Moving the tip underneath the cantilever, the researchers can scan the whole calcium-fluoride sample. “As you move it along, you get more or less signal depending on the shape and size of the sample,” Mamin says. Finally, the researchers use these signals to reconstruct the sample’s image on a computer.
The image in the paper shows the calcium-fluoride samples on the cantilever pillars and the distance between the pillars with a resolution of 90 nanometers. The volume of the calcium fluoride is 60,000 times smaller than the volume that conventional MRI microscopy can detect.
While the images created so far are two-dimensional images, making 3-D images is a matter of making more scans, Rugar says. The researchers would have to move the magnetic tip up and down to image slices of the sample at different depths, and then simply put the slices together and create a 3-D image.
The method could just as easily be used on molecules containing other atoms with magnetic nuclei, including hydrogen, Rugar says. To achieve their ultimate goal of viewing a protein’s structure in 3-D, the researchers would need to precisely detect the locations of single hydrogen atoms in the protein. For this, the researchers would have to detect the magnetism, or spin, of a single nucleus, a resolution of about 0.1 nanometers. This is a challenge, says Chris Hammel, a physicist who does magnetic resonance research at Ohio State University. But, adds Hammel, the IBM group has made significant strides toward this goal.
The results in the new paper are promising because they show that the imaging technique is robust and that the IBM group’s ideas to improve imaging resolution are working out well, Hammel adds. “Single nuclear spin detection is just an amazing thing to even contemplate, and several years ago it was hard for most people to imagine that it was achievable, but this is starting to seem possible now,” he says. “There’s no indication that it cannot be done. This paper is a significant milestone in that quest.”