Studying nanoparticles in-flight: applications of size-selected free nanoparticles

Experimental investigation of nanoparticles in form of free particles in an inert gas is advantageous due to absence of substrate effects. Gas-phase synthesis techniques offer many possibilities for producing and manipulating nanoparticles. The most advanced technique produces well-defined nanoparticles, by means of inert-gas evaporation in a flowing gas, size-selection on the basis of the electrical mobility and subsequent sintering into monocrystalline and quasispherical nanoparticles. The electrical charge obtained by nanoparticles allows further manipulation, such as the generation of well-defined nanoparticle pairs, in which the sizes of both the particles can be selected. The application of these well-defined nanoparticles for studying the sintering of metallic nanoparticles is demonstrated. The ability to deliver size-selected nanoparticle aerosols at larger flowrates, in this study up to 30 l/min, allows to deliver larger quantities of well-defined nanoparticles. The size-selection necessitates the charging of the nanoparticle aerosol. We show that photoionization by means of UV irradiation is able to charge nanoparticles with a high efficiency and that by optimizing the radiation intensity the amount of multiple charges can be brought to a minimum, resulting in a geometric standard deviation of the size distribution of 1.05.