Interestingly, it is found that substrate thickness can affect the number of layers of graphene grown on the substrate. Growing graphene on different thicknesses of Cu substrates, Yilmaz and Eker have shown that the grain size of the substrate decreases with an increase in the substrate's thickness . In the thickness range of 9-250 µm, the results of single-layer graphene grown on all substrates show that 150 µm gave the best quality graphene, while the other substrates had few-layer graphene in addition.