Physikhttps://kops.uni-konstanz.de:443/handle/123456789/102017-11-23T15:16:23Z2017-11-23T15:16:23ZThermal conductance of metallic atomic-size contacts : Phonon transport and Wiedemann-Franz lawKlöckner, Jan C.pop212308Matt, Manuelpop139824Nielaba, Peterpop14804Pauly, Fabianpop238339Cuevas, Juan Carlospop508513123456789/406812017-11-22T02:13:58Z2017Thermal conductance of metallic atomic-size contacts : Phonon transport and Wiedemann-Franz law
Klöckner, Jan C.; Matt, Manuel; Nielaba, Peter; Pauly, Fabian; Cuevas, Juan Carlos
Motivated by recent experiments [Science 355, 1192 (2017); Nat. Nanotechnol. 12, 430 (2017)], we present here an extensive theoretical analysis of the thermal conductance of atomic-size contacts made of three different metals, namely gold (Au), platinum (Pt), and aluminum (Al). The main goal of this work is to elucidate the role of phonons in the thermal transport through these atomic contacts as well as to study the validity of the Wiedemann-Franz law, which relates the electrical and the thermal conductance. For this purpose, we have employed two different custom-developed theoretical approaches. The first one is a transport method based on density functional theory (DFT) that allows one to accurately compute the contributions of both electrons and phonons to the thermal transport in few-atom-thick contacts. The second technique is based on a combination of classical molecular dynamics (MD) simulations and a tight-binding model that enables the efficient calculation of the electronic contribution to the thermal conductance of atomic contacts of larger size. Our DFT-based calculations show that the thermal conductance of few-atom contacts of Au and Pt is dominated by electrons, with phonons giving a contribution typically below 10% of the total thermal conductance, depending on the contact geometry. For these two metals we find that the small deviations from the Wiedemann-Franz law, reported experimentally, largely stem from phonons. In the case of Al contacts we predict that the phononic contribution can be considerably larger with up to 40% of the total thermal conductance. We show that these differences in the phononic contribution across metals originate mainly from their distinct Debye energies. On the other hand, our MD-based calculations demonstrate that the electronic contribution to the thermal conductance follows very closely the Wiedemann-Franz law, irrespective of the material and the contact size. Finally, the ensemble of our results consistently shows that the reported observation of quantized thermal transport at room temperature is restricted to few-atom contacts of Au, a monovalent metal in which the transport is dominated by the s valence orbitals. In the case of multivalent metals like Pt and Al this quantization is statistically absent due to the fact that additional orbitals contribute to the transport with conduction channels that have intermediate transmissions between 0 and 1, even in the case of single-atom contacts.
2017Klöckner, Jan C.Matt, ManuelNielaba, PeterPauly, FabianCuevas, Juan Carlos530Motivated by recent experiments [Science 355, 1192 (2017); Nat. Nanotechnol. 12, 430 (2017)], we present here an extensive theoretical analysis of the thermal conductance of atomic-size contacts made of three different metals, namely gold (Au), platinum (Pt), and aluminum (Al). The main goal of this work is to elucidate the role of phonons in the thermal transport through these atomic contacts as well as to study the validity of the Wiedemann-Franz law, which relates the electrical and the thermal conductance. For this purpose, we have employed two different custom-developed theoretical approaches. The first one is a transport method based on density functional theory (DFT) that allows one to accurately compute the contributions of both electrons and phonons to the thermal transport in few-atom-thick contacts. The second technique is based on a combination of classical molecular dynamics (MD) simulations and a tight-binding model that enables the efficient calculation of the electronic contribution to the thermal conductance of atomic contacts of larger size. Our DFT-based calculations show that the thermal conductance of few-atom contacts of Au and Pt is dominated by electrons, with phonons giving a contribution typically below 10% of the total thermal conductance, depending on the contact geometry. For these two metals we find that the small deviations from the Wiedemann-Franz law, reported experimentally, largely stem from phonons. In the case of Al contacts we predict that the phononic contribution can be considerably larger with up to 40% of the total thermal conductance. We show that these differences in the phononic contribution across metals originate mainly from their distinct Debye energies. On the other hand, our MD-based calculations demonstrate that the electronic contribution to the thermal conductance follows very closely the Wiedemann-Franz law, irrespective of the material and the contact size. Finally, the ensemble of our results consistently shows that the reported observation of quantized thermal transport at room temperature is restricted to few-atom contacts of Au, a monovalent metal in which the transport is dominated by the s valence orbitals. In the case of multivalent metals like Pt and Al this quantization is statistically absent due to the fact that additional orbitals contribute to the transport with conduction channels that have intermediate transmissions between 0 and 1, even in the case of single-atom contacts.JOURNAL_ARTICLEurn:nbn:de:bsz:352-2-1jnsf5z52vejo8eng10.1103/PhysRevB.96.2054052469-99502470-00109620Physical Review B2017-11-21T15:09:59+01:00123456789/41Physical Review B ; 96 (2017), 20. - 205405. - ISSN 2469-9950. - eISSN 2470-00102017-11-21T14:09:59ZCharacterization of interface adhesion and acoustic attenuation in multilayer systemsGroßmann, Martinpop139823123456789/406402017-11-16T06:25:34Z2017Characterization of interface adhesion and acoustic attenuation in multilayer systems
Großmann, Martin
2017Großmann, Martin530DOCTORAL_THESISurn:nbn:de:bsz:352-2--16cebclocrdui0eng2017-11-16T07:17:31+01:00123456789/412017-11-16T06:17:31ZOn the linewidth in photoelectron spectra of size-selected clustersKoop, Alexanderpop212188Ganteför, Gerdpop08476123456789/406302017-11-16T02:13:57Z2017On the linewidth in photoelectron spectra of size-selected clusters
Koop, Alexander; Ganteför, Gerd
A systematic analysis of the average linewidth of features in the photoelectron spectra of size-selected elemental clusters consisting of up to 10 atoms is presented. With increasing atomic weight, the average linewidth decreases. Several possible reasons for this trend are discussed. Obvious effects such as experimental resolution, vibrational temperature, and lifetime broadening can be excluded. The only remaining explanation is a mass-dependence of the Franck-Condon envelope. Each photoelectron peak corresponds to an electronic transition, which exhibits a Frank-Condon envelope. Its full width of half maximum depends on the spatial expansion of the nuclear wave functions in the initial state. With increasing atomic mass, the nuclear wave functions narrow down.
2017Koop, AlexanderGanteför, Gerd530A systematic analysis of the average linewidth of features in the photoelectron spectra of size-selected elemental clusters consisting of up to 10 atoms is presented. With increasing atomic weight, the average linewidth decreases. Several possible reasons for this trend are discussed. Obvious effects such as experimental resolution, vibrational temperature, and lifetime broadening can be excluded. The only remaining explanation is a mass-dependence of the Franck-Condon envelope. Each photoelectron peak corresponds to an electronic transition, which exhibits a Frank-Condon envelope. Its full width of half maximum depends on the spatial expansion of the nuclear wave functions in the initial state. With increasing atomic mass, the nuclear wave functions narrow down.JOURNAL_ARTICLEeng10.1063/1.50043990021-96061089-769014712The Journal of chemical physics2017-11-15T11:40:03+01:00123456789/41The Journal of chemical physics ; 147 (2017), 12. - 124307. - ISSN 0021-9606. - eISSN 1089-76902017-11-15T10:40:03ZBasic Theory of Electron Transport Through Molecular ContactsBergvall, AndersFogelström, MikaelHolmqvist, Ceciliapop226927Löfwander, TomasMoth-Poulsen, Kasperedae29fc-3584-44ca-89e4-af0ab2b3d86b123456789/406232017-11-16T02:14:42Z2016Basic Theory of Electron Transport Through Molecular Contacts
Bergvall, Anders; Fogelström, Mikael; Holmqvist, Cecilia; Löfwander, Tomas
2016Bergvall, AndersFogelström, MikaelHolmqvist, CeciliaLöfwander, Tomas530Pan Stanford PublishingMoth-Poulsen, KasperINCOLLECTIONeng97898144633863178Handbook of single-molecule electronics2017-11-15T10:23:12+01:00123456789/41Handbook of single-molecule electronics / Moth-Poulsen, Kasper (Hrsg.). - Singapore : Pan Stanford Publishing, 2016. - S. 31-78. - ISBN 97898144633862017-11-15T09:23:12Z