Backscatter imaging is primarily a compositional imaging mode, although it can be used on samples which exhibit excessive charging or on samples which provide poor SE images. The BSE detector can detect the greatest amount of signal if the stage is at zero degrees tilt. The user may need to adjust the current or spot size to increase contrast in the image.
1. Select Analysis mode in the Column SetUp window. Normal and UHR-A modes may also be used. If you use Normal or UHR-A modes and need to increase current:
1.1. Raise the emission current to no more than 20 µA. This will increase the signal to noise ratio without affecting the resolution or alignment settings.
1.2. Increase the spot size using the Cond Lens 1 setting in the Column Set-up window. The lens is set to a default of 5. A setting of 1 creates the largest spot size and 16 the smallest.
2. Before switching to BSE collection, perform alignments and stigmation in SE mode. It is important to keep the beam current higher while in BSE mode.
3. Click on the Signal Control icon in the bottom right of the screen. Check the SE/BSE box and using the slider, adjust the voltage -50 to -70 V. Next, adjust the brightness and contrast and re-focus the image.
4. The default settings are:
- Emission current = 10 µA
- Condenser Lens 1 = 5.0 to 8.0
- Aperture = 50 µm