Gas Chromatography (GC) is routinely used in the laboratory to temporally separate chemical mixtures into their constituent components for improved chemical identification. This paper will provide a overview of more than twenty years of development of one-dimensional field-portable micro GC systems, highlighting key experimental results that illustrate how a reduction in false alarm rate (FAR) is achieved in real-world environments. Significantly, we will also present recent results on a micro two-dimensional GC (micro GCxGC) technology. This ultra-small system consists of microfabricated columns, NanoElectroMechanical System (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator. The separation of a 29-component polar mixture in less than 7 seconds is demonstrated along with peak widths in the second dimension ranging from 10-60 ms. For this system, a peak capacity of just over 300 was calculated for separation in about 6 s. This work has important implications for field detection, to drastically reduce FAR and significantly improve chemical selectivity and identification. This separation performance was demonstrated with the NEMS resonator and bench scale FID. But other detectors, suitably fast and sensitive can work as well. Recent research has shown that the identification power of GCxGC-FID can match that of GC-MS. This result indicates a path to improved size, weight, power, and performance in micro GCxGC systems outfitted with relatively non-specific, lightweight detectors. We will briefly discuss the performance of possible options, such as the pulsed discharge helium ionization detector (PDHID) and miniature correlation ion mobility spectrometer (mini-CIMS).

We describe for the first time hydrogen bonded acid (HBA) polymer, poly{methyl[3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane}, (DKAP), as stationary phase for gas chromatography (μGC) of organophosphate (OP), chemical warfare agent (CWA) surrogates, dimethylmethylphosphonate (DMMP), diisopropylmethylphosphonate (DIMP), diethylmethylphosphonate (DEMP), and trimethylphosphate (TMP), with high selectivity. Absorption of OPs to DKAP was one-to-several orders of magnitude higher relative to commercial polar, mid-polar, and nonpolar stationary phases. We also present for the first-time thermodynamic studies on the absorption of OP vapors and quantitative binding energy data for interactions with various stationary phases. These data help to identify the best pair of hetero-polar columns for a two-dimensional GC system, employing a nonpolar stationary phase as GC1 and DKAP as the GC2 stationary phase, for selective and rapid field detection of CWAs.

A small, consumable-free, low-power, ultra-high-speed comprehensive GC×GC system consisting of microfabricated columns, nanoelectromechanical system (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator is demonstrated. The separation of a highly polar 29-component mixture covering a boiling point range of 46 to 253 °C on a pair of microfabricated columns using a Staiger valve manifold in less than 7 seconds, and just over 4 seconds after the ensemble holdup time is demonstrated with a downstream FID. The analysis time of the second dimension was 160 ms, and peak widths in the second dimension range from 10-60 ms. A peak capacity of just over 300 was calculated for a separation of just over 6 s. Data from a continuous operation testing over 40 days and 20 000 runs of the GC×GC columns with the NEMS resonators using a 4-component test set is presented. The GC×GC-NEMS resonator system generated second-dimension peak widths as narrow as 8 ms with no discernable peak distortion due to under-sampling from the detector.

Using scanning tunneling microscopy (STM), we investigate oxide-induced growth pits in Si thin films deposited by molecular beam epitaxy. In the transition temperature range from 2D adatom islanding to step-flow growth, systematic controlled air leaks into the growth chamber induce pits in the growth surface. We show that pits are also correlated with oxygen-contaminated flux from Si sublimation sources. From a thermodynamic standpoint, multilayer growth pits are unexpected in relaxed homoepitaxial growth, whereas oxidation is a known cause for step pinning, roughening, and faceting on elemental surfaces, both with and without growth flux. Not surprisingly, pits are thermodynamically metastable and heal by annealing to recover a smooth periodic step arrangement. STM reveals new details about the pits' atomistic origins and growth dynamics. We give a model for heterogeneous nucleation of pits by preferential adsorption of Å-sized oxide nuclei at intrinsic growth antiphase boundaries, and subsequent step pinning and bunching around the nuclei.

To quantify the resolution limits of scanning microwave impedance microscopy (sMIM), we created scanning tunneling microscope (STM)-patterned donor nanostructures in silicon composed of 10 nm lines of highly conductive silicon buried under a protective top cap of silicon, and imaged them with sMIM. This dopant pattern is an ideal test of the resolution and sensitivity of the sMIM technique, as it is made with nm-resolution and offers minimal complications from topography convolution. It has been determined that typical sMIM tips can resolve lines down to similar to 80 nm spacing, while resolution is independent of tip geometry as extreme tip wear does not change the resolving power, contrary to traditional scanning capacitance microscopy (SCM). Going forward, sMIM is an ideal technique for qualifying buried patterned devices, potentially allowing for quantitative post-fabrication characterization of donor structures, which may be an important tool for the study of atomic-scale transistors and state of the art quantum computation schemes. (C) 2017 Elsevier B.V. All rights reserved.

Nitrogen and phosphorus atoms are constituents of some of the most toxic chemical vapors. Nitrogen-phosphorus gas chromatograph detectors (NPDs) rely on selective ionization of such compounds using ionization temperatures typically greater than 600°C. NPDs have previously been reported to be 7×104× and 105× more sensitive for nitrogen and phosphorus, respectively, than for carbon. Presented here is an investigation of the structure-based selectivity of a microfabricated nitrogen-phosphorus detector (μNPD). The μNPD presented here is smaller than a dime and can be placed in a system that is 1/100th the size of a commercial NPD. Comparison of responses of such devices to homologous anilines (p-methoxyaniline, p-fluoroaniline, and aniline) revealed that detection selectivity, determined by the ratio of μNPD to nonselective flame ionization detector (FID) peak areas, is correlated with acid disassociation pKa values for the respective analine. Selectivity was determined to be greatest for p-methoxyaniline, followed by p-fluoroaniline, with aniline having the smallest response. The limit of detection for a nitrogen containing chemical, p-methoxyaniline, using the μNPD was determined to be 0.29ng compared to 59ng for a carbon chemical containing no nitrogen or phosphorus, 1,3,5-trimethybenzene. The μNPD presented here has increased detection for nitrogen and phosphorus compared to the FID and with a slight increase in detection of carbon compounds compared to commercial NPD's sensitivity to nitrogen and carbon.

such devices to homologous anilines (p-methoxyaniline, p-fluoroaniline, and aniline) revealed that detection selectivity, determined by the ratio of μNPD to nonselective flame ionization detector (FID) peak areas, is correlated with acid disassociation pKa values for the respective analine. Selectivity was determined to be greatest for p-methoxyaniline, followed by p-fluoroaniline, with aniline having the smallest response. The limit of detection for a nitrogen containing chemical, p-methoxyaniline, using the μNPD was determined to be 0.29 ng compared to 59 ng for a carbon chemical containing no nitrogen or phosphorus, 1,3,5-trimethybenzene. Furthermore, the μNPD presented here has increased detection for nitrogen and phosphorus compared to the FID and with a slight increase in detection of carbon compounds compared to commercial NPD's sensitivity to nitrogen and carbon.