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- Buyanova, Irina, et al.
(författare)
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Spin dynamics in ZnO-based materials
- 2010
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Ingår i: Journal of Superconductivity and Novel Magnetism. - New York, USA : Springer-Verlag New York. - 1557-1939 .- 1557-1947. ; 23:1, s. 161-165
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we address the issue of spin relaxation and its relevance to spin detection in ZnO-based materials, by spin-polarized, time-resolved magneto-optical spectroscopy. We have found that spin relaxation is very fast, i.e. about 100 ps for donor bound excitons in wurtzite ZnO, despite of a weak spin–orbit interaction. We also reveal that alloying of ZnO with Cd enhances spin relaxation, prohibiting ZnCdO/ZnO structures for efficient optical spin detection. On the other hand, a variation in strain field induced by lattice mismatch with substrates does not seem to lead to a noticeable change in spin relaxation. The observed fast spin relaxation, together with the limitation imposed by the band structure, are thus identified as the two most important factors that limit the efficiency of optical spin detection in the studied ZnO-based materials.
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- Campa, Daniele, et al.
(författare)
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Leukocyte telomere length in relation to pancreatic cancer risk: a prospective study.
- 2014
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Ingår i: Cancer Epidemiology Biomarkers & Prevention. - 1538-7755 .- 1055-9965. ; 23:11, s. 2447-2454
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Tidskriftsartikel (refereegranskat)abstract
- Background: Several studies have examined leukocyte telomere length (LTL) as a possible predictor for cancer at various organ sites. The hypothesis originally motivating many of these studies was that shorter telomeres would be associated with an increase in cancer risk, the results of epidemiologic studies have been inconsistent, however, and suggested positive, negative, or null associations. Two studies have addressed the association of LTL in relation to pancreatic cancer risk and the results are contrasting. Methods: we measured LTL in a prospective study of 331 pancreatic cancer cases and 331 controls in the context of the European Prospective Investigation into Cancer and Nutrition (EPIC). Results: We observed that the mean LTL was higher in cases (0.59±0.20) than in controls (0.57±0.17), although this difference was not statistically significant (p=0.07), and a basic logistic regression model showed no association of LTL with pancreas cancer risk. When adjusting for levels of HbA1c and C-Peptide, however, there was a weakly positive association between longer LTL and pancreatic cancer risk , OR=1.13 (1.01-1.27). Additional analyses by cubic spline regression suggested a possible non-linear relationship between RTL and pancreatic cancer risk (P=0.022), with a statistically non-significant increase in risk at very low LTL, as well as a significant increase at high LTL. Conclusion: Taken together, the results from our study do not support LTL as a uniform and strong predictor of pancreatic cancer. Impact: The results of this manuscript can provide insights into telomere dynamics and highlight the complex relationship between LTL and pancreatic cancer risk.
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- Dagnelund, Daniel, et al.
(författare)
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Phosphorus-related interfacial defect complex at a GaP/GaNP heterojunction
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For full exploration of dilute nitrides in device applications, a better understanding and control of defects located at interfaces involving e.g. Ga(In)NP are required. In this work we report on the first identification of a point defect situated at an interface between two semiconductors: GaNP and GaP. The defect is concluded to be a complex involving a P antisite or a P interstitial in its core, partnered with a neighboring impurity/defect aligned along a <111> direction, from detailed angular dependence studies of the optically detected magnetic resonance (ODMR) spectra at both X- and Q-band microwave frequencies. The principal g and A values, g┴=2.013, g║=2.002, A┴=130x10-4 cm-1 and A║=330x10-4 cm-1, are obtained from a spin Hamiltonian analysis. The interface nature of the defect is clearly evident from the absence of the ODMR lines originating from two out of four equivalent <111> orientations. Defect formation is shown to be facilitated by severe nitrogen ion bombardment under non-equilibrium growth conditions during solid-source molecular beam epitaxy and the defect is thermally stable upon post-growth thermal annealing.
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- Dobrovolsky, Alexandr, et al.
(författare)
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Energy Upconversion in GaP/GaNP Core/Shell Nanowires for Enhanced Near-Infrared Light Harvesting
- 2014
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Ingår i: Small. - : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 10:21, s. 4403-4408
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires (NWs) have recently gained increasing interest due to their great potential for photovoltaics. A novel material system based on GaNP NWs is considered to be highly suitable for applications in efficient multi-junction and intermediate band solar cells. This work shows that though the bandgap energies of GaNx P1-x alloys lie within the visible spectral range (i.e., within 540-650 nm for the currently achievable x < 3%), coaxial GaNP NWs grown on Si substrates can also harvest infrared light utilizing energy upconversion. This energy upconversion can be monitored via anti-Stokes near-band-edge photoluminescence (PL) from GaNP, visible even from a single NW. The dominant process responsible for this effect is identified as being due to two-step two-photon absorption (TS-TPA) via a deep level lying at about 1.28 eV above the valence band, based on the measured dependences of the anti-Stokes PL on excitation power and wavelength. The formation of the defect participating in the TS-TPA process is concluded to be promoted by nitrogen incorporation. The revealed defect-mediated TS-TPA process can boost efficiency of harvesting solar energy in GaNP NWs, beneficial for applications of this novel material system in third-generation photovoltaic devices.
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- Dobrovolsky, Alexandr, et al.
(författare)
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Mechanism for radiative recombination and defect properties of GaP/GaNP core/shell nanowires
- 2012
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 101:16, s. 163106-1-163106-4
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Tidskriftsartikel (refereegranskat)abstract
- Recombination processes in GaP/GaNP core/shell nanowires (NWs) grown on a Si substrate by molecular beam epitaxy are examined using a variety of optical characterization techniques, including cw- and time-resolved photoluminescence and optically detected magnetic resonance (ODMR). Superior optical quality of the structures is demonstrated based on the observation of intense emission from a single NW at room temperature. This emission is shown to originate from radiative transitions within N-related localized states. From ODMR, growth of GaP/GaNP NWs is also found to facilitate formation of complex defects containing a P atom at its core that act as centers of competing non-radiative recombination.
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