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1.
Materials (Basel) ; 13(10)2020 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-32443648

RESUMO

Novel functionalities of disorder-induced scattering effect in random lasers, attributed to low spatial coherence, draw remarkable attention in high-contrast to superior quality speckle-free imaging applications. This paper demonstrates perovskite-polystyrene (PS)-based random lasing action with robust optical performance at room temperature. Optical characterizations are carried out upon perovskite thin films addition with polystyrene of different mixing concentrations (wt.%). A low threshold lasing operation is achieved with an increasing concentration of polystyrene, accompanying a wavy surface texture with high surface roughness. The rough surface dominating multiple scattering effects leads to enhanced feedback efficiency. Moreover, this study also elucidates efficient fabrication process steps for the development of high quality and durable PS-based random lasers. With the advantages of reduced coherent artifacts and low spatial coherence, speckle free projection images of the USAF (U. S. Air Force MIL-STD-150A standard of 1951) resolution test chart are shown for different PS-based random lasers.

2.
Macromol Rapid Commun ; 41(11): e2000088, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32329178

RESUMO

Surface properties are essential for substrates exhibiting high sensitivity in surface-enhanced Raman scattering (SERS) applications. In this work, novel SERS hybrid substrates using polystyrene-block-poly(methyl methacrylate) and anodic aluminum oxide templates is presented. The hybrid substrates not only possess hierarchical porous nanostructures but also exhibit superhydrophilic surface properties with the water contact angle ≈0°. Such surfaces play an important role in providing uniform enhanced intensities over large areas (relative standard deviation ≈10%); moreover, these substrates are found to be highly sensitive (limit of detection ≈10-12 m for rhodamine 6G (R6G)). The results show that the hybrid SERS substrates can achieve the simultaneous detection of multicomponent mixtures of different target molecules, such as R6G, crystal violet, and methylene blue. Furthermore, the bending experiments show that about 70% of the SERS intensities are maintained after bending from ≈30° to 150°.

3.
ACS Nano ; 2020 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-32298575

RESUMO

Artificial color pixels based on dielectric Mie resonators are appealing for scientific research as well as practical design. Vivid colors are imperative for displays and imaging. Dielectric metasurface-based artificial pixels are promising candidates for developing flat, flexible, and/or wearable displays. Considering the application feasibility of artificial color pixels, wide color gamuts are crucial for contemporary display technology. To achieve a wide color gamut, ensuring the purity and efficiency of nanostructure resonance peaks in the visible spectrum is necessary for structural color design. Low-loss dielectric materials are suitable for achieving vivid colors with structural color pixels. However, high-order Mie resonances prevent color pixels based on dielectric metasurfaces from efficiently generating highly saturated colors. In particular, fundamental Mie resonances (electric/magnetic dipole) for red can result in not only a strong resonance peak at 650 nm but also high-order Mie resonances at shorter wavelengths, which reduces the saturation of the target color. To address these problems, we fabricated silicon nitride metasurfaces on quartz substrates and applied Rayleigh anomalies at relatively short wavelengths to successfully suppress high-order Mie resonances, thus creating vivid color pixels. We performed numerical design, semianalytic considerations, and experimental proof-of-concept examinations to demonstrate the performance of the silicon nitride metasurfaces. Apart from traditional metasurface designs that involve transmission and reflection modes, we determined that lateral light incidence on silicon nitride metasurfaces can provide vivid colors through long-range dipole interactions; this can thus extend the applications of such surfaces to eyewear displays and guided-wave illumination techniques.

4.
Sci Rep ; 9(1): 13055, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31506495

RESUMO

We reported on GaN microcavity (MC) lasers combined with one rigid TiO2 high-contrast grating (HCG) structure as the output mirror. The HCG structure was directly fabricated on the GaN structure without an airgap. The entire MC structure comprised a bottom dielectric distributed Bragg reflector; a GaN cavity; and a top HCG reflector, which was designed to yield high reflectance for transverse magnetic (TM)- or transverse electric (TE)-polarized light. The MC device revealed an operation threshold of approximately 0.79 MW/cm2 when pulsed optical pumping was conducted using the HCG structure at room temperature. The laser emission was TM polarized with a degree of polarization of 99.2% and had a small divergence angle of 14° (full width at half maximum). This laser operation demonstration for the GaN-based MC structure employing an HCG exhibited the advantages of HCGs in semiconductor lasers at wavelengths from green to ultraviolet.

5.
Nano Lett ; 19(8): 5017-5024, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31268338

RESUMO

Graphene is a two-dimensional (2D) structure that creates a linear relationship between energy and momentum that not only forms massless Dirac fermions with extremely high group velocity but also exhibits a broadband transmission from 300 to 2500 nm that can be applied to many optoelectronic applications, such as solar cells, light-emitting devices, touchscreens, ultrafast photodetectors, and lasers. Although the plasmonic resonance of graphene occurs in the terahertz band, graphene can be combined with a noble metal to provide a versatile platform for supporting surface plasmon waves. In this study, we propose a hybrid graphene-insulator-metal (GIM) structure that can modulate the surface plasmon polariton (SPP) dispersion characteristics and thus influence the performance of plasmonic nanolasers. Compared with values obtained when graphene is not used on an Al template, the propagation length of SPP waves can be increased 2-fold, and the threshold of nanolasers is reduced by 50% when graphene is incorporated on the template. The GIM structure can be further applied in the future to realize electrical control or electrical injection of plasmonic devices through graphene.

6.
ACS Nano ; 13(5): 5421-5429, 2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-31009199

RESUMO

Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.

7.
Macromol Rapid Commun ; 39(23): e1800424, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30142232

RESUMO

Fibrillar materials have gained much attention recently because of their unique properties and potential applications. Although many methods have been developed to fabricate materials, it remains challenging to prepare fibrillar materials containing multicomponent materials or even with complex structures. Here, a facile strategy is developed to fabricate bamboo-shaped fibers by treating electrospun polymer core-shell fibers with solvent vapor annealing. Electrospun polystyrene (PS)/poly(methyl methacrylate) (PMMA) core-shell fibers are first prepared by electrospinning PS/PMMA blend solutions via a phase separation process. When the PS/PMMA core-shell fibers are annealed with the vapor of cyclohexane, which swells and delocalizes the PS domains selectively, the fibers transform into bamboo-shaped structures. The bamboo-shaped structures can be further examined by swelling and delocalizing the PMMA domains selectively, revealing the undulated PS structures. The thermal insulation properties of the fibers with bamboo-shaped structures are observed to be enhanced compared with the original polymer core-shell fibers.


Assuntos
Acetatos/química , Polimetil Metacrilato/química , Poliestirenos/química , Temperatura , Estrutura Molecular , Tamanho da Partícula , Solventes/química , Propriedades de Superfície
8.
Nano Lett ; 18(2): 747-753, 2018 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-29320208

RESUMO

Concentrating light at the deep subwavelength scale by utilizing plasmonic effects has been reported in various optoelectronic devices with intriguing phenomena and functionality. Plasmonic waveguides with a planar structure exhibit a two-dimensional degree of freedom for the surface plasmon; the degree of freedom can be further reduced by utilizing metallic nanostructures or nanoparticles for surface plasmon resonance. Reduction leads to different lightwave confinement capabilities, which can be utilized to construct plasmonic nanolaser cavities. However, most theoretical and experimental research efforts have focused on planar surface plasmon polariton (SPP) nanolasers. In this study, we combined nanometallic structures intersecting with ZnO nanowires and realized the first laser emission based on pseudowedge SPP waveguides. Relative to current plasmonic nanolasers, the pseudowedge plasmonic lasers reported in our study exhibit extremely small mode volumes, high group indices, high spontaneous emission factors, and high Purell factors beneficial for the strong interaction between light and matter. Furthermore, we demonstrated that compact plasmonic laser arrays can be constructed, which could benefit integrated plasmonic circuits.

9.
Opt Lett ; 42(21): 4533-4536, 2017 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-29088206

RESUMO

In this work, III-nitride based ∼370 nm UVA light-emitting diodes (LEDs) grown on Si substrates are demonstrated. We also reveal the impact of the AlN composition in the AlGaN quantum barrier on the carrier injection for the studied LEDs. We find that, by properly increasing the AlN composition, both the electron and hole concentrations in the multiple quantum wells (MQWs) are enhanced. We attribute the increased electron concentration to the better electron confinement within the MQW region when increasing the AlN composition for the AlGaN barrier. The improved hole concentration in the MQW region is ascribed to the reduced hole blocking effect by the p-type electron blocking layer (p-EBL). This is enabled by the reduced density of the polarization-induced positive charges at the AlGaN last quantum barrier (LB)/p-EBL interface, which correspondingly suppresses the hole depletion at the AlGaN LB/p-EBL interface and decreases the valence band barrier height for the p-EBL. As a result, the optical power is improved.

10.
Nano Lett ; 17(10): 6228-6234, 2017 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-28926272

RESUMO

We demonstrated a monolithic GaN-InGaN core-shell nanorod lattice lasing under room temperature. The threshold pumping density was as low as 140 kW/cm2 with a quality factor as high as 1940. The narrow mode spacing between lasing peaks suggested a strong coupling between adjacent whisper gallery modes (WGM), which was confirmed with the far-field patterns. Excitation area dependent photoluminescence revealed that the long-wavelength lasing modes dominated the collective lasing behavior under a large excitation area. The excitation-area-dependent lasing behavior resulted from the prominent optical coupling among rods. According to the optical mode simulations and truncated-rod experiments, we confirmed that the fine-splitting of lasing peaks originated from the coupled supermodes existing in the periodic nanorod lattices. With wavelength-tunable active materials and a wafer-level scalable processing, patterning optically coupled GaN-InGaN core-shell nanorods is a highly practical approach for building various on-chip optical components including emitters and coupled resonator waveguides in visible and ultraviolet spectral range.

11.
Sci Rep ; 7(1): 9515, 2017 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-28842628

RESUMO

We consider finite temperature effects in a non-standard Bose-Hubbard model for an exciton- polariton Josephson junction (JJ) that is characterised by complicated potential energy landscapes (PEL) consisting of sets of barriers and wells. We show that the transition between thermal activation (classical) and tunneling (quantum) regimes exhibits universal features of the first and second order phase transition (PT) depending on the PEL for two polariton condensates that might be described as transition from the thermal to the quantum annealing regime. In the presence of dissipation the relative phase of two condensates exhibits non-equilibrium PT from the quantum regime characterized by efficient tunneling of polaritons to the regime of permanent Josephson or Rabi oscillations, where the tunneling is suppressed, respectively. This analysis paves the way for the application of coupled polariton condensates for the realisation of a quantum annealing algorithm in presently experimentally accessible semiconductor microcavities possessing high (105 and more) Q-factors.

12.
Materials (Basel) ; 10(2)2017 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-28772476

RESUMO

This paper reviews the formation of nanoscale V-shaped pits on GaN-based light emitting diodes (LEDs) grown by the metal organic chemical vapor deposition (MOCVD) system and studies the effect of V-shaped pits on quantum efficiency. Since V-pits could provide potential barriers around threading dislocations to lessen non-radiative recombinations in such a high defect environment. In our study, multiple InGaN/GaN quantum well samples with different emission wavelengths of 380, 420, 460, and 500 nm were grown, each with different nanoscale V-shaped pits of three diameters for 150, 200, and 250 nm, respectively. It was found that the multiple quantum well (MQW) sample with larger V-pits had a lower pit density, but a relatively larger total V-pits defected area. The optimum diameter of V-pits showing the highest quantum efficiency from the MQW sample depended on the emission wavelength. MQW samples with wavelengths of 380 and 500 nm exhibited the best internal quantum efficiency (IQE) performance at the smallest V-pits area; however, the best performance for MQW samples with wavelength around 420 and 460 nm occurred when large V-pit areas were presented. Photoluminescence (PL) peak shifts and Raman shifts can provide a relationship between quantum-confined Stark effect (QCSE) and IQE, as well as a comparison between strain and IQE. The results obtained in this phenomenological study shall provide a useful guide line in making high-performance GaN-based LEDs with wide emission spectra.

13.
Sci Rep ; 7: 45519, 2017 03 30.
Artigo em Inglês | MEDLINE | ID: mdl-28358119

RESUMO

We performed depth-resolved PL and Raman spectral mappings of a GaN-based LED structure grown on a patterned sapphire substrate (PSS). Our results showed that the Raman mapping in the PSS-GaN heterointerface and the PL mapping in the InxGa1-xN/GaN MQWs active layer are spatially correlated. Based on the 3D construction of E2(high) Raman peak intensity and frequency shift, V-shaped pits in the MQWs can be traced down to the dislocations originated in the cone tip area of PSS. Detail analysis of the PL peak distribution further revealed that the indium composition in the MQWs is related to the residual strain propagating from the PSS-GaN heterointerface toward the LED surface. Numerical simulation based on the indium composition distribution also led to a radiative recombination rate distribution that shows agreement with the experimental PL intensity distribution in the InxGa1-xN/GaN MQWs active layer.

14.
Sci Rep ; 7: 39813, 2017 01 03.
Artigo em Inglês | MEDLINE | ID: mdl-28045127

RESUMO

We systematically investigate the effects of surface roughness on the characteristics of ultraviolet zinc oxide plasmonic nanolasers fabricated on aluminium films with two different degrees of surface roughness. We demonstrate that the effective dielectric functions of aluminium interfaces with distinct roughness can be analysed from reflectivity measurements. By considering the scattering losses, including Rayleigh scattering, electron scattering, and grain boundary scattering, we adopt the modified Drude-Lorentz model to describe the scattering effect caused by surface roughness and obtain the effective dielectric functions of different Al samples. The sample with higher surface roughness induces more electron scattering and light scattering for SPP modes, leading to a higher threshold gain for the plasmonic nanolaser. By considering the pumping efficiency, our theoretical analysis shows that diminishing the detrimental optical losses caused by the roughness of the metallic interface could effectively lower (~33.1%) the pumping threshold of the plasmonic nanolasers, which is consistent with the experimental results.

15.
Nanoscale Res Lett ; 12(1): 15, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28058649

RESUMO

In this work, we report on electrically pumped III-N microcavity (MC) light emitters incorporating oxide confinement apertures. The utilized SiO2 aperture can provide a planar ITO design with a higher index contrast (~1) over other previously reported approaches. The fabricated MC light emitter with a 15-µm-aperture shows a turn-on voltage of 3.3 V, which is comparable to conventional light emitting diodes (LEDs), showing a good electrical property of the proposed structure. A uniform light output profile within the emission aperture suggesting the good capability of current spreading and current confinement of ITO and SiO2 aperture, respectively. Although the quality factor (Q) of fabricated MC is not high enough to achieve lasing action (~500), a superlinear emission can still be reached under a high current injection density (2.83 kA/cm2) at 77 K through the exciton-exciton scattering, indicating the high potential of this structure for realizing excitonic vertical-cavity surface-emitting laser (VCSEL) action or even polariton laser after fabrication optimization.

16.
Nanoscale ; 8(43): 18483-18488, 2016 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-27778006

RESUMO

Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of optoelectronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 µJ cm-2 in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.

17.
Opt Express ; 24(18): 20696-702, 2016 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-27607673

RESUMO

A promising method to promote the lasing performance of solution-processed organic-inorganic lead-halide perovskites has been demonstrated. With the adding Ag and PMMA thin films, the threshold excitation power for low-temperature lasing action in perovskites can be greatly reduced by over two orders of magnitude than that acquired in bare perovskite layers, ascribing to the strong exciton-plasmon coupling between the Ag and perovskite films. Also, the PMMA layer can be exploited to prevent the perovskite degradation from the hydrolysis in ambient environment, achieving long-lasting light-emitting performance. The advantages exhibited by the hybrid perovskite configuration would be very promising in making practical laser devices.

18.
Nanoscale Res Lett ; 11(1): 319, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27364999

RESUMO

We reported an easy fabrication method to realize ZnO-based microcavities with various cavity shapes by focused ion beam (FIB) milling. The optical characteristics of different shaped microcavities have been systematically carried out and analyzed. Through comprehensive studies of cathodoluminescence and photoluminescence spectra, the whispering gallery mode (WGM) was observed in different shaped microcavities. Up further increasing excitation, the lasing action was dominated by these WGMs and matched very well to the simulated results. Our experiment shows that ZnO microcavities with different shapes can be made with high quality by FIB milling for specific applications of microlight sources and optical devices.

19.
Nano Lett ; 16(5): 3179-86, 2016 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-27089144

RESUMO

The recent development of plasmonics has overcome the optical diffraction limit and fostered the development of several important components including nanolasers, low-operation-power modulators, and high-speed detectors. In particular, the advent of surface-plasmon-polariton (SPP) nanolasers has enabled the development of coherent emitters approaching the nanoscale. SPP nanolasers widely adopted metal-insulator-semiconductor structures because the presence of an insulator can prevent large metal loss. However, the insulator is not necessary if permittivity combination of laser structures is properly designed. Here, we experimentally demonstrate a SPP nanolaser with a ZnO nanowire on the as-grown single-crystalline aluminum. The average lasing threshold of this simple structure is 20 MW/cm(2), which is four-times lower than that of structures with additional insulator layers. Furthermore, single-mode laser operation can be sustained at temperatures up to 353 K. Our study represents a major step toward the practical realization of SPP nanolasers.

20.
Sci Rep ; 6: 20581, 2016 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-26838665

RESUMO

Unlike conventional photon lasing, in which the threshold is limited by the population inversion of the electron-hole plasma, the exciton lasing generated by exciton-exciton scattering and the polariton lasing generated by dynamical condensates have received considerable attention in recent years because of the sub-Mott density and low-threshold operation. This paper presents a novel approach to generate both exciton and polariton lasing in a strongly coupled microcavity (MC) and determine the critical driving requirements for simultaneously triggering these two lasing operation in temperature <140 K and large negative polariton-exciton offset (<-133 meV) conditions. In addition, the corresponding lasing behaviors, such as threshold energy, linewidth, phase diagram, and angular dispersion are verified. The results afford a basis from which to understand the complicated lasing mechanisms in strongly coupled MCs and verify a new method with which to trigger dual laser emission based on exciton and polariton.

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