Two-step Anodization Approach Research Articles

Development of a Capacitive Pressure Sensor Based on Nanoporous Anodic Aluminium Oxide

Capacitive pressure sensors make pressure sensing technology more accessible to a wider range of applications and industries, including consumer electronics, automotive, healthcare etc. However, developing a capacitive pressure sensor with brilliant performance using a lowcost technique remains a difficulty. In this work, the development of a capacitive pressure sensor based on nanoporous AAO fabricated by a two-step anodization approach which offers a promising solution for precise pressure measurement is fabricated by a two-step anodization approach. A parallel plate capacitive sensor was fabricated by placing two AAO deposited sheets are placed face to face, with the non-anodized aluminum component at the base functioning as the top and bottom electrodes. A variation in the capacitance value of the as fabricated sensor was observed over an applied pressure range (100 Pa-100 kPa). This change in capacitance can be attributed to the decrease in the distance between the two plates and the non-homogenous distribution of contact stress and strain due to the presence of nanoporous AAO structure. In this pressure range the sensor showed high sensitivity, short response time and excellent repeatability which indicates a promising future of the fabricated sensor in consumer electronics, intelligent robotics etc.

Fabrication of silver nanoparticles decorated anodic aluminum oxide as the SERS substrate for the detection of pesticide thiram

An efficient surface-enhanced Raman scattering (SERS) substrate is developed based on silver nanoparticles decorated anodic aluminum oxide (Ag/AAO). The AAO templates were fabricated using a two-step anodization approach, and silver nanoparticles (AgNPs) were obtained by thermal decomposition of Ag nitrate in AAO. The structure of Ag/AAO hybrid substrate is characterized by scanning electron microscopy (SEM). The results show that the as-prepared SERS substrates consist of high-density AgNPs with sizes of tens of nanometers. The AgNPs are adsorbed on the surface of AAO template in the form of network structure which is called “hot spot”. The SERS enhancement ability of the nanostructure is verified using thiram as probing molecules. The limit of detection is as low as 1×10−9 mol/L. The results indicate that the as-prepared substrate possesses excellent SERS sensitivity, high stability and uniformity enhancement.

Highly Ordered Porous Anodic Alumina with Large Diameter Pores Fabricated by an Improved Two-Step Anodization Approach.

The aim of this study is to prepare highly ordered porous anodic alumina (PAA) with large pore sizes (> 200 nm) by an improved two-step anodization approach which combines the first hard anodization in oxalic acid-water-ethanol system and second mild anodization in phosphoric acid-water-ethanol system. The surface morphology and elemental composition of PAA are characterized by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectrometer (EDS). The effects of matching of two-step anodizing voltages on the regularity of pore arrangement is evaluated and discussed. Moreover, the pore formation mechanism is also discussed. The results show that the nanopore arrays on all the PAA samples are in a highly regular arrangement and the pore size is adjustable in the range of 200-300 nm. EDS analysis suggests that the main elements of the as-prepared PAA are oxygen, aluminum and a small amount of phosphorus. Furthermore, the voltage in the first anodization must match well with that in the second anodization, which has significant influence on the PAA regularity. The addition of ethanol to the electrolytes effectively accelerates the diffusion of the heat that evolves from the sample, and decreases the steady current to keep the steady growth of PAA film. The improved two-step anodization approach in this study breaks through the restriction of small pore size in oxalic acid and overcomes the drawbacks of irregular pore morphology in phosphoric acid, and is an efficient way to fabricate large diameter ordered PAA.

Fabrication of Hierarchical TiO2Nanotubes in a New HBF4-Based Electrolyte for Enhanced Morphology and Photocatalytic Activities

The present work introduces a new HBF4-based electrolyte for the preparation of anodic TiO2 nanotubes (NTs). It is shown that, by optimizing the preparation parameters, highly ordered and extremely smooth TiO2 NTs can be successfully fabricated in the HBF4-containing electrolyte via a two-step anodization approach (so-called the BF4–TiO2 NTs). The obtained BF4–TiO2 NTs have unique hierarchical upper-nanopore/lower-nanotube structure and show both enhanced photoelectrochemical and photocatalytic performances than the referenced TiO2 NTs formed in the F–-containing electrolyte (i.e., the F–TiO2 NTs). We consider that the decomposition of BF4– into F– under high electric field is the key for the formation of anodic BF4–TiO2 NTs, and this allows the growth of BF4–TiO2 NTs going through a quite different way as compared to that of the F–TiO2 NTs. These findings may pave an alternative way for the preparation of TiO2 NTs with enhanced geometrical features and application properties.

Influence of substrate morphology on the growth and properties of TiO2 nanotubes in HBF4-based electrolyte

The present work demonstrates how the growth and photoelectrochemical (PEC) properties of anodic TiO2 nanotubes (NTs) are influenced by Ti substrates in the new HBF4 containing electrolyte. Three different Ti substrates, the rough abraded Ti foil, the smooth electropolished Ti and the two-step Ti plate (i.e. the Ti substrate with ordered dimples left by removing the TiO2 NTs formed in the first-step anodization), are employed for the preparation of TiO2 NTs. It is revealed that the Ti substrate morphology can largely influence the formation of TiO2 NTs, particularly in the initial tube generation stage. The two-step Ti substrate has ordered hexagonally distributed dimples which play the role of template for the formation of new TiO2 NTs. As a result, the TiO2 NTs grown via a two-step anodization approach have highly ordered structure and extremely smooth sidewalls, hence possess the best PEC performance among the three kinds of substrates.

A reliable TiO 2 nanotube membrane transfer method and its application in photovoltaic devices

In this work we present a highly reproducible method to fabricate front-illuminated TiO 2 nanotube-based dye-sensitized solar-cell. The well oriented nature of the nanotube arrays ensures favorable electron percolation pathways for charge transfer between interfaces. Our two-step anodization approach allows for a nearly 100% reliable production of uniform films with a greater flexibility in the thickness of the nanotube membranes suitable for both liquid and solid electrolyte dye-sensitized solar-cells (DSCs). Large area nanotube membranes fabricated by this method were successfully detached and transferred onto fluorine-doped tin oxide (FTO) and other substrates without crack formation. In contrast to earlier methods, the method presented here does not require steps that may damage the nanotube membrane quality such as prolonged ultrasonication or acid treatment. We systematically study the current–time profile and analyze the detachment mechanism. Front-illuminated nanotube-based dye-sensitized solar-cells using this method reach an efficiency of 6.3% with liquid electrolytes (of which at least 6.1% originate from the transferred membrane) and 1.9% when using the solid state hole conductor CuSCN under AM1.5 1 sun illumination.

用于快速、无损检测阳极氧化铝阻挡层厚度的光谱方法

A novel method was established for the rapid and nondestructive determination of the barrier layer thickness of anodic aluminum oxide (AAO) films based on their optical transmission spectra. Nanoporous AAO films with highly ordered pores have been prepared by a two-step anodization approach. Series UV-VIS-NIR transmission spectra of AAO with different barrier layer thickness have been studied. Oscillatory waves were observed at visible-near infrared region in the spectrum of AAO with the existence of barrier layer. Furthermore, a linear relationship between the number of wave crests and the thickness of barrier layer was established, for which the correlation coefficient is 0.99979. This relationship affords a simple and efficient method for rapid and nondestructive detection of the barrier layer thickness of AAO films.

Improved two-step anodization technique for ordered porous anodic aluminum membranes

We report on an improved two-step anodization technique through combining the first hard anodization in C 2H 2O 4 with the second mild anodization in H 3PO 4, which successfully overcome the drawbacks of irregular top surfaces in the conventional two-step hard anodization in C 2H 2O 4 and disordered pore arrays in the two-step mild anodization in H 3PO 4. The key success of our method is the strong guidance effect of the first hard anodization on the second mild anodization. Highly-ordered (both top and bottom surfaces) porous anodic aluminum (PAA) membranes with interpore spacing from 220 to 350 nm have been realized under anodizing voltages from 100 to 150 V. The interpore spacing is only determined by the first anodizing voltage, while the pore diameter can be manipulated in the second step by adding ethanol in the H 3PO 4 electrolyte, changing the H 3PO 4 bath temperature, and altering the second anodizing voltage. The bath temperature for the steady growth of ordered structures can be expanded up to 20 °C, from which the average activation energy can be yielded. The present novel two-step anodization approach is simple, efficient, and cost-effective. It expands the self-ordering regime of PAA membranes, which is of great value for applications in diverse areas of nanotechnology.

Fabrication of Silver Decorated Anodic Aluminum Oxide Substrate and Its Optical Properties on Surface-Enhanced Raman Scattering and Thin Film Interference

In this paper, a simple method to fabricate a three-dimensional (3D) nanostructure decorated with Ag nanoparticles for surface-enhanced Raman scattering (SERS) is demonstrated. Highly ordered porous anodic aluminum oxide (AAO) templates were employed to construct these compound nanostructures. First, the AAO templates were fabricated using a two-step anodization approach. Second, an alternating current (AC) electrochemical deposition was used to fill AAO templates with Ag nanoparticles. Taking 4-mercaptopyridine (4-MPy) as the probing molecule, high-quality SERS spectra were observed. The UV-vis mirror reflection spectra were measured to investigate the surface plasma resonance (SPR) absorbance. An interesting phenomenon of SPR-affected thin film interference was observed. SERS mapping was performed to characterize the homogeneity of as-prepared substrates. Good homogeneity and stability make these substrates good candidates for SERS spectroscopy.

Electrochemical fabrication of sandwich nanostructures based on anodic alumina

A sandwich porous anodic alumina (PAA/Al2O3/PAA) film was successfully designed and fabricated using the customary two-step anodization approach on both sides of an aluminum foil. The structure of the film was determined with field emission scanning electron microscopy (SEM). The SEM shows the PAA membranes has a well-defined nanostructure. All nanoholes stand symmetrically on both sides of the barrier layer. The average pore diameter reaches 40 nm.

A facile approach to formation of through-hole porous anodic aluminum oxide film

Highly ordered through-hole anodic porous alumina film was fabricated using a facile single side and two-step anodization approach without any special pretreatment. The as-fabricated anodic aluminum oxide (AAO) film has a mean pore diameter of 80 nm and the interpore distance is ∼150 nm. The pore density can be high as 1.0×10 10 cm −2. During the processes of removal of aluminum substrate and pore opening, a simple setup was used. The evolution of surface morphology of the AAO film was characterized by scanning electron microscopy (SEM). The fabricated pore-through AAO film can then be used as templates for growth of well aligned nanowire, nanotube and nanodevice.