Dopant reactivation

Based on the study of the Arl/doped systems, three distinct differences have been delineated between the ablative regime and the very low fluences regime. Specifically, differences are observed concerning (a) efficient formation of biaryl-type products, (b) efficiency of ArH-like photoproduct formation, and (c) kinetics of product formation. These results demonstrate that dopant reactivity is both qualitatively and quantitatively modified from that at low laser fluences. 

Rottman, C., Grader, G., De Kazan, Y., Melchior, S., and Avnir, D. (1999) Surfactant-induced modification of dopants reactivity in sol-gel matrixes. 

The neutralization of shallow dopants by hydrogen can also be used to create resistive regions for electrical insulation between different components by using proper masking. Reactivation of neutralized dopants by local heating, using laser beam direct writing for example, can be useful if interconnection pathways are desired. 

The hydrolytic polycondensation of silicon alkoxides of general formula Si(OR)4 or R/ Si(OR)4 , where the non-reactive organofunc-tional group R acts as a network modifier, is carried out in the presence of dopant molecules resulting in the formation of highly porous, reactive organosilicates whose applications span many traditional domains of chemistry. 

Instead of applying synthetic methods to alter chromophore reactivity, this new way of controlling chemical reactivity involves choosing an appropriate solid micellar system (from the available multitude) and exploiting it to manipulate the chemistry of the entrapped compound. The sol-gel matrix and the micellar solubilization, in fact, have a synergetic effect. Their combination produces effects stronger and more tuneable than in solution, so that a careful selection of sol-gel entrapped surfactants allows one to induce enormous changes in the dopant properties. 

Indeed, the mobility of the entrapped dopant is crucial in promoting the reactivity of the final materials. Thus, provided that the dopant molecules are at the surface and enjoy enough freedom, high porosity will certainly promote reactivity by limiting intraparticle diffusion but that will not be the case if microporous xerogels of different HLB are compared (c/. entrapped lipase and tetra-//-propy 1 am monium perruthe-nate (TPAP) where ORMOSIL with the smaller pores are more reactive). 

Chatteijee, A. 2006. A reactivity index study to rationalize the effect of dopants on Bronsted and Lewis acidity occurring in MeAlPOs. J. Mol. Graphics Model. 24 262-270. 

Defects in carbon nanostructures can be classified into (a) structural defects, (b) topological defects, (c) high curvature and (d) non-sp2 carbon defects. Even slight changes within the carbon nanostructure can modify the chemical and physical properties. Some defects in carbon systems results in high chemical reactivity, mainly due to the accumulation of electrons in the vicinity of the dopant. These defects can be used as anchoring sites in order to make the carbon nanostructures more compatible with ceramic or polymer matrices, thus enhancing interactions between carbon structures (filler) and the host matrices. 

Lattice defects also play a prominent role in the reactivity of pyrotechnic materials, where the displacement or absence of atoms or ions from their normal positions within a lattice can have a pronounced effect on properties, as can the introduction of foreign species or dopants within a crystal. 

K —> 71 transitions. Also, in the case of jt —> 7t transitions, efficient energy dissipation occurs in polyimides although dris latter absorption may lead to a weaker n-bond and long-lived excited states. Subsequent reactions (possibly with a reactive ambient) can lead to modification or ablation. The UV absorbance spectrum of BPDA-PDA is shown in Figure 5.7. At 308nm, o BPOA-PDA 1 X 10 cm Thus, polyimides, theoretically, are ideal dopant candidates for PTFE. However, the critical problem of incorporating polyimide evenly and at a suitable dopant-domain size in the PTFE matrix was only recently solved. 2... 

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