Twinning of cubic diamond explains reported nanodiamond polymorphs

Abstract

The unusual physical properties and formation conditions attributed to h-, i-, m-, and n-nanodiamond polymorphs has resulted in their receiving much attention in the materials and planetary science literature. Their identification is based on diffraction features that are absent in ordinary cubic (c-) diamond (space group: Fd-3m). We show, using ultra-high-resolution transmission electron microscope (HRTEM) images of natural and synthetic nanodiamonds, that the diffraction features attributed to the reported polymorphs are consistent with c-diamond containing abundant defects. Combinations of {113} reflection and <011> rotation twins produce HRTEM images and d-spacings that match those attributed to h-, i-, and m-diamond. The diagnostic features of n-diamond in TEM images can arise from thickness effects of c-diamonds. Our data and interpretations strongly suggest that the reported nanodiamond polymorphs are in fact twinned c-diamond. We also report a new type of twin (<11> rotational), which can give rise to grains with dodecagonal symmetry. Our results show that twins are widespread in diamond nanocrystals. A high density of twins could strongly influence their applications.

Structural characterization of natural diamond shocked to 60 GPa; implications for Earth and planetary systems

“…Such twinning is commonly observed in face-centered cubic (fcc) structures including CVD diamond (Hoffmeister, 1999). However this symmetry might also be consistent with12-fold symmetry as observed for diamond nanocrystals, which was interpreted as {113} twins (Nemeth et al, 2015). We can see the emergence of the separate features at slightly smaller diffraction angles that give rise to the main shoulder at larger d-spacing observed in the integrated diffraction patterns (Fig.…”

“…Thus, in addition to the impact crater-related occurrences (eg (Bunch et al, 2008), "lonsdaleite" in ultra-high pressure (UHP) rocks may record shockdamaged crust (Smith et al, 2011). Hexagonal-diamonds in airfall carbon-rich layers of Younger Dryas age, are interpreted as evidence for a large cosmic impact at the end of the last ice-age (Israde-Alcántara et al, 2012;Kennet et al, (2009)) although these data have been questioned (Nemeth et al, 2015). "Lonsdaleite" associated with nanodiamond has been reported in interplanetary dust particles (IDPs) and widely in meteorites with a variety of growth mechanisms, which include primitive nebular vapor condensates, large body HPHT growth, collision shock-modification of low-P carbon phases, and chemical vapor deposition (CVD), including crystalline graphite (Tielens et al, 1987) to which we now add diamond precursors.…”

An Affordable Wet Chemical Route to Grow Conducting Hybrid Graphite-Diamond Nanowires: Demonstration by A Single Nanowire Device

“…3 . Further to note, the diffraction distance 0.206 nm was corresponds to nanodiamond (111) pattern 48 . In addition, the TEM also tells about the existence of defects or impurity channels in the grains of diamond nanoparticles.…”

A Blind Test of the Younger Dryas Impact Hypothesis

“…YDIH proponents have argued that some species of magnetic microspheres and nanodiamonds are of terrestrial origin, while others are likely of impact origin [ 9 , 38 ], but no agreement exists on these issues [ 12 , 17 , 43 – 48 ]. Bunch et al [ 7 ] rejected a criticism of the YDIH noting that the investigators who authored the critique “performed no SEM or EDS analyses to determine whether their spherules are volcanic, cosmic, or impact-related, as stipulated by Firestone et al (2007).” But Firestone et al [ 2 ] state (p. 16019) that they were unable to use compositional analyses: “the similarity in composition of YDB magnetic microspherules and magnetic grains (e.g., high Ti) from many sites across North America cannot be explained at this time, but the YDB abundance of microspherules and magnetic grains most likely resulted from the influx of ejecta from an unidentified, unusually Ti-rich, terrestrial source region and/or from a new and unknown type of impactor.”…”