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- Hirvonen Grytzelius, Joakim, 1975-, et al.
(författare)
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Coverage dependence and surface atomic structure of Mn/Si(111)-√3×√3 studied by scanning tunneling microscopy and spectroscopy
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - Washington : American Institute of Physics (AIP). - 1098-0121 .- 1550-235X. ; 80, s. 235324-1-235324-6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Hirvonen Grytzelius, Joakim, 1975-, et al.
(författare)
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Mn5Ge3 film formation on Ge(111)c(2×8)
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - New York : American Physical Society. - 1098-0121 .- 1550-235X. ; 86:12, s. 125313-1-125313-7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Hirvonen Grytzelius, Joakim, 1975-, et al.
(författare)
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Surface atomic and electronic structure of Mn5Ge3 on Ge(111)
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - New York : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:19, s. 195306-1-195306-6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Hirvonen Grytzelius, Joakim, 1975-, et al.
(författare)
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Surface electronic structure of Mn/Si(111)-√3×√3
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - New York : American Institute of Physics. - 1098-0121 .- 1550-235X. ; 78:15, s. 155406-1-155406-6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Jemander, S.T., et al.
(författare)
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STM study of the C-induced Si(100)-c(4×4) reconstruction
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Sociaty. - 1098-0121 .- 1550-235X. ; 65:11, s. 115321-
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Tidskriftsartikel (refereegranskat)abstract
- We report a direct and reliable way to produce the Si(100)-c(4×4) reconstruction by submonolayer deposition from a SiC source and subsequent annealing. Auger electron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy (STM) investigations reveal that a C amount equivalent to 0.07 monolayers (ML’s) is sufficient to obtain full coverage of the c(4×4) reconstruction. A deposition of 0.035 ML’s C produces a c(4×4) coverage of only 19%, indicating that C is not only present in the c(4×4) areas, but also in the 2×1 areas. There is not enough C to make it a regular part of the c(4×4) reconstruction and we therefore conclude that the c(4×4) reconstruction is strain induced. We find that a combination of the mixed ad-dimer and buckled ad-dimer models explains all main features observed in the STM images. Images of freshly prepared c(4×4) surfaces exhibit a decoration of approximately 50% of the unit cells, which is attributed to perpendicular ad-dimers. Long exposures (>20 h) to the UHV background gas quench these features and the c(4×4) reconstruction appears as if more homogeneous.
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- Razado Colambo, Ivy, et al.
(författare)
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Electronic structure of H/Ge(111)1×1 studied by angle-resolved photoelectron spectroscopy
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical society. - 1098-0121 .- 1550-235X. ; 80:19, s. 193403-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of H/Ge(111)1×1 was investigated using angle-resolved photoelectron spectroscopy. Spectra were measured along the high-symmetry lines of the 1×1 surface Brillouin zone. In the Γ̅ −K̅ −M̅ direction, two surface states, labeled a and a′, were found in the lower and upper band-gap pockets. The a and a′ surface states are associated with the Ge-H bonds and the Ge-Ge backbonds, respectively. In the Γ̅ −M̅ direction, only the Ge-H surface state, a, can be identified. It is found in the band-gap pocket around the M̅ point. The two hydrogen-induced surface states on H/Ge(111)1×1 show strong similarities with the corresponding surface states on H/Si(111)1×1. Results from H/Ge(111)1×1 and H/Si(111)1×1 are compared in this Brief Report.
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| 9. |
- Razado-Colambo, Ivy, 1977-, et al.
(författare)
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STM study of site selective hydrogen adsorption on Si(111) 7×7
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 71:23, s. 235411-
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of atomic hydrogen has been studied by scanning tunneling microscopy (STM) and photoelectron spectroscopy with a focus on the different adsorption sites provided by the Si(111) 7×7 surface. At low temperature, the hydrogen atoms adsorb preferentially on adatoms while at elevated temperatures the rest atoms are the first to become hydrogen terminated. The hydrogen-terminated rest atoms are no longer visible in the STM images and the surrounding adatoms appear brighter compared to the clean 7×7 surface. This indicates that there is a local charge transfer back to the adatoms from the rest atoms. Three kinds of modified triangular subunit cells of the 7×7 reconstruction have been identified corresponding to one, two, and three hydrogen-terminated rest atoms, respectively. A detailed study of the apparent height using STM line profiles through the adatom and rest atom positions on the surface is presented. These line profiles show a characteristic and reproducible variation of the apparent heights of the adatoms for the different kinds of triangular subunit cells and the changes are interpreted in terms of charge transfer. The very local nature of the charge transfer is concluded from the fact that only the hydrogen termination of neighboring rest atoms is significantly affecting the apparent height of an adatom.
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| 10. |
- Razado, Ivy, et al.
(författare)
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Electronic structure of Ge(111)c(2x8) : STM, angle-resolved photoemission, and theory
- 2009
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 79
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Tidskriftsartikel (refereegranskat)abstract
- The surface electronic structure of Ge(111)c(2x8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (A(T),A(R)) and rest atoms (R-T,R-R) confirming the presence of asymmetries within the c(2x8) cell. The ARPES study resulted in a more detailed picture of the surface electronic structure of the Ge(111)c(2x8) surface compared to earlier studies. The energy dispersion curves showed the presence of seven surface bands labeled A1, A2, A2(), A3, A4, A4(), and A5. The experimental surface bands were compared to the calculated band structure of the full c(2x8) unit cell. The most important results are (i) we have identified a split surface-state band in the photoemission data that matches a split between R-T and R-R derived rest atom bands in the calculated surface band structure. This allows us to identify the upper A2 band with the R-R and the lower A2() band with the R-T rest atoms. (ii) The uppermost highly dispersive band (A1) originates from states below the adatom and rest atom layers and should not be confused with rest atom bands A2 and A2(). (iii) The bias-dependent changes in the adatom/rest atom contrast in the experimental STM images were closely reproduced by simulated STM images generated from the calculated electronic structure. (iv) A split was observed in the back-bond derived surface band at higher emission angles (A4 and A4()).
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