Diamond and Cubic Boron Nitride Alloy Form Superhard Material

Diamonds are forever, except when they oxidize while cutting through iron, cobalt, nickel, chromium, or vanadium at high temperatures. Conversely, cubic boron nitride possesses superior chemical inertness but only about half of the hardness of diamonds. In an attempt to create a superhard material better suited for a wide variety of materials on an industrial scale, researchers at Sichuan University in Chengdu, China, have created an alloy composed of diamonds and cubic boron nitride (cBN) that boasts the benefits of both.

"Diamond and cubic boron nitride could readily form alloys that can potentially fill the performance gap because of their affinity in structure lattices and covalent bonding character," said Duanwei He, a professor at Sichauan University's Institute of Atomic and Molecular Physics. "However, the idea has never been demonstrated because samples obtained in previous studies are too small to test their practical performance."

In the image above, both A and B a bulk diamond-cubic boron nitride (cBN) alloy samples synthesized at 20 GPa/2200 °C with a diameter of ~3 mm, over a copper screen to exhibit its transparency. Image C and D show polished rake faces of diamond-cBN alloy cutters.

Lasers Used to Levitate Diamond

Researchers have, for the first time, levitated individual nanodiamonds in vacuum. The research team is led by Nick Vamivakas at the University of Rochester who thinks their work will make extremely sensitive instruments for sensing tiny forces and torques possible, as well as a way to physically create larger-scale quantum systems known as macroscopic Schrödinger Cat states.

While other researchers have trapped other types of nanoparticles in vacuum, those were not optically active. The nanodiamonds, on the other hand, can contain nitrogen-vacancy (NV) centers that emit light and also have a spin quantum number of one. In the paper, published in Nature Photonics, the researchers from Rochester's Institute of Optics explain this is the first step towards creating a "hybrid quantum system." Their system combines the mechanical motion of the nanodiamond with the internal spin of the vacancy and its optical properties to make it particularly promising for a number of applications.

In a previous paper, the researchers had shown that nanodiamonds could be levitated in air using a trapping laser. The new paper now shows this can be done in vacuum, which they say is "a critical advance over previous nanodiamond optical tweezer experiments performed in liquids or at atmospheric pressure."

Nanodiamonds trapped at atmospheric pressure are continuously agitated by collisions with the air molecules around them. Trapping the diamonds in vacuum removes the effect of all these air molecules. "This allows us to exert mechanical control over them," said Levi Neukirch, lead author of the paper and a Ph.D. student in Vamivakas' group at Rochester. "They turn into little harmonic oscillators."