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Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy, and density functional theory
University of Regensburg , Germany ; Kanazawa University, Japan.
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. (Condensed Matter Physics)ORCID iD: 0000-0003-2659-4161
University of Regensburg, Germany.
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
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2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 16, 165415Article in journal (Refereed) Published
Abstract [en]

Achieving a high intensity in inelastic scanning tunneling spectroscopy (IETS) is important for precise measurements. The intensity of the IETS signal can vary by up to a factor of 3 for various tips without an apparent reason accessible by scanning tunneling microscopy (STM) alone. Here, we show that combining STM and IETS with atomic force microscopy enables carbon monoxide front-atom identification, revealing that high IETS intensities for CO/Cu(111) are obtained for single-atom tips, while the intensity drops sharply for multiatom tips. Adsorption of the CO molecule on a Cu adatom [CO/Cu/Cu(111)] such that the molecule is elevated over the substrate strongly diminishes the tip dependence of IETS intensity, showing that an elevated position channels most of the tunneling current through the CO molecule even for multiatom tips, while a large fraction of the tunneling current bypasses the CO molecule in the case of CO/Cu(111).

Place, publisher, year, edition, pages
2016. Vol. 93, no 16, 165415
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics, Electrotechnology
Identifiers
URN: urn:nbn:se:lnu:diva-46508DOI: 10.1103/PhysRevB.93.165415Scopus ID: 2-s2.0-84963756980OAI: oai:DiVA.org:lnu-46508DiVA: diva2:857071
Available from: 2015-09-28 Created: 2015-09-28 Last updated: 2017-05-31Bibliographically 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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