Transmission electron imaging in the Delft multibeam scanning electron microscope 1

Our group is developing a multibeam scanning electron microscope (SEM) with 196 beams in order to increase the throughput of SEM. Three imaging systems using, respectively, transmission electron detection, secondary electron detection, and backscatter electron detection are designed in order to make it as versatile as a single beam SEM. This paper focuses on the realization of the transmission electron imaging system, which is motivated by biologists' interest in the particular contrast this can give. A thin sample is placed on fluorescent material which converts the transmitted electrons to photons. Then, the 196 photon beams are focused with a large magnification onto a camera via a high quality optical microscope integrated inside the vacuum chamber. Intensities of the transmission beams are retrieved from the camera images and constructed to form each beam's image using an off line image processing program. Experimental results prove the working principle of transmission electron imaging and show that details of 10-20 nm in images of biological specimen are visible. Problems encountered in the results are discussed and plans for future improvements are suggested.