Can You Keep Zooming In Infinitely?

The central breakthrough behind modern “atom-seeing” electron microscopes is not simply stronger magnification—it’s the ability to correct a fundamental blur called spherical aberration. For decades, transmission electron microscopes (TEMs) could get close to atomic resolution, but a built-in flaw in radially symmetric electromagnetic lenses spread the focus, preventing electrons from landing sharply enough to distinguish individual atoms. That limit shaped the field until researchers found a way to cancel the aberration rather than fight it head-on.

The path to this solution starts with why atoms are hard to view at all. Visible light can’t resolve atoms because its wavelength (380–750 nanometers) is vastly larger than atomic dimensions (about 0.1 nanometers). The workaround is to use matter waves: in 1924, Louis de Broglie showed that particles have wavelengths inversely related to momentum. Accelerated electrons at 300 kilovolts move at roughly 80% of the speed of light, giving them wavelengths on the order of 2–3 picometers—over 100,000 times smaller than visible light—making far finer resolution theoretically possible.

Early electron microscopes followed quickly. Hans Busch proposed electromagnetic lenses in 1926, and Ernst Ruska built prototypes that steered electron beams using magnetic fields shaped by a coil and a gap. By 1931, Ruska and Max Knoll produced the first working TEM design: electrons pass through an ultra-thin sample (around 100 nanometers thick), and a second lens projects the resulting imprint onto a detector. Magnification rose rapidly—by the mid-1930s, TEMs surpassed 10,000× and could image insects, bacteria, and viruses.

Then Otto Scherzer’s 1936 analysis landed like a ceiling. In a radially symmetric magnetic lens, the magnetic field strengthens near the edges, causing electrons farther from the optical axis to over-deflect. Instead of focusing into a single point, the beam spreads along the axis, producing spherical aberration. The same issue exists in ordinary spherical lenses, but for TEMs it became a persistent, unavoidable roadblock because magnetic lenses inherently converge rather than diverge.

Progress stalled for years, and alternative approaches emerged. Field ion microscopy achieved early accepted atomic images by ionizing helium or neon atoms near a sharp needle tip, but it mainly revealed the very surface of the tip. Probe microscopes later mapped surfaces using quantum or nanoscale force interactions, producing 3D images without lens-based spherical aberration—yet they often “felt” atoms rather than directly imaging them.

The decisive fix came from breaking symmetry. Scherzer’s theorem said a diverging radially symmetric lens can’t be made, but it doesn’t apply if the lens isn’t radially symmetric. Knut Urban, Max Haider, and Harold Rose built a system using multipole magnetic elements—hexapole, octopole, and decapole magnets—to intentionally distort the beam into a saddle-like shape, then pass it through a second, oppositely configured multipole that restores circular symmetry while leaving behind a tiny effective divergence. When tuned correctly, the residual divergence cancels the original spherical aberration.

After years of skepticism and funding pressure, their lens stabilized in July 1997, producing clear atomic images. The corrected TEM reached about 0.13 nanometers resolution, and the method spread quickly. Independent work by Orndrej Krivanek extended aberration correction to scanning TEM, and in 2020 Urban, Rose, Haider, and Krivanek received the Kavli Prize in Nanoscience. Today, aberration-corrected electron microscopy is widely treated as essential for materials science because atomic-scale structure is required to connect observed properties to the underlying arrangement of atoms.