Chiromagnetoptics of Au and Ag Nanoparticulate Systems

Abstract

Photoelectron excitations into unoccupied energy states are fundamental in solid-state physics and many modern applications. The operation of such internal electronic transitions relies not only on photon absorption efficiency, which is pivotal in sensing, photovoltaics, active plasmonics, etc., but also on light-matter interactions and near/far-field spectroscopic techniques. Here, we report on a spectroscopic absorption fingerprint in magnetic circular dichroism (MCD) responses of various nanoparticulate systems. MCD spectra acquired at low temperatures on assemblies of uncoupled/coupled Ag and Au nanoparticles reveal asymmetric MCD spectral line shapes strongly depending on the nature and shape of nanoparticles and on their interparticular interactions. Assembling for instance the NPs into 2D networks with interparticle distances allowing dipolar interactions or transforming the spherical nanoparticles into disks was found to significantly alter the magneto-optic response in the spectral line shape. The findings are interpreted within the framework of chiral magneto-plasmonic effects by considering the k-dependent electronic states involved in both inter-and intraband electronic transitions.

Magneto-optical methods for magnetoplasmonics in noble metal nanostructures

“…A confirmation of the importance of inter-band transition in determining the asymmetry of the MCD signal was also provided by Kovalenko et al through a comparison between Au and Ag NPs. 65 The authors also reported that inter-particle coupling in 2D networks of Au NPs can significantly alter the MCD line shape, red shifting the LSPR and reducing the asymmetry of the signal.…”

Dielectric Effects in FeOx-Coated Au Nanoparticles Boost the Magnetoplasmonic Response: Implications for Active Plasmonic Devices

“…In the MCD spectrum, the effect of the overlapping between LSPR and interband transitions is observed with the asymmetry of the signal, where the high energy lobe of the signal is the one which is closer to the interband transitions, and it is thus more damped. 11 , 67 …”

“…Indeed, for Au NPs, a significant damping occurs when the LSPR is overlapped with interband transitions of Au (close to 500 nm), and the red-shift of the LSPR position reduces the overlapping, resulting in a sharper and more intense extinction cross section. In the MCD spectrum, the effect of the overlapping between LSPR and interband transitions is observed with the asymmetry of the signal, where the high energy lobe of the signal is the one which is closer to the interband transitions, and it is thus more damped. , …”

“…In the MCD spectrum, the effect of the overlapping between LSPR and interband transitions is observed with the asymmetry of the signal, where the high energy lobe of the signal is the one which is closer to the interband transitions, and it is thus more damped. 11,67 For samples CS1 and CS2, in order to consider the effect of the shell on the optical and MCD response, a core@shell model was employed for the quasi-static polarizability, according to Bohren and Huffman, 57 modified to take into account the magnetic field effect according to Gu and Kornev (Supporting Information). 63 Assuming that the magnetic field effect on the shell is small and comparable to that of the medium, as suggested by the low magnetic moment detected at room temperature, we can write a simplified equation for the quasi-static fieldand helicity-dependent core@shell polarizability (eq 1).…”

Photothermal Plasmonic Actuation of Micromechanical Cantilever Beams

“…A specific absorption peak (∼ 545 nm), induced by intra-band collective plasmonic excitations of conduction electrons is revealed. By substituting the Au NPs with a continuous metallic Au film, it is shown that interband electronic transitions -not being part of plasma oscillations but occurring in NPs as well [60,61] -already induce a specific absorption of light in the visible range. This permits a deeper understanding of the photoinduced oscillations as a function of wavelength.…”