Generalized ellipsometry, a non-destructive optical characterization technique, is employed to determine geometrical structure parameters and anisotropic dielectric properties of highly spatially coherent three-dimensionally nanostructured thin films in the spectral range from 400 to 1700 nm. The analysis of metal slanted columnar thin films fabricated by glancing angle deposition reveals their monoclinic optical properties and their optical response can be modeled with a single homogeneous biaxial layer. This homogeneous biaxial layer approach is universally applicable to sculptured thin films and effective optical properties of the nanostructured thin films are attained. We provide a nomenclature and categorization for sculptured thin films based on their geometry and structure. A piecewise homogeneous biaxial layer approach is described, which allows for the determination of principal optical constants of chiral and achiral multi-fold and helical sculptured thin films. It is confirmed that such sculptured thin films have modular optical properties. This characteristic can be exploited to predict the optical response of sculptured thin films grown with arbitrary sequential substrate rotations. As an alternative model approach, an anisotropic effective medium approximation based on the Bruggeman formula is presented, which provides results comparable to the homogeneous biaxial layer approach and in addition provides the volume fraction parameters for slanted columnar thin films and their depolarization factors.
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