“Hello my name is Xiaoxia Gao from the user
nano technology from the University of Washington.
Today we are going to operate the transmission
electron microscope the model is FEI Tecnai
F20”
In a transmission electron microscope an electron
beam from the electron gun, passes through
an electromagnetic condenser lens , through
the sample, through an objective lens and
then down to a phosphor screen or CCD camera.
The condenser lens controls the size and intensity
of the beam hitting the sample. The objective
lens controls the magnification.
TEM images show internal structures of specimens
with magnification up to one million times
revealing structures in atomic resolution.
The first step is to prepare the sample and
mount it in the holder.
Remove the cover tube from the single tilt
holder. Insert the tool into the hole and
gently lift the clamp.
Place tissue paper beneath in case the sample
falls off. This sample has gold nanoparticles
on a copper grid. Place the side with the
particles facing down inside the specimen
carrier. Gently lower the clamp. Replace the
cover tube.
Carry the sample with a hand over the end
so that arm can’t slide out.
Place the copper cold fingers slowly into
a Dewar of liquid nitrogen. Top- off the Dewar
with additional liquid nitrogen. This will
keep the sample cold.
The TEM uses four pieces of software which
should be opened in order.
Open tecnai user interface software PEUOL
and you will hear a “click click” which
confirms that the microscope is communicating
with the computer.
On the second monitor we see the DigitalMicrograph
software.
The third software is TIA- “TEM imaging
and analysis” which is used for recording
Scanning TEM and EDS.
The last software is the RTEM Control.
Select “setup”, “vacuum” and “turbo
on” and hear the vacuum pump sound. After
3 minutes the “Turbo On” boxes changes
to yellow.
In the user interface software the box on
the lower left tells the magnification and
the microscope mode, currently TEM bright
field and 175,000 magnification.
To the right the beam energy and spot size
are shown. While setting- up the spot size
will be 5 and during operation it will be
3. The exposure time tells you the brightness
and illumination of the beam.
The lower left box with L1, L2, L3s reflect
the left control panel and the R1, R2 and
R3 shows the state of the right control panel.
The multifunction controls are used for several
functions in different modes.
In the right bottom box select “vacuum overview”
to show the status of the vacuum system and
valves.
Now the “Turbo on” button is yellow indicating
the turbo pump has reached its full function
and the TEM is ready to receive the sample.
Take the holder out of the support . Place
the little pin on the holder in the 5 o’clock
position with a twist adjustment.
The light goes on, the valves are opened and
the pump evacuates the sample chamber. You
must wait for several minutes until the light
goes off or you could crash the vacuum.
You must also tell the computer that it is
a single tilt holder so that the holder can
be controlled with a joystick.
When the light goes out and the “airlock”
status changes to “column valves” the
sample chamber has been evacuated.
Now turn the holder counterclockwise and hold
it as the vacuum sucks the holder slowly in.
Now turn off the “turbo” pump.
After the holder has been inserted the vacuum
in column should read 6 and you can start
to adjust the beam.
Click the “column valves closed” and the
button changes from yellow to gray and the
status reads “ready”.
Take the cover off the phosphor screen.
If you don’t see a beam, decrease the magnification
with the magnification dial on the right control
panel.
At low magnification you see a bright spot.
As you increase the magnification you can
see the copper grid.
Use the joystick to move the sample.
When you change the magnification you also
have to adjust the intensity to illuminate
the whole field of view.
Counter clockwise condenses the beam and clockwise
spreads the beam.
Next we will do alignment
Use the trackball to move the beam to the
center, spread the beam, increase magnification
and then condense the beam.
The rings are caused by diffraction.
Click “eucentric focus” button on the
right control panel to reset the objective
to the default value.
Use the z button on the right control panel
and try to make the rings disappear.
Increase the magnification to 125K. Again
use the trackball to center the beam, condense
the beam and use the z buttons again to make
the rings go away.
Next we must center the C2 aperture.
Set the C3 aperture to position 3.
Use the trackball to center the beam. Use
the intensity control to condense the beam
and then spread the beam. Notice that the
beam expands off center indicating the C2
aperture should be adjusted.
Rotate the C2 dials to center the beam, one
dial moves it in the x and the other dial
moves centers it in the y direction
Again condense the beam with the intensity
button and open it to confirm that the beam
remains on center.
Next we adjust the condenser stigmation. Click
on “tune”, and “condenser” from the
stigmator menu.
Use the “Multifunction knobs (MF)” on
either side of the scope to adjust the condenser
stigmation in both x and y directions to ensure
the beam is round and expands concentrically.
After you are finished, be sure to click “none”
otherwise the multifunction will continue
to control the stigmation.
Now we do direct alignments.
Select “ Tune”, “user interface”,
“Direct alignments” and beam tilt ppX.
Notice that there appears to be two beams.
Adjust multifunction X and Y until the two
beams merge to one.
Click Done to save this setting.
Repeat for beam tilt ppY, and adjust the multifunction
X and Y knob until there is one beam image.
Select “Beam shift and center the beam it
with the multifunction key and then click
Done.
This saves the position of the beam so it
can be recalled later if it gets lost. The
trackball position can not be saved.
Select “Rotation center”.
The beam begins to wobble and the image moves.
Adjust the multifunction dial until the movement
of the image is minimized and the edge appears
simply to go in and out of focus.
Click done to finish the direct alignments
Click Gun, FEG registers. Type a name like
“TEM” and save the alignment settings
for future use.
