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1.
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.

2.
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.

3.
Nat Commun ; 8(1): 187, 2017 08 04.
Artigo em Inglês | MEDLINE | ID: mdl-28775300

RESUMO

Among various flat optical devices, metasurfaces have presented their great ability in efficient manipulation of light fields and have been proposed for variety of devices with specific functionalities. However, due to the high phase dispersion of their building blocks, metasurfaces significantly suffer from large chromatic aberration. Here we propose a design principle to realize achromatic metasurface devices which successfully eliminate the chromatic aberration over a continuous wavelength region from 1200 to 1680 nm for circularly-polarized incidences in a reflection scheme. For this proof-of-concept, we demonstrate broadband achromatic metalenses (with the efficiency on the order of ∼12%) which are capable of focusing light with arbitrary wavelength at the same focal plane. A broadband achromatic gradient metasurface is also implemented, which is able to deflect wide-band light by the same angle. Through this approach, various flat achromatic devices that were previously impossible can be realized, which will allow innovation in full-color detection and imaging.Metasurfaces suffer from large chromatic aberration due to the high phase dispersion of their building blocks, limiting their applications. Here, Wang et al. design achromatic metasurface devices which eliminate the chromatic aberration over a continuous region from 1200 to 1680 nm in a reflection schleme.

4.
Nanotechnology ; 28(42): 425301, 2017 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-28714459

RESUMO

In this study, we propose a set of single-spot experiment to construct a comprehensive model of electron-beam lithography to describe the relation among the incident electrons, resist, and the development conditions such as durations and temperatures. Through the experiments, small feature can be achieved by performing a short-time development due to the high acceleration voltage and large depth of focus of electron-beam system. The singular point in the beginning of the development is also observed in our model and supported by the experimental data. In addition, we verify the characteristic region of each incident spot induced by the point spread function of the electron-beam system. We further fabricate the single line with narrow groove width by utilizing the results from single-spot experiment at low developing temperatures. The line is formed by arranging a series of incident points with a distance close to the characteristic radius. This method can eliminate the proximity effect effectively and thus the groove width is scaled down to 8 nm. By adopting the successful experience in the single line formation, dense array with narrow linewidth is also demonstrated under well suppression of the proximity effect. The minimum groove width of 9 nm with 30 nm pitch is achieved with 5 s development time at -10 °C. Finally, the exceptional capability of pattern transfer is presented due to the high aspect ratio of the resist.

5.
Nanoscale Res Lett ; 12(1): 420, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28629208

RESUMO

We present new normally off GaN high-electron-mobility transistors (HEMTs) that overcome the typical limitations in multi-mesa-channel (MMC) width through modulation of the via-hole-length to regulate the charge neutrality screen effect. We have prepared enhancement-mode (E-mode) GaN HEMTs having widths of up to 300 nm, based on an enhanced surface pinning effect. E-mode GaN HEMTs having MMC structures and widths as well as via-hole-lengths of 100 nm/2 µm and 300 nm/6 µm, respectively, exhibited positive threshold voltages (V th) of 0.79 and 0.46 V, respectively. The on-resistances of the MMC and via-hole-length structures were lower than those of typical tri-gate nanoribbon GaN HEMTs. In addition, the devices not only achieved the E-mode but also improved the power performance of the GaN HEMTs and effectively mitigated the device thermal effect. We controlled the via-hole-length sidewall surface pinning effect to obtain the E-mode GaN HEMTs. Our findings suggest that via-hole-length normally off GaN HEMTs have great potential for use in next-generation power electronics.

6.
Nanotechnology ; 26(16): 165301, 2015 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-25815515

RESUMO

In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm(-2), the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm(-1) at 300.7 cm(-1), which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

7.
Nanotechnology ; 25(47): 475301, 2014 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-25369731

RESUMO

Thermally activated redistribution of Si surface atoms is found to be a crucial factor for the growth of aligned Ge dots on pit-patterned Si(001) substrates. A phenomenon of Si accumulation around the edge of pits significantly alters the substrate surface morphology. As the pit spacing is reduced to below 100 nm, a convex morphology developed between adjacent pits causes a chemical potential distribution that drives the Ge dots into the pits. In addition, the pits of an etching depth greater than 60 nm will evolve into truncated inverted pyramids with sharp base corners that provide deep potential wells for the confinement of Ge dots. Perfectly aligned Ge dots are obtained on pit-patterned Si substrates with this range of pit spacing and etching depth. We also find that the initial geometric shape of the pits does not affect the spatial arrangement of Ge dots.

8.
Nanoscale Res Lett ; 9(1): 596, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25392706

RESUMO

This paper aims to investigate the light output power (LOP) of InGaN-based light-emitting diodes (LEDs) grown on patterned sapphire substrates (PSSs) with different symmetry. The GaN epitaxial layers grown on the hexagonal lattice arrangement PSS (HLAPSS) have a lower compressive strain than the ones grown on the square lattice arrangement PSS (SLAPSS). The quantum-confined Stark effect (QCSE) is also affected by the residual compressive strain. Based on the experimentally measured data and the ray tracing simulation results, the InGaN-based LED with the HLAPSS has a higher LOP than the one with the SLAPSS due to the weaker QCSE within multiple-quantum wells (MQWs).

9.
Am J Ophthalmol ; 155(4): 750-6, 756.e1, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23317649

RESUMO

PURPOSE: To introduce a new approach for short-term external scleral buckling with pneumatic retinopexy for the management of rhegmatogenous retinal detachment with inferior retinal breaks. DESIGN: Retrospective, noncomparative, interventional case series. METHODS: A review of 33 consecutive eyes of 31 patients who underwent external buckling with pneumatic retinopexy for uncomplicated rhegmatogenous retinal detachment with inferior retinal breaks from December 2006 through December 2010. An external buckle was made of a 505 sponge sutured along the blunt side of a 279 tyre (MIRA Inc). The buckle was inserted deeply into the inferior fornix without suture after pneumatic retinopexy and was kept in place for 3 days. Primary and final anatomic outcomes, visual acuity, and adverse events were recorded. RESULTS: All patients tolerated the procedure. The mean follow-up period was 24.0 months (range, 9 to 61 months). Primary success, defined as successful retinal reattachment within 6 months without further treatment, was achieved in 29 (87.9%) eyes. All patients attained final retinal reattachment (100%). Overall, the mean best-corrected visual acuity improved significantly at the end of follow-up (0.30 logarithm of the minimal angle of resolution units; Snellen equivalent, 6/12), compared with the preoperative best-corrected visual acuity (0.82 logarithm of the minimal angle of resolution units; Snellen equivalent, 6/38; P < .001). CONCLUSIONS: Short-term external buckling with pneumatic retinopexy is a novel and effective treatment for rhegmatogenous retinal detachment with inferior retinal breaks, with a comparable success rate with other treatment methods. This approach also can avoid complications of long-term buckle implantation. Further comparative cohort studies may be necessary to compare the clinical efficacy with other conventional operations.


Assuntos
Criocirurgia , Descolamento Retiniano/cirurgia , Perfurações Retinianas/cirurgia , Recurvamento da Esclera/métodos , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Tamponamento Interno , Feminino , Fluorcarbonetos/administração & dosagem , Seguimentos , Humanos , Masculino , Pessoa de Meia-Idade , Decúbito Ventral , Descolamento Retiniano/fisiopatologia , Perfurações Retinianas/fisiopatologia , Estudos Retrospectivos , Resultado do Tratamento , Acuidade Visual/fisiologia , Adulto Jovem
10.
Opt Express ; 21(24): 30065-73, 2013 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-24514556

RESUMO

This paper demonstrates that quantum-confined Stark effect (QCSE) within the multiple quantum wells (MQWs) can be suppressed by the growths of InGaN-based light-emitting diodes (LEDs) on the nano-sized patterned c-plane sapphire substrates (PCSSs) with reducing the space. The efficiency droop is also determined by QCSE. As verified by the experimentally measured data and the ray-tracing simulation results, the suppressed efficiency droop for the InGaN-based LED having the nano-sized PCSS with a smaller space of 200 nm can be acquired due to the weaker function of the QCSE within the MQWs as a result of the smaller polarization fields coming from the lower compressive strain in the corresponding epitaxial layers.

11.
J Nanosci Nanotechnol ; 12(10): 7975-9, 2012 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-23421166

RESUMO

In an aluminum/silicon system, contact conductance (Gc) and Al crystallization can improve by using the hole array on Si, which is built by electron-beam lithography, and increase with decreasing hole size; this improves Gc from 0.004 microS to 13.390 microS. TEM results show Al crystals located inside and near the holes. The ratio of the total Al grain area over the pad area, defined in short form as Ac, is improved from 0.007 to 0.359. An experimental model demonstrates that Gc is proportional to Ac, divided by the square of the interfacial oxygen content. The well-known Al/Si system, chosen as a vehicle, verifies this paper's methodology and provides an alternative to a highly doped or annealing process for Gc improvement. Most significantly, it yields a more robust and well-controlled interface and overcomes obstacles in the newly introduced material system. It also addresses devices with the size narrowed into the deep nanoscale domain. The methodology prevents an inherently non-planar Al/Si interface.

12.
Nanotechnology ; 23(1): 015303, 2012 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-22155926

RESUMO

We demonstrate the effect of the pre-growth heat treatment process on the nucleation properties of Ge dots grown on pit-patterned Si(001) substrates. The prefabricated 200 nm diameter pits inherently evolve into truncated inverted pyramids (TIPs) with (110) base edges and a 7°-9° sidewall slope during heat treatment; this morphology transformation is robust against variations in shape and orientation of the pit patterns. Uniform Ge dots with an areal density of 4 × 10(9) cm(-2) were obtained on the Si substrates having TIPs. Each TIP contains four aligned Ge dots locating symmetrically with respect to (110). These dots exhibit an elliptical dome shape with major axis oriented along (100). The nucleation position, shape and spatial orientation of these Ge dots coincide with the calculated surface chemical potential distribution of the TIP.

13.
Opt Express ; 18(19): 19665-71, 2010 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-20940861

RESUMO

The Taiji symbol is a very old schematic representation of two opposing but complementary patterns in oriental civilization. Using electron beam lithography, we fabricated an array of 70 × 70 gold Taiji marks with 30 nm thickness and a total area of 50 × 50 µm(2) on a fused silica substrate. The diameter of each Taiji mark is 500 nm, while the period of the array is 700 nm. Here we present experimental as well as numerical simulation results pertaining to plasmonic resonances of several Taiji nano-structures under normal illumination. We have identified a Taiji structure with a particularly interesting vortex-like Poynting vector profile, which could be attributed to the special shape and dimensions of the Taiji symbol.


Assuntos
Modelos Teóricos , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Simulação por Computador , Desenho Assistido por Computador , Campos Eletromagnéticos , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Espalhamento de Radiação
14.
Opt Express ; 15(18): 11608-15, 2007 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-19547520

RESUMO

The effect of coupled mode surface plasmon polaritons (SPPs) on the active emission of a nanostructure grating with organic semiconductor material, Alq(3), on the surface was investigated in this study. We report surface plasmon grating coupled emission (SPGCE) from excited organic layer on metal grating in both organic/metal (2-Layer) and organic/metal/organic/metal (4-Layer) structures. The dispersion relation was obtained from angle-resolved photoluminescence measurement. The resultant emission intensity can have up to 6 times enhancement on the 4- Layer device and the Full-Width Half-Maximum (FWHM) is less than 50 nm. The combination of SPPs on organic/metal interface allows specific directional emission and color appearance of Alq(3) fluorophores. Potential applications of such an active plasmonics with enhanced resonant energy emission due to interactions on the organic/metal nano-grating as biosensor were presented and discussed.

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