21 research outputs found
Extremely short-length surface plasmon resonance sensors
The impact of the system design on the control of coupling between planar
waveguide modes and surface plasmon polaritons (SPP) is analyzed. We examine
how the efficiency of the coupling can be enhanced by an appropriate
dimensioning of a multi-layer device structure without using additional
gratings. We demonstrate that by proper design the length of the device can be
dramatically reduced through fabrication a surface plasmon resonance sensor
based on the SPP-photon transformation rather then on SPP dissipation
Research of Structural, Strength and Thermal Properties of ZrO<sub>2</sub>âCeO<sub>2</sub> Ceramics Doped with Yttrium
In this work, using a mechanochemical solid-phase synthesis method, ZrO2âCeO2 ceramics doped with yttrium were obtained, which have great prospects for use as a basis for dispersed nuclear fuel materials or inert nuclear fuel matrices. The purpose of this work was to study the formation of the ZrO2âCeO2 phase composition, depending on the concentration of yttrium dopant, as well as to study their structural and strength properties. The relevance of this study is in obtaining new data on the properties of composite ceramics based on oxides having a cermet structure, as well as the effect of doping with yttrium on increasing the resistance of ceramics to deformation and thermal properties. During the studies, the dynamics of the phase transformations depending on the concentration of the dopant, as well as changes in the structural characteristics and dislocation density, were established. It was found that at a dopant concentration of 0.25 mol, the main phase in the structure was Ce3ZrO8âtriclinic P1 (1), the formation of which led to an increase in the mechanical and strength properties of the ceramics as well as a 1.5-fold increase in the thermal conductivity coefficient
The Role of Plasmon-Generated Near Fields for Enhanced Circular Dichroism Spectroscopy
Plasmon-enhanced
circular dichroism has established itself as a promising candidate
to push the limits of molecular handedness detection to the extremes,
namely, toward a monolayer or even to a single molecule. A multitude
of intricate mechanisms, both chemical and physical, have to contribute
individually or in unison to an enhancement that is large enough that
it may bridge the several orders of magnitude of lacking signal strength
when detecting small analyte quantities in a circular dichroism scheme.
Here, we assess in isolation the contribution arising from electromagnetic
interactions between a homogeneous chiral medium and plasmonic structures.
Using a suitably modified full-field electromagnetic simulation environment,
we are able to investigate the viability of various canonical achiral
and chiral plasmonic configurations for substrate-enhanced chiroptical
spectroscopy. A clear hierarchy in enhancement factors is revealed
that places achiral plasmonic gap antennas at the top, thus outperforming
its chiral equivalent, the BornâKuhn-type plasmonic dimer.
Moreover, the importance of coplanarity of the incident rotating circular
polarization field vector with the resonantly enhanced field vector
in the plasmonic hot-spot is demonstrated. Taking everything into
account, we obtain an enhancement of 3 orders of magnitude from purely
electromagnetic interactions, thereby charting this part of the CD
enhancement landscape
Graphene Plasmon Reflection by Corrugations
Graphene
plasmons (GPs) exhibit extreme confinement of the associated
electromagnetic fields. For that reason, they are promising candidates
for controlling light in nanoscale devices. However, despite the ubiquitous
presence of surface corrugations in graphene, very little is known
on how they affect the propagation of GPs. Here we perform a comprehensive
theoretical analysis of GP scattering by both smooth and sharp corrugations.
For smooth corrugations, we demonstrate that scattering of GPs depends
on the dielectric environment, being strongly suppressed when graphene
is placed between two dielectrics with the same refractive indices.
We also show that sharp corrugations can act as effective GP reflectors,
even when their dimensions are small in comparison with the GP wavelength.
Additionally, we provide simple analytical expressions for the reflectance
of GPs valid in an ample parametric range. Finally, we connect these
results with potential experiments based on scattering scanning near-field
optical microscopy (s-SNOM) showing how to extract the GP reflectance
from s-SNOM images
High Catalytic Activity of Vanadium Complexes in Alkane Oxidations with Hydrogen Peroxide: An Effect of 8âHydroxyquinoline Derivatives as Noninnocent Ligands
Five monomeric oxovanadiumÂ(V)
complexes [VOÂ(OMe)Â(N<sup>â©</sup>O)<sub>2</sub>] with the nitro
or halogen substituted quinolin-8-olate ligands were synthesized and
characterized using Fourier transform infrared, <sup>1</sup>H and <sup>13</sup>C NMR, high-resolution mass spectrometryâelectrospray
ionization as well as X-ray diffraction and UVâvis spectroscopy.
These complexes exhibit high catalytic activity toward oxidation of
inert alkanes to alkyl hydroperoxides by H<sub>2</sub>O<sub>2</sub> in aqueous acetonitrile with the yield of oxygenate products up
to 39% and turnover number 1780 for 1 h. The experimental kinetic
study, the C<sub>6</sub>D<sub>12</sub> and <sup>18</sup>O<sub>2</sub> labeled experiments, and density functional theory (DFT) calculations
allowed to propose the reaction mechanism, which includes the formation
of HO· radicals as active oxidizing species. The mechanism of
the HO· formation appears to be different from those usually
accepted for the Fenton or Fenton-like systems. The activation of
H<sub>2</sub>O<sub>2</sub> toward homolysis occurs upon simple coordination
of hydrogen peroxide to the metal center of the catalyst molecule
and does not require the change of the metal oxidation state and formation
of the HOO· radical. Such an activation is associated with the
redox-active nature of the quinolin-8-olate ligands. The experimentally
determined activation energy for the oxidation of cyclohexane with
complex [VOÂ(OCH<sub>3</sub>)Â(5-Cl-quin)<sub>2</sub>] (quin = quinolin-8-olate)
is 23 ± 3 kcal/mol correlating well with the estimate obtained
from the DFT calculations
Strong Plasmon Reflection at Nanometer-Size Gaps in Monolayer Graphene on SiC
We employ tip-enhanced infrared near-field
microscopy to study
the plasmonic properties of epitaxial quasi-free-standing monolayer
graphene on silicon carbide. The near-field images reveal propagating
graphene plasmons, as well as a strong plasmon reflection at gaps
in the graphene layer, which appear at the steps between the SiC terraces.
When the step height is around 1.5 nm, which is two orders of magnitude
smaller than the plasmon wavelength, the reflection signal reaches
20% of its value at graphene edges, and it approaches 50% for step
heights as small as 5 nm. This intriguing observation is corroborated
by numerical simulations and explained by the accumulation of a line
charge at the graphene termination. The associated electromagnetic
fields at the graphene termination decay within a few nanometers,
thus preventing efficient plasmon transmission across nanoscale gaps.
Our work suggests that plasmon propagation in graphene-based circuits
can be tailored using extremely compact nanostructures, such as ultranarrow
gaps. It also demonstrates that tip-enhanced near-field microscopy
is a powerful contactless tool to examine nanoscale defects in graphene
Strong Plasmon Reflection at Nanometer-Size Gaps in Monolayer Graphene on SiC
We employ tip-enhanced infrared near-field microscopy to study the plasmonic
properties of epitaxial quasi-free-standing monolayer graphene on silicon
carbide. The near-field images reveal propagating graphene plasmons, as well as
a strong plasmon reflection at gaps in the graphene layer, which appear at the
steps between the SiC terraces. When the step height is around 1.5 nm, which is
two orders of magnitude smaller than the plasmon wavelength, the reflection
signal reaches 20% of its value at graphene edges, and it approaches 50% for
step heights as small as 5 nm. This intriguing observation is corroborated by
numerical simulations, and explained by the accumulation of a line charge at
the graphene termination. The associated electromagnetic fields at the graphene
termination decay within a few nanometers, thus preventing efficient plasmon
transmission across nanoscale gaps. Our work suggests that plasmon propagation
in graphene-based circuits can be tailored using extremely compact
nanostructures, such as ultra-narrow gaps. It also demonstrates that
tip-enhanced near-field microscopy is a powerful contactless tool to examine
nanoscale defects in graphene.Comment: Nano Letters (2013); manuscript + supporting informatio