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The synthesis of the Li-ion conversion candidates, FeF2 and CoF2, obtained from the single source organometallic precursors [Fe(tta)3] (tta = C8H4F3O2S), and [Co(hfac)2[middle dot]2H2O] (hfac = C5H1F6O2), respectively, via a novel supercritical fluid (SCF) method is presented. The nature of the synthesis led to highly-crystalline FeF2 and CoF2 powders requiring no additional thermal treatment. The as-obtained powders were investigated for use as potential positive Li-ion conversion electrodes by means of chronopotentiometric measurements. The FeF2 cells displayed high initial capacities following electrochemical conversion (up to [similar]1100 mA h g-1 at a potential of 1.0 V vs. Li/Li+), with appreciable cyclic behaviour over 25 discharge-charge cycles. The deposition of a [similar]5 nm layer of amorphous carbon onto the surface of the active material following SCF treatment, likely facilitated adequate electron transport through an otherwise poorly conducting FeF2 phase. Similarly, CoF2 cells displayed high initial capacities (up to [similar]650 mA h g-1 at a potential of 1.2 V vs. Li/Li+), although significant capacity fading ensued in the subsequent cycles. Ex situ XRD measurements confirmed a poor reversibility in the conversion sequence for CoF2, with a complete loss of CoF2 crystallinity and the sole presence of a crystalline LiF phase following charging

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We report for the first time the self-catalyzed, single-step growth of branched GeSn nanostructures by a vapor–liquid–solid mechanism. These typical GeSn nanostructures consist of ⟨111⟩-oriented, Sn-rich (∼8 atom %) GeSn “branches” grown epitaxially on GeSn “trunks”, with a Sn content of ∼4 atom %. The trunks were seeded from Au0.80Ag0.20 nanoparticles followed by the catalytic growth of secondary branches (diameter ∼ 50 nm) from the excess of Sn on the sidewalls of the trunks, as determined by high-resolution electron microscopy and energy-dispersive X-ray analysis. The nanowires, with ⟨111⟩-directed GeSn branches oriented at ∼70° to the trunks, have no apparent defects or change in crystal structure at the trunk–branch interface; structural quality is retained at the interface with epitaxial crystallographic relation. The electrochemical performance of these highly ordered GeSn nanostructures was explored as a potential anode material for Li-ion batteries, due to their high surface-to-volume ratio and increased charge carrier pathways. The unique structure of the branched nanowires led to high specific capacities comparable to, or greater than, those of conventional Ge nanowire anode materials and Ge1–x Sn x nanocrystals.

We report the controlled self-seeded growth of highly crystalline Ge nanowires, in the absence of conventional metal seed catalysts, using a variety of oligosilylgermane precursors and mixtures of germane and silane compounds (Ge:Si ratios between 1:4 and 1:1). The nanowires produced were encased in an amorphous shell of material derived from the precursors, which acted to isolate the Ge seed particles from which the nanowires were nucleated. The mode diameter and size distribution of the nanowires were found to increase as the growth temperature and Ge content in the precursors increased. Specifically, a model was developed to describe the main stages of self-seeded Ge nanowire growth (nucleation, coalescence, and Ostwald ripening) from the oligosilylgermane precursors and, in conjunction with TEM analysis, a mechanism of growth was proposed.

Access to the full text of the published version may require a subscription. Rights KEYWORDS : PZT, Block copolymer, PFM, nanodot, piezoelectricABSTRACT: This article presents a simple methodology for the fabrication of two dimensional arrays of lead zirconate titanate (PZT) nanodots on n-doped Si substrates via the directed self-assembly of PS-b-PEO block copolymer templates. The approach produces highly ordered PZT nanodot patterns, with lateral widths and heights as small as 20 and 10 nm respectively, and a coverage density as high as ~ 68 × 10 9 nanodots cm -2 . The existence of a pervoskite phase in the nanodots was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The piezo-amplitude and ferroelectric domain response obtained from the nanodots, through piezoresponse force microscopy, confirmed the presence of ferroelectricity in the PZT arrays. Notably, PZT nanodots with a thickness ~ 10 nm, which is close to the critical size limit of PZT, showed ferroelectric behavior. The presence of a multi-a/c domain structure in the nanodots was attributed to their polycrystalline nature.

Access to the full text of the published version may require a subscription. Rights AbstractThe synthesis of Ge nanowires with very high-aspect ratios (greater than 1000) and uniform crystal growth directions is highly desirable, not only for investigating the fundamental properties of nanoscale materials, but also for fabricating integrated functional nanodevices. In this article, we present a unique approach for manipulating the supersaturation, and thus the growth kinetics, of Ge nanowires using Au/Ge bilayer films. Ge nanowires were synthesized on substrates consisting of two parts: a Au film on one half of a Si substrate and a Au/Ge bilayer film on the other half of the 2 substrate. Upon annealing the substrate, Au and Au/Ge binary alloy catalysts were formed on the Au-side and Au/Ge-side of the substrates respectively, under identical conditions. The mean lengths of Ge nanowires produced were found to be significantly longer on the Au/Ge bilayer side of the substrate compared to the Au-coated side, as a result of a reduced incubation time for nucleation on the bi-layer side. The mean length and growth rate on the bilayer side (with a 1 nm Ge film) was found to be 5.5 ± 2.3 µm and 3.7 × 10 -3 µm s -1 respectively, and 2.7 ± 0.8 µm and 1.8 × 10 -3 µm s -1for the Au film. Additionally, the lengths and growth rates of the nanowires further increased as the thickness of the Ge layer in the Au/Ge bilayer was increased. In-situ TEM experiments were performed to probe the kinetics of Ge nanowire growth from the Au/Ge bilayer substrates.Diffraction contrast during in-situ heating of the bilayer films clarified the fact that thinner Ge films,i.e. lower Ge concentration, take longer to alloy with Au than thicker films. Phase separation was also more significant for thicker Ge films upon cooling. The use of binary alloy catalyst particles, instead of the more commonly used elementary metal catalyst, enabled the supersaturation of Ge during nanowire growth to be readily tailored, offering a unique approach to producing very long high aspect ratio nanowires.

We present the facile synthesis of crystalline V 2 O 5 nanorods and V 2 O 5 /TiO 2 nanocomposites structures by a carbon nanocage (CNC)-assisted growth process, using vanadium triisopropoxide oxide and titanium isopropoxide precursors in air at 500 C. The diameters of the resultant V 2 O 5 nanorods ranged between $10 and 70 nm, while the crystalline V 2 O 5 /TiO 2 nanocomposite structures adopted a unique morphology, due to both crystallisation and templating processes, with V 2 O 5 adopting small-diameter nanowire and nanorod morphologies surrounded by sub-30 nm TiO 2 nanoparticles. The V 2 O 5 nanorods and V 2 O 5 /TiO 2 nanocomposites were characterised by electron microscopy and X-ray diffraction techniques and subsequently reviewed as positive Li-ion electrodes. The phase-pure V 2 O 5 nanorod structures exhibited appreciable Li + storage properties over the potential range of 2.0-4.0 V vs. Li/Li + , displaying capacities of up to 288 mA h g À1 with appreciable cyclic behaviour at test rates of up to $1 C. The crystalline V 2 O 5 /TiO 2 nanocomposite structures displayed similar Li + storage properties, however, increasing molar fractions of TiO 2 led to a decline in the overall capacity versus the single-phase V 2 O 5 counterparts. Interestingly, the Li + insertion behaviour of the V 2 O 5 /TiO 2 nanocomposite displayed character more-typical of amorphous V 2 O 5 , which was ascribed to a structural buffering effect of the inactive TiO 2 phase.