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Spontaneous Self-agglomeration of Magnetic Nanoparticles into Nanowires

机译：磁性纳米粒子自发自团聚成纳米线

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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.
机译：本文提出了一种新开发的通过纳米粒子自聚集形成纳米线的方法。将分散在有孔碳网格上的Co3C，富Co和Ni纳米颗粒插入真空炉中，并在375°C下与聚氯三氟乙烯（PCTFE）共同退火。没有施加外部电场或磁场。高分辨率电子显微镜（HREM）被广泛用于确定起始原料和生产原料的形状，尺寸分布和结晶相。有趣的是，在72小时的退火循环后，纳米粒子似乎会自聚集成纳米线，纳米线的直径在5-20 nm范围内，长度超过案例1微米。产生的线材的直径与初始纳米粒子的直径在相同范围内，进一步支持了纳米线已经由纳米粒子团聚形成的观点。对纳米线HREM图像的仔细检查显示，宽于约11 nm的纳米线的核心结构类似于链接的纳米粒子。还使用HREM图像进行了相鉴定，以揭示核与起始纳米粒子具有相同的相/材料。由于纳米线似乎在多孔碳网格上的孔上形成，因此提出了一种基本的生长机理。碳氟化合物蒸气在过渡金属纳米粒子上分解，碳管开始生长。纳米颗粒似乎被捕获在小管中，在小管中它们的近距离增强了它们融合成连续核的能力。在研究的温度下，纳米粒子的融合受到纳米粒子尺寸的限制，纳米粒子的尺寸仅由细纳米线中的连续核显示。此处介绍的过程表明，纳米粒子可以自发地自对准纳米线，其方式和程度在以前从未报道过。因此，当然有必要进一步研究该方法，以揭示有关过渡金属对烃的催化作用以及确切的纳米线形成机理的更多信息。尽管目前尚在推测中，但此过程可能会导致在构建微型电路时毫不费力地在特定位置生长纳米线。

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