Vibrational properties of carbon nanostructures

Since 1996 the lab has been studying carbon-based materials by Raman and Brillouin scattering. We investigated acoustic modes in carbon nanotubes, in PTFE films and the elastic properties of ultrathin (2-4 nm) DLC films. Cluster assembled carbon films have been investigated in collaboration with Molecular Jets and Nanocrystalline Materials Lab (prof. P. Milani). Raman spectrosocpy revealed a correlation between the inertial focusing effects of supersonic cluster beams on material structural properties (degree of structural order/disorder). Brillouin spectrosocpy permitted the determination of film mesoscopic elastic constants and to observe a cross-over between a propagating and a localized regime of acoustic vibrations as a function of the nano- and mesostructure.

In years 2001-2004, in collaboration with Molecular Jets and Nanocrystalline Materials Lab (prof. P. Milani) and thanks to an official agreement on nanotechnologies between Politecnico di Milano and Universita' di Milano, a Pulsed Microplasma Cluster Source (PMCS) hosted in the CLARA (Cluster Assembling Roaming Apparatus) apparatus for supersonic cluster beam deposition (SCBD) was connected to a UHV deposition chamber for in situ Raman charaterization. Since then research activity is being devoted to in situ Raman studies of cluster assembled carbon films. We showed the presence of metastable carbon structures with sp hybridization (polyynes and cumulenes). These structures reacts both with inert (He, Ar, N2) and reactive gases (H2, O2) and show a peculiar thermal stability.

In situ (red line) and ex situ (black line) Raman spectra of cluster assembled carbon films.

From 2004 we are also investigating isolated linear carbon chains (polyynes). Polyynes are produced by prof. F. Cataldo (Rome) and are studied by Raman and SERS (Surface Enhanced Raman Scattering) in collaboration with the Molecular Dynamics and Vibrational Spectroscopy Lab (prof. G. Zerbi), Chemistry Department of the Politecnico di Milano. Such activity is in the framework of the NEMAS Center.

Selected publications :

• C.S. Casari, A. Li Bassi, A. Baserga, L. Ravagnan, P. Piseri, C. Lenardi M. Tommasini, A. Milani, D. Fazzi, C.E. Bottani, P. Milani
  Low-frequency modes in the Raman spectrum of sp-sp 2 nanostructured carbon
  Physical Review B 77, 195444 (2008)
  Selected for the Virtual Journal of Nanoscale Science and Technology

• L. Ravagnan, P. Piseri, M. Bruzzi, S. Miglio, G. Bongiorno, A. Baserga, C.S. Casari, A. Li Bassi, C. Lenardi, Y. Yamaguchi, T. Wakabayashi, C.E. Bottani, P. Milani
  Influence of cumulenic chains on the vibrational and electronic properties of sp/sp 2 amorphous carbon.
  Physical Review Letters 98 , 216103 ( 2007)

• C.S. Casari , V. Russo, A. Li Bassi, C.E. Bottani, F. Cataldo, A. Lucotti, M. Tommasini, M. Del Zoppo, C. Castiglioni, G. Zerbi
  Stabilization of linear carbon structures in a solid Ag nanoparticle assembly
  Applied Physics Letters 90 , 013111 (2007)
  Selected for the Virtual Journal of Nanoscale Science and Technology

• A. Lucotti, M. Tommasini, M. Del Zoppo, C. Castiglioni, G. Zerbi, F. Cataldo, C.S. Casari , A. Li Bassi, V. Russo, M. Bogana, C.E. Bottani
  Raman and SERS investigation of isolated sp carbon chains
  Chemical Physics Letters 417 , 78-82 (2006)

• C.S. Casari, A. Li Bassi, L. Ravagnan, F. Siviero, C. Lenardi, P. Piseri, G. Bongiorno, C.E. Bottani, P. Milani,
  Carbynoid structures in cluster-assembled carbons: synthesis, chemical and thermal stability
  Physical Review B, 69, 075422 (2004)

• C.E.Bottani, A. Li Bassi, M.G. Beghi, A. Podestà, P. Milani, A. Zakhidov, R. Baughman, D. A. Walters and R. E. Smalley
  Dynamic light scattering from acoustic modes in single-walled carbon nanotubes
  Physical Review B 67, 155407 (2003)
  Selected for the Virtual Journal of Nanoscale Science and Technology

• L. Ravagnan, F.Siviero, C. Lenardi, E. Barborini, P. Piseri, P. Milani, C.S. Casari, A. Li Bassi and C. E. Bottani,
  Cluster Beam Deposition and in situ Characterization of Carbyne-rich Carbon Films,
  Physical Review Letters, 89, 28, 285506-1 (2002)

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