Optical characterization of porous alumina from vacuum ultraviolet to midinfrared

Abstract

Porous alumina was fabricated and optically characterized over a wide spectral range. Layers were formed electrochemically in oxalic acid solution from 10-m-thick aluminum films evaporated onto silicon wafers. The layer formation was monitored with in situ spectroscopic ellipsometry in the visible and near-infrared wavelength range to accurately determine the thickness and dielectric functions. Anisotropy due to the columnar nature of the porous structure was determined using optical modeling. The porous alumina layer was found to have a small but significant absorption tail throughout the visible region. Atomic force microscopy and scanning electron microscopy were used throughout the process to assess the quality of pore formation. The mean pore center-to-center spacing was approximately 100 nm with thicknesses up to 5 m. The infrared spectra revealed absorption peaks previously seen in ceramic alumina and peaks not associated with bulk alumina.

Influence of TiO2-Coating Layer on Nanoporous Alumina Membranes by ALD Technique

“…Application of spectroscopic ellipsometry to the study of optical properties of nanoporous alumina structures obtained by electrochemical aluminum anodization has already been performed by different authors [24,25], and differences depending on the pore radii/porosity of the studied samples have been reported [26]. Ellipsometry measures a change in the polarization as light reflects or transmits from a material structure, and the ellipsometric angles Ψ and ∆, determine the differential changes in amplitude and phase, respectively (tan(Ψ) e i∆ = r p /r s , where r p y r s are the amount of light reflected in the perpendicular and parallel planes of incidence [27]).…”

Optical properties of copper and silver nanowires grown in a nanoporous alumina template

“…For obtaining ε , Goad and Moskovits [8] used the Maxwell-Garnett approximation, which is strictly valid for very small metal inclusions in the dielectric [12]. Given the nature of the present samples (parallel cylindrical metallic NW in a dielectric matrix), Bruggeman's effective medium approximation [12] is used instead; which already has been used for the unfilled PAM [11,17]. It is more appropriate for the rather high metal filling fraction f m of these samples.…”

Optical properties of nanoporous Al2O3 obtained by aluminium anodization

“…The relation between the optical and structural properties of PAA has been studied by spectroscopic ellipsometry [9]. Similar ellipsometric studies have recently identified resonant transitions in the IR and UV regions [10]. It has been also shown that PAA PL depends on the preparation conditions, like annealing [6] or substrate [11,12].…”