Mo tips 50-100 Si tips 50-100 p-type diamond 160 Defective CVD diamond 30-120 Amorphic diamond 20-40 Cesium-coated diamond 20-30 Graphite powders 10-20 Nano-diamond 3-5 (unstable > 30 mA/cm2) Carbon Nanotubes 1-2 (stable >4000mA/cm 2) Table 1. Threshold fields for various cathode materials and some CNT emission characteristics.

A breadboard setup constructed at MOXTEK, Inc., is capable of capturing both x-ray diffraction (XRD) and x-ray fluorescence (XRF) information simultaneously using a charge-coupled device (CCD) as the x-ray detector. This preliminary setup will lead to a prototype simultaneous XRD/XRF instrument. NASA is funding the instrument's construction because of its capabilities and small size; it could be used for future Mars missions for analysis of rocks. The instrument uses a CCD to capture both the energy and the spatial information of an incoming x-ray. This is possible because each pixel acts as a spatially addressable energy-dispersive detector. A powdered sample of material is placed in front of the CCD, which in turn is bombarded by a collimated x-ray beam. The instrument's critical features-namely the x-ray source, collimation optics and x-ray transparent windows-allow for the first time, to the best of our knowledge, mounting the sample outside the CCD camera. In this paper the instrument's design parameters as well as the properties of both a front-side-illuminated (FSI) CCD and backside illuminated (BSI) CCD as x-ray detectors are investigated.

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A new sample support film for small spot XRF analysis has been developed that improves detection limits by a factor of 10 over traditional polymer supports. The surface characteristics of this new film are excellent for retaining drops of sample solution in one place and allowing the solution to dry into a single spot A dimpling technique was developed to further aid in concentrating the evaporated samples to the prescribed spot size and position. The film showed good resistance to chemical attacfc from the solution, even some strong acids and bases. The detection limits achieved using micro sample XRF with the ultra thin sample support were sufficient to be a comparable alternative to ICP-MS and GFAAS for elemental analysis.

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