A newly developed method for the formation of nanowires by self-aggregation of
nanoparticles is presented in this paper. Co3C, Co-rich and Ni nanoparticles dispersed on holey
carbon grids are inserted in a vacuum oven and are co-annealed with PolyChloroTriFluoroEthylene
(PCTFE) at 375 °C. No external electric or magnetic fields were applied. High resolution
electron microscopy (HREM) was extensively used to determine the shape, size distribution and
crystallographic phase of the starting and produced materials. Interestingly, after an annealing
circle of 72 hours, the nanoparticles seem to self-agglomerate into nanowires which have diameters
in the 5-20 nm range and lengths exceeding at cases 1 micron. The diameter of the produced wires
is in the same range as the diameter of the initial nanoparticles, further supporting the notion
that the nanowires have formed out of nanoparticle agglomeration. Close inspection of nanowire
HREM images shows that the core structure of nanowires wider than approximately 11 nm resembles
linked nanoparticles. Phase identification has also been performed using the HREM images to reveal
the core is of the same phase/material as the starting nanoparticles.
Since nanowires appear to form over holes on the holey carbon grid, a base growth mechanism is proposed. The fluorocarbon vapour decomposes over the transitional metal nanoparticles and carbon tubules start growing. The nanoparticles appear to be trapped inside the tubules where their close proximity enhances their fusion into a continuous core. At the studied temperature, the nanoparticle fusion is seen to be limited by the size of the nanoparticles manifested by continuous cores only in the thin nanowires. The process presented here shows that nanoparticles can spontaneously selfalign into nanowires in a way and to an extent never reported before. Therefore there is certainly scope for studying this method further to reveal more information about the catalytic action of transitional metals on hydrocarbons and the exact nanowire formation mechanism. Although it is currently a matter of speculation, this process might lead to the effortless growth of nanowires at particular places when building miniature circuits.
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