Uniform Diamond Films Research Articles

Optimization of electrostatic seeding technique for wafer-scale diamond fabrication on β-Ga2O3

Integrating diamonds with β-Ga2O3 is a promising solution for addressing the problem of poor thermal conductivity and limited p-type dopability of β-Ga2O3. However, growing diamonds on β-Ga2O3 is challenging, especially without any interfacial layer, and achieving large-scale uniform diamond films is also tricky. This paper explores the vital role of an electrostatic seeding technique involving the use of Polydiallyldimethylammonium chloride (PDDAC) polymer with a positive zeta potential and diamond nano slurries with a negative zeta potential to facilitate the integration of diamond with β-Ga2O3. We conduct a detailed analysis of each step of this seeding technique, adjusting the spinning speed of the polymer coating, spinning period, baking period, and ultrasonication period to understand the underlying mechanisms preventing large-scale diamond growth and to identify strategies for achieving wafer-scale diamond fabrication on single crystal β-Ga2O3 film. This process facilitates the attainment of a uniform dispersion of diamond nanoparticles on β-Ga2O3 at a seeding density of ∼1.82 × 1011 cm−2. The optimized seeding technique has enabled the successful growth of wafer-scale diamond films on β-Ga2O3, as confirmed by scanning electron microscopy (SEM). Additionally, the high quality of the diamond film is affirmed by a quality factor of 96.75 % and a narrow full-width half maximum of 10.28 cm−1 in the T2g peak of the Raman spectra. The X-ray diffraction pattern reinforces the excellent quality of polycrystalline diamond films with minimum stress. In summary, this research provides valuable insights into the polymer-assisted electrostatic seeding technique, paving the way for the uniform growth of wafer-scale diamond films on β-Ga2O3, which is critical for realizing β-Ga2O3-based heterostructure devices.

Deposition of uniform diamond films on three dimensional Si spheres by using faraday cage in MPCVD reactor

Deposition of a consistent diamond coating on intricate surfaces has historically posed a difficulty. This article presents the advancement in research on depositing a uniform diamond coating on three-dimensional (3D) silicon spheres, utilizing a faraday cage within a microwave plasma chemical vapor deposition (MPCVD) reactor. A self-consistent three-dimensional multi-physics field model has been established for simulating the microwave electric field and plasma inside a reactor with or without a faraday cage. Results indicate the cage effectively reduces the discharge at the top of the silicon sphere and improves uniformity of the distribution of the microwave electric field and plasma electron density on the sphere's surface. MPCVD trials have demonstrated that a powerful discharge takes place at the apex of the silicon sphere resulting in an excessive thermal gradient if the cage is not added. The apex of the silicon sphere is covered with a blend of diamond and graphite phases. Due to the excessive internal stress of the coating, approximately 50 % of the samples experience coating detachment. After the addition of the cage, the strong discharge is transferred to the top of the cage, effectively suppressing the microwave electric field and plasma inside the cage. Improved quality, reduced internal stress, and enhanced uniformity of the polycrystalline diamond coating are achievable on the silicon spheres within the cage. Moreover, this technique offers a novel approach to coat diamond on complex 3D geometries.

Mapping the effect of substrate temperature inhomogeneity during microwave plasma-enhanced chemical vapour deposition nanocrystalline diamond growth

It is important to account for variance in substrate temperature during microwave plasma-enhanced chemical vapour deposition (MPECVD) nanocrystalline diamond growth, as this has a significant impact on the uniformity of the grown film. In this work, an in-situ method of mapping the substrate temperature under MPECVD growth conditions is demonstrated, employing a mirror galvanometer to scan the field of view of a dual-wavelength pyrometer across the substrate. Temperature maps generated were compared to plasma electron densities simulated using a finite element model. An increase in temperature and simulated plasma density were seen towards the centre of the holder. The properties of nanocrystalline diamond films were mapped using ex-situ Raman spectroscopy and spectroscopic ellipsometry (SE). A greater SE-measured bulk thickness and bulk sp3 fraction, as well as a greater first-order diamond Raman intensity and lower full width at half maximum were seen in the higher-temperature central region, demonstrating the impact of substrate temperature inhomogeneity during growth. The temperature mapping technique demonstrated allows easy evaluation of the impact of substrate holder design, microwave power and chamber pressure on substrate temperature homogeneity, and therefore optimisation of growth conditions for uniform diamond film growth.

Design and simulation of a novel MPCVD reactor with three-cylinder cavity

A novel microwave plasma chemical vapor deposition (MPCVD) reactor with three-cylinder cavity and outstanding tuning capability was proposed. The electric field and plasma in the reactor were simulated, and four geometric parameters were optimized. After optimization, the electric field intensity above the substrate exceeded 5×103V/m (input power of 1 W), which was 1.6 times that of the similar cylindrical reactors. Only one strong plasma formed above the substrate surface with an input power of 5 kW once the gas pressure exceeds 8 kPa. But the plasma coverage area was decreased with the increase of the gas pressure. The plasma coverage area could be restored by adjusting the height difference between the adjusting mechanism 1 and 2. The frequency detuning caused by the microwave frequency changes also could be returned by adjusting the adjusting mechanisms. The subsequent experimental results showed that uniform and high-quality diamond films could be deposited under the simulation condition (5 kW and 12 kPa). It could verify the accuracy of the simulation and the excellent performance of the new MPCVD reactor.

Effects of the electric field at the edge of a substrate to deposit a Ø100 mm uniform diamond film in a 2.45 GHz MPCVD system

In this study, uniform diamond films with a diameter of 100 mm were deposited in a 15 kW/2.45 GHz ellipsoidal microwave plasma chemical vapour deposition system. A phenomenological model previously developed by our group was used to simulate the distribution of the electric strength and electron density of plasma. Results indicate that the electric field in the cavity includes multiple modes, i.e. TM02 and TM03. When the gas pressure exceeds 10 kPa, the electron density of plasma increases and plasma volume decreases. A T-shaped substrate was developed to achieve uniform temperature, and the substrate was suspended in air from Ø70 to 100 mm, thus eliminating vertical heat dissipation. An edge electric field was added to the system after the introduction of the T-shaped substrate. Moreover, the plasma volume in this case was greater than that in the central electric field but smaller than that in the periphery electric field of the TM02 mode. This indicates that the electric field above and below the edge benefits the plasma volume rather than the periphery electric field of the TM02 mode. The quality, uniformity and surface morphology of the deposited diamond films were primarily investigated to maintain substrate temperature uniformity. When employing the improved substrate, the thickness unevenness of the Ø100 mm diamond film decreased from 22% to 7%.

Study on the Large Area Diamond Film Deposition in a Self- built Overmoded Microwave Power Chemical Vapor Deposition Device

With a self-built overmoded microwave plasma chemical vapor deposition device, the effect of the gas flow rate variation on the uniform deposition of diamond films on molybdenum of 100 millimeter diameter was studied. The plasma density was 1.0×1019/m3 when the microwave power was 5.0 kW and the gas pressure was 10.0 kPa. The ovemoded MPCVD device presented good stability of the gas flow rate field distribution. The substrate surface can be well covered when the hydrogen flow rate varied from 50 to 800 sccm. The uniform diamond film with good quality was obtained at an intermediate gas flow rate, 300 sccm. The diamond film with good quality, 5.74 cm-1 as FWHM value and high growth rate, 5.8 μm/h was deposited when the gas flow rate was 300 sccm.

Optimization of depositing uniform and wear-resistant diamond films on massive mechanical seals

PurposeThis study aims to obtain diamond-coated mechanical seals with improved sealing performance and considerable cost. To achieve this purpose, the study focuses on depositing uniform, wear-resistant and easily polished diamond coatings on massive mechanical seals in a large-scale vacuum chamber.Design/methodology/approachThe computational fluid dynamics simulation test and its corresponding deposition experiment are carried out to improve the uniformity of diamond films on massive mechanical seals. The polishing properties and sealing performance of mechanical seals coated with three different diamond films (microcrystalline diamond [MCD], nanocrystalline diamond [NCD] and microcrystalline/nanocrystalline diamond [MNCD]) and uncoated mechanical seals are comparatively studied using the polishing tests and dynamic seal tests to obtain the optimized diamond coating type on the mechanical seals.FindingsThe substrate rotation and four gas outlets distribution are helpful for depositing uniform diamond coatings on massive mechanical seals. The MNCD-coated mechanical seal shows the advantages of high polishing efficiency in the initial polishing process and excellent wear resistance and self-lubrication property in the follow-up polishing period because of its unique composite diamond film structures. The MNCD-coated mechanical seal shows the longest working life under dry friction condition, about 14, 1.27 and 1.9 times of that for the uncoated, MCD and NCD coated mechanical seals, respectively.Originality/valueThe effect of substrate rotation and gas outlets distribution on temperature and gas flow field during diamond deposition procedure is simulated. The MNCD-coated mechanical seal exhibits a superior sealing performance compared with the MCD-coated, NCD-coated and uncoated mechanical seals, which is helpful for decreasing the operating system shut-down frequency and saving operating energy consumption.

Deposition of large area uniform diamond films by microwave plasma CVD

Diamond films with 70 mm in diameter were deposited on silicon substrates with Ar/CH4/H2 gas mixture, using microwave plasma chemical vapor deposition (MPCVD) technique. One designed water-cooling substrate stage was used to improve the uniformity of the surface temperature across the substrate. An uniform substrate surface temperature was obtained at the pressure of 10 kPa when the input microwave power was 5500 W. The condition of the plasma was diagnosed by optical emission spectrum (OES) and the grown diamond films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The results show that higher microwave power can further improve the uniformity of the temperature distribution across the substrate which in turn increases the uniformity of diamond film. And introducing more H2 into Ar/CH4/H2 gas mixture at high microwave power is effective on the improvement of the quality and the decrease of the stress in the deposited diamond films. The diamond films with low average intrinsic stress of 0.32 GPa were finally deposited with introducing 100 sccm H2 into Ar/CH4/H2 gas mixture at 5500 W.

A novel approach of deposition for uniform diamond films on circular saw blades

Uniform diamond films are highly desirable for cutting industries, due to their high performance and long lifetime used on cutting tools. Nevertheless, they are difficult to obtain on cutting tools with complicated shapes, greatly limiting the applications of diamond films. In this study, a novel approach of deposition for uniform diamond films is proposed, on circular saw blades made of cemented carbide using reflectors of brass sheets. Diamond films are deposited using hot filament chemical vapor deposition (HFCVD). A novel concave structure of brass sheets is designed and fabricated, improving the distribution of temperature field, and overcoming the disadvantages of the conventional HFCVD systems. This increases the energy efficiency of use without changing the structure and increasing the cost of HFCVD. The grains are refined and the intensities of diamond peaks are strengthened obviously, which is confirmed by scanning electron microscopy and Raman spectra respectively.

Plateholder design for deposition of uniform diamond coatings on WC-Co substrates by microwave plasma CVD for efficient turning application

Polycrystalline diamond coatings have been grown on cemented carbide WC-6% Co substrates with different aspect ratios by microwave plasma CVD in CH4/H2 gas mixtures. Special plateholder with holes for group growth has been used to protect the edges of the substrates from non-uniform heating due to the plasma edge effect. The difference in heights Δh of the substrates and plateholder, and its influence on the diamond film mean grain size, growth rate, phase composition and stress was investigated. Diamond growth rate of 0.3–1μm/h and compressive stress of 2.2–2.5GPa, respectively were determined in the optimal Δh region. The substrate temperature range of 740–760°C, within which uniform diamond films are produced with good adhesion, is determined. The diamond-coated samples produced at optimized process conditions exhibited a reduction of cutting force and wear resistance by a factor of two, and increase of cutting path length up to 8150m or by 4.3 times upon turning А390 Al-Si alloy as compared to performance of uncoated tools. Prime noveltyPolycrystalline diamond coatings with uniform structure and thickness distribution are grown by microwave plasma CVD (MPCVD) on WC-6% Co substrates using an optimized pocket-type substrate holder. Edge effect during MPCVD on high substrates (height/diameter>0.1) was suppressed. Influence of distance between the substrate holder and substrate surface on deposition temperature and other parameters was investigated. Cutting force and wear rate of the coated samples upon cutting of Si-Al abrasive alloy were twice less than that of uncoated WC-6% Co.

A step forward into hierarchically nanostructured materials for high performance micro-supercapacitors: Diamond-coated SiNW electrodes in protic ionic liquid electrolyte

Silicon nanowires (SiNWs) were successfully coated by uniform, adherent and homogenous ultra-thin crystalline diamond films through microwave enhanced chemical vapor deposition (MWCVD). The as-grown functionalized nanowires were employed as electrodes in a symmetric micro-supercapacitor (MSC) using a protic ionic liquid electrolyte [triethylammonium bis(trifluoromethylsulfonyl)imide; Et3NH TFSI]. The electrochemical performance of the device delivered a specific capacitance of 1.5mFcm−2 and a power density of 25mWcm−2 using an enlarged cell voltage of 4V. Furthermore, a remarkable cycling stability was evaluated after 1·106galvanostatic cycles at a high current density of 10mAcm−2 with an excellent capacitive behavior. These results confirm that diamond-coated SiNW micro-supercapacitors exhibit very promising performances dealing with MSCs based on CVD-grown SiNWs.

A dome-shaped cavity type microwave plasma chemical vapor deposition reactor for diamond films deposition

In this paper, a new type of microwave plasma chemical vapor deposition (MPCVD) reactor possessing a novel dome-shaped resonant cavity is described. Such a MPCVD reactor is required for efficient preparation of diamond films. It will be shown that by adopting a design outlined in this paper, a MPCVD reactor fulfilling all different requirements for reliable, long-time operation at high input microwave power levels could be optimized. Experimental results will be given showing that with the new MPCVD reactor, an input microwave power of up to 10 kW at 2.45 GHz could be applied, and at an input power of 8.5 kW, uniform and transparent polycrystalline diamond film of high quality and high purity could be deposited on 2 inch diameter silicon substrates, at a deposition rate of about 3.5 μm/h.

A novel microwave plasma reactor with a unique structure for chemical vapor deposition of diamond films

With the aid of numerical simulation, a novel microwave plasma reactor for diamond films deposition has been designed. The new reactor possesses a unique structure, neither purely cylindrical nor purely ellipsoidal, but a combination of the both. In this paper, the design strategy of the new reactor together with a simple but reliable phenomenological simulation method will be described. Preliminary experiments show that uniform diamond films of high quality could be deposited using the new reactor, and the deposition rate of diamond films is typically about 3 μm/h at 6 kW input power level on a 2 inch diameter silicon substrate. • The proposed microwave plasma reactor has a novel structure, which is the combination of cylinder and ellipsoid. • A simple but effective simulation method is established to design the microwave plasma reactor. • An ingenious design has been adopted to solve the problem of parasitic plasma, which has not been reported before. • The results of both simulation and experiments show a good performance of the newly designed reactor.

Investigation of depositing large area uniform diamond films in multi-mode MPCVD chamber

In this work, diamond films were deposited in a 10kW, 2450MHz MPCVD apparatus, of which the chamber allows a multi-mode microwave electric field to be overlapped and high microwave power to be employed. The two primary modes of TM01 and TM02 overlap around the substrate and generate a large scale plasma ball which ensures the deposition of large area diamond films. The deposition temperature across the substrate was primarily investigated in order to deposit uniform diamond films in the multi-mode chamber. And the optical emission spectra, scanning electron microscope and Raman were used to characterize the diamond films. The results showed that higher microwave power should be selected to generate large plasma ball and obtain needed temperature uniformity for a given deposition pressure. And the temperature variation was decreased obviously when the substrate holder was improved. With the optimized parameter and the improved stage configuration, the diamond thin films deposited on Φ=80mm silicon wafers obtained excellent uniformity in morphology, thickness and quality. And the results of investigating growth rate further confirm that the improved substrate holder and the employment of high microwave power are useful to achieve uniform diamond films with large area and high deposition rate.

Diamond films grown without seeding treatment and bias by hot-filament CVD system

Diamond film growth without seeding treatment has been the subject of numerous studies. In the present study, diamond films with/without seeding treatment were grown on silicon using hot-filament chemical vapour deposition. An inexpensive and simple approach, namely, “dry ultrasonic treatment”, was introduced in which full coverage of diamond film was achieved on unseeded substrate. For comparison, one substrate was seeded with 5μm diamond particles, prior to deposition. The resulting diamond films were examined through standard characterization tools and distinct features were observed in each film. Here we present the results of uniform and high purity diamond film, free from nano-sized grains, which is grown without seeding treatment and is expected to be potential candidate for electro-optical applications, particularly as heat sinks.

Effect of surface treatment on hot-filament chemical vapour deposition grown diamond films

Diamond film growth without seeding treatment has been the subject of numerous studies. In this study, diamond films with/without seeding treatment were grown on silicon using hot-filament chemical vapour deposition. An inexpensive and simple approach, namely ‘dry ultrasonic treatment’, was introduced in which full coverage of the diamond film was achieved over the substrate having no prior seeding treatment. For comparison purposes, two substrates were seeded with different sizes of diamond particles, 5 µm by hand and 30–40 µm by ultrasonic agitation, prior to deposition. The produced diamond films were examined through standard characterization tools and distinct features were observed in each film. The diamond film grown without the seeding treatment shows slightly lower growth rate (1 µm h−1) but bigger grain size up to 8 µm compared with seeded films. Here we show the growth of uniform and high-purity diamond films free from nano-sized grains, which are grown without any seeding treatment.

Improvement on the Cutting Performance of CVD Diamond Coated Drills in Drilling CFRP

Carbon fiber reinforced plastics (CFRP) is difficult to machine because of the extremely abrasive nature of the carbon fibers and its low thermal conductivity. CVD diamond films have many excellent properties such as wonderful wear resistance, high thermal conductivity and low friction coefficient, therefore depositing diamond films on the surface of drills is thought to be an effective way to elongate the lifetime of drills and improve the cutting performance. In this study, diamond films are deposited on the WC-Co drill using hot filament chemical vapor deposition (HFCVD) method. The results of characterization by the scanning electron microscope (SEM) and Raman spectrum indicate that the fabricated CVD diamond coated drill is covered with a layer of uniform and high-purity diamond films. The cutting performance of as-fabricated CVD diamond coated drill is evaluated in dry drilling CFRP, comparing with the uncoated WC-Co drill. The results demonstrate that the CVD diamond coated drill exhibits much stronger wear resistance. Its flank wear is about 50μm after drilling 30 holes, about one-third of that of WC-Co drill. Machining quality of the exit and internal wall of drilled holes shows better surface finish obtained by coated drill, which suggests that CVD diamond coated tool has great advantages in drilling CFRP.

Design of novel plasma reactor for diamond film deposition

Development of microwave plasma reactors is a key factor for improving microwave plasma chemical vapor deposition (MPCVD) techniques for producing high quality diamond films. In this paper, a new microwave plasma reactor operated at 2.45 GHz was proposed on the basis of numerical simulation. The Finite Element Method (FEM) was used to optimize the geometry, and the Finite Difference Time Domain (FDTD) method was employed to calculate the electric field and the plasma density. The proposed reactor works mainly at the TM 021 mode, and it has an excellent power handing capability. Preliminary experiment showed that high density hemispherical plasma could be ignited inside the reactor, and uniform diamond film could be deposited on substrates at high input microwave power.

High Current Extended DC Arc Plasma CVD for Mass Production of Diamond Film Coated Hard Metal Cutting Tools

Diamond film coated hard metal cutting tools are indispensible for high efficiency machining of materials which are difficult to cut by ordinary tools, and are successfully used in the dry cutting of high silicon content Al-Si cast alloys, graphite, carbon reinforced composite (CRFC) and metal matrix composite (MMC) , ceramics, and many other materials. In the present presentation, a novel process of High Current Extended DC Arc (HCEDCA) plasma CVD for mass production of diamond film coated hard metal cutting tools is presented. Besides, a novel process for the pretreatment of the hard metal cutting tool substrate, which involves the idea of “surface engineering” consisting of boronizing and alkaline and acidic etching is also discussed, by which the adhesion of the diamond film coating to the hard metal substrate can be greatly enhanced. Highly adherent and uniform diamond film coatings are successfully obtained. Diamond film coated WC-6wt%Co indexable tool bits, drills, endmill samples have been produced and been shown having excellent cutting performance by field cutting tests in dry cutting of Al-12%Si cast alloy and Al-15% SiC MMC materials.

Fabrication of nanogranular diamond films by MPJCVD system

Nanogranular diamond films have been prepared by microwave plasma jet chemical vapor deposition system (MPJCVD) with argon-rich (Ar/H2:90%) plasma. In this work, the plasma pre-carbonization (P.P.) pre-treatment was employed to obtain uniform and smooth (13.3nm rms) diamond films with high nucleation density. The diamond films were fabricated in various Ar/H2 concentrations from 0% to 100% and fixed at CH4 concentration of 1%. It can be clearly observed that the grain size of diamond films changed from micrometer to nanometer scale and down to 5nm at the concentration of 90% Ar/H2. The reason is due to the rise of C2 dimer in the plasma, which could be proved from the analysis of OES analysis.