By 2018 they had figured out how to reconstruct two-dimensional samples with the technique, producing what Muller calls “the highest-resolution image by any method in the world” (and winning that Guinness record). Just in the past several years Muller and his team developed a detector good enough for electron ptychography to work experimentally. “You had to be a true believer in ptychography to be paying attention to it,” Muller says. Meanwhile scientists kept improving electron microscopes. Early versions worked far better with visible light and x-rays than the electrons needed to image atomic-size objects. But because of computing and detector limitations and the complex math required, the technique was not put into practice for decades. Researchers theorized ptychography in the 1960s and conceived its use to overcome electron lenses' limits in the 1980s. Ptychography, in contrast, uses a detector that can record all the different angles the beam can scatter to at every beam position, getting much more information with the same wavelength and lens. But electron microscopes had a limit: increasing their resolution required raising the electron beam's energy, and eventually the necessary energy would become so great that it would damage the sample. Invented in the early 1930s, standard electron microscopes made it possible to see objects such as polioviruses, which are smaller than the wavelengths of visible light. This result marks an important advancement in the world of electron microscopy. (This is smaller than the length your fingernails grow in a minute but many times thicker than what electron ptychography could image in the past.) “They can actually look at stacks of atoms now, so it's amazing,” says University of Sheffield engineer Andrew Maiden, who helped to develop ptychography but was not part of the new study. This makes the technique much more relevant to materials scientists, who typically study the properties of samples with a thickness of about 30 to 50 nanometers. But Muller and his colleagues' new study in Science describes capturing multiple layers tens to hundreds of atoms thick. Previously, electron ptychography had only been used to image extremely flat samples just one to a few atoms thick. Based on the speckle pattern generated by billions of these electrons as they hit a detector, machine-learning algorithms can calculate where the atoms were in the sample and what their shapes might be, thus creating an image. Although Muller cannot see the targets, he can detect where the “dodgeballs” end up. The dodgeballs are electrons, and their targets are individual atoms. Cornell physicist David Muller likens the technique to playing dodgeball against opponents who are standing in the dark. The beam moves infinitesimally as the electrons are fired, so they hit the sample from slightly different angles-sometimes they pass through cleanly other times they collide with atoms and bounce around inside the sample before exiting. It involves shooting a beam of electrons, about a billion per second, at a target material. The scientists obtained the image using a technique called electron ptychography. Their imaging process could help develop materials for designing more powerful and efficient phones, computers and other electronics, as well as longer-lasting batteries. To create it, Cornell University researchers captured a sample from a crystal in three dimensions and magnified it 100 million times, doubling the resolution that earned the same scientists a Guinness World Record in 2018. Behold the highest-resolution image of atoms ever taken.
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