Scan Speed/Dwell Time in TEM/STEM Imaging and Elemental Mapping
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The signal in STEM images is typically smaller than that in equivalent CTEM images. Therefore, because we need a certain dwell time to collect sufficient signal, we normally take relatively small fields of view in STEM imaging in order to avoid taking an unfeasibly long time for large fields of view.

Typical high-dose STEM imaging conditions with a dose of ~1.0 x 108 e-2 are an electron beam current of ~50 pA, a pixel dwell time of 20 µs, and a pixel size of 0.05 Å2. However, the most straightforward method to lower the electron dose is to reduce the pixel dwell time (i.e., increasing the STEM scanning speed). Typical low dose STEM imaging can be performed at a dose of ~15-20 e-2 with a probe current of ~1 pA and a scan speed of 1.0 µs per pixel.

In EELS data acquisition, higher energy edges require longer dwell times.

 

 

 

 

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