A More Precise Way to Make Nanodiamonds

Nanosized diamonds can be useful, e.g., in drug delivery, sensing, and quantum computing. Producing uniformly sized diamond nanoparticles is important for such applications. Carbon can be transformed to its diamond allotrope under high-pressure and high-temperature conditions. Nanodiamonds can, for example, be created in the laboratory by detonating an explosive, such as trinitrotoluene (TNT), in a sealed stainless-steel container. The blast converts the carbon in the explosive material into tiny diamond particles. However, this method is hard to control and the formed crystals are generally uneven in size.

Hao Yan, University of North Texas, Denton, USA, and colleagues have developed a method to grow ultra-uniform nanodiamonds without the need for explosives. The technique also could be used to add beneficial single-atom defects to diamond nanocrystals. The team designed a process aiming to imitate the creation of diamonds in the Earth’s mantle at sites that contain a lot of iron and iron–carbon compounds, including carbides and carbonates. First, they prepared evenly sized nanoparticles of iron carbide as the carbon source and mixed them into an iron oxide matrix. The resulting precursor material was placed in a high-pressure and high-temperature environment. This approach gave very uniform nanodiamonds, down to 2 nm wide with size differences of less than 1 nm.

Nanodiamond materials with defects, such as the replacement of carbon atoms with nitrogen, silicon, nickel, or another element, can be useful. Because the non-carbon atoms color the material slightly, they are called “color centers.” Nanoparticles with only one color center are desirable because they can securely store information in quantum computers and telecommunication devices. Usually, a high-energy beam of atoms such as nitrogen or silicon is used to bombard the diamond and embed these elements. However, this method cannot control how many color centers are added to one diamond, requiring post-processing steps to obtain crystals with a single-atom defect. The researchers propose that replacing carbon atoms in their precursor could be used to create single-color-center nanodiamonds.