The 1945eV band is the dominant end product of annealing radiation damage in diamonds containing isolated substitutional nitrogen atoms In this paper uniaxial stress experiments are described which show the band to be a transition between A 1 (ground) and E (excited) electronic states of a trigonal centre, the E state being coupled predominantly to A 1 modes of vibration Annealing experiments suggest that the centre is either a substitutional nitrogen atom plus an interstitial nitrogen atom, or a substitutional nitrogen atom plus a vacancy Small differences between the luminescence and absorption bands are shown to be consistent with the double minima vibrational potential of the nitrogenvacancy model

Optical Studies of the 1.945 eV Vibronic Band in Diamond

Nitrogen-vacancy (NV) centers in millimeter-scale diamond samples were produced by irradiation and subsequent annealing under varied conditions. The optical and spin-relaxation properties of these samples were characterized using confocal microscopy, visible and infrared absorption, and optically detected magnetic resonance. The sample with the highest ${\text{NV}}^{\ensuremath{-}}$ concentration, approximately 16 ppm $(2.8\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3})$, was prepared with no observable traces of neutrally charged vacancy defects. The effective transverse spin-relaxation time for this sample was ${T}_{2}^{\ensuremath{\ast}}=118(48)\text{ }\text{ns}$, predominately limited by residual paramagnetic nitrogen which was determined to have a concentration of 49(7) ppm. Under ideal conditions, the shot-noise limited sensitivity is projected to be $\ensuremath{\sim}150\text{ }\text{fT}/\sqrt{\text{Hz}}$ for a $100\text{ }\ensuremath{\mu}\text{m}$-scale magnetometer based on this sample. Other samples with ${\text{NV}}^{\ensuremath{-}}$ concentrations from 0.007 to 12 ppm and effective relaxation times ranging from 27 to over 291 ns were prepared and characterized.

/pdf/diamonds-with-a-high-density-of-nitrogen-vacancy-centers-for-d0326hhgg6.pdf

Diamonds with a high density of nitrogen-vacancy centers for magnetometry applications

Micro-inclusions in diamonds from Zaire and Botswana differ in composition from the more common large inclusions of the peridotitic or eclogitic assemblages. These sub-micrometre inclusions resemble potassic magmas in their composition, but are enriched in H_2O, CO^(2−)_3 and K_2O and depleted in MgO. This composition represents a volatile-rich fluid or melt from the upper mantle, which was trapped in the diamonds as they grew.

Mantle-derived fluids in diamond micro-inclusions

### Introduction

Earth’s carbon, derived from planetesimals in the 1 AU region during accretion of the Solar System, still retains similarities to carbon found in meteorites (Marty et al. 2013) even after 4.57 billion years of geological processing. The range in isotopic composition of carbon on Earth versus meteorites is nearly identical and, for both, diamond is a common, if volumetrically minor, carbon mineral (Haggerty 1999). Diamond is one of the three native carbon minerals on Earth (the other two being graphite and lonsdaleite). It can crystallize throughout the mantle below about 150 km and can occur metastably in the crust. Diamond is a rare mineral, occurring at the part-per-billion level even within the most diamondiferous volcanic host rock although some rare eclogites have been known to contain 10–15% diamond. As a trace mineral it is unevenly distributed and, except for occurrences in metamorphosed crustal rocks, it is a xenocrystic phase within the series of volcanic rocks (kimberlites, lamproites, ultramafic lamprohyres), which bring it to the surface and host it. The occurrence of diamond on Earth’s surface results from its unique resistance to alteration/dissolution and the sometimes accidental circumstances of its sampling by the volcanic host rock. Diamonds are usually the chief minerals left from their depth of formation, because intact diamondiferous mantle xenoliths are rare.

Diamond has been intensively studied over the last 40 years to provide extraordinary information on our planet’s interior. For example, from the study of its inclusions, diamond is recognized as the only material sampling the “very deep” mantle to depths exceeding 800 km (Harte et al. 1999; McCammon 2001; Stachel and Harris 2009; Harte 2010) although most crystals (~95%) derive from shallower depths (150 to 250 km). Diamonds are less useful in determining carbon fluxes on Earth because they provide only a small, …

Diamonds and the Geology of Mantle Carbon

It is established that vacancies in diamond migrate, during annealing, primarily in their neutral charge state, with an activation energy of 2.3\ifmmode\pm\else\textpm\fi{}0.3 eV. Negative vacancies are destroyed by first converting to neutral centers in a reversible charge transfer process. In relatively pure diamonds (type IIa) and in diamonds (type I) containing large concentrations of nitrogen, effectively all the vacancies in the samples after irradiation can be accounted for in their neutral (${\mathit{V}}^{0}$) and negative (${\mathit{V}}^{\mathrm{\ensuremath{-}}}$) charge states. In nitrogen-rich diamonds, the vacancies are predominantly trapped during annealing at the nitrogen. From the annealing data we derive the relative oscillator strengths of the main absorption bands of ${\mathit{V}}^{0}$, ${\mathit{V}}^{\mathrm{\ensuremath{-}}}$, and of one vacancy combined either with a single N atom, a pair of N atoms, or the larger ``B'' aggregate of nitrogen. In the absence of the intrinsic nonradiative decay channels of luminescence from ${\mathit{V}}^{0}$, we show that the radiative decay time would be 35\ifmmode\pm\else\textpm\fi{}7 ns. In common natural (``type IaA'') diamonds, variations of absorption linewidths during annealing imply that about 40% of the vacancies are created within a few atomic sites of the nitrogen impurity, and direct observation confirms that vacancy production is enhanced in these diamonds. About half the vacancies, including those created near the nitrogen, anneal at each temperature about 12 times faster than those vacancies whose creation is not correlated with the nitrogen.

Vacancy-related centers in diamond

High temperature–high pressure annealing experiments on diamond transform type IB dispersed nitrogen into type IA aggregate nitrogen. The activation energy for the transformation is approximately 60 kcal mol−l (2.6 eV). An estimate is given for the diffusivity of nitrogen in diamond for this transformation

Transformation of the state of nitrogen in diamond

A mass of diamond crystals contacting a mass of elemental silicon are confined within a pressure-transmitting medium. The resulting charge assembly is subjected to a pressure of at least 25 kilobars causing application of isostatic pressure to the contacting masses which dimensionally stabilizes them and increases the density of the mass of diamond crystals. The resulting pressure-maintained charge assembly is heated to a temperature sufficient to melt the silicon and at which no significant graphitization of the diamond occurs whereby the silicon is infiltrated through the interstices between the diamond crystals producing, upon cooling, an adherently bonded integral body.

Silicon carbide and silicon bonded polycrystalline diamond body and method of making it

A curve relating dispersed paramagnetic nitrogen concentrations in laboratory diamonds to their infra-red or ultra-violet absorption spectra has been obtained. Good quality laboratory diamonds ranging in size from 14 to 130 mg were used in this work. From this curve one can obtain dispersed paramagnetic nitrogen concentrations in the range between 0·1 and 500 atomic p.p.m. This curve extends previous results two orders of magnitude toward lower nitrogen concentrations and shows a higher dispersed paramagnetic nitrogen concentration for a given absorption coefficient.

Dispersed paramagnetic nitrogen content of large laboratory diamonds

A polycrystalline diamond body infiltrated by a silicon atom-containing metal (e.g., silicon alloy) is bonded to a substrate comprising cemented carbide with a barrier of refractory material extending between the diamonds cemented together with silicon atom-containing binder and the substrate substantially precluding migration of the cementing medium (e.g., cobalt) from the carbide substrate into contact with the silicon atom-containing bonding medium in the diamond body. The process comprises subjecting a mass of diamond powder, a quantity of silicon atom-containing metal binder material, a cemented carbide body and a barrier made of material selected from the group consisting of tantalum, vanadium, molybdenum, zirconium, tungsten and alloys thereof to the simultaneous application of elevated temperature and pressure.

Polycrystalline diamond and cemented carbide substrate and synthesizing process therefor

Improvements are provided in reaction vessel construction used in the growth of diamond by the process disclosed in U.S. Pat. No. 3,297,407 -- Wentorf, Jr. In assembly of the reaction vessel of this invention, the plug of catalyst-solvent material is disposed between the source of carbon and the diamond seed material as in the Wentorf, Jr. patent and, in addition, the diamond seed material is separated from the catalyst-solvent plug by means for isolating the diamond seed material from the catalyst-solvent material until after the latter has become saturated with carbon from the source of carbon. In addition, preferably the under surface of the plug of catalyst-solvent metal is covered with means for suppressing diamond nucleation. The nucleation suppressing means is usually in the form of a disc and may completely cover the underside of the catalyst-solvent plug or may have a hole therethrough in juxtaposition to the diamond seed/isolating means combination(s). When both the isolating means and the nucleation suppressing means are employed, capability is provided for simultaneously preventing dissolution of the diamond seed and suppressing spurious diamond nucleation.

Method and high pressure reaction vessel for quality control of diamond growth on diamond seed

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