Acquire a spectrum
- Find the general region of interest at low magnification; once located increase the magnification. Ensure that you chose an area with suitable thickness. A t/λ thickness map is ideal for this determination.
- Reduce the spot size and condenser aperture to typical values for microanalysis
- Put the beam on the feature of interest; select a region that appears highly electron transparent
- 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
- Make sure the center spot (disc) is in the center of the screen
- Lift the screen, then click the View button on the EELS palette to start a continuous view of the low-loss spectrum
- Click on the EELS status text to control the dispersion, aperture and energy offset. You can choose the energy offset by element from the periodic table icon.
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.
- Select Auto in the Exposure field of the EELS palette to use the auto exposure function.
- If you prefer manual mode, disable Auto and enter the Exposure time. Alternately, with the live EELS window front most, hitting the up/down arrow keys will double/half the current Exposure time.
- Choose among the four EELS detector settings (SNR, View, HDR, User) as needed for the experiment.
- SNR uses the lowest noise settings and is ideal for weak signals
- View provides a fast refresh of the spectrum with good dynamic range
- HDR is preferred when viewing strong signals and delivers the cleanest spectra
- 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.
- Use the Align ZLP button to adjust the ZLP to 0 eV
- Select Thickness button in the EELS Processing palette to estimate the thickness of your region of interest