carbon nanotubes for Electrospray nanofluidic Applications

Electrospray is the technique to soft-ionize liquids by applying a high electric potential to a liquid meniscus. The liquid meniscus is deformed into a cone [1], and charged species are emitted from its apex. The emission can be solvated ions, charged droplets, or a mix of the two. This low-divergence charged species source can be used in diverse applications such as mass spectrometry, propulsion, printing, and etching. Our research group has successfully developed several multiplexed MEMS electrospray sources, mainly intended for space propulsion applications. These devices include internal pressure-fed spouts that emit charged droplets [2] and externally surface tension fed spouts that emit solvated ions [3]. In all cases, the emitter field enhancers and the hydraulic impedance are provided using silicon-based structures. Furthermore, the devices use a 3D packaging technology that allows decoupling the process flows of the subsystems without loss in emitter density [4]. Consequently, it is possible to use radically different fabrication techniques and materials to implement MEMS electrospray arrays. This project intends to investigate the application of Plasma Enhanced Chemical Vapor Deposition Carbon Nanotubes (PECVD CNTs) in multiplexed electrospray sources. Two research directions are currently pursued: the use of CNTs as hydraulic impedance to ballast the emitter array (both in internal and external architectures) and the use of CNTs as emitter field enhancers. On the one hand, PECVD CNT forests can be custom tailored to match a desired morphology. On the other hand, PECVD CNTs have remarkable field enhancing properties. Figure 1 shows a silicon-based externally fed electrospray linear emitter array that uses PECVD CNTs as hydraulic impedance, while Figure 2 shows the PECVD CNT forest grown on top of the silicon structures, using our group’s reactor. Current research is focused on exploring the wettability of CNT forests using different liquids, catalysts, and growth conditions. These results will be used to choose the proper nanostructure to be used in an externally fed MEMS electrospray head that will eventually include CNT-based field enhancers.