Diamond Metal Research Articles

Microscopic Insights into Metallization of Diamond with Transition Metals

AbstractMetallization of diamond with transition metals (TMs) has attracted much attention as they play an important role in the development of precision machining, high‐end thermal management, especially for electronic devices. However, it is found that the solid‐state reaction does not stop at the interface, potentially hampering interface engineering. To unleash the full potential of diamond devices, deeper reactions are investigated in monocrystalline intrinsic diamond metallized with Ti/Pt/Au ohmic contacts combing experiments and theoretical calculations. Apart from exhibiting TiC, graphite, TMs, and diamond nanocrystallites at the interface, a unique ion‐implanted‐like multilayered structure is observed at micrometer depth. TM atoms penetrate through diamond produce a buried amorphous carbon layer under the damaged diamond lattice. In addition, these theoretical calculations reveal that the structural amorphization is catalyzed by the incorporation of TM atoms through vacancy‐mediated diffusion, which induces the closure of the bandgap of the diamond. This facilitates carriers crossing the bandgap via impurity band conduction and promotes the formation of the ohmic contact. This study provides critical insight into the microscopic mechanisms of the metallization between diamonds and TMs and could facilitate the development of diamond‐based electronic devices with a tailored electronic property.

Characteristics of silicon-based polycrystalline diamond MOSFETs prepared by three-step growth method

Hydrogen-terminated diamond (H-diamond) metal oxide field effect transistors (MOSFETs) were successfully fabricated on polished first-grown and unpolished secondary-grown silicon-based polycrystalline diamond films. The devices have a gate length of 8 μm, while an Al2O3 dielectric bilayer was deposited at 200 °C and 100 °C using atomic layer deposition (ALD). Compared to the first-grown diamond films with a root-mean-square roughness (Rq) of 257 nm, the films after polishing and subsequent second growth change the diamond growth mode, resulting in a mixed surface morphology characterized by faceted and step-bunching structures with a roughness (Rq) of 16.6 nm, and also leading to a decrease in grain boundary density and polishing-induced defects. Device analysis demonstrates that these changes result in an increase in the on/off ratio from 102 to 107 at a gate leakage current of 10−7 mA/mm. Meanwhile, although polished first-grown diamond films have atomic-level smoothness, the devices channels on unpolished secondary-grown diamond films show higher carrier concentration and mobility. The improvement in device performance indicates that the three-step growth method provides a new opportunity for the application of large-sized silicon-based polycrystalline diamond films in electronic devices.

Dynamic switching operation of diamond MOSFETs with NO2 p-type doping and Al2O3 gate insulation and passivation

Diamond metal–oxide–semiconductor field-effect transistor (MOSFET) exhibited durable and stable dynamic switching characteristics at an unprecedentedly high voltage of −105 V. Switching turn-on and turn-off times were measured to be 7.64 and 4.93 ns, respectively, with a corresponding total switching loss of 20.03 pJ for a load resistance of 50 Ω. No Miller effect was observed due to the low Miller capacitance of 11 pF/mm. This study suggests the potentiality of diamond MOSFETs in prospective high-voltage, high-speed applications.

Unveiling the Structure of Metal–Nanodiamonds Bonds: Experiment and Theory

In this study, we conducted a theoretical simulation to compare the effects of various factors on the atomic and electronic structures and the magnetic properties of copper and gadolinium ions bonded to carboxylated species of (111) diamond surfaces. It was experimentally found that in the temperature range above 120 K, the magnetic moments of chelated Gd3+ and Cu2+ equal 6.73 and 0.981 Bohr magnetons, respectively. In the temperature range from 12 to 2 K, these magnetic moments sharply decrease to 6.38 and 0.88 Bohr magnetons. Specifically, we examined the effects of the number of covalent adatom–diamond substrate bridges, coordination of water molecules, and shallow carbon-inherited spins in the substrate on the physical properties of the metal center. Our simulation predicted that increasing the number of bonds between the chelated metal ion and substrate while decreasing the number of coordinating water molecules corresponded to a decrease in the magnetic moment of metal ions in a metal–diamond system. This is due to the redistribution of the electron charge density in an asymmetric metal–diamond system. By comparing our theoretical results with experimental data, we proposed configurations involving one and, in a minor number of cases, two surface –COO− groups and maximum coordination of water molecules as the most realistic options for Cu- and Gd-complexes.

Influence of grit friability and grit distribution pattern on dry grindability of WC-6Co by single layered brazed diamond wheels

Single-layered brazed diamond wheels, composed of uni-layered diamond grits, metal binder, and metal core, have potentially good thermal conductivity to dissipate heat from the grinding zone. Considering this characteristic feature, the current study aims to explore the performance and suitability of various indigenously developed single-layered brazed diamond tools in plunge-grinding of fine-grained cemented carbide in a challenging dry atmospheric condition. Single crystalline synthetic diamond particles with different strengths and friability were utilized to develop indigenous diamond wheels with random and patterned grit distribution. The current study explores the role of diamond-grit friability and grit distribution patterns to identify the most suitable wheel for dry grinding of WC-6Co composite. Detailed analysis of the wheel morphology, signifying the fracture behavior of the diamond grit used, justified the variation in the grinding forces, tool life, and ground surface roughness. Irrespective of the grit and distribution type, all wheels showed saturation of dynamic changes in work-surface topography with the number of passes and more sensitively to the degree of increase of uncut chip thickness. Grinding wheels containing friable diamond grits with irregular granular structures performed better than the high-strength, cubo-octahedral grains during the dry grinding experiments.

Synthesis and Mechanism Study of Carbon Nanowires, Carbon Nanotubes, and Carbon Pompons on Single-Crystal Diamonds

Carbon nanomaterials are in high demand owing to their exceptional physical and chemical properties. This study employed a mixture of CH4, H2, and N2 to create carbon nanostructures on a single-crystal diamond using microwave plasma chemical vapor deposition (MPCVD) under high-power conditions. By controlling the substrate surface and nitrogen flow rate, carbon nanowires, carbon nanotubes, and carbon pompons could be selectively deposited. The results obtained from OES, SEM, TEM, and Raman spectroscopy revealed that the nitrogen flow rate and substrate surface conditions were crucial for the growth of carbon nanostructures. The changes in the plasma shape enhanced the etching effect, promoting the growth of carbon pompons. The CN and C2 groups play vital catalytic roles in the formation of carbon nanotubes and nanowires, guiding the precipitation and composite growth of carbon atoms at the interface between the Mo metal catalysts and diamond. This study demonstrated that heterostructures of diamond–carbon nanomaterials could be produced under high-power conditions, offering a new approach to integrating diamond and carbon nanomaterials.

Ultrastable halide perovskite CsPbBr3 photoanodes achieved with electrocatalytic glassy-carbon and boron-doped diamond sheets

Halide perovskites exhibit exceptional optoelectronic properties for photoelectrochemical production of solar fuels and chemicals but their instability in aqueous electrolytes hampers their application. Here we present ultrastable perovskite CsPbBr3-based photoanodes achieved with both multifunctional glassy carbon and boron-doped diamond sheets coated with Ni nanopyramids and NiFeOOH. These perovskite photoanodes achieve record operational stability in aqueous electrolytes, preserving 95% of their initial photocurrent density for 168 h of continuous operation with the glassy carbon sheets and 97% for 210 h with the boron-doped diamond sheets, due to the excellent mechanical and chemical stability of glassy carbon, boron-doped diamond, and nickel metal. Moreover, these photoanodes reach a low water-oxidation onset potential close to +0.4 VRHE and photocurrent densities close to 8 mA cm−2 at 1.23 VRHE, owing to the high conductivity of glassy carbon and boron-doped diamond and the catalytic activity of NiFeOOH. The applied catalytic, protective sheets employ only earth-abundant elements and straightforward fabrication methods, engineering a solution for the success of halide perovskites in stable photoelectrochemical cells.

Impact of water vapor annealing treatments on Al2O3/diamond interface

Our group developed the first inversion-type p-channel diamond metal–oxide–semiconductor field-effect transistor, which featured normally off properties by employing water vapor annealing treatments for the oxygen-terminated diamond surface. Despite the comprehensive device-grade characterization, the impact of water vapor annealing treatments on the Al2O3/diamond interface has not been investigated in detail. In this work, we fabricated four diamond metal–oxide–semiconductor (MOS) capacitors without and with water vapor annealing treatments for various times of 30 min, 1 h, and 2 h and conducted the cycle capacitance–voltage (C–V) and simultaneous C–V measurements. The large cycle C–V shift existed in the sample without water vapor annealing treatment, whereas it was significantly suppressed by water vapor annealing treatments, indicating the effective passivation of the traps with long time constants. The simultaneous C–V results showed a similar trend that the frequency dispersion of the simultaneous C–V was dramatically reduced with water vapor annealing treatments, and the interface quality of Al2O3/diamond had a slight dependence on the water vapor annealing times. Based on simultaneous C–V measurements, the interface state density (Dit) at an energy level of 0.2–0.6 eV from the valence band edge of diamond was extracted for the different MOS capacitors. The Dit was reduced by one order of magnitude with water vapor annealing treatments, and it almost did not change with the water vapor annealing times. Besides, the flat band voltage shift and effective fixed charge were also dramatically reduced by water vapor annealing. The possible physical reason for the interface improvement by water vapor annealing treatments was discussed.

Electrical property improvement for boron-doped diamond metal–oxide–semiconductor field-effect transistors

High-performance boron-doped diamond (B-diamond) metal–oxide–semiconductor field-effect transistors (MOSFETs) are fabricated by improving fabrication process and device structures. Drain current maximum values for the B-diamond MOSFETs operating at room temperature and 300 °C are −1.2 and −10.9 mA/mm, respectively. Both exhibit on/off ratios higher than 109 and their extrinsic transconductance maximum values are 29.0 and 215.7 μS/mm, respectively. These properties surpass the values reported in previous studies.

Deposition characteristics and tribological performance of atmospheric plasma sprayed diamond metal matrix composite (DMMC) coatings

Diamond-reinforced metal matrix composites (DMMC) have great potential for wear-resistance applications due to the superior hardness imparted by diamond. Atmospheric plasma spraying involving axial injection of suitable feedstock is a convenient pathway to fabricate DMMC coatings for tribological applications. In this paper, thick DMMC coatings were deposited by plasma spraying Ni–P clad diamond particles under varying spray conditions. It was found that the phase characteristics of DMMC coatings as well as extent of diamond retention and fragmentation were significantly influenced by spray conditions such as, stand-off distance (SOD) and carrier gas flow rate (CGFR). Mechanical characterization (by micro-indentation) on all DMMC coatings developed in this work showed that coatings sprayed with longer SOD and higher CGFR has relatively higher hardness than other two coatings. However, on nanoindentation, the diamond hardness was found overestimated due to effect of diamond roughness on fragmentation. Ball-on-disc wear testing showed excellent tribological properties in all cases, with enhanced wear performance being noted when more diamond is retained in the coating.

Calculation of positron annihilation lifetime in diamond doped with B, Cr, Mo, Ti, W, Zr

Metal-matrix diamond composites have been extensively used and studied, but vacancies, doping, and other defects caused by the pretreatment of the diamond surface significantly affect the interface property between the metal base and diamond. Although techniques like transmission electron microscopy and spectroscopy analysis have been used to detect defects, they present certain limitations. Calculating the positron annihilation lifetime in diamond provides an accurate assessment of interface defect in the diamond. This study uses first-principles calculation methods and adopts various positron annihilation algorithms and enhancement factors, to compute the positron annihilation lifetimes in ideal diamond crystals, single vacancies, and diamond crystals doped with B, Cr, Mo, Ti, W, and Zr. The results, obtained by using local density functional in combination with Boronski & Nieminen algorithms and random-phase approximation restriction as annihilation enhancement factors, indicate that the computed positron annihilation lifetime of diamond is 119.87 ps, which is consistent closely with the experimental result in the literature. Furthermore, after B, Cr, Mo, Ti, W, and Zr atoms are doped into diamond (doping atomic concentration of 1.6%), the positron annihilation lifetimes change from a single vacancy 119.87 ps to 148.57, 156.82, 119.05, 116.5, 117.62, and 115.74 ps respectively. This implies that the defects due to doped atoms in diamond change their positron annihilation lifetimes, with the influence varying according to the different atoms doped. Based on the calculated electron density in diamond vacancies and doped atom areas, it is discovered that doping atoms do not cause severe distortion in the diamond lattice. However, after B and Cr atoms are doped, the positron annihilation lifetime increases significantly. The primary reason is that the relatively low positron affinity of B and Cr atoms results in an extended positron residence time in the vacancy, thereby increasing the annihilation lifetime. Overall, vacancies and doped atom defects in diamond will cause its positron annihilation lifetime to change. The above conclusions provide crucial theoretical references for detecting and identifying interface defects caused by doping treatment on the diamond surface during the preparation of metal-matrix diamond composites.

Robust diamond-embedded microwave antenna for optimizing quantum sensing using nitrogen-vacancy center ensembles

The nitrogen-vacancy (NV) color center in diamond has emerged as a promising candidate for quantum sensing. In this study, we propose a diamond-embedded metal antenna for magnetic detection utilizing NV center ensembles. Our approach involved employing nanofabrication and microwave plasma chemical vapor deposition techniques to fabricate the metal antenna and diamond epilayer. By directly embedding the antenna into the diamond, we effectively minimize external environmental interference, leading to improved device stability and reusability. Moreover, this integration enhances the device's compactness, making it highly suitable for on-chip quantum sensing applications. The innovative antenna design holds great potential for the development of future integrated quantum sensing devices based on NV centers in diamond.

Effect of Cu-coated diamond on the formation of Cu–Sn-based diamond composites fabricated by laser-powder bed fusion

In this study, Cu–Sn-based diamond composites were fabricated using L-PBF. The effects of the Cu-coated diamond on the melt-pool evolution, diamond–metal matrix bonding, thermal damage, and friction behavior of Cu in the Cu–Sn-based diamond composites were investigated. Moreover, the optimum L-PBF parameters for processing Cu-coated diamond/Cu–Sn composites were investigated. A convolutional neural network based on deep learning was used to process laser-scanned diamond images and evaluate the diamond thermal damage by model-feature visualization. The thermally damaged Cu-coated diamond and percentage of severely damaged parts were reduced compared to those of the uncoated diamond. Thick Cu coating changed the wettability of the diamond and matrix, thereby increasing the friction of the molten pool and unmelted metal particles and introducing the friction of the Cu microfluidic flow on the diamond. Hence, the mechanical holding force of the CuSn alloy matrix on the diamond substantially increased, and the bending strength of the Cu-coated diamond/Cu–Sn composites fabricated using L-PBF reached 720 MPa, which is approximately twice that of diamond/Cu–Sn (365 MPa).

Interface regulation of diamond-doped GaInSn composites

Diamond-doped GaInSn thermal interface materials have broad application prospects in the field of electronic thermal management. However, the poor wettability of diamond and liquid metal makes the fabrication of composites through simple mechanical agitation difficult. In this study, the wettability between GaInSn and diamond was improved by reducing the surface tension of liquid metal and improving the anisotropy of the diamond surface. The diamond/liquid metal (Dia/LM) interface structure was regulated by controlling the gallium oxide content. Ga2O3 was enriched in the GaInSn and diamond contact surface, which can reduce the surface tension of the liquid metal, improve the wettability of GaInSn to diamond, produce a mechanical locking force with the diamond surface, strengthen the bonding between the liquid metal and the diamond, and reduce the thermal resistance of the liquid metal/diamond interface. The Dia/LM interface structure was controlled by using crushed diamond. Result shows that the wettability of the surface (111) of the diamond was the best. The (100) and (110) planes with poor wettability were cut by the crushed diamond cleavage step, and the area of the crystal plane with poor wettability was reduced, thus improving the wettability of the liquid metal. The improvement of the crushed diamonds' wettability was verified by molecular dynamics calculation. The composite preparation technology of diamond and the GaInSn liquid metal was optimized, and the high-performance Dia/LM thermal interface material was prepared by ultrasonic-assisted and micro-oxidation methods.

Next Generation High Powered RF and Optical Packages

RF signals are radio waves that are very crucial for telecommunications. Quality communications require reliable materials which are appropriately processed to house high-powered semiconductors such as GaN and GaAs. It is equally crucial to accommodate passive electronic components along with these semiconductors into the housings for the Next Generation RF package or GenPack™. Evolving semiconductor technologies demand fail-safe packages to protect the devices in all applications and environmental conditions. Future aircraft, EV cars, spacecraft, augmented and/ or virtual reality headsets, medical devices and many more technologies require operating at a higher power and frequency with a proper thermal and power management platform. The higher speeds of telecommunications hinge on the performance of semiconductors and their packages. Therefore, the GenPack™ and packaging process are becoming crucial pieces of the supply chain. Rugged GenPack™ RF packages differ in several ways compared to the traditional air cavity packages. For instance, FR-4 or Flame-Retardant glass-reinforced epoxy laminate material can be replaced with Aluminum Nitride or Alumina Oxide, Silicon Nitride or even Sapphire. The switch offers mechanical bonding directly onto the thermal spreader. Traditional circuits created on printed circuit boards have limited ability to dissipate heat due to the low thermal conductivity of FR4. Circuits created on ceramic can dissipate higher amounts of heat. As in the organic FR4 boards, multiple vias can be formed in the ceramic substrates to create metal pads top the ceramic that are grounded to the flange beneath the ceramic. A metal flange can be positioned beneath the ceramic to provide a heat spreader and electrical ground that can be bolted onto a heatsink. Flanges can be made from a diamond metal matrix composite instead of lower thermal conductivity materials to provide much more efficient thermal transfer. Furthermore, narrow leads offer optimized impedance at RF and microwave frequencies. A range of ceramic and flange materials can be selected to optimize GenPack™ RF Packages with cost, quality, and performance in considerations for the respective applications.

Grain size dependence of wear resistance of polycrystalline diamond compact

Polycrystalline diamond compact (PDC) with different grain sizes were fabricated and the multi-physical behaviors, including mechanical-, thermal-, and magnetic performances, and the microscopic features were examined to study the grain size dependence of wear behavior while cutting dense granite. The results showed that the coarse grade PDC had higher impact resistance and fracture toughness. However, the fine grade PDC had higher cobalt content, hardness and thermal resistance. Among these properties, the wear resistance changed the same way as thermal expansion properties proving the strong correlation. Moreover, the crack network caused by thermal mismatch, and the peeling/fracture of metallic phases and diamond promoted fracture wear and played the critical roles in the wear of coarse grade PDC.

Mechanical Alloying of Copper- or Iron-Based Metallic Binders for Diamond Tools

Powder mixtures based on copper or iron are used as metal binder materials in the manufacturing of abrasive and cutting tools. This article discusses some aspects and possibilities of using a high-energy ball milling process to modify the structure and properties of Cu-Sn, Cu-Sn-Ti and Fe-Ti powders, their sintered materials and composites with diamond. The structures of powders and sintered materials, as well as the binder-to-diamond interfaces in metal matrix composites with diamond fillers, were studied by XRD analysis, scanning electron microscopy and X-ray spectroscopy. Tribological properties and thermal stability of materials in the temperature range of 250–800 °C were investigated. Various mechanisms of dispersion strengthening during the heating of sintered materials are described. It is shown that due to the grain boundary distribution of titanium, it is possible to obtain single-phase powders in the form of a supersaturated solid solution of CuSn20Ti5 and FeTi20, which ensure the formation of thermally hardened alloys with a microhardness of 357–408 HV and 561–622 HV, respectively, in the temperature range of 350–800 °C. The wear resistance of sintered powder alloys increases more than twice. Furthermore, the simultaneous enhancement in both the strength and ductility of metal–diamond titanium-containing composites is achieved through the nanostructural state and the formation of a thin layer (up to 2 μm) of titanium carbide at the interface between the metal matrix and diamond. The developed alloy shows great potential as a binder in diamond tools which are designed for machining abrasive materials.

Tribological Behavior of Ti-Coated Diamond/Copper Composite Coating Fabricated via Supersonic Laser Deposition

Diamond/copper composite coating is promising for wear-resistant applications, owing to the extreme hardness of the diamond reinforcement. Ti-coated diamond/copper composite coatings with various laser powers were successfully fabricated employing the novel manufacturing technology of supersonic laser deposition (SLD). Ti-coated diamond, which was able to enhance the wettability between diamond and copper, was prepared at the optimal parameters via salt bath. Nano-spherical titanium carbides were uniformly distributed on the diamond’s surface to generate a favorable interface bonding with a copper matrix though mechanical interlocking and metallurgical bonding during impact. Furthermore, the results showed that the transition layer acted as a buffer, preventing the breakage of the diamond in the coating. SLD can prevent the graphitization of the diamonds in the coating due to its low processing temperature. The coordination of laser and diamond metallization significantly improved the tribological properties of the diamond/copper composite coatings with the SLD technique. The microhardness of the diamond/copper composite coating at a laser power of 1000 W reached about 172.58 HV0.1, which was clearly harder than that of the cold sprayed copper. The wear test illustrated that the diamond/copper composite coating at a laser power of 1000 W exhibited a low friction coefficient of 0.44 and a minimal wear rate of 11.85 μm3·N−1·mm−1. SLD technology shows great potential in the field of preparing wear-resistant hard reinforced phase composite coatings.

Development and printability of diamond-containing composite filament for material extrusion

PurposeMaterial extrusion technology is considered to be an effective way to realize the accurate and integrated manufacturing of high-performance metal diamond tools with complex structures. The present work aims to report the G4 binder that can be used to create metal composite filament loading high concentrations of large diamond particles through comparative experiments.Design/methodology/approachThe quality of filaments was evaluated by surface topography observation and porosity measurement. And the printability of filaments was further studied by the tensile test, rheological test, shear analysis and printing test.FindingsThe results show that the G4 binder exhibits the best capacity for loading diamonds among G1–G4. The L4 filament created with G4 has no defects such as pores, cracks and patterns on the surface and section, and has the lowest porosity, which is about 1/3 of the L1. Therefore, the diamond-containing composite filament based on G4 binder exhibits the best quality. On the other hand, the results of the tensile test of L5–L8 filaments reveal that as the diamond content increases from 10% to 30%, the tensile strength of the filament decreases by 29.52%, and the retention force coefficient decreases by 15.74%. This can be attributed to the formation of inefficient bonding areas of the clustered diamond particles inside the composite filament, which also leads to a weakening of the shear strength. Despite this, the results of the printing test show that the diamond-containing composite filament based on the G4 binder has reliable printability.Originality/valueTherefore, the G4 binder is considered to solve the most critical first challenge in the development of diamond-containing filament.

Growth mechanisms of interfacial carbides in solid-state reaction between single-crystal diamond and chromium

Interfacial bonding is one of the most challenging issues in the fabrication, and hence comprehensively influences the properties of diamond-based metal matrix composites (MMCs) materials. In this work, solid-state (S/S) interface reaction between single-crystal synthetic diamond and chromium (Cr) metal was critically examined with special attention given to unveil the role of crystal orientation in the formation and growth of interfacial products. It has been revealed that catalytically converted carbon (CCC) was formed prior to chromium carbides, which is counterintuitive to previous studies. Cr7C3 was the first carbide formed in the S/S interface reaction, aided by the relaxation of diamond lattices that reduces the interfacial mismatch. Interfacial Cr7C3 and Cr3C2 carbides were formed at 600 and 800 °C, respectively, with the growth preferred on diamond (100) plane, because of its higher density of surface defects than (111) plane. Interfacial strain distribution was quasi-quantitively measured using windowed Fourier Transform-Geometric Phase Analysis (WFT-GPA) analysis and an ameliorated strain concentration was found after the ripening of interfacial carbides. Textured morphologies of Cr3C2 grown on diamond (100) and (111) planes were perceived after S/S interface reaction at 1000 °C, which is reported for the first time. The underlying mechanisms of Cr-induced phase transformation on diamond surface, as well as the crystal orientation dependent growth of interfacial carbides were unveiled using the first-principles calculation. The formation and growth mechanisms of Cr3C2 were elucidated using TEM and XRD analyses. Finally, an approach for tailoring the interfacial microstructure between synthetic diamond and bonding metals was proposed.