I've always felt vaguely uncomfortable that the electrons don't turn round after passing the anode, I always just thought they're going so fast at that point that they are out of reach before they've got too far away. But of course - free electrons don't know the anode is "positive". Saying it is the field suddenly makes it all make sense ! 👍
Ben... I have been loving your videos ever since I got back into the TEM and SEM repair business with my Dad, who retired after 50 years of EM love. I have decommissioned many instruments and have acquired many, many pumps, gauges, valves, apertures, specimen holders, etc. Let me know if I can help you with anything EM related. I love your channel. Professional and accurate for sure! Keep up the great work!
BEN! This is so great. I am curious how an electron gun from a television differs from an SEM. The obvious is that the scanning area of a TV is much larger and I would also assume that the precision beam itself isn't as critical. Have you wondered if it would be possible use a TV's electron gun? Also if a TV's tungsten electrode lasts for so long, why doesn't your electrodes last very long? Thanks!
I am someone with 2 left-hands and something between my ears that seems to be a brain. Most of the time my hands are jobless and my brain is boiling. I always say that "I live in theory". But watching this video really amazes me! These engineers are very smart people. Good to have this diversity among us!!!
Thanks a lot for the explanation! It was difficult for me to understand how the electron can leave the gun. But example with a flat capacitor has made it. And a mistake with voltages made the understanding even more deep.
Thank you for saying "equipotential." Another video I just watched only called them "field lines," which bothered me (and took a minute for me to realize what was meant) and seemed like it could be confusing for anyone with basic knowledge of electric fields who has seen flux lines drawn and called "field lines," which seems more common.
An electron gun from an old b/w television includes: filament heated cathode(with surface coated to lower workfunction), suppression grid and focal lens.
let me assure you, your explanation have been as good as can be... If one doesn't understand what you talking about he should change his field of interest.
so I've been thinking about making an sem. I'm just curious why you didn't just use a CRT gun assembly and play with the parameters to see if you could make that work. Its almost the same thing. perhaps the beam current is too high and the pin holes are too large?
Hey, Im an electrical engineering college student and need to build an electron gun for part of my senior design project. Could you say what your balancing resistor values are and the explanation as to why you chose those values? thanks!
Hello Mr. Ben The video is great with satisfactory explanation. I also recommend you to explain types of electron sources/guns that would be very useful for students studying SEM, if possible. Thank you.
There are two basic type- 1. Thermionic Emission source In this type work function of source material is overcome by giving energy in the form of heat. Two most common used sources in thermionic Emission are- Tungsten and Lanthanum Hexaboride (LaB6) 2. Field Emission Gun- In this type of source, electric field is applied to extract electrons. Both have their own advantage and disadvantage.
Hello Ben, I know this is an old thread, but i have one question about your electron gun explanation: I don't see the current loop for the emission current you are measuring. The electrons are emitted from the cathode and fly away and it seems they never come back to form a current loop. Where is the return path for emitted electrons.
+fogl2 That is a good question. The high voltage supply ("HV") in the diagram pumps electrons through the current meter and biasing resistor, and out the cathode. They are emitted, and fly through the vacuum of the microscope where they eventually hit the inner metal surface of the microscope column, or hit the sample, releasing secondary electrons, which drift toward the detector or hit the metal of the column. The high voltage supply is referenced to the metal column (the ground symbol in the diagram), and so the column itself forms the return path.
1. The lines shown here are not the electric field, but the iso-lines (planes) of same electrical potential. 2. The electrons are accelerated along the fieldlines (The electrical field results in a forcefield, which is, due to the mass of the electron, an acceleration field), which is (infinitessimally) perpendicular to the iso-planes. Note: the acceleration field is not the field of velocities or trajectory. It's the acceleration field - the field of change of velocity. Sorry for being a knowitall, but when explaining in detail, the explaination schould be correct.
Here am I ... 8 years later figuring that I will FINNALY make this (for some small EBM 3D Printer). But I still don't have a UVAC pump nor a HVAC .... But I do have a CNC machine and a lathe so.... I'll try to make my own pumps.. that'll be the most challenging part I guess...
@paul beenis Hopefully I will, it's going to take a while thou because I need a decent pump, the HV stuff will be easy (and getting materials) but the culprits are the pumps) I have a double piston(membrane) pump that will most likely need servicing. Also, I need to finish the design and machine parts (which I can only do during weekends)
can you please show the assembly of the electron gun? I am designing mine now. I want to see how you did yours. I plan on using a commercial electron gun cartridge
Excellent video! I am venturing into making my own SEM. Care to share a wiring diagram of your high voltage and filament supply of your electron gun column? I watched all the videos related to your SEM and its still not quite clear.
Hi bendo your videos for your S.E.M build run in order I seem to find them all over the place I have subscribed to you channel. I'm quite new to tube so bear with me. I have over eleven years with a company called VG Scientific involved in S.I.M.S and E.S.C.A I have worked with both ION and Electron guns in my time and a few different analysers as well that coupled with high vacuum pumps and sample manipulation. VG split into a few little factions mine was called VG IONEX based in Burgess Hill. Now get to my point I had a thought to make a simple S.E.M for educational purposes why cant I cut the screen of a CRT Oscilloscope and with a mucking about with power supplies or making software controlled supplies via "Arduino" So basically I stand the tube screen down I have a filament source condenser lenses scan plates I have extraction and focus, yep I no I need a PM tube and a whole host of other bits and bobs. Also a roughing pump plus DIFF or turbo ION I have my own electron multiplier "French horn type" heheh! was gonna put one piece at a time in my lunch box , think theirs a song about that but pretty sure it was about a car. So do you see what I mean ? has it been done or can it be done your opinion please when you have a moment contact me via U tube I'm not sure how that works yet but will figure it out or you have my address here - andy.brown100@yahoo.com The way I see it is that a scope is an electron optical coloum in its self .Or have I gone mad.............................squeak!
Hi! very nice video. Why you don't apply magnetic field to minimize electron focuse spot? Your construction is very comfortable to make longitudinal solenoid. I think, if thermoelectron energy is about 1 eV, for beam 30 cm long and 5 kV forsing voltage we have ideal focus spot about 0.5 cm without magnetic field and any aperture. So you should use 1.5 mm aperture in anode and it decrease max beam current. Applying field must let avoid this limitations. But it is only theory, I never do it :)
With these kinds of kV levels in a high vacuum, do you have any problems with coronal discharge and whatnot off the sharp edges of your electrical shenanigans?
Once you have a hard enough vacuum it becomes an insulator. Residual gas remains a problem and this is why high kV (RF, x-Ray, microscope) electrodes are radiused to reduce the field intensities at edges where the corona discharge would first start.
As i've seen your HV-PSU as able to produce 0-10kV. How did you manage to make negative voltage? You can't just switch the ends and call it negative. And why it was so crucial for you making 0V anode and wehnelt negative?
If you do not connect to ground you have 'floating' voltages that are not referenced to ground. If you ground the negative end of a battery then the other terminal will be positive with respect to ground. If you ground the positive terminal then the other will be negative with respect to ground. Ground is simply a convention that we use because we work on the principle that the earth is at the same potential everywhere. You can pick any point as your reference voltage. You can even change it later if there is no connection to other circuits.
@@DarthZackTheFirstI don't give false information. *IF I RECALL CORRECTLY*, high energy electrons are radioactive and the midway point between alpha radiation and gamma radiation, so they're pretty ionizing, but are blocked by metal.
In almost all cases the electrons stay inside the vacuum chamber. If you have a good energy beam and a suitable thin window you can have the electrons exit into air but the beam is attenuated quickly.
They form a virtual centre tap in the absence of a bipolar power supply. If he has a 2V filament supply the resistors will have about 1V at their junction. The reason it is done with a bare filament here is so that the tip of the filament is kept at the same voltage relative to the aperture even if he changes the filament power supply voltage. I suspect that with the voltages in question of 400V and 1V it may not make any difference but I am not sure, maybe it will make a significant difference.
11 YEARS!!! you looked like such a baby back then! So much great content over the years. Keep it up old friend!
I used my milling machine with a very small drill bit held in a pin vise.
I've always felt vaguely uncomfortable that the electrons don't turn round after passing the anode, I always just thought they're going so fast at that point that they are out of reach before they've got too far away. But of course - free electrons don't know the anode is "positive". Saying it is the field suddenly makes it all make sense ! 👍
Ben... I have been loving your videos ever since I got back into the TEM and SEM repair business with my Dad, who retired after 50 years of EM love. I have decommissioned many instruments and have acquired many, many pumps, gauges, valves, apertures, specimen holders, etc. Let me know if I can help you with anything EM related. I love your channel. Professional and accurate for sure! Keep up the great work!
I would love to work at your business, I am currently a diesel mechanic and heavy equipment/truck technician.
BEN! This is so great. I am curious how an electron gun from a television differs from an SEM. The obvious is that the scanning area of a TV is much larger and I would also assume that the precision beam itself isn't as critical. Have you wondered if it would be possible use a TV's electron gun? Also if a TV's tungsten electrode lasts for so long, why doesn't your electrodes last very long? Thanks!
I am someone with 2 left-hands and something between my ears that seems to be a brain. Most of the time my hands are jobless and my brain is boiling. I always say that "I live in theory". But watching this video really amazes me! These engineers are very smart people. Good to have this diversity among us!!!
Thanks a lot for the explanation! It was difficult for me to understand how the electron can leave the gun. But example with a flat capacitor has made it. And a mistake with voltages made the understanding even more deep.
Thank you for saying "equipotential." Another video I just watched only called them "field lines," which bothered me (and took a minute for me to realize what was meant) and seemed like it could be confusing for anyone with basic knowledge of electric fields who has seen flux lines drawn and called "field lines," which seems more common.
"hey guys
it is saturday morning
I've got my cup of coffee
And i wanna talk particle physics"
that's my life now.
An electron gun from an old b/w television includes: filament heated cathode(with surface coated to lower workfunction), suppression grid and focal lens.
This is super cool, now I want to make my own SEM
let me assure you, your explanation have been as good as can be... If one doesn't understand what you talking about he should change his field of interest.
so I've been thinking about making an sem. I'm just curious why you didn't just use a CRT gun assembly and play with the parameters to see if you could make that work. Its almost the same thing. perhaps the beam current is too high and the pin holes are too large?
can you make a detailed a video on how to make the electron microscope
Great description of a self biased electron gun. Keep up the good videos.
awesome video! how did they publish the periodic table before there was an electron microscope?
Hey, Im an electrical engineering college student and need to build an electron gun for part of my senior design project. Could you say what your balancing resistor values are and the explanation as to why you chose those values? thanks!
Hey man! This is such a great explanation. Thank you for making these outstanding videos.
Very lucid explanation. Sharing the heck out of this series:)
Fascinating design! Although I’m curious about something, couldn’t a spark gap be used in place of a filament?🤪
Hello Mr. Ben
The video is great with satisfactory explanation. I also recommend you to explain types of electron sources/guns that would be very useful for students studying SEM, if possible.
Thank you.
There are two basic type-
1. Thermionic Emission source
In this type work function of source material is overcome by giving energy in the form of heat. Two most common used sources in thermionic Emission are- Tungsten and Lanthanum Hexaboride (LaB6)
2. Field Emission Gun-
In this type of source, electric field is applied to extract electrons.
Both have their own advantage and disadvantage.
@@arjunbarwal1502 thank you
Hello Ben,
I know this is an old thread, but i have one question about your electron gun explanation: I don't see the current loop for the emission current you are measuring. The electrons are emitted from the cathode and fly away and it seems they never come back to form a current loop. Where is the return path for emitted electrons.
+fogl2 That is a good question. The high voltage supply ("HV") in the diagram pumps electrons through the current meter and biasing resistor, and out the cathode. They are emitted, and fly through the vacuum of the microscope where they eventually hit the inner metal surface of the microscope column, or hit the sample, releasing secondary electrons, which drift toward the detector or hit the metal of the column. The high voltage supply is referenced to the metal column (the ground symbol in the diagram), and so the column itself forms the return path.
Hi Ben, Could you ascertain the rough size of the focused electron beam hitting the specimen ( or spot size )
Is the potential voltage also the other way around? The emitted electrons do experience the biggest potential just after being released?
Hi there great video I'm really enjoying the series. If you have, where did you get schematics to build this machine. Cheers
1. The lines shown here are not the electric field, but the iso-lines (planes) of same electrical potential.
2. The electrons are accelerated along the fieldlines (The electrical field results in a forcefield, which is, due to the mass of the electron, an acceleration field), which is (infinitessimally) perpendicular to the iso-planes. Note: the acceleration field is not the field of velocities or trajectory. It's the acceleration field - the field of change of velocity.
Sorry for being a knowitall, but when explaining in detail, the explaination schould be correct.
영상의 의미는 알고있습니다.
알고싶은것은 방출된전자가 반사된것을 어떻게 수신하고 어떤장치가 사용돼며 영상화 시키는지가 궁금합니다. 이장치를 사용하고 대략적인 내부도 보았으나 그것이 가장 의문입니다. 알고싶은 부분이기도 합니다.
Here am I ... 8 years later figuring that I will FINNALY make this (for some small EBM 3D Printer). But I still don't have a UVAC pump nor a HVAC .... But I do have a CNC machine and a lathe so.... I'll try to make my own pumps.. that'll be the most challenging part I guess...
@paul beenis Hopefully I will, it's going to take a while thou because I need a decent pump, the HV stuff will be easy (and getting materials) but the culprits are the pumps) I have a double piston(membrane) pump that will most likely need servicing. Also, I need to finish the design and machine parts (which I can only do during weekends)
Great! Thank you!
These are brass screws? Is this important? Like they are non magnetic? Why not aluminum?
can you please show the assembly of the electron gun? I am designing mine now. I want to see how you did yours. I plan on using a commercial electron gun cartridge
thank you so much sir for your wonderful demonstration i wish much more about depostion video
Hi everyone. Can I hijack a CRT and get the cathode ray. Is that the EXACT same thing as a Electron gun?
Excellent video! I am venturing into making my own SEM. Care to share a wiring diagram of your high voltage and filament supply of your electron gun column? I watched all the videos related to your SEM and its still not quite clear.
Hi. Do you have a list of materials needed to make this,but most importantly,do you have a list of dimensions? Thanks
Excellent
Isn't the Wehnelt cylinder the focussing grid (G3) ? and the first grid after the cathode the intensity control grid (G1) ?
Hi bendo your videos for your S.E.M build run in order I seem to find them all over the place I have subscribed to you channel. I'm quite new to tube so bear with me. I have over eleven years with a company called VG Scientific involved in S.I.M.S and E.S.C.A I have worked with both ION and Electron guns in my time and a few different analysers as well that coupled with high vacuum pumps and sample manipulation. VG split into a few little factions mine was called VG IONEX based in Burgess Hill. Now get to my point I had a thought to make a simple S.E.M for educational purposes why cant I cut the screen of a CRT Oscilloscope and with a mucking about with power supplies or making software controlled supplies via "Arduino" So basically I stand the tube screen down I have a filament source condenser lenses scan plates I have extraction and focus, yep I no I need a PM tube and a whole host of other bits and bobs. Also a roughing pump plus DIFF or turbo ION I have my own electron multiplier "French horn type" heheh! was gonna put one piece at a time in my lunch box , think theirs a song about that but pretty sure it was about a car. So do you see what I mean ? has it been done or can it be done your opinion please when you have a moment contact me via U tube I'm not sure how that works yet but will figure it out or you have my address here - andy.brown100@yahoo.com The way I see it is that a scope is an electron optical coloum in its self .Or have I gone mad.............................squeak!
Hi! very nice video. Why you don't apply magnetic field to minimize electron focuse spot? Your construction is very comfortable to make longitudinal solenoid. I think, if thermoelectron energy is about 1 eV, for beam 30 cm long and 5 kV forsing voltage we have ideal focus spot about 0.5 cm without magnetic field and any aperture. So you should use 1.5 mm aperture in anode and it decrease max beam current. Applying field must let avoid this limitations. But it is only theory, I never do it :)
With these kinds of kV levels in a high vacuum, do you have any problems with coronal discharge and whatnot off the sharp edges of your electrical shenanigans?
Once you have a hard enough vacuum it becomes an insulator. Residual gas remains a problem and this is why high kV (RF, x-Ray, microscope) electrodes are radiused to reduce the field intensities at edges where the corona discharge would first start.
It's the potential difference.
Has there ever been a laser heated cathode?
Hi Ben, how did you make such small holes on the Wennelt plate and the anode?
Good idea, and it should bring some improvement :)
the explanation is great ,, just keep these videos coming :)
I think my IQ went up 10 points just watching this!
As i've seen your HV-PSU as able to produce 0-10kV. How did you manage to make negative voltage? You can't just switch the ends and call it negative.
And why it was so crucial for you making 0V anode and wehnelt negative?
If you do not connect to ground you have 'floating' voltages that are not referenced to ground. If you ground the negative end of a battery then the other terminal will be positive with respect to ground. If you ground the positive terminal then the other will be negative with respect to ground. Ground is simply a convention that we use because we work on the principle that the earth is at the same potential everywhere.
You can pick any point as your reference voltage. You can even change it later if there is no connection to other circuits.
I am your fan. How can i meet with you?
Hey guys it's Monday mid afternoon and I've got my coffee, let's talk particle physics. I'm wanting to look into my body at my cancer. Can I do it?
Very nice video. Thanks! If you're not a lecturer for your day job, you should be.
Quality.
how dangerous is a fully functioning electron gun where the electrons leave the apparatus? ]
kinda the same as a microwave i would assume at worst :p
@@DarthZackTheFirstI don't give false information. *IF I RECALL CORRECTLY*, high energy electrons are radioactive and the midway point between alpha radiation and gamma radiation, so they're pretty ionizing, but are blocked by metal.
i suppose your skin isnt made out of metal...
@@DarthZackTheFirstI yep
In almost all cases the electrons stay inside the vacuum chamber. If you have a good energy beam and a suitable thin window you can have the electrons exit into air but the beam is attenuated quickly.
I don't see how the two resistors across the filament are effective at anything other than burning battery power.
They form a virtual centre tap in the absence of a bipolar power supply. If he has a 2V filament supply the resistors will have about 1V at their junction.
The reason it is done with a bare filament here is so that the tip of the filament is kept at the same voltage relative to the aperture even if he changes the filament power supply voltage. I suspect that with the voltages in question of 400V and 1V it may not make any difference but I am not sure, maybe it will make a significant difference.
try to align such a gun........