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Elastic and Inelastic Electron Tunneling in Molecular Devices
KTH, School of Biotechnology (BIO).
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

A theoretical framework for calculating electron transport through molecular junctions is presented. It is based on scattering theory using a Green's function formalism. The model can take both elastic and inelastic scattering into account and treats chemical and physical bonds on equal footing. It is shown that it is quite reliable with respect to the choice of functional and basis set. Applications concerning both elastic and inelastic transport are presented, though the emphasis is on the inelastic transport properties. The elastic scattering application part is divided in two part. The first part demonstrates how the current magnitude is strongly related to the junction width, which provides an explanation why experimentalists get two orders of magnitude differences when performing measurements on the same type of system. The second part is devoted to a study of how hydrogenbonding affects the current-voltage (I-V) characteristics. It is shown that for a conjugated molecule with functional groups, the effects can be quite dramatic. This shows the importance of taking possible intermolecular interactions into account when evaluating and comparing experimental data. The inelastic scattering part is devoted to get accurate predictions of inelastic electron tunneling spectroscopy (IETS) experiments. The emphasis has been on elucidating the importance of various bonding conditions for the IETS. It is shown that the IETS is very sensitive to the shape of the electrodes and it can also be used to discriminate between different intramolecular conformations. Temperature dependence is nicely reproduced. The junction width is shown to be of importance and comparisons between experiment as well as other theoretical predictions are made.

Place, publisher, year, edition, pages
Stockholm: Bioteknologi , 2006. , 46 p.
Keyword [en]
molecular electronics, inelastic electron tunneling spectroscopy, IETS, Green's function, scattering
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-3958ISBN: 91-7178-362-8 (print)OAI: oai:DiVA.org:kth-3958DiVA: diva2:10186
Presentation
2006-05-31, FB52, AlbaNova Main Building, Roslagstullsbacken 21, SE-106 91, Stockholm, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101118Available from: 2006-05-11 Created: 2006-05-11 Last updated: 2010-11-18Bibliographically approved
List of papers
1. First-principles simulations of inelastic electron tunneling spectroscopy of molecular electronic devices
Open this publication in new window or tab >>First-principles simulations of inelastic electron tunneling spectroscopy of molecular electronic devices
2005 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 5, no 8, 1551-1555 p.Article in journal (Refereed) Published
Abstract [en]

Inelastic electron tunneling spectroscopy (IETS) is a powerful experimental tool for studying the molecular and metal contact geometries in molecular electronic devices. A first-principles computational method based on the hybrid density functional theory is developed to simulate the IETS of realistic molecular electronic devices. The calculated spectra of a real device with an octanedithiolate embedded between two gold contacts are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intramolecular conformation and the molecule-metal contact geometry changes. With the help of theoretical calculations, it has finally become possible to fully understand and assign the complicated experimental IETS and, more importantly, provide the structural information of the molecular electronic devices.

Keyword
Computer simulation; Electron tunneling; Probability density function; Spectroscopy; Thermal effects; Inelastic electron tunneling spectroscopy (IETS); Intramolecular conformations; Molecular electronic devices; Structural information; article; chemical model; chemistry; computer simulation; electronics; equipment; evaluation; feasibility study; materials testing; methodology; scanning tunneling microscopy; spectroscopy; Computer Simulation; Electronics; Equipment Failure Analysis; Feasibility Studies; Materials Testing; Microscopy, Scanning Tunneling; Models, Chemical; Nanostructures; Spectrum Analysis
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-6988 (URN)10.1021/nl050789h (DOI)000231211300005 ()2-s2.0-24344435119 (Scopus ID)
Note
QC 20100730. Titeln ändrad från "First-principles simulations of inelastic electron tunneling spectroscopy of molecular junctions"Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2010-12-03Bibliographically approved
2. A generalized quantum chemical approach for elastic and inelastic electron transports in molecular electronics devices
Open this publication in new window or tab >>A generalized quantum chemical approach for elastic and inelastic electron transports in molecular electronics devices
2006 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 3, 034708-1-034708-10 p.Article in journal (Refereed) Published
Abstract [en]

A generalized quantum chemical approach for electron transport in molecular devices is developed. It allows one to treat devices where the metal electrodes and the molecule are either chemically or physically bonded on equal footing. An extension to include the vibration motions of the molecule has also been implemented which has produced the inelastic electron-tunneling spectroscopy of molecular electronics devices with unprecedented accuracy. Important information about the structure of the molecule and of metal-molecule contacts that are not accessible in the experiment are revealed. The calculated current-voltage (I-V) characteristics of different molecular devices, including benzene-1,4-dithiolate, octanemonothiolate [H(CH2)(8)S], and octanedithiolate [S(CH2)(8)S] bonded to gold electrodes, are in very good agreement with experimental measurements.

Keyword
Current voltage characteristics; Electrodes; Electron tunneling; Spectroscopic analysis; Gold electrodes; Molecular devices; Molecular electronics devices; Vibration motions; Quantum theory
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-6982 (URN)10.1063/1.2159490 (DOI)000234757400042 ()2-s2.0-31144451119 (Scopus ID)
Note
QC 20100730Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2010-07-30Bibliographically approved
3. Effects of Hydrogen Bonding on Current−Voltage Characteristics of Molecular Junctions
Open this publication in new window or tab >>Effects of Hydrogen Bonding on Current−Voltage Characteristics of Molecular Junctions
2006 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 19, 194703-1-194703-7 p.Article in journal (Refereed) Published
Abstract [en]

We present a first-principles study of hydrogen bonding effect on current-voltage characteristics of molecular junctions. Three model charge-transfer molecules, 2'-amino-4,4'-di(ethynylphenyl)-1-benzenethiolate (DEPBT-D), 4,4'-di(ethynylphenyl)-2'-nitro-1-benzenethiolate (DEPBT-A), and 2'-amino-4,4'-di(ethynylphenyl)-5'-nitro-1-benzenethiolate (DEPBT-DA), have been examined and compared with the corresponding hydrogen bonded complexes formed with different water molecules. Large differences in current-voltage characteristics are observed for DEPBT-D and DEPBT-A molecules with or without hydrogen bonded waters, while relatively small differences are found for DEPBT-DA. It is predicted that the presence of water clusters can drastically reduce the conductivities of the charge-transfer molecules. The underlying microscopic mechanism has been discussed.

Keyword
Charge transfer, Current voltage characteristics, Electric conductivity, Hydrogen bonds;, Mathematical models, Water, Charge transfer molecules, Molecular junctions, Aromatic compounds
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-7524 (URN)10.1063/1.2364494 (DOI)000242181800066 ()2-s2.0-33845301692 (Scopus ID)
Note
QC 20100804Available from: 2007-09-28 Created: 2007-09-28 Last updated: 2010-12-03Bibliographically approved
4. Probing molecule-metal bonding in molecular junctions by inelastic electron tunneling spectroscopy
Open this publication in new window or tab >>Probing molecule-metal bonding in molecular junctions by inelastic electron tunneling spectroscopy
2006 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 6, no 8, 1693-1698 p.Article in journal (Refereed) Published
Abstract [en]

We present first-principles calculations for the inelastic electron tunneling spectra ( IETS) of three molecules, 1-undecane thiol (C11), alpha, omega-bis(thioacetyl)oligophenylenethynylene (OPE), and alpha,omega-bis(thioacetyl) oligophenylenevinylene (OPV), sandwiched between two gold electrodes. We have demonstrated that IETS is very sensitive to the bonding between the molecule and electrodes. In comparison with experiment of Kushmerick et al. (Nano Lett. 2004, 4, 639), it has been concluded that the C11 forms a strong chemical bond, while the bonding of the OPE and OPV systems are slightly weaker. All experimental spectral features have been correctly assigned.

Keyword
Chemical bonds; Electrodes; Electron tunneling; Organic compounds; First principles calculations; Inelastic electron tunneling spectra (IETS); Molecular junctions; Molecule-metal bonding; article; binding site; chemical model; chemical structure; chemistry; computer simulation; elasticity; electron transport; energy filtered transmission electron microscopy; methodology; microelectrode; scanning tunneling microscopy; Binding Sites; Computer Simulation; Elasticity; Electron Transport; Metals; Microelectrodes; Microscopy, Energy-Filtering Transmission Electron; Microscopy, Scanning Tunneling; Models, Chemical; Models, Molecular; Nanostructures; Polymers
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-6989 (URN)10.1021/nl060951w (DOI)000239623900021 ()2-s2.0-33748329697 (Scopus ID)
Note
QC 20100730Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2010-07-30Bibliographically approved

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