#ElectronMicroscopy : What is the typical electron beam size in a) Analytical Transmission Electron Microscope b) High Resolution TEM c) Scanning Electron Microscope and d) Electron Probe Micro Analyser?
In terms of electron optic SEM and EPMA are basically the same thing (one optimized for imaging, another - for spectroscopy). Their minimal beam size is close to their resolution. TEM employs unfocused, mostly parallel beam. For best results it should be just a bit bigger than the field of view.
Dear Mohit Rattanpal , you gave a wrong answer. EPMA beam could be much smaller than 0.5 micron (up to a few nanometers). I have not worked with EPMA for 30 years, but even then resolution (and correspondintly a beam size) was about 7 nanometers.
Vladimir Dusevich Thanks for pointing out this. Let me again check and revert back to you.
Vladimir Dusevich Please check this.
Ref: Physical Metallurgy: Principles and Practice by V. Raghavan, PHI Publications.
However I will ask expert also and let you know.
Mohit Rattanpal , the book is wrong. With errors like this one I would not recommed cited book to anyone.
Having run both SEM and EPMA, I would like to weigh in. The answer is a bit nuanced. I agree with Vladimir that the book is probably not to be recommended. They do not give a very precise answer. The beam on an EPMA can be measured in nm. That is especially true on the newer, field -emission probes. However,
Probe beams are often not run as small as they can be. They are often defocused to illuminate an area of several microns to limit the electron flux at the sample. Too high a flux can lead to significant heating and migration and loss of elements. Look up analysis of Na in geological samples. Many of my samples were homogeneous and I often opened up the beam to 10 um.
Also, for x-ray analysis, the issue is not so much the beam size as the interaction volume. Look into Monte Carlo simulators and check out the diameter of the interaction volume for various voltages in your samples. That alone is a reason to not run analyses at high voltages whenever possible. One of our users was looking at the gradients in linescans at the edges of phases in a Al-Ag-Cu alloy. At 20 kV, it took about 2 um to fully transition from one composition to the next. At 8 kV, it took about 0.5 um. The spot size was just a very few nm in both cases. The interaction volume dominated the effects and was the principle of most importance. (In that sense, the book quote was close to the right answer but really needed to provide more explanation.)
Illustration to the post of Warren Straszheim from Article X-ray Microanalysis Artifacts Visualized
Poor understanding of X-ray microanalysis can lead some authors to "discovery" of unusuial diffusion (some papers were published even in respected journals).
Thank you. I hadn't thought to add pictures. Now that you have, and that I am presenting this material this afternoon, here you go with scaled interaction volumes overlaid.
Vladimir Dusevich , can you please stop spamming RG with your unreflected and unedited ChatGPT answers? You're really not helpful and confuse people.
Ronald Zallocco, I seriously doubt that Vladimir Dusevich is using AI in his answers. I have seen AI in other answers from people I do not know. I have known of Vladimir for many years and I suggest he knows what he is talking about. He is a resource to be valued.
On the other hand, I know nothing about you. Please give some substance to support your objections.
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