Nonmetallic crystals with high thermal conductivity

Diamond may be grown at low pressures where it is the metastable form of carbon. Recent advances in a wide variety of plasma and electrical discharge methods have led to dramatic increases in growth rates. All of these methods have certain aspects in common, namely, the presence of atomic hydrogen and the production of energetic carbon-containing fragments under conditions that support high mobilities on the diamond surface. Some understanding of the processes taking place during nucleation and growth of diamond has been achieved, but detailed molecular mechanisms are not yet known. Related research has led to the discovery of a new class of materials, the "diamondlike" phases. Vapor-grown diamond and diamondlike materials may have eventual applications in abrasives, tool coatings, bearing surfaces, electronics, optics, tribological surfaces, and corrosion protection.

https://science.sciencemag.org/content/sci/241/4868/913.full.pdf

Low-Pressure, Metastable Growth of Diamond and "Diamondlike" Phases

▪ Abstract The synthesis of the two currently used superhard materials, diamond and cubic boron nitride, is briefly described with indications of the factors influencing the quality of the crystals obtained. The physics of hardness is discussed and the importance of covalent bonding and fixed atomic positions in the crystal structure, which determine high hardness values, is outlined. The materials investigated to date are described and new potentially superhard materials are presented. No material that is thermodynamically stable under ambient conditions and composed of light (small) atoms will have a hardness greater than that of diamond. Materials with hardness values similar to that of cubic boron nitride (cBN) can be obtained. However, increasing the capabilities of the high-pressure devices could lead to the production of better quality cBN compacts without binders.

Synthesis and Design of Superhard Materials

Materials emitting light in the deep ultraviolet region around 200 nanometers are essential in a wide-range of applications, such as information storage technology, environmental protection, and medical treatment Hexagonal boron nitride (hBN), which was recently found to be a promising deep ultraviolet light emitter, has traditionally been synthesized under high pressure and at high temperature We successfully synthesized high-purity hBN crystals at atmospheric pressure by using a nickel-molybdenum solvent The obtained hBN crystals emitted intense 215-nanometer luminescence at room temperature This study demonstrates an easier way to grow high-quality hBN crystals, through their liquid-phase deposition on a substrate at atmospheric pressure

http://science.sciencemag.org/content/sci/317/5840/932.full.pdf

Deep Ultraviolet Light-Emitting Hexagonal Boron Nitride Synthesized at Atmospheric Pressure

The isolated electronic spin system of the nitrogen-vacancy (NV) centre in diamond offers unique possibilities to be employed as a nanoscale sensor for detection and imaging of weak magnetic fields. Magnetic imaging with nanometric resolution and field detection capabilities in the nanotesla range are enabled by the atomic-size and exceptionally long spin-coherence times of this naturally occurring defect. The exciting perspectives that ensue from these characteristics have triggered vivid experimental activities in the emerging field of 'NV magnetometry'. It is the purpose of this article to review the recent progress in high-sensitivity nanoscale NV magnetometry, generate an overview of the most pertinent results of the last years and highlight perspectives for future developments. We will present the physical principles that allow for magnetic field detection with NV centres and discuss first applications of NV magnetometers that have been demonstrated in the context of nano magnetism, mesoscopic physics and the life sciences.

https://iopscience.iop.org/article/10.1088/0034-4885/77/5/056503/pdf

Magnetometry with nitrogen-vacancy defects in diamond

Claims of the conversion of carbon to diamond date back to 1880, but it was not until 1955 that the first reproducible synthesis was reported. Bundy et al. describe the high-pressure, high-temperature apparatus that enabled them to reach the stability field of diamond, and prove that the material obtained was indeed diamond. Ironically, some of the same authors discovered 38 years later that the very first diamond grown by their technique was not synthetic after all, but a fragment of a natural diamond that got into the experiment. Fortunately, however, the technique was sound, and marked the beginning of the present synthetic-diamond industry.

Man-Made Diamonds

Cubic Form of Boron Nitride

Diamond tools and superpressure processes for the preparation thereof are described wherein the diamond content is present either in the form of a mass comprising diamond crystals bonded to each other or of a thin skin of diamond crystals bonded to each other. In each instance the diamond content is supported on and directly bonded to an extremely stiff sintered carbide substrate in order to provide mechanical support therefor to more effectively utilize the high elastic modulus of the diamond.

Diamond tools for machining

It would be good to be able to write a paper entitled \"The Preparation of Diamond\", in which all the factors affecting diamonds were nicely accounted for and the formation of diamond was completely explained. But the work which has been carried out on this problem indicates that diamond can form in several different ways, and that stubborn mysteries still surround some of them. This article, therefore, is more of the

Preparation of Diamond

Diamond or cubic boron nitride particles can be sintered into strong masses at high temperatures and very high pressures at which these crystalline forms are stable. Most of the desirable physical properties of the sintered masses, such as hardness and thermal conductivity, approach those of large single crystals; their resistance to wear and catastrophic splitting is superior. The sintered masses are produced on a commercial scale and are increasingly used as cutting tools on hard or abrasive materials, as wire-drawing dies, in rock drills, and in special high-pressure apparatus.

https://science.sciencemag.org/content/sci/208/4446/873.full.pdf

Robert H. Wentorf

Papers

Man-Made Diamonds

Cubic Form of Boron Nitride

Diamond tools for machining

Preparation of Diamond

Sintered superhard materials.