We numerically design and experimentally test a SERS-active substrate for enhancing the SERS signal of a monolayer of graphene in water. The monolayer is placed on top of an array of silver-covered nanoholes in a polymer and is covered with water. Here we report a large enhancement of up to 200000 in the SERS signal of the graphene monolayer on the patterned plasmonic nanostructure for a 532 nm excitation laser wavelength. Our numerical calculations of both the excitation field and the emission rate enhancements support the experimental results. We also propose a highly compact structure for near total light absorption in a monolayer of graphene in the visible. The structure consists of a grating slab covered with the graphene monolayer. The grating slab is separated from a metallic back reflector by a dielectric spacer. The proposed structure could find applications in the design of efficient nanoscale visible-light photodetectors and modulators.
It has been shown that surface enhanced Raman spectroscopy (SERS) has many promising applications in ultrasensitive detection of Raman signal of substances. However, optimizing the enhancement in SERS signal for different applications typically requires several levels of fabrication of active plasmonic SERS substrates. In this paper, we report the enhancement of SERS signal of a single layer of graphene located on a plasmonic nano-Lycurgus cup array after placing water droplets on it. The experimental data shows that addition of water droplets can enhance the SERS signal of the single layer of graphene about 10 times without requiring any modifications to the nano-Lycurgus cup array. Using fullwave electromagnetic simulations, we show that addition of water droplets enhances the local electric field at the graphene layer, resulting in stronger light-graphene interaction at the excitation pump laser wavelength. We also show that the addition of water droplets on the graphene layer enables us to modify the band diagram of the structure, in order to enhance the local density of optical states at the Raman emission wavelengths of the graphene layer. Numerical calculations of both the excitation field enhancement at the location of the graphene layer, and the emission enhancement due to enhanced local density of optical states, support the experimental results. Our results demonstrate an approach to boost the SERS signal of a target material by controlling the band diagram of the active nanostructured SERS substrate through the use of fluidic dielectrics. These results could find potential applications in biomedical and environmental technologies.
In this paper, we fabricated gold particle array substrate by thermal dewetting technique. The fabrication process is
simple, reliable, cost efficient with comparing to other techniques. From optical characteristic it shows light trapping
ability to reduce reflectance around 75%. Combining light trapping and its localized plasmonic properties, this substrate
has significant advantages on plasmonic based sensing methods such as surface enhanced Raman scattering (SERS).
SERS measurement has been performed and the enhancement factor is 2.58×105. Further more, after silver thin film
deposition the enhancement can be increased up to 2 orders and the enhancement factor is 3.66×107.
Improvement of energy conversion efficiency of solar cells has led to innovative approaches, in particular the
introduction of nanopillar photovoltaics [1]. Previous work on nanopillar Si photovoltaic has shown broadband reduction
in optical reflection and enhancement of absorption [2]. Radial or axial PN junctions [3, 4] have been of high interest for
improved photovoltaic devices. However, with the PN junction incorporated as part of the pillar, the discreteness of
individual pillar requires additional conductive layer that would electrically short the top of each pillar for efficient
carrier extraction. The fragile structure of the surface pillars would also require a protection layer for possible
mechanical scratch to prevent pillars from breaking. Any additional layer that is applied, either for electrical contact or
for mechanical properties may introduce additional recombination sites and also reduce the actual light absorption by the
photovoltaic material. In this paper, nanopore Si photovoltaics that not only provides the advantages but also addresses
the challenges of nanopillers is demonstrated. PN junction substrate of 250 nm thick N-type polycrystalline Si on P-type
Si wafer is prepared. The nanopore structure is formed by using anodized aluminum oxide (AAO) as an etching mask
against deep reactive ionic etching (DRIE). The device consists of semi-ordered pores of ~70 nm diameter.
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