Circular Nanoholes Research Articles

Local instability of a plate with a circular nanohole under uniaxial tension

The problem of the influence of surface tension on the local instability of a plate under tension is investigated by the example of an infinite plate with a circular nanohole. The method for solving the problem under consideration is based on a previously developed approach for solving problems on local buckling of a thin uniaxially stretched elastic sheet with variously shaped macroholes. The critical (Euler) load, at which the instability occurs, is sought by the Ritz method in framework of the linearized Karman set of equations based on the principle of virtual motions as the smallest positive load giving the minimum of the potential energy of the plate deformation. The generalized plane stress state of the plate with a nanohole is found for its application taking into account surface stresses. The linearized Gurtin-Murdoch relationships for the surface elasticity, the generalized Young-Laplace law, and the Goursat-Kolosov complex potentials are used when deriving analytical dependences for the stress in this plane problem. The deflection of the plate is represented by a double row satisfying the damping condition at infinity and ensuring freedom of motion of hole edges. Numerical calculations are performed for the aluminum plate. Two variants of the elastic properties of a circular hole are considered. Zones of compressing circumferential tensions near the edges of the circular hole with radii 1, 2, and 4 nm under uniaxial tension are constructed. It is shown that the account of the surface stresses decreases the critical load, which has a tendency to decrease in both cases with a decrease in the cut radius in a nanometer variation range.

Fractal Holey Metal Microlenses with Significantly Suppressed Side Lobes and High‐Order Diffractions in Focusing

A fractal holey metal microlens based on finite areas of two‐dimensional arrays of circular nanoholes is reported. Both experimental and simulation results confirm that the fractal holey metal microlens can significantly suppress both the side lobes and high‐order diffractions. The ultra‐thin, planar, and compact design of the fractal holey metal microlenses with excellent focusing performance will benefit many applications such as bioimaging, optical trapping, and integrated optics.

FINITE ELEMENT ANALYSIS OF THE INTERFACE/SURFACE EFFECT ON THE ELASTIC WAVE BAND STRUCTURE OF TWO-DIMENSIONAL NANOSIZED PHONONIC CRYSTALS

In this paper, an interface/surface element is formulated based on the Gurtin–Murdoch interface/surface elasticity theory for accounting the interface/surface effect on the elastic wave propagation in two-dimensional nanosized phononic crystals. The interface/surface element is subsequently incorporated into the finite element procedure for calculating the elastic wave band structure of two-dimensional nanosized phononic crystals with consideration of the interface/surface effect. Elastic wave band structures of two-dimensional phononic crystals comprising a square array of circular or elliptical cylindrical nanoholes embedded in an aluminum matrix are analyzed. Numerical results evidence that the interface/surface effect on the elastic wave band structure can be remarkable when the characteristic size reduces to nanometers.

Nonresonant enhanced optical transmission through the metallic circular nanohole arrays

The nonresonant extraordinary optical transmission (EOT) can achieve broadband transmission, which is significant for the collection and excitation of the broadband light. To obtain broadband transmission, in this paper, we proposed a subwavelength metallic circular nanohole arrays. The transmission properties of the metallic circular nanohole arrays were investigated using the finite element method. Results show that this paradigm structure can achieve broadband transmission. In addition, the effects of the polarization direction, the radius of the holes and the period of the arrays on the transmission property were also studied.

Radiative behaviors of crystalline silicon nanowire and nanohole arrays for photovoltaic applications

The optical absorption of four square arrays of crystalline silicon nanostructures, i.e., circular nanowire array, circular nanohole arrays, square nanowire arrays, and square nanohole arrays, are numerically investigated. The method of rigorous coupled-wave analysis (RCWA) is employed to calculate the absorptivity for the arrays with lattice constant from 100nm to 1500nm. The results indicated that the lattice constant is the foremost structural parameter to determine the ultimate efficiency, and the peaks of ultimate efficiencies for the four different nanostructures always appear around the lattice constant of 600nm. It demonstrates that square nanowire arrays and circular nanohole arrays have great potentials for photovoltaic applications with high ultimate efficiencies and low filling ratios. Moreover, high ultimate efficiencies of all structures can be maintained over a large range of incident angles.

Nanoarchitectures with Controllable Anisotropic Features in Structures and Properties from Simple and Robust Holographic Lithography

Anisotropic nanostructures with precise orientations or sharp corners display unique properties that may be useful in a variety of applications; however, precise control over the anisotropy of geometric features, using a simple and reproducible large-area fabrication technique, remains a challenge. Here, we report the fabrication of highly uniform polymeric and metallic nanostructure arrays prepared using prism holographic lithography (HL) in such a way that the isotropy that can be readily and continuously tuned. The prism position on the sample stage was laterally translated to vary the relative intensities of the four split beams, thereby tuning the isotropy of the resulting polymer nanostructures through the following shapes: circular nanoholes, elliptical nanoholes, and zigzag-shaped nanoarrays. Corresponding large-area, defect-free anisotropic metallic nanostructures could then be fabricated using an HL-featured porous polymer structure as a milling mask. Removal of the polymer mask left zigzag-shaped metallic nanostructure arrays in which nanogaps separated adjacent sharp edges. These structures displayed two distinct optical properties, depending on the direction along which the excitation beam was polarized (longitudinal and transverse modes) incident on the array. Furthermore, bidirectional anisotropic wetting was observed on the anisotropic polymer nanowall array surface.

Surface-Enhanced Resonance Raman Scattering (SERRS) Using Au Nanohole Arrays on Optical Fiber Tips

Circular and bow tie-shaped Au nanoholes arrays were fabricated on gold films deposited on the tips of single-mode optical fibers. The nanostructures were milled using focused ion beam with a high quality control of their shapes and sizes. The optical fiber devices were used for surface-enhanced resonance Raman scattering (SERRS) measurements in both back- and forward-scattering geometries, yielding promising performance in both detection arrangements. The effect of the hole shape on the SERRS performance was explored with the bow tie nanostructures presenting a better SERRS performance than the circular holes arrays. The results present here are another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications.

Light Output Enhancement of InGaN/GaN Light‐Emitting Diodes with Contrasting Indium Tin‐Oxide Nanopatterned Structures

Various nanopatterns on the transparent conducting indium tin oxide (ITO) layer are investigated to enhance the light extraction efficiency of the InGaN/GaN light‐emitting diodes (LEDs). Triangular, square, and circular nanohole patterns with the square and hexagonal lattices are fabricated on the ITO layer by an electron beam lithography and inductively coupled plasma dry etching processes. The circular hole pattern with a hexagonal geometry is found to be the most effective among the studied structures. Light output intensity measurements reveal that the circular hole nanopatterned ITO LEDs with a hexagonal lattice show up to 35.6% enhancement of output intensity compared to the sample without nanopatterns.

Integrated lithography to prepare periodic arrays of nano-objects

We present an integrated lithography method to prepare versatile nano-objects with variable shape and nano-scaled substructure, in wavelength-scaled periodic arrays with arbitrary symmetry. The idea is to illuminate colloid sphere monolayers by polarized beams possessing periodic lateral intensity modulations. Finite element method was applied to determine the effects of the wavelength, polarization and angle of incidence of the incoming beam, and to predict the characteristics of nano-objects, which can be fabricated on thin metal layer covered substrates due to the near-field enhancement under silica colloid spheres. The inter-object distance is controlled by varying the relative orientation of the periodic intensity modulation with respect to the silica colloid sphere monolayer. It is shown that illuminating silica colloid sphere monolayers by two interfering beams, linear patterns made of elliptical holes appear in case of linear polarization, while circularly polarized beams result in co-existent rounded objects, as more circular nano-holes and nano-crescents. The size of the nano-objects and their sub-structure is determined by the spheres diameter and by the wavelength. We present various complex plasmonic patterns made of versatile nano-objects that can be uniquely fabricated applying the inherent symmetry breaking possibilities in the integrated lithography method.

Optical behaviour of thick gold and silver films with periodic circular nanohole arrays

To better understand the enhanced optical transmission observed with an array of nanoholes on optically thick metallic films, an extensive numerical calculation is presented in this paper to relate the scattering modes observed to transmittance spectral behaviour. Surface plasmon polariton Bloch waves, Wood's anomalies and localized surface plasmon resonances at the rim of the nanoholes are investigated based on scattering modes that form the features of the transmission spectrum. The finite difference time-domain method is applied to calculate the transmission intensity from films of gold and silver subjected to variations in geometrical parameters such as film thickness, spatial period of the structures and hole diameter. Analysis of transmission spectra showed that the cut-off frequency of the array of subwavelength holes is mostly defined by the thickness of the film and the diameter of the holes rather than the periodicity of the structures.

Chiroptical Effects in Planar Achiral Plasmonic Oriented Nanohole Arrays

Chiroptical effects are routinely observed in three dimensional objects lacking mirror symmetry or quasi-two-dimensional thin films lacking in-plane mirror symmetry. Here we show that symmetric plasmonic planar arrays of circular nanoholes produced strong chiroptical responses at visible wavelengths on tilting them with respect to the incident light beam due to the collective asymmetric nature of their surface plasmon excitations. This extrinsic chiroptical effect can be stronger than the local chiroptical response in arrays of intrinsically chiral nanoholes and may be useful for chiral sensing and negative refraction.

Two Interacting Circular Nano-Holes with Interface Effect Under Anti-Plane Shear Waves

Two Interacting Circular Nano-Holes with Interface Effect Under Anti-Plane Shear Waves

Development of a mass-producible on-chip plasmonic nanohole array biosensor

We have developed a polymer film based plasmonic device whose optical properties are tuned for measuring biological samples. The device has a circular nanohole array structure fabricated with a nanoimprint technique using a UV curable polymer, and then gold thin film is deposited by electron beam deposition. Therefore, the device is mass-producible, which is also very important for bioaffinity sensors. First the gold film thickness and hole depth were optimized to obtain the maximum dip shift for the reflection spectra. The dip shift is equivalent to the sensitivity to refractive index changes at the plasmonic device surface. We also calculated the variation in reflection spectra by changing the above conditions using the finite-difference time domain method, and we obtained agreement between the theoretical and experimental curves. The nanohole periodicity was adjusted from 400 to 900 nm to make it possible to perform measurements in the visible wavelength region to measure the aqueous samples with less optical absorption. The tuned bottom filled gold nanohole array was incorporated in a microfluidic device covered with a PDMS based microchannel that was 2 mm wide and 20 μm deep. As a proof of concept, the device was used to detect TNF-α by employing a direct immunochemical reaction on the plasmonic array, and a detection limit of 21 ng mL(-1) was obtained by amplification with colloidal gold labeling instead of enzymatic amplification.

Broadband plasmonic microlenses based on patches of nanoholes.

This paper reports a new type of diffractive microlens based on finite-areas of two-dimensional arrays of circular nanoholes (patches). The plasmonic microlenses can focus single wavelengths of light across the entire visible spectrum as well as broadband white light with little divergence. The focal length is determined primarily by the overall size of the patch and is tolerant to significant changes in patch substructure, including lattice geometry and local order of the circular nanoholes. The optical throughput, however, depends sensitively on the patch substructure and is determined by the wavelengths of surface plasmon resonances. This simple diffractive lens design enables millions of broadband plasmonic microlenses to be fabricated in parallel using soft nanolithographic techniques.

Femtosecond laser near-field nanoablation patterning using Mie resonance high dielectric constant particle with small size parameter

We demonstrate near-field nanohole patterning using a Mie resonance, small size parameter particle for nanofabrication technology regardless of substrate’s refractive index. Maximal enhancement factor and nearly smallest spot diameter among the same size dielectric particles are simultaneously obtainable on both low-refractive-index SiO2 and high-refractive-index Si substrates with a 200 nm particle of magnetic quadrupole resonance scattering mode (n∼2.7) at 400 nm excitation wavelength. Circular nanoholes with approximately 100 nm in diameter were fabricated on both substrates using a 200 nm amorphous TiO2 particle (n=2.66+0.024i) even with lower laser fluences than a half ablation threshold of the bare substrates.

Electromagnetic Analysis of Plasmon-Resonance Based All-Optical Magnetic Recording

The electromagnetic analysis of plasmon-resonance-based all-optical magnetic recording is performed. This analysis is based on the treatment of plasmon resonances as an eigenvalue problem for specific boundary integral equations. The plasmon modes which can be excited in circular nanoholes and cylindrical nanoshells by circularly polarized light are theoretically and numerically studied. Dramatic enhancement of circularly polarized light intensity on the nanoscale through the excitation of specific plasmon modes in uniaxial nanostructures is demonstrated.

Lateral confinement of surface plasmons and polarization-dependent optical transmission using nanohole arrays with a surrounding rectangular Bragg resonator

Enhanced optical transmission and surface plasmon resonant cavity effects are studied for subwavelength aperture arrays surrounded by rectangular-shaped Bragg mirrors. A circular nanohole array with a surrounding rectangular Bragg resonator exhibits the introduction of polarization-dependent enhanced optical transmission by constructive and destructive interference effects generated within the cavity. The feasibility for high-density packing of several individually distinct nanohole arrays is demonstrated by also using the Bragg mirrors to block surface plasmon interference between multiple such neighboring devices spaced 5μm apart.

Propagation of Femtosecond Surface Plasmon Polariton Pulses on the Surface of a Nanostructured Metallic Film: Space-Time Complex Amplitude Characterization

Ultrashort surface plasmon polariton (SPP) pulses, propagating on the surface of a nanostructured metallic film, are characterized in space and time using time-resolved spatial-heterodyne imaging. Optical pulses are coupled from free space into various surface modes using a 2D array of circular nanoholes, and spatial amplitude and phase characteristics of the scattered surface field are measured with femtosecond-scale time resolution. Demonstrated in-plane focusing of SPP pulse provides additional electromagnetic field localization with possible applications in SPP nanophotonics, nonlinear surface dynamics, biochemical sensing, and ultrafast surface studies.