Surface science with nanosized particles in a carrier gas

The dynamics of nanoparticles in a carrier gas are governed by the physical and chemical nature of the surface. The total surface area can be divided into an “active” and a “passive” part. The active surface is the surface on which transfer of momentum, energy, and mass from the gas to the particle takes place. The experiments show that the active surface may be determined in physically very different in situ experiments such as measuring the mobility b, the diffusion constant D, or the mass transfer coefficient K of the particle. The concept of the active surface manifests itself in scaling laws $\mathrm{Kb=}\mathrm{const},$ $\mathrm{KD=}\mathrm{const},$ and $\mathrm{Yb=}\mathrm{const},$ found valid over a large range of particle shapes and sizes. Y is the yield of low energy photoelectrons from the particles upon irradiating the carrier gas with light of energy below the ionization energy of the carrier gas molecules but above the photoelectric threshold of the particles. While K, D and b are independent of the chemical nature of the particles as far as we know today, the simultaneous measurement of Y provides a chemical fingerprint of the particles and allows one to observe, in combination with pulsed lasers as sources of light, the dynamical changes of the active surface while the nanoparticle is interacting with the carrier gas.