452 research outputs found
Dramatic impact of pumping mechanism on photon entanglement in microcavity
A theory of entangled photons emission from quantum dot in microcavity under
continuous and pulsed incoherent pumping is presented. It is shown that the
time-resolved two-photon correlations drastically depend on the pumping
mechanism: the continuous pumping quenches the polarization entanglement and
strongly suppresses photon correlation times. Analytical theory of the effect
is presented.Comment: 6 pages, 3 figure
Effect of quantum confinement on the dielectric function of PbSe
Monolayers of lead selenide nanocrystals of a few nanometers in height have been made by electrodeposition on a Au(111) substrate. These layers show a thickness-dependent dielectric function, which was determined using spectroscopic ellipsometry. The experimental results are compared with electronic structure calculations of the imaginary part of the dielectric function of PbSe nanocrystals. We demonstrate that the size-dependent variation of the dielectric function is affected by quantum confinement at well-identifiable points in the Brillouin zone, different from the position of the band-gap transition
Heterointerface effects on the charging energy of shallow D- ground state in silicon: the role of dielectric mismatch
Donor states in Si nanodevices can be strongly modified by nearby insulating
barriers and metallic gates. We report here experimental results indicating a
strong reduction in the charging energy of isolated As dopants in Si FinFETs
relative to the bulk value. By studying the problem of two electrons bound to a
shallow donor within the effective mass approach, we find that the measured
small charging energy may be due to a combined effect of the insulator
screening and the proximity of metallic gates.Comment: 7 pages, 6 figure
Anomalous Suppression of Valley Splittings in Lead Salt Nanocrystals without Inversion Center
Atomistic sp3d5s* tight-binding theory of PbSe and PbS nanocrystals is
developed. It is demonstrated, that the valley splittings of confined electrons
and holes strongly and peculiarly depend on the geometry of a nanocrystal. When
the nanocrystal lacks a microscopic center of inversion and has T_d symmetry,
the splitting is strongly suppressed as compared to the more symmetric
nanocrystals with O_h symmetry, having an inversion center.Comment: 5 pages, 4 figures, 1 tabl
National cultural values and the perceived relational risks in biotechnology alliance relationships
Cross-cultural interactions are growing at an exponential pace. Consequently, it is becoming important to be aware of the existence and precise nature of cultural differences in risk perceptions. Do national cultural values influence relational risk perception in alliance relationships? This is the issue addressed in this article. Through analyzing risk perception in 344 alliance relationships, the evidence presented demonstrates the importance of cultural values
Preconcentration and sensitive determination of the anti-inflammatory drug diclofenac on a paper-based electroanalytical platform
This work describes the development of a paper-based platform for highly sensitive detection of diclofenac. The quantification of this anti-inflammatory drug is of importance in clinical (e.g. quality and therapeutic control) and environmental (e.g. emerging contaminant determination) areas. The easy-to-handle platform here described consists of a carbon-ink paper-based working electrode and two metallic wires, provided by a gold-plated standard connector, as reference and counter electrodes. The porous paper matrix enables the preconcentration of the sample, decoupling sample and detection solutions. Thus, relatively large sample volumes can be used, which significantly improves the sensitivity of the method. A wide dynamic range of four orders of magnitude, between 0.10 and 100 μM, was obtained for diclofenac determination. Due to the predominance of adsorption at the lowest concentrations, there were two linear concentration ranges: one comprised between 0.10 and 5.0 μM (with a slope of 0.85 μA μM-1) and the other between 5.0 and 100 μM (with a slope of 0.48 μA μM-1). A limit of detection of 70 nM was achieved with this simple device that provided accurate results with an RSD of ca. 5%. The platform was applied for diclofenac quantification in spiked tap water samples. The versatility of this design enabled the fabrication of a multiplexed platform containing eight electrochemical cells that work independently. The low cost, small size and simplicity of the device allow on-site analysis, which is very useful for environmental monitoring.The authors would like to thank the EU and FCT/UEFISCDI/FORMAS for funding, in the frame of the collaborative internationalconsortium REWATERfinanced under the ERA-NET CofundWaterWorks 2015 Call. This ERA-NET is an integral part of the 2016Joint Activities developed by the Water Challenges for a ChangingWorld Joint Programme Initiative (Water JPI). This work was alsosupported by the EU (FEDER funds through COMPETE) and FCT(project FOODnanoHEALTH, Portugal2020, Norte-01-0145-FEDER-000011 and project UID/QUI/50006/2013) and by the SpanishMinistry of Economy and Competitiveness (MINECO, projectCTQ2014-58826-R). Estefanía Costa Rama thanks the Governmentof Principado de Asturias and Marie Curie-Cofund Actions for thepost-doctoral grant“Clarín-Cofund”ACA17-20.info:eu-repo/semantics/publishedVersio
Model for the on-site matrix elements of the tight-binding hamiltonian of a strained crystal: Application to silicon, germanium and their alloys
We discuss a model for the on-site matrix elements of the sp3d5s*
tight-binding hamiltonian of a strained diamond or zinc-blende crystal or
nanostructure. This model features on-site, off-diagonal couplings between the
s, p and d orbitals, and is able to reproduce the effects of arbitrary strains
on the band energies and effective masses in the full Brillouin zone. It
introduces only a few additional parameters and is free from any ambiguities
that might arise from the definition of the macroscopic strains as a function
of the atomic positions. We apply this model to silicon, germanium and their
alloys as an illustration. In particular, we make a detailed comparison of
tight-binding and ab initio data on strained Si, Ge and SiGe.Comment: Submitted to Phys. Rev.
Size-Dependence of the Wavefunction of Self-Assembled Quantum Dots
The radiative and non-radiative decay rates of InAs quantum dots are measured
by controlling the local density of optical states near an interface. From
time-resolved measurements we extract the oscillator strength and the quantum
efficiency and their dependence on emission energy. From our results and a
theoretical model we determine the striking dependence of the overlap of the
electron and hole wavefunctions on the quantum dot size. We conclude that the
optical quality is best for large quantum dots, which is important in order to
optimally tailor quantum dot emitters for, e.g., quantum electrodynamics
experiments.Comment: 5 pages, 3 figure
Beam Profile Measurements and Simulations of the PETRA Laser-Wire
The Laser-wire will be an essential diagnostic tool at the International
Linear Collider. It uses a finely focussed laser beam to measure the transverse
profile of electron bunches by detecting the Compton-scattered photons (or
degraded electrons) downstream of where the laser beam intersects the electron
beam. Such a system has been installed at the PETRA storage ring at DESY, which
uses a piezo-driven mirror to scan the laser-light across the electron beam.
Lat- est results of experimental data taking are presented and compared to
detailed simulations using the Geant4 based program BDSIM.Comment: 3 pagesm 4 figures. Submitted as a conference paper for the Particle
Accelerator Conference 2005 (PAC05
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