Oxide-Film Effect on Infrared Radiative Properties of Grating Structures of Aluminum

• Published in: Journal of thermophysics and heat transfer 2011-01, Vol.25 (1), p.80-86
• Main Authors: Qiu, J, Liu, L. H, Hsu, P.-F
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of surfaces; Physics
• ISSN: 0887-8722; 1533-6808
• DOI: 10.2514/1.49834

Aluminum tends to oxidize naturally, which hence changes the radiative properties of the metallic structure. The focus of this study is on the effect of oxide film on the infrared radiative properties of grating structures made of aluminum. Two kinds of grating-surface geometries (namely, square-wave grating and sawtooth grating) with alumina thin film are considered. The impact of the size of the oxide coating on the infrared radiative properties is predicted numerically by the finite difference time-domain method within an incident-wavelength range of 2 to 12μm12μm. The effect of the alumina film on the cavity resonance of square-wave gratings and the surface wave of sawtooth gratings is discussed. For the oxidized square-wave grating with a given film thickness, four different modes of cavity resonances are observed at different wavelengths. The resonance wavelengths will be changed as the oxide-film thickness increases. Because of the absorption characteristics of alumina, one mode of resonance is only formed in alumina films, while the others are excited in both alumina films and cavity. The energy of the resonance is mainly absorbed by alumina films when the resonance wavelength within the range of 10.2 to 12μm12μm, and it is transmitted and absorbed by aluminum substrate within the range of 2 to 10.2μm10.2μm. For the oxidized sawtooth grating, no cavity-resonance absorption peaks are observed; only one absorption peak exists, which is due to the surface waves absorbed by alumina films. The finding of this work may facilitate the design and applications of metallic gratings in cases in which the metal is easily oxidized. [PUBLISHER ABSTRACT]