James Ferreira

Non-DNA Methods for Biological Signatures

Publisher Summary This chapter focuses on the methods that can determine chemical or structural features of biological agent particles that are signatures of particular methods of growth and post-growth processing (often referred to as “weaponization”). The detection of these signatures in a sample of a bio-weapon (BW) agent can aid the attribution by indicating: (1) the level of sophistication of the producer, (2) the access to particular types of agent weaponization information, (3) the likelihood that the material could be or has been produced at a significant scale, (4) and by providing essential sample matching data for ascertaining a putative relationship with other samples obtained in other venues. An example of the use of biologicals in forensic science is DNA, amplied by the Polymerase Chain Reaction (PCR) technique, legally admissible in courtas evidence. DNA evidence is successfully used in the court to convict or clear people of crimes because each persons DNA is unique. High-resolution techniques are being applied to investigations; such as Environmental scanning electron microscopy (ESEM) is used for taking high-resolution images under hydrated conditions; this avoids any artifacts associated with the critical point drying process that is required under normal Scanning Electron Microscopy (SEM) operations. ESEM is also equipped with Energy Dispersive X-ray (EDX) microanalysis and Backscatter capabilities. SEM is a standard “workhorse” technique for characterizing particulate samples, found in many laboratories worldwide. It provides excellent imaging of the surfaces of agent particles and other material in a sample, and is used for identifying likely agent particles for analysis by other instruments. When combined with EDX, the elemental composition of the material in the imaged region can be determined. These techniques continue to signature libraries of correlations between analyses and growth and processing conditions of growth, it will be necessary to develop an information system which combines types of data to determine unique signatures.

Large Area Deposition of Field Emission Cathodes for Flat Panel Displays

The convention for field emission cathode (FEC) synthesis involves coating with a very-high tolerance in thickness uniformity using a planetary substrate fixture and a large source-to-substrate separation. New criteria for a deposition process must facilitate a reduction in the operating voltage by increasing the density of emitters through a reduction of cathode size and spacing. The objective of scaling the substrate size from small (less than 30 cm{sup 2}) to large (greater than 500 cm{sup 2}) areas further compounds manufacturing requirements to a point beyond that easily obtained by modifications to the convention for FEC deposition. A new patented approach to design, assemble, and operate a coating system enables FEC deposition over large areas through process control of source divergence coupled to incremental substrate positioning.

Corrosion of Ferritic Steels in High Temperature Molten Salt Coolants for Nuclear Applications

Corrosion of ferritic steels, including oxide dispersion strengthened (ODS) variants, in high temperature molten fluoride salts may limit the life of advanced reactors, including some hybrid systems that are now under consideration. In some cases, the steel may be protected through galvanic coupling with other less noble materials with special neutronic properties such as beryllium. This paper reports the development of a model for predicting corrosion rates for various ferritic steels, with and without oxide dispersion strengthening, in FLiBe (Li 2 BeF 4 ) and FLiNaK (Li-Na-K-F) coolants at temperatures up to 800 °C. Mixed potential theory is used to account for the protection of steel by beryllium, Tafel kinetics are used to predict rates of dissolution as a function of temperature and potential, and the thinning of the mass-transfer boundary layer with increasing Reynolds number is accounted for with dimensionless correlations. The model also accounts for the deceleration of corrosion as the coolants become saturated with dissolved chromium and iron. Electrochemical impedance spectroscopy has been used for the initial in situ study of an ODS ferritic steel in high-temperature molten fluoride salt environments, with the complex impedance spectra obtained at its open circuit corrosion potential (OCP) interpreted in terms of the basic components of the equivalent circuit, which include the electrolyte conductivity, the interfacial charge transfer resistance, and the interfacial capacitance. Such in situ measurement techniques may provide valuable insight into the degradation of materials under realistic conditions.

PASSIVATION OF SEMICONDUCTOR SURFACES FOR IMPROVED RADIATION DETECTORS: X-RAY PHOTOEMISSION ANALYSIS

Surface passivation of device-grade radiation detector materials was investigated using x-ray photoelectron spectroscopy in combination with transport property measurements before and after various chemical treatments. Specifically Br-MeOH (2% Br), KOH with NH{sub 4}F/H{sub 2}O{sub 2} and NH{sub 4}OH solutions were used to etch, reduce and oxidize the surface of Cd{sub (1-x)}Zn{sub x}Te semiconductor crystals. Scanning electron microscopy was used to evaluate the resultant microscopic surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the Schottky barrier height for improved radiation detector devices.

Characterization of Vapor Deposited, NanoStructured Membranes

The vapor deposition methods of planar magnetron sputtering and electron-beam evaporation are used to synthesize materials with nano structured morphological features that have ultra-high surface areas with continuous open porosity at the nano scale. These nano structured membranes are used in a variety of fuel cells to provide electrode and catalytic functions. Specifically, stand alone and composite nickel electrodes for use in thin film solid-oxide, and molten carbonate fuel cells are formed by sputter deposition and electron bean evaporation, respectively. Also, a potentially high-performance catalyst material for the direct reformation of hydrocarbon fuels at low temperatures is deposited as a nano structure by the reactive sputtering of a copper-zinc alloy using a partial pressure of oxygen at an elevated substrate temperature.