Electron Beam Attenuation and Energy Dissipation between 0 eV and Relativistic Energies

Abstract

The status quo of quantitative nanoanalysis using medium energy electrons will be briefly reviewed, demonstrating the impressive progress which has been made over the past fifty years.

This is in stark contrast to the understanding of the interaction of low energy electrons (LEEs) with surfaces which is rapidly gaining attention due to its importance for a variety of processes on the nanoscale: LEEs are not only essential for nanoscale analysis such as microscopy, CD metrology or attosecond physics but also act as agents inducing physico-chemical processes as in, e.g., electron lithography, electron beam induced deposition, astrochemistry and, last but not least, DNA-bond breaking induced by high energy ionising radiation striking biological tissue. Improvement in this field is complicated by the lack of benchmark experiments specifically designed to obtain information on individual physical parameters or processes.

In the present talk, a recently proposed experimental approach will be described in which the quantitative knowledge of the medium energy range is used to gain information about the (poorly understood) low energy range. This is done by using medium energy primary electrons as messengers of the depth of creation of low energy secondaries. Measuring the secondary electron intensity as a function of depth of creation, the attenuation law in the low energy range is quantified.

In the case of polymethylmethacrylate, it is found that the attenuation law is non-exponential, but is rather made up of two exponential functions, corresponding to two different groups of electrons playing a role in the energy dissipation process. The attenuation lengths of both groups are measured and essentially agree with a theory used for decades in astrophysics ––albeit with units expressed in nm rather than lightyears–– and providing electron attenuation lengths in the range between 0 eV and relativistic energies.

Bio Wolfgang S.M. Werner is Professor of Physics at Vienna University of Technology in Austria. His main field of research is electron spectroscopy, in particular, the quantitative interpretation of electron spectra for surface analysis.