Spectroscopic analysis of ALD-coated 3D structures and origin of the Berreman effect

The Berreman effect shed light on various phenomena in 2D systems. However, coatings of 3D systems in soft-lithography and photonic devices, or 3D fibers suggest that the Berreman effect in 3D structures could be different. Experimental and computational infrared spectroscopy studies of 3D structures conformally coated with Al$_{2}$O$_{3}$ and ZnO layers using atomic layer deposition support this conclusion. In 2D systems, defining $\theta _{0}$ the macroscopic incidence angle of the IR beam on a sample, the LO mode absorbance increases as [Sin($\theta _{0})$]$^{4}$ when $\theta _{0}$ becomes grazing. On the other hand, in 3D systems a linear combination of [Sin($\theta _{0})$]$^{4}$ with appropriate coefficients must be considered. Accounting for Snell's law in the simulation model is essential to explain these results and the origin of the Berreman effect. We conclude that sample geometry determines infrared absorbance of LO modes versus $\theta $ and vice-versa Our results promise a new tool to investigate topography of insulating ionic oxide layers.