Fabrication Of Photonic Crystals Research Articles

Computer simulations of complicated photonic crystal fabrication based on one-step holographic interference method

A one-step holographic interference method is proposed to create two-dimensional complicated photonic crystals. Only four beams are needed and their wave vector differences comprise two sets of independent reciprocal basic vectors to produce complicated triangular photonic crystals. In our computer simulations, various unitcell patterns are achieved by adjusting the polarization or initial phase of the fourth beam conveniently. These results hold potential in fabrication of abundant complicated periodic microstructures.

Large area colloidal photonic crystals for light trapping in flexible organic photovoltaic modules applied using a roll-to-roll Langmuir-Blodgett method

For the first time, the application of large-area 2D colloidal photonic crystals for light trapping in flexible OPV modules is demonstrated via the study of a broad range of light trapping structures deposited simply and cheaply using our novel roll-to-roll Langmuir–Blodgett technique. Commercially available flexible OPV modules with a size of 10 cm × 14 cm were used. Colloidal silica spheres with diameters ranging from 50 nm to 740 nm were used for the photonic crystal fabrication. The photonic structures made from SiO2 spheres with diameters of 50 nm and 120 nm demonstrate good antireflective properties in the visible and near-infrared spectral range, which have a pronounced positive effect on the photocurrent and the power conversion efficiency in OPV modules at all angles of the light incidence. The 2D photonic crystals made from SiO2 spheres with diameters of 600 nm and 740 nm show strong diffractive scattering of incident light in the forward direction, which results in significant light trapping effects in the OPV modules which again gives rise to an improvement in the cell characteristics. The observed light trapping effects vary only slightly with angle of incidence, suggesting that such photonic crystal layers could be of direct benefit in terms of the response of the OPV modules without the need to track the sun position as it moves across the sky.

Fabrication and Characterization of Polystyrene Colloidal Photonic Crystals on Soft Sodium Alginate Film

Fabrication and Characterization of Polystyrene Colloidal Photonic Crystals on Soft Sodium Alginate Film

Study on the fabrication of composite photonic crystals with high structural stability by co-sedimentation self-assembly on fabric substrates

The Silica/Poly(methylmethacrylate-butylacrylate)[SiO2/P(MMA-BA)] photonic crystals(PCs) with brilliant structural colors were fabricated on fabric substrates by co-sedimentation self-assembly, in which the relatively smaller P(MMA-BA) copolymer particles filled in the interstices among the larger SiO2 microspheres. The fabricated composite PCs were mechanically robust and strongly bonded to the substrate because of the cementing effect caused by the soft P(MMA-BA) copolymer particles filling in the interstices of the SiO2 microspheres like cement filling in the gap and tightly holding stones in a sturdy cement wall. The volume fraction and the size ratios of the two components significantly influenced the structural colors of the composite PCs, and the larger volume fraction could improve the structural stability of the composite PCs, while the smaller size ratios could enhance the brightness of the structural colors of the composite PCs. The composite PCs with both high structural stability and brilliant structural colors have great application prospect for structural coloration of textiles.

Hydrogenated TiO2 nanotube photonic crystals for enhanced photoelectrochemical water splitting

We report the design, fabrication and characterization of novel TiO2 nanotube photonic crystals with a crystalline core/disordered shell structure as well as substantial oxygen vacancies for photoelectrochemical (PEC) water splitting. The novel TiO2 nanotube photonic crystals are fabricated by annealing of anodized TiO2 nanotube photonic crystals in hydrogen atmosphere at various temperatures. The optimized novel TiO2 nanotube photonic crystals produce a maximal photocurrent density of 2.2 mA cm–2 at 0.22 V versus Ag/AgCl, which is two times higher that of the TiO2 nanotube photonic crystals annealed in air. Such significant PEC performance improvement can be ascribed to synergistic effects of the disordered surface layer and oxygen vacancies. The reduced band gap owing to the disordered surface layer and localized states induced by oxygen vacancies can enhance the efficient utilization of visible light. In addition, the disordered surface layer and substantial oxygen vacancies can promote the efficiency for separation and transport of the photogenerated carriers. This work may open up new opportunities for the design and construction of the high efficient and low-cost PEC water splitting system.

Large scale fabrication of asymmetric 2D and 3D micro/nano array pattern structures using multi-beam interference lithography technique for Solar cell texturing application

A method for the large scale fabrication of nano/micro array patterned structure for solar Photovoltaics (PV) is demonstrated by the use of laser interference lithography (LIL) technique. Since micro/nano array patterned structures for photonic arrangement are of increasing importance in higher efficiency solar PV cell concepts, structuring technique and miniaturization in size play a vital role in their realization/fabrication. In this paper, we have designed and modelled multi-beam interference lithography technique (MBIL) for the fabrication of solar PV cells. The generated periodic 1D, 2D and 3D micro/nano array structures are done using MATLAB. The obtained results show that the complexity of the pattern structures varies with the variation in position of beams and angle of incidence. The interference parameters such as wavelength, slit separation, distance between slit and screen influence in generation of periodic array pattern structures. The maximum intensity occurs at an angle of incidence 45 degree. The obtained pattern structures have the periodicity of 0.19 µm for 1064 nm, 0.18 µm for 1024 nm, 0.14 µm for 780 nm, 0.12 µm for 650 nm and 0.07 µm for 565 nm. Depth of the focus is found to be 0.029 µm for 1064 nm, 0.028 µm for 1024 nm, 0.024 µm for 780 nm, 0.020 µm for 650 nm and 0.015 µm for 565 nm. MBIL can be applied in fabrication of 3D photonic crystals, magnetic storage, solar cells, waveguides, calibration grids, Organic Light Emitting Diodes (OLEDs) and functional surfaces of sensors.

Tuning the optical properties of nanoporous anodic alumina photonic crystals by control of allowed voltage range via mixed acid concentration

This study investigates the tunable fabrication of photonic crystals (PCs) based on nanoporous anodic alumina (NAA) templates through modification of nanopore diameter, affecting the PCs optical response. This was realized by controlling phosphoric acid concentration (CPh) and anodization current density. This approach along with chemical etching offers the opportunity to adjust optical band gap in a wide range of wavelengths (from about 400 to 1100 nm). To this end, the effect of CPh on current density and threshold voltage was investigated. To analyze formation mechanism of resulting multilayers and optimize their optical characteristics, the potential ratio, span, cycles and charge density were examined, thereby providing a band gap as narrow as 6 nm. The sensing analysis revealed that the modified multilayer shows enhanced sensitivity to the changes of effective media inside the nanopores. These findings provide insights into the development of both optical sensors and optoelectronic nanodevices based on the NAA-based PCs.

Preparation of perovskite-embedded monodisperse copolymer particles and their application for high purity down-conversion LEDs

Fabrication of angle-independent 3D photonic crystals with organic–inorganic hybrid perovskite nanoparticle-embedded copolymer particles for the extraction of a narrow emissive spectrum without angle-dependency.

Trapping Structural Coloration by a Bioinspired Gyroid Microstructure in Solid State.

In theory, gyroid photonic crystals in butterfly wings exhibit advanced optical properties as a result of their highly interconnected microstructures. Because of the difficulties in synthesizing artificial gyroid materials having periodicity corresponding to visible wavelengths, human-made visible gyroid photonic crystals are still unachievable by self-assembly. In this study, we develop a physical approach-trapping of structural coloration (TOSC)-through which the visible structural coloration of an expanded gyroid lattice in a solvated state can be preserved in the solid state, thereby allowing the fabrication of visible-wavelength gyroid photonic crystals. Through control over the diffusivity and diffusive distance for solvent evaporation, the single-molecular-weight gyroid block copolymer photonic crystal can exhibit desired structural coloration in the solid state without the need to introduce any additives, namely, evapochromism. Also, greatly enhanced reflectivity is observed arising from the formation of porous gyroid nanochannels, similar to those in butterfly wings. As a result, TOSC facilitates the fabrication of the human-made solid gyroid photonic crystal featuring tunable and switchable structural coloration without the synthesis to alter the molecular weight. It appears to be applicable in the fields of optical communication, energy, light-emission, sensors, and displays.

Microsphere lithography for scalable polycrystalline diamond-based near-infrared photonic crystals fabrication

We demonstrate the fabrication of a polycrystalline diamond-based two-dimensional photonic crystal (PhC) slab using microsphere lithography (MSL). First, the essential issues of MSL on rough diamond surfaces are demonstrated. The peak-to-valley value of the rough surfaces is shown as the most important parameter in choosing the appropriate sphere size for the MSL technique. Second, we fabricate a diamond-based PhC composed of a hexagonal lattice of air holes and tuned to have a leaky mode in the near-infrared wavelength region at 1.31μm which is an important telecommunication window. A monolayer of plasma-treated polystyrene microspheres with controllable size and periodicity, combined with a metal mask, are utilised as templates in the fabrication process. The prepared diamond films and photonic crystal are characterised using scanning electron microscopy, atomic force microscopy, Raman spectroscopy, reflection, and transmission measurements. In order to investigate the optical properties of the PhC, the experimental measurements are compared with simulation outputs. The successful employment of MSL on rough diamond films with their unique properties opens the road to the large scale fabrication of highly durable and chemically inert scalable structures.

Experimental sol-gel fabrication and theoretical simulation of one-dimensional photonic crystals with a defect state

One-dimensional multilayer structures of the periodically alternating low refractive index (silica) and high refractive index (titania) materials have been deposited by sol–gel spincoating. The possibility of creating an optical filter by introducing a structural defect in the form of a layer of double thickness is shown theoretically and experimentally. All experimental spectra are in agreement with theoretical spectra calculated by transfer matrix method.

Fabrication of submicron chalcogenide glass photonic crystal by resist-free nanoimprint lithography

We reported the fabrication of submicron photonic crystal with As40Se40Te20 chalcogenide glass by resist-free thermal nanoimprint using a soft stamp. The As40Se40Te20 glass was prepared with melt-quenching method, and measured to have broad transmission range, high linear and nonlinear refractive index, and good thermal stability. Due to the very low glass transition temperature, the thermal nanoimprint was accomplished directly on the resist-free bulk glass with the soft stamp. By choosing suitable imprint condition, submicron chalcogenide glass photonic crystal with the band gap covering telecom wavelength was obtained. Taking advantage of the high nonlinearity of As40Se40Te20 glass, the imprinted PC structure may have potential applications for all-optical switch in optical communications.

Design and fabrication of spectrally selective emitter for thermophotovoltaic system by using nano-imprint lithography

Thermophotovoltaic (TPV) systems have attracted attention as promising power generation systems that can directly convert the radiant energy produced by the combustion of fuel into electrical energy. However, there is a fundamental limit of their conversion efficiency due to the broadband distribution of the radiant spectrum. To overcome this problem, several spectrally selective thermal emitter technologies have been investigated, including the fabrication of photonic crystal (PhC) structures. In this paper, we present some design rules based on finite-a difference time-domain (FDTD) simulation results for tungsten (W) PhC emitter. The W 2D PhC was fabricated by a simple nano-imprint lithography (NIL) process, and inductive coupled plasma reactive ion etching (ICP-RIE) with an isotropic etching process, the benefits and parameters of which are presented. The fabricated W PhC emitter showed spectrally selective emission near the infrared wavelength range, and the optical properties varied depending on the size of the nano-patterns. The measured results of the fabricated prototype structure correspond well to the simulated values. Finally, compared with the performance of a flat W emitter, the total thermal emitter efficiency was almost 3.25 times better with the 2D W PhC structure.

Constructing photocatalyst from β-Bi2O3 photonic crystals for enhanced photocatalytic performance

Photonic crystals with highly ordered structure have presented a prospective application in the design of photocatalysts. Herein, we fabricated visible-light active β-Bi2O3 photonic crystals via a modified sandwich infiltration method. By using the acetylacetone-complexed metal ion precursors, pure β-Bi2O3 photonic crystals with highly ordered structure could be obtained at a calcination temperature of 400 °C. Benefited from the facilitated mass transport in the highly ordered structure, β-Bi2O3 photonic crystals exhibited higher photocatalytic activity towards organic pollutions degradation than porous β-Bi2O3 and β-Bi2O3 nanocrystals. Furthermore, the photonic band gap of β-Bi2O3 photonic crystals could be modulated to overlap its electronic band gap by changing the macropore diameter into 220 nm. Slow photon effect could be observed over the β-Bi2O3 photonic crystals with a pore diameter of 220 nm, which enhanced the electronic band gap absorption and further improved the corresponding photocatalytic activity. The enhanced activity stability of β-Bi2O3 photonic crystals could also be observed. Based on the detection of active species, the degradation mechanism over β-Bi2O3 photonic crystals was discussed. The fabrication of β-Bi2O3 photonic crystals in this study provides experimental guidance for developing photonic crystals with enhanced visible light absorption and photocatalytic activities.

Fabrication of TiO2 photonic crystal by anodic oxidation and their optical sensing properties

TiO2 nanotube arrays with a highly ordered porous structure have been attracting much attention as photocatalysts, membranes, gas sensors, and photoelectrodes in dye-sensitized solar cells, optical interferometric sensing chips and so on. TiO2 nanotube arrays are stable in acid and easy to make using an anodic oxidation process in organic and inorganic electrolytes. Furthermore, photonic crystals, which cause monochromatic or other unique reflection of visible light by a photonic band gap, are very useful materials for light scattering, light harvesting, light reuse, waveguides, optical filters, and lasers. Their periodic potentials cause a photonic band gap and affect electromagnetic wave propagation. In this study, to fabricate TiO2 photonic crystals, we used the anodic oxidation process with the anodizing voltage of the potentiostatic pulse wave, controlling for many variables: high voltage, low voltage, voltage amplitude, the wavelength of the voltage wave, temperature and the surface morphology of titanium foil. The anodizing electrolyte was composed of ammonium fluoride, deionized water and ethylene glycol. The microstructure, periodicity, thickness, and pore diameter of the TiO2 photonic crystals were observed by field emission scanning electron microscope. A periodic structure like a bamboo was observed and the distance between nodes was ∼150nm. The TiO2 photonic crystals were put into the various materials: air, ethyl alcohol, and isopropyl alcohol. The wavelength spectrum from the TiO2 photonic crystals was measured for each material by a charge-coupled device camera. The TiO2 nanotube arrays fabricated by anodic oxidation are shown to be useful for photonic crystals.

Fabrication of two-dimensional special photonic crystals by symmetry-lost beam interference lithography

An optical interference holographic setup with a symmetry-lost five or four-beam configuration is used to obtain two-dimensional special photonic crystals. By altering beam configuration and polarization combinations, novel structures can be achieved, such as tai chi-like, tadpole-like, and flag-like patterns. The experimental results with SU8 photoresist are the same with simulation. Process of two-dimensional special photonic crystals could provide an effective guidance for experimental design and fabrication of other complex structures, and thereby, promote the development and applications of novel photonic crystals.

Photonic crystal waveguides on silicon rich nitride platform.

We demonstrate design, fabrication, and characterization of two-dimensional photonic crystal (PhC) waveguides on a suspended silicon rich nitride (SRN) platform for applications at telecom wavelengths. Simulation results suggest that a 210 nm photonic band gap can be achieved in such PhC structures. We also developed a fabrication process to realize suspended PhC waveguides with a transmission bandwidth of 20 nm for a W1 PhC waveguide and over 70 nm for a W0.7 PhC waveguide. Using the Fabry-Pérot oscillations of the transmission spectrum we estimated a group index of over 110 for W1 PhC waveguides. For a W1 waveguide we estimated a propagation loss of 53 dB/cm for a group index of 37 and for a W0.7 waveguide the lowest propagation was 4.6 dB/cm.

Telecom wavelength emitting single quantum dots coupled to InP-based photonic crystal microcavities

Here we report on the fabrication and optical characterization of InP-based L3 photonic crystal (PhC) microcavities embedded with a medium density InAs/InP quantum dots (QDs) emitting at telecom wavelengths. The QDs are grown by solid source molecular beam epitaxy using a ripening technique. Micro-photoluminescence (μ-PL) measurements of PhC samples reveal sharp cavity modes with quality factors exceeding 8500. QDs emit highly linear-polarized light at telecom wavelengths with resolution-limited spectral linewidth below 50 μeV. Enhanced PL intensity of QDs in PhC is observed in comparison to the PL intensity of QDs in bulk semiconductors. The combination of excitation power-dependent and polarization-resolved μ-PL measurements reveal the existence of an exciton-biexciton system with a small fine-structure splitting.

Fabrication and stabilization of silicon-based photonic crystals with tuned morphology for multi-band optical filtering

One-dimensional silicon-based photonic crystals are formed by the electrochemical anodization of silicon substrates in hydrofluoric acid-based solution using an appropriate current density profile. In order to create a multi-band optical filter, two fabrication approaches are compared and discussed. The first approach utilizes a current profile composed of a linear combination of sinusoidal current waveforms having different frequencies. The individual frequency of the waveform maps to a characteristic stop band in the reflectance spectrum. The stopbands of the optical filter created by the second approach, on the other hand, are controlled by stacking multiple porous silicon rugate multilayers having different fabrication conditions. The morphology of the resulting optical filters is tuned by controlling the electrolyte composition and the type of the silicon substrate. The reduction of sidelobes arising from the interference in the multilayers is observed by applying an index matching current profile to the anodizing current waveform. In order to stabilize the resulting optical filters against natural oxidation, atomic layer deposition of silicon dioxide on the pore wall is employed.

Controllable fabrication of metallic photonic crystals for ultra-sensitive SERS and photodetectors

Metallic photonic crystals with strong light harvesting capabilities for SERS and photodetectors.