In situ characterization of strontium surface segregation in epitaxial La0.7Sr0.3MnO3 thin films as a function of oxygen partial pressure

Using in situ synchrotron measurements of total reflection x-ray fluorescence, we find evidence of strontium surface segregation in (001)-oriented La0.7Sr0.3MnO3 thin films over a wide range of temperatures (25-900 degrees C) and oxygen partial pressures (pO(2)=0.15-150 Torr). The strontium surface concentration is observed to increase with decreasing pO(2), suggesting that the surface oxygen vacancy concentration plays a significant role in controlling the degree of segregation. Interestingly, the enthalpy of segregation becomes less exothermic with increasing pO(2), varying from -9.5 to -2.0 kJ/mol. In contrast, the La0.7Sr0.3MnO3 film thickness and epitaxial strain state have little impact on segregation behavior. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2987731]