Sculptured thin films - I. Concepts

A report on the conceptualization of sculptured thin films (STFs), as well as on recent theoretical advances thereon, is presented. The morphology of a STF is described in terms of a spatially varying unit vector called the director, whose piecewise specification assists in setting up frequency-dependent constitutive relations of the STF. These relations lead in turn to a 4×4 matrix differential equation for the propagation of electromagnetic waves in the STF. Optical, suboptical, infrared and even millimeter-wave applications are possible, as well as acoustic and piezoelectric ones.