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| Paper IPM / P / 9560 |
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The structural stability and vibrational properties of different sizes and charge states of the hydrogen saturated
spherical and cagelike C nanoparticles were investigated by means of ab initio density-functional theory.
The cagelike nanoparticles remain stable and stiff under structural relaxation, whereas specific sizes and charge
states of spherical C nanoparticles deform dramatically and dissociate under the relaxation. In order to see the
possibility of observation this effect in other semiconductor nanoparticles, two smallest sizes of spherical Si
nanoparticles were also examined and similar instabilities were obtained. We explain the induced large amount
of positive strain of unstable spherical C and Si nanoparticles by the presence of CH3 and SiH3 terminations on
the surface. These terminations result in a very packed arrangement of polar C-H bonds and consequently a
large value of Coulombic potential on the surface and corresponding strain in the volume of the clusters,
respectively. We demonstrate that the variation in formation and electronic properties with size correlate with
the variation in CH/CH2+CH3 ratio of the surface with size in agreement with the recently reported empirical
correlation suggested by x-ray absorption spectroscopy measurements. Likewise, we discuss the reported
empirical correlation between H coverage and strain in porous Si and some other corresponding experimental
evidences in porous Si. The calculation of the vibrational properties supports the reported structural
instabilities.
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