Nanocrystalline diamond

Diamond properties are significantly affected by crystallite size. High surface to volume fractions result in enhanced disorder, sp² bonding, hydrogen content and scattering of electrons and phonons. Most of these properties are common to all low dimensional materials, but the addition of carbon allotropes introduces sp² bonding, a significant disadvantage over systems such as amorphous silicon. Increased sp² bonding results in enhanced disorder, a significantly more complex density of states within the bandgap, reduction of Young's modulus, increased optical absorption etc. At sizes below 10 nm, many diamond particle and film properties deviate substantially from that of bulk diamond, mostly due not only to the contribution of sp² bonding, but also at the extreme low dimensions due to size effects. Despite these drawbacks, nano-diamond films and particles are powerful systems for a variety of applications and the study of fundamental science. Knowledge of the fundamental properties of these materials allows a far greater exploitation of their attributes for specific applications. This review attempts to guide the reader between the various nanocrystalline diamond forms and applications, with a particular focus on thin films grown by chemical vapour deposition.     

Nanocrystalline diamond film for biosensor applications

In this study, we have developed a novel capacitive biosensor based on interdigitated gold nanodiamond (GID-NCD) electrode for detection of C-reactive protein (CRP) antigen. CRP is one of the plasma proteins known as acute-phase proteins and its levels rise dramatically during inflammatory processes occurring in the body. It has been reported that CRP in serum can be used for risk assessment of cardiovascular diseases. The antibodies immobilization were confirmed by fourier transform spectroscopy (FTIR) and contact angle measurements. In this capacitive biosensor, nanocrystalline diamond acting as a dielectric layer between the electrodes. The CRP antigen detection was performed by capacitive/dielectric-constant measurements. Our results showed that the response of NCD-based capacitive-based biosensor for CRP antigen was dependent on both concentration (25–800 ng/ml) as well as frequency (50–350 MHz). Furthermore, using optimized conditions, the biosensors developed in this study can be potentially used for detection of elevated level of risk markers protein in suspected subjects for early diagnosis of disease.     

Nanocrystalline diamond growth in a surface-wave plasma

A surface-wave excited plasma is exploited in a diamond growth process by microwave plasma chemical vapor deposition method. Nanocrystalline diamond films with smooth surfaces are obtained from the plasma. As well as characterizing the deposited diamond films, the electron density and the electron temperature of the plasma are determined by using double-probe measurements. The plasma diagnosis reveals low electron temperatures of 2–3 eV in the process region, which is a distinctive characteristic of the surface-wave plasma. The low electron temperature is essential for the continuous re-nucleation of diamond in a hydrogen-rich plasma during the nanocrystalline diamond growth for a wide range of substrate temperature from under 100 to over 700 ^°C.     

Nanocrystalline diamond coating of fusion plasma facing components

Nanocrystalline diamond layers were deposited by hot-filament CVD on several substrates including molybdenum tiles and foils, graphite blocks and silicon wafers. The structural characterisation of the deposited layers, achieved by SEM, AFM, Raman and X-ray photoelectron spectroscopies, showed the typical features of nanocrystalline diamond.A nanocrystalline diamond coated molybdenum tile was exposed to a fusion grade deuterium plasma in the MAST tokamak, with a plasma current of 700 kA, core electron temperature of about 0.6 keV, and total exposure time of about 1 s. The diamond coating showed good resistance to the extremely harsh conditions of the fusion plasma edge.     

A parametric relationship for synthesized diamond powder

Diamond powders synthesized in different solvent/catalyst systems at high pressure and high temperature conditions contain crystals that could be separated into groups of distinct size and defect morphology. These groups differ by their mechanical compressive resistance, given by the fracture load, which could be used to classify them for potential industrial applications. In the present work a parametric relationship between the defect morphological aspects, the granulometry and the compressive resistance of diamond powders synthesized in a concave anvil high-pressure device at 4.7 GPa and 1250 °C was established. Results were obtained by measuring the fracture load, using the single grit test of individual crystals, and comparing the average value for crystals with different defect morphology and corresponding grain sizes. The parametric relationship permitted to classify each diamond crystal by its size and defect morphology in association with its compressive resistance. It is therefore suggested that this parametric relationship be used as a new method to evaluate a diamond powder in terms of crystal size, defect morphological aspects and mechanical resistance.     

Nanocrystalline diamond containing hydrogels and coatings for acceleration of osteogenesis

In the present study, we have compared the effects of ultrananocrystalline diamond/amorphous carbon composite films (UNCD/a-C) and nanocrystalline diamond (NCD) containing hydrogels to support the osteogenesis of endothelial progenitor cells (EPCs). The course of EPCs osteogenic differentiation was followed 21 days and assayed by measuring cell-associated alkaline phosphatase activity, calcium deposition, and expression of fibronectin. We found that EPCs were capable to adhere to both surfaces in flattened and elongated morphology. The attachment and spreading on the UNCD/a-C films were faster as compared to the hydrogels containing NCDs (by day 7), and this was connected with the release and adsorption of fibronectin to the surfaces. During the process of EPCs differentiation, the release of fibronectin was favored by hydrogels + NCD (day 21). The formation of calcium nodules, characteristic of osteoblastic mineralization, was detected by Alizarin Red S staining. Differentiation-induced calcium nodules were detected in EPCs growing on both surfaces. The EPCs cultured on hydrogels containing NCD deposited more extracellular calcium in comparison with those on UNCD/a-C films on day 21. These results were consistent with the data about the alkaline phosphatase activity on the same day and verified that an active EPC transformation to osteoblast phenotype occurred on both substrates. Our results could have direct implications in the use of biomaterials in tissue engineering strategies, and this work might be useful for the improvement of the methodologies for substrate preparation (including scaffolds). Thus both surfaces studied could be used for modification of bone implants (bone-anchoring parts of joint prostheses or bone replacements) in order to improve their integration with the surrounding bone tissue, for which improved cell-substrate adhesion is also needed.     

Nanocrystalline erbium oxide powders synthesized by the solid-state method from carbonates, oxalates, and hydroxides

Nanocrystalline erbium oxide powders are synthesized by the solid-state method from carbonates, oxalates, and hydroxides. Depending on the prehistory of their preparation, the average particle size decreases in the series: oxalates > carbonates > hydroxides; being 10 to 20 nm at a thermal treatment temperature of 680°C     

粉末材料合成金刚石中工艺参数的选取

合理地选取工艺参数,有利于合成优质金刚石.文章综述了粉末材料合成金刚石中工艺参数对合成效果的影响以及粉末材料合成金刚石中工艺参数的选取原则.     

铁基触媒合成工业金刚石中包裹体研究

借助穆斯堡尔谱的测试方法,对不同铁基粉末触媒合成的工业金刚石中的包裹体进行了检测,结果表明,纯Fe触媒合成的金刚石晶体中的包裹体为α-Fe和Fe3C;Fe90Nil10和Fe80Ni20合成的金刚石晶体中的包裹体主要以FeNi合金和Fe3C形式存在,同时随着触媒中的Fe含量的降低,包裹体Fe3C的相对含量随之降低.另外,对包裹体的形成机制进行了分析.通过对包裹体的成分和形成机制的研究,提出了有效减少金刚石中包裹体的方法.     

Study on the preparation and the catalytic performance of Ni-modified shock-wave synthesized diamond blends and nanodispersed diamond

The possibility to use shock-wave synthesized diamond blend and ultradispersed diamond powder isolated from it as supports for catalytically active nickel metal phase has been studied. The influence of the pre-treatment conditions for the metal precursor decomposition and generation of Ni⁰ upon reduction have been investigated. The present findings reveal that the state of the supported nickel is predetermined by the conditions of the catalysts preparation. The reaction test showed that the graphite containing diamond blend is not appropriate as a support. In contrast, the ultradisperssed diamond powder appears very promising for disposition of metallic nickel active in the catalytic hydrogenation of toluene.     

Transparent diamond ceramics from diamond powder

Diamond possesses a unique combination of excellent optical, thermal, and mechanical properties, and is therefore an ideal transparent ceramic material for harsh and extreme environments. Due to its important applications in technology, transparent diamond ceramic (TDC) has been explored and prepared by chemical vapor deposition (CVD) or direct conversions of non-diamond carbon precursors at high pressure and high temperature (HPHT), but the preparation of large-size TDC with high mechanical strength remains a challenge. Here, we report for the first time, a transparent polycrystalline diamond ceramic from diamond powder with a transmittance of ～60 % at wavelengths of 400–1600 nm. The analyses of phase composition, residual stress and microstructure evolution of the sintered samples with different sintering conditions indicate that compression at high temperatures (>2000 ?C) facilitates the deformation of diamond grains, allowing for densification and diamond-diamond bonding formation. The sintering pressure of the diamond powders with an optimized particle size distribution was dramatically reduced from 16 GPa to 10 GPa. Our results, based on successfully preparing centimeter-sized TDC, set the standard and the precedent for the large-scale preparation of larger TDC in proximity to industrial conditions.     

Boron-doped ultrananocrystalline diamond synthesized with an H-rich/Ar-lean gas system

This paper reports the recent development and applications of conductive boron-doped ultrananocrystalline diamond (BD-UNCD). The authors have determined that BD-UNCD can be synthesized with an H-rich gaseous chemistry and a high CH₄/H₂ ratio, which is opposite to previously reported methods with Ar-rich or H-rich gas compositions but utilizing very low CH₄/H₂ ratios. The BD-UNCD reported here has a resistivity as low as 0.01 ohm cm, with low roughness (<10 nm) and a wide deposition temperature range (450–850 °C). The properties of this BD-UNCD were studied systematically using resistivity characterization, scanning and transmission electron microscopy, Raman spectroscopy, and roughness measurements. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy confirms that up to 97% of the UNCD is deposited as sp³ carbon. These various measurements also reveal additional special properties for this material, such as an “M” shape Raman signature, line-granular nano-cluster texture and high CH bond surface content. A hypothesis is provided to explain why this new deposition strategy, with H-rich/Ar-lean gas chemistry and a high CH₄/H₂ ratio, is able to produce high sp³-content and/or heavily doped UNCD. In addition, a few emerging applications of BD-UNCD in the field of atomic force microscopy, electrochemistry and biosensing are reviewed here.     

Nanocrystalline diamond on SiO2 fiber: A new class of hybrid material

We report a template technique for the fabrication of high density nanocrystalline diamond (NCD)-coated silica (a-SiO₂) nanofibers with diameters of 1–5 μm. This method includes the synthesis of templates (a-SiO₂ nanofibers) by conventional Vapor–Liquid–Solid method and the conformal coating of the nanofibers with nanodiamond by Microwave Plasma Chemical Vapor Deposition technique in hydrogen-deficient conditions. A detailed micro-structural analysis was performed to probe the interaction of the NCD grains with a-SiO₂ nanofibers. The specimen for Transmission Electron Microscopy was prepared using Focused Ion Beam lift-out method. Room temperature micro-Raman was performed to study the crystalline quality of the NCD-coated silica nanofibers. Field electron emission of as-synthesized NCD-coated silica nanofibers was observed with a threshold field of ~ 3 V/µm.     

Diffusion of cobalt in diamond films synthesized by combustion flame method

It is well known that Cobalt (Co) plays an important role during diamond deposition on cemented carbide substrates (WC). The presence of cobalt on the substrate lead to decrease adhesion and increase the formation of non-diamond compounds phases. However, the diffusion phenomenon of cobalt in diamond coatings is not well understood.We have carried out a detailed study to investigate the diffusion of cobalt during the nucleation and growth of diamond on WC-Co substrate by combustion-flame method, and the influence of it on the structure and quality of the diamond coatings. At high substrate temperature T_s>800 °C, ball-sharp of cobalt with a ball size about 0.7 μm was observed on the top surface of diamond coatings (thickness >50 μm). The constraints in the coating are very high, the Raman peak appearance at 1341.1 cm⁻¹. At relatively low substrate temperature, T_s is about 550 °C, ball sharp of cobalt was not observed by MEB but a lot of cobalt particles dissolution carbon films were detected by EDX.Based on the above results, the influence of cobalt on the structure, the quality and the constraints in the diamond films are discussed, a model suggesting the nucleation and growth mechanisms of diamond, to explain the cobalt diffusion in diamond films, is presented.     

高温高压温度梯度法合成板状宝石级金刚石单晶

板状宝石级金刚石单晶具有重要的应用价值.它可以作为红外透明窗口和高功率激光器的散热片等.文章研究了温度梯度法合成宝石级金刚石与籽晶的生长面以及合成温度之间的关系,在低温区用籽晶(100)面合成了4mm的优质板状晶体.     

Characterization of phases synthesized close to the boundary of C60 collapse at high temperature high pressure conditions

Two sets of samples were synthesized at high pressure high temperature conditions in the P–T region where C₆₀ molecules collapse into a nearly amorphous graphite-like hard carbon phase. For the first set, heating temperature was varied at fixed pressure and preparation time. For the second set, synthesis time was varied at fixed pressure and fixed temperature. Detailed structural characterization of samples was performed using Raman spectroscopy and powder XRD. Mechanical properties of the samples have been studied by nanoindentation method. It has been found that duration of heat treatment under high pressure is an important parameter which influences the temperature of fullerene cage collapse. Both tetragonal and rhombohedral polymeric phases transform into hard carbon phase over a rather narrow temperature interval, but the tetragonal phase shows somewhat increased stability against C₆₀ collapse. Viscoelastic mechanical behavior during nanoindentation was observed for fullerene polymers but not for graphite-like hard carbon phase. Possible mechanism for nucleation of the hard carbon phase in polymeric C₆₀ networks is discussed.     

Nanocrystalline diamond microspikes increase the efficiency of ultrasonic cell lysis in a microfluidic lab-on-a-chip

This research demonstrates that use of Nanocrystalline Diamond (NCD) microspikes in a microfluidic chamber increases the efficiency of mechanical cell lysis, as compared to a standard microfluidic surface such as glass. Microspikes made of nanocrystalline diamond were fabricated using standard MEMS techniques, and were incorporated in microfluidic chamber developed as part of a lab on a chip system. Mechanical cell lysis was performed on B16-F10 (ATCC CRL-6475) murine melanoma cells using ultrasonic vibration and the efficiency of cell lysis was determined. The microspikes puncture the cell membranes on collision greatly increasing the efficiency of cell lysis (about 400% as per fluorescence measurements) as compared to a non-textured glass surface. The effect of using cell disruption glass beads during ultrasonic lyses was also explored. This methodology of cell disruption could potentially make mechanical cell lysis a viable and preferred lysis option for lab-on-a-chip applications.     

间接加热合成工业金刚石工艺的研究

在工业金刚石的合成过程中,合成工艺对其有着重要的影响。文章在国产六面顶高压设备上,利用膜生长法,在F e-N i-C体系中对影响金刚石合成的工艺参数进行了考察,通过对合成工艺的调整,成功实现了对生长速度的有效控制,并成功合成出平均粒度为0.6mm的优质金刚石单晶。     

NEXAFS characterization of nanocrystalline diamond thin films synthesized with high methane concentrations

Diamond thin films were deposited on silicon in gas mixtures of methane and hydrogen with different methane concentrations ranging from 1% to 100% using microwave plasma assisted chemical vapor deposition. Both Raman spectroscopy and synchrotron near edge extended X-ray absorption fine structure spectroscopy (NEXAFS) were used to characterize the electronic structure and chemical bonding of the synthesized films. The NEXAFS spectra of the nanocrystalline diamond (NCD) films exhibit clear spectral characteristics of diamond. Close observation reveals that the films (10% CH₄ or above) exhibit a slightly broadened exciton transition with a 0.25 eV blue shift. With the increase in methane concentration, the growth rate, the surface smoothness, and the sp² carbon concentration of the films increase while the grain size decreases. Well-faceted microcrystalline diamond films were synthesized with a methane concentration of 5% or lower, while NCD films were formed with a methane concentration of 10% or higher. Diamond thin films with low surface roughness and fine nanocrystalline structure have been synthesized with high methane concentrations (50% or above). It has been observed that the diamond growth rate increases with methane concentration. The growth rate at 100% methane concentration is approximately 10 times higher than at 1%.