Zn/F-doped tin oxide nanoparticles synthesized by laser pyrolysis: structural and optical properties

Zn/F co-doped SnO2 nanoparticles with a mean diameter of less than 15 nm and a narrow size distribution were synthesized by a one-step laser pyrolysis technique using a reactive mixture containing tetramethyltin (SnMe4) and diethylzinc (ZnEt2) vapors, diluted Ar, O2 and SF6. Their structural, morphological, optical and electrical properties are reported in this work. The X-ray diffraction (XRD) analysis shows that the nanoparticles possess a tetragonal SnO2 crystalline structure. The main diffraction patterns of stannous fluoride (SnF2) were also identified and a reduction in intensity with increasing Zn percentage was evidenced. For the elemental composition estimation, energy dispersion X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) measurements were performed. In general, both analyses showed that the Zn percentage increases with increasing ZnEt2 flow, accompanied at the same time by a decrease in the amount of F in the nanopowders when the same SF6 flow was employed. The Raman spectra of the nanoparticles show the influence of both Zn and F content and crystallite size. The fluorine presence is due to the catalytic partial decomposition of the SF6 laser energy transfer agent. In direct correlation with the increase in the Zn doping level, the bandgap of co-doped nanoparticles shifts to lower energy (from 3.55 to 2.88 eV for the highest Zn dopant concentration)

Chitosan-coated iron oxide nanoparticles obtained by laser pyrolysis

The structural and magnetic properties of iron oxide nanoparticles (NPs) synthesized by laser pyrolysis, as well as their chitosan-stabilized aqueous suspensions were studied in regards to the ratio between O2 and Ar. During the synthesis, the flow of Fe(CO)5 precursor vapors and C2H4 sensitizer molecules was kept constant, while the ratio between O2 and Ar in the reactive mixture was increased (1:4, 1:2, 1:1, and 2:1). The formation of small particles (under 4 nm in size) was observed at lower O2 concentrations, whereas their mean crystallite size increased to ∼14 nm for those formed from the richest O2 content, which also induced the formation of particles with the highest magnetization saturation (101.4 emu/g). Maghemite and/or magnetite phases were identified as the main components in all samples, while a small amount of α iron/iron carbides presence was detected with the exception of sample obtained at 1:1 O2 to Ar ratio. The formation of these minor phases reveals the interplay between oxidative and reductive processes which depend on O2 content and C2H4 reactivity at different temperatures. After chitosan loading, all aqueous suspensions presented excellent stability (zeta potential values over 76 mV). Moreover, the samples stabilized using low polymer concentration (0.05 g/l) displayed relatively low hydrodynamic sizes (110–125 nm)