Type IIa Diamond Research Articles

Brown diamonds from an eclogite xenolith from Udachnaya kimberlite, Yakutia, Russia

Abstract We have performed petrographic and spectroscopic studies of brown diamonds from an eclogite xenolith from the Udachnaya pipe (Yakutia, Russia). Brown diamonds are randomly intermixed with colorless ones in the rock and often located at the grain boundaries of clinopyroxene and garnet. Brown diamonds can be characterized by a set of defects (H4, N2D and a line at 490.7 nm) which are absent in colorless diamonds. This set of defects is typical for plastically deformed diamonds and indicates that diamonds were likely annealed for a relatively short period after deformation had occurred. Excitation of brown colored zones with a 632.8 nm He–Ne laser produced the typical diamond band plus two additional bands at 1730 cm −1 and 3350 cm −1. These spectral features are not genuine Raman bands, and can be attributed to photoluminescence at ∼ 710 nm (1.75 eV) and ∼ 802 nm (1.54 eV). No Raman peak corresponding to graphite was observed in regions of brown coloration. Comparison with previous reports of brown diamonds from eclogites showed our eclogitic sample to have a typical structure without signs of apparent deformation. Two mechanisms with regard to diamond deformation are proposed: deformation of eclogite by external forces followed by subsequent recrystallization of silicates or, alternatively, deformation by local stress arising due to decompression and expansion of silicates during ascent of the xenolith to surface conditions.

Physicochemical study of the nanodiamond surface

Suspensions of five types of ultrafine diamond of a detonation synthesis in distilled water and 0.9 mol/l NaCl solution were found to have pHs in the range of 3–6, which results from the intrinsic acidity of their surfaces. The possibility of quantitatively determining the protogenic groups of a surface is found using the pH-potentiometric method. The data on the kinetics of the varying pH of suspensions in water and 0.9 mol/l NaCl solution and the data on the curves of the alkali titration of the suspensions of nanodiamond in the indicated systems make it possible to infer the presence of one or two types of acid groups on the surface of a diamond. The constants of dissociation (pK 1) of these groups on the assumption of their single-base nature are estimated. From 1 × 10−3−5 × 10−2 mol/l chloride solutions of H[AuCl4] and RhCl3 on the surface of diamond, gold(III) and rhodium(III) are found to be adsorbed; the adsorption of methylene blue from its 2.5 × 10−4−5 × 10−4 mol/l solutions reaches more than 90% (upon adsorption from 5 ml of the initial solution by a 0.05-g nanodiamond).

Wear Characteristics of Impregnated Diamond Bit in Drilling Armor Ceramic

This paper describes the wear characteristics of impregnated diamond bits when drilling in Al2O3 armor ceramic. With different bits being developed, drilling experiments and scanning electron microscope (SEM) examinations were conducted, and the results show that diamond wear types consist of complete crystal shape, micro fragmentation, whole fragmentation, wearing flat and falling off of diamond; abrasive wear, impact abrasion and erosion exist in the wear of diamond and bond; diamond grain size and concentration have their optimal value under fixed machining conditions; diamonds of high quality could increase bit drilling efficiency and serving life; the bit whose abrasion rate of bond matches that of diamonds presents the best comprehensive properties.

Luminescence of diamonds from metamorphic rocks

This study explores the effects of metamorphism on luminescence of diamond. Four diamond suites extracted from metamorphic rocks were characterized using optical cathodoluminescence, FTIR spectroscopy, photoluminescence at the liquid nitrogen temperature, and cathodoluminescence spectroscopy. The studied diamonds are from sedimentary conglomerate and lamprophyric breccia metamorphosed to the greenschist facies (Wawa, Canada), and from the ultrahigh-pressure (UHP) terranes of Kokchetav (Kazakhstan) and Erzgebirge (Germany). The majority of studied diamonds that experienced metamorphism have distinct cathodoluminescence and photoluminescence when compared to diamonds from unmetamorphosed rocks, i.e., kimberlites or placers. Diamonds in metamorphic rocks do not show the prevalent blue cathodoluminescence emittance at 415–440 and 480–490 nm typical of common kimberlite and placer diamonds. Ultrahigh-pressure diamonds are mostly non-luminescent, whereas diamonds from greenschists display green, yellow, orange, and red cathodoluminescent colors emitting light at 520 and 576 nm, and between 586 and 664 nm. The shift of cathodoluminescence in octahedrally grown Type Ia diamonds metamorphosed in the greenschist facies results from the presence of optical centers with zero-phonon lines at 575 and 637 nm detected via photoluminescence spectroscopy. The centers may have formed due to irradiation of diamonds in the upper crust followed by annealing at T > 500 °C. This process creates vacancies that diffuse through the diamond lattice and get trapped at N sites, creating NV o and NV − optical centers. The distinct luminescence of metamorphosed diamonds can persist for billions of years in the crust, but is annealed in the mantle.

Laser annealing of neutron irradiated boron-10 isotope doped diamond

10B isotope doped p-type diamond epilayer grown by chemical vapor deposition on (110) oriented type IIa diamond single crystal substrate was subjected to neutron transmutation at a fluence of 2.4 × 1020 thermal and 2.4 × 1020 fast neutrons. After neutron irradiation, the epilayer and the diamond substrate were laser annealed using Nd–YAG laser irradiation with wave length, 266 nm and energy, 150 mJ per pulse. The neutron irradiated diamond epilayer and the substrate were characterized before and after laser annealing using different techniques. The characterization techniques include optical microscopy, secondary ion mass spectrometry, X-ray diffraction, Raman, photoluminescence and Fourier Transform Infrared spectroscopy, and electrical sheet conductance measurement. The results indicate that the structure of the irradiation induced amorphous epilayer changes to disordered graphite upon laser annealing. The irradiated substrate retains the (110) crystalline structure with neutron irradiation induced defects.

Simulations of chemical vapor deposition diamond film growth using a kinetic Monte Carlo model and two-dimensional models of microwave plasma and hot filament chemical vapor deposition reactors

A one-dimensional kinetic Monte Carlo (KMC) model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model considers adsorption, etching/desorption, lattice incorporation and surface migration but not defect formation or renucleation processes. Two methods have been devised for estimation of the gas phase concentrations of species at the growing diamond surface, and are used to determine adsorption rates for C1Hx hydrocarbons for the different conditions. The rate of migration of adsorbed carbon species is governed by the availability of neighboring radical sites, which, in turn, depend upon the rates of H abstraction and of surface-radical migration. The KMC model predicts growth rates and surface roughness for each of diamond types consistent with experiment. In the absence of defect formation and renucleation the average surface diffusion length, ℓ, is a key parameter controlling surface morphology. When ℓ<2, surface migration is limited by the lack of availability of surface radical sites, and the migrating surface species simply hop back and forth between two adjacent sites but do not travel far beyond their initial adsorption site. Thus, Eley–Rideal processes dominate the growth, leading to the rough surfaces seen in NCD and UNCD. The maximum or “intrinsic” surface roughness occurs for nominally zero-migration conditions (ℓ=0) with an rms value of approximately five carbon atoms. Conversely, when migration occurs over greater distances (ℓ>2), Langmuir–Hinshelwood processes dominate the growth producing the smoother surfaces of MCD and SCD. By extrapolation, we predict that atomically smooth surfaces over large areas should occur once migrating species can travel approximately five sites (ℓ∼5). β-scission processes are found to be unimportant for MCD and SCD growth conditions, but can remove up to 5% of the adsorbing carbon for NCD and UNCD growth. C1Hx insertion reactions also contribute <1% to the growth for nearly all conditions, while C2Hx (x<2) insertion reactions are negligible due their very low concentrations at the surface. Finally, the predictions for growth rate and morphology for UNCD deposition in a microwave system were found to be anomalous compared to those for all the other growth conditions, suggesting that carbonaceous particulates created in these plasmas may significantly affect the gas chemistry.

Mosaic Diamond Pad Conditioners for Improved CMP Performance

A mosaic design of diamond disks that incorporates different cutting characteristics of diamond grits can allow faster polishing of wafers with less pad consumption. Larger diamond grits can make pad asperities with large peak to valley ratios for achieving high polishing rate. On the other hand, Sharp grits can shave the pad effectively as to eliminate the glazed layer. The conventional diamond disks employ similar type of diamond grits across the entire disk. These grits cannot dress and cut the pad with optimization. By combining different types of diamond grits in a cocktail combination, the pad asperities can be controlled to enhance removal rates of the wafer. The glazed layer may also be removed cleaner so wafer defectivity is minimized.

Raman characterization of carbon materials under non-hydrostatic conditions

Raman spectroscopy experiments on double-wall carbon nanotube and highly oriented pyrolytic graphite (HOPG) samples subjected to non-hydrostatic conditions have been conducted in anvil cells to study the effect of the pressure/stress on the bands assigned to defects. Typical diamond anvils used in high pressure experiments have been substituted by moissanite (6H-SiC) and sapphire (Al 2O 3) anvils to allow the observation of the D band (around 1350 cm −1) and the second-order Raman scattering without interference. We demonstrate that Raman experiments at high pressure provide unique information to probe the mechanical behaviour of carbon materials (CMs). We also show that this can be also a powerful technique to assign controversial spectral features such as those appearing in the second order region of the spectra of CMs. In HOPG samples we find that the D′/D band intensity ratio is independent of stress. The results indicate that an increase of non-hydrostatic stresses on HOPG generates graphitic domains with sizes around 20–30 nm when the sample is recovered to room conditions.

Field emission stability and properties of simultaneously grown microcrystalline diamond and carbon nanostructure films

The temporal stability and electron field emission characteristics of simultaneously grown microcrystalline diamond and carbon nanostructures were investigated. The films were prepared by hot filament chemical vapor deposition using typical diamond deposition parameters, and iron oxide nanoparticles on the molybdenum substrate were employed as catalyst for their induction. The hybrid system presented better emission characteristics compared with microcrystalline diamond with turn-on fields as low as 2.45 V/μm (at 1 μA/cm2), and a current density of up to 0.24 mA/cm2 was achieved. The films showed relatively stable emission behavior for a period of 24 h.

High-Temperature Dielectric Behavior of Nanocrystalline and Microcrystalline Diamond Thin Films

This paper presents high-temperature electrical properties of polycrystalline, microcrystalline and nanocrystalline diamond films synthesized with varying proportions of nitrogen and argon in the gas phase. Resistivity data, activation energies, barrier heights, dielectric constants and quality factors are reported for these films up to 823 K. Results indicate that high N2 (0.5 %) and Ar (85 %) levels in the gas phase degrade the electrical quality of the diamond films. This degradation is attributed to a combined effect of decreasing grain size and higher sp2 carbon content in the films. A gas ratio of 60:39:1 of Ar:H2:CH4 was found to produce improved dielectric quality with resistivities comparable to those of typical microcrystalline diamond films. A proprietary seeding technique which produced a dense diamond nucleation layer is also presented. This research resulted in the development of process conditions for diamond deposition on device substrates that incurred no observable damage to device metallization.

Single-crystal diamond MIS diode for deep UV detection

Due to its exceptional physical properties, synthetic diamond is an ideal material for the realization of UV and X-ray detectors to be used for the characterization of laser-generated plasmas. Diamond detectors are able to operate at high temperatures and in the presence of high fluxes of ionizing radiation, where traditional silicon-based detectors usually fail. In this paper, we report on Raman and electro-optical characterization of a structure consisting of intrinsic diamond/boron-doped diamond homoepitaxially grown by chemical vapor deposition onto a commercial high pressure high temperature Ib-type diamond substrate using a 1% CH4/H2 gas mixture. A metal–insulator–semiconductor (MIS) diode was obtained by thermally evaporating an aluminum contact on the growth surface of the intrinsic layer. The detection capability of this device operating in transverse configuration was measured in the deep UV spectral range. The device sensitivity has been estimated at different biasing voltages and at two wavelengths having different penetration depths into the material. The device was also tested at zero biasing voltage (photovoltaic mode operation), showing quite a good photoresponse. These results suggest that MIS structures based on high-quality homoepitaxial diamonds may be successfully utilized for photodetection even at zero bias.

Modelling wafer bow in silicon–polycrystalline CVD diamond substrates for GaN-based devices

Composite silicon–polycrystalline chemical vapour deposition (CVD) diamond wafers are potential substrates for GaN-based devices for use in harsh environments due to their high thermal conductivity and chemical stability. When cooled from a typical diamond deposition temperature of approximately 800 to 25 °C wafer bowing arises from a mismatch in the coefficients of thermal expansion of silicon and polycrystalline diamond. In this paper 100 mm diameter silicon–polycrystalline diamond wafers have been modelled using ANSYS finite element software to investigate their bowing behaviour as a function of temperature and geometry. The maximum bow of a wafer occurred where the thicknesses of both the silicon and polycrystalline diamond layers was almost identical; this has been confirmed using analytical methods. Strategies are discussed for reducing wafer bow.

Nanodiamonds for optical bioimaging

Diamond has received increasing attention for its promising biomedical applications. The material is highly biocompatible and can be easily conjugated with bioactive molecules. Recently, nanoscale diamond has been applied as light scattering labels and luminescent optical markers. The luminescence, arising from photoexcitation of colour centres, can be substantially enhanced when type Ib diamond nanocrystals are bombarded by a high-energy particle beam and then annealed to form negatively charged nitrogen-vacancy centres. The centre absorbs strongly at 560 nm, fluoresces efficiently in the far-red region and is exceptionally photostable (without photoblinking and photobleaching). It is an ideal candidate for long-term imaging and tracking in complex cellular environments. This review summarizes recent advances in the development of fluorescent nanodiamonds for optical bioimaging with single particle sensitivity and nanometric resolution.

Dislocation electrical conductivity of plastically deformed natural diamonds

The temperature dependence of the electrical conductivity of natural semiconducting diamonds of Ic type has been studied. The activation energies of the dislocation acceptor centers (induced by plastic deformation) are found to be ɛ3 = 0.29–0.36 eV. Four natural diamonds of IIa type with a resistivity of 1015–1016 Ω cm were plastically deformed to prove the formation of levels with the activation energy ɛ3 in semiconducting diamonds. The deformation led to a decrease in resistivity by one to two orders of magnitude and to the formation of a new level with ɛ3 = 0.29 eV, which is characteristic of semiconducting diamonds. We expect deformation to induce dislocation centers, not only in Ic-type diamonds, but also in natural semiconducting diamonds of IIb type.

Electron emission by current injection from n‐type diamond film surface with negative electron affinity

AbstractWe found current injection‐stimulated electron emission from n‐type diamond (001) surfaces with negative electron affinity (NEA) and band conduction, while no emission was observed from heavily phosphorous‐doped n+‐type diamond (111) surfaces with NEA and hopping conduction even though the injected current level was four to five orders of magnitude higher than that of the (001) case. Sweeping the potential of the collector electrode implies that electrons are emitted mainly from the positively biased electrode side, where the upward‐band bending should be reduced. These results support the intrinsic upward‐band bending model of the n‐type diamond surfaces with NEA, which was previously indicated by photoelectron emission experiments and theoretical prediction.

Polish Properties of Nano-Cluster Diamonds on Glass Substrates

Hard disk substrates play a key role in the data storage process of magnetic storage hard disk drives (HDDs). However, a potential failure mode exists with the head clearance requirements caused by surface variation which is induced by substrate nano-asperities. Consequently, developing a polish process to eliminate surface asperities and residual surface defects in the glass substrate disks process is therefore a necessity to meet the challenges of future technology. Currently, the leading candidate utilizes nano cluster diamond (NCD) abrasive which is a synthetic diamond created in a controlled explosion process. A great effort is now underway to modify these NCD clusters to reduce light scratches and asperities in the perpendicular magnetic recording media polish process. Three distinct diamond types of NCD-90, NCD-80 and NCD-70 were utilized in this study. The major difference among these three distinct cluster diamond types is the diamond percentage amounts. Because of the differing diamond percentage content, one achieves a different structure which changes the polish properties. HRTEM, XPS, Raman, BET, AFM, Optical Surface Analyzer and disk defect testers were used for the diamond particles, polished substrate and disk analysis. The detail shall be discussed in this study.

Back Cover (Phys. Status Solidi A 8/2010)

Diamond Schottky barrier diodes (SBDs) are promising candidates for high current operation. Towards achieving this, the device series resistance (Rs) has to be manipulated carefully, and the parasitic resistance [R(p+)] originating from the p+ layer of the diamond SBDs has a significant influence in constituting the device Rs. For the first time, Kumaresan et al. (see the article on pp. 1997-2001) carried out a systematic analysis of the parasitic resistance of pseudo-vertical type diamond SBDs, and for this the authors designed an elegant structure, as shown in the cover image at top. The left bottom image is a curve fitting analysis result of device Rs which reveals the significance of parasitic resistance on device Rs, and the right bottom image reveals that the parasitic resistance from p+ layer can be engineered by varying its thickness suitably. This study paves a way towards designing the p+ layer thickness for achieving a high current transport of the fabricated device, by means of minimizing the parasitic resistance of the p+ layer.

Ultraviolet photoresponse properties of zinc oxide on type IIb diamond heterojunction

Heterojunctions between ZnO and diamond are difficult to synthesize due to doping problems. In this work, a successful heterojunction that is sensitive to ultraviolet (UV) light has been fabricated using sputtered ZnO thin film on type IIb diamond, where boron activation at room temperature is possible at low concentrations. Current–voltage measurements show a p–n characteristic with significant UV photoresponse properties. The threshold voltage under UV illumination is decreased by 0.4 V, which can be predicted using a theoretical model.

Mantle-related carbonados? Geochemical insights from diamonds from the Dachine komatiite (French Guiana)

Carbonado is a unique type of polycrystalline diamond characterised, among others, by 13C-depleted isotope compositions (δ 13C ∼ -25‰ vs. PDB), little advanced nitrogen aggregation (Ib-IaA) and sintered (ceramic-like) diamond grains. Its origin remains an enigma, with models proposing a formation either in the Earth's crust or even within an exploding super-nova. The possibility that carbonado formed in the Earth's mantle is often rejected because diamond with carbonado-like geochemical features has never been found in rocks, such as kimberlites, that carry diamonds from the mantle. In this study, it is shown that the C- and N- stable isotope compositions, nitrogen contents and nitrogen speciation of diamonds from the Dachine komatiite (French Guyana) exhibit unambiguous similarities with carbonados. These include C-isotopes (from -32.6 to + 0.15‰, mode at ∼-27‰), N-aggregation (only Ib-IaA diamonds, from 2 to 76% of N-pairs) and N-isotopes (from -4.1 to + 6.9‰, average ∼ + 2.1 ± 2.9‰), which all strikingly match the carbonado data. This evidence illustrates that the main geochemical arguments usually called to reject a mantle origin of carbonado are no longer valid. A model linking carbonado crystallisation from komatiite volatiles is developed. In this model, the sintering is produced by the high temperature of the komatiite magma thus accounting for their absence in colder kimberlites. The low δ 13C compositions of carbonados would be inherited from the transition zone (> 300 km depths), which is known to yield diamonds with distinct C-isotope distributions compared to most lithospheric diamonds (150–300 km depths). This model can account for most available observations of carbonados, including their large size, sintering, photoluminescense/cathodoluminescence features and geochemical characteristics.

Atomic structure-colour relationship in natural diamonds

Colour is a physical attribute that can be very difficult to characterise in diamond and consequently it receives regular attention from scientists working in the gem industry. In this work we compare natural brown (the most common colour) and colourless type IIa diamonds containing only trace quantities (< 1 at. ppm) of nitrogen. Numerous attempts have been made to trace the origin of brown tints in natural diamond, with the most likely culprits, i.e. dislocations and nitrogen impurities, ruled out through the application of various analytical techniques. Consequently more emphasis has recently been placed on the study of smaller defects in the diamond structure and their influence on colour. The focus of this research work is the analysis of vacancy defects having a size of the order of 1nm using aberration corrected scanning transmission electron microscopy (AC-STEM). The small electron probe size and depth of focus afforded by this technique allows such defect structures together with their position to be resolved far more readily than with conventional HR-TEM. Small-scale contrast variations are apparent in the lattice images of brown and not of colourless diamonds. These features have been compared to simulated phase contrast images of vacancy clusters in diamond. In addition, both experimental and simulated defocus series indicate that such features are not restricted to the surface of the specimen.