Vapor Deposited Diamond Films Research Articles

The Stability of Straightened Ta Filament During Chemical Vapor Deposition of Diamond Film

Maintaining the geometrical stability of hot filament is a challenge in chemical vapor deposition (CVD) over a larger area since deformation varies the distance between the filament and the substrate and, consequently, destroys the uniformity of diamond deposition. Herein, Ta filament is straightened with a tensile stress ranging from 4.40 to 11 MPa to suppress deformation, and the stability during the CVD process of diamond film is evaluated. Scanning electron microscopy and energy dispersive X‐ray are further utilized to investigate the morphological and structural evolutions of Ta filament. Results show that straightened Ta filament maintains geometrical stability without any visible deformation or breakage and uniform deposition of diamond film is obtained through Ta filament undergone a transformation from Ta to Ta2C and then to TaC. At high deposition pressure (7 kPa) or a low concentration of methane (1%), the straightened Ta filament goes through a moderate transformation, which implies the cracks caused by rough transformation can be avoided, thus prolonging the lifetime of straightened Ta filament. These works provide significant guidelines for the large‐scale manufacture of diamond deposition.

Super High-Concentration Si and N Doping of CVD Diamond Film by Thermal Decomposition of Silicon Nitride Substrate.

The high-concentration N doping of diamond film is still a challenge since nitrogen is limited during diamond growth. In this work, a novel method combined with the thermal decomposition of silicon nitride was proposed to form the activated N and Si components in the reactor gas that surrounded the substrate, with which the high-concentration N and Si doping of diamond film was performed. Meanwhile, graphene oxide (GO) particles were also employed as an adsorbent to further increase the concentration of the N element in diamond film by capturing the more decomposed N components. All the as-deposited diamond films were characterized by scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. For the pure diamond film with a growth time of 0.5 h, the N and Si concentrations were 20.78 and 41.21 at%, respectively. For the GO-diamond film, they reached 47.47 and 21.66 at%, which set a new record for super high-concentration N doping of diamond film. Hence, thermal decomposition for the substrate can be regarded as a potential and alternative method to deposit the chemical vapor deposition (CVD) diamond film with high-concentration N, which be favorable for the widespread application of diamond in the electric field.

Effects of metal layers on chemical vapor deposition of diamond films

Abstract Diamond is recognized as one of the most promising wide bandgap materials for advanced electronic applications. However, for many practical uses, hybrid diamond growth combining metal electrodes is often demanded. Here, we present the influence of thin metal (Ni, Ir, Au) layers on diamond growth by microwave plasma chemical vapor deposition (MWCVD) employing two different concepts. In the first concept, a flat substrate (GaN) was initially coated with a thin metal layer, then exposed to the diamond MWCVD process. In the second concept, the thin diamond film was firstly formed, then it was overcoated with the metal layer and finally, once again exposed to the diamond MWCVD. It should be mentioned that this concept allows the implementation of the metal electrode into the diamond bulk. It was confirmed that the Ni thin films (15 nm) hinder the formation of diamond crystals resulting in the formation of an amorphous carbon layer. Contrary to this finding, the Ir layer resulted in a successful overgrowth by the fully closed diamond film. However, by employing concept 2 (ie hybrid diamond/metal/diamond composite), the thin Ir layer was found to be unstable and transferred into the isolated clusters, which were overgrown by the diamond film. Using the Au/Ir (30/15 nm) bilayer system stabilized the metallization and no diamond growth was observed on the metal layer.

Suppression and compensation effect of oxygen on the behavior of heavily boron-doped diamond films

This work investigates the suppression and compensation effect of oxygen on the behaviors and characteristics of heavily boron-doped microwave plasma chemical vapor deposition (MPCVD) diamond films. The suppression effect of oxygen on boron incorporation is observed by an improvement in crystal quality when oxygen is added during the diamond doping process. A relatively low hole concentration is expected and verified by Hall effect measurements due to the compensation effect of oxygen as a deep donor in diamond. A low acceptor concentration, high compensation donor concentration and relatively larger acceptor ionization energy are then induced by the incorporation of oxygen; however, a heavily boron-doped diamond film with high crystal quality can also be expected. The formation of an oxygen–boron complex structure instead of oxygen substitution, as indicated by the results of x-ray photoelectron spectroscopy, is suggested to be more responsible for the observed enhanced compensation effect due to its predicted low formation energy. Meanwhile, density functional theory calculations show that the boron–oxygen complex structure is easily formed in diamond with a formation energy of –0.83 eV. This work provides a comprehensive understanding of oxygen compensation in heavily boron-doped diamond.

Control of Spindle Position and Stiffness of Aerostatic-Bearing-Type Air Turbine Spindle

Air turbine spindles with aerostatic bearings are widely used in ultraprecision machining equipment. Ultraprecision grinding processes using air turbine spindles with aerostatic bearings include constant-pressure dry lapping of nano-polycrystalline diamond (NPD) tools and ultraviolet irradiation polishing of chemical vapor deposition diamond films. In the dry lapping of NPD tools, it is necessary to achieve constant-pressure grinding while flexibly adjusting the contact force between the NPD tool and the truer fixed on the end face of the aerostatic spindle to form a nose bite with a cutting-edge rounding radius, R, of 0.1 nm. However, it is common for operators to manually adjust the cut depth and the air pressure supplied to the aerostatic bearing by relying on the noise and rotation speed during machining. Moreover, aerostatic spindles without a control mechanism, such as active bearings, are widely used because of their low costs and versatility. For several years, the authors have been developing a method to control air bearing stiffness by controlling the bearing supply pressure with high speeds and precision using a high-precision quick response regulator for aerostatic spindles without a control mechanism, such as active bearings. In this study, the compliance control (control of spindle position and stiffness) of aerostatic bearings was investigated using the proposed method, and the effectiveness of the method to ultraprecision grinding applications was demonstrated.

Fracture mechanics of microcrystalline/nanocrystalline composited multilayer chemical vapor deposition self-standing diamond films

Though microwave plasma chemical vapor deposition (MPCVD) diamond films exhibit extraordinary strength, the toughness improvement is still a huge challenge. The catastrophic fracture of the diamond films is undesirable in many applications, especially for the application of fabricating cutting tools. In the present study, adopting the pre-notched and unnotched cantilever bending tests, fracture behaviors of monolayer microcrystalline diamond (m-M), monolayer nanocrystalline diamond (m-N), and microcrystalline/nanocrystalline composited multilayer diamond films were observed and compared. Typical fracture mechanics, including Young's modulus (E), fracture strength (σF), and fracture toughness (KIC) of different diamond films were investigated. Effects of diamond crystal structure, intrinsic stress, and tensile-side roughness were systematically analyzed. Grain size and graphite phase content dominated the E of self-standing diamond films. Tensive-side surface roughness and intergranular bonding strength affected the σF. When the growth side in tension, E of the multilayer film (modulation period Λ = 3 h) was 16.0% lower than m-M and 26.6% higher than m-N, σF of multilayer film was 16.8% higher than m-M and 8.3% lower than m-N. At fixed Λ, doubling the total deposition period, E, σF, and KIC of the multilayer film increased 72.3%, 22.3%, and 2.7%, respectively. MCD/NCD composited multilayer architecture presented significant strengthening and toughening effects on self-standing diamond films.

Microscopic Insight into the Inhomogeneous Broadening of Zero-Phonon Lines of GeV– Color Centers in Chemical Vapor Deposition Diamond Films Synthesized from Gaseous Germane

Microscopic Insight into the Inhomogeneous Broadening of Zero-Phonon Lines of GeV^– Color Centers in Chemical Vapor Deposition Diamond Films Synthesized from Gaseous Germane

Laser cladding of vanadium carbide interlayer for CVD diamond growth on steel substrate

The chemical vapor deposition of diamond film on steel substrate remains with main drawbacks demanding a proper solution. Some proposed interlayers tackled with the high carbon diffusivity into steel and with the graphitic sp2 bonds catalyzed by transition metal. However, the large mismatch of the coefficient of thermal expansion between steel and diamond produces cracked and delaminated diamond films. Thermodiffused vanadium carbide (TDVC) interlayer for straight CVD diamond deposition on steel, showed disruptive results; nevertheless, the coating thickening is limited to substrate with high carbon content and low alloy steel. This work introduces the use of laser cladding (LC) to form an intermediate layer of vanadium carbide (VC) from V4C3 powder. The LC process has a short cycle time and a high VC growth rate (5.6 μm/min). Comparing with TDVC, it represents a reduction of approximately 26 times in the process cycle time. We used AISI D6 steel as substrate and overlapped VC layers to raise the coat thickness up to 25 μm. The layers showed good adherence, low porosity, and the formation of V8C7 phase. Diamond films 2.8 μm thick were deposited by hot filament chemical vapor deposition (HFCVD) at 700 °C. The Raman spectroscopy of the diamond film on four overlapped VC layers (25 μm thick) showed a compressive residual stress of 2.7 GPa. The residual stress reduction was 1.8 GPa, when compared with the 7 μm thick single cladded VC layer.

Thermoluminescence properties of high-dose gamma-irradiated diamond films

Thermoluminescence (TL) properties of gamma-irradiated chemical vapor deposition (CVD) diamond films at high doses are presented. Samples of undoped and nitrogen-doped CVD diamonds were exposed to 60Co gamma sources and TL intensity as a function of the dose was analyzed. To evaluate the feasibility of using these materials as TL high-dose dosimeters, reproducibility of the TL signal, and the TL response as a function of absorbed dose from 100 Gy up to 10 kGy were studied. Furthermore, the fading of the TL glow curve was analyzed. Finally, to estimate the kinetics parameter values associated with the trap distribution in the CVD diamond, a computerized deconvolution was carried out by using the general order kinetics (GOK) model.

Tribological Properties of Chemical Vapor Deposited Diamond Film on YT14 Cemented Carbide under Water Lubrication Condition

Abstract A diamond film was deposited on YT14 cemented carbide using chemical vapor deposition technique. The surface and cross-section morphologies and chemical compositions of obtained diamond film were analyzed using a scanning electron microscope, energy dispersive spectroscopy, Raman spectroscope, and X–ray diffractometer, respectively. The friction and wear tests of diamond film under the water lubrication condition were conducted using a wear tester with the minimum quantity lubrication system, and the effects of wear loads on tribological properties of diamond film were also discussed. The results show that the chemical vapor deposited diamond film is primarily composed of diamond (111) peak, and its hardness, elastic modulus, bonding strength, and roughness are 16.27 GPa, 166.18 GPa, 26.2 N, and 79.2 nm, respectively. Under the water lubrication condition, the average coefficients of friction (COF) of diamond film under the wear loads of 4, 6, and 8 N are 0.117, 0.139, and 0.163, respectively, and the corresponding wear rates of diamond film under the wear loads of 4, 6, and 8 N are 3.87 × 10−7, 4.26 × 10−7, and 4.67 × 10−7 mm3/N • m. This shows that the average COFs and wear rates increase with an increase of wear loads and that the wear mechanism is abrasive wear.

Diamond Deposition on Iron and Steel Substrates: A Review.

This article presents an overview of the research in chemical vapor deposition (CVD) diamond films on steel substrates. Since the steels are the most commonly used and cost-effective structural materials in modern industry, CVD coating diamond films on steel substrates are extremely important, combining the unique surface properties of diamond with the superior toughness and strength of the core steel substrates, and will open up many new applications in the industry. However, CVD diamond deposition on steel substrates continues to be a persistent problem. We go through the most relevant results of the last two and a half decades, including recent advances in our group. This review discusses the essential reason of the thick catalytic graphite interlayer formed on steel substrates before diamond deposition. The high carbon diffusion in iron would induce severe internal carburization, and then voluminous graphite precipitated from the substrate. In order to hinder the catalytic graphite formation, various methods have been applied for the adherent diamond film deposition, such as pre-imposed various interlayers or multi-interlayers, special controls of the deposition process, the approaches of substrate alloying and so on. We found that adherent diamond films can be directly deposited on Al alloying steel substrates, and then the role of Al alloying element was examined. That is a thin dense amorphous alumina sublayer in situ formed on the alloying substrate, which played a critical role in preventing the formation of graphite phase and consequently enhancing diamond growth and adhesion. The mechanism of Al alloying suggests that the way used to improve hot corrosion resistance is also applicable. Then, some of the hot corrosion resistance methods, such as aluminizing, siliconizing, and so on, which have been used by some researchers examining CVD diamond films on steel substrates, are reviewed. Another way is to prepare diamond-like carbon (DLC) films on steel substrates at low temperature, and then the precipitated graphite from the internal carburization can be effectively avoided. In addition, based on some new findings, the understanding of the diamond nucleation and metastable growth is discussed.

Microstructure, hardness and optical properties of Er2O3 films deposited on diamond-coated and Si(100) substrates by radio frequency magnetron sputtering

Er2O3 anti-reflection films were deposited on the surface of the chemical vapor deposited diamond films and Si(100) substrates by radio frequency magnetron sputtering. The microstructure of the Er2O3 thin films and the interfacial layer were investigated by means of scanning electron microscopy, X-ray diffraction, atomic force microscopy and transmission electron microscopy. The refractive index, hardness and transmittance of the films were measured by ellipsometry, nanoindentation measurements, and Fourier transformed infrared spectroscopy. Results revealed that the bias induces the formation of a monoclinic phase and the nucleation of the Er2O3 thin films is mainly observed along the (222) plane. A high-resolution TEM image revealed a 2.5-nm-thick amorphous layer at the interface between the Si substrate and Er2O3 film. Notably, monoclinic Er2O3 films can considerably improve the transmittance of the diamond film in the long-wavelength infrared range of 8–12 μm via the reduction of the refractive index. However, the introduction of the monoclinic phase led to the decrease of the hardness and elastic modulus of the films; hence, controlling a suitable amount of the monoclinic phase may play an extremely important role in the mechanical and optical properties of the Er2O3 films.

Investigating the Possible Origin of Raman Bands in Defective sp2/sp3 Carbons below 900 cm−1: Phonon Density of States or Double Resonance Mechanism at Play?

Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp2 and sp3 carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 °C and highly oriented pyrolytic graphite exposed to a radio-frequent deuterium plasma. We found evidence that the lower part of the phonon density of states (PDOS) spectral region (300–900 cm−1) that rises when defects are introduced in crystals can give more information on the structure than expected. For example, the height of the PDOS, taken at 400 cm−1 and compared to the height of the G band, depends on the sp2 content, estimated by electron energy-loss spectroscopy. This ratio measured with 633 nm laser is more intense than with 514 nm laser. It is also correlated for diamond to the relative intensity ratio between the diamond band at 1332 cm−1 and the G band at ≈1500–1600 cm−1 when using 325 nm laser. Moreover, it is found that the shape of the PDOS of the exposed graphite samples is different when changing the wavelength of the laser used, giving evidence of a double resonance mechanism origin with the rise of the associated D3, D4 and D5 bands, which is not the case for a-C:H samples.

Superhydrophilic surface of oxidized freestanding CVD diamond films: Preparation and application to test solution conductivity

This work reports the surface features, wettability properties and application of the thermally oxidized freestanding chemical vapor deposited diamond films. The oxygen-terminated micrometer-sized diamond grains on growth side and the pyramid-shaped diamond nanotips on nucleation side of diamond films, having superhydrophilic feature, are realized by a thermal oxidation treatment process in air. The superhydrophilic surfaces were proposed to examine the conductivity properties of micro-solution droplets (with varying ion concentrations) spreading fast on the film surface. The corresponding conductivities of the micro-solutions are nearly linearly increased with increasing the ion-concentration in a large region. It is demonstrated that the chemical inert diamond films with the functionalized surfaces are favorable for fabricating high efficient, sensitive, and washable detectors.

The Influence of B, N and Si Doping on the CH3 Adsorption on the Diamond Surface Based on DFT Calculations

To better understand the influence mechanism of boron, nitrogen and silicon dopants on the growth of chemical vapor deposition (CVD) diamond film, density functional calculations have been performed to reveal the different impact of the impurities on the CH3 adsorption on diamond surface. The substituted doping and radical doping of diamond (111) and (100) − 2 × 1 surface are both considered. The calculation results indicate that the CH3 radicals are hardly adsorbed on nitrogen atoms and thus may cause vacancy in the diamond lattice easily. Boron substituted doping will disfavor the adsorption of CH3 due to the lacking of valence electron. However, the empty p orbitals of boron atom will help the chemical adsorbing of CH3 radicals. The substituted silicon doping has little influence on the CH3 adsorption, as Si atom has the same outer valence electron structure with C atom. In the case of radical doping, the adsorption energy of CH3 will be reduced due to the steric hindrance between NH2 or SiH3 with CH3. The adsorption energy can be slightly enhanced when BH2 radical is pre-adsorbed on diamond (111) surface. However, the BH2 pre-adsorbed on diamond (100) − 2 × 1 surface may interact with surface radical carbon site and result in a large reduction of CH3 adsorption energy. Thus, the boron doping may hinder the formation of the (100) facet during the CVD diamond deposition under a certain condition.

Atmospheric-Pressure Microwave Plasma Torch for CVD Technology of Diamond Synthesis

An electrodeless microwave jet plasma source is considered, and its various applications in the technology of chemical vapor deposition of diamond films and dimension increasing of small diamond single crystals synthesized at high pressures and temperatures are discussed. The plasma jet is ignited in an atmospheric-pressure gas (argon) flow with hydrogen and methane additives. The operation of the microwave jet reactor is described, and the plasma characteristics measured using emission spectroscopy are presented. The brightly glowing atmospheric-pressure plasma jet is ignited and stably burns at a microwave power of ≤1 kW supplied from a microwave oven magnetron. The specific microwave power density absorbed by the compact plasma jet (≤104 W/cm3) is comparable with that absorbed by a dc arc. The growth rate of the polycrystalline diamond layer amounts to 40 µm/h. The process of film deposition on the substrate can be controlled by scanning the substrate surface with the jet.

Kinetic studies of few-layer graphene grown by flame deposition from the perspective of gas composition and temperature.

Studies on depositions of chemical vapour deposition (CVD) diamond films have shown that flame combustion has the highest deposition rates without involving microwave plasma and direct current arc. Thus, here we report on our study of few-layer graphene grown by flame deposition. A horizontal CVD reactor was modified for the synthesis of flame deposition of few-layer graphene on a Cu substrate. It was found that graphene obtained has comparable quality to that obtained with other flame deposition setups reported in the literature as determined from Raman spectroscopy, sheet resistance, and transmission electron microscopy. Calculation of the chemical kinetics reveals a gas phase species that has a close correlation to the growth rate of graphene. This was further correlated with van't Hoff analysis of the reaction, which shows that the growth reaction has a single dominating mechanism for temperatures in the range of 400 °C to 1000 °C. Arrhenius analysis also was found to be in good agreement with this result. This study shows few-layer graphene growth proceeds through different pathways from a CVD grown graphene and also highlights flame deposition as a viable method for graphene growth.

Physics and application of gas discharge in millimeter wave beams

The microwave discharge produced in gases by millimeter wave radiation in wave beams is characterized by high plasma density, and wave beams allow one to control the form and size of plasma maintained both in free space and near surfaces of various materials. This paper reviews the results of studying dense plasmas in microwave discharges, which are produced in four and two crossing wave beams by continuous wave radiation of a gyrotron at frequencies of 30 GHz and 28 GHz, respectively. The results of using such discharges for advancing the technique of chemical vapor deposition of diamond films are described. Furthermore, new results on discharge characteristics at extreme values of power density up to 1000–1500 W cm−3 and the homoepitaxial growth of diamond under these conditions are presented.

Solar Thermionic‐Thermoelectric Generator (ST2G): Concept, Materials Engineering, and Prototype Demonstration

AbstractThe thermionic‐thermoelectric solid‐state technology, characterized by solar‐to‐electric conversion efficiency feasibly >40%, is comprehensively proposed and discussed for conversion of concentrating solar power. For the first time, the related solar generator prototype is designed and fabricated by developing advanced materials functionalized for the specific application, such as thermally resistant hafnium carbide‐based radiation absorbers, surface‐textured at the nanoscale to obtain a solar absorptance >90%, and chemical vapor deposition diamond films, acting as low‐work‐function (2.06 eV) thermionic emitters. Commercial thermoelectric generators and encapsulation vacuum components complete the prototype. The conversion efficiency is here evaluated under outdoor concentrated sunlight, demonstrating thermionic stage output power of 130 mW at 756 °C, combined to the maximum thermoelectric output power of 290 mW. The related solar‐to‐electric conversion efficiency is found to be 0.4%, but, once the net thermal flux fed to the conversion stages is considered, a thermal‐to‐electric efficiency of 6% is revealed. Factors affecting the performance of the present prototype are analyzed and discussed, as well as a strategy to rapidly overcome limitations, in order to prepare an efficient and highly competitive solid‐state conversion alternative for future concentrating solar plants.

Spin-Rayleigh wave interaction in CVD diamond films

It has been suggested that surface acoustic waves can couple remote quantum bits (qubits). Bulk diamond and chemical vapor deposition diamond films host the negatively charged nitrogen-vacancy color center (NV−1) which carry an electronic spin-1. The latter is among the most promising qubits for implementing scalable quantum information processing. The characteristic features of the Rayleigh surface acoustic wave which can propagate near the free surface of a diamond thin film are investigated. The texture of the film is taken into account. A phenomenological theory of the spin-phonon interaction is applied to describe the coupling between the Rayleigh surface acoustic wave and the NV−1 spin-qubits.