Vapor Deposited Diamond Films Research Articles

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.

J044094 研摩ダイヤモンド膜と金属の間の低摩擦摺動における速度依存性評価([J04409]知的材料・構造システム(9))

Institute of Fluid Science, Tohoku University Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, JapanChemical vapor deposition (CVD) diamond film is well known as the material of high hardness, good wear resistance and so on. It is suitable for the maintenance free solid lubrication film for sliding bearing, but as-deposited CVD diamond films have a rough surface which induces high friction and severe abrasion. To realize the low frictional properties, diamond films have to be well polished or deposited as smooth surfaces. We have developed the deposition process for easy abrasable diamond films. These kinds of diamond films are moderately polished and show a stable low friction between films and steel pins in dry air. In addition, the extremely low friction phenomena of noiseless sliding between films and counter metals were realized as relatively higher sliding speed. These phenomena are similar to a certain type of air bearing. In the present study, we evaluate the sliding speed and contact pressure dependency of the friction properties on polished diamond films. The friction properties between polished diamond films and an AISI440C pin under dry condition were performed in the atmosphere. Definite reductions of the friction coefficient obtained by the sliding speed and contact pressure dependence measurements were clearly observed.

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.

Zero-bias operation of polycrystalline chemically vapour deposited diamond films for Intensity Modulated Radiation Therapy

A detailed investigation of the performance as a dosimeter of state-of-art polycrystalline CVD (pCVD) diamond detectors operated in photovoltaic regime for applications in clinical radiotherapy has been carried out with conventional 6–10–18 MV X-photons, as well as with a 10 MV photon Intensity Modulated Radiation Therapy (IMRT) beam from a linear accelerator. Our results show that the performances of a pCVD diamond dosimeter improves dramatically when operated in null-bias conditions. Main improvements with respect to operation with an external voltage applied are: a reduced pre-irradiation dose; an excellent time stability, characterised by standard deviations less than 0.5%; a rise-time comparable to that of commercial reference dosimeters; a linearity with dose proven over three decades; a reduced deviation from linearity of the current vs. dose–rate curve, output factors comparable to that of commercial reference dosimeters. These results represent a significant step towards clinical applications as IMRT with synthetic polycrystalline CVD diamond films.

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.

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.

Alternating-current and direct-current electrical transport properties of diamond diodes with diamond surfaces of the different morphology

The alternating current (ac) conductance (f=200 Hz) was measured as a function of applied voltage at ambient temperature for two diodes with aluminium/diamond rectifying contacts on chemical vapour-deposited diamond films of 5 μm in thickness with different morphology, nucleation and growth surfaces. Comparison of direct current (dc) conductance curves (deduced from experimental current–voltage curves) with ac conductance curves for the diodes revealed different transport mechanisms for two interfaces. The current–voltage characteristic of gold/diamond/gold structures shows that the two interfaces have different resistance values. The results demonstrate that the nucleation surface has a greater surface density of states than the growth surface, and this contributes to electrical transport through the potential barrier. Cole–Cole curves show a discrepancy between the Debye semicircle and experimental results and illustrate the fundamental differences between the two diodes. These results provide additional proof that the principal source of dispersion admittance is the surface states. The current–voltage characteristic of diamond diodes with diamond films of 1 μm in thickness shows two distinct resistance states (high and low resistance). By applying an appropriate bias, resistance switching from one state to the other state can be achieved. The experimental results are discussed on the basis of filamentary conduction

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.

A Survey of the Machining Characteristics and Mechanical Polishing Technology of CVD Diamond Films

The rough surfaces and non-uniform thicknesses of chemically vapor-deposited (CVD) diamond films and substrates affect their industrial application. In recent years, many polishing and planarization methods have been reported, but each method has its relative merits. This paper reviews the necessity for processing of the CVD diamond films first. Then the processing mechanism of micro-cracking and the characteristics of mechanical polishing of diamond films are discussed. The remove form of the material and surface characteristics are compared by three mechanical polishing method, including free abrasive polishing, fixation abrasive polishing and membrane on the membrane polishing method. No matter what form of mechanical polishing process is adopted, because of its inherent characteristics and the principles of processing, mechanical polishing CVD diamond films can only be as polish processing to remove large residual. The macro-surface roughness of processing is about the 2μm. The micro-rough surface roughness is for the 40nm or so. The material removal rate is 10nm/h.