Optical trapping is a powerful tool for studying fundamental physics on the nanoscale as described by electric field-based light-matter interactions. However, the range of capabilities would be greatly enhanced by understanding its magnetic counterpart. Our studies provide experimental evidence of optical magnetic trapping. In particular, our work identifies new forces in optical trapping of Si nanoparticles stemming from the Photonic Hall Effect. We also discovered optical-driven Brownian engines at the single-particle level whose counterintuitive behavior originates from optical magnetic light-matter interactions. As a result, optical magnetic trapping now offers new opportunities for particle manipulation in optical beams.
Resonant excitation and manipulation of high-index dielectric nanostructures (such as Silicon, Germanium) provide great opportunities for engineering novel optical phenomena and applications. Here, we report selective excitation and enhancement of multipolar resonances, and non-radiating optical anapoles in silicon nanospheres using cylindrical vector beams (CVBs). Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances as well as a straightforward alternate route to excite electrodynamic anapoles at the optical frequencies.
Directed self-assembly (DSA) of block copolymers (BCPs) is a rising technique for sub-20 nm patterning. To fully harness DSA capabilities for patterning, a detailed understanding of the three dimensional (3D) structure of BCPs is needed. By combining sequential infiltration synthesis (SIS) and scanning transmission electron microscopy (STEM) tomography, we have characterized the 3D structure of self-assembled and DSA BCPs films with high precision and resolution. SIS is an emerging technique for enhancing pattern transfer in BCPs through the selective growth of inorganic material in polar BCP domains. Here, Al2O3 SIS was used to enhance the imaging contrast and enable tomographic characterization of BCPs with high fidelity. Moreover, by utilizing SIS for both 3D characterization and hard mask fabrication, we were able to characterize the BCP morphology as well as the alumina nanostructures that would be used for pattern transfer.
Photoluminescence (PL) studies of the surface exciton peak in ZnO nanostructures at ~3.367 eV are
reported to elucidate the nature and origin of the emission and its relationship to nanostructure
morphology. Localised voltage application in high vacuum and different gas atmospheres show a
consistent PL variation (and recovery), allowing an association of the PL to a bound excitonic
transition at the ZnO surface modified by an adsorbate. Studies of samples treated by plasma and of
samples exposed to UV light under high vacuum conditions show no consistent effects on the
surface exciton peak indicating no involvement of oxygen species. X-ray photoelectron spectroscopy
data indicate involvement of adsorbed OH species. The relationship of the surface exciton peak to
the nanostructure morphology is discussed in light of x-ray diffraction, scanning and transmission
electron microscopy data.
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