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Reduced graphene oxide-coated carbon nanotubes (RGO-CNT) electrodes have been prepared by hot filament chemical vapour deposition system in one-step growth process. We studied RGO-CNT electrodes behaviour as cold cathode in field emission test. Our results show that RGO-CNT retain the low threshold voltage typical of CNTs, but with greatly improved emission current stability. The field emission enhancement value is significantly higher than that expected being caused by geometric effect (height divided by the radius of nanotube). This suggested that the field emission of this hybrid structure is not only from a single tip, but eventually it is from several tips with contribution of graphene nanosheets at CNT's walls. This phenomenon explains why the graphenated carbon nanotubes do not burn out as quickly as CNT does until emission ceases completely. These preliminaries results make nanocarbon materials good candidates for applications as electron sources for several devices.

Reduced graphene oxide (RGO) and vertically aligned carbon nanotubes (VACNT) superhydrophilic films were prepared by chemical vapor deposition techniques for electrical energy storage investigations. These electrodes were characterized in terms of their material and electrochemical properties by scanning electron microscopy (SEM), surface wettability, Fourier transform infrared spectroscopy (FTIR), energy dispersive and Raman spectroscopies, cyclic voltammetry (CV) and galvanostatic charge–discharge. We observed several physical structural and electrochemical similarities between these carbon-based materials with particular attention to very good specific capacitance, ultra-high energy storage and fast power delivery. Our results showed that the main difference between specific capacitance values is attributed to pseudocapacitive contribution and high density of multiwall nanotubes tips. In this work we have tested a supercapacitor device using the VACNT electrodes.

Microcrystalline (MCD) and nanocrystalline (NCD) magnetic diamond samples were produced by hot-filament chemical vapour deposition (HFCVD) on AISI 316 substrates. Energy Dispersive X-ray Spectroscopy (EDS) measurements indicated the presence of Fe, Cr and Ni in the MCD and NCD samples, and all samples showed similar magnetisation properties. Cell viability tests were realised using Vero cells, a type of fibroblastic cell line. Polystyrene was used as a negative control for toxicity (NCT). The cells were cultured under standard cell culture conditions. The proliferation indicated that these magnetic diamond samples were not cytotoxic.

Chemical vapor deposited diamond is a new potential biomedical material which has the advantage of chemical inertness, extreme hardness and low coefficient of friction, among others. In orthopedics and maxillofacial surgery, these properties could improve implant performance, reducing metallic corrosion, particle wear, inflammatory reactions and bone loss. In the present study, two types of chemical vapor deposition (CVD) diamonds have been analyzed: microcrystalline diamonds (MD) and nanocrystalline diamonds (ND), both produced by hot-filament chemical vapor deposition. The diamond tubes were previously characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman scattering spectroscopy (RSS). The aim of this study was to verify the interface between bone and MD and ND, surgically implanted in the femoral diaphysis of Wistar rats, after 4 and 8 weeks. The outcome was evaluated by scanning electron and optical microscopy using a semi quantitative method. The results suggest that nanocrystalline diamonds (ND) elicits a richer biological response than microcrystalline diamonds (MD) when in interaction with bone.

Sulfur doping of diamond samples produced by the hot-filament chemical vapor deposition (CVD) process using carbon disulfide highly diluted in ethanol and hydrogen has been investigated. The polycrystalline morphology observed by Scanning Electron Microscopy (SEM) and the characteristic diamond Raman peak were practically not affected by addition of CS2 in the range of 0.8–2.0% by volume. The electrical resistivity dependence due to CS2 addition showed a “down-and-up” curve with minimum resistivity of about 3.6 × 10−4 Ωcm. Hall mobility as high as 325.9 cm2V−1s−1 have been achieved. PIXE and XRF measurements showed that sulfur (100–400 ppm) was incorporated during the deposition independent of the CS2 added. Unintentional contaminations with Si, W, Cu and Cr have been detected. All the samples, measured by hot-point method and Hall effect, showed p-type characteristics.

Nanostructured diamond doped with sulphur has been prepared using a hot-filament assisted chemical vapour deposition system fed with an ethyl alcohol, carbon disulfide, hydrogen, and argon mixture. The reduction of diamond grains to the nanoscale is relevant to create a network of defective grain boundaries which may be n-type doped to facilitate the transport and injection of electrons to the diamond grains located at the vacuum interface, enhancing the electron field-emission properties of the samples. The downsizing was produced by secondary nucleation and defects induced by sulphur and argon atoms in the chemical vapour deposition surface reactions. Sulphur also acts as an n-type dopant of diamond. Raman measurements show that the samples are nanodiamonds embedded in a matrix of graphite and disordered carbon grains and the morphology, revealed by field electron scanning microscopy, shows that the grains are in the range of 10 to 30 nm. The lowest threshold achieved for field emission was 13.20 V/μm.

Diamond coatings on pure titanium substrates are of interest for tribological and biomedical implants, among others, however, due to the different thermal expansion coefficients of the two materials, it is difficult to grow adherent thick diamond layers on Ti. The aim of this work was to investigate the influence of cooling down the substrate from the deposition temperature to the room temperature and then repeat the deposition process several times, on the quality and stress of the deposited diamond. This process intended to allow a partial relaxation of the diamond/Ti thermal stresses by accommodating the diamond nuclei onto the titanium carbide formed interlayer without detachment from the substrate. A hot-filament chemical vapor deposition system fed with ethanol, highly diluted in hydrogen was employed. Coatings of complete surface coverage with faceted grains of lateral size of about 4 μm and 0.38 GPa have been obtained.

Atomic force microscopy (AFM) was used to study the morphology and coagulation of human blood cells in contact with solid surfaces. Blood was extracted from the veins of healthy adult donors and the samples were used immediately after extraction, deposited either on borosilicate glass or diamond substrates. Some blood samples were anti-coagulated by adding heparin for single cell AFM imaging. No chemicals were used for attaching or immobilizing the cells. The diamond substrates were produced by chemical vapour deposition (CVD diamond) using a hot-filament CVD system fed with ethanol highly diluted in hydrogen. AFM imaging of isolated cells (anti-coagulated by heparin) was only possible on the glass substrates due to the lack of adherence of the cells to the diamond surface. The coagulation results suggest that blood clotting on diamond produces a less rough surface than blood clotting on glass.

Nanostructured diamond and diamond-like materials having good field electron emission properties have been prepared using a hot-filament assisted chemical vapour deposition system fed with ethanol/hydrogen/helium mixtures. The changes in the structure of the samples were determined by the hydrogen content in the gas mixture and varied from samples of nanocrystalline diamond with graphitic connection between the grains (for helium concentration 40 vol %). Although the samples had such structural differences, low threshold values for electron field emission in vacuum were observed for representative samples of low and high hydrogen concentrations in the gas feed.

A hot-filament chemical vapor deposition system fed with ethanol highly diluted in hydrogen was employed to grow self-supported diamond tubes with external diameter to wall thickness aspect ratio between ∼5 and ∼60, and 30 mm in length. Tungsten wires of diameters between 238 and 586 μm were used as substrates for the deposition, and were subsequently completely removed by etching, to leave stress-free diamond tubes, as demonstrated by micro-Raman spectroscopy. Scanning electron microscopy revealed cross-sections with diamond grains growing radially, forming well-faceted top-surface grains on the tube's external surface.

The fabrication and characterization of ‘self-supporting’ diamond tubes grown by chemical vapor deposition (CVD) are reported. Diamond layers were deposited onto tungsten wires with diameters of 238 μm; the tungsten cores were subsequently completely removed by etching to leave ‘self-supporting’ diamond tubes with a diameter of approximately 400 μm and length of 20 mm. A hot-filament CVD system fed with ethanol highly diluted in hydrogen was employed. Growth rates of 7.8 μm h −1 have been measured and incubation times >3 h have been estimated. Scanning electron microscopy of cross-sections revealed columnar structures, which terminate on sharp (111) facets on the tube's external surface. Raman spectroscopy showed that the tube structure is predominantly composed of CC sp 3 bonds, with intrinsic tensile stresses.

Atomic force microscopy (AFM) was used to study the relation between the surface morphology of SnO2 coatings with their room-temperature resistivities. A hot-plate chemical vapor deposition system fed with vapors of tin tetrachloride and methyl alcohol diluted in a nitrogen gas carrier was used to deposit the SnO2 films on soda-lime glass. It was found that above a critical deposition temperature (T=643 K), the film resistivity reaches its minimum value, which is almost constant over the wide range of the SnCl4 vapor concentration used. AFM revealed that the increase in the deposition temperature increased the grain size and that the surface roughness increases with greater SnCl4 vapor concentration. Therefore films of the same resistivity (deposited at the same temperature) may have different roughnesses.

Diamond-like carbon films were grown on pyrolised bamboo substrates by hot filament-chemical vapor deposition from ethanol/hydrogen mixtures. Different stages of deposition of films grown on untreated substrates and substrates seeded with diamond dust were compared. Changes in film morphology and structure under changes in these parameters were investigated using scanning electron microscopy and Raman spectroscopy. Diamond-like carbon (DLC) with ball-like morphology on the micrometer scale and glassy DLC with a stacked planar structure were observed for depositions of >2 h on unseeded and seeded substrates, respectively. Gasification of the fibers by hydrogen in the early stages of growth may play a role in film growth, but this requires further study. Nevertheless, DLC films can be grown on pyrolised bamboo substrates, which suggests that other carbonaceous substrates for film fabrication by hot-filament chemical vapor deposition also merit systematic investigation.

Porous diamond and porous carbon structures were deposited by hot-filament chemical vapor deposition (HFCVD) onto natural fibers derived from pyrolized bamboo substrates. 'Seeding' of the substrate with diamond dust prior the HFCVD process, allowed the fabrication of porous diamond, replicating the porous surface geometry of the bamboo fibers. As indicated by scanning electron microscopy and Raman spectroscopy, respectively, the films deposited on 'seeded' substrates are poly-faceted and are composed predominantly of C-C sp bonds. 2001 Elsevier Science B.V. All rights reserved. 3

Tungsten wires were used as templates for the deposition of tubes of micro-crystalline diamond or of 'spongy' carbon nano- structures. A hot-filament chemical vapor deposition system fed with highly diluted ethanol in hydrogen and argon was used. Argon was intentionally added to the feed at different concentrations to affect the crystalline growth. As the argon concentration was increased beyond 65 vol.% in the reactor feed, the morphology drastically changed from micro-crystalline diamond to complex carbon nano-structures. While the samples produced at argon concentrations of 65 vol.% or less resulted in a radial columnar structure of micro-crystalline diamond, the samples produced at higher argon concentrations showed radial flaws and 'spongy' structures. Each type of morphology is of potential interest for the use of these tubes as molecular filters or in electron emission devices. 2001 Elsevier Science B.V. All rights reserved.

Diamond-coated stainless-steel blades promise smoother cutting and greater durability. In this work the feasibility of coating stainless-steel blades with diamond and diamond-like carbon (DLC) by hot-filament chemical vapor deposition was investigated. Two pre-deposition seeding procedures using either diamond dust or oil droplets were tested. As revealed by scanning electron microscopy and Raman spectroscopy, both seeding methods allow the production of diamond films also containing some DLC. The oil-seeding method, however, is the most successful in promoting diamond nucleation. Film deposition along the blade edge is also enhanced by its curvature.

Diamond films of small roughness have been deposited onto thermally oxidized Si substrates by a process of anisotropic crystalline growth induced by nitrogen in a hot-filament chemical vapor deposition reactor. Ethanol (C2H5OH), diluted in hydrogen and nitrogen, was used as the source of carbon. At high concentrations, nitrogen tends to suppress the diamond growth in the 〈100〉 direction, which allows the growth of square mesoscopic-like crystals (“plates”) of large area in the directions parallel to the surface of the substrate. These plates stack upon each other, forming a thick diamond coating of uniform thickness. Analysis of the films made by micro-Raman spectroscopy and atomic force microscopy revealed that it is possible to obtain diamond coatings of high quality with a roughness comparable to that of the SiO2 at the diamond/SiO2 interface, and of nanometric roughness on the surface of the plates. A model to explain the morphology of the plates based on the microscopic mechanisms that involve the possible passivation of the (100) plane and an increase of vacancies by nitrogen is also discussed.

Micro-crystalline diamond films and nano-carbon structures in the form of wires have been grown by the introduction of argon at very high concentrations (60%–87.5% vol Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament chemical vapor deposition reactor. The argon, in addition to acting as an inert diluent, also modified the kinetics of the carbon deposition process; its presence apparently minimized the deposition of intergranular hydrogenated species, induced an increase in the number of flaws between the diamond grains, increased the porosity of the films, and formed new carbon structures. Well-faceted diamond films, diamond-like carbon (DLC) balls, spongy-like wires, and multilayer structures were observed at different concentrations of Ar. Raman spectroscopy of the deposited material showed that structures of high quality diamond (60%–65% vol Ar) and carbon structures related to DLC, fullerenes and carbon nanotubes, may be deposited by this process.

In this work, we undertook a unique study of the growth kinetics of diamond in a hot-filament chemical vapor deposition (HF-CVD) reactor fed with the mixture C2H5OH+H2+Ne, varying the concentration of Ne from 0% vol. to 60% vol. Images obtained by scanning electron microscopy (SEM) show that the addition of neon influenced the grain morphology, but diamond films with well-defined crystalline facets and good Raman quality were obtained up to a concentration of 60% vol. Ne. We verified that neon changes the diamond growth mechanism in the space between the grains, probably by the minimization of the hydrogenation kinetics in these regions. There is an apparent increase in the grain size and an increase in the flaws between the grains. The presence of Ne in the feed mixture also induces a broadening of the Raman peak characteristic of diamond, and this broadening may be related to an increase in the density of vacancies within the diamond grains.

We present experimental results of chemical vapor deposition (CVD) diamond growth from ethanol vapor with the substitution of hydrogen by helium in concentrations varying from 0 to 95 vol.% He. Scanning electron microscopy (SEM) analysis revealed that the addition of helium to the gas phase influenced the growth rate and film structure. The deposition rate of diamond increases up to a helium concentration of 40 vol.% and then decreases. We attribute this behavior to an increase in the density of vacancies in the film or to a change in the reaction kinetics provoked by the chemical inertness of helium. Diamond films with well-defined crystalline facets and of good quality (measured by Raman spectroscopy) were obtained with the addition of up to 70 vol.% He. Use of helium also provokes an increase in film porosity, with the appearance of a strong room temperature photoluminescence with a Gaussian peak at approximately 635 nm. The intensity of the luminescence increases with the concentration of helium and is probably related to nanoporous defects introduced into the diamond structure.

We studied the effects on the growth kinetics and properties of diamond and carbon-like diamond films obtained by the introduction of argon at low to high concentrations (0–85 vol.% Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament chemical vapor deposition (CVD) reactor. Scanning electron microscopy (SEM) analysis revealed that the addition of argon induces an increase in the diamond grain size, and increases the flaws between the grains and the density of vacancy defects. Well-faceted diamond films of good quality (measured by Raman spectroscopy) have been obtained using up to 65 vol.% of argon in the gaseous mixture, while higher concentrations (85 vol.% Ar) produce diamond-like carbon or other complex carbon structures. We also observed an increase in the diamond growth rate with argon addition that was associated with an increase in carbon free radicals (up to ∼40 vol.% Ar) or to the increase in the filament temperature necessary to keep the substrate temperature constant at higher Ar concentrations (above ∼40 vol.% Ar). Room temperature photoluminescence spectroscopy also confirmed that argon addition increases the density of vacancy defects in the diamond structure.

Diamond growth on non-diamond substrates initially requires a heterogeneous nucleation step on the substrate surface and, depending on the substrate material, the nucleation time may be very long and the nuclei density may also be very low, compromising the film quality. Seeding of substrates prior to chemical vapor deposition (CVD), typically using diamond grains, is commonly employed to increase nucleation of the growing film. Alternative nucleation methods are of great interest. In this work, we demonstrate the feasibility of using natural hematite to increase nucleation on silicon. This mineral in lamellae form is very soft and minimizes damage to the substrate surface. Hematite grains of a silica-rich phase improved the crystalline faceting and the coalescence of the growing diamond, indicating that complex oxides, such as iron silicates, may favor diamond nucleation. The nucleation density was approximately 0.8 × 10 6 nuclei cm -2 , which is a thousand times greater than that obtained on the 'unseeded' silicon surface. Samples 'seeded' with hematite grains of the silica-rich phase presented sharper peaks at 1332 cm -1 (higher aspect-ratio), indicating a higher diamond quality.

We demonstrate the enhancement of diamond nucleation through the use of the equilibrium forces at the solid-liquid-gas interface on a substrate wetted with droplets of an oil of low vapor pressure. Such a process is shown to produce well-faceted grains with densities of roughly 107 nuclei cm−2 (boundary), 105 nuclei cm−2 (oil-coated area), and 104 nuclei cm−2 (uncoated area) without the need for scratching or seeding the substrate. Diamond deposition was undertaken on silicon using ethanol and hydrogen in the feed of a hot-filament chemical vapor deposition reactor. The oil-covered regions, in addition to showing higher nucleation densities, have the merit that the intergrain spaces are covered with diamond structures, while the parts uncovered with oil exhibit intergrain spaces covered with diamond-like carbon.

Diamond coatings on porous silicon (PS) samples have been obtained by the hot-filament chemical vapor deposition(CVD) technique. We focused our attention on the coating morphology, showing experimentally that high quality diamond coatings may be produced with the PS sample kept at 710°C. The deposited patterns consist of polycrystalline grains with a plane interface with the PS layer.At 790°C, the quality of the coating is improved but the PS layer becomes damaged, and at 650°C the coating consists of diamond-like carbon particles. Besides the temperature, other factors such as the porosity, roughness and chemical activity of the PS layer deserve attention. We observed that one of the limiting factors of the deposition process was the high nucleation time. Two nucleation mechanisms are involved in the growth process. The first nucleation mechanism occurs on the top of the sharp PS features, subsequently to the nucleation a superficial film, and then a second nucleation mechanism occurs over this surface, which allows the growth process to continue. We also observed the presence of ablue-shift in the luminescence spectra following the coating.

Porous silicon (PS) is a nanostructured material obtained by etching pores into crystalline Si wafers. In this paper, we report on the nucleation and growth of diamond on very thick PS films (130–220 μm) of very high porosity (10–50%). The edges of the pores were in the form of small crosses, which followed the original directions of the 〈100〉 c-Si. The diamond coating was made by chemical vapor deposition (CVD) in a hot-filament reactor. We observed that the diamond nucleation occurs mainly at the edges of the pores but relatively few nuclei follow a preferential orientation axis. As the nucleation density is very low, coalescence does not occur even after 11 h and 30 min of deposition. Using a pre-deposition ‘seeding’ process with diamond grains, it was possible to produce a complete diamond CVD coating. A cross-section analysis of the diamond/PS/c-Si structure by scanning electron microscopy (SEM), micro-Raman and photoluminescence spectroscopies revealed interesting results: the luminescence of the PS under the diamond layer is preserved. There is no diamond deposition inside of the pores, but a small permeation of carbon was identified which forms diamond-like phases at the bottom of the pores. The Raman analyses indicated also a small contamination of the diamond layer by Si nano-crystals.

The effect of nitrogen incorporation on the electrical properties of diamond is currently under intense study. In this work, diamond grown by hot filament chemical vapor deposition was exposed to a radiofrequency (40 MHz) glow discharge of pure nitrogen for times of between 5 min and 1 h. The effect of this exposure on the chemical and elemental composition of the samples was assessed by Raman and X-ray photoelectron spectroscopy. Changes in the electrical resistance with increasing film nitrogenation and temperature were measured. The scope and limitations of this approach to nitrogenation are evaluated.

Thick porous silicon (PS) layers, made by anodic etching of crystalline Si wafers, have been coated with diamond films using the hot-filament chemical vapor deposition (CVD) technique. Ethanol diluted in hydrogen was used as the carbon source for diamond deposition. We observed that diamond nucleation occurs predominantly on the top of the PS spikes, creating individual islands of growth. Nucleation is apparently homogeneous over the PS surface and the islands grow independently until the complete coalescence of the diamond film. Although the diamond film is polycrystalline, it does not have the usual columnar structure of diamond deposited on c-Si. A good adherence between diamond and PS was observed in diamond–PS and diamond–PS–diamond structures. The problems of the intrinsic and thermal stresses have been addressed. Samples were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Raman and photoluminescence spectroscopy.

Carbon nanostructures have been prepared from the catalytic conversion of polyethylene glycol using a rapid immersion in hot-filament system fed with ethanol, hydrogen and argon. Fiber structures of external diameter about 30 nm have been observed by field emission scanning electron microscopy (FESEM). Raman measurements indicate high degree of C–C sp2 ordering which suggests that the samples correspond to CNTs of good tube crystallinity. The samples presented remarkable field emission properties. Lowest threshold field achieved for electron emission was 1.0 V/μm.

Tetrafluoromethane (CF4) was added to standard CH4/H2 mixtures for diamond growth in hot-filament-assisted chemical vapour deposition. CF4 concentrations in the range of 0.3%–3% were studied. Mass spectrometry of the exhaust gas showed that only a small fraction (< 15%) of CF4 was thermally dissociated for filament temperatures over 1800 °C. The observed stable products of its dissociation were mainly C2H2, CH4 and HF. This CF4 addition considerably enhanced the nucleation and growth characteristics on silicon and molybdenum. Diamond growth was observed with substrate temperature as low as 390 °C. A comparative study for the growth dependence on substrate temperature with and without CF4 addition in the gas mixture is presented. The growth rate was measured by post-growth weighing with a micro balance. An activation energy of 11 kcal mol-1 for growth with CF4 addition was obtained. Raman spectra and atomic force microscopy were used to characterize the diamond films.

Some studies about application devices that have been developed in our laboratory are presented. Some characterizations show the quality of free-standing CVD diamond film. An improvement of CVD diamond burrs will be presented, including laser cutting of diamond film, processes for soldering the film to the stainless steel tips, and statistical performance of the burrs. Basic studies were carried out in order to improve the film quality. These results gave us support for the scaling-up of a hot-filament system for the manufacturing of CVD diamond burrs.

We report here the improvement of the adhesion of CVD diamond films on WC-Co (6%) tools and the enhancement in the cutting tool life-time by the introduction of CF4 in the CH 4 H 2 gas mixture. By the use of this halogen precursor it was possible to reduce the substrate temperature during the deposition without degradation in the diamond film quality. The low-temperature deposition improves the smoothness of the coating and minimizes the thermal stress induced by the CVD process.

Boron-doped diamond (BDD) films were deposited onto either silicon or niobium cylindrical substrates with areas up to 35 cm^2 for electrochemical applications. BDD electrodes were characterised in terms of their material and electrochemical properties by scanning electron microscopy, Raman spectroscopy and linear sweep voltammetry. These characterisation techniques indicated conductive polycrystalline BDD with low quantities of non-diamond carbon impurities. Electrochemical oxidations of pharmaceutical compounds were performed using these cylindrical electrodes and monitored by UV/Vis spectroscopy, chemical oxygen demand and total organic carbon. Mixtures of chlortetracycline, oxytetracycline and diclofenac were electrolyzed on a 9.42 cm^2 (∅ = 6 mm, h = 50 mm) cylindrical Si/BDD anode using a current density of 8.2 mA cm^−2. Ibuprofen was electrolyzed on an 18.0 cm^2 (∅ = 10 mm, h = 60 mm) cylindrical Nb/BDD anode using a current density of 25 mA cm^−2. Cylindrical-shape diamond electrodes present several advantages with respect to conventional plate-shape BDD electrodes such as handling, sealing and cell assembly. The obtained results show that BDD cylindrical anodes are promising for electrochemical wastewater treatment.

Agradecimentos: The electron microscopy work was performed with the JSM-5900LV microscope of the LME/LNLS - Campinas. We wish to express sincere thanks to Dr. Kanad Mallik of University of Oxford, UK, for his technical assistance. We also gratefully acknowledge the Brazilian agencies FAPESP, CAPES and CNPq for financial support Abstract: Solar induced chemical vapor deposition (S-CVD) process using the concentrated solar radiation flux provided at the focus of a Fresnel lens (diameter 40 cm, focal length 40 cm) has been investigated. Carbon deposits on silicon and on silica have been produced using ethanol as the carbon precursor, highly diluted in hydrogen. A simple optical modeling results in a spot of 0.36 cm diameter with maximum radiation flux of 0.388 kW cm(-2). The deposited spots morphology observed by Scanning Electron Microscopy (SEM) are round shaped with dimensions smaller than 500 x 500 mu m(2). Several flakes and holes of diameters around 2 mu m are easily seen on both substrates. Raman results suggest that the deposits may be composed of complex structured carbon FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

This study reports the first results obtained by cutting/etching high quality synthesized diamond wafers of thickness up to 525 μm using a Nd: YAG laser. Energy pulses of 1–5 mJ, repetition rates of 100–50000 Hz and pulse width of 250 ns have been used. The diamond wafers/films were synthesized by CVD of carbon from a diluted methane/freon gas mixture in hydrogen using a hot-filament reactor. It was found that the laser-material cutting/etching mechanisms involve first the graphitization of the grains and then oxidation in air. SEM microscopy was used to observe the surface morphology of the laser cuts revealing a columnar CVD grain growth which is very useful for heat dissipation elements in electro-optical devices. It was found that for deep grooves the cutting width is limited by the grain size of the polycrystalline wafers/films. High profile cutting aspect ratios of the order of 7–12 were obtained. Specific cutting energies employed were of the order of 200 kJ/g.

The field emission properties of “porous diamond-like” carbon structures have been characterized. A hot filament chemical vapor deposition system fed with ethyl alcohol vapor diluted in helium was used to deposit the samples. Morphological analysis by field emission scanning electron microscopy revealed that they had a highly porous structure, which was attributed to the modification of the kinetics of the carbon deposition process due to the presence of helium as a buffer gas. Micro-Raman spectroscopy showed two peaks in the graphene and microcrystalline graphite frequencies and a new peak at 1620 cm−1. Low threshold fields (Et) and hysteresis in the current versus voltage characteristic have been observed, and a model to explain the hysteresis is proposed.

Deposition of Y2O3 films on Si is of interest due to its use as a heteroepitaxial dielectric material to obtain Si‐on‐insulator or as an epitaxial buffer layer for the growth of YBa2Cu3Ox, high temperature superconductors on Si. In this investigation, Y2O3 films have been deposited in the downstream location in an electron cyclotron resonance oxygen plasma using an organometallic Y source. The reactor pressure was varied which resulted in changes in the ionic and atomic oxygen flux as well as the energetic ion bombardment of the substrate. The deposited material has been characterized by reflected high‐energy electron diffraction, x‐ray diffraction, Rutherford backscattering spectrometry, and atomic force microscopy. The majority of the films appear to be highly oriented, textured films. Deposition of the (111) phase is preferred, even on the (100) substrate.

We show that the electrical properties of nitrogen-doped nominally undoped polycrystalline chemical vapor deposited diamond films are modified by post-deposition heating in an oxidizing atmosphere. We found that the first heating cycle in air in the temperature range of 300–673 K decreased the graphitization content still present in the diamond surface and that after the second heating cycle the electrical resistance versus temperature curves became stabilized. Using a flow of argon with residues of oxygen over the surface of the sample during the heating cycles, the stabilization of the resistance-temperature dependence also occurred but only after the fourth heating cycle. The results suggest the existence of an oxidation mechanism of the nondiamond carbon atoms present at the diamond surface. After stabilization, the deep donor ionization energy was found to be Ed=1.62±0.02 eV. All results brought together strongly suggest that this level is due to single nitrogen atoms that occupy substitutional latti...

Diamond polycrystals deposited by the hot‐filament chemical vapor deposition method on silicon (100) substrates have been examined by atomic force microscopy (AFM) in air. Measurements of the diamond unit cell show periodic spacings between 0.34 to 0.37 nm in a very good agreement with the theoretical value of the bulk constant of natural diamond (0.356 nm). Hybridized sp3 bonds can also be observed at the (111) surface.

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:18:05Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:28:22Z : No. of bitstreams: 1 2-s2.0-0000950115.pdf: 514956 bytes, checksum: 6c9c0de1741231e5c99740d865b2cd63 (MD5) Made available in DSpace on 2014-05-27T11:18:05Z (GMT). No. of bitstreams: 0 Previous issue date: 1996-05-01 The fabrication of boring tools (burrs) for dentistry with the use of a hot-filament chemical vapor deposition (CVD) system, to form the diamond abrading structure, is reported here. The diamond was synthesized from a methane/freon gas mixture diluted in hydrogen. Comparative drilling tests with conventional diamond burrs and the CVD diamond burrs in borosilicate glasses demonstrated a lifetime more than 20 times larger for the CVD diamond burrs. Also, heat flow experiments in dentine showed that the CVD diamond burrs induce temperature gradients of the same order as the conventional ones. These characteristics of the CVD diamond burrs are highly desirable for odontological applications where the burrs' lifetime and the low temperature processing are essential to the quality and comfort of the treatment. © 1996 American Institute of Physics. Inst. Nac. de Pesquisas Espaciais, 12201-970 Sao Jose dos Campos, SP Universidade Estadual Paulista, 12245-001 Sao Jose dos Campos, SP Universidade Estadual de Campinas, 13081-970 Campinas, SP Universidade Estadual Paulista, Presidente Prudente, SP Universidade Estadual Paulista, 12245-001 Sao Jose dos Campos, SP Universidade Estadual Paulista, Presidente Prudente, SP

Diamond films have been deposited by hot-filament CVD on silicon using either a gas mixture of pure methane-hydrogen or a mixture of methane-hydrogen and carbon-tetrafluoride, for the study of the influenceof the fluorine radicals in the growth process. Raman spectra shows that the fluorine is effective in the etchingof non-diamond bonds since the corresponding Raman shift at 1550 cm1 due to sp2 was not observed in the films deposited with the CF1JCH4 gas mixture. Also the FTIR spectra of these films show a better transmittance in the range from 500 cm1 to 4000 cm1, and an apparent increase of the SiC layer thickness.Using the same thermodinamical conditions, with the CF1JCH4 gas mixture diamond films of high quality aredeposited at a higher growth rate. AFM measurements of the surface morphology indicates apparently thesame vertical roughness in both kinds of films but larger lateral coalescence in the films produced with CF4-content.1. INTRODUCTIONThe diamond transparency for photons from U.V. to I.R. range, combined with its high chemical inertness,high hardness and high thermal conductivity, make this material an ideal choice as protective coatings for

Boron-doped carbon nanotubes have been prepared by chemical vapour deposition of ethyl alcohol doped with B2O3 using a hot-filament system. Multi-wall carbon nanotubes of diameters in the range of 30 – 100 nm have been observed by field emission scanning electron microscopy (FESEM). Raman measurements indicated that the degree of C-C sp2 order decreased with boron doping. Lowest threshold fields achieved were 1.0 V/μm and 2.1 V/μm for undoped and boron-doped samples, respectively.

Nanostructured diamond doped with boron was prepared using a hot-filament assisted chemical vapour deposition system fed with an ethyl alcohol, hydrogen and argon mixture. The reduction of the diamond grains to the nanoscale was produced by secondary nucleation and defects induced by argon and boron atoms via surface reactions during chemical vapour deposition. Raman measurements show that the samples are nanodiamonds embedded in a matrix of graphite and disordered carbon grains, while morphological investigations using field electron scanning microscopy show that the size of the grains ranges from 20 to 100 nm. The lowest threshold fields achieved were in the 1.6 to 2.4 V/μm range.

The friction and wear behavior of chemical vapor deposition grown diamond films has been investigated under strong ultrasound conditions at the friction interface. Experiments were performed on an alternating ‘‘pin‐on‐plate’’ tribometer constructed as an ultrasonic motor with excited bimodal mechanical vibrations at the frequency of 20 kHz. Ultrasound sliding of the films was done against alumina ceramics and with the diamond film itself. We have shown that chemical vapor deposition diamond films can be fast polished mechanically without significant graphitization by ultrasonic treatment. The initial film roughness was reduced from an average Ra ≊3000 nm to Ra ≊10 nm. The polishing decreased the static coefficient of friction of the diamond film from about 0.53 to about 0.12. The operative mechanism for the polishing in the case of initially rough diamond samples appears to be asperity fracture. For smooth diamond samples it is suggested that tribochemical oxidation is also a polishing mechanism.

Polycrystalline Si films with average grain sizes of ∼8 μm have been grown by laser‐induced chemical vapor deposition from SiCl4. A cw CO2 laser operated at 10.6 μm was used to provide local heating of quartz substrates in an otherwise cool reactor to initiate the endothermic decomposition reaction. Deposition rates of 5.1 μm/min were obtained for films grown at an incident laser power of 18.9 W, resulting in sharply defined mesa structures due to the occurrence of the reverse reaction, etching of free Si, at cooler regions of the substrate surface closer to the edge of the 6‐mm irradiated zone. The diameter of the mesas was 1.4 mm with thicknesses up to 26 μm. Three modes of film growth, depending on the incident laser power, were observed.