Electrons, Cameras, Action!

Upgrade of electron microscopy cameras offers cleaner, more-efficient imaging data at the CNSI

Figure 1: Image of the Titan 80-300. The monitors for each of the computers are labeled. The inset shows the stack of detectors below the microscope column. The Direct Electron DE64 is placed below the STEM detector to allow for maximum usage of its 28 cm2 sensor area, which is over 12 times larger than the Gatan Ultrascan 1000 CCD below it. (Image credit: Marc Roseboro/CNSI)

The California NanoSystems Institute at UCLA has changed or added five cameras connected to its suite of six transmission electron microscopes. Taken together, the upgrades will dramatically reduce noise in imaging while increasing efficiency and offering options to meet the distinct needs of different types of investigations. These instruments are available to users from UCLA and beyond at the EICN.Researchers in a variety of fields, from biology to materials science, rely on transmission electron microscopy to explore details and phenomena invisible to optical microscopes. Too often, though, traditional CMOS and CCD cameras can lead transient events being missed due to pixel read noise and inefficient electron detection. “With scintillator cameras only part of the image is reproduced in the chain of events involved in detecting electrons,” said Matthew Mecklenburg, Director of the Electron Imaging Center for NanoMachines, a CNSI Technology Center.

Figure 2: The two images show gold on carbon exposed to a 1200 e/Å2/s flux of electrons after two second of exposure in each case. The differences between the CCD (left) and direct electron camera in integrating mode (right) are clear. The contrast and detail in the latter camera shows sharper white-to-black detail between the atomic columns. The Fourier transform in each case is inset, and the detail in the rings (which correspond to different lattice spacings) show much more detail and contrast in the newer camera, compared to the decade older model. The new camera is 70 times faster, and is an excellent tool for in situ experiments.

In response to this problem, users at the EICN now have access to direct electron detecting cameras on all three of its field-emission-sourced instruments, the Titan 80-300, Titan Krios and TF20. With these state-of-the-art cameras, electrons are counted one-by-one and are only affected by the shot noise in the illuminating electron beam. The detectors improve the ability to reveal information out to single angstrom periodicities and improve the contrast acquired in an image to almost maximal efficiency.

“Electron counting cameras have revolutionized electron microscopy of biological structures,” said Matthew Mecklenburg, “and their high speed and increased sensitivity can also be a benefit for in situ TEM experiments, imaging of radiation sensitive materials, and high-resolution imaging.” The EICN’s Tecnai series of microscopes has gained two 16-megapixel CCD cameras — a Gatan Ultrascan for the T20 and a TVIPS TemCam F415MP for the T12 Cryo. In addition, a Gatan K2 direct electron-counting camera has been moved to the TF20. To the Titan series, the EICN has added a 4-megapixel CCD camera and a 64-megapixel camera, the Direct Electron DE-64.

“This camera will reveal the elusive atomic structure of radiation-sensitive materials and their nanoscale interfaces (e.g., lithium metal batteries, carbon-capture porous materials) that are critical for our transition to clean energy technologies,” said Yuzhang Li, assistant professor in chemical and biomolecular engineering.”The direct electron cameras have a linear mode and counting mode. The linear mode allows for higher fluence to facilitate imaging of materials science samples that are not sensitive to electron dosage. The counting mode operates at a limited fluence to prevent coincidence loss on a pixel and in this mode radiation-sensitive samples can be imaged to the highest degree of efficiency.

Figure 3: Zeolite ZIF 8 imaged in counting mode on the DE64 camera. The total fluence in the sample is approximately 2 e/Å2, which is low enough to preserve delicate materials such as zeolites and lithium metal at room temperature

EICN has sustained its operations through the pandemic, although applications to use its equipment must comport with campus guidance designed to help control the spread of the coronavirus. Investigators interested in using the upgraded cameras can contact eicnhelp@cnsi.ucla.edu.