Surgical devices and methods are described herein that provide energy density control during tissue sealing. In general, these devices include a handle portion, an elongate shaft, and an end effector having a first jaw having a first tissue engaging surface and a second jaw having a second tissue engaging surface. The first tissue engaging surface can include an energy delivering electrode having a selected pattern of varying conductivity which may include a discrete region or a continuous pattern. The energy delivering electrode may be formed from a polymer substrate that includes a metal. The metal may be mixed into the substrate using an ion beam process. The amount of ions in the ion beam, the energy of the ion beam, or both may be varied to create the selected pattern of varying conductivity.