Valence-band offset and forward-backward charge transfer in manganite/NiO and manganite/LaNiO3 heterostructures†
The valence-band offset (VBO) of the La0.67Sr0.33MnO3/NiO (LSMO/NiO), LaMnO3/NiO (LMO/NiO), LSMO/LaNiO3 (LSMO/LNO) and LMO/LaNiO3 (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 Mn3.3+ + 0.7e → Mn2.6+, Mn3.3+ + 0.1e → Mn3.2+, Mn3.0+ − 0.4e → Mn3.4+ and Mn3.0+ − 0.5e → Mn3.5+ 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.