Electronic properties, carbon compared with silicon

In the more distant future it is quite possible that nanotubes (and other carbon based structures for that matter) may find their way into electronics [165, 145,148,183-185]. This would of course be a spectacular development, in an area which has been dominated by silicon for so long. On the other hand nanotubes will have to demonstrate vastly superior properties compared with silicon to be a serious contender in this game. At the moment, nanotubes have been little more than rather curious objects from an electronics point of view. In fact, very much... 

The influence of both the steric and electronic properties of the silyl group on the rate of epoxidation have been examined experimentally [104], Two rate effects were considered. First, the overall rate of epoxidation of the silyl allylic alcohols was found to be one-fifth to one-sixth that of the similar carbon analogs. This rate difference was attributed to electronic differences between the silicon and carbon substituents. Second, the increase in k[el to 700 for silyl allylic alcohols compared with carbon analogs (e.g., 104 for entry 3, Table 6A.8) was attributed to the steric effect of the large trimethylsilyl group. As expected, when abulky (-butyl group was placed at C-3, k[e] increased to 300 [104],... 

The experimental and theoretical research activities in the field of materials with hardness comparable to or higher than diamond have been stimulated in recent years by the discovery and postulation of novel carbon aUotropes and novel carbon- and boron-based materials. Comparison of the experimental and theoretical results obtained in the past shows that first principles quantum mechanical and semi-empirical calculations are very useful for the screening of the structural and electronic properties of new materials. The fascinating variety of new possible carbon aUotropes which have been calculated to be stable relative to diamond or can be stabilized for kinetic reasons refiects the high potential and the topicality of modem carbon chemistry. Novel carbon aUotropes and carbon and silicon nitrides are subjects of discussion in Part I in the chapter written by G. Jungnickel et al. and J. E. Lowther. 

Selected physical properties of the tetrahalides of C and Si are listed in Table 13.3. The carbon tetrahalides differ markedly from those of the later group 14 elements they are inert towards water and dilute alkali and do not form complexes with metal halides. The distinction has been attributed to the absence of d orbitals in the valence shell of a C atom look back at the electronic versus steric debate, outlined in Section 13.3. However, one must be cautious. In the case of CX4 being inert towards attack by water, the lack of C d orbitals presupposes that the reaction would proceed through a 5-coordinate intermediate (i.e. as is proposed for hydrolysis of silicon halides). Of course, it is impossible to establish the mechanism of a reaction that does not occur Certainly, CF4 and CCI4 are thermodynamically unstable with respect to hydrolysis compare the value of AjG° for equation 13.35 with that of —290 kJ mol for the hydrolysis of SiCl4. 

Suwanpratech and Hattapanit [104] compared the use of black rice husk ash as a filler in epoxy resins used for embedding electrical and electronic devices to the use of commercial fillers, fused silica, and crystalline silica in various weight fractions between 20% and 60%. This led to an increased mixing viscosity, thermal expansion, and water absorption, with slightly lower tensile properties, compared to conunercial silicon fillers. It was suggested that the use of different combustion conditions for the rice husk ash, to lower the carbon content, may make the results more comparable. 

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