No abstract

A transmission electron microscopy study of oxidation kinetics of NiSi2 for both dry and wet oxidation has been carried out. Care was taken to determine the activation energies of oxidation in the temperature and time regime where the islanding of NiSi2 did not occur. For dry oxidation, activation energies for parabolic and linear growth were found to be 1.87 and 1.94 eV (with an error bar of ±0.1 eV), respectively. On the other hand, activation energies for parabolic and linear growth were found to be 1.72 and 1.59 eV (with an error bar of ±0.1 eV), respectively, for wet oxidation. The activation energy of parabolic rate constant is seen to be substantially different from those obtained previously. The difference is attributed to the occurrence and absence of islanding during oxidation in the previous and present study, correspondingly. Compared to the oxidation of TiSi2 and pure silicon, a model based on the dominant diffusing species through silicide, i.e., metal and Si for NiSi2 and TiSi2, respectively, is proposed to explain the substantial difference and closeness in linear activation energies of wet oxidation between NiSi2, TiSi2, and pure silicon, respectively.

The catalytic conversion of CO2 into valuable commodities has the potential to balance ongoing energy and environmental issues. To this end, the reverse water–gas shift (RWGS) reaction is a key process that converts CO2 into CO for various industrial processes. However, the competitive CO2 methanation reaction severely limits the CO production yield; therefore, a highly CO-selective catalyst is needed. To address this issue, we have developed a bimetallic nanocatalyst comprising Pd nanoparticles on the cobalt oxide support (denoted as CoPd) via a wet chemical reduction method. Furthermore, the as-prepared CoPd nanocatalyst was exposed to sub-millisecond laser irradiation with per-pulse energies of 1 mJ (denoted as CoPd-1) and 10 mJ (denoted as CoPd-10) for a fixed duration of 10 s to optimize the catalytic activity and selectivity. For the optimum case, the CoPd-10 nanocatalyst exhibited the highest CO production yield of ∼1667 μmol g−1catalyst, with a CO selectivity of ∼88% at a temperature of 573 K, which is a 41% improvement over pristine CoPd (~976 μmol g−1catalyst). The in-depth analysis of structural characterizations along with gas chromatography (GC) and electrochemical analysis suggested that such a high catalytic activity and selectivity of the CoPd-10 nanocatalyst originated from the sub-millisecond laser-irradiation-assisted facile surface restructure of cobalt oxide supported Pd nanoparticles, where atomic CoOx species were observed in the defect sites of the Pd nanoparticles. Such an atomic manipulation led to the formation of heteroatomic reaction sites, where atomic CoOx species and adjacent Pd domains, respectively, promoted the CO2 activation and H2 splitting steps. In addition, the cobalt oxide support helped to donate electrons to Pd, thereby enhancing its ability of H2 splitting. These results provide a strong foundation to use sub-millisecond laser irradiation for catalytic applications.

Oxidation kinetics of epitaxial Nisi2 (200 nm)/(OOl)Si samples for both dry and wet oxidation and polycrystalline Nisi2 EDMS'94 8-8-28 EDMS94 8-8-31

Oxidation kinetics for both dry and wet oxidation of epitaxial NiSi2 (200 nm)/(001)Si samples as well as dry oxidation of polycrystalline NiSi2 (200 nm)/(111)Si and epitaxial NiSi2 (600 nm)/(111)Si samples have been studied by transmission electron microscopy. Comparing oxidation kinetics data of 200-nm-thick epitaxial NiSi2 on (001) and (111)Si, activation energies of the parabolic rate constants are rather close, whereas those for linear rate constants are substantially different. The orientation dependence of the linear activation energies is explained in terms of the total number of available Si atoms for oxidation as a function of the substrate orientation. Oxide growth rate was found to be higher in polycrystalline NiSi2/(111)Si samples than that in epitaxial NiSi2/(111)Si samples. Strong influence of the grain boundaries of NiSi2 on oxidation kinetics was observed with the grain boundaries serving as fast paths for oxidation. For dry oxidation of epitaxial NiSi2 (600 nm)/(111)Si samples, both parabolic and linear activation energies are higher than those of Ni(200 nm)/(111)Si samples.