Nanocrystalline Diamond Research Articles

Corrosion resistance of diamond films with different grain sizes

Titanium alloys are widely used in the aerospace industry due to their excellent comprehensive properties. However, as the application becomes more and more extensive, higher requirements are put forward for the corrosion resistance of titanium alloys. Due to its natural chemical stability, diamond has become a good corrosion-resistant material. Diamond films with three different grain sizes were prepared on the surface of titanium alloy by hot-filament chemical vapor deposition (HFCVD). The protective efficiency of the three kinds of films to the substrate is above 90 %. The corrosion resistance of the nanocrystalline diamond (NCD) films is obviously better than that of the microcrystalline diamond (MCD) films. For NCD films, as the diamond grain size decreases, a cluster structure of particle stacking is formed, which hinders the arrival of corrosive substances to the substrate and further improves the corrosion resistance.

Tribological properties of HFCVD diamond coatings over wide temperature range

Single and gradient multilayered diamond coatings, deposited on silicon nitride (Si3N4), were prepared by hot filament chemical vapour deposition. The tribological properties were evaluated in a wide temperature range (26 °C–300 °C), against Si3N4 ceramic balls, as the friction counterpart. The results showed that with the increase of temperature from 26 °C to 300 °C, the wear rate of NCD (nanocrystalline diamond) and GCD (gradient diamond) coatings rapidly increases. When the temperature reaches 300 °C, obvious cracks and detachment appear on the surface of the NCD coatings. Due to the special interlayer, the wear rate of the GCD coatings is lower than that of the NCD coatings. In the range of 26 °C to 100 °C, GCD exhibits excellent wear resistance and low friction coefficient due to its special gradient structure. When the temperature increases to 200 °C, NCD films with smaller grain sizes exhibit higher wear rates. From the wear morphology, it can be seen that cracks are generated in the NCD film, and as the temperature increases, the cracks continue to expand until the film spalling. GCD shows relatively good wear resistance at high temperatures. This study found that gradient multilayered diamond coatings exhibited superior wear resistance at high temperatures, compared with single-layer coatings tested in identical conditions.

Morphology evolution and non-uniformity removal mechanism analysis of diamond nanocone arrays by reactive ion etching

Microstructures of diamond can be fabricated by reactive ion etching and during this process the evolution of surface morphology can affect the electric field near the microstructure. These changes in the electric field will alter the trajectory of ions, thereby affecting the number of ion bombardments on the surface regions of the microstructure. Consequently, this will affect the removal rate of the material on the microstructure surface and consequently affects the evolution of microstructure morphology. In order to understand the morphology evolution process of diamond during etching. H2 and Ar were used as the reactive gases to etch the nanocrystalline diamond (NCD) films with masks. The electric field near the microstructure and the trajectories of reactive ions was stimulated. The number of H+ and Ar+ bombardments at various regions on the diamond microstructure surface has been recorded and analyzed. By observing the cross-sectional morphology of the microstructure at different periods, the etching process of nanocones was analyzed. The study found that the microstructure of the diamond surface would gradually be etched into convex shaped and waist drum shaped and cone. By stimulating the electric field near the microstructure, it was found that the electric field distorted near the microstructure, causing the electric field lines initially perpendicular to the diamond surface to be diverted. As a result, the trajectory of the particles originally arrived perpendicularly to the diamond surface was distorted and hence they bombarded against the sidewall of the diamond microstructures. The angle between the ion trajectory and the electric field line also increased gradually.

Inhomogeneities across boron-doped nanocrystalline diamond films

For large-scale device fabrication, information about film inhomogeneities is crucial for high fabrication yield. In this work, inhomogeneities in two-inch diameter heavily boron-doped nanocrystalline diamond (BNCD) films have been studied. Two BNCD films were grown using chemical vapour deposition (CVD) with different boron-to-carbon (B/C) ratios. Their superconducting properties were measured as a function of distance from the centre of the film. The critical temperature (Tc) and critical magnetic field (Hc2) decreased radially outwards from the centre for both films. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were done on the samples to pinpoint the underlying explanation for the observed behaviour. Raman spectroscopy suggested a reduction in boron concentration and diamond purity over both films while moving radially outwards from the centre. XPS data from both films, however, did not show similar behaviours to that observed from the Raman data for the B/C ratios or diamond content. The AFM scans and SEM analysis showed a decreasing grain size further away from the film centre irrespective of the B/C ratio. This is due to the film being thinner at the edges when compared with the centre of the film. Raman analysis showed that the film with the higher B/C ratio had a higher diamond purity across the film. As expected, the film with a higher B/C ratio showed a more robust superconducting behaviour. The observed reductions in boron concentration, diamond purity, film thickness and decreased grain sizes are responsible for the diminishing superconductivity at the edge of the films.

XMEA: A New Hybrid Diamond Multielectrode Array for the In Situ Assessment of the Radiation Dose Enhancement by Nanoparticles.

This work presents a novel multielectrode array (MEA) to quantitatively assess the dose enhancement factor (DEF) produced in a medium by embedded nanoparticles. The MEA has 16 nanocrystalline diamond electrodes (in a cell-culture well), and a single-crystal diamond divided into four quadrants for X-ray dosimetry. DEF was assessed in water solutions with up to a 1000 µg/mL concentration of silver, platinum, and gold nanoparticles. The X-ray detectors showed a linear response to radiation dose (r2 ≥ 0.9999). Overall, platinum and gold nanoparticles produced a dose enhancement in the medium (maximum of 1.9 and 3.1, respectively), while silver nanoparticles produced a shielding effect (maximum of 37%), lowering the dose in the medium. This work shows that the novel MEA can be a useful tool in the quantitative assessment of radiation dose enhancement due to nanoparticles. Together with its suitability for cells' exocytosis studies, it proves to be a highly versatile device for several applications.

Reduced temperature in lateral (AlxGa1−x)2O3/Ga2O3 heterojunction field effect transistor capped with nanocrystalline diamond

The low thermal conductivity of β-Ga2O3 is a significant concern for maximizing the potential of this ultra-wide bandgap semiconductor as a power switching device technology. Here, we report on the use of nanocrystalline diamond (NCD) deposited via microwave plasma enhanced chemical vapor deposition (MP-CVD) as a top-side, device-level thermal management solution on a lateral β-Ga2O3 transistor. NCD was grown via MP-CVD on β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures prior to the gate formation of the field-effect transistor. A reduced growth temperature of 400 °C and a SiNx barrier layer were used to protect the oxide semiconductors from etching in the MP-CVD H2 plasma environment. Raman spectroscopy showed a highly sp3-bonded NCD film was obtained at 400 °C, with grain size of about 50–100 nm imaged via atomic force microscopy. The incorporation of the NCD heat-spreading layer resulted in a β-(AlxGa1−x)2O3/β-Ga2O3 heterostructure field-effect transistor showing a decrease in the total thermal resistance at the gate by 42%. The fabrication process, including the NCD etch in the gate region, will need to be improved to minimize the impact of these processes on important device characteristics (i.e., drain current, threshold voltage, and leakage current).

Weak oxidant fraction in the microwave plasma influencing the evolution of nanocrystalline-diamond–imbedded diamond–like carbon network at low temperatures and its orbital hybridization dependent wide optical band gaps

The diamond-like carbon (DLC) thin films having intrinsic nanocrystalline diamond (NCD) components were synthesized on bare glass substrates at 300 °C, employing a (C2H2/CO2/H2/) gas mixture in MW-PECVD. Relevant influence of the weak oxidant fraction [F = CO2/(CO2 + C2H2)] in the plasma on the specific hybridized constituents (sp3 and sp2) in the C-network, optical transmission characteristics of the film, and its accomplished degree of nanocrystallinity were investigated. A substantial segment of the NCD was achieved in the DLC matrix. An optimized diamond-phase component corresponding to the minimized bond angle disorder in the matrix was accounted from the manifestation of the maxima of IDia/IG and IDia/ID simultaneous to the minimum of ID/IG ratio in Raman response, along with an allied diamond peak appearing near 1332 cm−1. The optimal DLC film at F = 0.23 revealed a wide optical band gap (Eg) of ∼3.60 eV, ∼59% sp3-hybridized C component of the diamond phase, and a significant sp3/sp2 ratio of ∼2.1. The film microstructure seemed homogeneous with uniformly distributed NCDs of average diameter ∼7.5 nm and dominant 〈111〉 crystallographic orientation. The sp3/sp2 fraction in the film matrix has been correlated directly to the IDia/IG and IDia/ID, and inversely to ID/IG ratios of the Raman data. Atomic-O, including atomic-H, remains instrumental in chemical reactions, facilitating the etching of graphitic and a-C phases while preserving the superior sp3-hybridized NCD component growing uninterruptedly in the DLC network that subsists shielded from the high-energy ion impact within secondary plasma under the shadow mask.

Disappearance of cobalt particles above nanocrystalline diamond films by HF-CVD on cemented tungsten carbide

Abstract In this study, the possibility of the disappearance of Co particles on the surface of nanocrystalline diamond (NCD) films with large thicknesses was examined. It is shown that the number of Co particles decreased clearly with larger thicknesses. In the thickest case, the Co particles disappeared almost completely. Investigation with energy-dispersive spectroscopy for the cross section of the NCD films suggested that the Co particle was embedded during the growth of the NCD film. Our observations will contribute to depositing smooth NCD films on tools without the embrittlement of substrates by Co etching.

Single-photon emission from silicon-vacancy color centers in polycrystalline diamond membranes

Single-color centers in thin polycrystalline diamond membranes allow the platform to be used in integrated quantum photonics, hybrid quantum systems, and other complex functional materials. While single-crystal diamond membranes are still technologically challenging to fabricate as they cannot be grown on a non-diamond substrate, free-standing polycrystalline diamond membranes can be conveniently fabricated at large-scale from nanocrystalline diamond seeds on a substrate that can be selectively etched. However, their practical application for quantum photonics is so far limited by crystallographic defects, impurities, graphitic grain boundaries, small grain sizes, scattering loss, and strain. In this paper, we report on a single-photon source based on silicon-vacancy color centers in a polycrystalline diamond membrane. We discuss the spectroscopic approach and quantify the photon statistics, obtaining a g2(0) ≈ 0.04. Our findings hold promise for introducing polycrystalline diamond to quantum photonics and hybrid quantum systems.

Impact of surface treatments on the electron affinity of nitrogen-doped ultrananocrystalline diamond

In recent years, various forms of nanocrystalline diamond (NCD) have emerged as an attractive group of diamond/graphite mixed-phase materials for a range of applications from electron emission sources to electrodes for neural interfacing. To tailor their properties for different uses, NCD surfaces can be terminated with various chemical functionalities, in particular hydrogen and oxygen, which shift the band edge positions and electron affinity values. While the band edge positions of chemically terminated single crystal diamond are well understood, the same is not true for nanocrystalline diamond, which has uncontrolled crystallographic surfaces with a variety of chemical states as well as graphitic grain boundary regions. In this work, the relative band edge positions of as-grown, hydrogen terminated, and oxygen terminated nitrogen-doped ultrananocrystalline diamond (N-UNCD) are determined using ultraviolet photoelectron spectroscopy (UPS), while the band bending is investigated using photoelectrochemical measurements. In contrast to the widely reported negative electrode affinity of hydrogen terminated single crystal diamond, our work demonstrates that hydrogen terminated N-UNCD exhibits a positive electron affinity owing to the increased surface and bulk defect densities. These findings elucidate the marked differences in electrochemical properties of hydrogen and oxygen terminated N-UNCD, such as the dramatic changes in electrochemical capacitance.

High performance field emission cathode based on the diamond nanowires prepared by nanocrystalline diamond films annealed in air

This paper reports the field emission (FE) characteristics of a diamond nanowires (DNWs) array. The nanocrystalline diamond (NCD) film was deposited on silicon by microwave plasma chemical vapor deposition (MPCVD) and then annealed in air forming DNWs and hydrogenated at last. A high-field flat-plate emission test structure with a 1.03 μm gap between anode and cathode was prepared and the electrical properties proved it feasible. The FE performance of DNWs array was measured in a vacuum test system and that of NCDs film as a comparison. Finally, their FE parameters were analyzed and extracted based on the Fowler–Nordheim (F-N) theory. The results show that transforming NCDs film into DNWs array can improve the FE characteristics greatly. The turn-on field is as low as 1.36 V μm−1 dropping by one order of magnitude, while the field enhancement factor and FE current density are up to 156.68 and 484.75 mA cm−2 respectively rising both by two orders of magnitude. This excellent FE performance stems from the characteristics of large aspect ratio, very small tip radius and high density of DNWs.

Design and Fabrication of Piezoresistive Strain-Gauges for Harsh Environment Applications

Maximum operating temperature is usuallyone of the limiting factors for using of conventional sensors and other electronic devices. High-temperature sensors and electronics are required in some special applications e.g. measurement of deformations, stresses and pressures inside power generators. The design methodology of the some piezoresistive sensors utilizing FEM simulations is presented. Piezoresistive sensors based on thin-film metal sputtered layers, silicon-on-insulator (SOI) and nanocrystalline diamond layers (NCD) were successfully designed, fabricated and measured. The fabricated sensors are able to operate at temperatures up to 250 °C. Extensive study of sensor parameters e.g. deformation sensitivity, edge and contact resistances, temperature dependences gauge factor, bridge output voltage was performed. The measured values and investigated findings can be used for calibration of simulation software and in prospective design of more complex sensor structures.

Nano- and micro-crystalline diamond film structuring with electron beam lithography mask

Direct current plasma enhanced chemical vapor deposition (CVD) was employed to create polycrystalline diamond films from CH4/H2 gaseous mixture at 98 mbar pressure and various substrate temperatures between 720 °C and 960 °C. The Si chips with patterns of periodic masked and open seeded zones were used as substrates. The mask free seeded areas evolved into polycrystalline diamond films after CVD process. The diamond crystallites of the films featured single crystal ordering individually with distinct cubic (100) or octahedral (111) facets on the film surfaces. Notably, specific growth conditions were determined for obtaining diamond films composed of the crystallites of nanometre and micrometre scale. These conditions are differing from those observed for non-pattern-prepared Si substrates. The nano-crystalline diamonds emerged within the 4.5–5 A current range, with growth conditions involving 3% CH4/H2 mixture at 98 mbar. The micro-crystalline diamonds (MCDs) predominantly characterized by well-developed rectangular (100) crystal faces on the film surface were successfully grown with current settings of 5.5–6 A, under 3% CH4/H2 mixture at 98 mbar. Furthermore, MCDs characterized by entirely crystalline (111) diamond faces forming CVD film surface were attained within a growth parameter range of 4.5–5.8 A, employing 3% CH4/H2 mixture for certain samples, or alternatively, utilizing 5 A with a 1.5% CH4/H2 mixture for others. Upon thorough evaluation, it was established that SiO2, TiO2, and Cr masks are well-suited materials for the planar patterning of both nano- and micro-crystalline diamond films, and the bottom-up approach can pave the way for the production of diamond planar structures through CVD, facilitated by electron beam lithography (EBL).

Piezoresistive Sensor for Strain Measurement on Turbine Blade with Wireless Telemetry Data Acquisition

In the paper, strain-gauge sensor design and its application for wireless measurement of blade deformations and strains are presented. The strain sensor was designed using FEM (Finite Element Modeling) and uses piezoresistive strain sensitive boron doped nanocrystalline layers or insulated silicon layers (SOI). Nanocrystalline Diamond (NCD) is a very promising material for fabrication of harsh-environment devices because of its unique mechanical and electrical properties. The prospective of using diamond is not only in sensors (MEMS) but in RF and power electronic as well. Selection of method for data transfer is the key problem in rotating mechanisms. Traditional approach is using the slip ring, but it is not suitable for multisensor applications due to the requirement of one slip ring per sensing element. Telemetry can be related to transfer a data over any media, but is typically applied on wireless communications. A basic telemetry system consists of a measuring element or sensor, a device for sending the transmission, a receiver, and an output controller which records and displays data.

Micromechanical properties of micro- and nanocrystalline CVD diamond thin films with gradient microstructures and stresses

Chemical vapor deposition produced diamonds attract considerable scientific and industrial interest due to their exceptional mechanical and functional properties. Here, hot filament (HF) chemical vapor deposition was used to synthesize two diamond thin films with different cross-sectional microstructure and residual stresses. Structural characterization by scanning electron microscopy, Raman spectroscopy, and cross-sectional synchrotron x-ray nanodiffraction revealed different diamond morphologies. While the microcrystalline diamond film exhibits pronounced microstructural gradients expressed by gradually increasing (i) intensities of the 111 Debye-Scherrer rings, (ii) ⟨110⟩ fiber texture sharpness, (iii) grain size, and (iv) slightly oscillating residual stress at the level of −0.5 GPa, the nanocrystalline diamond film showed no pronounced cross-sectional variation of microstructure above the nucleation zone of ∼0.5 μm and a steady stress level of 0.25 GPa. In situ micromechanical cantilever bending tests revealed highly different mechanical properties of the two films. In detail, Young's modulus of 830 ± 53 and 459 ± 53 GPa, fracture stress of 12.4 ± 0.8 and 7.8 ± 1.0 GPa, and fracture toughness values of 6.9 ± 0.4 and 3.6 ± 0.3 MPa⋅m½ were evaluated for the micro- and nanocrystalline diamond films, respectively. In summary, this study provides valuable insights into the microstructure-residual stress correlation in micro- and nanocrystalline diamond films, especially illuminating their influence on micromechanical properties.

Crystal orientation control of HFCVD diamond spherical film tools and tribological behavior on steel

(111)-oriented micron-crystalline diamond (111MCD), (110)-oriented micron-crystalline diamond (110MCD) and (110)-oriented nano-crystalline diamond (110NCD) spherical films were prepared on the surface of spherical WC-Co polishing tools by hot filament chemical vapor deposition technology. The microstructure, molecular structure, crystal orientation and surface roughness of spherical films were characterized by SEM, XRD, EBSD and White-light interferometer. The friction performance and material removal mechanisms were studied by friction experiments on steel. The results showed that both crystal orientation and grain size variation significantly influenced the tool properties. The roughness and friction coefficient of 111MCD, 110MCD, and 110NCD films decreased successively. During the friction process, the transformation of diamond to graphite reduced the friction coefficient but accelerated film delamination. 111MCD has the fastest material removal rate, but the graphitization rate and wear rate of the film are the highest, and there are a lot of abrasive chips in the friction interface. Diamond of (110) orientation can improve the wear resistance of the film and reduce the abrasive wear of the workpiece. Compared to 111MCD, 110NCD exhibited a 29.3 % reduction in friction coefficient, a 90 % improvement in wear resistance, a 49.4 % increase in surface smoothness of the processed workpiece, and the highest ID/IG value of 1.45 after film wear, demonstrating superior polishing performance and anti-graphitization properties. These results indicate that 110NCD tool is a highly efficient polishing tool with great potential.

Enhanced Gas Sensing Performance of Heterostructure Sensors Based on H-NCD, MoS₂, and Functionalized Graphene Oxide for Ethanol, NH₃, and NO₂ Detection

This study investigates the gas-sensing capabilities of heterostructure sensors based on hydrogen-terminated nanocrystalline diamond (H-NCD), molybdenum disulfide (MoS₂), and functionalized graphene oxide (SH-GO, GO) for detecting ethanol, ammonia (NH₃), and nitrogen dioxide (NO₂) gases at 100 ppm concentrations. Sensors were tested at two distinct temperatures: 125°C and room temperature (22°C). Among the tested sensors, the SH-GO/H-NCD exhibited the highest sensitivity to ethanol, with a response of 634% at 22°C and 554% at 125°C. The Au NPs/H-NCD sensor showed the second-best ethanol response of 587% at 125°C. For NH₃, SH-GO/H-NCD demonstrated the best response at 125°C with a value of 76%, while at room temperature, it showed 41%. NO₂ sensing showed negative responses, with the SH-GO/H-NCD sensor exhibiting the least degradation at -47% at 125°C and -19% at 22°C. The results highlight those combining materials into heterostructures significantly enhances gas detection performance, even at room temperature, showing comparable responses to commercial sensors.

New diamond coatings for peroxosulphate production

In this work new diamonds coating, named as nanocrystalline diamond (ND) and ultrananocrystalline diamond (UND) are evaluated for the production of peroxospecies derived from the electrolysis of sulphuric acid and their performance is compared to that of a commercial diamond coating widely used in the literature and well-known by its outstanding performance. The oxidant production was tested at two different current densities and significant differences were found in oxidant production between the electrodes applied in the different conditions studied. Results demonstrate that when the lowest current is applied (25 mA cm−2), the ND and UND electrodes are more efficient in the persulfate formation. For ND electrode, this behavior can be explained in terms of the promoted hydroxyl radical formation at these conditions. However, the UND electrode presented different behavior: the lesser hydroxyl formation and highest peroxospecies formation. This behavior may be attributed to the sum of two factors: the high sp2 content in the diamond film and its porosity, that can increase the sulphate adsorption at the surface that, in turn, facilitates the persulfate generation. This behavior can be proved by the Tafel plots and are explained by the electrode’s features discussed by Raman spectra. When the operation current is increased to harsher conditions (300 mA cm−2), the commercial electrode increases importantly the production of the studied oxidant. One more time it can be attributed to the hydroxyl radical generation at this condition. Considering the energy consumption and the process efficiency, it can be concluded that the UND electrode is more attractive for this application in the studied conditions.

Effect of substrate roughness on the nucleation and growth behaviour of microwave plasma enhanced CVD diamond films – a case study

The influence of substrate surface roughness on the nucleation and growth of diamond films by chemical vapour deposition (CVD) is investigated. Silicon substrates were grinded with six different grit sizes of abrasive papers with a rotating wheel. Si was also etched by Ar+ ions to produce average surface roughness Ra = 11.29 nm on the mirror polished side (Ra = 1.17 nm). A comparison of the results of the effect of substrate roughness, on the growth behaviour of nanocrystalline diamond (NCD) films, by using both the resonant cavity and the linear antenna CVD systems, are presented here. Scanning electron microscopy (SEM) images and Raman spectroscopy reveal that under both the linear antenna and the resonant cavity microwave plasma CVD conditions, grown films are NCD. The diamond nanocrystals sizes vary from 80 to 180 nm, grown by both the reactors after few hours of deposition, irrespective of the substrate roughness, whereas their quality (defined by the relative percentage ratios of the Raman sp3 peak intensity to the non-sp3 peak intensity) varies from 33% to 45%, depending on the substrate surface roughness. Such nanocrystals grew into plate-like flat 1–6 μm size diamond grains after prolonged hours (64–69 h) of CVD growth. It is found specifically that the roughness created by the argon plasma treatment of the silicon substrate surfaces effectively enhances the nucleation and growth behaviour of the diamond films.

Three-dimensional opal-like photonic crystals made of diamond shells by chemical vapor deposition

3D ordered hollow diamond spheres packed into opal structure have been synthesized by chemical vapor deposition using silicon inverse opal template which, in turn, was produced by molding of a bulk silica opal template. These 3D diamond opals demonstrate optical properties of photonic crystal with Bragg reflection peak in the visible range. Numerical modeling of the reflection spectra is performed using a scattering matrix calculation, and agrees well with the measured Bragg peak positions. The porous structure consisting of nanocrystalline diamond shells with thickness of the order of 10 nm composes the light-weight material with density of ≈0.50 g/cm3. The diamond opals showed bright photoluminescence at 738 nm wavelength due to silicon-vacancy centers formation in course of the growth process. The diamond opals can be a new promising platform for versatile applications, primarily in photonics, due to wide transparency window, high chemical resistance and mechanical strength inherent to diamond.