LabAdviser/314/Microscopy 314-307/Technique/Holo/Off-axis ETEM: Difference between revisions
| Line 83: | Line 83: | ||
# Put the viewing screen down (with R1 button) | # Put the viewing screen down (with R1 button) | ||
# Reset the TEM to its initial conditions: | # Reset the TEM to its initial conditions: | ||
::* Switch to TEM mode ( | ::* Switch to TEM mode (Gun → BeamSettings → Click on TEM button).Turn down the volume knob of the biprism. Then turn off this box. | ||
::* Reset the FEG: Gun | ::* Reset the FEG: Gun tab → FEG Register → Choose the correct register → Click on Set | ||
:::* This will reset the monochromator to its initial state aswell | :::* This will reset the monochromator to its initial state aswell | ||
# Turn off the power supply box in the back of the room. | # Turn off the power supply box in the back of the room. | ||
# Swap the cables at the SAD apertures (from “Power” to “Ground”) | # Swap the cables at the SAD apertures (from “Power” to “Ground”) | ||
# Remove the biprism/SAD aperture (lever from left to right) | # Remove the biprism/SAD aperture (lever from left to right) | ||
== Image Analysis in GMS3 == | |||
Instead of relying solely on post-mortem image analysis, GMS3 on the ETEM has the necessary image analysis for holograms. To do in-situ image analysis, the Holography mode in GMS3 can be used. | |||
# Click the Holo3 tab: Reconstruct | |||
::* If you have a reference hologram acquired, specify this in the pop-up window. | |||
::* Check off the “Choose sideband manually” (it is unchecked per default) | |||
::* In the pop-up FFT, click either of the sidebands by left-click | |||
::* Press enter | |||
::* Set the radius of the applied mask → The default of 1/3 the distance to the center band is usually sufficient | |||
# Afterwards, 3 windows will open: The amplitude image (“A”) and the phase image (“P”) and the contrast (“C”) | |||
# If you want to unwrap the phase: | |||
::* Click the phase image (“P”) | |||
::* Right click the image and select ROI | |||
::* Draw the ROI over the interference pattern (you don’t need to unwrap parts outside the interference pattern) | |||
::* In the holography section, click “Unwrap Phase” | |||
# Draw line profiles in the unwrapped phase and measure the potential (e.g. the MIP) | |||
::* You can increase the ROI by pressing crtl+ | |||
::* window will also pop up, the width is set by the pixel size of the ROI | |||
== Notes/Tips == | |||
# Black lines appear in the image: | |||
This occurs due to the dark/Gain reference image is not correct. In order to fix this, remove the biprism/SAD (lever from left to right). Reset the FEG (Gun tab → FEG Register → Choose the correct register → Click on Set) and set it to TEM mode (Gun → BeamSettings → Click on TEM button) | |||
First, prepare the gain reference: | |||
One the OneView Computer (GMS3), go to Help → User → Power User. Lift the screen (R1) | |||
In GMS3 click camera → Prepare Gain reference → Follow the directions in GMS3 by tuning the condenser lens strength (Intensity) to a signal of 1000e- and later 4000e- (tune the monochromator if necessary) | |||
After Gain reference, prepare dark reference by first lowering the screen and turning off the beam (Column valves): | |||
In GMS3, click camera → Prepare Dark Reference (roughly 25min) | |||
# Avoid Fresnel fringe in the camera’s field of view, so center the biprism wire accordingly | |||
::* Fresnel fringes occur on the edge of the intereference pattern due to the edge of the biprism. It can be observed when setting the biprism to 0V | |||
# Obtain reference holograms directly after each object hologram for every condition | |||
# Acquire at least 3 of each pair per feature/setting used | |||
# Do the rotation centering before adjusting objective focus | |||
# Go to a high enough biprism voltage to have fine enough fringes that will lead to non-overlapping central and side bands in the FFT | |||
# If you see features in the FOV that were not intended to be there, it means that there are features in the reference wave. Do not be confused, move the sample a bit and see what is what in the interference pattern | |||
# If you see a blister on the biprism, it means the biprism is contaminated at this region. Move the biprism by adjusting the knobs on the SAD aperture until the blister is not there | |||
::* You don’t want a curved interference pattern, the lines should be straight | |||
# Do not jump around or cause vibrations Move the chair and yourself away from the desk if necessary | |||
# If the biprism is not stable, even after waiting, tab either of the knobs of the SAD ever so slightly. It is possible the SAD aperture is moving, tabbing will help it fall into a stable position. | |||
# Name the reference and object holograms appropriately. I usually have a string for the file along the lines: Sample_Magnification_BiprismVoltage_ExposureTime_Obj_Number for object holograms, and “Obj” is “Ref” for reference holograms. | |||
::* You need to know the biprism voltage and exposure time for later documentation, since these values determine the width and carrier frequency and are always reported in literature. | |||