UC Irvine

ABSTRACT OF THE DISSERTATION

Multiplexing of electrospray sources for space propulsion and physical sputtering

By

Enric Lluís Grustan Gutiérrez

Doctor of Philosophy in Mechanical and Aerospace Engineering

University of California, Irvine, 2015

Professor Manuel Gamero Castaño, Chair

The present work explores what can be achieved when the fields of microfabrication and electrospray atomization intersect. The electrospraying of conductive liquids is a well documented technique used heavily for mass spectrometry but also for drug encapsulation or electric propulsion among other applications.

Chapters 2 and 3 of the dissertation focus on the development of a miniaturized array of sixty-four electrospray sources, determining the design requirements and how to adapt them to microfabrication processes. The prototypes response to mass flux and emitting voltage variations is characterized by recording the currents at the emitter, extractor and collector. To determine whether the source can run continuously for prolonged periods of time, it is left operating until malfunction; the maximum life span is 12 hours.

The most advanced prototype undergoes Time-of-flight spectrometry analysis to evaluate its capabilities for satellite propulsion; with resulting mass flux ranging from 2.07·10-9 to 2.81·10-8 kg/s, a total maximum thrust of 34 µN, an Isp varying from 124 to 245s, with specific charge between 697 and 3142 C/kg and a maximum thrust efficiency of 70%.

In the final portion of the document we present the effects of bombarding Si, SiC, InAs, InP, Ge, GaAs, GaSb and GaN with high kinetic energy projectiles from a single emitter electrospray source. We investigate the structure of the damaged surface and sputtered volume by atomic force and scanning electron microscopy and stylus profilometry. The dependance of substrate nature, kinetic energy and projectile dosage on the final topography of the processed slice is discussed together with sputtering rate and yield. The maximum sputtering rates for the technologically interesting SiC and GaN are 220 and 630 nm/min respectively.

Gold, AZ4620 and Shipley 1827 photoresists layers are deposited on a silicon substrate and sputtered to find their adequacy as microfabrication masks. The sputtering rate selectivity between mask and substrate is calculated for different impact velocities; the maximum value for gold is 64.17, at low speeds Shipley and AZ selectivity is virtually infinite. Finally as proof of concept some intricate structures are carved on silicon using AZ4620.