Advanced Hybrid GaN/ZnO Nanoarchitectured Microtubes for Fluorescent Micromotors Driven by UV Light.

The development of functional microstructures with designed hierarchical and complex morphologies and large free active surfaces offers new potential for improvement of the pristine microstructures properties by the synergistic combination of microscopic as well as nanoscopic effects. In this contribution, dedicated methods of transmission electron microscopy (TEM) including tomography are used to characterize the complex hierarchically structured hybrid GaN/ZnO:Au microtubes containing a dense nanowire network on their interior. The presence of an epitaxially stabilized and chemically extremely stable ultrathin layer of ZnO on the inner wall of the produced GaN microtubes is evidenced. Gold nanoparticles initially trigger the catalytic growth of solid solution phase (Ga1- x Znx )(N1- x Ox ) nanowires into the interior space of the microtube, which are found to be terminated by AuGa-alloy nanodots coated in a shell of amorphous GaOx species after the hydride vapor phase epitaxy process. The structural characterization suggests that this hierarchical design of GaN/ZnO microtubes could offer the potential to exhibit improved photocatalytic properties, which are initially demonstrated under UV light irradiation. As a proof of concept, the produced microtubes are used as photocatalytic micromotors in the presence of hydrogen peroxide solution with luminescent properties, which are appealing for future environmental applications and active matter fundamental studies.

Electromagnetic interference shielding in X-band with aero-GaN.

We investigate the electromagnetic shielding properties of an ultra-porous lightweight nanomaterial named aerogalnite (aero-GaN). Aero-GaN is made up of randomly arranged hollow GaN microtetrapods, which are obtained by direct growth using hydride vapor phase epitaxy of GaN on the sacrificial network of ZnO microtetrapods. A 2 mm thick aero-GaN sample exhibits electromagnetic shielding properties in the X-band similar to solid structures based on metal foams or carbon nanomaterials. Aero-GaN has a weight four to five orders of magnitude lower than the weight of metals.

Nanostructured Fibrous Membranes with Rose Spike-Like Architecture.

Nanoparticles have been used for engineering composite materials to improve the intrinsic properties and/or add functionalities to pristine polymers. The majority of the studies have focused on the incorporation of spherical nanoparticles within the composite fibers. Herein, we incorporate anisotropic branched-shaped zinc oxide (ZnO) nanoparticles into fibrous scaffolds fabricated by electrospinning. The addition of the branched particles resulted in their protrusion from fibers, mimicking the architecture of a rose stem. We demonstrated that the encapsulation of different-shape particles significantly influences the physicochemical and biological activities of the resultant composite scaffolds. In particular, the branched nanoparticles induced heterogeneous crystallization of the polymeric matrix and enhance the ultimate mechanical strain and strength. Moreover, the three-dimensional (3D) nature of the branched ZnO nanoparticles enhanced adhesion properties of the composite scaffolds to the tissues. In addition, the rose stem-like constructs offered excellent antibacterial activity, while supporting the growth of eukaryote cells.

Buckminsterfullerene hybridized zinc oxide tetrapods: defects and charge transfer induced optical and electrical response.

Buckminster fullerene (C60) based hybrid metal oxide materials are receiving considerable attention because of their excellent fundamental and applied aspects, like semiconducting, electron transfer, luminescent behaviors, etc. and this work briefly discusses the successful fabrication of C60 decorated ZnO tetrapod materials and their detailed structure-property relationships including device sensing applications. The electron microscopy investigations indicate that a quite dense surface coverage of ZnO tetrapods with C60 clusters is achieved. The spectroscopy studies confirmed the identification of the C60 vibrational modes and the C60 induced changes in the absorption and luminescence properties of the ZnO tetrapods. An increased C60 concentration on ZnO results in steeper ZnO bandgap absorption followed by well-defined free exciton and 3.31 eV line emissions. As expected, higher amounts of C60 increase the intensity of C60-related visible absorption bands. Pumping the samples with photons with an energy corresponding to these absorption band maxima leads to additional emission from ZnO showing an effective charge transfer phenomenon from C60 to the ZnO host. The density of states model obtained from DFT studies for pure and C60 coated ZnO surfaces confirms the experimental observations. The fabricated C60-ZnO hybrid tetrapod based micro- and nanodevices showed interesting ethanol gas sensing characteristics.

Light, Force, and Heat: A Multi-Stimuli Composite that Reveals its Violent Past.

A self-reporting polythiourethane/tetrapodal-ZnO (PTU/T-ZnO) composite is produced using spiropyran as an additive at a concentration as low as 0.5 wt %. Exposure to heat, UV light and mechanical force caused the spiropyran to undergo reversible isomerization indicated by a reversible color change. The studies have been conducted with a constant spiropyran concentration at 0.5 wt %, meanwhile varying the T-ZnO concentration from 0 to 7.5 wt %. The tetrapodal ZnO served as a prism: the light scattering effect of T-ZnO created a visual impression of uniform color distribution. The interconnected network of the tetrapodal of ZnO embedded in the PTU matrix enhanced the mechanical stability of the polymer leading to high impact resistance up to ∼232 kPa. PTU/spiropyran also emerged as a possible thermal sensing coating, due to its temperature sensitivity. Due to the broad green luminescence band (∼535 nm) in T-ZnO, the colored merocyanine form which absorbs in this region of the spectrum switches back to spiropyran at this wavelength. High concentrations of T-ZnO were shown to reduce the effect one of the switching triggers i.e., ultraviolet light. Using this property of T-ZnO it was possible to achieve a switchable system with the possibility of separating the stimuli.