Researchers build 3D GaN-based networks on carbon 'foam'
Scientists from universities in Germany, Moldova and Australia have grown a 3D GaN hybrid network on a novel flexible carbon 'foam' called Aerographite, using a single step hydride vapour phase epitaxy process (HVPE).
The work, which was published in Nature Scientific Reports, opens up the possibility of making flexible, semiconducting composites that could be used as next generation materials for electronic, photonic, and sensors applications.
Aerographite is a synthetic foam made from a mechanically flexible, porous interconnected network of hollow carbon tubes with micron-scale diameters and a wall thickness of around 15nm. Researchers at the University of Kiel and the Technical University of Hamburg in Germany, who were involved in this recent work, developed the foam a couple of years ago.
GaN's direct and wide bandgap (~3.4eV at room temperature), high mechanical stability, and large electrical/thermal conductivity mean that nano- and microstructures based on GaN are promising candidates for next generation nanoelectronic, nanopiezotronic, and photonic devices, LEDs and lasers, chemical and biosensors.
Various techniques have been used for versatile growth of different GaN structures, however almost all are based on one or 2D epitaxially grown architectures, such a nanorods, nanowires, nanotubes etc. and their arrays on particular substrates.
Unusually, in this case, the researchers used a single step HVPE process to grow the GaN nano- and microstructures on the surface of Aerographite tubes. In the HVPE process, homogeneous growth of GaN nano- and microstructures occurs on both the inner and the outer surfaces of the carbon tubes in the entire Aerographite network while several growth directions are indicative of the direct free growth, according to the paper.
(a-c) Growth of the GaN nano- and microcrystals on Aerographite network from partial to complete coverage. (d-f) Uniformity and morphology of the grown GaN nano- and microstructures on the AG tubes. (g) Growth of GaN nano- and microcrystals on inner and outer surfaces. (h-i) Low and corresponding high magnification SEM images demonstrating growth of hexagonally facetted GaN nanocrystals at the inner surface of the tube.
The team found that the grown GaN nano- and microstructures were strongly attached on the surface of the thin graphite walls which prevent their agglomeration. Studies also revealed the highly crystalline nature of these GaN structures. Cathodoluminescence results showed that they exhibited intense near-band-edge UV emission, and yellow emission usually attributed to host defects.
The scientists say that the 3D network retains the flexible behavior of the Aerographite template, which opens up a wide range of application opportunities. In particular, the stress dependent electrical conductivity of the Aerographite-GaN hybrid 3D network might be useful for designing different kinds of sensors and self-reporting materials, the team suggest.
'Three-dimensional Aerographite-GaN hybrid networks: Single step fabrication of porous and mechanically flexible materials for multifunctional applications' by Arnim Schuchardt et al, Scientific Reports 5, Article number: 8839 doi:10.1038/srep08839
