Chemically synthesized metal nanoparticles with morphological chiral features are known to exhibit strong circular dichroism. However, we still lack understanding of the correlation between... Show moreChemically synthesized metal nanoparticles with morphological chiral features are known to exhibit strong circular dichroism. However, we still lack understanding of the correlation between morphological and chiroptical features of plasmonic nanoparticles. To shed light on that question, single nanoparticle experiments are required. We performed photothermal circular dichroism measurements of single chiral and achiral gold nanoparticles and correlated the chiroptical response to the 3D morphology of the same nanoparticles retrieved by electron tomography. In contrast to an ensemble measurement, we show that individual particles within the ensemble display a broad distribution of strength and handedness of circular dichroism signals. Whereas obvious structural chiral features, such as helical wrinkles, translate into chiroptical ones, nanoparticles with less obvious chiral morphological features can also display strong circular dichroism signals. Interestingly, we find that even seemingly achiral nanoparticles can display large g-factors. The origin of this circular dichroism signal is discussed in terms of plasmonics and other potentially relevant factors. Show less
Magnetic imaging is a versatile tool in biological andcondensed-matter physics. Existing magnetic imaging techniqueseither require demanding experimental conditions which restrict therange of their... Show moreMagnetic imaging is a versatile tool in biological andcondensed-matter physics. Existing magnetic imaging techniqueseither require demanding experimental conditions which restrict therange of their applications or lack the spatial resolution required forsingle-particle measurements. Here, we combine photothermal (PT)microscopy with magnetic circular dichroism (MCD) to develop aversatile magnetic imaging technique using visible light. Unlike mostmagnetic imaging techniques, photothermal magnetic circulardichroism (PT MCD) microscopy works particularly well for singlenanoparticles immersed in liquids. As a proof of principle, wedemonstrate magnetic CD imaging of superparamagnetic magnetitenanoparticulate clusters immersed in microscope immersion oil. Thesensitivity of our method allowed us to probe the magnetizationcurve of single similar to 400-nm-diameter magnetite nanoparticulate clusters Show less