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<111> platelets

Of the models so far suggested for the <111> platelet, TEM studies and calculations, favour the structure with a pair of hydrogen atoms saturating each broken bond between (111) planes displaced apart by ~3 Å. This structure does not include any silicon vacancies. Using the AIMPRO code, the vibrational modes of a H2 molecule trapped within a platelet have been calculated. The stretch frequencies for the molecule lie at 4385 cm-1 for H2, 3796 and 3804 for HD, and 3101 cm-1 for D2. The modes of the hydrogen saturating the surrounding silicon atoms fall between 2117 and 2098 cm-1. The experimental values for platelets lie at ~2110 and ~1960 cm-1. The molecule has a bond length of 0.748 Å when sited in the platelet, and is centred 2.459 (3.255) Å from the nearest passivating hydrogen (structural silicon) atoms.

Antonio Resende