FEI Themis Z S/TEM: XFEG + monochromator operation (unfiltered)

[@samadabdus5920]

Great video, I was just wondering what is the reason behind +ve focus for STEM and -ve for TEM? Also, why do alignments change over time, especially monochromator focus changes/deflects every couple of hours? Thank you

[@stanbilly6823]

thanks for the perfect video! I got a question about c3 off mode. Why do we need to pass the crossover counterclockwise when doing the alignment?

[@NicholasRudawski]

Hi Stan: expanding the beam CCW from crossover with C3 off results in the incident beam being convergent to parallel; if the beam was expanded CW from crossover with C3 off, the beam would be divergent (or spreading). The convergent to parallel beam geometry is needed to produce the best possible TEM images.

[@stanbilly6823]

Thank u!!!@@NicholasRudawski

[@NicholasRudawski]

@@stanbilly6823 sure thing; glad I could help

[@rayshen9739]

Just ask a silly question: what is the difference between FEI themis vs Thermofisher spectra?

[@NicholasRudawski]

Hi Ray: ThermoFisher acquired FEI company a couple years ago, so they now call all the microscopes by "ThermoFisher" instead of FEI. The Themis is now technically at a "ThermoFisher" Themis, but since most of us historically remember the brand as FEI, we still tend to call it by that brand. So the Themis and Spectra are two different models of S/TEMs; I think on paper the performance of the two instruments is probably pretty similar, but I'm not very familiar with the Spectra.

[@rayshen9739]

@@NicholasRudawski Understood! Really appreciate your answer!

[@toninegi01]

what does +ve and -ve Focus mean: over and under focus?

[@NicholasRudawski]

Hi Anuj: yes, you are correct; I actually am planning to do a video specifically about "focusing" so do be on the lookout for it!