2,935 research outputs found
Optical characteristics of single wavelength-tunable InAs/InGaAsP/InP(100) quantum dots emitting at 1.55 um
We have studied the emission properties of individual InAs quantum dots (QDs)
grown in an InGaAsP matrix on InP(100) by metal-organic vapor-phase epitaxy.
Low-temperature microphotoluminescence spectroscopy shows emission from single
QDs around 1550 nm with characteristic exciton-biexciton behavior, and a
biexciton antibinding energy of more than 2 meV. Temperature-dependent
measurements reveal negligible optical-phonon induced broadening of the exciton
line up to 50 K, and emission from the exciton state clearly persists above 70
K. Furthermore, we find no measurable polarized fine structure splitting of the
exciton state within the experimental precision. These results are encouraging
for the development of a controllable photon source for fiber-based quantum
information and cryptography systems.Comment: 3 pages, 4 figures, submitted AP
Charged exciton emission at 1.3 m from single InAs quantum dots grown by metalorganic chemical vapor deposition
We have studied the emission properties of self-organized InAs quantum dots
(QDs) grown in an InGaAs quantum well by metalorganic chemical vapor
deposition. Low-temperature photoluminescence spectroscopy shows emission from
single QDs around 1300 nm; we clearly observe the formation of neutral and
charged exciton and biexciton states, and we obtain a biexciton binding energy
of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV,
indicating strong confinement.Comment: 3 pages, 3 figures, submitted AP
Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at 1.3 um
We present a detailed investigation into the optical characteristics of
individual InAs quantum dots (QDs) grown by metalorganic chemical vapor
deposition, with low temperature emission in the telecoms window around 1300
nm. Using micro-photoluminescence (PL) spectroscopy we have identified neutral,
positively charged, and negatively charged exciton and biexciton states.
Temperature-dependent measurements reveal dot-charging effects due to
differences in carrier diffusivity. We observe a pronounced linearly polarized
splitting of the neutral exciton and biexciton lines (~250 ueV) resulting from
asymmetry in the QD structure. This asymmetry also causes a mixing of the
excited trion states which is manifested in the fine structure and polarization
of the charged biexciton emission; from this data we obtain values for the
ratio between the anisotropic and isotropic electron-hole exchange energies of
(Delta1)/(Delta0)= 0.2--0.5. Magneto-PL spectroscopy has been used to
investigate the diamagnetic response and Zeeman splitting of the various
exciton complexes. We find a significant variation in g-factor between the
exciton, the positive biexciton, and the negative biexciton; this is also
attributed to anisotropy effects and the difference in lateral extent of the
electron and hole wavefunctions.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Emergent Phases of Nodeless and Nodal Superconductivity Separated by Antiferromagnetic Order in Iron-based Superconductor (Ca4Al2O6)Fe2(As1-xPx)2: 75As- and 31P-NMR Studies
We report P- and As-NMR studies on
(CaAlO)Fe(AsP) with an isovalent substitution
of P for As. We present the novel evolution of emergent phases that the
nodeless superconductivity (SC) in 00.4 and the nodal one around
=1 are intimately separated by the onset of a commensurate stripe-type
antiferromagnetic (AFM) order in 0.5 0.95, as an isovalent
substitution of P for As decreases a pnictogen height measured from
the Fe plane. It is demonstrated that the AFM order takes place under a
condition of 1.32\AA1.42\AA, which is also the case for other
Fe-pnictides with the Fe state in (Fe) layers. This novel
phase evolution with the variation in points to the importance of
electron correlation for the emergence of SC as well as AFM order.Comment: 5pages, 4figures; accepted for publication as a Rapid Communication
in Phys. Rev.
Graphitization behavior of iodine-treated Bombyx mori silk fibroin fiber
The original publication is available at www.springerlink.comArticleJOURNAL OF MATERIALS SCIENCE. 44(16):4235-4240 (2009)journal articl
SPH based numerical treatment of the interfacial interaction of flow with porous media
In this paper, the macroscopic equations of mass and momentum are developed and discretised based on the Smoothed Particle Hydrodynamics (SPH) formulation for the interaction at an interface of flow with porous media. The theoretical background of flow through porous media is investigated in order to highlight the key constraints which should be satisfied, particularly at the interface between the porous media flow and the overlying free flow. The study aims to investigate the derivation of the porous flow equations, computation of the porosity, and treatment of the interfacial boundary layer. It addresses weak assumptions that are commonly adopted for interfacial flow simulation in particle‐based methods. As support to the theoretical analysis, a 2D weakly compressible SPH (WCSPH) model is developed based on the proposed interfacial treatment. The equations in this model are written in terms of the intrinsic averages and in the Lagrangian form. The effect of particle volume change due to the spatial change of porosity is taken into account and the extra stress terms in the momentum equation are approximated by using Ergun's equation and the Sub‐Particle Scale (SPS) model to represent the drag and turbulence effects, respectively. Four benchmark test cases covering a range of flow scenarios are simulated to examine the influence of the porous boundary on the internal, interface and external flow. The capacity of the modified SPH model to predict velocity distributions and water surface behaviour is fully examined with a focus on the flow conditions at the interfacial boundary between the overlying free flow and the underlying porous media
An Estimate of Vacancy Migration Energy from Aging Experiments in an Iron 3.8 at% Molybdenum Alloy(Physics)
Resistivity change during isochronal aging of a high purity Fe-3.8 at.% Mo alloy is investigated. The resistivity first decreases between 300℃ and 400℃, passing through a minimum it increases to a maximum at 650℃ and decreases again. Molybdenum atoms are considered to form clusters in the first stage of resistivity decrease. The clustering at temperatures below 400℃ is possible only when quenched-in excess vacancies are present and enhance the solute atom diffusion. This observation implies that vacancies in pure iron also migrate at an appreciable rate at around 350℃ with an activation energy of about 1.2 eV
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