Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 103
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nano Lett ; 19(12): 8972-8978, 2019 12 11.
Artigo em Inglês | MEDLINE | ID: mdl-31693379

RESUMO

Dielectric metasurfaces have recently been shown to provide an excellent platform for the harmonic generation of light due to their low optical absorption and to the strong electromagnetic field enhancement that can be designed into their constituent meta-atoms. Here, we demonstrate vacuum ultraviolet (VUV) third harmonic generation from a specially designed dielectric metasurface consisting of a titanium dioxide (TiO2) nanostructure array. The metasurface was designed to enhance the generation of VUV light at a wavelength of 185 nm by tailoring its geometric design parameters to achieve an optical resonance at the fundamental laser wavelength of 555 nm. The metasurface exhibits an enhancement factor of nominally 180 compared to an unpatterned TiO2 thin film of the same thickness, evidence of strong field enhancement at the fundamental wavelength. Mode analysis reveals that the origin of the enhancement is an anapole resonance near the pump wavelength. This work demonstrates an effective strategy for the compact generation of VUV light that could enable expanded access to this useful region of the electromagnetic spectrum.

2.
Light Sci Appl ; 8: 99, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31728191

RESUMO

Tomography is an informative imaging modality that is usually implemented by mechanical scanning, owing to the limited depth-of-field (DOF) in conventional systems. However, recent imaging systems are working towards more compact and stable architectures; therefore, developing nonmotion tomography is highly desirable. Here, we propose a metalens-based spectral imaging system with an aplanatic GaN metalens (NA = 0.78), in which large chromatic dispersion is used to access spectral focus tuning and optical zooming in the visible spectrum. After the function of wavelength-switched tomography was confirmed on cascaded samples, this aplanatic metalens is utilized to image microscopic frog egg cells and shows excellent tomographic images with distinct DOF features of the cell membrane and nucleus. Our approach makes good use of the large diffractive dispersion of the metalens and develops a new imaging technique that advances recent informative optical devices.

3.
ACS Sens ; 4(11): 2900-2907, 2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31602973

RESUMO

We present experimental and theoretical studies of a metamaterial-based plasmonic structure to build a plasmonic-molecular coupling detection system. High molecular sensitivity is realized only when molecules are located in the vicinity of the enhanced field (hot spot region); thus, introducing target molecules in the hot spot region to maximize plasmonic-molecular coupling is crucial to developing the sensing technology. We design a metamaterial consisting of a vertically oriented metal insulator metal (MIM) structure with a 25 nm channel sandwiched between two metal films, which enables the delivery of molecules into the large ravinelike hot spot region, offering an ultrasensitive platform for molecular sensing. This metamaterial is applied to carbon dioxide and butane detection. We design the structure to exhibit resonances at 4033 and 2945 cm-1, which overlap with the C═O and -CH2 vibration modes, respectively. The mutual coupling of these two resonance modes creates a Fano resonance, and their distinct peaks are clearly observed in the corresponding transmission dips. In addition, owing to its small footprint, such a vertical-oriented MIM structure enables us to increase the integration density and allows the detection of a 20 ppm concentration with negligible background noise and high selectivity in the mid-infrared region.

4.
ACS Appl Mater Interfaces ; 11(29): 25882-25890, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31257841

RESUMO

With the rise of Internet of Things, the presence of flexible devices has attracted significant attention owing to design flexibility. A ferroelectric field-effect transistor (FeFET), showing the advantages of high speed, nondestructive readout, and low-power consumption, plays a key role in next-generation technology. However, the performance of these devices is restricted since conventional flexible substrates show poor thermal stability to integrate traditional ferroelectric materials, limiting the compatibility of wearable devices. In this study, we adopt flexible muscovite mica as a substrate due to its good thermal properties and epitaxial integration ability. A flexible FeFET composed of oxide heteroepitaxy on muscovite is realized by combining an aluminum-doped zinc oxide film as the semiconductor channel layer and a Pb(Zr0.7Ti0.3)O3 film as the ferroelectric gate dielectric. The excellent characteristics of the transistor together with superior thermal stability and mechanical flexibility are demonstrated through various mechanical bending and temperature measurements. The on/off current ratio of the FeFET is higher than 103, which based on the field effect in the transfer curve. The smallest bending radius that can be achieved is 5 mm with a cyclability of 300 times and a retention of 100 h. This study opens an avenue to use oxide heteroepitaxy to construct a FeFET for next-generation flexible electronic systems.

5.
Nat Nanotechnol ; 14(3): 227-231, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30664753

RESUMO

A light-field camera captures both the intensity and the direction of incoming light1-5. This enables a user to refocus pictures and afterwards reconstruct information on the depth of field. Research on light-field imaging can be divided into two components: acquisition and rendering. Microlens arrays have been used for acquisition, but obtaining broadband achromatic images with no spherical aberration remains challenging. Here, we describe a metalens array made of gallium nitride (GaN) nanoantennas6 that can be used to capture light-field information and demonstrate a full-colour light-field camera devoid of chromatic aberration. The metalens array contains an array of 60 × 60 metalenses with diameters of 21.65 µm. The camera has a diffraction-limited resolution of 1.95 µm under white light illumination. The depth of every object in the scene can be reconstructed slice by slice from a series of rendered images with different depths of focus. Full-colour, achromatic light-field cameras could find applications in a variety of fields such as robotic vision, self-driving vehicles and virtual and augmented reality.

6.
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.

7.
Opt Express ; 26(18): 23397-23410, 2018 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-30184841

RESUMO

Enabling laser white-lighting at a correlated color temperature (CCT) of 6500K with the use of only red/green/blue (RGB) tri-color laser diodes (LDs) is demonstrated, which can further perform wavelength division multiplexing (WDM) communication with a high-spectral-usage 16 QAM-OFDM data stream at 11.2 Gbps over 0.5 m. The sampling rate of encoded data is optimized to avoid the aliasing effect and to effectively amplify the signal with high on/off extinction and modulation depth. Proper oversampling can decrease the peak-to-average power ratio (PAPR) of the OFDM data and filter out unwanted noise. There are also six different diffusers used to diverge the white-light mixed by the RGB LD beam. By analyzing the color-casting transmittance, surface roughness, CCT uniformity, divergent angle of the diffuser, and the data transmission capacity, the frosted glass (FG2.8) diffuser with high transmittance diverges the white light with the divergent angle of ± 20° and supports the highest data rate of 14 Gbps over 0.5 m. To fit the day-light CCT, the blue LD power at an optimized bias current is further attenuated with a 0.6-optical density filter for reducing CCT from 100000K to 6500K; however, such an adjustment also degrades the SNR ratio to sacrifice the achievable data rate of the blue LD. The polycarbonate (PC1.5) diffuser with proper surface roughness diverged white-light exhibits the best CCT uniformity and a divergent angle of ± 30° but supports a data rate of only 6.4 Gbps over 0.5 m. The poly (methyl methacrylate) PMMA1.5 diffuser scatters the white light with the largest angle of ± 40°; however, the data rate also decreases to 4.8 Gbps over 0.5 m.

8.
ACS Appl Mater Interfaces ; 10(36): 30574-30580, 2018 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-30118205

RESUMO

In the era of Internet of Things, the demand for flexible and transparent electronic devices has shifted to the forefront of materials science research. However, the radiation damage to key performance of transparent devices under radiative environment remains as a critical issue. Here, we present a promising technology for nonvolatile transparent electronic devices based on flexible oxide heteroepitaxy. A direct fabrication of epitaxial lead lanthanum zirconate titanate on transparent flexible mica substrate with indium tin oxide electrodes is presented. The transparent flexible ferroelectric heterostructures not only retain their superior performance, thermal stability, reliability, and mechanical durability, but also exhibit remarkably robust properties against to a strong radiation exposure. Our study demonstrates an extraordinary concept to realize transparent flexible nonvolatile electronic devices for the design and development of next-generation smart devices with potential application in electronics, automotive, aerospace, and nuclear systems.

9.
Nano Lett ; 18(9): 5738-5743, 2018 09 12.
Artigo em Inglês | MEDLINE | ID: mdl-30067376

RESUMO

Vacuum ultraviolet (VUV) light has important applications in many fields, ranging from device fabrication to photochemistry, from environmental remediation to microscopy and spectroscopy. Methods to produce coherent VUV light frequently utilize high harmonic generation in media such as rare gases or atomic vapors; nonlinear optical crystals that support second harmonic generation into the VUV are quite rare. Here, we demonstrate an all-dielectric metasurface designed for the nonlinear optical generation of VUV light. Consisting of an array of zinc oxide nanoresonators, the device exhibits a magnetic dipole resonance at a wavelength of 394 nm. When excited with ultrafast laser pulses at this wavelength, the second harmonic at 197 nm is readily generated. Manipulation of the metasurface design enables control over the radiation pattern. This work has the potential to open the door toward simple and compact VUV sources for new applications.

10.
ACS Omega ; 3(2): 1627-1634, 2018 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-30023811

RESUMO

The matrix metalloproteinases (MMPs) are well-known mediators that are activated in tumor progression. MMP2 is a kind of gelatinase in extracellular matrix remodeling and cancer metastasis processes. MMP2 secretion increased in many types of cancer diseases, and its abnormal expression is associated with a poor prognosis. We fabricated a nanocomposite that sensed MMP2 expression by a red and blue light change. This nanocomposite consisted of an upconversion nanoparticle (UCNP), MMP2-sensitive peptide, and CuInS2/ZnS quantum dot (CIS/ZnS QD). An UCNP is composed of NaYF4:Tm/Yb@NaYF4:Nd/Yb, which has multiple emissions at UV/blue-visible wavelengths under 808 nm laser excitation. The conjugated CIS/ZnS QD showed the red-visible fluorescence though the FRET process. The two fluorophores were connected by a MMP2-sensitive peptide to form a novel MMP2 biosensor, named UCNP@p-QD. UCNP@p-QD was highly biocompatible according to cell viability assay. The FRET-based biosensor was employed in the MMP2 determination in vitro and in vivo. Furthermore, it was administrated into the tumor-bearing mouse to check MMP2 expression. UCNP@p-QD could be a promising tool for biological study and biomedical application. In this study, we demonstrated that the CIS/ZnS QD improved the upconversion intensity through a near-infrared-induced FRET process. This nanocomposite has the advantage of light penetration, excellent biocompatibility, and high sensitivity to sense MMP2. The near-infrared-induced composites are a potential inspiration for use in biomedical applications.

11.
Opt Express ; 26(10): 13148-13182, 2018 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-29801344

RESUMO

The research and development of optical metasurfaces has been primarily driven by the curiosity for novel optical phenomena that are unattainable from materials that exist in nature and by the desire for miniaturization of optical devices. Metasurfaces constructed of artificial patterns of subwavelength depth make it possible to achieve flat, ultrathin optical devices of high performance. A wide variety of fabrication techniques have been developed to explore their unconventional functionalities which in many ways have revolutionized the means with which we control and manipulate electromagnetic waves. The relevant research community could benefit from an overview on recent progress in the fabrication and applications of the metasurfaces. This review article is intended to serve that purpose by reviewing the state-of-the-art fabrication methods and surveying their cutting-edge applications.

12.
Adv Mater ; 30(21): e1706918, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29633385

RESUMO

Given the high demand for miniaturized optoelectronic circuits, plasmonic devices with the capability of generating coherent radiation at deep subwavelength scales have attracted great interest for diverse applications such as nanoantennas, single photon sources, and nanosensors. However, the design of such lasing devices remains a challenging issue because of the long structure requirements for producing strong radiation feedback. Here, a plasmonic laser made by using a nanoscale hyperbolic metamaterial cube, called hyperbolic metacavity, on a multiple quantum-well (MQW), deep-ultraviolet emitter is presented. The specifically designed metacavity merges plasmon resonant modes within the cube and provides a unique resonant radiation feedback to the MQW. This unique plasmon field allows the dipoles of the MQW with various orientations into radiative emission, achieving enhancement of spontaneous emission rate by a factor of 33 and of quantum efficiency by a factor of 2.5, which is beneficial for coherent laser action. The hyperbolic metacavity laser shows a clear clamping of spontaneous emission above the threshold, which demonstrates a near complete radiation coupling of the MQW with the metacavity. This approach shown here can greatly simplify the requirements of plasmonic nanolaser with a long plasmonic structure, and the metacavity effect can be extended to many other material systems.

13.
Small ; 14(17): e1703920, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29611338

RESUMO

An ultrathin planar cavity metasurface is proposed based on ultrathin film interference and its practicability for light manipulation in visible region is experimentally demonstrated. Phase of reflected light is modulated by finely adjusting the thickness of amorphous silicon (a-Si) by a few nanometers on an aluminum (Al) substrate via nontrivial phase shifts at the interfaces and interference of multireflections generated from the planar cavity. A phase shift of π, the basic requirement for two-level phase metasurface systems, can be accomplished with an 8 nm thick difference. For proof of concept, gradient metasurfaces for beam deflection, Fresnel zone plate metalens for light focusing, and metaholograms for image reconstruction are presented, demonstrating polarization-independent and broadband characteristics. This novel mechanism for phase modulation with ultrathin planar cavity provides diverse routes to construct advanced flat optical devices with versatile applications.

14.
Sci Adv ; 4(1): eaao0773, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29326979

RESUMO

The past two decades have witnessed the revolutionary development of optical trapping of nanoparticles, most of which deal with trapping stiffness larger than 10-8 N/m. In this conventional regime, however, it remains a formidable challenge to sort out sub-50-nm nanoparticles with single-nanometer precision, isolating us from a rich flatland with advanced applications of micromanipulation. With an insightfully established roadmap of damping, the synchronization between optical force and flow drag force can be coordinated to attempt the loosely overdamped realm (stiffness, 10-10 to 10-8 N/m), which has been challenging. This paper intuitively demonstrates the remarkable functionality to sort out single gold nanoparticles with radii ranging from 30 to 50 nm, as well as 100- and 150-nm polystyrene nanoparticles, with single nanometer precision. The quasi-Bessel optical profile and the loosely overdamped potential wells in the microchannel enable those aforementioned nanoparticles to be separated, positioned, and microscopically oscillated. This work reveals an unprecedentedly meaningful damping scenario that enriches our fundamental understanding of particle kinetics in intriguing optical systems, and offers new opportunities for tumor targeting, intracellular imaging, and sorting small particles such as viruses and DNA.

15.
ACS Nano ; 12(2): 1920-1927, 2018 02 27.
Artigo em Inglês | MEDLINE | ID: mdl-29376312

RESUMO

The toroidal dipole is a localized electromagnetic excitation independent from the familiar magnetic and electric dipoles. It corresponds to currents flowing along minor loops of a torus. Interference of radiating induced toroidal and electric dipoles leads to anapole, a nonradiating charge-current configuration. Interactions of induced toroidal dipoles with electromagnetic waves have recently been observed in artificial media at microwave, terahertz, and optical frequencies. Here, we demonstrate a quasi-planar plasmonic metamaterial, a combination of dumbbell aperture and vertical split-ring resonator, that exhibits transverse toroidal moment and resonant anapole behavior in the optical part of the spectrum upon excitation with a normally incident electromagnetic wave. Our results prove experimentally that toroidal modes and anapole modes can provide distinct and physically significant contributions to the absorption and dispersion of slabs of matter in the optical part of the spectrum in conventional transmission and reflection experiments.

16.
Nat Nanotechnol ; 13(3): 227-232, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29379204

RESUMO

Metalenses consist of an array of optical nanoantennas on a surface capable of manipulating the properties of an incoming light wavefront. Various flat optical components, such as polarizers, optical imaging encoders, tunable phase modulators and a retroreflector, have been demonstrated using a metalens design. An open issue, especially problematic for colour imaging and display applications, is the correction of chromatic aberration, an intrinsic effect originating from the specific resonance and limited working bandwidth of each nanoantenna. As a result, no metalens has demonstrated full-colour imaging in the visible wavelength. Here, we show a design and fabrication that consists of GaN-based integrated-resonant unit elements to achieve an achromatic metalens operating in the entire visible region in transmission mode. The focal length of our metalenses remains unchanged as the incident wavelength is varied from 400 to 660 nm, demonstrating complete elimination of chromatic aberration at about 49% bandwidth of the central working wavelength. The average efficiency of a metalens with a numerical aperture of 0.106 is about 40% over the whole visible spectrum. We also show some examples of full-colour imaging based on this design.

18.
Sci Rep ; 7(1): 17130, 2017 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-29203927

RESUMO

A correction to this article has been published and is linked from the HTML version of this paper. The error has not been fixed in the paper.

19.
Sci Rep ; 7(1): 11096, 2017 09 11.
Artigo em Inglês | MEDLINE | ID: mdl-28894227

RESUMO

An electron bunch passing through a periodic metal grating can emit Smith-Purcell radiation (SPR). Recently, it has been found that SPR can be locked and enhanced at some emission wavelength and angle by excitation of surface plasmon (SP) on the metal substrate. In this work, the generation of a convergent light beam via using the SP-locked SPR is proposed and investigated by computer simulations. The proposed structure is composed of an insulator-metal-insulator (IMI) substrate with chirped gratings on the substrate. The chirped gratings are designed such that a convergent beam containing a single wavelength is formed directly above the gratings when an electron bunch passes beneath the substrate. The wavelength of the convergent beam changes with the refractive index of dielectric layer of the IMI structure, which is determined by the frequency of SP on the IMI substrate excited by the electron bunch. Moreover, reversing the direction of electron bunch will make the emitted light from the proposed structure to switch from a convergent beam to a divergent beam. Finally, the formation of a convergent beam containing red, green and blue lights just above the chirped gratings is also demonstrated. This work offers potential applications in the fields of optical imaging, optical beam steering, holography, microdisplay, cryptography and light source.

20.
Nano Lett ; 17(10): 6345-6352, 2017 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-28892632

RESUMO

Metasurface-based components are known to be one of the promising candidates for developing flat optical systems. However, their low working efficiency highly limits the use of such flat components for feasible applications. Although the introduction of the metallic mirror has been demonstrated to successfully enhance the efficiency, it is still somehow limited for imaging and sensing applications because they are only available for devices operating in a reflection fashion. Here, we demonstrate three individual GaN-based metalenses working in a transmission window with extremely high operation efficiency at visible light (87%, 91.6%, and 50.6% for blue, green, and red light, respectively). For the proof of concept, a multiplex color router with dielectric metalens, which is capable of guiding individual primary colors into different spatial positions, is experimentally verified based on the design of out-of-plane focusing metalens. Our approach with low-cost, semiconductor fabrication compatibility and high working efficiency characteristics offers a way for establishing a complete set of flat optical components for a wide range of applications such as compact imaging sensors, optical spectroscopy, and high-resolution lithography, just named a few.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA