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-substrate separation, Dts , using atomic force microscopy AFM.and high resolution scanning electron microscopy HRSEM.. For low energy density Eds1.04 Jrcm2. ablation of Si into He at pressures of 0.5, 1.5, 4 and 10 Torr, large nanoparticles were most numerous at Dtss10 mm, with smaller nanoparticles found at 20 mm and 40 mm. For each Dts 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 Eds0.74 Jrcm2 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 Dts were qualitatively similar to those found for Si in He. q1998 Elsevier Science B.V.