronic properties of the constituent molecules, but also the local electrostatic potentials formed by these molecules and coadsorbed inert molecules.
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Affiliation(s)
- Yasuyuki Yokota
- Surface and Interface Science Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
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Mete E, Yılmaz A, Danışman MF. A van der Waals density functional investigation of carboranethiol self-assembled monolayers on Au(111). Phys Chem Chem Phys 2016; 18:12920-7. [PMID: 27108565 DOI: 10.1039/c6cp01485b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Isolated and full monolayer adsorption of various carboranethiol (C2B10H12S) isomers on the gold(111) surface has been investigated using both the standard and van der Waals density functional theory calculations. The effect of different molecular dipole moment orientations on the low energy adlayer geometries, the binding characteristics and the electronic properties of the self-assembled monolayers of these isomers has been studied. Specifically, the binding energy and work function changes associated with different molecules show a correlation with their dipole moments. The adsorption is favored for the isomers with dipole moments parallel to the surface. Of the two possible unit cell structures, (5 × 5) was found to be more stable than .
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Affiliation(s)
- Ersen Mete
- Department of Physics, Balıkesir University, Balıkesir 10145, Turkey.
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Nakaya M, Shikishima M, Shibuta M, Hirata N, Eguchi T, Nakajima A. Molecular-scale and wide-energy-range tunneling spectroscopy on self-assembled monolayers of alkanethiol molecules. ACS NANO 2012; 6:8728-8734. [PMID: 22958159 DOI: 10.1021/nn302405r] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The electronic properties of alkanethiol self-assembled monolayers (alkanethiolate SAMs) associated with their molecular-scale geometry are investigated using scanning tunneling microscopy and spectroscopy (STM/STS). We have selectively formed the three types of alkanethiolate SAMs with standing-up, lying-down, and lattice-gas phases by precise thermal annealing of the SAMs which are conventionally prepared by depositing alkanethiol molecules onto Au(111) surface in solution. The empty and filled states of each SAM are evaluated over a wide energy range covering 6 eV above/below the Fermi level (E(F)) using two types of STS on the basis of tunneling current-voltage and distance-voltage measurements. Electronic states originating from rigid covalent bonds between the thiol group and substrate surface are observed near E(F) in the standing-up and lying-down phases but not in the lattice-gas phase. These states contribute to electrical conduction in the tunneling junction at a low bias voltage. At a higher energy, a highly conductive state stemming from the alkyl chain and an image potential state (IPS) formed in a vacuum gap appear in all phases. The IPS shifts toward a higher energy through the change in the geometry of the SAM from the standing-up phase to the lattice-gas phase through the lying-down phase. This is explained by the increasing work function of alkanethiolate/Au(111) with decreasing density of surface molecules.
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Affiliation(s)
- Masato Nakaya
- Nakajima Designer Nanocluster Assembly Project, ERATO, JST, KSP, 3-2-1 Sakado, Kawasaki 213-0012, Japan
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Ma Z, Rissner F, Wang L, Heimel G, Li Q, Shuai Z, Zojer E. Electronic structure of pyridine-based SAMs on flat Au(111) surfaces: extended charge rearrangements and Fermi level pinning. Phys Chem Chem Phys 2011; 13:9747-60. [PMID: 21503307 DOI: 10.1039/c0cp02168g] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Density functional theory calculations are used to investigate the electronic structure of pyridine-based self-assembled monolayers (SAMs) on an Au(111) surface. We find that, when using pyridine docking groups, the bonding-induced charge rearrangements are frequently found to extend well onto the molecular backbone. This is in contrast to previous observations for the chemisorption of other SAMs, e.g., organic thiolates on gold, and can be explained by a pinning of the lowest unoccupied states of the SAM at the metal Fermi-level. The details of the pinning process, especially the parts of the molecules most affected by the charge rearrangements, strongly depend on the length of the molecular backbone and the tail-group substituent. We also mention methodological shortcomings of conventional density functional theory that can impact the quantitative details regarding the circumstances under which pinning occurs and highlight a number of peculiarities associated with bond dipoles that arise from Fermi-level pinning.
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Affiliation(s)
- ZhongYun Ma
- Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing, People's Republic of China
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Sushko ML, Sushko PV, Abarenkov IV, Shluger AL. QM/MM method for metal-organic interfaces. J Comput Chem 2011; 31:2955-66. [PMID: 20645296 DOI: 10.1002/jcc.21591] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We present a QM/MM method for modeling metal/organic interfaces, which incorporates contributions from long-range electron correlation, characteristic to metals and non-bonded interactions in organic systems. This method can be used to study structurally irregular systems. We apply the method to model finite size domains of self-assembled monolayers on the gold (111) surface and discuss the influence of boundary effects on the electrostatic and electronic properties of these systems.
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Affiliation(s)
- Maria L Sushko
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
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Heimel G, Rissner F, Zojer E. Modeling the electronic properties of pi-conjugated self-assembled monolayers. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2010; 22:2494-513. [PMID: 20414885 DOI: 10.1002/adma.200903855] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The modification of electrode surfaces by depositing self-assembled monolayers (SAMs) provides the possibility for controlled adjustment of various key parameters in organic and molecular electronic devices. Most important among them are the work function of the electrode and the relative alignment of its Fermi level with the conducting states in the SAM itself and with those in a subsequently deposited organic semiconductor. For the efficient application of such interface modifications it is crucial to reach a proper understanding of the relation between the chemical structure of a molecule, its molecular electronic characteristics, and the properties of the SAM formed by such molecules. Over the past years, quantum-mechanical calculations have proven to be a valuable tool for reaching a fundamental understanding of the relevant structure-property relations. Here, we provide a review over the field and report on recent progress in the modeling of the interfacial electronic properties of pi-conjugated SAMs. In addition to the insight that can be gained from simple electrostatic considerations, we focus on the quantum-mechanical description of the roles played by substituents, molecular backbones, chemical anchoring groups, and the packing density of molecules on the surface. Furthermore, we explicitly address the energy-level alignment at the interface between a prototypical organic semiconductor and a SAM-covered metal electrode and describe an approach suitable for extending the metallic character of the substrate onto the monolayer.
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Affiliation(s)
- Georg Heimel
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstrasse 15, 12489 Berlin, Germany.
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Wang L, Rangger GM, Ma Z, Li Q, Shuai Z, Zojer E, Heimel G. Is there a Au–S bond dipole in self-assembled monolayers on gold? Phys Chem Chem Phys 2010; 12:4287-90. [PMID: 20407696 DOI: 10.1039/b924306m] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Linjun Wang
- Department of Chemistry, Tsinghua University, 100084 Beijing, PR China
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Xia JL, Diez-Perez I, Tao NJ. Electron transport in single molecules measured by a distance-modulation assisted break junction method. NANO LETTERS 2008; 8:1960-4. [PMID: 18543978 DOI: 10.1021/nl080857a] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We describe a method to determine whether a measured current in a break junction is due to electron tunneling via space or conduction through a molecule bridged between two electrodes. By modulating the electrode separation, we monitor both the DC and the AC components of the current. The AC component indicates if a molecule is connected to the electrodes while the DC component is the transport current through the molecule. This method allows us to remove the tunneling background from conductance histograms and unambiguously measure the I- V characteristic of single molecules. Furthermore, it provides valuable information about the electromechanical properties of single molecules.
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Affiliation(s)
- J L Xia
- Department of Electrical Engineering, Arizona State University, Tempe, Arizona 85287, USA
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Wang JG, Selloni A. Influence of End Group and Surface Structure on the Current−Voltage Characteristics of Alkanethiol Monolayers on Au(111). J Phys Chem A 2007; 111:12381-5. [DOI: 10.1021/jp075875f] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jian-guo Wang
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540
| | - Annabella Selloni
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540
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De Angelis F, Fantacci S, Selloni A, Grätzel M, Nazeeruddin MK. Influence of the sensitizer adsorption mode on the open-circuit potential of dye-sensitized solar cells. NANO LETTERS 2007; 7:3189-95. [PMID: 17854229 DOI: 10.1021/nl071835b] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We report a combined experimental and theoretical study on the origin of the different open circuit potentials observed in dye-sensitized solar cells using Ru(II)-polypyridyl homoleptic and heteroleptic sensitizers. We have measured the photovoltaic data of different sensitizers and used DFT calculations to analyze the electronic structure of dye-sensitized TiO(2) nanoparticles. Heteroleptic sensitizers adsorb onto TiO(2) via a single bipyridine, leading to a TiO(2) conduction band downshift and overall reduction of the cell open circuit potential.
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Affiliation(s)
- Filippo De Angelis
- Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR), c/o Dipartimento di Chimica, Università di Perugia, Via elce di Sotto 8, I-06213, Perugia, Italy.
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Zangmeister CD, Picraux LB, van Zee RD, Yao Y, Tour JM. Energy-level alignment and work function shifts for thiol-bound monolayers of conjugated molecules self-assembled on Ag, Cu, Au, and Pt. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.06.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Deutsch D, Natan A, Shapira Y, Kronik L. Electrostatic properties of adsorbed polar molecules: opposite behavior of a single molecule and a molecular monolayer. J Am Chem Soc 2007; 129:2989-97. [PMID: 17305341 DOI: 10.1021/ja068417d] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We compare the electrostatic behavior of a single polar molecule adsorbed on a solid substrate with that of an adsorbed polar monolayer. This is accomplished by comparing first principles calculations obtained within a cluster model and a periodic slab model, using benzene derivatives on the Si(111) surface as a representative test case. We find that the two models offer diametrically opposite descriptions of the surface electrostatic phenomena. Slab electrostatics is dominated by dipole reduction due to intermolecular dipole-dipole interactions that partially depolarize the molecules, with charge migration to the substrate playing a negligible role due to electric field suppression outside the monolayer. Conversely, cluster electrostatics is dominated by dipole enhancement due to charge migration to/from the substrate, with only a small polarization of the molecule. This establishes the important role played by long-range interactions, in addition to local chemical properties, in tailoring surface chemistry via polar molecule adsorption.
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Affiliation(s)
- Dudi Deutsch
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
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