Probing Individual Layers in Functional Oxide Multilayers by Wavelength‐Dependent Raman Scattering

Abstract

International audienceThe integration of functional oxides on silicon requires the use of complex heterostructures involving oxides of which the structure and properties strongly depend on the strain state and strain-mediated interface coupling. The experimental observation of strain-related effects of the individual components remains challenging. Here, a Raman scattering investigation of complex multilayer BaTiO3/LaNiO3/CeO2/YSZ thin-film structures on silicon is reported. It is shown that the Raman signature of the multilayers differs significantly for three different laser wavelengths (633, 442, and 325 nm). The results demonstrate that Raman scattering at various wavelengths allows both the identification of the individual layers of functional oxide multilayers and monitoring of their strain state. It is shown that all of the layers are strained with respect to the bulk reference samples, and that strain induces a new crystal structure in the embedded LaNiO3. Based on this, it is demonstrated that Raman scattering at various wavelengths offers a well-adapted, non-destructive probe for the investigation of strain and structure changes, even in complex thin-film heterostructures

Structural evolution of cobalt oxide–tungsten oxide nanowire heterostructures for photocatalysis

“…This is consistent with the XRD observation in Fig. 3A and probably because the sputtered WO 3 shell brought extra strain to the lattice of Co 3 O 4 nanowires, which resulted in frequency change to the equilibrium vibration of cobalt and oxygen atoms [41]. As mentioned above, the amount sputtered WO 3 was very less as compared with that of Co 3 O 4 , and thus only weak signal can be found for WO 3 Fig.…”

Raman spectroscopy of rare-earth orthoferrites RFeO3 ( R =La, Sm, Eu, Gd, Tb, Dy)

“…Further to this, RS is an ideal probe for the investigation of spinphonon coupling phenomena [19][20][21][22][23]. Finally, RS is a now widely used technique for probing even subtle straininduced structural modifications in oxide thin films [24][25][26]. All such investigations rely on thorough reference spectra, solid knowledge of the relations between structural distortions phonon modes, and on a proper band assignment of vibrational bands in terms of symmetry and atomic displacement patterns.…”

Multiple strain-induced phase transitions inLaNiO3thin films

“…Here we tackle the problem of structural analysis of LNO ultrathin films by using Raman scattering, known to be a well-adapted technique for the observation of strain effects [14][15][16][17] and structural transitions in thin films [16,18,19], in combination with x-ray diffraction, electron microscopy, and DFT simulations. LNO films of various thicknesses have been grown on substrates imposing either compressive (LAO) or tensile stress [(LaAlO 3 ) 0.3 (Sr 2 TaAlO 6 ) 0.7 ; LSAT] on the films.…”