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Nature and extent of charge/energy transfer at the nanocarbonmetal oxide interface

Cherevan, Alexey (Technische Universität Wien, Vienna, AUT); Kemnade, Nina (Westfälische Wilhelms-Universität Münster, Münster, GER); Gebhardt, Paul (Technische Universität Wien, Vienna, AUT); Wilde, Gerhard (Westfälische Wilhelms-Universität Münster, Münster, GER); Eder, Dominik (Technische Universität Wien, Vienna, AUT)

Nanocarbon-inorganic hybrids constitute a novel class of composite materials that have recently attracted considerable attention for use in applications where efficient charge extraction is required. Key to these hybrids is the rational hybridization of two complementary compounds, i.e. a nanocarbon and an active inorganic nanomaterial, in a way that creates tight interface between them. Such hybridization enhances interfacial charge and energy transfer processes, which in turn can further facilitate efficient charge separation and extraction. So far the majority of published works in this field have merely assumed the presence of charge transfer in nanocarbon containing hybrids and only few have tried to experimentally evaluate these processes e.g. by using fluorescence quenching. These works, however, have not considered potential energy transfer process as well as light absorption and scattering by the nanocarbon. Furthermore, the reported samples showed non-attached metal oxide agglomerates and non-uniform morphology, which does not allow for accounting for other quenching contributions such as inter-particle quenching and particle size effects. In this work we have designed a unique model system that allowed for reliable and in-depth investigations of interfacial charge and energy transfer in nanocarbon hybrids. We used a modified atomic layer deposition (ALD) process to create new sandwich structures comprising of a central carbon nanotube (CNT) core, thin films of Al2O3 and a decorating layer of photoluminescent ZnO nanoparticles. The novelty of our model originates from the introduction of a dielectric barrier layer between the hybrid components with atomically precise control of thickness varied between 2 nm and 100 nm. This has, for the first time, allowed for distance-dependent photoluminescence quenching studies in CNT containing nanocarbon hybrids and provided some intriguing mechanistic findings. 

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