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11.
Jarjour AF Oliver RA Tahraoui A Kappers MJ Humphreys CJ Taylor RA 《Physical review letters》2007,99(19):197403
We report direct evidence for the control of the oscillator strength of the exciton state in a single quantum dot by the application of a vertical electric field. This is achieved through the study of the radiative lifetime of a single InGaN-GaN quantum dot in a p-i-n diode structure. Our results are in good quantitative agreement with theoretical predictions from an atomistic tight-binding model. Furthermore, the increase of the overlap between the electron and hole wave functions due to the applied field is shown experimentally to increase the attractive Coulomb interaction leading to a change in the sign of the biexcitonic binding energy. 相似文献
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J. Humphreys E. L. V. Lewis I. M. Ward E. L. Nix J. C. McGrath 《Journal of Polymer Science.Polymer Physics》1988,26(1):141-158
The mechanical anisotropy of oriented PVDF sheet is examined using a variety of experimental techniques. The mechanical behavior is similar to that observed previously for low-density polyethylene and nylon and consistent with a parallel lamellar crystalline structure. The s31 compliance is reduced in magnitude by drawing to higher draw ratio, but the reduction in the piezoelectric coefficient d31 is less marked, suggesting that the piezoelectric response cannot be related solely to dimensional changes under stress. Drawing to high draw ratio increases the s33 compliance, and this is further increased by introducing voids. The corresponding d33 piezoelectric coefficient is not changed significantly by drawing to high draw ratio, or by the introduction of voids, again indicating that the piezoelectric behavior relates to factors other than dimensional changes. 相似文献
15.
N. Ketteniss C. McAleese M.J. Kappers Y. Zhang C.J. Humphreys 《Applied Surface Science》2008,254(7):2124-2130
Treatment of GaN with SiH4 and NH3 increases the size of surface pits associated with threading dislocations, allowing them to be easily imaged by atomic force microscopy. Here, we assess the effect of a similar treatment on AlxGa1−xN surfaces for x ≤ 0.4. For relaxed AlxGa1−xN epilayers, an increase in the observed size and density of threading dislocation pits is observed. However, if the AlxGa1−xN is under tensile strain, the treatment results in the appearance of nanometre-scale surface hillocks. These hillocks may prevent observation of the dislocation pits. The hillocks are found to consist of crystalline AlxGa1−xN, and hence are suggested to be formed by strain driven etching or transformation of the surface by SiH4 and NH3. 相似文献
16.
Humphreys AS Filipovska A Berners-Price SJ Koutsantonis GA Skelton BW White AH 《Dalton transactions (Cambridge, England : 2003)》2007,(43):4943-4950
The novel water soluble bidentate phosphine ligand 1,3-bis(di-2-pyridylphosphino)propane (d2pypp) has been synthesized by a convenient route involving treatment of 2-pyridyllithium with Cl(2)P(CH(2))(3)PCl(2) and isolation in crystalline form as the hydrochloride salt. The synthesis of the precursor Cl(2)P(CH(2))(3)PCl(2) has been optimized by the use of triphosgene as the chlorinating agent. The 2 : 1 and 1 : 2 AuCl : d2pypp adducts have been synthesized and characterized by NMR spectroscopy and single crystal X-ray studies, and shown to be of the form (AuCl)(2)(mu-d2pypp-P,P') and [Au(d2pypp-P,P')(2)]Cl(.3.75H(2)O), respectively. The latter is more lipophilic than analogous 1 : 2 adducts of gold(I) chloride with the diphosphine ligands 1,2-bis(di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4, based on measurement of the n-octanol-water partition coefficient (log P = -0.46). A single crystal structure determination of the 1 : 2 Au(I) complex of the 3-pyridyl ethane ligand shows it to be of the form [Au(d3pype-P,P')(2)]Cl.5H(2)O. The in vitro cytotoxic activity of [Au(d2pypp)(2)]Cl was assessed in human normal and cancer breast cells and selective toxicity to the cancer cells found. The significance of these results to the antitumour properties of chelated 1 : 2 Au(I) diphosphine complexes is discussed. 相似文献
17.
J.F. Humphreys 《代数通讯》2013,41(14):5777-5802
18.
M.A. Moram C.F. JohnstonM.J. Kappers C.J. Humphreys 《Journal of Crystal Growth》2009,311(12):3239-3242
Nonpolar (1 1 2¯ 0) and semipolar (1 1 2¯ 2) GaN films were grown on sapphire by metalorganic vapour phase epitaxy using ScN interlayers of varying thicknesses. A 5 nm interlayer reduced basal plane stacking fault (BSF) densities in nonpolar films by a factor of 2 and threading dislocation (TD) densities by a factor of 100 to (1.8±0.2)×109 cm−2. An 8.5 nm interlayer reduced BSF densities in semipolar films by a factor of 5 and reduced TD densities by a factor of 200 to (1.5±0.3)×108 cm−2. Nonpolar film surface roughnesses were reduced by a factor of 20. 相似文献
19.
Neil P. Humphreys Roy Maartens David R. Matravers 《General Relativity and Gravitation》2012,44(12):3197-3215
Physical (and weak) regularity conditions are used to determine and classify all the possible types of spherically symmetric dust spacetimes in general relativity. This work unifies and completes various earlier results. The junction conditions are described for general non-comoving (and non-null) surfaces, and the limits of kinematical quantities are given on all comoving surfaces where there is Darmois matching. We show that an inhomogeneous generalisation of the Kantowski-Sachs metric may be joined to the Lema?tre-Tolman-Bondi metric. All the possible spacetimes are explicitly divided into four groups according to topology, including a group in which the spatial sections have the topology of a 3-torus. The recollapse conjecture (for these spacetimes) follows naturally in this approach. 相似文献
20.
Conditions for smooth cosmological models are set out and applied to inhomogeneous spherically symmetric models constructed by matching together different Lemaître–Tolman–Bondi solutions to the Einstein field equations. As an illustration the methods are applied to a collapsing dust sphere in a curved background. This describes a region which expands and then collapses to form a black hole in an Einstein de Sitter background. We show that in all such models if there is no vacuum region then the singularity must go on accreting matter for an infinite LTB time. 相似文献