Diamond Microstructures Research Articles

Limiting Aspect Ratio of Diamond Microstructure Fabricated by Model Copy Technology

Model copy technology is an ideal approach for diamond patterning. However, incomplete filling were discovered in some of the diamond microstructures which were produced by model copy method. The effect of structural aspect ratio on the filling was investigated. The growth form of CVD diamond in the micro mould was analyzed. Results show that the nonuniformity of gas velocity distribution in the mould is the main course of incomplete filling, and an aspect ratio larger than 0.5 is necessary to achieve a complete filling.

The microstructure, mechanical and friction properties of protective diamond like carbon films on magnesium alloy

Protective hard coatings deposited on magnesium alloys are believed to be effective for overcoming their poor wear properties. In this work, diamond-like carbon (DLC) films as hard protective films were deposited on AZ91 magnesium alloy by arc ion plating under negative pulse bias voltages ranging from 0 to −200V. The microstructure, composition and mechanical properties of the DLC films were analyzed by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and nanoindentation. The tribological behavior of uncoated and coated AZ91 magnesium alloy was investigated using a ball-on-disk tribotester. The results show that the negative pulse bias voltage used for film deposition has a significant effect on the sp3 carbon content and mechanical properties of the deposited DLC films. A maximum sp3 content of 33.3% was obtained at −100V, resulting in a high hardness of 28.6GPa and elastic modulus of 300.0GPa. The DLC films showed very good adhesion to the AZ91 magnesium alloy with no observable cracks and delamination even during friction testing. Compared with the uncoated AZ91 magnesium alloy, the magnesium alloy coated with DLC films exhibits a low friction coefficient and a narrow, shallow wear track. The wear resistance and surface hardness of AZ91 magnesium alloy can be significantly improved by coating a layer of DLC protective film due to its high hardness and low friction coefficient.

Effect of coating on the microstructure and thermal conductivities of diamond–Cu composites prepared by powder metallurgy

Diamond–Cu composites from the direct combination of diamond and Cu show low thermal conductivities due to weak interface and high thermal resistance as a result of chemical incompatibility. In this paper, a new method is proposed to strengthen interfacial binding between diamond and Cu by coating strong carbide-forming elements, e.g., Ti or Cr on the surface of the diamond through vacuum micro-deposition. Interfacial thermal resistance of diamond–Cu composites is greatly decreased when diamond particles are coated by a Cr or Ti layer of a certain thickness before combining with Cu. Thermal conductivity is also increased several times. Cr coating can reduce more effectively interface thermal resistance between diamond and Cu than Ti coating. Moreover, it has a smaller negative impact on the thermal conductivity of the Cu matrix, resulting in higher thermal conductivity of Cr-coated diamond–Cu composites. Through the vacuum micro-deposition technology, Cr on the diamond particle surface is present in the form Cr 7C 3 near diamond and a pure Cr outer layer at 2:1. The optimum thickness is within 0.6–0.9 μm; at this depth, the thermal conductivities of 70 vol% diamond–Cu composites can be increased four times and reach as high as 657 W/m K. In this work, an original theoretical model is proposed to estimate the thermal conductivities of composite materials with an interlayer of a certain thickness. The predicted values from this model are in good agreement with the experimental values.

Microstructure, residual stresses and shear strength of diamond–steel-joints brazed with a Cu–Sn-based active filler alloy

Brazing of diamonds is important in grinding technology. The brazing parameters can strongly influence the grinding tool's performance. In this work a Cu–Sn-based active filler alloy (73.9 Cu–14.4 Sn–10.2 Ti–1.5 Zr, wt.%) was applied to join monocrystalline block-shaped diamonds onto a stainless steel substrate using three different brazing temperatures (880, 930 and 980 °C) and two different dwell times (10 and 30 min), respectively. The characteristics of the joints were investigated by means of scanning electron microscopy and energy dispersive X-ray spectroscopy (microstructure and phase composition), by Raman-spectroscopy (residual stress) as well as by shear testing (bond strength). The microstructural investigations revealed an intermetallic interlayer of type Fe 2Ti at the steel-filler alloy interface, which grew with increasing brazing temperatures and longer dwell durations. The brazing parameters strongly affected the residual stresses in the diamond. Compressive residual stresses with a maximum value of − 350 MPa were found in the samples brazed at 880 and 930 °C, whereas tensile stresses of maximum + 150 MPa were determined in samples joined at 980 °C. The effect of the brazing parameters on the shear strength is very pronounced. The shear strength decreased from (321 ± 107) MPa at 880 °C, 10 min to (78 ± 30) MPa at 980 °C, 30 min.

Investigation of Interface Microstructure of Diamond and Ti Coated Diamond Brazed with Cu-Sn-Ti Alloy

Cu-Sn-Ti brazing alloys are gaining importance as active brazing alloys for brazing diamond tools. The microstructure at the interface between diamond or Ti-coated diamond grits and Cu-Sn-Ti brazing alloy and bonding strength have been investigated in this paper. The results show that TiC layer forms between diamond and alloy matrix during the brazing process and Sn- and Ti-based intermetallic phase forms between TiC and the bonding matrix. And compound SnTi3forms between the Ti-coated diamond grits and Cu-Sn-Ti brazing alloy. Furthermore, the bonding strength between Ti-coated diamond grits and brazing alloy is higher than that between diamond grits and brazing alloy.

Directly Grown Nanocrystalline Diamond Field-Effect Transistor Microstructures

Nanocrystalline diamond microscopic structures (5 m width) are grown directly on Si/SiO2 substrates by patterning of a nucleation layer using photolithography prior to the diamond growth. The diamond in a thickness of 300 nm is grown by a microwave chemical vapor deposition on the nucleation patterns. Morphology and material composition of the microstructures are characterized by scanning electron microscopy and atomic force microscopy. The diamond microstructures exhibit clear transistor characteristics in both solid-state and solution-gated field-effect transistor configurations. The conductivity is generated by a transfer doping of hydrogen-terminated diamond surface. Gating of the transistors is realized by a deposition of Al electrode or by an immersion into a pH buffer in contact with Ag/AgCl electrode. The solution-gated field-effect transistors are sensitive to pH.

グラファイト-ダイヤモンド相転移プロセスと微細組織 －局所応力とグラファイト結晶度の影響－

グラファイト-ダイヤモンド相転移プロセスと微細組織 －局所応力とグラファイト結晶度の影響－

Diamond deposition on hardmetal substrates – Comparison of substrate pre-treatments and industrial applications

Abstract Diamond deposition on various hardmetal tools is widely used. For applications where the mechanical forces are low diamond coatings have long lifetimes, but especially for heavy duty applications the reproducibility of the diamond coating adhesion is not adequate. Wear and lifetime of diamond coated tools are determined by the diamond microstructure, the coating thickness, and the adhesion of the coating. The diamond substrate interface is important for layer adhesion, but in the case of diamond deposition on hardmetal tools, the interface can change during the diamond deposition. For this reason, surface pre-treatments are important, not only for a better diamond nucleation, but also to create a stable interface that allows good coating adhesion. The various aspects of different surface pre-treatments of hardmetal tools will be discussed.

Influence of the brazing parameters on microstructure, residual stresses and shear strength of diamond–metal joints

The reliability and integrity of diamond cutting tools depend on the properties of diamond–metal joints as created by a brazing process. Block-shaped monocrystalline diamonds were brazed onto a steel substrate (X2CrNiMo 18-14-3), using silver–copper based Cusil-ABA™ (Ag–35wt%Cu–1.75wt%Ti) filler alloy. The experimental procedure includes a thorough microstructural investigation of the filler alloy, the determination of the induced residual stresses by Raman spectroscopy as well as the joint’s shear strength utilizing a special shear device. The brazing processes were carried out at 850, 880 and 910 °C for dwell durations of 10 and 30 min, respectively. At the steel interface two interlayers develop. The layers grow with extended dwell duration and higher brazing temperature. The residual stresses only slightly depend on the brazing parameters and exhibit a maximum value of −400 MPa. Unlike the residual stresses, the shear strength strongly depends on the brazing parameters and thus on the microstructure. Three failure modes could be identified; a ductile fracture in the filler alloy, a brittle fracture in the interlayers and a partly shattering of the diamond.

Realisation and characterisation of mass-based diamond micro-transducers working in dynamic mode

We report on novel MEMS micro-transducers made of diamond and targeted for bio-sensing applications. To overcome the non-straightforward micromachining of diamond, we developed a bottom up process for the fabrication of synthetic diamond micro-structures involving the patterned growth of diamond using the CVD (chemical vapour deposition) technique, inside micro-machined silicon moulds. Here typical resonant MEMS structures including cantilevers fabricated using this method were characterized by measuring their first mode resonance (frequency and Q-factor) by Doppler laser interferometry. The experimental data matched the simulation data. Data from bare diamond cantilevers and from diamond cantilevers with actuation gold track on the surface were compared and showed a significant decrease in the resonant frequency in the presence of gold tracks. Nevertheless, comparisons with equivalent silicon structures demonstrated the superior performances of diamond cantilevers: the resonance frequencies were twice higher and the Q-factors 2.5 times higher for the diamond transducers. Diamond cantilevers sensitivity were measured using PMMA deposition and values as high as 227.4 Hz ng −1 were found. It was shown that diamond mass sensitivity values are typically two times higher than identical silicon devices. Finally, the limit of detection (LOD) of diamond cantilevers was found experimentally to be as low as 0.86 pg using our set up. This is suitable for many bio-sensing applications.

Simplified procedure for patterned growth of nanocrystalline diamond micro-structures

Two technological strategies to generate patterned diamond growth have been tested. The diamond micro-structures (i.e. linear stripes and 5 µm narrow channels) were grown in the thickness of 450 nm on Si/SiO 2 substrates by a microwave plasma chemical vapor deposition process. Strategy 1, employing a metal mask, resulted in unsatisfying patterned diamond growth due to instability of metal mask. Strategy 2 was based on a direct lithographic patterning of the seeding layer and resulted in a strongly selective, homogenous, and compact growth of diamond on the polymer-coated seeding patterns. This is assigned to the high seeding yield. The diamond micro-structures formed in this way exhibit surface conductivity of 10 − 7 (Ω/□) − 1 as assessed by I– V characteristics. The observed results appear promising for the development of directly grown diamond-based transistors.

Growth and field emission characteristics of diamond films on macroporous silicon substrate

The effect of substrate pretreatments such as ultrasonication or scratching by diamond powder on the microstructure and field emission characteristics of diamond grown over silicon and macroporous (anodized) silicon substrates was investigated. These films were grown in a hot filament chemical vapor deposition (CVD) system. Scanning electron microscope (SEM) studies revealed that ultrasonic pretreatment of the substrates increases nucleation density of CVD diamond by two orders of magnitude. Atomic force microscopy and energy dispersive x-ray analysis of the substrates showed that seeding is responsible for the enhanced nucleation density of diamond. SEM study showed that diamond powder scratching of porous silicon leads to uniform coverage of the substrate by the CVD diamond. Cross-sectional SEM showed growth of diamond inside the pores only after pretreating porous silicon with diamond powder. Raman spectroscopy of all the samples showed a scattering peak corresponding to diamond. Discontinuous diamond films also exhibited Raman bands corresponding to nanocrystalline diamond, diamondlike carbon, graphite, and silicon carbide. The presence of these phases of carbon was further confirmed by high resolution transmission electron microscopy studies. Field emission studies revealed that discontinuous diamond films grown on porous silicon (after diamond powder ultrasonic pretreatment) had the lowest threshold field (5.4 V/μm).

Fabrication of diamond micro-structures by ink-jet printed diamond seeding and microwave plasma assisted chemical vapor deposition

Ink-jet printing has the advantage of easy formation of micro-patterns on rigid as well as flexible surfaces without needing conventional lithographic processes. By means of printing in selected areas, diamond seeding in designed patterns and areas is achieved. Properly designed ink with a desirable composition helps the formation of patterned structures with tailored functions. Ink containing nano-diamond particles was designed and used to print micro-structures, which were applied for further CVD growth of diamond by means of microwave plasma CVD. Promising applications of this technique are discussed.

825 ナノ結晶ダイヤモンド薄膜の弾性定数と内部組織との関係(GS-3・4 ミクロ・ナノ材料)

825 ナノ結晶ダイヤモンド薄膜の弾性定数と内部組織との関係(GS-3・4 ミクロ・ナノ材料)

Impurity diffusion and microstructure in diamonds deformed at high pressures and temperatures

Results of a comprehensive study of the influence of deformation at high-pressure and high-temperature conditions on diamond microstructure and nitrogen diffusion are presented. Selection of the pressure medium allows the introduction of different types of extended defects (dislocations, mechanical twins). Despite clear differences in microstructure of diamonds deformed in variable pressure mediums, the relationship between the deformation and the rate of aggregation of the C to A nitrogen defects is still not clear. In some cases the deformation apparently increases the aggregation rate; in others no effect or even a decrease in the conversion rate was observed.

FIB and TEM studies of interface structure in diamond–SiC composites

The microstructure of diamond–SiC interfaces was studied by transmission electron microscopy (TEM). Specimens were prepared by focused ion beam (FIB) etching from a diamond–SiC composite bulk material. The diamond–SiC interfaces were easily located by high contrast in FIB images of the bulk surface, and site-specific specimen preparation was possible. The possible origin of this high contrast in FIB images compared to SEM images is discussed. TEM images and electron diffraction patterns showed that the diamond and SiC crystals away from the interface region are relatively defect-free, but numerous defects are present at the diamond–SiC interface over a dimension of 600 nm, much larger than the physical interface.

Microstructure and Mechanical Behaviors of Nano-polycrystalline Diamonds Synthesized by Direct Conversion Sintering under HPHT

AbstractHigh-purity nano-polycrystalline diamonds have been synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures. The polycrystalline diamond synthesized from graphite at ≥15 GPa and 2300-2600 °C has a mixed texture comprising a homogeneous fine structure (particle size: 10-30 nm, formed in a diffusion process) and a lamellar structure (formed in a martensitic process), and has a very high Knoop hardness of 120-145 GPa. In contrast, the polycrystalline diamonds made from the non-graphitic carbons at ≥15 GPa and 1600-2000 °C have a single texture consisting of a very fine homogeneous structure (5-10 nm, formed in a diffusion process) without a lamellar structure. The hardness values of the nano-polycrystalline diamonds made from non-graphitic carbons (70-90 GPa) are significantly lower than that of polycrystalline diamond made from graphite. The investigation of the microstructure beneath the indentation of these nano-polycrystalline diamonds revealed that the existence of the lamellar structure and the bonding strength of the grain boundary have a decisive effect on the hardness.

Microstructure of diamond–SiC nanocomposites determined by X-ray line profile analysis

Diamond composites with nanosize diamond crystals and nanosize SiC matrix were obtained at 8 GPa and temperatures varied between 1800 and 2000 °C. Multiple Whole Profile fitting method applied to X-ray diffractograms of sintered composites provided information on crystallite size and population of dislocations. When the temperature was increased at a constant pressure, it led to a growth of crystallite sizes in both phases and reduced population of dislocations. Porosity was limiting hardness of the specimens indicating importance of sample preparation prior to sintering nanosize diamond powders.

Diamond microstructures fabricated using silicon molds

We have fabricated diamond microstructures using silicon molds into which microcrystalline diamond was deposited by plasma assisted chemical vapor deposition. Prior to diamond deposition the silicon molds were seeded with the diamond powder of two different grain sizes, 14 and 1μm. Scanning electron microscopy and atomic force microscopy were used to view and characterize the resultant diamond microstructures. Analysis of the diamond replicas indicates better reproduction fidelity for the 14μm diamond powder, and a surface roughness of 20 nm.

Characterization of amorphous and nanocrystalline carbon films

Amorphous and nanocrystalline carbon films possess special chemical and physical properties such as high chemical inertness, diamond-like properties, and favorable tribological proprieties. The materials usually consist of graphite and diamond microstructures and thus possess properties that lie between the two. Amorphous and nanocrystalline carbon films can exist in different kinds of matrices and are usually doped with a large amount of hydrogen. Thus, carbon films can be classified as polymer-like, diamond-like, or graphite-like based on the main binding framework. In order to characterize the structure, either direct bonding characterization methods or the indirect bonding characterization methods are employed. Examples of techniques utilized to identify the chemical bonds and microstructure of amorphous and nanocrystalline carbon films include optical characterization methods such as Raman spectroscopy, Ultra-violet (UV) Raman spectroscopy, and infrared spectroscopy, electron spectroscopic and microscopic methods such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy, surface morphology characterization techniques such as scanning probe microscopy (SPM) as well as other characterization methods such as X-ray reflectivity and nuclear magnetic resonance. In this review, the structures of various types of amorphous carbon films and common characterization techniques are described.