Dynamics of Ternary Cu–Fe–S2 Nanoparticles Stabilized by Organic Ligands

Chalcopyrite-type (Cu–Fe–S2) ternary nanocrystals stabilized by long aliphatic chain ligands could be considered as isolated hard nanoobjects dispersed in a soft network of organic ligands. The main attention was paid to the behavior of the particles whose average size was varied in a controllable manner from 3 to 20 nm. Dynamics of the nanoparticles was studied by applying Mossbauer spectroscopy. The fast dynamics could be described by a two-level environment. The deeper level (atomic) was practically the same as for bulk material except for the Debye temperature, but the higher level (particle motion) was described by the classical harmonic oscillator with the spring constant dramatically softening with increasing temperature. Such behavior led to a fast decrease of the fraction detectable by Mossbauer spectroscopy with increasing temperature. The induced internal oscillations within a particle by the surrounding thermal bath additionally contribute to the shift of measured spectra. Slow dynamics was ch...