| 51. |
- Israr, Muhammad Qadir, et al.
(författare)
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Natural oxidation based controlled synthesis and characterization of ZnO nanodisks through structural transition of ZnO nanorods at 55 °C
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A novel, reproducible and natural oxidation based low temperature (55 °C) synthesis of ZnO nanodisks has been carried out using metallic zinc foil and formamide solution. The concentration of the formamide and the reaction duration are optimized to achieve the controlled fabrication. The morphological evolution of the ZnO nanodisks has been observed using scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. It is observed that ZnO nanodisks are of a good crystalline quality and have hexagonal wurtzite structure. The mechanism behind the growth and the breaking of nanorods into nanodisks is also suggested. Microphotoluminescence spectrum exhibits a strong ultraviolet emission and a very weak deep level related emission. In addition, temperature dependent studies reveal a decrease in the emission intensity of the ultraviolet peak combined with a red shift with increasing temperature from 20 to 300 K.
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| 52. |
- Israr Qadir, Muhammad, et al.
(författare)
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Fabrication of ZnO nanodisks from structural transformation of ZnO nanorods through natural oxidation and their emission characteristics
- 2014
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Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 40:1, s. 2435-2439
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Tidskriftsartikel (refereegranskat)abstract
- An environmentally benign natural oxidation based synthetic technique has been developed to grow and transform the ZnO nanorods into nanodisks at a very mild temperature of 55 degrees C with excellent features of its novelty and reproducibility. Metallic zinc foil and formamide solution have been utilized as substrate and reacting solution, respectively, for the growth of ZnO nanostructures. The optimized values of temperature, concentration of formamide and the reaction time are achieved to obtain the controlled and desired nanoscale morphologies. Detailed mechanism of the structural transformation of the nanorods into nanodisks has been discussed. Strong ultraviolet emission peak along with the much weaker deep level defects related emission has been realized in the microphotoluminescence spectrum. A visible red-shift and decrease in the intensity of ultraviolet peak are observed with increasing range of temperature from 20 to 300 K.
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| 53. |
- Jahnson, S, et al.
(författare)
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Anastomotic blood-flow reduction in rat small intestine with chronic radiation damage.
- 1998
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Ingår i: Digestion. - 0012-2823 .- 1421-9867. ; 59:2, s. 134-41
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND/AIMS: Anastomoses in previously irradiated intestine are prone to leakage, possibly due to an impeded blood supply. Whether or not chronic radiation damage actually predisposes to a disturbed blood flow in the vicinity of anastomoses was investigated in the rat small bowel.METHOD: A 2-cm segment of rat ileum was irradiated with a single dose (21 Gy). After 20 weeks an anastomosis was created in the irradiated segment and in the corresponding segment of controls. Another 4 days later local blood flow was studied with the 14C-iodoantipyrine autoradiography technique in 16 sectors around the circumference both in the anastomotic segment and in a segment 4 mm apart.RESULTS: In the anastomotic segment, the average blood flow was reduced in irradiated compared with non-irradiated animals in the mucosal layer (p = 0.034), but not in the muscular layer (p = 0.08). In the mesenteric quadrant blood flow was reduced in irradiated compared with non-irradiated animals, both in the mucosal layer (p = 0.012) and in the muscular layer (p = 0.05). More irradiated than non-irradiated animals showed a blood-flow reduction to 15% or more in 13-16 sectors both in the mucosal (p = 0.015) and the muscular layer (p = 0.04).CONCLUSIONS: The results favor the hypothesis that anastomoses in previously irradiated intestine are vascularly compromized and thereby have an increased risk of leakage.
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| 54. |
- Karim, Amir, 1976-, et al.
(författare)
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Photoluminescence Studies of Sn Quantum Dots in Si Grown by MBE
- 2005
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 27:5, s. 836-840
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Tidskriftsartikel (refereegranskat)abstract
- A few nanometer thick SnxSi1−x layers with x 0.1 grown on silicon (1 0 0) surfaces can be used to form tin (α-Sn) quantum dots as a result of heat treatment of such structures up to 800 °C. These quantum dots with a well-defined shape are expected to be a candidate for obtaining a low-energy direct band gap structure in Si. Absorption measurements reported by Ragan et al. have shown the onset of absorption at 0.27 eV indicating that the MBE-grown α-Sn quantum dots could be used, e.g. in infrared detectors or emitters. We have performed low temperature photoluminescence (PL) studies of some of the structures produced in this first study and observed no emission peak near 0.27 eV. The PL spectra are instead characterised by a broadband emission in the range 0.7–1 eV. Furthermore there are narrow features that have previously been described as the 789 meV C–O band and 1018 meV W or I1 band. The broad emission at 0.7–1 eV is attributed to the presence of defects introduced by the grown layers, which have suppressed the emission peaks related to the substrate as well. We have also grown α-Sn quantum dot samples on Si (1 0 0) substrates with very low doping concentrations. These samples show PL spectra with Si-substrate related peaks and a relatively lower broad feature at 0.7–1 eV. However, no emission was observed near 0.27 eV.
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| 55. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Photoluminescence study of basal plane stacking faults in ZnO nanowires
- 2014
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 50-53
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the photoluminescence (PL) of ZnO nanowires (NWs) containing a high density (similar to 1 x 10(6) cm(-1)) of basal plane stacking faults (BSFs). It was observed that the BSFs result in a specific PL peak at similar to 3.329 eV along with a donor bound excitonic emission (D degrees X) peak at 5 K. The observed BSF-related emission is of excitonic type and possesses longer PL lifetime than D degrees X (similar to 360 ps vs. similar to 70 ps). Via comparison of the microstructural and the PL properties of the ZnO NWs, it is shown that the observed BSF-related emission is due to the formation of crystal phase quantum wells (QWs). This is explained by the fact that BSF in wurtzite (WZ) ZnO is the thinnest segment of zinc blende (ZB) phase ZnO inserted in the WZ matrix, resulting in band alignment of type II due to the conduction and valence band offsets of ZB with respect to WZ ZnO. The mechanism of the BSF related PL is suggested to be an indirect exciton transitions clue to the recombination of electrons confined in the ZB QWs to holes in the WZ barriers localized near the BSFs.
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| 56. |
- Larsson, L. A., et al.
(författare)
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Quantum Dot Charging By Means Of Temperature And Magnetic Field
- 2011
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A micro‐photoluminescence study of individual InAs/GaAs quantum dots is presented. It is demonstrated that by varying the strength of an applied magnetic field and/or the temperature, the charge state of a quantum dot can be tuned. The charge tuning mechanism is shown to be due to the modification of the electron and hole transport in the wetting layer plane prior to their capture into the quantum dot.
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| 57. |
- Larsson, L. A., et al.
(författare)
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Spin Polarizing Neutral Excitons In Quantum Dots
- 2011
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A high degree of spin polarization for the neutral exciton in individual InAs quantum dots, without any external magnetic field applied, is demonstrated. The polarization mechanism is shown to be due to the difference in capture time into the QD for the electrons and holes after photo excitation in the wetting layer. This leads to optical pumping of the QD nuclei by spin polarized electrons and hence suppression of the anisotropic electron—hole exchange interaction.
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| 58. |
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| 59. |
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| 60. |
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