Study of deposition of Al$_2$O$_3$ nanolayers by atomic layer deposition on the structured ito films

In this work, the antireflective nanostructured ITO/Al$_2$O$_3$ coatings that have a gradient of the effective refractive index in the direction perpendicular to the substrate plane have been studied. The coatings were obtained by the atomic layer deposition (ALD) of aluminum oxide on the structured ITO films. The transmission electron microscopy showed that the deposited nanosized aluminum oxide layer was of good quality and uniformly covered the ITO whiskers. As shown in experiments, the thickness of the resulting Al$_2$O$_3$ layer is affected by the thickness and, hence, by the degree of surface roughness of the initial ITO film. The resulting thicknesses can be several times lower than that planned in the experiment, based both on the calculations of the parameters of the ALD process and on the direct measurements of the aluminum oxide deposition rate for unstructured ITO films. A possible reason that affects the growth rate of Al$_2$O$_3$ layers in nanostructured ITO films is a strong increase in the surface area of the ITO film during its structuring. So, the transmission and scanning microscopy data for a 700 nm-thick structured ITO film have shown that its surface area is more than 20 times greater than that of a smooth film.