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Molecular Electronics: Insight from Ab-Initio Transport Simulations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents the theoretical studies of electronic transport in molecular electronic devices. Such devices have been proposed and investigated as a promising new approach that complements conventional silicon-based electronics. To design and fabricate future nanoelectronic devices, it is essential to understand the conduction mechanism at a molecular or atomic level. Our approach is based on the non-equilibrium Green's function method (NEGF) combined with density functional theory (DFT). We apply the method to study the electronic transport properties of two-probe systems consisting of molecules or atomic wires sandwiched between leads. A few molecular electronic devices are characterized; namely, conducting molecular wires, molecular switches and molecular recognition sensors. The considered applications are interconnection of different nanoelectronic units with cumulene molecular wires; adding switching functionality to the molecular connectors by applying stress to the CNT-cumulene-CNT junction or by introducing phthalocyanine unit; sensing of individual nucleotides, e.g., for DNA sequencing applications. The obtained results provide useful insights into the electron transport properties of molecules. Several interesting and significant features are analyzed and explained in particular such as, level pinning, negative differential resistance, interfering of conducting channels etc.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 875
Keyword [en]
Molecular Electronics, Ab Initio, DNA Sequencing, Nanoscience, Graphene
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-160474ISBN: 978-91-554-8208-4 (print)OAI: oai:DiVA.org:uu-160474DiVA: diva2:451150
Public defence
2011-12-08, Å80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-11-17 Created: 2011-10-24 Last updated: 2014-01-27Bibliographically approved
List of papers
1. Cumulene molecular wire conductance from first principles
Open this publication in new window or tab >>Cumulene molecular wire conductance from first principles
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 11, 115404- p.Article in journal (Refereed) Published
Abstract [en]

We present first principles calculations of current-voltage characteristics (IVC) and conductance of Au(111):S-2-cumulene-S-2:Au(111) molecular wire junctions with realistic contacts. The transport properties are calculated using full self-consistent ab initio nonequilibrium Green's function density-functional theory methods under external bias. The conductance of the cumulene wires shows oscillatory behavior depending on the number of carbon atoms (double bonds). Among all conjugated oligomers, we find that cumulene wires with odd number of carbon atoms yield the highest conductance with metalliclike ballistic transport behavior. The reason is the high density of states in broad lowest unoccupied molecular orbital levels spanning the Fermi level of the electrodes. The transmission spectrum and the conductance depend only weakly on applied bias, and the IVC is nearly linear over a bias region of +/- 1 V. Cumulene wires are therefore potential candidates for metallic connections in nanoelectronic applications.

National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-137108 (URN)10.1103/PhysRevB.81.115404 (DOI)000276248800117 ()
Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11Bibliographically approved
2. Conductance of linear carbon wires bridging carbon nanotubes
Open this publication in new window or tab >>Conductance of linear carbon wires bridging carbon nanotubes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The cumulenes bridging two-dimensional electrodes provide a model for interconnecting molecular electronics circuit with one of the most conductive molecular wires known. In recent experiments cumulene molecules bridging graphene sheets were observed [PRL 102, 205501 (2009)], thus demonstrating the mechanical way of producing cumulenes. Appearance of carbon wires: cumulenes and polynes, is also feasible between graphene sheets or carbon nanotubes (CNTs). In this work, we study structure and conductance of these wires  suspended between CNTs of different chirality (zigzag and armchair), and graphene sheets (infinite radii CNTs) and corresponding conductance variation upon stretching. We find the geometrical structures of the carbon wire bridging CNT similar to the experimentally observed in the carbon wires obtained between graphene electrodes. We show a capability to modulate the conductance by changing bridging sites between the carbon wire and CNT without breaking the wire. Observed current modulation via cumulene wire stretching/elongation together with CNT stability makes it a promising candidate for mechano-switching device in molecular nanoelectronics.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-160469 (URN)
Projects
KoF U3MEC
Available from: 2011-10-24 Created: 2011-10-24 Last updated: 2012-04-25
3. Interference effects in phtalocyanine controlled by H-H tautomerization: Potential two-terminal unimolecular electronic switch
Open this publication in new window or tab >>Interference effects in phtalocyanine controlled by H-H tautomerization: Potential two-terminal unimolecular electronic switch
2011 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 84, no 16, 165437- p.Article in journal (Refereed) Published
Abstract [en]

We investigate the electrical transport properties of two hydrogen tautomer configurations of phthalocyanine (H2Pc) connected to cumulene and gold leads. Hydrogen tautomerization affects the electronic state of H2Pc by switching the character of molecular orbitals with the same symmetry close to the Fermi level. The near degeneracy between the HOMO and HOMO-1 leads to pronounced interference effects, causing a large change in current for the two tautomer configurations, especially in the low-bias regime. Two types of planar junctions are considered: cumulene-H2Pc-cumulene and gold-H2Pc-gold. Both demonstrate a prominent difference in molecular conductance between ON and OFF states. In addition, junctions with gold leads show pronounced negative differential resistance (NDR) at high bias voltage, as well as weak NDR at intermediate bias.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-160466 (URN)10.1103/PhysRevB.84.165437 (DOI)000296371200009 ()
Projects
KoF U3MEC
Available from: 2011-10-24 Created: 2011-10-24 Last updated: 2017-12-08Bibliographically approved
4. Transverse Conductance of DNA Nucleotides in a Graphene Nanogap from First Principles
Open this publication in new window or tab >>Transverse Conductance of DNA Nucleotides in a Graphene Nanogap from First Principles
Show others...
2011 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 5, 1941-1945 p.Article in journal (Refereed) Published
Abstract [en]

The fabrication of nanopores in atomically thin graphene has recently been achieved, and translocation of DNA has been demonstrated. Taken together with an earlier proposal to use graphene nanogaps for the purpose of DNA sequencing, this approach can resolve the technical problem of achieving single-base resolution in electronic nucleobase detection. We have theoretically evaluated the performance of a graphene nanogap setup for the purpose of whole-genome sequencing, by employing density functional theory and the nonequilibrium Green's function method to investigate the transverse conductance properties of nucleotides inside the gap. In particular, we determined the electrical tunneling current variation at finite bias due to changes in the nucleotides orientation and lateral position. Although the resulting tunneling current is found to fluctuate over several orders of magnitude, a distinction between the four DNA bases appears possible, thus ranking the approach promising for rapid whole-genome sequencing applications.

Keyword
DNA sequencing, graphene, nanogap, ab initio, electronic transport, molecular electronics
National Category
Atom and Molecular Physics and Optics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-153682 (URN)10.1021/nl200147x (DOI)000290373000015 ()21495701 (PubMedID)
Projects
KoFF U3MEC
Funder
Swedish Research Council, 113501971
Available from: 2011-05-18 Created: 2011-05-17 Last updated: 2017-12-11Bibliographically approved
5. Theoretical Study of Electronic Transport through DNA Nucleotides in a Double-Functionalized Graphene Nanogap
Open this publication in new window or tab >>Theoretical Study of Electronic Transport through DNA Nucleotides in a Double-Functionalized Graphene Nanogap
Show others...
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 29, 15421-15428 p.Article in journal (Refereed) Published
Abstract [en]

Graphene nanogaps and nanopores show potential for the purpose of electrical DNA sequencing, in particular because single-base resolution appears to be readily achievable. Here, we evaluated from first principles the advantages of a nanogap setup with functionalized graphene edges. To this end, we employed density functional theory and the non-equilibrium Green's function method to investigate the transverse conductance properties of the four nucleotides occurring in DNA when located between opposing functionalized graphene electrodes. In particular, we determined the electrical tunneling current variation as a function of the applied bias and analyzed the associated differential conductance at a voltage which appears suitable to distinguish between the four nucleotides. Intriguingly, we predict for one of the nucleotides (deoxyguanosine monophosphate) a negative differential resistance effect.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-208163 (URN)10.1021/jp4048743 (DOI)000322503600064 ()
Available from: 2013-09-24 Created: 2013-09-24 Last updated: 2017-12-06Bibliographically approved

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