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Understanding Electron Transport Properties of Molecular Electronic Devices
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

his thesis has been devoted to the study of underlying mechanisms for electron transport in molecular electronic devices. Not only has focus been on describing the elastic and inelastic electron transport processes with a Green's function based scattering theory approach, but also on how to construct computational models that are relevant to experimental systems. The thesis is essentially divided into two parts. While the rst part covers basic assumptions and the elastic transport properties, the second part covers the inelastic transport properties and its applications.

It is discussed how di erent experimental approaches may give rise to di erent junction widths and thereby di erences in coupling strength between the bridging molecules and the contacts. This di erence in coupling strength is then directly related to the magnitude of the current that passes through the molecule and may thus explain observed di erences between di erent experiments. Another focus is the role of intermolecular interactions on the current-voltage (I-V) characteristics, where water molecules interacting with functional groups in a set of conjugated molecules are considered. This is interesting from several aspects; many experiments are performed under ambient conditions, which means that water molecules will be present and may interfere with the experiment. Another point is that many measurement are done on self-assembled monolayers, which raises the question of how such a measurement relates to that of a single molecule. By looking at the perturbations caused by the water molecules, one may get an understanding of what impact a neighboring molecule may have. The theoretical predictions show that intermolecular e ects may play a crucial role and is related to the functional groups, which has to be taken into consideration when looking at experimental data.

In the second part, the inelastic contribution to the total current is shown to be quite small and its real importance lies in probing the device geometry. Several molecules are studied for which experimental data is available for comparison. It is demonstrated that the IETS is very sensitive to the molecular conformation, contact geometry and junction width. It is also found that some of the spectral features that appear in experiment cannot be attributed to the molecular device, but to the background contributions, which shows how theory may be used to complement experiment. This part concludes with a study of the temperature dependence of the inelastic transport. This is very important not only from a theoretical point of view, but also for the experiments since it gives experimentalists a sense of which temperature ranges they can operate for measuring IETS.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , 54 p.
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4500ISBN: 978-91-7178-768-2 (print)OAI: oai:DiVA.org:kth-4500DiVA: diva2:12579
Public defence
2007-10-18, FB52, AlbaNova Universitetscentrum, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100804. Ändrat titeln från: "Understanding Electron Transport Properties in Molecular Devices" 20100804.Available from: 2007-09-28 Created: 2007-09-28 Last updated: 2010-08-04Bibliographically approved
List of papers
1. 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: 2017-12-14Bibliographically approved
2. 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: 2017-12-14Bibliographically approved
3. 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: 2017-12-14Bibliographically 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: 2017-12-14Bibliographically approved
5. Effects of intermolecular interaction on inelastic electron tunneling spectra
Open this publication in new window or tab >>Effects of intermolecular interaction on inelastic electron tunneling spectra
2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 6, 064705- p.Article in journal (Refereed) Published
Abstract [en]

We have examined the effects of intermolecular interactions on the inelastic electron tunneling spectroscopy (IETS) of model systems: a pair of benzenethiol or a pair of benzenedithiol sandwiched between gold electrodes. The dependence of the IETS on the mutual position of and distance between the paired molecules has been predicted and discussed in detailed. It is shown that, although in most cases, there are clear spectral fingerprints present which allow identification of the actual structures of the molecules inside the junction. Caution must be exercised since some characteristic lines can disappear at certain symmetries. The importance of theoretical simulation is emphasized.

Keyword
Aromatic hydrocarbons; Electrodes; Gold compounds; Inelastic scattering; Molecular interactions; Scanning tunneling microscopy; Spectrum analyzers; Inelastic electron tunneling spectroscopy (IETS); Mutual position; Spectral fingerprints; Electron tunneling
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-7527 (URN)10.1063/1.2832304 (DOI)000253238200047 ()2-s2.0-39349098310 (Scopus ID)
Note
QC 20100804. Tidigare titel: "Effects of internolecular interaction on inelastic electron tunneling spectra". Uppdaterad från Submitted till Published 20100804.Available from: 2007-09-28 Created: 2007-09-28 Last updated: 2017-12-14Bibliographically approved
6. Temperature dependence of inelastic electron transport in molecular junctions
Open this publication in new window or tab >>Temperature dependence of inelastic electron transport in molecular junctions
(English)Manuscript (Other academic)
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-7528 (URN)
Note
QC 20100804Available from: 2007-09-28 Created: 2007-09-28 Last updated: 2010-08-04Bibliographically approved

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