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
In this work, we investigate the minute circular dichroism effects of single nanoparticles.To this aim, we apply photothermal imaging with a polarization-modulated heating beam. This new technique,... Show moreIn this work, we investigate the minute circular dichroism effects of single nanoparticles.To this aim, we apply photothermal imaging with a polarization-modulated heating beam. This new technique, which we call photothermal circular dichroism microscopy, probes circular dichroism in an absorption measurement, unlike other techniques which usually probe the extinction. We also investigate in detail how to avoid measurement artefacts such as leakage of linear dichroism and residual intensity modulation.We then study the CD of formally achiral and wet-chemically synthesized chiral nanoparticles. We find that the achiral spherical-like particles, can exhibit considerable circular dichroism, some of them display almost as strong CD as specially designed chiral particles. Furthermore, we find that the control of handedness of the synthesized chiral particles is only limited and that, even from a geometric perspective, the relation between the 3D shape of these particles and their handedness is not straightforward.In the last chapter, we apply our method to magnetic samples which exhibit circular dichroism through their magnetization but not due to their shape. The excellent sensitivity of photothermal microscopy not only allows us to perform magnetic imaging of particles, but we also succeeded in obtaining magnetization curves of single particles and estimating their magnetization. Show less
