Joseph Thomas Mcginn

Classification and selective collection of individual aerosol particles using laser-induced fluorescence.

We describe the development and performance evaluation of a system for optical interrogation, subsequent selection, and collection of individual aerosol particles entrained in an inlet air stream. Elastic scatter and laser-induced fluorescence obtained from single particles on-the-fly provide compositional information for classification criteria. Individual particles could then be selectively electrically charged and captured to a conductive substrate with an electric potential. The optical subsystem also includes a novel two-beam velocimeter to provide accurate downstream timing. Good overall quantitative performance values are reported for particles in the size range of 1-8 μm at mean rates up to 4 kHz.

Formation of fault structures during coalescence and growth of gold particles in a fused silica matrix—I

Abstract The fault structures formed during annealing of gold particles in a fused silica matrix were examined employing transmission electron microscopy. For higher volume fractions of gold and short annealing times at 900°C particle-particle coalescence by bridge formation was observed. After longer annealing times, particles assumed a nearly spherical shape approximately 500 A in diameter. A limited number of planar boundaries were found to have formed as the result of particle-particle coalescences and grain growth. The predominant structural configuration was a series of parallel or nonparallel planar twin boundaries within the gold particles. In the case of intersecting twins a specific planar coincidence lattice boundary was also observed. No evidence of high angle grain boundaries and dislocation structure was observed. It is believed that the various twin structures observed are metastable, with little mobility and may be used to examine mechanisms of grain boundary migration and annealing twin formation.

A mechanism for fault formation in fine particles and implications for theories of annealing twins in f.c.c. metals—II

Abstract A mechanism is proposed for fault structure formation in annealed f.c.c. metals on the basis of experimental observations during annealing of gold particles in a fused silica matrix. The proposed model is an extension of the ‘growth accident’ model of Gleiter and accounts for particle-particle impingement and coalescence. The model explains how the high angle boundaries formed upon impingement and coalescence of two or more particles migrate to form metastable twin boundary structures. All structures observed are explained successfully by the modified growth accident model. Other theories were critically examined, but fail to explain the observed morphologies. The gold particle-fused silica matrix system may be viewed as a model system for understanding the nature of particle impingement, grain boundary migration, and annealing twin formation. The observations made and mechanism developed may be extended to recrystallization, grain growth, and annealing twin formation in bulk, polycrystalline materials.

The effects of oxygen doping and subsequent annealing in nitrogen on the structure of polycrystalline silicon

We have used reflection high‐energy electron diffraction (RHEED) to study (i) the structure (surface crystallinity) of semi‐insulating polycrystalline silicon (SIPOS) layers having a wide range of oxygen doping and (ii) the effect of subsequent annealing on that structure. Our results are consistent with a model in which (i) excess O exists in the form of silicon oxide at the intergrain boundaries, (ii) the presence of this intergrain oxide tends to prevent grain growth during annealing, and (iii) sufficiently large O doping completely suppresses observable grain growth during annealing.

Dependence of buried CoSi sub 2 resistivity on ion implantation and annealing conditions

We have investigated the dependence of electrical and material properties of buried CoSi{sub 2} layers on Co+ implantation and annealing conditions. The results indicated that the electrical resistivity and crystalline quality of the implanted buried CoSi{sub 2} layers depend strongly on the implantation temperature. CoSi{sub 2} layers with the lowest resistivity and best crystalline quality ({chi}{sub min} as low as 3.6%) were obtained from samples implanted at 300{degrees}C--400{degrees}C. Implantation at higher temperatures (e.g., 580{degrees}C) produced cobalt disilicide layers with significantly higher electrical resistivity and a {chi}{sub min} of about 10.7%.

Recent advances in the development of a novel aerosol sorting and deposition system for bio-threat sensing applications

Sarnoff Corporation and the Naval Research Laboratory, through support of the U.S. Department of Homeland Security, are developing an automated, high throughput bio-aerosol physical enrichment system designed for use as part of a biological-threat protection system. The Biological Aerosol-Capture-Enrichment (BioACE) system is a bio-aerosol collection system that combines three unique technologies to create physically enriched aerosol samples that can be subsequently interrogated by any number of bio-threat detection systems for the presence of threat agents. An air-to-air concentrator uses an inertial separation technique to highly concentrate an aerosol sample presented to a dual wavelength ultra-violet laser induced fluorescence (UVLIF) optical trigger used to discriminate potential threat particles from non-threat particles conveyed in a collimated particle stream. This particle classification information is used to trigger an electrostatic deposition mechanism to deposit only those particles determined to be potential bio-threats onto a stainless steel substrate. Non-threat particles are discarded with the exiting airflow. The goal for the most recent development effort has been the integration and optimization of these technologies into a unit capable of producing highly enriched particulate samples from ambient air containing variable background aerosol loading and type. Several key technical and engineering challenges were overcome during the course of this development including a unique solution for compensating particle velocity dispersion within the airflow, development of a real-time signal acquisition and detection algorithm for determining material type on a particle by particle basis at rates greater than 2000 particles per second, and the introduction of a robust method for transferring deposited particulate into a 50ul wet sample suitable for most advanced bio-detection techniques. This paper will briefly describe the overall system architecture and then concentrate on the various component and system design tradeoffs required to optimize sample enrichment performance. A system performance model will be presented along with detailed analysis of the optical system components and electronic signal processing needed for achieving high concentration sample enrichment. Experimental methods and data obtained in the laboratory setting and from real world environments will be described and used to support the performance model of the system. Finally, a number of air sampling scenarios will be analyzed using the system performance model to determine the applicability of the BioACE system to the various concepts of operation perceived to be needed for achieving a high performance bio-threat detect-to-protect system.

A study of aerosol particle sorting to provide enriched samples for improved bio-threat analysis

Detection of biological threats in room air is a challenging problem due to their low concentration and the relatively high concentration of background. Dynamic sorting of threat particles from background clutter and dust prior to collection for analysis can provide substantially enriched samples with the advantages of greater analytical accuracy in shorter periods of time. The conceptually simple process of capturing threat particles and rejecting background in fact requires sophisticated particle detection and classification, timing, capture and final threat identification subsystems operating in concert. The effectiveness of the process is also strongly influenced by the operational conditions including threat and background loads as well as the time allotted for sample collection. The requirements of the final threat identification system will dictate the form factor for the collected sample and if collection is to be done dry or into a liquid. A number of sorting systems are currently under development to achieve enrichment for subsequent analysis. Enrichment factors, a common figure of merit for these systems, will be shown to be an inadequate indicator for comparing these systems unless standard operating conditions are used and other parameters are well defined. A set of parameters will be suggested that better allows characterization of the collection component of the sorting system.

Experimental performance of a novel aerosol sorting and deposition system for bio-threat sensing applications

Sarnoff Corporation and the Naval Research Laboratory, through support from HSARPA, are developing an automated, high throughput bio-aerosol physical enrichment system designed for use as part of a biological-threat protection system. The Biological Aerosol-Capture-Enrichment (BioACE) system is a bio-aerosol collection system that combines three unique technologies to create physically enriched aerosol samples that can be subsequently interrogated by any number of bio-threat detection systems for the presence of threat agents. An air-to-air concentrator uses an inertial separation technique to highly concentrate an aerosol sample presented to a dual wavelength ultra-violet laser induced fluorescence (UVLIF) optical trigger used to discriminate potential threat particles from non-threat particles conveyed in a collimated particle stream. This particle classification information is used to trigger an electrostatic deposition mechanism to deposit only those particles determined to be potential bio-threats onto a stainless steel substrate. Non-threat particles are discarded with the exiting airflow. A prototype laboratory system in which particle size dependent elastic scatter rater than fluorescence provides the triggering signal has been experimentally qualified. This paper will present a detailed overview of the prototype system and discuss the physical enrichment results achieved.