liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Structural and electronic transitions in potassium doped pentacene
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, Vol. 73, no 18Article in journal (Refereed) Published
Abstract [en]

We calculate the ground state geometrical structure of potassium-intercalated pentacene lattices using molecular mechanics and the density-functional theory. Both methods result in a structural phase transition in going from the pristine form to the intercalated state with one potassium ion per pentacene molecule. The phase transition is characterized by a sliding of adjacent pentacene molecules relative to each other. The electronic properties of this phase is studied with the density-functional theory. As a result of the geometrical changes, the - overlap in the direction perpendicular to the molecular planes of the layered pristine pentacene structure increases substantially and many of the electronic bands show strong dispersion in this direction. The Fermi energy of the doped phase appears in the middle of the conduction band where the density of states is maximum. The bandwidth of the conduction band is 0.7  eV.

Place, publisher, year, edition, pages
2006. Vol. 73, no 18
Keyword [en]
potassium, organic semiconductors, density functional theory, solid-state phase transformations, conduction bands, Fermi level, electronic density of states, ground states
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-14063DOI: 10.1103/PhysRevB.73.184114OAI: oai:DiVA.org:liu-14063DiVA: diva2:22555
Available from: 2006-10-05 Created: 2006-10-05 Last updated: 2013-11-14
In thesis
1. Electronic Structure and Transport Properties of Carbon Based Materials
Open this publication in new window or tab >>Electronic Structure and Transport Properties of Carbon Based Materials
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the past decade the interest in molecular electronic devices has escalated. The synthesis of molecular crystals has improved, providing single crystals or thin films with mobility comparable with or even higher than amorphous silicon. Their mechanical flexibility admits new types of applications and usage of electronic devices. Some of these organic crystals also display magnetic effects. Furthermore, the fullerene and carbon nanotube allotropes of carbon are prominent candidates for various types of applications. The carbon nanotubes, in particular, are suitable for molecular wire applications with their robust, hollow and almost one-dimensional structure and diverse band structure. In this thesis, we have theoretically investigated carbon based materials, such as carbon nanotubes, pentacene and spiro-biphenalenyl neutral radical molecular crystals. The work mainly deals with the electron structure and the transport properties thereof. The first studies concerns effects and defects in devices of finite carbon nanotubes. The transport properties, that is, conductance, are calculated with the Landauer approach. The device setup contains two metallic leads attached to the carbon nanotubes. Structural defects as vacancies and bending are considered for single-walled carbon nanotubes. For the multi-walled carbon nanotubes the focus is on inter-shell interaction and telescopic junctions. The current voltage characteristics of these systems show clear marks of quantum dot behaviour. The influence of defects as vacancies and geometrical deformations are significant for infinite systems, but in these devices they play a minor role. The rest of the studies concern molecular crystals, treated with density-functional theory (DFT). Inspired by the enhance of the electrical conductivity obtained experimentally by doping similar materials with alkali metals, calculations were performed on bundles of single-walled carbon nanotubes and pentacene crystals doped with potassium. The most prominent effect of the potassium intercalation is the shift of Fermi level in the nanotube bands. A sign of charge transfer of the valence electrons of the potassium atoms. Semi-conducting bundles become metallic and metallic bundles gain density of states at the Fermi level. In the semi-conducting pristine pentacene crystals structural transitions occur upon doping. The herringbone arrangement of the pristine pentacene molecules relaxes to a more π-stacked structure causing more dispersive bands. The charge transfer shifts the Fermi level into the lowest unoccupied molecular orbital band and turns the crystal metallic. Finally, we have studied molecular crystals of spiro-biphenalenyl neutral radicals. According to experimental studies, some of these materials show simultaneous electrical, optical and magnetical bistability. The electronic properties of these crystals are investigated by means of DFT with a focus on the possible intermolecular interactions of radical spins.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1001
Keyword
Molecular crystals, Organic crystals, Nano technique, Density-Functional Theory (DFT), Fermi
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-7544 (URN)9185497118 (ISBN)
Public defence
2006-01-27, Schr¨odinger, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Available from: 2006-10-05 Created: 2006-10-05 Last updated: 2017-12-12
2. Molecular electronics : a theoretical study of electronic structure in molecular crystals and surfaces
Open this publication in new window or tab >>Molecular electronics : a theoretical study of electronic structure in molecular crystals and surfaces
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

  

This thesis deals with theoretical studies of the electronic structures of molecules in organic crystal and molecules adsorbed on metal surfaces. Both studies with first principle calculations and classical mechanics were performed. The materials include pentacene and bis(9-cyclohexylimino-l-oxyphenalenyl)boron and the

Tetrakis( dimethylamino )ethylene (TDAE) molecule chemisorbed on a gold surface. Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field effect transistors, and are therefore suitable to be the active material in such devices. The increase in conductivity obtained experimentally by doping with alkali metals showed great promise, and we therefore performed calculations on pentacene crystals doped with potassium. Phase transitions occured upon doping, and the herringbone arrangement of the pristine pentacene molecules relaxes towards a 1r stacked structure. Charge transfer between the crystal and the potassium occurs, which shifts the Fermi level into the lowest unoccupied molecular orbitals bands and turns the crystal metallic. The study of bis(9-cyclohexylimino-l-oxyphenalenyl)boron, a biphenalenyl based neutral radical, was performed in order to investigate the electronic properties since experimental studies had shown simultaneous electrical, optical and magnetical bistability. The system is quasi one-dimensional, as shown from band structure calculations.. The injection of charge carriers from metals to organic semiconductors is one of the most central processes when it comes to the performance of organic devices. The interface between the metal and the semiconductor is one of the device parameters that will significantly influence the device performance. The addition of a molecular layer on the interface can, by the introduction of a dipole, reduce the energy barrier for charge injection. ·we found that a molecular layer of TDAE deposited on a gold surface results in a charge transfer from the molecule to the surface which reduced the charge injection barrier by as much as 2.4 eV.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2007. 34 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1315
Series
LIU-TEK-LIC, 24
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-38440 (URN)44368 (Local ID)978-91-85831-76-0 (ISBN)44368 (Archive number)44368 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-14

Open Access in DiVA

No full text

Other links

Publisher's full textLink to Ph.D. thesis

Authority records BETA

Hansson, AndersBöhlin, JohanStafström, Sven

Search in DiVA

By author/editor
Hansson, AndersBöhlin, JohanStafström, Sven
By organisation
Computational Physics The Institute of Technology
In the same journal
Physical Review B. Condensed Matter and Materials Physics
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 282 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf