Flow rate and interface roughness of zinc oxide thin films deposited by spray pyrolysis technique

The interface growth and topology of sprayed ZnO thin films are examined here using the spatial scaling approach to the film surface in relation with the effect of a spraying deposition flow rate, f, ranging between 1 and 8 mil min−1. This thermally activated process is performed at the optimal temperature of the material (T=723 K). Two different growth mechanisms are identified, each of them characteristic of a particular f region. These related regions are separated from each other at a critical growth rate value of fc=5 mil min−1. The mechanism evolved below fc leads to a Hurst exponent α=0.4 typical of simple ballistic deposition growth modes. The morphology evolution in this f region corresponds to smoothing of the film surface with an increase of the flow rate. The growth kinetic exponent n=0.9 obtained in this region could be assigned to the elimination of some groove. Beyond fc, the spraying process engenders duplicate roughness exponents. The first value relative to the lowest scan lengths increases with f from α1=0.40 until unity. The second one, always evaluated at α2=0.16, is free of the f value. The growth kinetic exponent obtained in this f region, n=1.6, confirms a change of the growth mechanism, the last probably linked to incorporation of Zn particles at the growing film surface.