Aggregation effect on the infrared absorption spectrum of small ionic crystals

Abstract

The frequency spectrum of clusters of small ionic particles is calculated when the particle mutual interaction is described by a dipole-dipole interaction Hamiltonian. The crystallites are spheres of known bulk dielectric properties. The actual geometry of the cluster is taken into account. Clusters of increasing size (pair, triplet, quadruplet, etc. ) have been solved analytically. As expected, the dipolar broadening of the frequency spectrum of (optically active or inactive) surface modes increases with cluster size and compactness. From the spectrum of few-particle clusters, one obtains the long-wavelength modes of large linear or planar aggregates of such clusters by application of the Bloch-Floquet theorem. Application is made to ir optical absorption of NiO. The present approach is intermediate between the continuum model of a structureless powder on the one hand and microscopic calculations for single microcrystals of prescribed shape on the other hand.

Pore structure of thermally treated goethite (α-FeOOH)

“…Se). Subsequently, the IR spectra of he-usually broad absorption bands, presumably due to large anharmonicity contribution (26) or to particle aggregation (27). Nevertheless, when these effects are taken into account, the experimental IR spectra ofFigs.…”

Plasmon-induced near-infrared electrochromism based on transparent conducting nanoparticles: Approximate performance limits

“…The limitation to a dilute composite of nanospheres is important, though, since otherwise particleparticle interaction widens the plasmon absorption 26 compared to what is seen in Fig. 1 so that strong absorption in the NIR tends to extend also into the luminous range, and the same is true if nanoparticle clustering 27 or non-spherical shapes 28 are prevalent. Actually, such broadening effects are clearly visible in optical spectra for the nanoparticle films reported on in Ref.…”

Second Harmonic Generation from Coupled Surface‐Plasmon Resonances in Self‐Assembled Gold‐Nanoparticle Monolayers Coated with an Aminosilane

“…3). Clippe et al [20] offered the first theoretical explanation for the coupled resonance modes of two identical clusters. The clusters could be arranged as a linear chain of particles on a larger scale, an equilateral triangle, a tetrahedron, or face-centered-cubic-packed clusters, where each particle has a resonance mode.…”