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| 2. |
- Johansson, Leif, 1945-, et al.
(författare)
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A comparative photoemission study of polar and nonpolar SiC surfaces oxidized in N2O
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 552:1-3, s. 251-259
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission studies of oxidized SiC samples grown ex situ in N 2O, at a temperature of 900 °C, on the (0001), (0001̄), (112̄0) and (101̄0) surfaces are reported. Angle resolved data from the Si 1s and Si 2p core levels and the Si KL2,3L2,3 Auger transitions are analyzed and compared to data from a sample grown in O2 on the (0001) surface. The results show oxide growth and no oxy-nitride formation. The growth rate is found to be smallest for the Si-terminated (0001) surface and highest for the nonpolar (101̄0) surface. The presence of two oxidation states, Si+4 and a suboxide, are required to explain and model recorded Si 1s, Si 2p and Si KLL spectra. The SiO2 shift is found to be smaller on the (0001) surface than on the other three surfaces, which is attributed to an oxide thickness dependence of the shift. A layer attenuation model describes satisfactorily the intensity variations observed in the core level components versus electron emission angle when assuming the suboxide at the interface. Estimates made of the thickness of the oxide layers show that the oxidation rate for the (0001) surfaces is about half of that for the (101̄0) surface and that the oxidation rate for the (112̄0) and (0001̄) surfaces are similar but somewhat smaller than for the (101̄0) surface. The amount of suboxide is found to be smaller on the nonpolar than on the polar surfaces. © 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Johansson, Leif, et al.
(författare)
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A photoemission study of polar and non-polar SiC surfaces oxidized in N2O.
- 2004
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2. - : Trans Tech Publications Inc.. ; , s. 1329-1332
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Konferensbidrag (refereegranskat)abstract
- Angle resolved photoemission studies of SiO2/SiC samples grown ex situ in N2O on polar and non-polar 4H-SiC surfaces are reported. Data from the Si 1s and Si 2p core levels and the Si KL2,3L2,3 Auger transitions are analyzed and compared to data from a sample grown in O-2 on the (0001) surface. The results show oxide growth without nitride or oxy-nitride formation. Presence of two oxidation states, SiO2 and a sub-oxide explains recorded Si 1s. Si 2p and Si KLL spectra. Estimates of the oxide layer thickness show that the oxidation rate is highest for the (10 (1) under bar0) surface, somewhat smaller and similar for the (11 (2) under bar0) and (000 (1) under bar) surfaces, and smaller by a factor of about two for the (0001) surface.
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| 4. |
- Johansson, Leif, et al.
(författare)
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Angle-resolved studies of SiO2/SiC samples
- 2002
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS - 2002. - : Trans Tech Publications Inc.. ; , s. 539-542
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Konferensbidrag (refereegranskat)abstract
- Angle resolved studies of SiO2/SiC samples utilizing the Si 2p and Si 1s core levels and the Si KLL Auger transitions are reported. Samples with total oxide thicknesses from ca. 5 to 118 A are investigated. The data collected show that two oxidation states only, Si+1 and Si+4, are required to explain and model recorded Si 2p, Si 1s and Si KLL spectra. For all samples investigated the intensity variations observed in the core level components versus electron emission angle are found to be well described by a layer attenuation model when assuming that the sub-oxide, Si+1, is located at the interface. The SiO2 chemical shift is found to be larger in the Si 1s level than in the Si 2p level and moreover to depend on the thickness of the oxide layer.
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| 5. |
- Johansson, Leif, et al.
(författare)
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Properties of the SiO2/SiC interface investigated by angle resolved studies of the Si 2p and Si 1s levels and the Si KLL Auger transitions
- 2003
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 529:3, s. 515-526
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Tidskriftsartikel (refereegranskat)abstract
- Angle resolved photoemission studies of the Si 2p and Si 1s core levels and the Si KL2,3L2,3 Auger transitions from SiO2/SiC samples are reported. Most samples investigated were grown in situ on initially clean and well ordered v3 × v3 reconstructed 4H-SiC(0 0 0 1) surfaces but some samples were grown ex situ using a standard dry oxidation procedure. The results presented cover samples with total oxide thicknesses from about 5 to 118 Å. The angle resolved data show that two oxidation states only, Si+1 and Si+4, are required to explain and model recorded Si 2p, Si 1s and Si KLL spectra. The intensity variations observed in the core level components versus electron emission angle are found to be well described by a layer attenuation model for all samples when assuming a sub-oxide (Si2O) at the interface with a thickness ranging from 2.5 to 4 Å. We conclude that the sub-oxide is located at the interface and that the thickness of this layer does not increase much when the total oxide thickness is increased from about 5 to 118 Å. The SiO2 chemical shift is found to be larger in the Si 1s level than in the Si 2p level and to depend on the thickness of the oxide layer. The SiO2 shift is found to be fairly constant for oxides less than about 10 Å thick, to increase by 0.5 eV when increasing the oxide thickness to around 25 Å and then to be fairly constant for thicker oxides. An even more pronounced dependence is observed in the Si KLL transitions where a relative energy shift of 0.9 eV is determined. The relative final state relaxation energy dR(2p) is determined from the modified Auger parameter. This yields a value of dR(2p) = -1.7 eV and implies, for SiO2/SiC, a "true" chemical shift in the Si 2p level of only ˜0.4 eV for oxide layers of up to 10 Å thick. © 2003 Elsevier Science B.V. All rights reserved.
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| 6. |
- Mukherjee, S., et al.
(författare)
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Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions
- 2015
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Ingår i: Physical Review B. - 1098-0121 .- 1550-235X. ; 91:8
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Tidskriftsartikel (refereegranskat)abstract
- Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeBmagnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.
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| 7. |
- Schlueter, C., et al.
(författare)
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New HAXPES Applications at PETRA III
- 2018
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Ingår i: Synchrotron Radiation News. - : Informa UK Limited. - 0894-0886 .- 1931-7344. ; 31:4, s. 29-35
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Tidskriftsartikel (refereegranskat)
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| 8. |
- Schlueter, C., et al.
(författare)
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The new dedicated HAXPES beamline P22 at PETRAIII
- 2019
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Ingår i: 13th International Conference on Synchrotron Radiation Instrumentation (SRI2018). - : American Institute of Physics (AIP). - 9780735417823
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Konferensbidrag (refereegranskat)abstract
- A new undulator beamline (P22) for hard X-ray photoelectron spectroscopy (HAXPES) was built at PETRA III (DESY, Hamburg) to meet the increasing demand for HAXPES-based techniques. It provides four special instruments for high-resolution studies of the electronic and chemical structure of functional nano-materials and catalytic interfaces, with a focus on measurements under operando and/or ambient conditions: (i) a versatile solid-state spectroscopy setup with optional wide-angle lens and in-situ electrical characterization, (ii) a HAXPEEM instrument for sub-µm spectro-microscopy applications, (iii) an ambient pressure system (> 1 bar) for operando studies of catalytic reactions and (iv) a time-of-flight spectrometer as a full-field k-microscope for measurements of the 4D spectral function ρ(EB,k). The X-ray optics were designed to deliver high brightness photon flux within the HAXPES energy range 2.4 – 15 keV. An LN2-cooled double-crystal monochromator with interchangeable pairs of Si(111) and (311) crystals is optionally combined with a double channel-cut post-monochromator to generate X-rays with variable energy bandpass adapted to the needs of the experiment. Additionally, the beam polarization can be varied using a diamond phase plate integrated into the beamline. Adaptive beam focusing is realized by Be compound refractive lenses and/or horizontally deflecting mirrors down to a spot size of ∼20x17 µm2 with a flux of up to 1.1x1013 ph/s (for Si(111) at 6 keV).
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| 9. |
- Virojanadara, Chariya, et al.
(författare)
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High energy photoemission investigations of SiO2/SiC samples
- 2001
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 172:3-4, s. 253-259
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Tidskriftsartikel (refereegranskat)abstract
- Chemically etched and directly load-locked SiO2/SiC samples are investigated using a photon energy of 3.0 keV. Si 2p and C 1s spectra recorded at different electron emission angles each show two components originating from SiC, SiO2 and graphite like carbon, respectively. The relative intensity of these are extracted and compared to calculated intensity variations. For the samples investigated, best agreement between experimental and calculated intensity variations is obtained when assuming a graphite like layer on top of the oxide. No graphite like carbon at the SiO2/SiC interface was detected, even on a sample for which the graphite like carbon contribution at the surface corresponds to a layer thickness of only 0.05 angstrom. The energy separation between the oxide and carbide components in the Si 2p spectrum was monitored before and after Ar+ sputtering cycles and before and after in situ heating. The separation increased directly upon sputtering while only in situ heating does not affect it. We suggest that defects induced by the sputtering give rise to the increase, observed in the energy separation.
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| 10. |
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