Highly c-axis-oriented apatite-type lanthanum silicate thin films fabricated by magnetron sputtering under bias

The development of apatite-type lanthanum silicate (LSO) thin films with enhanced c-axis orientation has received attention because highly c-axis oriented LSO is an attractive electrolyte for lowering the operating temperature of solid oxide cells. In this study, the effect of thin-film conditions in magnetron sputtering on the c-axis orientation of LSO thin films after crystallization were investigated. X-ray diffraction and X-ray reflectivity measurements revealed that the c-axis orientation of LSO thin films after crystallization is correlated with the density of the amorphous thin films deposited by magnetron sputtering. Bias application during magnetron sputtering effectively increased the c-axis orientation of crystallized LSO thin films, which showed extremely high c-axis orientation (Lotgering factor of 0.99). This thin film consisted of columnar grains, most of which were c-axis oriented, as confirmed by direct observation using scanning transmission electron microscopy.