arXiv subjects

Nicklas Anttu

Publications and source records attributed to Nicklas Anttu.

4 recordsLinked to original sources

arXiv2024

Chiro-Optical Structures with Magnetizable Plasmonic Elements for Modulating the Chiral Transmission of Light

Manipulating external stimuli is crucial for enhancing and controlling the optical response in chiral structures. This study introduces chiral structures composed of single, dimer, or trimer arrays of plasmonic and magneto-plasmonic trapezoidal and triangular nanoantennas. Through modeling, we demonstrate how these systems can (i) function as chiral metasurfaces, (ii) modulate chiral light absorption via an external magnetic field, (iii) magnetically enhance the chiro-optical response, and (iv) improve the chiro-optical and magneto-chiral response through structural engineering. By optimizing the nanoantenna geometry, we achieve enhancements larger than 100 in the chiro-optical signal of a magnetized Ni monomer compared to a non-magnetized system. Additionally, we model bimetallic systems, showing a ~2-fold increase in chiro-optical response for hybrid Au and Ni magneto-plasmonic systems compared to purely plasmonic Au systems, while simultaneously enabling magnetic tuning of the optical response. Our results highlight the potential of structurally engineered magneto-plasmonic nanoantennas for advanced applications in chiro-optical sensing and tunable photonic devices.

physics.optics↗

arXiv2024

Fluorophore signal detection and imaging enhancement in high refractive index nanowire biosensors

High refractive index semiconductor nanowires have recently been demonstrated experimentally as an efficient platform for enhancing the signal in fluorescence-based biosensors. Here, we study through modelling how a vertical GaP nanowire (i) enhances the excitation intensity at the position of the fluorophore attached to the nanowire sidewall, (ii) enhances the probability to collect photons emitted from the fluorophore by directing them preferentially into the numerical aperture of the collection objective, and (iii) through the Purcell effect increases the quantum yield of the fluorophore. With appropriate choice for the geometry of the nanowire, we can reach a larger than $10^2$ enhancement in signal compared to a corresponding conventional planar biosensor platform. We model also imaging-based detection. There, we find that thanks to waveguiding in the nanowire, we can beat the limitations set by the depth of view in conventional microscopy, enabling the use of a long nanowire to enhance the binding-area for fluorophores. As an example, we can focus to the top of a 4000 nm long nanowire and reach a 25 times sharper image from a fluorophore at the bottom of the nanowire, as compared to such a 4000 nm defocusing in a conventional planar biosensor platform.

physics.optics↗

arXiv2023

Optimized Absorption of Light in Perovskite Nanowire Solar Cells

Metal halide perovskite nanowires (PrvNWs) have recently emerged as an interesting path for nanostructured solar cells. Here, we model the absorption of light in PrvNW arrays for varying diameter and length of the PrvNWs and period for the array by solving the Maxwell equations. For long enough bare PrvNW arrays, we find that the optimum diameter is fixed to that which places the absorption peak from the HE$_{11}$ waveguide mode in the PrvNWs to the vicinity of the bandgap wavelength. In contrast, when we include a transparent conductive oxide (TCO) top contact layer, the optimum diameter shifts to a larger value by 100 nm. The origin of this shift is traced to a reduced reflection at the interface between the TCO layer and the PrvNW array when the PrvNW's diameter is larger. Overall, we find that 1500 nm long PrvNWs can reach 90% of the broadband absorption potential, making this system of high interest for photovoltaics.

physics.optics↗

arXiv2017

Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage

Compared to traditional pn-junction photovoltaics, hot carrier solar cells offer potentially higher efficiency by extracting work from the kinetic energy of photogenerated "hot carriers" before they cool to the lattice temperature. Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap materials, where the potential efficiency gain is highest. Recently, a high open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire with a low bandgap of 0.39 eV, and was interpreted in terms of a photothermoelectric effect. Here, we point out that this device is a hot carrier solar cell and discuss its performance in those terms. In the demonstrated devices, InP heterostructures are used as energy filters in order to thermoelectrically harvest the energy of hot electrons photogenerated in InAs absorber segments. The obtained photovoltage depends on the heterostructure design of the energy filter and is therefore tunable. By using a high-resistance, thermionic barrier an open-circuit voltage is obtained that is in excess of the Shockley-Queisser limit. These results provide generalizable insight into how to realize high voltage hot carrier solar cells in low-bandgap materials, and therefore are a step towards the demonstration of higher efficiency hot carrier solar cells.

physics.app-ph↗