Evidence of the matrix effect on a compositionally graded oxide thin film
A heterostructure of Ba$_{1-x}$Sr$_x$TiO$_3$/La$_{1.1}$Sr$_{0.9}$NiO$_3$ /SrTiO$_3$ has been analysed by magnetic sector secondary ion mass spectrometry (SIMS). The stoichiometry parameter $x$ of the top layer was made varying continuously from 0 to 1 along the width of the sample by combinatorial pulsed laser deposition. Prior to SIMS analysis, the composition gradient of Ba$_{1-x}$Sr$_x$TiO$_3$ was quantitatively characterized by chemical characterizations including wavelength and energy dispersive X-ray spectroscopies. Even if the Ti content is constant into Ba$_{1-x}$Sr$_x$TiO$_3${}, its ionic yield exhibits an increasing trend as Ba is substituted by Sr. Such a phenomenon can be explained by the variation of the neighbouring atoms chemistry which affects the ionization probability of titanium during the sputtering process. In addition to the continuously varying composition, the oxide multilayer sample features sharp interfaces hence the in-depth resolution under our analysing conditions has been investigated too. The modelling of the interface crossing profiles reveals that the instrumental contribution to the profile broadening is as low as 5 nm.