I'm not so expert in diffraction, so I cannot answer for the SAED part of question (EBSD is usually a SEM technique, as far as I know), but the main advantages I see in using a 300 kV machine is the penetration depth (higher @ 300 kV) and a tiny theoretical improvement in resolution (but this depends very much on the parameters of the electron optical systems of the 2 hypothetical instruments). Also the kind beam damage is slightly different, but whether 300 is better or not, this depends on the samples you need to study.

Resolution can be effected by the wavelength of the light (the electron in the TEM), so the resolution will be better in the 300 KV TEM (the resolution can reach 1.75 A), also it depends on the type of the TEM, such as aberration corrected TEM (the resolution can be better at the same voltage than the TEM). EBSD is usually equipped in the SEM, to my best knowledge. Hoping this reply can help you!

Higher accelerating voltage will give higher brightness. This will help for high resolution and large diffraction regions.

But all these are materials dependent also.

Hello everyone,

Thank you for your comments. That was pretty enlightening. Today we at our centre had a similar discussion with the TEM Vendor (name not mentioned here) and he was also telling us the same thing about the differences between a 300 and 200KV systems. The price difference is pretty phenomenal (USD 300,000). But the major difference in the resolution for imaging is pretty low (1.7A for 300KV while 1.9A for 200KV). The vendor also mentioned that EELS would be a better option than a EBSD (as you have mentioned). They have mentioned about an omega filter (that comes with the EELS detector) that is in-situ placed under the sample holder that improves the imaging quality.

Abberation corrected TEM of course is a very sophisticated instrument and costs wayyyyyyyyy more than the generic ones.

Now my doubt from the interaction with 2 of the vendors is that : One of them says that 300KV electrons are faster than 200KV and hence the interaction time with the sample is very less and so cause much less damage to the material.

The second vendor said that 300KV electrons are like fast moving bullets and hence cause much more sample damage than the 200KV electrons.

So I would like to understand which of the statements holds true.

Thanks in advance,

Teja

Hi Tejabhiram,

Second vendor is wrong: at the same beam intensity damage to a specimen is less at higher accelerating voltages, because number of interactions is lower (even if each of interactions is more powerful). It is well known phenomena, and vendor should know it better.

At 300 kV the only thing you can have for granted is ability to use thicker specimens (it is often important). Resolution depends very much on the electron optics. TEMs are manufactured mostly in two flavors: biological TEM (increased contrast, a little bit worse resolution) and universal TEM (highest possible resolution). If 20 years ago biological TEMs were limited to 120 kV, now they may have accelerating voltage up to 300 kV (for cryo applications). So, first you have to choose which one you need. You can find best in resolution microscopes (with aberration correction) both with 200 and 300 kV voltage. So, things are a bit complicated in choosing right instrument. I would recommend to see (and discuss with vendors) which one is better suited for your applications. For example, even if you do not need slight improvement in resolution at 300 kV, you may find that 300 kV is better for electron tomography (thicker specimens – important for tomography).

Good luck in acquiring TEM!

Dear Vladimir,

Thank you for the comment. that gives me a better understanding of the TEM. I hope we get the best of instruments.

There are two main types of electron beam damage: Knock-on damage, in which atoms are displaced creating point defects, and damage due to inelastic interactions. the first type occurrs mainly in metals and can be minimized by going to lower voltages. The second occurrs mainly in ceramics and polymers and can be minimized by limiting exposure, increasing electron voltage, and using thin specimens. However, the same inelastic interactions that can cause damage are also the source of the EELS signal. EELS works better at lower voltages. So again, it depends...200 kV seems like a good compromise. Also ask your vendor why you should use an omega filter as opposed to a GIF, which is a better spectrometer for many applications.

Hello Claudia Maam,

First of all thank you for the explanation you have given for the electron sample interaction.

I think the reason for use of omega filter rather than GIF is the cost difference he is quoting between the two. I guess Omega filter comes at a lower price compared to the GIF filter maam. I would definitely ask the vendor to quote for the same.

Thank you,

Teja

As in theory 300kV might give a better resolution as they are working with a higher energy and, thus, lower wanvelength, it will be limited to amount of aberration correction. In that sense, final resolution will depend of the equipment hardware and must a point of discussion with the equipment manufacturer. The FEI Titan has been shown to provide1.4A atomic resolution at 80kV as well, for example.

What is for certain is that the number of interaction will be lower and the beam penetration higher. So... I would like to point that if you are considering working with thicker tomography samples or frozen specimens, you could carefully consider the 300kV as an option. Nevertheless, it should also be pointed that several implementations should be considered for working with tomography and cryosamples and, thus, lot of care will need to be taken during negotiation.

Dear Fabio Gomes,

Sir I had a small doubt even while talking to the vendors... what would be the maximum difference in the sample thicknesses that we would be able to analyze in the case of 300 and 200 KV?

I don't know if there is a short answer to that. There might be some way to calculate this taking into account the regular electron absorption of biological samples even though one would need to take into account Epon, Water and different embedding media. I am currently not aware of safe estimate though. You could check on section thickness people have reported for electron tomography with 200 and 300kV for a real life estimate.

Sure 3oo kv better

Dear Teja,

another thing to consider when deciding between the 2 voltages is depth of focus. Because of the higher energy, 300Kv instruments have a much larger range at which the specimen is "in focus". This is another reason they are better for tomography: more of the sample when tilted is at the same defocus. But it can also be useful for cryo single particle reconstruction work if larger particles are to be considered. It can be very difficult to get to the highest resolution in a reconstruction if the top of a particle is at one defocus and the bottom is at another. And for smaller particles the same principal applies if the whole image area is not exactly flat. If you plan to do any CTF correction in processing images, I would definitely recommend 300kv.

If I remember correctly that an electron mean free path is proportional to a square of accelerating voltage, then you can expect you can use twice as thick specimens at 300 kV. Of course, for best resolution you still need as thin specimens as possible.

Have a look at an excellent review on the properties of electron microscopes by Richard Henderson in Q. Rev. Biophys (1995) 28 (2): 171-93. This deals directly with the effects of different energies on resolution and other effects (eg. charging of the specimen). http://www.ncbi.nlm.nih.gov/pubmed/7568675