Chemischer Transport oxidischer Mischphasen mit ZnO, Ga2O3 und TiO3 als Wirtsgitter

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Electrical Properties of Thin ZrSe3 Films for Device Applications

Measurements of key properties of the two-dimensional transition metal trichalcogenide ZrSe3are reported. The bulk material was created by chemical vapor deposition and subsequently exfoliated to obtain thin films of varying thicknesses. The samples were then characterized by atomic force microscopy measurements and Raman spectroscopy and contacted by e-beam lithography. Electrical measurements give values for the band gap energy of 0.6 eV increasing for thinner samples. Transistor measurements show ZrSe3to be an n-type semiconductor. By looking at several samples with varying thicknesses, it was possible to determine a mean free path of 103 nm for the bulk material which opens the possibility for new electronic devices

Inside/Outside : Post-Synthetic Modification of the Zr-Benzophenonedicarboxylate Metal–Organic Framework

The Zr-based metal–organic framework, Zr-bzpdc-MOF, contains the photoreactive linker molecule benzophenone-4,4'-dicarboxylate (bzpdc) which imparts the possibility for photochemical post-synthetic modification. Upon irradiation with UV light, the keto group of the benzophenone moiety will react with nearly every C-H bond-containing molecule. Within this paper, we further explore the photochemical reactivity of the Zr-bzpdc-MOF, especially with regard to which restrictions govern internal versus external reactions. We show that apart from reactions with C-H bond-containing molecules, the MOF reacts also with water. By studying the reactivity versus linear alcohols we find a clear delineation in that shorter alcohol molecules (up to butanol as a borderline case) react with photoexcited keto groups throughout the whole crystals whereas longer ones react only with surface-standing keto groups. In addition, we show that with the alkanes n-butane to n-octane, the reaction is restricted to the outer surface. We hypothesize that the reactivity of the Zr-bzpdc-MOF versus different reagents depends on the accessibility of the pore system which in turn depends mainly on the size of the reagents and on their polarity. The possibility to direct the post-synthetic modification of the Zr-bzpdc-MOF (selective modification of the whole pore system versus surface modification) gives additional degrees of freedom in the design of this metal–organic framework for shaping and for applications. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Design of Active Defects in Semiconductors: 3D Electron Diffraction Revealed Novel Organometallic Lead Bromide Phases Containing Ferrocene as Redox Switches

Once the optical, electronic, or photocatalytic properties of a semiconductor are set by adjusting composition, crystal phase, and morphology, one cannot change them anymore, respectively, on demand. Materials enabling postsynthetic and reversible switching of features such as absorption coefficient, bandgap, or charge carrier dynamics are highly desired. Hybrid perovskites facilitate exceptional possibilities for progress in the field of smart semiconductors because active organic molecules become an integral constituent of the crystalline structure. This paper reports the integration of ferrocene ligands into semiconducting 2D phases based on lead bromide. The complex crystal structures of the resulting, novel ferrovskite (≃ ferrocene perovskite) phases are determined by 3D electron diffraction. The ferrocene ligands exhibit strong structure-directing effects on the 2D hybrid phases, which is why the formation of exotic types of face- and edge-sharing lead bromide octahedra is observed. The bandgap of the materials ranges from 3.06 up to 3.51 eV, depending on the connectivity of the octahedra. By deploying the redox features of ferrocene, one can create defect states or even a defect band leading to control over the direction of exciton migration and energy transport in the semiconductor, enabling fluorescence via indirect to direct gap transition. © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH

Microcrystals as amplifiers to learn about the facet- and point de-fect-dependent lability and stabilization of hybrid perovskite semi-conductors against humidity and light

Shape-controlled methyl ammonium lead bromide microcrystals are used to unravel the facet-selective differences in the reactivity of hybrid perovskite semiconductors against chemical and physical triggers. The microstructure of thin films made of hybrid perovskites is highly dynamic because it is prone to small deviations in external conditions, e.g. the presence of traces of water. During operation in photovoltaics, even the exposure to light or the infusion of heat can induce unpredictable changes. Because such films consist of irregular microcrystalline domains fused together, it is very hard to study the mentioned processes directly. The investigation of isolated microcrys-tals as models can solve this problem. Herein, two types of well-defined CH3NH3PbBr3 microcrystals are compared to each other, one with cubic shape terminated by (100) facets, the other with rhombododecahedral shape and exclusively (110) facets. Those microcrys-tals amplify the sensitivity of hybrid perovskites against humidity, against irradiation or to heat. The surfaces of the cubic particles are thermodynamically more stable, but their reactivity is much higher. Although chemically equivalent, rhombodocecahedral microcrystals are much more stable. However, it is demonstrated that cubic microcrystals are significantly less labile, when a small fraction of CH3NH3+ is substituted by Cs+

Design of Active Defects in Semiconductors: 3D Electron Diffraction Revealed Novel Organometallic Lead Bromide Phases Containing Ferrocene as Redox Switches

Once the optical, electronic or photocatalytic properties of a semiconductor are set by adjusting composition, crystal phase and morphology, one cannot change them anymore, respectively on demand. Materials enabling a post-synthetic and reversible switching of features such as absorption coefficient, band-gap or charge carrier dynamics represent are highly desired. Hybrid perovskites facilitate exceptional possibilities for progress in the field of smart semiconductors because active organic molecules become an integral constituent of the crystalline structure. We report the integration of ferrocene ligands into semiconducting 2D phases based on lead bromide. The complex crystal structures of the resulting, novel ferrovskite phases were determined by 3D electron diffraction. The ferrocene ligands exhibit strong structure directing effects on the 2D hybrid phases, which is why the formation of exotic types of face and edge sharing lead bromide octahedra is observed. The band gap of the materials ranges from 3.06 eV up to 3.51 eV, depending on the connectivity of the octahedra. Deploying the redox features of ferrocene, one can create defect states or even a defect band leading to the control over the direction of exciton migration and energy transport in the semiconductor