Mechanism of contact electrification-induced microscale breakdown between separating electrodes

Since the 1990s, there has been a debate on whether the contact electrification (CE)-induced discharge mode is continuous or intermittent, and the understanding of the relationship between the electrode potential and Paschen's curve remains controversial. In the present work, we demonstrate CE-induced microscale breakdown between two separating metal electrodes without an external voltage source and successfully reveal that continuous and intermittent discharge modes can both be realized by adjusting the electrode separation velocity. The CE-induced initial charge, electrode separation velocity, and breakdown time delay are identified as key factors, and their combined effects explicitly determine the breakdown mode. Further, it is found that in continuous breakdown mode with a sufficiently high initial charge, the electrode potential versus gap distance exactly follows the modified Paschen's curve, which incorporates the field emission regime. This discovery suggests that a microscale breakdown curve can be determined based on a single characterization of the separating electrode potential without the need to perform redundant repeated experiments. The results of this study elucidate microscale breakdown physics with moving electrodes and inform better control and optimization of microelectromechanical devices for applications including energy harvesters, microsensors, and detectors.