Silicon binding energy curves

Figure Al.3.23. Phase diagram of silicon in various polymorphs from an ab initio pseudopotential calculation [34], The volume is nonnalized to the experimental volume. The binding energy is the total electronic energy of the valence electrons. The slope of the dashed curve gives the pressure to transfomi silicon in the diamond structure to the p-Sn structure. Otlier polymorphs listed include face-centred cubic (fee), body-centred cubic (bee), simple hexagonal (sh), simple cubic (sc) and hexagonal close-packed (licp) structures.

Fig. 5. Kinetic energy distributions of SiF4 etch products evolved from a silicon surface exposed to 3-keV Ar+ ions and 5 x 10 SF molecules/cm s, at two surface temperatures, 50 and 100 K. Solid curves represent collision cascade distributions with a surface binding energy (Co) of 0.05 eV. (From Osstra et al., 1986.)...

The above observations all indicate that substitution of iron for aluminum in the octahedral layer and of aluminum for silicon in the tetrahedral layer both cause dehydroxylation to commence at a lower temperature. This, combined with the fact that the binding energy of the hydroxyl groups also affects the results, explains the extreme complexity of the curves obtained for this subgroup. Yet all have a potential diagnostic feature in the size and configuration of the low-temperature endothermic peak. 

Figure 11.4 The cohesive energies per atom as a function of nearest-neighbor distance for silicon in different crystalline structures. The solid curves are the tight-binding approximations and the dashed curves are the local density approximations (after [35]).

We report a representative picture to show the tight-binding results for silicon nanocrystals. Figure 5.1 shows the absorption cross section for a set of silicon nanocrystals upon increasing their size. It can be seen that the absorption spectra move from a multipeak structure that is typical of molecules to a broad, continuous curve that is typical of bulk systems. This is due to the increase in the number of transitions, which makes a nanocrystal as a molecular system that is in the middle between a small molecule and a bulk system. An interesting feature emerges from the analysis of the first transition, defined as the transition between the HOMO and LUMO energy levels. 

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