“…Moreover, as can be clearly seen from the Table 1and Figure 3, the band gap values of the CuO thin films decreased from 1.42 to 1.30 eV with increasing the film thickness. The decrease in the band gap value with increasing the film thickness can be ascribed to the morphological alteration of the films, improvement in crystallization and changes in interatomic distances of the films (Ateş et al, 2007, Akaltun et al, 2011, Yıldırım et al, 2010, Akaltun et al, 2015. The refractive index of the thin films was determined according to the Moss relation (Hannachi et al, 2009) which is directly associated with the fundamental energy band gap,…”