Physics Seminar

The properties of the matter at the atomic scale are complex and often differ from those observed at larger scales. Computer modeling provides deep insights into the nature and properties of matter at the atomic scale, and is essential in predicting the structure and properties of novel materials and nanomaterials, reducing often the time spent on expensive lab experiments.In this talk I will present my recent results on first-principles density functional calculations for two different systems:

1. Iron-hydrogen interactions in bulk silicon

Iron and its complexes in silicon have been intensively investigated for more than 50 years because they are unwanted recombination centers. In particular, interstitial iron (Fe_i) and iron-acceptor pairs in p-type silicon form deep levels. One of the proposed approaches to reduce the number of iron related deep levels is by hydrogen passivation. Iron is also known to occupy substitutional sites (Fe_s) but its electronic properties and possible interactions with H are not well explored. In this work, I investigated the interaction of hydrogen with Fe_i, Fe_s, and the {Fe_iB_s} pair in silicon. The configurations, charge and spin states, electronic structures, binding energies, and approximate acceptor and donor level positions will be presented. The vibrational spectra of the most stable complexes will be also shown.

2. Boron fullerenes and nanotubes

The chemistry of boron resembles that of carbon in its ability to catenate and form molecular networks. Therefore it is natural to believe that not only carbon but also boron possesses molecular fullerene-like allotropes. Starting from a known stable structure, a boron double-ring, I will show how a family of very stable cages can be constructed. All of them have icosahedral symmetry and round shape. I will also show that these fullerenes and the recently proposed novel boron nanotubes are closely related structures.