| AVS 66th International Symposium & Exhibition | |
| Complex Oxides: Fundamental Properties and Applications Focus Topic | Wednesday Sessions |
| Session OX+EM+MI+SS-WeM |
| Session: | Electronic and Magnetic Properties of Complex Oxide Surfaces and Interfaces |
| Presenter: | Le Wang, Pacific Northwest National Laboratory |
| Authors: | L. Wang, Pacific Northwest National Laboratory Z. Yang, Pacific Northwest National Laboratory M.E. Bowden, Pacific Northwest National Laboratory J.W. Freeland, Argonne National Laboratory Y. Du, Pacific Northwest National Laboratory S.A. Chambers, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Charge transfer at oxide interfaces can drive emergent phenomena that do not occur in the bulk, thereby significantly enriching our fundamental understanding of these material systems and their applications. Designing oxide heterostructures and seeking new and novel interfacial phenomena has been an active area of research for some time. We have synthesized a series of [(LaFeO3)m/(SrNiO3-d)n]z ([(LFO)m/(SNO)n]z) superlattices (SLs) (z = 7 to 21) by oxide molecular beam epitaxy on (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (001) substrates. In situ RHEED patterns and x-ray diffraction measurements reveal a high degree of structural quality in the SLs. X-ray photoemission spectroscopy (XPS) shows that the Fe is Fe4+ in the (LFO1/SNO1)21 SL. However, the Fe 2p binding energy shifts to lower values with increasing LFO layer thickness in (LFOm/SNO1)z SLs, suggesting that the volume averaged Fe valence decreases. Fe L-edge X-ray absorption spectroscopy (XAS) measurements corroborate the XPS results, indicating that Fe is 4+ for the (LFO1/SNO1)21 SL and mostly 3+ for the (LFO5/SNO1)10 SL. On the other hand, Ni L-edge XAS shows that Ni valence is Ni3+ for the (LFO1/SNO1)21 SL as is also true for insulating NdNiO3, suggesting that the Ni layers in this SL are insulating, which is consistent with our in-plane transport measurements. However, for the (LFO5/SNO1)10 SL, the Ni valence is larger than 3+. The measured energy shifts suggest that Ni is close to 4+. The thicker LFO layer in the (LFO5/SNO1)10 SL may result in a larger band offset and create a potential well to trap the holes in the Ni layer, inducing the formation of Ni4+. Our ongoing studies are probing the impact of the SNO layer thickness on material structure as well as the evolution of the Fe and Ni valences in (LFO5/SNOn)z SLs. Additional planned experimental and theoretical investigations will address how charge transfer from Fe to Ni occurs at the LFO/SNO interface, and how to stabilize the unusual high 4+ valence in Fe4+ and Ni4+ by means of interfacial engineering.