The Figure 6b shows the current den

The Figure 6b shows the current density-electrical field graph of MLV composite that is plotted according to Equation 3 as a function of temperature from -50 to 75 °C. The activation energy of ZnO-PEI multilayer composite calculated from Figure 6c is 0.50 eV, which is in good agreement with activation energies of ZnO- metal oxides based varistors.39 The difference between this value and the earlier value obtained from modulus spectroscopy is thought to be due to a difference in measurement methods, as it is well known in research on semiconductors.40 Another possible reason is that energy barrier attributed to the 0.50 eV was not observed in Fig.5 because it was outside the measured temperature-frequency range. Unfortunately, the temperature range of Fig.5 was limited by the stability of PEI and the frequency lower than 0.01 Hz was also unrealistic for the spectroscopic measurement. In any case, it remains true that ZnO/PEI interface formed a potential barrier providing the enhanced resistance and non-linear I-V characteristics. Thus, we avoid further discussion in this paper. Beyond all discussion, it is important to point out that the Figure 4 and 6 reflect the main idea of this novelty and it is an excellent facility to demonstrate micro/nano structure - electrical property relationship by the grain boundary engineering.