Jaroslava Z. Wilcox

Silicon bulk micromachined vibratory gyroscope for microspacecraft

This paper reports on the design, modeling, fabrication, and characterization of a novel silicon bulk micromachined vibratory rate gyroscope and a 3-axes rotation sensing system using this new type of microgyroscopes designed for microspacecraft applications. The new microgyroscope consists of a silicon four leaf clover structure with a post attached to the center. The whole structure is suspended by four thin silicon cantilevers. This device is electrostatically actuated and detects Coriolis induced motions of the leaves capacitively. A prototype of this microgyroscope has a rotation responsivity (scale factor) of 10.4 mV/deg/sec with scale factor nonlinearity of less than 1%, and a minimum detectable noise equivalent rotation rate of 90 deg/hr, at an integration time of 1 second. The bias stability of this microgyroscope is better than 29 deg/hr. The performance of this microgyroscope is limited by the electronic circuit noise and drift. Planned improvements in the fabrication and assembly of the microgyroscope will allow the use of Q-factor amplification to increase the sensitivity of the device by at least two to three orders of magnitude. This new vibratory microgyroscope offers potential advantages of almost unlimited operational life, high performance, extremely compact size, low power operation, and low cost for inertial navigation and altitude control.

Elemental surface analysis at ambient pressure by electron-induced x-ray fluorescence

The development of a portable surface elemental analysis tool, based on the excitation of characteristic x rays from samples at ambient pressure with a focused electron beam is described. This instrument relies on the use of a thin electron transmissive membrane to isolate the vacuum of the electron source from the ambient atmosphere. The major attributes of this instrument include rapid (several minutes) spectrum acquisition, nondestructive evaluation of elemental composition, no sample preparation, and high-to-medium (several hundreds μm) spatial resolution. The instrument proof-of-principle has been demonstrated in a laboratory setup by obtaining energy dispersive x-ray spectra from metal and mineral samples.

Atmospheric electron X-ray spectrometer development

The development of a portable surface elemental analysis tool based on the excitation of characteristic X-rays at ambient pressure with an electron beam is described. This instrument relies on the use of a thin electron transmissive membrane to isolate the vacuum of the electron source from the ambient atmosphere. The major advantages offered by this instrument include rapid spectrum acquisition, nondestructive evaluation of elemental composition, and high spatial resolution in comparison to similar portable instruments. The instrument proof-of-principle has been demonstrated by obtaining energy dispersive X-ray spectra from metal and mineral samples. SEM experiments have been carried out to determine beam spot size and quantitative analysis limits. Modeling has been performed to study performance limits and to understand the influence of membrane and atmosphere interactions on the focused electron beam.

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.

Beam splitting mirrors for miniature Fourier transform soft x-ray(FTXR) interferometer

The development of Fourier Transform (FT) spectral techniques in the soft X-ray spectral region has been advocated in the past as a possible route to constructing a bench-top size spectral imager with high spatial and spectral resolution. The crux of the imager is a soft X-ray interferometer. Auxiliary subsystems include a wide-band soft X-ray source, focusing optics and detection systems. When tuned over a sufficiently large range of path delays, the interferometer will sinusoidally modulate the source spectrum centered at the core wavelength of interest, the spectrum illuminates a target, the reflected signal is imaged onto a CCD, and data acquired for different frames is converted to spectra in software by using FT methods similar to those used in IR spectrometry producing spectral image per each pixel. The use of shorter wavelengths results in dramatic increase in imaging resolution, the modulation across the beam width results in highly efficient use of the beam spectral content, facilitating construction of a bench-top instrument. With the predicted <0.1eV spectral and <100 nm spatial resolution, the imager would be able to map core-level shift spectra for elements such as Carbon, which can be used as a chemical compound fingerprint and imaging intracellular structures. We report on our progress in the development of a Fourier Transform X-ray (FTXR) interferometer. The enabling technology is X-ray beam splitting mirrors. The mirrors are not available commercially; multi layers of quarter-wave films (used in IR and visible) are not suitable, and several efforts by other researchers who used parallel slits met only a very limited success. In contrast, our beam splitters use thin (about 200 nm) SiN membranes perforated with a large number of very small holes prepared in our micro-fabrication laboratory at JPL. Precise control of surface roughness and high planarity are needed to achieve the requisite wave coherency. The beam splitters prepared-to-date had surface RMS and planarity better that <0.3 nm over a 0.45 mm x 1.4 mm area, meeting requirements for spectral imaging at 100eV. Efforts to improve the mirror flatness to a level required for core-level shifts of Carbon are under way.

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...

Electron beam enabled surface composition, charge, and adsorbed gas determination [of Mars]

The Human Exploration and Development of Space Roadmap calls for Human Missions to Mars and other planets in the 2010 to 2023 timeframe. This paper describes a proposal written in response to the Announcement of Opportunity (A099-HEDS-01) for definition studies preparing for the human exploration of Mars. Specifically, the proposal addressed the call for the development of innovative instrument concepts aimed at studying soil, dust, and environmental interactions for 2005 Mission Opportunities. The objective of the proposed study was to determine the feasibility, under simulated Martian ambient conditions, of a suite of miniature instruments performing correlated measurements of sample surfaces. A novel Atmospheric Electron X-ray Spectrometer (AEXS), an optical microscope capable of producing low magnification images, an electrometer, and a fiber optic oxygen sensor fitted with a resistive heater comprised the proposed instrument suite.