Growth Of Polycrystalline Diamond Films Research Articles

Combined HF+MW CVD Approach for the Growth of Polycrystalline Diamond Films with Reduced Bow

A combination of two methods of chemical vapor deposition (CVD) of diamond films, microwave plasma–assisted (MW CVD) and hot filament (HF CVD), was used for the growth of 100 µm-thick polycrystalline diamond (PCD) layers on Si substrates. The bow of HF CVD and MW CVD films showed opposite convex\concave trends; thus, the combined material allowed reducing the overall bow by a factor of 2–3. Using MW CVD for the growth of the initial 25 µm-thick PCD layer allowed achieving much higher thermal conductivity of the combined 110 µm-thick film at 210 W/m·K in comparison to 130 W/m·K for the 93 µm-thick pure HF CVD film.

Photoluminescence in Raman Scattering: Effects of HfO2 Template Layer on Ultrananocrystalline Diamond (UNCD) Films Grown on Stainless Steel Substrates

The growth of polycrystalline diamond films can play an important role in industry if they can be grown on industrially used materials like aluminum (Al) or stainless steel (SS). A critical issue related to the growth of ultrananocrystalline diamond (UNCD) thin films on metals like SS, in a Hydrogen rich environment like the one present during growth of UNCD films, is the diffusion of Hydrogen (H) into the SS substrate, as it has been observed in prior research, which results in hydride formation in the SS that induce brittleness in the SS substrate. Several interface layers have been proposed described to avoid the H diffusion into the SS. However, HfO2 has not been explored. The work reported here was focused on investigating the growth of UNCD films on commercially available SS substrates by using an interface layer of HfO2, which was found to be a good diffusion barrier for H to inhibit penetration into the SS substrate. The samples where characterized with SEM and Raman spectroscopy. A photoluminescence (PL) effect, observed in the Raman scattering analysis, is present in all the samples. The PL effect may be due to the interaction of the UNCD / HfO2 interface. and the SS substrate rather than UNCD film alone. The novel result from the experiments described here, is the fact that it is possible to grow UNCD films on unseeded HfO2 layers on SS substrates.Keywords: Poly-crystalline diamond, photoluminescence, UNCD, Stainless Steel, Hafnium Dioxide

Field-emission diodes based on semiconductor—polycrystalline diamond heterojunctions

A complex of electrophysical and technological studies of solid-state field-emission diodes is carried out. Emission comes from an array of nanometer objects near the semiconductor—polycrystalline diamond interface. The process route of the diode heterostructures includes the fabrication of nanometer masks and nanometer cone (tip) arrays, as well as plasma-assisted growth of polycrystalline diamond films on the surface of structures with nanometer cone arrays. In field-emission diodes thus formed, a current density as high as 20 A/cm2 is achieved at a threshold of field emission from the nanotip arrays into the diamond of about 0.5 V.

Study of microwave plasma-assisted chemical vapor deposition of poly-and single-crystalline diamond films

We study conditions for microwave plasma-assisted chemical vapor deposition of high-quality single-crystal diamond films in a CVD reactor. These conditions are studied using the results of homoepitaxial growth of polycrystalline diamond films on diamond substrates and on the basis of numerical simulation of the microwave discharge in a CVD reactor. A high-quality single-crystal diamond layer is synthesized on a synthetic, type Ib diamond substrate. The properties of the obtained monolayer are studied by means of Raman and X-ray diffraction spectroscopy as well as optical and atomic-force microscopy.

Diamond coated molybdenum dental tools for machining orthodontic bridgework materials

The growth of polycrystalline diamond films on molybdenum dental burs using a new hot filament Chemical Vapour Deposition (CVD) system has been investigated. A negative d.c. bias voltage relative to the filament was applied to the molybdenum substrate prior to deposition and showed improved film adhesion and increased diamond nucleation density. The CVD coated molybdenum dental bur was found to give much improved performance and lifetime compared to the conventional sintered diamond burs. This paper describes the performance of diamond coated molybdenum dental burs machining orthodontic bridge such as cobalt-chromium alloys, and also portrays an interesting picture of how these alloys react to machining with diamond using a finite element method.

100]-textured growth of polycrystalline diamond films on alumina substrates by microwave plasma chemical vapor deposition

In order to grow diamond film on alumina ceramic, it is essential to control the diamond nucleation properly. Under a gas pressure lower than that used for growth, a high nucleation density of diamond films on alumina, as high as 10 8/cm 2, is successfully achieved by microwave plasma-enhanced chemical vapor deposition method. Based on this, [100]-textured diamond films are successfully deposited on alumina by controlling the substrate temperature. From the results on SEM, XRD and Raman measurements, the substrate temperature has a strong influence on the textured growth and quality of diamond films on alumina substrates. Too low or too high temperature cannot obtain [100]-textured and good-quality films. The optimum substrate temperature range, for the growth of [100]-textured and good-quality diamond films on alumina, should be 800∼860 °C in our experiments.

Chemical vapour deposition of diamond coatings onto molybdenum dental tools

The growth of polycrystalline diamond films onto molybdenum rods and dentalburrs by using a new hot filament chemical vapour deposition (CVD) system hasbeen investigated. Negative dc bias voltage relative to the filament was appliedto the molybdenum substrate prior to deposition. This led to much improvedfilm adhesion and increased nucleation density. There was a factor of fourimprovement in the adhesive force from 20 to 80 N when a bias voltage of−300 Vwas employed to the substrate.The CVD coated molybdenum dental burr was found to give much improvedperformance and lifetime compared to the conventional sintered diamond burr. TheCVD diamond burr showed no signs of deterioration even after 1000 operationswhereas the conventional sintered diamond burrs were ineffective after between 30and 60 operations. This represents a 30-fold improvement when CVD is applied.CVD diamond growth onto dental burrs has the potential for replacing excitingtechnology by achieving better performance and lifetime in a cost-effective manner.

Grain-Scale Modeling of CVD of Polycrystalline Diamond Films

The evolution of grain size, grain-size distribution, morphological and crystallographic texture, surface roughness, and the contribution of various surface facets to the growth of polycrystalline diamond films is performed by carrying out a series of two-dimensional computer simulations. The films are assumed to grow from a set of randomly oriented, {100}- and {111}-faceted nuclei by the motion of their vertices (the points where the adjoining facets of the same or neighboring grains meet). The vertex velocities are found to be a function of the orientation and the growth rate of the adjoining facets. To quantify the latter, a {100} to {111} growth-rate parameter is used. The results show that the evolution of the grain size and its distribution, surface roughness, morphological and crystallographic texture, and the portion of the film grown from different surface facets are all mutually linked and governed by the magnitude of the growth-rate parameter. The latter can be controlled by the CVD processing conditions, such as the substrate temperature, reactor pressure, mole fraction of carbon-source gas (e.g., CH4, C2H2).

Growth of Polycrystalline Diamond Films Including Diborane and Oxygen in the Source Gas

Boron‐doped polycrystalline diamond with both (100) and (111) facets were grown by microwave plasma chemical vapor deposition with and without oxygen to study effects of on surface morphology, crystal quality, and boron‐doping concentration of the films. It was found by Raman spectroscopy that the addition of improved the film quality as evidenced by the decrease of both the full width at half‐maximum of the diamond peak and the background level. By the addition of , the boron concentrations in the diamond decreased to the same extent by two orders of magnitude for both (100) and (111) facets, indicating that the oxygen is playing a role in the gas phase in suppressing the involvement of diborane. It was also observed by scanning electron microscopy that the (100) facets of the diamond grown with appeared darker than the (111) facets, while the opposite is the case for the films grown without . This is because the secondary electron emission was suppressed by a higher concentration of terminating species on the (100) facets as compared to the (111) planes, indicating the added oxygen is also affecting the chemistry of the diamond surface. © 1999 The Electrochemical Society. All rights reserved.

Growth of polycrystalline diamond films on stainless steel without external barrier layers using oxy-acetylene flame

Polycrystalline diamond films have been successfully deposited on stainless steel substrates using oxy-acetylene flame. Films have been characterized using scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Good quality diamond films were obtained by employing a short duration pretreatment of the substrates by the oxidizing outer zone of the flame, prior to film deposition using inner zone (acetylene feather) of the flame. Low growth temperatures (∼625 °C) and formation of oxides at the steel surfaces during pretreatment are suggested to be responsible for the growth of diamond films.

Transmission electron microscope observation of diamond/WC interface

Abstract The growth of polycrystalline diamond films on WC substrate has been investigated by transmission electron microscopy. Preferential growth of columnar subgrains of 10–50 nm in diameter results in the formation of large grains with 4 μm spacing. The interfacial stress between diamond and WC is accommodated by twins and stacking faults. Graphite layers of 10–40 nm in thickness are observed locally, but mostly the diamond is deposited directly on WC grains.

Deposition of diamond films on metal substrates

In this paper we report on the growth of polycrystalline diamond films on Mo, W, and Ni substrates using oxy-acetylene combustion flame technique. Effect of substrate temperature on the growth of diamond films has been studied in the temperature range 600–1100°C. The deposits and their surface morphology has been characterized by X-ray diffraction and scanning electron microscopy (SEM). A short duration pretreatment of Mo substrates by outer zone of the oxy-acetylene flame at lower substrate temperatures, results in the improvement of quality and adherence of the films. Growth of diamond as well as other intermediate compounds depending on the nature of substrates and interface layers is discussed.

CVD diamond films on bio-medical ceramics

In this study, the growth of diamond films by the hot filament chemical vapour deposition method on ceramic substrates is presented. The ceramics, used in teeth implants, were sintered at 970 °C, and were mainly constituted by SiO 2 , Al 2 O 3 and other oxides. To avoid substrate damaging, the diamond deposition was carried out at a lower temperature than usual. Raman spectroscopy demonstrated the growth of polycrystalline diamond films with a very low content of amorphous carbon phases at a temperature as low as 750 °C. The thermal expansion mismatch between film and substrate causes the films thicker than 0.2 μm to break, but the high nucleation density of diamond obtained when the ceramic was scratched with diamond powder allowed the formation of compact and well-adhered diamond films, even with this small thickness. Optical analysis of the reflection spectra of the coating in the visible range, when compared with the spectra of the bare ceramic, showed that diamond films do not appreciably affect the reflection of light.

Photoelectron spectroscopy of CVD diamond

We report a study of the electronic structure of thin diamond films by core state (X-ray photoelectron spectroscopy (XPS)) and valence band (UV photoelectron spectroscopy (UPS)) photoelectron spectroscopy. These techniques were used to investigate the different phases in the initial growth of polycrystalline diamond films on Si(100) substrates. The films were deposited by a standard microwave technique as well as by bias-enhanced microwave plasma chemical vapour deposition in a dilute mixture of methane in hydrogen. The influence of sample preparation (such as prebiasing or prescratching of the silicon surface with different sized diamond powder prior to deposition) on nucleation density and electronic structure was also investigated by scanning electron microscopy and photoelectron spectroscopy (PES) respectively. The surface composition was probed as a function of deposition time. The XPS data reveal the formation of an SiC phase at the early stage on nucleation, preceding the gradual growth of diamond. At intermediate stages a combination of different carbon phases was observed. The atomic structure of the interface phases is discussed and a growth model is proposed. Valence band spectra of the different samples show the extreme sensitivity of PES to impurities and to surface properties such as reconstruction. The obtained data were compared to valence band measurements of natural diamond and other forms of carbon and to some extent to data obtained with Raman spectroscopy.

Low temperature (∼400 °C) growth of polycrystalline diamond films in the microwave plasma of CO/H2 and CO/H2/Ar systems

In order to elucidate the growth conditions for pure diamond of good crystallinity, the correlation of the properties of deposited films and gas phase species in microwave plasma of CO/H2 and CO/H2/Ar systems was investigated through film characterization and optical emission spectroscopic measurements. It was found that the increase of gas phase atomic hydrogen and the suppression of gas phase acetylene were effective for the growth of pure diamond of good crystallinity. Low temperature growth was proposed to realize these growth conditions. It was confirmed that diamond films with good crystallinity and optical transparency could be synthesized at 410 °C (diamond film growth was possible even at 365 °C). The growth rate was accelerated in a CO/H2/Ar system (0.33 μm/h at 410 °C), which was several times faster than that obtained in a CO/H2 system (0.14 μm/h at 450 °C).

Intermediate layers for the deposition of polycrystalline diamond films

Thin films of BN, hard carbon, a-C:H, and SiC have been deposited onto ZnS or (100)-silicon as precursors to the growth of polycrystalline diamond films. These layers must protect the substrate from chemical attack at the deposition temperatures used in microwave plasma chemical vapor deposition (CVD) and also promote the nucleation of crystalline diamond. The thermal stability, the optical properties of these coatings, and their ability to nucleate diamond growth are investigated. BN thin films appear to be the best interlayer for both protection and nucleation enhancement. Hard carbon and a-C:H interlayers provide no real benefit in themselves. Silicon carbide was identified at the interface between one type of hard carbon film and the silicon substrate using x-ray photoelectron spectroscopy (XPS). Si–C islands may provide nucleation sites for CVD diamond. Silicon carbide can provide both protection and nucleation enhancement if the crystallinity and texture are optimized.

The role of the tungsten filament in the growth of polycrystalline diamond films by filament-assisted CVD of hydrocarbons

The role of the tungsten filament in the growth of polycrystalline diamond films by filament-assisted CVD of hydrocarbons was investigated. Besides the well known phenomenon of catalytic dissociation of molecular hydrogen on a hot W-filament, we found that the filament undergoes carburization and converts into α-W 2C. The kinetics of this carburization process and its effects on the nucleation of the diamond films can be investigated by studying the resistance of the filament during the carburization stage. The carburized filament was found to be a better electron emitter. This together with the fact that electron bombardment of the substrate leads to higher nucleation rate suggests that an α-W 2C filament will lead to more efficient growth of diamond thin films.

Synthesis of diamonds by use of microwave plasma chemical-vapor deposition: Morphology and growth of diamond films.

An investigation is made of the surface morphology and growth of polycrystalline diamond films deposited on Si substrates using the microwave plasma chemical-vapor-deposition (CVD) method. For the source gas, ${\mathrm{CH}}_{4}$ and ${\mathrm{H}}_{2}$ gases mixed in different concentrations are used. Scanning electron microscope pictures of the diamond films synthesized for 7 h show that the film surface consists of triangular (111) diamond faces for ${\mathrm{CH}}_{4}$ concentrations c0.4 vol %, whereas square (100) faces are predominant above c\ensuremath{\simeq}0.4 vol %. For c\ensuremath{\gtrsim}1.2 vol %, the number density of (100) faces decreases with c and finally at c\ensuremath{\simeq}1.6 vol % the film surface becomes entirely structureless, consisting of microcrystallites only. For characterization of the films, x-ray and electron diffraction are measured along with Raman and infrared spectra. In the study of the evolution of surface morphology during film growth, it is found that diamond particles grown on the substrate initially increase their size almost uniformly until the substrate is entirely covered. Then a secondary growth takes place, followed by surface-restructuring processes such as ``fusion'' and ``absorption'' among secondary crystallites. As a result, well-defined diamond faces are formed progressively on the film surface. Higher-order growths followed by the restructuring processes occur periodically as the CVD synthesis proceeds.

Infrared detection of gaseous species during the filament-assisted growth of diamond

Infrared diode laser absorption spectroscopy is employed as an in situ method to examine gas phase species present during filament-assisted deposition of diamond films. From a reactant mixture of 0.5% methane in hydrogen, methyl radical (CH3 ), acetylene (C2H2), and ethylene (C2H4 ) are detected above the growing surface, while ethane (C2H6 ), various C3 hydrocarbons, and methylene (CH2) radicals are below our sensitivity levels. The growth of polycrystalline diamond films on Si wafers and polycrystalline Ni is confirmed with x-ray and Raman scattering, scanning electron microscopy, and Auger electron spectroscopy.