The valence-band offset (VBO) of the La(0.67)Sr(0.33)MnO(3)/NiO (LSMO/NiO), LaMnO(3)/NiO (LMO/NiO), LSMO/LaNiO(3) (LSMO/LNO) and LMO/LaNiO(3) (LSMO/LNO) heterostructures has been investigated using X-ray photoemission spectroscopy. The VBO values are calculated to be -0.72, -0.05, +1.43 and +1.51 eV for the LSMO/NiO, LSMO/LNO, LMO/LNO and LMO/NiO heterostructures, respectively. Hence, when compared with NiO and LNO, the valence band of LSMO is shifted to a lower binding energy, whereas that of LMO is shifted to a higher binding energy. In addition, the charge transfer at the interfaces has been depicted as Mn(3.3+) + 0.7e→ Mn(2.6+), Mn(3.3+) + 0.1e→ Mn(3.2+), Mn(3.0+)- 0.4e→ Mn(3.4+) and Mn(3.0+)- 0.5e→ Mn(3.5+) for the LSMO/NiO, LSMO/LNO, LMO/LNO and LMO/NiO heterostructures, respectively. Thus, the charge transfer procedure can be described as electron hopping from NiO and LNO to LSMO in the LSMO/NiO and LSMO/LNO heterostructures, and electron hopping from LMO to NiO and LNO in the LMO/NiO and LSMO/LNO heterostructures. Therefore, the charge transfer is dependent on the VBO, and the charge transfer direction can be determined from the negative or positive values of the VBO.

In this study, the effect of microwave irradiation on reduction of graphene oxide films was investigated.

Coherently strained BiFeO3 epitaxial films deposited on (001)-oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 have a tetragonal crystal form, a stress-distorted version of the rhombohedral phase. A conversion from coherent BiFeO3 to a new, tilted pseudotetragonal phase with the c/a ratio exceeding 1.2 is observed beyond the critical thickness of 60 nm. X-ray reciprocal space maps display that this highly elongated metastable structure is monoclinically distorted by ∼0.2° and exhibits an out-of-plane tilt of ∼3°. These observations are at odds with traditional understandings that a coherent epilayer should turn into its parent structure upon increasing the thickness, providing a new insight into the strain relaxation mechanism of epitaxial films. We show that in the heating and cooling cycles, the transition between these two phases is completely reversible and is associated with the alleviation of thermal stress. Our results reveal that the coherent BiFeO3 epilayer with tetragonal symmetry stabilized by moderate compressive strain behaves as a structural bridge that links the thermally stable rhombohedral phase and the metastable tetragonal-like phase with a giant axial ratio. Moreover, the finding of a BiFeO3 phase mixture in our study extends the threshold in-plane strain of the stress-driven morphotropic phase boundary to a value as low as −2.3%.

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