doing forensics at the moment and was giving myself a headache trying to understand the different forms of electrons & how they actually worked - this cleared up almost everything! thanks for uploading :)
Thanks for the video! I am taking a university course in engineering on materials science and we had to explain in lab report how this device worked. With your great explanation I can understand much better.
Sorry for taking so long to get back to you. We were on break and the book I needed was in my office at the college. This is a weird one, so I went back to my textbook for an explanation. Yes, the anode is negatively charged, but relative to the filament on the scope it is positive. Here is a quote from the text: "If one induces the emission of electrons from a filament as described above, this will result in the emanation of electrons in all directions. Without a mechanism for guiding them, most of the electrons would not enter the illumination system. A second part of the electron gun, the shield (also called Wehnelt cylinder, bias shield, or grid cap), is a caplike structure that covers the filament and is maintained at a slightly more negative voltage potential than the filament. Because it is several hundred more negative than the 50 to 100 kV electrons, the shield surrounds the electrons with a repulsive field that is breachable only through a 2 to 3 mm aperture directly in front of the filament tip. Electrons exit the shield aperture and and are drawn toward the apertured disc, or anode, the third part of the electron gun. The anode is connected to ground so that the highly negative electrons are are strongly attracted to it. THUS IT IS POSITIVE WITH RESPECT TO THE GUN. In fact, the highly attractive pull of the anode in combination with the negative surface of the shield act as an electrostatic "lens" to generate a crossover image of the electron source near the anode." Bozzola, John J., and Lonnie D. Russell. Electron Microscopy. 2nd ed. Sudbury: Jones and Bartlett, 1999. Print. 0-7637-0192-5 I could not agree with you more - it seems backwards. The anode is negative, but it is positive related to the beam. Let me know what you think. There is also an illustration in the text I would be glad to photograph and send to you if you provide me an e-mail or text address. Many thanks for your comment. Murry
I appreciate your comment and I agree that this is not a research-level explanation - it was not intended to be. I demonstrate a Hitachi TM1000 to elementary, middle, and high school students. This is one of the videos I forward to the teachers ahead of time to prepare their classes. I also use it as a basic introduction to electron microscope for some of the students I teach at a community college - many of whom are not science majors. But I do appreciate your comment.
My understanding is that there needs to be a vaccume inside the microscope, that way electrons aren’t going to come into contact with anything other than the target specimen. My question is, how does a specimen stay where they need it to? Glass slides would get in the way of the electrons and a vaccume would move the specimen...wouldn’t it?🤔
Secondary electrons come right off the surface. Yes, backscattered electrons penetrate deeper (relatively) and then come off the specimen. Both are given off - different detectors are tuned to pick up the different frequencies. Depending on your em you can combine both into a single image.
You should have talked about the raster scanning meathod. you should have also explained about the EDAX spectrum and explained the way to read/uncode the EDAX spectrum. over all its a good video. it has explained all the basic points but not that good for a research level thing. I hope you include the above mentioned things and make an other video.
For my SEM, a Hitachi S3400, the theoretical resolution is 1.7 nm. Hitachi claims 3.0 nm. It is a 30 kV scope with a max mag of 300 kx. My lab does not have a sputter coater so we are imaging uncoated samples. I did some imaging of an aluminum sample with holes from 10 to 20 nm in diameter. I was able to image it, but with aperture 4 in place and low probe current. BSE dectector at 15 kV. The result is a pretty grainy image, but it does show the holes. My concern, and I think this is what you mean by bias (not sensitivity of the detector) is that the edges of the holes are indistinct making the accuracy of the measurements poor. If this isn't what you meant please let me know. M. Gans
@@murrygans1786 thanks for replying! yes it is what i meant, i am seeking the full knowledge of this technology since i am a medical student and i am interested in doing a research in the medical field in the near future!
@@anasomar1473 Let me add a couple of more things then. Scanning electron microscopy only shows surface features. Medical facilities have SEMs, but they also have at least two other devices for preparing specimens. The first is a critical point drier (CPD). The inside of an SEM is a very nasty place. The specimen is under a high vacuum and being bombarded by high energy electrons. This can cause the specimen to dry out. The CPD is a machine that uses high pressure and temperature to replace the water in a specimen with acetone or ethanol. When the specimen comes out of the CPD the acetone evaporates and you have a dry specimen that will not shrink in the SEM. Second is a sputter coater. This device will cover the specimen with a very thin layer of metal, usually gold, iridium, or palladium. This gives a bright, high contrast SEM image. The second technique is not SEM but TEM - transmission electron microscopy. In this procedure the specimen is cut into extremely thin sections. The TEM sends electrons through the specimen to make the image, kind of like a light microscope, but the small wavelength of the electron beam give outstanding resolution. The prep for this technique is complex. Best of luck to you. If you have any other questions let me know. M. Gans
How come primary and secondary electrons don't get mixed ? How come secondary electrons are attracted to the positively charge Faraday cage while primary electrons are not? How do we use the information from those electrons to form a picture ?
It's important to notice is that the BS electrons have a much higher energy than the SE. This way, those 300V won't be enough to attract too many BS electrons to the SE detector. The BS electrons detector is placed to capture a fraction of the backscattered electrons that depends on the solid angle that it covers. Since there is a scanning being made, for every dot there is a certain number of BS and secondary electrons. The secondary electrons that can be detected are "released" from very near the surface (about 2nm) because they interact a lot then can't travel through the solid too much. This way, the amount of electrons that can leave the solid will depend on its topography. The image generated reveals topographic contrast. The number of backscattered electrons will depend on the atomic number Z of the atoms. Then, the image generated from this detector shows variations in chemical composition of the specimen. Hope it helps ;)
How can SEM be used to image higher resolution than light microscopes, and how is this different for typical thermionic and field emission electron source microscopes.
The main reason it CAN image with higher resolution is because visible light have a diffraction limit much higher than electrons. It DOES by focusing a very small beam in the sample. About the source of electrons I guess there is no difference on the imaging. Since the electrons are accelerated to form a beam they're essentially the same. I'm not completely sure about this, though. Hope it helps ;)
Resolution means distance between two points! Light has wavelength 300-700 nm while electron has 4pm for example! Smallest distance can be resolved is directly proportional to wavelength!!
There are two different detectors on the microscope and I can choose which one the microscope uses - in fact, I can use them both at the same time under full vacuum. On my SEM, and because I am often imaging insects and other organic materials, I get a build up of static charge which can flood the detector with electrons - meaning I lose detail on the image. The backscatter detector on my SEM operates under variable pressure which means I can control the amount of atmosphere in the microscope - from 6 to 279 Pascals. This allows the charging to dissipate. This option is not available when using the secondary detector on my microscope, but other SEM models allow variable atmosphere on the SE detector. So the best answer to your question is that I can pick which detector I use based on the nature of the specimen. I hope this helps and I answered your question. Best wishes, Murry
Another important thing to notice is that the BS electrons have a much higher energy than the SE. This way, those 300V won't be enough to attract too many BS electrons to the SE detector. The BS electrons detector is placed to capture a fraction of the backscattered electrons that depends on the solid angle that it covers. Is this correct, Murry?
By now you've had some experience using the small electron microscope the TM 1000 now we're going to add some theory behind what's actually happening inside the electron microscope and I actually delayed this until now until you had a chance to use the small electron microscope because hopefully it'll help it make a little bit more sense to you so here's a cutaway of what the inside of our electron microscopes look like this is not exactly ours but it's going to be very similar inside essentially what we have is we have an electron gun up here which we're going to induce to send a beam of electrons down to our specimen down here in the chamber and to focus that specimen we'll be using a series of electromagnets now we can't use glass lenses like you find on the regular microscope because electron beam won't go through glass but the electrons have a charge which means that they're influenced by magnetic fields so these rings right here these condenser lenses if you will are actually just electromagnets and the idea is to get those electrons finally focused right down here on the sample so first of all. let's look let's take a look at the electron gun electron gun here's a photo photograph taken with the like a dissecting microscope this is called a thermionic electron gun which basically means we're going to heat it up it's going to give off a bunch of electrons to give some idea of the scale here this is just a penny I had in my pocket I stuck down there with it so you could see what's going on by the way just show you a nice image from the from the Leica here you can see that this this film it's actually burned out so so this wears a way as we use it we put that 15,000 volts through there or on the big scope we'll put up to 30,000 volts through this filament and it eventually burns away all right so let's go back and look at our cutaway again so the way we get these electrons to head down toward the specimen is the fact that under this you will see a disc called an anode and anodes have a positive charge and of course negatively charged electrons are going to be attracted to our positively charged anode so they head off in that direction but there's a hole right in the middle the anode so once these guys start moving toward the anode some of them will simply go right through it also the stage down here on which you're going to mount your specimen also has a positive charge so that also keeps electrons moving in this direction this can cause a problem all things we look at normal our microscopes are non-conductive and as you found out with the hopefully with the team 1000 if so you have something that's non-conductive it can actually gather a charge and then it gives off lots of electrons in it all we see is a glow so let's take a look at what happens when the electron beam hits a specimen and how that ends up making an image on our computer screen so here you can see like Tron beam heading down it hits the specimen here and then there's actually two types of electrons that are going to come off of this in one case we're going to get the what are known as secondary electrons and that is when the electron beam comes down and hits the atoms of the specimen the those atoms absorb the energy and give off their own electron there's a detector to pick up secondary electrons over here as you can see and that detector to attract those electrons has a positive charge on it it's about 300 volts which is actually quite a lot and then once those electrons come in to the Faraday cage which is positively charged they hit the detector and then the detector uses the information from those electrons to form the image on our computer screen now the second type of electrons are called back scatter electrons and these electrons actually don't come from the atoms actually reflect off the surface and they actually can come even from deeper down the specimen and we have a second detector that it can actually detect those so this is to show you this little illustration will actually show you where these electrons are going to come from so you can see or the secondary electrons are going to be surface electrons so they're very shallow but these are very good for getting surface features and of course that's one of the main reasons for using a scan electron microscope the back scatter electrons are going to come from deeper in the specimen so someone will bounce right off the surface some will go deeper and then the ones that are really deep actually never get back out again so when they get absorbed they give off x-rays now we actually don't have an x-ray detector for our scope but you can do an elemental analysis by using by looking x-rays so the detectors that we have on our scope are the secondary electron detectors and the back scatter detectors so why is it called a scanning electron microscope well as you can see from this illustration here's our primary beam coming down and it's actually making the picture pixel by pixel it's hitting from left to right top the ball and every time it hits we get electrons from that particular part of the specimen interestingly enough if you want to magnify all we do instead of actually scanning across a big image like this so we just would scan over a smaller box so this is actually showing the setup as you can see here we've got the column here so all the electromagnets are up above there the electrons come out through the pole piece here they hit our specimen the secondary electrons over here to the side and then of course our backscatter detector is actually going to be up here mounted to the pole piece and you saw a picture of that on inside of the TM 1000.
Thanks and God bless John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
Anodes are for the attraction of anions (negatively charged) and cathodes are for cations (positively charged). They have to be oppositely charged from what they are attracting. Therefore, anodes are positively charged and cathodes are negatively charged.
Hi everyone .If you read this message please read the Holy Quran the direct words and the final message from Almighty God.It will guide you to peace truth and happiness in this world and the afterworld with my lovely wishes
This is the best practical SEM lecture I have ever seen!.
Thank you. This is the best & easiest to understand explanation so far. So clear & simplified.
Thank you so much for this video! You definitely saved me for this part of my nanotechnology quiz tomorrow!
doing forensics at the moment and was giving myself a headache trying to understand the different forms of electrons & how they actually worked - this cleared up almost everything! thanks for uploading :)
Thanks for the video! I am taking a university course in engineering on materials science and we had to explain in lab report how this device worked. With your great explanation I can understand much better.
Thanks for this explanation Mr. Gans! Due to my SEM presentation for exam, I'd like to use your video and put your name as courtesy.
Sorry for taking so long to get back to you. We were on break and the book I needed was in my office at the college.
This is a weird one, so I went back to my textbook for an explanation. Yes, the anode is negatively charged, but relative to the filament on the scope it is positive. Here is a quote from the text:
"If one induces the emission of electrons from a filament as described above, this will result in the emanation of electrons in all directions. Without a mechanism for guiding them, most of the electrons would not enter the illumination system. A second part of the electron gun, the shield (also called Wehnelt cylinder, bias shield, or grid cap), is a caplike structure that covers the filament and is maintained at a slightly more negative voltage potential than the filament. Because it is several hundred more negative than the 50 to 100 kV electrons, the shield surrounds the electrons with a repulsive field that is breachable only through a 2 to 3 mm aperture directly in front of the filament tip. Electrons exit the shield aperture and and are drawn toward the apertured disc, or anode, the third part of the electron gun. The anode is connected to ground so that the highly negative electrons are are strongly attracted to it. THUS IT IS POSITIVE WITH RESPECT TO THE GUN. In fact, the highly attractive pull of the anode in combination with the negative surface of the shield act as an electrostatic "lens" to generate a crossover image of the electron source near the anode."
Bozzola, John J., and Lonnie D. Russell. Electron Microscopy. 2nd ed. Sudbury: Jones and Bartlett, 1999. Print. 0-7637-0192-5
I could not agree with you more - it seems backwards. The anode is negative, but it is positive related to the beam.
Let me know what you think. There is also an illustration in the text I would be glad to photograph and send to you if you provide me an e-mail or text address.
Many thanks for your comment.
Murry
I appreciate your comment and I agree that this is not a research-level explanation - it was not intended to be. I demonstrate a Hitachi TM1000 to elementary, middle, and high school students. This is one of the videos I forward to the teachers ahead of time to prepare their classes. I also use it as a basic introduction to electron microscope for some of the students I teach at a community college - many of whom are not science majors. But I do appreciate your comment.
very good science video. really help understand how does a SEM work. highly recommended
Murry, you are the Man. Great video!
My understanding is that there needs to be a vaccume inside the microscope, that way electrons aren’t going to come into contact with anything other than the target specimen.
My question is, how does a specimen stay where they need it to? Glass slides would get in the way of the electrons and a vaccume would move the specimen...wouldn’t it?🤔
sir, why the secondary electron are from the surface of sample,and the X-ray are from the deeper within the specimen? Thank you .
best best best video explaining the working principle ^_^ thank you so much
So the back scattered electrons are the electrons given off by the atoms of the specimen that are located deeper within?
Secondary electrons come right off the surface. Yes, backscattered electrons penetrate deeper (relatively) and then come off the specimen. Both are given off - different detectors are tuned to pick up the different frequencies. Depending on your em you can combine both into a single image.
excellent video
Is inside the scope vacuum?
Sir ,why we coat the sample with gold?
To make it conductive
You should have talked about the raster scanning meathod. you should have also explained about the EDAX spectrum and explained the way to read/uncode the EDAX spectrum. over all its a good video. it has explained all the basic points but not that good for a research level thing. I hope you include the above mentioned things and make an other video.
very useful, thank you. however, it is weird to scan a Cockroach with SEM......
Bold of you to assume im starting with the small one and not just going right for the big chungus
what is the possibility of bias for a 5 nano meter specimen ?
For my SEM, a Hitachi S3400, the theoretical resolution is 1.7 nm. Hitachi claims 3.0 nm. It is a 30 kV scope with a max mag of 300 kx. My lab does not have a sputter coater so we are imaging uncoated samples.
I did some imaging of an aluminum sample with holes from 10 to 20 nm in diameter. I was able to image it, but with aperture 4 in place and low probe current. BSE dectector at 15 kV. The result is a pretty grainy image, but it does show the holes.
My concern, and I think this is what you mean by bias (not sensitivity of the detector) is that the edges of the holes are indistinct making the accuracy of the measurements poor.
If this isn't what you meant please let me know.
M. Gans
@@murrygans1786 thanks for replying! yes it is what i meant, i am seeking the full knowledge of this technology since i am a medical student and i am interested in doing a research in the medical field in the near future!
@@anasomar1473 Let me add a couple of more things then.
Scanning electron microscopy only shows surface features. Medical facilities have SEMs, but they also have at least two other devices for preparing specimens. The first is a critical point drier (CPD). The inside of an SEM is a very nasty place. The specimen is under a high vacuum and being bombarded by high energy electrons. This can cause the specimen to dry out. The CPD is a machine that uses high pressure and temperature to replace the water in a specimen with acetone or ethanol. When the specimen comes out of the CPD the acetone evaporates and you have a dry specimen that will not shrink in the SEM.
Second is a sputter coater. This device will cover the specimen with a very thin layer of metal, usually gold, iridium, or palladium. This gives a bright, high contrast SEM image.
The second technique is not SEM but TEM - transmission electron microscopy. In this procedure the specimen is cut into extremely thin sections. The TEM sends electrons through the specimen to make the image, kind of like a light microscope, but the small wavelength of the electron beam give outstanding resolution. The prep for this technique is complex.
Best of luck to you. If you have any other questions let me know.
M. Gans
@@murrygans1786 thank you so much doctor Gens, I have learned a lot!
How come primary and secondary electrons don't get mixed ? How come secondary electrons are attracted to the positively charge Faraday cage while primary electrons are not? How do we use the information from those electrons to form a picture ?
It's important to notice is that the BS electrons have a much higher energy than the SE. This way, those 300V won't be enough to attract too many BS electrons to the SE detector. The BS electrons detector is placed to capture a fraction of the backscattered electrons that depends on the solid angle that it covers.
Since there is a scanning being made, for every dot there is a certain number of BS and secondary electrons.
The secondary electrons that can be detected are "released" from very near the surface (about 2nm) because they interact a lot then can't travel through the solid too much. This way, the amount of electrons that can leave the solid will depend on its topography. The image generated reveals topographic contrast.
The number of backscattered electrons will depend on the atomic number Z of the atoms. Then, the image generated from this detector shows variations in chemical composition of the specimen.
Hope it helps ;)
How can SEM be used to image higher resolution than light microscopes, and how is this different for typical thermionic and field emission electron source microscopes.
The main reason it CAN image with higher resolution is because visible light have a diffraction limit much higher than electrons.
It DOES by focusing a very small beam in the sample.
About the source of electrons I guess there is no difference on the imaging. Since the electrons are accelerated to form a beam they're essentially the same. I'm not completely sure about this, though.
Hope it helps ;)
Resolution means distance between two points! Light has wavelength 300-700 nm while electron has 4pm for example! Smallest distance can be resolved is directly proportional to wavelength!!
I’m not from your college, I’m still in high school actually, but an amazing video to watch nevertheless
How the microscope differentiates secondary and backscattering electrons?
There are two different detectors on the microscope and I can choose which one the microscope uses - in fact, I can use them both at the same time under full vacuum. On my SEM, and because I am often imaging insects and other organic materials, I get a build up of static charge which can flood the detector with electrons - meaning I lose detail on the image. The backscatter detector on my SEM operates under variable pressure which means I can control the amount of atmosphere in the microscope - from 6 to 279 Pascals. This allows the charging to dissipate. This option is not available when using the secondary detector on my microscope, but other SEM models allow variable atmosphere on the SE detector. So the best answer to your question is that I can pick which detector I use based on the nature of the specimen.
I hope this helps and I answered your question.
Best wishes,
Murry
+Murry Gans yes, i got the idea. Thank you so much :)
Another important thing to notice is that the BS electrons have a much higher energy than the SE. This way, those 300V won't be enough to attract too many BS electrons to the SE detector. The BS electrons detector is placed to capture a fraction of the backscattered electrons that depends on the solid angle that it covers.
Is this correct, Murry?
Excellent information, thank you
good and nice explanation.
thank you alot for information
Thank you 🙏
Thank u so much :) the video was of great help
❤Thank you so much this was so helpfull❤
good informative one.Thanks murry
Thank you very much
it is very well explained.
I swear the narrator is Jay Santos of the Citizens Auxiliary Police
Thank you very much
The 25 dislikes are burned out filaments.
By now you've had some experience using the small electron microscope the TM 1000 now we're going to add some theory behind what's actually happening inside the electron microscope and I actually delayed this until now until you had a chance to use the small electron microscope because hopefully it'll help it make a little bit more sense to you so here's a cutaway of what the inside of our electron microscopes look like this is not exactly ours but it's going to be very similar inside essentially what we have is we have an electron gun up here which we're going to induce to send a beam of electrons down to our specimen down here in the chamber and to focus that specimen we'll be using a series of electromagnets now we can't use glass lenses like you find on the regular microscope because electron beam won't go through glass but the electrons have a charge which means that they're influenced by magnetic fields so these rings right here these condenser lenses if you will are actually just electromagnets and the idea is to get those electrons finally focused right down here on the sample so first of all. let's look let's take a look at the electron gun electron gun here's a photo photograph taken with the like a dissecting microscope this is called a thermionic electron gun which basically means we're going to heat it up it's going to give off a bunch of electrons to give some idea of the scale here this is just a penny I had in my pocket I stuck down there with it so you could see what's going on by the way just show you a nice image from the from the Leica here you can see that this this film it's actually burned out so so this wears a way as we use it we put that 15,000 volts through there or on the big scope we'll put up to 30,000 volts through this filament and it eventually burns away all right so let's go back and look at our cutaway again so the way we get these electrons to head down toward the specimen is the fact that under this you will see a disc called an anode and anodes have a positive charge and of course negatively charged electrons are going to be attracted to our positively charged anode so they head off in that direction but there's a hole right in the middle the anode so once these guys start moving toward the anode some of them will simply go right through it also the stage down here on which you're going to mount your specimen also has a positive charge so that also keeps electrons moving in this direction this can cause a problem all things we look at normal our microscopes are non-conductive and as you found out with the hopefully with the team 1000 if so you have something that's non-conductive it can actually gather a charge and then it gives off lots of electrons in it all we see is a glow so let's take a look at what happens when the electron beam hits a specimen and how that ends up making an image on our computer screen so here you can see like Tron beam heading down it hits the specimen here and then there's actually two types of electrons that are going to come off of this in one case we're going to get the what are known as secondary electrons and that is when the electron beam comes down and hits the atoms of the specimen the those atoms absorb the energy and give off their own electron there's a detector to pick up secondary electrons over here as you can see and that detector to attract those electrons has a positive charge on it it's about 300 volts which is actually quite a lot and then once those electrons come in to the Faraday cage which is positively charged they hit the detector and then the detector uses the information from those electrons to form the image on our computer screen now the second type of electrons are called back scatter electrons and these electrons actually don't come from the atoms actually reflect off the surface and they actually can come even from deeper down the specimen and we have a second detector that it can actually detect those so this is to show you this little illustration will actually show you where these electrons are going to come from so you can see or the secondary electrons are going to be surface electrons so they're very shallow but these are very good for getting surface features and of course that's one of the main reasons for using a scan electron microscope the back scatter electrons are going to come from deeper in the specimen so someone will bounce right off the surface some will go deeper and then the ones that are really deep actually never get back out again so when they get absorbed they give off x-rays now we actually don't have an x-ray detector for our scope but you can do an elemental analysis by using by looking x-rays so the detectors that we have on our scope are the secondary electron detectors and the back scatter detectors so why is it called a scanning electron microscope well as you can see from this illustration here's our primary beam coming down and it's actually making the picture pixel by pixel it's hitting from left to right top the ball and every time it hits we get electrons from that particular part of the specimen interestingly enough if you want to magnify all we do instead of actually scanning across a big image like this so we just would scan over a smaller box so this is actually showing the setup as you can see here we've got the column here so all the electromagnets are up above there the electrons come out through the pole piece here they hit our specimen the secondary electrons over here to the side and then of course our backscatter detector is actually going to be up here mounted to the pole piece and you saw a picture of that on inside of the TM 1000.
thank you
This was cool and gud thank u very much...
thanks
fascinating
informative presentation
really interesting
thx
great
thank uuuuu
Gk paham tapi pengen paham
Dead leagents after 8 yerrs ...corona
Thanks and God bless
John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
The anode is not positively charged, it is negatively charged,and it attracts positive charges.
Anodes are for the attraction of anions (negatively charged) and cathodes are for cations (positively charged).
They have to be oppositely charged from what they are attracting. Therefore, anodes are positively charged and cathodes are negatively charged.
Hi everyone .If you read this message please read the Holy Quran the direct words and the final message from Almighty God.It will guide you to peace truth and happiness in this world and the afterworld with my lovely wishes
thanks
thank you
Thank you
thanks