# A Review on the Deformation Behavior of Silver Nanowire Networks under Many Bending Cycles
## 5 Deformation Behavior of Silver Nanowire Network with Protective Coating
Figure 16: (**a**) Cyclic bending test results of silver nanowire networks with and without RGO coating after exposing them at 70 \({}^{\circ}\)C for 132 h. (**b**) Sheet resistance change of silver nanowire networks with and without RGO coating as a function of exposure time in air at 70 \({}^{\circ}\)C. Resistance change of bare silver nanowire networks with GO and RGO coatings exposed to air (**c**) at 120 \({}^{\circ}\)C and (**d**) at 85 \({}^{\circ}\)C with 85% relative humidity. Reproduced with permission from ref. [49] with permission from The Royal Society of Chemistry. Reproduced with permission from ref. [50]. Copyright 2018, Elsevier. Figure 15: SEM images of RGO-coated silver nanowire networks after (**a**) 10,000, (**b**) 100,000, and (**c**,**d**) 800,000 bending cycles. Reproduced with permission from ref. [49] with permission from The Royal Society of Chemistry. The native brittleness of oxide and concentration of the stress around the oxide resulted in several failures in the network [51]. Furthermore, the formation of silver oxide, which has a higher resistivity than pure silver, hinders the electrical conduction within the network and reduces the area of the electric percolation pathway [38]. Thus, a smaller increase in the fraction resistance of the RGO-coated silver nanowire network is in line with lesser oxidation of the silver nanowire network. As demonstrated above, coating the silver nanowire network with RGO did not affect its deformation behavior, but increased the chemical stability against oxidation and ultimately increased the network's mechanical reliability. Therefore, combining RGO with a silver nanowire network seemed a promising method to fabricate a mechanically reliable silver nanowire network. Metal oxide is another example for the protective coating to enhance the chemical and thermal stabilities of silver nanowire electrodes [52; 53; 54; 55; 56; 57]. [PERSON] et al. investigated the effect of a metal oxide coating on the fracture behavior of silver nanowire networks [52]. Al\({}_{2}\)O\({}_{3}\), HfO\({}_{2}\), and TiO\({}_{2}\) films were deposited on silver nanowire electrodes by atomic layer deposition at a low temperature of 100 \({}^{\circ}\)C. Cyclic bending tests with in situ resistance measurements were conducted for up to 300,000 cycles. Thicker metal oxide films resulted in a greater increase in the resistance of composite electrodes under cyclic bending, owing to the reduced fracture strength of thicker films as shown in Figure 18. Regardless of the type of metal oxides, however, a similar tendency of resistance change in response to cyclic bending was observed, which revealed that the critical thickness calculation based on [PERSON]'s theory for the evaluation of the brittle-to-ductile transition was not applicable. Damaged Al\({}_{2}\)O\({}_{3}\)-coated silver nanowire composite electrodes sustained excellent chemical stability without showing an increase in resistance, even after 500 h of exposure at 85 \({}^{\circ}\)C (Figure 19a). Regarding the thermal stability, the damaged silver nanowire composite electrode with a 1 nm Al\({}_{2}\)O\({}_{3}\) film showed an increased sheet resistance at 200 \({}^{\circ}\)C. The other damaged samples with Al\({}_{2}\)O\({}_{3}\) layers thicker than 3 nm showed excellent stability up to the maximum test temperature of 250 \({}^{\circ}\)C (Figure 19b). The analysis of the optoelectronic properties revealed that silver nanowires with Al\({}_{2}\)O\({}_{3}\) layers thicker than 5 nm showed the degradation of the optical transmittance due to increased light reflection at the film  
Figure 17: SEM images of silver nanowire networks (**a**–**c**) without and (**d**–**f**) with RGO coating as a function of the exposure time in air at 70 \({}^{\circ}\)C. Reproduced with permission from ref. [49] with permission from The Royal Society of Chemistry. substrate interfaces (Figure 19c).