Researchers at the University of Lyon led by Matthias Hillenkamp have shown that, in very small nanoparticles (<10 nm in diameter), the surface plasmon resonance is indeed influenced by quantum effects, but that these are sometimes quenched depending on the environment. The work helps explain inconsistencies seen in earlier work on localized surface-plasmon resonance, or LSPR. This is is a collective excitation of electrons that can be tuned over a large spectral range depending on the material, its size and shape and appears in metal particles the smaller they get. The result will be important for better understanding how quantum mechanics affects LSPR and it also helps advance applications that exploit the effect – such as photocatalysis and biomedical imaging.
The researchers obtained their results by studying ensembles of silica-embedded silver nanoparticles using optical absorption spectroscopy and looked at particles ranging in size down to less than 1 nm diameter. This is where quantum size effects are expected. They found that all but the very smallest particles strongly absorb light at a bandwidth of 2.95 eV, irrespective of their size.
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