We present a theoretical study on narrow armchair graphene nanoribbons (AGNRs) with hydroxyl functionalized edges. Although this kind of passivation strongly affects the structure of the ribbon, a high degree of edge functionalization proves to be particularly stable. An important consequence of the geometric deviations is a severe reduction of the band-gap of the investigated 7-AGNR. This shift follows a linear dependence on the number of added hydroxyl groups per unit cell and thus offers the prospect of a tunable band-gap by edge functionalization. We furthermore cover the behavior of characteristic phonons for the ribbon itself as well as fingerprint modes of the hydroxyl groups. A large down-shift of prominent Raman active modes allows the experimental determination of the degree of edge functionalization.

We report first-principles studies on the electronic and vibrational properties of uniaxially strained graphene and graphene nanoribbons. The band structure of extended graphene shows an interesting behavior under uniaxial strain in directions other than the zigzag or armchair direction. While strained graphene remains semi-metallic, one-dimensional graphene nanoribbons allow band-gap tuning via strain. The shift of the strain-induced band-gap in armachair nanoribbons depends on their family. At small strain the band-gap of all AGNRs depends linearly on the amount of strain. Concerning the vibrational spectra, we compare straininduced shift rates of the G modes in two-dimensional graphene and AGNRs. The shift rates of the G − and G + modes in AGNRs strongly reflect the common classification into three families. For large ribbon widths all shift rates converge to their counterparts in graphene.

The semitrimer picotube is a ring-shaped hydrocarbon closely related to a very short (3,3) carbon nanotube. We study the vibrational properties of the semitrimer by means of Raman spectroscopy and find the structural similarity to nanotubes to be reflected also in the vibrational spectra. In particular, combining polarization-dependent Raman measurements and ab inito calculations we can identify a fully symmetric vibration corresponding to the radial breathing mode in nanotubes.

Four different picotubes have been synthesized up to now. These highly symmetric, ringlike hydrocarbons are closely related to the smallest armchair nanotubes available. We investigate vibrational properties of the different picotubes using first principles calculations and polarization‐dependent Raman spectroscopy. Our results emphasize the strong relationship between picotubes and nanotubes.In this context, two features in the picotube spectra are of particular interest: The high‐energy bands and breathing‐like modes. Vibrational patterns calculated for the high‐energy modes of picotubes are similar to the axial and transversal high‐energy vibrations of armchair nanotubes. Concerning the radial breathing modes of picotubes, our calculations suggest a d–1‐dependence of the radial breathing mode (RBM) frequency, which is again in analogy to nanotubes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carbon picotubes are a promising starting point for the specific synthesis of nanotubes. In this context the interaction between nanotubes and picotubes is of particular interest. One potentially useful configuration evolves from inserting picotubes into a nanotube in a row in analogy to fullerene peapods. We perform temperature-dependent molecular dynamics simulations on such a system consisting of three tetramer picotubes arranged along the axis of a (9,9) nanotube. Covering a temperature range from room temperature up to 3000 K we observe two different effects: First, our studies show oscillations of the tetramer molecules inside the nanotube. These eigenmodes include axial motion of the picotubes as well as various rotational patterns. Moreover, at sufficiently high temperatures breaking and formation of new bonds results in a structural reorganization, which under suitable conditions might yield a second, inner nanotube of defined chirality.