Eduardo Urgiles

Application specific electrode-integrated nanotube cathodes (ASINCs) for miniature analytical instruments for space exploration

JPL has developed high performance cold cathodes using arrays of carbon nanotube bundles that routinely produce > 15 A/cm2 at applied fields of 5 to 8 V/μm without any beam focusing. They have exhibited robust operation in poor vacuums of 10-6 to 10-4 Torr- a typically achievable range inside hermetically sealed microcavities. A new double-SOI process to monolithically integrate gate and additional beam tailoring electrodes has been developed. These electrodes are designed according to application requirements making carbon nanotube field emission sources application specific (Application Specific electrode-Integrated Nanotube Cathodes or ASINCs). ASINCs, vacuum packaged using COTS parts and a reflow bonding process, when tested after 6-month shelf life have shown little emission degradation. Lifetime of ASINCs is found to be affected by two effects- a gradual decay of emission due to anode sputtering, and dislodging of CNT bundles at high fields (> 10 V/μm). Using ASINCs miniature X-ray tubes and mass ionizers have been developed for future XRD/XRF and miniature mass spectrometer instruments for lander missions to Venus, Mars, Titan, and other planetary bodies.

Atmospheric electron-induced X-ray spectrometer (AEXS) development

The progress in the development of the Atmospheric Electron X-ray Spectrometer (AEXS) is described. The AEXS is a surface analysis tool based on excitation of characteristic X-ray fluorescence (XRF) spectra from samples in ambient atmospheres using a focused electron beam. Operation in ambient atmospheres with moderate-to-high spatial resolution in comparison to similar instruments is obtained through the use of a thin electron transmissive membrane to isolate the vacuum of the electron probe, obviating the need for the samples to be drawn into the probe vacuum. Our initial setup consisted of an actively pumped chamber from within which the electrons were transmitted -not a portable instrument. The instrument that has been assembled and used to acquire XRF spectra in our laboratory during the past two years consists of a 20 keV electron tube sealed with a SiN membrane and requires no active pumping -a big step towards the development of a stand-alone instrument. The microprobe was used to perform elemental analysis of NIST and USGS standards, with good agreement with the certified composition for samples in up to about 90 Torr-cm thick atmosphere, and for resolving the composition of mm-sized mineral grains in inhomogeneous samples, a big improvement over the several cm-scale spatial resolution of the APXS instrument that flew on NASAs MER mission.

Electron-induced luminescence and x-ray spectrometer development: progress report

The progress in the development of a surface analysis tool based on the excitation of characteristic luminescence and x-ray spectra at ambient pressure with an electron beam is described.

MEMS-Based Micro Instruments for In-Situ Planetary Exploration

NASAs planetary exploration strategy is primarily targeted to the detection of extant or extinct signs of life. Thus, the agency is moving towards more in-situ landed missions as evidenced by the recent, successful demonstration of twin Mars Exploration Rovers. Also, future robotic exploration platforms are expected to evolve towards sophisticated analytical laboratories composed of multi-instrument suites. MEMS technology is very attractive for in-situ planetary exploration because of the promise of a diverse and capable set of advanced, low mass and low-power devices and instruments. At JPL, we are exploiting this diversity of MEMS for the development of a new class of miniaturized instruments for planetary exploration. In particular, two examples of this approach are the development of an Electron Luminescence X-ray Spectrometer (ELXS), and a Force-Detected Nuclear Magnetic Resonance (FDNMR) Spectrometer. The ELXS is a compact (< 1 kg) electron-beam based microinstrument that can determine the chemical composition of samples in air via electron-excited x-ray fluorescence and cathodoluminescence. The enabling technology is a 200-nm-thick, MEMS-fabricated silicon nitride membrane that encapsulates the evacuated electron column while yet being thin enough to allow electron transmission into the ambient atmosphere. The MEMS FDNMR spectrometer, at 2-mm diameter, will be the smallest NMR spectrometer in the world. The significant innovation in this technology is the ability to immerse the sample in a homogenous, uniform magnetic field required for high-resolution NMR spectroscopy. The NMR signal is detected using the principle of modulated dipole-dipole interaction between the samples nuclear magnetic moment and a 60-micron-diameter detector magnet. Finally, the future development path for both of these technologies, culminating ultimately in infusion into space missions, is discussed.

Development of Atmospheric Electron-Induced X-Ray Spectrometer (AEXS) Instrument with High Spatial Resolution for Surface Elemental Analysis in Planetary Atmosphere

One of the most powerful techniques for the characterization of mineral samples is Electron-induced Energy-Dispersive X-ray Fluorescence Spectroscopy (EDX-XRF). If used for resolving the elemental composition for samples in their natural state, high spatial resolution data will provide insight into geological processes and formation mechanisms of planets and other solar system objects. By correlating the XRF with other spectra (eg XUV and optical luminescence) additional information could be obtained about the bonding structure and oxidation states for the minerals. To date, all in situ missions have carried some form of an XRF instrument. For example, the APXS instrument aboard the Mars Pathfinder and MER determined bulk averaged elemental composition over areas of several cm in diameter. The spectrum acquisition time required to resolve the XRF spectrum was several hours. In order to obtain spatial maps, the spectrum acquisition time must be decreased and the spatial resolution of future XRF instruments increased in comparison to the current methods.

Surface elemental analysis in ambient atmosphere using electron-induced x-ray fluorescence

The progress in the development of the atmospheric electron x-ray spectrometer (AEXS) is described. The AEXS is a surface analysis tool based on excitation of characteristic x-ray fluorescence (XRF) spectra from samples in ambient atmospheres using a focused electron beam. Operation in ambient atmospheres with moderate-to-high spatial resolution in comparison to similar instruments is obtained through the use of a thin electron-transmissive membrane to isolate the vacuum of the electron probe, obviating the need for the samples to be drawn into the probe vacuum. Our initial setup that was used for the demonstration of the ability of the transmitted electrons to excite the XRF spectra in the external atmosphere consisted of an actively pumped chamber from within which the electrons were transmitted—not a portable instrument. The AEXS instrument that has been assembled in our laboratory during the past year consists of a miniature 20 keV electron microprobe that is vacuum sealed with a thin SiN membrane and...