This review is devoted to the angular selectivity that can be obtained in thin films prepared under conditions such that they contain inclined absorbing regions of sizes much smaller than the wavelength of visible light. The films are of considerable interest as window coatings for energy-conscious architecture and, potentially, in the automotive sector. The theoretical basis for modelling the optical properties is presented, comprising rigorous bounds on the dielectric function, effective medium theories pertinent to different microgeometries and equations for treating the optics of anisotropic thin films. Experimental data are reported for films made by oblique-angle evaporation of Cr and for reactive and non-reactive oblique-angle sputtering of Cr, Al, Ti and W. The highest angular selectivity was obtained with evaporated Cr, whereas the highest luminous transmittance, combined with some angular selectivity, was found with reactively sputtered Al. Films made from Ti showed angular selectivity mainly in the infrared, whereas films made from W could display angular selective electrochromism. Samples of several types were subjected to elaborate theoretical analysis using effective-medium theories and it was seen that theory and experiment could be reconciled using plausible parameters to specify the microstructures of the films. Thus it appears that the angular, spectral and polarization dependences of obliquely deposited films can be understood, at least approximately, in terms of conceptually simple theoretical models.

Tungsten oxide films were made by magnetron sputtering with a large angle between the substrate normal and the direction of the deposition flux. Scanning electron microscopy displayed a microstructure composed of inclined columns. Spectrophotometric measurements on films with different amounts of electrochemically intercalated Li+ ions showed pronounced angular selective transmittance together with electrochromism.

Thin chromium films were prepared by oblique sputtering, i.e. by letting deposition species impinge onto a substrate from a significantly off-normal angle. The surface structure was studied by Atomic Force Microscopy. The images indicated a non-fractal structure at short length scales. Exponents describing the scaling of the r.m.s. roughness with film thickness and lateral length scale were found to be close to unity. The results disagree with oblique ballistic deposition simulations, and a more complex behaviour is clearly present. Unstable growth of columnar features due to Schwoebel barriers for diffusing atoms at steps in the surface may be important for our films.

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