Type IIa Diamond Research Articles

Conductive diamond hollow fiber membranes

Boron-doped diamond hollow fiber membrane (BDD–HFM) was fabricated as a novel type of porous conductive diamond. BDD–HFM was obtained by deposition of BDD polycrystalline film onto a quartz filter substrate consisting of quartz fibers, followed by etching of the substrate in HF/HNO 3 aqueous solution. Cross-sectional scanning electron microscope (SEM) observation showed the inner diameter and wall thickness of the BDD hollow fibers were in the range of 0.4–2 and 0.2–2 μm, respectively. The BDD–HFM electrode exhibited a relatively large double-layer capacitance (ca. 13 F g −1) in 0.1 M H 2SO 4. Electrochemical AC impedance properties were simulated using an equivalent circuit model containing a transmission line model, which indicated characteristics of a porous electrode material.

Nanoinclusions in microdiamonds from Neogenic sands of the Ukraine (Samotkan’ placer): A TEM study

Mineral and fluid inclusions in seven microdiamonds (ca. 0.2 mm in diameter) from the Neogene, Samotkan’ placer of the Ukrainian shield were investigated by TEM. Various types of submicron- or nanometre-sized inclusions such as olivine and orthopyroxene, Fe,Sn oxide and assemblages of mineral multi-phases were observed.In an octahedral microdiamond crystal numerous olivine and enstatite micro- and nanocrystals were observed. Their composition is close to that of other olivine and enstatite inclusions found in kimberlitic diamonds worldwide. An unusual feature of these minerals in the samples studied, however, is a relatively high NiO content: 0.50–0.80 wt.% in olivine (Fo91.3–92.1) and 0.40–0.70 wt.% in enstatite (Fo94.1–95.4). These peridotitic mineral associations represent the host (possibly lherzolitic mantle) in which the diamonds grew. The mean Mg# values of olivine and enstatite inclusions in Samotkan’s microdiamond are, respectively, 91.43 and 94.83, which are closer to Mg#-values of these minerals in lherzolite, rather than in harzburgite assemblages (included in diamond). In addition, enstatite–clinoenstatite, K-richterite, graphite, and Fe,Sn oxide were also identified as nanoinclusions in Samotkan’ diamond; the Fe,Sn oxides and magnetite were found in two microdiamonds of the transitional {111}+{110} form. The K-richterite and graphite have been attributed to epigenetic inclusions. The origin of Fe,Sn oxide is not clear.Assemblages of multi-phase, minerals were observed in four microdiamonds of variable morphology: octahedron, transitional {111}+{110} form, cube and cube-coated diamond. These phases belong to fluid-bearing inclusions and are enclosed in cavities which, as a rule, are not filled completely by the solid phases. The remainder of the volume is occupied by a fluid that for the most part has been released during sample preparation. In the majority of cases the multi-phase assemblages consist of carbonate, mica, rutile, ilmenite, apatite and sylvite. Carbonates are the most abundant phases in the fluid inclusions; they are calcium-rich carbonates, frequently with admixtures of Fe, Mg and Sr. The mica inclusions are enriched in silicon, with Si varying from ca. 6.7 to 7.0 a.p.f.u. The multi-phase mineral assemblages present in Samotkan’s microdiamond are similar to fluid-bearing, microinclusions found previously in other diamond types (e.g., fibrous diamonds, the fibrous coat of coated diamonds or the internal clouds of octahedral diamonds) from kimberlites of different provinces worldwide. They represent the carbonate-, alkali-, and chlorine-rich mantle fluid composition present during crystallisation of the Samotkan’s microdiamond. Judging from the composition of the multi-phase assemblages it may be assumed that the Samotkan’s microdiamond grew from a carbonatitic to a slightly silicic melt, rich in alkali and volatile components.

On the unusual characteristics of the diamonds from Letšeng-la-Terae kimberlites, Lesotho

The Letšeng-la-Terae kimberlites are situated 3100 m above sea level in the Maloti Mountains of Lesotho, southern Africa. The principal economic bodies are two Late Cretaceous, low grade, 1–3.5 carats/hundred ton (cpht), kimberlite pipes that host high-value diamonds realising US$ 2000–2500/carat ($/ct) in 2008 terms. Locally, the larger kimberlite body is referred to as the Main Pipe (17.2 ha) and the smaller one is called the Satellite Pipe (5.2 ha). These pipes, and their associated eluvial and proximal alluvial deposits, are renowned for yielding large, “D” colour, gem quality diamonds, including + 100 carat (ct) stones. Earlier artisanal effort (1959–1977) and formal mining (1977–1982) produced 335,000 carats (cts), including the 601 ct Lesotho Brown in 1968. In 2003, Letšeng Diamonds Limited re-commenced mining operations and had produced 265,000 cts by the end of July 2008, including 24 + 100 ct diamonds, the largest of which was the 603 ct Lesotho Promise. We report here on the unusual characteristics of the Letšeng diamond population that include: i. 75% gem quality that is more commonly associated with alluvial diamond deposits, ii. large average stone size of ca. 1 carat/stone (ct/stn) that is also more typical of certain alluvial diamond placers, iii. high-yielding, rounded to flattened irregular, resorbed dodecahedral shapes (Main Pipe 67% and Satellite Pipe 87%) with subordinate dodecahedral macle (Main Pipe 32% and Satellite Pipe 12%) and broken (ca. 1%) forms. In both pipes the octahedral component is virtually absent (< 0.1%), iv. economically favourable colour mix (ca. 33% white colour diamonds in both pipes), v. abundance of nitrogen-free, “D” colour, Type IIa diamonds that dominate the internationally recognised “special” stone size fraction which covers all diamonds larger than + 10.8 cts (Main Pipe 32% and Satellite Pipe 51%). During 2008, these larger, “special” diamonds commanded prices in excess of US$ 15,000/ct, contributing ca. 75% of the revenue generated by the Letšeng mine. Furthermore, of the 24 + 100 ct diamonds recovered between November 2003 and July 2008, 18 (75%) were Type IIa “D” colour diamonds that also fetched prices mostly in excess of US$ 25,000/ct. Therefore the Type IIa diamonds boost significantly the revenue per unit measure (in this case, the US$/ton) of the Letšeng-la-Terae pipes, making these low grade kimberlites economic to mine.

A comparison of diamonds irradiated by high fluence neutrons or electrons, before and after annealing

Neutron- and electron-irradiated type Ia “black” diamonds were analyzed: three near colorless type Ia diamonds were treated in a nuclear reactor with a dose of 1.8 × 10 17 neutrons/cm 2 and three equivalent samples were irradiated in an electron accelerator with a dose of approximately 0.5 GGy 10 MeV electrons. The diamonds were then annealed and analyzed after the different steps of the treatment. The samples turned from near colorless to very dark green to opaque black upon irradiation and deep greenish yellow to deep orangy brown upon annealing ( Fig. 1). The amount of brown color developed during the treatment was found to relate to the type of irradiation used and likely to the total dose of irradiation. The absorption and photoluminescence features as well as the color changes that were observed were found to be unusual and characteristic for diamonds treated with such high irradiation doses. Certain spectral features such as the 644/649 nm, the 724/734/738 nm, the 920 nm and the 967 nm absorptions were only detected in the neutron-irradiated diamonds while others such as the 6165 cm − 1 and the 805 nm absorptions were only found in the spectra of the electron-irradiated stones. In addition to these treatment experiments some neutron-irradiated very dark green (appearing black) diamonds were heated from 300 to 1100 °C in increments of 50 °C to get a precise idea of the temperature at which color changes occur and the various absorption peaks form. All diamonds turned yellowish to orangy brown after annealing above 700 °C and most of them exhibited unusually strong H1b and/or H1c absorptions after annealing at > 900 °C.

Dependence of nitrogen concentration in type Ib diamonds on synthesis temperature

Type Ib diamonds were grown by the temperature gradient method (TGM) at 5.5 GPa and 1500–1560 K in a china-type cubic anvil high pressure apparatus using Ni70Mn25Co5 alloy as solvent/catalyst. The concentration of nitrogen (CN) in type Ib diamonds synthesized at different synthesis temperatures was measured by a Fourier transform infrared (FTIR) spectrometer. The dependence of CN in diamond on synthesis temperature was studied. For the type Ib diamonds synthesized using Ni70Mn25Co5 as catalyst, its CN decreases along with the increase of synthesis temperature.

Lattice relaxation at V−, NV−,and NVN− defects in diamond investigated by positron annihilation

Experimental positron lifetime data for three vacancy-related defects in synthetic type Ibdiamonds with well known structures are uniquely suitable for comparison with theoreticalinvestigations of lattice relaxation.

Brown diamonds and high pressure high temperature treatment

Much progress has been made in recent years towards greater understanding of the various point and extended defects that give rise to colour in diamond and how such defects can be modified via treatment to change a diamond's colour. Such fundamental understanding has been vital in providing reliable means for gemmological laboratories to identify treated diamonds and ensure maintenance of consumer confidence in diamond. The application of high pressure high temperature treatment to remove a brown colour component has prompted significant research recently into the cause of brown colour. This article reviews progress to date and the evidence that indicates that clusters of around 60 vacancies are the defects responsible for the absorption causing brown colour. The general principles and techniques applied to the detection of diamonds subjected to high pressure high temperature treatment are also discussed. Detailed comparison between photoluminescence spectra from treated and untreated diamonds is vital in the identification of Type IIa diamonds, whilst absorption features provide a robust means of identification for Type I diamonds. A detection scheme based on the shape of the platelet-related infrared absorption is presented.

Development of CMP Conditioner for Sub-50 nm Technology Nodes

Several key conditioner design parameters including diamond size, shape, and concentration were selected and optimized to tune wafer removal rate and pad cut rate for various types of CMP pads. Among various diamond types, two types of diamonds were selected for conditioner applications and numerous conditioners were manufactured to generate pad surface roughness on a regular polyurethane porous pad, hard porous pad, and hard solid pad. Furthermore pad cut rate stability curves and wafer removal rate were generated to correlate conditioner design with pad surface texture and wafer removal rate and defects. Experimental results revealed the effect of conditioner design on pad surface roughness was significant and wafer removal rate varied significantly depending on a specific set of conditioner and pad.

Growth of Nanocrystalline Diamond Thin Films on Titanium Silicon Carbide Using Different Chemical Vapour Deposition Processes

Diamond deposition on Ti3SiC2, a newly developed metallic ceramic material, was studied using microwave plasma enhanced chemical vapour deposition (MPCVD) and hot filament chemical vapour deposition (HFCVD) in hydrogen and methane gas mixtures under different conditions. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and synchrotron near edge extended X-ray absorption fine structure spectroscopy (NEXAFS) were used to characterize the synthesized films. Results show that high diamond nucleation density has been achieved on Ti3SiC2, thus nanocrystalline diamond (NCD) thin films can be feasibly synthesized on Ti3SiC2 under typical microcrystalline diamond growth conditions.

The effect of grain boundaries and adsorbates on the electrical properties of hydrogenated ultra nano crystalline diamond

The results of a comprehensive study on the temperature dependence of the electrical properties of hydrogenated and air exposed undoped UNCD layers following heating/cooling cycles are presented. The results clearly show that, in contrast to hydrogenated and air exposed single crystal type IIa diamond, which exhibits a clear highly conductive p-type surface layer, the electrical properties of hydrogen and H 2O exposure of UNCD are determined by the properties of the entire layer. The changes in the electrical conductivity of UNCD as a result of heating are governed by two different processes: (i) Loss of water from the external surface that takes place at about 150 °C. This process is reversible, reviving the electrical properties upon exposure to humidity, just like in single crystalline diamond.(ii) Modification of the inter-grain material, which occurs at higher temperatures possibly due to H diffusion and passivation of some dangling bonds in the inter-grain material. This increases the resistivity in an irreversible manner. The conduction mechanism in the inter-grain material is characterized by variable range hopping in band tails thus indirectly proving that the material between the grains is some kind of amorphous carbon.

A snapshot of mantle metasomatism: Trace element analysis of coexisting fluid (LA-ICP-MS) and silicate (SIMS) inclusions in fibrous diamonds

We have determined the trace element compositions of coexisting fluid (carbonate–K-chloride–H 2O) and single-phase mineral inclusions in peridotitic (Cr-diopside) and eclogitic (omphacite, garnet) inclusions in fibrous diamonds from the Panda kimberlite (Slave craton, Canada). These diamonds provide a unique insight into the nature of the metasomatic agent, the metasomatised minerals and the pre-metasomatic protolith. The fluid component is strongly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE). Co-existing peridotitic minerals record a melt extraction event (high Cr and Ni) in the protolith prior to the influx of the trapped metasomatic fluid. The silicate minerals are also strongly enriched in LREE. Calculated partition coefficients agree with experimentally determined values in the literature, despite the complex composition of the natural fluid. This indicates that the minerals have re-equilibrated with the metasomatic fluid. The trace element compositions of the mineral inclusions are comparable to many equivalent phases in monocrystalline diamonds. This suggests that the metasomatic fluid and the process recorded in these samples may also be responsible for the growth of some types of monocrystalline diamonds.

On the reduction of the non-diamond phase in nanocrystalline CVD diamond films

We present photocurrent spectra of nominally undoped nanocrystalline diamond (NCD) films grown on glass substrates by hot filament (HF) and microwave (MW) plasma enhanced chemical vapor deposition (CVD). The spectra were measured in a broad optical range (200–2000 nm) by dual-beam photocurrent spectroscopy (DBP) and Fourier-transform photocurrent spectroscopy (FTPS) in amplitude modulated step scan mode. The NCD films with carefully oxidized surface show photosensitivity and high dark resistivity. Unlike single crystal type IIa diamond with the photonization threshold at 5.5 eV, the photocurrent spectra of NCD films are dominated by the “non-diamond phase” with the photo-ionization threshold at about 0.8 eV. Some HF CVD samples have lower sub-band gap absorption (non-diamond phase contamination). The non-diamond phase content increases after annealing at elevated temperature. The non-diamond phase content can be reduced by exposing NCD to hydrogen plasma at temperature below 350 °C.

Spectroscopic methods for the identification of natural yellow gem-quality diamonds

The present study shows how spectroscopic methods are implemented during the identification of diamonds. Specifically, this article presents the characteristic spectroscopic features and criteria of identification for different types of yellow diamonds, including varieties of naturally occurring yellow color and varieties of artificially produced yellow color. Due to the numerous causes of yellow color in diamonds, yellow diamonds are ideal for illustrating the value of spectroscopic methods for identification. The spectroscopic techniques discussed include infrared (IR) spectroscopy, optical absorption spectroscopy, and most importantly laser-induced photoluminescence (PL) spectroscopy.

Multivariable study on homoepitaxial diamond growth using isotopically enriched carbon-13 gas mixtures

We report our observations on the homoepitaxial diamond growth by microwave plasma chemical vapor deposition (MPCVD) experiments on Type Ib diamond substrates conducted by varying three independent variables. In a feed gas mixture of H2, N2, O2, and 13CH4, the amount of nitrogen was varied in the range of 0 to 4000 ppm, the amount of methane was varied from 2% CH4/H2 to 6% CH4/H2, and the substrate temperature was varied in the range of 850 to 1200 °C. We used isotopically enriched carbon-13 methane gas as the source of carbon in the plasma to clearly distinguish the grown diamond layer from the underlying substrate using Raman spectroscopy. The x-ray rocking curve measurements confirmed the homoepitaxial nature of the deposited layers with a slight increase in the full width at half-maximum for sample grown with the highest nitrogen content in the plasma. Optical and atomic force microscopy revealed dramatic changes in surface morphology with variation in each parameter. The nitrogen incorporation in carbon-13 diamond layers was monitored through photoluminescence spectroscopy of nitrogen–vacancy complexes. A twentyfold increase in diamond growth rate was clearly achieved in this multivariable study.

CH2 group migration between the H-terminated 2×1 reconstructed {100} and {111} surfaces of diamond

AbstractVarious possible routes for the migration of a CH2 group between the H-terminated 2×1 reconstructed {100} surface and the H-terminated {111} surface of diamond have been explored using a hybrid quantum mechanical/molecular mechanical method. The calculated energies suggest that movement of such surface bound species across step edges should be a facile process under typical diamond growth conditions, and that such migrations are significant contributors to the observed morphologies of diamond grown by chemical vapor deposition methods.

Characterization of Natural Type-Ia Diamonds by Using Electron Beam Irradiation

Characterization of Natural Type-Ia Diamonds by Using Electron Beam Irradiation

Pulsed laser processing of nano-polycrystalline diamond: A comparative study with single crystal diamond

We have conducted laser processing of ultrahard nano-polycrystalline and single crystalline diamonds (NPD, SCD, respectively) using nano-pulsed near-ultraviolet laser, and the machining properties were compared through microstructural examinations by SEM, TEM and Raman spectroscopy. The cut depth of the laser-cut grooves was observed to be deeper for the NPD than for the SCD. This is probably due to the lower thermal conductivity feature of NPD, which provides higher absorption efficiency of the laser energy and decreases the laser ablation threshold. TEM cross-section observation showed that the processed grooves in the both types of diamonds are covered with identical laser-modified layers (~ 1 µm thick) composed of roughly oriented nanocrystalline graphite. A marked difference was observed between the laser-processed surfaces of NPD and SCD: in the former the diamond–graphite interface is almost linear and undamaged, whereas in the latter the boundary is slightly folded and significantly distorted. These textural features suggest that different laser-machining processes are involved between NPD and SCD in the microscopic scale. Our results demonstrate that pulsed laser can be used even more effectively for the fabrication of nano-polycrystalline diamond than the case for single crystal diamond.

Impaired Reproduction of Three-Dimensional Objects by Cocaine-Dependent Subjects

Impaired Reproduction of Three-Dimensional Objects by Cocaine-Dependent Subjects

Effects of Al and Ti/Cu on Synthesis of Type-IIa Diamond Crystals in Ni70Mn25Co5-C System at HPHT

High-quality type-Ma gem diamond crystals are successfully synthesized in a Ni70Mn25 C05-C system by temperature gradient method (TGM) at about 5.5 GPa and 1560 K. Al and Ti/Cu are used as nitrogen getters respectively. While nitrogen getter Al or Ti/Cu is added into the synthesis system, some inclusions and caves tend to be introduced into the crystals. When Al is added into the solvent alloy, we would hardly gain high-quality type-IIa diamond crystals with nitrogen concentration Nc < 1 ppm because of the reversible reaction of Al and N at high pressure and high temperature (HPHT). However, when Ti/Cu is added into the solvent alloy, high-quality type-IIa diamond crystals with Nc < 1 ppm can be grown by decreasing the growth rate of diamonds.

Electrical properties of a B doped layer in diamond formed by hot B implantation and high-temperature annealing

The influence of hot B implantation into diamond and postimplantation high-temperature annealing at 1600 °C on doping properties has been investigated. B multiple ion implantation was performed at 30–360 keV into high-pressure, high-temperature synthetic type-IIa diamond or high-quality homoepitaxially grown diamond films at 400 °C, followed by 1450 °C and higher temperature (1600 °C) annealing. Optical transmission spectra indicated that radiation damage was almost removed with an increase in annealing temperatures up to 1600 °C. In the sample of 5 × 10 18 cm − 3 using a type-IIa substrate, the hole concentration and the Hall mobility were 2 × 10 13 cm − 3 and 55 cm 2/Vs after 1450 °C annealing, respectively. After 1600 °C annealing, their values increased to 6.5 × 10 13 cm − 3 and 82 cm 2/Vs, respectively. The doping efficiency of the sample after 1600 °C annealing ~ 50% is the highest ever reported for B implanted diamond. By contrast, in the sample of 5 × 10 19 cm − 3 using a type-IIa substrate, high-temperature annealing at 1600 °C resulted in the appearance of hopping conduction in the low-temperature region below 400 K. In the case of a homoepitaxial film B doped at 5 × 10 19 cm − 3 , band conduction is still dominant even after such 1600 °C annealing, giving an increase in the hole concentration in the valence band. The resultant resistivity of the film became much lower than that of annealing at 1450 °C.