Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles

Abstract

We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. First, aerosol photoemission studies can be performed for many different materials, including liquids. Second, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles.

Nanofocusing, shadowing, and electron mean free path in the photoemission from aerosol droplets

“…Details of the photoelectron velocity map imaging (VMI) spectrometers used in this study have been provided in previous publications [13,[19][20][21]. A sketch of the setup is shown in the SI, Figure S1.…”

“…1 in ref. [13]). However, these small droplets also do not exhibit nanofocusing because their size is below the limit where resonance phenomena occur…”

“…Wilson et al [10,11], the DESIRS beamline team at SOLEIL [12] and our group [13] used angle-resolved photoelectron spectroscopy and VUV radiation to visualize shadowing effects in the photoelectron angular distributions of small dielectric particles. The introduction of velocity map imaging for probing particle photoemission was crucial because it is currently the only method that allows one to obtain detailed information on the PEY, the eKE, and the PAD for small dielectric particles (~10 to 300 nm in radius).…”

“…In principle, this opens up the possibility to exploit aerosol photoemission for the study of other intriguing phenomena. We have recently proposed angle-resolved photoelectron spectroscopy of aerosol particles as a new way to determine the mean free path of electrons (eMFP) in condensed matter [13].…”

“…For details on the calculations of the internal electric field intensities (light intensity inside the droplet), the modelling of the photoelectron images for H 2 O, and the extraction of eMFPs for H 2 O we refer the reader to the SI, Figure S3 and section B and ref. [13]. Briefly, the internal electromagnetic field intensity is calculated with classical electrodynamics using frequency-dependent refractive index data [1,25,26] and SI, Table T1.…”