3 research outputs found
Impact of Metal-Optical Properties on Surface-Enhanced Infrared Absorption
Surface-enhanced
infrared absorption (SEIRA) spectroscopy using
resonant metallic nanostructures is increasingly attracting interest
during the last decade. Nevertheless, the impact of the metals’
intrinsic properties on SEIRA is still little studied. We present
an experimental work on this topic, examining the infrared-optical
resonance spectra of linear nanoantennas made of five of the most
common metals (gold, silver, copper, aluminum, and iron) with respect
to the intrinsic and radiation damping. Highly material- and size-dependent
ratios of the two damping contributions were found and discussed.
Using layers of organic probe molecules, we obtained SEIRA enhancement
factors for the different nanoantennas and experimentally verified
the predicted relationship between the plasmonic damping mechanisms
and the SEIRA enhancement. The multitude of our experimental data
for the ratio between the intrinsic electronic damping and the radiation
damping is compared with the measured SEIRA enhancement of the various
nanoantennas and therefore deliver the proof that the best SEIRA enhancement
is achieved when both damping mechanisms equally contribute. Furthermore,
it is shown that for a given nanoantenna geometry, the red-shift away
from the plasmonic extinction maximum is strongly dependent on material
parameters
Chemical Identification of Individual Fine Dust Particles with Resonant Plasmonic Enhancement of Nanoslits in the Infrared
We
demonstrate the capability of single plasmonically active nanoslits
for sensing of small fine dust particles via surface-enhanced infrared
absorption (SEIRA) spectroscopy. Investigating phononic excitations
of individual spherical silica particles coupled to the plasmonic
excitation of single nanoslits, we are able to detect and chemically
identify single spheres with diameters of 240 nm by their enhanced
phononic signal. The single silica spheres in nanoslits lead to Fano-type
phononic signals on the plasmonic background. The enhancement of the
phononic silica signal is highest for particles located in the middle
of the slit, in accordance with the FDTD-simulated near-field distribution
along the slit at resonance. Our results reveal, that resonant plasmonic
nanoslits are promising substrates for SEIRA spectroscopy of fine
and ultra fine dust particles and guide the way toward SEIRA based
dust sensing devices
A<sub>2</sub>MnXO<sub>4</sub> Family (A = Li, Na, Ag; X = Si, Ge): Structural and Magnetic Properties
Four new manganese
germanates and silicates, A<sub>2</sub>MnGeO<sub>4</sub> (A = Li,
Na) and A<sub>2</sub>MnSiO<sub>4</sub> (A = Na, Ag), were prepared,
and their crystal structures were determined using the X-ray Rietveld
method. All of them contain all components in tetrahedral coordination.
Li<sub>2</sub>MnGeO<sub>4</sub> is orthorhombic (<i>Pmn</i>2<sub>1</sub>) layered, isostructural with Li<sub>2</sub>CdGeO<sub>4</sub>, and the three other compounds are monoclinic (<i>Pn</i>) cristobalite-related frameworks. As in other stuffed cristobalites
of various symmetry (<i>Pn</i> A<sub>2</sub>MXO<sub>4</sub>, <i>Pna</i>2<sub>1</sub> and <i>Pbca</i> AMO<sub>2</sub>), average bond angles on bridging oxygens (here, Mn–O–X)
increase with increasing A/X and/or A/M radius ratios, indicating
the trend to the ideal cubic (<i>Fd</i>3Ì…<i>m</i>) structure typified by CsAlO<sub>2</sub>. The sublattices of the
magnetic Mn<sup>2+</sup> ions in both structure types under study
(<i>Pmn</i>2<sub>1</sub> and <i>Pn</i>) are essentially
the same; namely, they are pseudocubic eutaxy with 12 nearest neighbors.
The magnetic properties of the four new phases plus Li<sub>2</sub>MnSiO<sub>4</sub> were characterized by carrying out magnetic susceptibility,
specific heat, magnetization, and electron spin resonance measurements
and also by performing energy-mapping analysis to evaluate their spin
exchange constants. Ag<sub>2</sub>MnSiO<sub>4</sub> remains paramagnetic
down to 2 K, but A<sub>2</sub>MnXO<sub>4</sub> (A = Li, Na; X = Si,
Ge) undergo a three-dimensional antiferromagnetic ordering. All five
phases exhibit short-range AFM ordering correlations, hence showing
them to be low-dimensional magnets and a magnetic field induced spin-reorientation
transition at <i>T</i> < <i>T</i><sub>N</sub> for all AFM phases. We constructed the magnetic phase diagrams for
A<sub>2</sub>MnXO<sub>4</sub> (A = Li, Na; X = Si, Ge) on the basis
of the thermodynamic data in magnetic fields up to 9 T. The magnetic
properties of all five phases experimentally determined are well explained
by their spin exchange constants evaluated by performing energy-mapping
analysis