[♪ 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]
