How to capture the TEM Images?

How to capture the TEM Image?

  1. Adjust "Selector", "Brightness" knob, and "Shift X" & "Shift Y" knob, where necessary.

  2. Press "Screen" (Lift up the fluorescence screen) so that the electron beam can reach the underneath CCD.

  3. On the software, press "Start View". Select a suitable exposure time, like "0.5s".

  4. Focus the sample with the "Obj Focus" using the Coarse and Fine knob.
    Clockwise rotation --> Increase the focusing power
    Anti-clockwise rotation --> Decrease the focusing power

  5. How to focus?
    Bright edge --> Underfocused --> Clockwise --> Until the edge is at minimal contrast
    Dark edge --> Overfocused --> Anti-clockwise --> Until the edge is at minimal contrast

  6. To capture the images, click "Start Acquire" or "START View". Then, save the images in Gatan Format “.dm3”.
    "    Start Acquire" allows you to acquire the TEM images with many frames, you can save all of them at the end of your TEM session. However, it takes some time to freeze the TEM image, which may degrade the quality of TEM images due to drifting. "Start View" is best for high-resolution TEM imaging as it freezes the TEM image instantaneously. However, the image needs to be saved immediately.

Notes:
1. Underfocus, In-focus, and overfocus

  • Overfocus: The current passing through the coil is too strong, so turning the "Obj Focus" knob anticlockwise reduces the current.

  • Underfocus: The current passing through the coil is too weak, so turning the "Obj Focus" knob clockwise increases the current.

Overfocus is also known as positive defocus; Underfocus is also known as negative defocus.
When you are not doing imaging, diffuse the electron beam to avoid the sample get sdegraded (the stoichiometric ratio, etc.).

2. Under low magnification, we sometimes intentionally capture the image at slightly underfocused conditions for better image contrast. However, the image has to be in focus at high magnification to see the lattice fringe.