Phonons in Hybrid Lamellar Supercrystals

Phonons in hybrid lamellar supercrystals are investigated by Raman scattering. Special attention is paid to low-frequency vibrations as a mean to shed some light onto the structure at the nanometer scale. In particular, little is known about the structure of the organic capping agents in supercrystals made of colloidal nanopoarticles. This is due to the fact that characterization tools such as electron microscopy and X-ray diffraction are mostly sensitive to the inorganic phase due to its larger electronic density. Raman scattering does not suffer from this limitation. In this class of materials, synthesized following the ``benzyl alcohol route'', the inorganic layers are kept together by pi-pi conjugated interactions. Low frequency Raman spectra have been measured for yttrium and neodymium oxide-based lamellar organic inorganic supercrystals synthesized with three benzyl alcohol derivatives. The spectra strongly depend on the nature of both the inorganic and organic phase despite the resulting lamellar structure being similar in terms of layer thickness and crystalline structure for all the samples. This makes low-frequency Raman spectroscopy the tool of choice for the study of the assembling process driving the formation of colloidal supercrystals.