Papers by Keyword: Nanocrystalline Diamond

Abstract: A flame combustion method enables the synthesis of diamond using acetylene-oxygen in ambient atmosphere. It has various advantages over other methods, such as in terms of speed, safety and cost. Tungsten carbide (WC) is used as cutting tools in the machining industry. In this study, to obtain nanocrystalline diamond films and to achieve good adhesion on the WC substrate, diamond films were synthesized by flame combustion using a mixture of high-purity acetylene and oxygen gas with the addition of nitrogen gas. Nitrogen gas added as the nanocrystalline diamond promotion agent; nitrogen flow rate was varied. The results indicated that, at the mixture of high-purity acetylene and oxygen gas, the diamond nanocrystallites was not synthesized on the diamond microcrystallites at nitrogen flow rate 0.000 cm³/s. As nitrogen flow rate was increased, the diamond nanocrystallites was synthesized on the microcrystallites. The diamond nanocrystallites was synthesized with high density all over the diamond microcrystallites.

Abstract: In this work, a solar cell structure of nitrogen-doped nanocrystalline diamond (NCD:N)/p-type silicon was fabricated using microwave plasma jet chemical vapour deposition technique. The effects of nitrogen doping level on the structure, optical, and electrical of the as-grown NCD:N was discussed. The results showed that the micro structure, surface roughness, electrical properties, and optical properties were affected by the nitrogen doping. Additionally, the agglomeration of the film was increased with the higher concentration of CN species when the ratio of doped nitrogen increased. The roughness of the film was Rms:16.5 nm ~ 20.4 nm and the wettability was increased (contact angle 94.4^o ~ 64.6^o). The optical transmittance was decreased (87% ~ 72%) with the higher nitrogen. The results of Hall measurements showed that the carrier concentration increased 2 order (1016 cm^-3 to 1018 cm^-3) through nitrogen doping. The solar cell was made by NCD: N compound with p-type silicon. The photoelectric conversion efficiency was 2.8%. The open-circuit voltage was 0.52 V. The short-circuit current was 3 mA and the fill factor was 0.38.

Abstract: The morphology and structure of nanocrystalline diamond films as well as the plasma chemistry were studied by altering the plasma impedance. These impedances related to electron density were altered via the matching system. Two films were grown by the microwave plasma under different values of the plasma impedance, resulting in low and high electron densities in the plasma. By the use of measurements of plasma impedance and optical emission, the lowering of an inductive component of the impedance, indicating an increasing electron density, encouraged H-radical concentration present in the plasma. As the plasma was changed to the high electron density, Raman spectra of the films showed the sp³ Raman peak shifted from 1325 to 1328.5 cm^-1 with narrower broadening. This behavior arose from an increase in grain size, corresponding to images from a field emission scanning electron microscope. Raman spectra of G-peak position and white light reflectometry showed a reduction in sp² carbon content of the film. The G-peak shifted from 1564 to 1541 cm^-1 and refractive index increased from 1.84 to 2.16. The formation of the films related to the concentrations of H and CH₃ radicals. The plasma impedance affected the radical concentrations.

Abstract: Nanocrystalline diamond films, as other forms of diamond, possess a set of extreme properties, such as high thermal conductivity, hardness and resistance to hazard environments. Although an enormous focus has been placed into the deposition of nanocrystalline diamond films, most of this research uses microwave plasma assisted CVD systems. However, the growth conditions used in microwave systems cannot be directly used in hot-filament CVD systems. In this paper, it is meant to enlarge the knowledge of the process of depositing nanocrystalline films on different engineering materials, by means of hot-filament CVD systems. The coated materials include silicon (Si); titanium (Ti); tungsten carbide with cobalt as binder (WC-Co); and tungsten carbide with nickel as binder (WC-Ni). On the former two substrates, the diamond films were achieved on the bare substrates and with the use of an interlayer. The interlayers used were chromium nitride (CrN) and titanium aluminium nitride (TiAlN). Additionally, the as-grown films were characterized for hardness, quality and microstructure using scanning electron microscopy, Raman spectroscopy and nanohardness testing.

Abstract: Nitrogen-incorporated, n-type nanocrystalline diamond (NCD) films are deposited on p-type Si(001) and 4H-SiC(0001) substrates by moderate-pressure, microwave plasma-enhanced chemical vapor deposition using a mixture of 1%CH4-30%N2-69%Ar. X-ray diffraction and visible Raman spectroscopy reveal that the structure of the NCD films is identical independent of the substrate materials, such that diamond nanoparticles with apparent crystal sizes of 5-8 nm are embedded in amorphous sp² carbon matrix. For p-Si/n-NCD heterojunctions in a diode configuration, the rectifying behavior in current-voltage curves depends upon the substrate temperature for film deposition, and the rectification ratio reaches a maximum of about 300 when the film is deposited at 830 °C. For p-4H-SiC/n-NCD heterojunctions, the rectification ratio increases greatly to about 10000 when the film is deposited at 830 °C due exclusively to suppression of the reverse leakage current.

Abstract: Nanocrystalline diamond films were grown by hot filament chemical vapour deposition (HFCVD) in a mixture of methane and hydrogen gases. Three straight parallel wires filament configuration were used in the HFCVD system for the deposition of the films studied in this work. The deposition pressure for the growth of diamond films in this hot filament chemical vapour deposition (HFCVD) reactor have been optimized to be at 20 torr with the methane and hydrogen flow-rates fixed at 2 and 200 sccm respectively. The films studied in this work were grown at low deposition pressures of 2 and 5 torr using the same gas flow-rates used for the optimized diamond film growth including an additional film grown at pressure of 5 mbar with the methane flow-rate reduced to 1 sccm. The morphology showed the formation of closed packed diamond grains for the film grown at 5 torr with methane and hydrogen flow-rates fixed at 2 and 200 sccm. Decrease in pressure and methane flow-rate produced significant changes to the morphology of the diamond grains formed. X-ray diffraction showed that diamond phase phases were dominant in the films deposited at higher pressure. Raman and photoluminescence (PL) spectral analysis were performed using spectra acquired at 325 and 514 nm excitation energies. Raman analysis revealed that increase in deposition pressure from 2 to 5 Torr resulted in the transformation of the film structure from diamond-like-carbon to nanocrystalline diamond structure. UV excitation produced high PL emission intensity at 2.1 eV and the PL intensity was highest for the films deposited at the lowest pressure. Visible excitation on the other hand produced low intensity broad PL emission for all the films between 1.2 and 2.5 eV and the PL intensity was high for the films deposited at the highest deposition pressure.

Abstract: Nanocrystalline diamond films have been synthesized by microwave plasma enhanced chemical vapour deposition using H₂/CH₄ as the reactant gas. Nanocrystalline diamond thin films with surface roughness of 11.8 nm were obtained on silicon substrates. The nanocrystallinity, surface roughness and hardness were characterized by the Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy and Nano Indentation, respectively. The Raman spectra of the films exhibit a band near 1145 cm^-1 and XRD patterns indicate the presence of nanocrystalline diamond. The hardness value of individual test point is approximately 102 GPa and the average hardness of thin film could reach 86 GPa.

Abstract: Nanocrystalline diamond (NCD)/3C-SiC layered films are deposited on Si substrates by using a moderate-pressure microwave plasma apparatus. The epitaxial 3C-SiC thin layer is grown on p-type Si(001) above 1200°C in 2%CH4/98%H2 by plasma-assisted carbonization and the n-type NCD overlayer is subsequently grown at 830°C in 1%CH4/30%N2/69%Ar by plasma-enhanced chemical vapor deposition (CVD). According to cross sectional TEM observations, the initial thickness of the 3C-SiC layer (~20 nm) is reduced to 10 nm or less in the beginning of the NCD growth due most likely to etching. A rectifying current-voltage characteristic is obtained for an n-type NCD/epitaxial 3C-SiC/p-type Si(001) junction in a diode configuration.

Abstract: Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band (9.4 GHz) and W-band (94 GHz) have been used to study defects in natural diamond nanocrystals, detonation nanodiamond (ND) with a size of  4.5 nm and detonation ND after high-pressure high-temperature (HTHP) sintering with a size of  8.5 nm. Based on identification of atomic nitrogen centers N0 and nitrogen pairs N2+ detected by means of the high frequency EPR and ESE in natural diamond nanocrystals, atomic nitrogen centers N0 have been discovered in nanodiamond core in detonation ND and detonation ND after sintering. In addition EPR signal of multi-vacancy centers with spin 3/2 seems to be observed in diamond core of detonation ND.

Abstract: Nanocrystalline diamond (NCD) films were deposited using plasma-enhanced chemical vapor deposition. The NCD films were Boron-doped for p-type conductivity, yielding sheet resistances from 6.17x1011 to 522.5 /. Four different metals were deposited as Ohmic contacts and investigated for contact resistance and thermal stability. Contact and film annealing was performed under different atmospheric conditions with variable N2 content.