Μm Diamond Powder Research Articles

Preparation and Property Modulation of Multi-Grit Diamond/Aluminum Composites Based on Interfacial Strategy

The development of electronic devices has a tendency to become more complicated in structure, more integrated in function, and smaller in size. The heat flow density of components continues to escalate, which urgently requires the development of heat sink materials with high thermal conductivity and a low coefficient of expansion. Diamond/aluminum composites have become the research hotspot of thermal management materials with excellent thermophysical and mechanical properties, taking into account the advantages of light weight. In this paper, diamond/Al composites are prepared by combining aluminum as matrix and diamond reinforcement through the discharge plasma sintering (SPS) method. The micro-interfacial bonding state of diamond and aluminum is changed by adjusting the particle size of diamond, and the macroscopic morphology performance of the composites is regulated. Through this, the flexible design of diamond/Al performance can be achieved. As a result, when 150 μm diamond powder and A1-12Si powder were used for the composite, the thermal conductivity of the obtained specimens was up to 660.1 W/mK, and the coefficient of thermal expansion was 5.63 × 10−6/K, which was a good match for the semiconductor material. At the same time, the bending strength is 304.6 MPa, which can satisfy the performance requirements of heat-sinking materials in the field of electronic packaging.

3D gel-printing of phenolic resin-based diamond tool parts

In this study, the phenolic resin-based diamond tool parts were successfully prepared by 3D gel-printing (3DGP), the rheological properties of printing slurries and mechanical properties of the prepared resin-based diamond parts were characterizated. The results show that when the amount of phenolic resin to anhydrous ethanol was 2:1, the slurry was suitable for extrusion printing, and it was also easy to keep the shape of the printed product. When the needle size was 0.60 mm, the layer height was 0.48 mm, and the line width was 0.48 mm, the printed products had superior surface quality. For dense parts, the three-point bending strength of diamond part printed was about 27.0 MPa. The Rockwell hardness values of the dense parts prepared from the two powders were 81.0 for 1.58 μm and 85.1 for 2.61 μm, and their roughness (Ra) was about 6.99 μm and 6.15 μm, respectively. For porous parts, the bending strength of parts prepared from 1.58 μm diamond powder was from 11.8 MPa to 18.2 MPa and that of parts prepared from 2.61 μm diamond powder was from 15.5 MPa to 21.6 MPa when the porosity was 20–50%. The dense and porous resin-based diamond parts with controllable structure and porosity were successfully prepared by 3DGP, which has a promising future application in the field of abrasive materials.

Investigation of Nucleation and Growth of Nanocrystalline Diamond Films Deposited at Low Temperature Using In Situ Laser Reflectance Interferometry

The nucleation and growth of nanocrystalline diamond (NCD) films deposited at low temperature on silicon substrates with a distributed antenna array (DAA) plasma enhanced chemical vapor deposition (PECVD) system is investigated using in situ laser reflectance interferometry (LRI). An optical model is developed using an effective media theory in order to describe the LRI signal recorded during NCD growth and to extract the nucleation density. The model is validated through comparisons with nuclei counting from Scanning Electron Microscopy (SEM) micrographs. LRI is then employed to investigate the influence of several ex situ pre‐treatments of silicon substrates. The nucleation density is estimated between 7.3 × 109 for ultrasonic abrasion with 40 μm diamond powder and 5.9 × 1010 for seeding with 4.2 nm nanodiamond solution. The LRI technique is also employed to estimate in real time the critical thickness leading to the film delamination. The critical thickness for seeding methods is estimated in the range 485–545 nm, whereas no delamination is observed for the sample achieved on Si substrate pre‐treated by ultrasonic abrasion that reaches a thickness of 674 nm after a deposition of 20 h.

Burnishing of Aluminium Alloy Surface Using Diamond Matrix Composite Tools

To make the most of unique properties of diamond and to diminish an influence its disadvantageous properties new diamond tool composites with ceramic bonding phase (MAX) has been proposed. Ti3(Si,Ge)C2 and Ti3SiC2 were produced by self-propagating high temperature synthesis (SHS). 3-6 µm (MDA, De Beers) diamond powder was mechanically mixed with 10 wt% Ti3(Si,Ge)C2 or 30 wt% Ti3SiC2, pressed and the compacts were sintered at 1962 °C at 8.0 GPa in a Bridgman-type high pressure apparatus. These mechanical properties were determined: Vickers hardness HV1, Young’s modulus, tensile strength, fracture toughness and wear resistance.Microstructure and phase composition were studied by scanning and transmission electron microscopy and X-ray and electron diffraction techniques. To improve the final quality of the AlCu4MgSi(A) alloy, balls of diamond-new composites were incorporated into the burnishing tools. The influence of burnishing parameters, such as burnishing force and feed, on surface geometry parameters were measured and profilograms of the surface roughness recorded.

The role of surface activation prior to seeding on CVD diamond adhesion

A special surface pre-treatment protocol consisting of four steps is proposed to provide high adhesion levels for CVD diamond by hot-filament technique. In step 1, the silicon nitride ceramic substrates are surface ground with 15 µm diamond slurry and mirror-like polished with colloidal silica (0.05 µm). In step 2, plasma etching with CF 4 (PE), mechanical anchoring is promoted due to the surface roughness increment. Surface activation (SA) is the following step, where the substrates are subjected to CVD diamond growth conditions for a short time (30 min), leading to the deposition of an amorphous carbon layer responsible for enhancing the nucleation density and the further growth of diamond during early stages of deposition. The final step 4 is 0.5–1 µm diamond powder seeding in an ultrasonic bath. The results show that the Si 3 N 4 ceramic surface modified by the surface pre-treatment protocol allowed a high nucleation density promoting a continuous and homogeneous film of equally sized diamond grains, at a growth rate of ap. 1.5 µm h − 1 . Brale tip indentation tests confirmed that highly adherent films are thus produced (no delamination under 900 N).

High pressure and high temperature sintering of fine-grained PCD using bi-layered assembly

This work presents the study of the synthesis and characterization of polycrystalline diamond (PCD) compacts using a bi-layered assembly method and solving the catastrophic nature of failure molding when using single-layered assembly and 0.5–1.5 μm diamond powder as starting materials. The well-sintered PCD compacts are prepared on WC-16wt% Co substrates at temperatures from 1350 °C to 1500 °C for 15 min at static high pressure of 5.2 GPa, using the bi-layered assembly method. According to our scanning electron microscope observation, the specimens sintered at 1450 °C have a homogeneous microstructure. The graphitization of the diamond appears at 1500 °C according to X-ray diffraction analysis. The specimens sintered at 1450 °C show the best performance according to the wear resistance test.

Fabrication of MgB 2/Au/Nb and MgB 2/Nb Josephson junctions

We have fabricated planar type Josephson junctions from MgB 2 thin films by using a Nb thin film as the counter electrode with and without a normal Au barrier layer. The superconducting MgB 2 layer was prepared by diffusion-annealing of B precursor film on a sapphire substrate in Mg vapor. The film surface was mechanically dry-polished with 1/4 μm diamond powder to remove nonsuperconducting residues and subsequently cleaned using argon ion beam. Junction was defined on an area of 4 μm × 4 μm through a 150 nm thick SiO x insulating layer by argon ion milling with photolithography and completed by depositing a normal thin Au layer (0–10 nm) and a 150 nm thick Nb counter electrode. The offset T c was at least 30 K for the MgB 2 electrode and 9 K for the Nb electrode. Current–voltage curves showed typical Josephson transition characteristics. Periodic modulation of the junction critical current under magnetic field was observed in agreement with the standard Fraunhoffer diffraction pattern of a Josephson junction.

Carbon Nanotubes and Nanofibers Grown by Microwave Plasma Enhanced Chemical Vapor Deposition on a Nickel Substrate

ABSTRACTBoth carbon nanotubes and carbon nanofibers were grown on a thick nickel substrate by means of microwave plasma enhanced chemical vapor deposition (MPECVD) process using 20% CH4 and 80% H2 at a temperature of 750°C and a pressure of 50 Torr. The substrate was pre-abraded with 1.0μm diamond powder and 15.0 μm diamond paste to increase the rate of nucleation. When the substrate is taken out of the reactor the film detaches itself completely from the nickel. Unusual outgrowth structures appear jutted on one section of the substrate in a symmetrical manner. These structures were very hard and, when analyzed using environmental scanning electron microscope (ESEM), Raman microscopy and transmission electron microscope (TEM), micro-trees and an abundance of multi wall carbon nanotubes (MWCNTs) and nanofibers were observed. An attempt to measure the hardness of the film using a nano-indenter was inconclusive due to the extreme hardness of the material produced.

CVD diamond nucleation enhanced by ultrasonic pretreatment using diamond and mixture of diamond and TaC powders

Effects of ultrasonic pretreatment on chemical vapor deposition (CVD) diamond nucleation on Si substrates were systematically studied. Pure 1.5–40 μm-diamond powder and mixtures of 1.5–5 μm-diamond as well as 5–20 μm-Tantalum Carbide (TaC) powder were used in ultrasonic pretreatment. The root-mean-square (Rms) surface roughness of the pretreated substrates, residual diamond and TaC powders left on the substrates were examined using atomic force microscopy (AFM), Raman spectroscopy and X-ray diffraction (XRD), respectively. It was observed that the Rms surface roughness increases with increasing diamond or TaC powder size, and there is some diamond or TaC powder left on the substrates after ultrasonic pretreatment. Diamond films were deposited using microwave plasma chemical vapor deposition (MPCVD) technique and characterized by field emission scanning electron microscopy (FE-SEM). It was found that CVD diamond nucleation density strongly depends on particle size of diamond or TaC powder used, the nucleation density increases with increasing diamond or TaC powder size. A mixture of diamond and TaC powders enhances CVD diamond nucleation much more significantly than that of pure diamond powder. A mixture of 1.5 μm-diamond and 20 μm-TaC powders has an equivalent nucleation enhancement efficiency, which could be caused by pure 40 μm-diamond powder.

Growth of nanocrystalline diamond protective coatings on quartz glass

Transparent diamond films with a crystallite size well controlled below 70 nm were grown by hydrogen and methane microwave plasma-enhanced chemical vapor deposition on quartz glass substrates, which had been scratched with 0.5 μm diamond powder. A complementary set of analyzing tools was employed to study the microstructure, the optical and mechanical properties of the deposits. Transmission electron microscopy revealed a nucleation density generally larger than 1011/cm2, which is of the same order of magnitude as the spotlike defects on the pretreated surface of the substrates. The Vicker’s hardness of the deposits scatters between 61 and 95 GPa. An optimal transmittance of 65% in the visible light range is achieved in coatings of 1.0 μm in thickness when the surface roughness measures about 10 nm or less. The nanocrystalline diamond films thus prepared can meet the requirements on transparent protective coatings for optical components.

Growth, characterization, optical and X-ray absorption studies of nano-crystalline diamond films

Abstract We report here the growth of thin diamond films, with an average grain size ranged from 3.6 nm to 5 μm, by microwave plasma enhanced chemical vapor deposition via different substrate pretreatment and varying methane fraction in the source gas. Specifically, the substrate pretreatment involved using two different grain sizes, 4 nm and 0.1 μm, of the diamond powder for ultrasonic agitation. Transmission electron microscopy, optical transmission spectra, and X-ray absorption spectra have been employed to characterize the resultant films. For each film, the grain size distribution was obtained by directly analyzing the dark-field images of the film. For films deposited with 0.1 μm diamond powder pretreatment, the grain size of the film decreased as the methane fraction increased. The opposite trend was observed for 4 nm diamond powder pretreated films. X-ray absorption spectra at the C K-edge showed clear bulk diamond excitonic and sp3 features with little evidence of sp2 bonding even for films with an average grain size as low as 3.6 nm. Furthermore, a blue shift of the exciton state and conduction band edge was observed with the decrease of the grain size of the film, indicating a quantum confinement effect. On the other hand, no direct relationship between the grain size of the film and the optical transmission was observed. The key parameter that dictated the optical transparency of the film was the surface roughness provided that the film maintained high sp3 content.

The annealing effect on the electrical property of the Al/undoped diamond film

Abstract Polycrystalline diamond films were deposited using a methane–hydrogen gas mixture in a microwave plasma assisted chemical vapor deposition system. Prior to deposition the silicon substrate was seeded, by photoresist, with 0.1 μm diamond powder. Then, the polycrystalline diamond films were annealed at 800°C under N2 gas flow for 1 h. From the ESCA analyses, it was observed that the oxygen signal increases substantially, the carbon signal became very weak and the silicon (Si) signal showed up appreciably after the 800°C annealing process. In this study, a conduction mechanism was successfully established for the Al/annealed undoped diamond structure in the temperature ranges of 30–300°C. It was considered that a Schottky contact was also formed in the diamond grain boundaries. The modified equivalent circuit for the Al/annealed undoped diamond structure is an ideal Schottky diode in series with the bulk resistance for the bulk diamond crystallites, which is also in parallel with an opposite pole of the ideal Schottky diode in series with the grain boundary resistance for the diamond grain boundaries. It was observed that the electrical characteristics of the Al/annealed undoped diamond structure showed more ohmic behavior at high temperatures. It was suggested that the oxidation layer in the Al/annealed diamond interface was degraded after the high temperature measuring process. It was found that the field-activated transport mechanism, in which the series resistance can be represented by the modified Frenkel–Poole equation, the effective oxidation layer thickness and the electromigration effects both being included, gave a better fit to the experimental data.

The surface properties on both sides of the isolated diamond film

The polycrystalline diamond films in this research were deposited on silicon substrates using a methane–hydrogen gas mixture by the microwave plasma chemical vapor deposition (MPCVD) system. Prior to deposition, the silicon wafers were pretreated by a photoresist in which 0.1 μm diamond powder is suspended. The isolated diamond film was then obtained by etching the backside of the silicon wafer with KOH solution. The bottom surface of the isolated diamond film exhibited a much smoother surface profile than the top surface of the isolated diamond film. From XPS analysis, the oxygenated phenomenon was detected for the as-deposited diamond film and increased for both surfaces of the isolated diamond film after the back-etching process. It was noted that the oxygenated phenomenon did not degrade the film quality since the quality of the isolated diamond film improved after the back-etching process. An estimated 600 Å thick SiC layer and an amorphous carbon interlayer was found on the bottom surface, which is in the diamond–Si interfacial region of the isolated diamond film. Experimental results showed that the film quality was not dependent on the grain size and roughness of the diamond film. The shift of the characteristic diamond peak was due to the strain force that was formed in the interface of diamond–Si during the cooling-down period of the deposition process. The thick layer of SiC and the amorphous carbon interlayer also affected the film quality in the interfacial region during diamond deposition and the noise of the Raman spectrum increased for the bottom surface of the isolated diamond film.

Surface analysis of boron-doped polycrystalline diamond films deposited by a microwave plasma chemical vapor deposition system

Polycrystalline diamond films were deposited on silicon substrates by a microwave plasma chemical vapor deposition (MPCVD) system. Raman, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used for the analyses of the diamond films. Prior to deposition the silicon substrate was seeded, by photoresist, with 0.1 μm (micron) diamond powder. Using this pretreatment technique results in an oxygen-rich phase on the substrate surface, oxygen is easily incorporated into diamond grain boundaries during the synthesis of the diamond films. The oxygenated phenomenon also increased after the diamond films were exposed to air for a period of time. Experiments showed that the diamond crystallite surfaces and the diamond grain boundaries are the two major sources causing the adsorption of oxygen on the surface layers of the diamond films. At room temperature, the reaction between the diamond grain boundaries and air is fast and oxidized dangling bonds are hard to remove. The oxidized dangling bonds are gradually formed on the diamond crystallite surfaces and are easily removed. The quality of the diamond film degraded after the boron ion implantation. The oxygenated phenomenon increased considerably after the boron-doped diamond films were annealed at 800°C and the quality of the boron-doped diamond films degraded appreciably. The oxygenation layer which is formed on the surface of the annealed boron-doped diamond film is difficult to be etched away.

Coalesced oriented diamond films on nickel

The growth of coalesced, highly oriented diamond films has been achieved on nickel substrates using a multistep process that consisted of (i) seeding the Ni surface with 0.5 μm diamond powder, (ii) annealing at 1100 °C in a hydrogen atmosphere, and (iii) growth at 900 °C in a mixture of hydrogen and 0.5% methane. Auger depth profile analysis of a sample quenched after the annealing stage showed the presence of significant amounts of carbon (6 at. %) close to the substrate surface and about 3 at.% deeper in the substrate. The loss of carbon into the substrate resulted in relatively low nucleation density. The addition of methane into the gas phase during the annealing stage proved very effective in compensating for the diffusion. An addition of 0.5% methane in the gas phase produced optimum results, as the nucleation density, orientation of diamond particles, and uniformity were substantially improved. Substrates nucleated under these conditions were grown out into coalesced, 30 μm thick films. Both (100) and (111) oriented films showed a high degree of orientation and Raman spectra obtained from these orientations showed intense and narrow diamond signature peaks with FWHM's of 5 and 8 cm-1, respectively.

Studies on CVD-diamond on Ti6Al4V alloy surface using hot filament assisted technique

Diamond growth on Ti6Al4V substrate has been studied using a hot filament assisted technique. The substrate surface pretreatment consisted of polishing with 1- μm diamond paste using oxalic acid followed by pitting in an ultrasonic bath with a 0.25- μm diamond powder suspension in n-hexane for 20 min. The main parameters of the diamond growth with CH 4/H 2 gas mixture and the mechanical properties of the substrate have been studied as a dependence of substrate temperature. The film was completely formed after 20 min at a 800°C substrate temperature. The adherence between film and substrate has been shown to be strongly dependent on substrate temperature and growth time. Adherent and good quality CVD diamond films, as thick as 10 μm, have been obtained at a 600°C growth temperature. Stress dependence on growth parameters has been studied by Raman spectroscopy.

Method for achieving high selectivity and resolution in selectively deposited diamond films

A process for depositing CVD diamond selectively on silicon is presented. Using standard photolithography techniques, wafers are patterned with 0.6 μm resist features. Chromium is then deposited through electron beam evaporation and lifted off of the desired growth areas with acetone. After scratching with 0.5 μm diamond powder, the chrome film is etched off and diamond deposited in a hot filament CVD system. Micrographs demonstrating a high degree of selectivity and micron-scale resolution are presented. These include contiguous, single crystallite wide lines and square arrays of individual nuclei with 10 μm periodicity

Effect of the substrate state on the formation of diamond film in a low temperature microwave-plasma-enhanced chemical vapor deposition system

Diamond films were deposited on substrates using a low temperature microwave-plasma-enhanced chemical vapor deposition system. Low temperature (below 500 °C) deposition can be achieved only by making the substrate position remote from the plasma under the normal deposition condition. The substrate was untreated or was pre-treated by 30 μm diamond powder. Among various substrates (untreated silicon, pre-treated silicon, pre-treated quartz, untreated glass, and pre-treated glass), pre-treated quartz and pre-treated glass enhance the diamond formation, while untreated glass gives only graphite formation even under the same deposition conditions. We understand that the better formation of diamond on pre-treated glass and pre-treated quartz was due to the existence of a diamond particle on the substrates. We also deposited diamond films on pre-treated glass at various CH4 concentrations. The largest grain size can be acquired at 3% of CH4 concentration and the growth rate of the film increases with increasing CH4 concentration.

Ultrahigh nucleation density for growth of smooth diamond films

An ultrahigh density seeding process of diamond thin-film deposition is demonstrated. Diamond powders with average grain sizes of 0.038 and 0.101 μm were used to study the surface roughness as a function of deposition time, film thickness, and nucleation density. The diamond films, prepared by hot filament chemical vapor deposition, were characterized by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. An extremely high nucleation density on the order of 1011 cm−2 was achieved by coating 0.038 μm diamond powder on the surface of the Si substrate. One micron thick films were obtained with the mean surface roughness of 30 nm.

Effect of Surface Finish on Nuclear Glass Dissolution Rate

ABSTRACTThe influence of the surface finish on nuclear glass dissolution was investigated. Seven different surface finishes were tested: a specimen as cut, three specimens polished with 220, 600 and 4000 mesh SiC paper and one with 1 μm diamond powder, a flame-polished specimen and a thermal rupture specimen.The initial glass corrosion rates were measured after 7 and 28 days of Soxhlet leaching at 100°C. The surface finish of each glass coupon was also assessed by three-dimensional analysis before and after leaching for 28 days. Leaching solution analyses showed that the mean apparent leach rate for the first 7 days was highly dependent on the surface finish: the measured rates ranged from 3.8·g.m-2d-1 for the as-cut specimen to 1.3 g·m-2d-1 for the flamepolished specimen. The differences in the leach rates diminished considerably after 28 days of leaching: the mean rate measured between 7 and 28 days for the as-cut and polished specimens was identical (1.7 g·m-2d-1), but was still lower for the remaining two specimens. Three-dimensional surface analysis showed that leaching revealed surface defects (superficial microcracks) produced by cutting or polishing. These effects were less perceptible on the flame-polished or thermally ruptured specimens. The actual surface area of the cut and polished specimens exceeded the apparent geometrical area.In another experiment, the leach rates measured for as-cut specimens and flamepolished specimens were measured over periods of five months or more using a thermogravity balance placed above the Soxhlet device. The experiment confirmed the existence of an initial period during which the dissolution rate for the as-cut specimen was much higher than the mean corrosion rate.