Crystalline Diamond Research Articles

Advances in RF Glow Discharge Optical Emission Spectrometry Characterization of Intrinsic and Boron-Doped Diamond Coatings

Accurate determination of the effective doping range within diamond thin films is important for fine-tuning of electrical conductivity. Nevertheless, it is not easily attainable by the commonly adopted techniques. In this work, pulsed RF glow discharge optical emission spectrometry (GD-OES) combined with ultrafast sputtering (UFS) is applied for the first time to acquire elemental depth profiles of intrinsic diamond coatings and boron content bulk distribution in films. The GD-OES practical advances presented here enabled quick elemental profiling with noteworthy depth resolution and determination of the film interfaces. The erosion rates and layer thicknesses were measured using differential interferometric profiling (DIP), demonstrating a close correlation between the coating thickness and the carbon/hydrogen gas ratio. Moreover, DIP and the adopted semiquantification methodology revealed a nonhomogeneous bulk distribution of boron within the diamond crystalline structure, i.e., boron doping is both substitutional and interstitial within the diamond framework. DIP measurements also showed that effective boron doping is not linearly correlated to the increasing content introduced into the diamond coating. This is a finding well supported by X-ray diffraction (XRD) Rietveld refinement and X-ray photoelectron spectroscopy (XPS). This work demonstrates the advantage of applying advanced GD-OES operation modes due to its ease of use, affordability, accuracy, and high-speed depth profile analysis capability.

Diamond MOSFET with MoO3/Si3N4 doubly stacked gate dielectric

A hydrogen terminated diamond MOSFET with MoO3/Si3N4 doubly stacked gate dielectrics was fabricated on a single crystalline diamond sample. Compared to a device with single MoO3 layer gate dielectrics, the device performance was improved due to the improvement in the gate voltage, which benefited from the doubly stacked gate dielectric. The device with 4 μm gate length shows a maximum output current of 118.67 mA/mm and an ultra-low resistance of 36.15 Ω mm at the gate voltage of −5 V. In addition, the device shows a maximum transconductance of 35 mS/mm. These results indicate that the dielectric with high work function has high potential to achieve a high-performance diamond MOSFET.

Characteristics of hydrogen terminated single crystalline diamond logic inverter

Diamond has a wide band gap, high carrier mobility, and high thermal conductivity, thereby possessing great potential applications in high power, and high temperature electronics devices, and also inhigh temperature logic circuit. In this work, we fabricate a hydrogen terminated diamond metal-oxide-semiconductor field effect transistor (MOSFET) by using the atomic layer deposition grown Al<sub>2</sub>O<sub>3</sub> as a gate dielectric and passivation layer. The device has a gate length and width of 4 μm and 50 μm, respectively. The device delivers a maximum output current of about 113.4 mA/mm at <i>V</i><sub>GS</sub> of –6 V and an ultra-high on/off ratio of 10<sup>9</sup>. In addition, we fabricate three resistors, respectively, with an interelectrode distance of 20, 80 and 160 μm, corresponding to the resistance value of 16.7, 69.5 and 136.4 kΩ, respectively. The logic inverter is realized by combining the MOSFET with the load resistance, and the characteristics of the logic inverter are demonstrated successfully, which indicates that the diamond MOSFET has great potential applications in future logic circuits.

Magnetic Properties of Crystalline Diamond Powders Synthesized at High Pressure and High Temperature in the Graphite–Nickel–Aluminum System

Magnetic Properties of Crystalline Diamond Powders Synthesized at High Pressure and High Temperature in the Graphite–Nickel–Aluminum System

Multiple regression analysis on drilling performance of Al 2219 – SiCp metal matrix composite by Response surface Methodology (RSM) technique

In this work, Response Surface Methodology (RSM) based multiple performance analysis was used to investigate in detail about the influences of most dominating machining process parameters on responses like thrust force and surface roughness in the drilling of aluminium metal matrix composites developed through powder metallurgy process. Cylindrical specimens of Al 2219 aluminium alloy with silicon carbide particulates of average particle size 23, 37 and 67 µm as reinforcement are used in the experiment. Drilling test was carried out using poly crystalline diamond (PCD) coated solid tungsten carbide drill of diameter 5 mm at normal atmospheric conditions and different combinations of machining conditions. The RSM based multiple performance analysis was carried out to develop the input output relationships of the machining process parameters. The developed mathematical models were subjected to test their capability using analysis of variance (ANOVA). The main and interaction effect of the input variables on the responses was also investigated. The entire adequacy R2 has been more than 95%, which is within the desirable limit and indicate that the model is accurate and fit.

Influence of B/N co-doping on electrical and photoluminescence properties of CVD grown homoepitaxial diamond films

Boron doped diamond (BDD) has great potential in electrical, and electrochemical sensing applications. The growth parameters, substrates, and synthesis method play a vital role in the preparation of semiconducting BDD to metallic BDD. Doping of other elements along with boron (B) into diamond demonstrated improved efficacy of B doping and exceptional properties. In the present study, B and nitrogen (N) co-doped diamond has been synthesized on single crystalline diamond (SCD) IIa and SCD Ib substrates in a microwave plasma-assisted chemical vapor deposition process. The B/N co-doping into CVD diamond has been conducted at constant N flow of N/C ∼ 0.02 with three different B/C doping concentrations of B/C ∼ 2500 ppm, 5000 ppm, 7500 ppm. Atomic force microscopy topography depicted the flat and smooth surface with low surface roughness for low B doping, whereas surface features like hillock structures and un-epitaxial diamond crystals with high surface roughness were observed for high B doping concentrations. KPFM measurements revealed that the work function (4.74–4.94 eV) has not varied significantly for CVD diamond synthesized with different B/C concentrations. Raman spectroscopy measurements described the growth of high-quality diamond and photoluminescence studies revealed the formation of high-density nitrogen-vacancy centers in CVD diamond layers. X-ray photoelectron spectroscopy results confirmed the successful B doping and the increase in N doping with B doping concentration. The room temperature electrical resistance measurements of CVD diamond layers (B/C ∼ 7500 ppm) have shown the low resistance value ∼9.29 Ω for CVD diamond/SCD IIa, and the resistance value ∼16.55 Ω for CVD diamond/SCD Ib samples.

Diamond-Based Electrodes for Detection of Metal Ions and Anions.

Diamond electrodes have long been a well-known candidate in electrochemical analyte detection. Nano- and micro-level modifications on the diamond electrodes can lead to diverse analytical applications. Doping of crystalline diamond allows the fabrication of suitable electrodes towards specific analyte monitoring. In particular, boron-doped diamond (BDD) electrodes have been reported for metal ions, anions, biomolecules, drugs, beverage hazards, pesticides, organic molecules, dyes, growth stimulant, etc., with exceptional performance in discriminations. Therefore, numerous reviews on the diamond electrode-based sensory utilities towards the specified analyte quantifications were published by many researchers. However, reviews on the nanodiamond-based electrodes for metal ions and anions are still not readily available nowadays. To advance the development of diamond electrodes towards the detection of diverse metal ions and anions, it is essential to provide clear and focused information on the diamond electrode synthesis, structure, and electrical properties. This review provides indispensable information on the diamond-based electrodes towards the determination of metal ions and anions.

Resonant boron acceptor states in semiconducting diamond

High-excited discrete states of boron hydrogenlike acceptors in crystalline diamond have been measured by temperature-dependent infrared absorption spectroscopy. We distinguish the boron resonant states in diamond crystals from the localized boron states in the band gap by differentiating the impurity transitions within state continua of the valence light- and heavy-hole subbands on the basis of their relative oscillator strengths, specific selection rules, and temperature dependences. Constraints on the boron binding energy and spin-orbit splitting of the valence band have been derived by analysis of the structure of the infrared absorption spectra of boron-doped diamond, in particular by a comparison with boron spectra in other semiconductors with a diamond lattice.

The crack propagation and surface formation mechanism of single crystalline diamond by a nanosecond pulsed laser

In this article, the surface formation mechanism of single crystalline diamond (SCD) by a nanosecond pulsed laser is performed, where surface cracking, phase transformation, and typical surface morphology are involved. The nanometric surface characteristics of the ablated micro-grooves on the diamond caused by the thermal effect are first studied, where the crack generation and propagation are discussed by the thermoelastic bending model for the laser irradiation process. In addition, the composed phases and the formation mechanism of the induced metamorphic layer (IML) and deposited metamorphic layer (DML) near the ablated groove are investigated, where the diamond/graphite transition layer is the coexistence of the distributed crystalline diamond and the oriented graphite, the direction of which is at an angle of 60°–80° to the laser scanning direction and toward the center of the ablated groove. Based on the subsurface exploration and the grain growth kinetics analysis, the formation process of the DML is proposed as follows: the nucleation → the formation of carbon islands → the combination of the carbon islands → the formation of the deposited metamorphic layer.

Milling of an Aluminium Matrix Composite Using MCD-Tipped Tools with Adjusted Corner and Minor Cutting Edge Geometries

Aluminium matrix composites (AMCs) represent suitable materials for lightweight design applications. The abrasive ceramic reinforcements typically require diamond cutting materials to prevent excessive tool wear. In milling with diamond cutting materials the influence of cutting parameters was already examined to a significant extent. Investigations concerning the effect of modified tool geometries are limited and the potentials with regard to the geometrical and physical surface properties are unclear. Accordingly, experimental investigations in milling of a 10 vol.% SiC particle-reinforced aluminium wrought alloy EN AW-2017 T4 were addressed. The effect of modified corner and minor cutting edge geometries were investigated based on mono crystalline diamond (MCD)-tipped tools to benefit stable process conditions. The results indicated achievable areal roughness values in the range around 0.2μm. Especially the application of the lowest cutting edge angle and a trailing minor cutting edge led to strong fluctuations of the surface parameters. The lowest valley void volumes were achieved with an arched minor cutting edge. Generally, finish machining led to stronger compressive residual stresses compared to the state prior to machining. The strongest increase was achieved using a corner radius combined with a straight minor cutting edge. It is concluded that reduced effective radii generating the surface enable an acceptable surface structure and strong compressive residual stresses and should be addressed in further investigations.

Antibacterial properties of polycrystalline diamond films

Electronic and mechanical properties, and their biocompatibility, make diamond-based materials promising biomedical applications. The cost required to produce high quality single crystalline diamond films is still a hurdle to prevent them from commercial applications, but the emergence of polycrystalline diamond (PCD) films grown by chemical vapour deposition (CVD) method has provided an affordable strategy. PCD films grown on silicon wafer have been used throughout and were fully characterised by SEM, XPS, Raman spectroscopy and FTIR. The samples contain nearly pure carbon, with impurities originated from the CVD growth and the silicon etching process. Raman spectroscopy revealed it contained tetrahedral amorphous carbon with small tensile stress. The sp2 carbon content, comprised between 16.1 and 18.8%, is attributed to the diamond grain boundaries and iron-catalysed graphitisation. Antibacterial properties of PCD films were performed with two model bacteria, i.e. Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using direct contact and shaking flask methods. The samples showed strong bacteriostatic properties against S. aureus and E. coli with the direct contact method and no influence on planktonic bacterial growth. These results suggest that the bacteriostatic mechanism of PCD films is linked to their surface functional groups (carbon radicals and –NH2 and –COOH groups) and that no diffusible molecules or components were involved.

Research on variation law of geophysical drill-bit downhole flow field under the interaction of multiple hydraulic factors.

Mountain geophysical prospecting operations play an important role in the entire petroleum exploration field. Geophysical drill-bit is the main tool for mountain geophysical prospecting operations. Its hydraulic structure directly affects the downhole flow field and then affects the chip removal efficiency and drilling efficiency of the bit. At present, most of the scholars' research is focused on Poly Diamond Crystalline bit, roller bit, etc., and the research on geophysical drill-bit is less, and most of them study the downhole flow field based on the change of single hydraulic structure. The primary objective of this research is to study the variation law of the downhole flow field under the interaction of multiple hydraulic structure factors. The drilling time and cuttings size of two geophysical drill-bits with different hydraulic structures are compared, and the key hydraulic structure factors are selected for analysis. Using numerical simulation software, take different levels of key hydraulic structure parameters and carry out orthogonal experiments. Under the interaction of various factors, study the flow field distribution in the flow channel, the downhole, and the annulus area of the shaft lining. The hydraulic structure of the geophysical drill-bit is closely related to the drilling speed and chip removal efficiency. When multiple hydraulic factors are changed, the diameter of the flow channel is the best when it is 10-12.5 mm, the inclination of the flow channel should be set as close as possible to the center of the downhole, and the length of the chip groove increases, the movement of cuttings is more stable. Variation law of downhole flow field under the interaction of multiple hydraulic factors is studied. This study provides a basis for the hydraulic structure design and optimization of the geophysical drill-bit.

Impact of the I-value of diamond on the energy deposition in different beam qualities

Diamond detectors are increasingly employed in dosimetry. Their response has been investigated by means of Monte Carlo (MC) methods, but there is no consensus on what mass density ρ, mean excitation energy I and number of conduction electrons per atom n ce to use in the simulations. The ambiguity occurs due to its seeming similarity with graphite (both are carbon allotropes). Except for the difference in ρ between crystalline graphite (2.265 g cm−3) and diamond (3.515 g cm−3), their dielectric properties are assumed to be identical. This is incorrect, and the two materials should be distinguished: (ρ = 2.265 g cm−3, I = 81.0 eV, n ce = 1) for graphite and (ρ = 3.515 g cm−3, I = 88.5 eV, n ce = 0) for diamond. Simulations done with the MC code penelope show that the energy imparted in diamond decreases by up to 1% with respect to ‘pseudo-diamond’ (ρ = 3.515 g cm−3, I = 81.0 eV, n ce = 0) depending on the beam quality and cavity thickness. The energy imparted changed the most in cavities that are small compared with the range of electrons. The difference in the density-effect term relative to graphite was the smallest for diamond owing to an interplay effect that ρ, I and n ce have on this term, in contrast to pseudo-diamond media when either ρ or I alone were adjusted. The study also presents a parameterized density-effect correction function for diamond that may be used by MC codes like EGSnrc. The estar program assumes that n ce = 2 for all carbon-based materials, hence it delivers an erroneous density-effect correction term for graphite and diamond. Despite the small changes of the energy imparted in diamond simulated with two different I values and expected close-to-negligible deviation from the published small-field output correction data, it is important to pay attention to material properties and model the medium faithfully.

Chemical vapor deposition diamond dental burs for high speed air turbine handpieces

Abstract Background The objectives were, establishment of diamond coating using Chemical Vapor Deposition (CVD) on tungsten carbide burs and, assessment of diamond film adherence at 250,000 rpm after cavity preparations on teeth. Methods Hot Filament CVD (HFCVD) was used to deposit a thin diamond film on tungsten carbide burs using 1–1.5% methane in excess hydrogen at 1800–2200 °C and 2700 - 6700 Pa pressure. Consistent and repeated film deposition of Microcrystalline diamond (MCD) and Nano crystalline diamond (NCD) could be achieved. Raman spectrometry and scanning electron microscopy (SEM) were used to confirm diamond deposition. Adherence of the films was checked after cavity preparations on human teeth at speeds of ~250,000 rpm, and flank wear was determined using SEM. Results SEM images confirmed presence of microcrystalline and nanocrystalline forms. MCD had a 3–7 μm cubo-octahedral crystal formation. NCD was seen as 25–50 nm cuboidal facets in columnar formation. Raman spectrometry corroborated these findings. SEM of NCD showed no loss of diamond film or blunting of blades after three cavity preparations followed by a maximum loss of 33 μm after nine repeated cavity preparations. MCD showed partial loss of diamond film after third cavity with a maximum loss of 91 μm after nine repeated cavities. Conclusion Successful deposition of uniform diamond coating on tungsten carbide burs that remain adherent even at high rotational speeds was achieved and NCD coating adhered better compared to MCD. Practical implication The newly developed dental bur which combines the cutting action of bladed instruments and the hardness of diamond and provides a new area of clinical application.

Modeling of the temperature field in nanosecond pulsed laser ablation of single crystalline diamond

In this paper, a comprehensive finite element (FE) simulation model of the heat transfer for laser ablation of a single crystalline diamond (SCD) with a scanning laser beam in Gaussian shape is developed. The model takes into account the material properties, the geometric structure, and the thermal boundary conditions. It is employed to study the dependence of the temperature distribution under varying laser machining parameters. The distribution characteristics of the temperature field, the temperature evolution, and the heat conduction on the diamond surface are obtained, analyzed, and discussed. The law describing the influence of the laser parameters on the temperature field on the diamond surface is established. After comparing the numerically estimated thermal penetration depth of the pulsed laser in the diamond with the experimentally ablated groove characterized by a scanning electron microscope (SEM), a white light interferometer (WLI) and the Raman spectroscopy analysis of the deposited metamorphic layer, it is found that the developed model shows an excellent predictive capability and provides a promising tool for the future optimization of the machining parameters.

Spherical Lame-type problem in second strain gradient theory

Second strain gradient theory (SSGT) is employed to examine the spherical single/double-phase Lame-type problem. Due to the capability of SSGT to capture the effects of surface, size, and discrete nature of materials, the pertinent relaxed configuration is sought. SSGT is written in the spherical coordinate system and the corresponding governing equilibrium equations, stress and strain components, constitutive relations, and boundary tractions are derived. With spherical symmetry consideration of the problem, the relaxed configuration is obtained for both the diamond crystalline carbon and carbon coated crystalline silicon shell. Afterwards, the external symmetric loading is applied on the nanostructure relaxed configuration to analyze the mechanical response. The SSGT elastic material parameters for carbon and silicon are calculated via the quantum computations and lattice dynamics combined with the material continuum description. Analysis shows that the nanostructures mechanical response in SSGT is significantly different from that in the classical elasticity. For example, in the single-phase problem with inner and outer radius equal to two and ten lattice parameter, respectively, under an external pressure of about 0.0001 , the classic elasticity predicts an approximately constant radial stress of about -0.0001 in the nanoshell. However, in the framework of SSGT, the radial stress is varying from about -0.001 and -0.0002 in the vicinity of the inner and outer boundaries, respectively, to about 0.0003 in the middle of the hollow nanoshell. With increasing the inner radius, the difference between the two results in the middle points decreases.

Grinding characteristics of CVD diamond grits in single grit grinding of SiC ceramics

Single crystalline diamond (SCD) grits are usually made by a high-pressure and high-temperature (HPHT) method and exhibit cuboctahedral shapes and smooth surfaces. In this paper, we synthesized new kinds of SCD grits and nanocrystalline diamond (NCD) grits by a chemical vapor deposition (CVD) method and explored their grinding performance by single grit grinding of SiC ceramics. Grinding by HPHT grits was also conducted for comparison. The CVD-SCD grits exhibit cuboctahedral shapes, but surfaces are covered by protruded twin crystals of several microns, while the NCD grits are spherical agglomerations of nano-grains. We demonstrated that these morphological features have profound influences on material removal behavior. Results show that the wear of NCD grits is dominated by wear flat and intergranular cracks. The worn NCD grits can exert intense rubbing and ploughing effects on the workpiece. In contrast, the wear of CVD-SCD grits is dominated by fracture of the protruded twin crystals. It is proved that the twins on the grit surface are effective cutting edges to remove the material in a micro scale and thus lead to the formation of fine grinding striations and smaller cracking pits, but this process has little influence on specific grinding energy. Besides, grits with rough twins, especially on the flank face, tend to exhibit lower grinding force ratios and thus better sharpness. Moreover, for grits with smooth rake faces, there exists an explicit critical undeformed chip thickness value around 0.4–0.6 μm, above which the material removal mechanism changes from ductile to brittle rapidly. However, for grits with rough twins on rake faces, this transition process becomes vague.

Isotope Effect in Thermal Conductivity of Polycrystalline CVD-Diamond: Experiment and Theory

We measured the thermal conductivity κ(T) of polycrystalline diamond with natural (natC) and isotopically enriched (12C content up to 99.96 at.%) compositions over a broad temperature T range, from 5 to 410 K. The high quality polycrystalline diamond wafers were produced by microwave plasma chemical vapor deposition in CH4-H2 mixtures. The thermal conductivity of 12C diamond along the wafer, as precisely determined using a steady-state longitudinal heat flow method, exceeds much that of the natC sample at T>60 K. The enriched sample demonstrates the value of κ(298K)=25.1±0.5 W cm−1 K−1 that is higher than the ever reported conductivity of natural and synthetic single crystalline diamonds with natural isotopic composition. A phenomenological theoretical model based on the full version of Callaway theory of thermal conductivity is developed which provides a good approximation of the experimental data. The role of different resistive scattering processes, including due to minor isotope 13C atoms, defects, and grain boundaries, is estimated from the data analysis. The model predicts about a 37% increase of thermal conductivity for impurity and dislocation free polycrystalline chemical vapor deposition (CVD)-diamond with the 12C-enriched isotopic composition at room temperature.

Surface microstructuring of single crystalline diamond based on the accumulated energy homogenization in the nanosecond pulsed laser ablation

In this paper, surface microstructuring of single crystalline diamond (SCD) by a nanosecond pulsed laser is performed. The nanometric surface characteristics of the ablated micro-grooves on the diamond caused by the thermal effect are firstly studied, where the deposited metamorphic layer, the irregular cross-sectional profile of the ablated groove and the non-uniform surface morphology are involved, and the dependence of the obtained surface characteristics on the ablation parameters of the infrared nanosecond pulsed laser, including the laser energy density, the pulse frequency, the scanning speed and the scanning times, is then analyzed and discussed. Finally, based on the mathematic analysis of the laser energy distribution and the accumulated energy intensity homogenization, the scanning path of the laser beam is programmed and five different types of surface microstructures are then fabricated on the diamond by controlling the scanning path with the optimized laser machining parameters to achieve the high surface quality of less cracking and better uniformity.

Behavioral Contrast of Electron and Hole Transport in High-Resolution Diamond Detectors: A Biparametric Correlation Study

In this letter we investigate for the first time the behavioral differences of transport properties of electrons and holes observed in high-resolution radiation detectors fabricated on high-purity single crystalline diamond using biparametric (BP) correlation studies. The chemical vapor deposition (CVD) grown 500 μm thick diamonds exhibited an excellent energy resolution of 0.5% for 5486 keV alpha particles for both electron and hole transport in a vertical electrode geometry. Interestingly, the behavior of the electron and hole transport were found to be vastly different at bias voltages less than 100 V. No discernable detector signal was observed due to electron transit below an applied bias of -100 V. The hole transit on the other hand, resulted in resolvable pulse height spectrum (PHS) from bias voltages as low as +10 V. Digital biparametric correlation studies of the rise-times and induced charge from each interaction of the incident alpha particles, revealed that the observed difference is due to the excessive electron trapping below bias voltages of -100 V. At lower biases, the width of the alpha peak in the PHS due to hole movement, was hardly affected by trapping and was observed to be limited due to lower hole drift velocities. The developed method with new insights of correlating the biparametric plots and the detector performance can be extended to vast range of semiconductor detectors.