FEI Quanta FEG 250, User'S Operation Manual

Page: 91 / 228

Operating Procedures: Detector Types and Usage
5-19
Removing the GSED
CAUTION!
DO NOT change the order of the following procedure! Otherwise you
can damage the detector.
1. Remove the detector head from the lens insert first. Do this by
catching a fingernail or thumbnail (of the gloved hand) on the
FRONT of the yellow Torlon ring and pull down (there is a shoulder
machined into the Torlon ring which is specifically designed for this
purpose).
2. Pull the other end of the detector out from the connector.
PLA CONES
In some cases it is possible to install a cone on the actual gaseous
detector to achieve some special characteristic. Here are the
possibilities available for the user:
• The Standard Insert is installed at all times. Gaseous detector
and / or the PLA cone are pressed onto the insert to form a gas
seal. Chamber gas (flowing through the detector / PLA aperture) is
pumped out through the holes in the sides of the insert. A gas-
restricting aperture is found at the top of the insert.
Note:
This aperture also acts as a final or objective aperture. The
pressure above this aperture is considered to be very low. Any
pollution that accumulates on this aperture greatly affects the
image. If astigmatism is not possible to correct, it is usually a sign
that this aperture needs to be cleaned or replaced.
• The X-ray PLA cone (option - 500 µm aperture) is used for EDX
analysis (see Chapter 9) at a longer working distance (profile
extends down to 8.5 mm). Samples are imaged at 10 mm working
distance, which is the stage eucentric position and the collection
point of the EDX detector. It is used in conjunction with the LFD.
The longer profile of this cone minimizes the low voltage beam
dispersion and skirting of the primary beam in the gaseous
environment of the chamber, allowing more electrons to interact with
the specimen when focused and increasing the signal to noise ratio.
To fit the X-ray PLA cone, remove any existing detector or PLA cone
from the standard insert, then press the X-ray PLA cone into place.
• The Low kV PLA cone (500 µm aperture) is installed onto the
standard insert in case the LFD is used for low vacuum and low
voltage imaging (i.e. below 5 kV) to reduce beam loss in the gas. It
is used when imaging at shorter working distances (< 9 mm) and
restricts the lower magnification limit.
• The Hot Stage cone (option - 1000 µm aperture) is used with the
heating stage in combination with the hook wire or LFD. It can be
used without the hot stage when beam protection is desired with a
larger field of view.
Note:
When the Pole-Piece Configuration dialogue appears, select the
appropriate cone according to the figure and the name.