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Tai Nguyen

    Tai Nguyen

    Multilayer structures of W/C, WC/C, and Ru/C, of various periods were prepared and studied by high-resolution transmission electron microscopy. Comparison of the phases in the layered structures is made for as-prepared and annealed... more
    Multilayer structures of W/C, WC/C, and Ru/C, of various periods were prepared and studied by high-resolution transmission electron microscopy. Comparison of the phases in the layered structures is made for as-prepared and annealed samples. Both as-prepared and annealed WC/C multilayers are predominantly amorphous, while the phases in the W/C depend on the periods. The 2 nm period W/C multilayer remains amorphous after annealing, and the longer periods recrystallize to form W2C. The layered microstructures of W/C and WC/C are stable on annealing at all periods, while the amorphous Ru-rich layers in the 2 nm period Ru/C multilayer agglomerate upon annealing to form elemental hexagonal Ru crystallites. Larger period Ru/C multilayers show stable layered structures, and indicate hexagonal Ru in the Ru-rich layers. X-ray measurements show that the multilayer periods expand on annealing for all metal-carbon multilayers studied.
    ABSTRACTDiffusion-induced precipitation in arsenosilicate glass (AsSG) under high temperature anneal is studied by high resolution Transmission Electron Microscopy (TEM), and other techniques. Polycrystalline precipitates of a few hundred... more
    ABSTRACTDiffusion-induced precipitation in arsenosilicate glass (AsSG) under high temperature anneal is studied by high resolution Transmission Electron Microscopy (TEM), and other techniques. Polycrystalline precipitates of a few hundred angstroms in size have been observed near the interface of AsSG and the silicon substrate, covering the entire interface area after high temperature anneal. It is proposed that high concentrations of arsenic (above the solid solubility limit) precipitate initially at nucleation sites near the AsSG/silicon interface. Further anneal-induced diffusion of arsenic to the interface promotes growth of the precipitates. As a result, the precipitates cover the entire interface area, and impede further As diffusion into the Si substrate. Techniques to avoid the precipitation process without compromising the thermal budget or reduced arsenic diffusion have been explored and will be discussed.
    Forty‐nine fortified wines, dessert wines, aperitifs and fruit wines were tested for mutagenicity using a standardised Ames test system in the presence or absence of S9 rat liver homogenate and faecalase. In general, little or no... more
    Forty‐nine fortified wines, dessert wines, aperitifs and fruit wines were tested for mutagenicity using a standardised Ames test system in the presence or absence of S9 rat liver homogenate and faecalase. In general, little or no mutagenic activity was detected in the samples of aperitifs, sherries, madeiras, marsalas, dessert wines, most ports and most fruit wines. Thirty‐seven of the beverage samples contained mutagenic activity equivalent to less than 1 mg quercetin l under all test conditions. The beverages possessing higher direct‐acting mutagenic activity included one fruit wine made from raspberries, and wine beverages made from red grapes, including black muscat dessert wines, ports and a sangria. Treatment of concentrated wine beverage samples with S9 and faecalase, or S9 alone, generally had little effect on mutagenic activity, but increases of up to 1.7 mg equivalents of quercetin l were observed in specific samples.
    Abstract Vintners often use fining agents such as gelatin, casein or polyvinylpolypyrrolidone (PVPP) to remove bitter and astringent phenolic compounds from wine prior to bottling. One of these fining agents, PVPP, also efficiently... more
    Abstract Vintners often use fining agents such as gelatin, casein or polyvinylpolypyrrolidone (PVPP) to remove bitter and astringent phenolic compounds from wine prior to bottling. One of these fining agents, PVPP, also efficiently removes the direct‐acting mutagenic activity ...
    The reaction mechanism of thin cobalt (Co) films with silicon dioxide (SiO2) substrate under rapid thermal annealing conditions has been investigated. Reaction of thin cobalt film (12.5 nm) with a SiO2 substrate is observed in an inert... more
    The reaction mechanism of thin cobalt (Co) films with silicon dioxide (SiO2) substrate under rapid thermal annealing conditions has been investigated. Reaction of thin cobalt film (12.5 nm) with a SiO2 substrate is observed in an inert ambient (N2) and in vacuum (∼10−8 Torr). The reaction is manifested by the formation of craterlike depressions on the SiO2 substrate and by the presence of a Co2SiO4 reaction product determined by transmission electron microscopy diffraction patterns. Much less damage is observed with no reaction product observed if the samples are annealed in a forming gas ambient (90% N2/10% H2), the cobalt film is much thicker (150 nm), or the cobalt film is in situ cleaned (e.g., 5 min in 400 °C, forming gas ambient) prior to annealing in either inert or vacuum ambient. It is proposed that the presence of oxygen is required in order to initiate the reaction between cobalt and SiO2. The source of the oxygen contaminant, in our studies, is the oxygen on the surface ...
    The ongoing threat of the potential use of biothreat agents (such as Bacillus anthracis) as a biochemical weapon emphasizes the need for a rapid, miniature, fully automated, and highly specific detection assay. An integrated and... more
    The ongoing threat of the potential use of biothreat agents (such as Bacillus anthracis) as a biochemical weapon emphasizes the need for a rapid, miniature, fully automated, and highly specific detection assay. An integrated and self-contained microfluidic device has been developed to rapidly detect B. anthracis and many other bacteria. The device consists of a semiconductor-based DNA microarray chip with 12,000 features and a microfluidic cartridge that automates the fluid handling steps required to carry out a genotyping assay for pathogen identification. This fully integrated and disposable device consists of low-cost microfluidic pumps, mixers, valves, fluid channels, reagent storage chambers, and DNA microarray silicon chip. Microarray hybridization and subsequent fluid handling and reactions were performed in this fully automated and miniature device before fluorescent image scanning of the microarray chip. The genotyping results showed that the device was able to identify and...