NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NFx+F and NHx+H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the atomic hydrogen from the ammonia does not react with SiO2.

Background: Oxidative damage is one of the most frequent types of cell components damage leading to oxidation of lipids, proteins and the molecule of DNA. As a consequence, there is a higher occurrence of several pathologies such as atherosclerosis, neurodegenerative diseases, cancer; or diabetes. In our study, influence of whole body anesthesia during minor surgery on the level of DNA damage was examined using comet assay technique. Methods: The basic principle of this method is fixing the cells (lymphocytes) in agarose, their lysis for the removal of membranes, incubation with the specific enzymes and electrophoresis of the released cell nuclei. During the electrophoresis, free low-molecular weight and negatively charged fragments of DNA move towards anode which causes the formation of the typical comet cell shape. Finally, the gels are stained by ethidium bromide (DNA intercalating dye) and visualized. Results: We have observed single strand breakages (SSBs) and, with the use of modified assay using specific enzymes for detection of specific lesions, also oxidized purines and pyrimidines. The extent of DNA damage as determined by the intensity of the tail of the comet was quantified using LUCIA Comet Assay (Laboratory Imaging, Czech Republic) software for image analysis. The results were used...

Melatonin is a neurohormone produced by the pineal gland in the brain. It functions as an antioxidant to scavenge free radicals. Free radicals are reactive species; they often oxidize the cells leading to oxidative stress which may lead to severe health complications. Reaction of melatonin with free radicals is known to be stepwise, as such the stability of the intermediates can be examined. Thus, the possibility of using melatonin as an in vivo spin trap can be determined. Spin traps allow characterization of unstable radical species using electron spin resonance spectroscopy. In this research, ab initio quantum chemistry techniques were used to calculate the energies of selected intermediates formed during the partial oxidation of melatonin by hydroxyl radical. Specifically, optimized geometries for melatonin, and selected intermediates with ·OH were obtained at the DFT/B3LYP/cc-pVXZ and HF/cc-pVXZ (X = D, T, Q) levels of theory. Extrapolations to the complete basis set limit were also performed.

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NiSi and Ni(Pt)Si, and of the effects of dissociated ammonia on oxide reduction was carried out under controlled ultrahigh vacuum (UHV) conditions. X-ray photoelectron spectroscopy (XPS) has been used to characterize the evolution of surface composition. Vicinal surfaces on NiSi and Ni(Pt)Si were formed in UHV by a combination of Ar+ sputtering and thermal annealing. Oxidation of these surfaces in the presence of either O+O2 or pure O2 at room temperature results in the initial formation of a SiO2 layer ~ 7 Å thick. Subsequent exposure to O2 yields no further oxidation. Continued exposure to O+O2, however, results in rapid silicon consumption and, at higher exposures, the kinetically-driven oxidation of the transition metal(s), with oxides >35Ǻ thick formed on all samples, without passivation. The addition of Pt retards but does not eliminate oxide growth or Ni oxidation. At higher exposures, in Ni(Pt)Si surface the kinetically-limited oxidation of Pt results in Pt silicate formation. Substrate dopant type has almost no effect on oxidation rate. Reduction of the silicon oxide/metal silicate is carried out by reacting with dissociated NH3 at room temperature. The reduction from dissociated ammonia (NHx+H) on silicon oxide/ metal silicate layer shows selective reduction of the metal oxide/silicate layer, but does not react with SiO2 at ambient temperature.

The focus of the following research was to (1) understand the chemistry involved in nitriding an organosilicate glass substrate prior to tantalum deposition, as well as the effect nitrogen incorporation plays on subsequent tantalum deposition and (2) the reduction of a native oxide, the removal of surface contaminants, and the etching of a HgCdTe surface utilizing atomic hydrogen. These studies were investigated utilizing XPS, TEM and AFM. XPS data show that bombardment of an OSG substrate with NH3 and Ar ions results in the removal of carbon species and the incorporation of nitrogen into the surface. Tantalum deposition onto a nitrided OSG surface results in the initial formation of tantalum nitride with continued deposition resulting in the formation of tantalum. This process is a direct method for forming a thin TaN/Ta bilayer for use in micro- and nanoelectronic devices. Exposure to atomic hydrogen is shown to increase the surface roughness of both air exposed and etched samples. XPS results indicate that atomic hydrogen reduces tellurium oxide observed on air exposed samples via first-order kinetics. The removal of surface contaminants is an important step prior to continued device fabrication for optimum device performance. It is shown here that atomic hydrogen effectively removes adsorbed chlorine from the HgCdTe surface.

The presence of excess free radicals in the body can result in severe health consequences because of oxidative damage to cells. Spin traps may be used as a probe to examine radical reactions in cells, but there is a need for less toxic and more lipid soluble examples. Melatonin is one of the numerous antioxidants used to scavenge free radicals in the body and reportedly one of the most efficient radical scavengers known. It is relatively nontoxic and easily crosses the lipid bilayer in cell membranes. Melatonin is thought to undergo a multistep oxidation process and this work investigates the potential for it to be used as a spin trap. The presence of electron withdrawing or donating groups added to melatonin may stabilize an intermediate and allow it to function as a spin trap. The essence of this study is to conduct a computational inquiry into the relative stability of melatonin, selected derivatives, and the partial oxidation products formed from the scavenging of hydroxyl radical. To determine this, geometries were optimized for each molecule at the DFT/B3LYP/6-31G(d) and HF/6-31G(d) levels of theory.

The effects of oxidatively modified low density lipoprotein (oxLDL) on atherogenesis may be partly mediated by alterations in the production of nitric oxide (NO) by vascular cells. Lipid hydroperoxides (LOOH) and lysophosphatidylcholine (lysoPC) are the major primary products of LDL oxidation. The purpose of this study was to characterize the effects of oxLDL, LOOH and lysoPC on NO production and the expression of inducible nitric oxide synthase (iNOS) gene in lipopolysaccharide (LPS) stimulated macrophages. LDL was oxidized using an azo-initiator 2,2'-azobis (2- amidinopropane) HCl (ABAP) and octadecadienoic acid was oxidized by lipoxygenase to generate 13-hydroperoxyl octadecadienoic acid (13-HPODE). Our study showed that oxLDL markedly decreased the production of NO, the levels of iNOS protein and iNOS mRNA in LPS stimulated macrophages. The inhibition potential of oxLDL on NO production and iNOS gene expression depended on the levels of LOOH formed in oxLDL and was not due to oxLDL cytotoxicity. Furthermore, 13-HPODE markedly reduced NO production and iNOS protein levels, whereas lysoPC showed only slight reduction. The effects of 13-HPODE and lysoPC did not require an acetylated LDL carrier. Our results suggest that 13-HPODE is a much more potent inhibitor of NO production and iNOS gene expression than lysoPC in LPS stimulated RAW264.7 macrophages.

The effect of chronic treatment with vitamin E (VE) on acute l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity, as assessed by striatal dopamine (DA) depletion, was studied. Male C57B1/6J mice were fed VE (48 mg kg-1 per day, intragastric) for 4, 8, or 12 weeks prior to administration of MPTP (20 mg kg-1, i.p. X 3, 2 h intervals) or its diluent. Brain VE concentration was increased by exogenous supplements for 12 weeks. Striatal DA content was reduced by 85% to 90% after MPTP in control and VE-treated mice. Mice with elevated cerebral VE were not protected from MPTP toxicity, with DA content as an indicator. In conclusion, these findings indicate that moderate elevation of brain VE is not adequate for protecting DA-containing neurons against the toxic actions of a high dose of MPTP.

Superoxide dismutase scavenges oxygen radicals, which have been implicated in ischemia/reperfusion (I/R) injury in the heart. Our experiments were designed to study the effect of a moderate increase of copper/zinc superoxide dismutase (CuZnSOD) on myocardial I/R injury in TgN(SOD1)3Cje transgenic mice. A species of 0.8 kb human CuZnSOD mRNA was expressed, and a 273% increase in CuZnSOD activity was detected in the hearts of transgenic mice with no changes in the activities of other antioxidant enzymes. Furthermore, immunoblot analysis revealed no changes in the levels of HSP-70 or HSP-25 levels. Immunocytochemical study indicated that there was increased labeling of CuZnSOD in the cytosolic fractions of both endothelial cells and smooth muscle cells, but not in the myocytes of the hearts from transgenic mice. When these hearts were perfused as Langendorff preparations for 45 min after 35 min of global ischemia, the functional recovery of the hearts, expressed as heart rate x LVDP, was 48 ± 3% in the transgenic hearts as compared to 30 ± 5% in the nontransgenic hearts (p < .05). The improved cardiac function was accompanied by a significant reduction in lactate dehydrogenase release from the transgenic hearts. Our results demonstrate that overexpression of CuZnSOD in coronary vascular cells renders the heart more resistant to I/R injury.