Kind: captions
Language: en
this is a tiny piece of metal just 3 mm
across and here's what happens if you
just keep zooming in 1 thousand
times 100,000 times 50 million times
each of these blobs is an actual
atom I saw this the other day at the
University of Sydney and it kind of blew
my mind because up until just 30 years
ago directly seeing atoms like this was
thought to be impossible the rooms that
you going to see here are perhaps the
most shielded rooms on campus or even in
the Hall of Sydney I would say and
perhaps also the most expensive that's
wild so why is it so hard to see
atoms well you can't actually see atoms
with visible light that's because while
light has wavelengths between 380 and
750 NM and atom is still over 3,000
times smaller just .1 NM and if the
wavelength of light is much bigger than
the thing you're trying to see the light
will just defract or bend around it so
you won't be able to see it so if you
want to see atams you need something
with a much much smaller wavelength the
best candidate isn't even
light it's
electrons in 1924 a French physicist
named Lou de broi worked out that
everything was sort of wavelike not just
light but matter too atoms molecules
even you yourself have a wavelength and
the formula for this wavelength is
Plank's constant divided by the object's
momentum that is mass time velocity so
here what you actually see that's the
column of the microscope where we
accelerate the 300 KV electrons down 300
Kilts these electrons yes so they are
relativistic particles how fast are they
moving 99% the speed of light or uh well
around 80 80% of the speed of light yes
so what would be their wavelength the
wavelength is the plank constant over
the momentum right so uh if we calculate
that we come to around between 2 to 3
Pomers wa yeah that's over 100,000 times
smaller than visible light so
theoretically you get 100,000 times more
resolution shortly after de Broly's
Discovery a group of scientists in
Germany started working on a microscope
that would use these high-speed
electrons the only problem is you can't
bend electrons using glass lenses so how
do you focus them Hans Bush a German
physicist suggested that an
electromagnetic lens might do the trick
he published his results in 1926 but
never actually built one fortunately a
copy of his paper fell into the hands of
an eager young PhD student erns
rusa rusa built his first prototype by
coiling up some wire and surrounding it
with iron taking care to leave a gap in
the middle then when he passed a current
through the coil it induced a
donut-shaped magnetic field through the
metal and across this Gap this was his
lens to test it rusa first boiled
electrons off a Tungsten filament the
same kind of filament you'd find in an
incandescent light bulb he accelerated
these free electrons through a
positively charged anode down to his
electromagnetic lens as an electron
approaches the lens the magnetic field
exerts a force on it so if an electron
is traveling in the y direction and the
magnetic fields are in the X Direction
This Force called the lorence force
pushes it in the Z Direction but as the
electron moves this way and encounters
other magnetic field lines along the
donut shape which constantly Point its
motion in a circle but then this
circular motion means the lorence force
starts pushing the electron inwards as
well spiraling it into the center of the
lens now if you trace the path of the
whole beam of electrons you'll see they
all get steered into the center focusing
the
beam by 1931 rusa and his colleague Max
null used this kind of design to build
the first working electron microscope it
was pretty basic made of brass roughly
bolted together but it
worked the image itself was created once
the focused Electron Beam hit a sample
sitting at the focal point the sample
needed to be incredibly thin only around
100 nanm thick more electrons would make
it through the thinner parts of the
sample than the thicker Parts creating
an electron imprint of the sample then a
second electromagnetic lens magnified
this imprint down onto a fluorescent
detector producing the final image this
was known as a transmission electron
microscope or
temm now early versions of the
microscope barely magnified at all in
fact it wasn't even better than an
optical microscope but rusa was
determined over the next few years he
experimented with adding more lenses
onto the microscope to create bigger and
bigger images by the mid 1930s rusa had
gotten the tem way past 10,000 times
magnification it could produce close-ups
of insects bacteria and even viruses at
a level far surpassing the optical
microscope but right as RCA's temm was
taking off a German physicist named uto
Sherer published a paper claiming that
the microscope was about to hit a brick
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wall there was a flaw in the
electromagnetic lens he wrote that was
completely unavoidable
for an electron to make it to the focus
of the lens it needs to be deflected by
a specific amount if you simplify its
trajectory you can Define that ideal
deflection with this angle Theta this
angle depends on the horizontal distance
of the electron from the optical axis
and how far down the axis the focus is
also known as the focal length the
shorter the focal length the stronger
the magnification if you graph this
angle as a function of distance to the
optical axis you'll see that it can be
approx oximated as linear the problem is
that the magnetic field doesn't scale
linearly it's much stronger near the
edges of the magnet so if you plot the
curve for the actual deflection of the
electrons you'll see that the magnetic
field over deflects the electrons
further out their angles are bigger than
they should be so they end up focusing
before the Rays in the middle and as a
result the focus is spread across the
optical axis instead of being contained
in a single point the blur starts out
around the edges of the image but it
gets worse the higher the magnification
this is called spherical aberration and
it distorts every radially symmetric
magnetic
lens in fact it doesn't just affect
magnetic lenses every spherical lens
from a camera to a telescope to a
magnifying glass also suffers from it
but there is a surprisingly simple way
to minimize spherical aberration just
add a second lens one that diverges
light instead of converging in end now a
diverging lens also suffers from
spherical aberration but if it has the
same amount of aberration as your
converging lens Just In Reverse you can
stack the two to essentially cancel out
their effects and that removes the
aberration almost entirely almost all
modern lens systems in cameras and
microscopes use some sort of correcting
Divergent lens so you might imagine that
the tem simply needs its own version of
a diverging spherical lens to magnify
further but with magnets this is
physically impossible every magnet has
two poles a north and a South it's
impossible to just have one even if you
split a magnet down the middle it
creates two smaller magnets both with a
north and a South and all magnetic field
lines have to start at one pole and end
at the other forming a closed loop is a
direct result of the second Maxell
equation because the field that you you
create has field lines that start and
end at the same magnet so electrons will
always cross through two lines the first
time it passes through by the luren
force it's brought into the spiraling
motion and then the second time from
that spiraling motion which has then a
slightly different direction it's pushed
towards the
axis that's why all electromagnetic
lenses by default will converge the beam
and never diverge
it even if you shot electrons in from
the other side of the lens they would
still get focused
this is what Auto sherer's paper proved
in 1936 stopping progress on the tem it
is impossible to produce a radially
symmetric magnetic lens that
diverges and this was of course a big
roadblock for the development of
electron microscopy because people saw
okay we can accelerate electrons as much
as we want the presence of the ccal
aberation will always be in the
way because of this roadblock
advancements in the microscope's
resolution slowed significant ific L by
1955 another microscope beat the tem to
the punch and took the first generally
accepted image of
atoms this was called the field ion
microscope and it worked by shooting
helium or neon atoms at an atomically
sharp needle tip the tip was positively
charged so when the gas atoms hit the
needle they got ionized and were ejected
off perpendicular to the surface and
that could form an impression of the
atomic structure of the tip but this
method was limited you could only get a
sense of the atomic structure of the
very tip of the needle and the images
weren't all that
impressive luckily RCA's electron
microscope wouldn't stay stuck in the
realm of insects and bacteria
forever now you might not be an insect
getting bombarded with relativistic
electrons but it can sometimes feel like
it when you're getting bombarded with
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incognitum and now back to the electron
microscope despite sherer's abberation
limit work on the transmission electron
microscope continued during the next
four decades people tried boosting the
resolution with clever workarounds and
perhaps none more so than British
American physicist Albert
crew his idea was to replace the
tungsten filament which fired off
electrons at random with a more directed
source so instead of boiling electron
off the surface he tried pulling them
off with a stronger electric field and
by sharpening the tungsten into a fine
tip he was able to create a narrow beam
which was over a thousand times brighter
than
before he paired his new narrow Beam
with an unlikely
technology the cathode ray tube TV these
TVs worked by scanning an electron beam
across a screen the screen was Co in a
phosphor that produced light when hit by
electrons and by varying the intensity
of the Electron Beam you could vary the
brightness of the screen giving you a
black and white
image crew was inspired to design a
similar Electron Beam for the tem that
would scan across the nanoscopic sample
so instead of creating an imprint of the
whole sample at once Cruz Electron Beam
made smaller imprints mapping the sample
out bit by bit this wasn't the first
time someone had tried to make a
scanning version of the tem German
researcher Manfred Von built an early
prototype in the
1930s but it was destroyed during World
War II when crew revived ardan's design
he made several drastic improvements and
by 1970 he had this the first image of
single atoms taken with the electron
microscope researchers quickly jumped to
employ his Tech producing countless
images of
atams after nearly a century of
improvements from rusa crew and many
others the magnification upgrades on the
temm had reached their
Peak but sherer's problem
persisted spherical aberration set a
hard limit on how small you could see
even crew himself gave up on trying to
get around it after over 10 years of
work unfortunately we could never make
it work after many heartbreaking
attempts we were forced to admit defeat
around this time other microscopes
emerged that could also image atoms
these probe microscopes work by gliding
an incredibly small stylus across the
sample the stylus detects variations in
Quantum effects or nanoscale forces to
then map the surface structure of the
sample these were easier to build and
because they didn't use any lenses they
weren't limited by spherical aberration
their images were even 3D but the
looming issue was that these probes
weren't really seeing atoms it was more
like feeling atoms throughout the ' 80s
and '90s this was all we had but what if
there was another way sh's theorem
proved that a diverging radial symmetric
lens isn't possible but if you're
willing to give up on that symmetry the
theorem no longer applies the problem is
that radial symmetry is arguably the
most important property of any lens
because if you break the Symmetry you
also break the
image but three Maverick scientists
thought there might be a way
n Urban Max hater and Harold Rose were
known in the electron microscope
Community as troublemakers and for years
barely anyone had been interested in
their research or more importantly in
funding it and for a good reason too
their idea was kind of crazy I mean they
purposfully wanted to break the image
using a lens that wasn't symmetric their
Hope was that there would be a small
part of this distorted image that would
be slightly diverging and maybe just
maybe this small part could correct the
spherical aberration of the original
lens so they got to
work to distort the image they used a
massive nest of electromagnets with six
eight or even 10 separate coils and
magnets with bumpy magnetic fields these
were known as the hexapole octopole and
decapo magnets so as the Electron Beam
passed through a hexapole it would twist
and squeeze the flat 2D image into a
triangular saddle and the circumference
of the original beam would be pushed
into the three corners with the rest of
the Interior stretched out but now the
middle of the image would have a slight
concave bow giving the effect of a small
Divergence then Rose haer and urban
forced the beam through a second
hexapole one that worked the opposite
way so it would unbend the distorted
image back into a circular shape but now
they calculated this new image might
have the remant of that tiny Divergence
still in its center with spherical
aberration pointing in the opposite way
so if they got their maths and
Engineering exactly right they could
feed an image with spherical aberration
through these two lenses to almost
completely counteract the effect and I
imagine a lot of people in the field
thought it was a crazy idea when it was
proposed right not only the concept but
um that this is like technical feasible
I believe it was thought that this is
not possible
by May 1997 the group had just 2 months
of development time left before their
last sponsor withdrew their backing and
to make matters worse their latest lens
iteration was still just on the drawing
board but somehow by the 23rd of July
just a week before their funding ran out
the new lens was ready to test they
gingerly placed it into the microscope
but like every time before it the lens
was unstable and failed so they decided
to switch off the equipment for 24 hours
to allow the magnets to settle and then
at 2: a.m. on the 24th they turned it on
again and almost magically the picture
started to
stabilize suddenly there was no
aberration only beautiful clear images
of
Adams after more than 60 years of failed
attempts Urban Rose and hater pulled off
the seemingly impossible with this
method they cut the resolution of the
temm down to only only .13 nanm an
average tem image went from looking like
this to
this a few months after the group's
breakthrough n Urban attended a
microscopy conference to share these
results but because of the group's
reputation he was relegated to a small
back room that barely anyone
noticed soon however words spread that
Against All Odds his pictures seemed
real then a crowd of hundreds formed
people were lining up outside hoping to
get a glimpse of their stunningly Sharp
[Music]
Images so we're going to get a sample
holder yes now we got a sample holder
out we put that under the optical
microscope so the sample itself is a
small Lamela that you can't see without
the optical
microscope yeah have a look through that
beautiful on top of the be there's a
prong yeah and on the very top of that
on the left hand side looks like a
little bit of dust that's our actual
[Music]
sample okay and now I simply go up with
a
magnification and I do a very few like
more basic alignments in this electron
microscope because it's called
transmission electronic microscope the
electrons always transmit the sample
here we look through our entire sample
at the same time and that's why it's so
important that we um align the sample if
you imagine atoms in a high symmetry
direction are lined up like PS on a
string when we look down it well we can
see an image but if we're in like some
random Direction then everything would
be just blurred so that's why we have to
do some tilting in the end and this is
where the actual sample starts the
stonum Titanite and this is a thin
region where where we hope to get Atomic
resolution so this is 5,000 times yes
wow and we see strum titanium we see
oxygen we see carbon that's
contamination so most likely what we're
looking at here is carbon
contamination when you do this Focus
what are you really looking for I look
for this Edge to become
[Music]
sharp see atoms
what just like
that that's
wild shortly after the group
successfully corrected the aberration in
the temm Andre cranic independently
achieved the same for Cruz version of
the microscope the scanning
temm and in 2020 all four were awarded
the prestigious cavali prize in
nanoscience for accomplishing what so
many others thought impossible through
their persistence and Ingenuity seeing
atoms like this is well
normal how big of a difference does
aberration correction make if you want
to see atoms and if you want to for
example measure interatomic distances
and if you want to learn what type of
atoms you have you need aberation
correction any research that's material
science materials engineering chemical
engineering you need to see what's
happening at the atomic level because
you want to relate the properties to the
structure if you can't see the structure
at the atomic level you only have half
of the information so that was a game
Cher that's why nowadays every
University in principle needs a
microscope like that