Column Use Cases - Thermo Scientific Apreo User's Operation Manual

Column Use cases

The electron column can be operated in different Use cases
optimized for specific applications. To select the desired Use
case, use the Use cases module drop down list box.
You can immediately switch from one Use case to another. If high
voltage or beam current is out of the operating range of the new
Use case, it is set automatically to the closest possible value. If
the newly set conditions do not allow imaging, (e.g. it is not
possible to focus), transition is not allowed, and a warning is
shown in the application status window.
• Standard
This is the survey mode ideal for navigating and reviewing sites at lower magnifications. The A-Tube is on the
ground potential, and the default detector is the ETD in the Secondary Electron mode. Maximum probe current
is limited to 13 nA.
Probe currents above 13 nA are available for analytical applications such as EDS, WDS or EBSD. It should be
used when higher probe currents are required. Currents can be as high as 400 nA; the accelerating voltages
above 13 nA are available within 5 to 30 kV. The A-Tube is on the ground potential, the ETD detector should be
used for secondary electrons and T1 or DBS (optional) for backscattered electron imaging.
• OptiPlan
Here primary electrons are accelerated by the potential of the
Acceleration tube (A-Tube) and pass through the column at
high energy. They are decelerated back in between the T1
detector and the sample. Secondary as well as backscattered
electrons are also collimated into the final lens by the A-Tube
electrostatic field and detected by the Trinity detectors (T1, T2,
T3).
This mode is used for ultrahigh resolution electron imaging of
the sample at short working distances (1 – 2 mm). The A-tube
is at the highest potential and the T1 and T2 detectors should
be used. The full range of the Beam Deceleration mode (if
installed) is available for this Use case.
In this mode, the maximal working distance depends on the
landing energy (Beam Deceleration mode). It ranges linearly
from 5 mm (at 200 eV) to 70 mm (> 10 keV). It is possible to
use overview imaging at the maximal field of view, so there is
no need to switch the Use Case for navigation purposes.

Note
For detailed high resolution electron imaging, see the Help menu /
User Guidance item / High Resolution Imaging.
• Immersion
This Use case is available only with the Immersion lens
(option). The primary electrons are accelerated by the
potential of the A-Tube (Acceleration tube) and pass through the column at high energy. They are decelerated
back in between the T1 detector and the sample. Moreover, immersion magnetic field is applied in between the
pole piece and the sample to form the smallest possible beam diameter. The secondary as well as backscattered
electrons are collimated into the final lens and detected by the Trinity detectors (T1, T2,T3). Described
combination of the electro-static and magnetic lenses is called Compound lens (see Chapter 3 – Compound
Lens Filter module).
The Immersion Use case should be used to reach the ultimate performance – the best resolution. The optimal
working distance for ultra-high resolution imaging is suggested to the user by the Working distance indicator,
typically the lower the landing energy the shorter the optimal working distance. The maximal working distance
depends on the landing energy. It ranges linearly from 5 mm (at 200 eV) to 70 mm (> 10 keV). The maximal
field of view is working distance dependent and it ranges from one hundred micrometers to three millimeters.
Model difference
The low Vac mode can be used only with OptiPlan and Standard Use cases depending on the PLA (pressure limiting
aperture) installed on the pole piece.
5-16 User Manual
Operating Procedures: Optimizing Imaging
C O N F I D E N T I A L – limited rights
Feb 2018 Revision A