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Scanning tunneling microscopy current from localized basis orbital density functional theory
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).ORCID-id: 0000-0003-2659-4161
Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
2016 (engelsk)Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, nr 11, artikkel-id 115434Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
2016. Vol. 93, nr 11, artikkel-id 115434
HSV kategori
Identifikatorer
URN: urn:nbn:se:lnu:diva-46504DOI: 10.1103/PhysRevB.93.115434ISI: 000372715600004Scopus ID: 2-s2.0-84962071169OAI: oai:DiVA.org:lnu-46504DiVA, id: diva2:857068
Tilgjengelig fra: 2015-09-28 Laget: 2015-09-28 Sist oppdatert: 2017-12-01bibliografisk kontrollert
Inngår i avhandling
1. Modeling of non-equilibrium scanning probe microscopy
Åpne denne publikasjonen i ny fane eller vindu >>Modeling of non-equilibrium scanning probe microscopy
2015 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Växjö: Linnaeus University, 2015. s. 80
Emneord
scanning tunneling microscopy, molecular dynamics, density functional theory, non-equilibrium Green's functions
HSV kategori
Forskningsprogram
Fysik, Kondenserade materians fysik
Identifikatorer
urn:nbn:se:lnu:diva-46448 (URN)978-91-87925-73-3 (ISBN)
Presentation
2015-09-17, Ny227, Kalmar Nyckel, Kalmar, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2015-09-28 Laget: 2015-09-23 Sist oppdatert: 2018-01-10bibliografisk kontrollert

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