| 1. |
- Adell, Johan, 1980, et al.
(författare)
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Electron spectroscopic studies of nanowires formed by (GaMn)As growth on GaAs(111)B
- 2011
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 151:11, s. 850-854
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Tidskriftsartikel (refereegranskat)abstract
- Valence band photoemission with photon energies around the Mn2p excitation threshold has been used to study the development of nanowires catalyzed by MnAs particles. A gradual change in the spectra with increasing nanowire length is observed, such that the resonant photoemission eventually dominates over the Auger decay channel. The change is ascribed to dilution of Mn, showing that Mn is transferred from the MnAs particles into the nanowires. (C) 2011 Elsevier Ltd. All rights reserved.
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| 2. |
- Adell, Johan, et al.
(författare)
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Formation of epitaxial MnBi layers on (Ga,Mn)As
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 2469-9950 .- 2469-9969. ; 80:7
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Adell, Johan, 1980, et al.
(författare)
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Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As
- 2011
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 23:8
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Tidskriftsartikel (refereegranskat)abstract
- Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.
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| 4. |
- Guziewicz, E., et al.
(författare)
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Mn on the surface of ZnO(0001) - a resonant photoemisson study
- 2005
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T115, s. 541-544
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of Mn/ZnO system has been invesigated by synchrotron radiation photoemission. Manganese vacuum deposition was done at room temperature onto a ZnO(0001) single crystal for coverage Mn-Theta <= 4 ML. Photoemission spectra taken near the Mn3p-Mn3d absorption edge after each deposition step show resonant enhancement of Mn3d states within 10 eV of the Fermi edge. The experimentally deduced partial Mn3d density of states for Theta >= 1.2 ML shows at least three features: a major Mn3d structure at 3.8-4.5 eV below the Fermi edge, a valence structure at lower binding energy (1-3 eV) and a broad satelite in the 5.5-9 eV range. The branching ratio of satellite/main structure increases with depostion from 0.33 for 0.4 ML to 0.65 for 4 ML. After annealing up to 500 degrees C the satellite/main ratio decreases to 0.43 indicating a high degree of hybridization between the Mn3d states and valence band of ZnO. After annealing no manganese cap layer was found at the crystal surfaces as was confirmed by the lack of metallic Fermi edge in photoemission spectra and by scanning Auger spectroscopy experiment. The photoemission Mn3p core level spectra taken after annealing consist of two components separated by about 4 eV, which shows that at least two manganese states are observed in the Mn-ZnO interface region.
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| 5. |
- Kanski, Janusz, 1946, et al.
(författare)
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Electronic structure of (Ga,Mn)As revisited
- 2017
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Ingår i: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 19:2, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The detailed nature of electronic states mediating ferromagnetic coupling in dilute magnetic semiconductors, specifically (Ga,Mn)As, has been an issue of long debate. Two confronting models have been discussed emphasizing host band vs. impurity band carriers. Using angle resolved photoemission we show that the electronic structure of the (Ga,Mn)As system is significantly modified from that of GaAs throughout the valence band. Close to the Fermi energy, the presence of Mn induces a strong mixing of the bulk bands of GaAs, which results in the appearance of a highly dispersive band in the gap region of GaAs.For Mn concentrations above 1% the band reaches the Fermi level, and can thus host the delocalized holes needed for ferromagnetic coupling. Overall, our data provide a firm evidence of delocalized carriers belonging to the modified host valence band.
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| 6. |
- Kanski, Janusz, 1946, et al.
(författare)
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Mn-induced modifications of Ga 3d photoemission from (Ga, Mn)As: evidence for long range effects
- 2012
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:43, s. 1-435802
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Tidskriftsartikel (refereegranskat)abstract
- Using synchrotron based photoemission, we have investigated the Mn-induced changes in Ga 3d core level spectra from as-grown Ga(1-x)Mn(x)As. Although Mn is located in Ga substitutional sites, and therefore does not have any Ga nearest neighbors, the impact of Mn on the Ga core level spectra is pronounced even at Mn concentrations in the region of 0.5%. The analysis shows that each Mn atom affects a volume corresponding to a sphere with around 1.4 nm diameter.
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| 7. |
- Kasama, T., et al.
(författare)
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Direct observation of doping incorporation pathways in self-catalytic GaMnAs nanowires
- 2015
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 118:5
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Tidskriftsartikel (refereegranskat)abstract
- Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 degrees C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography, Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga0.82Mn0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22 +/- 4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga0.82Mn0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process. (C) 2015 AIP Publishing LLC.
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| 8. |
- Kowalik, I. A., et al.
(författare)
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MnAs dots grown on GaN( 000(1)over-bar)-(1x1) surface
- 2007
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 75:23, s. 11-
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Laukkanen, P., et al.
(författare)
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Anomalous bismuth-stabilized (2x1) reconstructions on GaAs(100) and InP(100) surfaces
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 100, s. 086101-
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Tidskriftsartikel (refereegranskat)abstract
- First-principles phase diagrams of bismuth-stabilized GaAs- and InP(100) surfaces demonstrate for the first time the presence of anomalous (2 x 1) reconstructions, which disobey the common electron counting principle. Combining these theoretical results with our scanning-tunneling-microscopy and photoemission measurements, we identify novel (2 x 1) surface structures, which are composed of symmetric Bi-Bi and asymmetric mixed Bi-As and Bi-P dimers, and find that they are stabilized by stress relief and pseudogap formation.
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| 10. |
- Laukkanen, P., et al.
(författare)
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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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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 81:3
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Tidskriftsartikel (refereegranskat)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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