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| 2. |
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| 3. |
- 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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| 4. |
- Adell, Johan, 1980
(författare)
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Synchrotron light based spectroscopy of MBE-grown (GaMn)As structures
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Structures based on the diluted magnetic semiconductor (GaMn)As have been grown by low temperature molecular beam epitaxy and studied using synchrotron radiation based electron spectroscopy. An investigation of modifications due to in situ low temperature annealing under amorphous As capping has been performed. A clear accumulation of Mn is observed. This is ascribed to a reaction between diffusing Mn interstitials and the As capping. The reacted surface is smooth and well ordered with a 1x2 reconstruction. All data indicate that the annealed (GaMn)As is terminated by a monolayer MnAs in zinc-blende structure. The good surface quality of the MnAs-terminated layer allows further epitaxial growth. As an example, it was possible to deposit a 3 ML thick MnBi film layer-by-layer. MnBi is particularly interesting in this context due to its predicted half-metal characteristics The GaAs/(GaMn)As interface has been studied with focus on the electrostatic properties. No band offset between the two systems was observed. The continuous transition is explained as an effect of electronic smearing of the atomically abrupt interface. Annealing induced diffusion of Mn interstitials through GaAs films grown on (GaMn)As during thermal treatment was also studied. It was found that GaAs layers thicker than 8 monolayers effectively hinder all Mn out diffusion. The effect was ascribed to the electrostatic potential barrier due to band bending in the GaAs film. Nanowires catalyzed by MnAs particles were studied using valence band photoemission with photon energies around the Mn2p threshold. It was found that with increasing nanowire length the resonant photoemission eventually dominated over the Auger decay channel. This was ascribed to dilution of Mn in the wires.
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| 5. |
- 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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| 6. |
- Kowalski, B. J., et al.
(författare)
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Angle-resolved photoemission study and pseudopotential calculations of GeTe and Ge1-xMnxTe band structure
- 2010
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3892. ; 3:2, s. 1357-1362
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Tidskriftsartikel (refereegranskat)abstract
- The valence band structure along the Γ-T and T-W-L directions in the Brillouin zone of GeTe is studied by means of angle-resolved photoemission and compared with the results of ab initio pseudopotential calculations. For Ge1-xMnxTe surface alloy, changes in the valence band induced by presence of Mn atoms are revealed.
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| 7. |
- Lang, J. J. K., et al.
(författare)
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Tin-stabilized (1 x 2) and (1 x 4) reconstructions on GaAs(100) and InAs(100) studied by scanning tunneling microscopy, photoelectron spectroscopy, and ab initio calculations
- 2011
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 605:9-10, s. 883-888
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Tidskriftsartikel (refereegranskat)abstract
- Tin (Sn) induced (1 x 2) reconstructions on GaAs(100) and InAs(100) substrates have been studied by low energy electron diffraction (LEED), photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy (STM/STS) and ab initio calculations. The comparison of measured and calculated STM images and surface core-level shifts shows that these surfaces can be well described with the energetically stable building blocks that consist of Sn-III dimers. Furthermore, a new Sn-induced (1 x 4) reconstruction was found. In this reconstruction the occupied dangling bonds are closer to each other than in the more symmetric (1 x 2) reconstruction, and it is shown that the (1 x 4) reconstruction is stabilized as the adatom size increases.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Laukkanen, P., et al.
(författare)
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Core-level shifts of the c(8 x 2)-reconstructed InAs(100) and InSb(100) surfaces
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 177:1, s. 52-57
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Tidskriftsartikel (refereegranskat)abstract
- We have studied In-stabilized c(8 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III-V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the zeta and zeta a models, which have been previously established to describe the atomic structures of the III-V(1 00)c(8 x 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III-V(1 00)c(8 x 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated zeta and zeta a SCLS values shows that the InSb spectra are reproduced by the zeta SCLSs better than by the zeta a SCLSs. Interestingly, the zeta a fits agree better with the InAs spectra than the zeta fits do, indicating that the zeta a model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III-V(1 0 0)c(8 x 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges.
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| 11. |
- Punkkinen, M. P. J., et al.
(författare)
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Bismuth-stabilized (2x1) and (2x4) reconstructions on GaAs(100) surfaces : Combined first-principles, photoemission, and scanning tunneling microscopy study
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78, s. 195304-
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth adsorbate-stabilized (2x1) and (2x4) reconstructions of the GaAs(100) surfaces have been studied by first-principles calculations, valence-band and core-level photoelectron spectroscopies, and scanning tunneling microscopy. It is demonstrated that large Bi atom size leads to the formation of the pseudogap at the Fermi energy and to the lower energy of an adsorbate-derived surface band, which contributes to the stabilization of the exceptional Bi/GaAs(100)(2x1) reconstruction. It is proposed that the Bi/GaAs(100)(2x4) reconstructions include asymmetric mixed Bi-As dimers, in addition to the Bi-Bi dimers. Based on the calculations, we solve the atomic origins of the surface core-level shifts (SCLSs) of the Bi 5d photoemission spectra from the Bi/GaAs(100)(2x4) surfaces. This allows for resolving the puzzle related to the identification of two SCLS components often found in the measurements of the Bi 5d and Sb 4d core-level emissions of the Bi/III-V and Sb/III-V(100)(2x4) surfaces. Finally, the reason for the absence of the common (2x4)-beta 2 structure and additional support for the stability of the (2x1) structure on the Bi/III-V(100) surfaces are discussed in terms of Bi atom size and subsurface stress.
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| 12. |
- Ulfat, Intikhab, 1966, et al.
(författare)
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As3d core level studies of (GaMn)As annealed under As capping
- 2010
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 604:2, s. 125-128
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Tidskriftsartikel (refereegranskat)abstract
- The surface of a Ga(0.95)Mn(0.05)As layer subjected to low temperature annealing under As capping has been studied by core level photoemission with focus on As3d spectrum. By detailed comparison with the surface of pure GaAs subjected to the same surface treatment, the As spectral component of the reacted surface layer has been identified. The relative intensity of this component is consistent with the notion of an MnAs monolayer terminating the annealed (GaMn)As surface.
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| 13. |
- Ulfat, Intikhab, 1966, et al.
(författare)
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Electron Spectroscopic Studies of Homogenous (GaMn)As layers
- 2012
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Ingår i: Advanced Materials Research. - 1662-8985 .- 1022-6680. - 9783037853634 ; 463-464, s. 380-384
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Konferensbidrag (refereegranskat)abstract
- By incorporating magnetism into semiconductors, it may possibly be viable to enhance the functionality of materials. An exceptionally important material in this context is GaAs, which can be doped with Mn atoms. (GaMn)As has fascinated research community as a promising candidate for spintronic application. It is quite appealing due to both its compatibility with existing HI-V technology and great progress in improving its magnetic properties. Being fabricated by low temperature molecular beam epitaxy (LT-MBE), due to thermal instability at elevated temperatures, the material contains a high density of various defects compensating Mn acceptors. It is a well-established fact that the ferromagnetic state of (GaMn)As can be stabilized via post growth annealing. Nevertheless, in general, the annealed (GaMn)As layers do not remain useful for further epitaxial overgrowth that might be included in multilayer structure. We present a summary of our investigations regarding the synchrotron-based characterization of (GaMn)As layers grown via molecular beam epitaxy carried out at the Swedish National Facility of Synchrotron Radiation-the MAX-lab aiming at the reduction of the density of Mn interstitial and increase in the content of Mn.
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| 14. |
- Ulfat, Intikhab, 1966, et al.
(författare)
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Post-growth annealing of (Ga,Mn)As under Sb capping
- 2012
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Ingår i: Applied Mechanics and Materials. - 1660-9336. - 9783037855102 ; 243-246, s. 243-246
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Konferensbidrag (refereegranskat)abstract
- (Ga,Mn)As is a model diluted ferromagnet system in which the atomic spins of Mn ions are ferromagnetically arranged due to the exchange interaction with valence band holes. An important tecchnological concern regarding this system has been approaches that might result in reduction of the density of Mn interstitial and increase in the content of Mn in order to make the system practically feasible. To accomplish the objective we report the results of our recent synchrotron radiation based spectroscopic investigations concening annealing induced modification of as-grown (Ga,Mn)As layers covered with Sb capping.
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