Apreo ChemiSEM System Features

In a conventional SEM, backscattered electrons are typically detected either with a below-the-lens detector or an in-column detector. One of the major advantages of the Trinity Detection System is the intense BSE signal detected by T1. The T1 detector is positioned at the bottom of the final lens, just a few millimeters above the pole piece. This placement allows a much larger opening angle for backscattered electrons to reach the detector compared to typical systems, which position the detector higher. As a result, the system achieves an outstanding signal-to-noise ratio (SNR), even at an analytical working distance of 10 mm. High SNR is essential for low-voltage and low-dose imaging, making this system particularly beneficial for examining beam- and charge-sensitive materials like polymers and polymer composites. Until now, these measurements would be performed with a BSE detector positioned below the pole piece. That space is now free, granting remarkable freedom and safety while tilting and moving the stage. 

Backscattered electrons emitted at angles close to the optical axis (high-angle BSE) provide compositional (atomic number) contrast, while those collected perpendicularly to the optical axis (low-angle BSE) offer topographic information. It is worth noting that, due to the T1 detector’s position and high SNR, the Apreo ChemiSEM System enables selective BSE detection by combining data from different detectors with the versatility of selecting the signals depending on the sample’s working distance. Both high-angle and low-angle BSEs can be segmented using the T1 and ETD detectors.

At longer working distances, the angular range of the T1 detector narrows, capturing only high-angle BSEs, while the ETD detector captures low-angle BSEs. Although the T1 and ETD detectors cover nearly the entire angular range, the highest-angle BSEs are not collected by T1. These electrons, which are almost parallel to the beam axis, provide strong compositional contrast that is lost in this setup. This issue can be resolved by moving the sample to a 5 mm working distance. By reducing the working distance, the highest-angle BSEs are directed through the T1 hole and onto T2, while T1 and ETD still capture high-angle and low-angle BSEs, respectively. This configuration simultaneously captures the complete range of backscattered electrons, separated into high, middle, and low angles. 

Secondary electrons (SE) are typically used to characterize surface morphology and, like backscattered electrons (BSEs), provide different information based on their emission angle. Low-energy SEs, emitted parallel to the optical axis with energies between 0 and 2 eV, are the most surface-sensitive. They offer detailed information about surface features and, under specific conditions, deliver charge contrast information. SEs with higher angles and energies (greater than 2 eV but still less than 50 eV) are less sensitive to sample charging but still provide morphological information.

In the Trinity Detection System, both high-angle and low-angle SEs are detectable simultaneously. Low-angle SEs are detected by T2, providing morphological information, while high-angle SEs pass through the opening in the T2 detector and are collected further up the column by T3. Because T3 is more sensitive to surface information and local charge, it can provide insights about the presence of organic residues or oxidation. Using only the T2 detector can be beneficial for insulating materials, as it avoids capturing charging artifacts, which would be clearly visible with T3.

Electron detection is one of the key determinants of quality for state-of-the-art SEMs. The unique design of the Trinity Detection System allows for selective detection based on energy and angle, providing enhanced contrast and information for both BSE and SE. For BSE, the entire angular distribution can be collected in a single scan. And thanks to the high signal-to-noise ratio of the T1 detector, BSE imaging can take place at low beam energies and currents. This is an ideal solution for beam-sensitive and insulating materials. Finally, low-energy and low-emission-angle SEs provide excellent surface information and charge contrast, whereas high-energy SEs allow for detailed morphological observations.