We report the design, fabrication, and experimental characterization of dense, monolithic, and planar arrays of externally-fed electrospray emitters with an integrated extractor grid and carbon nanotube flow control structures for low-voltage and high-throughput electrospray of the ionic liquid EMI-BF 4 in vacuum. Microfabricated arrays with as many as 1900 emitters in 1 cm 2 were fabricated and tested. Per-emitter currents as high as 5 µA in both polarities were measured, with start-up bias voltages as low as 470 V and extractor grid transmission as high as 80%. Maximum array emission currents of 1.35 mA (1.35 mA/cm 2 ) were measured using arrays of 1900 emitters in 1 cm 2 . A conformal carbon nanotube forest grown on the surface of the emitters acts as a wicking structure that transports liquid to the emitter tips, providing hydraulic impedance to regulate and uniformize the emission across the array. Mass spectrometry of the electrospray beam confirms that emission in both polarities is composed of solvated ions, and etching of the silicon collector electrode is observed. Collector imprints and per-emitter current-voltage characteristics for different emitter array sizes spanning three orders of magnitude show excellent emission uniformity across the array. Performance estimates of the devices as nanosatellite thrusters are provided.

We report the design, fabrication, and proof-ofconcept characterization of an X-ray generator for improved X-ray absorption imaging that uses a nanostructured field emission cathode as the electron source and a microstructured transmission anode as the X-ray generating structure. Field emission cathodes consume less power, respond faster, and tolerate lower vacuum than the thermionic cathodes used in conventional X-ray generators. The use of a transmission anode, instead of a conventional reflection anode, allows filtering of the background radiation (bremsstrahlung) while allowing efficient generation of X-ray at lower voltages by exciting atomic shell transitions, resulting in emission of X-ray with narrow spectral linewidth for sharper imaging of biological tissue. The fabricated field emission cathode contains arrays of self-aligned and gated silicon field emitters. The field emission cathodes turn on at bias voltages as low as 25 V, and their gates transmit almost 100% of the electrons to the anode. The cathodes produce per-emitter electron currents in excess of 2 µA (current density >2 A/cm 2 ) at a bias voltage of 80 V. A desktop rig is built to generate X-ray with a field emission cathode and transmission anode. Using the facility, we obtained X-ray absorption images of several objects. The images clearly show details under 500 µm in size, as well as soft tissue and fine bone structures without using contrast agents.[ 2014-0087]Index Terms-Field emission, medical imaging, X-ray generation.

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We report the design, fabrication, and characterization of planar arrays of externally-fed silicon electrospinning emitters for high-throughput generation of polymer nanofibers. Arrays with as many as 225 emitters and with emitter density as large as 100 emitters cm(-2) were characterized using a solution of dissolved PEO in water and ethanol. Devices with emitter density as high as 25 emitters cm(-2) deposit uniform imprints comprising fibers with diameters on the order of a few hundred nanometers. Mass flux rates as high as 417 g hr(-1) m(-2) were measured, i.e., four times the reported production rate of the leading commercial free-surface electrospinning sources. Throughput increases with increasing array size at constant emitter density, suggesting the design can be scaled up with no loss of productivity. Devices with emitter density equal to 100 emitters cm(-2) fail to generate fibers but uniformly generate electrosprayed droplets. For the arrays tested, the largest measured mass flux resulted from arrays with larger emitter separation operating at larger bias voltages, indicating the strong influence of electrical field enhancement on the performance of the devices. Incorporation of a ground electrode surrounding the array tips helps equalize the emitter field enhancement across the array as well as control the spread of the imprints over larger distances.

We report the design, fabrication, and preliminary characterization of a microfabricated retarding potential analyzer (RPA) that ensures unprecedented grid alignment accuracy. Through refined manufacturing methods, improved tolerances upon assembly serve to increase the signal to noise ratio (SNR). Furthermore, microfabrication permits smaller features overcoming sensor limitations previously barring RPAs from use in very dense plasmas such as those during reentry. Preliminary results show more than a twofold increase in signal strength compared to conventional RPAs. Finally, a new batch-fabricated RPA design that uses MEMS springs for grid assembly is demonstrated to help drive down cost while improving device reliability.