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1.
Sci Adv ; 8(35): eabn9252, 2022 Sep 02.
Article in English | MEDLINE | ID: mdl-36054351

ABSTRACT

Realization of quantum optical circuits is at the heart of quantum photonic information processing. A long-standing obstacle, however, has been the absence of a suitable platform of single photon sources (SPSs). Such SPSs need to be in spatially ordered arrays and produce, on-demand, highly pure, and indistinguishable single photons with sufficiently uniform emission characteristics to enable controlled interference between photons from distinct sources underpinning functional quantum optical networks. We report on such a platform of SPSs based on a unique class of epitaxial quantum dots dubbed mesa-top single quantum dot. Under resonant excitation, the spatially ordered SPSs (without Purcell enhancement) show single photon purity of >99% [g(2)(0) ~ 0.015], high two-photon Hong-Ou-Mandel interference visibilities of 0.82 ± 0.03 (at 11.5 kelvin, without cavity), and spectral nonuniformity of <3 nanometers, within established locally tunable technology. Our platform of SPSs paves the path to creating on-chip scalable quantum photonic networks for communication, computation, simulation, sensing and imaging.

2.
Opt Express ; 24(26): 29955-29962, 2016 Dec 26.
Article in English | MEDLINE | ID: mdl-28059380

ABSTRACT

We demonstrate triggered single photon emission up to 77K from an ordered 5x8 array of InGaAs single quantum dots (SQDs). The SQDs are grown selectively on patterned mesa tops utilizing substrate-encoded size-reducing epitaxy (SESRE). It exploits designed surface-curvature stress gradients to preferentially direct atom migration from mesa sidewalls to the top during growth. The emission from the SQDs exhibits a g(2)(0) of 0.19 ± 0.03 at 8K and decent emission spectral uniformity (standard deviation <1% of emission wavelength). The SESRE QDs are inherently compatible with on-chip integrated light manipulation elements, thereby enabling a path towards integrated nanophotonic systems for quantum information processing.

3.
Nanomedicine ; 9(2): 293-301, 2013 Feb.
Article in English | MEDLINE | ID: mdl-22841911

ABSTRACT

Recently we reported an analysis that examined the potential of synthesized photovoltaic functional abiotic nanosystems (PVFANs) to modulate membrane potential and activate action potential firing in neurons. Here we extend the analysis to delineate the requirements on the electronic energy levels and the attendant photophysical properties of the PVFANs to induce repetitive action potential under continuous light, a capability essential for the proposed potential application of PVFANs as retinal cellular prostheses to compensate for loss of photoreceptors. We find that repetitive action potential firing demands two basic characteristics in the electronic response of the PVFANs: an exponential dependence of the PVFAN excited state decay rate on the membrane potential and a three-state system such that, following photon absorption, the electron decay from the excited state to the ground state is via intermediate state(s) whose lifetime is comparable to the refractory time following an action potential. FROM THE CLINICAL EDITOR: In this study, the potential of synthetic photovoltaic functional abiotic nanosystems (PVFANs) is examined under continuous light to modulate membrane potential and activate action potential firing in neurons with the proposed potential application of PVFANs as retinal cellular prostheses.


Subject(s)
Action Potentials , Artificial Cells/chemistry , Nanostructures/chemistry , Neurons/physiology , Retina/cytology , Electric Stimulation , Humans , Models, Biological , Prostheses and Implants , Prosthesis Design
4.
Nano Lett ; 11(7): 2887-91, 2011 Jul 13.
Article in English | MEDLINE | ID: mdl-21707024

ABSTRACT

We present a new approach to ligand exchange on lead sulfide (PbS) quantum dots (QDs) in which the QDs are reacted with preformed Pb cation-ligand exchange units designed to promote reactions that replace surface Pb and oleate groups on the as-grown QDs. This process introduces negligible surface defects as the high quantum efficiency (∼55%) of the as-grown QDs is maintained. Infrared spectroscopy and electron microscopy are used to confirm the replacement of ligands and time-resolved photoluminescence to demonstrate the expected inverse sixth power dependence of the nonradiative resonant energy transfer rate on inter-QD spacing.


Subject(s)
Lead/chemistry , Quantum Dots , Quantum Theory , Sulfides/chemistry , Energy Transfer , Ligands , Nanotechnology , Particle Size , Surface Properties
5.
PLoS One ; 5(10): e13437, 2010 Oct 18.
Article in English | MEDLINE | ID: mdl-20976135

ABSTRACT

Quantitative information on the dynamics of multiple molecular processes in individual live cells under controlled stress is central to the understanding of the cell behavior of interest and the establishment of reliable models. Here, the dynamics of the apoptosis regulator intracellular Ca(2+), apoptosis effector caspase-3/7, and morphological changes, as well as temporal correlation between them at the single cell level, are examined in retinal gangling cell line (differentiated RGC-5 cells) undergoing apoptosis at elevated hydrostatic pressure using a custom-designed imaging platform that allows long-term real-time simultaneous imaging of morphological and molecular-level physiological changes in large numbers of live cells (beyond the field-of-view of typical microscopy) under controlled hydrostatic pressure. This examination revealed intracellular Ca(2+) elevation with transient single or multiple peaks of less than 0.5 hour duration appearing at the early stages (typically less than 5 hours after the onset of 100 mmHg pressure) followed by gradual caspase-3/7 activation at late stages (typically later than 5 hours). The data reveal a strong temporal correlation between the Ca(2+) peak occurrence and morphological changes of neurite retraction and cell body shrinkage. This suggests that Ca(2+) elevation, through its impact on ion channel activity and water efflux, is likely responsible for the onset of apoptotic morphological changes. Moreover, the data show a significant cell-to-cell variation in the onset of caspase-3/7 activation, an inevitable consequence of the stochastic nature of the underlying biochemical reactions not captured by conventional assays based on population-averaged cellular responses. This real-time imaging study provides, for the first time, statistically significant data on simultaneous multiple molecular level changes to enable refinements and testing of models of the dynamics of mitochondria-mediated apoptosis. Further, the platform developed and the approach has direct significance to the study of a variety of signaling pathway phenomena.


Subject(s)
Apoptosis , Calcium/metabolism , Caspase 3/metabolism , Caspase 7/metabolism , Ganglia/metabolism , Retina/metabolism , Animals , Cell Line , Ganglia/cytology , Pressure , Retina/cytology
6.
Nanomedicine ; 6(3): 409-18, 2010 Jun.
Article in English | MEDLINE | ID: mdl-20116456

ABSTRACT

A class of nanoscale (approximately 1-10 nm) structures designed to probe, manipulate, or endow function by direct interfacing with live cells is considered. Such a concept of cellular-level prostheses is illustrated via the example of light-activated nanoscale photodiodes capable of creating local electric fields that modulate existing voltage-gated ion channels in excitable cells. The dynamics of the membrane potential modulation by such photovoltaic functional abiotic nanosystems (PV-FANs) is modeled through an appropriate equivalent circuit. The feasibility of exceeding the typical approximately 10 mV depolarization threshold for activating the action potentials is examined. In view of the continuing advances in the ability to design, synthesize, and characterize abiotic nanoscale systems that can provide desired function, several approaches to the implementation of PV-FANs are discussed. The FANs as "cellular prostheses" can provide a variety of functions in response to different stimuli and represent a paradigm-changing opportunity at the frontiers of nanomedicine. FROM THE CLINICAL EDITOR: A class of nanoscale (approximately 1-10nm) structures designed to probe, manipulate, or endow live cell functions is demonstrated in this work. More specifically, light-activated nanoscale photodiodes were found capable of creating local electric fields that modulate existing voltage gated ion channels in excitable cells, thus allowing the generation of action potentials in excitable cells via external light stimulus in a controlled fashion.


Subject(s)
Nanotechnology/methods , Neurons/physiology , Action Potentials/physiology , Animals , Cell Membrane/physiology , Cell Survival , Models, Biological , Photochemistry , Surface Properties
7.
Nano Lett ; 9(12): 4548-52, 2009 Dec.
Article in English | MEDLINE | ID: mdl-19856942

ABSTRACT

We report the observation of photocurrent in silicon nanowires induced by nonradiative resonant energy transfer (NRET) from adjacent layers of lead sulfide nanocrystal quantum dots using time-resolved photocurrent measurements. This demonstration supports the feasibility of a new solar cell paradigm (Lu, S.; Madhukar, A. Nano Lett. 2007, 7, 3443-3451) that exploits NRET between efficient photon absorbers and adjacent nanowire/quantum well high-mobility charge transport channels and could offer a viable alternative to the limitations of carrier transport and collection faced by excitonic solar cells.


Subject(s)
Crystallization/methods , Electrochemistry/methods , Nanostructures/chemistry , Nanotechnology/methods , Photochemistry/methods , Quantum Dots , Silicon/chemistry , Electric Conductivity , Electric Power Supplies , Electromagnetic Fields , Energy Transfer , Light , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Nanostructures/radiation effects , Nanostructures/ultrastructure , Particle Size , Solar Energy , Surface Properties
8.
Nano Lett ; 7(11): 3443-51, 2007 Nov.
Article in English | MEDLINE | ID: mdl-17956142

ABSTRACT

Evidence is provided for nonradiative resonant energy transfer (NRET) from excitons in nanocrystal quantum dots (NCQDs) to the confined states of an adjacent quantum well (QW) at low excitation power and rate competitive with the quantum dot radiative decay. This indicates that NRET in optimized NCQD-QW/nanowire systems may provide a solar energy conversion approach with a viable tradeoff with the bottlenecks of charge carrier generation and/or transport to/in electrodes faced by excitonic solar cells.


Subject(s)
Nanoparticles/chemistry , Nanotechnology/methods , Quantum Dots , Absorption , Crystallization , Electrodes , Energy Transfer , Equipment Design , Ligands , Models, Chemical , Nanostructures , Nanowires , Quantum Theory , Solar Energy , Temperature , Time Factors
9.
Nano Lett ; 6(9): 1977-81, 2006 Sep.
Article in English | MEDLINE | ID: mdl-16968011

ABSTRACT

Cell adhesion through binding between specific cell membrane receptors and corresponding cell-adhesion-molecule (CAM)-coated solid surfaces is examined. The morphology of surfaces at various modification steps leading to functionalization with cell-binding CAMs is characterized. In one week neuron cultures, enhanced growth on surfaces modified with neuron-binding versus astrocyte-binding CAMs is observed. However, nonspecific adhesion on a poly-D-lysine-coated positive control surface is found to be even higher. Potential reasons and further studies needed are discussed.


Subject(s)
Cell Adhesion Molecules/chemistry , Cell Adhesion Molecules/metabolism , Cell Culture Techniques/methods , Hippocampus/cytology , Hippocampus/physiology , Neurons/cytology , Neurons/physiology , Animals , Biomimetics/methods , Cell Adhesion/physiology , Cells, Cultured , Coated Materials, Biocompatible/chemistry , Coated Materials, Biocompatible/pharmacology , Glass , Humans
10.
Nano Lett ; 6(6): 1279-83, 2006 Jun.
Article in English | MEDLINE | ID: mdl-16771594

ABSTRACT

We investigate the behavior of the island vertical pairing probability in multilayer systems of Ge island quantum dots (QDs) in Si(001). By combining a simple kinetic rate model with our previously reported atomistic simulation results on the nature of the stress field from buried shallow Ge islands having {105}-oriented sidewalls, we derive an analytical expression for correlation probability as a function of the parameters characterizing the multi-QD systems. The approach is based upon continuum mechanochemical potential model, which allows one to introduce necessary elements of the kinetics of island formation in a simple way. We compare the model predictions with available experimental data and find that the model provides a satisfactory description of the coupling probability. The correlation probability behavior as a function of capping layer thickness, Ge island size, interisland distance, and Ge adatom diffusion length is investigated within the framework of the developed model.


Subject(s)
Crystallization/methods , Germanium/chemistry , Models, Chemical , Models, Molecular , Nanostructures/chemistry , Nanostructures/ultrastructure , Quantum Dots , Silicon/chemistry , Computer Simulation , Models, Statistical , Particle Size , Statistics as Topic , Surface Properties
11.
Nano Lett ; 5(5): 969-73, 2005 May.
Article in English | MEDLINE | ID: mdl-15884904

ABSTRACT

We report on high-resolution transmission electron microscope structural studies of InAs colloidal semiconductor nanocrystal quantum dots (NCQDs) on ultrathin GaAs (001) semiconductor single-crystal substrates. We employ a benign method for preparing electron transparent specimens that is suitable for the study of such fragile samples. The image contrast comprises contributions from electron scattering from both the NCs and the GaAs substrate. Long-term electron exposure studies reveal different damage mechanisms operative in the nanocrystals and the substrate.


Subject(s)
Arsenicals/chemistry , Crystallization/methods , Gallium/chemistry , Indium/chemistry , Microscopy, Electron, Transmission/methods , Nanostructures/ultrastructure , Nanotechnology/methods , Quantum Dots , Semiconductors , Arsenicals/analysis , Gallium/analysis , Indium/analysis , Materials Testing/methods , Nanostructures/chemistry , Particle Size
12.
Nano Lett ; 5(3): 479-82, 2005 Mar.
Article in English | MEDLINE | ID: mdl-15755098

ABSTRACT

Integration of semiconductor epitaxical nanostructures and nanocrystals into two classes of quantum structures, uncovered adsorbed nanocrystals or buried via epitaxical overgrowth, is successfully demonstrated through structural and optical studies. The combination InGaAs/GaAs epitaxical structures and InAs nanocrystals is employed as a vehicle with the functional aim of exploiting the well developed optoelectronic communication technology based on the former with the biochemical and biomedical applications for which the latter are well suited.


Subject(s)
Arsenicals/chemistry , Crystallization/methods , Gallium/chemistry , Indium/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/instrumentation , Optics and Photonics/instrumentation , Arsenicals/analysis , Equipment Design , Equipment Failure Analysis , Gallium/analysis , Indium/analysis , Macromolecular Substances/analysis , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Nanostructures/analysis , Nanotechnology/methods , Particle Size , Quantum Dots , Semiconductors , Systems Integration
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