The 3D Position of Atoms Spotted for the First Time Ever

Atoms are the building blocks of all matter on Earth. Now, though, scientists have used a powerful microscope to image the three-dimensional positions of individual atoms to a precision of 19 trillionths of a meter, which is several times smaller than a hydrogen atom.

For more than 100 years, researchers have inferred how atoms are arranged in three-dimensional space using a technique called X-ray crystallography, which involves measuring how light waves scatter off of a crystal. However, X-ray crystallography only yields information about the average positions of many billions of atoms in the crystal, and not about individual atoms' precise coordinates.

"It's like taking an average of people on earth," said Jianwei (John) Miao, one of the researchers, in a news release. "Most people have a head, two eyes, a nose and two ears. But an image of the average person will still look different from you and me."

Now, though, researchers have identified a way in which to better see the atom. The researchers used a technique known as scanning transmission electron microscopy, in which a beam of electrons smaller than the size of a hydrogen atom is scanned over a sample and measures how many electrons interact with the atoms at each scan position. The method reveals the atomic structure of materials because different arrangements of atoms cause electrons to interact in different ways.

However, scanning transmission electron microscopes only produce two-dimensional images. This means that created a 3D picture requires scientists to scan the sample once, tilt it by a few degrees and re-scan it. Then they need to repeat the process until the desired spatial resolution is achieved.

In this case, the researchers used a scanning transmission microscope to analyze a small piece of tungsten. They showed that the atoms in the tip of the tungsten sample were arranged in nine layers, the sixth of which contained a point defect. The researchers believe the defect was either a hole in an otherwise filled layer of atoms or one or more interloping atoms of a light element such as carbon.

Regardless of the nature of the point defect, the fact that the researchers were able to detect its presence is significant, and could lead to future findings.

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