Artifacts can exist in the low dose TEM/STEM images. For instance, the STEM image in Figure 1412 only has thousands of counts (normally millions of counts for good data acquisitions) so that the image is streaking and noisy and does not present a clear structure of the TEM specimen.

Figure 1412. Streaking and noisy STEM image.

In general, the streaking and noise mechanisms are very complicated and the troubleshooting process is very time-consuming if you are not lucky. For instance, the origins of such artifacts are mainly:
        i) A streaking artifact parallel to the scanning direction. Such streaking artifact is caused by a slow reaction time of the photomultiplier/readout electronics (e.g. Figure 1412). This streaking effect can be significantly reduced by increasing the dwell time (scanning slower) or increase the electron dose. Selecting intense diffraction spots or discs can also help increase the image intensity.
        ii) An artifact due to a random horizontal offset of scan lines. Such random horizontal offset can be induced by poorly electrical grounding, e.g. in Gatan DigiScan. In this case, the problem would be periodic.This problem can be fixed by changing a new firewire cable into a different working socket on the back of the DigiScan and/or on the firewire board on the computer, or a new DigiScan.
        iii) Instability of electron beam.
        vi) Defects or charging on STEM detector.
        v) Noisy environment. In this case, significant image shift is normally visible as well.
        vi) Multiple beams from the electron gun in the microscope.