Nanocrystalline Diamond Grains Research Articles

Synthesis of High Quality Transparent Nanocrystalline Diamond Films on Glass Substrates Using a Distributed Antenna Array Microwave System

Diamond is a material of choice for the fabrication of optical windows and for protective and anti-reflecting coatings for optical materials. For these kinds of applications, the diamond coating must have a high purity and a low surface roughness to guarantee a high transparency. It should also be synthesized at low surface temperature to allow the deposition on low melting-point substrates such as glasses. In this work, the ability of a Distributed Antenna Array (DAA) microwave system operating at low temperature and low pressure in H2/CH4/CO2 gas mixture to synthesize nanocrystalline diamond (NCD) films on borosilicate and soda-lime glass substrates is investigated aiming at optical applications. The influence of the substrate temperature and deposition time on the film microstructure and optical properties is examined. The best film properties are obtained for a substrate temperature below 300 °C. In these conditions, the growth rate is around 50 nm·h−1 and the films are homogeneous and formed of spherical aggregates composed of nanocrystalline diamond grains of 12 nm in size. The resulting surface roughness is then very low, typically below 10 nm, and the diamond fraction is higher than 80%. This leads to a high transmittance of the NCD/glass systems, above 75%, and to a low absorption coefficient of the NCD film below 103 cm−1 in the visible range. The resulting optical band gap is estimated at 3.55 eV. The wettability of the surface evolves from a hydrophilic regime on the bare glass substrates to a more hydrophobic regime after NCD deposition, as assessed by the increase of the measured contact angle from less than 55° to 76° after the deposition of 100 nm thick NCD film. This study emphasizes that such transparent diamond films deposited at low surface temperature on glass substrate using the DAA microwave technology can find applications for optical devices.

Synthesis of nanocrystalline diamond embedded diamond-like carbon films on untreated glass substrates at low temperature using (C2H2 + H2) gas composition in microwave plasma CVD

Diamond-like carbon (DLC) films with well distinguished nanocrystalline diamond (NCD) grains embedded in the matrix are grown at ∼300 °C on glass substrates without any pre-treatment, using a specially-designed stainless-steel shadow-mask assembly creating diffuse secondary plasma that shields the growth zone from high energy ion bombardment. The effects of different compositions of the precursor gas, R = C2H2 / (C2H2 + H2), and gas pressure in the plasma at 500 W of microwave power demonstrate their significant influences on controlling the relative composition of the sp3 to sp2 hybridized carbon phases in the films. The maximum intensity ratio of IDia/IG (∼1.05) and IDia/ID (∼1.05) along with the corresponding minimum of ID/IG (∼1.0) appearing in the Raman spectrum at R = 0.33 and 25 Torr pressure, correlate a superior diamond-phase containing ∼55% sp3-hybridized carbon in the DLC network having high optical transmittance of ∼87% at 600 nm wavelength. A homogeneous microstructure with uniform distribution of the NCD grains of average size ∼10 nm and 〈111〉 crystallographic orientation, and smooth surface morphology with average roughness ∼2.1 nm is obtained in the optimum NCD embedded DLC film, the growth mechanism of which is discussed on the basis of parametric changes.

(100) oriented diamond film prepared on amorphous carbon buffer layer containing nano-crystalline diamond grains

In this study, amorphous carbon buffer layer containing nano-crystalline diamond grains was pre-deposited on single crystal silicon (Si) wafers. (100) oriented diamond films were prepared on the buffer layer by increasing deposition temperature. Morphology observation demonstrated that (100) oriented diamond plates appear on the buffer layer, thus realizing the deposition of (100) oriented diamond film. Transmission electron microscopy confirmed that (100) oriented diamond dominates deposition at high temperatures, leading to the formation of the (100) oriented diamond plates. The fast lateral growth of nano-crystalline diamond grains with (100) orientation in the buffer layer is the main driving force for the deposition of (100) oriented diamond film, providing a new route for the preparation of (100) oriented diamond films.

Microstructure and electrochemical properties of nanocrystalline diamond and graphene hybridized films

We have successfully grown a series of nanocrystalline diamond and graphene hybridized (NCD-G) films with various morphologies and compositions of grain boundaries by adjusting the growth pressure by hot-filament chemical vapor deposition and extensively investigated their electrochemical performances. In the case of low growth pressure, such as 1.0 and 1.3 kPa, there is a large amount of graphene in the NCD-G films, and graphene exhibits better crystallinity and a bigger size. These produce quicker electron exchange, rising background current, and reduced potential window. As the growth pressure increases to above 1.6 kPa, the grain boundaries are reduced, so that the NCD-G films possess fewer graphene components. As the growth pressure is 1.6 kPa, the “bridge”-like graphene stands on the neighboring nanocrystalline diamond grains, providing degraded electrochemical properties of smaller redox current. With the growth pressure further increasing to 1.9 kPa, the least trans-polyacetylene wrapped diamond grains produce slightly rising redox current, wider potential windows, and smaller background current. Graphene exists as a small slice and is distributed parallel with the grains with the growth pressure increasing to 2.2 kPa, exhibiting a significant rising redox current accompanied with wider potential windows and lower background current. It is concluded that the high diamond content is beneficial to enlarge the potential windows and decrease the background current, and the graphene components take advantage of improving the redox current. Moreover, the ordered and small graphene surrounding the diamond grains is positive to improve the electrochemical response without the rising background current. Thus, we prepare an electrochemical electrode material with excellent performance by adjusting the state and the content of each component in the NCD-G films.

Oxygen ion implanted grains dominantly contributed electron field emission of nanocrystalline diamond films

We have performed O ion implantation and annealing on nanocrystalline diamond (NCD) films with novel microstructure consisted of nanocrystalline diamond grains and intergranular interfaces instead of amorphous carbon grain boundaries. With annealing temperature increasing from 500 to 900 °C, a turn-on field of NCD films decreases from 4.5 to 5.9 V/μm to 3.6 V/μm, and its current density dramatically increases to 216 μA/cm2 at 8.0 V/μm. X-ray photoelectron spectroscopy results show that the content of sp3 carbon increases with lower C-O and C=O contents on the film surface, suggesting that fewer diamond grains are oxidized in the case of 900 °C annealing, dramatically improving the EFE properties. This reveals that O-doped diamond grains make main contribution to the enhanced EFE properties, which is further proved by the fact that EFE properties are not observed in C ion implanted and 900 °C annealed NCD film with the same structure. This is different from the typical NCD and ultrananocrystalline diamond (UNCD) films that the EFE properties were enhanced by the formation of nanographtic phase.

Effects of Air Exposure on Hard and Soft X-ray Photoemission Spectra of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films

Hard X-ray photoemission spectroscopy (HAXPES) was employed for the structural evaluation of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films deposited on cemented carbide substrates, at substrate temperatures up to 550 °C by coaxial arc plasma deposition. The results were compared with those of soft X-ray photoemission spectroscopy (SXPES). Since nanocrystalline diamond grains are easily destroyed by argon ion bombardment, the structural evaluation of UNCD/a-C films, without the argon ion bombardment, is preferable for precise evaluation. For samples that were preserved in a vacuum box after film preparation, the sp3 fraction estimated from HAXPES is in good agreement with that of SXPES. The substrate temperature dependencies also exhibited good correspondence with that of hardness and Young’s modulus of the films. On the other hand, the sp3 fraction estimated from SXPES for samples that were not preserved in the vacuum box had an apparent deviation from those of HAXPES. Since it is possible for HAXPES to precisely estimate the sp3 fraction without the ion bombardment treatment, HAXPES is a feasible method for UNCD/a-C films, comprising nanocrystalline diamond grains.

The effects of deposition parameters on the grain morphology and wear mechanism of monolayer diamond grinding tools fabricated by hot filament CVD method

The hot filament chemical vapor deposition technique (HFCVD) is used to fabricate monolayer grinding tools with high quality diamond abrasive grains. The high pressure and high temperature (HPHT) diamond seeds are distributed on SiC substrate randomly by a spin coater machine. Then epitaxial growth of CVD diamonds is conducted on both seeds and substrate simultaneously. The heteroepitaxial diamond film on substrate serves as a bonding layer to anchor the seeds, and the homoepitaxial growth of the seeds leads to changes in their morphology, purity, as well as mechanical properties. The grown seeds can be used as abrasive grains of the grinding tools. In this work, a systematic study is presented into the effects of deposition parameters (substrate temperature, carbon concentration, reactive pressure, bias current) on the growth behavior of diamond seeds. As a result, it is found that the well-faceted single crystal diamond (SCD) grains can be grown at 800 °C, 4.5 KPa, carbon concentration of 1.5% and bias current of 2 A. Besides, the increase of temperature and decrease of pressure allow the changes from SCD grains to microcrystalline diamond (MCD) clusters or further, to nanocrystalline diamond (NCD) clusters, while the high bias current and carbon concentration promote the growth of dislocated planes and secondary nucleation. Moreover, it is found that the protrusion of the diamond abrasives can be controlled by the difference in growth rates between seeds and diamond bonding films under various conditions. Finally, the wear resistance of diamond grains is tested. Results show that the wear of SCD grains is dominated by a high rate of wear flat and few fractures, and the wear of MCD grains exhibits less wear flat but more fractures, while the NCD grains exhibit the worst wear resistance in terms of both fracture and wear flat.

Thermal oxidation induced high electrochemical activity of boron-doped nanocrystalline diamond electrodes

Thermal oxidation treatment was executed on boron-doped nano-crystalline diamond (B-NCD) films to change both the microstructure and the terminal groups of grains and grain boundaries. Their contributions to the electrochemical activity and electrical properties were investigated. The grain boundaries become narrowing, with ordered graphite phase firstly, and then they become disordered for long time oxidized treatment. This causes that the mobility of the B-NCD electrodes increases to 84.97cm2/Vs after 30min oxidation and then it decreases obviously with oxidation time further increasing. Nanocrystalline diamond grains with high carrier concentration are growing larger and naked on the B-NCD electrode’s surface after oxidization. Also, part of the terminal CH groups on the grain phases turn to CO groups with positive electron affinity, which is prone to attract electrons from nearby anions. These results lead to larger electrochemical activity area with quick charge transfer rate in the surface of B-NCD electrode. The silane is used to shield the OH sites from electrochemical activity. The covered area become less with the oxidized time, further confirming that the electrochemical reaction mainly occurs on the grain phases and the OH groups is mainly growing in grain boundaries.

Bottom-up diamond nanorod growth in HFCVD from nanocrystalline diamond film as a template-free method

Nanocrystalline diamond (NCD) films are being used in a large number of applications. Also, diamond nanorods (DNRs) exhibit distinctive features that are not present in diamond films, because of the tunable large surface-to-volume ratio and tubular configuration. In this work, we report on the synthesis of DNRs by means of the bottom-up and template-free method from NCD films by the hot filament chemical vapor deposition system. The substrate materials used for diamond deposition were stainless steel (AISI 316) and chromium nitride-coated stainless steel. On both substrates, NCD films and then DNRs have been synthesized. The micro-Raman confirms that the synthesized structure is NCD. In addition, the grazing incident x-ray diffraction pattern confirms the presence of cubic diamond and rhombohedral diamond as a film on the CrN and Cr2N interlayer. Also, the DNRs are encased in an amorphous carbon (a-C) shell. The DNRs are grown on the NCD grains by a bottom-up technology and template-free method. Their orientations are almost random in the diamond thin-film surface. In addition, the density of DNRs on the NCD film for the CrN interlayer is more than for the stainless-steel substrate. The NCD/DNR films are dense, adhesive, continuous, and almost uniform on the CrN-coated stainless-steel substrate.

Hexagonal boron nitride particles for determining the thermal conductivity of diamond films based on near-ultraviolet micro-Raman mapping

Studies are reported of the thermal conductivity () for a supported ~1 µm thick diamond membrane. Near-ultraviolet micro-Raman spectroscopy is used to map the temperature rise produced in the diamond by a micro-fabricated heater and in hexagonal boron nitride micro/nano-particles which are dispersed on the surface as local temperature sensors. Thermal conductivity is determined analytically from Raman temperature rise and also by fitting data via simulation, using a Monte Carlo optimization approach. The low value obtained for , W m−1 · K, is attributed to the nanocrystalline diamond grain structure as analyzed by transmission electron microscopy (TEM). TEM identifies a disordered silicon-carbon interfacial layer ~2 nm thick which is expected to affect the diamond/silicon thermal boundary resistance.

SiV center photoluminescence induced by C=O termination in nanocrystalline diamond and graphite loops hybridized films

We performed a series of thermal oxidation at different temperatures on nanocrystalline diamond (NCD) films to construct various surface termination states of NCD grains and investigated their effects on silicon-vacancy (SiV) photoluminescence (PL) at 738 nm. Experiments and first principles calculations show that the negative electron affinity surface induced by C-H bond termination quenches the SiV PL, while the positive electron affinity surface originating from C=O bond termination removes this quenching. Moreover, oxidation at 600 °C results in the transition from amorphous carbon to graphite loops with an interlayer space of 0.4 nm, so that NCD and graphite loops' hybridized structure is formed. This allows oxygen atoms to contact with inside NCD grains to form more C=O bonds on the surface, producing much larger positive electron affinity in the surface. It traps the excited state electrons, lets them scatter back to the ground state, and emits SiV PL. These results reveal that C=O bonds play a crucial role in SiV PL of NCD grains and well explain the experimentally observed quenching effect. A novel way by changing the surface termination states is proposed to control the PL of NCD grains with SiV centers for potential quantum information processing and biological sensing.

Development and growth time optimization of boron-doped micro-crystalline, undoped micro-crystalline and undoped nano-crystalline composite diamond film

Based on a well-designed growth procedure, a tri-material, namely, a three-layer boron-doped micro-crystalline, undoped micro-crystalline and undoped nano-crystalline composite diamond film, is deposited on the pretreated WC–6 wt% Co substrate, the basic characters of which are systematically studied and compared with some other commonly used diamond films. Besides, the growth times for three respective layers are accordingly determined. It is further clarified that the underlying boron-doped micro-crystalline diamond layer can well adhere to the WC–Co substrate due to either the reduction in the residual stress or the formation of B–Co compounds. There is no doubt that the surface undoped nano-crystalline diamond layer with relatively lower hardness and initial surface roughness is more convenient to be polished to the required surface roughness. Moreover, when the growth times for the middle undoped micro-crystalline diamond layer and the surface undoped nano-crystalline diamond layer are both appropriate, the undoped micro-crystalline diamond layer with extremely high diamond quality and hardness can effectively reinforce the surface hardness of the whole composite film. Based on the discussions on the influences of the growth times for the different layers on the performance of the composite diamond film, the growth times for the boron-doped micro-crystalline diamond, undoped micro-crystalline diamond and undoped nano-crystalline diamond layers are, respectively, determined as 4, 4 and 2 h. Under such conditions, the reinforcement effect of the middle layer on the surface hardness can be guaranteed, and the undoped nano-crystalline diamond grains have totally covered the undoped micro-crystalline diamond layer.

The impact of nanocrystalline diamond grain boundary chemistry on frictional response in sliding contact with 319Al alloy

Due to its exceptional mechanical and tribological properties, nanocrystalline diamond (NCD) has the potential to be used for tool coatings that can enable dry machining of Al alloys. This study explores the friction response of NCD coatings in sliding contact with 319 Al. NCD coatings were grown using microwave plasma CVD with a range of growth conditions to explore key growth modulators governing the tribological response of this material. These coatings were then characterized with Raman spectroscopic analysis at three different wavelengths. Pin-on-disc friction response of these coatings with 319 Al showed that the trans-polyacetylene content as determined by the respective Raman spectrum in NCD is the critical factor controlling friction behavior. This finding can have significant implications in other similar applications where friction response of NCD is a key design factor.

Boron Doped Nanocrystalline Diamond Grown on Reticulated Vitreous Carbon: Morphological, Structural, and Electrochemical Characterizations

Reticulated vitreous carbon (RVC) is a macroporous material with high surface area, rigid structure, low resistance to fluid flow and high thermal and electrical conductivities. RVC has a wide range of applications as porous electrodes, high temperature insulation, filters, storage batteries, among others. Composites formed from diamond grown on sp2 bonded carbonaceous materials have already been studied, but there are still few publications about the electrochemical properties of this material. Then, the study of new hybrid nanomaterials is very important for understanding and promoting new technologies. In this work, boron-doped nanocrystalline diamond (BDND) films were deposited on RVC heat treated until 1000 °C and 1700 °C in order to evaluate the influence of different structural organization indexes of RVC on the nanocrystalline diamond grains formation as well as on their electrochemical performance. RVC was processed using poly(furfuryl) alcohol and polyurethane foams with 70 ppi (pores per inch) as mold. RVC substrates surfaces were prepared using seeding treatment in which samples are dipped in a 10 wt% solution of Poly diallyldimethylammonium chloride (PDDA) during 30 min followed by immersion in a nanodiamond (4nm) seeding dispersion for 10 min. The seeding step is necessary to improve diamond growth on carbon fiber in order to keep the surface carbon in sp3 configuration dominant over sp2 bond etching during diamond film growth. BDND films were grown on RVC heat treated until 1000 °C and 1700 °C using a hot-filament chemical vapor deposition (HFCVD) reactor. The boron doping was performed by dissolving B2O3 in methanol in a bubbler attached to the reactor. The solution was prepared with a concentration of B2O3 dissolved in CH3OH that correspond to B/C ratio of 30000 ppm. Hydrogen gas was used as a carrier with a constant flow of 30 sccm. The composites were evaluated by Scanning Electron Microscopy (SEM), Raman spectroscopy and cyclic voltammetry. Raman spectra and SEM images confirmed the BDND films achievement showing the RVC completely covered by a diamond coating. The electrochemical measurements were made by using Autolab PGSTAT 302 equipment with a three-electrode cell. The BDND/RVC composites obtained with different RVC heat treatment temperature (HTT), were used as working electrode. A platinum coil wire served as the counter electrode and Ag/AgCl was used as the reference electrode. The voltammetric curves (VC) were taken in H2SO4 0.5 mol.L-1 and showed a standard wide potential window as expected for BDND electrodes. In order to characterize the electrochemical kinetic we have applied CV using the redox couple of Fe(CN)6 3-/4- with different scan rates. This redox system includes reactions that depend on the specific interactions with the surface electrode. Besides, the electrode kinetics for this kind of redox couple tends to be more sensitive to the surface functionalities on sp2-bonded carbon electrodes. The BDND grown on RVC with higher HTT demonstrated the fast kinetics attributed to the better conductivity of such substrate.

Effects of Various Seeding Methods on Multi-Layered Diamond Coatings Deposited via Hot Filament Chemical Vapor Deposition

Multi-layer alternating nanocrystalline diamond (NCD) layer and polycrystalline diamond (PCD) layer was successfully deposited on pretreated tungsten carbide (WC) substrates with various seeding sizes (<0.1μm synthetic, <0.5μm synthetic, <0.25μm natural, <0.5μm natural, and <1μm natural) diamond with and without hammering by silicon carbide. X-rays penetrate through the coating to the substrate from XRD method was able to show strong peaks of diamond relative to WC despite the diamond film being 4μm thick only. It is found that substrates with no hammering produce stronger signals. The coating was cross sectioned and analysed using field emission scanning electron microscopy showing the multi-layer with NCD grains that has coalesced and columnar structure for PCD. None of the diamond coating delaminated during cross sectioning showing good adhesion. Raman was able to capture data from the 1-1.6μm thick NCD layer only while AFM measured the extreme low roughness of the NCD surface.

Local bond length variations in boron-doped nanocrystalline diamond measured by spatially resolved electron energy-loss spectroscopy

Variations in local bond length and coordination in boron-doped nanocrystalline diamond (NCD) films have been studied through changes in the fine structure of boron and carbon K-edges in electron energy-loss spectra, acquired in a scanning transmission electron microscope. The presence of high concentrations of B in pristine diamond regions and enrichment of B at defects in single NCD grains is demonstrated. Local bond length variations are evidenced through an energy shift of the carbon 1s → σ* edge at B-rich defective regions within single diamond grains, indicating an expansion of the diamond bond length at sites with local high B content.

Mechanisms of time-modulated polarized nano-crystalline diamond growth

Two bilayer systems (TaN/Mo and ZrN/Mo) have been deposited onto WC–Co cermets in order to limit the cobalt diffusion from this substrate and to promote the diamond nucleation. Mo was the top layer. The diamond CVD coating process includes two steps: 1) Bias Enhance Nucleation (BEN) step for diamond nucleation control, 2) diamond growth step with a time-modulated negative substrate polarization to form nanocrystalline diamond grains (NCD). Original cluster morphology of diamond film was obtained, and patented under the name PyrNCD (for pyramidal NCD). Clusters are multilayered and composed of two diamond layers (resp. grain sizes: about 1nm and 10nm) periodically repeated. Thermomechanical computations have been carried out to understand the stress distribution inside the multilayer systems before and after diamond deposition. Computation results demonstrate that the architecture of the system is optimized and the morphology of PyrNCD diamond clusters should not degrade their substrate adhesion. A mechanism for the formation of the diamond layer is proposed for a time-modulated polarized diamond growth process to understand the formation of both the specific morphology and the NCD grains.

Effects of annealing temperature on the microstructure and p-type conduction of B-doped nanocrystalline diamond films

Annealing of different temperatures was performed on boron-doped nanocrystalline diamond (BDND) films synthesized by hot filament chemical vapor deposition (HFCVD). Effects of annealing temperature on the microstructural and electrical properties of BDND films were systematically investigated. The Hall-effect results show that smaller resistivity and Hall mobility values as well as higher carrier concentration exist in the 5000 ppm boron-doped nanocrystalline diamond film (NHB) as compared with those in 500 ppm boron-doped nanocrystalline diamond film (NLB). After 1000 ℃ annealing, the Hall mobility of NLB and NHB samples were 53.3 and 39.3 cm2·V-1·s-1, respectively, indicating that annealing increases the Hall mobility and decreases the resistivity of the films. HRTEM, UV, and visible Raman spectroscopic results show that the content of diamond phase in NLB samples is larger than that in NHB samples because higher B-doping concentration results in a greater lattice distortion. After 1000 ℃ annealing, the amount of nano-diamond phase of NLB and NHB samples both increase, indicating that a part of the amorphous carbon transforms into the diamond phase. This provides an opportunity for boron atoms located at the grain boundaries to diffuse into the nano-diamond grains, which increases the concentration of boron in the nano-diamond grains and improves the conductivity of nanocrystalline diamond grains. It is observed that 1000 ℃ annealing treatment is beneficial for lattice perfection of BDND films and reduction of internal stress caused by doping, so that the electrical properties of BDND films are improved. Visible Raman spectra show that the trans-polyacetylene (TPA) peak (1140 cm-1) disappears after 1000 ℃ annealing, which improves the electrical properties of BDND films. It is suggested that the larger the diamond phase content, the better lattice perfection and the less the TPA amount in the annealed BDND samples that prefer to improve the electrical properties of BDND films.

Sensitivity of Diamond-Capped Impedance Transducer to Tröger’s Base Derivative

Sensitivity of an intrinsic nanocrystalline diamond (NCD) layer to naphthalene Tröger's base derivative decorated with pyrrole groups (TBPyr) was characterized by impedance spectroscopy. The transducer was made of Au interdigitated electrodes (IDE) with 50 μm spacing on alumina substrate which were capped with the NCD layer. The NCD-capped transducer with H-termination was able to electrically distinguish TBPyr molecules (the change of surface resistance within 30-60 kΩ) adsorbed from methanol in concentrations of 0.04 mg/mL to 40 mg/mL. An exponential decay of the surface resistance with time was observed and attributed to the readsorption of air moisture after methanol evaporation. After surface oxidation the NCD cap layer did not show any leakage due to NCD grain boundaries. We analyzed electronic transport in the transducer and propose a model for the sensing mechanism based on surface ion replacement.

Nanocrystalline diamond coating on carbon fibers produced at different temperatures: Morphological, structural and electrochemical study

In this paper, the morphological, structural and electrochemical properties of nanocrystalline diamond (NCD) films grown on carbon fibers (CF) were investigated. The CF substrates were produced at three different heat treatment temperatures (HTT):1000, 1500 and 2000°C. The HTT variation promoted different organization indexes on the CF structures. Consequently, the NCD coating formation was strongly affected by the substrate HTT. The changes in the properties of the diamond films were discussed as a function of the film morphology evolution using CH4 flow rate of 0.25, 0.5 and 1.0sccm in the feed gas. The X-ray diffraction measurements for the CF and NCD/CF composites were determinant to characterize the crystallinity of the NCD films as a function of the CF HTT and of the CH4 addition. Based on the diffractograms, the Scherrer's equation was applied to the (111) NCD peak, resulting in grain size values varying from 11.0 to 5.0nm depending on the CH4 flow rate and on the CF HTT. The scanning electron microscopy images confirmed the deposition of a continuous NCD coating with high nucleation rate covering the whole CF, while their quality was analyzed by Raman spectroscopy measurements. The NCD grain agglomerates increased as a function of the increase in the CH4 flow rate from 0.25 to 1.0sccm, showing similar film morphology to that of the unfaceted diamond balls obtained by chemical vapor deposition. This behavior confirmed the expected tendency by decreasing the diamond quality with the CH4 addition, especially for the films grown on CF treated at 1500 and 2000°C. This performance was also corroborated by the cyclic voltammetry measurements concerning the electrode potential window and their responses in a redox couple.