Roles of spin-state dangling bonds and strain on the electronic structure of polytetrafluoroethylene for charge transfer from first-principles

Abstract

Utilizing first-principles density functional theory, we computed the surface electronic structure of a polytetrafluoroethylene (PTFE) slab with various dangling bond (DB) configurations. As the number of surface DBs increases, the lowest unoccupied level (LUL) associated with electron affinity (EA) decreases, resulting in a rise in DBs' formation energy, indicating an unstable state and electron deficiency. Particularly in spinless DB states, only one localized lowest unoccupied surface state (LUSS) forms below the conduction band minimum (CBM). To investigate charge transfer, a contact model between various spin-state DBs and aluminum slab was performed. Furthermore, axial or radial extension in the DB-PTFE system confirms reduced LUL (CBM or LUSS), attributed to F atoms moving away, facilitating easier electron entry from the external environment. These calculations lead to the proposal of an electron transfer model between the metal and DB-PTFE.