This image shows the 3D positions of individual atoms in a tungsten tip, consisting of nine atomic layers, labeled with crimson (dark red), red, orange, yellow, green, cyan, blue, magenta and purple from layers one (top) to nine (bottom), respectively. Image: Mary Scott and Jianwei (John) Miao/UCLA.Atoms are the building blocks of all matter on Earth, and the patterns in which they are arranged dictate how strong, conductive or flexible a material will be. Now, scientists at the University of California, Los Angeles (UCLA) have used a powerful microscope to image the three-dimensional (3D) positions of individual atoms to a precision of 19 trillionths of a meter, several times smaller than a hydrogen atom.
Their observations make it possible, for the first time, to infer the macroscopic properties of materials based on the structural arrangements of their atoms, helping to guide scientists and engineers in their development of new materials such as aircraft components. The research, led by Jianwei (John) Miao, a UCLA professor of physics and astronomy and a member of UCLA's California NanoSystems Institute, is published in Nature Materials.
For more than 100 years, researchers have inferred how atoms are arranged in 3D space using a technique called X-ray crystallography, which involves measuring how light waves scatter from a crystal. However, X-ray crystallography only yields information about the average positions of many billions of atoms in the crystal, not about the precise coordinates of individual atoms.
"It's like taking an average of people on Earth," Miao said. "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."
Because X-ray crystallography doesn't reveal the structure of a material on an atom-by-atom basis, the technique can't identify tiny imperfections in materials such as the absence of a single atom. These imperfections, known as point defects, can weaken materials, which can be dangerous when the materials are components of machines like jet engines.
"Point defects are very important to modern science and technology," Miao said.
Miao and his team used a technique known as scanning transmission electron microscopy, which involves scanning a beam of electrons smaller than the size of a hydrogen atom over a sample and then measuring how many electrons interact with the atoms at each scan position. This technique reveals the atomic structure of materials because different arrangements of atoms cause electrons to interact in different ways.
Ordinarily, scanning transmission electron microscopes can only produce two-dimensional images. In order to create a 3D image, scientists need to scan the sample once, tilt it by a few degrees and then re-scan it – repeating the process until the desired spatial resolution is achieved – before combining the data from each scan using a computer algorithm. The downside of this technique is that the repeated electron beam radiation can progressively damage the sample.
Using a scanning transmission electron microscope at the Lawrence Berkeley National Laboratory's Molecular Foundry, Miao and his colleagues analyzed a small piece of tungsten, an element used in incandescent light bulbs. By tilting the sample 62 times, the researchers were slowly able to assemble a 3D model of 3769 atoms in the tip of the tungsten sample.
The experiment was time consuming because the researchers had to wait several minutes after each tilt for the setup to stabilize. "Our measurements are so precise, and any vibrations – like a person walking by – can affect what we measure," explained Peter Ercius, a staff scientist at Lawrence Berkeley National Laboratory and one of the authors of the paper. The researchers also made sure to keep the energy of the electron beam below the radiation damage threshold of tungsten, confirming that the tungsten had not been damaged by comparing the images from the first and last scans.
Producing 3D images in this way allowed the researchers to show 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 lighter element such as carbon.
Regardless of the nature of the point defect, the researchers' ability to detect its presence is significant, demonstrating for the first time that the coordinates of individual atoms and point defects can be recorded in three dimensions. "We made a big breakthrough," Miao asserted.
Miao and his team now plan to build on their results by studying how atoms are arranged in materials that possess magnetism or energy storage abilities, which will help inform our understanding of the properties of these important materials at the most fundamental scale.
"I think this work will create a paradigm shift in how materials are characterized in the 21st century," Miao said. "Point defects strongly influence a material's properties and are discussed in many physics and materials science textbooks. Our results are the first experimental determination of a point defect inside a material in three dimensions."
This story is adapted from material from UCLA, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.