Low-energy photoelectron transmission through aerosol overlayers

Abstract

The transmission of low-energy (<1.8 eV) photoelectrons through the shell of core-shell aerosol particles is studied for liquid squalane, squalene, and di-ethyl-hexyl-sebacate shells. The photoelectrons are exclusively formed in the core of the particles by two-photon ionization. The total photoelectron yield recorded as a function of shell thicknesses (1-80 nm) shows a bi-exponential attenuation. For all substances, the damping parameter for shell thicknesses below 15 nm lies around 8 to 9 nm and is tentatively assigned to the electron attenuation length at electron kinetic energies of ≲1 eV. The significantly larger damping parameters for thick shells (>20 nm) are presumably a consequence of distorted core-shell structures. A first comparison of aerosol and traditional thin film overlayer methods is provided.

FIG. 1.

Scheme of the experimental setup consisting of devices for aerosol formation (aerosol atomizer, aerosol coating device), devices for aerosol selection and characterization (SMPS), the VMI photoelectron spectrometer with an ADL for the transfer of aerosols into the spectrometer, and a laser for photoionization of the aerosol particles.

FIG. 2.

Semi-log plot of the relative electron yield $\frac{Y}{Y_0}$ as a function of the shell thickness d for the example of squalane coatings. (a) Full squares: original experimental data assuming a constant core yield, Y₀ = Y₀(0). Open circles: experimental data after correction for optical effects in aerosol particles [Eq. (2)]. (b) Corrected experimental data (open circles); bi-exponential fit (full line); and fit with two single exponentials (dashed lines).

FIG. 3.

Square of the local light intensity $I^2$ relative to the square of the light intensity $I_0^2$ of the incoming light (not shown) for the 266 nm light in a plane through the center of the particle that is spanned by the directions of polarization (y) and propagation (x) of the light. Note the logarithmic color scale. Upper panel: bare NaB core with r = 74 nm. Lower panel: NaB core with r = 74 nm coated with a squalane shell of d = 77 nm.

FIG. 4.

eKE distributions of bare NaB cores (thick black line) and NaB particles with a 20 nm coating of squalane (thin red lines). The dashed red line is the unscaled spectrum, and the full red line is the scaled spectrum.