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

A₂MnXO₄ Family (A = Li, Na, Ag; X = Si, Ge): Structural and Magnetic Properties

Four new manganese germanates and silicates, A₂MnGeO₄ (A = Li, Na) and A₂MnSiO₄ (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. Li₂MnGeO₄ is orthorhombic (<i>Pmn</i>2₁) layered, isostructural with Li₂CdGeO₄, and the three other compounds are monoclinic (<i>Pn</i>) cristobalite-related frameworks. As in other stuffed cristobalites of various symmetry (<i>Pn</i> A₂MXO₄, <i>Pna</i>2₁ and <i>Pbca</i> AMO₂), 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>3̅<i>m</i>) structure typified by CsAlO₂. The sublattices of the magnetic Mn²⁺ ions in both structure types under study (<i>Pmn</i>2₁ 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 Li₂MnSiO₄ 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. Ag₂MnSiO₄ remains paramagnetic down to 2 K, but A₂MnXO₄ (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>_N for all AFM phases. We constructed the magnetic phase diagrams for A₂MnXO₄ (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