Transmission electron microscopes (TEM) primarily employ indirect cameras for electron detection in imaging, diffraction, and electron energy loss spectroscopy (EELS). Such cameras convert incident electrons to photons, which, through a fiber-optic network or lens, are coupled to a light-sensitive camera. This indirect detection method typically has a negative impact on the point spread function (PSF) and detective quantum efficiency (DQE) of the camera. Over the last decade, radiation-tolerant CMOS active pixel sensors, which directly detect individual, high-energy incident electrons, have been used in detectors to improve the PSF and DQE greatly. Such direct detection cameras have revolutionized the cryo-TEM field as well as have strong advantages for in-situ TEM in both imaging and diffraction applications.
EELS applications can benefit from improved PSF and the ability to count electrons. The improved PSF allows spectra to be acquired over larger energy ranges while maintaining sharp features and significantly reduced spectral tails. The ability to count electrons nearly eliminates the noise associated with detector readout and dramatically reduces the proportional noise associated with detector gain variations. This effectively leaves the shot noise as the limiting noise source present. The implication for EELS acquisition is that fine structure analysis becomes more straightforward for typical conditions and even possible for the case of low signal levels.
In this presentation, we review the current state of electrons counting detectors for electron microscopy with an emphasis on the system for EELS measurements.
Presenter
Liam Spillane, Ph.D., Analytical Applications Specialist
