Orientation specific synthesis of kinked silicon nanowires grown by the vapour-liquid-solid mechanism.

Kinked silicon nanowires (Si-NWs) were synthesized in a well reproducible manner using gold nanocluster-catalyzed quasi-one-dimensional growth on Si(111) substrates with silane (SiH(4)) as the precursor gas. The kinking is considered to be due to the change in the growth direction induced by the sudden change of the pressure during Si-NW synthesis. Structural high resolution transmission electron microscopy (HRTEM) characterization of the sample shows that epitaxial Si-NWs synthesized on Si(111) substrates at a total pressure of 3 mbar grow along the {111} direction, while the ones at 15 mbar favour the {112} direction. By dynamically changing the system pressure during the growth process morphological changes of the NW growth directions along their length have been shown, resulting in kinked nanowires. The crystallographic orientation relation of the kinking between the 3 and 15 mbar ranges has been analysed by TEM. It is shown that no defects or grain boundaries in the intersection between the two sections of the Si-NWs are necessary to form such kinks between different wire directions.

Air pollution and asthma among children in Seoul, Korea.

BACKGROUND: As information about the health risks associated with air pollution has become available, attention has focused increasingly on susceptible persons such as children and persons with preexisting respiratory diseases, such as asthma. METHODS: We investigated the association between outdoor air pollution and asthma attacks among children under 15 years of age in Seoul, Korea. We estimated the relative risks of hospitalization associated with an interquartile range (IQR) increase in pollutant concentrations and used time series analysis of the counts by means of the generalized additive Poisson model. RESULTS: The estimated relative risk of hospitalization for asthma was 1.07 (95% confidence interval [CI] = 1.04-1.11) for particulate matters less than or equal to 10 microm in aerodynamic diameter (IQR = 40.4 microg/m3); 1.11 (95% CI = 1.06-1.17) for sulfur dioxide (IQR = 4.4 ppb); 1.15 (95% CI = 1.10-1.20) for nitrogen dioxide (IQR = 14.6 ppb); 1.12 (95% CI = 1.07-1.16) for ozone (IQR = 21.7 ppb); and 1.16 (95% CI = 1.10-1.22) for carbon monoxide (IQR = 1.0 ppm). CONCLUSIONS: These findings support the hypothesis that air pollution at levels below the current standards of Korea is harmful to sensitive subjects such as asthmatic children.