[♪ INTRO]
In the late 1970s, two physicists in Zurich, Switzerland,
wanted to do something no one had done before:
see the individual atoms in a sheet of metal.
Their names were Gerd Binnig and Heinrich Rohrer,
and at the time, they were both interested in studying materials
that could be used in electronics, like silicon.
They thought that if scientists could just see these surfaces
at an atomic level, they’d be able to understand them better,
and then, maybe, they could make electronics that were more
efficient and compact.
The problem was, Binnig and Rohrer would have to invent
new technology before they had any hope of doing that.
But they were excited about the challenge and the chance
to explore new areas of physics.
So they decided to go for it.
And decades later, we’re glad they did.
Because along the way, these two scientists invented a new type
of microscope that’s made its way into labs all around the world,
where it’s transformed our study of things ranging
from data storage to blood.
Just a few decades ago, seeing a single atom was absurdly difficult.
A few microscopes had managed it under special circumstances,
like if the atoms were isolated on a thin needle.
But this wouldn’t be enough for Binnig and Rohrer.
They wanted to see all the individual atoms on a whole surface.
Because, well, electronics components aren’t just made of
single atoms; they’re made of much larger materials.
Unfortunately, at this scale, regular optical microscopes —
like the kind you might have seen in science class —
are totally useless.
They’re able to see small objects because of how light passes
through them or reflects off them.
But the wavelength of light is much bigger than the length of an atom,
they can’t make out anything near the size of a single atom.
So the first microscopes to look at these things worked differently.
For example, electron microscopes (which showed up in the 1930s)
fired beams of electrons through their samples and then
focused them onto a screen.
There, the pattern they made revealed the structure of the object
they had passed through.
Which is amazing!
But these microscopes still didn’t have high enough resolution
to capture every atom.
They relied a lot on computers to fill in the blanks.
So Binnig and Rohrer wanted to invent a new kind of microscope
that could do even better.
They came up with a design that could potentially zoom in on things
10 times smaller than the best existing microscopes.
According to their plan, it would work kind of like a needle
hovering over a record.
The resolution would come from the sharpness of their needle —
because the more detail a needle can trace,
the more detail it can reveal.
In this case, Binnig and Rohrer wanted to be able to detect
each and every atom on a surface, so their needle needed
to be really sharp.
In fact, its tip had to be on the order of one atom thick.
That was the first big challenge.
The two researchers used a technique called electrochemical etching
to make a super-sharp metal tip.
To make a needle this way, you start with a regular piece of wire.
Binnig and Rohrer went with one made of tungsten.
You connect that wire to another piece of metal —
something like stainless steel.
Then, you dunk the whole thing in a hydroxide solution
and leave part of the tungsten wire poking out.
Since that tip is exposed, the liquid forms what’s called
a meniscus around it, meaning the liquid gets slightly drawn upward.
Next, if you apply a voltage between the two metals, charge will
start moving between them.
And that will set off a chemical reaction at the meniscus.
The submerged tungsten will react with hydroxide in the solution,
producing something called tungstate.
This tungstate dissolves away, leaving the wire to get thinner
and thinner at the meniscus.
Essentially, the metal gets chemically eroded away.
Eventually, the wire becomes so thin that it breaks!
And it leaves behind an extremely sharp tip — ideally one-atom thick.
But this process isn’t perfect, so the tip normally still needs
to be sharpened a little.
Fortunately, even on their first attempt,
Binning and Rohrer were prepared.
They were able to sharpen the tip by exposing it
to very high electric fields.
And I mean very high — like, high enough to make the molecules
restructure themselves, which created a sharper point.
But making the tip was only half the battle.
Next, Binnig and Rohrer had to lower it into the surface
they wanted to study.
Except first, since they were dealing with such fine detail,
they needed to completely control any vibrations —
otherwise the tip or the sample could move in unpredictable ways.
And that wasn’t easy.
Because all sorts of things create vibrations — people talking,
cars driving, the wind blowing.
At the atomic level, even a footstep can seem like an earthquake.
So the two researchers decided to levitate the entire apparatus
using magnets.
Which is super practical and as a bonus, gives your experiment
a nice sci-fi vibe.
Once their contraption was finally in place, it was time
to actually trace the atoms in the silicon and get a reading.
But to do that, they needed a way of determining when the needle
was directly over an atom.
Because, again, the needle itself was around the size of an atom,
so to it, the metal didn’t look like a smooth sheet —
it looked like a bunch of atoms bound together
in some complex structure.
So, they called on one of the quantum mechanics’ best party tricks,
which just had been discovered a few decades before: quantum tunneling.
Quantum tunneling is a phenomenon that happens because atoms
are super strange.
They don’t look or behave like anything we’re familiar
with in the everyday world.
And they don’t look anything like that classic model that was
probably on the cover of at least half your science textbooks.
In fact, they’re not even solid particles at all.
They’re little nuclei surrounded by electrons.
The thing is, those electrons don’t follow nice neat orbits.
And—stick with me here—they truly don’t exist
in a physical place at all.
The most we can say is that an electron has a certain probability
of being somewhere at a given time.
And that’s not because we can’t see it or because we don’t have
the precision to measure it or something.
They actually don’t have a specific position.
In fact, there is even some probability of electrons jumping
from one location to another.
And that jump is called quantum tunneling.
Binnig and Rohrer encouraged the electrons to jump
by giving the needle and the sample each
a different electric potential.
To try to even things out, electrons would jump between
the two and create what’s called a tunneling current.
And the strength of the tunneling current would depend
a lot on how close the needle was to a given atom.
This was the key that made the rest of the experiment fall into place.
If there was a lot of current, that would basically mean
the needle was hovering right on top of an atom.
If the tunneling current was very weak, then the needle
was probably far from an individual atom.
This understanding was the breakthrough that made
the whole technique possible.
It sounds like the kind of mission that could take a lifetime
to make into reality.
You’re combining chemistry, electromagnetism, materials science,
and quantum physics.
Making this microscope was a tall order.
But just three years later, in 1981, Binnig and Rohrer
had a needle scanning the surface of a sample of silicon.
Using what they knew about tunneling current,
they used computer software to create a topographic map
of the surface.
And that year, they created the first images of atoms
with their new technique.
It was incredibly exciting for scientists to see these atoms.
And, as they’d hoped, being able to probe metals this way
did reveal new things about what they were like at the simplest level.
It made it possible to see what the structure of metals looked like
at the surface, and to better understand how atoms at the surface
interacted with the elements of their environment.
But the thing that had the widest impact on science
was not the discovery itself but the tool Binnig and Rohrer
invented to make it.
The microscope they created came to be called
a scanning tunneling microscope, better known as an STM.
And since then, scientists have poured a ton of effort
into perfecting it.
Today, many STMs are inside soundproof rooms on top of powerful vacuum
pumps that completely isolate them from outside vibrations.
Usually they’re even inside a Faraday cage — which is
a large metal cage designed to block electromagnetic fields
from getting inside.
And to snuff out any last possible vibrations, some STMs
are kept just fractions of a degree above absolute zero—
about negative 273 degrees Celsius.
These machines have been used to image materials like silicon,
nickel, and even oxygen and carbon.
Materials that are important for things like life
as well as electronics.
And just a few years after the STM was invented,
IBM began using it not only to look at atoms but to manipulate them.
By holding the tip of the needle close to an atom,
they were able to use the attraction between the two surfaces
to pick up the atom and move it to a new position.
The ability to do that opened up a new field called
nanoscale engineering, which is all about constructing
and researching structures on the scale of molecules.
Today, STMs are used in a huge range of scientific fields.
In microbiology research, they can not only take images,
but also videos of atomic and molecular movement.
These scientists have been able to record video
of individual molecules coming together to form a blood clot.
Being able to witness events like this gives scientists
incredible insight into complex interactions.
STMs may also help engineers create new technology
for data storage, which is a constant challenge these days.
Instead of relying on conventional hard drives,
which store information in magnets representing a one or a zero,
researchers hope to magnetize individual atoms,
which might make it possible to store information at an atomic level.
Not only is that efficient, but certain atoms have
incredible magnetic stability.
So, if they could be used for storage, you wouldn’t have to worry
about a magnet or extreme heat erasing your precious data.
So, decades after it was invented to solve one problem,
the STM is still pushing science forward in all different directions.
All because of two curious physicists in Zurich who thought
it would be pretty handy if they could take a closer look at silicon.
Thanks for watching this episode of SciShow!
And if you’re curious what an atom really looks like,
you might want to check out our video about how we came up
with our model of the atom.
Incidentally, we had a decent idea what atoms looked like even
before we could ever see one.
To find out how, you can watch this episode next.
[♪ OUTRO]