Synthesis and crystal structure of n-diamond

Abstract

Allotropes of carbon based materials, such as graphite, fullerenes and nanotubes, and diamond are currently a focus of great interest. New diamond (n-diamond) has been proposed as a new carbon allotrope; its electron diffraction pattern matches that of cubic (Fd3 m) diamond apart from some additional reflections that are forbidden for diamond, indexed as {200}, {222} and {420}. n-Diamond has been found experimentally for more than 10 years, yet its structure and stability are not unambiguously resolved, and some controversies still exist. A comprehensive review of recent developments in the experimental and theoretical knowledge of n-diamond is presented. Synthesis methods reported for n-diamond and transformation mechanisms from other carbon allotropes are discussed. The various crystal structure models proposed for n-diamond are summarised and critically assessed. The stability to aging and other properties of n-diamond are briefly considered. Finally, the potential for technological application of n-diamond as an electromagnetic absorber is discussed.

Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

“…Crystal morphologies vary from angular to rounded and from monocrystalline to twinned, and ND diameters average 3-4 nm (range: 1 nm-2.9 mm), with most measuring between 1 and 20 nm, a typical size for detonation-formed NDs (Wen et al 2007). The quantification method discussed above was used to estimate abundances of NDs and revealed concentrations in carbon spherules of 10-3680 ppb (mean: 755 ppb) and in bulk sediment of 11-494 ppb (mean: 200 ppb).…”

“…Hough et al (1997) suggested that the K-Pg NDs formed by the CVD process, which requires a source of carbon vapor and the reducing atmosphere of the fireball (Wen et al 2007). For the K-Pg, it is proposed that the NDs formed when the impactor collided with carbon-rich Yucatan bedrock, e.g., limestones and dolostones containing hydrocarbons (Belcher et al 2005).…”

“…The YDB layer contains two diamond-like polytypes, ndiamonds and i-carbon, that were first synthesized in the laboratory (Wen et al 2007 and references therein). Outside of the laboratory, face-centered cubic NDs (another name for n-diamonds) were first reported within carbon spherules from nearsurface sediments of unknown age across northern Europe by Rö sler et al (2006).…”

“…Ongoing investigations have been examining whether these polymorphs are simply cubic diamonds with atomic substitution of carbon by hydrogen or other elements (Wen et al 2011) or are new forms of diamond-like carbon (Hu et al 2012). Regardless, the nanoparticles in question form under exotic temperatures and pressures not present naturally at the Earth's surface or lower atmosphere but similar to conditions related to cosmic impact (Wen et al 2007) and are unlike other forms of carbon typically found naturally on Earth. For simplicity, we refer to all forms as NDs, even though n-diamonds and i-carbon may actually be only diamond-like.…”

“…A-D available online). These latter two types of nanocrystals, almost as hard as cubic NDs, are frequently used in thin, polycrystalline films for industrial applications requiring hardness and abrasion resistance (Wen et al 2007). Ongoing investigations have been examining whether these polymorphs are simply cubic diamonds with atomic substitution of carbon by hydrogen or other elements (Wen et al 2011) or are new forms of diamond-like carbon (Hu et al 2012).…”