Space charge drives electromechanical conversion via a piezoelectric-like effect in ion implanted polymers

Ion implantation is a powerful tool to modify materials chemistry and structure. The implantation process was considered to result in a net-neutral material, due to implanted ionic charge being compensated by the host materials lattice. Here, we show ion implantation into polytetrafluoroethylene (PTFE) results in an uncompensated ‘space charge’ region – requiring a reconsideration of ion implantation into polymers. This is demonstrated via electromechanical testing of Cu implanted PTFE as a triboelectric nanogenerator (TENG). Previously, ion implantation into polymers has shown to increase TENG performance, attributed to increasing the prevalence of electron transfer during contact-separation testing. This attribution to electron transfer is incorrect, with significant electromechanical conversion being observed in 1 x 10 ¹⁶ Cu ions cm ^− 2 implanted polytetrafluoroethylene (PTFE) in both piezoelectric mode testing and in non-contact induction measurements – where electron transfer cannot occur. These results, indicate that the implantation of Cu ions creates a space charge effect in the PTFE matrix, and the subsequent charge asymmetry creates an electric field enhancing TENG performance, analogous to hybrid piezoelectric-TENGs. These results demonstrate that ion implanted polymers possess space charge and can be used directly for sensing, creating a new pathway for electromechanical conversion materials.