Ultra-uniform lab-grown nanodiamonds are now a reality

“It’s fascinating that even though a diamond is chemically quite simple – it’s an element, carbon – making this material at the nanometer scale is extremely difficult,” Hao Yan, the project’s principal investigator, said in A press release.

Carbon becomes a diamond when the atoms of this element are arranged in a rigid 3D cubic pattern under conditions of high pressure and high temperature. Researchers have previously created nanodiamonds in the lab by detonating explosives such as TNT in a sealed stainless steel container.

The explosion converts the carbon in the explosive material into tiny diamond particles. However, this crude method is difficult to control, and the crystals that form are uneven in size, requiring additional steps to sort them for different technologies.

Scientists have developed a method to grow ultra-uniform nanodiamonds (scale bar is 5 nm) without using explosives. (Image by Tengteng Lyu, courtesy of the American Chemical Society).

To design a more precise way to make nanodiamonds, Yan’s group looked at the chemistry used by nature.

“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,” the scientist said. “And when iron carbide reacts with iron oxide between the crust and the upper mantle, diamonds develop.”

Armed with this knowledge, Tengteng Lyu, a graduate student in Yan’s lab, devised a chemical process to mimic the lithospheric environment found beneath the planet’s surface.

First, Lyu created uniformly sized iron carbide nanoparticles as a carbon source for diamonds. The tiny particles were embedded in a matrix of iron oxide, analogous to iron carbide being chocolate chips in cookie dough.

Next, Lyu placed the carbon precursor “dough” in a high-pressure, high-temperature environment, similar to conditions where natural diamonds form. The compounds reacted and very uniform nanodiamonds resulted. The new method makes crystals as small as 2 nm wide with differences between them of less than a nanometer. Yan says that’s an order of magnitude greater than anyone can do without additional post-synthetic processing or purification steps.

Beyond Perfect

According to Yan, creating uniform and perfect nanodiamonds is great, but these materials can be even more useful when they have flaws, such as empty spots in the diamond structure and the replacement of neighboring carbon atoms by nitrogen. , silicon, nickel or another element.

As the atoms other than carbon lightly color the material, they are called “color centers”. Nanoparticles with a single color center are highly desirable because they can securely store information in quantum computers and telecommunication devices.

Traditionally, a beam of high-energy 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 the number of color centers added to a diamond, requiring post-processing steps to obtain crystals with a single atom defect. Moreover, when diamond diameters shrink to 2-3 nm – the size range Yan’s team can now consistently establish – this atom-beam approach becomes energetically unfavorable.

But with their new method, Yan thinks they could devise a way to replace one of the thousands of carbons in their “dough” of carbon precursors. He estimates that they could now make enough single-color center nanodiamonds for a few thousand quantum computers with just one synthesis experiment.

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