Superlattices*

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. We have synthesized a series of (SrNiO₃)₁/(LaFeO₃)_n superlattices (SLs) by oxide molecular beam epitaxy on (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7 (001) substrates. Our structural characterization results indicate that cubic perovskite SrNiO₃ (SNO), which does not exist in the bulk, can be stabilized as a single unit cell level in SLs with LaFeO₃. Our in-situ X-ray photoemission spectroscopy and X-ray absorption spectroscopy measurements indicate that depending on the value of n, the Ni and Fe valences are either 3+ or 4+. The n = 1 SL contains Ni³⁺ and Fe⁴⁺, while Ni⁴⁺ and Fe³⁺ are observed in the n = 5 SL. These results are consistent with valence band offset measurements which indicate that a potential well for holes is present in the LFO (SNO) layers for n = 1 (5). The insights gained from these spectroscopies shed considerable light on the associated two dimensional (2D) semiconducting transport behavior in these SLs, thereby positioning us to utilize these materials systems in new and novel electronic devices.