Methods and apparatus for processing a substrate are provided herein. For example, a method for processing a substrate includes applying at least one of low frequency RF power or DC power to an upper electrode formed from a high secondary electron emission coefficient material disposed adjacent to a process volume; generating a plasma comprising ions in the process volume; bombarding the upper electrode with the ions to cause the upper electrode to emit electrons and form an electron beam; and applying a bias power comprising at least one of low frequency RF power or high frequency RF power to a lower electrode disposed in the process volume to accelerate electrons of the electron beam toward the lower electrode.