Quality Diamond Research Articles

Undoped CVD diamond films for electrochemical applications

By using different deposition conditions, the CVD diamond films with different qualities and orientation were grown by the hot-filament CVD technique.The object of this article is to summarize and discuss relation between structural, physical and electrochemical properties of different diamond electrodes. The physical properties of the Hot Filament CVD microcrystalline diamond films are analyzed by scanning electron microscopy and Raman spectroscopy. In presented studies two different electrodes were used of the diamond grain sizes around 200nm and 10μm, as it was estimated from SEM picture. The diamond layers quality was checked on basis of FWHM (Full width at Half Maximum) of 1332cm−1 diamond Raman peak. The ratio of sp3/sp2 carbon bonds was determined by 1550cm−1 G band and 1350cm−1 D band in the Raman spectrum. The electrochemical properties were analyzed using (CV) cyclic voltammetry measurements in aqueous solutions. The sensitivity of undoped diamond electrodes depends strongly on diamond film quality and concentration of amorphous carbon phase in the diamond layer.

Silicon vacancy color center photoluminescence enhancement in nanodiamond particles by isolated substitutional nitrogen on {100} surfaces.

Fluorescent nanodiamonds were produced by incorporation of silicon-vacancy (Si-V) defect centers in as-received diamonds of averaged size ∼255 nm using microwave plasma chemical vapor deposition. The potential for further enhancement of Si-V emission in nanodiamonds (NDs) is demonstrated through controlled nitrogen doping by adding varying amounts of N(2) in a H(2) + CH(4) feedgas mixture. Nitrogen doping promoted strong narrow-band (FWHM ∼ 10 nm) emission from the Si-V defects in NDs, as confirmed by room temperature photoluminescence. At low levels, isolated substitutional nitrogen in {100} growth sectors is believed to act as a donor to increase the population of optically active (Si-V)(-) at the expense of optically inactive Si-V defects, thus increasing the observed luminescence from this center. At higher levels, clustered nitrogen leads to deterioration of diamond quality with twinning and increased surface roughness primarily on {111} faces, leading to a quenching of the Si-V luminescence. Enhancement of the Si-V defect through controlled nitrogen doping offers a viable alternative to nitrogen-vacancy defects in biolabeling/sensing applications involving sub-10 nm diamonds for which luminescent activity and stability are reportedly poor.

Seed-Free Growth of Diamond Patterns on Silicon Predefined by Femtosecond Laser Direct Writing

Seed-free growth of diamond patterns on Si surfaces was realized by surface patterning via femtosecond laser direct writing followed by laser-assisted combustion synthesis in open air. Prepatterned Si surfaces provide active nucleation sites for diamond growth. The dimension and shape of the diamond patterns can be precisely controlled at micrometer scales. Field-enhanced thermionic emission current was measured to monitor diamond nucleation and growth process in real time. The diamond nucleation density and quality depend strongly on the surface roughness of the prepatterned Si patterns. A higher surface roughness leads to more nucleation sites and higher nucleation density. However, high local temperature at peaks due to a large exposed surface to the flame on an excessively rough surface degrades the diamond quality. The easy fabrication of diamond patterns on nondiamond surfaces suggests potential applications such as cutting tools, protective coatings, heat sinks, etc.

Cyclic voltammetry and impedance studies of undoped diamond films

The undoped, polycrystalline diamond films were deposited on tungsten wire substrates by hot filament chemical vapor deposition (HF CVD), using a precursor gas mixture of methanol with excess of hydrogen. The morphology and quality of the as-deposited films were monitored by scanning electron microscopy (SEM) and Raman spectroscopy. The surface morphology analyzed by SEM resembles a continuous and well faceted diamond film. Raman results showed essential differences in qualities of diamond films grown at different hydrocarbon concentrations. The electrochemical properties of diamond electrodes were examined with cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS). The CV experiments revealed a large chemical window (>∼4.3 V) of undoped diamond. Analysis of the ferrocyanide-ferricyanide couple at a diamond electrode suggests some extent of electrochemical quasi-reversibility, but the rates of charge transfer across the diamond substrate interface vary with diamond quality.

Seed-Free Growth of Diamond Patterns on Femtosecond Laser Processed Silicon Substrates

ABSTRACTDue to its outstanding properties, diamond is considered as an ideal material for mechanical and electric applications at high temperatures, voltages, radiation, etc. It is known that femtosecond lasers exhibit extremely high precision and minimized thermal effect in material processing. In this study, a seed-free diamond pattern growth method was developed by patterning silicon substrates using a femtosecond laser before diamond deposition through laser-assisted combustion flame synthesis. The resolution of the diamond patterns reaches micro scales. Peak position, full width at half maximum (FWHM), and diamond quality parameter were calculated from Raman spectra. The mechanism of the seed-free diamond growth based on the femtosecond laser patterning was discussed. The influence of substrates surface roughness on the diamond nucleation and subsequent growth was studied, indicating that the nucleation density is proportional to the surface roughness.

Doping level influence on chemical surface of diamond electrodes

The modification of surface bond termination promoted by the doping level on diamond electrodes is analyzed. The films were prepared by hot filament chemical vapor deposition technique using the standard mixture of H2/CH4 with an extra H2 flux passing through a bubbler containing different concentrations of B2O3 dissolved in methanol. Diamond morphology and quality were characterized by scanning electron microscopy and Raman scattering spectroscopy techniques while the changes in film surfaces were analyzed by contact angle, cyclic voltammetry and synchrotron X-ray photoelectron spectroscopy (XPS). The boron-doped diamond (BDD) films hydrophobicity, reversibility, and work potential window characteristics were related to their physical properties and chemical surface, as a function of the doping level. From the Mott–Schottky plots (MSP) and XPS analyzes, for the lightly (1018cm−3) and highly (1020cm−3) BDD films, the relationship between the BDD electrochemical responses and their surface bond terminations is discussed.

Diamond MESFET performance improvement by layout optimisation

Hydrogen terminated diamond is a promising material for metal semi-conductor field effect transistor (MESFETs) fabrication and research effort is focused on diamond quality improvement. In this reported work, the focus of attention is on device layout and structure to improve RF performances, designed on the basis of diamond physical properties, taking into account the characterisation of previously fabricated devices. Significant increase of current gain cutoff frequency fT, from 3.4 to 6.7 GHz, has been obtained, while maximum oscillation frequency fMAX is raised from 10.4 to 11.8 GHz.

Optical study of defects in nano‐diamond films grown in linear antenna microwave plasma CVD from H2/CH4/CO2 gas mixture

AbstractWe present the study on optical quality of nanocrystalline diamond (NCD) films with submicron grain size grown from H2/CH4/CO2 gas mixture on alkali‐free borosilicate glass substrates using the commercially available large area linear antenna pulsed microwave plasma chemical vapor deposition (CVD) system. The NCD films were characterized by Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. The NCD layers are optically transparent and show low optical scattering. The defect states measured by photo‐thermal deflection spectroscopy (PDS) and dual beam photocurrent spectroscopy (DBPS) are dominated by the non‐diamond carbon phases localized at grain boundaries with the characteristic shape of the optical absorption spectrum and the photo‐ionization threshold in a near infrared region. The sp2‐related defect density increases for samples grown at higher pressure. From DBPS we estimate the concentration of substitutional nitrogen to be below 10 ppm. The optimized NCD layers show the photoionization threshold in UV region above 5 eV and a broad exponential tail below 5 eV.

Fabrication and characterizations of large homoepitaxial single crystal diamond grown by DC arc plasma jet CVD

Homoepitaxial diamond layers have been grown on HPHT synthetic type Ib (100) single crystal diamond plates brazed on a Φ65mm Mo holder using a commercial type 30kW dc arc plasma jet CVD with rotating arc root and operating at gas recycling mode with gas mixture of Ar/H2/CH4. The effects of substrate temperature and CH4/H2 ratio on the surface morphology, the growth rate and the quality of the synthesized diamond have been studied using optical microscopy and Raman spectroscopy. The growth rate up to 17.4μm/h has been obtained in the single crystal diamond sample deposited at 1000°C with CH4/H2=0.813%, exhibiting relatively smooth surface morphology with the typical feature of step-flow growth, without any non-epitaxial diamond crystallites. Under the optimum synthesis conditions, large size (7.5mm×7.5mm) polished freestanding single crystal diamond plate up to 1.03mm thickness has been produced and characterized by UV–vis–IR absorption, photoluminescence and Raman spectroscopy, as well as high-resolution X-ray diffraction. It was demonstrated that the quality of the as-grown CVD single crystal diamond was close to that of the natural type IIa single crystal diamond. It was shown that the epitaxial growth of high quality CVD single crystal diamonds could be achieved over the entire Φ65mm Mo holder on which a large quantity of CVD single crystal diamonds could be grown simultaneously. This is of economical importance in the development of high power DC arc plasma jet CVD systems for fabricating large size, high quality CVD single crystal diamond.

Influence of annealing treatment on as-grown Ib-type diamond crystal at a high temperature and high pressure

In this paper, we report on the influence of annealing treatment on as-grown Ib-type diamond crystal under high pressure and high temperature in a china-type cubic anvil high-pressure apparatus. Experiments are carried out at a pressure of 7.0 GPa and temperatures ranging from 1700 °C to 1900 °C for 1 h. Annealing treatment of the diamond crystal shows that the aggregation rate constant of nitrogen atoms in the as-grown Ib-type diamond crystal strongly depends on diamond morphology and annealing temperature. The aggregation rate constant of nitrogen remarkably increases with the increase of annealing temperature and its value in octahedral diamond is much higher than that in cubic diamond annealed at the same temperature. The colour of octahedral diamond crystal is obviously reduced from yellow to nearly colorless after annealing treatment for 1 h at 1900 °C, which is induced by nitrogen aggregation in a diamond lattice. The extent of nitrogen aggregation in an annealed diamond could approach approximately 98% indicated from the infrared absorption spectra. The micro-Raman spectrum reveals that the annealing treatment can improve the crystalline quality of Ib-type diamond characterized by a half width at full maximum at first order Raman peak, and therefore the annealed diamond crystals exhibit nearly the same properties as the natural IaA-type diamond stones of high quality in the Raman measurements.

High purity diamond films synthesised by chemical vapour deposition

Defect free diamond films have tremendous potential in a variety of areas including optoelectronics and have been the focus of several studies. Before diamond growth, a seeding treatment to substrate is mandatory, which itself is a source of contamination and degrades the quality of diamond. In the present study, diamond films without seeding treatment were grown on silicon using hot filament chemical vapour deposition. As a result of dry ultrasonic process, the diamond film with continuous layer was grown over unseeded substrate. At nucleation stage, carbon containing species were trapped by the uniformly created network of pits. Film grown at 2·0 vol.-% CH4 in H2 and substrate temperature of 850°C showed higher purity than that grown at 3·0 vol.-%CH4 in H2 and substrate temperature of 1000°C. Films grown over seedless substrates were also compared with those grown with seeding treatment.

Research on Removing of Pyrophyllite in Synthetic Diamond by the Physical Method Instead of Chemical Method

As a harmful impurity, Pyrophyllite must be remove in synthetic diamond purification process. It commonly use chemical method. A trial research is made on the removing of pyrophyllite impurity in synthetic diamond by physical method. As a result, after synthetic diamond materials containing pyrophyllite are selectively interground in the ball grinding machine, the pyrophyllite is effectively broken and removed from the coarse – medium grade diamond only by physical method, but diamond quality is not affected.

Recent Advances in CVD Synthetic Diamond Quality

Recent Advances in CVD Synthetic Diamond Quality

The influence of boron doping level on quality and stability of diamond film on Ti substrate

In this study, we investigate the influence of boron doping level on film quality and stability of boron doped diamond (BDD) film deposited on titanium substrate (Ti/BDD) using microwave plasma chemical vapor deposition system. The results demonstrate that high boron concentration will improve the film conductivity, whereas the diamond film quality and adhesion are deteriorated obviously. The increase of total internal stress in the film and the variation of components within the interlayer will weaken the coating adhesion. According to the analysis of electrode inactivation mechanism, high boron doping level will be harmful to the electrode stability in the view of diamond quality and adhesion deterioration. In this study, 5000ppm B/C ratio in the reaction gas is optimized for Ti/BDD electrode preparation.

Nanocrystalline diamond coating on carbon fibers produced at different temperatures: Morphological, structural and electrochemical study

In this paper, the morphological, structural and electrochemical properties of nanocrystalline diamond (NCD) films grown on carbon fibers (CF) were investigated. The CF substrates were produced at three different heat treatment temperatures (HTT):1000, 1500 and 2000°C. The HTT variation promoted different organization indexes on the CF structures. Consequently, the NCD coating formation was strongly affected by the substrate HTT. The changes in the properties of the diamond films were discussed as a function of the film morphology evolution using CH4 flow rate of 0.25, 0.5 and 1.0sccm in the feed gas. The X-ray diffraction measurements for the CF and NCD/CF composites were determinant to characterize the crystallinity of the NCD films as a function of the CF HTT and of the CH4 addition. Based on the diffractograms, the Scherrer's equation was applied to the (111) NCD peak, resulting in grain size values varying from 11.0 to 5.0nm depending on the CH4 flow rate and on the CF HTT. The scanning electron microscopy images confirmed the deposition of a continuous NCD coating with high nucleation rate covering the whole CF, while their quality was analyzed by Raman spectroscopy measurements. The NCD grain agglomerates increased as a function of the increase in the CH4 flow rate from 0.25 to 1.0sccm, showing similar film morphology to that of the unfaceted diamond balls obtained by chemical vapor deposition. This behavior confirmed the expected tendency by decreasing the diamond quality with the CH4 addition, especially for the films grown on CF treated at 1500 and 2000°C. This performance was also corroborated by the cyclic voltammetry measurements concerning the electrode potential window and their responses in a redox couple.

Characterisation of diamond coatings with different morphologies by Raman spectroscopy using various laser wavelengths

Since the beginning of low-pressure diamond synthesis, Raman spectroscopy has been widely used to identify and characterise the quality of diamonds. The diamond crystal is characterised by a Raman peak at about 1,332cm(-1). Other peaks are associated with miscellaneous carbon structures, e.g. graphite and amorphous phases. In recent years, both well-faceted crystalline diamonds and nanocrystalline and ultrananocrystalline diamonds have been investigated. For these fine-grained materials, the diamond peak at 1,332cm(-1) disappears and the intensities of peaks at other wavelengths increase. To study the influence of the Raman laser wavelength, three lasers were used (472.681nm, blue; 532.1nm, green; 632.81nm, red). For well-faceted diamonds, the Raman spectra with blue and green laser light were similar. A shift of the peak maxima and different intensities were observed. With use of the red laser, a strong luminescence peak and low peak intensities for the various carbon-related peaks occurred. When the diamond morphology changes from well-faceted to fine-grained ballas diamond, the spectra are similar for all three lasers.

Parallel Algorithm for the Voltage Profile Simulation for the Synthesis of Superhard Materials Under High Pressure and High Temperature

This article shows a parallel algorithm developed to simulate the electric voltage profile applied to the heating of the compression chamber used in the process of superhard materials synthesis, specifically, diamonds. The computational simulation for the determination of the distribution of the eletrical potential (d.d.p. in volt) is necessary to permit to get, with precision, the value of the heat (in W/mm) that is generated by the eletric current flux in the process. The analysis of temperature distribution let us investigate the graphite to diamond transformation process and also get diamonds of better quality and lower cost. The computational simulation is an important tool in the superhard materials syntesis research, once the real tests show a very high cost and many times they do not show satisfactory answers. We hope we can contribute with the techniques of computational simulation for the diamond synthesis process, using resources of parallelism shown in this article. The purpose to the use of paralelism techniques in the computational simulations is situated in the possibility of offering an ampler research of the superhard material synthesis process, through enlargement of the volume studied in a time of the reduced processing. In the simulations carried out in a small part of the compression chamber of 10mm of ray per 10mm of height, using a matrix 100x100, it was necessary nearly one hour of processing in a SUN FIRE machine with one SPARC III 750 MHz processor. A completed chamber, used in the diamond synthesis, has measurements from 60mm to 100mm and that can be enlarged if there is interest in analysing other parts of the high pressure apparatus that permit the coupling of the compression chamber to the hydraulic press.

Fabricating microstructures on CVD diamond film

Diamond has many advanced properties which may provide potential solutions to various engineering problems. This study focuses on fabricating micro-structures on CVD diamond film. A thin layer of Au or Pt together with thermal annealing process is used to form micro-masks and reactive ion etching (RIE) method was subsequently adopted in this research to etch and fabricate micro-structures. Field emission scanning electron microscope (FESEM) and micro Raman spectroscopy were used to observe and analyse the morphology and composition of the obtained microstructures. Results show that different coated materials and thickness can produce different types of micro-masks and, as a consequence, different microstructures. Depending on the micro-mask, whisker-like or pillar-like microstructures are successfully produced and, based on the micro Raman spectrum; these microstructures still retains good diamond quality.

The influence of working gas on CVD diamond quality

Abstract The effect of the working gas pressure and its composition on diamond quality and particles size was investigated. The diamond layers were grown in Hot Filament Chemical Vapor Deposition (HF CVD) reactor. A methanol–hydrogen gas mixture was used as the precursor gas. The structure of these films was characterized by scanning electron microscopy (SEM) and micro-Raman spectroscopy. Typically, the diamond's crystallite size decreased with increasing pressure and increasing with methanol concentration. Additionally the admixture of non-diamond (sp2-hybridized carbon) phase also increased with increasing both of deposition pressure and of methanol concentration. It was observed that the deposition pressure has a weaker influence on diamond quality than the methanol concentration.

Influence of Alignment Errors on Measuring Nose Roundness of Diamond Cutting Tools with a Novel Method

The nose roundness is one of the most important indexes of lapping quality of rounded diamond cutting tools. Due to its special characters and requirements, a new measuring method was proposed based on atomic force microscope (AFM) and precision-revolution spindle. However, in the measurement the alignment errors of tools with the spindle axis have great influence on the measuring result. By a carefully deducting, the relations between the deviation and the alignment errors were presented. The deviation increases with the eccentric linearly, and has the same value with the eccentric. But it varies with θ dramatically and forms a parabola curve when the deflection angle is negative, otherwise, varies with θ gently and forms a flat Gaussian curve.