Graphitization Of Diamond Research Articles

Non-damaged preparation and energy band structure modulation of silicon-based nitrogen-terminated diamond films

The surface terminal structure of diamond film determines its surface physical properties. In this paper, the surface of silicon-based polycrystalline diamond film was nitrided by radio frequency (RF) plasma, and the evolution of the diamond surface termination structure under different nitridation temperatures and times was investigated. In-situ X-ray photoelectron spectroscopy (XPS) analysis showed that nitridation at 600 °C is beneficial for the more effective formation of nitrogen terminal diamond (N-diamond) structure dominated by CN bonds on the diamond surface. In-situ ultraviolet photoelectron spectroscopy (UPS) indicated that the electron affinity of diamond surface can gradually change from negative to positive with prolonged nitridation time. The increased positive electron affinity (PEA) of surface terminations made it more difficult for electrons to escape from the diamond surface, resulting in a significant decrease in the intensity of the secondary electron peak. Furthermore, AFM and Raman measurements indicated that nitridation treatment does not significantly improve the surface roughness of diamond or form graphite phase, which realized the preparation of non-damaged N-diamond.

First Voltammetric Determination of Karbutylate via Pencil Graphite, Glassy Carbon, and Boron-Doped Diamond Electrodes in Soil Sample

We investigated the electrochemical behavior of carbamate pesticide-type karbutylate (KB) with boron-doped diamond (BDD), glassy carbon (GC), and pencil graphite (PG) electrode, and analytical determination in real samples. Similar to organophosphate insecticides, carbamate pesticides are produced from carbamic acid and are extensively utilized in agriculture, gardens, and residences. Therefore, a rapid and simple detection of KB in real samples is important. Carbon-based electrodes are widely used in electroanalytical chemistry due to their rich surface chemistry, chemical inertness, broad potential window, low background current, and congruency for various demanding applications. Three different carbon-based electrodes were used. The effect of buffer solutions, scan rate, square wave (SWV), and differential pulse voltammetry parameters on the voltammetric response of KB was tested. The optimum working media for all three electrodes was determined as pH 2.00 phosphate buffer solution and voltammetric measurements were carried out in this media. Under optimum experimental conditions, linear calibration dependences for KB were obtained as 6.00 × 10−7–8.00 × 10−5 M, 4.00 × 10−7–8.00 × 10−5 M, and 8.00 × 10−8–8.00 × 10−5 M with a limit of detection of 2.18 × 10−7, 3.71 × 10−8 M, and 2.66 × 10−8 M by the BDD, GC, and PG electrodes, respectively, using SWV. As a result, sensitive determination of KB has been successfully performed using different carbon-based electrodes in real soil samples.

Controllable phase transition process of polycrystalline diamond surface for low friction via suppressing oxygen involved tribochemical reactions

The diamond inner wall of drawing die is crucial for the precise formation of ultra-fine wires during the drawing process. Unexpectedly, when drawing soft metal wire, a significant wear occurs on hard-phase diamond surface, resulting in increased friction at the drawing interface, which leads to the wire cross-section distortion, uneven wire diameter, surface scratches and burrs. In this study, the interface interaction and friction products between diamond and iron were investigated, focusing on the primary factors influencing diamond phase transitions by adjusting friction atmosphere. Whether in air or nitrogen, the friction coefficient (CoF) decreases with the increase of load, but CoF value is relatively lower in nitrogen environment. The friction curve of diamond against iron stabilized after an initial downward trend, reaching a minimum CoF of 0.08 in nitrogen under a load of 15 N. The friction mechanism is explained through material transfer, friction products, phase transition, tribolayer formation, and interfaces interactions. It is speculated that in nitrogen, even if a small amount of oxide forms on iron surface, iron remains in contact with diamond, generating a large amount of iron carbide and inducing the graphitization of diamond, which would act as a lubricating role. In contrast, in air, oxygen atoms continuously interact with iron, forming a dense oxide film at the friction interface, which prevents carbon from continuous contacting iron atoms and limits the formation of iron carbide. Overall, the discovery provides new insights into the interaction between metals and diamonds, and offers theoretical guidance for the drawing of iron wires.

Optical characteristics and wavefront control of femtosecond laser pulses and their effect on the performance of diamond graphite electrodes

High purity diamond is an excellent material for making radiation hard detectors suitable for high-energy particle detection, cancer treatment and other fields. Electrodes are formed by the localized graphitization of the diamond bulk, where fine control of the manufacturing process is essential to the performance of the detector. The resistivity of the electrode formed by diamond graphitization significantly affects the performance of the detector. Femtosecond laser pulses interact with the material for a very short time (10-13 s), exhibiting a cold processing. In this paper, we utilize Spatial Light Modulators (SLM) to optimize the optical characteristics of the 800 nm femtosecond laser pulse and control the graphitization process. Our research focuses on the analysis of the influence exerted by the pulse characteristics on the diameter and resistivity of inscribed graphite structures. By examining these parameters, the study aims to refine the graphitization process, thereby optimizing the functional characteristics of the diamond-based detectors.

Balling behavior and diamond graphitization of metal-matrix diamond composites by selective laser melting: A quantitative investigation

Selective laser melting (SLM) is an effective and potential technology to prepare metal-matrix diamond composites (MDC). In this study, balling phenomenon and graphitization of diamond of CuSn10-diamond composites by SLM were investigated. By univariate analysis of laser power and scanning speed on the morphology of single track, the balling phenomenon is directly affected by the flowability and wettability of the molten pool. By introducing the concept of laser energy density, balling and diamond graphitization are quantitatively evaluated by the standard deviation σ of surface balling height and IG: ID value, respectively. Balling degree increases with laser energy density, but diamond-graphitization turns out to be the opposite. The CuSn10-diamond composites with low balling and no diamond-graphitization can be obtained at moderate laser energy density of 0.17 J/mm. In terms of performances, bending strength is mainly affected the defects caused by balling, and wear properties is determined by the graphitization of diamond abrasives. Graphitization of diamond results in the transformation of wear mechanism from abrasive to adhesive wear. The optimal properties of 185.36 MPa in bending strength, 0.41 in coefficient of friction and minimum wear loss is obtained in the composite sample prepared at 0.17 J/mm.

Modulating the thermophysical properties of diamond/SiC composites via controlling the diamond graphitization

Modulating the thermophysical properties of diamond/SiC composites via controlling the diamond graphitization

High-temperature tribological properties and wear mechanisms of multilayered cubic-BN/nanocrystalline diamond tool coatings

Wear failure of cutting inserts is the main form of failure that occurs when cutting difficult-to-machine materials at high speeds. To obtain cutting inserts with outstanding tribological properties, multilayered cubic boron nitride (cBN) and nanocrystalline diamond (NCD) coatings (cBN/NCD) were prepared on WC-6 wt% Co tool substrates. The tribological properties of the multilayered cBN/NCD coatings were studied at different temperatures, and the results showed that the coefficient of friction (COF) and wear rate of the coatings were closely interrelated to the temperatures, and the COF gradually decrease and the wear rate gradually increase as the temperature increased from room temperature (25 °C) to 600 °C. The COF and wear rate of the multilayer coatings at 600 °C were ∼0.05 and 8.43 × 10−6 mm3/(N⋅m), respectively. The wear resistance of the cBN/NCD coatings was higher than that of TiAlN coatings and PcBN tool materials by more than 3 and 4.5 times, respectively. The high-temperature wear failure modes of the multilayered cBN/NCD coatings were abrasive wear, diamond graphitization, and BN hydrolysis. Coating wear accelerated when pores were formed on the cBN surface of a multilayered cBN/NCD coating due to the low nucleation density of diamond. These results would guide the application of cBN/NCD-coated cutting tools in high-speed cutting processes.

Thermal-mechanical evolution behaviors of metal matrix diamond composite by powder bed fusion-laser beam

The thermal damage of diamond and the residual stress have always been the critical issues to be resolved in the development of metal matrix diamond composites. In the presented study, FeCoCrNi high entropy alloys (HEAs)-diamond composites were fabricated by powder bed fusion-laser beam of metals (PBF-LB/M), using un-coated diamond and Ti–Ni coated diamond, respectively. Based on the numerical and experimental analysis, the effect of thermal-mechanical behavior on the microstructures and mechanical properties of the composites was systematically investigated. By establishing the temperature field of the PBF-LB molten pool, the defects, diamond graphitization and in-situ TiC formation were studied. The start-temperature for diamond graphitization in coated samples was 365 °C higher than that of un-coated samples, due to the diffusion barrier effect of TiC. Subsequently, by thermo-mechanical coupling, the property and value of the residual stress exhibited sudden change at the diamond/matrix interface. The TiC intermediate layer significantly relieved the stress concentration at interface, and effectively avoided cleavage fracture of the diamond and the initiation of interfacial cracks. At the moderate molten-pool temperature, the coated diamond composites exhibited optimal performance, as bending strength of 913 MPa, friction coefficient of 0.25 and worn mass loss of 0.67 mg. Finally, the quantitative relationship between PBF-LB molten-pool temperature and the relative density, graphitization degree, residual stress, retention(bending strength) and wear performance was established, to demonstrate the thermal-mechanical evolution of the HEAs-diamond composites by PBF-LB.

Improving frictional state at fretting interfaces through the covalent structure of diamond–graphite–graphene

This study proposes a novel approach based on the covalent structure of diamond–graphite–graphene (CDGG) to integrate the outstanding properties of diamond, graphite, and graphene, synergistically improving frictional behavior of fretting interfaces. The results demonstrated that in-situ CDGG significantly reduced the alternating stress at the contact interface, the friction coefficient decreased by 40–62 % over pristine diamond coatings under gross slip regime, accompanied by a shorter running-in period. The counterpart pair wear corresponding to in-situ CDGG was lower, and no delamination caused by metal adhesion. The surface graphene/graphite exhibited good frictional toughness, effectively absorbing the relative displacement at contact interface, enabling CDGG to exhibit partial slip regime under higher loads and smaller displacement amplitudes.

Experimental Parametric Investigation of Nanosecond Laser-Induced Surface Graphitization of Nano-Crystalline Diamond.

While nano-crystalline diamond (NCD) is a promising engineering composite material for its unique mechanical properties, achieving the ultrahigh surface quality of NCD-based components through conventional grinding and polishing is challenging due to its exceptional hardness and brittleness. In the present work, we experimentally investigate the nanosecond laser ablation-induced graphitization characteristics of NCD, which provides a critical pretreatment method of NCD for realizing its superlative surface finish. Specifically, systematic experimental investigations of the nanosecond pulsed laser ablation of NCD are carried out, in which the characteristics of graphitization are qualitatively characterized by the Raman spectroscopy detection of the ablated area of the microhole and microgroove. Subsequently, the influence of laser processing parameters on the degree and morphological characteristics of graphitization is evaluated based on experimental data and related interpretation, from which optimized parameters for maximizing the graphitization of NCD are then identified. The findings reported in the current work provide guidance for promoting the machinability of NCD via laser irradiation-induced surface modification.

Effects of spark plasma sintering and nanodiamond amount on titanium-nanodiamond composite properties

Titanium/nanodiamond (ND) mixtures were sintered using spark plasma sintering (SPS). Densification was studied for Ti + x wt% ND mixtures (where x = 2, 5, 10 and 15) to determine the optimized cycles. Ti/ND mixtures were then sintered under these optimized conditions achieving relative densities higher than 96 %. The SPS temperatures for the Ti + 2 wt% ND, Ti + 5 wt% ND, Ti + 10 wt% ND and Ti + 15 wt% ND mixtures were 1000 °C, 1050 °C, 1150 °C and 1150 °C, respectively. Numerical simulation by finite elements were used to check the thermal homogeneity in the sample and to determine the maximal temperature in the sample to ensure avoiding graphitization. The effects of ND on the Ti/ND mixtures were investigated. Microstructural characterizations reveal the presence of three different phases including a Ti phase, a non-stoichiometric TiCx solid phase and NDs located inside the TiCx grains. Indeed, NDs react with Ti to form the TiCx solid phase. However, a fast sintering with temperature below graphitization of diamond allows to keep nanodiamond structure into the Ti/ND mixtures. Hardness and electrical conductivity of the Ti/ND mixtures were measured. The results show that the higher the ND content, the more the hardness of the composite increases and the more the electrical conductivity decreases. Hardness increased from 340 HV to 1346 HV for Ti and the Ti + 15 wt% ND mixture, respectively. Electrical conductivity is reduced by a factor of three for the Ti + 15 wt% ND mixture relative to Ti which can be explained by the microstructure exhibiting fewer Ti grains in favor of the TiCx solid phase when ND content was increased in the composite.

Electrochemical Hydrogen Peroxide Generation and Removal of Moxifloxacin by Electro-Fenton Process

In this study, the removal of moxifloxacin, an antibiotic of the fluoroquinolone group, from aqueous solutions was investigated using the electro-Fenton process. As the efficiency of the electro-Fenton process is highly dependent on the amount of H2O2 produced during process, the formation of H2O2 under acidic conditions was also investigated. In this context, the effects of applied current, cathode type and O2 flow rate on H2O2 production were investigated using boron-doped diamond anode. The highest H2O2 production was achieved using the boron-doped diamond anode and the graphite felt cathode. In addition, the optimum conditions for the applied current and oxygen flow rate for H2O2 production were determined to be 0.25 A and 0.1 L min−1, respectively. The effects of applied current and Fe2+ concentration in the electro-Fenton process on the removal of moxifloxacin were investigated. It was found that the moxifloxacin removal rate increased with increasing applied current. The highest H2O2 accumulation was observed at 0.25 A applied current, and moxifloxacin removal also reached 93.6% after 60 min. The moxifloxacin removal rate reached the highest value at Fe2+ concentration of 0.01 mM. This study provides promising results for the efficient treatment of moxifloxacin-containing wastewater by the electro-Fenton process without the addition of H2O2 using boron-doped diamond anode anode and graphite felt cathode.

Origin of the surface facet dependence in the thermal degradation of the diamond (111) and (100) surfaces in vacuum investigated by machine learning molecular dynamics simulations

We perform machine learning molecular dynamics simulations to gain an atomic-level understanding of the dependence of the graphitization and thermal degradation behavior of diamond to the (111) and (100) surface facets. The interatomic potential is constructed using graph neural network model, trained using energies and forces from spin-polarized van der Walls-corrected density functional theory calculations. Our results show that the C(111) surface is more susceptible to thermal degradation, which occurs from 2850 K through synchronized bilayer exfoliation mechanism. In comparison, the C(100) surface thermally degrade from a higher temperature of 3680 K through the formation of sp1 carbon chains and amorphous sp2-sp3 carbon network. Due to the dangling bonds at the step edges, the stepped surfaces are more susceptible to thermal degradation compared to the corresponding flat surfaces, with the stepped C(111) and C(100) surfaces thermally degrading from 1810 K and 3070 K, respectively. We propose potential applications of this study in diamond tool wear suppression, diamond polishing, and production of graphene directly from the diamond surface.

High Temperature Graphitization of Diamond during Heat Treatment in Air and in a Vacuum

High Temperature Graphitization of Diamond during Heat Treatment in Air and in a Vacuum

Electrochemical detection of phenacetin with graphite/boron-doped diamond electrode grown at high methane concentration

We have developed a composite electrode containing boron-doped diamond and high graphite content (HGBDD) by microwave plasma chemical vapor deposition system at high methane concentration. The electrode is applied to test the trace level of phenacetin. Scanning rate studies have exhibited that electrochemical oxidation is controlled by adsorption with scanning speed ranging from 20 to 100 mV s−1, while at a higher scanning rate, electrochemical oxidation is controlled by diffusion process. Voltammetry of phenacetin researched on the HGBDD electrode reveals the redox mechanism of phenacetin, the HGBDD has a high current response with a sensitive detection limit of 0.058 μM and a wide linear detection range of 0.5 μM - 400 μM. The high performance could be attributed to the presence of a higher carrier concentration for HGBDD electrode. Based on the density functional theory caculations, the graphite on the diamond surface could adsorb phenacetin strongly and provide more active sites for the redox reaction. Due to the unique properties of diamond, the electrode shows stability, repeatability, and accuracy for detecting phenacetin.

Thermal annealing induced graphite/diamond structure processed by high-voltage hydroxide ion treatments

Ohmic contacts with low specific contact resistance are necessary for fabrication of diamond electronic devices. This work reports that graphite/diamond ohmic contacts can be obtained by thermal annealing of diamond, patterned by hydroxide ion treatment. Surface graphitization of diamond is achieved through rapid thermal annealing at 1050 °C in vacuum. The thickness of graphite layer is found to be dependent on the duration of annealing with an approximate rate of 3.3 ∼ 3.6 nm/minute. The alteration in surface structure is analyzed using Raman spectra, showing a continuously enhanced G peak with increasing annealing time. Early stages of graphitization are discovered by X-ray photoelectron spectroscopy, after annealing diamond samples for merely 0.5 ∼ 2 min. Additionally, a distinct atomic interface between graphite and diamond is observed via cross-sectional transmission electron microscopy. Further, the surface graphite is selectively etched by hydroxide ion treatments, protected by gold patterns. In the end, the specific contact resistance of the graphite/diamond contact is determined to be 2.53 × 10-4 Ω cm2 employing the transmission line model.

Effect of crystallographic orientation on the potential barrier and conductivity of Bessel written graphitic electrodes in diamond

Ultrafast laser micromachining can be used to promote diamond graphitization, enabling the creation of electrically conductive wires embedded in the diamond matrix. In this context, the presence of a potential barrier in the conductivity of transverse graphitic wires fabricated by pulsed Bessel beams without sample translation across 500 μm thick monocrystalline CVD diamond has been studied. In particular, the role of the crystallographic orientation has been analysed. The morphology and the conductivity of the obtained electrodes have been studied using optical microscopy and current-voltage measurements, while the structural changes have been investigated by means of micro-Raman spectroscopy. By using different laser writing parameters, we have explored the features of different electrodes in a (100) and a (110) oriented diamond crystal respectively. We show that in addition to the use of specific pulse energies and durations (in the fs and ps regimes), the crystallographic orientation of the sample plays an important role in reducing or eliminating the potential barrier height of the IV electrical characterization curves. In a (110) oriented sample, it is possible to eradicate the potential barrier completely even for graphitic wires fabricated at low pulse energy and in the fs pulse duration regime, in contrast to the (100) oriented-crystal case where the barrier is generally observed. The effect of thermal annealing of the diamond samples on the resistivity of the fabricated micro-electrodes has also been investigated. In (110) oriented diamond, resistivities lower than 0.015 Ω cm have been obtained.

Effect of SPS frequency on the transformation of diamond to graphite in WC-Co composite

(WC–6wt%Co)/5Vol% diamond composites were successfully fabricated at 1150–1300 °C and 40 MPa for 5 minutes under the thermodynamically unstable conditions of the Spark Plasma Sintering method. The influence of on-off time, and frequency of the DC pulse of SPS on diamond stability, microstructure, and mechanical properties of WC–Co/diamond composites were investigated. The diamond particles are strongly bounded with the cemented carbide matrix by a transition layer composed of a solid solution of tungsten and carbon in cobalt. The amount of graphitization was low in the sintered composites at 1300 °C due to the low temperature and short sintering time. Reduction of SPS frequency effectively inhibited graphite preformation, and no graphite was detected in the sintered composites at 1150 °C. Diamond morphology was not affected during SPS as examined by SEM, and Raman scattering spectra. The uniform dispersion of the super-hard diamond phase in matrix which good bonded, caused the high hardness, fracture toughness and flexural strength of this composite. The reduction of pulse frequency of SPS leads to a significant enhancement in the hardness, fracture toughness, and flexural strength of the composites, overcoming the graphitization of diamond typically observed in SPS. The sample sintered with 4 Hz showed simultaneously the highest hardness (23.6 GPa), the highest fracture toughness (24.6 MPa.m½), and the highest flexural strength (2050 MPa).

Instantaneous formation of covalently bonded diamond–graphite–graphene with synergistic properties

Diamond and graphene are the most widely used carbon allotropes and offer great potential for developing mechanical, electronic, energy-storage, and sensor applications. Their combination, especially interfacial covalent bonding, can impart excellent properties. However, achieving interfacial covalent bonding with superior performance using flexible and low-power strategies remains challenging. This study developed a novel instantaneous transformation method from diamond to graphene to prepare a new covalent structure of diamond–nano-graphite–graphene (CDGG). That is, a nanosecond-pulse laser induces sp3-to-sp2 instantaneous transformations from diamond to graphite in air, and the subsequent mechanical cleavage overcomes the weak van der Waals forces to achieve the final transformation of graphite to graphene. First, the key factors influencing laser-induced graphitization and mechanical cleavage were investigated, and a covalent carbon structure with multidirectional graphene was obtained. Furthermore, the mechanisms encompassing the lattice transformation, interface relationships, transformation time, and interface bonding were elucidated. The obtained new structure synergized the excellent properties of diamond, nano-graphite, and graphene, exhibiting superior lubrication, mechanochemical wear resistance, durability, and load-capacity. Compared to polished diamond, the obtained structure exhibited a significant decrease in the stable coefficient of friction by 49–59 % and a reduction of more than one order of magnitude in the relative wear rate under high friction against ferrous metals with a normal load of 1–9 N. Even under a heavy load of 100 N, it still exhibited superior lubrication and mechanochemical wear resistance. Finally, the preparation and patterning of covalent carbon structures were achieved on various diamond surfaces with high efficiency, environmental friendliness, and low power. This study is expected to broaden the scope of developing and applying diamond, diamond films, and graphene devices.

Enhanced properties of a novel medium-entropy alloy base diamond composite by introducing coherent L12 phase at interface

In this study, a medium-entropy alloy (MEA) was used as a new binder to fabricate diamond composite. The MEA base diamond composite (MEA-Comp) shows a much higher transverse rupture strength (TRS, 1453.5 MPa) and a stronger bonding interface than the referenced Co base diamond composite (TRS, 744.9 MPa). It is for the first time found that a (Ni, Co)3Al L12-type phase was in-situ formed between diamond and the MEA matrix. The L12 phase is fully coherent with the diamond in orientation relationship of [001]L12//[001]Diamond and (010)L12//(010)Diamond. Thus, the metallurgical bonding between diamond and metal matrix can be greatly improved, resulting in an enhanced wearing performance. Additionally, chromium carbides (majority Cr7C3 and minor Cr3C2) were also in-situ formed in the interlayer between diamond and matrix. The interlayer composed of L12 phase and chromium carbides can also block the direct contact between diamond and metal matrix, which might slow down the graphitization of diamond under service condition.