Alan W. Staton

High-speed two-dimensional gas chromatography using microfabricated GC columns combined with nanoelectromechanical mass sensors

We report here for the first time the combination of microfabricated gas chromatography (GC) columns with pneumatic modulation to achieve high-speed comprehensive two-dimensional gas chromatography (GCxGC) using microfabricated components. The GCxGC system is in turn combined with nanoelectromechanical (NEMS) resonator mass sensors that have been coated with a chemically-selective polymer to enhance detection of phosphonate compounds that are useful surrogates for chemical warfare agents (CWA). GC elution peak widths on the order of 20 msec have been achieved. Retention times on the order of 2–4 seconds have been demonstrated for polar compounds, indicating that this microfabricated GCxGC system can be applied for rapid analyses.

Micro-analytical systems for national security applications

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.

Detection of volatile organics using a surface acoustic-wave array system

A chemical sensor system based on arrays of surface acoustic wave (SAW) delay lines has been developed for identification and quantification of volatile organic compounds. The individual SAW chemical sensors consist of interdigital transducers patterned on the surface of an ST-cut quartz substrate to launch and detect the acoustic waves and a thin film coating in the SAW propagation path to perturb the acoustic wave velocity and attenuation during analyte sorption.

Single-monolayer in situ modulus measurements using a SAW device: Photocrosslinking of a diacetylenic thiol-based monolayer

We report direct measurement of the modulus change that accompanies the crosslinking of a single molecular monolayer. We measured a change in elastic modulus of 5×1010 dyn cm-2 as a result of UV-induced photocrosslinking of a single surface-confined monolayer of the conjugated diacetylenic thiol HS(CH2)10Câ–·CCâ–·C(CH2)10CO2H (DAT). The modulus measurement was made on a monolayer of DAT chemisorbed upon a gold film on the surface of a 97-MHz ST-quartz surface acoustic wave (SAW) delay line. The ratio of the changes recorded in SAW velocity and attenuation, ca. 4:1, suggests that the measured effect is mainly a change in the elastic (real) component of the complex shear modulus, viscous changes playing a lesser role. In relation to typical polymer modulus values, the change of 5×1010 dyn cm-2 is consistent with a change from a rubbery material (G′≈107–108 dyn cm-2) to a fairly rigid, glassy material (G′≈1010 dyn cm-2), reasonable for comparison of the monolayer in its as-adsorbed and crosslinked forms. This report of the direct measurement of the modulus change that accompanies the crosslinking of a single molecular monolayer is consistent with previous insitu measurements of this process using thickness-shear mode resonators

Thermally-activated pentanol delivery from precursor poly(p-phenylenevinylene)s for MEMS lubrication.

The synthesis of two new polyphenylene vinylene (PPV) precursor polymers which can be thermally induced to eliminate pentanol is presented. Pentanol has recently been discovered to be a very useful lubricant in MicroElectroMechanical Systems. The utilization of the elimination reaction of precursor polymers to PPV as a small molecule delivery platform has, to the best of our knowledge, not been previously reported. The elimination reactions were examined using thermal gravimetric analysis, gas chromatography, and UV-Vis spectroscopy. Using PPV precursors allows for (1) a high loading of lubricant (one molecule per monomeric unit), (2) a platform that requires relatively high temperatures (>145 °C) to eliminate the lubricant, and (3) a non-volatile, mechanically and chemically stable by-product of the elimination reaction (PPV).

Viscoelastic coupling of nanoelectromechanical resonators.

This report summarizes work to date on a new collaboration between Sandia National Laboratories and the California Institute of Technology (Caltech) to utilize nanoelectromechanical resonators designed at Caltech as platforms to measure the mechanical properties of polymeric materials at length scales on the order of 10-50 nm. Caltech has succeeded in reproducibly building cantilever resonators having major dimensions on the order of 2-5 microns. These devices are fabricated in pairs, with free ends separated by reproducible gaps having dimensions on the order of 10-50 nm. By controlled placement of materials that bridge the very small gap between resonators, the mechanical devices become coupled through the test material, and the transmission of energy between the devices can be monitored. This should allow for measurements of viscoelastic properties of polymeric materials at high frequency over short distances. Our work to date has been directed toward establishing this measurement capability at Sandia.