金属纳米颗粒分形聚集体中局域电磁场的各向异性和巨增强
Local anisotropy and giant enhancement of local electromagnetic fields in fractal aggregates of metal nanoparticles
摘要：
我们已经表明，在准静态近似下，银纳米球的随机分形聚集体中的局部电磁场的巨大波动与本文定义的局部各向异性因子S强烈相关。后者是一个纯粹的几何参数，其特征在于一个给定的纳米球的局部环境从球形对称的聚集体的偏差。因此，它是可能的预测网站与异常大的局部领域在一个聚合物没有明确解决电磁问题。我们还证明了S的平均值（在纳米球上）并不明显取决于分形维数D，除非D接近平凡极限D=3。在这种情况下，正如人们所预期的，平均局部环境变得球对称，并且S接近于零。这对应于众所周知的事实，即在平凡聚集体中，局部电磁场的波动比分形聚集体弱得多。因此，我们发现，在准静态，大规模的几何形状不具有显着的影响，在很宽的分形维数的纳米聚集体的局部电磁响应。然而，这种预测预计是不正确的聚集体是足够大的中间和辐射区的相互作用的个别纳米球变得重要。
英文摘要：
We have shown within the quasistatic approximation that the giant fluctuations of local electromagnetic field in random fractal aggregates of silver nanospheres are strongly correlated with a local anisotropy factor S which is defined in this paper. The latter is a purely geometrical parameter which characterizes the deviation of local environment of a given nanosphere in an aggregate from spherical symmetry. Therefore, it is possible to predict the sites with anomalously large local fields in an aggregate without explicitly solving the electromagnetic problem. We have also demonstrated that the average (over nanospheres) value of S does not depend noticeably on the fractal dimension D, except when D approaches the trivial limit D=3. In this case, as one can expect, the average local environment becomes spherically symmetrical and S approaches zero. This corresponds to the well-known fact that in trivial aggregates fluctuations of local electromagnetic fields are much weaker than in fractal aggregates. Thus, we find that, within the quasistatics, the large-scale geometry does not have a significant impact on local electromagnetic responses in nanoaggregates in a wide range of fractal dimensions. However, this prediction is expected to be not correct in aggregates which are sufficiently large for the intermediate- and radiation-zone interaction of individual nanospheres to become important.
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