A model for the optical response of obliquely deposited thin films

Abstract

An effective medium model, capable of explaining both the unusual transmittance characteristics and the pronounced biaxial response observed in obliquely deposited metal and metal-insulator composites, is used to model experimental data. Short-range interactions between neighbouring columns dominate the response. This in turn leads to biaxial behaviour, provided the columns are packed anisotropically.

Angular selective window coatings: theory and experiments

“…Al Evaporation [8][9][10] Reactive sputtering [13,17] Cathodic arc deposition [9,10] Ti Reactive evaporation [13,18] Cathodic arc deposition [9] Cr Evaporation [3-7, 13, 14, 22, 23] Reactive sputtering [13,15,16] Cathodic arc deposition [9,10] Ag Evaporation [11,12,20] Cathodic arc deposition [12,20] W Reactive sputtering [19] the vapour species incident at a large off-normal angle with respect to the substrate. Table 1 summarizes the base metals and experimental techniques employed in previous work.…”

“…Equation (8) is a generalization of the usual optical theorem [64] for non-absorbing media and C ext can be either positive or negative. From the definition of an effective medium it follows that C ext = 0; that is, S(0) = 0 (10) which expresses the fundamental property of an effective medium. This condition has been put forward earlier [65,66] in somewhat different contexts.…”

Angular-selective optical transmittance through obliquely evaporated Cr films: Experiments and theory

“…Attempts to model the optical properties by employing Maxwell-Garnett theory 20 and touching-cylinder-array theory 11 were unsuccessful, which indicates that the columns and voids have a fair degree of topological equivalence in the obliquely evaporated films.…”

“…Earlier work has been centered on effective medium concepts, 18 and the Bruggeman theory 19 was found suitable to represent the optical data for nonreactively sputtered Cr films, 9 whereas the Maxwell-Garnett theory 20 could account for the data of reactively sputtered Al-oxide-based films. 13 Other theories, such as a touching-cylinder-array theory, 11 have been successfully employed to some data. 10,11 The present work considers obliquely evaporated Cr films-having superior angular selectivity, as seen before 7 -and shows that the optical properties can be reconciled with a Bruggeman approach.…”

“…13 Other theories, such as a touching-cylinder-array theory, 11 have been successfully employed to some data. 10,11 The present work considers obliquely evaporated Cr films-having superior angular selectivity, as seen before 7 -and shows that the optical properties can be reconciled with a Bruggeman approach.…”