Thickness effects on the texture development of fluorine-doped SnO2 thin films: The role of surface and strain energy

Polycrystalline fluorine-doped SnO2 thin films have been grown by ultrasonic spray pyrolysis with a thickness varying in the range of 40 to 600 nm. A texture transition from < 110 > to < 100 > and < 301 > crystallographic orientations has experimentally been shown by x-ray diffraction measurements as film thickness is increased, showing that a process of abnormal grain growth has occurred. The texture effects are considered within a thermodynamic approach, in which the minimization of total free energy constitutes the driving force for grain growth. For very small film thickness, it is found that the < 110 > preferred orientation is due to surface energy minimization, as the (110) planes have the lowest surface energy in the rutile structure. In contrast, as film thickness is increased, the < 100 > and < 301 > crystallographic orientations are progressively predominant, owing to elastic strain energy minimization in which the anisotropic character is considered in the elastic biaxial modulus. A texture map is eventually determined, revealing the expected texture as a function of elastic strain and film thickness. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684543]