Sheath electron heating in surface wave discharges driven at microwave frequencies

Using fully electromagnetic particle-in-cell/Monte Carlo simulations, the electron heating due to interaction with a moving sheath is demonstrated to dominate in surface wave-driven discharges at microwave frequencies and relatively low pressures. Electrons impinging on the rapidly expanding sheath gain energy by repulsion from its strongly negative potential, similarly to the corresponding mechanism in capacitively coupled discharges driven at radio frequencies. This results in generation of energetic electron beams propagating towards the bulk plasma. In contrast to the expectations from previous theoretical studies, the electron heating due to plasma resonance is not observed.