This was a great lecture! I have been wanting to learn more about the EM scope for quite some time now, and this really helped. I am excited to watch the rest of your TH-cam lectures.
🎯 Key Takeaways for quick navigation: 00:05 *Electrons escape a bent wire due to collisions, akin to water molecules evaporating from a stream.* 01:48 *In electron microscopes, electrons are accelerated downwards towards the sample using strong electric fields.* 03:20 *A Wehnelt cylinder focuses electron spray towards a central point.* 03:50 *Accelerator stacks gradually increase electron voltage, reaching speeds of 76% of the speed of light.* 06:05 *Electron wavelengths in microscopes are small enough to visualize details smaller than a single atom.* 08:28 *Electron guns require conditioning to clean and stabilize the system.* 09:09 *Sulfur hexafluoride gas is used for insulation in high-voltage tanks, posing asphyxiation risks if leaked.* 11:18 *Electron guns require spatial and temporal coherence for clear imaging.* 13:48 *Tungsten, LaB6, and field emission guns are common filament types, differing in coherence and cost.* 16:54 *Field emission guns provide the highest coherence but are costly and require precise temperature control.* Made with HARPA AI
Can someone explain why the electric field lines in the accelerator stack are perpendicular to the path of the beam? I would have thought that the electric field lines should point in the direction of decreasing potential, from 0 V to - 270kV, anti-parallel to the path of the beam. Also, if the electric field lines are perpendicular to the path of the beam, why is the electron beam not deflected, as it would be experiencing a force perpendicular to its velocity?
You are right in questioning the horizontal lines being called the field lines. They should appropriately be called equipotential surfaces. The field lines are perpendicular to the equipotential surfaces and so will be parallel to the path of the beam, as you have rightly suggested.
You are right in questioning the horizontal lines being called the field lines. They should appropriately be called equipotential surfaces. The field lines are perpendicular to the equipotential surfaces and so will be vertical as you have rightly pointed out.
Are y'all REAL fans? this is the material he presents to lab members to teach em, formalized in a video format for public consumption. Real fans watch the intro video smh
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I smoked some weed and wanted to listen to some electronic music, now i am stuck here.
I operate TEM and believe me this is one of the best lecture on TEM with indepth insights... Thank you sir for such videos
The cap with the lowest voltage is called "Wehnelt cylinder", in case you were wondering how it's spelled.
Thanks a lot!
The top most "box" does not contain the filament.
The filament resides just below that box, which is an IGP (a vacuum pump).
This was a great lecture! I have been wanting to learn more about the EM scope for quite some time now, and this really helped. I am excited to watch the rest of your TH-cam lectures.
New grad student trying to prepare myself for a cryo-EM project. This was so helpful! Thank you!
What is the advantage of the accelerator stack over a single anode? Is it just to focus the beam better and increase temporal coherence?
To accelerate the velocity of electrons
🎯 Key Takeaways for quick navigation:
00:05 *Electrons escape a bent wire due to collisions, akin to water molecules evaporating from a stream.*
01:48 *In electron microscopes, electrons are accelerated downwards towards the sample using strong electric fields.*
03:20 *A Wehnelt cylinder focuses electron spray towards a central point.*
03:50 *Accelerator stacks gradually increase electron voltage, reaching speeds of 76% of the speed of light.*
06:05 *Electron wavelengths in microscopes are small enough to visualize details smaller than a single atom.*
08:28 *Electron guns require conditioning to clean and stabilize the system.*
09:09 *Sulfur hexafluoride gas is used for insulation in high-voltage tanks, posing asphyxiation risks if leaked.*
11:18 *Electron guns require spatial and temporal coherence for clear imaging.*
13:48 *Tungsten, LaB6, and field emission guns are common filament types, differing in coherence and cost.*
16:54 *Field emission guns provide the highest coherence but are costly and require precise temperature control.*
Made with HARPA AI
perfect toefl listening tests
Is it possible to change the beam wavelength in electron microscopy for solving the Anamolos structures?
Can someone explain why the electric field lines in the accelerator stack are perpendicular to the path of the beam?
I would have thought that the electric field lines should point in the direction of decreasing potential, from 0 V to - 270kV, anti-parallel to the path of the beam.
Also, if the electric field lines are perpendicular to the path of the beam, why is the electron beam not deflected, as it would be experiencing a force perpendicular to its velocity?
You are right in questioning the horizontal lines being called the field lines. They should appropriately be called equipotential surfaces. The field lines are perpendicular to the equipotential surfaces and so will be parallel to the path of the beam, as you have rightly suggested.
Thank you very much for this awesome tutorial...
The best interpretation
is there a part 2 for this?
Electric field line should be vertical not horizontal. F=qE, the force applied on electron is the same direction of electric field direction
That's what I was thinking...
You are right in questioning the horizontal lines being called the field lines. They should appropriately be called equipotential surfaces. The field lines are perpendicular to the equipotential surfaces and so will be vertical as you have rightly pointed out.
300kV "a very low voltage"
negative
Great video
i guess u meant equipotential lines instead of field lines at ~5:10?
yes, I think he made a mistake by accvident.
Thank you, I was confused by his statement. Your suggestion makes much more sense.
That would make a lot of sense
You are right. They should appropriately be called equipotential surfaces.
Similar thing called pentode in another field
Lanthanum hexaboride (LaB6) crystals
6:06 should be 0.02 angstrom for 2 picoM
well, he just said so - two hundredths :)
What's amazing
Viktor grebenikov used this principle to fly
Is this what they are teaching at Cal- Tech?
Yes, that's why there's a teacher lecturing on the topic at caltech
Are y'all REAL fans? this is the material he presents to lab members to teach em, formalized in a video format for public consumption. Real fans watch the intro video smh
thank you so much you did a great job dud !
300kv negative is a is not a low voltage
It's a high negative number, which is why it's "very low" (because it's so much below zero).
Cant even
Awesome tutorial