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First-principles simulations of inelastic electron tunneling spectroscopy of molecular electronic devices
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
National Lab for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.ORCID iD: 0000-0003-0007-0394
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.

Place, publisher, year, edition, pages
2005. Vol. 5, no 8, 1551-1555 p.
Keyword [en]
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: urn:nbn:se:kth:diva-6988DOI: 10.1021/nl050789hISI: 000231211300005Scopus ID: 2-s2.0-24344435119OAI: oai:DiVA.org:kth-6988DiVA: diva2:11855
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
In thesis
1. Understanding Electron Transport Properties of Molecular Electronic Devices
Open this publication in new window or tab >>Understanding Electron Transport Properties of Molecular Electronic Devices
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:nbn:se:kth:diva-4500 (URN)978-91-7178-768-2 (ISBN)
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
2. Elastic and Inelastic Electron Tunneling in Molecular Devices
Open this publication in new window or tab >>Elastic and Inelastic Electron Tunneling in Molecular Devices
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
molecular electronics, inelastic electron tunneling spectroscopy, IETS, Green's function, scattering
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3958 (URN)91-7178-362-8 (ISBN)
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
3. A Quantum Chemical View of Molecular and Nano-Electronics
Open this publication in new window or tab >>A Quantum Chemical View of Molecular and Nano-Electronics
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This dissertation presents a generalized quantum chemical approach for electron transport in molecular electronic devices based on Green's function scattering theory. It allows to describe both elastic and inelastic electron transport processes at first principles levels of theory, and to treat devices with metal electrodes either chemically or physically bonded to the molecules on equal footing. Special attention has been paid to understand the molecular length dependence of current-voltage characteristics of molecular junctions. Effects of external electric fields have been taken into account non-perturbatively, allowing to treat electrochemical gate-controlled single molecular field effect transistors for the first time. Inelastic electron tunneling spectroscopy of molecular junctions has been simulated by including electron-vibration couplings. The calculated spectra are often in excellent agreement with experiment, revealing detailed structure information about the molecule and the bonding between molecule and metal electrodes that are not accessible in the experiment.

An effective central insertion scheme (CIS) has been introduced to study electronic structures of nanomaterials at first principles levels. It takes advantage of the partial periodicity of a system and uses the fact that long range interaction in a big system dies out quickly. CIS method can save significant computational time without loss of accuracy and has been successfully applied to calculate electronic structures of one- , two- , and three-dimensional nanomaterials, such as sub-116 nm long conjugated polymers, sub-200nm long single-walled carbon nanotubes, sub-60 base pairs DNA segments, nanodiamondoids of sub-7.3nm in diameter and Si-nanoparticles of sub-6.5nm in diameter at the hybrid density functional theory level. The largest system under investigation consists of 100,000 electrons. The formation of energy bands and quantum confinement effects in these nanostructures have been revealed. Electron transport properties of polymers, SWCNTs and DNA have also been calculated.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 70 p.
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-4335 (URN)978-91-7178-618-0 (ISBN)
Public defence
2007-04-24, FA32, AlbaNova, Roslagstullsbacken, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100729. Ändrat felaktig titel "Theoretical Chemistry, Molecular and Nano-electronics" 20100729.Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2010-07-30Bibliographically approved
4. A generalized quantum chemical approach for nano- and bio-electronics
Open this publication in new window or tab >>A generalized quantum chemical approach for nano- and bio-electronics
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

A generalized quantum chemical approach for electron transport in molecular devices is developed. It allows to treat the devices where the metal electrodes and the molecule are either chemically or physically bonded on equal footing. Effects of molecular length and hydrogen bonding on the current-voltage (I-V) characteristics of molecular devices are discussed. An extension to include the vibration motions of the molecule has been derived and implemented. It provides the inelastic electron tunneling spectroscopy (IETS) of molecular devices with unprecedented accuracy, and reveals important information about the molecular structures that are not accessible in the experiment. The IETS is shown to be a powerful characterization tool for molecular devices.

An effective elongation method has been developed to study the electron transport in nanoand bio-electronic devices at hybrid density functional theory level. It enables to study electronic structures and transportation properties of a 40 nm long self-assembled conjugated polymer junction, a 21 nm long single-walled carbon nanotubes (SWCNT), and a 60 basepairs DNA molecule. It is the first time that systems consisting of more than 10,000 electrons have been described at such a sophisticated level. The calculations have shown that the electron transport in sub-22 nm long SWCNT and short DNA molecules is dominated by the coherent scattering through the delocalized unoccupied states. The derived length dependence of coherent electron transport in these nanostructured systems will be useful for the future experiments. Moreover, some unexpected behaviors of these devices have been discovered.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 48 p.
Keyword
Biotechnology, Bioteknik
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-286 (URN)91-7178-022-X (ISBN)
Presentation
2005-05-24, Sal FB53, AlbaNova, 10:00
Opponent
Supervisors
Note
QC 20101203Available from: 2005-07-06 Created: 2005-07-06 Last updated: 2011-11-23Bibliographically approved

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