Point-Spread Function of the Optics in Scanning Electron Microscopes

TL;DR

This paper reports the first measurement of the point-spread function of optics in an uncorrected SEM by reconstructing probe wavefunctions from focal-series images, enabling potential aberration correction and improved imaging.

Contribution

It introduces a method to recover probe phase information and determine the PSF of SEM optics without multipole correctors, advancing SEM imaging techniques.

Findings

Reconstructed probe intensities from focal-series images.

Reported PSF for 20 keV SEM without aberration correction.

Demonstrated potential for aberration-free SEM imaging.

Abstract

Point-spread function of the probe forming optics ($PSF_{optics} $) is reported for the first time in an uncorrected (without multipole correctors) scanning electron microscope (SEM). In an SEM, the electron probe information is lost as the beam interacts with the specimen. We show how the probe phase information can be recovered from reconstructed probe intensity estimates. Controlled defocus was used to capture a focal-series of SEM images of $28.5\;nm $ gold ($\mathrm{Au} $) nanoparticles ($\mathrm{NPs} $) on a carbon ($\mathrm C $) film. These images were used to reconstruct their respective probe intensities to create a focal-series of probe intensities, which were the input to the phase retrieval pipeline. Using the complete description (intensity and phase) of the electron probe wavefunction at the specimen plane, we report the $PSF_{optics} $ for multiple data sets for beam energy $E\;=20\;keV\; $. This work opens up new possibilities for an alternative way of aberration correction and aberration-free imaging in scanning electron microscopy.