Chemical Vapor Deposited Diamond Films Research Articles

Orientation degree characterization of diamond etched with Ce-7%Fe alloy

An increasing {110} orientation degree behavior was observed during etching of chemical vapor deposition (CVD) diamond films by partially melting Ce-7%Fe alloys. In order to accurately investigate this phenomenon, the X-ray diffraction method was used to identify the changes in the surface crystal orientation of the diamond films etched by Ce-7%Fe alloys, and evolution of orientation along the growth direction of the un-etched diamond film was analyzed by electron backscattering diffraction (EBSD), and then the morphology of etched diamond surface was observed by scanning electron microscopy (SEM). The results showed that the {110} orientation degree of diamond surface increased due to the anisotropy in diamond etching with Ce-7%Fe, which was verified by the etching “pit” in SEM micrographs.

Priming effect on a polycrystalline CVD diamond detector under 60Co γ-rays irradiation

The priming effect on a polycrystalline chemical vapor deposition (CVD) diamond film detector caused by irradiation with 60Co γ-rays has been investigated. Charge collection efficiencies of the detector for α-particles and γ-rays detection were determined in both the normal state and the pumped state. The duration of the priming effect and its relationship with bias voltage were also studied. The results show that the priming effect may clearly improve charge collection efficiency, with an increase of 6% for α-particles and 13% for γ-rays at 600V saturation bias voltage. The priming effect can be completely retained for 40min after irradiation, and it begins to gradually disappear within 12h. In addition, the effect is more easily induced when bias voltage is applied than in the absence of any bias voltage. The experiments also demonstrated that irradiation incident on the growth surface may induce higher charge collection efficiency than irradiation incident on the substrate surface.

Freestanding single crystal chemical vapor deposited diamond films produced using a lift-off method: Response to α-particles from 241Am and crystallinity

Thick (∼100μm) undoped diamond films were grown homoepitaxially on single crystal (SC) diamond substrates by microwave plasma chemical vapor deposition (CVD). To form a freestanding SC diamond film (plate), the substrate was pre-ion-implanted with high-energy ion beams before the film growth, and after the thick-film deposition, the substrate was eliminated using a lift-off method, resulting in fabrication of a SC CVD diamond plate. Two samples were prepared; sample 1 was grown on a (001) oriented, nitrogen doped CVD SC diamond at ∼900°C with the input microwave power of 1.7kW, while sample 2 was grown on a (001) oriented, high-pressure high-temperature synthesized type-Ib SC diamond at ∼900°C with the input microwave power of 1.25kW. The formed SC plates have high optical transparencies, indicating no remarkable optical absorptions seen in the wavelength from ultraviolet to near infrared. The photoluminescence (PL) spectra of both samples show strong free exciton FE peaks, while in sample 2 relatively strong optical emissions corresponding to nitrogen related centers were observed in the visible region. After the metal electrodes were formed on both faces of the SC diamond plate to fabricate a sandwich-type diamond particle detector, the energy spectra of 5.486MeV α-particles from 241Am were measured. The charge collection efficiencies (CCEs) of sample 1 were CCE=98% for a hole transport and CCE=89% for an electron transport, respectively, while CCEs of sample 2 were CCE=80% for a hole transport and CCE=78% for an electron transport, respectively. These results indicate that both holes and electrons in sample 2 were trapped much more than those in sample 1. Possible candidates of carrier capture centers are nitrogen and/or nitrogen-vacancy centers observed in PL, nonradiative defect (complex) centers, extended defects such as threading dislocations observed in micrographs taken with polarizers. The different growth conditions most likely affected crystallinity and responses to α-particles of the samples.

Growth and electron field emission of ZnO nanorods on diamond films

Zinc oxide (ZnO) nanorods grown on chemical vapor deposited diamond films by thermal vapor transport method have been investigated. In the initial growth status, the semi-spherical ZnO nuclei were preferably deposited near the growth steps on the terraces and the boundaries of diamond grains. With increasing the growth time, the [0 0 0 1] orientated ZnO nanorods appeared and further covered the whole diamond film. It is found that the size of diamond grains would determine the diameter of ZnO nanorods. The electron field emission properties of the ZnO nanorods/diamond system have been significantly improved with respect to pure diamond film. The feature of the ZnO nanorods grown on diamond films played an important role in further enhancing the electron field emission performances.

微喇曼和红外光谱法研究化学气相沉积金刚石多晶膜结晶质量特性

The relation between macro-properties and micro-quantities of the large-grained polycrystalline chemical vapour deposited diamond films was investigated.Considering the growth non-uniformity,the micro-Raman spectra measured on the top growth surface show large variation from spot to spot.Whereas,the micro-Raman spectra taken on the fine-grained smooth interface of the diamond films show that small deviation and generally can represent the overall quality of the large-grained polycrystaline diamond films,and correlate well with hydrogen content of the film measured by Fourier-transform infrared spectroscopy.It can be concluded that a diamond film with darker color or lower transparency has lower quality and lower phase purity characterized by the larger full width at half maximum(FWHM) and lower intensity of the diamond Raman peak around 1 332 cm-1.

Simulations of chemical vapor deposition diamond film growth using a kinetic Monte Carlo model and two-dimensional models of microwave plasma and hot filament chemical vapor deposition reactors

A one-dimensional kinetic Monte Carlo (KMC) model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model considers adsorption, etching/desorption, lattice incorporation and surface migration but not defect formation or renucleation processes. Two methods have been devised for estimation of the gas phase concentrations of species at the growing diamond surface, and are used to determine adsorption rates for C1Hx hydrocarbons for the different conditions. The rate of migration of adsorbed carbon species is governed by the availability of neighboring radical sites, which, in turn, depend upon the rates of H abstraction and of surface-radical migration. The KMC model predicts growth rates and surface roughness for each of diamond types consistent with experiment. In the absence of defect formation and renucleation the average surface diffusion length, ℓ, is a key parameter controlling surface morphology. When ℓ<2, surface migration is limited by the lack of availability of surface radical sites, and the migrating surface species simply hop back and forth between two adjacent sites but do not travel far beyond their initial adsorption site. Thus, Eley–Rideal processes dominate the growth, leading to the rough surfaces seen in NCD and UNCD. The maximum or “intrinsic” surface roughness occurs for nominally zero-migration conditions (ℓ=0) with an rms value of approximately five carbon atoms. Conversely, when migration occurs over greater distances (ℓ>2), Langmuir–Hinshelwood processes dominate the growth producing the smoother surfaces of MCD and SCD. By extrapolation, we predict that atomically smooth surfaces over large areas should occur once migrating species can travel approximately five sites (ℓ∼5). β-scission processes are found to be unimportant for MCD and SCD growth conditions, but can remove up to 5% of the adsorbing carbon for NCD and UNCD growth. C1Hx insertion reactions also contribute <1% to the growth for nearly all conditions, while C2Hx (x<2) insertion reactions are negligible due their very low concentrations at the surface. Finally, the predictions for growth rate and morphology for UNCD deposition in a microwave system were found to be anomalous compared to those for all the other growth conditions, suggesting that carbonaceous particulates created in these plasmas may significantly affect the gas chemistry.

Microstructure and tribological performance of self-lubricating diamond/tetrahedral amorphous carbon composite film

In order to smooth the rough surface and further improve the wear-resistance of coarse chemical vapor deposition diamond films, diamond/tetrahedral amorphous carbon composite films were synthesized by a two-step preparation technique including hot-filament chemical vapor deposition for polycrystalline diamond (PCD) and subsequent filtered cathodic vacuum arc growth for tetrahedral amorphous carbon (ta-C). The microstructure and tribological performance of the composite films were investigated by means of various characterization techniques. The results indicated that the composite films consisted of a thick well-grained diamond base layer with a thickness up to 150μm and a thin covering ta-C layer with a thickness of about 0.3μm, and sp3-C fraction up to 73.93%. Deposition of a smooth ta-C film on coarse polycrystalline diamond films was proved to be an effective tool to lower the surface roughness of the polycrystalline diamond film. The wear-resistance of the diamond film was also enhanced by the self-lubricating effect of the covering ta-C film due to graphitic phase transformation. Under dry pin-on-disk wear test against Si3N4 ball, the friction coefficients of the composite films were much lower than that of the single PCD film. An extremely low friction coefficient (∼0.05) was achieved for the PCD/ta-C composite film. Moreover, the addition of Ti interlayer between the ta-C and the PCD layers can further reduce the surface roughness of the composite film. The main wear mechanism of the composite films was abrasive wear.

Field Emission Property of Hydrogenated Chemical Vapor Deposited Diamond Films Studied by Scanning Tunneling Microscopy

By using scanning tunneling microscopy, the plots of tunneling current versus applied voltage, at the local points for hydrogenated and oxygenated chemical vapor deposited diamond films, were investigated. For comparison, the measurement points were adopted on the centers of the crystalline grains and at the grain boundaries, respectively. The results indicated that, for the hydrogenated chemical vapor deposited diamond, the field emission character is much better on the center of the crystalline grains than at the grain boundary. In contrast, for the oxygenated samples, the crystalline grains show a poor field emission character. The two diamond surfaces exhibit similar field emission characters at the grain boundaries. The surface emission mechanisms of the hydrogenated chemical vapor deposited diamond films were also discussed.

Thermodiffused vanadium carbide interface for diamond films on steel and cemented carbides substrates

In this work an interface is studied and proposed for chemical vapour deposition (CVD) diamond films on sintered carbides and steel substrates, the most relevant tooling materials for mechanical applications. It consists of a thermoreactive deposited and diffused vanadium carbide layer. This interface presents good characteristics for diamond films deposition: high adherence to substrates, favourable thermal expansion coefficient, high hardness and high mechanical strength. Good quality and adherent diamond films are obtained and its characteristics are evaluated by SEM, X-ray diffraction, Raman spectroscopy and indentation tests. For sintered carbides substrates, typical Raman shift of 4·1 cm−1 is obtained, equivalent to compressive residual stresses of 1·4 GPa applied from the substrate to CVD diamond films through vanadium carbide interlayer. For steel substrates, Raman shift reached 20·1 cm−1, corresponding to 6·93 GPa compressive stress applied from substrate to diamond films through VC interlayer, evidencing the mechanical strength of the VC diamond film coatings.

Newly Designed Glass Scribing Wheel Made of Chemical Vapor Deposition Diamond Film

Scribing wheel (SW) is an important tool for separating glass panels in thin-film transistor liquid crystal display industry. In this study, unlike the traditional SW completely made of polycrystalline diamond (PCD) or cemented tungsten carbide (c-WC), an alternative partially taking advantage of chemical vapor deposition diamond (CVDD) was newly developed. The fabrication of such unique sandwich-like CVDD-SW combined hot filament chemical vapor deposition (HFCVD), welding, and other machining processes. Both hard CVDD scribing edge and tough c-WC supporting layers contributed to SW structure. CVDD was prepared by adjusting the concentration of methane fed into HFCVD chamber. Morphological observation confirmed the reproducibility of microcrystal diamond (MCD), submicrocrystal diamond (SMCD), and nanocrystal diamond (NCD) diamond. Besides grain size, the existence of columnar structure, the nondiamond carbon content, the residual stress, and I(220)/I(111) ratio of CVDD films were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Based on results, SMCD was predicted as the optimized CVDD for making a scribing edge. After three CVDD films were respectively integrated into SW, this prediction was supported by preliminary scribing test. Selecting Corning-1737 as the cutting object, among three CVDD-SWs and one self-made PCD-SW, only the scribing edge of SMCD-SW kept almost undamaged. The outperformance of our design was thus confirmed.

Linear–supralinear–sublinear beta‐ray dose dependences of TL, OSL and afterglow in undoped CVD diamond

AbstractThe thermoluminescence (TL), optically stimulated luminescence (OSL) and afterglow (AG) properties of chemical vapour deposition (CVD) diamond film irradiated by beta rays with doses from 0.5 to 1000 Gy have been studied. The film (23 µm) was grown for 47 h on monocrystalline silicon. The TL dose responses are similar for all the peaks and exhibit the typical linear–supralinear–sublinear behaviour. The supralinear growth starts at about 1.0 Gy and goes up to 100 Gy. At higher doses the dose responses go to saturation. The AG and OSL dose responses are similar to the TL one and exhibit the supralinear–sublinear behaviour. The linear part (if it exists) is not observed due to low AG and OSL intensity at doses lower than 2.0 Gy. The diamond film that had been irradiated with high doses, partially preheated and irradiated again with low test dose, exhibits increased TL, OSL and AG sensitivity that can be considered as a mixture of the supralinearity and sensitization. Pure sensitization is observed for the 350 and 400 K TL peaks and AG after preheating the sample to temperatures higher than 500 K. This sensitization gradually decreases from 10 to 1 as the preheating increases from 500 to 770 K.

Comparative Studies on the Cutting Performance of HFCVD Diamond and DLC Coated WC-Co Milling Tools in Dry Machining Al/SiC-MMC

The chemical vapor deposition (CVD) diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC-Co) cutting tools respectively using the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode. The scanning electron microscope (SEM), optical interferometer profiler and Raman spectroscopy were adopted to characterize the as-deposited diamond and DLC films. The cutting performance of as-fabricated CVD diamond and DLC coated milling tools is evaluated in dry milling SiC particulate reinforced Al-metal matrix composite material (Al/SiC-MMCs), comparing with the uncoated WC-Co milling tool. The milling results demonstrate that the uncoated WC-Co milling tool suffers severest wear in its circumferential cutting edge, while the wear of DLC coated milling tool is slightly lower. Comparatively, the CVD diamond coated milling tool exhibits much stronger wear resistance. The wear on its circumferential cutting edge is less than 0.07 mm at the end of milling test, only a half of that of DLC coated milling tool. This result is attributed to the extremely high hardness and strong adhesive strength of CVD diamond film covered on the WC-Co milling tool.

Dose rate effects on the performance of MWCVD diamond films as TL gamma radiation dosimeter

AbstractDose rate effects on the thermoluminescence (TL) properties of undoped and 750 ppm nitrogen doped microwave chemical vapor deposition (MWCVD) diamond films were analyzed. The diamond samples were exposed to 2.4–20.67 Gy/min dose rates from a 60Co source. The TL glow curve of undoped sample showed no apparent dose rate effects. The doped diamond film exhibited dose rate effects consisting in a 10–30% integrated TL increase as the dose rate increased. The TL response as a function of dose rates showed a nonlinear behavior for the doped sample contrary to the undoped diamond film. The dose rate effects were evaluated through the determination of the kinetics parameters by fitting of the TL glow curves. The results indicate that chemical vapor deposition (CVD) diamond may present some dose rate effects on the TL properties in a given dose range, implying that some care should be exercised in order to use CVD diamond films in radiation dose assessments.

Morphology and bonding states of chemical vapor deposition diamond films nucleation surface

The morphology and chemical bonding of the nucleation surface of polycrystalline diamond films were studied following the removal of the silicon substrate by acid etching and mild plasma cleaning. Atomic force microscopy characterization of this surface revealed a mosaic structure of cracks arranged in hexagonal patterns. These cracks are correlated with etched twin grain boundaries that surrounded hexagonal diamond crystals at the initial growth stages of the diamond films. High resolution electron energy loss spectroscopy studies indicate that mild annealing of the diamond film caused desorption of various oxides exposing a damaged diamond surface.

Investigating point defects in irradiated boron-doped diamond films by temperature-dependent electrical properties and scanning tunneling microscopy and spectroscopy

We report temperature-dependent electrical resistivity (or dc conductivity, σdc) down to 4 K for pristine and gamma-irradiated microwave plasma-assisted chemical vapor-deposited boron-doped diamond films with [B]/[C]gas = 4000 ppm to gain insights into the nature of conduction mechanism, distribution, and kinetics of point defects generated due to gamma irradiation prompted by the article [Gupta et al., J. Mater. Res.24, 1498 (2009)]. The pristine samples exhibit typical metallic conduction up to 50 K and with reduction in temperature to 25 K, the σdc decreases monotonically followed by saturation at 4 K, suggesting “disordered” metal or “localized” behavior. For irradiated films, continuous increasing resistivity with decreasing temperature demonstrates semiconducting behavior with thermal activation/hopping conduction phenomena. It is intriguing to propose that irradiation leads to substantial hydrogen redistribution leading to unexpected low-temperature resistivity behavior. Scanning tunneling microscopy/spectroscopy helped to illustrate local grain and grain boundary effects.

A review of crystallographic textures in chemical vapor-deposited diamond films

Diamond is one of the most important functional materials for film applications due to its extreme physical and mechanical properties, many of which depend on the crystallographic texture. The influence of various deposition parameters matters to the texture formation and evolution during chemical vapor deposition (CVD) of diamond films. In this overview, the texture evolutions are presented in terms of both simulations and experimental observations. The crystallographic textures in diamond are simulated based on the van der Drift growth selection mechanism. The film morphology and textures associated with the growth parameters α (proportional to the ratio of the growth rate along the 〈100〉 direction to that along the 〈111〉 direction) are presented and determined by applying the fastest growth directions. Thick films with variations in substrate temperature, methane concentration, film thickness, and nitrogen addition were analyzed using high-resolution electron back-scattering diffraction (HR-EBSD) as well as X-ray diffraction (XRD), and the fraction variations of fiber textures with these deposition parameters were explained. In conjunction with the focused ion beam (FIB) technique for specimen preparation, the grain orientations in the beginning nucleation zones were studied using HR-EBSD (50 nm step size) in another two sets of thin films deposited with variations in methane concentration and substrate material. The microstructures, textures, and grain boundary character were characterized. Based on the combination of an FIB unit for serial sectioning and HR-EBSD, diamond growth dynamics was observed using a 3D EBSD technique, with which individual diamond grains were investigated in 3D. Microscopic defects were observed in the vicinity of the high-angle grain boundaries by using the transmission electron microscopy (TEM) technique, and the advances of TEM orientation microscopy make it possible to identify the grain orientations in nano-crystalline diamond.

Microtexture and Grain Boundaries in Freestanding CVD Diamond Films: Growth and Twinning Mechanisms

AbstractThree groups of free‐standing chemical vapor deposition (CVD) diamond films formed with variations in substrate temperature, methane concentration, and film thickness are analyzed using high‐resolution electron back‐scattering diffraction. Primarily {001}, {110}, and {111} fiber textures are observed. In addition, corresponding primary and higher order twinning components are found. As interfaces, high angle, low angle, primary twin, and secondary twin boundaries are observed. A growth and a twinning model are proposed based on the sp3 hybridization of the bond in the CH4 molecule that is used as the deposition medium.

Simultaneous measurement of thermal conductivity and interface thermal conductance of diamond thin film

The authors developed an experimental method that can measure the in-plane thermal conductivity of a thin film and the interface thermal conductance between the film and the metal strip, simultaneously. This technique, the in-plane 3ω method, can be applied to the films with very high thermal conductivity such as diamond films. To guarantee the reliability of the measurement, the factors causing error were analyzed rigorously. Then, the method was demonstrated on silicon dioxide and silicon nitride films and was valid in experiments performed in the open atmosphere. They also applied the method on several chemical vapor deposited diamond films of different thicknesses and pretreatment methods. The data are comparable with those from previous researches.

Enhanced field emission from ZnO nanoneedles on chemical vapour deposited diamond films

ZnO nanoneedles were coated on hot filament chemical vapour deposited diamond thin films to enhance the field emission properties of ZnO nanoneedles. The virgin diamond films and ZnO nanoneedles on diamond films were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The field emission studies reveal that the ZnO nanoneedles coated on diamond film exhibit better emission characteristics, with minimum threshold field (required to draw a current density ~ 1 μA/cm 2) as compared to ZnO needles on silicon and virgin diamond films. The better emission characteristic of ZnO nanoneedles on diamond film is attributed to the high field-enhancement factor resulting due to the combined effect of the ZnO nanoneedles and diamond film.

Modulation of Electron Transfer Activity at Diamond Films by Dissolved Oxygen in Aqueous Solution

The electron transfer activities of conductive undoped, boron-doped, and sulfur-doped chemical vapor-deposited diamond films were observed in terms of increases or decreases in both hydrogen and oxygen evolution, i.e., over a wide potential range, as modulated by the presence or the absence of dissolved oxygen as a typical oxidant in an aqueous acid solution. The electrochemical behavior of n-type sulfur-doped nanocrystalline chemical-vapor-deposited diamond films was such that the current corresponding to the electrochemical hydrogen evolution decreased reversibly in the presence of dissolved oxygen in the solution, in contrast to the behavior of the p-type materials, boron-doped (microcrystalline) and undoped (nanocrystalline) diamonds. For the sulfur-doped film, we propose that the presence of oxygen at the interface may cause a decrease in the number of majority carrier electrons near the surface. The influence of the doping levels of sulfur in the diamond films on the films’ oxygen sensitivities was examined in detail. We propose that the electron transfer activity, modulated by the concentration of oxygen dissolved in an aqueous solution, necessitates the development of a model for the electrochemical behavior of the types of diamond films examined in the present work.