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1.
Sci Adv ; 5(10): eaax6973, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31692752

RESUMO

The dynamic characterization of water multilayers on oxide surfaces is hard to achieve by currently available techniques. Despite this, there is an increasing interest in the evolution of water nanostructures on oxides to fully understand the complex dynamics of ice nucleation and growth in natural and artificial environments. Here, we report the in situ detection of the dynamic evolution of nanoscale water layers on an amorphous oxide surface probed by optical resonances. In the water nanolayer growth process, we find an initial nanocluster morphology that turns into a planar layer beyond a critical thickness. In the reverse process, the planar water film converts to nanoclusters, accompanied by a transition from a planar amorphous layer to crystalline nanoclusters. Our results are explained by a simple thermodynamic model as well as kinetic considerations. Our work represents an approach to reveal the nanostructure and dynamics at the water-oxide interface using resonant light probing.

2.
Adv Mater ; 31(33): e1901263, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31243831

RESUMO

High-performance nanostructured electro-optical switches and logic gates are highly desirable as essential building blocks in integrated photonics. In contrast to silicon-based optoelectronic devices, with their inherent indirect optical bandgap, weak light-modulation mechanism, and sophisticated device configuration, direct-bandgap-semiconductor nanostructures with attractive electro-optical properties are promising candidates for the construction of nanoscale optical switches for on-chip photonic integrations. However, previously reported semiconductor-nanostructure optical switches suffer from serious drawbacks such as high drive voltage, limited operation spectral range, and low modulation depth. High-efficiency electro-optical switches based on single CdS nanobelts with low drive voltage, ultra-high on/off ratio, and broad operation wavelength range, properties resulting from unique electric-field-dependent phonon-assisted optical transitions, are demonstrated. Furthermore, functional NOT, NOR, and NAND optical logic gates are demonstrated based on these switches. These switches and optical logic gates represent an important step toward integrated photonic circuits.

3.
ACS Sens ; 4(6): 1476-1496, 2019 06 28.
Artigo em Inglês | MEDLINE | ID: mdl-31132252

RESUMO

The rapid advance of micro-/nanofabrication technologies opens up new opportunities for miniaturized sensing devices based on novel three-dimensional (3D) architectures. Notably, microtubular geometry exhibits natural advantages for sensing applications due to its unique properties including the hollow sensing channel, high surface-volume ratio, well-controlled shape parameters and compatibility to on-chip integration. Here the state-of-the-art sensing techniques based on microtubular devices are reviewed. The developed microtubular sensors cover microcapillaries, rolled-up nanomembranes, chemically synthesized tubular arrays, and photoresist-based tubular structures via 3D printing. Various types of microtubular sensors working in optical, electrical, and magnetic principles exhibit an extremely broad scope of sensing targets including liquids, biomolecules, micrometer-sized/nanosized objects, and gases. Moreover, they have also been applied for the detection of mechanical, acoustic, and magnetic fields as well as fluorescence signals in labeling-based analyses. At last, a comprehensive outlook of future research on microtubular sensors is discussed on pushing the detection limit, extending the functionality, and taking a step forward to a compact and integrable core module in a lab-on-a-chip analytical system for understanding fundamental biological events or performing accurate point-of-care diagnostics.

4.
ACS Appl Mater Interfaces ; 11(17): 15891-15897, 2019 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-30964264

RESUMO

Graphene, with its excellent chemical stability, biocompatibility, and capability of electric field enhancement, has a great potential in optical and optoelectronic applications with superior performances by integrating with conventional optical and plasmonic devices. Here, we design and demonstrate graphene-activated optoplasmonic cavities based on rolled-up nanomembranes, which are employed for in situ monitoring the photodegradation dynamics of organic dye molecules on the molecular level in real time. The presence of the graphene layer significantly enhances the electric field of hybrid optoplasmonic modes at the cavity surface, enabling a highly sensitive surface detection. The degradation of rhodamine 6G molecules on the graphene-activated sensor surface is triggered by localized laser irradiation and monitored by measuring the optical resonance shift. Our demonstration paves the way for real-time, high-precision analysis of photodegradation by resonance-based optical sensors, which promises the comprehensive understanding of degradation mechanism and exploration of effective photocatalysts.

5.
Nano Lett ; 18(11): 7261-7267, 2018 11 14.
Artigo em Inglês | MEDLINE | ID: mdl-30339757

RESUMO

We report the mode interactions and resonant hybridization in nanomembrane-formed concentric dual ring cavities supporting whispering gallery mode resonances. Utilizing a rolled-up nanomembrane with subwavelength thickness as an interlayer, dual concentric microring cavities are formed by coating high-index nanomembranes on the inner and outer surfaces of the rolled-up dielectric nanomembrane. In such a hybrid cavity system, the conventional fundamental mode resonating along a single ring orbit splits into symmetric and antisymmetric modes confined by concentric dual ring orbits. Detuning of the coupled supermodes is realized by spatially resolved measurements along the cavity axial direction. A spectral anticrossing feature is observed as a clear evidence of strong coupling. Upon strong coupling, the resonant orbits of symmetric and antisymmetric modes cross over each other in the form of superwaves oscillating between the concentric rings with opposite phase. Notably, the present system provides high flexibilities in controlling the coupling strength by varying the thickness of the spacer layer and thus enables switching between strong and weak coupling regimes. Our work offers a compact and robust scheme using curved nanomembranes to realize novel cavity mode interactions for both fundamental and applied studies.

6.
Opt Lett ; 43(19): 4703-4706, 2018 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-30272719

RESUMO

In this Letter, we experimentally demonstrate a monolithic integration of two vertically rolled-up microtube resonators (VRUMs) on polymer-based 1×5 multimode interference waveguides to achieve 3D multi-channel coupling. In this configuration, different sets of resonant modes are simultaneously excited at S-, C-, and L- telecom bands, demonstrating an on-chip multiplexing, based on a vertical-coupling configuration. Moreover, the resonant wavelength tuning and consequently the overlapping of resonant modes are accomplished via covering the integrated VRUMs by liquid. A maximum sensitivity of 330 nm/refractive index unit is achieved. The present work would be a critical step for the realization of massively parallel optofluidic sensors with higher sensitivity and flexibility for signal processing, particularly in a 3D-integrated photonic chip.

7.
ACS Nano ; 12(6): 6170-6178, 2018 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-29890082

RESUMO

Cesium lead halide perovskite nanowires have emerged as promising low-dimensional semiconductor structures for integrated photonic applications. Understanding light-matter interactions in a nanowire cavity is of both fundamental and practical interest in designing low-power-consumption nanoscale light sources. In this work, high-quality in-plane aligned halide perovskite CsPbX3 (X = Cl, Br, I) nanowires are synthesized by a vapor growth method on an annealed M-plane sapphire substrate. Large-area nanowire laser arrays have been achieved based on the as-grown aligned CsPbX3 nanowires at room temperature with quite low pumping thresholds, very high quality factors, and a high degree of linear polarization. More importantly, it is found that exciton-polaritons are formed in the nanowires under the excitation of a pulsed laser, indicating a strong exciton-photon coupling in the optical microcavities made of cesium lead halide perovskites. The coupling strength in these CsPbX3 nanowires is dependent on the atomic composition, where the obtained room-temperature Rabi splitting energy is ∼210 ± 13, 146 ± 9, and 103 ± 5 meV for the CsPbCl3, CsPbBr3, and CsPbI3 nanowires, respectively. This work provides fundamental insights for the practical applications of all-inorganic perovskite CsPbX3 nanowires in designing light-emitting devices and integrated nanophotonic systems.

8.
ACS Nano ; 12(4): 3726-3732, 2018 04 24.
Artigo em Inglês | MEDLINE | ID: mdl-29630816

RESUMO

In situ generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery modes (WGMs) is investigated by spatially resolved laser dewetting on microtube cavities. The size and morphology of the silver nanoparticles are changed by adjusting the laser power and irradiation time, which in turn effectively tune the photon-plasmon coupling strength. Depending on the relative position of the plasmonic nanoparticles spot and resonant field distribution of WGMs, selective coupling between the localized surface plasmon resonances (LSPRs) and WGMs is experimentally demonstrated. Moreover, by creating multiple plasmonic-nanoparticle spots on the microtube cavity, the field distribution of optical axial modes is freely tuned due to multicoupling between LSPRs and WGMs. The multicoupling mechanism is theoretically investigated by a modified quasipotential model based on perturbation theory. This work provides an in situ fabrication of plasmonic nanoparticles on three-dimensional microtube cavities for manipulating photon-plasmon coupling which is of interest for optical tuning abilities and enhanced light-matter interactions.

9.
Adv Mater ; 30(10)2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29349814

RESUMO

Vanadium dioxide/titanium nitride (VO2 /TiN) smart coatings are prepared by hybridizing thermochromic VO2 with plasmonic TiN nanoparticles. The VO2 /TiN coatings can control infrared (IR) radiation dynamically in accordance with the ambient temperature and illumination intensity. It blocks IR light under strong illumination at 28 °C but is IR transparent under weak irradiation conditions or at a low temperature of 20 °C. The VO2 /TiN coatings exhibit a good integral visible transmittance of up to 51% and excellent IR switching efficiency of 48% at 2000 nm. These unique advantages make VO2 /TiN promising as smart energy-saving windows.

10.
ACS Appl Mater Interfaces ; 9(41): 36199-36205, 2017 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-28948758

RESUMO

We report on design and fabrication of patterned plasmonic dimer arrays by using an ultrathin anodic aluminum oxide (AAO) membrane as a shadow mask. This strategy allows for controllable fabrication of plasmonic dimers where the location, size, and orientation of each particle in the dimer pairs can be independently tuned. Particularly, plasmonic dimers with ultrasmall nanogaps down to the sub-10 nm scale as well as a large dimer density up to 1.0 × 1010 cm-2 are fabricated over a centimeter-sized area. The plasmonic dimers exhibit significant surface-enhanced Raman scattering (SERS) enhancement with a polarization-dependent behavior, which is well interpreted by finite-difference time-domain (FDTD) simulations. Our results reveal a facile approach for controllable fabrication of large-area dimer arrays, which is of fundamental interest for plasmon-based applications in surface-enhanced spectroscopy, biochemical sensing, and optoelectronics.

11.
Opt Lett ; 42(3): 486-489, 2017 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-28146508

RESUMO

Microtubular optical resonators are monolithically integrated on photonic chips to demonstrate optofluidic functionality. Due to the compact subwavelength-thin tube wall and a well-defined nanogap between polymer photonic waveguides and the microtube, excellent optical coupling with extinction ratios up to 32 dB are observed in the telecommunication relevant wavelength range. For the first time, optofluidic applications of fully on-chip integrated microtubular systems are investigated both by filling the core of the microtube and by the microtube being covered by a liquid droplet. Total shifts over the full free spectral range are observed in response to the presence of the liquid medium in the vicinity of the microtube resonators. This work provides a vertical coupling scheme for optofluidic applications in monolithically integrated so-called "lab-in-a-tube" systems.

12.
Phys Rev Lett ; 116(25): 253904, 2016 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-27391725

RESUMO

Vertical gold nanogaps are created on microtubular cavities to explore the coupling between resonant light supported by the microcavities and surface plasmons localized at the nanogaps. Selective coupling of optical axial modes and localized surface plasmons critically depends on the exact location of the gold nanogap on the microcavities, which is conveniently achieved by rolling up specially designed thin dielectric films into three-dimensional microtube cavities. The coupling phenomenon is explained by a modified quasipotential model based on perturbation theory. Our work reveals the coupling of surface plasmon resonances localized at the nanoscale to optical resonances confined in microtubular cavities at the microscale, implying a promising strategy for the investigation of light-matter interactions.

13.
Nanoscale ; 8(18): 9498-503, 2016 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-27102146

RESUMO

Luminescent nanoparticles (NPs) are deposited onto two dimensional (2D) pre-strained TiO2 nanomembranes by spin-coating. After rolling up the 2D differentially strained TiO2 nanomembranes into 3D microtube structures, the NPs are embedded within the tube windings. The embedded NPs serve as a light source for optical whispering-gallery-mode resonances under laser excitation, and therefore allow the TiO2 microtube to work as an active microcavity operating in emission mode. The spectral range of resonant modes can be tuned from the visible to the near infrared by embedding the proper NPs in the TiO2 tube wall. Rolled-up TiO2 microcavities combined with luminescent NPs could offer interesting opportunities in a variety of research fields, such as bio- and nanophotonics, optoelectronics, and optofluidics.

14.
Opt Lett ; 40(16): 3826-9, 2015 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-26274670

RESUMO

We demonstrate full integration of vertical optical ring resonators with silicon nanophotonic waveguides on silicon-on-insulator substrates to accomplish a significant step toward 3D photonic integration. The on-chip integration is realized by rolling up 2D differentially strained TiO(2) nanomembranes into 3D microtube cavities on a nanophotonic microchip. The integration configuration allows for out-of-plane optical coupling between the in-plane nanowaveguides and the vertical microtube cavities as a compact and mechanically stable optical unit, which could enable refined vertical light transfer in 3D stacks of multiple photonic layers. In this vertical transmission scheme, resonant filtering of optical signals at telecommunication wavelengths is demonstrated based on subwavelength thick-walled microcavities. Moreover, an array of microtube cavities is prepared, and each microtube cavity is integrated with multiple waveguides, which opens up interesting perspectives toward parallel and multi-routing through a single-cavity device as well as high-throughput optofluidic sensing schemes.

15.
Carbohydr Polym ; 125: 352-9, 2015 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-25857992

RESUMO

The master-batch method provides a simple way to apply cellulose nanocrystal (CNC) as reinforcement in a hydrophobic matrix. The two-stage process includes making high-CNC content (70 wt%) master batch pellets, then mixing acrylonitrile-butadiene-styrene (ABS) and maleic anhydride grafted polyethylene with the master batch pellets to prepare the ABS/CNC nanocomposite in extruder. SEM image indicates that self-assembled CNC nanosheets disperse evenly throughout the polymer matrix. The improved mechanical properties shown in tensile and DMA tests reveal that the CNC combines well with the ABS. TGA results show that the thermal degradation temperature of CNC in the master batch increases because of the protection of the ABS coating. This approach not only improves the dispersion ability and the thermal stability of CNC, but it is also applicable to use with other hydrophobic thermoplastics in industrial scale production.


Assuntos
Resinas Acrílicas/química , Butadienos/química , Celulose/química , Técnicas de Química Sintética/métodos , Nanocompostos/química , Nanopartículas/química , Poliestirenos/química
17.
Opt Lett ; 37(20): 4284-6, 2012 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-23073438

RESUMO

Asymmetric cone-like microtube cavities have been fabricated by unevenly rolling-up prestrained SiO/SiO(2) circular-shaped nanomembranes. Spatially localized axial resonant modes are obtained due to an axial confinement mechanism that is defined by the variation of the tube radius and windings along the tube axis. A theoretical model is applied to quantitatively explain and confirm our experimental results.

18.
Sheng Li Xue Bao ; 63(5): 463-71, 2011 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-22002237

RESUMO

Efficient coding theory proposes that sensory systems in the brain have been adapted to process natural scenes efficiently over the long history of evolution. Computational modeling the statistical regularities of natural images is therefore beneficial to our understanding of the mechanisms of visual information processing. In this paper, we briefly review the recent progress in using efficient coding approaches to study the encoding of natural images in the visual system.


Assuntos
Potenciais Evocados Visuais/fisiologia , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Animais , Humanos , Modelos Estatísticos , Estimulação Luminosa
19.
Opt Lett ; 36(19): 3840-2, 2011 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-21964115

RESUMO

We tune optical resonances in rolled-up SiO/SiO(2) microtube cavities by gradually modifying the tube structure through asymmetrical postdeposition of SiO(2). Spectral blueshifts followed by redshifts of the resonant modes are observed in a thin-walled microtube (tube-I), which is attributed to a competition between shape deformation and effective increase of tube wall thickness. In contrast, only a monotonic redshift is detected when asymmetrical deposition is performed on a thick-walled microtube (tube-II). Distinct wavelength-dependent tuning was revealed in both kinds of tubes. Numerical calculations based on perturbation theory are carried out to explain and confirm the experimental results.

20.
Sci China C Life Sci ; 51(6): 526-36, 2008 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-18488173

RESUMO

Perception of objects and motions in the visual scene is one of the basic problems in the visual system. There exist 'What' and 'Where' pathways in the superior visual cortex, starting from the simple cells in the primary visual cortex. The former is able to perceive objects such as forms, color, and texture, and the latter perceives 'where', for example, velocity and direction of spatial movement of objects. This paper explores brain-like computational architectures of visual information processing. We propose a visual perceptual model and computational mechanism for training the perceptual model. The computational model is a three-layer network. The first layer is the input layer which is used to receive the stimuli from natural environments. The second layer is designed for representing the internal neural information. The connections between the first layer and the second layer, called the receptive fields of neurons, are self-adaptively learned based on principle of sparse neural representation. To this end, we introduce Kullback-Leibler divergence as the measure of independence between neural responses and derive the learning algorithm based on minimizing the cost function. The proposed algorithm is applied to train the basis functions, namely receptive fields, which are localized, oriented, and bandpassed. The resultant receptive fields of neurons in the second layer have the characteristics resembling that of simple cells in the primary visual cortex. Based on these basis functions, we further construct the third layer for perception of what and where in the superior visual cortex. The proposed model is able to perceive objects and their motions with a high accuracy and strong robustness against additive noise. Computer simulation results in the final section show the feasibility of the proposed perceptual model and high efficiency of the learning algorithm.


Assuntos
Simulação por Computador , Modelos Neurológicos , Percepção de Movimento , Algoritmos , Humanos , Aprendizagem
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