We present active electrostatic MEMS gas valves for Micro-Gas-Analyzer (MGA) flow control. These unique valves enable extremely low dead volume, highly integrated flow control chips for the MGA application, and potentially others (e.g., propulsion, pneumatic, and thermodynamic microsystems). We have demonstrated low leak rates ( <; 0.025 sccm, <; 0.0025 sccm on a similar passive valve design), high operating pressures 6.9×10 5 N/m 2 (100 psig), a high-pressure record for valves of this size and type, and high flow rates (>; 25 sccm) using control voltages on the order of 100 V. The valve designs presented eliminate charge build-up issues associated with insulating materials and are closely tied to a base-lined microfabrication process (SUMMiT), allowing mass production. Using this process, which incorporates only CMOS compatible materials, eliminates outgassing and absorption problems inherent to microvalve designs that incorporate elastomers or organic bonding layers, and reduces contamination when the valve is part of the chemical analysis flowpath. The results obtained indicate that even higher performance level valves (>; 1.4 × 10 6 N/m 2 or 200 psig operating pressure, at similar control voltage, flow rates, and leak rates) are possible.

Miniaturized gas chromatography (GC) systems can provide fast, quantitative analysis of chemical vapors in an ultrasmall package. We describe a chemical sensor technology based on resonant nanoelectromechanical systems (NEMS) mass detectors that provides the speed, sensitivity, specificity, and size required by the microscale GC paradigm. Such NEMS sensors have demonstrated detection of subparts per billion (ppb) concentrations of a phosphonate analyte. By combining two channels of NEMS detection with an ultrafast GC front-end, chromatographic analysis of 13 chemicals was performed within a 5 s time window.

Cross-linked assemblies of nanoparticles are of great value as chemiresistor-type sensors. Herein, we report a simple method to fabricate a chemiresistor-type sensor that minimizes the swelling transduction mechanism while optimizing the change in dielectric response. Sensors prepared with this methodology showed enhanced chemoselectivity for phosphonates which are useful surrogates for chemical weapons. Chemoselective sensors were fabricated using an aqueous solution of gold nanoparticles that were then cross-linked in the presence of the silica precursor, tetraethyl orthosilicate with the α-, ω-dithiolate (which is derived from the in situ deprotection of 1,4-di(Phenylethynyl-4′,4″-diacetylthio)-benzene (1) with wet triethylamine). The cross-linked nanoparticles and silica matrix were drop coated onto interdigitated electrodes having 8 μm spacing. Samples were exposed to a series of analytes including dimethyl methylphosphonate (DMMP), octane, and toluene. A limit of detection was obtained for each analyte. Sensors assembled in this fashion were more sensitive to dimethyl methylphosphonate than to octane by a factor of 1000.

Sandia National Laboratories has a long tradition of technology development for national security applications. In recent years, significant effort has been focused on micro-analytical systems - handheld, miniature, or portable instruments built around microfabricated components. Many of these systems include microsensor concepts and target detection and analysis of chemical and biological agents. The ultimate development goal for these instruments is to produce fully integrated sensored microsystems. Described here are a few new components and systems being explored: (1) A new microcalibrator chip, consisting of a thermally labile solid matrix on an array of suspended-membrane microhotplates, that when actuated delivers controlled quantities of chemical vapors. (2) New chemical vapor detectors, based on a suspended-membrane micro-hotplate design, which are amenable to array configurations. (3) Micron-scale cylindrical ion traps, fabricated using a molded tungsten process, which form the critical elements for a micro-mass analyzer. (4) Monolithically integrated micro-chemical analysis systems fabricated in silicon that incorporate chemical preconcentrators, gas chromatography columns, detector arrays, and MEMS valves.

Optical lithography based on microfabrication techniques was employed to fabricate one-dimensional nanogaps with micrometre edge lengths in silicon. These one-dimensional nanogaps served as a platform on which organic/nanoparticle films were assembled. Characterization of the gaps was performed with high-resolution TEM, SEM, and electrical measurements. Novel self-assembling attachment chemistry, based on the interaction of silicon with a diazonium salt, was used to iteratively build a multi-layer nanoparticle film across a 7 nm gap. By using nanoparticles capped with an easily displaced ligand, a variable conductive path was created across the 1D nanogap. Electrical measurements of the gap showed a dramatic change in the I(V) characteristics after assembly of the nanoparticle film.

This article details a simple four-step procedure to create a one-dimensional nanogap on a buried oxide substrate that relies on conventional photolithography performed on a stack of silicon/silicon oxide/silicon, metal evaporation, and hydrofluoric acid oxide removal. Once the nanogap was fabricated it was bridged with an assembly of 1,8-octanedithiol and 5 nm Au nanoparticles capped with a sacrificial dodecylamine coating. Before assembly, characterization of the nanogaps was performed through electrical measurements and SEM imaging. Post assembly, the resistance of the nanogaps was evaluated. The current increased from 70 fA to 200 microA at +1 V bias, clearly indicating a modification due to nanoparticle molecule assembly. Control experiments without nanoparticles or octanedithiol did not show an increase in current.

Many data analysis algorithms that are currently employed in SAW sensors lack the ability to easily maintain calibration models in the presence of unmodeled interferents or sensor drift. The classical least squares/partial least squares (CLS/PLS) hybrid algorithm is tested in this study for its ability to update calibration models for unmodeled interferents and sensor drift with information from only a single recalibration standard. Use of the CLS/PLS hybrid algorithm for calibration and calibration maintenance of surface acoustic wave (SAW) devices was investigated for synthetic mixtures of iso-octane-methanol-water and with synthetic mixtures of nerve agent analogs, di-iso-propyl methyl phosphonate (DIMP)-kerosene-water along with a true ternary mixture of dimethyl methyl phosphonate (DMMP)-kerosene-water. Calibration statistics using the hybrid algorithm were found to be as good as those obtained from a standard partial least squares (PLS) analysis. In prediction, the hybrid algorithm models were found to perform equivalently to PLS models in the absence of unmodeled interferents or sensor drift, with an accuracy of 5-10% of the reference values and a high degree of precision. In the case of prediction in the presence of unmodeled interferents and/or sensor drift, PLS models and prediction augmented CLS/PLS (PACLS/PLS) hybrid models were compared using a single standard more » sample to update each model for prediction. For the cases studied, PACLS/PLS hybrid models were comparable to or outperformed updated PLS models that used subset recalibration or piece-wise direct standardization. « less

The downstream etching of tungsten and tungsten oxide has been investigated. Etching of chemical vapor deposited tungsten and e-beam deposited tungsten oxide samples was performed using atomic fluorine generated by a microwave discharge of argon and NF3. Etching was found to be highly activated with activation energies approximated to be 6.0±0.5 kcal/mol and 5.4±0.4 kcal/mol for W and WO3, respectively. In the case of F etching of tungsten, the addition of undischarged nitric oxide (NO) directly into the reaction chamber results in the competing effects of catalytic etch rate enhancement and the formation of a nearly stoichiometric WO3 passivating tungsten oxide film, which ultimately stops the etching process. For F etching of tungsten oxide, the introduction of downstream NO reduces the etch rate.