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Thin Mn silicide and germanide layers studied by photoemission and STM
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialfysik)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The research presented in this thesis concerns experimental studies of thin manganese silicide and germanide layers, grown by solid phase epitaxy on the Si(111)7×7 and the Ge(111)c(2×8) surfaces, respectively. The atomic and electronic structures, as well as growth modes of the epitaxial Mn-Si and Mn-Ge layers, were investigated by low-energy electron diffraction (LEED), angle-resolved photoelectron spectroscopy (ARPES), core-level spectroscopy (CLS), and scanning tunneling microscopy and spectroscopy (STM and STS). The magnetic properties of the Mn-Ge films were investigated by X-ray magnetic circular dichroism (XMCD).

The Mn-Si layers, annealed at 400 °C, showed a √3×√3 LEED pattern, consistent with the formation of the stoichiometric monosilicide MnSi. Up to 4 monolayers (ML) of Mn coverage, island formation was observed. For higher Mn coverages, uniform film growth was found. Our results concerning morphology and the atomic and electronic structure of the Mn/Si(111)-√3×√3 surface, are in good agreement with a recent theoretical model for a layered MnSi structure and the √3×√3 surface structure.

Similar to the Mn-Si case, the grown Mn-Ge films, annealed at 330 °C and 450 °C, showed a √3×√3 LEED pattern. This indicated the formation of the ordered Mn5Ge3 germanide. A strong tendency to island formation was observed for the Mn5Ge3 films, and a Mn coverage of about 32 ML was needed to obtain a continuous film. Our STM and CLS results are in good agreement with the established model for the bulk Mn5Ge3 germanide, with a surface termination of Mn atoms arranged in a honeycomb pattern. Mn-Ge films grown at a lower annealing temperature, 260 °C, showed a continuous film at lower coverages, with a film structure that is different compared to the structure of the Mn5Ge3 film. XMCD studies showed that the low-temperature films are ferromagnetic for 16 ML Mn coverage and above, with a Curie temperature of ~250 K.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2012. , 46 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2012:41
Keyword [en]
Semiconductor surfaces, Si(111), Ge(111), manganese, Mn, silicides, germanides, atomic structure, electronic structure, magnetic properties, LEED, ARPES, XPS, core-level spectroscopy, STM, STS, XMCD
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kau:diva-14488ISBN: 978-91-7063-448-2 (print)OAI: oai:DiVA.org:kau-14488DiVA: diva2:545486
Public defence
2012-09-28, 21A 342, Universitetsgatan 2, Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2012-09-11 Created: 2012-08-13 Last updated: 2015-04-15Bibliographically approved
List of papers
1. Surface electronic structure of Mn/Si(111)-√3×√3
Open this publication in new window or tab >>Surface electronic structure of Mn/Si(111)-√3×√3
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 15, 155406-1-155406-6 p.Article in journal (Refereed) Published
Abstract [en]

The Mn/Si(111)-√3×√3 surface has been studied in detail by low energy electron diffraction (LEED), angle-resolved photoelectron spectroscopy (ARPES), and core-level photoelectron spectroscopy (CLS). Annealing of the deposited manganese resulted in a well-ordered surface as seen by intense √3×√3 LEED spots. ARPES spectra recorded in the Γ̅ -K̅ -M̅ direction of the √3×√3 surface Brillouin zone show five surface related features in the band gap while in the Γ̅ -M̅ -Γ̅ direction four surface features are observed. The high-resolution Si 2p CLS data were recorded at photon energies between 108–140 eV both at normal and 60° emission angle. The bulk component was identified from the bulk sensitive spectrum recorded at a photon energy of 108 eV. To achieve a consistent core-level fitting over the whole energy and angular range, five components were introduced in the line-shape analysis. The photoemission data from the √3×√3 surface have been discussed and compared with a recent theoretical model. The findings here support a layered Mn silicide film structure.

Place, publisher, year, edition, pages
New York: American Institute of Physics, 2008
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-14484 (URN)10.1103/PhysRevB.78.155406 (DOI)
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
2. Coverage dependence and surface atomic structure of Mn/Si(111)-√3×√3 studied by scanning tunneling microscopy and spectroscopy
Open this publication in new window or tab >>Coverage dependence and surface atomic structure of Mn/Si(111)-√3×√3 studied by scanning tunneling microscopy and spectroscopy
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, 235324-1-235324-6 p.Article in journal (Refereed) Published
Abstract [en]

Thin manganese silicide films of different thicknesses on Si(111) have been studied in detail by low-energy electron diffraction (LEED), scanning tunneling microscopy, and scanning tunneling spectroscopy (STM/STS). Up to a Mn coverage of 3–4 monolayers (ML), island formation is favored. For higher Mn coverages up to 12 ML uniform film growth is found. The silicide film morphology at low coverages supports a layered Mn-Si film structure. The silicide surfaces displayed a √3×√3 LEED pattern. STM images recorded from the √3×√3 surfaces mostly show a hexagonal pattern but a honeycomb pattern has also been observed. A surface atomic structure based on chained Mn triangles is proposed. Our STM results are in good agreement with a recent theoretical model. The high-quality STS spectra recorded from the different surfaces show a clear metallic character at 1.5 ML and higher coverages. The filled-state features in the STS spectra at surfaces with 3–4 ML Mn coverages are similar to earlier published angle-resolved photoelectron spectroscopy data.

Place, publisher, year, edition, pages
Washington: American Institute of Physics (AIP), 2009
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-14486 (URN)10.1103/PhysRevB.80.235324 (DOI)
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
3. Surface atomic and electronic structure of Mn5Ge3 on Ge(111)
Open this publication in new window or tab >>Surface atomic and electronic structure of Mn5Ge3 on Ge(111)
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, ISSN 1098-0121, Vol. 84, no 19, 195306-1-195306-6 p.Article in journal (Refereed) Published
Abstract [en]

The atomic and electronic structure of the Mn5Ge3(001) surface grown on Ge(111) c(2×8) has been studied in detail by angle-resolved photoelectron spectroscopy (ARPES), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy. ARPES spectra recorded from the Γ̅ -K̅ -M̅ and Γ̅ -M̅ -Γ̅ directions of the surface Brillouin zone show six surface-related features. The STM images recorded at biases higher/lower than ±0.4 V always show a honeycomb pattern with two bright protrusions in each unit cell. At lower biases, a hexagonal, intermediate transition, and a honeycomb pattern are observed. These can be explained as arising from Mn and Ge atoms in the sublayer arranged in triangular structures and Mn atoms in the top layer arranged in a honeycomb structure, respectively. The photoemission and STM data from the germanide surface are discussed and compared to earlier published theoretical, photoelectron spectroscopy, and scanning tunneling microscopy studies.

Place, publisher, year, edition, pages
New York: American Physical Society, 2011
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-8996 (URN)10.1103/PhysRevB.84.195306 (DOI)000296865600008 ()
Funder
Swedish Research Council
Note

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

Available from: 2011-12-21 Created: 2011-12-21 Last updated: 2017-12-08Bibliographically approved
4. Mn5Ge3 film formation on Ge(111)c(2×8)
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, 125313-1-125313-7 p.Article 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
Keyword
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
5. Thin Mn germanide films studied with XPS, STM, and XMCD
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, 045311-1-045311-6 p.Article 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

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