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HL: Fachverband Halbleiterphysik

HL 11: C/diamond

HL 11.6: Vortrag

Montag, 25. Februar 2008, 12:15–12:30, EW 202

Ab initio calculation of the lattice dynamics of graphene nanoribbons — •Roland Gillen, Marcel Mohr, Janina Maultzsch, and Christian Thomsen — Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin

During the past decades, graphite-related materials of nanoscale, such as fullerenes and nanotubes, have been subject to scientific interest. Their remarkable optical and electronical properties make them promising for use in future nanotechnology. Recently, another type of nanoscale materials, narrow stripes of graphene (single layer graphite) have been fabricated and were investigated regarding their electrical transport properties. Those graphene nanoribbons are, depending on the direction of their edges, classified into armchair (AGNR), zig-zag (ZGNR) and chiral nanoribbons (CGNR). They correspond to "unrolled" carbon nanotubes, i.e. the model system used in zone-folding calculations of carbon nanotube properties. We use DFT calculations to obtain the band structure and phonon dispersion of various AGNR and ZGNR. Group theory was applied to classify the resulting phonon modes. We show that most of the phonon modes can be interpreted as "overtones" of a few fundamental modes. These overtone frequencies can be understood from zone folding the phonon dispersion of graphene. Shape and size dependences of the phonon frequencies of the nanoribbons are found. Similarities between nanoribbons and carbon nanotubes will be discussed.