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WonderAtomic imaging technology

The scanning tunnelling microscope, invented at IBM's Zurich laboratory in 1981, can show individual atoms on a surface. It moves a needle-sharp tip just above the sample and measures the tiny electric current that leaks across the gap, which changes sharply with distance.

Scanning tunnelling microscope

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The story behind the card

In everyday physics an electron cannot cross an empty gap, but when the gap is only about a billionth of a metre wide, quantum mechanics lets some electrons slip across anyway; this is called tunnelling. The current drops roughly tenfold for every extra tenth of a nanometre, so the tip's height can be controlled with extraordinary precision. A feedback system keeps the current steady as the tip scans, and the recorded height traces the surface. The method needs samples that conduct electricity. Gerd Binnig and Heinrich Rohrer built the first working instrument in 1981, and in 1983 they published an image of a silicon surface resolved atom by atom. They shared the 1986 Nobel Prize in Physics with Ernst Ruska, inventor of the electron microscope. In 1989 IBM researchers used such a tip to spell the company's name in 35 xenon atoms.

Türkçe oku
1981'de IBM'in Zürih laboratuvarında icat edilen taramalı tünelleme mikroskobu, bir yüzeydeki atomları tek tek gösterebilir. Aygıt iğne gibi sivri bir ucu örneğin hemen üzerinde gezdirir ve aradaki boşluktan sızan çok küçük elektrik akımını ölçer; bu akım uzaklıkla birlikte çok hızlı değişir.

Gündelik fizikte bir elektron boş bir aralıktan geçemez; ama aralık metrenin milyarda biri kadar daraldığında kuantum mekaniği bazı elektronların yine de öbür yana geçmesine izin verir. Buna tünelleme denir. Uç ile yüzey arasındaki mesafe nanometrenin onda biri kadar arttığında akım yaklaşık on kat düşer; bu yüzden ucun yüksekliği olağanüstü bir hassasiyetle denetlenebilir. Tarama sırasında bir geri besleme sistemi akımı sabit tutar; ucun kaydedilen yüksekliği yüzeyin haritasını çıkarır. Yöntem yalnızca elektriği ileten örneklerde işe yarar. Gerd Binnig ile Heinrich Rohrer ilk çalışan aygıtı 1981'de yaptı; 1983'te bir silisyum yüzeyini atom atom gösteren bir görüntü yayımladılar. 1986 Nobel Fizik Ödülü'nü elektron mikroskobunun mucidi Ernst Ruska ile paylaştılar. 1989'da IBM araştırmacıları böyle bir uçla şirketin adını 35 ksenon atomuyla yazdı.

Sources and further reading

Background reading: Scanning tunneling microscope
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Next card in the archiveElectron microscopes use beams of electrons, focused by magnets instead of glass lenses, to show details far smaller than any light microscope can, down to viruses and even rows of atoms. Ernst Ruska and Max Knoll built the first one in Berlin in 1931.Read next →