Abstract:
In this paper we report on new techniques for making self-ordered porous layers of alumina of varying aspect ratios on
glass, without the use of lithographic or masking techniques. Use of RF etching in one of the hole forming steps and also
when filling the holes with sputtered metal is shown to be advantageous over additional anodisation. These hole arrays
have intrinsically interesting optical responses which will be reported, but their main use is for nano-patterning of
subsequent deposited layers either as templates or as masks. High resolution images demonstrate the uniformity in nanohole
diameter and in the spacing between holes, which can be achieved when care is used in production.
While many nanostructured materials can be deposited using these Porous Anodic Alumina (PAA) templates we focus
here on filling the vertical cylindrical holes with silver. Etching during hole filling leads to better-controlled structures
and more efficient processes. Novel optical data on the resultant conducting columnar rings will be presented. Spectrally
much sharper plasmon resonant features are found than those reported for classical and more random silver column and
island arrays. The optical properties are analysed from an effective medium perspective using data from
spectrophotometry and ellipsometry. Fitting this data gives modelled layer thickness and the vertical profile in close
agreement with direct SEM imaging. The effective refractive indices of the silver columnar layer have interesting and
potentially useful dispersion characteristics.
