The bottom-up approach can synthesize microscopic diamonds for bio-imaging, quantum computing

Scientists are excited about diamonds, not about the types that adorn jewelry, but about the microscopic variety that is smaller than the width of a human hair. These so-called "nanodiamonds" are composed almost entirely of carbon. But by introducing other elements into the crystalline lattice of the nanodiamond – a method known as "doping" – researchers could produce useful traits in medical research, computation and beyond.

In an article published on May 3 in Progress of scienceResearchers from the University of Washington, the US Naval Research Laboratory, and the Pacific Northwest National Laboratory have announced that they can use extremely high pressure and temperature to dope nanodiamonds. The team used this approach to dope nanodiamonds with silicon, which causes the diamonds to glow deep red, a property that would make them useful for cell and tissue imaging.

The team discovered that their method could also dope nanodiamonds with argon, a rare gas and a helium-related non-reactive element present in the balloons. Nanodiamonds doped with such elements could be applied to the science of quantum information, a rapidly expanding field that includes quantum communication and quantum computing.

"Our approach allows us to intentionally integrate other elements into diamond nanocrystals by carefully selecting the molecular starting materials used in their synthesis," said corresponding author Peter Pauzauskie, a professor. Associate Professor of Materials Science and Engineering at UW and researcher at Pacific Northwest National Laboratory.

There are other methods of doping nanodiamonds, such as ion implantation, but this process often damages the crystal structure and the introduced elements are randomly placed, which limits performance and applications. Here, the researchers decided not to dope nanodiamonds after their synthesis. Instead, they doped the molecular ingredients to make nanodiamonds with the element they wanted to introduce, and then used a high temperature and pressure to synthesize nanodiamonds with the included elements.

In principle, it is like making a cake: It is much simpler and more effective to add sugar to the dough instead of trying to add sugar to the cake after baking.

The team's starting point for the nanodiamonds was a carbon-rich material – similar to charcoal, said Pauzauskie – that the researchers turned into a light and porous matrix known as airgel. . They then doped the carbon airgel with a molecule containing silicon, tetraethyl orthosilicate, chemically integrated into the carbon airgel. The researchers sealed the reagents in the seal of a diamond anvil cell, which could generate pressures of up to 15 gigapascals inside the joint. As a reference, 1 gigapascal corresponds to about 10,000 atmospheres of pressure, or 10 times the pressure in the deepest part of the ocean.

To prevent the airgel from being crushed at such extreme pressures, they used argon, which becomes solid at 1.8 gigapascals, as a pressure medium. After charging the material at high pressure, the researchers used a laser to heat the cell to a temperature above 3,100 F, more than a third of the temperature of the sun's surface. In collaboration with E. James Davis, Emeritus Professor of Chemical Engineering at the University of Washington, they found that at these temperatures, solid argon melted to form a supercritical fluid.

During this process, the carbon airgel was converted to nanodiamonds containing point defects of luminescence formed from silicon-based dopant molecules. The nanodiamonds emitted a dark red light at a wavelength of about 740 nanometers, which is useful in medical imaging. Nanodiamonds doped with other elements could emit other colors.

"We can throw an arrow at the periodic table and, as long as the element we touch is soluble in the diamond – we could deliberately incorporate it into the nanodiamond using this method," said Pauzauskie. "You can create a wide range of nanodiamonds that emit different colors for imaging purposes, or we could use this molecular doping approach to create more complex point defects with two or more different dopant atoms, including totally new defects that have not been detected yet created before. "

Surprisingly, the researchers discovered that their nanodiamonds also contained two other elements they did not intend to introduce: argon used as a pressure medium and nitrogen in the air. Just like the silicon that the researchers had intended to introduce, the nitrogen and argon atoms were fully integrated into the crystal structure of the nanodiamond.

This is the first time that scientists have used a high temperature and high pressure assembly to introduce a rare gas element, argon, into a nanodiamond lattice structure. It is not easy to force non-reactive atoms to associate with other materials in a compound.

"It was an unexpected surprise," said Pauzauskie. "But the fact that argon has been incorporated into nanodiamonds means that this method is potentially useful for creating other point defects likely to be used in information science research." quantum. "

The researchers then hopefully intentionally dope the nanodiamonds with xenon, another rare gas, for possible use in areas such as quantum communications and quantum detection.

Finally, the team's method could also help solve a cosmic mystery: nanodiamonds were found in outer space and something – like supernovae or high-energy collisions – dope them with noble gases. Although the methods developed by Pauzauskie and his team concern the doping of nanodiamonds on Earth, their discoveries could help scientists to determine what types of extraterrestrial events trigger cosmic doping away from home.