Optical properties of ultrafine aluminum particles

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Abstract
Ultrafine Al particles with median diameters of 3–4 nm were produced by gas evaporation in He+O2. Optical transmittance measurements for wavelengths of 0.3–2.5 μm gave reproducible results. These can be reconciled with the Maxwell Garnett theory with one exception: the parallel band absorption, occurring at 0.85 μm in bulklike specimens, is much less visible than theoretically predicted. This is possibly caused by defect scattering inside the particles, which increases the featureless Drude absorption, although other mechanisms may also be operative. The study provides a basis for modeling ’’integrally’’ colored anodic Al2O3.