Optic and acustic phonons in nanostructured films

Inelastic light scattering (Raman and Brillouin) permits to investigate dynamic structural properties of materials (vibrational spectrum). In details Raman scattering is sensitive to molecular vibrations in disordered materials and to optical phonons in crystals, whereas Brillouin scattering reveals acoustic wave propagation due to thermal excitations (acoustic phonons). These tecniques give useful information on material structure at different scales: molecular/microscopic scale (1-10 nm) with Raman and mesoscopic scale(10 - hundreds nm) with Brillouin. In this way the frequency range from 1 GHz to 100 THz is entirely covered.

This line, started in 1992, involved different projects and collaborations for the investigation of a great variety of structural properties of micro and nano structured materials:
  • Titanium oxide nanocrystals
  • Advanced glasses for photonics
  • Quantum dots
  • Tin nanoparticles
  • PdO catalysts
  • Bi2Te3 thermolectric films
  • Nanostructured metal oxides
  • SERS active substrates
  • Si/SiO2 systems for MEMS

Computational codes have been developed in our lab for the calculation of surface and bulk acoustic phonon density of state and for incident electromagnetic field coupling in order to simulate the Brillouin cross section in multilayers. It has been developed a software for calculation of elastic constants starting from surface acoustic phonon dispersion relation.

Selected publications :

  • V. Russo, A. Bailini , M. Zamboni, M. Passoni, C. Conti, C.S. Casari , A. Li Bassi , C.E. Bottani
    Raman spectroscopy of Bi-Te thin films
    Journal of Raman Spectroscopy 39 (2), 205 - 210 (2008)
  • T. Mazza, E. Barborini, P. Piseri, P. Milani, D. Cattaneo, A. Li Bassi, C. E. Bottani, C. Ducati
    Raman spectroscopy characterization of TiO2 rutile nanocrystals
    Physical Review B 75, 045416 (2007)
  • T. Mazza, E. Barborini, I. N. Kholmanov, P. Piseri, G. Bongiorno, S. Vinati, P. Milani, C. Ducati, D. Cattaneo, A. Li Bassi, C. E. Bottani, A. M. Taurino, P. Siciliano
    Libraries of cluster-assembled titania films for chemical sensing
    Appl. Phys. Lett. 87, 103108 (2005)
  • A.Li Bassi, D. Cattaneo, V. Russo, C.E. Bottani, E. Barborini, T. Mazza, P. Piseri, P. Milani, F.O. Ernst, K. Wegner, S.E. Pratsinis
    Raman spectroscopy characterization of titania nanoparticles produced by flame pyrolisis: the influence of size and stoichiometry
    J. Appl. Physics 98, 074305-(1-9) (2005)
  • Bottani CE; Li Bassi A; Tanner BK; Stella A; Tognini P; Cheyssac P; Kofman R
    Melting in metallic Sn nanoparticles studied by surface Brillouin scattering and synchrotron-x-ray diffraction
    Physical Review B-Rapid Communications Vol 59, pp R15601-R15604 (1999)
  • C.E.Bottani, C.Mantini, M.Manfredini, P.Milani, A.Stella, P.Tognini,P.Cheyssac and R.Kofman
    Raman, optical absorption and transmission electron microscopy study of size effects in germanium quantum dots
    Appl. Phys. Lett., 69 , 2409 (1996)

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Low frequency spheroidal modes of tin nanoparticles during melting


Simulation of the Layer Projected Phonon Density of States LPPDOS


Raman spectra of nanostructured tungsten oxide

Micro and Nanostructured Materials Lab, Department of Energy Politecnico di Milano Via Ponzio 34/3 I-20133 Milan, Italy