211 research outputs found
Controlling the charge environment of single quantum dots in a photonic-crystal cavity
We demonstrate that the presence of charge around a semiconductor quantum dot
(QD) strongly affects its optical properties and produces non-resonant coupling
to the modes of a microcavity. We first show that, besides (multi)exciton
lines, a QD generates a spectrally broad emission which efficiently couples to
cavity modes. Its temporal dynamics shows that it is related to the Coulomb
interaction between the QD (multi)excitons and carriers in the adjacent wetting
layer. This mechanism can be suppressed by the application of an electric
field, making the QD closer to an ideal two-level system.Comment: 12 pages, 4 figure
Bachelor of Arts in Communication Students Asked: “What is my Contextual Communication Competence Level?”
In general, students need to be able to interact and communicate with one another from all walks of life, whether they are in personal or professional settings. Therefore, it is essential to examine students’ communication skills to ascertain whether they have adequate competence or not. In this regard, this research endeavored to determine the contextual communication competence of 266 Bachelor of Arts in Communication (BA Comm) students in one prime state university in Cordillera Administrative Region, Philippines. Through a quantitative-descriptive research design, one result revealed that BA Comm students are able to use their understanding of successful and appropriate communication patterns in public, meeting, group, and dyad situations with an average level of contextual communication competence. On the same level, BA Comm majors are committed to the field because they have the necessary communication abilities to adapt and improve various communication tactics when conversing with friends, acquaintances, and strangers. Lastly, compared to female BA Comm students, male students are more self-assured and open to communicating in various communication contexts, such as in public, meeting, group, or dyad contexts, as well as with strangers, friends, and acquaintances. Further, BA Comm students see a growth in their level of contextual communication competence as they move through their year levels because of their communication classes and social involvement. Recommendations are also included for future research directions
Single photonics at telecom wavelengths using nanowire superconducting detectors
Single photonic applications - such as quantum key distribution - rely on the
transmission of single photons, and require the ultimate sensitivity that an
optical detector can achieve. Single-photon detectors must convert the energy
of an optical pulse containing a single photon into a measurable electrical
signal. We report on fiber-coupled superconducting single-photon detectors
(SSPDs) with specifications that exceed those of avalanche photodiodes (APDs),
operating at telecommunication wavelength, in sensitivity, temporal resolution
and repetition frequency. The improved performance is demonstrated by measuring
the intensity correlation function g(2)(t) of single-photon states at 1300nm
produced by single semiconductor quantum dots (QDs).Comment: 7 pages, 5 figures - submitted 12 OCT 200
Tuning optical modes in slab photonic crystal by atomic layer deposition and laser-assisted oxidation
The authors experimentally investigate the effects of atomic layer deposition (ALD) and laser-assisted oxidation on the optical modes in GaAs L3 photonic crystal air-bridge cavities, using layers of InAs quantum dots as internal light source. Four distinct optical mode peaks are observed in the photonic bandgap and they show different wavelength-redshifts (0–6.5 nm) as the photonic crystal surface is coated with an Al2O3 layer (0–5.4 nm thick). Numerical finite-difference time-domain (FDTD) simulations can well-reproduce the experimental result and give insight into the origin of the shifts of modes with different spatial profiles. By combining the ALD coating with in situ laser-assisted oxidation, we are able to both redshift and blueshift the optical modes and we attribute the blueshift to the formation of a GaAs-oxide at the expense of GaAs at the interface between GaAs and the Al2O3 layer. This result can be quantitatively reproduced by including a GaAs-oxide layer into the FDTD model. Selective etching experiments, confirm that this GaAs-oxide layer is mainly at the interface between GaAs and Al2O3 layers
Enhanced spontaneous emission in a photonic crystal light-emitting diode
We report direct evidence of enhanced spontaneous emission in a photonic
crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction
embedded in a suspended membrane, comprising a layer of self-assembled quantum
dots. Current is injected laterally from the periphery to the center of the
PhC. A well-isolated emission peak at 1300nm from the PhC cavity mode is
observed, and the enhancement of the spontaneous emission rate is clearly
evidenced by time-resolved electroluminescence measurements, showing that our
diode switches off in a time shorter than the bulk radiative and nonradiative
lifetimesComment: 10 page
Physicochemical properties of mixed micellar aggregates containing CCK peptides and Gd complexes designed as tumor specific contrast agents in MRI
New amphiphilic molecules containing a bioactive peptide or a claw moiety have been prepared
in order to obtain mixed micelles as target-specific contrast agents in magnetic resonance imaging. The
first molecule, C18H37CONH(AdOO)2-G-CCK8 (C18CCK8), contains a C18 hydrophobic moiety bound to
the C-terminal cholecystokinin octapeptide amide (CCK 26-33 or CCK8). The second amphiphilic
compound, C18H37CONHLys(DTPAGlu)CONH2 (C18DTPAGlu) or its gadolinium complex, (C18DTPAGlu-
(Gd)), contains the same C18 hydrophobic moiety bound, through a lysine residue, to the DTPAGlu chelating
agent. The mixed aggregates as well as the pure C18DTPAGlu aggregate, in the presence and absence
of Gd, have been fully characterized by surface tension measurements, FT-PGSE-NMR, fluorescence
quenching, and small-angle neutron scattering measurements. The structural characterization of the mixed
aggregates C18DTPAGlu(Gd)-C18CCK8 indicates a spherical arrangement of the micelles with an external
shell of 21 Ă… and an inner core of 20 Ă…. Both the DTPAGlu(Gd) complexes and the CCK8 peptides
point toward the external surface. The measured values for relaxivity in saline medium at 20 MHz proton
Larmor frequency and 25 °C are 18.7 mM-1 s-1. These values show a large enhancement in comparison
with the isolated DTPAGlu(Gd) complex
Controlling the Cassie-to-Wenzel Transition: an Easy Route towards the Realization of Tridimensional Arrays of Biological Objects
In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited as an effective micro-fabrication strategy to obtain highly ordered arrays of biological objects. To this purpose we fabricated a patterned surface wetted in the Cassie state, where we deposited a droplet containing genomic DNA. We observed that, when the droplet wets the surface in the Cassie state, an array of DNA filaments pinned on the top edges between pillars is formed. Conversely, when the Cassie-to-Wenzel transition occurs, DNA can be pinned at different height between pillars. These results open the way to the realization of tridimensional arrays of biological objects
The Gas Sensing Properties of Porphyrins-coated Laterally Grown ZnO Nanorods
AbstractPorphyrins coated ZnO is an interesting material where the exposure to light and gas may cooperate to modulate the respective sensitivities. In this work, the gas sensing properties of porphyrins functionalized laterally grown ZnO nanorods are introduced. The porphyrin layer incompletely coats the semiconductor surface in order to keep both ZnO and porphyrins in contact with analyte. It is known that UV light may prompt the chemical sensitivity of ZnO replacing the high temperature condition. Here we demonstrate that because of the photo-injection of electrons from porphyrin to the ZnO, the same impact could be acquired with visible light
Post-fabrication control of evanescent tunnelling in photonic crystal molecules
The post-fabrication control of evanescent tunnelling in photonic crystal molecules is demonstrated through the combination of selective infiltration and oxidation. By laser non thermal oxidation, we reduce the photonic coupling by more than 30% while by means of water micro-infiltration, we increase it by 28%. Fine-tuning of the photonic coupling is achieved by low-power laser oxidation and forced evaporation, opening the route to post-fabrication control of array of coupled cavities
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