Type IIa Diamond Research Articles

Enhancing the wear resistance of WC–Co cutting inserts using synthetic diamond coatings

PurposeThe purpose of this study is to investigate the mechanical and tribological properties of the synthetic diamond coatings deposited on WC-Co cutting tools for their prospective applications in mechanical industry. In this work, the concept of nanocrystalline diamond, microcrystalline diamond and multilayer-diamond coating systems were proposed and deposited on WC-Co substrates with the top-layer nanocrystallinity, optimum thickness and interfacial adhesion strength for load-bearing tribological and machining applications. Also, the overall mechanical and tribological properties of all synthetic diamond coatings were compared for the purpose of selecting a suitable type of protective layer used on the surfaces of WC-Co cutting tools or mechanical dies.Design/methodology/approachSmooth and adhesive single layered and multilayered synthetic deposited on chemically etched cemented tungsten carbide (WC-Co) substrates using predetermined process parameters in hot filament chemical vapor deposition (HFCVD) method. A comparison has been documented between diamond coatings having different nature and architecture for the purpose of studying their mechanical and tribological characteristics. The friction characteristics were studied experimentally using ball-on-disc type linear reciprocating micro-tribometer under the influence of varying load conditions and within dry sliding conditions. Nanoindentation tests were conducted on each diamond coating using Berkovich nanoindenter for the measurement of their hardness and elastic modulus values. Also, the wear characteristics of all sliding bodies were studied under varying load conditions using cumulative weight loss and density method.FindingsDepositing any type of diamond coating on the cemented carbide tool insert increases its all mechanical and tribological characteristics. When using boron-doping onto the top-layer surface of diamond coatings decrease slightly their mechanical properties but increases the tribological characteristics. Present analysis reveals that friction coefficient of all diamond-coated WC-Co substrates decreases with the increase of normal load. Therefore, maintaining an appropriate level of normal load, sliding time, sliding distance, atmospheric conditions and type of diamond coating, the friction coefficient may be kept to some lower value to improve mechanical processes.Originality/valueAs the single layered synthetic diamond coatings have not given the full requirements of mechanical and tribological properties when deposited on cutting tools. Therefore, the multilayered diamond coatings were proposed and developed to enhance the interfacial integrity of the nanocrystalline and microcrystalline layers (by eliminating the sharp interface) as well as increasing the hardness of tungsten carbide substrate. However, when using boron doping onto the top-layer surface of diamond, coatings decreases slightly their mechanical characteristics but also decreases the value of friction coefficient.

Blue boron-bearing diamonds from Earth's lower mantle.

Geological pathways for the recycling of Earth's surface materials into the mantle are both driven and obscured by plate tectonics1-3. Gauging the extent of this recycling is difficult because subducted crustal components are often released at relatively shallow depths, below arc volcanoes4-7. The conspicuous existence of blue boron-bearing diamonds (typeIIb)8,9 reveals that boron, an element abundant in the continental and oceanic crust, is present in certain diamond-forming fluids at mantle depths. However, both the provenance of the boron and the geological setting of diamond crystallization were unknown. Here we show that boron-bearing diamonds carry previously unrecognized mineral assemblages whose high-pressure precursors were stable in metamorphosed oceanic lithospheric slabs at depths reaching the lower mantle. We propose that some of the boron in seawater-serpentinized oceanic lithosphere is subducted into the deep mantle, where it is released with hydrous fluids that enable diamond growth10. TypeIIb diamonds are thus among the deepest diamonds ever found and indicate a viable pathway for the deep-mantle recycling of crustal elements.

Laser heated diamond anvil cell facility for high temperature high pressure research: application to material synthesis and melting studies

Laser-heated diamond anvil cell (LHDAC) technique is a unique and powerful experimental tool for studying the phase behaviour of materials at thermodynamic conditions comparable to the Earth’s deep interior. Fine tuning of the two thermodynamic variables viz., pressure and temperature enables one to manipulate matter on an atomic scale leading to the synthesis of novel compounds or transformation of the properties of existing materials. In this article the details of an ytterbium doped fibre laser based LHDAC facility are presented. The advantages and excellent performance of the off-axis angular heating geometry is demonstrated through results of high pressure melting experiments on KBr up to 24 GPa and high temperature high pressure synthesis of γ-Mo2N carried out by laser heating molybdenum metal and molecular nitrogen at 7 GPa and 2000 K in a Mao–Bell type diamond anvil cell.

A 4.5 [formula omitted]m PIN diamond diode for detecting slow neutrons

The response of a PIN diamond diode with a 4.5 μm thick i-layer to α-particles from a 210Po radioactive source has been measured and compared to the response from a 300 μm thick single crystal type IIa diamond. The results show that this PIN diamond diode with thin i-layer can be employed to detect slow neutrons following absorption on a converter boron layer. Such a detector will operate at low voltages and be rather insensitive to gamma background and neutron radiation damage.

Experimental study of rectangular groove texture in the surface of photovoltaic silicon with diamond coated micro-milling tools

Microstructure in the surface of photovoltaic silicon can decrease the reflectance of light and improve absorption efficiency of silicon solar cell, and mechanical texturization is a kind of clean method to fabricate light trap microstructure in the surface of silicon. This paper is an experimental study to verify reflectance simulation of rectangular groove texture in the surface of photovoltaic silicon. In this paper, two types of micro-end diamond coated cemented carbide tools in different diameters were used to carry out mechanical texturization in single crystal silicon along <111> and <100> crystal orientation. Firstly, formulas aiming to achieve ductile mode milling are derived and offering guidelines for subsequent parameters set of rectangular light trap machining, and then cutting parameters such as axial depth of cut, feed rate and uncut width (width of wall between adjacent rectangular grooves) were studied for diamond different coated tools. The finish and integrity of structures obtained by machining along < 111 > and < 100 > crystal orientations were compared and analyzed, and machining along < 100 > crystal orientation showed a better surface finish and integrity of light trap than along < 111 > under the same conditions. Finally, the appearance of worn tools were observed and the reflectance of fabricated light trap microstructure was analyzed, and a satisfying reflectance below 15% for 0.4–1.1 µm wavelength lights can be achieved in the texture obtained when the principle angle of light incidence > 20°.

Characterization of Various Centers in Synthetic Type Ib Diamond under HPHT Annealing

In this study, type Ib diamond annealing experiments were successfully performed under a pressure of 2.5 GPa and a high temperature range between 1680 and 2060 °C. The color of the diamond changed ...

Microstructural modification of diamond-graphite nanohybrid films via adjusting deposition temperatures for enhanced electron field emission

To achieve enhanced electron field emission, diamond-graphite nanohybrid films are deposited on Si substrates by means of a microwave plasma chemical vapor deposition (MPCVD) reactor. Liquid diethylamine is used as a sole reactive source. An increase of deposition temperature from 730 °C to 830 °C leads to remarkable changes of morphology and microstructure of diamond-graphite nanohybrid films, namely from a typical planar ultrananocrystalline diamond (UNCD) film at 730 °C to a novel nanocrystalline diamond/graphene nanowall (ND/GNW) film at 830 °C. The electrical conductivity of a ND/GNW film is measured to be 762.4 Ω−1·cm−1, while for a UNCD film it is 18.0 Ω−1·cm−1. Moreover, the electron field emission is significantly enhanced on a ND/GNW film. With an applied electrical field of 9.9 V μm−1 its emission current density is 1.6 mA cm−2, 8-time larger than that for a UNCD film. The possible electron emission mechanism is then discussed based on the Fowler-Nordheim theory. This work offers a simple way to alter effectively the microstructures of sp2/sp3 nanohybrid films that benefit greatly to develop carbon-based field emission cold cathodes featuring high performance.

Minimal surface designs for porous materials: from microstructures to mechanical properties

In this work, we present four types of topological bicontinuous porous structures, namely Gyroid (G), Schwarz Diamond (D), Schwarz Primitive (P), and iWp (W), which are generated from mathematically defined triply periodic minimal surfaces. A systematic semi-theoretical investigation is performed to analyze the relations between the microstructures and the macroscopic mechanical behavior. Benefiting from the straightforward controllability on parameters, the scaling laws of the geometrical properties and mechanical properties are determined as functions of the relative density according to numerical analysis and computational simulation. An application to additive manufacturing accompanying with uniaxial compression testing is also performed, and the results show a highly agreement with the above scaling laws. Moreover, the simulation results indicate that the mechanical properties are highly dependent on topological architectures, which affect the deformation behavior of porous materials. It is shown that P topology has the highest stiffness and strength with stretching-dominated mode, while the rest exhibit a flexibly bending-dominated deformation behavior. The present study provides not only new insights into the structure–property relations of such topologies, but also a practical guide for their fabrication and application.

Comparison of the quality of single-crystal diamonds grown on two types of seed substrates by MPCVD

Microwave plasma chemical vapor deposition (MPCVD) was used to grow single-crystal diamonds on two types of single-crystal diamond seed substrates prepared by high-pressure, high-temperature (HPHT) and chemical vapor deposition (CVD) methods. The quality of diamonds grown on the different seed substrates was compared. Fluorescence characteristics showed that the sectors of the HPHT seed substrates were obviously partitioned. Raman and absorption spectra showed that the CVD seed substrate produced higher-quality crystals with fewer nitrogen impurities. X-ray topography showed that the HPHT seed substrate had obvious growth sector boundaries, inclusions, dislocations, and stacking faults. The polarization characteristics of HPHT seed substrate were obvious, and the stress distribution was not uniform. When etching HPHT and CVD seed substrates using the same parameters, the etching morphology and extent of different growth sectors of the two substrates differed. Although extended defects were inevitably formed at the interface and propagated in the CVD layer, the dislocation density of a 1 mm-thick CVD layer grown on a CVD seed substrate was only half that of a 1 mm-thick CVD layer grown on an HPHT seed substrate. Therefore, the use of CVD seed substrate enabled the growth of a relatively higher-quality CVD single-crystal diamond.

Preferentially aligned nitrogen-vacancy centers in heteroepitaxial (111) diamonds on Si substrates via 3C-SiC intermediate layers

Nitrogen-vacancy (NV) centers in diamonds are expected for high-performance quantum sensing devices. The NV centers in heteroepitaxial diamond films on Si substrates have more potential to enable low-cost and large-area sensors than typical single-crystal diamond substrates and to support the emergence of diamond/Si hybrid devices. In this paper, NV centers were formed in (111) heteroepitaxial diamond films on Si substrates with preferential atomic alignment in the [111] direction. In addition, incorporation of silicon-vacancy centers, which decrease the sensitivity of sensors, from the 3C-SiC/Si substrate was effectively suppressed using oxygen gas in the growth environment.

Quantum-optical characterization of single-photon emitters created by MeV proton irradiation of HPHT diamond nanocrystals

Deterministic single-photon sources are a fundamental tool for several emerging applications in quantum sensing and quantum metrology. In these fields, the exploitation of individual quantum systems could significantly improve the current measuring capabilities and define a new generation of standard measure units. In addition, the availability of nanoscale-sized single-photon emitters is also of considerable interest, as it enables a further integration with external structures or biological samples.In this work, we investigate the role of MeV proton irradiation in the production of single-photon emitters based on the nitrogen-vacancy complex (NV center) in nanodiamonds (NDs). Powders of nitrogen-containing type Ib diamond nanocrystals with a median size distribution of 80 nm were irradiated with 2 MeV protons at 5 × 1013 cm−2 fluence with the purpose of creating vacancies and thus promote the formation of NV centers upon a subsequent thermal annealing. Following a suitable chemical processing, the ND powders were characterized in their opto-physical properties by means of a single-photon-sensitive confocal photoluminescence microscopy setup equipped with a “Hanbury Brown & Twiss” interferometer, enabling the measurement of the second-order autocorrelation function characterizing the PL emission. A comparison with two reference batches of unirradiated NDs powder, which only underwent the chemical, and the chemical and thermal treatment, respectively, enabled to assess the role of ion implantation in the production of single-photon sources.

Fabrication of (111)-faced single-crystal diamond plates by laser nucleated cleaving

Single-crystal diamond plates with surfaces oriented in a (111) crystal plane are required for high-performance solid-state device platforms ranging from power electronics to quantum information processing architectures. However, producing plates with this orientation has proven challenging. In this paper, we demonstrate a method for reliably and precisely fabricating (111)-faced plates from commercially available, chemical-vapor-deposition-grown, type-IIa single-crystal diamond substrates with (100) faces. Our method uses a nanosecond-pulsed visible laser to nucleate and propagate a mechanical cleave in a chosen (111) crystal plane, resulting in faces as large as 3.0mm × 0.3mm with atomically flat surfaces, negligible miscut angles, and near zero kerf loss. We discuss the underlying physical mechanisms of the process along with potential improvements that will enable the production of millimeter-scale (111)-faced single-crystal diamond plates for a variety of emerging devices and applications.

Imaging the atomic structure and local chemistry of platelets in natural type Ia diamond.

In the past decades, many efforts have been devoted to characterizing {001} platelet defects in type Ia diamond. It is known that N is concentrated at the defect core. However, an accurate description of the atomic structure of the defect and the role that N plays in it is still unknown. Here, by using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy we have determined the atomic arrangement within platelet defects in a natural type Ia diamond and matched it to a prevalent theoretical model. The platelet has an anisotropic atomic structure with a zigzag ordering of defect pairs along the defect line. The electron energy-loss near-edge fine structure of both carbon K- and nitrogen K-edges obtained from the platelet core is consistent with a trigonal bonding arrangement at interstitial sites. The experimental observations support an interstitial aggregate mode of formation for platelet defects in natural diamond.

The luminescence emitted from the type Ib and IIa diamonds under the SiO2 polishing process

The luminescence of triboplasma during diamond polishing was investigated. The main luminescence in the ultraviolet range came from N2 molecules in the air. The colors of the visible range of triboplasma were the same as those observed in the photoluminescence images, excited by the ultraviolet light. The color of the triboplasma luminescence was green for type Ib diamond, which was mainly from the H3 center. The blue luminescence for type IIa diamond was mainly from Band A. The correlation between the diamond temperature and periphery speed indicate that that the mechanical abrasion component also increased linearly. However the polishing rate showed a threshold at the periphery speed of 26 km/h which corresponds well with the threshold of the triboplasma generation. These results imply that the electrical and optical energy of the triboplasma excited the defect level at the diamond surface and enhanced the chemical polishing rate of the diamond.

Formation of the nitrogen aggregates in annealed diamond by neutron irradiation

Neutron heavy irradiation was performed on synthetic diamonds contain nitrogen atoms in isolated substitutional form (called “type Ib diamond”) and they were annealed under a pressure of 6 GPa. A large number of nitrogen B-aggregate which consists of four substitutional nitrogen atoms symmetrically surrounding a vacancy was formed within 30 m from single nitrogen atoms. Furthermore it is observed that, in these diamonds, single nitrogen atoms coexist with the B-aggregates, which is unexplainable by the simple nitrogen aggregation model.

Diamond in the Rough.

The article offers information on formation of rare diamonds. It mentions that when a meteorite containing graphite slams into the earth, the collision's heat and pressure can transform this form of carbon into a rare and extremely hard type of diamond. It presents the views of Yogendra Gupta, from Washington State University, on formation of hexagonal diamond. It mentions the views of Lorin Benedict, from Lawrence Livermore National Laboratory, on the crystal structure of diamond.

UV-photodetector based on NiO/diamond film

In this study, a NiO/diamond UV-photodetector has been fabricated and investigated. A single crystal diamond (SCD) layer was grown on a high-pressure-high-temperature Ib-type diamond substrate by using a microwave plasma chemical vapor deposition system. NiO films were deposited directly by the reactive magnetron sputtering technique in a mixture gas of oxygen and argon onto the SCD layer. Gold films were patterned on NiO films as electrodes to form the metal-semiconductor-metal UV-photodetector which shows good repeatability and a 2 orders of magnitude UV/visible rejection ratio. Also, the NiO/diamond photodetector has a higher responsivity and a wider response range in contrast to a diamond photodetector.

Nano-polycrystalline diamond synthesized from neutron-irradiated highly oriented pyrolytic graphite (HOPG)

Highly oriented pyrolytic graphite (HOPG) is a unique source material for the synthesis of new types of diamond. It can transform to layered nano-polycrystalline diamond (NPD) under static high pressure and high temperature (HPHT) and to “amorphous diamond” by introducing structural defects by neutron irradiation followed by shock compression. Here, we investigated the structural change of the neutron-irradiated HOPG through a HPHT treatment at 2300°C and 15GPa by Raman, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray absorption near edge structure (XANES) analyses. The recovered sample consists of randomly oriented nanodiamonds (50–100nm), showing clearly a different microtexture from those of the layered NPD and “amorphous diamond” reported by the previous studies. This is likely as a result of competing effects of the introduction of irradiation-induced defects, which provided the preferential nucleation sites for cubic diamond, and their partial recovery upon annealing during the HPHT treatment. The present result suggests that NPDs with various crystalline structures can potentially be synthesized from neutron-irradiated HOPG by controlling the density and distribution of the defects introduced.

Millimetre-wave and terahertz IMPATT sources: influence of inter-carrier interactions

A major amount of energy of mobile electrons and holes in a semiconductor under electric field are lost due to inter-carrier collisions prior to ionising collision. This fact causes a decrease in the ionisation probability which leads to the deterioration in ionisation rates especially when the doping density is high. The effects of this phenomenon on the high frequency and noise properties of highly doped impact avalanche transit time (IMPATT) devices based on different wide bandgap (WBG) semiconductors, like 4H-SiC, Wurtzite-GaN (Wz-GaN) and type-IIb diamond (C) have been studied in this paper. Significant deteriorations in the diodes' high frequency and noise performance have been observed in the simulation results. The simulation results have been compared with the experimental data in order to validate those.

Crystallographic Basis for the Stability of Abundant (Popular) Structure Types

In compliance with the hypothesis that the crystal structure stability increases with a decrease in the degrees of freedom of the constituent atoms, we propose quantitative criteria for structures: the ratio between the amount of the degrees of freedom of atoms to their number in a primitive cell (S) and the fundamental volume (V*)–the quotient of the cell volume (asymmetric unit) and the order of the symmetry group (M) that is the general position multiplicity. The crystallographic analysis of diamond and spinel structure types and their comparative analysis with stability and packing criteria are performed. The study uses the findings from the analysis of abundant less symmetrical tourmaline and apatite structure types which confirm the existence of standard frameworks–symmetrical spatial configurations of atomic sites that can be taken by atoms of various types.