Surfaces of the perovskite manganites ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$

Angle-resolved core-level photoemission has been utilized to study the surfaces of crystalline thin films of manganite ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ ($x=0.1\mathrm{}$ and 0.35). It is found that both the surface termination and Ca surface concentration depend on the bulk Ca concentration. For ${\mathrm{La}}_{0.65}{\mathrm{Ca}}_{0.35}{\mathrm{MnO}}_3,$ the terminal layer is predominately Mn-O, while for ${\mathrm{La}}_{0.9}{\mathrm{Ca}}_{0.1}{\mathrm{MnO}}_3,$ the majority of the surface is La/Ca-O terminated. Both surfaces exhibit a large enhancement in the Ca concentration compared to the bulk with the ${\mathrm{La}}_{0.9}{\mathrm{Ca}}_{0.1}{\mathrm{MnO}}_3$ sample, having a larger surface Ca concentration than for the ${\mathrm{La}}_{0.65}{\mathrm{Ca}}_{0.35}{\mathrm{MnO}}_3$ material.