It is shown that a pulsed direct current (dc) bias is capable of discharging insulating surfaces and providing a good means of controlling the energy of the ions extracted from the sputter magnetron plasma. Numerical calculations were made for surface potentials of an insulating thin film exposed to a plasma, placed on a conductor with a pulsed de bias. Surface potentials are calculated as a function of time for pulses of variable frequency and duty. Average ion energy is shown to converge to applied de biases at higher frequencies. Thin aluminum films were deposited on SiO2 substrates as a function of pulse frequency. Atomic force microscopy scans of the surface show that increasing the frequency of the pulses produces drastic changes in resulting film surface morphology.