Voltage Contrast in Scanning Electron Microscopy to Distinguish Conducting Ag Nanowire Networks from Nonconducting Ag Nanowire Networks

A study of the electrical properties of metallic nanowires requires a clear analysis of conductive networks. In this study, we demonstrated that the conducting networks of Ag nanowires (AgNW) could be visually observed by examination of the voltage contrast of the scanning electron microscopy (SEM) images, which was caused by the differences in the degrees of charging of AgNWs. When AgNWs dispersed on a quartz glass were irradiated by primary electrons, the substrate became negatively charged. This induced positive charges on the AgNWs in contact with the electrodes. As a result, AgNW networks connected to electrodes appeared dark in the SEM image, while the isolated AgNWs appeared brighter. By varying the acceleration voltage of the primary electrons, the extent of charging could be controlled, which, in turn, enabled the observation of the voltage contrast of AgNWs. Using the voltage contrast of SEM images, we could visually distinguish the AgNW networks having an electrical connection with the electrode from the ones that were not connected to the electrode.