Electron microscope image capture with an oscilloscope----make money online

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

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