Ultraviolet-Raman studies of SrTiO3 ultrathin films on Si

Abstract

Few-layer epitaxial graphene grown on vicinal 6H-SiC studied by deep ultraviolet Raman spectroscopy Appl. Phys. Lett. 97, 033108 (2010); 10.1063/1.3466150Combinatorial ( Ba , Sr ) TiO 3 thin film growth: X-ray diffraction and Raman spectroscopy Stoichiometric and nonstoichiometric SrTiO 3 ͑STO͒ films less than 50 nm were grown by molecular beam epitaxy on Si substrates for characterization with UV-Raman spectroscopy. All the films grown have first order phonon Raman scattering as the crystal symmetry has been altered due to threading dislocations and local vicinal strain at defect sites. Strong phonon scattering and hardening of the phonon modes is seen in Ti-rich films while Sr-rich films have a decrease in the phonon scattering intensity when compared with stoichiometric thin films. Excess Ti leads to a high density of planar boundaries and different chemical phases lowering the overall crystal symmetry of STO. The Sr-rich sample compensates for excess Sr by forming SrO Ruddlesden-Popper layers in the perovskite structure.

Raman Spectroscopy of Ferroelectric Thin Films and Superlattices

“…So far, UV Raman spectroscopy has not been widely used for ferroelectric films because of technical difficulties such as lower throughput efficiency, insufficient dispersion, and higher stray light level of UV Raman spectrometers compared with those operating in the visible range. Only a room temperature measurement of SrTiO 3 films using 325‐nm excitation has been reported 127 . Recent progress in UV Raman instrumentation has made measurement of ferroelectric ultrathin films possible.…”

Probing Nanoscale Ferroelectricity by Ultraviolet Raman Spectroscopy

“…Recently, room temperature measurement of SrTiO 3 films using 325 nm excitation has been reported (11).…”

Optoelectronic and microstructure attributes of epitaxial SrTiO3 on Si

“…23 On the other hand, the corresponding Raman signature from the center region of the wafer in 300-nm-thick epi-STO is very "bulklike" in nature (although the data does exhibit some first-order activity at 180 cm −1 ). The weak optical modes reported here from the 300-nm-thick epi-STO wafer edge region are similar to those observed from the Ti-rich ultrathin STO.…”