Microfabricated out-of-plane arrays of integrated capillary nano-electrospray emitters

We present the fabrication and operation of an integrated nano-electrospray thruster consisting of an array of microfabricated silicon capillary emitters and microfabricated silicon extractor electrodes. Based on previous work in which we showed operation of single microfabricated capillaries, the improved microfabricated thruster presented here allows simultaneously operation of arrays of emitters. In addition, we control the hydraulic impedance of the capillaries by filling them with silica beads, thus tailoring the flow rate in order to spray either in droplet regime or in ionic regime for two ionic liquids (EMI-BF4 and EMI-Im). Operation in both modes is confirmed by mass spectrometry and retarding potential analysis. In ion regime, a specific impulse of 3500 s is obtained at 1.2 kV for the ionic liquid EMI-BF4.