Scientists from the University of North Texas have learned how to create crystals with a width of only 2 nm without the use of TNT. The researchers will present their findings at the American Chemical Society’s spring meeting, ACS Spring 2022.

The smallest diamonds, only a few nanometers wide, are widely used in sensors and processors of quantum computers. In this regard, obtaining diamond nanoparticles of a constant size is of great importance for the development of technologies.

Scientists report a method for growing ultra-homogeneous nanodiamonds without the use of explosives. The second advantage of the new method is the addition of useful monatomic defects to otherwise ideal diamonds.

“It’s amazing that although diamond is chemically quite simple – it’s one element, carbon – it’s extremely difficult to fabricate this material at the nanometer scale,” says Hao Yang, the project’s principal investigator.

Carbon becomes diamond when the atoms of this element are arranged in a rigid three-dimensional cubic pattern under conditions of high pressure and high temperature. Researchers have previously created nanodiamonds in the lab by detonating an explosive such as trinitrotoluene in a sealed stainless steel container. The explosion turns the carbon in the explosive material into tiny diamond particles. However, this method is difficult to control, the researchers explain. In addition, the resulting crystals are not uniform in size, requiring additional steps to sort them.

To develop a more precise way to produce nanodiamonds, scientists have studied the “chemistry” that nature uses.

“We realized that the places where diamonds form in the Earth’s mantle contain a lot of iron and iron-carbon compounds, including carbides and carbonates,” Yang says.

And when iron carbide reacts with iron oxide between the crust and the upper mantle, diamonds grow.

Armed with this knowledge, scientists have developed a chemical process to mimic the lithospheric environment below the Earth’s surface. To do this, they created iron carbide nanoparticles of the same size as a carbon source for diamonds. After that, the particles were placed in an environment with high pressure and high temperature, similar to the conditions in places where natural diamonds are formed. The compounds reacted, resulting in very homogeneous nanodiamonds.

The new method makes it possible to create crystals as narrow as 2 nm with differences between them of less than a nanometer. Previously, such results have not been obtained. The scientists claim that this is an order of magnitude better than anyone can do without additional post-synthetic processing or purification steps.

Creating uniform, perfect nanodiamonds is good in itself, the researchers say, but these materials can be even more useful when they have imperfections, such as voids in the diamond structure. These voids can be replaced by carbon, nitrogen, silicon, nickel, or another element. Embedded non-carbon atoms slightly color the material, they are called “color centers”.

Traditionally, a high-energy beam of atoms such as nitrogen or silicon is used to bombard the diamond and embed these elements into the crystal structure. However, this method cannot control how many color centers are added to a single diamond, requiring post-processing steps to produce crystals with a one-atom defect. The scientists believe that with the new method, they could develop a way to replace just one of the thousands of carbons present in a nanodiamond. Nanoparticles with only one color center are highly desirable as they can securely store information in quantum computers and telecommunications devices.

“Now we have an ideal platform to develop a way to make a single-color central nanodiamond, which is a breakthrough for a number of diamond-related technologies. But also, in a broader sense, it would be a fascinating demonstration of how you can control one atom in a much larger structure,” Yang says.