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Paulsson, Magnus
Publications (10 of 56) Show all publications
Okabayashi, N., Peronio, A., Paulsson, M., Arai, T. & Giessibl, F. J. (2018). Vibrations of a molecule in an external force field. Proceedings of the National Academy of Sciences of the United States of America, 115(18), 4571-4576
Open this publication in new window or tab >>Vibrations of a molecule in an external force field
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2018 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 115, no 18, p. 4571-4576Article in journal (Refereed) Published
Abstract [en]

The vibration of a molecule adsorbed on a surface contains essential information on the molecule–surface bond, which is important to understand the surface reactions that occur, e.g., in catalytic reactions. Accessing the vibrational energies of a single molecule is possible by combining scanning tunneling microscopy with inelastic electron spectroscopy. However, the tip of a microscope exerts a force on a nearby molecule, and possibly even induces slight structural changes. To study this problem, we have further incorporated atomic force microscopy. The relationship between the exerted forces and vibrational energies is well reproduced by a classical mechanical model. This combined technique opens the possibility to study the atomic-scale interaction of a molecule on a surface with unprecedented precision.The oscillation frequencies of a molecule on a surface are determined by the mass distribution in the molecule and the restoring forces that occur when the molecule bends. The restoring force originates from the atomic-scale interaction within the molecule and with the surface, which plays an essential role in the dynamics and reactivity of the molecule. In 1998, a combination of scanning tunneling microscopy with inelastic tunneling spectroscopy revealed the vibrational frequencies of single molecules adsorbed on a surface. However, the probe tip itself exerts forces on the molecule, changing its oscillation frequencies. Here, we combine atomic force microscopy with inelastic tunneling spectroscopy and measure the influence of the forces exerted by the tip on the lateral vibrational modes of a carbon monoxide molecule on a copper surface. Comparing the experimental data to a mechanical model of the vibrating molecule shows that the bonds within the molecule and with the surface are weakened by the proximity of the tip. This combination of techniques can be applied to analyze complex molecular vibrations and the mechanics of forming and loosening chemical bonds, as well as to study the mechanics of bond breaking in chemical reactions and atomic manipulation.

Place, publisher, year, edition, pages
National Academy of Sciences, 2018
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-73705 (URN)10.1073/pnas.1721498115 (DOI)000431119600037 ()29666274 (PubMedID)
Available from: 2018-04-26 Created: 2018-04-26 Last updated: 2018-07-11Bibliographically approved
Gustafsson, A., Okabayashi, N., Peronio, A., Giessibl, F. J. & Paulsson, M. (2017). Analysis of STM images with pure and CO-functionalized tips: A first-principles and experimental study. Physical Review B, 96(8), Article ID 085415.
Open this publication in new window or tab >>Analysis of STM images with pure and CO-functionalized tips: A first-principles and experimental study
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 8, article id 085415Article in journal (Refereed) Published
Abstract [en]

We describe a first-principles method to calculate scanning tunneling microscopy (STM) images, and compare the results to well-characterized experiments combining STM with atomic force microscopy (AFM). The theory is based on density functional theory with a localized basis set, where the wave functions in the vacuum gap are computed by propagating the localized-basis wave functions into the gap using a real-space grid. Constant-height STM images are computed using Bardeen's approximation method, including averaging over the reciprocal space. We consider copper adatoms and single CO molecules adsorbed on Cu(111), scanned with a single-atom copper tip with and without CO functionalization. The calculated images agree with state-of-the-art experiments, where the atomic structure of the tip apex is determined by AFM. The comparison further allows for detailed interpretation of the STM images.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-67497 (URN)10.1103/PhysRevB.96.085415 (DOI)000407266100004 ()
Available from: 2017-08-29 Created: 2017-08-29 Last updated: 2017-11-29Bibliographically approved
Gustafsson, A. & Paulsson, M. (2017). STM contrast of a CO dimer on a Cu(111) surface: a wave-function analysis. Journal of Physics: Condensed Matter, 29(505301)
Open this publication in new window or tab >>STM contrast of a CO dimer on a Cu(111) surface: a wave-function analysis
2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 505301Article in journal (Refereed) Published
Abstract [en]

We present a method used to intuitively interpret the scanning tunneling microscopy (STM) contrast by investigating individual wave functions originating from the substrate and tip side. We use localized basis orbital density functional theory, and propagate the wave functions into the vacuum region at a real-space grid, including averaging over the lateral reciprocal space. Optimization by means of the method of Lagrange multipliers is implemented to perform a unitary transformation of the wave functions in the middle of the vacuum region. The method enables (i) reduction of the number of contributing tip-substrate wave function combinations used in the corresponding transmission matrix, and (ii) to bundle up wave functions with similar symmetry in the lateral plane, so that (iii) an intuitive understanding of the STM contrast can be achieved. The theory is applied to a CO dimer adsorbed on a Cu(1 1 1) surface scanned by a single-atom Cu tip, whose STM image is discussed in detail by the outlined method.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-69702 (URN)10.1088/1361-648X/aa986d (DOI)
Available from: 2018-01-10 Created: 2018-01-10 Last updated: 2018-01-18Bibliographically approved
Okabayashi, N., Gustafsson, A., Peronio, A., Paulsson, M., Arai, T. & Giessibl, F. (2016). 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. Physical Review B, 93(16), Article ID 165415.
Open this publication in new window or tab >>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
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2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 16, article id 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).

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-46508 (URN)10.1103/PhysRevB.93.165415 (DOI)000373878100002 ()2-s2.0-84963756980 (Scopus ID)
Available from: 2015-09-28 Created: 2015-09-28 Last updated: 2017-12-01Bibliographically approved
Gustafsson, A. & Paulsson, M. (2016). Scanning tunneling microscopy current from localized basis orbital density functional theory. Physical Review B, 93(11), Article ID 115434.
Open this publication in new window or tab >>Scanning tunneling microscopy current from localized basis orbital density functional theory
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 11, article id 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.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:lnu:diva-46504 (URN)10.1103/PhysRevB.93.115434 (DOI)000372715600004 ()2-s2.0-84962071169 (Scopus ID)
Available from: 2015-09-28 Created: 2015-09-28 Last updated: 2017-12-01Bibliographically approved
Kitaguchi, Y., Habuka, S., Okuyama, H., Hatta, S., Aruga, T., Frederiksen, T., . . . Ueba, H. (2015). Controlled switching of single-molecule junctions by mechanical motion of a phenyl ring. Beilstein Journal of Nanotechnology, 6, 2088-2095
Open this publication in new window or tab >>Controlled switching of single-molecule junctions by mechanical motion of a phenyl ring
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2015 (English)In: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 6, p. 2088-2095Article in journal (Refereed) Published
Abstract [en]

Mechanical methods for single-molecule control have potential for wide application in nanodevices and machines. Here we demonstrate the operation of a single-molecule switch made functional by the motion of a phenyl ring, analogous to the lever in a conventional toggle switch. The switch can be actuated by dual triggers, either by a voltage pulse or by displacement of the electrode, and electronic manipulation of the ring by chemical substitution enables rational control of the on-state conductance. Owing to its simple mechanics, structural robustness, and chemical accessibility, we propose that phenyl rings are promising components in mechanical molecular devices.

Keywords
density functional theory, phenyl rings, quantum transport simulations, scanning tunneling microscopy, single-molecule switches
National Category
Materials Chemistry Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-47379 (URN)10.3762/bjnano.6.213 (DOI)000363840300001 ()2-s2.0-84947910268 (Scopus ID)
Available from: 2015-11-24 Created: 2015-11-24 Last updated: 2017-12-01Bibliographically approved
Kitaguchi, Y., Habuka, S., Okuyama, H., Hatta, S., Aruga, T., Frederiksen, T., . . . Ueba, H. (2015). Controlling single-molecule junction conductance by molecular interactions. Scientific Reports, 5, Article ID 11796.
Open this publication in new window or tab >>Controlling single-molecule junction conductance by molecular interactions
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2015 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 11796Article in journal (Refereed) Published
Abstract [en]

For the rational design of single-molecular electronic devices, it is essential to understand environmental effects on the electronic properties of a working molecule. Here we investigate the impact of molecular interactions on the single-molecule conductance by accurately positioning individual molecules on the electrode. To achieve reproducible and precise conductivity measurements, we utilize relatively weak pi-bonding between a phenoxy molecule and a STM-tip to form and cleave one contact to the molecule. The anchoring to the other electrode is kept stable using a chalcogen atom with strong bonding to a Cu(110) substrate. These non-destructive measurements permit us to investigate the variation in single-molecule conductance under different but controlled environmental conditions. Combined with density functional theory calculations, we clarify the role of the electrostatic field in the environmental effect that influences the molecular level alignment.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-45786 (URN)10.1038/srep11796 (DOI)000357263200003 ()26135251 (PubMedID)2-s2.0-84934324836 (Scopus ID)
Available from: 2015-08-20 Created: 2015-08-19 Last updated: 2017-12-04Bibliographically approved
Shchadilova, Y. E., Tikhodeev, S. G., Paulsson, M. & Ueba, H. (2014). Isotope effect in acetylene C2H2 and C2D2 rotations on Cu(001). Physical Review B. Condensed Matter and Materials Physics, 89(16), Article ID: 165418
Open this publication in new window or tab >>Isotope effect in acetylene C2H2 and C2D2 rotations on Cu(001)
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 16, p. Article ID: 165418-Article in journal (Refereed) Published
Abstract [en]

A comprehensive analysis of the elementary processes behind the scanning tunneling microscope controlled rotation of C2H2 and C2D2, isotopologues of a single acetylene molecule adsorbed on the Cu(001) surface, is given, with a focus on the isotope effects. With the help of density-functional theory we calculate the vibrational modes of C2H2 and C2D2 on Cu(001) and estimate the anharmonic couplings between them, using a simple strings-on-rods model. The probability of the elementary processes, nonlinear and combination band, is estimated using the Keldysh diagram technique. This allows us to clarify the main peculiarities and the isotope effects of the C2H2 and C2D2 on Cu(001) rotation, discovered in the pioneering work [B. C. Stipe et al., Phys. Rev. Lett. 81, 1263 (1998)], which have not been previously understood.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-34643 (URN)10.1103/PhysRevB.89.165418 (DOI)000335233000015 ()2-s2.0-84899728464 (Scopus ID)
Available from: 2014-06-04 Created: 2014-06-04 Last updated: 2017-12-05Bibliographically approved
Frederiksen, T., Paulsson, M. & Ueba, H. (2014). Theory of action spectroscopy for single-molecule reactions induced by vibrational excitations with STM. Physical Review B. Condensed Matter and Materials Physics, 89(3), 035427
Open this publication in new window or tab >>Theory of action spectroscopy for single-molecule reactions induced by vibrational excitations with STM
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 3, p. 035427-Article in journal (Refereed) Published
Abstract [en]

A theory of action spectroscopy, i.e., a reaction rate or yield as a function of bias voltage, is presented for single-molecule reactions induced by the inelastic tunneling current with a scanning tunneling microscope. A formula for the reaction yield is derived using the adsorbate resonance model, which provides a versatile tool to analyze vibrationally mediated reactions of single adsorbates on conductive surfaces. This allows us to determine the energy quantum of the excited vibrational mode, the effective broadening of the vibrational density of states (as described by Gaussian or Lorentzian functions), and a prefactor characterizing the elementary process behind the reaction. The underlying approximations are critically discussed. We point out that observation of reaction yields at both bias voltage polarities can provide additional insight into the adsorbate density of states near the Fermi level. As an example, we apply the theory to the case of flip motion of a hydroxyl dimer (OD)(2) on Cu(110) which was experimentally observed by Kumagai et al. [Phys. Rev. B 79, 035423 (2009)]. In combination with density functional theory calculations for the vibrational modes, the vibrational damping due to electron-hole pair generation, and the potential energy landscape for the flip motion, a detailed microscopic picture for the switching process is established. This picture reveals that the predominant mechanism is excitation of the OD stretch modes which couple anharmonically to the low-energy frustrated rotation mode.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-33350 (URN)10.1103/PhysRevB.89.035427 (DOI)000332232300004 ()2-s2.0-84893139363 (Scopus ID)
Available from: 2014-03-27 Created: 2014-03-27 Last updated: 2017-12-05Bibliographically approved
Gustafsson, A., Ueba, H. & Paulsson, M. (2014). Theory of vibrationally assisted tunneling for hydroxyl monomer flipping on Cu(110). Physical Review B. Condensed Matter and Materials Physics, 90(16), Article ID: 165413
Open this publication in new window or tab >>Theory of vibrationally assisted tunneling for hydroxyl monomer flipping on Cu(110)
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 16, p. Article ID: 165413-Article in journal (Refereed) Published
Abstract [en]

To describe vibrationally mediated configuration changes of adsorbates on surfaces we have developed a theory to calculate both reaction rates and pathways. The method uses the T-matrix to describe excitations of vibrational states by the electrons of the substrate, adsorbate, and tunneling electrons from a scanning tunneling probe. In addition to reaction rates, the theory also provides the reaction pathways by going beyond the harmonic approximation and using the full potential energy surface of the adsorbate which contains local minima corresponding to the adsorbates different configurations. To describe the theory, we reproduce the experimental results in [T. Kumagai et al., Phys. Rev. B 79, 035423 (2009)], where the hydrogen/deuterium atom of an adsorbed hydroxyl (OH/OD) exhibits back and forth flipping between two equivalent configurations on a Cu(110) surface at T = 6 K. We estimate the potential energy surface and the reaction barrier, similar to 160 meV, from DFT calculations. The calculated flipping processes arise from (i) at low bias, tunneling of the hydrogen through the barrier, (ii) intermediate bias, tunneling electrons excite the vibrations increasing the reaction rate although over the barrier processes are rare, and (iii) higher bias, overtone excitations increase the reaction rate further.

National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-38309 (URN)10.1103/PhysRevB.90.165413 (DOI)000343771900005 ()2-s2.0-84908052258 (Scopus ID)
Available from: 2014-11-24 Created: 2014-11-24 Last updated: 2017-12-05Bibliographically approved
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