Vibrational properties of nanoscale ferroelectric heterostructures probed by UV Raman spectroscopy

A. BRUCHHAUSEN; A. FAINSTEIN; A. SOUKIASSIAN; D. A. TENNE; D. G. SCHLOM; X. X. XI

Cargèse, Consega, Francia

Conferencia; Son et Lumière: from microphotonics to nanophononics; 2006

Institut d' Etudes Scientifiques de Cargèse

We investigate the vibrational properties of ultrathin heterostructures of ferroelectric and piezoelectric oxide materials (BaTiO3, SrTiO3) grown by reactive molecular-beam epitaxy, using ultraviolet Raman spectroscopy (UV-RS). The reduction of size to the nanoscale changes the ferroelectric properties of the layered materials, and enables the tuning of the para-ferro transition temperature (Tc) by varying the layer thickness of both materials [1]. Since the vibrational state is closely related to the ferroelectricity, it is shown that UV-RS is a suited technique to measure Tc. Folded acoustic phonons are observed at the expected energies in many superlattices with different (BaTiO3)m/(SrTiO3)n relations, and the corresponding sound velocities are derived. In addition, our experimental observations agree well with photoelastic model calculations. The results presented demonstrate the viability of these materials with superior acoustic properties to be used to design and build devices like acoustic Bragg mirrors and cavities operating at THz frequencies. [1] D. A. Tenne et al., Science, to be published Sept. 15th, 2006