| 1. |
- Adell, Johan, et al.
(author)
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Formation of epitaxial MnBi layers on (Ga,Mn)As
- 2009
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 2469-9950 .- 2469-9969. ; 80:7
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Journal article (peer-reviewed)abstract
- The initial growth of MnBi on MnAs-terminated (GaMn)As is studied by means of synchrotron-based photoelectron spectroscopy. From analysis of surface core-level shifts we conclude that a continued epitaxial MnBi layer is formed, in which the MnAs/MnBi interface occurs between As and Bi atomic planes. The well-defined 1×2 surface reconstruction of the MnAs surface is preserved for up to 2 ML of MnBi before clear surface degradation occurs. The MnBi layer appears to be free from intermixed As.
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| 2. |
- Adell, M, et al.
(author)
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Photoemission studies of the annealing-induced modifications of Ga0.95Mn0.05As
- 2004
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:12: 125204
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Journal article (peer-reviewed)abstract
- Using angle resolved photoemission we have investigated annealing-induced changes in Ga1-xMnxAs with x=0.05. We find that the position of the Fermi energy is a function of annealing time and temperature. It is also established that the Curie temperature is strongly correlated to the separation between the Fermi level and the valence band maximum. Valence band photoemission shows that the Mn3d spectrum is modified by the annealing treatments.
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| 3. |
- Asklund, H, et al.
(author)
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Photoemission study of GaAs (100) grown at low temperature
- 2002
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 65:11
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Journal article (peer-reviewed)abstract
- GaAs(100) layers grown by low-temperature (LT) molecular beam epitaxy were studied by means of valence-band and core-level photoelectron spectroscopy. Small differences were found between valence-band spectra from the LT layers and corresponding layers grown at high temperature. In the Ga 3d spectra a new component was found in the LT-GaAs. The relative intensity of this component was found to be practically constant with varying probing depth. It is proposed that this component represents sites coordinated to the five-atom As clusters formed at As-Ga antisites. This interpretation implies a higher density of antisite defects in the near-surface region than typically found in the bulk.
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| 4. |
- Gryglas-Borysiewicz, M., et al.
(author)
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Hydrostatic pressure study of the paramagnetic-ferromagnetic phase transition in (Ga,Mn)As
- 2010
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 82:15
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Journal article (peer-reviewed)abstract
- The effect of hydrostatic pressure on the paramagnetic-ferromagnetic phase transition has been studied in (Ga,Mn)As. The variation in the Curie temperature (T-C) with pressure was monitored by two transport methods: (1) measurement of zero-field resistivity versus temperature rho(T) and (2) dependence on temperature of the Hall voltage hysteresis loop. Two specimens of different resistivity characteristics were examined. The measured pressure-induced changes in T-C were relatively small (on the order of 1 K/GPa) for both samples, however they were opposite for the two.
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| 5. |
- Kowalik, I. A., et al.
(author)
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MnAs dots grown on GaN( 000(1)over-bar)-(1x1) surface
- 2007
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 75:23, s. 11-
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Journal article (peer-reviewed)abstract
- MnAs has been grown by means of MBE on the GaN(000 (1) over bar)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1x10(11) cm(-2) and 2.5x10(11) cm(-2), respectively (as observed by atomic force microscopy), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d-related contribution to the total density of states distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both systems behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intradot Curie temperatures substantially different. The intradot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure, and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.
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| 6. |
- Laukkanen, P., et al.
(author)
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Bismuth-stabilized c(2X6) reconstruction on a InSb(100) substrate : Violation of the electron counting model
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 81:3
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Journal article (peer-reviewed)abstract
- By means of scanning tunneling microscopy/spectroscopy (STM/STS), photoelectron spectroscopy, and first-principles calculations, we have studied the bismuth (Bi) adsorbate-stabilized InSb(100) substrate surface which shows a c(2X6) low-energy electron diffraction pattern [thus labeled Bi/InSb(100)c(2X6) surface] and which includes areas with metallic STS curves as well as areas with semiconducting STS curves. The first-principles phase diagram of the Bi/InSb(100) surface demonstrates the presence of the Bi-stabilized metallic c(2X6) reconstruction and semiconducting (4X3) reconstruction depending on the chemical potentials, in good agreement with STS results. The existence of the metallic c(2X6) phase, which does not obey the electron counting model, is attributed to the partial prohibition of the relaxation in the direction perpendicular to dimer rows in the competing reconstructions and the peculiar stability of the Bi-stabilized dimer rows. Based on (i) first-principles phase diagram, (ii) STS results, and (iii) comparison of the measured and calculated STM and photoemission data, we show that the measured Bi/InSb(100)c(2X6) surface includes metallic areas with the stable c(2X6) atomic structure and semiconducting areas with the stable (4X3) atomic structure.
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| 7. |
- Laukkanen, P, et al.
(author)
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Electronic and structural analysis of Sb-induced GaAs(100)(2x4) and (2x8) surfaces
- 2004
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 69:20
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Journal article (peer-reviewed)abstract
- Electronic and structural properties of Sb-induced GaAs(100)(2x4) and (2x8) surfaces are studied by means of core-level and valence-band photoelectron spectroscopy utilizing synchrotron radiation and scanning tunneling microscopy. Combining these results and showing good consistency among them, we demonstrate that the Sb/GaAs(100)(2x4) surface is well compatible with the delta structural model, which includes one Sb dimer in both the first and third atomic layers and two second-layer Ga dimers per unit cell (i.e., the Sb coverage of 0.5 ML), giving experimental support to generality of the delta-type model for III-V(100)(2x4) surfaces, proposed previously on the basis of ab-initio calculations. Deconvolution of the Sb 4d core-level spectrum from the (2x4) surface shows two components, which are tentatively connected to two inequivalent Sb-dimer sites in the delta unit cell. Angle-resolved valence-band photoelectron spectroscopy reveals Sb-induced surface-derived states at near 0.4 and 0.6 eV below the valence-band maximum (VBM) for the Sb/GaAs(100)(2x4) surface, which have not been found in earlier measurements. These two surface-derived features mapped along symmetry lines of the surface Brillouin zone are identified with previous electronic-structure calculations. The results are also compared to band-structure measurements of the As/GaAs(100)(2x4) surface found in the literature. For the Sb/GaAs(100)(2x8) surface, we propose a structural model which, in contrast to the recent model, obeys the electron counting rule and consists of Sb dimers in three atomic layers, showing the Sb coverage of 1.25 ML for the (2x8) surface. The Sb 4d core-level spectrum from this surface exhibits three components, which are discussed within the determined structural model. The valence-band measurements of the (2x8) surface propose a new Sb-induced surface state at near 0.5 eV below the VBM.
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| 8. |
- Laukkanen, P, et al.
(author)
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Electronic and structural properties of GaAs(100)(2x4) and InAs(100)(2x4) surfaces studied by core-level photoemission and scanning tunneling microscopy
- 2005
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:4
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Journal article (peer-reviewed)abstract
- Electronic and structural properties of GaAs(100)(2x4), InAs(100)(2x4), and Sb/InAs(100)(2x4) reconstructed surfaces have been studied by synchrotron-radiation photoelectron spectroscopy and scanning tunneling microscopy (STM). Based on the difference spectrum of As 3d core-level spectra of III-As(100)(2x4), measured in different surface-sensitivity conditions, as well as the line shape of the As 3d emission from the Sb-induced (2x4) surface, we give evidence that the As 3d spectra of GaAs(100)(2x4) and InAs(100)(2x4) consist of two surface-core-level-shifted components. One of them is shifted about 0.2 eV to the lower kinetic energy from the bulk component. On the basis of the relative component intensities, this surface-shifted As 3d component is assigned to the emission from the first-layer As dimers in the established model of the (2x4) surface. The other component, shifted about 0.3 eV to the higher kinetic energy, is connected to the third-layer As-dimer site. The comparison of the core-level results between GaAs(100)(2x4) and InAs(100)(2x4) suggests that the alpha 2 phase, which has one As dimer in both the first and third atomic layers per unit cell, exists on GaAs(100)(2x4), similarly to the case of InAs(100)(2x4), as predicted in theory but not observed to date. Furthermore, the STM observation of the GaAs(100)(2x4)alpha 2 phase is reported.
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| 9. |
- Mathieu, R, et al.
(author)
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Magnetization of ultrathin (Ga,Mn)As layers
- 2003
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 68:18: 184421
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Journal article (peer-reviewed)abstract
- Kerr rotation and superconducting quantum interference device magnetometry measurements were performed on ultrathin (Ga0.95Mn0.05)As layers. The thinner layers (below 250 A) exhibit magnetic properties different than those of thicker ones, associated with different microstructure, and some degree of inhomogeneity. The temperature dependence of the field-cooled magnetization of the layers is recorded after successive low temperature annealings. While the Curie temperature of the thicker layer (250 A) is nearly unchanged, the critical temperature of the thinner layers is enhanced by more than 23 K after two annealings. Secondary ion mass spectrometry experiments on similar layers show that Mn is displaced upon annealing. The results are discussed considering a possible segregation of substitutional and interstitial Mn atoms at the surface of the (Ga,Mn)As layers.
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| 10. |
- Mikkelsen, Anders, et al.
(author)
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Defect structure of Ga1-xMnxAs: A cross-sectional scanning tunneling microscopy study
- 2004
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:8
-
Journal article (peer-reviewed)abstract
- We have studied the atomic scale structure of molecular beam epitaxy grown Ga1-xMnxAs compounds with various Mn concentrations by cross-sectional scanning tunneling microscopy and first principles calculations. Only bright protrusions close to the top layer As atoms are directly correlated with the bulk Mn concentration. Atomically resolved filled and empty states images of this defect are compared to images derived from first principles calculations. We identify the Mn related defect as substitutional Mn in the second layer Ga site. Surprisingly no substitutional Mn is observed in the top-most Ga layer. The experimental results are consistent with the energetics of our first principles total energy calculations.
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