Hydrothermal Synthesis of Ordered ZnO Nanorod Arrays by Nanosphere Lithography Method

Ordered ZnO nanorod arrays were hydrothermally synthesized on a patterned GaN substrate formed by a nanosphere lithography method.Firstly,polystyrene(PS)nanospheres were used to self-assemble a close-packed monolayer on the surface of water.Then the monolayer was transferred onto a GaN substrate.Subsequently,magnetron sputtering of SiO2 was used to reduce the size of PS nanospheres and cover the interstitial space between PS nanospheres by SiO_(2) at the same time.After removing the PS nanospheres,periodic seed sites were accomplished on the GaN substrate for ZnO growth.Finally,ordered ZnO nanorod arrays,perpendicular to the substrate,were grown on GaN substrates by a hydrothermal method.This work provides a potential low-cost hydrothermal method for the preparation of ordered semiconductor nanorod arrays.

Nanosphere lithography for optical fiber tip nanoprobes

This paper reports a simple and economical method for the fabrication of nanopatterned optical fiber nanotips.The proposed patterning approach relies on the use of the nanosphere lithography of the optical fiber end facet.Polystyrene(PS)nanospheres are initially self-assembled in a hexagonal array on the surface of water.The created pattern is then transferred onto an optical fiber tip(OFT).The PS monolayer colloidal crystal on the OFT is the basic building block that is used to obtain different periodic structures by applying further treatment to the fiber,such as metal coating,nanosphere size reduction and sphere removal.Ordered dielectric and metallo-dielectric sphere arrays,metallic nanoisland arrays and hole-patterned metallic films with feature sizes down to the submicron scale are achievable using this approach.Furthermore,the sizes and shapes of these periodic structures can be tailored by altering the fabrication conditions.The results indicate that the proposed self-assembly approach is a valuable route for the development of highly repeatable metallo-dielectric periodic patterns on OFTs with a high degree of order and low fabrication cost.The method can be easily extended to simultaneously produce multiple fibers,opening a new route to the development of fiber-optic nanoprobes.Finally,we demonstrate the effective application of the patterned OFTs as surface-enhanced Raman spectroscopy nanoprobes.

Large-scale SiO_2 photonic crystal for high efficiency GaN LEDs by nanospherical-lens lithography

Wafer-scale SiO2 photonic crystal （PhC） patterns （SiO2 air-hole PhC, SiO2-pillar PhC） on indium tin oxide （ITO） layer of GaN-based light-emitting diode （LED） are fabricated via novel nanospherical-lens lithography. Nanoscale polystyrene spheres are self-assembled into a hexagonal closed-packed monolayer array acting as convex lens for expo- sure using conventional lithography instrument. The light output power is enhanced by as great as 40.5% and 61% over those of as-grown LEDs, for SiO2-hole PhC and SiO2-pillar PhC LEDs, respectively. No degradation to LED electrical properties is found due to the fact that SiO2 PhC structures are fabricated on ITO current spreading electrode. For SiO2- pillar PhC LEDs, which have the largest light output power in all LEDs, no dry etching, which would introduce etching damage, was involved. Our method is demonstrated to be a simple, low cost, and high-yield technique for fabricating the PhC LEDs. Furthermore, the finite difference time domain simulation is also performed to further reveal the emission characteristics of LEDs with PhC structures.

Discrete Dipole Approximation Aided Design Method for Nanostructure Arrays

A discrete dipole approximation （DDA） aided design method is proposed to determine the parameters of nanostructure arrays. The relationship between the thickness, period and extinction efficiency of nanostructure arrays for the given shape can be calculated using the DDA. Based on the calculated curves, the main parameters of the nanostructure arrays such as thickness and period can be determined. Using this aided method, a rhombic sliver nanostructure array is designed with the determinant parameters of thickness （40 nm） and period （440 nm）. We further fabricate the rhombic sliver nanostructure arrays and testify the character of the extinction spectra. The obtained extinction spectra is within the visible range and the full width at half maximum is 99nm, as is expected.

Enhanced light emission from InGaN/GaN quantum wells by using surface plasmonic resonances of silver nanoparticle array

The effect of silver nanostructures prepared by nanosphere lithography on the photoluminescence（PL） properties of blue-emitting In Ga N/Ga N quantum wells（QWs） is studied. Arrays of silver nanoparticles are fabricated to yield a collective surface plasmonic resonance（SPR） near to the QWs emission wavelength. A large enhancement in peak PL intensity is observed, when the induced SPR wavelength of the nanoparticles on the QWs sample matches the QWs emission wavelength. The study proves that the SPRs could enhance the light emission efficiency of semiconductor material.

Enhancing light extraction of GaN-based blue light-emitting diodes by a tuned nanopillar array

Surface patterning of p-GaN to improve the light extraction efficiency of GaN-based blue light-emitting diodes(LEDs) has been investigated. Periodic nanopillar arrays on p-GaN have been fabricated by polystyrene(PS) nanosphere lithography; the diameter of the nanopillars can be tuned to optimize the electrical and optical properties of the LEDs. The electroluminescence intensity of the nanopillar-patterned LEDs is better than that of conventional LEDs; the greatest enhancement increased the intensity by a factor of 1.41 at a 20 mA injection current. The enhancements can be explained by a model of bilayer film on a GaN substrate. This method may serve as a practical approach to improve the efficiency of light extraction from LEDs.

Nonlinear optical behaviors in a silver nanoparticle array at different wavelengths

The optical nonlinearities of an Ag nanoparticle array are investigated by performing Z-scan measurements at the selected wavelengths （400, 600, 650, and 800 nm）. The nonlinear refraction index in the resonant region （around 400 nm） exhibits a significant enhancement by two orders compared with that in the off-resonant region （around 800 nm））, and exhibits an sign alternation of the resonant nonlinear absorption, which results in a negligible nonlinear absorption at a certain excitation intensity. Moreover, a low degree of nonlinear absorption was measured at the edges of the resonant region （600 and 650 nm）, which is attributed to the competition of the saturated absorption and the two-photon absorption processes.

Light trapping and optical absorption enhancement in vertical semiconductor Si/SiO_2 nanowire arrays

The full potential of optical absorption property must be further cultivated before silicon（Si） semiconductor nanowire（NW） arrays become available for mainstream applications in optoelectronic devices. In this paper, we demonstrate both experimentally and theoretically that an SiO_2 coating can substantially improve the absorption of light in Si NW arrays.When the transparent SiO_2 shell is coated on the outer layer of Si NW, the incident light penetrates better into the absorbing NW core. We provide the detailed theoretical analysis by a combination of finite-difference time-domain（FDTD） analysis.It is demonstrated that increasing the thickness of the dielectric shell, we achieve 1.72 times stronger absorption in the NWs than in uncoated NWs.

Biomimetic Corrugated Silicon Nanocone Arrays for Self-Cleaning Antireflection Coatings

Corrugated silicon nanocone(SiNC)arrays have been fabricated on a silicon wafer by two polystyrene-sphere-monolayer-masked etching steps in order to create high-performance antireflective coatings.The reflectance was reduced from above 35%to less than 0.7%in the range 400-1050 nm,and it remained below 0.5%at incidence angles up to 70°at 632.8 nm for both s-and p-polarized light.The fluorinated corrugated SiNC array surface exhibits superhydrophobic properties with a water contact angle of 164°.

Highly effective and reproducible surface-enhanced Raman scattering substrates based on Ag pyramidal arrays

Close-packed Ag pyramidal arrays have been fabricated by using inverted pyramidal pits on Si as a template and used to generate plentiful and homogeneous surface-enhanced Raman scattering （SERS） hot sites. The sharp nanotip and the four edges of the Ag pyramid result in strong electromagnetic field enhancement with an average enhancement factor （EF） of 2.84 × 10^7. Moreover, the features of the close-packed Ag pyramidal array can be well controlled, which allows SERS substrates with good reproducibility to be obtained. The relative standard deviation （RSD） was lower than 8.78% both across a single substrate and different batches of substrates.

Silver-coated elevated bowtie nanoantenna arrays： Improving the near-field enhancement of gap cavities for highly active surface-enhanced Raman scattering

Improving hot-spot intensity is a key issue in surface-enhanced Raman scattering （SERS）. The bowtie nanoantenna （BNA） is an effective device used to concentrate light energy into a nanoscale volume and produce strong hot spots. Nanosphere lithography （NSL） is a large-area and low-cost technique to produce BNA arrays; however, the SERS activity of NSL-fabricated BNAs is limited. In this paper, we present a simple method to improve the SERS activity of conventional NSL-fabricated BNAs by modifying their geometry. The new configuration is termed ＂silver-coated elevated bowtie nanoantenna＂ （SCEBNA）. SCEBNAs perform intensive near-field enhancement in the gap cavities owing to the integrated contribution of the ＂lightning rod＂ effect, resonance coupling, and the formation of the plasmonic Fabry-Perot cavity. Experimental measurements and finite-difference time-domain simulations revealed that the hot-spot intensity and the substrate enhancement factor can be optimized by adjusting the silver thickness. The optimal sample has the capability of trace-amount detection with fine reproducibility.

Fabrication and properties of well-ordered arrays of single-crystalline NiSi2 nanowires and epitaxial NiSi2/Si heterostructures

In this study, we reported the design, fabrication, and characterization of well- ordered arrays of vertically-aligned, epitaxial NiSi2/Si heterostructures and single- crystalline NiSi2 nanowires on （001）Si substrates. The epitaxial NiSi2 with {111} facets was found to be the first and the only silicide phase formed inside the Si nanowires after annealing at a temperature as low as 300℃. Upon annealing at 500 ℃ for 4 h, the residual parts of Si nanowires were completely consumed and the NiSi2/Si heterostructured nanowires were transformed to fully silicided NiSi2 nanowires. XRD, TEM and SAED analyses indicated that all the NiSi2 nanowires were single crystalline and their axial orientations were parallel to the [001] direction. The obtained vertically-aligned NiSi2 nanowires, owing to their well-ordered arrangement, single-crystalline structure, and low effective work function, exhibit excellent field-emission properties with a very low turn-on field of 1.1 V/m. The surface wettability of the nanowires was found to switch from hydrophobic to hydrophilic after the formation of NiSi2 phase and the measured water contact angle decreased with increasing extent of Ni silicidation. The increased hydrophilicity can be explained by the Wenzel model. The obtained results present the exciting prospect that the new approach proposed here will provide the capability to fabricate other highly-ordered, vertically-aligned fully silicided nanowire arrays and may offer potential applications in constructing vertical silicide-based nanodevices.

To increase more than 10% in efficiency of perovskite solar cells by using nanoholes SnO_(2)

The perovskite solar cells have been intensively investigated these years due to their premium electrical and optical properties as well as huge potential for application.In order to further increase the power conversion efficiency(PCE) of the thin film perovskite solar cells, light management should be taken into consideration. Herein, we apply a lithography method to transfer randomly distributed polystyrene(PS) nanospheres into the electron transporting SnO_(2) layer, by means of which, a nanoholes structure is formed. Finally, we get a nanostructured perovskite layer under low temperature(less than 150 ℃).The depth of SnO_(2) nanoholes is around 60 nm when the device is fabricated with 300-nm PS, and 150 nm in depth when 500-nm PS is used. The device gains PCE of 17.97%,which is 12.3% higher than that with planar electrontransporting SnO_(2) layer and 300-nm CH_(3)NH_(3)PbI_(3) layer.Our findings provide an applicable method to improve the light absorption, which can not only make the absorbing layer of lead-based perovskite solar cells thinner to help decrease the content of lead, but also increase the PCE of non-lead perovskite devices.