Jorit Gröttrup

Hybridization of Zinc Oxide Tetrapods for Selective Gas Sensing Applications

In this work, the exceptionally improved sensing capability of highly porous three-dimensional (3-D) hybrid ceramic networks toward reducing gases is demonstrated for the first time. The 3-D hybrid ceramic networks are based on doped metal oxides (MexOy and ZnxMe1-xOy, Me = Fe, Cu, Al) and alloyed zinc oxide tetrapods (ZnO-T) forming numerous junctions and heterojunctions. A change in morphology of the samples and formation of different complex microstructures is achieved by mixing the metallic (Fe, Cu, Al) microparticles with ZnO-T grown by the flame transport synthesis (FTS) in different weight ratios (ZnO-T:Me, e.g., 20:1) followed by subsequent thermal annealing in air. The gas sensing studies reveal the possibility to control and change/tune the selectivity of the materials, depending on the elemental content ratio and the type of added metal oxide in the 3-D ZnO-T hybrid networks. While pristine ZnO-T networks showed a good response to H2 gas, a change/tune in selectivity to ethanol vapor with a decrease in optimal operating temperature was observed in the networks hybridized with Fe-oxide and Cu-oxide. In the case of hybridization with ZnAl2O4, an improvement of H2 gas response (to ∼7.5) was reached at lower doping concentrations (20:1), whereas the increase in concentration of ZnAl2O4 (ZnO-T:Al, 10:1), the selectivity changes to methane CH4 gas (response is about 28). Selectivity tuning to different gases is attributed to the catalytic properties of the metal oxides after hybridization, while the gas sensitivity improvement is mainly associated with additional modulation of the electrical resistance by the built-in potential barriers between n-n and n-p heterojunctions, during adsorption and desorption of gaseous species. Density functional theory based calculations provided the mechanistic insights into the interactions between different hybrid networks and gas molecules to support the experimentally observed results. The studied networked materials and sensor structures performances would provide particular advantages in the field of fundamental research, applied physics studies, and industrial and ecological applications.

Strong light scattering and broadband (UV to IR) photoabsorption in stretchable 3D hybrid architectures based on Aerographite decorated by ZnO nanocrystallites

In present work, the nano- and microscale tetrapods from zinc oxide were integrated on the surface of Aerographite material (as backbone) in carbon-metal oxide hybrid hierarchical network via a simple and single step magnetron sputtering process. The fabricated hybrid networks are characterized for morphology, microstructural and optical properties. The cathodoluminescence investigations revealed interesting luminescence features related to carbon impurities and inherent host defects in zinc oxide. Because of the wide bandgap of zinc oxide and its intrinsic defects, the hybrid network absorbs light in the UV and visible regions, however, this broadband photoabsorption behavior extends to the infrared (IR) region due to the dependence of the optical properties of ZnO architectures upon size and shape of constituent nanostructures and their doping by carbon impurities. Such a phenomenon of broadband photoabsorption ranging from UV to IR for zinc oxide based hybrid materials is novel. Additionally, the fabricated network exhibits strong visible light scattering behavior. The developed Aerographite/nanocrystalline ZnO hybrid network materials, equipped with broadband photoabsorption and strong light scattering, are very promising candidates for optoelectronic technologies.

Individual Bi 2 O 3 -Functionalized ZnO Microwire for Hydrogen Gas Detection

Individual micro- and nanostructures of metal oxides are known to be highly sensitive to surface phenomena due to their enhanced surface-to-volume ratio. In this work, an individual Bi2O3-functionalized ZnO microwire (Bi2O3/ZnO MW) with a diameter of ~2.2 μm was integrated into a sensing device using its direct transfer and placement in a focused ion beam (FIB)/scanning electron microscopy (SEM) equipment. The fabricated device was exposed to H2 gas at room temperature showing a detectable response. The gas response to 1000 ppm is ~28%.

Flame based growth of ZnO nano- and microstructures for advanced optical, multifunctional devices, and biomedical applications (Conference Presentation)

The recent flame based growth strategy offers a simple and versatile fabrication of various (one, two, and three-dimensional) nano- and microstructures from different metal oxides (ZnO, SnO2, Fe2O3, etc.) in a desired manner.[1] ZnO structures ranging from nanoscales wires to macroscopic and highly porous 3D interconnected tetrapod networks have been successfully synthesized, characterized and utilized for various applications. The ZnO micro- and nanoneedles grown at walls in silicon trenches showed excellent whispering gallery mode resonances and photocatalytic properties.[2] Using the same strategy, large polycrystalline micro- and nanostructured ZnO platelets can be grown with grains interconnected together via grain boundaries and these grain boundaries exhibit a higher conductivity as compared to individual grains.[3] This flame transport synthesis (FTS) approach offers the growth of a large amount of ZnO tetrapods which have shown interesting applications because of their 3D spatial shape and micro-and nanoscale size, for example, interconnected tetrapods based devices for UV-detection and gas sensing.[4-5] Because of their complex 3D shape, ZnO tetrapods can be used as efficient filler particles for designing self-reporting,[6] and other interesting composites. The nanostructured materials exhibit an important role with respect to advanced biomedical applications as grown ZnO structures have shown strong potentials for antiviral applications.[7] Being mechanically strong and micro-and nanoscale in dimensions, these ZnO tetrapods can be easily doped with other elements or hybridized with various nanoparticles in form of hybrid ZnO tetrapods which are suitable for various multifunctional applications, for example, these hybrid tetrapods showed improved gas sensing properties.[8] The sacrificial nature of ZnO allows the for growth of new tetrapods and 3D network materials for various advanced applications, for example, highly porous and ultra light carbon based Aerographite materials[9] and hollow silicon tetrapods.[10] These carbon based highly porous network can be further utilized for growth of new hybrid 3D nanomaterials, for example, Aerographite- GaN[11] and Aerographite-ZnO[12] for advanced optical and other applications.