Profiling of Particle Composition

Depth profiling of single airborne particles has been reported by Carson et al. (1995, 1997a), who showed that the use of variable laser fluences in single-particle laser ionization mass spectrometry can be used to probe thin films on particles in laboratory systems. At low laser intensities, only the surface layer is volatilized and ionized, whereas the entire particle can be vaporized and detected at higher intensities. 

Emission of electrons from the particle surface has also been used in laboratory studies to probe surface composition. Electron emission has been induced by UV irradiation, for example, by Burtscher and Schmidt-Ott (1986) to probe perylene on the surface of carbon particles. In a series of laboratory studies, Zie-mann et al. (1995, 1997, 1998) have demonstrated the potential utility of secondary electron yield measurements as a technique for probing particle surface composition. In this method, particles are bombarded with 

FIGURE 11.75 Measured secondary electron yields from the electron bombardment of 89-nm KC1 particles, 128-nm particles of dioctyl subacate (DOS), and KC1 coated with DOS of film thickness (in nm) shown (adapted from Ziemann and McMurry, f998). 

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