Silicon electronic structures

Silicon cluster reactions are an example of a newly emerging field of research which is very amenable to study with electronic structure methods. This exercise will examine the potential surface for silicon cation reacting with silane (SiH4). Such reactions are central to the growth of large silicon clusters, which occurs by sequential additions of -SiHj ... 

The general understanding of the electronic structure and the bonding properties of transition-metal silicides is in terms of low-lying Si(3.s) and metal-d silicon-p hybridization. There are two dominant contributions to the bonding in transition-metal compounds, the decrease of the d band width and the covalent hybridization of atomic states. The former is caused by the increase in the distance between the transition-metal atoms due to the insertion of the silicon atoms, which decreases the d band broadening contribution to the stability of the lattice. 

OFETs constructed on a silicon wafer do not lake advantage of one of the main interest of organic materials, namely the possibility of building electronic devices on plastic substrates. A second important drawback of the silicon-based structure is the difficulty to individually address the gale of transistors built on the same wafer, which would prevent the achievement of integrated circuits. 

Molecular and electronic structures of penta- and hexa-coordinate silicon compounds. S. N. Tan-dura, M. G. Voronkov and N. V. Alekseev, Top. Curr. Chem., 1986,131, 99 (1008). 

A. Y. Liu and M. L. Cohen, Structural Properties and Electronic Structure of Low-Compressibility Materials P-silicon Nitride and Hypothetical Carbon Nitride (P-C3N4), Phys. Rev. B, 41(15), 10727-34 (1990). 

Stroscio JA, Feenstra RM, Fein AP (1986) Electronic structure of the silicon(lll) 2x1 surface by scanning-tunneling microscopy. Phys Rev Lett 57 2579-2582... 

Fig. 1. Ligand-field model for the electronic structure of substitutional hydrogen in silicon in terms of the interactions between the vacancy orbitals and the atomic-hydrogen orbitals [Although the a state is shown as being not entirely passivated (still below the bottom of the conduction-band edge), it could in fact be in the conduction band, but with a host-like state pushed down slightly into the band gap.] (Reprinted with permission from the American Physical Society, DeLeo, G.G., Fowler, W.B., Watkins, G.D. (1984). Phys. Rev. B 29, 1819.)...

In summary, the H-acceptor pairs appear to be very similar to their silicon counterparts, which we have discussed in depth. The H-donor pairs are similar in that the H occupies a silicon-antibonding site however, this is an antibonding site to the defect and not to the host as is found in silicon. It is also interesting to note that the computed hydrogen frequencies appropriate to the latter pairs are better described by theory than the silicon counterparts discussed earlier. It is not clear whether this is a consequence of the electronic-structure method used here, a natural consequence of the differences between the silicon and compound-semiconductor hosts, or simply an accident. 

Figure 10.9. (a) Schematic structure of a silicon quantum dot crystal and (b) its calculated electronic structure as a function of interparticle distance H. The size of the nanoparticles is L = 6.5 nm. At small H, a splitting of the quantized energy levels of single dots results in the formation of three-dimensional minibands. Reproduced from Ref. 64, Copyright 2001, with permission from the American Institute of Physics. 

Figure 11.11. Integration of nanowire photonics with silicon electronics. Schematic illustrating fabrication of hybrid structures. A silicon-on-insulator (SOI) substrate is patterned by standard electron-beam or photolithography followed by reactive ion etching. Emissive NWs are then aligned onto the patterned SOI substrate to form photonic sources. [Reprinted with permission from Ref. 59. Copyright 2005 Wiley-VCH Verlag.]...

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

In contrast to carbon, which forms structures derived from both sp2 and sp3 bonds, silicon is unable to form sp2 related structures. Since one out of four sp3 bonds of a given atom is pointing out of the cage, the most stable fullerene-like structure in this case is a network of connected cages. This kind of network is realized in alkali metal doped silicon clathrate (19), which were identified to have a connected fullerene-like structure (20). In these compounds, Si polyhe-dra of 12 five-fold rings and 2 or 4 more six-fold rings share faces, and form a network of hollow cage structures, which can accommodate endohedral metal atoms. Recently, the clathrate compound (Na,Ba), has been synthesized and demonstrated a transition into a superconductor at 4 K (21). The electronic structure of these compounds is drastically different from that of sp3 Si solid (22). 

Michl, J. West, R. Electronic Structure and Spectroscopy of Polysilanes. In Silicon-based Polymers The Science and Technology of their Synthesis and Application-, Jones, R. G., Ando, W., Chojnowski, J., Eds. Kluwer Dordrecht, 2000 pp 499-529. 

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