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Analysis of the chiral composition of a carbon nanotube surface by means of second harmonic generation
Author(s) -
De Dominicis L.,
Fantoni R.,
Botti S.,
Ciardi R.,
Asilyan L.,
Fiori A.,
Orlanducci S.
Publication year - 2005
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1268
Subject(s) - hyperpolarizability , second harmonic generation , carbon nanotube , anisotropy , raman spectroscopy , laser , molecular physics , polarization (electrochemistry) , materials science , wavenumber , chemistry , optics , nonlinear system , nanotechnology , physics , nonlinear optical , quantum mechanics
The second‐order susceptibility tensor χ (2) (2ω;ω, ω) of a carbon nanotube (CNT) surface was determined as a function both of the average tube orientation and CNT topology distribution. The transformation properties of the hyperpolarizability β tensor, as rooted in the CNT isogonal symmetry point group, make non‐vanishing only the chiral component of χ (2) (2ω;ω, ω), thus denying second harmonic generation (SHG) in racemic samples. Nevertheless, the rupture of the CNT spatial symmetry due to local deformations and to finite size can act as a source for SHG even in racemic samples. The study of SHG polarization and of the anisotropic dependence of the signal intensity on the angle Ω between the surface normal and the exciting laser beam direction are proposed as methods to discriminate between the two contributions. An experimental test of such a statement was performed on a sample grown by the laser annealing technique. A massive presence of chiral CNTs with strong local deformations was revealed by the low‐ and medium‐wavenumber Raman spectra measured on the sample. The SHG polarization and the anisotropic dependence of the signal intensity as a function of Ω were studied experimentally, allowing the racemic nature of the investigated sample to be elucidated. Copyright © 2005 John Wiley & Sons, Ltd.