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  • [♪ 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 tipideally 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 highlike, 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 vibrationspeople 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.

  • Andstick with me herethey 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 cagewhich 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]

[♪ INTRO]

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利用量子物理學追蹤原子的顯微鏡 (The Microscope That Uses Quantum Physics to Trace Atoms)

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    林宜悉 發佈於 2021 年 01 月 14 日
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