When the solution was not continuously stirred, the final nanoparticles obtained after annealing are irregular in shape and easily formed agglomerates [15]. It is found by AFM images that the higher total metal concentration causes the higher nanoparticle size in sample S2 against S1. In addition, the higher particle size in S4 illustrated in SEM images can be related to the effect of oxygen presence in annealing treatment [15], [16] and [17].