In a nanoplasmonic context, copper (Cu) is a potential and interesting surrogate to less accessible metals such as gold, silver or platinum. We demonstrate optical trapping of individual Cu nanoparticles with diameters between 25 and 70 nm and of two ionic Cu nanoparticle species, CuFe2O4 and CuZnFe2O4, with diameters of 90 nm using a near infrared laser and quantify their interaction with the electromagnetic field experimentally and theoretically. We find that, despite the similarity in size, the trapping stiffness and polarizability of the ferrites are significantly lower than those of Cu nanoparticles, thus inferring a different light-particle interaction. One challenge with using Cu nanoparticles in practice is that upon exposure to the normal atmosphere, Cu is spontaneously passivated by an oxide layer, thus altering its physicochemical properties. We theoretically investigate how the presence of an oxide layer influences the optical properties of Cu nanoparticles. Comparisons to experimental observations infer that oxidation of CuNPs is minimal during optical trapping. By finite element modelling we map out the expected temperature increase of the plasmonic Cu nanoparticles during optical trapping and retrieve temperature increases high enough to change the catalytic properties of the particles.

译文

在纳米等离子体的背景下,铜 (Cu) 是一种潜在且有趣的替代物,可以替代不易接近的金属,例如金,银或铂。我们证明了使用近红外激光对直径在25至70  nm之间的单个Cu纳米颗粒以及直径为90  nm的两种离子Cu纳米颗粒物种CuFe2O4和CuZnFe2O4的光学捕获,并通过实验和理论上量化了它们与电磁场的相互作用。我们发现,尽管尺寸相似,但铁氧体的俘获刚度和极化率明显低于Cu纳米颗粒,从而推断出不同的光粒子相互作用。在实践中使用Cu纳米颗粒的一个挑战是,在暴露于正常大气中,Cu会被氧化物层自发钝化,从而改变其理化性质。我们从理论上研究了氧化物层的存在如何影响Cu纳米颗粒的光学性能。与实验观察结果的比较表明,在光学捕获过程中,CuNPs的氧化最小。通过有限元建模,我们绘制出了等离子体Cu纳米颗粒在光学捕获过程中的预期温度升高,并且回收温度升高到足以改变颗粒的催化性能。

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