Small Al cluster ion implantation into Si and 4H-SiC.

RATIONALE: Continuously downscaling integrated circuit devices requires fabrication of shallower p-n junctions. The ion implantation approach at low energy is subject to low beam current due to the Coulomb repulsion. To overcome this problem cluster ions can be used for implantation. In comparison with single ions, cluster ions possess lower energy per atom and reduced Coulomb repulsion resulting in high equivalent current. METHODS: In this study to carry out low-energy implantation into single crystalline silicon and 4H-SiC samples we employ Aln - (n = 1-5) clusters with energy in the range of 5-20 keV. The Al clusters are obtained by Cs sputtering of Al rod. Time-of-flight secondary ion mass spectrometry (TOF-SIMS; IONTOF TOF.SIMS-5) is used to study aluminum and oxygen sputter depth profiles for different cluster sizes and implantation energies before and after annealing treatment. RESULTS: A distinguishable effect of the energy per atom in the cluster on reduction of the projected range Rp is revealed. The lowest Rp of 3 ± 1 nm has been achieved in SiC samples at the energy per atom of 1.66 keV. After annealing of Si samples, a considerable change in the Al profiles due to redistribution of Al atoms during motion of the front of recrystallization is observed. The influence of the number of atoms in the cluster at the same energy per atom within the experimental uncertainty is not observed. CONCLUSIONS: The transient effects of the sputtering by the primary ion beam distort the shape of the Al profiles in Si samples. In the case of SiC, due to its relatively lower surface chemical activity, more informative TOF-SIMS depth profiling of the shallow cluster implantation is feasible.

Bench scale production of butyramide using free and immobilized cells of Bacillus sp. APB-6.

Butyramide is a commodity chemical having wide range of applications from material science to biological sciences including synthesis of therapeutic drugs, hydroxamic acids, and electrorheological fluids. The nitrile hydratase protein of Bacillus sp. APB-6 was explored to develop an efficient biocatalytic process for the biotransformation of butyronitrile to butyramide using free and immobilized cells. The reaction conditions for nitrile hydratase activity were not affected after immobilization of the free cells and the optimum pH and temperature for both free and immobilized cells were 8.0 and 55 °C, respectively. In a 1-l batch reaction, complete conversion of 3000 mM butyronitrile to butyramide was achieved using free and immobilized cells. Immobilization of the cells further enhanced their operational stability and reusability in repetitive cycles of butyramide production. This bioconversion resulted in the formation of butyramide at a rate of 522.0 g h-1 g-1 dcw.

Thermostable Fe/Mn superoxide dismutase from Bacillus licheniformis SPB-13 from thermal springs of Himalayan region: Purification, characterization and antioxidative potential.

Superoxide dismutase (SOD; EC 1.15.1.1) is an enzyme that scavenges free radicals and increases the longevity. In this study, a thermostable superoxide dismutase (SOD) from Bacillus licheniformis SPB-13, from Himalayan region was purified to homogeneity using ion exchange chromatography (DEAE-Sepharose). The SDS and native PAGE analysis showed that SOD is composed of two subunits of 32 kDa each and total molecular mass of the enzyme was estimated as 68 kDa. The specific activity of enzyme was 3965.51 U/mg and was purified to 16.17 folds. The SOD showed maximum activity with 60 mM Tris-HCl buffer at pH 8.0 for 2 min of incubation. Enzyme along with FeCl3 as metal ion remained active till 70 °C. After reaction variables optimization, enzyme activity increased from 3965.51 to 4015.72 U/mg. Kinetic analysis of SOD showed km of 1.4 mM of NADH and Vmax of 10000 U/mg of protein. Turnover number (kcat) and catalytic efficiency (kcat/Km) were found to be 11,333 s-1 and 7092.2 s-1·mM-1 NADH. The activation energy (Ea) was calculated as 2.67 kJ·mol-1. After typing, it was found to be a member of Fe/Mn SOD family with IC50 value of 25 µg/ml, prevented the cell death at a concentration of 30 µg/ml and it increased the cell viability by 30%.

RBS Depth Profiling Analysis of (Ti, Al)N/MoN and CrN/MoN Multilayers.

(Ti, Al)N/MoN and CrN/MoN multilayered films were synthesized on Si (100) surface by multi-cathodic arc ion plating system with various bilayer periods. The elemental composition and depth profiling of the films were investigated by Rutherford backscattering spectroscopy (RBS) using 2.42 and 1.52 MeV Li2+ ion beams and different incident angles (0°, 15°, 37°, and 53°). The microstructures of (Ti, Al)N/MoN multilayered films were evaluated by X-ray diffraction. The multilayer periods and thickness of the multilayered films were characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) and then compared with RBS results.