Electron microscope image capture with an oscilloscope

check out my scanning electron microscope collection this is the SEM that I built myself a couple years ago but the newest addition is this jeol J SMT 200 this was sent to me by Richard Anderson who rescued it from his University's trash heap and offered to send it to me if I paid for shipping from Sweden which I thought was a great deal so in this video today I'm going to talk about how I'm getting digital images off this piece of equipment and into videos also if you're interested in supporting the channel I've got a t-shirt design on teespring comm I'll put a link in the description and it's a 14 bucks for a quality t-shirt you got the logo on the front and applied science on the back so I go ahead and pick up one of those if you're interested before the crate left Sweden someone maybe FedEx dropped it on its back and surprisingly the force was high enough word actually knocked the socket connector off the back of the CRT inside here even more surprisingly just replacing the connector and then refilling the pump with some oil was all it took to bring this up to fully functional status so currently we're looking at a MEMS gyroscope and you can see we're live here we can zoom in and out and pan around like this and the state-of-the-art image capture technology at the time was this polaroid camera adapter so you'd actually put a film camera here and then set up the scope to do one single frame exposure while the camera shutter was open however there's another reason why using a camera it will give you a better image than just looking at it on the CRT the electron microscope works by focusing a beam of electrons down onto the sample and then measuring the amount of emitted electrons coming back from that point so the signal is very small just for argument's sake let's say that when the beam is over this part of the sample we're only getting one electron per second and over here we're getting two electrons per second now we want to amplify this signal into something we can actually see in an image however no matter how good our amplifier is this is going to make a pretty terrible looking image because there's so few gradations in fact there's only three values zero one or two and we can multiply that by a million and then we have 0 1 million and two million in the image would look basically the same this problem is referred to as shot noise and it stems from the fact that the electrons have a discrete charge and once we've counted them we can't really amplify the signal anymore because we've already counted all the electrons that we have in the real world the amplifier adds its own kind of noise and there's also other signal problems too but this is a fundamental problem that the best technology cannot get around so if the sample is only emitting two electrons per second and we're capturing all of them all two of them and we're amplifying them as best as we can what else can we do to get more signal well we could just shoot more electrons at the sample if we just dump more electrons in will get more electrons out however the problem is that electrons are like charged and they repel each other so if we have more electrons in the beam the beam will necessarily be fatter at low magnification this isn't a problem but at high magnifications we really need this beam to be as tightly focused as possible to get a good image so alternatively we could put more energy into each photon so we're not actually adding more photon or we're not adding more electrons but we are making them go faster and this is the you know the kilovolt acceleration value that you'll see on lots of scanning electron microscope micrographs however this has a limit as well eventually the electrons will have so much energy that they'll be buried deep into the sample and we actually won't get any more of this signal coming out the realistic upper end is about thirty kilovolts and any faster than that the electrons don't actually give us much more information about the surface of the sample so we're running out of tricks but there is something else we can do we can actually slow down the speed at which we scan the beam along the sample so if we're only getting two electrons per second here if we stayed over that spot for a good 10 seconds we might find out that we collected a total of 21 electrons and if we move to the next value whereas before we collected nothing in one second we might collect four electrons sitting there for 10 seconds so what we've done is we've sort of traded our poor signal collection ability for with times we're spending more time and getting a better signal all scanning electron microscopes including the latest cutting-edge models have to get around this problem of dealing with low signal so when resumed in like this we're in video mode now which is kind of like a low resolution fast scan rate and this is so that we can move around and get the image set up and focus it and then to actually take an image we slowed down the scan rate to something very low in fact it's it's too low to even see the image it's just a line that's tracing down however if we had a camera with its shutter open or if we had a digital acquisition system we could collect that high-resolution image and remember the only reason that we're doing this slowly is just to collect basing more electrons from the sample this device has three basic modes it has the full video mode which is approximately 30 frames a second and then it has this scan rate which is about 10 seconds for a full scan and then it also has a super slow rate that's meant for use with the camera and in full the full scan takes about 60 seconds and like I say even modern cutting-edge scanning electron microscopes still require the same amount of time to collect a high-quality image just because the problem is actually physically based it's just the number of electrons that we're trying to capture so lucky for me I have nearly the complete schematic for the whole scanning electron microscope and probe the board at the point where I get the video signal for these slow 10 and 60 second scan readouts the signal was quite high amplitude we're at five volts per division and you can see that there's a negative pulse here in a negative pulse here which is what I'm triggering off of and these are the horizontal sync pulses so between these two pulses this represents one line of video or one string of values that we're pulling out from the scanning electron microscope and as the scan moves from the top of the screen to the bottom you can see the shape of the scan line change or the intensity of the scan line change so the first thing we want to do is maximize the dynamic range that we can capture with the oscilloscope so what we're going to get here is eight bits of data that are going to span the top the bottom to the top of the screen so since we're basically not capturing any signal from down here what we can do is move the horizontal or the vertical position down and then I'm going to fine tune gain not quite that much something like that so now our video signal is basically filling up the whole screen and it's okay that the sync pulse goes negative second I'm going to go to the acquire menu and change the sampling mode to high-resolution since we're going to be sampling at a relatively low rate much slower than the scope can sample we want to take all those values and average them together so that we don't get sampling noise next we're going to change the record length so since we know that the whole scan is going to take 10 seconds for the scanning electron microscope to finish and let's say we want you know a two or three megapixel image or at least a 1 megapixel image we're going to want to record at least 1 million or 2 million points and so our options are 1 million or 5 million and 1 million is probably not quite enough because we're going to lose some of those acquisition points to the horizontal sync pulses which happen pretty frequently so I'm going to change the record length to 5 million right now the scope is just triggering on every horizontal sync pulse that it gets however a slightly more elegant way of doing it to set up the trigger so that it will only trigger on the vertical sync pulses so that when the scope starts or when the scanning electromicroscope starts a scan the scope will be triggered and we'll have the data at the right point so instead of a simple edge trigger I'm going to set up a pulse width trigger and we are going to trigger when the pulse is greater than 500 microseconds actually like the data entry on this since you can just dial in a number directly like 505 per second so just have it set like that and if I set the level properly you'll notice that it's actually not triggering what's going on well the vertical sync pulse is so infrequent it only happens once every 10 seconds the scope has gone into its auto trigger mode so we'll change this to a normal trigger and as you can see the scope is not running right now it's a trigger the question mark meaning it hasn't gotten one pouch here it's going to trigger now and that was because the microscope just started a new frame so now all we have to do is set the horizontal scale so that we get this whole ten-second capture in one block so we'll change the horizontal scale to one second per division would be just not quite enough so we'll go with two seconds per division and then we'll also change the trigger point to be right about there so at this trigger point this is going to indicate the start of a frame so the scope just triggered and unfortunately in the normal trigger mode with these very slow capture rates you know two hundred and fifty thousand samples per second it doesn't actually show you the buffer filling as it's acquiring data so there it is this is a whole video frame you can actually see the divisions this is the start of the next frame this is the end of the previous frame and this is the whole frame as you can see there might be just a few very very sparse Peaks that are actually going off scale but otherwise it's a very good image because we're using as much dynamic range as we can so now we want to save this data to a file that you can get onto a PC so I'm going to use my USB Drive here and the tech has an interesting feature what we can do is set up the cursors to just select the data that we want so what I'm going to do is basically just kind of give it some buffer but basically just select that frame and then we'll go to the save menu and say save waveform so we're going to save channel 1 and instead of saving it to r1 we're going to save it to a file and it automatically picks a name that doesn't exist already on the drive and then for gating we'll say between cursors so we could have it save just the screen or the full record but this will actually save us some data since we don't care about the other frames stay ok I'm using octave which is an open-source MATLAB alternative to take the data in the CSV file and produce an image so here you can see the horizontal pulses in the raw data so this represents one scanline and my script just goes through and puts those scan lines together filling up the image in sort of a raster pattern and so here we can see the image that we just captured this is the MEMS gyroscope and as you can see there's actually a little bit distortion at the side here mainly because the scanning electron microscope does not intend for the video signal to be picked off the circuit board at that point where I grabbed it so when you tell it to make a photo what it does is it actually uses a sub section of the screen in fact just this middle may probably about the middle 25% or so here's an image of a housefly that I captured without actually coding the fly with metal typically non conductive specimens have to be sputter coated with metal to show up well however this is just a dried out fly here's a close-up of the fly's eye and head area I was also able to capture an image of red blood cells this is just a tiny drop of blood that I put onto a metal holder and the blood cells are drying out but aren't completely dry yet I was kind of surprised how much signal I got out of this okay see you next time bye

Channel: Applied Science

Views: 253,694

Keywords: SEM, scanning electron microscope, microscopy, oscilloscope, Tektronix, MDO3000, data capture, digital image, JEOL, JSM-T200, Electron Microscope (Invention), Image Capture (Software)

Id: SWVu-qPR-Ws

Length: 12min 14sec (734 seconds)

Published: Mon Sep 01 2014

Reddit Comments

[u/rlrl]

First I was like "you can't do that in your garage". Then I saw it was Ben Krasnow.

[u/AmericanGeezus]

I have a feeling that man has more dollar value worth of oscilloscope than I will have ever earned in my life.

[u/[deleted]]

I really want an electron microscope (and vapor deposition chamber).

I gotta figure out how to salvage one like this guy did. All of the older ones will have through-hole components that would be relatively easy to replace.

[u/spainguy]

It's just using the scope as a basic frame store, nothing special, but quite pretty

http://www.techmind.org/vd/vidmk2.html

[u/sdmike21]

Holy shit this is so cool!

[u/dmayan]

Awesome!!!!!

[u/[deleted]]

Okay question, when he saved the data on the scope, was that the entire image data he saved or just one scan line? If it was one scan line, that seems like it would take forever to do manually so surely it must have been the entire image data?

[u/marmz111]

That was awesome!

[u/[deleted]]

I'm a smarter person now. I like this video.