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Version: publishedVersion × Subject: nanocrystals ×

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    Nonclassical Recrystallization
    (Weinheim : Wiley-VCH, 2020) Brunner, Julian; Maier, Britta; Rosenberg, Rose; Sturm, Sebastian; Cölfen, Helmut; Sturm, Elena V.
    Applications in the fields of materials science and nanotechnology increasingly demand monodisperse nanoparticles in size and shape. Up to now, no general purification procedure exists to thoroughly narrow the size and shape distributions of nanoparticles. Here, we show by analytical ultracentrifugation (AUC) as an absolute and quantitative high-resolution method that multiple recrystallizations of nanocrystals to mesocrystals is a very efficient tool to generate nanocrystals with an excellent and so-far unsurpassed size-distribution (PDIc=1.0001) and shape. Similar to the crystallization of molecular building blocks, nonclassical recrystallization removes “colloidal” impurities (i.e., nanoparticles, which are different in shape and size from the majority) by assembling them into a mesocrystal. In the case of nanocrystals, this assembly can be size- and shape-selective, since mesocrystals show both long-range packing ordering and preferable crystallographic orientation of nanocrystals. Besides the generation of highly monodisperse nanoparticles, these findings provide highly relevant insights into the crystallization of mesocrystals. © 2020 The Authors. Published by Wiley-VCH GmbH
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    Modeling Photodetection at the Graphene/Ag2S Interface
    (Weinheim : Wiley-VCH, 2021) Spirito, Davide; Martín-García, Beatriz; Mišeikis, Vaidotas; Coletti, Camilla; Bonaccorso, Francesco; Krahne, Roman
    Mixed-dimensional systems host interesting phenomena that involve electron and ion transport along or across the interface, with promising applications in optoelectronic and electrochemical devices. Herein, a heterosystem consisting of a graphene monolayer with a colloidal Ag2S nanocrystal film atop, in which both ions and electrons are involved in photoelectrical effects, is studied. An investigation of the transport at the interface in different configurations by using a phototransistor configuration with graphene as a charge-transport layer and semiconductor nanocrystals as a light-sensitive layer is performed. The key feature of charge transfer is investigated as a function of gate voltage, frequency, and incident light power. A simple analytical model of the photoresponse is developed, to gain information on the device operation, revealing that the nanocrystals transfer electrons to graphene in the dark, but the opposite process occurs upon illumination. A frequency-dependence analysis suggests a fractal interface between the two materials. This interface can be modified using solid-state electrochemical reactions, leading to the formation of metallic Ag particles, which affect the graphene properties by additional doping, while keeping the photoresponse. Overall, these results provide analytical tools and guidelines for the evaluation of coupled electron/ion transport in hybrid systems.