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Low frequency Raman scattering in characterization of nanostructured materials

Mile Ivanda 1Davor Ristic 1Kresimir Furic 1Svetozar Music 1Mira Ristić 1Marijan Gotić 1Goran Štefanić 1Uros V. Desnica 1Maja Buljan 1Maurizio Montagna 2Maurizio Ferrari 3Alesandro Chisaera 3Yoann Jestin 3

1. Ruđer Bošković Institute, Bijenička 54, Zagreb 10000, Croatia
2. Dipartimento di Fisica, Universita' di Trento, via Sommarive, 14, Trento 38050, Italy
3. CNR-IFN, CSMFO group (CSMFO), via Sommarive 14, Trento 38050, Italy


A short theoretical introduction of the Lamb theory on the vibrations of elastic spheres will be described for the free nanoparticles as well as for the nanoparticles embedded in matrix. The spherical case is well understood – the normal modes of the sphere are divided into torsional and spheroidal and, experimentally, have been measured in various situations. Here, the application of the Lamb theory will be illustrated by the low frequency Raman scattering (LFRS) measurements on different powder samples: TiO2, SnO2, and CdS. The effects of sintering of nanoparticles will be described with the ZrO2 nanoparticles doped with Sn, Ge and Cu. For the nanoparticles embedded in matrix a theoretical treatment of polarization-dependent low-frequency off-resonant Raman scattering which establishes a relation between the particle size, the frequencies, and the widths of various phonons. The selection rules for the Raman scattering of the spherical particles and of the particles of irregular shape will be discussed. Polarized and depolarized scattering from confined acoustic phonons were distinctly resolved near the laser line. A good agreement between the experimental and the theoretical results will be illustrated by TiO2, CdSxSe1-x, and HfO2 nanoparticles in glass matrix. The nanoparticle sizes and even sizes distribution obtained from Raman scattering agree well with those obtained from transmission electron microscope proving the LFRS to be a simple, fast and reliable method for the size distribution measurements. By inverse procedure, starting from the Raman spectra and known particles size distribution, the mean sound velocities of longitudinal and transverse phonons of nanoparticles could be deduced, providing LFRS to be unique technique for determination of the sound velocities in nanoparticles. The possibility of coherent Raman scattering will be illustrated by the LFRS on the self-organized Ge superlattice.


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Presentation: Invited oral at E-MRS Fall Meeting 2008, Symposium A, by Mile Ivanda
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-20 10:40
Revised:   2008-06-13 16:19