Christopher G. Bailey

Separation of Explosives Using Capillary Electrochromatography

The identification of explosives and their degradation products is important in forensic and environmental applications. Complete separation of these structurally similar compounds using reversed-phase liquid chromatography has proven to be a challenge. Here we present a demonstration of the use of capillary electrochromatography on the separation of a series of 14 nitroaromatic and nitramine explosive compounds. A separation with baseline resolution is achieved for all of the compounds in under 7 min, featuring efficiencies of over 500 000 theoretical plates/m. Using more aggressive running conditions, 13 of the 14 compounds are separated in under 2 min.

Efficacy of liquid and foam decontamination technologies for chemical warfare agents on indoor surfaces.

Bench-scale testing was used to evaluate the efficacy of four decontamination formulations on typical indoor surfaces following exposure to the liquid chemical warfare agents sarin (GB), soman (GD), sulfur mustard (HD), and VX. Residual surface contamination on coupons was periodically measured for up to 24h after applying one of four selected decontamination technologies [0.5% bleach solution with trisodium phosphate, Allen Vanguard Surface Decontamination Foam (SDF™), U.S. military Decon Green™, and Modec Inc. and EnviroFoam Technologies Sandia Decontamination Foam (DF-200)]. All decontamination technologies tested, except for the bleach solution, performed well on nonporous and nonpermeable glass and stainless-steel surfaces. However, chemical agent residual contamination typically remained on porous and permeable surfaces, especially for the more persistent agents, HD and VX. Solvent-based Decon Green™ performed better than aqueous-based bleach or foams on polymeric surfaces, possibly because the solvent is able to penetrate the polymer matrix. Bleach and foams out-performed Decon Green for penetrating the highly polar concrete surface. Results suggest that the different characteristics needed for an ideal and universal decontamination technology may be incompatible in a single formulation and a strategy for decontaminating a complex facility will require a range of technologies.

Decontamination after a release of B. anthracis spores.

Decontaminating civilian facilities or large urban areas following an attack with Bacillus anthracis poses daunting challenges because of the lack of resources and proven technologies. Nevertheless, lessons learned from the 2001 cleanups together with advances derived from recent research have improved our understanding of what is required for effective decontamination. This article reviews current decontamination technologies appropriate for use in outdoor environments, on material surfaces, within large enclosed spaces, in water, and on waste contaminated with aerosolized B. anthracis spores.

In vitro double transposition for DNA identification

We present a double transposition technique that inserts two different transposons into target DNA to act as priming sites for amplifying the region between the two transposons for sequencing applications. Unlike some current sequencing approaches, the genome of the unknown target remains intact in this method. The transposition reaction, DNA repair, and subsequent sequencing were performed entirely in vitro, without the need for transformation into bacteria, and resulted in sequence homology with the plasmid DNA target. This approach can reduce the time required for the assay by more than a day compared with standard techniques and reduces the number of required enzymatic steps. In addition, the in vitro method enables transposition to be carried out in automated microfluidic platforms without the need for significant sample manipulation. As a demonstration of incorporating transposition techniques into high-throughput technologies, single transposition reactions were carried out in picoliter-sized droplets generated on a microfluidic platform.

Engineering precision relocation capability into a large-cantilevered telescoping diagnostic for a Kirkpatrick Baez x-ray Optic

The Kirkpatrick Baez Optic (KBO) diagnostic designed for the National Ignition Facility (NIF) requires very precise alignment between four pairs of mirrors that make up four x-ray imaging channels. Furthermore, the overlapping image axis of the four pairs must be aligned to within a 50 μm radius of the NIF target center. In order to achieve this the diagnostic utilizes a telescoping snout that when extended, locates the mirrors at the end of a Diagnostic Load Package (DLP), cantilevered more than three meters out from its bolted connection points. Discussed in this paper are the structural challenges and the mechanical design solutions that were implemented to achieve the ±50 μm pointing accuracy. During an Inertial Confinement Fusion (ICF) experiment, the KBO diagnostic will be 117 mm away from the extremely high impulse, target implosion shock wave, which requires a unique approach to protecting the sensitive optics which will also be discussed.

Investigation of spectral responsivity of InAs QD-embedded GaAs solar cells

GaAs p-i-n solar cells embedded with varying number of QD layers (0-60) were grown by OMVPE. 1x1 cm2 cells were fabricated and standard solar cell testing was performed. Illuminated AM0 current-voltage characteristics were measured of both a baseline and 10-layer quantum dot (QD) embedded GaAs p-i-n. The QD solar cell (QDSC) gave an short circuit current of 23.1 mA/cm2 increase in of 0.7mA/cm2 above the baseline with no QDs. The QD embedded cell also showed limited loss in open circuit voltage characteristics of 0.99 V compared to 1.04 V of the baseline. Conversion efficiencies were 13.4 and 13.8 for the QDSC and baseline solar cell, respectively. Spectral responsivity measurements revealed equivalent GaAs response in the visible for the baseline, 10x and 20x layer QD samples, while systematically degraded emitter lifetime was found to be responsible for loss in visible responsivities for the 60x QDSC. Sub-GaAs bandgap response gave a systematic increase of 0.25 mA/QD layer. Spectral responsivity modeling was used and found that bulk GaAs emitter and i-region lifetimes degraded from 102 ns to 102 ps, with increasing number of QD layers.

Target material collection for High-Energy Imaging Diagnostic

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory uses the world’s largest and most energetic laser system to explore Inertial Confinement Fusion (ICF) and High-Energy-Density (HED) physics, with the potential of creating pressure and density conditions normally found in the cores of stars or large planets. During NIF experiments, the laser energy is directed to the target, driving the desired physics conditions, and the breakup of the target. During this breakup there is the potential to generate debris fields with both vaporized and solid target material, traveling at extremely high velocities (~10 km/s). For future shots, it is desirable to minimize distribution of the certain target materials within NIF. The High Energy Imaging Diagnostic (HEIDI), which comes within 8 cm of the target, will be modified to minimize the distribution of the ejected material. An external cone will be added to HEIDI which will block a larger angle than the existing hardware. Internal shielding will be added to isolate target material within the front portion of the diagnostic. A thin aluminum bumper will slow low-density vaporized material and contribute to the breakup of high velocity particles, while a thicker wall will block solid chunks. After the shot, an external cover will be installed, to contain any stray material that might be disturbed by regular operations. The target material will be retrieved from the various shielding mechanisms and assayed.

Quantum Dot Space Solar Cells

The state-of-the-art in space solar cells utilizes epitaxially grown III-V multi-junction cells. Champion lattice matched triple-junction space cells now exceed the 30% efficiency barrier. The ultimate efficiency of such cells is restricted by the available bandgaps offered by the lattice-matching requirement and the necessity of having current-matching between the various junctions. It has been theoretically shown that efficiency improvements are possible if the spectral bandwidth of the GaAs or middle junction of a conventional lattice- matched triple junction cell (grown on Ge) could be extended to longer wavelengths. We have been investigating a method of providing this additional sub-gap absorption, and corresponding improvement of short-circuit current of this junction, through the use of self- organized InAs quantum dots. These quantum dots are incorporated using a Stranski- Krastanov organometallic vapor phase epitaxy growth mode in a sequentially stacked array of InAs quantum dots (QD) and GaAs cladding layers within the p-type / intrinsic / n-type (pin) GaAs cell structure. Spectral response results have demonstrated enhanced sub GaAs bandgap response and improvements in short-circuit current densities. We will discuss the potential that exists and the challenges associated with multi-junction device growth with the inclusion of quantum dot arrays. The unique challenges associated with the characterization of this type of device will also be presented. Finally, we will discuss the opportunities that these devices may hold for future space power systems.

Progress Towards III-V Photovoltaics on Flexible Substrates

Presented here is the recent progress of the NASA Glenn Research Center OMVPE group’s efforts in the development of high efficiency thin-film polycrystalline III-V photovoltaics on optimum substrates. By using bulk polycrystalline germanium (Ge) films, devices of high efficiency and low mass will be developed and incorporated onto low-cost flexible substrates. Our progress towards the integration of high efficiency polycrystalline III-V devices and recrystallized Ge films on thin metal foils is discussed.