Alumina Photonic Crystals Research Articles

Semiconductor Nanoporous Anodic Alumina Photonic Crystals as a Model Photoelectrocatalytic Platform for Solar Light‐Driven Reactions

In this study, nanoporous anodic alumina distributed‐Bragg reflectors (NAA–DBRs) functionalized with tungsten trioxide (WO3) are used as prototype photoelectrocatalysts (PEC) for harnessing the slow photon effect to maximize photon‐to‐electron conversion efficiency under UV–visible–NIR illumination. NAA–DBR structures are structurally engineered by anodization, where their characteristic photonic stopband is precisely tuned along specific positions of the UV–visible spectrum. Subsequent atomic layer deposition is employed to coat the inner surface of these porous structures with WO3 semiconductor layers. Upon the application of overpotential bias, these platforms reveal excellent electron–hole pair separation to boost photoelectrocatalytic reactions. Photoelectrochemical degradation of methylene blue is used as a model reaction to elucidate enhancements associated with structural and optoelectronic arrangements. Notably, precise spectral alignment between the photonic stopband's red edge and the absorbance band of methylene blue enhances the degradation performance through the slow photon effect. Applying an overpotential bias further improves the photodegradation performance through efficient charge separation. These systems outperform comparable structures in this model reaction, achieving a maximum kinetic rate of 13.7 ± 2.0 h−1. The findings create new opportunities to develop high‐performing PEC technologies harnessing light–matter interactions.

Nanoscale Photonic Barcodes Based on Anodic Alumina Photonic Crystal Heterostructures: Implications for Optical Communications, Data Storage, and Sensing

Nanoscale Photonic Barcodes Based on Anodic Alumina Photonic Crystal Heterostructures: Implications for Optical Communications, Data Storage, and Sensing

Tailoring Tamm Plasmon Resonances in Dielectric Nanoporous Photonic Crystals.

The fields of plasmonics and photonic crystals (PCs) have been combined to generate model light-confining Tamm plasmon (TMM) cavities. This approach effectively overcomes the intrinsic limit of diffraction faced by dielectric cavities and mitigates losses associated with the inherent properties of plasmonic materials. In this study, nanoporous anodic alumina PCs, produced by two-step sinusoidal pulse anodization, are used as a model dielectric platform to establish the methodology for tailoring light confinement through TMM resonances. These model dielectric mirrors feature highly organized nanopores and narrow bandwidth photonic stopbands (PSBs) across different positions of the spectrum. Different types of metallic films (gold, silver, and aluminum) were coated on the top of these model dielectric mirrors. By structuring the features of the plasmonic and photonic components of these hybrid structures, the characteristics of TMM resonances were studied to elucidate effective approaches to optimize the light-confining capability of this hybrid TMM model system. Our findings indicate that the coupling of photonic and plasmonic modes is maximized when the PSB of the model dielectric mirror is broad and located within the midvisible region. It was also found that thicker metal films enhance the quality of the confined light. Gas sensing experiments were performed on optimized TMM systems, and their sensitivity was assessed in real time to demonstrate their applicability. Ag films provide superior performance in achieving the highest sensitivity (S = 0.038 ± 0.001 nm ppm-1) based on specific binding interactions between thiol-containing molecules and metal films.

Desorption Kinetics Profiling of Volatile Organic Compounds in Nanoporous Anodic Alumina Photonic Crystal Optical Microcavities

Desorption Kinetics Profiling of Volatile Organic Compounds in Nanoporous Anodic Alumina Photonic Crystal Optical Microcavities

(Invited) tamm Plasmon Resonance Sensors Based on Nanoporous Anodic Alumina Photonic Crystals

Nanoporous Anodic Alumina (NAA) is a material with growing interest in nanotechnology and for biological and medical applications. It is a cost-effective nanostructured material obtained by the electrochemical etching of aluminum in acidic electrolytes at the adequate conditions of applied voltage or current, temperature and electrolyte composition [1-4]. The precise control over the diameter of the nanopore allows to create periodic variations of nanopore’s diameter in deep and obtain different photonic crystals e.g.., Gradient-index filters, microcavities, Distributed Bragg Reflectors, etc [5-6]. The optical properties of NAA depend on its nanoporous structure and of its functionalized surface. NAA can be used to fabricate hybrid photonic structures by gold coating on nanoporous anodic alumina photonic crystals surface (NAA-PCs) [7]. In this metal-dielectric photonic structure, we can observe effects of an enhancement of the surface plasmon resonance due to absorption of the light at the interface of metallic layer and the NAA photonic crystal.Tamm plasmon resonance (TPR) can be tuned by engineering the properties and characteristics of the metal film and the porous photonic structure, providing new opportunities to achieve unique plasmonic−photonic structures for different applications (optical switching, lasing, light emission, surface-enhanced spectroscopy, and sensing). One interesting application of TPR is the use as a sensing platform taking advantage of its exceptional optical properties to confine/amplify the light-matter interactions [8-9]. The sensing performance of TPR-NAA−PCs is assessed by the infiltration of their structure with analytical solutions, producing a spectral shift in the Tamm plasmonic resonance. In this work, we evaluate the structural geometry and the optical properties of TPR-NAA-PCs and the assessment of TPR-NAA-PCs as a sensing platform.Figure 1a shows the reflectance spectrum for a TPR-NAA–PCs structure. The spectrum shows the photonic bandgap and the absorption narrow-line associated with the resonant recirculation of light within the plasmon-photonic system. Figure 1b shows the sensing performance of TPR-NAA-PCS. Red-shift on the position of the TPR-NAA-PCs is observed due to the refractive index variation when the nanopores are infiltrated of different analytical solutions (water- ethylene glycol)AcknowledgmentsThis work was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) PDI2021- 128342OB-I00, by the Agency for Management of University and Research Grants (AGAUR) ref. 2017- SGR-1527, COST Action 20126 - NETPORE and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award.

Anodic alumina photonic crystals: Structure engineering, optical properties and prospective applications

Anodic alumina photonic crystals: Structure engineering, optical properties and prospective applications

Structural stability and optical properties of 1D photonic crystals based on porous anodic alumina after annealing at different temperatures

Porous anodic alumina (PAA) photonic crystals with a photonic stop-band (PSB) placed in the mid-infrared (MIR) spectral region represent a promising approach for increasing of gas sensors sensitivity. An onion-like layered distribution of anionic impurities is a hallmark of PAA, and its presence is generally considered to demarcate the boundary between transparent and opaque ranges in the infrared spectral region. Here, we study the effect of annealing in the temperature range of 450 °C–1 100 °C on the structural stability and optical properties in photonic crystals based on PAA fabricated by pulse anodization in oxalic acid. Pulse sequences were selected in a way to obtain photonic crystals of different periodic structures with a PSB located in visible and MIR spectral regions. The first photonic crystal was composed of layers with gradually changing porosity, whereas the second photonic crystal consisted of a sequentially repeated double-layer unit with an abrupt change in porosity. We investigated the response of alumina with rationally designed porosities and different arrangements of porous layers for high-temperature treatment. The microstructure (scanning electron microscopy), phase composition (x-ray diffraction), and optical properties (optical spectroscopy) were analysed to track possible changes after annealing. Both photonic crystals demonstrated an excellent structural stability after 24 h annealing up to 950 °C. At the same time, the evaporation of the anionic impurities from PAA walls caused a shift of the PSB towards the shorter wavelengths. Furthermore, the annealing at 1 100 °C induced a high transparency (up to 90%) of alumina in MIR spectral region. It was shown thus that properly selected electrochemical and annealing conditions enable the fabrication of porous photonic crystals with the high transparency spanning the spectral range up to around 10 μm.

Engineering of Solid-State Random Lasing in Nanoporous Anodic Alumina Photonic Crystals

Engineering of Solid-State Random Lasing in Nanoporous Anodic Alumina Photonic Crystals

Tuning intrinsic photoluminescence from light-emitting multispectral nanoporous anodic alumina photonic crystals

To control and harness the intrinsic photoluminescence of solid-state, light-emitting materials produced by self-organization approaches remain challenging. This study demonstrates how the intrinsic broadband photoluminescence emission from nanoporous anodic alumina (NAA) produced by anodization of aluminum in oxalic acid electrolyte can be precisely tuned by engineering its structure in the form of photonic crystals (PCs). A combination of pulse and constant anodization in distinct acid electrolytes makes it possible to engineer a novel heterogeneous optical structure consisting of two layers: (i) a non-emitting, light-filtering layer in the form of multi-spectral nanoporous anodic alumina photonic crystals (MS–NAA–PCs) on its top (i.e., 58 µm thick and average pore diameter of 17 nm) and (ii) an intrinsically light-emitting layer of NAA at its bottom (i.e., 50 µm thick an average pore diameter of 40 nm). MS–NAA–PCs are engineered to feature three intense, well-resolved photonic stopbands (PSBs), the positions of which are spaced at specific regions of the visible spectrum from ∼380 to 560 nm. It is demonstrated that the PSBs of the non-emitting MS–NAA–PCs on top of the heterogeneous optical structure act as a light-filtering component, which makes it possible to narrow and tune the characteristically broad, Gaussian-like photoluminescence emission from the underlying light-emitting NAA layer. This structural design makes it possible to narrow the width of photoluminescence emission up to ∼50 nm and blue shift its position for ∼15 nm. Our advances pave the way for novel designs of intrinsic, light-emitting NAA-based PC structures, which could find broad applicability across light technologies, such as sensing and biosensing, photodetection, and solar light harvesting.

Spectral Engineering of Tamm Plasmon Resonances in Dielectric Nanoporous Photonic Crystal Sensors.

Model light-confining Tamm plasmon cavities based on gold-coated nanoporous anodic alumina photonic crystals (TMM-NAA-PCs) with spectrally tunable resonance bands were engineered. Laplacian and Lorentzian NAA-PCs produced by a modified Gaussian-like pulse anodization approach showed well-resolved, high-quality photonic stopbands, the position of which was precisely controlled across the visible spectrum by the periodicity in the input anodization profile. These PC structures were used as a platform material to develop highly reflective distributed Bragg mirrors, the top sides of which were coated with a thin gold film. The resulting nanoporous hybrid plasmonic-photonic crystals showed strong light-confining properties attributed to Tamm plasmon resonances at three specific positions of the visible spectrum. These structures achieved high sensitivity to changes in refractive index, with a sensitivity of ∼106 nm RIU-1. The optical sensitivity of TMM-NAA-PCs was assessed in real time, using a model chemically selective binding interaction between thiol-containing molecules and gold. The optical sensitivity was found to rely linearly on the spectral position of the Tamm resonance band, for both Laplacian and Lorentzian TMM-NAA-PCs. The density of self-assembled monolayers of thiol-containing analyte molecules formed on the surface of the metallic film directly contributes to the dependence of sensitivity on TMM resonance position in these optical transducers. Our findings provide opportunities to integrate TMM modes in NAA-based photonic crystal structures, with promising potential for optical technologies and applications requiring high-quality surface plasmon resonance bands.

Optical engineering of nanoporous photonic crystals by Gaussian-Like pulse anodization

Abstract A new class of nanoporous anodic alumina photonic crystals (NAA–PCs) are optically engineered by four distinct forms of Gaussian-like pulse anodization (GLPA) – Gaussian, Lorentzian, logarithmic normal, and Laplacian. NAA–PCs produced by GLPA under current density control conditions show well-resolved, spectrally tunable photonic stopbands (PSBs), the features of which – central wavelength, full width at half maximum, intensity, and quality factor – can be precisely tuned across the UV–visible spectrum by the input Gaussian-like current density pulses. Effects of type, width, and period of Gaussian-like current density pulses on the structural and optical properties of NAA–PCs are systematically assessed. Comprehensive electrochemical, structural, and optical characterizations allow us to elucidate the interplay of input GLPA profile and structural features in determining forbidden light propagation within these NAA–PCs. Sensitivity of these PC structures toward changes in their effective medium are determined by quantifying spectral shifts in their characteristic PSB upon infiltration of their nanoporous structure with analytical solutions of alcohol mixtures with varying refractive index, from 1.362 to 1.383 RIU. It is found that, at fixed anodization period, NAA–PCs produced by Laplacian current density pulses achieve the highest sensitivity (105 ± 4 nm RIU−1) and, for a given type of GLPA, NAA–PCs produced with longer anodization period achieve higher sensitivity (123 ± 10 nm RIU−1 for NAA–PCs fabricated by Gaussian pulses with a 1400 s-period). Our advances provide exciting new opportunities for future developments of high-quality NAA–PCs with broad applicability across various photonic technologies, including optical sensing, photocatalysis, lasing, and optical encoding.

Control of high-order photonic band gaps in one-dimensional anodic alumina photonic crystals

Abstract One-dimensional (1D) photonic crystals based on porous anodic alumina are of high practical importance in modern materials science owing to their promising applications in the field of photonics. Although the positions of photonic band gaps can be controlled precisely by electric charge passed during the formation of repeating layers of anodic alumina, the methods for tuning the transmittance and reflectance within the photonic band gaps are limited. Here we demonstrate a simple and highly reproducible method for obtaining 1D anodic alumina photonic crystals with several reflecting layers in the unit cell. A theoretical model for the calculation of the optical properties of the prepared 1D anodic alumina photonic crystals is suggested and used for the design of an anodizing profile. The ability to tune the transmittance and reflectance within high-order photonic band gaps by controlling the position of the reflecting layers in the unit cell of the photonic crystal is demonstrated.

Rapid fabrication of iridescent alumina films supported on an aluminium substrate by high voltage anodization

Porous alumina photonic crystals supported on an aluminium substrate were successfully fabricated by applying a high voltage for a short period of time in an oxalic acid solution. These films show brilliant structural colors, and the highest applied voltage was 250 V. The experimental results indicate that a photonic crystal supported on an aluminium substrate shows a uniform structural colour when a voltage is increased to 150 V and, with oxidation time increasing, the colour gradually turns blue. A reasonable explanation was given for this phenomenon through a theoretical analysis combined with microstructure measurement. In this study, the growth process and colour generation mechanism of porous anodic alumina under a linear anodizing voltage were discussed and analyzed in detail. These films may have great potential in colour display, decoration, anti-counterfeiting, sensing and other fields.

Tunable Nanoporous Anodic Alumina Photonic Crystals by Gaussian Pulse Anodization.

This study presents a Gaussian pulse anodization approach to generate nanoporous photonic crystals with highly tunable and controllable optical properties across the visible-NIR spectrum. Nanoporous anodic alumina Gaussian photonic crystals (NAA-GPCs) are fabricated in oxalic acid electrolyte by Gaussian pulse anodization, a novel form of pulse-like anodization. The effect of the Gaussian pulse width in the anodization profile on the optical properties of these photonic crystals is assessed by systematically varying this fabrication parameter from 5 to 60 s. The optical features of the characteristic photonic stopband (PSB) of NAA-GPCs-the position of the central wavelength, full width at half-maximum, and intensity-are found to be highly dependent on the Gaussian pulse width, the angle of incidence of incoming photons, and the nanopore diameter of NAA-GPCs. The effective medium of NAA-GPCs is assessed by monitoring spectral shifts in their characteristic PSB upon infiltration of their nanoporous structure with analytical solutions of d-glucose of varying concentration (0.0125-1 M). Experimental results are validated and mechanistically described by theoretical simulations, using the Looyenga-Landau-Lifshitz effective medium approximation model. Our findings demonstrate that Gaussian pulse anodization is an effective nanofabrication approach to producing highly sensitive NAA-based PC structures with versatile and tunable PSBs across the spectral regions. The findings provide new exiting opportunities to integrate these unique PC structures into photonic sensors and other platform materials for light-based technologies.

The effect of the voltage waveform on the microstructure and optical properties of porous anodic alumina photonic crystals

Porous anodic alumina photonic crystals (PAA-PhCs) with brilliant colours were successfully fabricated by pulse anodization of aluminium in an oxalic acid electrolyte. The influence of the voltage waveform on the microstructure of the PAA-PhCs was investigated by adjusting the anodization period, anodization amplitude, and anodization offset. Here, we report a simplified method for compensation of the photonic band gap (PBG) drift using AC waveforms instead of the periodic length-controlled method. Scanning electron microscopy (SEM) results showed that the layer thickness of the PAA-PhC prepared by an AC pulse was gradually reduced from 360 nm to 290 nm, which was completely different from a previous report showing that the layer thickness of a sample prepared by a DC pulse remained unchanged. In addition, the effect of chemical corrosion in a phosphoric acid solution on the microstructures of the PAA-PhCs was analysed by comparative experiments. PBG drift caused by minor defects in the nanostructure during the anodization process could also be compensated for by adjusting the anodizing time and corrosion time. Our approach may help to broaden the potential applications of and provide important guidance for photonic crystal display and new devices.

Anodic Alumina Photonic Crystals as Refractive Index Sensors for Controlling the Composition of Liquid Mixtures

Photonic crystals based on anodic aluminum oxide films are examined as refractive index sensors for controlling the composition of water-alcohol liquid mixtures. The position of the reflectance maximum corresponding to the first photonic stop band is used as the analytical signal. Impregnation of a photonic crystal with water-ethanol and water-glycerol mixtures results in a redshift of the reflectance maximum. A fairly high refractive index sensitivity, sufficient to determine the composition of water-ethanol and water-glycerol mixtures with an accuracy of about 1 wt.%, is observed. The detailed dependencies of the analytical signal on the composition of mixtures are experimentally investigated and compared with numerical calculations. Prospects and limitations of the refractive index sensors based on anodic alumina photonic crystals are discussed.

Selenic acid anodizing of aluminium for preparation of 1D photonic crystals

Anodizing of aluminium under oscillating conditions is a reproducible, scalable, and low-cost method for the preparation of one-dimensional photonic crystals with photonic band gaps in the visible and near-infrared regions. For this purpose, sulfuric and oxalic acid electrolytes are used, because in such baths transparent anodic alumina films are formed. In the present study, selenic acid electrolyte is utilized for the fabrication of anodic alumina photonic crystals for the first time. The choice of a rational range of voltage/current modulation is performed on the basis of linear voltammetry. The dispersion of the effective refractive index and the porosity of prepared photonic crystals are measured. High transmittance of the anodic alumina obtained in selenic acid electrolyte makes this bath promising for the preparation of 1D photonic crystals with photonic band gaps from the ultraviolet to infrared regions.

Rational Management of Photons for Enhanced Photocatalysis in Structurally-Colored Nanoporous Anodic Alumina Photonic Crystals

A comprehensive study on the engineering of titanium dioxide-functionalized nanoporous anodic alumina distributed Bragg reflectors (TiO2–NAA-DBRs) for photocatalysis enhanced by the “slow photon” effect is presented. The photocatalytic performance of these composite photonic crystals (PCs) is assessed by monitoring photodegradation of a variety of organic molecules with absorbance bands across the spectral regions. This study demonstrates that photocatalytic performance of TiO2–NAA-DBRs is enhanced by the “slow photon” effect when the edges of the PC’s photonic stopband (PSB) fall within the absorbance band of the organic molecules. The photocatalytic performance is significantly enhanced when the PSB’s red edge is in close proximity to the absorbance band of the organic molecules. Overall photocatalytic degradation is also dependent on the total pore length of the PC structure, charge of the organic molecules, percentage of vis–near-IR irradiation, and matrix complexity (i.e., interfering ions and molecu...

Integrating surface plasmon resonance and slow photon effects in nanoporous anodic alumina photonic crystals for photocatalysis

This study explores the potential of gold-coated titania-functionalized nanoporous anodic alumina distributed Bragg reflectors (Au-TiO2-NAA-DBRs) as platforms to enhance photocatalytic reactions by integrating “slow photons” and surface plasmon resonance (SPR).

Unidirectional Slow Light Transmission in Heterostructure Photonic Crystal Waveguide

In conventional photonic crystal systems, extrinsic scattering resulting from random manufacturing defects or environmental changes is a major source of loss that causes performance degradation, and the backscattering loss is amplified as the group velocity slows down. In order to overcome the limitations in slow light systems, we propose a backscattering-immune slow light waveguide design. The waveguide is based on an interface between a square lattice of magneto-optical photonic crystal with precisely tailored rod radii of the first two rows and a titled 45 degrees square lattice of Alumina photonic crystal with an aligned band gap. High group indices of 77, 68, 64, and 60 with the normalized frequency bandwidths of 0.444%, 0.481%, 0.485%, and 0.491% are obtained, respectively. The corresponding normalized delay-bandwidth products remain around 0.32 for all cases, which are higher than previously reported works based on rod radius adjustment. The robustness for the edge modes against different types of interfacial defects is observed for the lack of backward propagation modes at the same frequencies as the unidirectional edge modes. Furthermore, the transmission direction can be controlled by the sign of the externally applied magnetic field normal to the plane.