Polycrystalline Diamond Surfaces Research Articles

Depth profiling of microwave nitrogen-terminated polycrystalline diamond surfaces by energy-dependent X-ray photoelectron spectroscopy

Nitrogen-terminated diamonds hold promise for stabilizing near-surface NV− centers, which is essential for reliable quantum sensing. Among various surface preparation methods, microwave (MW) nitrogen plasma, known for its minimal surface damage, appears as the most effective choice. In this investigation, we explore the nature of nitrogen bonding of polycrystalline diamond (PCD) surfaces exposed to MW nitrogen plasma using X-ray Photoelectron Spectroscopy (XPS) depth profiling and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the C K- and N K-edges. XPS depth profiling with atomic resolution, achieved by varying the probing photon energy using synchrotron radiation and supported by a physical model considering the associated inelastic mean free path, suggests a surface of almost fully saturated nitrogen in two main bonding configurations of similar contribution and a low coverage of ∼5 % of graphene-like islands residing atop the nitrogen-terminated diamond surface. The thermal stability of these surface groups is monitored by in situ annealing up to 700 °C. The depth profiles reveal that nitrogen atoms do not diffuse in the diamond crystal, resulting in excellent diamond crystallinity in the first atomic planes below the surface. C K-edge NEXAFS analysis reveals the position of unoccupied surface states within the diamond bandgap, opening new perspective on the stabilization of near-surface NV− centers.

Machine learning for predicting laser ablation groove characteristics in polycrystalline diamond

This paper explores machine learning’s role in predicting laser-machined micro-groove texture on Polycrystalline Diamond (PCD) surfaces. PCD has been used for manufacturing ideal cutting insert due to its exceptional attributes, including hardness and thermal conductivity. Surface micro-texturing enhances accuracy and tool lifespan through micro-textures on tool surfaces. Laser micromachining, especially for its precision and efficiency, stands out among methods. Six regression models—Elastic Net, Random Forest, Gradient Boosting Regression, XGBoost Regression, Bayesian Regression, and Gaussian Process Regression—are used to predict groove depth and width based on laser parameters like energy, defocus, and speed. Experiments involve a nanosecond laser system and a commercial PCD tool. Results indicate both Gradient Boosting and XGBoost excel in predicting micro-groove texture. XGBoost slightly outperforms, credited to its enhancements over Gradient Boosting. This paper concludes that machine learning models, especially XGBoost and Gradient Boosting, effectively forecast micro-groove features on laser-machined PCD surfaces, offering insights for further research and practical applications in this domain.

Monitoring of Carbonated Hydroxyapatite Growth on Modified Polycrystalline CVD-Diamond Coatings on Titanium Substrates

Production of diamond coatings on titanium substrates has demonstrated as a promising strategy for applications ranging from biosensing to hard tissue engineering. The present study focuses on monitoring the nucleation and growth of bone-like carbonated-hydroxyapatite (C-HA) on polycrystalline diamond (PCD) synthetized on titanium substrate by means of a hot filament chemical vapor deposition (HF-CVD) method. The surface terminations of diamond coatings were selectively modified by oxidative treatments. The process of the C-HA deposition, accomplished by precipitation from simulated body fluid (SBF), was monitored from 3 to 20 days by Raman spectroscopy analysis. The coupling of morphological and structural investigations suggests that the modulation of the PCD surface chemistry enhances the bioactivity of the produced materials, allowing for the formation of continuous C-HA coatings with needle-like texture and chemical composition typical of those of the bone mineral. Specifically, after 20 days of immersion in SBF the calculated carbonate weight percent and the Ca/P ratio are 5.5% and 2.1, respectively. Based on these results, this study brings a novelty in tailoring the CVD-diamond properties for advanced biomedical and technological applications.

Unveiling the site-dependent characteristics and atomic mechanism of graphene growth on the polycrystalline diamond: Insight from the experiments and ReaxFF studies

The synthesis of graphene on functional materials has been an issue of great interest in the field of new-functional nanomaterials. As a promising semiconductor and mechanical material, the need for direct growing graphene on the polycrystalline diamond for modification has been strongly inspired nowadays. Herein, we completed the catalytic thermal annealing synthesis of graphene on the polycrystalline diamond without any additional carbon source, and the site-dependent growth characteristics of graphene on the diamond materials were captured. To explain such growth characteristics in detail, the graphene in-situ growth mechanism based on the polycrystalline diamond surface was clarified for the first time by using the reactive molecular dynamics method. Essentially, the growth mechanism of graphene in the vicinity of the diamond grain boundary follows the principle of “counter-precipitation”. Furthermore, the graphene growth is driven by the amorphization of the diamond lattice, and the pristine diamond surface has been proven can be used as the only solid carbon source to accomplish the growth of graphene on it. By contrast, the grain boundary plays the role of supplementary solid carbon source to accelerate the graphene growth rate during the graphene growth, which is the underlying cause of the site-dependent growth characteristics of graphene on the polycrystalline diamond.

Experimental study on surface physical behaviour and integrity of polycrystalline diamond (PCD) in micron-scale abrasive flow assisted impulse-discharge machining

The superhard polycrystalline diamond (PCD) includes cobalt bonding, but it is difficult to remove the composited material in fabrication. Hence, an impulse-discharge is assisted by micron-scale abrasive flow to machine PCD surface. The objective is to understand how the impulse-discharge machining of conductive cobalt complements abrasive flow machining of non-conductive diamond in process. First, the rheological and bonding behaviour of loose-abrasive was analyzed in relation to electric field. Then, the surface machining procedure was modelled in relation to impulse-discharge energy, stress wave and removal force, etc. Finally, the non-conductive diamond integrity was investigated in impulse-discharge machining. It is shown that the electric field causes abrasive to aggregate and impulse-spark expansion promotes hydrated particle cluster to bond strongly and flexibly. When the resulted instantaneous stress drives loose-abrasive to flow towards the diamond surface through micron-scale removal force, the instantaneous temperature generates diamond graphitization and cobalt melting but abrasive flow improves diamond surface integrity. Although the surface electrode adhesion and residual compressive stress are higher with larger discharge energy, the diamond graphitization is reduced with grain refinement. The removal force and ratio are subject to impulse-discharge energy, electrode material and loose-abrasive size. As a result, the nanoscale-roughness surface with the material removal of 150% higher, and high diamond surface integrity can be achieved in short processing time.

The influence of hydrogen plasma etching on the surface conductivity of the polycrystalline diamond surface and the temperature-dependent properties

With the development of carbon-based electronics, the polycrystalline diamond has drawn much attention in diamond electronic devices; as compared to single crystalline diamond, the scale of the polycrystalline diamond can be fabricated over 4 in. much more easily. However, until now, the influence factors on the surface conductivity of hydrogen-terminated polycrystalline diamond (H-PCD) are still unclear. In this work, the carrier concentration and mobility of H-PCD were investigated through Hall effect measurement. It was found that besides surface roughness, the temperature at which the equilibrium states of adsorption and desorption of H-PCD surface adsorbates are established also plays an important role in carrier concentration and mobility. With the increase of the establishment temperature, both carrier concentration and mobility show a decreasing tendency, which may be determined by the coefficient of the surface ionic scattering, phonon scattering, and the grain boundaries on the H-PCD surface. The investigation of this work will give some insight into the control of the surface conductivity on H-PCD from the aspect of the equilibrium state established temperature and surface roughness.

Electrochemical surface rehydrogenation of boron-doped diamond electrodes after electrochemical polishing

Non-diamond carbon impurity and surface roughness are features that can affect the response of boron-doped diamond (BDD) electrodes. Herein, we report on the electropolishing of BDD electrodes carried out in the presence of acetic and sulfuric acid for different times (1, 2, and 4 h). The wet electrochemical treatment smooths the polycrystalline diamond surface and reduces the non-diamond sp2 carbon impurity content while increasing the surface oxygen content. Changes in surface texture and microstructure were revealed by atomic force microscopy, Raman spectroscopy, and cyclic voltammetry. Subsequently, the surface oxygen content was reduced by increasingly severe cathodic pretreatments (CPTs). This was revealed by changes in the voltametric response for the [Fe(CN)6]3−/4– and ascorbic acid (AA) redox systems, as both exhibit electron transfer kinetics sensitive to the level of oxidation of the BDD surface. For [Fe(CN)6]3−/4–, greater ∆Ep values were obtained for the electropolished (EP-BDD) electrodes, as compared to the as received (AR-BDD) electrode. However, after CPTs the EP-BDD electrodes exhibited smaller ∆Ep values (∼60 mV), which indicate significantly improved electrochemical reversibility and faster electron-transfer kinetics caused by the decreased level of surface oxidation (greater hydrogenation). The increased surface oxygen content brought on by the electropolishing process had also a significant effect on the AA oxidation peak potential (Eap), making it at least ∼140 mV more positive than that for the AR–BDD electrode. However, after CPTs the Eap values for the EP–BDD electrodes became at least ∼0.1 V less positive than that for the AR–BDD electrode, indicating that the surface of the EP-BDD electrodes possesses less surface carbon‑oxygen functional groups (i.e., it is more hydrogenated). The combination of electropolishing and cathodic pretreatment is a way to process the BDD electrode surface to create a smoother, low oxygen surface in much the same way as a hydrogen plasma treatment does.

Capillary adhesion governs the friction behavior of electrochemically corroded polycrystalline diamond

The friction behavior of rough polycrystalline diamond (PCD) surfaces is important in many applications and devices that are required to operate in various harsh environments and it can be argued that a thorough understanding of the friction behavior is essential to the application performance. However, the interplay between electrochemical corrosion, capillary adhesion and friction behavior of PCD in multi-asperity contacts is still poorly understood. In this work, we quantify the interfacial capillary adhesion at contact interfaces and its effect on the friction response, between a colloidal microsphere and rough PCD films before and after electrochemical corrosion, for water-immersed, low RH, and humid air conditions. For these multi-asperity contacts, we demonstrate how electrochemical corrosion influences the surface hydrophilicity of the PCD surfaces, and how capillary adhesion due to water condensation contributes to the friction force. We estimate the capillary forces from both the microscopic lateral force experiments and elastoplastic boundary element method (BEM) contact calculations. The combined results indicate strongly that the observed increase in friction force on electrochemically-corroded PCD surfaces is governed by enhanced capillary adhesion at the contact interface, as affected by surface hydrophilicity and environmental humidity.

Entrapment and thermal stability of low energy Argon implanted into diamond studied by in-situ X-ray photoelectron spectroscopy and thermal programmed desorption

The retention and thermal stability of Ar implanted into polycrystalline diamond surfaces with 700 and 5000 eV Ar ions, with high dose (HD) and low dose (LD) of 1016 and 1014 ions/cm2 at room temperature (RT) and 400 °C were investigated. Upon implantation at 400 °C, the thermal stability of the retained Ar is very high and can exceed 1000 °C, whereas, upon RT implantation at the same energy, it is below ∼800 °C. Ar entrapped in a local high crystalline diamond environment possesses a very high thermal stability compared to when it is entrapped in a graphite/amorphous local carbon environment. Ar thermal desorption occurs via diffusion between local defects, greatly enhanced between 600 and 700 °C. Implantation at 400 °C (at HD) results in two distinct regions: graphitic and highly crystalline diamond with low defect density due to dynamic annealing and direct desorption of Ar entrapped within the graphitic/damaged region during the implantation. Ar entrapped in a high crystalline diamond matrix is under higher compressive stress than in graphitic/amorphous carbon.

Formation mechanism and regulation of silicon vacancy centers in polycrystalline diamond films

Diamond silicon vacancy centers (SiV centers) have important application prospects in quantum information technology and biomarkers. In this work, the formation mechanism and regulation method of SiV center during the growth of polycrystalline diamond on silicon substrate are studied. By changing the ratio of nitrogen content to oxygen content in the growing atmosphere of diamond, the photoluminescence intensity of SiV center can be controlled effectively, and polycrystalline diamond samples with the ratios of SiV center photoluminescence peak to diamond intrinsic peak as high as 334.46 and as low as 1.48 are prepared. It is found that nitrogen promotes the formation of SiV center in the growth process, and the inhibition of oxygen. The surface morphology and photoluminescence spectrum for each of these samples show that the photoluminescence peak intensity of SiV center is positively correlated with the grain size of diamond, and the SiV center’s photoluminescence peak in the diamond film with obvious preferred orientation of crystal plane is higher. The distribution of Si centers and SiV centers on the surface of polycrystalline diamond are further characterized and analyzed by photoluminescence, Raman surface scanning and depth scanning spectroscopy. It is found that during the growth of polycrystalline diamond, the substrate silicon diffuses first into the diamond grain and then into the crystal structure to form the SiV center. This paper provides a theoretical basis for the development and application of SiV centers in diamond.

Effects of urea versus N2 addition on growth and mechanical properties of HFCVD diamond films on WC-Co substrates

Nitrogen doped diamonds with great application potentials can be synthesized by using different doping sources (i.e., urea and N2), effects of which on growth behavior and properties of diamond films on WC-Co substrates were presented in this paper. The doping efficiency of urea was always higher than 0.12, much higher than that of N2 (always lower than 0.04). The sufficient N2 addition could increase growth rate, and induce apparent grain nanocrystallization, by modifying reactant gas phase chemistry. The grain nanocrystallization contributed more to the reduction of the surface roughness, and degradation of the diamond purity and mechanical properties. On the contrary, the urea doping resulted in much less degradation of the diamond purity and mechanical properties, while providing sufficient N incorporations into the diamonds. Besides, urea doping promoted the formation of the diamond (220) planes on the polycrystalline diamond surfaces, which had a close relationship with the actual N doping concentration in the diamond. The controllable adjustment of the growth and properties of diamond films, by selecting the doping source and optimizing the doping ratio, could help to meet distinctive application requirements, and balance the machining efficiency and application performance of diamond coated components.

Nanoscale smooth and damage-free polycrystalline diamond surface ground by coarse diamond grinding wheel

Fabrication of smooth damage-free diamond surfaces has been a popular subject in the manufacturing research field. In this study, the polycrystalline diamond was ground by a vitrified bonded diamond wheel to obtain damage-free diamond surfaces with low surface roughness and high quality. Atomic force microscopy verified that surface roughness of Sa 4.20 nm, Sa 2.06 nm, and Sa 0.548 nm were achieved under grinding speeds of 750, 1050, and 1350 rpm, respectively. Electron energy loss spectroscopy spectra confirmed the existence of a graphitic layer (black layer) with a thickness of ~15 nm in the subsurface after grinding. The “black layer” showed an easy ability to be removed under scratch and high-temperature oxidation. Moreover, transmission electron microscopy demonstrated that no damaged layer was observed in the subsurfaces at 750 rpm and 1050 rpm grinding speed. For grinding speed of 1350 rpm, stacking faults and micro-crack appear in the subsurface, thus forming a damaged layer with several microns in thickness. Our work proposes a new strategy to efficiently fabricate nanoscale smooth and damage-free diamond surfaces by diamond wheel grinding. More innovatively, this work demonstrates a unique removal mechanism for abrasive processing of hard-and-brittle materials, as distinct from either mechanical grinding or chemical mechanical grinding.

Micro-hole texture prepared on PCD tool by nanosecond laser

Plenty of experimental studies have shown that the performance of the cutting tools can be improved through fabrication micro-texture on the rake surface. In this paper, a nanosecond laser with wavelength of 1064 nm is used to create micro-holes on the rake surface of polycrystalline diamond (PCD) tool, the influence of laser process parameters (laser power, frequency and defocusing amount) on the diameter, depth and recast layer area of micro-hole is investigated by single factor and multi-objective optimization experiments. The diameter, depth and recast layer area of micro-hole are converted into a single gray correlation degree as the detection index of micro-hole quality by the gray correlation method combined with the principal component analysis. The mathematical model between laser process parameters and gray correlation degree (GRG) is established based on the response surface method (RSM), and the adequacy of the mode for gray correlation degree is studied by ANVOA, and the optimum process parameters are obtained and verified. The results show that the average relative error of the gray correlation model is 2.67%. Ultimately, the required micro-holes are prepared by laser power of 20 W, pulse frequency of 90 kHz, and defocusing amount of-0.5468 μm.

Nitrogen-Terminated Polycrystalline Diamond Surfaces by Microwave Chemical Vapor Deposition: Thermal Stability, Chemical States, and Electronic Structure

In this work, we investigate the interaction of microwave (MW) N2 plasma with polycrystalline diamond surfaces. Optical emission spectroscopy (OES) was used to identify different species present in...

Assessment machining of micro-channel textures on PCD by laser-induced plasma and ultra-short pulsed laser ablation

Micro-channels are one of the most common surface textures for applications, however, the machining of micro-channels on polycrystalline diamond (PCD) is still facing challenges due to its intrinsic properties of high brittleness and hardness. In this paper, fabrication of micro-channels by laser induced plasma (LIP) and laser ablation directly (LAD) machining methods on PCD surface is experimentally investigated. For comparing the processing capacity, the influence of different laser process parameters (including overlap, power, frequency, scanning speed and the number of passes) on the geometry and material removal rate of micro-channels is assessed. Results show that the process parameters have a significant influence on the formation of micro-channels, and LIP exhibits higher efficiency compared to LAD in the case of the plasma formation with the high overlap and laser power. The micro-channel depth and width produced by LIP increase with the increasing overlap, laser power and number passes, and that reduce with the increasing frequency and scanning speed; the MRR produced by LIP increases with the increasing overlap, laser power and scanning speed, and that reduces with the increasing frequency and number of passes. Meanwhile, LIP reduces the oxidation reaction inside the micro-channels compared to LAD due to the shielding effect of distilled water.

Optical properties of laser-modified diamond: From visible to microwave range

We have measured the optical properties of a graphitised layer with dc conductivity of 305 Ω−1 cm−1 produced by excimer laser irradiation (KrF, τ = 20 ns, λ = 248 nm) of a polycrystalline diamond surface grown by chemical vapour deposition. Studies have been conducted in a wide range of wavelengths: from far-IR to visible spectral regions. The resulting constants of the Drude model are the basic parameters for calculating the electromagnetic response of diamond/graphite photon elements or metamaterials fabricated using the direct laser writing method.

Deoxyribonucleic-acid-sensitive Polycrystalline Diamond Solution-gate Field-effect Transistor with a Carboxyl-terminated Boron-doped Channel.

This paper describes a deoxyribonucleic-acid-sensitive electrolyte solution-gate field-effect transistor (SGFET) sensor utilizing a partial carboxyl-terminated boron-doped polycrystalline diamond surface as a linker to connect a deoxyribonucleic acid (DNA) probe. A high density of carboxyl termination on the polycrystalline diamond surface that was employed as a FET channel was achieved using a vacuum ultraviolet system with oxygen gas. A single-stranded DNA probe was immobilized on the polycrystalline diamond channel via amino coupling. The current-voltage characteristics of the polycrystalline diamond SGFET sensor was examined with bias voltages within its potential voltage window. The characteristics of the drain-source current verses the drain-source voltage showed a pinch-off, a shift voltage of up to 40 mV with a coefficient of variation of 4 - 11% was obtained between hybridization and denaturation. In addition, a single nucleotide mutation of DNA sequence was selectively recognized by the shift voltage up to ca. 10 mV.

Processing of polycrystalline diamond surface by IR laser pulses without interior damage

A new approach to improve quality of diamond surface treatment by near IR short laser pulses is considered. The main problem being addressed is optical breakdown in diamond bulk occurred in the process of the surface ablation that causes multifold decrease of the machined surface transmittance. To eliminate laser-induced subsurface damaging, preliminary deposition of different absorbing coatings (titanium, graphite) on the diamond surface was proposed and experimentally tested. When the diamond surface is ablated by 10 ns laser pulses, both examined coatings significantly reduce the surface ablation threshold that makes possible to avoid completely the optical breakdowns in the diamond bulk. As a result, transmittance of the machined diamond drastically increases and surface roughness decreases. But the absorbing coatings have negligible influence on ablation of diamond by 1 ps pulses and don’t solve the problem of the interior damaging under these conditions. Other essential differences in processing of the polycrystalline diamond by the picosecond and nanosecond pulses are also analyzed including uniformity of laser-induced graphitized layer and surface roughening.

Study on fabrication of PCD micro-milling tool by picosecond pulsed laser

For the purpose of processing some forms of diamond, such as polycrystalline diamond (PCD) and chemical vapor deposition diamond, picosecond pulsed laser (PSPL) has the decisive advantage of wear-free material removal. This availability of picosecond pulsed laser sources enables the efficient applications of cutting diamond to generate sharp and regular cutting edge. Therefore, in this study, picosecond pulsed laser is used to fabricate polycrystalline diamond (PCD) micro tool. In order to optimize the picosecond pulsed laser processing, the effects of PSPL cutting parameters including the pulse energy, pulse pitch, and grain size of PCD on the cutting results are investigated. The results indicate the grain size has the greatest impact on the cutting edge radius and pulse energy has great effect on the processed surface of PCD. The results prove that PSPL is a better choice for precision fabrication of PCD micro tool. Finally, the fabrication of PCD micro tools by PSPL has been demonstrated.

Enhanced tribological behaviors of sintered polycrystalline diamond by annealing treatment under humid condition

The tribological behaviors of the 700 °C annealed sintered polycrystalline diamond (PCD) at various relative humidity (RH) levels were systematically investigated. The comparison of tribological behaviors between the 700 °C annealed PCD and the pristine PCD was made to further understand the tribological mechanisms. The results reveal that the friction inducing carbonaceous transfer film and oxidation and hydrolysis induced tribochemistry reaction dominant the tribological behaviors of the annealed PCD at various RH levels. The low coefficient of friction (COF) obtained in dry environments is attributed to carbonaceous transfer film on the worn Si3N4 surface, which was formed by the layers shearing action of massive tiny diamond grains exfoliated from the annealed PCD surface. The graphitization, oxidation and stress relaxation of the PCD induced by the 700 °C annealing treatment make the tiny diamond grains more easily to exfoliate and be grinded on the Si3N4 interface. It facilitates the formation of friction reducing carbonaceous transfer film, and finally results in the 30% lower COFs than those of pristine PCD at low RH levels (5%–50% RH). Meanwhile, an enhanced wear resistance of PCD can be achieved after 700 °C annealing treatment. The tribochemistry reaction induced by the oxidation and hydrolysis of Si3N4 governs the tribological behaviors of the annealed PCD at high RH levels (60%–99.9% RH). It reveals higher COFs accompanied with serious wear of Si3N4 ball and nearly no wear loss of annealed PCD. The produced SiO2 and silicic acid embeds into massive spalling pits on the annealed PCD surface, resulting in slighter wear of the PCD and Si3N4 than that of the pristine PCD/Si3N4. These results propose that the tribological behaviors of PCD under humid environment can be significantly improved by the 700 °C annealing treatment.