Pressure dependence of the Raman active vibrations in InP-CdS hybrid nanoparticles

The effects of pressure on the confined and surface-optical (SO) vibrations in core-shell InP-CdS colloidal nanoparticles are explored experimentally by Raman scattering and theoretically using the phenomenological macroscopic approach (PMA) (F. Comas and C. Trallero-Giner, Phys. Rev. B 67, 115301 (2003); C. Trallero-Giner et al., to be published). Experiments on two sample ensembles are carried out to P=6.5 GPa at 373 K and 230 K (including laser heating) using diamond-cells with 4:1 methanol:ethanol and pyridine media. We observe the pressure-induced shifts of the peaks due to the confined LO- and TO-like core modes, and of the broad feature assigned to SO vibrations at the CdS-shell surface. PMA calculations are performed for the confined modes and the l=1,2 SO modes in spherical geometry using pressure-dependent bulk parameters as input. We compute the frequencies for different core radii and shell-to-core radius ratios γ. The best fit to the pressure data is found for an InP core diameter of 45±10 A, and γ∝1.1-1.4 depending on the sample ensemble and the value of l. The effects of pressure on the InP-CdS core-shell modes appear to be well described by the PMA formalism. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)