Ultra-low dose rate cryo-EELS mapping at atomic resolution with dose-fractionated spectrum imaging

Gatan instruments used

GIF Continuum^® K3^® IS, Gatan liquid nitrogen cooling holder, and eaSI™ spectrum imaging with DigiScan™ 3

Background

Beam-sensitive materials prove to be a challenge for atomic-resolution electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) even with modern high-brightness probes and highly efficient energy loss spectrometers. These materials cannot withstand the high probe currents typically applied in an analytical STEM. Cryogenic cooling of the specimen improves dose sensitivity but adds the complication of specimen drift and instabilities. Multi-frame spectrum imaging (SI) summation was proposed and successfully demonstrated as a means of improving both STEM image resolution and signal-to-noise ratio (SNR) [1]. For EELS, scintillator-based CMOS and CCD detectors are inadequate for multi-frame SI at low-dose and high speeds due to the detrimental effects of read noise. Direct detection, counting cameras are capable of nearly noise-free readout, making them ideal for multi-frame EELS SI acquisition at low dose [2]. Here, we demonstrate some of the advantages of this method for cryo-EELS mapping at atomic resolution of beam-sensitive material performed at atomic resolution.