Effect of dopants on the fracture toughness of silicon

Fracture experiments were conducted on p-type and n-type Si in the presence and absence of hydrogen. It was found that fracture toughness is slightly less than the fracture toughness of n-type silicon. Annealing silicon in an Ar/H atmosphere gave a hydrogen concentration of less than 0.1 ppm, which did not have any measurable effect on fracture toughness. Likewise, the exposure of pre-cracked specimens to H did not cause any measurable change in fracture toughness.

New solid bases for biodiesel synthesis

Biodiesel is a promising non-toxic and biodegradable renewable fuel, synthesized by the homogeneous base-catalyzed transesterification of vegetable oils or animal fats with methanol or ethanol. Removal of the base, typically Na or K alkoxide, after reaction is a major problem since aqueous quenching results in stable emulsions and saponification. The use of a solid base catalyst offers several process advantages including the elimination of a quenching step (and associated basic water waste) to isolate the products, and the opportunity to operate in a continuous process. The synthesis and characterization of a series of Li-doped CaO and Mg-Al hydrotalcite solid base catalysts were presented and their physicochemical properties were correlated with their activity in biodiesel synthesis. Both catalysts were effective solid bases for the transesterification of triglycerides to the methyl ester, with catalyst activity related to the electronic properties of Li and Mg dopants. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005).

Highly photosensitive polymethyl methacrylate microstructured polymer optical fiber with doped core

In this Letter, we report the fabrication of a highly photosensitive, microstructured polymer optical fiber using benzyl dimethyl ketal as a dopant, as well as the inscription of a fiber Bragg grating in the fiber. A refractive index change in the core of at least 3.2 × 10 has been achieved, providing a grating with a strong transmission rejection of -23 dB with an inscription time of only 13 min. The fabrication method has a big advantage compared to doping step index fiber since it enables doping of the fiber without using extra dopants to compensate for the index reduction in the core introduced by the photosensitive agent. © 2013 Optical Society of America.