Porous Anodic Aluminum Oxide Template Research Articles

Au nanostructures with controllable morphology in porous anodic aluminum oxide templates

We report the controllable fabrication of Au nanostructures with different morphology inside the nanochannels of the Al-surrounded porous anodic aluminum oxide (AAO) templates. It has been found that the morphology of the Au nanostructures is influenced by the pore diameter of the AAO templates and the bottom Au layer sputtering on the surface of the AAO templates. Au nanowires are formed in the AAO templates with smaller pore diameters (40–60 nm), and rice spike-like Au nanostructures are formed in the AAO templates with larger pore diameters (∼130 nm). When the AAO templates with bottom Au layer were used, almost all of the nanochannels were filled with Au nanostructures. As the AAO templates without bottom Au layer were employed, longer Au nanostructures are formed inside some nanochannels near the Al-AAO boundary.

Ultrabroadband absorptive refractory plasmonics for photocatalytic hydrogen evolution reactions

As an environmentally friendly and renewable method for hydrogen production powered by solar energy, photocatalytic hydrogen evolution reactions (HERs) using broadband absorbers have received much attention. Here, we report the fabrication and characterization of an ultrabroadband absorber for the photocatalytic HER. The absorber is composed of titanium nitride and titanium dioxide heterostructures deposited onto a porous anodized aluminum oxide template. The absorber shows ultrabroadband absorption in both the visible and near-infrared regions (400–2500 nm), with averages of 99.1% and 80.1%, respectively. Additionally, the presence of the TiO2 layer within the absorber extends the lifetime of the hot carriers by 2.7 times longer than that without the TiO2 layer, enhancing the transfer of hot electrons and improving the efficiency of hydrogen production by 1.9 times. This novel ultrabroadband absorber has potential use in advanced photocatalytic HER applications, providing a sustainable and cost-effective route for hydrogen generation from solar energy.

The experimental Young’s modulus of polythiophene nanofibers

The Young’s modulus of polythiophene (PT) nanofibers has not been reported so far. In this paper, PT nanofibers were electrolytically prepared from thiophene monomer with a porous anodic aluminum oxide template. The Young's modulus of individual PT nanofibers was measured using atomic force microscopy. The average Young's modulus of PT nanofibers with diameters around 90 nm was 64.5 ± 5.0 GPa, which is an order of magnitude higher than its bulk value. We attribute the high Young’s modulus of PT nanofibers to the alignment of the molecular chain.

Anisotropic Plasmonic Property of Al Nanowires Obtained by AC Electrodeposition Using Anodic Porous Alumina Template

Anisotropic Plasmonic Property of Al Nanowires Obtained by AC Electrodeposition Using Anodic Porous Alumina Template

Magnetic saturation enhancement of gold-capped nickel nanorods

Nickel nanorods (NRs) capped with gold (Au/Ni) were grown into porous anodic aluminum oxide templates and subsequently transferred onto Au/Si (100) substrates. A high dense 2D array of Ni and Au/Ni nanorods was analyzed by vibrating sample magnetometry; it was found that an increase in 14.8% of the magnetic moment following the deposition of Au caps. In order to further investigate this phenomenon, the magnetic distribution of Au/Ni nanorods was studied by off-axis electron holography. The magnetization and induction strengths were evaluated to be 4.7 × 105 A/m and 0.62 T, respectively, which is equivalent to magnetometry measurements of the Ni NR arrays. Remarkably, a vortex state configuration was imaged in the Au segment by the retrieved magnetic phase of the electron holograms under free lens conditions of the transmission electron microscope column. It was concluded that the magnetic distribution in the Au segment is associated with a ferromagnetic coupling with Ni and correlated with the magnetometry measurements.

High-performance flexible pressure sensor based on ordered double-level nanopillar array films: Design, development, and modeling

To improve the sensitivity and broaden the range of flexible pressure sensors, we proposed a high-performance flexible pressure sensor based on ordered double-level nanopillar array films. In this work, polypyrrole/multi-walled carbon nanotube/polyurethane (PPy/MWCNT/PU) conductive films with double-level nanopillar array microstructures were prepared by continuously adjusting the oxidation and pore expansion parameters of a porous anodic alumina template (AAO), where the high pillar height was 1243.0 ± 7.0 nm, and the low pillar height was 868.0 ± 4.70 nm. We studied the influence of the structural characteristics of ordered double-level nanopillar array conductive films and a flexible pressure sensor on the sensing performance using finite element simulations, the establishment of sensing mechanism, and sensor performance measurements. The results showed that the pressure was positively correlated with the change rate of strain and the surface microstructure contact area of the ordered double-level nanopillar array films. The sensor sensitivity reached 208.353 kPa−1, and its range was extended by 267%. In addition, the sensor, which could monitor vocalization, drinking pulse and finger movements, could be used in a wide range of applications, including wearable medical monitoring and smart sign language textiles.

Nanoconfinement-Dependent Chain Orientation of Polymorphs in Poly(3-dodecylthiophene)s

Nanoconfinement of conjugated polymers (CPs) is an effective strategy to control the orientations and orderings of CPs, which determine their electrical properties. We investigate the chain orientations of two crystal polymorphs, Form I and Form II, in poly(3-dodecylthiophene)s (P3DDTs) using a porous anodic aluminum oxide (AAO) template. The control of regioregularity (RR) of P3DDTs results in well-defined Form II/Form I ratios of crystal polymorphs. Interestingly, Form I and Form II crystals show considerably different orientational changes depending on the pore diameter (Dpore) of the porous AAO template. As Dpore decreases from 100 to 30 nm, Form II crystals change their orientations from face-on to edge-on dominant morphologies, whereas Form I crystals consistently exhibit edge-on dominant morphologies. In addition, for a fixed Dpore of 100 nm, temperature-dependent orientational changes of Form I and Form II are investigated. While Form II crystals show a significant orientational change with increasing temperature, Form I crystals only experience chain reconfiguration. This finding provides useful guidelines for achieving the CPs with controlled intermolecular assembly and chain orientations.

Overview of Engineering Carbon Nanomaterials Such As Carbon Nanotubes (CNTs), Carbon Nanofibers (CNFs), Graphene and Nanodiamonds and Other Carbon Allotropes inside Porous Anodic Alumina (PAA) Templates

The fabrication and design of carbon-based hierarchical structures with tailored nano-architectures have attracted the enormous attention of the materials science community due to their exceptional chemical and physical properties. The collective control of nano-objects, in terms of their dimensionality, orientation and size, is of paramount importance to expand the implementation of carbon nanomaterials across a large variety of applications. In this context, porous anodic alumina (PAA) has become an attractive template where the pore morphologies can be straightforwardly modulated. The synthesis of diverse carbon nanomaterials can be performed using PAA templates, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and nanodiamonds, or can act as support for other carbon allotropes such as graphene and other carbon nanoforms. However, the successful growth of carbon nanomaterials within ordered PAA templates typically requires a series of stages involving the template fabrication, nanostructure growth and finally an etching or electrode metallization steps, which all encounter different challenges towards a nanodevice fabrication. The present review article describes the advantages and challenges associated with the fabrication of carbon materials in PAA based materials and aims to give a renewed momentum to this topic within the materials science community by providing an exhaustive overview of the current synthesis approaches and the most relevant applications based on PAA/Carbon nanostructures materials. Finally, the perspective and opportunities in the field are presented.

Influence of Ethanol on Porous Anodic Alumina Growth in Etidronic Acid Solutions at Various Temperatures.

Etidronic acid, used in aluminum anodization, has a great potential for the fabrication of porous anodic alumina (PAA) with large cell sizes (>540 nm). PAAs are particularly suited to applications in optics and photonics where large-scale periodicity corresponding to visible or infrared light is needed. Additionally, such PAAs should be characterized by long-range pore ordering. However, to obtain regular pore arrangement in an etidronic electrolyte, the anodization should be performed at high electric fields using relatively high temperatures, which makes the process challenging in terms of its stability. To stabilize the process, the electrolyte can be modified with ethanol. In this work, the impact of ethanol on pore geometry and a level of pore ordering is systematically analyzed. It is shown that the additive tends to reduce pore ordering. Moreover, by changing the anodizing temperature and the amount of ethanol, it is possible to tune the porosity of the PAA template. At 20 °C, porosity drops from 14% in PAA grown in a pure water-based electrolyte to ca. 8% in PAA fabricated in the 1:3 v/v EtOH:H2O electrolyte. The larger PAA thickness obtained for the same charge density strongly suggests that PAA formation efficiency increases in the 1:3 v/v EtOH:H2O mixture.

Rapid fabrication of the Au hexagonal cone arrays for SERS applications

This study performed trace detection using surface-enhanced Raman scattering (SERS) on Au hexagonal cone arrays (Au-HCAs). Uniform porous anodized aluminum oxide (AAO) templates were used, and an Ag film with a cone cavity was prepared using a thermal deposition technique. Next, a series of homogeneous Au-HCAs were prepared controllably via electrodeposition growth technology. The prepared Au-HCAs were used as SERS substrates, and according to the experimental results, the optimal electrodeposition time is 600 s. At this time, Au-HCAs had the highest SERS activity. The detection limit of R6G was 10−9 M, exhibiting high reproducibility and high uniformity at 10−6 M, indicating that Au-HCAs had good stability. Moreover, a good linear correlation between the Raman intensity and the molecular concentration endowed Au-HCAs with good quantitative analysis ability. Therefore, the Au-HCAs exhibited great potential for qualitative and quantitative detection.

Key role of longitudinal disarranged growth in porous anodic alumina: Crystallographic orientation

Porous anodic alumina (PAA) is a typical template for electrochemical deposition. The longitudinal disarranged growth (LDG) in a PAA template directly causes a distortion of deposited nanomaterials. Crystallographic orientation is an important parameter of aluminum (Al) and its influence on PAA longitudinal growth is the key to high-quality PAA templates. In this study, PAA films prepared from polycrystalline pure Al foils were used to investigate the key effects of crystallographic orientation on PAA LDG. A spatial mapping relationship between crystallographic orientation and PAA morphology was built using a scratch marking method with a combination of electron backscatter diffraction and scanning electron microscopy. The results showed that PAA LDG manifested as LDG regions, whose size was positively correlated with grain boundary misorientation. The effect of misorientation on the LDG was explained based on the volume expansion model. This study contributed to a further understanding of the PAA longitudinal growth mechanism.

Synthesis and Magnetic Properties of FeCo Alloy Nanowires via AC Frequency Conversion Electrodeposition

Binary alloy nanowires of Fe₃CoSUB7/SUB system are synthesized in the highly ordered porous anodic aluminum oxide (PAA) templates by AC frequency (5, 50, 120, and 200 Hz) conversion electrodeposition method. High resolution field emission transmission electron microscope (HRTEM) and Lorenz TEM (LTEM) were used to study the morphology and the magnetic domain structure of the Fe₃CoSUB7/SUB alloy nanowires, respectively. Magnetic measurements showed that the M-H curves presented a discontinuity in a restricted magnetic field, but with high squareness (about 90 %). Quantitative local measurements of the magnetic properties of the nanowires are explored by differential phase contrast (DPC) imaging. The magnetic properties, however, were significantly affected by the AC frequency, which is correlated with the specific magnetic structure formation of Bloch line. We reported herein a detailed investigation on Fe₃CoSUB7/SUB alloy nanowires and their magnetic properties.

Integration of supercapacitor with solar cell based on NiO 2 and CdS nanopillars embedded in porous anodic alumina templates

Integration of supercapacitor with solar cell based on <scp> NiO ₂ </scp> and <scp>CdS</scp> nanopillars embedded in porous anodic alumina templates

SEM Image Analysis on the Formation of Porous Anodic Alumina Templates

SEM Image Analysis on the Formation of Porous Anodic Alumina Templates

Superhydrophobic Ag‐Decorated CuO Nanowire Arrays with Analyte‐Concentrating and Self‐Cleaning Binary Functions for Ultrasensitive and Recyclable Surface‐Enhanced Raman Scattering

AbstractSurface‐enhanced Raman scattering (SERS) is considered a promising analytical technique for the detection of analytes. Considering the practical SERS detection, it is necessary to develop low‐cost, highly sensitive, and recyclable SERS‐active substrates. Here, a simple and flexible approach is proposed to fabricate a superhydrophobic Ag‐decorated CuO (named as CuO@Ag) nanowire array substrate with analyte‐concentrating and self‐cleaning binary functions for ultrasensitive and recyclable SERS detection. During this process, a superhydrophobic CuO@Ag nanowire array is made via fabrication of a CuO nanowire array by oxidizing and calcinating an ordered porous anodic aluminum oxide template on Cu foil, and following with Ag sputtering deposition on CuO nanowire array. Remarkably, this SERS substrate exhibits ultrasensitive SERS detection ability attributed to superhydrophobic plasmonic metal nanostructured arrays with high analyte‐concentrating ability and excellent photocatalytic capability due to this metal‐semiconductor composite nanostructure. These advantageous properties allow for SERS detection of malachite green with a limit of detection of 6.73 × 10−13 m and self‐cleaning via photodegradation of adsorbed analytes with visible‐light illumination. Consequently, it achieves recyclable SERS detection. This research demonstrates a simple and flexible approach for fabricating recyclable SERS‐active substrate, which expands the practical SERS applications in chemical and biological analysis, food safety, and healthcare.

Directional controllable electrodeposition growth of homogeneous Au nano-rampart arrays and its reliable SERS applications

High-yield large-area uniform metal nanoarrays have shown attractive application potential in many fields. Electrodeposition growth has unique advantages in the construction of metal nanostructures due to its high efficiency. However, the uniformity and stability of electrodeposition are still remain challenging. Here, an efficient, stable and cost-effective directional electrodeposition route was proposed to construct large-scale uniform metal nanoarrays, which could be further used as reliable SERS substrates. Assisted with uniform porous anodized aluminum oxide (AAO) templates, a series of homogeneous Au nano-rampart arrays (Au-NRAs) were prepared controllably by directional electrodeposition growth technology. Using the prepared Au-NRAs as SERS substrates, the results showed that the optimal electrodeposition growth is 600 s. At this time, Au-NRAs showed highest SERS activity and the low relative standard deviation (RSD) value of Raman intensity at 619 cm−1 mode of R6G (with concentration of 10-5 M) was 2.08%, which indicated excellent SERS stability. This method integrated not only cost-effectiveness, but also good directional controllability and repeatability, showing great potential in constructing large-area uniform metal nanostructures.

Templated electrodeposition as a scalable and surfactant-free approach to the synthesis of Au nanoparticles with tunable aspect ratios.

A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.

Nanoimprinted and Anodized Templates for Large-Scale and Low-Cost Nanopatterning.

Nanopatterning to fabricate advanced nanostructured materials is a widely employed technology in a broad spectrum of applications going from spintronics and nanoelectronics to nanophotonics. This work reports on an easy route for nanopatterning making use of ordered porous templates with geometries ranging from straight lines to square, triangular or rhombohedral lattices, to be employed for the designed growth of sputtered materials with engineered properties. The procedure is based on large-scale nanoimprinting using patterned low-cost commercial disks, as 1-D grating stamps, followed by a single electrochemical process that allows one to obtain 1-D ordered porous anodic templates. Multiple imprinting steps at different angles enable more complex 2-D patterned templates. Subsequently, sputtering facilitates the growth of ferromagnetic antidot thin films (e.g., from 20 to 100 nm Co thick layers) with designed symmetries. This technique constitutes a non-expensive method for massive mold production and pattern generation avoiding standard lithographical techniques. In addition, it overcomes current challenges of the two-stage electrochemical porous anodic alumina templates: (i) allowing the patterning of large areas with high ordering and/or complex antidot geometries, and (ii) being less-time consuming.

Preparation and Characterization of Pure SiC Ceramics by HTPVT Induced by Seeding with SiC Nanoarrays.

Dense SiC ceramics were fabricated by high-temperature physical vapor transport (HTPVT) growth process using SiC nanoarrays as the crystal seeds, which was obtained by vacuum heat treatment of amorphous SiC films prepared by plasma-enhanced chemical vapor deposition (PECVD) with a porous anodic aluminum oxide (AAO) template. In the HTPVT process, two-step holding was adopted, and the temperature at the first step was controlled at 2100 and 2150 °C to avoid SiC nanoarrays evaporation, and the grain size of SiC crystal increased with the increase in temperature and decrease in the pressure of Ar. The temperature of the second step was 2300 °C, and rapid SiC grain growth and gradual densification were achieved. The prepared SiC ceramics exhibited a relative density of more than 99%, an average grain size of about 100 μm, a preferred orientation along the (0 0 0 6) plane, a Vickers hardness of about 29 GPa, a flexural strength of about 360 MPa, and thermal conductivity at room temperature of more than 200 W·m−1·K−1.

(Invited) The Role of Surface Inhibition in Deterministic Controlled Electrodeposition

Templated electrodeposition is a common practice for the fabrication of metal nanostructures. The nanostructure architecture is set by that of the nanoporous template. For complex nano-architectures such as the metal nanomesh (see Figure) which was developed in our group [1,2], templates will remain necessary. Nonetheless, the 3D nanoporous anodized aluminum oxide (AAO) used for the templated electrodeposition, did form by self-assembly. Regular AAO made from pure Al has only vertical pores with a hexagonal arrangement. The additional horizontal pores in the 3D-AAO are formed with regular interval by doping of the aluminum with Cu [1]. Such level of deterministic control on the growth direction is not yet achievable with electrodeposition. Yet, directed growth of pillars and nanowires has been achieved by control of current inhibiting surface layers, either introduced by additives [3] or intrinsic to the metal electrochemistry [4]. We will shortly discuss the example of indium electrodeposition where InCl intermediate adsorbate is believed to form a coating around electrodeposited indium, leading to large single crystalline morphologies and nanowires when guided by a shallow pattern [3].Conformal deposition of thin-film coatings on high aspect ratio structures is typically claimed by Atomic and Molecular Layer Deposition (ALD and MLD). The nature of the surface limited reactions of these vapor-phase methods allows for the formation of continuous sub-nanometer to a few tens of nanometer thin films with uniform thickness over the most complex architectures. The accuracy of the technique goes at the cost of long deposition cycles especially when very large surface areas with extreme aspect ratios (>100) are involved. In recent years, electrodeposition processes have shown where the metal electrodeposition reaction for e.g. Ni or Pt can be inhibited early on, similarly leading to sub-nanometer to few nanometer thick coatings by cycling [5, 6]. In this paper, we will show examples where this process can be used also to coat nano-architectures such as our nanomesh with very large surface area (100 cm2 per planar cm2) and aspect ratio (100x).Finally, the electrochemical fabrication of oxide thin-films by electro-precipitation and electrochemically induced sol-gel reactions will be discussed. The poor electronic conductivity of oxides makes that the reaction is maintained by ionic conduction through the films, similar as for oxide formation by anodization. The resistive nature of the layers typically allows also for good conformality over high aspect ratio substrates [7]. Similarly, thin polymer films such as poly-phenylene oxide or PPO can be made conformally [8].[1] "The Formation Mechanism of 3D Porous Anodized Aluminum Oxide Templates from an Aluminum Film with Copper Impurities" Johannes Vanpaemel, Alaa Abd-Elnaiem, Stefan De Gendt, Philippe M. Vereecken, J. Phys. Chem. C, 119 (4), 2105–2112 (2015); [2] “Combining High Porosity with High Surface Area in Flexible Interconnected Nanowire Meshes for Hydrogen Generation and Beyond" Stanislaw Zankowski and Philippe M. Vereecken, ACS Appl. Mater. Interfaces, 10 (51), pp 44634–44644 (2018); [3] “Electrodeposited free-standing single-crystal indium nanowires" G. Hautier, J. D’Haen, K. Maex and P.M. Vereecken, ESL 11, K49 (2008); [4] “Fabrication of complex architectures using electrodeposition into patterned self-assembled monolayers” N.S.Pesika, A. Radisic, K.J. Stebe, P.C. Searson, Nano Letters. 6, 1023-1026 (2006); [5] Electro-chemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014); [6] “Self-Terminating Growth of Platinum Films by Electrochemical Deposition” Yihua Liu, Dincer Gokcen, Dincer Gokcen, Ugo Bertocci, Tom Moffat, Science 338(6112):1327-30 (2012); [7] "Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes" Marina Timmermans, Nouha Labyedh, Felix Mattelaer, Stanislaw Zankowski, Stella Deheryan, Christophe Detavernier, and Philippe M. Vereecken, J. Electrochem. Soc. 164 , 14, D954-D963 (2017); [8] “Self-limiting electropolymerisation of ultrathin, pinhole free poly(phenylene oxide) film on Carbon Nanosheets” S. Deheryan, D. J. Cott, R. Muller, M. Heyns and P. M. Vereecken, Carbon, , 88, 42-50, (2015). Figure 1