Dose fractionation using multi-pass in-situ spectrum imaging

Gatan instruments

GIF Continuum^® K3^® System

Background

Traditionally, electron energy-loss spectroscopy (EELS) spectrum images were acquired using a single pass with dwell times on the order of 10's to 100's of milliseconds to limit the effect of detector read noise in optically coupled cameras. Drift, sample damage, and contamination were not apparent until several minutes into the acquisition or until it was finished. Multi-pass spectrum imaging (SI) sums several rapidly acquired passes until the desired accumulated dwell time is achieved. This allows for fast feedback on sample integrity and the ability to correct sample drift between frames. Summing multiple passes acquired with the K3 increases the signal-to-noise ratio (SNR) since direct detection is only limited by shot noise. Saving passes separately, rather than summing, allows for the removal of compromised passes post-acquisition and the ability to study the evolution of beam damage. This provides critical feedback for the design of future experiments.