Silicon cluster reactions

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 ... 

Silicon Cluster Reactions S t 2 Reaction Hydration Reactions... 

A few clusters of interest containing germanium and transition metals have been reported.136-138 Dimethylgermane was found to replace only the bridging carbonyls between cobalt in a mixed germanium/cobalt/iron cluster complex (Equation (107)), and replacement of the carbonyl bridging the iron metal centers was not observed.137 A similar reaction leads to replacement of a bridging carbonyl in a mixed cobalt/silicon cluster (Equation (108)).136... 

Clusters of the elements aluminum to thallium containing only one or two carbon atoms and strong direct element-element interactions, similar to boron rich car-baboranes, have not yet been synthesized, and also the corresponding silicon derivatives are relatively rare. To the best of our knowledge only one aluminum-silicon and one gallium-silicon cluster (1 and 2) has been reported in the literature. The reaction of metastable aluminum(I) chloride with decamethylsilicocene or with a mixture of SiCl4 and (AlCp )4, respectively, afforded black crystals of... 

Figure 5.18. Calculated reaction path and optimized structures using DFT for (a) N—H dissociation and (b) N—CH3 dissociation of dimethylamine on the one-dimer silicon cluster. Figure reused with permission from Collin Mui, Journal of Chemical Physics, 114, 10170 (2001). Copyright 2001, American Institute of Physics [279].

So-called clustering reactions of SiH + ions (n = 0-3) with silanes and other small molecules have attracted considerable interest. In particular, the reaction sequences which might lead to the formation of large-sized clusters have received attention, as these processes are thought to be involved in undesirable dust-formation which occurs during silicon-film depositions from silane plasmas and vapors97-99. Thus, Mandich and Reents... 

The clustering reactions of SiD + (n = 0-3) and Si2D + (n = 0-6) cations with deuterated disilane, Si2D6, have been measured in a FTMS study110. The dominant pathway for these reactions was found to correspond to silylene transfer and SiD4 elimination. The overall reactivity of disilane compared to monosilane was found to be higher, and this was explained by the fact that the silicon-silicon bond in disilane is considerably weaker (76 kcalmol-1) than the Si—H bond of SiFLt (88 kcalmol-1)111. Thus the insertion of Si+ into the Si—Si bond was calculated to be 17 kcalmol-1 more favorable than Si+ insertion into the Si—H bond of SiFFt106,112. 

A number of other groups have investigated the clustering reactions of small cation silicon species with silanes and other small molecules. The ion-molecule reactions occurring between SiHv+ (x = 0-3) cations and neutral ammonia, as well as the reactions between NHt+ cations and SiH4 were studied by FIMS113,114. The main channel for the reaction between SiHv+ ions and NH3 was found to correspond to the elimination-addition reaction, well-known for silanes (equation 20), which formally corresponds to the transfer of a nitrene-unit (NH)113. 

The structure of ionic silicon clusters, the mixed silicon-carbon species and their reactions with neutral molecules have been investigated by a number of experimental151,120-133 and theoretical groups134-137. Ion-molecule reactions of the silicon clusters have also been thoroughly studied by larrold and coworkers51. These... 

So far few reports have dealt with the reaction chemistry of transition-metal silicon clusters, but the diversity of structural types and the interesting ways in which silicon-based ligands can become incorporated into clusters suggest that new and useful types of transformations should be possible. 

Reents W D Jr, Mandich M L and Bondybey V E 1986 Reaction of anionic and cationic silicon clusters with tungsten hexafluoride studied by Fourier transform ion cyclotron resonance mass spectrometry Chem. Phys. Lett. 131 12... 

Copolymerization of SiCl4 with Me2SiCl2 was less successful because this reaction is difficult to control, due to favored formation of oxidation-sensitive silicon clusters, and the reaction is often incomplete providing only low yields of soluble materials consisting of a high proportion of low molecular oligomers. 

The non-dissociated SiELr molecules also participate in the surface reactions, but mostly as deactivating chemical agents. Detailed kinetics of the gas-phase processes in the silane discharges is much more comphcated (Kushner, 1988). In particular, the kinetics of silicon clusterization in the silane discharges will be discussed later in this chapter in connection with the formation of nanoparticles. 

To date, neural network potentials have been most frequently applied to represent low-dimensional, molecular PESs. Apart from the central role of molecules in chemistry the main reason for this is certainly the comparably simple mapping of the reference points using electronic structure methods. Low-dimensional NN PESs have been constructed for example for the of ground state and excited state PESs and transition dipole moments of the HCl" ion, " for the OH radical in order to calculate the vibrational levels,for Hi " to calculate rovibrational spectra,for the free H2O molecule, for the dissociation of a Si02 molecule, for the HOOH molecule, for the NOCl molecule, for formaldehyde, for the cis-trans isomerization and dissociation dynamics of nitrous add, " for H + HBr, " for the reaction 0H + H2 H20 + H, for the reaction BeH + H2->BeH2 + H, " for small silicon clusters, " for vinyl bromide, to describe the three-body interaction energies in the H2O-... 

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