Sculptured Thin Films: Accomplishments and Emerging Uses

Sculptured thin films (STFs) are nano-engineered materials whose columnar morphology is tailored to elicit desired optical responses upon excitation. Two canonical forms of STFs have been identified. Linear constitutive relations for general STFs as unidirectionally nonhomogeneous (continuously or piecewise uniformly) and locally bianisotropic continuums are presented, along with a 4$\times$4 matrix ordinary differential equation for wave propagation therein. A nominal model for the macroscopic properties of linear STFs is devised from nanoscopic considerations. The accomplished implementation of STFs as circular polarization filters and spectral hole filters is discussed, as also are emerging applications such as bioluminescence sensors and optical interconnects.