Mapping the Space Charge at Nanoscale in Dielectric Polymer Nanocomposites

Heterogeneous dielectric materials such as dielectric polymer nanocomposites have attracted extensive attention because of their exceptional insulating and dielectric performance, which originates from the unique space charge dynamics associated with the various interfacial regions. However, the space charge distribution and transport in polymer nanocomposites remain elusive due to the lack of analytical methods that can precisely probe the charge profile at the nanoscale resolution. Although a few studies have explored the possibility of using scanning probe techniques for characterizing the local charge distribution, the interference from induced electrical polarization of the material has been unfortunately ignored, leading to inaccurate results. In this contribution, we report an open-loop Kelvin probe force microscopy (KPFM) method with nanoscale resolution for the direct detection of the space charge profile in dielectric polymer nanocomposites. Unlike the conventional studies where a vertical direct current (DC) voltage is applied on the sample through the probe to evoke the charge injection and transport in dielectric polymer nanocomposites, the present method is established based on a delicate electrode configuration where a lateral electric field is allowed to be applied on the sample during the KPFM test. This special testing configuration enables real-time charge injection and transport without inducing the electrical polarization of material along the vertical direction, which gives rise to clean mapping of space charges and reveals the interfacial charge trapping in polymer nanocomposites. This work provides a robust and reliable method for studying the sophisticated charge transport properties associated with the various interfacial regions in heterogeneous dielectric materials.