| 1. |
- Levchenko, K., et al.
(author)
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Evidence for the homogeneous ferromagnetic phase in (Ga, Mn) (Bi, As) epitaxial layers from muon spin relaxation spectroscopy
- 2019
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In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9, s. 1-8
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Journal article (peer-reviewed)abstract
- Ferromagnetic semiconductor thin layers of the quaternary (Ga,Mn)(Bi,As) and reference, ternary (Ga, Mn) As compounds, epitaxially grown under either compressive or tensile strain, have been characterized from a perspective of structural and magnetization homogeneity. The quality and composition of the layers have been confirmed by secondary-ion mass spectrometry (SIMS). A thorough evaluation of the magnetic properties as a function of temperature and applied magnetic field has been performed by means of SQUID magnetometry and low-energy muon spin relaxation (mu SR) spectroscopy, which enables studying local (on the nanometer scale) magnetic properties of the layers. The results testify that the ferromagnetic order builds up almost homogeneously below the Curie temperature in the full volume fraction of both the (Ga, Mn) As and (Ga, Mn)(Bi, As) layers. Incorporation of a small amount of heavy Bi atoms into (Ga, Mn) As, which distinctly enhances the strength of spin-orbit coupling in the quaternary (Ga, Mn)(Bi, As) layers, does not deteriorate noticeably their magnetic properties.
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| 2. |
- Curado, M. A., et al.
(author)
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Front passivation of Cu(In,Ga)Se-2 solar cells using Al2O3 : Culprits and benefits
- 2020
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In: APPLIED MATERIALS TODAY. - : ELSEVIER. - 2352-9407. ; 21
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Journal article (peer-reviewed)abstract
- In the past years, the strategies used to break the Cu(In,Ga)Se-2 (CIGS) light to power conversion efficiency world record value were based on improvements of the absorber optoelectronic and crystalline properties, mainly using complex post-deposition treatments. To reach even higher efficiency values, further advances in the solar cell architecture are needed, in particular, with respect to the CIGS interfaces. In this study, we evaluate the structural, morphological and optoelectronic impact of an Al2O3 layer as a potential front passivation layer on the CIGS properties, as well as an Al2O3 tunneling layer between CIGS and CdS. Morphological and structural analyses reveal that the use of Al2O3 alone is not detrimental to CIGS, although it does not resist to the CdS chemical bath deposition. The CIGS optoelectronic properties degrade when the CdS is deposited on top of Al2O3. Nonetheless, when Al2O3 is used alone, the optoelectronic measurements reveal a positive impact of this inclusion such as a very low concentration of interface defects while keeping the same CIGS recombination channels. Thus, we suggest that an Al2O3 front passivation layer can be successfully used with alternative buffer layers. Depth-resolved microscopic analysis of the CIGS interface with slow-muons strongly suggests for the first time that low-energy muon spin spectroscopy (LE-mu SR) is sensitive to both charge carrier separation and bulk recombination in complex semiconductors. The demonstration that Al2O3 has the potential to be used as a front passivation layer is of significant importance, considering that Al2O3 has been widely studied as rear interface passivation material. (C) 2020 Published by Elsevier Ltd.
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| 3. |
- Kozhevnikov, V., et al.
(author)
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Nonlocal effect and dimensions of Cooper pairs measured by low-energy muons and polarized neutrons in type-I superconductors
- 2013
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In: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 87:10, s. 104508-
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Journal article (peer-reviewed)abstract
- The Pippard coherence length xi(0) (the size of a Cooper pair) in two extreme type-I superconductors (In and Sn) was determined directly through high-resolution measurement of the nonlocal electrodynamic effect combining low-energy muon spin rotation spectroscopy and polarized neutron reflectometry. The renormalization factor Z = m*(cp)/2m (m*(cp) and m are the mass of the Cooper pair and the electron, respectively) resulting from the electron-phonon interaction, and the temperature-dependent London penetration depth lambda(L)(T) were determined as well. An expression linking xi(0), Z, and lambda(L)(0) is introduced and experimentally verified. This expression allows one to determine experimentally the Pippard coherence length in any superconductor, independent of whether the superconductor is local or nonlocal, conventional or unconventional.
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| 4. |
- Alberto, H. V., et al.
(author)
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Low energy muon study of the p-n interface in chalcopyrite solar cells
- 2023
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In: Journal of Physics, Conference Series. - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596. ; 2462
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Journal article (peer-reviewed)abstract
- The slow muon technique was used to study the p-n junction of chalcopyrite solar cells. A defect layer near the interface was identified and the passivation of the defects by buffer layers was studied. Several cover layers on top of the chalcopyrite Cu(In,Ga)Se2 (CIGS) semiconductor absorber were investigated in this work, namely CdS, ZnSnO, Al2O3 and SiO2. Quantitative results were obtained: The defect layer extends about 50 nm into the CIGS absorber, the relevant disturbance is strain in the lattice, and CdS provides the best passivation, oxides have a minor effect. In the present contribution, specific aspects of the low-energy muon technique in connection with this research are discussed.
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| 5. |
- Alberto, H. V., et al.
(author)
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Slow-muon study of quaternary solar-cell materials : Single layers and p-n junctions
- 2018
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In: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:2
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Journal article (peer-reviewed)abstract
- Thin films and p-n junctions for solar cells based on the absorber materials Cu(In, Ga) Se-2 and Cu2ZnSnS4 were investigated as a function of depth using implanted low energy muons. The most significant result is a clear decrease of the formation probability of the Mu(+) state at the heterojunction interface as well as at the surface of the Cu(In, Ga)Se-2 film. This reduction is attributed to a reduced bonding reaction of the muon in the absorber defect layer at its surface. In addition, the activation energies for the conversion from a muon in an atomiclike configuration to a anion-bound position are determined from temperature-dependence measurements. It is concluded that the muon probe provides a measurement of the effective surface defect layer width, both at the heterojunctions and at the films. The CIGS surface defect layer is crucial for solar-cell electrical performance and additional information can be used for further optimizations of the surface.
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| 6. |
- Ofer, O., et al.
(author)
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Absolute value and temperature dependence of the magnetic penetration depth in Ba(Co 0.074Fe 0.926) 2As 2
- 2012
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:6, s. 060506-
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Journal article (peer-reviewed)abstract
- The absolute value and temperature dependence of the in-plane magnetic penetration depth lambda have been measured on a single crystal of Ba(Co0.074Fe0.926)(2)As-2 using low-energy muon-spin rotation and microwave cavity perturbation. The magnetic field profiles in the Meissner state are consistent with a local London model beyond a depth of 15 nm. We determine the gap symmetry through measurements of the temperature dependence of the superfluid density which follows a two-gap s-wave model over the entire temperature range below T-c. While the intermediate to high temperature data is well fit by an energy gap model in the BCS-like (weak-coupling) limit, a second smaller gap becomes apparent at low temperatures.
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| 7. |
- Stilp, E., et al.
(author)
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Magnetic phase diagram of low-doped La2-xSrxCuO4 thin films studied by low-energy muon-spin rotation
- 2013
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 88:6, s. 064419-1-064419-11
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Journal article (peer-reviewed)abstract
- The magnetic phase diagram of La2-xSrxCuO4 thin films grown on single-crystal LaSrAlO4 substrates has been determined by low-energy muon-spin rotation. The diagram shows the same features as the one of bulk La2-xSrxCuO4, but the transition temperatures between distinct magnetic states are significantly different. In the antiferromagnetic phase the Neel temperature T-N is strongly reduced, and no hole spin freezing is observed at low temperatures. In the disordered magnetic phase (x greater than or similar to 0.02) the transition temperature to the cluster spin-glass state T-g is enhanced. Possible reasons for the pronounced differences between the magnetic phase diagrams of thin-film and bulk samples are discussed.
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| 8. |
- Wojek, Bastian M., et al.
(author)
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Magnetism, superconductivity, and coupling in cuprate heterostructures probed by low-energy muon-spin rotation
- 2012
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:2, s. 024505-
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Journal article (peer-reviewed)abstract
- We present a low-energy muon-spin-rotation study of the magnetic and superconducting properties of YBa(2)Cu(3)O(7-delta)/PrBa(2)Cu(3)O(7-delta) trilayer and bilayer heterostructures. By determining the magnetic-field profiles throughout these structures, we show that a finite superfluid density can be induced in otherwise semiconducting PrBa(2)Cu(3)O(7-delta) layers when juxtaposed to YBa(2)Cu(3)O(7-delta) "electrodes," while the intrinsic antiferromagnetic order is unaffected.
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