Chemical Vapor Deposited Diamond Films Research Articles

Diamond and biology

A summary of photo- and electrochemical surface modifications applied on single-crystalline chemical vapour deposition diamond films is given. The covalently bonded formation of amine and phenyl linker molecular layers is characterized using X-ray photoelectron spectroscopy, atomic force microscopy (AFM), cyclic voltammetry and field-effect transistor characterization experiments. Amine and phenyl layers are very different with respect to formation, growth, thickness and molecular arrangement. We deduce a sub-monolayer of amine linker molecules on diamond with approximately 10% coverage of 1.510(15) cm(-2) carbon bonds. Amine is bonded only on initially H-terminated surface areas. In the case of electrochemical deposition of phenyl layers, multilayer properties are detected with three-dimensional nitrophenyl growth properties. This leads to the formation of typically 25 A thick layers. The electrochemical bonding to boron-doped diamond works on H-terminated and oxidized surfaces. After reacting such films with heterobifunctional cross-linker molecules, thiol-modified ss-DNA markers are bonded to the organic system. Application of fluorescence and AFM on hybridized DNA films shows dense arrangements with densities up to 10(13) cm(-2). The DNA is tilted by an angle of approximately 35 degrees with respect to the diamond surface. Shortening the bonding time of thiol-modified ss-DNA to 10 min causes a decrease in DNA density to approximately 10(12) cm(-2). Application of AFM scratching experiments shows threshold removal forces of approximately 75 and 45 nN for the DNA bonded to the phenyl and the amine linker molecules, respectively. First, DNA sensor applications using Fe(CN6) 3-/4- mediator redox molecules and DNA field-effect transistor devices are introduced and discussed.

Study of the stress in doped CVD diamond films

Sulphur-doped and boron-sulphur co-doped diamond thin films were prepared using chemical vapour deposition (CVD) on Si substrates under different conditions. The influence of doping on stress in CVD diamond films were investigated with X-ray diffraction and Raman spectra. The results show that the sp2-carbon content, the concentration of defects and the residual compressive stress in CVD diamond films increase with increasing of sulphur content. Compared with sulphur doping of diamond films, the boron-sulphur co-doping with few boron atoms facilitates sulphur atom incorporation into diamond crystal. The boron-sulphur complexes in diamond can reduce crystal lattice distortion and crystal imperfection. As a result, sp2-carbon content and residual compressive stress in boron-sulphur co-doped diamond are reduced, and diamond crystal prefection is improved.

2834 基板上のCVDダイヤモンド薄膜の疲労損傷過程(S08-2 微小機械設計・開発のための実験力学の新展開(2),S08 微小機械設計・開発のための実験力学の新展開)

This paper describes the fatigue characteristics of Chemical Vapor Deposition diamond films on a silicon substrate. Repeated indentation load was applied to the diamond film surface with a spherical indenter to introduce mechanical fatigue damage in the films and interfaces with a minimum amount of tribological surface damage. The stress field applied to the sample is analyzed in detail, and fatigue behavior was clarified as an S-N diagram. Detailed observation of fatigue damage revealed that damage initiated on the substrate surface leading to interface debonding.

Fabrication and wear of nitrogen-doped diamond microtools

Chemical vapour deposited diamond films have many industrial applications but are assuming increasing importance in the area of microfabrication, most notably in the development of diamond-coated microtools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness and the degree of sp³ character have a profound effect on the machining properties of the films deposited. In this paper, experimental results are presented on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of microtools. It is concluded that the magnitude of tensile stresses induced in the diamond grain by grinding forces at the rake face is the best indicator of tool wear during the grinding process.

Investigation of Thermo-Chemical Polishing of CVD Diamond Film

ZnO/Diamond structure has attracted a lot of attentions and heavy investment recently just because diamond has the capability of producing very high surface acoustic wave (around 10,000m/s). In this present study, the microwave chemical vapor deposition (CVD) method was employed to produce diamond films on silicon single crystal. Thermo-chemical polishing experiments were then conducted on the obtained diamond films. The underlying material removal mechanisms, microstructure of the machined surface and related machining conditions were also investigated. Thermo-chemical polishing was proved to be able to remove the diamond film very effectively (4.8μm deep of diamond film was removed in 30 minutes when polishing at 550oC and 5.7m/s). The material removal rate was increased with polishing speed and pressure. Higher polishing temperature would improve the chemical reaction and result in better surface finish.

SURFACE TEMPERATURE FIELD MODEL AND INFLUENCE FACTORS OF HF CVD DIAMOND FILMS ON WC–Co ALLOYS

The surface temperature field model of hot filament chemical vapor deposition (HF CVD) diamond films on WC – Co alloys was constructed and calculated by taking into account the influences of both thermal source properties and physical properties of substrates. Under the certain conditions of some parameters, the effects of the influence factors such as the maximum specific heat flux (q m ), the heat conductivity coefficient (λ) of the substrate and the substrate height (h) on the surface temperature field were exhibited quickly and clearly by the computer modeling. The theoretical calculating data are close to the experimental results. It is found that the influences of the thermal source parameter, the substrate height, and the heat conductivity coefficient of the substrate materials on the surface temperature field of diamond films on WC – Co alloys are almost equally important.

Hexagonal diamond synthesis on h-GaN strained films

Chemical vapor deposited diamond films grown on strained gallium nitride-coated quartz substrate are found to display a dominantly hexagonal diamond phase. The phase identification is done using Raman spectroscopy and orientation imaging microscopy (OIM). The presence of a 1324.4cm−1 band in the Raman spectra is attributed to a hexagonal diamond symmetry, but the unambiguous signature of the hexagonal phase is confirmed by OIM. A phase map of the sample clearly shows that 88% of the scanned sample area is hexagonal diamond.

Evaluation research of polishing methods for large area diamond films produced by chemical vapor deposition

The current study compared several polishing techniques of chemical vapor deposition (CVD) diamond films. Although research on various diamond polishing techniques has been carried for years, some issues still need to be examined in order to facilitate application on large areas in a cost-efficient manner. In the present work, microwave plasma enhanced chemical vapor deposition (CVD) was used to obtain diamond films with full width half magnitude (FWHM) less than 10 wavenumbers at 1332 cm − 1 Raman peak. The diamond films were processed through mechanical polishing, chemical-assisted mechanical polishing, thermo-chemical polishing, excimer laser ablation, and catalytic reaction assisted grinding. A profilometer, an atomic force microscope, and a scanning electron microscope have been used to evaluate the surface morphology of diamond films before and after polishing. The results obtained by using the above mentioned techniques were analyzed and compared.

Hydrogen plasma etching mechanism on (0 0 1) diamond

We studied the hydrogen plasma etching mechanism on (0 0 1) diamond surfaces as a parameter of misorientation angle ( θ off). After hydrogen plasma etching, for θ off < 1.5 ° , atomically flat surfaces were observed by atomic force microscopy, while for θ off > 1.5 ° , rough surfaces with high etch pit density and large (200 nm) periodic pattern due to mechanical polishing were observed on diamond substrates. In addition, mean roughness ( R a) increased with the increase in θ off. A simple model is presented taking into account anisotropic etching depending on θ off. Simulated results based on the model well explain the experimental results. Based on these results, we discuss the effect of hydrogen plasma etching on the growth of atomically flat homoepitaxial chemical vapor deposition diamond film at low CH 4/H 2 ratio with low θ off.

Study on EDM Polishing of CVD Diamond Films

Chemical vapor deposition (CVD) diamond is known for its superior characteristics such as hardness, toughness and wear resistance. However, due to these factors, machining CVD diamond is a difficult material removal process. A new technique to polish CVD diamond film efficiently is reported in the present paper. In the CVD deposition process, boron was doped into diamond to fabricate high-quality semi-conductive film, which make it possible to machine diamond film by electro discharged machining (EDM) method. The relationship between EDM parameter and removal processing was investigated in details. The machined surface of boron doped (B-doped) diamond films was studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that EDM polishing is a highspeed material removal and low cost method for CVD diamond polishing. When the discharge current and pulse-on time increase in a certain range, the cutting-off speed and roughness will increase correspondingly. The roughness of EDM polished CVD diamond film surface is Ra&lt;0.5μm when the discharge current is at 4A and pulse-on time is at 200μs.

Influence of intermittently etching on quality of CVD diamond thin films

A new method, called growing-etching repetitional process based on hot filament chemical vapor deposition, was proposed to improve the quality of diamond film. During the deposition carbon source was intermittently closed letting hydrogen etch the surface of the diamond film from time to time. In order to find whether it is helpful to the films' quality, a series of experiments were done. The results show that the new method can enhance the orientation of the chemical vapor deposition diamond films, reduce the graphite phase and increase the film's surface resistivity.

Diamond Ablators for Inertial Confinement Fusion

Diamond has a unique combination of physical properties for the inertial confinement fusion ablator application, such as appropriate optical properties, high atomic density, high yield strength, and high thermal conductivity. Here, we present a feasible concept for fabrication of diamond ablator shells. The fabrication of diamond capsules is a multi-step process which involves diamond chemical vapor deposition on silicon mandrels followed by polishing, microfabrication of holes, and removing of the silicon mandrel by an etch process. We also discuss the pros and cons of coarse-grained optical quality and nanocrystalline chemical vapor deposition diamond films for the ablator application.

Soft X-ray angle-resolved photoemission spectroscopy of heavily boron-doped superconducting diamond films

We have performed soft X-ray angle-resolved photoemission spectroscopy (SXARPES) of microwave plasma-assisted chemical vapor deposition diamond films with different B concentrations in order to study the origin of the metallic behaviorof superconducting diamond. SXARPES results clearly show valence band dispersions with a bandwidth of ~ 23 eV and with a top of the valence band at gamma point in the Brillouin zone, which are consistent with the calculated valenceband dispersions of pure diamond. Boron concentration-dependent band dispersions near the Fermi level (Ef) exhibit asystematic shift of Ef, indicating depopulation of electrons due to hole doping. These SXARPES results indicate that diamond bands retain for heavy boron doping and holes in the diamond band are responsible for the metallic states leading to superconductivity at low temperature. A high-resolution photoemission spectroscopy spectrum near Ef of a heavily boron-doped diamond superconductor is also presented.

Grain orientation dependence on distance to surface of CVD diamond film

Free standing chemical vapour deposition (CVD) diamond films were prepared under the gas recycling mode, where the substrate temperature ranged from 820 to 1050°C. Macro- and microtextures of the films were investigated based on the orientation distribution function (ODF) and electron backscatter diffraction (EBSD) analysis. The texture consisted of 〈001〉, 〈112〉, 〈111〉, 〈221〉 and 〈110〉 fibre components. Very high twinning frequency was observed because of the reduced purity of the deposition gas. The multi-twins appearing in series as well as in paratactic form reduced the grain size and randomised the orientation distribution. It is believed that the residual strain and stress in diamond films should relate to the fibre textures in certain extent because of the anisotropic elastic characteristics of diamond crystals.

Preparation of diamond whiskers using Ar/O 2 plasma etching

Radio frequency (RF) plasma etching of chemical vapor deposition (CVD) diamond film has been investigated in Ar/O 2 plasmas, with an emphasis to elucidate the effects of reacting gas on the fabrication of diamond whiskers. Diamond whiskers were formed on diamond films pre-coated with Al. It was found that diamond whiskers preferentially formed at the diamond grain boundaries. The densities of diamond whiskers increased with O 2 / Ar ratio. Whiskers obtained in pure O 2 plasma etching were 50 nm in diameter and 1 μm in height. The etching rate was increased by mixing Ar with appropriate volume of O 2. Al coated on the diamond surface reacted with O 2 to form Al 2O 3, serving as mask to restrain the etching underneath. Raman spectroscopy measurement confirmed that the whiskers kept sp 3 diamond bonding structure after RF plasma etching. The field emission characteristics of the whiskers were also inspected.

P-type doping by B ion implantation into diamond at elevated temperatures

We have studied B ion implantation at 400 °C into undoped homoepitaxial chemical vapor deposition diamond films and high-pressure and high-temperature (HPHT) synthetic IIa substrates. The highest Hall mobility at room temperature is 268 cm 2/Vs among B implanted homoepitaxial films, while it is 38 cm 2/Vs for the B implanted HPHT synthetic IIa substrate. The present result reveals that the quality of a doped layer is strongly dependent upon that of a diamond substrate employed for ion implantation.

Characterization of N-Doped Polycrystalline Diamond Films Deposited on Microgrinding Tools

Chemical vapor deposited diamond films have many industrial applications but are assuming increasing importance in the area of microengineering, most notably in the development of diamond coated microgrinding tools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness, and the degree of sp 3 character have a profound effect on the tribological properties of the films deposited. In this article, we present experimental results on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of microgrinding tools. The sp 3 character optimizes at 200 ppm nitrogen, and above this value the surface becomes much smoother and crystal sizes decrease considerably. Fracture-induced wear of the diamond grain is the most important mechanism of material removal from a microgrinding tool during the grinding process. Fracture occurs as a consequence of tensile stresses induced into diamond grains by grinding forces to which they are subjected. The relationship between the wear of diamond coated grinding tools, component grinding forces, and induced stresses in the model diamond grains is described in detail. A significant correlation was found between the maximum value of tensile stress induced in the diamond grain and the appropriate wheel-wear parameter (grinding ratio). It was concluded that the magnitude of tensile stresses induced in the diamond grain by grinding forces at the rake face is the best indicator of tool wear during the grinding process.

Field emission from nitrogen-implanted CVD diamond film grown on silicon wafer

Nitrogen was implanted into chemical vapor deposition (CVD) diamond films and the electron field emission properties of the nitrogenated diamond films were investigated. Nitrogen implantation was carried out using 10 keV in the dose range from 1×1016 to 5×1017 cm-2 at room temperature. Raman and X-ray photoelectron spectroscopy measurements revealed that nitrogen implantation damaged the structure of the diamond film and promoted the formation of sp2 C–C and sp2 C–N bondings. Increasing the implantation dose could lower the threshold field of the emission of the diamond film from 18 V/μm to 4 V/μm. The effective work function of the nitrogen-implanted CVD diamond films was estimated to be in the range of 0.01–0.1 eV. The enhancement of field emission for nitrogen-implanted CVD diamond films was attributed to the increase of the sp2 C bonds fraction and the formation of defect bands within the bulk diamond band gap induced by nitrogen implantation, which could alter the work function and elevate the Fermi level. Consequently, the energy barrier for electron tunneling was reduced.

Study of diamond film by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

Three chemical vapor deposited diamond films were studied by dynamic nuclear polarization (DNP)-enhanced high-resolution solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy. Enhanced C-13 direct-poiarization spectra of diamond Films were obtained by irradiating the samples with microwaves at or near electron spin resonance Larmor frequency of carbon center free radicals. No NMR signal for sp(2) hybridized carbons could be observed. From the Curve of the DNP enhancement as a function of Frequency, it is found that the dominant DNP mechanism is the solid-state effect. The C-13 cross-polarization spectrum, which is an evidence for existence of the proton defect in the lattice of diamond films, is much broader than the C-13 single Pulse spectrum. The reason is discussed shortly.

Characterization of chemical vapour deposited diamond films: correlation betweenhydrogen incorporation and film morphology and quality

In order to tailor diamond synthesized through chemical vapour deposition (CVD)for different applications, many diamond films of different colours and variablequality were deposited by a 5 kW microwave plasma CVD reactor under differentgrowth conditions. The morphology, quality and hydrogen incorporation of thesefilms were characterized using scanning electron microscopy (SEM), Raman andFourier-transform infrared (FTIR) spectroscopy, respectively. From this study, a generaltrend between hydrogen incorporation and film colour, morphology and quality was found.That is, as the films sorted by colour gradually become darker, ranging fromwhite through grey to black, high magnification SEM images illustrate that thesmoothness of the well defined crystalline facet gradually decreases and secondnucleation starts to appear on it, indicating gradual degradation of the crystallinequality. Correspondingly, Raman spectra evidence that the diamond Raman peak at1332 cm−1 becomes broader and the non-diamond carbon band around1500 cm−1 starts to appear and becomes stronger, confirming increase of the non-diamondcomponent and decrease of the phase purity of the film, while FTIR spectra showthat the CH stretching band and the two CVD diamond specific peaks around2830 cm−1 rise rapidly, and this indicates that the total amount of hydrogen incorporated into the filmincreases significantly.