111 research outputs found
Direct observation of dynamic surface acoustic wave controlled carrier injection into single quantum posts using phase-resolved optical spectroscopy
A versatile stroboscopic technique based on active phase-locking of a surface
acoustic wave to picosecond laser pulses is used to monitor dynamic
acoustoelectric effects. Time-integrated multi-channel detection is applied to
probe the modulation of the emission of a quantum well for different
frequencies of the surface acoustic wave. For quantum posts we resolve
dynamically controlled generation of neutral and charged excitons and
preferential injection of holes into localized states within the nanostructure.Comment: 10 pages, 4 figure
Polymer/Nanocrystal Hybrid Solar Cells: Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance
Structure and Stability of Si(114)-(2x1)
We describe a recently discovered stable planar surface of silicon, Si(114).
This high-index surface, oriented 19.5 degrees away from (001) toward (111),
undergoes a 2x1 reconstruction. We propose a complete model for the
reconstructed surface based on scanning tunneling microscopy images and
first-principles total-energy calculations. The structure and stability of
Si(114)-(2x1) arises from a balance between surface dangling bond reduction and
surface stress relief, and provides a key to understanding the morphology of a
family of surfaces oriented between (001) and (114).Comment: REVTeX, 4 pages + 3 figures. A preprint with high-resolution figures
is available at http://cst-www.nrl.navy.mil/papers/si114.ps . To be published
in Phys. Rev. Let
Surface acoustic wave controlled carrier injection into self-assembled quantum dots and quantum posts
We report on recent progress in the acousto-electrical control of
self-assembled quantum dot and quantum post using radio frequency surface
acoustic waves (SAWs). We show that the occupancy state of these optically
active nanostructures can be controlled via the SAW-induced dissociation of
photogenerated excitons and the resulting sequential bipolar carrier injection
which strongly favors the formation of neutral excitons for quantum posts in
contrast to conventional quantum dots. We demonstrate high fidelity preparation
of the neutral biexciton which makes this approach suitable for deterministic
entangled photon pair generation. The SAW driven acoustic charge conveyance is
found to be highly efficient within the wide quantum well surrounding the
quantum posts. Finally we present the direct observation of acoustically
triggered carrier injection into remotely positioned, individual quantum posts
which is required for a low-jitter SAW-triggered single photon source.Comment: Proceedings of ISCS 2011; to appear in physics status solidi (c
Para to Ortho transition of metallic dimers on Si(001)
Extensive electronic structure calculations are performed to obtain the
stable geometries of metals like Al, Ga and In on the Si(001) surface at 0.5 ML
and 1 ML coverages. Our results coupled with previous theoretical findings
explain the recent experimental data in a comprehensive fashion. At low
coverages, as shown by previous works, `Para' dimers give the lowest energy
structure. With increasing coverage beyond 0.5 ML, `Ortho' dimers become part
of low energy configurations leading toward a `Para' to `Ortho' transition at 1
ML coverage. For In mixed staggered dimers (`Ortho' and `Para') give the lowest
energy configuration. For Ga, mixed dimers are non-staggered, while for Al
`Para' to `Ortho' transition of dimers is complete. Thus at intermediate
coverages between 0.5 and 1 ML, the `Ortho' and `Para' dimers may coexist on
the surface. Consequently, this may be an explanation of the fact that the
experimental observations can be successfully interpreted using either
orientation. A supported zigzag structure at 0.5 ML, which resembles , does not undergo a dimerization transition, and hence stays
semi-metallic. Also, unlike the soliton formation is ruled out
for this structure.Comment: 8 pages, 6 figure
Development of a Boston-area 50-km fiber quantum network testbed
Distributing quantum information between remote systems will necessitate the
integration of emerging quantum components with existing communication
infrastructure. This requires understanding the channel-induced degradations of
the transmitted quantum signals, beyond the typical characterization methods
for classical communication systems. Here we report on a comprehensive
characterization of a Boston-Area Quantum Network (BARQNET) telecom fiber
testbed, measuring the time-of-flight, polarization, and phase noise imparted
on transmitted signals. We further design and demonstrate a compensation system
that is both resilient to these noise sources and compatible with integration
of emerging quantum memory components on the deployed link. These results have
utility for future work on the BARQNET as well as other quantum network
testbeds in development, enabling near-term quantum networking demonstrations
and informing what areas of technology development will be most impactful in
advancing future system capabilities.Comment: 9 pages, 5 figures + Supplemental Material
Recommended from our members
Competing Interface and Bulk Effect-Driven Magnetoelectric Coupling in Vertically Aligned Nanocomposites.
Room-temperature magnetoelectric (ME) coupling is developed in artificial multilayers and nanocomposites composed of magnetostrictive and electrostrictive materials. While the coupling mechanisms and strengths in multilayers are widely studied, they are largely unexplored in vertically aligned nanocomposites (VANs), even though theory has predicted that VANs exhibit much larger ME coupling coefficients than multilayer structures. Here, strong transverse and longitudinal ME coupling in epitaxial BaTiO3:CoFe2O4 VANs measured by both optical second harmonic generation and piezoresponse force microscopy under magnetic fields is reported. Phase field simulations have shown that the ME coupling strength strongly depends on the vertical interfacial area which is ultimately controlled by pillar size. The ME coupling in VANs is determined by the competition between the vertical interface coupling effect and the bulk volume conservation effect. The revealed mechanisms shed light on the physical insights of vertical interface coupling in VANs in general, which can be applied to a variety of nanocomposites with different functionalities beyond the studied ME coupling effect.The work at Los Alamos National Laboratory was supported by the NNSA's Laboratory Directed Research and Development Program and was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy Office of Science. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is managed by Triad National Security, LLC for the U.S. Department of Energy's NNSA, under contract 89233218CNA000001. Angularâdependent magnetization studies (L.C.) were partially supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division
Integrating Signals from the T-Cell Receptor and the Interleukin-2 Receptor
T cells orchestrate the adaptive immune response, making them targets for immunotherapy. Although immunosuppressive therapies prevent disease progression, they also leave patients susceptible to opportunistic infections. To identify novel drug targets, we established a logical model describing T-cell receptor (TCR) signaling. However, to have a model that is able to predict new therapeutic approaches, the current drug targets must be included. Therefore, as a next step we generated the interleukin-2 receptor (IL-2R) signaling network and developed a tool to merge logical models. For IL-2R signaling, we show that STAT activation is independent of both Src- and PI3-kinases, while ERK activation depends upon both kinases and additionally requires novel PKCs. In addition, our merged model correctly predicted TCR-induced STAT activation. The combined network also allows information transfer from one receptor to add detail to another, thereby predicting that LAT mediates JNK activation in IL-2R signaling. In summary, the merged model not only enables us to unravel potential cross-talk, but it also suggests new experimental designs and provides a critical step towards designing strategies to reprogram T cells
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