Stories from China

Dielectric materials are widely used for various electrical devices and equipment, including capacitors, transformers, gas-insulated switchgear, and so on; energy storage; electronic packaging; and mechanical support [1], [2]. Surface charge commonly exists on the surface of dielectric material due to the strong electromagnetic (electron injection or ionization) or mechanical stress (contact electrification). On one hand, surface charge accumulation is a critical factor that can greatly influence the flashover, especially in high-voltage direct-current equipment [3]. On the other hand, high surface charge density is greatly expected for energy storage or harvesting devices, such as triboelectric nanogenerators (TENG), supercapacitors, and so on [4], [5]. Because surface charges are imperceptible, surface charge characterization techniques play an important role in comprehensively understanding their characteristics.