Beam Deceleration Module - Thermo Scientific Apreo User's Operation Manual

Beam Deceleration module

The Beam Deceleration module has the following features:
• On button – switches the BD mode On / Off. This is available
only in the HiVac mode and with the Beam On. When
switching the beam off, the BD mode switches off
automatically.
• Stage Bias adjuster – reflects the voltage applied to a stage
up to –4 000 V.
When the BD mode is on, a hook mark is placed behind the HV. In this case, the value
represents the energy of electrons reaching a sample surface (it is also stored within the
TIF file header).
imRatio = (HV + bias) / HV
Beam Deceleration Mode Imaging Procedure
1. Put the sample into the chamber and pump down to HiVac.
In the BD mode, a sample becomes the electrode. Its position, size, tilt and surface roughness influence imaging
quality. At optimal conditions the sample should be symmetrical, planar, have a size comparable to the detector
size, and be placed perpendicular to the column axis. Under other conditions, distortion, astigmatism and
blurring caused by chromatic aberration appear. This is even worse when the Immersion Ratio is higher.
2. Select the suitable HV and find an area of interest. Set the Eucentric Position and tune an image with the Direct
Adjustments module / Beam and the Stigmator Centering tabs (see Chapter 5). Using various displays, get the SE
and BSE images so you can observe different images simultaneously.
3. Click the On button. Gradually raise the Stage Bias (lower voltage); the SE / BSE image gets dark / light.
At low magnifications, an ETD image should become dark symmetrically around the window center. In other
cases, the sample can be tilted.
When a dark area is shifted with a Stage Bias change, the sample is possibly not parallel with the detector. With
the use of the Compucentric stage rotation / stage tilt, try to keep the dark area in the center of the screen.

Note
When a retractable detector is inserted, stage tilt is restricted via the UI. Overcome it manually (confirmation is necessary)
to keep the dark area in the center of the screen.
An image shift when changing the Stage Bias can be caused by imaging near the sample edge or any other edge.
4. Set the Stage Bias, considering the sample material (charging compensation, material contrast) and optimizing
the signal. Set the brightness, contrast and WD as required.
5. Tune the Direct Adjustments module / Beam and the Stigmator Centering tabs (both factors remember the HV and
Stage Bias last used).
6. Repeat steps 4 and 5 to get the best results.

Note
For the column Use case application suitable for the Beam Deceleration mode, see the Help menu / User Guidance item.
C O N F I D E N T I A L – limited rights
Revision A Feb 2018
Operating Procedures: Beam Deceleration
User Manual 5-21