Nanodiamonds as Small as 4 Nanometres Exhibit 30% Lower Stiffness Than Larger Diamonds

Diamonds as small as 4 nanometres across become noticeably more elastic than larger diamonds, according to an experiment that pushed the frontier of such measurements tenfold smaller than previous work. The researchers clamped each nanodiamond between two diamond-tipped cylinders capable of compressing them.

The cylinders were connected to a force sensor that measured resistance and a special microscope that imaged the compressed diamond.

Measurements were performed in high vacuum. Chongxin Shan at Zhengzhou University in China and his colleagues repeated the experiment with about 100 different diamonds. As diamond diameter decreased from 12 to 4 nanometres, stiffness decreased by about 30 per cent.

The team combined those measurements with computer simulations of the diamonds. They determined that the ratio between surface-layer atoms and core atoms is large in 4-nm diamonds. Chemical bonds between surface layer and core are weak in nanodiamonds.

“Bulk diamonds are widely known for extreme stiffness and hardness. At the nanoscale, things can be different,” Chongxin Shan said. Yang Lu at the City University of Hong Kong, whose team completed some of the first studies showing that diamonds at the nanoscale can be less hard and brittle, reviewed the significance of the new work.

The experiment pushed the smallness level down tenfold compared with past studies. Tiny diamonds are becoming an increasingly popular material for building novel electronics as well as quantum devices, Yang Lu said. “And artificial diamonds are becoming extremely cheap nowadays so it’s a good time for putting diamonds in more and more [applications],” he added.