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Scanning tunneling microscopy current from localized basis orbital density functional theory
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.ORCID iD: 0000-0003-2659-4161
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 11, 115434Article in journal (Refereed) Published
Abstract [en]

We present a method capable of calculating elastic scanning tunneling microscopy (STM) currents from localized atomic orbital density functional theory (DFT). To overcome the poor accuracy of the localized orbital description of the wave functions far away from the atoms, we propagate the wave functions, using the total DFT potential. From the propagated wave functions, the Bardeen's perturbative approach provides the tunneling current. To illustrate the method we investigate carbon monoxide adsorbed on a Cu(111) surface and recover the depression/protrusion observed experimentally with normal/CO-functionalized STM tips. The theory furthermore allows us to discuss the significance of s- and p-wave tips.

Place, publisher, year, edition, pages
2016. Vol. 93, no 11, 115434
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:lnu:diva-46504DOI: 10.1103/PhysRevB.93.115434ISI: 000372715600004Scopus ID: 2-s2.0-84962071169OAI: oai:DiVA.org:lnu-46504DiVA: diva2:857068
Available from: 2015-09-28 Created: 2015-09-28 Last updated: 2017-04-18Bibliographically approved
In thesis
1. Modeling of non-equilibrium scanning probe microscopy
Open this publication in new window or tab >>Modeling of non-equilibrium scanning probe microscopy
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The work in this thesis is basically divided into two related but separate investigations.

The first part treats simple chemical reactions of adsorbate molecules on metallic surfaces, induced by means of a scanning tunneling probe (STM). The investigation serves as a parameter free extension to existing theories. The theoretical framework is based on a combination of density functional theory (DFT) and non-equilibrium Green's functions (NEGF). Tunneling electrons that pass the adsorbate molecule are assumed to heat up the molecule, and excite vibrations that directly correspond to the reaction coordinate. The theory is demonstrated for an OD molecule adsorbed on a bridge site on a Cu(110) surface, and critically compared to the corresponding experimental results. Both reaction rates and pathways are deduced, opening up the understanding of energy transfer between different configurational geometries, and suggests a deeper insight, and ultimately a higher control of the behaviour of adsorbate molecules on surfaces.

The second part describes a method to calculate STM images in the low bias regime in order to overcome the limitations of localized orbital DFT in the weak coupling limit, i.e., for large vacuum gaps between a tip and the adsorbate molecule. The theory is based on Bardeen's approach to tunneling, where the orbitals computed by DFT are used together with the single-particle Green's function formalism, to accurately describe the orbitals far away from the surface/tip. In particular, the theory successfully reproduces the experimentally well-observed characteristic dip in the tunneling current for a carbon monoxide (CO) molecule adsorbed on a Cu(111) surface. Constant height/current STM images provide direct comparisons to experiments, and from the developed method further insights into elastic tunneling are gained.

Place, publisher, year, edition, pages
Växjö: Linneaus Univesity, 2015. 80 p.
Keyword
scanning tunneling microscopy, molecular dynamics, density functional theory, non-equilibrium Green's functions
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-46448 (URN)978-91-87925-73-3 (ISBN)
Presentation
2015-09-17, Ny227, Kalmar Nyckel, Kalmar, 10:00 (English)
Opponent
Supervisors
Available from: 2015-09-28 Created: 2015-09-23 Last updated: 2015-09-28Bibliographically approved

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CiteExportLink to record
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