Efforts for the integration of ferroelectric materials in nonvolatile, low energy consuming memories have so far been focused on perovskite oxide materials. Their down-scaling for nanodevices is, however, hindered by finite-size effects, and alternative materials offering more robust polar properties are required. Layered ferroelectrics of the Aurivillius phase have since emerged as promising candidates with robust polarization at subunit-cell thicknesses. Their controlled growth in the epitaxial thin film form has unfortunately remained elusive. Here, we demonstrate the stabilization of the coalescent layer-by-layer growth mode of the Bi n+1 Fe n−3 Ti 3 O 3n+3 (BFTO) Aurivillius family homologues. We define the growth conditions for high-quality, single-crystalline thin films exhibiting ferroelectricity from the first half-unit-cell. We demonstrate the process to be effective for several homologous Aurivillius compositions, which highlights its general applicability. Our work thus provides the systematic framework for the integration of high-quality epitaxial layered ferroelectrics into oxide electronics.
Micrometer sized capsules are often used as single entities for the encapsulation and release of active ingredients, for example in food, cosmetics, and drug delivery. Important parameters that determine the stability of capsules and the release of reagents contained in them are the dimensions and composition of their shell. Most capsule shells are rather thick, thereby occupying a significant fraction of the capsule volume, or they are rigid, making the capsules fragile. This work introduces viscoelastic capsules with very thin shells of order 10 nm. Despite the thin nature of these shells, they are flexible, self‐healing, yet, for practical applications impermeable even to low molecular weight substances. These shells are formed by ionically crosslinking surfactants that are functionalized with catechol‐derivatives. This work investigates the influence of the number of chelators contained per surfactant and the crosslinking ion on the rheological properties of the membranes and relate it to the mechanical properties of the resulting capsules. This work demonstrates that these shells are impermeable to molecules as small as 340 Da even if loaded with cell culture media, indicating their potential for biomedical applications.
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