Nanoporous Alumina Structures Research Articles

Optical Characterization of ALD-Coated Nanoporous Alumina Structures: Effect of Sample Geometry or Coated Layer Material

Optical characterization of nanoporous alumina-based structures (NPA-bSs), obtained by ALD deposition of a thin conformal SiO2 layer on two alumina nanosupports with different geometrical parameters (pore size and interpore distance), was performed by two noninvasive and nondestructive techniques such as spectroscopic ellipsometry (SE) and photoluminescence (Ph) spectra. SE measurements allow us to estimate the refraction index and extinction coefficient for the studied samples and their dependence with wavelength for the 250–1700 nm interval, showing the effect of sample geometry and cover-layer material (SiO2, TiO2, or Fe2O3), which significantly affect the oscillatory character of both parameters, as well as changes associated with the light incidence angle, which are attributed to surface impurities and inhomogeneity. Photoluminescence curves exhibit a similar shape independently of sample pore-size/porosity, but they seem to affect intensity values. This analysis shows the potential application of these NPA-bSs platforms to nanophotonics, optical sensing, or biosensing.

Optical and Electrochemical Characterization of Nanoporous Alumina Structures: Pore Size, Porosity, and Structure Effect

Three nanoporous alumina structures (NPASs) obtained by the two-step anodization method were optically and electrochemically characterized. Two of the structures were symmetric (NPAS-Sf and NPAS-Ph) and one was asymmetric (NPAS-And); pore size ranged from 10 nm to 100 nm and porosity was 12% in the case of the symmetrical NPAS and 23% and 30% for each surface of the asymmetric structure NPAS-And(A) and (B), respectively. Optical parameters of the studied samples (refraction index and extinction coefficient) were obtained from ellypsometric spectroscopy measurements carried out for wavelengths ranging between 250 nm and 1700 nm (visible and near infrared regions), with the total average refraction indices being 1.54, 1.52, 1.14, and 1.05 for NPAS-Sf, NPAS-Ph, NPAS-And(A), and NPAS-And(B), respectively, which indicates porosity control of refraction index values. Electrochemical characterizations (concentration potential and impedance spectroscopy measurements) were performed with NaCl solutions, and they allowed us to estimate samples of effective fixed charge concentration (1.22 × 10−2 M, 1.13 × 10−3 M, and 1.15 × 10−3 M), ion transport numbers, permselectivity (33.0%, 3.1%, and 9.6%), and the electrical resistance of each solution/sample system as well as the interfacial effects associated to solution concentration–polarization, which seems to be mainly controlled by pore size and sample symmetry.

Formation of secondary Moiré patterns for characterization of nanoporous alumina structures in multiple domains with different orientations

We first report the formation of secondary Moiré patterns from electron Moiré fringes to characterize nanostructures in multiple domains with different orientations. The pitches and the orientations of the nanoporous alumina arrays in several domains are simultaneously measured using only one electron Moiré image.

Vertically Aligned Nanowires on Flexible Silicone using a Supported Alumina Template prepared by Pulsed Anodization

Carpets of vertically aligned nanowires on flexible substrates are successfully realized by a template method. Applying special pulsed anodization conditions, defect-free nanoporous alumina structures supported on polydimethylsiloxane (PDMS), a flexible silicone elastomer, are created. By using this template with nanopores ending on a conducting underlayer, a high-density nanowire array can be simply grown by direct DC-electrodeposition on the top of the silicone rubber.

Effect of voltammetric parameters on fabrication of highly ordered nanoporous alumina structures

The synthetic route of quantum wires, nanorods and nanotubes has recently acquired immense popularity, as the technique is easy, low cost and less skill dependent. In the present work, highly ordered, nanoporous alumina structures have been synthesised on aluminium in oxalic acid electrolyte using cyclic voltammetry by critically controlling the oxidation potential, temperature, time and concentration of the oxalic acid. Self–organised pores were developed over the anodic alumina. The effect of concentration of electrolyte, oxidation potential, temperature and treatment time were correlated with the morphology of the nanoporous alumina layers. The mechanism of the pore formation and its growth with respect to the changes in the nanostructures was also highlighted. Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray diffraction (XRD) were used as the characterisation tools in different stages of the experiment.

Fabrication of porous alumina on quartz crystal microbalances

Nanoporous alumina structures were fabricated on quartz crystal microbalances (QCMs) by electrochemically anodizing aluminum electrodes which had a typical thickness of 13μm. By varying the temperature and voltage of anodization, the diameter of the cylindrical pores could be controlled in the range of 12–40nm. Properties of the porous films were determined from scanning electron microscopy images and by analyzing isotherms of nitrogen, propane, and water. The isotherms showed signatures of capillary condensation and hysteresis. The mass sensitivity of the QCMs with porous alumina electrodes was increased by a factor of up to 120 compared to conventional QCMs with flat electrodes. Measurements at atmospheric pressure and room temperature in which the relative humidity was varied showed that QCMs with porous alumina electrodes are very sensitive to the partial pressure of water, and can be used as humidity sensors.