Ion-beam synthesis of zinc-based nanoparticles in SiO2

In this paper production process of Zn nanocrystals in SiO2 by using an implantation of high dose zinc ions with energy of 130 keV and annealing process in 700°C were described. Using electron microscopy was established that annealing causes extension of admixtures distribution on depth and zinc nanoparticles size increasing from approx. 1 - 6 nm to 12 - 18 nm. For prepared material AC conductivity measurements were made in temperatures range from liquid nitride temperature (LNT) to 373 K and at frequencies range from 50 Hz to 5 MHz. Strong frequency dependence on conductivity proves that in this nanocomposite Zn-SiO2 conduction takes place by electron hopping exchange (tunneling) between metallic phase nanoparticles. It was established that three activation energies of conductivity occurs in temperatures range of LNT – 373 K – in low temperatures ΔE1≈0.001 eV, in medium temperatures ΔE2≈0.025 eV and in higher temperatures area ΔE3≈0.096 eV. This is due to the presence of at least two types of nanoparticles. First there are zinc nanoparticles with zinc oxide coating, second there are nanoparticles without the coating. The highest activation energy occurs during electrons tunneling between nanoparticles with zinc oxide coating. Intermediate activation energy corresponds to tunneling from nanoparticle with coating to nanoparticle without coating or conversely. The lowest activation energy corresponds to electrons hopping between nanoparticles without coatings.