AVS 45th International Symposium
    Organic Electronic Materials Topical Conference Monday Sessions
       Session OE-MoP

Paper OE-MoP4
Second-Harmonic-Generation Spectroscopy and Hyper-Rayleigh Scattering in Langmuir Films of C60 and its Derivatives

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Organic Electronic Materials Poster Session
Presenter: E.D. Mishina, Moscow State University, Russia
Authors: E.D. Mishina, Moscow State University, Russia
T.V. Misuryaev, Moscow State University, Russia
A.A. Nikulin, Moscow State University, Russia
V.R. Novak, Institute of Physical Problems, Russia
Th. Rasing, University of Nijmegen, The Netherlands
O.A. Aktsipetrov, Moscow State University, Russia
Correspondent: Click to Email
We report here the results of experimental studies by second-harmonic-generation (SHG) spectroscopy and hyper-Rayleigh scattering (HRS) of thin Langmuir films of C60 and C60-derivatives: C60-tetracyanoethylene oxide derivative (C60[CN]) and C60-indopane derivative (C60[-ind]). Langmuir technique allows to fabricate thin films with controlled thickness with monolayer resolution and ordering the molecules within the layer, while the SHG probe provides a reliable diagnostic tool for such films. For the SHG measurements the output of a Ti:Sapphire laser in the range of the fundamental wavelength of 710-800 nm is used. SHG spectroscopic studies showed that, depending on the nature of organic group, the modification of C60 molecules can either increase (for C60[CN]) or decrease (for C60[-ind]) the SHG intensity in thin fullerene films, while the general character of the spectra remains unchanged. The obtained results can be interpreted as due to the following two mechanisms: nonuniform broadening of resonances due to fluctuations, that is also revealed in absorbtion spectra; breaking of the inversion symmetry of C60 molecules by the organic "grafts" resulting in appearence of dipole hyperpolarizability and its interference with the quadrupole hyperpolarizability of C60 "cage". Hyper-Rayleigh scattering allowed us to get information about the structural and statistical properties of these systems. In particular, the modification of C60 molecules with the [CN] "graft" does not noticeably change the structure of the Langmuir films: for both C60 and C60[CN] monolayer samples have a disordered island-like structure, whereas the multilayer C60 and C60[CN] samples indicate their more regular structure. The modification of C60 molecules with the [ind]-"graft" significantly increases homogeneity of the monolayer samples. In all films the characteristic spatial scale of in-plane fluctuations of the HRS sources has been estimated.