Periodic Nanohole Arrays Research Articles

Fabrication of periodic nano-hole array on GaN surface by fs laser for improvement of extraction efficiency in blue LED

For micro/nanofabrication of Gallium nitride (GaN), we developed wet-chemical-assisted femtosecond-laser ablation method. Obtained ablation craters exhibit higher quality and better uniformity without residual debris compared with those produced by femtosecond-laser ablation in air followed by etching. Multi-scan irradiation was performed to fabricate periodic structure composed of high aspect ratio nano-holes using the wet-chemical-assisted ablation method. The aspect ratio is much improved (∼1.6) compared to the case of using single pulse irradiation. This periodic structure of uniform nano-holls arranged on GaN surface can act as a two-dimensional photonic crystal which is expected to enhance a light extraction efficiency of blue LED.

Genetically Modifiable Flagella as Templates for Silica Fibers: From Hybrid Nanotubes to 1D Periodic Nanohole Arrays

Genetically Modifiable Flagella as Templates for Silica Fibers: From Hybrid Nanotubes to 1D Periodic Nanohole Arrays

Self-Assembled Plasmonic Nanohole Arrays

We present a simple and massively parallel nanofabrication technique to produce self-assembled periodic nanohole arrays over a millimeter-sized area of metallic film, with a tunable hole shape, diameter, and periodicity. Using this method, 30 x 30 microm(2) defect-free areas of 300 nm diameter or smaller holes were obtained in silver; this area threshold is critical because it is larger than the visible wavelength propagation length of surface plasmon waves ( approximately 27 microm) in the silver film. Measured optical transmission spectra show highly homogeneous characteristics across the millimeter-size patterned area, and they are in good agreement with FDTD simulations. The simulations also reveal intense electric fields concentrated near the air/silver interface, which was used for surface-enhanced Raman spectroscopy (SERS). Enhancement factors (EFs) measured with different hole shape and excitation wavelengths on the self-assembled nanohole arrays were 10(4)-10(6). With an additional Ag electroless plating step, the EF was further increased up to 3 x 10(6). The periodic nanohole arrays produced using this tunable self-assembly method show great promise as inexpensive SERS substrates as well as surface plasmon resonance biosensing platforms.

Extending nanosphere lithography for the fabrication of periodic arrays of subwavelength metallic nanoholes

In this work we extend the classical nanosphere lithography method to the fabrication of subwavelength metallic nanohole arrays. By combining the reactive ion etching of self-assembled films of polystyrene nanospheres with metal deposition, ordered arrays of nanoholes of different sizes were fabricated. These structures exhibit a well-defined optical response different from that of the regular triangular array and continuous metallic film.

Self‐Assembly of Ordered Semiconductor Nanoholes by Ion Beam Sputtering

Periodic nanohole arrays are formed on a Ge substrate by self-assembly using focused ion beam sputtering at normal incidence with an energy of 5 keV. The figure shows an SEM image of a hexagonally ordered hole domain that has hexagonally ordered quantum dots—20 nm diameter and 3 nm height—around each hole The structured Ge has high surface area and a considerably blue-shifted energy gap.

Localized surface-plasmon resonances in periodic nondiffracting metallic nanoparticle and nanohole arrays

We compare the optical response of periodic nondiffracting metallic nanoparticle and nanohole arrays. Experimental data from both structures show a pronounced minimum in their wavelength-dependent transmittance that, through numerical modeling, we identify as being due to the excitation of localized surface-plasmon resonances associated with the nanoparticles/nanoholes. Our main finding is that, while the optical response of the nanoparticle arrays is largely independent of interparticle separation, the response from nanohole arrays shows a marked dependence on interhole separation. We attribute this effect to coupling between localized surface-plasmon resonances mediated by the symmetric surface plasmon-polaritons associated with the metal film. Further numerical modeling supports this view.

Gold nanohole arrays for biochemical sensing fabricated by soft UV nanoimprint lithography

We report on results of fabrication and optical characterisation of sub-250 nm periodic gold nanohole arrays on glass by using UV nanoimprint lithography (UV-NIL) combined with both reactive ion etching (RIE) and Cr/Au lift-off processes. The transmission spectra of the fabricated nanohole gratings were measured for different hole diameters and periods. We also show preliminary results of chemical sensing after surface modification of the gold hole arrays. In agreement with the theoretical prediction, we found that any change in the dielectric index of the surrounding environment of the metallic array produces a transmission peak red shift.

LOCALIZED SURFACE PLASMON OF THIN GOLD FILM WITH PERIODIC ARRAYS OF NANOHOLES

The localized surface plasmon (LSP) resonances properties of periodic arrays of nanoholes in thin gold films are investigated by using the method of discrete dipole approximation (DDA). The surface plasmon polaritons (SPPs) play important roles in amplification or suppression of the LSP resonances in the film. The LSP-SPP coupling is affirmed based on the extinction spectra calculated by the DDA. The intensity of the LSP resonances can be controlled through changing the edge-to-edge separation distances between nanoholes, the number and the diameter of the nanoholes. The calculations also indicate that the LSP resonance peak decreases with increasing the thickness of the gold film.

Multifunctional plasmonic sensors on low-cost subwavelength metallic nanoholes arrays

Localized surface plasmon resonance (LSPR) sensing is combined with surface enhanced Raman scattering (SERS) detection on periodic arrays of subwavelength metallic nanoholes for the first time. LSPR sensors provide detection of molecular adsorption in both transmission and reflectivity modes with sensitivity greater that 300 nm/RIU and a spectral shift of 16 nm in the case of binding a monolayer of p-aminothiophenol (p-ATP) molecules. Subsequent SERS analysis enables identification of the adsorbed p-ATP molecule, its structure and orientation on the metal surface. This synergistic LSPR-SERS approach on low-cost metallic films perforated with periodic arrays of subwavelength nanoholes opens a route for molecular dual-modal detection to be integrated in lab-on-chip systems to increase the reliability of biological detection.

Genetically Modifiable Flagella as Templates for Silica Fibers: From Hybrid Nanotubes to 1D Periodic Nanohole Arrays

AbstractBacterial flagellum is a protein nanotube that is helically self‐assembled from thousands of a protein subunit called flagellin. The solvent‐exposed domain of each flagellin on the flagella is genetically modifiable, in that a foreign peptide can be genetically inserted into this domain, leading to the high‐density display of this foreign peptide on the surface of flagella. In this work, wild‐type and genetically engineered flagella (inner diameter of ∼2 nm and outer diameter of ∼14 nm) detached from the surface of Salmonella bacterial cells are used as templates to site‐specifically form silica sheaths on the flagellar surface, resulting in the formation of double‐layered silica/flagella nanotubes. The flagella templates inside the silica/flagella nanotubes can be removed to obtain silica nanotubes by calcining the nanotubes at high temperature (550°C). Further calcination of the silica nanotubes at a higher temperature (800 °C) leads to the formation of a periodic nanohole array along the silica fibers with a center‐to‐center nanohole spacing of ∼79 nm. It is demonstrated that the double‐layered silica‐flagella nanotubes can be used for selective CdTe quantum dot uptake into the inner channels or selective Au nanoparticle coating on the outer wall of the nanotubes due to the different chemistry between inner flagellum core (protein) and outer silica wall of the nanotubes. It is also found that flagella displaying different peptides result in different morphologies of the silica nanotubes. This work suggests that the monodisperse diameter and genetically tunable surface chemistry of the flagella can be exploited for the fabrication of silica nanotubes with uniform diameter and controllable morphologies as well as silica nanofibers decorated with periodic nanohole arrays.

Light modulation with nanopatterned diffractive microelectromechanical system pixels

The design, fabrication, and testing of a microelectromechanical system (MEMS) optical modulator is presented. Polarization effects of noncircular holes on reflectivity are examined. Thermal nanoimprint lithography is used to form an array of 150nm diameter nanoholes in a 60nm thick metal film on a silicon-on-insulator wafer. A quartz superstrate with an indium tin oxide electrode and a photoresist spacer is used to electrostatically actuate the MEMS pixel. The motion of the pixel in relation to the superstrate causes shifts in the wavelengths of optical interference from the periodic nanohole array. An optical modulation depth of over 67% is demonstrated with this modulation method. Dynamic modal analysis is also presented.

Fabrication of Large Area Periodic Nanostructures Using Nanosphere Photolithography

Large area periodic nanostructures exhibit unique optical and electronic properties and have found many applications, such as photonic band-gap materials, high dense data storage, and photonic devices. We have developed a maskless photolithography method—Nanosphere Photolithography (NSP)—to produce a large area of uniform nanopatterns in the photoresist utilizing the silica micro-spheres to focus UV light. Here, we will extend the idea to fabricate metallic nanostructures using the NSP method. We produced large areas of periodic uniform nanohole array perforated in different metallic films, such as gold and aluminum. The diameters of these nanoholes are much smaller than the wavelength of UV light used and they are very uniformly distributed. The method introduced here inherently has both the advantages of photolithography and self-assembled methods. Besides, it also generates very uniform repetitive nanopatterns because the focused beam waist is almost unchanged with different sphere sizes.

Nanoplasmonic biosensing with focus on short-range ordered nanoholes in thin metal films (Review)

The resonance conditions for excitation of propagating surface plasmons at planar metal/dielectric interfaces and localized surface plasmons associated with metal nanostructures are both sensitive to changes in the interfacial refractive index. This has made these phenomena increasingly popular as transducer principles in label-free sensing of biomolecular recognition reactions. In this article, the authors review the recent progress in the field of nanoplasmonic bioanalytical sensing in general, but set particular focus on certain unique possibilities provided by short-range ordered nanoholes in thin metal films. Although the latter structures are formed in continuous metal films, while nanoparticles are discrete entities, these two systems display striking similarities with respect to sensing capabilities, including bulk sensitivities, and the localization of the electromagnetic fields. In contrast, periodic arrays of nanoholes formed in metal films, most known for their ability to provide wavelength-tuned enhanced transmission, show more similarities with conventional propagating surface plasmon resonance. However, common for both short-range ordered and periodic nanoholes formed in metal films is that the substrate is electrically conductive. Some of the possibilities that emerge from sensor templates that are both electrically conductive and plasmon active are discussed and illustrated using recent results on synchronized nanoplasmonic and quartz crystal microbalance with dissipation monitoring of supported lipid bilayer formation and subsequent biomolecular recognition reactions. Besides the fact that this combination of techniques provides an independent measure of biomolecular structural changes, it is also shown to contribute with a general means to quantify the response from nanoplasmonic sensors in terms of bound molecular mass.

A MEMS light modulator based on diffractive nanohole gratings

We present the design, fabrication, and testing of a microelectromechanical systems (MEMS) light modulator based on pixels patterned with periodic nanohole arrays. Flexure-suspended silicon pixels are patterned with a two dimensional array of 150 nm diameter nanoholes using nanoimprint lithography. A top glass plate assembled above the pixel array is used to provide a counter electrode for electrostatic actuation. The nanohole pattern is designed so that normally-incident light is coupled into an in-plane grating resonance, resulting in an optical stop-band at a desired wavelength. When the pixel is switched into contact with the top plate, the pixel becomes highly reflective. A 3:1 contrast ratio at the resonant wavelength is demonstrated for gratings patterned on bulk Si substrates. The switching time is 0.08 ms and the switching voltage is less than 15V.

Templated fabrication of sub-100 nm periodic nanostructures

Periodic polymer nanoposts and metal nanohole arrays with tunable size have been fabricated by templating from spin-coated two-dimensional non close-packed colloidal crystal-polymer nanocomposites.

带有周期排列纳米孔结构金薄膜的散射光学性质

带有周期排列纳米孔结构金薄膜的散射光学性质

The surface plasmon resonance of metal-film nanohole arrays

In this paper we investigated the enhanced transmission and surface plasmon resonance through a thin gold film with a periodic array of subwavelength nanoholes. Both freestanding gold-film nanohole arrays and gold-film nanohole arrays deposited on a gallium arsenide (GaAs) substrate are considered. Periodic arrays of nanoholes exhibit two different surface plasmon resonance features: localized waveguide resonance and the well-recognized photonic crystal resonance. The tangential electric field component E y is nonzero only in the hole region for a freestanding gold-film nanohole array, but it can exist in the hole region and in the metallic region for a gold-film nanohole array deposited on a GaAs substrate.

Imaging three-dimensional light propagation through periodic nanohole arrays using scanning aperture microscopy

The authors introduce a technique for three-dimensional (3D) imaging of the light transmitted through periodic nanoapertures using a scanning probe to perform optical sectioning microscopy. For a 4×4 nanohole array, the transmitted light displays intensity modulations along the propagation axis, with the maximum intensity occurring at 450 μm above the surface. The propagating fields show low divergence, suggesting a beaming effect induced by the array. At distances within 25 μm from the surface, they observe subwavelength confinement of light propagating from the individual nanoholes. Hence, this technique can potentially be used to map the 3D distribution of propagating light, with high spatial resolution.

Periodic nanohole arrays with shape-enhanced plasmon resonance as real-time biosensors

The authors report a combination of the enhanced transmission effect and shape resonances in a periodic array of nanoscale double-hole structures in a gold film to enhance the detection sensitivity of surface plasmon biosensors. Finite-difference time-domain calculations are used to quantify field enhancement at the apexes of the double-hole structure. The double-hole array was used to measure the formation of a self-assembled monolayer and for real-time sensing of protein adsorption onto a gold surface. This result demonstrates the potential to integrate propagating surface plasmons and localized shape resonances to improve real-time biosensors.

Wafer-Scale Periodic Nanohole Arrays Templated from Two-Dimensional Nonclose-Packed Colloidal Crystals

This communication reports a simple yet versatile nonlithographic approach for fabricating wafer-scale periodic nanohole arrays from a large variety of functional materials, including metals, semiconductors, and dielectrics. Spin-coated two-dimensional (2D) nonclose-packed colloidal crystals are used as first-generation shadow masks during physical vapor deposition to produce isolated nanohole arrays. These regular nanoholes can then be used as second-generation etching masks to create submicrometer void arrays in the substrates underneath. Complex patterns with micrometer-scale resolution can be made by standard microfabrication techniques for potential device applications. These 2D-ordered nanohole arrays may find important technological applications ranging from subwavelength optics to interferometric biosensors.