Acquire a Spectrum

  1. Find the general region of interest at low magnification; once located, increase the magnification. Ensure that you choose an area with suitable thickness. A t/λ thickness map is ideal for this determination.

Acquire a spectrum
A typical TEM image of BN flakes on a lacy grid. Low magnification is used to identify ROI (left), and increased magnification is used further to identify ROI and sample thickness (right).

  1. Reduce the spot size and condenser aperture to typical values for microanalysis.

  2. Put the beam on the feature of interest; select a region that appears highly electron­ transparent.

  3. Select the diffraction mode on the TEM, then set the camera length to 5 – 20 cm to give a collection angle in the region of ~20 mrad.

  4. Make sure the center spot (disc) is in the center of the screen.

  5. Lift the screen, then click the View button on the EELS palette to start a continuous view of the low­-loss spectrum.

  6. Click on the EELS status text to control the dispersion, aperture, and energy offset. You can choose the energy offset by an element from the periodic table icon.

Acquire a spectrum

Note: Generally choose the smallest dispersion (largest eV/ch value) that still gives the required energy resolution. Assume at least 3 channels are needed to define the energy resolution (e.g., 0.5 eV/ch will yield at best 0.5 x 3 = 1.5 eV resolution). For systems with adjustable apertures, choose Hi-SNR (largest aperture) for mapping and general EELS, and choose Hi-Res for low-loss EELS and ELNES studies where the best energy resolution is needed.

  1. Select Auto in the Exposure field of the EELS palette to use the auto exposure function.

Acquire a spectrum

  1. If you prefer manual mode, disable Auto and enter the Exposure time. Alternately, with the live EELS window frontmost, hitting the up/down arrow keys will double/half the current Exposure time.

  2. Choose among the four EELS detector settings (SNR, View, HDR, User) as needed for the experiment.

    1. SNR uses the lowest noise settings and is ideal for weak signals

    2. View provides a fast refresh of the spectrum with a good dynamic range

    3. HDR is preferred when viewing strong signals and delivers the cleanest spectra

    4. Enables custom camera settings for the user; click on the setup icon to access and change the user settings

Note: View and Capture use the same camera settings.

  1. Use the Align ZLP button to adjust the ZLP to 0 eV.

Acquire a spectrum

  1. Select the Thickness button in the EELS Processing palette to estimate the thickness of your region of interest.

Acquire a spectrum