There are various ways to make artificial diamonds. Chemists have now developed a new method: the conversion of carbon-containing Adamantan molecules in diamonds by means of an electron beam. For a long time, experts thought that impossible, but the experiments confirm that nanodiamants can be generated in this way – at least from materials with suitable properties such as Adamantan. The advantage: This technology comes out without high temperatures and pressures and delivers synthetic diamonds with almost perfect crystal grilles.
Diamonds are desired because of their beauty, but primarily because of their great hardness. The gemstones occur naturally and in large numbers inside the earth, but are difficult to find and recover in the crust. It is therefore a cheaper alternative to make diamonds synthetically. For this purpose, carbon -containing materials are converted under extreme conditions. With very high pressures and temperatures, as they also occur in the ground mantle, the carbon is pressed into the compact configuration of the diamond grid. A team led by Jiaarui Fu from the University of Tokyo has now examined another approach that does not require such extreme pressures and temperatures as well as without catalysts and additives: the controlled radiation with electrons.
A carbon -rich molecule called Adamantan (C10H16) that already has a similar cage structure as diamond. Both materials consist of a tetra -medal symmetrical atomic frame in which the carbon atoms are arranged in the same spatial pattern. However, Adamantan consists of loosely arranged monomers and diamond of a robust three -dimensional grille. In order to make diamonds from Adamantan, its strong CH compounds at the edge of the monomers must be converted into weaker and more unstable CC bonds. The catch: “Nobody thought that was feasible,” says senior author Eiichi Nakamura from the University of Tokyo.
Looking for the best reaction conditions
It is known from previous studies that the atoms of Adamantan can be shot with individual electrons and thereby becoming ions. This facilitates the desired split of CH bonds and enables new CC bonds to form spontaneously. So far, however, nobody has succeeded in producing and isolating stable products through electron radiation. With the help of a transmission electron microscopy (TEM), the team around FU has now examined more closely what is happening under the electron beam and what conditions are best for conversion. To do this, they irradiated Adamantan crystals in a vacuum for a few seconds with electrons from 80 to 200 kiloelectron volts. The temperatures in the test were between 100 and 296 Kelvin, i.e. about minus 173 to plus 23 degrees Celsius.
“The common opinion among TEM specialists was that organic molecules quickly decompose if you point an electron beam at them,” says Nakamura. But he and his colleagues have now been able to prove that this is not always the case: their process led to tiny diamond balls with cube -shaped crystal structure and a diameter of two to four nanometers. “Longer radiation resulted in the merger of such nanodiamants, which resulted in twin crystals with a diameter of eight to 20 nanometers,” reports the team. Hydrogen gas was created as a by -product (H2). In contrast to other synthesis procedures or using similar starting materials, the now produced art diamonds from Adamantan showed no damage or deviations in the crystal grille. “These results underline that the tetrahedric-symmetrical Adamantan skeleton is the best building block for diamond synthesis,” write the chemists.
How does diamond formation work?
More detailed analyzes revealed how these seemingly perfect nanodiamants came about: First, flexible oligomer modules formed from the Adamantan monomors, which then merged into spherical and rigid polymers. CH bonds of the starting material were only preserved on the edge of the grid, the interior of the nanodiamants consisted exclusively of CC bonds. The pace of this process was dependent on how quickly the CH bonds could be split, as the team stated.
The energy for the conversion of the Adamantan into diamond came exclusively from the shot electrons, additional thermal energy was not necessary. Accordingly, the process runs both chilled and at room temperature. The release of hydrogen favored the process and was energetically beneficial for the chemical reaction. “This example of diamond synthesis is the ultimate proof that electrons do not destroy organic molecules, but let them go through precisely defined chemical reactions if the molecules to be irradiated,” says Nakamura.
The findings can now be used to produce nanodiamants. These are not suitable for jewelry, but for example for quantum sensors. The required Adamantan can be obtained from natural gas or oil. In addition to this practical benefit, the experiments primarily demonstrate that diamonds can arise under the influence of electrons – even outside the laboratory, in natural environments, where there are similar reaction conditions. Researchers have long suspected that such high -energy particles, for example the cosmic radiation, have shaped diamonds that occur in meteorites and in uranium sediments on earth. The study now confirms that this is possible.
Source: Jiarui Fu (University of Tokyo) et al.; Science, Doi: 10.1126/science.adw2025
