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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. J. & 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: 2019-11-04Bibliographically 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
Dou, Y., Peng, J., Li, W., Li, M., Liu, H. & Zhang, H. (2015). Effects of reducibility of graphene oxide nanosheets on preparation of AgNPs/GO nanocomposites and their electrocatalytic performance. Journal of nanoparticle research, 17(12), 1-10, Article ID 489.
Open this publication in new window or tab >>Effects of reducibility of graphene oxide nanosheets on preparation of AgNPs/GO nanocomposites and their electrocatalytic performance
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2015 (English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 17, no 12, p. 1-10, article id 489Article in journal (Refereed) Published
Abstract [en]

Silver nanoparticles/graphene oxide (AgNPs/GO) nanocomposites were prepared in a solution of AgNO3 and GO. The GO serves not only as a reductant but also as a substrate to support the as-reduced silver nanoparticles. The reducibility of GO was investigated by analyzing the influence factors such as pH, duration, the reaction temperature, and the weight ratio of AgNO3 and GO in the AgNP/GO nanocomposite mixture, which were evaluated by the UV–vis absorption spectroscopy. The results demonstrated that Ag nanoparticles with an average diameter of 5–10 nm were uniformly dispersed on the surface of GO nanosheets under the optimum synthesis conditions of pH between 8 and 11, weight ratio of AgNO3 and GO between 55 % and 60 %, and at 80 °C for 6 h. Moreover, the obtained AgNPs/GO nanocomposites exhibit good electrocatalytic activity for the reduction of p-nitrophenol to 4-(hydroxyamino) phenol.

Keywords
Silver nanoparticles/graphene oxide; Reducibility; Electrocatalytic; p-Nitrophenol
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-39042 (URN)10.1007/s11051-015-3300-2 (DOI)000367000900002 ()
Available from: 2016-01-20 Created: 2016-01-15 Last updated: 2019-07-10Bibliographically 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
Ericsson, L., Zhang, H. & Magnusson, K. (2013). Photoemission study of ZnO nanocrystals: Thermal annealing in UHV and induced band bending. Surface Science, 612, 10-15
Open this publication in new window or tab >>Photoemission study of ZnO nanocrystals: Thermal annealing in UHV and induced band bending
2013 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 612, p. 10-15Article in journal (Refereed) Published
Abstract [en]

ZnO nanocrystals distributed by spin-coating on SiO2/Si surfaces were annealed in UHV and studied in situ by synchrotron radiation based X-ray Photoelectron Spectroscopy. Changes in chemical composition and electronic structure of ZnO nanocrystal surfaces were found with increasing annealing temperatures. Annealing at 650 °C reduces the surface contaminant levels without any observed de-composition of ZnO. After annealing at 700 °C an initial de-composition of ZnO together with further reduction of contaminants was observed. As a result, 650 °C is found to be the optimal annealing temperature for thermal cleaning of ZnO nanocrystals. Chemical changes and induced point defect formation cause changes in the band structure of the ZnO/SiO2/Si system. An upward band bending of 0.7 eV on the surfaces of the ZnO nanocrystals was found after annealing at 300 °C. The bands on the surfaces of ZnO nanocrystals gradually bend downwards with increasing annealing temperatures. A downward band bending of 1.4 eV is the result after annealing at 750 °C for 1 h. This large downward band bending is explained as due to the change in balance of oxygen vacancies and zinc vacancies on the surfaces of ZnO nanocrystals.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2013
Keywords
ZnO, Nanocrystals, XPS, Annealing, Band bending
National Category
Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-27016 (URN)10.1016/j.susc.2013.02.001 (DOI)000317809100005 ()
Available from: 2013-04-22 Created: 2013-04-22 Last updated: 2017-12-06Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-4165-1515

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