9,092 research outputs found
2D materials coated plasmonic structures for SERS applications
Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride,
are new kind of materials that can serve as substrates for surface enhanced
Raman spectroscopy (SERS). When combined with traditional metallic plasmonic
structures, the hybrid 2D materials/metal SERS platform brings extra benefits,
including higher SERS enhancement factors, oxidation protection of metal
surface, and protection of molecules from photo-induced damage. This
perspective gives an overview of recent progress in 2D materials coated
plasmonic structure in SERS application. This paper focuses on the fabrication
of the hybrid 2D materials/metal SERS platform and their applications for Raman
enhancement.Comment: 10 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:1707.0546
Spatial damping of propagating sausage waves in coronal cylinders
Sausage modes are important in coronal seismology. Spatially damped
propagating sausage waves were recently observed in the solar atmosphere. We
examine how wave leakage influences the spatial damping of sausage waves
propagating along coronal structures modeled by a cylindrical density
enhancement embedded in a uniform magnetic field. Working in the framework of
cold magnetohydrodynamics, we solve the dispersion relation (DR) governing
sausage waves for complex-valued longitudinal wavenumber at given real
angular frequencies . For validation purposes, we also provide
analytical approximations to the DR in the low-frequency limit and in the
vicinity of , the critical angular frequency separating trapped
from leaky waves. In contrast to the standing case, propagating sausage waves
are allowed for much lower than . However, while able
to direct their energy upwards, these low-frequency waves are subject to
substantial spatial attenuation. The spatial damping length shows little
dependence on the density contrast between the cylinder and its surroundings,
and depends only weakly on frequency. This spatial damping length is of the
order of the cylinder radius for , where
and are the cylinder radius and the Alfv\'en speed in the
cylinder, respectively. We conclude that if a coronal cylinder is perturbed by
symmetric boundary drivers (e.g., granular motions) with a broadband spectrum,
wave leakage efficiently filters out the low-frequency components.Comment: 6 pages, 2 figures, to appear in Astronomy & Astrophysic
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