(Nanowerk News) A new technology to continuously place individual atoms exactly where they are needed could lead to new materials for devices that address critical needs for the field of quantum computing and communication that cannot be produced by conventional means, say scientists who developed it.
A research team at the Department of Energy’s Oak Ridge National Laboratory created a novel advanced microscopy tool to “write” with atoms, placing those atoms exactly where they are needed to give a material new properties.
“By working at the atomic scale, we also work at the scale where quantum properties naturally emerge and persist,” said Stephen Jesse, a materials scientist who leads this research and heads the Nanomaterials Characterizations section at ORNL’s Center for Nanophase Materials Sciences, or CNMS. “We aim to use this improved access to quantum behavior as a foundation for future devices that rely on uniquely quantum phenomena, like entanglement, for improving computers, creating more secure communications and enhancing the sensitivity of detectors.”
To accomplish improved control over atoms, the research team created a tool they call a synthescope for combining synthesis with advanced microscopy. The researchers used a scanning transmission electron microscope, or STEM, transformed into an atomic-scale material manipulation platform. The synthescope will advance the state of the art in fabrication down to the level of the individual building blocks of materials. This new approach (Advanced Materials, “Top-Down Fabrication of Atomic Patterns in Twisted Bilayer Graphene”) allows researchers to place different atoms into a material at specific locations; the new atoms and their locations can be selected to give the material new properties.
“Classical computers use bits, which can be either 0 or 1, and do calculations by flipping these bits,” said ORNL’s Ondrej Dyck, a materials scientist contributing to the research. “Quantum computers use qubits, which can be both 0 and 1 at the same time. The qubits can also become entangled, with one qubit connected to the state of another. This entangled system of qubits can be used to solve certain problems much faster than classical computers. The tricky part is keeping these delicate qubits stable and working correctly in the real world.
“One strategy to tackle these challenges is to build and operate at the scale where quantum mechanics exist more naturally—at the atomic scale. We realized that if we have a microscope that can resolve atoms, we may be able to use the same microscope to move atoms or alter materials with atomic precision. We also want to be able to add atoms to the structures we create, so we need a supply of atoms. The idea morphed into an atomic-scale synthesis platform—the synthescope.”
That is important because the ability to tailor materials atom-by-atom can be applied to many future technological applications in quantum information science, and more broadly in microelectronics and catalysis, and for gaining a deeper understanding of materials synthesis processes. This work could facilitate atomic-scale manufacturing, which is notoriously challenging.
“Simply by the fact that we can now start putting atoms where we want, we can think about creating arrays of atoms that are precisely positioned close enough together that they can entangle, and therefore share their quantum properties, which is key to making quantum devices more powerful than conventional ones,” Dyck said.
Such devices might include quantum computers — a proposed next generation of computers that may vastly outpace today’s fastest supercomputers; quantum sensors; and quantum communication devices that require a source of a single photon to create a secure quantum communications system.
“We are not just moving atoms around,” Jesse said. “We show that we can add a variety of atoms to a material that were not previously there and put them where we want them. Currently there is no technology that allows you to place different elements exactly where you want to place them and have the right bonding and structure. With this technology, we could build structures from the atom up, designed for their electronic, optical, chemical or structural properties.”
An artistic rendering depicts direct writing using ORNL’s synthescope, a novel microscopy technique, to continuously insert tin atoms into graphene, opening possibilities for materials fabrication atom-by-atom. (Image: Ondrej Dyck, ORNL)
The scientists, who are part of the CNMS, a nanoscience research center and DOE Office of Science user facility, detailed their research and their vision in a series of four papers in scientific journals over the course of a year starting with proof of principle that the synthescope could be realized. They have applied for a patent on the technology.
“With these papers, we are redirecting what atomic-scale fabrication will look like using electron beams,” Dyck said. “Together these manuscripts outline what we believe will be the direction atomic fabrication technology will take in the near future and the change in conceptualization that is needed to advance the field.”
By using an electron beam, or e-beam, to remove and deposit the atoms, the ORNL scientists could accomplish a direct writing procedure at the atomic level.
“The process is remarkably intuitive,” said ORNL’s Andrew Lupini, STEM group leader and a member of the research team. “STEMs work by transmitting a high-energy e-beam through a material. The e-beam is focused to a point smaller than the distance between atoms and scans across the material to create an image with atomic resolution. However, STEMs are notorious for damaging the very materials they are imaging.”
The scientists realized they could exploit this destructive “bug” and instead use it as a constructive feature and create holes on purpose. Then, they can put whatever atom they want in that hole, exactly where they made the defect. By purposely damaging the material, they create a new material with different and useful properties.
This artistic rendering shows a way to make materials atom-by-atom. The electron beam ejects a carbon atom from graphene, and a different atom bonds at the vacancy. (Image: Ondrej Dyck, ORNL)
“We’re exploring methods to create these defects on demand so we can place them where we want to,” Jesse said. “Since STEMs have atomic-scale imaging capabilities, and we work with very thin materials that are only a few atoms in thickness, we can see every atom. So, we are manipulating matter at the atomic scale in real time. That’s the goal, and we are actually achieving it.”
To demonstrate the method, the researchers moved an e-beam back and forth over a graphene lattice, creating minuscule holes. They inserted tin atoms into those holes and achieved a continuous, atom-by-atom, direct writing process thereby populating the exact same places where the carbon atom had been with tin atoms.
“We believe that atomic-scale synthesis processes could become a matter of routine using relatively simple strategies. When coupled with automated beam control and AI-driven analysis and discovery, the synthescope concept offers a window into atomic synthesis processes and a unique approach to atomic-scale manufacturing,” Jesse said.
