Regensburg 2022 – scientific programme

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O: Fachverband Oberflächenphysik

O 44: Focus Session: Surfaces and Interfaces of (Incipient) Ferroelectrics (joint session O/KFM)

O 44.1: Topical Talk

Wednesday, September 7, 2022, 15:00–15:30, H3

In search of electrostatic happiness at surfaces — •Nicola Spaldin — Materials Theory, ETH Zurich

We review the concept of surface charge in ionic insulators, first, in the context of the polarization in ferroelectric materials (traditionally discussed in the ferroelectrics community) and, second, in the context of layers of charged ions (traditionally discussed in the surface science community). In both cases, the surface charge leads to an electrostatic instability if it is not compensated, which is usually detrimental for the development of electronic devices based on ferroelectrics, but favorable for applications such as catalysis where surface reactivity is desirable.

Using the prototypical multiferroic bismuth ferrite, BiFeO3, as an example, we show how the spontaneous ferroelectric polarization and the charged ionic layers can in fact combine to yield stable, uncharged ``happy'' (100) surface geometries. Switching the polarization causes these (100) surfaces considerable electrostatic distress, which must be compensated by the introduction of charged point defects or adsorbates. We demonstrate that the relative happiness or unhappiness of the surfaces enables a cycle of alternating charged then neutral adsorbates on polarization switching, which can be exploited for water remediation and water splitting.

We close with a proposal that these physics can induce polarization in thin films of certain usually non-polar materials, and give a recipe for determining likely candidates.

In collaboration with Chiara Gattinoni, Ipek Efe and Marta Rossell