Iron Oxide Nanoparticles Employed as Seeds for the Induction of Microcrystalline Diamond Synthesis

Iron nanoparticles were employed to induce the synthesis of diamond on molybdenum, silicon, and quartz substrates. Diamond films were grown using conventional conditions for diamond synthesis by hot filament chemical vapor deposition, except that dispersed iron oxide nanoparticles replaced the seeding. X-ray diffraction, visible, and ultraviolet Raman Spectroscopy, energy-filtered transmission electron microscopy , electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to study the carbon bonding nature of the films and to analyze the carbon clustering around the seed nanoparticles leading to diamond synthesis. The results indicate that iron oxide nanoparticles lose the O atoms, becoming thus active C traps that induce the formation of a dense region of trigonally and tetrahedrally bonded carbon around them with the ensuing precipitation of diamond-type bonds that develop into microcrystalline diamond films under chemical vapor deposition conditions. This approach to diamond induction can be combined with dip pen nanolithography for the selective deposition of diamond and diamond patterning while avoiding surface damage associated to diamond-seeding methods.     

Carbon nanocapsules encapsulating cobalt nanoparticles by pulsed discharge plasma chemical vapor deposition

Silicon coated with a thin film of cobalt [Si/Co (10 nm)] is exposed to the plasma generated using CH₄–H₂ gas mixture by making a discharge between Si/Co substrates and Mo bent plate in pulsed discharge plasma chemical vapor deposition. At high plasma temperature and deposition pressure, carbon nanocapsules encapsulating Co nanoparticles are observed to form. They are investigated using high resolution transmission electron microscopy, scanning electron microscopy, visible Raman spectroscopy and X-ray diffraction. Present study indicates that the formation mechanism of carbon nanocapsules lie in the sputtering of Co thin film by the energetic ions from plasma at high deposition pressure which results in the formation of Co nanoparticles, on surface of which graphitic layers gets deposited at high plasma temperature. Present approach provides a novel strategy for the synthesis of high purity carbon nanocapsules encapsulating metal nanoparticles.     

The synthesis of graphene nanowalls on a diamond film on a silicon substrate by direct-current plasma chemical vapor deposition

Graphene nanowalls have been synthesized on diamond by direct-current plasma enhanced chemical vapor deposition (CVD) on silicon substrates pre-seeded with diamond nanoparticles in gas mixtures of methane and hydrogen. Switching from diamond CVD to graphene CVD is done by increasing the methane concentration and decreasing the plasma power without breaking the vacuum. Graphene nanowalls stand on the CVD diamond film to form a 3-dimensional network. Scanning electron microscopy, high-resolution transmission electron microscopy, UV and visible Raman scattering and electrochemical cyclic voltammetry measurements are used to characterize the multi-layer turbostratic graphitic carbon nanostructure and demonstrate its electrochemical durability with a low background current in a wide electrochemical potential window.     

Single-step route to diamond-nanotube composite

Candle wax was used as a precursor for the production of a diamond-nanotube composite in a single step. The composite films were fabricated by sulfur-assisted hot-filament chemical vapor deposition technique. The morphology of the composite films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectra of the films show characteristic diamond band at 1,332 cm⁻¹, D-band around 1,342 cm⁻¹, and graphitic G-band around 1,582 cm⁻¹. The electron energy-loss spectroscopy recorded at the carbon K-edge region shows signature features of diamond and carbon nanotube in the fabricated material. The ability to synthesize diamond-nanotube composites at relatively low temperatures by a single-step process opens up new possibilities for the fabrication of nanoelectronic devices.     

Experimental study of nucleation and quality of CVD diamond adopting two-step deposition approach using MPECVD

Effects of the deposition conditions on quality and nucleation density of CVD diamond were investigated using a microwave plasma enhanced chemical vapor deposition (MPECVD) method with methane-hydrogen gas mixtures. Diamond films were deposited at pressures of 665–4000 Pa, temperatures of 660–950 °C, and methane concentrations of 0.5–5 vol.%. Deposited diamond films were characterized by scanning electron microscopy, field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Diamond quality and nucleation density significantly affected by the deposition pressure, substrate temperature, and methane concentration. The findings of this work were discussed in terms of the effects of deposition conditions on the plasma composition. A two-step deposition approach was applied to improve nucleation density and quality of CVD diamond films. Polycrystalline diamond films were grown using the two-step deposition process changing a combination of parameters in the two steps. Growth and quality of the deposited diamond films were improved altering the deposition pressure and substrate temperature in the two steps.     

Investigation of the effect of the total pressure and methane concentration on the growth rate and quality of diamond thin films grown by MPCVD

The influence of total gas pressure (50–125 Torr) and methane concentration (0.75%–10%) on diamond growth by microwave plasma chemical vapor deposition (MPCVD) was investigated. Within the regimes studied, the growth rate was proportional to the methane concentration in the source gas while it exhibited a super-linear dependence on total pressure. For a fixed methane concentration, characterization by Raman spectroscopy, scanning electron microscopy and X-ray diffraction indicated there was a minimum pressure required for the growth of large grain diamond, and conversely, for a fixed pressure, there was a maximum methane concentration that yielded diamond deposition. Higher pressures and higher carbon concentrations yielded diamond growth rates more than 10 times higher than achieved by the conventional low pressure MPCVD process.     

Microwave plasma chemical vapor deposition of cone-like structure of diamond/SiC/Si on Si (100)

Diamond deposition on 1 × 1 cm² Si (100) substrates with bias was carried out by microwave plasma chemical vapor deposition (MPCVD). Distribution of deposited diamonds has been significantly improved in uniformity over all the Si substrate surface area by using a novel designed dome-shaped Mo anode. The deposits were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman analysis. SEM observations show that there is a high density of cone-like particles uniformly deposited on the surface of the substrate in short bias nucleation period. The average diameter, height and density of cone-like structure were increased with methane concentration in the bias stage. TEM reveals that the cone-like structure is actually composed of Si conic crystal covered with diamond. Between Si and diamond, a thin layer of cubic SiC is found in epitaxy with Si. Furthermore, for 3% CH₄ concentration, the range of diameter of cone-like structure was about 20–90 nm and the size of diamond was about 10–60 nm.     

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.     

The orientation effect of silicon grains on diamond deposition

Diamond deposition on mirror-polished polycrystalline silicon substrates which have grains in various orientations has been investigated using electron backscatter diffraction (EBSD) method with scanning electron microscopy (SEM). Diamond was deposited by microwave plasma chemical vapor deposition with application of a negative bias voltage on the substrate. The evidence from systematic SEM observations shows that silicon orientation determined by EBSD has a strong effect on diamond nucleation. In general, the diamond nucleation density on Si grains oriented close to <100> is the highest, while it is the lowest for those grains close to <111>, under the same experimental conditions for deposition. The same phenomena have been observed in the range of methane concentration from 2% to 4% in hydrogen.     

Magnetic response of CVD and PECVD iron filled multi-walled carbon nanotubes

Plasma enhanced chemical vapour deposition (PECVD) and injection chemical vapour deposition (CVD) methods have been used to produce superparamagnetic iron nanoparticles (NPs) encapsulated in carbon nanostructures (core@shell). Morphological and structural properties of the Fe-filled CNTs synthesized by PECVD and CVD were carried out using a scanning and transmission electron microscope (SEM, TEM), high resolution electron microscopy (HRTEM) and selected area electron diffraction (SAED). Magnetometry results and electron microscopy observations reveal magnetic responses with different characteristics associated to the iron particles depending on the deposition method. The magnetic properties of these samples have been described in terms of the carbon nanotube anisotropic structural effects. This magnetic behaviour has potential for biomedical applications.     

Carbon nanotubes coated with diamond nanocrystals and silicon carbide by hot-filament chemical vapor deposition below 200 °C substrate temperature

Multi-walled carbon nanotubes (MWCNTs) dispersed onto a silicon substrate have been coated with diamond nanocrystals (DNC) and silicon carbide (SiC) from solid carbon and silicon sources exposed to H₂ activated by hot filament chemical vapor deposition (HFCVD) at around 190 °C substrate temperature. MWCNT coating by DNC initiates during filament carburization process at 80 °C substrate temperature under conventional HFCVD conditions. The hybrid nanocarbon material was analyzed by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy, selected area electron diffraction, X-ray diffraction and Raman spectroscopy. The structure of the MWCNTs is preserved during coating and the smooth DNC/SiC coating is highly conformal. The average grain size is below 10 nm. The growth mechanism of DNC and SiC onto MWCNT surface is discussed.     

Adherent and low friction nano-crystalline diamond film grown on titanium using microwave CVD plasma

The use of titanium alloys for aerospace and biomedical applications could increase if their tribological behavior was improved. The deposition of an adherent diamond coating can resolve this issue. However, due to the different thermal expansion coefficients of the two materials, it is difficult to grow adherent thin diamond layers on Ti and its metallic alloys. In the present work microwave plasma chemical vapor deposition (MWPCVD) was used to deposit smooth nano-crystalline diamond (NCD) film on pure titanium substrate using Ar, CH₄ and H₂ gases at moderate deposition temperatures. Of particular interest in this study was the exceptional adhesion of approximately 2 μm-thick diamond film to the metal substrate as observed by indentation testing up to 150 kg load. The friction coefficient, which was measured with a cemented carbide ball of 10 mm diameter with 20 N load, was estimated to be around 0.04 in dry air. Morphology, surface roughness, diamond crystal orientation and quality were obtained by characterizing the sample with field emission electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy, respectively.     

Effect of ion beam nitriding on diamond nucleation and growth onto steel substrates

Ion beam nitriding was successfully employed to overcome the difficulty of diamond growth on ferrous base substrates. Commercial steels were pretreated by an ion beam method in an ambient environment of nitrogen gas, diamond was then deposited by hot filament chemical vapor deposition (CVD). The deposited films were characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Continuous diamond films with a sharp characteristic Raman peak of 1337.7 cm⁻¹ were grown and adhered well on the nitrided region of the steel substrates. On the other hand, a mixture of diamond crystallites, amorphous carbon and graphitic carbon was loosely deposited on the unnitrided region. A thin layer of iron and chromium nitrides, formed on the steel surface by ion beam nitriding, enabled the subsequent nucleation and growth of high-quality CVD diamond.     

Effect of substrate temperature on the selective deposition of diamond films

Selective diamond films on roughened Si(100) substrates with patternings have been achieved by microwave plasma chemical vapor deposition (MP-CVD). The films have been characterized by scanning electron microscopy (SEM) and Raman spectra. The influence of substrate temperature on the selective deposition of diamond films has been discussed in detail: the diamond nucleation density on the SiO₂ mask increased with substrate temperature while the effect of the selective deposition of diamond films deteriorated; the optimized deposition temperature conditions have been concluded.     

Planarizing CVD diamond films by using hydrogen plasma etching enhanced carbon diffusion process

Polycrystalline diamond films, deposited by microwave plasma chemical vapor deposition (MPCVD), were planarized in hydrogen plasma under the graphitization of iron film obtained by reduction of iron chloride under hydrogen plasma ambient. For this process, the free-standing diamond films were dipped in a saturated iron chloride solution and dried horizontally in atmospheric ambient. Then the diamond samples were heated by hydrogen plasma in the same MPCVD reactor. Under the effect of hydrogen reduction, iron thin film was formed on the surface of diamond films. Under ca. 800 °C, the carbon diffusion process was carried out under the graphitization effect of iron thin film. Since the iron film used in this process is very thin, the diffused carbon will diffuse from the diamond side to the hydrogen plasma side and then etched away by the plasma. Therefore, the etching rate of diamond film can be kept consistent. After etching the growth surface of a free-standing diamond film, we investigated the surface morphologies and the carbon phases on the etched surfaces of diamond films. Finally, compared with the result of mechanical lapping experiments, we suggest that the hydrogen plasma etching enhanced carbon diffusion process can serve as a new planarization method for rough diamond film surface. A mechanism for this enhanced etching effect is also presented and discussed.     

Deposition of diamond films on sapphire: studies of interfacial properties and patterning techniques

Polycrystalline diamond films were grown on single crystal sapphire substrates using hot filament chemical vapour deposition (CVD). Problems with poor adhesion, stress and film cracking became severe for deposited areas greater than about (100 μm)². Scanning electron microscopy analysis showed the films to be failing both at the interface and in the diamond layer itself. Transmission electron microscopy cross-sections of the interface showed that the interface was clean and free from non-diamond carbon impurities. Spallation problems in the diamond film could be reduced by introducing a barrier layer of epitaxial silicon grown on the sapphire prior to the diamond CVD step. Patterned silicon-on-sapphire wafers were then used as substrates for CVD of diamond in order to define features of linewidth more than 10 μm in the diamond films. Two methods were used: selective nucleation and lift off.     

The effect of HCl and NaOH treatment on structural transformations in a ball-milled anthracite after thermal and chemical processing

Nanocrystalline diamond (NCD) was observed after reactive ball milling of anthracite coal with cyclohexene, a high-temperature (1400 °C) thermal anneal, and a 4 M HCl treatment followed by a 10 M NaOH treatment. A crystalline carbon region was also observed when the thermal anneal was omitted. This crystalline region is highly unstable and converts to NCD and carbon onions via electron irradiation in the TEM. X-ray diffraction, Raman, ash content, and temperature-programmed oxidation (TPO) data suggest that tetrahedral amorphous carbon is formed during milling, iron carbides are formed during the thermal anneal step, and both the HCl and NaOH purification steps lead to changes in carbon structure. NaOH oxidizes metal carbides and this process may contribute to NCD formation.     

Growth and field emission study of a monolithic carbon nanotube/diamond composite

Carbon nanotube (CNT)/diamond composite has been fabricated by hot filament chemical vapor deposition on a silicon substrate using iron as catalyst. The material characteristics of this monolithic structure were examined by electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. The composite material shows the presence of carbon nanotubes of several microns in length together with conspicuous diamond microcrystals of sizes ranging from 0.5 to 2.0 μm. The CNTs protrude from the diamond microcrystals and become entangled around them as they grow. This monolithic CNT/diamond composite provides an intrinsic heat dissipation mechanism for CNTs during field emission and exhibits low turn on field, large field enhancement factor, and an excellent current stability over a period of 44 h.     

Structural investigation of nanocrystalline diamond/amorphous carbon composite films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films have been prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures. The complex nature of the coatings required the application of a variety of complementary analytical techniques in order to elucidate their structure. The crystallinity of the samples was studied by selected-area electron diffraction (SAED). The diffraction patterns revealed the presence of diamond crystallites within the films. From the images taken by transmission electron microscopy (TEM) the crystallite size was determined to be on the order of 3–5 nm. The results were confirmed by X-ray diffraction (XRD) measurements exhibiting broad (111) and (220) peaks of diamond from which the average size of the crystallites was calculated. The grain boundary width is 1–1.5 nm as observed by TEM images which corresponds to a matrix volume fraction of about 40–50%. This correlates very well with the crystalline phase content of about 50% in the films estimated from their density (2.75 g/cm³ as determined by X-ray reflectivity). The bonding structure of the composite films was studied by electron energy loss spectroscopy (EELS) in the region of carbon core level. The spectra were dominated by a peak at 292 eV indicating the diamond nature of the investigated films. In addition, the spectra of NCD/a-C films possessed a shoulder at 284 eV due to the presence of a small sp² bonded fraction. This phase was identified also by X-ray photoelectron spectroscopy (XPS). The sp²/sp³ ratio was on the order of 10% as determined by deconvolution of the C1s XPS peak.     

Transmission electron microscopy study of diamond nucleation and growth on smooth silicon surfaces coated with a thin amorphous carbon film

Amorphous carbon (a-C) films with high contents of tetrahedral carbon bonding (sp³) were synthesized on smooth Si(100) surfaces by cathodic arc deposition. Before diamond growth, the a-C films were pretreated with a low-temperature methane-rich hydrogen plasma in a microwave plasma-enhanced chemical vapor deposition system. The evolution of the morphology and microstructure of the a-C films during the pretreatment and subsequent diamond nucleation and initial growth stages was investigated by high-resolution transmission electron microscopy (TEM). Carbon-rich clusters with a density of ∼10¹⁰ cm⁻² were found on pretreated a-C film surfaces. The clusters comprised an a-C phase rich in sp³ carbon bonds with a high density of randomly oriented nanocrystallites and exhibited a high etching resistance to hydrogen plasma. Selected area diffraction patterns and associated dark-field TEM images of the residual clusters revealed diamond fingerprints in the nanocrystallites, which played the role of diamond nucleation sites. The presence of non-diamond fingerprints indicated the formation of Si–C-rich species at C/Si interfaces. The predominantly spherulitic growth of the clusters without apparent changes in density yielded numerous high surface free energy diamond nucleation sites. The rapid evolution of crystallographic facets in the clusters observed under diamond growth conditions suggested that the enhancement of diamond nucleation and growth resulted from the existing nanocrystallites and the crystallization of the a-C phase caused by the stabilization of sp³ carbon bonds by atomic hydrogen. The significant increase of the diamond nucleation density and growth is interpreted in terms of a simple three-step process which is in accord with the experimental observations.