Optics-based sensing platform working under unpolarized light illumination is of practical importance in the sensing applications. For this reason, sensing platforms based on localized surface plasmons are preferred to their integrated optics counterparts for their simple mode excitation and inexpensive implementation. However, their optical response under unpolarized light excitation is typically weak due to their strong polarization dependence. Herein, the role of rotational symmetry for realizing robust sensing platform exhibiting strong optical contrast and high sensitivity is explored. Specifically, gammadion and star-shaped gold nanostructures with different internal and external rotational symmetries are fabricated and studied in detail, from which their mode characteristics are demonstrated as superposition of their constituent longitudinal plasmons that are in conductive coupling with each other. We demonstrate that introducing and increasing internal rotational symmetry would lead to the enhancement in optical contrast up to ~3x under unpolarized light illumination. Finally, we compare the sensing performances of rotationally symmetric gold nanostructures with a more rigorous figure-of-merit based on sensitivity, Q-factor, and spectral contrast.

Strong light localization within metal nanostructures occurs by collective oscillations of plasmons in the form of electric and magnetic resonances. This so-called localized surface plasmon resonance (LSPR) has gained much interest in the development of low-cost sensing platforms in the visible spectrum. However, demonstrations of LSPR-based sensing are mostly limited to electric resonances due to the technological limitations for achieving magnetic resonances in the visible spectrum. In this work, we report the first demonstration of LSPR sensing based on fundamental magnetic resonance in the visible spectrum using ultrasmall gold v-shaped split ring resonators. Specifically, we show the ability for detecting adsorption of bovine serum albumin and cytochrome c biomolecules at monolayer levels, and the selective binding of protein A/G to immunoglobulin G.

Strong interactions between localized surface plasmons and nanoscale objects have led to the development of highly sensitive biochemical sensing in planar metallic nanostructures with sensing performance mainly dependent on the interaction volume and the local electric field. However, the sensitivity and the interaction volume of these planar structures have been limited by the achievable aspect ratios based on the standard lift-off process. We propose a new technique which involves cold sonicated development and pulsed electrodeposition to overcome this limitation, and demonstrate robust gold square dimers with sub-10 nm gaps and a gap aspect ratio of ∼8. We show that smooth gold surfaces can be achieved by growing the gold film directly on a transparent ITO substrate without a gold seed layer, and demonstrate a significant improvement in Q factors and resonance contrast in electrodeposited dimers compared to dimers fabricated by physical vapor deposition. We demonstrate that the electrodeposited dimers exhibit near 50% higher bulk refractive index sensitivity than their planar counterparts. The technique may be used to grow a variety of metals of arbitrary geometries and spatial arrangements.

The degradation mechanism of solar cells is studied operando by electrical biasing in a TEM. • Tyukalova, E.; Duchamp, M. Atomic Resolution Enabled STEM Imaging of Nanocrystals at Cryogenic Temperature J. Phys. Mater. 2020, 3, 034006. 3 Demonstrates the implementation of cryogenic STEM to delay degradation caused by radiation damage.

shape, size, and periodicity. [21,22] For a variety of applications, it is desirable to increase the interaction volume of incident radiation within the nanostructures. [23] Recently, electrochemical deposition of metal through nanometric templates has attracted much interest due to its advantages over physical deposition, [19,[24][25][26][27] such as lower material cost, better film morphology, and higher aspect ratio. [27] Typical plasmonic metals in the UVvis-NIR regions are silver, gold, aluminum, and copper, [28][29][30] all of which except aluminum can be electrodeposited using aqueous solutions. For plasmonic applications in the visible range, silver has the lowest loss. However, gold, having slightly higher loss, especially below its interband transition at 539 nm, is often preferred due its inertness and biocompatibility. [29,31] It is for these reasons that gold is the metal of choice for biological and chemical sensing applications. In addition to intrinsic metal