Silicon and zinc telluride nanoparticles synthesized by pulsed laser ablation: Size distributions and nanoscale structure

Size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure and target-sub strate separation, D _ts , using atomic force microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). For low energy density (E _d = 1.04 J/cm ² ) ablation of Si into He at pressures of 0.5, 1.5, 4 and 10 Torr, large nanoparticles were most numerous at D _ts = 10 mm, with smaller nanoparticles found at 20 mm and 40 mm. For each D _ts value a maximum of the mean nanoparticle diameter occurred for a He pressure near 6 Torr, in contrast to other recent measurements in which the size of Si nanoparticles increased monotonically with the He pressure. High resolution Z-contrast transmission electron microscopy (HRZTEM) and electron energy loss spectroscopy (EELS) revealed that ZnTe nanoparticles formed by ablation into nitrogen at E _d = 0.74 J/cm ² consisted of a crystalline ZnTe core surrounded by an amorphous ZnO shell. Growth defects and surface steps were clearly visible in the ZnTe crystalline core. The dependencies of the mean diameter of ZnTe nanocrystals on nitrogen pressure and D _ts were qualitatively similar to those found for Si in He.