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1.
Opt Express ; 28(12): 18018-18026, 2020 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-32680003

RESUMO

In this study, the optical properties of a meta-GMR consisting of a metasurface stacked on a planar dielectric slab waveguide were theoretically investigated. Two different metasurfaces, namely chiral split-ring resonator dimer arrays with/without a rod-shaped antenna, were investigated and compared. Conventional GMR filters utilize gratings to couple the free-space electromagnetic field to the waveguide. The highly dispersive nature of grating leads to low angular tolerance. Here, the grating is replaced by metasurfaces. The metasurface unit cell can be regarded as a polarizable dipole that couples the free-space electromagnetic field to the waveguide and decouples the waveguide mode to the radiation modes. Based on the localized nature of the resonant metasurfaces, the metasurface/GMR hybrid mode exhibits a superior angular tolerance as compared with a conventional GMR filter. This study can open a new avenue to tailor the optical properties of GMR-based devices.

2.
Aging Cell ; 18(4): e12989, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31183966

RESUMO

Multicellular signals are altered in the processes of both aging and neurodegenerative diseases, including Alzheimer's disease (AD). Similarities in behavioral and cellular functional changes suggest a common regulator between aging and AD that remains undetermined. Our genetics and behavioral approaches revealed the regulatory role of Akt in both aging and AD pathogenesis. In this study, we found that the activity of Akt is upregulated during aging through epidermal growth factor receptor activation by using the fruit fly as an in vivo model. Downregulation of Akt in neurons improved cell survival, locomotor activity, and starvation challenge in both aged and Aß42-expressing flies. Interestingly, increased cAMP levels attenuated both Akt activation-induced early death and Aß42-induced learning deficit in flies. At the molecular level, overexpression of Akt promoted Notch cleavage, suggesting that Akt is an endogenous activity regulator of γ-secretase. Taken together, this study revealed that Akt is involved in the aging process and Aß toxicity, and manipulating Akt can restore both neuronal functions and improve behavioral activity during the processes of aging and AD pathogenesis.

3.
Adv Mater ; 31(7): e1806479, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30549339

RESUMO

The second harmonic generation (SHG) of vertical and planar split-ring resonators (SRRs) that are broken centro-symmetry configurations at the interface of metal surface and air is investigated. Strong interactions, better electromagnetic field confinements, and less leakage into the substrate for vertical SRRs are found. Experimental results show a 2.6-fold enhancement of SHG nonlinearity, which is in good agreement with simulations and calculations. Demonstrations of 3D metastructures and vertical SRRs with strong SHG nonlinearity majorly result from magnetic dipole and electric quadrupole clearly provides potential applications for photonics and sensing.

4.
Sci Rep ; 8(1): 7684, 2018 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-29769619

RESUMO

In this paper, a tunable mid-infrared metasurface based on VO2 phase change material is proposed for temperature control. The proposed structure consisting of a VO2/SiO2/VO2 cavity supports a thermally switchable Fabry-Perot-like resonance mode at the transparency window of the atmosphere. Theoretically, the radiative cooling power density of the proposed metasurface can be switched to four-fold as the device temperature is below/above the phase change temperature of VO2. Besides radiative cooling, a passive temperature control application based on this huge cooling power switching ability is theoretically demonstrated. We believe the proposed device can be applied for small radiative cooling and temperature control applications.

5.
Sci Rep ; 7: 42076, 2017 02 06.
Artigo em Inglês | MEDLINE | ID: mdl-28165026

RESUMO

A high Q-value reflective type metasurface consisting of 1D Au nanorods, a SiO2 spacer and a Au back reflector is demonstrated. It is shown that the sideband of the resonant mode can be suppressed as the resonant wavelength close to the phonon absorption of SiO2. By combining both designed structured resonance and inherent property of the based materials, a low angle-dependent metasurface with a Q-value of 40 has been demonstrated. The proposed structure will be useful for high sensitivity sensing and narrow band thermal emitter.

6.
Opt Express ; 24(16): 18382-7, 2016 Aug 08.
Artigo em Inglês | MEDLINE | ID: mdl-27505801

RESUMO

In this paper, a narrow band thermal emission at 10 µm is demonstrated using a one dimensional metasurface. The proposed metasurface structure provides magnetic resonance mode that enhances the phonon absorption of SiO2. The proposed metasurface thermal emitter shows a Lambertian distribution. Additionally, 5.8-folds enhancement of emissivity is achieved by optimizing the cavity thickness of the metasurfaces. This type of thermal emitter will be useful for IR sensing applications.

7.
Opt Express ; 23(19): A1245-52, 2015 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-26406753

RESUMO

The contribution of graphene oxide (GO) on photocatalytic effects of Cu(x)O on plasmonic Au is investigated. It is found that the H(2) evolution rate from pure water is enhanced 1.4 fold using the visible-active Cu(x)O/GO photocatalyst, as compared with Cu(x)O without GO. In addition, the intensity of photoluminescence of Cu(x)O/GO can be enhanced as much as 2.85 fold as compared with Cu(x)O without GO. The enhancement is due to the negative fixed charge in GO, which can passivate the surface of Cu(x)O and suppress recombination of minority electrons at the surface. The results from optical characterization in this study can help to prove the proposed mechanism of passivation.

8.
Nano Lett ; 15(5): 3122-7, 2015 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-25844757

RESUMO

We report a phase-modulated multicolor meta-hologram (MCMH) that is polarization-dependent and capable of producing images in three primary colors. The MCMH structure is made of aluminum nanorods that are arranged in a two-dimensional array of pixels with surface plasmon resonances in red, green, and blue. The aluminum nanorod array is patterned on a 30 nm thick SiO2 spacer layer sputtered on top of a 130 nm thick aluminum mirror. With proper design of the structure, we obtain resonances of narrow bandwidths to allow for implementation of the multicolor scheme. Taking into account of the wavelength dependence of the diffraction angle, we can project images to specific locations with predetermined size and order. With tuning of aluminum nanorod size, we demonstrate that the image color can be continuously varied across the visible spectrum.


Assuntos
Alumínio/química , Holografia/métodos , Nanotecnologia , Nanotubos/química , Cor , Luz , Dióxido de Silício/química , Ressonância de Plasmônio de Superfície
9.
Sensors (Basel) ; 14(3): 5198-206, 2014 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-24625743

RESUMO

In this study, a polarization-control setup for intensity-resolved guided mode resonance sensors is proposed and demonstrated experimentally. The experimental results are in good agreement with the simulation data based on rigorous coupled wave approach calculations. The proposed intensity-resolved measurement setup transfers polarization ellipses, which are produced from guided mode resonance to a linear polarization state under a buffer solution condition, and then suppresses the signals to dark using a polarization-control set. Hence, any changes in the refractive index results in an increase in the intensity signals. Furthermore, no wavelength-resolved or angular-resolved measurement is needed in this scheme. According to the experimental results, a wide linear detection range of 0.014 refractive index units is achieved and the limit of detection is 1.62E-4 RIU.


Assuntos
Luz , Ressonância de Plasmônio de Superfície/instrumentação , Sistemas Computacionais , Refratometria
10.
Opt Express ; 22(2): 1313-8, 2014 Jan 27.
Artigo em Inglês | MEDLINE | ID: mdl-24515136

RESUMO

In this paper, the optical properties of a plasmonic nanoantenna array have been investigated. The proposed plasmonic structure presents omnidirectional resonance properties, such as omnidirectional reflection dip and omnidirectional emission peak. In addition, the reflection and emission of the plasmonic nanoantenna array with various metal/insulator/metal cavity thicknesses are theoretically and experimentally investigated. The simulation reveals a fair agreement with the experimental results.

11.
Nano Lett ; 14(1): 225-30, 2014 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-24329425

RESUMO

Holograms, the optical devices to reconstruct predesigned images, show many applications in our daily life. However, applications of hologram are still limited by the constituent materials and therefore their working range is trapped at a particular electromagnetic region. In recent years, the metasurfaces, an array of subwavelength antenna with varying sizes, show the abilities to manipulate the phase of incident electromagnetic wave from visible to microwave frequencies. Here, we present a reflective-type and high-efficiency meta-hologram fabricated by metasurface for visible wavelength. Using gold cross nanoantennas as building blocks to construct our meta-hologram devices with thickness ∼ λ/4, the reconstructed images of meta-hologram show polarization-controlled dual images with high contrast, functioning for both coherent and incoherent light sources within a broad spectral range and under a wide range of incidence angles. The flexibility demonstrated here for our meta-hologram paves the road to a wide range of applications related to holographic images at arbitrary electromagnetic wave region.


Assuntos
Ouro/química , Holografia/instrumentação , Lentes , Nanopartículas Metálicas/química , Nanopartículas Metálicas/ultraestrutura , Nanotecnologia/instrumentação , Refratometria/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento
12.
Opt Express ; 21 Suppl 2: A221-8, 2013 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-23482283

RESUMO

In this paper, Cu(x)O photocatalyst on plasmonic nanoporous Au film is proposed to enhancing the H(2) evolution rate of pure water splitting. The nanoporous Au film can simultaneously provide surface-enhanced absorption and built-in potential. The reflection spectrum shows that the surface plasmon (SP) assisted absorption wavelength of the Cu(x)O on the nanoporous Au film can be modified by changing the annealing temperature. It is found that the enhancement of the H(2) evolution rate highly depends on the SP-assisted absorption. As the annealing temperature is 220 ° C, the H(2) evolution rate is 58 µmol hr(-1) under the condition that the device area is 0.25 cm(2).

13.
Materials (Basel) ; 6(11): 5440-5446, 2013 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-28788400

RESUMO

Single crystal silicon solar cells are still predominant in the market due to the abundance of silicon on earth and their acceptable efficiency. Different solar-cell structures of single crystalline Si have been investigated to boost efficiency; the heterojunction with intrinsic thin layer (HIT) structure is currently the leading technology. The record efficiency values of state-of-the art HIT solar cells have always been based on n-type single-crystalline Si wafers. Improving the efficiency of cells based on p-type single-crystalline Si wafers could provide broader options for the development of HIT solar cells. In this study, we varied the thickness of intrinsic hydrogenated amorphous Si layer to improve the efficiency of HIT solar cells on p-type Si wafers.

14.
Nano Lett ; 12(12): 6223-9, 2012 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-23189928

RESUMO

We combine theory and experiment to demonstrate that a carefully designed gradient meta-surface supports high-efficiency anomalous reflections for near-infrared light following the generalized Snell's law, and the reflected wave becomes a bounded surface wave as the incident angle exceeds a critical value. Compared to previously fabricated gradient meta-surfaces in infrared regime, our samples work in a shorter wavelength regime with a broad bandwidth (750-900 nm), exhibit a much higher conversion efficiency (∼80%) to the anomalous reflection mode at normal incidence, and keep light polarization unchanged after the anomalous reflection. Finite-difference-time-domain (FDTD) simulations are in excellent agreement with experiments. Our findings may lead to many interesting applications, such as antireflection coating, polarization and spectral beam splitters, high-efficiency light absorbers, and surface plasmon couplers.

15.
Opt Express ; 20(16): 17952-61, 2012 Jul 30.
Artigo em Inglês | MEDLINE | ID: mdl-23038344

RESUMO

In this paper, the polarization dependent optical properties of GaN surface relief grating are investigated using dark field angle-resolved photoluminescence (ARPL) spectrometer. The light extraction efficiency with the transverse electric (TE) and transverse magnetic (TM) pumping source represents a TE polarized dominated property. It is found that the TE and TM waveguide modes cannot be simultaneously coupled out, therefore light extraction is polarization dependent. The ARPL spectrum also reveals that the extraction efficiency is relatively high as the dispersion line of the waveguide mode is coincident with the folded free-photon dispersion of the 1D GaN grating.

16.
Opt Express ; 20(13): 14584-95, 2012 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-22714520

RESUMO

In this paper, a metal layer assisted guide mode resonance (MaGMR) device with high sensitivity is proposed for bioanalytical applications and its functioning is experimentally proved. We find that the reflection spectra present a unique inversed response. The resonance mechanism is also discussed. Numerical calculation results indicate that the high sensitivity performance of MaGMR comes from the strongly asymmetric resonance modal profile and low propagation angle inside the waveguide. There is a one-fold enhancement of the evanescent wave in the analytes region compared to typical GMR. According to the experimental results, the proposed MaGMR achieved a bulk sensitivity of 376.78 nm/RIU in fundamental TM mode resonating at 0.809 µm with the first diffraction angle. Experiment results show a 264.78% enhancement in the sensitivity compared to that of the typical GMR sensor in the same resonance conditions of TM mode.


Assuntos
Técnicas Biossensoriais/instrumentação , Metais/química , Fotometria/instrumentação , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento
17.
Opt Lett ; 36(8): 1440-2, 2011 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-21499383

RESUMO

A plasmonic infrared (IR) filter assisted by localized surface plasmon polaritons (LSPPs) in a Ag/SiO2/Ag T-shaped array was theoretically and experimentally investigated. By using a Fourier transform infrared (FTIR) spectrometer, an angle-independent LSPP resonant mode caused by a Fabry-Pérot resonance in the structure was observed in agreement with the prediction from the rigorous coupled-wave analysis (RCWA) simulation. The resonant wavelength of the mode can also be controlled by modifying the geometry of the T-shaped structure. Such LSPP property can be used as an IR reflection-type band-stop filter with a single spectral bandwidth and an ultrahigh immunity to incident angles.

18.
Opt Express ; 18(25): 25608-14, 2010 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-21164906

RESUMO

In this paper, the polarization dependent optical properties of InGaN/GaN multi-quantum wells (MQWs) LED with cascading plasmonic gratings are investigated using an angle-resolved photoluminescence (ARPL) spectrometer. The plasmonic gratings consist of two Ag gratings with a half-pitch displacement. The ARPL spectra of the TE-TM state present a broadband emission with resonance dips occasioned by the SP resonance while the TM-TE state presents resonance peaks with low sideband emission. The resonance properties can be tuned by modifying the geometric parameters of the plasmonic grating. The ARPL spectrum of the LED sample with pure GaN 1D grating is also measured and discussed. The investigated plasmonics LED represents resonance optical properties different from the conventional surface relief LED, which can be used in special applications.


Assuntos
Iluminação/instrumentação , Refratometria/instrumentação , Semicondutores , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento/instrumentação
19.
Opt Lett ; 35(24): 4199-201, 2010 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-21165136

RESUMO

In this Letter, we present a method of reducing the spectral width of guided-mode resonance (GMR) in air-bridged resonant grating-waveguide structures to enhance the Q factor. The posttreatment of adding a dielectric film to the bottom of the membrane to manipulate the resonance behavior is practicable. The introduced underlayer is shown to be capable of effectively reducing the coupling and enhancing the resonant Q factor. The proposed method provides an effective means of adjusting the resonance property without varying the original GMR structure. The results also imply that TM resonance is more feasible for achieving narrow resonance and potentially in sensing applications, because it has higher sensitivity than TE resonance.

20.
Opt Express ; 18(11): 11763-71, 2010 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-20589037

RESUMO

The spatial dependence of absorption in a structured thin film solar cell is investigated through the rigorous coupled-wave analysis method. The investigated structure allows strong localized surface plasmon and surface plasmon polaritons, simultaneously. The absorptance of silver and amorphous silicon can be separately accounted for by calculating the time-averaged energy dissipation although only the absorption of amorphous silicon contributes to the photocurrent. In our studied case, the metallic material absorbs around 15%-20% of the total impinging sunlight while the active layer absorbs only approximately 50%.


Assuntos
Fontes de Energia Elétrica , Membranas Artificiais , Energia Solar , Ressonância de Plasmônio de Superfície/instrumentação , Absorção , Desenho Assistido por Computador , Transferência de Energia , Desenho de Equipamento , Análise de Falha de Equipamento , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
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