Abstrakt
The heterogeneous nanoparticles, i.e. the nanoparticles composed of parts from different materials, attracted significant attention nowadays because of their unique characteristics coming from the combination of properties of their individual counterparts. In our work we studied microstructural properties and the thermal stability and evolution of nanoparticles composed of silver core and polymeric shell.
Investigated core@shell nanoparticles were prepared by combination of magnetron-based gas aggregation cluster source (GAS) and simultaneous plasma enhanced chemical vapor deposition of hexamethyldisiloxane (HMDSO). The GAS was equipped with silver target and operated in DC mode.
A series of nanoparticles with various HMDSO concentration in the chamber was prepared. The properties of nanoparticles were investigated by combination of the small angle x-ray scattering - SAXS, x-ray diffraction - XRD, ultraviolet-visible spectroscopy and electron microscopy.
The changes in nanoparticles size distribution, shape, and the evolution of microstructural parameters with increasing temperature up to 450°C were described. Prepared samples differed in Ag core size and in thickness of the polymeric shell as well.
Besides, the size of Ag core and polymeric shell thickness strongly depends on the amount of HMDSO supplied to the system. The process without the HMDSO leads to the creation of Ag nanoparticles with mean diameter of around 40 nm.
The increase of HMDSO in the deposition chamber has the consequence in reduction of the nanoparticles size, the mean diameter of nanoparticles created with 9% of the HMDSO decreases to about 5 nm. The size of coherently diffracting domains (crystallite size) does not depend on amount of added HMDSO and stays around 5 nm.
However, the microstrain and stacking faults density increases with the concentration of HMDSO in the system. The annealing of nanoparticles to 450°C results in the annihilation of the crystal lattice defects, decay in the microstrain, stacking faults density and the relaxation of the lattice parameter.
The changes of nanoparticles sizes after annealing are obvious from measured SAXS and XRD patterns, see fig. 1. The comparison with pure silver nanoparticles shows that the polymeric shell around nanoparticles prevents nanoparticles fusion.
In the case of heterogeneous nanoparticles, the growth of nanoparticles occurs above 350°C, however this growth temperature for pure silver nanoparticles is fairly below 100°C.