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Cr3+ doped nanoporous anodic alumina: Facile microwave assisted doping to realize nanoporous ruby and phase dependent photoluminescence
摘要： Microwave-assisted solution technique (MAST) was used for the homogeneous doping of Cr3+ in nanoporous anodic alumina (NAA) which when heat-treated transforms into nanoporous ruby. The rise in annealing temperature led to the phase transition in the sequence: amorphous- δ- θ- α-alumina as evidenced by XRD. The dopant was homogenously distributed as seen from the elemental mapping and the Cr3+ content was 0.5 at%. Di?use re?ectance spectroscopy (DRS) displayed the characteristic blue and green absorption bands and the color-tone varied from light-green at 700 °C to the pink appearance at 1350 °C owing to the dopant di?usion. Two broad photoluminescence (PL) excitation bands centered at ～550 nm and ～400 nm were observed whose intensity increased with the annealing temperature. All the alumina phases exhibited characteristic phase dependent PL showing variation in the luminescence intensity and peak position. The characteristic R-line for α-phase was intense and observed at 694 nm with 4 m s lifetime in accordance with that expected for Ruby. Crystal ?eld parameters were obtained from the PL excitation spectra and Dq/B values were found to be higher than 2.3 for all the phases of NAA con?rming the presence of Cr3+ ions in the strong crystal ?eld. With annealing, the CIE coordinates moved towards the red region. The presented work shows a promising easy and inexpensive method for dopant incorporation into alumina and explores the understanding of phase-dependent emission of Cr3+ doped NAA for their potential applications in the areas of nano-optics and composite luminescent nanomaterials.
关键词： Nanoporous anodic alumina,Cr3+ doping,Photoluminescence,Phase transition
更新于2025-11-21 11:18:25
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Stacked Nanoporous Anodic Alumina Gradient-Index Filters with Tunable Multispectral Photonic Stopbands as Sensing Platforms
摘要： This study presents the development and optical engineering of stacked nanoporous anodic alumina gradient-index (NAA-GIFs) filters with tunable multi-spectral photonic stopbands for sensing applications. The structure of these photonic crystal (PC) is formed by stacked layers of NAA produced with sinusoidally modified effective medium. The progressive modification of the sinusoidal period during the anodization process enables the generation and precise tuning of the characteristic photonic stopbands (PSB) (i.e. one per sinusoidal period in the anodization profile) of these PC structures. Four types of NAA-GIFs featuring three distinctive PSBs positioned within the visible spectral region are developed. The sensitivity of the effective medium of these NAA-GIFs is systematically assessed by measuring spectral shifts in the characteristic PSBs upon infiltration of their nanoporous structure with analytical solutions of D-glucose with several concentrations (0.025 – 1 M). This study provides new insights into the intrinsic relationship between the nanoporous architecture of these PCs and their optical properties, generating opportunities to fabricate advanced optical sensing systems for high-throughput and multiplexed detection of analytes in a single sensing platform.
关键词： nanoporous anodic alumina,sensing platforms,stacked,multispectral bands,photonic crystals,gradient index filters
更新于2025-09-23 15:23:52
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On-chip sensor solution for hydrogen gas detection with the anodic niobium-oxide nanorod arrays
摘要： Two types of anodic niobium-oxide nanofilms were synthesized via anodization of an Al/Nb bilayer sputter-deposited onto a SiO2-coated Si wafer. Type I nanofilm was composed of a 200 nm thick NbO2 layer holding the upright-standing 650 nm long, 50 nm wide, and 70 nm spaced Nb2O5 nanorods, of 7·109 cm?2 density, whereas the Type II nanofilm had similarly long but bigger Nb2O5 nanorods, 100 nm wide, 220 nm spaced, and of 8·108 cm?2 density, aligned directly on a niobium metal without any buffering oxide layer, which was achieved for the first time. Each film was then incorporated in an advanced 3-D architecture and multilayer layout on a silicon chip comprising 33 microsensors, with variable sizes and tuned electrical characteristics, by combining the high-temperature vacuum or air annealing, sputter-deposition, and lift-off photolithography to form Pt/NiCr top electrodes and a multifunctional SiO2 interlayer, chemical etching, laser dicing, and ultrasonic wire-bonding. The proposed on-chip sensor solution allowed for a sensitive, fast, and highly selective (toward NH3 and CH4) detection of hydrogen gas. Comprehensive gas sensing tests performed for Type II nanofilm ultimately confirmed the presence of a Schottky-type sensing mechanism, the contribution, however, being substantially weaker than that due to reactions over the surface of the oxide nanorods, especially when the rods show a transition from fully to partially depleted states when interacting with H2 gas. The film formation and chip fabrication technologies may be transferable to other PAA-assisted 1-dimensional metal-oxide nanomaterials suitable for on-chip gas sensing.
关键词： niobium oxide nanorods,anodic alumina,hydrogen,Schottky barrier,anodizing,on-chip sensor
更新于2025-09-23 15:23:52
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Multisegmented Metallic Nanorods: Sub-10 nm Growth, Nanoscale Manipulation, and Subwavelength Imaging
摘要： Multisegmented metallic nanorods (MS-M-NRs) have attracted increasing attention thanks to their integrated structures and complex functions. The integration of nanoscale segments in 1D enables maximum exposure of each segment and enhanced interaction between adjacent segments. Such structural integration will induce functional complexity in the nanorods, leading to superior properties for the individual components. Herein, recent progress on the development of MS-M-NRs is reviewed. Their precise fabrication, nanoscale manipulation, and subwavelength imaging, as well as simultaneous manipulation and imaging are discussed, respectively. Specifically, precise fabrication of MS-M-NRs focuses on porous anodic alumina (PAA) templated electrodeposition, which enables sub-10 nm growth of the segments and their interfaces/fronts. Nanoscale manipulation of MS-M-NRs introduces the fundamental methods that are employed for delicate movement control on the nanorods through internal or external stimulations. Subwavelength imaging of MS-M-NRs highlights the achievements on identification and location of constituent nanoscale segments/gaps based on their differences and interactions. Simultaneous manipulation and imaging of MS-M-NRs addresses the significance and potential applications of the nanorods with magnetic–plasmonic dual modulation. The development of MS-M-NRs will greatly contribute to materials science and nanoscience/nanotechnology.
关键词： metallic nanorods,porous anodic alumina (PAA),electrodeposition,imaging,manipulation
更新于2025-09-23 15:22:29
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Ultrasensitive and Label-Free Detection of Cell Surface Glycan Using Nanochannel-Ionchannel Hybrid Coupled with Electrochemical Detector
摘要： In this work, asymmetric nanochannel-ionchannel of porous anodic alumina (PAA) coupled with electrochemical detector was used for sensitive and label-free detection of cell surface glycan. The amplified ionic current caused by array nanochannels as well as the ionic current rectification (ICR) caused by asymmetric geometry endows PAA with sensitive ionic current response. Functionalized with the special molecular probe, the constructed nanofluidic device can be used for selective recognition and detection of glycan in real-time and label-free format. In addition, due to the subnanosize of ionchannels, the probe immobilization and glycan recognition is carried out on the outer surface of PAA, avoiding the blockage of PAA nanochannel by samples, which promises the reproducibility and accuracy of the present method toward bioanalysis. Results show that the glycan concentration ranging from 10 fM to 10 nM can be successfully detected with a detection limit of ~10 aM, which is substantially lower than most previous works. The designed strategy provides a valuable platform for sensitive and label-free detection of cell surface glycan, which acts as a promising candidate in pathological research and cancer diagnosis.
关键词： porous anodic alumina,ionic current rectification,cell surface glycan,nanochannel-ionchannel hybrid,nanofluidics
更新于2025-09-23 15:19:57
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Reflection Spectra of Composite Photonic Crystals Based on Anodic Alumina Filled with Ferroelectric Sodium Nitrite
摘要： Re?ection spectra of a composite one-dimensional photonic crystal (PC) based on porous anodic alumina ?lled with ferroelectric sodium nitrite have been recorded in the wavelength range of 400 to 1200 nm. Signi?cant spectral shifts of the ?rst and second stopbands are revealed for the composite PC. The stopband spectral half-width is found to decrease by a factor of four to ?ve. The possibility of applying composite alumina-based photonic crystals as selective narrowband mirrors is discussed.
关键词： reflection spectra,ferroelectric sodium nitrite,photonic crystals,anodic alumina,stopbands
更新于2025-09-12 10:27:22
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On-substrate porous-anodic-alumina-assisted gold nanostructure arrays: Meeting the challenges of various sizes and interfaces
摘要： Arrays of 0- and 1-dimentional noble-metal nanostructures aligned on solid substrates are in demand for nanocatalysis, bio- and optical sensing, or biomolecular analysis. Here we introduce a range of advances based on a systematic research towards the porous-anodic-alumina (PAA)-assisted on- substrate arrays of gold nanostructures, such as rods and spheres, spatially-separated and highly aligned on a metal or semiconductor supporting layer via a blend of the anodizing, re-anodizing, and post- anodizing treatments applied to a thin layer of Al superimposed on selected valve metals (W, Ti, Hf), metal bilayers (W/Ti), or binary metal alloy layers (W-Ti). The achievements are due to (1) the improved self-organization in the PAA thin films during the self-localizing high-current anodization of the upper Al layer at challenging potentials ranging 100 to 250 V and 20 to 5 V, and (2) the enhanced penetration of the alumina barrier layer by the undergrowing metal oxide due to the increasing polarization (re- anodizing). The protrusions of the undergrown metal oxide can be either selectively dissolved away providing perfect nanoholes in the alumina barrier layer or left as formed in the barrier layer and annealed in vacuum to increase their electron conductance and serve as the supports for subsequent metal electrodeposition. Additionally, the in-situ amplitude-modulated constant-current pulse deposition mode combined with the original surface-wiping technique to remove the overdeposited gold allow for smooth nucleation and uniform finishing of perfect arrays of on-substrate gold nanospheres and nanorods, having diameters from 10 to over 250 nm and length up to 2.5 ?m.
关键词： gold nanorods,electrodeposition,barrier layer dissolution,nanodots,porous anodic alumina
更新于2025-09-10 09:29:36
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3D-FDTD modelling of optical biosensing based on gold-coated nanoporous anodic alumina
摘要： The suitability of using gold-coated nanoporous anodic alumina structures as a platform for reflectometry-based plasmonic biosensors is investigated by numerical simulation. Reflectance spectra of such structures has been obtained using 3D-FDTD while the sensing capabilities have been evaluated as the change in spectra upon the adsorption of a layer of a biological-related molecule (biolayer) on the gold coating and inner pore surface. Results show that the gold-coated nanoporous structure enables the coupling of normally incident light to a localized surface plasmon resonance, and that such resonance shifts upon the adsorption of the biolayer. A sensitivity can be defined as the resonance wavelength shift with the biolayer refractive index. It is demonstrated that smaller gold coating thicknesses result in an increase in sensitivity, but at the cost of a decrease in the resonance sharpness, what suggests the existence of an optimal gold coating thickness.
关键词： Gold-coated nanoporous anodic alumina,Biolayer,FDTD simulation,Reflectometry-based plasmonic biosensor
更新于2025-09-10 09:29:36
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Flow through polydisperse pores in an anodic alumina membrane: A new method to measure the mean pore diameter
摘要： We describe a novel technique for the characterization of the mean pore radius of self-ordered porous anodic alumina membranes. We have studied the flow of liquids through cylindrical membrane pores under conditions of very low Reynolds number (Re ? 1). We find that the flow data are well-described by Poiseuille’s law. Characterization is achieved through the application of the H?gen-Poiseuille equation on flow measurements conducted in a simple and compact experimental setup. This setup allows for the monitoring of flow as a result of the pressure difference between the two sides of the membrane without the use of sophisticated and costly laboratory equipment. The proposed method has been tested by flow experiments using liquids of various viscosities. Good agreement is found between the results obtained from the flow data and the pore radii measured by scanning electron microscopy. Consistent results for the mean pore radius for the same membrane have been obtained in all cases.
关键词： Poiseuille’s law,scanning electron microscopy,anodic alumina membrane,mean pore diameter,flow measurement
更新于2025-09-10 09:29:36
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Rapid Fabrication of Porous Anodic Alumina Films with Large Interpore Distances in an Ethylene Glycol and Ammonium Dihydrogen Phosphate-Based Electrolyte
摘要： Porous anodic alumina (PAA) ?lms have become popular nanotemplates due to the ordered hexagonal pore array structure. The fabrication of well-ordered PAA ?lms with larger interpore distances is still a challenge to date. Here, we develop a unique electrolyte system based on the reaction products of ethylene glycol (EG) with ammonium dihydrogen phosphate (ADP). In the novel electrolytes, stable high-voltage anodization with extremely high current densities (the peak value is close to 300 mA cm?2) can be realized at 400 V or even higher without breakdown. In 5 wt% EG-ADP-based electrolyte containing phosphoric acid, a well-ordered PAA ?lm with an interpore distance of ～610 nm can be fabricated at 250 V at a high growth rate of 1.3 μm · min?1.
关键词： Porous anodic alumina,high-voltage anodization,ethylene glycol,ammonium dihydrogen phosphate,interpore distance
更新于2025-09-09 09:28:46