DIY Scanning Electron Microscope - Overview--- make money online

hey guys I thought I'd show you my

latest project I haven't uploaded a

video in a while since I've been

spending pretty much all of my time on

this project this is an electron a

scanning electron microscope that I

built pretty much from scratch and it's

taken I've had some of these parts in my

garage for four years literally but I've

been spending just about every weekend

since January working on it so a pretty

involved project and I'll just give you

the basic overview and then show you

what I accomplished today which was

actually a huge milestone for this

project and we'll see where we go from

there so what we have here is a vacuum

chamber this is a glass bell jar that

seals on to a an aluminum plate here and

we'll just take the jar off so that we

can take a look at what's inside okay we

have three brass threaded rods which

just provide a support structure and a

bunch of copper piping which allows a

channel to be formed from the top of

this device to the bottom and at the top

we have an electron gun very similar to

the one that's in an old-style cathode

ray tube TVs so it fires electrons down

the copper pipe and it slams those

electrons into a sample the thing that

you're actually looking at and then

captures the resulting signal which is

also in the form of electrons and

eventually all this is displayed on an

oscilloscope which I'll show in a minute

so I'll probably end up making quite a

few videos showing how this project

works this is really just a very very

brief overview and I'll get into more

details later so let's move in and I'll

start on those details

okay so we're looking at the top of the

electron column that is the electron gun

at the top which I'll take apart and

show in a later video it basically

consists of a tungsten hairpin filament

so very similar to a filament in a

tungsten light bulb but it's not coiled

it's just a straight piece of wire

that's bent into into sort of an elbow

shape so the hot filament boils off

electrons through thermionic emission

and then there's a high voltage

accelerating potential of about about

five thousand volts I can adjust it but

I think five thousand has been a pretty

comfortable number so far so those

electrons come out of the electron gun

in a kind of a loose beam I found that

with the geometries of my electron gun I

had about a about a one inch diameter

spot about eighteen inches away so

that's you know a fairly tight beam for

for just the electron gun but to make a

useful electron microscope we need the

beam to be much more focused so as the

electrons travel down the column they

encounter this which is a an electron

lens so by exposing those moving

electrons to a specific kind of electric

field they can be focused just like

photons are focused when they move

through a glass lens or any let any

material that has a different refractive

index than the medium in which the

lenses are set this functions as a sort

of condenser lens so the electrons that

pass through here are focused to a point

that's very close in the lens so the

focal point of this lens is right about

here so as the electrons come through

here they're focused to this point here

and then diverge very very sharply and

the point of this is to D magnify the

image of the from the electron gun so

this is a way of increasing resolution

and it's also the reason that you would

want to have an electron

column that's you know relatively tall

the reason these devices aren't short

and squat is because optically it works

out a lot better if the if the electron

gun is farther away and for a similar

reason picture tubes in TVs are set up

that way to the electron source has to

be sort of far away in order for the

deflection and focusing to work so after

the electron beam passes through that

lens there is a set of deflection plates

so we are looking at it so that you can

see this bottom set of plates

you know edge on and the top set of

plates are side on so it looks like

there's just one plate there but it's

actually the same in both axes and by

putting a voltage difference across

those plates we can control how the

electron beam is scanned across so the

voltages are pretty low compared to the

rest of the system it's just about a few

hundred volts across the plates there at

most and the lower the voltage

differential the less the electron beam

moves and then we this is actually

another lens this top plate with a

there's an insulator but there's another

electrode in there and an electrode here

that's the focus for the beam that

focuses the electrons down and finally

they actually hit the sample which in

this case is that little lock washer

there just that little tiny washer and

when they hit the washer they emit a

cloud of secondary electrons and this is

the signal that a scanning electron

microscope actually senses and we'll

talk about how that thing is how the

electron cloud is sensed in in just a

minute

so here's that lock washer and this was

the thing that I use to actually test

this whole thing out today just because

it's a very simple object and it's

conductive but I'll get into that later

so we were talking about slamming

electrons into this thing the whole

point of this electron column with the

copper pipe and everything is just to

get a very fine very tightly focused

beam of electrons to hit the target in

this case that lock washer and when you

get an electron beam to hit something by

physics you you release more electrons

from the surface of that object so the

way this works is the beam is scanned

across the target object and these

resulting sort of secondary electrons as

they're called is sensed by this device

this this particular one is called a

never heart Thornley detector and the

way it works is by attracting those

secondary electrons that are liberated

from the surface of the object over to

here and it does that by putting a

voltage on this cage and inside here

there is a phosphor just like the

coating on a television screen or an

oscilloscope and when those electrons

are attracted over here there's their

accelerated and slammed into that

phosphor creating a little flash of

light and the flash of light is

conducted through a an acrylic light

guide and then up into here where there

is a photomultiplier tube which is

really just a fancy device that can

sense very low light levels so what we

end up is with a flickering sort of

light that's being sensed by the

photomultiplier inside here and the

reason this plastic bag is on is is just

to keep stray light out so the way an

image is formed is by synchronizing the

scanning that's going on in this

electron microscope with the scanning

that's going on on our display device

which is an oscilloscope in this case so

as the electron beam is scanned across

the surface of our sample

it's also scanned across the surface of

the oscilloscope and the signal that we

get from the secondary electron detector

is routed to the oscilloscope

brightness basically the beam brightness

on the oscilloscope so when we're

getting up as the beam moves across when

it's in a position where it's getting a

strong signal the oscilloscope will be

bright in that spot on the screen and

when it moves into a region where

there's not much signal coming out the

oscilloscope will be darker in that

region so an electron microscope

microscope doesn't actually form an

image in the microscope like a light

microscope does it actually scans across

and just sends that that information out

through this secondary electron detector

okay

so let's take a look at the front panel

here we've got all kinds of cool knobs

and gauges to look at I'll just start at

the top this top segment controls the

filament and the electron gun of the

device so this knob controls bias

voltage which regulates how much current

actually comes out of the electron gun

and this knob controls the filament

temperature the next one down is the

raster scan generator so this is what

actually applies voltages to those

deflection plates and there's controls

for x and y scale and offset so in both

axes you can control where the scanning

is happening and how big the scan is and

this is actually what controls the

magnification of the microscope so if

the scan is very small the magnification

is high because the size on the

oscilloscope screen is constant so if

the scan size gets progressively smaller

and smaller the overall magnification

goes higher and higher which is you

would think it would actually be you

would take more voltage or more signal

or something to get a higher

magnification but it's actually the

other way around

smaller deflections and smaller voltages

will lead to higher magnifications okay

and the this this is the the X&Y; signals

that are output to the oscilloscope so

Athy standby microscope scanning is

synchronized with the oscilloscope

display okay the next one down is the

secondary electron detector control so

this controls the voltage on that the

wire mesh cage it's usually about

between 0 and 500 volts this is the main

accelerating voltage for the phosphor

screen that's usually about 10,000 volts

this is the focus voltage that could be

hmm

couple thousand volts it depends on the

accelerating voltage these two bottom

things are commercially made supplies in

fact this one was the one that actually

inspired this whole project we'll get to

that this is a high voltage supply for

the photomultiplier tube and that uses

anywhere between 500 and 1500 volts you

can actually control the sensitivity or

the gain of the photomultiplier tube by

adjusting its supply voltage and this is

the main accelerating voltage for the

electron gun and it's set to six

kilovolts now but it could be anywhere

from zero to ten on this supply and

commercial scanning electron microscopes

actually go anywhere from a couple

hundred volts all the way up to 30 or 40

kilovolts even the vacuum system is two

parts this is a mechanical pump pretty

self-explanatory it's just it uses

mechanical means to actually remove most

of the air from the chamber but in order

to get an electron beam working

efficiently there needs to be an

additional vacuum pump which is hiding

behind these hoses here it's kind of

hard to see this is called a oil

diffusion pump and it has no moving

parts what it does is it actually boils

oil and uses the vapor debt to push more

air out of the chamber so I'll probably

do a whole video just on this by itself

the the basic idea is that it's very

easy to deal with since it has no moving

parts and it's it only has one drawback

which is that the boiling oil can get up

into the

cube chamber which is bad because you

know it make a mess and cover everything

so to get around that problem there's a

water-cooled baffle these are just foam

insulated rubber hoses and I'm using my

window air conditioner water chiller

concoction over here to condense that

stray oil vapors and get them to drip

back down into the pump instead of

contaminating the vacuum chamber so the

big success today was that I finally

formed an image with this microscope up

until today I've just been you know

doing preliminary tests and figuring out

how the electron beam was actually

moving it's it's actually a very

difficult thing to do because you can't

see the electron beam the only way to

tell what's happening is to put a

phosphor screen in the in the path of

the beam and that's I've been using this

oscilloscope screen that I cut off it's

coated with a green phosphor so I've

been putting that into the microscope so

that I can see what's going on otherwise

you have no idea where the beam is and

if this you know project generates some

interest I'll do a video on all the

problems I ran to lit basically took you

know to two or three months here to to

get the beam under control and working

the way I was you know hoping that it

would so so today we've finally got an

image in basically all the parts of this

system are working even though we still

have quite a few refinements to go

through at least the images there and I

can start refining it now so all the

parts are at least you know working as

planned so let me know what you think

let me know if you have any questions or

if this project is interesting to you

and we'll probably make more videos I

don't think I'm going to write up really

detailed instructions unless unless the

response is quite large but I'll

certainly make more videos and you know

make some great pictures actually once

the thing starts working a little better

ok see you next time byeTop Paid Keyword :  earn cash online, google make money from home, earn money online without investment by clicking ads, free earn money website, online money making jobs, earn money online without investment by typing, online work for money, best online earning sites, make money online with google, online earning websites, money making websites, online earning websites for students, invest online and earn money, best online money making, online money income, view ads and earn money without investment, earn money online by clicking, online money income site, money earning sites, online earning sites, best website to earn money,