Sputtering of silicon by a beamlet of electrosprayed nanodroplets

Advanced fabrication techniques use ion beams to sputter hard materials. Neutral molecules with sufficient energy are better projectiles because, in the absence of space charge, the beam's molecular flux and the sputtering rate can be orders of magnitude higher. This article describes the use of electrosprayed nanodroplets as projectiles for sputtering. Compared to ions, nanodroplets are massive groups of neutral molecules with several elementary charges. Acceleration voltages below 20 kV generate kinetic energies of tens of eV per molecule. When these energetic nanodroplets bombard a [1 0 0] Si wafer, atoms are ejected from the target surface. Depending on the energy of the projectiles, the impacts produce either a multitude of craters much larger than the nanodroplets, or a smooth surface. The two surface morphologies are carved at very high and different rates, suggesting the existence of two distinct sputtering mechanisms.