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- ItemTiOx/Pt3Ti(111) surface-directed formation of electronically responsive supramolecular assemblies of tungsten oxide clusters(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2021) Moors, Marco; An, Yun; Kuc, Agnieszka; Monakhov, Kirill YuHighly ordered titanium oxide films grown on a Pt3Ti(111) alloy surface were utilized for the controlled immobilization and tip-induced electric field-triggered electronic manipulation of nanoscopic W3O9 clusters. Depending on the operating conditions, two different stable oxide phases, z'-TiO x and w'-TiO x , were produced. These phases show a strong effect on the adsorption characteristics and reactivity of W3O9 clusters, which are formed as a result of thermal evaporation of WO3 powder on the complex TiO x /Pt3Ti(111) surfaces under ultra-high vacuum conditions. The physisorbed tritungsten nano-oxides were found as isolated single units located on the metallic attraction points or as supramolecular self-assemblies with a W3O9-capped hexagonal scaffold of W3O9 units. By applying scanning tunneling microscopy to the W3O9-(W3O9)6 structures, individual units underwent a tip-induced reduction to W3O8. At elevated temperatures, agglomeration and growth of large WO3 islands, which thickness is strongly limited to a maximum of two unit cells, were observed. The findings boost progress toward template-directed nucleation, growth, networking, and charge state manipulation of functional molecular nanostructures on surfaces using operando techniques.
- ItemHeterobimetallic conducting polymers based on salophen complexes via electrosynthesis(London [u.a.] : RSC, 2023) Bia, Francesca; Gualandi, Isacco; Griebel, Jan; Rasmussen, Leon; Hallak, Bassam; Tonelli, Domenica; Kersting, BertholdIn this work, we report the first electrochemical synthesis of two copolymeric bimetallic conducting polymers by a simple anodic electropolymerization method. The adopted precursors are electroactive transition metal (M = Ni, Cu and Fe) salophen complexes, which can be easily obtained by direct chemical synthesis. The resulting films, labeled poly-NiCu and poly-CuFe, were characterized by cyclic voltammetry in both organic and aqueous media, attenuated total reflectance Fourier transform infrared spectroscopy, UV-vis spectroscopy, scanning electron microscopy, and coupled energy dispersive X-ray spectroscopy. The films are conductive and exhibit great electrochemical stability in both organic and aqueous media (resistant over 100 cycles without significant loss in current response or changes in electrochemical behavior), which makes them good candidates for an array of potential applications. Electrochemical detection of ascorbic acid was performed using both materials.
- ItemCompositional Patterning in Carbon Implanted Titania Nanotubes(Weinheim : Wiley-VCH, 2021) Kupferer, Astrid; Holm, Alexander; Lotnyk, Andriy; Mändl, Stephan; Mayr, Stefan G.Ranging from novel solar cells to smart biosensors, titania nanotube arrays constitute a highly functional material for various applications. A promising route to modify material characteristics while preserving the amorphous nanotube structure is present when applying low-energy ion implantation. In this study, the interplay of phenomenological effects observed upon implantation of low fluences in the unique 3D structure is reported: sputtering versus readsorption and plastic flow, amorphization versus crystallization and compositional patterning. Patterning within the oxygen and carbon subsystem is revealed using transmission electron microscopy. By applying a Cahn–Hilliard approach within the framework of driven alloys, characteristic length scales are derived and it is demonstrated that compositional patterning is expected on free enthalpy grounds, as predicted by density functional theory based ab initio calculations. Hence, an attractive material with increased conductivity for advanced devices is provided. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemAntiphase Boundaries Constitute Fast Cation Diffusion Paths in SrTiO3 Memristive Devices(Weinheim : Wiley-VCH, 2020) Heisig, Thomas; Kler, Joe; Du, Hongchu; Baeumer, Christoph; Hensling, Felix; Glöß, Maria; Moors, Marco; Locatelli, Andrea; Menteş, Tevfik Onur; Genuzio, Francesca; Mayer, Joachim; De Souza, Roger A.; Dittmann, ReginaResistive switching in transition metal oxide-based metal-insulator-metal structures relies on the reversible drift of ions under an applied electric field on the nanoscale. In such structures, the formation of conductive filaments is believed to be induced by the electric-field driven migration of oxygen anions, while the cation sublattice is often considered to be inactive. This simple mechanistic picture of the switching process is incomplete as both oxygen anions and metal cations have been previously identified as mobile species under device operation. Here, spectromicroscopic techniques combined with atomistic simulations to elucidate the diffusion and drift processes that take place in the resistive switching model material SrTiO3 are used. It is demonstrated that the conductive filament in epitaxial SrTiO3 devices is not homogenous but exhibits a complex microstructure. Specifically, the filament consists of a conductive Ti3+-rich region and insulating Sr-rich islands. Transmission electron microscopy shows that the Sr-rich islands emerge above Ruddlesden–Popper type antiphase boundaries. The role of these extended defects is clarified by molecular static and molecular dynamic simulations, which reveal that the Ruddlesden–Popper antiphase boundaries constitute diffusion fast-paths for Sr cations in the perovskites structure. © 2020 The Authors. Published by Wiley-VCH GmbH