Among
the numerous point vapor sources, microsecond-pulsed spark
ablation at atmospheric pressure is a versatile and environmentally
friendly method for producing ultrapure inorganic nanoparticles ranging
from singlets having sizes smaller than 1 nm to larger agglomerated
structures. Due to its fast quenching and extremely high supersaturation,
coagulational growth already begins at the atomic scale at room temperature.
On the basis of this knowledge, we develop a simple semiempirical
yet versatile model for predicting the size distribution of singlet
particles as a function of the process conditions. The model assumes
that a plume of a turbulent aerosol flow flares out from a concentrated
point source, eventually reaching the walls of the confinement where
a fraction of the particles is deposited. Despite the complexity of
the entire process, the concentration and size evolution of particles
can be adequately described by a first-order differential equation
accounting for coagulation, turbulent dilution, and diffusional deposition
to the walls. The model provides a simple and practical tool that
can generally be used to design and control point vapor source reactors
for the synthesis of singlets with tunable sizes starting from that
of single atoms
