We identify a new noncatalytic growth regime for molecular beam epitaxially grown GaAs nanowires (NWs) that may provide a route toward axial heterostructures with discrete material boundaries and atomically sharp doping profiles. Upon increase of the As/Ga flux ratio, the growth mode of self-induced GaAs NWs on SiO(2)-masked Si(111) is found to exhibit a surprising discontinuous transition in morphology and aspect ratio. For effective As/Ga ratios <1, in situ reflection high-energy electron diffraction measurements reveal clear NW growth delay due to formation of liquid Ga droplets since the growth proceeds via the vapor-liquid-solid mechanism. In contrast, for effective As/Ga ratios >1 an immediate onset of NW growth is observed indicating a transition to droplet-free, facet-driven selective area growth with low vertical growth rates. Distinctly different microstructures, facet formation and either the presence or absence of Ga droplets at the apex of NWs, are further elucidated by transmission electron microscopy. The results show that the growth mode transition is caused by an abrupt change from As- to Ga-limited conditions at the (111)-oriented NW growth front, allowing precise tuning of the dominant growth mode.

Triboelectric nanogenerators (TENG) are one of the most promising candidates for powering wearable and portable devices. Example TENGs have demonstrated flexibility, light weight, biocompatibility, versatility and good performance. Textiles are a potential substrate onto, or into, which wearable technology is increasingly being incorporated but supplying power remains an enduring challenge. TENGs are a potential textile based mechanical energy harvesting power supply and there has been an increasing effort to combine TENGs with fabrics. A significant challenge exists in the integration without losing the performance of the TENG or the original properties (appearance, breathability, washability, and durability) and feel of the textile. Various approaches towards the realisation of textile-based TENGs (T-TENGs) have been demonstrated. Depending on its structure, T-TENGs can be divided into two main types, fabric-based TENG and fibre-based TENG. The fabric-based TENG is composed of conventional and/or modified fabrics, which serve as a substrate and/or a triboelectric material. The fibre-based TENG is fabricated as a single fibre or a collection of interlaced fibres. This paper provides an up to date review of the progress in the research of T-TENGs. The paper covers the basic operating principles, possible operation modes, textile manufacturing methods, material selections, T-TENG fabrication process, surface modification and structural designs. Issues, such as standardised measurement parameters, the challenges and limitations of T-TENG are discussed.

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A novel textile-based triboelectric nanogenerator (TENG) with woven structure operating in freestanding triboelectric-layer mode, defined as a woven-TENG, has been developed. Whereas most woven-structured TENGs operate in contact-separation mode and consist of one type of triboelectric material, this woven-TENG comprises woven electrodes and woven strips of positive and negative triboelectric material, which form a checker-like pattern over the electrodes with matching periodicity. The implementation of the positive and negative triboelectric material significantly improves the performance of the woven-TENG. Furthermore, in contrast to the conventional grating-structured and woven-structured TENG, which are designed to operate only in one moving direction, this new design also allows the woven-TENG to harvest energy from allplanar directions of movement. The woven-TENG with woven strips of nylon and polytetrafluoroethylenevinyl (PTFE) fabric can generate a root mean square (RMS) open-circuit voltage of 62.9 V, an RMS short-circuit current of 1.77 µA and a maximum RMS power of 34.8 µW at a load resistance of 50 MΩ, a mechanical oscillation of 2 Hz and a contact force of 5 N. This corresponds to a maximum RMS power density of 5.43 mW/m 2 .