Scanning Transmission Electron Microscopy (STEM) was first applied in a TEM. The idea is to navigate a beam over an area with a very fine probe similar as in SEM, but to collect transmitted electrons through a very thin sample (50-250 nm) to form images. In this mode, by varying the collection angle of the electron signals underneath the sample, Z-contrast imaging is possible of which the intensities render back directly to the composition or concentration. It also enables EDS mapping but with a much higher spatial resolution since the interaction volume is much reduced in the case of thin section samples.
Low-voltage STEM is a dedicated term for STEM mode performed in an SEM. The highest possible acceleration voltage of the electron beam in SEM is 30 kV, which is much lower than 80-300 kV in modern TEMs. Thus to avoid conflicts, the STEM imaging in SEM is referred to as LV-STEM, or Transmission SEM (TSEM).