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Johansson, Lars
Alternative names
Publications (10 of 69) Show all publications
Emanuelsson, C., Soldemo, M., Johansson, L. & Zhang, H. (2019). Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-2√3×2√3. Journal of Chemical Physics, 150(4)
Open this publication in new window or tab >>Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-2√3×2√3
2019 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 4Article in journal (Refereed) Published
Abstract [en]

Perylene tetracarboxylic diimide molecules were evaporated onto a Sn/Si(111)-2 root 3 x 2 root 3 surface and studied using scanning tunneling microscopy (STM) and low energy electron diffraction. At low coverages, single molecules are locked into specific adsorption geometries, which are investigated in detail using high resolution STM. The electronic structure of these individual molecules was studied using bias dependent STM images. The molecules form 1D rows that become more common with increasing coverages. Possible intermolecular O center dot center dot center dot H interactions within the rows have been identified. At around half of a monolayer (ML), the rows of molecules interact with each other and form a commensurate 4 root 3 x 2 root 3 reconstruction. In a complete monolayer, several structures emerge as molecules fill in the space between the 4 root 3 x 2 root 3 stripes. Possible intermolecular interactions within the 1 ML structures have been discussed. At coverages above 1 ML, the growth is characterized by island growth, where the molecules are arranged according to the canted structure within the layers.

Place, publisher, year, edition, pages
New York: American Institute of Physics (AIP), 2019
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-70247 (URN)10.1063/1.5070120 (DOI)000457414600075 ()
Funder
Swedish Research Council, 2013-5291
Note

Artikeln tidigare publicerad som manuskript i Emanuelssons (2018) doktorsavhandling Electronic Structure and Film Morphology Studies of PTCDI on Metal/Semiconductor Surfaces

Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2019-07-11Bibliographically approved
Emanuelsson, C., Johansson, L. & Zhang, H. (2018). Delicate Interactions of PTCDI molecules on Ag/Si(111)-√3×√3. Journal of Chemical Physics, 149(16), 164707
Open this publication in new window or tab >>Delicate Interactions of PTCDI molecules on Ag/Si(111)-√3×√3
2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 16, p. 164707-Article in journal (Refereed) Published
Abstract [en]

PTCDI molecules were evaporated onto a Ag/Si(111)√3×√3 surface and studied using scanning tun-resolution STM images are used to identify the delicate molecule/molecule and molecule/substrate interactions and the shapes of the molecular orbitals. The results show that the substrate/molecule interaction strongly modifies the electronic configuration of the molecules as their orbital shapes are quite different at 1 and 2 monolayer (ML) coverage. Simple models of molecular HOMO/LUMO levels and intermolecular hydrogen-bondings have been made for 1 and 2 ML PTCDI coverages to explain the STM images. Changes due to the interaction with the substrate are also found in ARUPS as extra states above the regular HOMO level at 1 ML PTCDI coverage. The ARUPS data also show that the electronic structure of the substrate remains unchanged after the deposition of molecules as the dispersion of the substrate related bands is unchanged. The changes in electronic structure ofthe molecules are discussed based on aHOMO/LUMO split.

Place, publisher, year, edition, pages
New York: American Institute of Physics (AIP), 2018
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-70246 (URN)10.1063/1.5053606 (DOI)000449103200074 ()
Projects
Organic molecular layers for photovoltaic applications
Funder
Swedish Research Council, 2013-5291
Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2018-12-19Bibliographically approved
Emanuelsson, C., Johansson, L. & Zhang, H. (2018). Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-root 3 x root 3. Journal of Chemical Physics, 149(4), Article ID 044702.
Open this publication in new window or tab >>Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-root 3 x root 3
2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 4, article id 044702Article in journal (Refereed) Published
Abstract [en]

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-root 3 x root 3 surface and studied using photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS). All core levels related to the imide group of the molecules showed a partial shift to lower binding energies at low coverages. In NEXAFS spectra, the first transitions to the unoccupied states were weaker at low coverages compared to thicker films. Also, extra states in the valence band between the regular highest occupied molecular orbital and the Fermi level were found at low coverages. These changes were explained by two types of molecules. Due to charge transfer from the surface, these two types have different interactions between the imide group and the substrate. As a result, one type has a partially filled lowest unoccupied molecular orbital while the other type does not. Published by AIP Publishing.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-69377 (URN)10.1063/1.5038721 (DOI)000440586200047 ()30068162 (PubMedID)
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2019-08-15Bibliographically approved
Starfelt, S., Zhang, H. & Johansson, L. (2018). Quantum-well states in thin Ag films grown on the Ga/Si(111)-root 3 x root 3 surface. Physical Review B, 97(19), Article ID 195430.
Open this publication in new window or tab >>Quantum-well states in thin Ag films grown on the Ga/Si(111)-root 3 x root 3 surface
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 19, article id 195430Article in journal (Refereed) Published
Abstract [en]

Silver thin films have been created by room temperature deposition on a Ga/Si(111)-root 3 x root 3 surface and their valence band structures and core levels have been measured by angle-resolved photoelectron spectroscopy (ARPES). Discrete quantum-well states (QWSs) quantized from the Ag sp valence band are observed already at 3 monolayers (ML). The characteristics of the QWSs have been examined in the phase accumulation model for thicknesses between 3 and 12 ML. The phase shift and QWSs binding energies dependence with Ag film thicknesses have all been consistently derived. In-plane energy dispersion follows a parabolic curve, and the effective mass of the QWSs shows an increasing trend with binding energies as well as with reduced film thicknesses. Furthermore, the ARPES measurements reveal umldapp mediated QWSs around the (M)over-bar points of the Si(111) 1 x 1 surface Brillouin zone. The study confirms that the Ga/Si(111)-root 3 x root 3 surface is a good substrate for growing uniform ultrathin Ag films in room temperature conditions.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-67486 (URN)10.1103/PhysRevB.97.195430 (DOI)000433009300010 ()
Available from: 2018-06-07 Created: 2018-06-07 Last updated: 2018-07-24Bibliographically approved
Zhang, H., Holleboom, T. & Johansson, L. (2017). Band splitting of quantum wells of thin Ag films on Sn/Si(111)√3×√3. Physical Review B, 96(4), 041402-1-041402-6
Open this publication in new window or tab >>Band splitting of quantum wells of thin Ag films on Sn/Si(111)√3×√3
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 4, p. 041402-1-041402-6Article in journal (Refereed) Published
Abstract [en]

High-resolution valence band spectra of ultrathin Ag films on Sn/Si(111)√3×√3 show intrinsic splitting of the quantum-well states (QWSs). Especially at low coverages, the QWSs of such a system display delicate coupling characters with the bulk bands from the substrate. The observed QWS splitting agrees well with the result of the theoretical calculation. We found that the splitting originates from an interface with a finite thickness. In addition, the interface also causes a large sp band splitting due to the Umklapp scattering in the Γ−M direction of the Ag(111) surface Brillouin zone.

Place, publisher, year, edition, pages
American Physical Society, 2017
Keywords
electronic structure, metals, semiconductors, quantum wells, thin films, first-principles calculation, photoemission spectroscopy
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-62779 (URN)10.1103/PhysRevB.96.041402 (DOI)000405026300008 ()
Funder
Swedish Research Council, 2013-5291
Available from: 2017-09-08 Created: 2017-09-08 Last updated: 2019-09-19Bibliographically approved
Emanuelsson, C., Zhang, H., Moons, E. & Johansson, L. (2017). Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-root 3 x root 3. Journal of Chemical Physics, 146(11), Article ID 114702.
Open this publication in new window or tab >>Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-root 3 x root 3
2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 11, article id 114702Article in journal (Refereed) Published
Abstract [en]

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-root 3 x root 3 surface and studied by scanning tunneling microscopy/spectroscopy and low energy electron diffraction (LEED). The growth mode was characterized as layer-by-layer growth with a single molecular unit cell in a short range order. The growth of the first two monolayers involves a molecule/substrate superstructure and a molecule/molecule superstructure. At higher coverages, the molecules in each layer were found to align so that unit cells are on top of each other. The experimentally obtained LEED pattern is described as a combination of patterns from the molecular unit cell and the molecule/substrate superstructure. The electronic structure was found to be strongly dependent on the film thickness for the first few layers: Several extra states are found at low coverages compared to higher coverages resulting in a very small pseudo gap of 0.9 eV for the first layer, which widens up to 4.0 eV for thicker films.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2017
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-65295 (URN)10.1063/1.4978470 (DOI)000397313600027 ()28330354 (PubMedID)
Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2019-07-10Bibliographically approved
Zhang, H. & Johansson, L. (2016). STM study of PTCDA on Sn/Si(111)-2 root 3 x 2 root 3. Journal of Chemical Physics, 144(12), Article ID 124701.
Open this publication in new window or tab >>STM study of PTCDA on Sn/Si(111)-2 root 3 x 2 root 3
2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 12, article id 124701Article in journal (Refereed) Published
Abstract [en]

The electronic structures of perylene tetracarboxylic dianhydride on Sn/Si(111)-2 root 3 x 2 root 3 have been studied by scanning tunneling microscopy and spectroscopy. Individual molecules have been investigated at 0.15 ML, while at 0.3 ML molecules formed short rods. At 0.6 ML, the molecular rods interacted with each other, coupling with the substrate and forming a new 4 root 3 x 2 root 3 super structure. At 0.9 ML, the surface was further reconstructed and consisted of strips with two and three rods of molecules. We found that these surface structures are strongly modified by the molecule/substrate and the intermolecular interactions. As a result, the HOMO-LUMO gaps of these molecules change with respect to the phases and the thickness. For a single molecular layer of the 4 root 3 x 2 root 3 phase, the HOMO-LUMO levels were split with a gap of approximately 2.1 eV, which is caused by charge transfer from the substrate to the molecules. (C) 2016 AIP Publishing LLC.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-42026 (URN)10.1063/1.4944389 (DOI)000373644400052 ()27036469 (PubMedID)
Available from: 2016-05-13 Created: 2016-05-13 Last updated: 2017-11-30Bibliographically approved
Zhang, H. & Johansson, L. (2014). Electronic structure of PTCDA on Sn/Si(111)-2√3×2√3. Chemical Physics, 439, 71-78
Open this publication in new window or tab >>Electronic structure of PTCDA on Sn/Si(111)-2√3×2√3
2014 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 439, p. 71-78Article in journal (Refereed) Published
Abstract [en]

The electronic structures of PTCDA on the Sn/Si(111)-2√3×2√3 surface have been thoroughly studied by high-resolution photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS). Upon deposition of PTCDA, there is an unusual charge transfer from the Sn/Si(111)-2√3×2√3 surface to the molecules. This is clearly shown by a new component in the Sn 4d core-level spectra that shifts towards higher binding energy. In contrast to the literature, the charge provided by Sn is donated to the carbonyl C instead of the O atoms. This is revealed by a new component in the C 1s core-level spectra that shifts towards lower binding energy. The charge transfer causes a splitting of the HOMO level in the valence band spectra. As indicated in the NEXAFS spectra, it also induces a splitting of the LUMO level of the molecules. For thick films the NEXAFS results suggest a layer by layer growth mode.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
PTCDA, XPS, NEXAFS, Electronic structure, Molecule-induced reconstruction, Metal/semiconductor surface
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-33743 (URN)10.1016/j.chemphys.2014.05.013 (DOI)000338705600010 ()
Funder
Swedish Research Council
Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2017-12-05Bibliographically approved
Zhang, H., Hirvonen Grytzelius, J. & Johansson, L. (2013). Thin Mn germanide films studied with XPS, STM, and XMCD. Physical Review B. Condensed Matter and Materials Physics, 88(4), 045311-1-045311-6
Open this publication in new window or tab >>Thin Mn germanide films studied with XPS, STM, and XMCD
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 4, p. 045311-1-045311-6Article in journal (Refereed) Published
Abstract [en]

Thin Mn germanide films with nanoscale thicknesses on Ge(111) have been studied by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), core-level spectroscopy (CLS), and x-ray magnetic circular dichroism. The 260 C annealing of 16 monolayers of Mn deposited on Ge(111)c(2×8) resulted in a uniform film with intense threefold split √3×√3 LEED spots and Moiré patterns in the STM images. This ultrathin film shows a clear ferromagnetism with a Curie temperature of ∼250 K. High-resolution Ge 3d CLS spectra were recorded with photon energies between 50 and 90 eV at normal and 60 emission angle. To achieve a consistent fit over the energy and angular range three components were used in the line-shape analysis. The low temperature (260 C) annealed film shows significant differences in terms of electronic structure and magnetism in contrast to the high temperature (330 C or above) annealed ones. Our results indicate that the annealing temperature and the Mn coverage play important roles in the formation of a thin magnetic Mn germanide film.

National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-14506 (URN)10.1103/PhysRevB.88.045311 (DOI)000321838800006 ()
Funder
Swedish Research Council
Available from: 2012-08-16 Created: 2012-08-16 Last updated: 2017-12-07Bibliographically approved
Hirvonen Grytzelius, J., Zhang, H. & Johansson, L. (2012). Mn5Ge3 film formation on Ge(111)c(2×8). Physical Review B. Condensed Matter and Materials Physics, 86(12), 125313-1-125313-7
Open this publication in new window or tab >>Mn5Ge3 film formation on Ge(111)c(2×8)
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 12, p. 125313-1-125313-7Article in journal (Refereed) Published
Abstract [en]

Thin manganese germanide films with different thicknesses on Ge(111) have been studied in detail by low-energy electron diffraction (LEED), scanning tunneling microscopy, and core-level spectroscopy (CLS). Annealing of the deposited Mn on Ge(111)c(2×8) between 330-450 C resulted in well-ordered Mn5Ge3 surfaces as seen by intense 3×3 LEED spots. Up to a coverage of 24 monolayers (ML), island formation is favored. At a coverage of 32 ML a well ordered Mn5Ge3 film was found to fully cover the surface. High-resolution Ge 3d CLS spectra were recorded with photon energies between 50 and 110 eV at normal and 60 emission angles. In contrast to earlier results, three components have been used in the line-shape analysis to achieve a consistent fit over the energy and angular range. In addition, three components have been identified for the Mn 2p CLS spectra. The two major components fit well with a layered Mn germanide structure suggested in the literature.

Place, publisher, year, edition, pages
New York: American Physical Society, 2012
Keywords
Scanning tunneling microscopy, Semiconductors, Diffusion; interface formation
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-14487 (URN)10.1103/PhysRevB.86.125313 (DOI)000308867300003 ()
Funder
Swedish Research Council
Note

Part of dissertation: Thin Mn silicide and germanide layers studied by photoemission and STM

Available from: 2012-08-13 Created: 2012-08-13 Last updated: 2017-12-07Bibliographically approved
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