Determination of localized surface phonons in nanocrystalline silicon by inelastic neutron scattering spectroscopy and its application to deuterium isotope enrichment

Matsumoto, Takahiro*; Nomata, Ikumi*; Ohara, Takashi   ; Kanemitsu, Yoshihiko*

The hydrogen isotope deuterium has attracted special interest for the manufacture of silicon (Si) semiconductors as well as for the synthesis of isotopically labeled compounds. However, the efficient production of D or H deuteride in a controlled manner is challenging, and rational H isotope enrichment protocols are still lacking. Here, we demonstrate a highly efficient exchange reaction from H to D on the surface of nanocrystalline Si. Fourfold enrichment of D termination was successfully achieved by dipping n-Si into a dilute D solution. By determining the surface-localized vibrational modes for H-and D-terminated n-Si using inelastic neutron scattering spectroscopy, we found that the physical mechanism responsible for this enrichment originates from the difference in the zero-point oscillation energies and entropies of the surface-localized vibrations.