By Knvul Sheikh
As our devices get smaller and more sophisticated, so do the materials we use to make them. That means we have to get up close to engineer new materials. Really close.
Different microscopy techniques allow scientists to see the nucleotide-by-nucleotide genetic sequences in cells down to the resolution of a couple atoms as seen in an atomic force microscopy image. But scientists at the IBM Almaden Research Center in San Jose, Calif., and the Institute for Basic Sciences in Seoul, have taken imaging a step further, developing a new magnetic resonance imaging technique that provides unprecedented detail, right down to the individual atoms of a sample.
The technique relies on the same basic physics behind the M.R.I. scans that are done in hospitals.
When doctors want to detect tumors, measure brain function or visualize the structure of joints, they employ huge M.R.I. machines, which apply a magnetic field across the human body. This temporarily disrupts the protons spinning in the nucleus of every atom in every cell. A subsequent, brief pulse of radio-frequency energy causes the protons to spin perpendicular to the pulse. Afterward, the protons return to their normal state, releasing energy that can be measured by sensors and made into an image.
But to gather enough diagnostic data, traditional hospital M.R.I.s must scan billions and billions of protons in a person’s body, said Christopher Lutz, a physicist at IBM. So he and his colleagues decided to pack the power of an M.R.I. machine into the tip of another specialized instrument known as a scanning tunneling microscope to see if they could image individual atoms.
Four M.R.I. scans, combined, of a single titanium atom, showing the magnetic field of the atom at different strengths.CreditWillke et al.
The tip of a scanning tunneling microscope is just a few atoms wide. And it moves along the surface of a sample, it picks up details about the size and conformation of molecules.
The researchers attached magnetized iron atoms to the tip, effectively combining scanning-tunneling microscope and M.R.I. technologies.
When the magnetized tip swept over a metal wafer of iron and titanium, it applied a magnetic field to the sample, disrupting the electrons (rather than the protons, as a typical M.R.I. would) within each atom. Then the researchers quickly turned a radio-frequency pulse on and off, so that the electrons would emit energy that could be visualized. The results were described Monday in the journal Nature Physics.
“It’s a really magnificent combination of imaging technologies,” said A. Duke Shereen, director of the M.R.I. Core Facility at the Advanced Science Research Center in New York. “Medical M.R.I.s can do great characterization of samples, but not at this small scale.”
The atomic M.R.I. provides subångström-level resolution, meaning it can distinguish neighboring atoms from one another, as well as reveal which types of atoms are visible based on their magnetic interactions.
“It is the ultimate way to miniaturization,” Dr. Lutz said. He hopes the new technology could one day be used to design atomic-scale methods of storing information, for quantum computers.
Current transistors are thousands of atoms wide and need to switch on and off to store a single bit of information in a computer. The ability to corral individual atoms could drastically increase computing power and enable researchers to tackle complex calculations such as predicting weather patterns or diagnosing illnesses with artificial intelligence.
Moving an atom from one location to another in a composite could also change and lead to the development of new ones.
The technique might also help scientists study how proteins fold and develop new drugs that bind to specific curves in a biological structure.
“We can now see something that we couldn’t see before,” Dr. Lutz said. “So our imagination can go to a whole bunch of new ideas that we can test out with this technology.”