Connecting structurally and dynamically detected signatures of supramolecular Debye liquids

The monohydroxy alcohol 2-ethyl-1-hexanol mixed with the halogen-substituted alkyl halides 2-ethyl-1-hexyl chloride and 2-ethyl-1-hexyl bromide was studied using synchrotron-based x-ray scattering. In the diffraction patterns, an oxygen-related prepeak appears. The concentration dependence of its intensity, shape, and position indicates that the formation of the hydrogen-bonded associates of monohydroxy alcohols is largely hindered by the halogen alkane admixture. Using dielectric spectroscopy and high-resolution rheology on the same liquid mixtures, it is shown that these structural features are correlated with the relaxation mechanisms giving rise to supramolecular low-frequency dynamics.

Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers

We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots.

Supramolecular x-ray signature of susceptibility amplification in hydrogen-bonded liquids

Mixing two nonconducting hydrogen-bonded liquids, each exhibiting a low dielectric relaxation strength, can result in a highly electrically absorbing fluid. This susceptibility amplification effect is demonstrated for mixtures of monohydroxy alcohols. Whereas in the pure liquids a tendency to form ringlike low-dipole moment clusters prevails, in the mixtures such supramolecular structures are disfavored leading to an up to tenfold enhancement of the dielectric loss. The compositional evolution of density and mean cluster-cluster separation is traced using x-ray scattering and indicates deviations from ideal mixing with decreased C-C but simultaneously increased O-O correlation lengths. Thus, the variation in the supramolecular absorption strength could be tracked using a static scattering technique. These observations are in harmony with volume exclusion and ring open effects that predict an optimized susceptibility amplification for mixtures in which the two components occupy equal volume fractions as experimentally observed.