sciencebriefs
13:00in productionCh. 1 · Getting close enough to tunnel/ 13:00 · ceiling 15 min
Physics · Materials

Scanning tunneling microscope

Binnig and Rohrer got a tip close enough to a surface that electrons crossed the gap by quantum tunnelling alone, turning that current into the first routine images of individual atoms.

Between 1978 and 1982, Gerd Binnig and Heinrich Rohrer at IBM's Zurich research laboratory built an instrument that held a sharp conducting tip within a few angstroms of a sample's surface, close enough that electrons crossed the gap by quantum tunnelling rather than any ordinary current, producing a signal so sensitive to distance that it could trace the position of individual atoms. Piezoelectric ceramics moved the tip with sub-nanometre precision, and by holding either the current or the tip height constant while scanning, the instrument built up an image of the surface's atomic structure. The scanning tunnelling microscope required a conducting sample, careful vibration isolation, and often an ultra-high vacuum, but it delivered resolution finer than a tenth of a nanometre. Binnig and Rohrer shared half the 1986 Nobel Prize in Physics for the invention, with Ernst Ruska recognised for his earlier work on the electron microscope.

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Chapters & takeaways6
  1. 0:08
    Getting close enough to tunnel

    The instrument works by holding a tip so close to a surface that electrons cross the gap through quantum tunnelling rather than ordinary conduction.

  2. 2:10
    Five years at IBM Zurich

    Binnig and Rohrer developed the microscope between 1978 and 1982, solving the mechanical and electronic problems needed to make tunnelling current usable as a signal.

  3. 4:20
    Two ways to scan

    Constant-current mode adjusts tip height to hold the current steady, while constant-height mode keeps the tip level and reads variations in current directly.

  4. 6:30
    Piezoelectric precision

    Ceramic scanners move the tip in steps of a fraction of a nanometre per volt applied, fine enough to trace individual atoms.

  5. 8:40
    What the sample has to be

    The technique only works on conducting or semiconducting samples and typically needs vacuum and strong vibration isolation to succeed.

  6. 10:50
    A shared Nobel Prize

    Binnig and Rohrer received half the 1986 Nobel Prize in Physics, with Ernst Ruska recognised separately for the earlier electron microscope.

Worth your time?

Yes. Study the whole thing.

4.5/ 5
What works
  • the explanation of why tunnelling current is so exquisitely sensitive to distance makes the resolution numbers feel earned rather than just stated
  • the two scanning modes are distinguished clearly enough to picture how an actual scan proceeds
  • the technical requirements, conducting samples, vacuum, vibration isolation, are given honestly rather than glossed over
What does not
  • the underlying quantum mechanics of tunnelling itself is invoked rather than explained from basic principles
  • Binnig and Rohrer's five years of development work is compressed into a short span with little sense of what made it difficult
Study it if
  • anyone who wants to understand how scientists actually see individual atoms
  • readers interested in quantum tunnelling as a working engineering principle rather than an abstract textbook effect
  • people who enjoyed the atomic force microscope story and want the original instrument it grew out of
Skip it if
  • readers wanting a full quantum-mechanical derivation of tunnelling current
  • anyone mainly interested in insulating or biological samples, which this technique cannot image directly
The written brief3 min read

Getting close enough to tunnel

The scanning tunnelling microscope works by exploiting a distinctly quantum effect: when a sharp, electrically conducting tip is brought within roughly four to seven angstroms of a conducting surface, a small voltage applied between them causes electrons to tunnel across the intervening vacuum gap even though no classical current could cross that distance. Gerd Binnig and Heinrich Rohrer, working at IBM’s research laboratory in Zurich, developed the instrument between 1978 and 1982, turning that tunnelling current into a genuinely usable imaging signal for the first time. The current that results is exponentially sensitive to the size of the gap, meaning even a change of a fraction of an atom’s width in the tip’s height produces a measurable shift in current, which is what gives the instrument its extraordinary resolution.

Five years at IBM Zurich

Making that sensitivity into a working microscope required solving a set of demanding mechanical and electronic problems. The tip has to be moved with precision far finer than an atom’s width, which Binnig and Rohrer achieved using piezoelectric ceramic scanners that shift position by roughly five nanometres for every volt applied, controllable in all three spatial directions. Two complementary ways of scanning emerged from this setup: in constant-current mode, feedback electronics continuously adjust the tip’s height to keep the tunnelling current steady, and the resulting height adjustments trace the surface’s contour directly; in constant-height mode, the tip stays at a fixed height while the microscope simply records how the current itself varies as it passes over atomic-scale bumps and depressions.

Two ways to scan

The resulting capability has held up as genuinely revolutionary and remains in active use decades later: the instrument can resolve features smaller than a tenth of a nanometre laterally and height differences as small as a hundredth of a nanometre, fine enough to image and, in later applications, even manipulate individual atoms on a surface. Binnig and Rohrer’s achievement was recognised quickly by the physics community, and in 1986 they shared half of the Nobel Prize in Physics for the invention, with the other half going to Ernst Ruska for his earlier, separate development of the electron microscope decades before, a pairing that placed the tunnelling microscope alongside one of the twentieth century’s other major imaging breakthroughs.

Piezoelectric precision

What the technique does not do is image anything indiscriminately. It requires a sample that conducts electricity or at least semiconducts, since the entire method depends on a tunnelling current flowing between tip and surface, which rules out most insulators, plastics, and untreated biological material outright, a limitation that later motivated the development of the atomic force microscope as a complementary instrument. Getting clean, reliable images also typically demands an ultra-high vacuum to keep contaminants off both tip and surface, sharp tips made from tungsten or platinum-iridium prepared with care, and serious vibration isolation, since at this scale of sensitivity even ordinary building vibrations or footsteps nearby can disrupt a scan, requiring systems such as magnetic levitation or spring suspension to keep the instrument stable.

What the sample has to be

The scanning tunnelling microscope’s significance extends well beyond its own images, since it opened the broader field now generally called scanning probe microscopy, in which a fine tip scanned close to a surface reveals information a lens-based microscope simply cannot access. It gave materials scientists a direct, routine way to see atomic arrangements on conducting surfaces, verify theoretical predictions about surface structure, and later to move individual atoms into deliberate arrangements, work that helped establish nanotechnology as a practical research area rather than a purely speculative one. Its conductivity requirement, rather than closing off other materials permanently, effectively defined the boundary that follow-on instruments like the atomic force microscope were built to cross.

A shared Nobel Prize

This is well worth the time, both as a piece of physics and as an engineering story: the underlying quantum tunnelling effect is genuinely elegant, and seeing how Binnig and Rohrer converted an exponentially sensitive but seemingly impractical phenomenon into a stable, controllable imaging tool over roughly five years gives a real sense of what separates a physical effect from a working instrument. It rewards patience with the technical requirements section in particular, since understanding why vibration isolation and vacuum conditions matter so much is part of appreciating just how demanding atomic-scale measurement actually is. Readers wanting to understand later instruments built on the same lineage, particularly the atomic force microscope, will find this a useful and clarifying starting point.

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