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Spherical quartz stones of around 1 cm in diameter have been exposed to anodic arc discharges in a helium atmosphere at 300 Torr. The arc current flowing between the graphite electrodes was set either in continuous DC mode (30–150 A) or in pulsed mode at 2 Hz (220 A peak). The ablation rate in each sample was systematically measured after several seconds of arc plasma treatment. Optical emission spectroscopy (OES) diagnostics and 2D fluid simulations of the arc discharge have shed light on the heat flux transport and the heating mechanisms of the quartz crystals. A linear correlation is found between the absorbed power density and the resulting rate of penetration, which yields a maximal value of 15 cm h−1 for approximately 150 W cm−2. The linear fit on the slope provides a specific energy of 40 kJ cm−3. The incident energy flux onto the sample surface promoted a phase transition from crystalline to glassy silica, as characterized via Raman spectroscopy. This study points out the strong potential of arc plasma technology for geothermal drilling applications.

Hydrogenated amorphous carbon (a-C:H) films with silicon and oxygen additions, which exhibit mechanical, tribological and wetting properties adequate for protective coating performance, have been synthesized at room temperature in a small- (0.1 m 3 ) and a large-scale (1 m 3 ) coaters by low-pressure Plasma-Activated Chemical Vapour Deposition (PACVD). Hence, a-C:H:Si and a-C:H:Si:O coatings were produced in atmospheres of tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO), respectively, excited either by radiofrequency (RF – small scale) or by pulsed-DC power (large scale). Argon was employed as a carrier gas to stabilize the glow discharge. Several series of 2–5 μm thick coatings have been prepared at different mass deposition rates, R m , by varying total gas flow, F , and input power, W . Arrhenius-type plots of R m / F vs. ( W / F ) −1 show linear behaviours for both plasma reactors, as expected for plasma polymerization processes at moderated energies. The calculation of apparent activation energy, E a , in each series permitted us to define the regimes of energy-deficient and monomer-deficient PACVD processes as a function of the key parameter W / F . Moreover, surface properties of the modified a-C:H coatings, such as contact angle, abrasive wear rate and hardness, appear also correlated to this parameter. This work shows an efficient methodology to scale up PACVD processes from small, lab-scale plasma machines to industrial plants by the unique evaluation of macroscopic parameters of deposition.

Diamond-Like Carbon (DLC) films find abundant applications as hard and protective coatings due to their excellent mechanical and tribological performances. The addition of new elements to the amorphous DLC matrix tunes the properties of this material, leading to an extension of its scope of applications. In order to scale up their production to a large plasma reactor, DLC films modified by silicon and oxygen additions have been grown in an industrial plant of 1m3 by means of pulsed-DC plasma-activated chemical vapour deposition (PACVD). The use of an additional microwave (MW) source has intensified the glow discharge, partly by electron cyclotron resonance (ECR), accelerating therefore the deposition process. Hence, acetylene, tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO) constituted the respective gas precursors for the deposition of a-C:H (DLC), a-C:H:Si and a-C:H:Si:O films by dual MW/pulsed-DC PACVD. This work presents systematic studies of the deposition rate, hardness, adhesion, abrasive wear and water contact angle aimed to optimize the technological parameters of deposition: gas pressure, relative gas flow of the monomers and input power. This study has been completed with measures of the atomic composition of the samples. Deposition rates around 1 μm/h, typical for standard processes held in the large reactor, were increased about by a factor 10 when the ionization source has been operated in ECR mode.

The relationship between metal-induced (W, Mo, Nb and Ti) structures and the surface properties of Me–DLC thin films is discussed. Nanocomposite films were deposited on c–Si wafers by pulsed-DC reactive magnetron sputtering controlling the gas ratio CH4/Ar. The sputtering process of metals such as Ti, Nb and Mo (unlike the tungsten) in the presence of methane shows a low reactivity at low methane concentration. The deposition rate and the spatial distribution of sputtered material depend of Z-ratio of each metal. The surface contamination of metal targets by carbon, owing to methane dilution, limits the incorporation of metals into DLC films according to an exponential decay. Results of electron probe microanalysis and X-ray photoelectron spectroscopy indicate a C rich Me/C composition ratio for low relative methane flows. According to the depth profile by secondary ion mass spectrometry, the films are systematically homogeneous in depth, whereas at high carbon contents they exhibit a metal-rich interfacial layer on the substrate. Moreover, high resolution transmission electron microscopy has evidenced important structural modifications with respect to DLC standard films, with marked differences for each Me/C combination, providing nanodendritic, nanocrystallized or multilayered structures. These particular nanostructures favour the stress decrease and induce significant changes in the tribological characteristics of the films. This study shows the possibilities of controlling the amorphous carbon films structure and surface properties by introducing metal in the DLC matrix. © 2007 Elsevier B.V. All rights reserved.

Diamond like carbon (DLC) thin films have been deposited at room temperature from a graphite target by asymmetric bipolar pulsed-DC reactive magnetron sputtering. DC bias was applied to the substrate holder between 0 and −300 V. Pulsed-DC power density and pressure were fixed at 4.4 W/cm 2 and 1.3 Pa. Pulse frequency was kept constant at 150 kHz. The results have been discussed in terms of the effects induced by substrate bias voltage. Pulsed-DC power increases the ionization of the plasma compared to processes using RF power. The conditions during the process can be described by a higher ion and electron density, the existence of more energetic species and an intense ion bombardment of substrate during the negative pulse. The substrate bias voltage induces considerable effects on deposition rate, intrinsic compressive stress and abrasive wear of the films, but it has no appreciable effect on the surface water contact angle of DLC films. Intrinsic compressive stress is limited by the carbon surface ion implantation, which in turn is controlled by the bias voltage applied to the substrate. The Davis model fitting indicates an increase in the averaged growth rate to ion flux ratio which could justify the decrease of compressive stress of the studied samples. © 2007 Elsevier B.V. All rights reserved.

A phenomenological kinetic model is proposed for describing the production of a thin film containing two components, A and B, by chemical and physical vapor deposition. The film was created by the “site-to-site” deposition of components A and B. The equations for the densities of components A and B in the surface layers were formed, and analytical and numerical solutions were obtained. The model includes the probabilities of different elementary processes for the interaction of gas phase components (molecules, radicals, atoms and ions) with those of A and B on the film surface. The deposition and erosion rates, the surface and volume densities of components A and B and the relative volume of micro-cavities inside the film were calculated as a function of the probabilities for the elementary processes of gas (plasma)-surface interactions. The experimental characteristics of a-Si: H thin films prepared by SiH4 plasma deposition and those of carbon nitride thin films deposited from r.f. — magnetron sputtering and ion beam-assisted processes are compared with model calculations.

Amorphous hydrogenated carbon (a-C:H) thin films were obtained at room temperature via asymmetric bipolar pulsed-dc methane glow discharge. The power frequency values were varied from 100 to 200 kHz and the maximum amplitude voltage from −600 to −1400 V. Such films present diamond-like carbon (DLC) properties [J.L. Andujar, M. Vives, C. Corbella, E. Bertran, Diamond Relat. Mater. 12 (2003) 98]. The plasma, powered by a pulse frequency of 100 kHz, was electrically studied by a Langmuir probe. The next parameters were calculated within the pulse cycle from I–V measurements with 1 μs resolution: plasma and floating potentials, electron temperature, and electron and ion densities. The presence of a population of hot electrons (10 eV) was detected at high bias voltage region. The density of cold electrons grows one order of magnitude after each negative pulse, whereas the ion density suffers a prompt increase during each positive pulse. The surface topography of DLC films was scanned by atomic force microscopy (AFM). A smoothly varying friction coefficient (between 0.2 and 0.3) was measured by AFM in contact mode. X-ray reflectivity (XRR) analysis provided a wide characterization of the films, involving density, thickness and roughness. The C/H ratio, as directly obtained by elemental analysis (EA), shows an increase at higher bias voltages. All these features are discussed in terms of process parameters varied in film growth.

6 pages, 5 figures.-- Printed version published Jun 22, 2005.-- Issue title: "EMRS 2004, Symposium J" (Strasbourg, May 24-28, 2004)., The addition of metal atoms within the matrix of diamond-like carbon films leads to the improvement of their mechanical properties. The present paper discusses the relationship between the composition and morphology of metal-containing (W, Nb, Mo, Ti) diamond-like carbon thin films deposited at room temperature by reactive magnetron sputtering from a metal target in an argon and methane atmosphere. Composition was measured either by electron microprobe technique or by X-ray photoelectron spectroscopy and shows a smooth variation with relative methane flow. High relative methane flows lead to a bulk saturation of carbon atoms, which leads to a lack of homogeneity in the films as confirmed by secondary ion mass spectrometry. Cross-section micrographs were observed by transmission electron microscopy and revealed a structure strongly influenced by the metal inserted and its abundance. The surface pattern obtained by scanning electrochemical potential microscopy provided the metallicity distribution. These measurements were completed with atomic force microscopy of the surface. Selected area electron diffraction and X-ray diffraction measurements provided data of the crystalline structure along with nano-crystallite size. High-resolution transmission electron microscopy provided images of these crystallites., This study was partially supported by the Generalitat de Catalunya (SGR 00078) and the CICYT of Spain (projects MAT 2002-04263-C04 and MAT 2003-02997).

Carbon/carbon‐nitride nanostructures were deposited by rf plasma enhanced and thermal chemical vapour deposition (PECVD and CVD). The growth of nanostructures was studied under several deposition conditions of negative self-bias (below −600V), C2H2∶NH3 and CH4∶NH3 ratios (varying from 0.5 to 1.0), substrate (Si and Cu) and substrate temperature (from 650°C to 800°C). It was found that the use of C2H2 or CH4 as the carbon source gave rise, respectively, to carbon nanotubes and carbon‐nitride nanorods under similar deposition conditions. The resulting films were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS) and Raman spectroscopy. The results have been discussed in terms of growth deposition conditions.

The addition of transition metal (Mo, Nb, Ti, W) atoms within the matrix of diamond-like carbon (DLC) films leads to the improving of their mechanical properties. In this work, we study the effects of the different metal induced structures on the electrical, optical and mechanical properties of DLC thin films. The samples were prepared at room temperature by pulsed-DC reactive magnetron sputtering, as a suitable way to vary their composition. X-ray photoelectron spectroscopy (XPS) evidenced a smooth variation of the composition with relative methane flow. Metal-DLC (Me-DLC) films are generally uniform in composition, as confirmed by secondary ion mass spectrometry (SIMS). Cross-section micrographs of the films, observed by transmission electron microscopy (TEM), showed relevant structural differences, which led to strong variations of physical properties. Among these variations, we can point to a better control of roughness, measured by atomic force microscopy (AFM), and stress. Indentation essays on W-DLC films have been performed in order to obtain the dependence of hardness with W concentration. Optical properties determined by UV–VIS spectroscopic ellipsometry evidenced the influence of methane dilution. The electrical measurements show a thermally activated conductivity, whose range of values and activation energy depend on the metal abundance. Me-DLC films suppose an advance in hard and wear-resistant coatings development.

The deposition process and physical properties (mechanical and surface) of diamond-like carbon (DLC) films prepared at room temperature by asymmetric bipolar pulsed-DC methane plasma-enhanced CVD (PECVD) are described in this study. The pulse frequency ranged from 100 to 200 kHz and voltage peaks ran between −600 and −1400 V. Plasma parameters within the pulse cycle were measured by a Langmuir probe with a time resolution of 1 μs. The results show a splitting of two electron populations at high positive bias voltage of the I–V plasma characteristics, the hotter one reaching a temperature of 10 eV. Plasma potential varied smoothly around 30 V and ion density increased promptly in the low-voltage region of the pulsed-DC cycle. Indentation and surface profilometry provided the results of hardness and stress, respectively. The behavior of the friction coefficient was analyzed by the scratch test method, using a 200 μm-diameter diamond spherical tip. Film characteristics are discussed as a function of technological parameters and compared to the characteristics of films grown using methane-glow discharge excited by rf power. For industrial purposes, pulsed-DC PECVD is a promising alternative to the more commonly used rf PECVD, because of the lower cost of its technology, lower film stress and higher deposition rate. DLC films grown by pulsed-DC PECVD with improved mechanical properties (high adherence and wear resistance, low stress, low roughness and low friction coefficient) are a real alternative for use as protective coatings on magnetic storage devices and sliding surfaces.

Metal-containing diamond-like carbon (Me-DLC) films were deposited by combining r.f. plasma-enhanced chemical vapour deposition (PECVD) and pulsed d.c. magnetron sputtering of several target materials (Mo, Nb, Ti and W) at different gas mixtures of methane and argon (relative methane flow ratios varying from 0 to 25%). Spectroscopic ellipsometric measurements from 1.5 to 4.1 eV were performed by a multichannel rotating analyser ellipsometer. It can detect a full spectrum in 20 ms at fixed positions of the analyser. IR ellipsometric spectra of the Me-DLC thin films as well as of the bare substrates were obtained from 900 to 3500 cm−1 with a FTIR phase-modulated ellipsometer that takes advantage of an optimized calibration method. The optical properties (refractive index and absorption) showed a clear dependence on concentration and type of metal on the film. When methane flow ratio increases, the size and concentration of nanocrystalline particles determine the variation from pure metal optical properties to typical DLC values. Optical results are discussed along with X-ray diffraction data and ellipsometry allows for a high sensitive analysis of Me-DLC films.

Diamond-like carbon films were prepared at room temperature from asymmetric bipolar pulsed-dc methane glow discharges, up to 1600 V of negative voltage pulse and 50–200 kHz of pulse frequency. Plasma parameters within a pulse cycle and at different peak voltage amplitudes were characterized by a Langmuir probe, which measured the I – V characteristics and the electron energy distribution function. Electron and ion density, electron temperature and averaged electron energy are found to increase along with negative peak voltage. Moreover, variations of electron temperature and density of charged species are registered between high- and low-pulse level. Meta-stable dissociation of methane was detected at electron energies of approximately 12 eV. Properties of the films are discussed as a function of the growth parameters obtained by plasma diagnostics, in order to establish their influence on film features. The deposition rate and residual stress of the film, which reached 50 nm/min and was minor than 1 GPa, respectively, were correlated to the enhancement of the degree of ionization at high power values. Surface topography shows an increase of roughness, up to 1 nm of RMS value, for films deposited at high peak voltages, whereas the friction coefficient, measured by atomic force microscopy in contact mode, is approximately constant. Surface energy was characterized by contact angle measures with water, which value is approximately 85°, and shows no dependence with deposition conditions. This deposition technique has an application in industry for deposition of large area coatings and it is especially indicated to process materials with plasma involving a great number of technological parameters.

We discuss the preparation of metal containing hydrogenated amorphous carbon (a-C:H) thin films by means of reactive magnetron sputtering with pulsed d.c. power of a metal target (W, Mo, Nb, Ti) and r.f. bias using different gas mixtures of methane and argon. The obtained samples comprised a thickness between 100 and 600 nm and a low internal stress when little quantities of metal were incorporated. The chemical composition was analysed by X-ray Photoelectron Spectroscopy (XPS). Depth profile composition was qualitatively displayed by secondary ion mass spectrometry (SIMS). The optical characterization of the films was carried out by transmittance measurements in the visible range and showed a relationship between the optical band gap and the composition. Structural information was obtained by X-ray diffraction (XRD), whose results showed a shift of the Bragg peaks from carbide crystallites as the metal amount increased. Peak width calculations situated particle sizes in the nanometric range. Surface topography from atomic force microscopy (AFM) measurements is also discussed. Surface energy was measured by the contact angle technique. The internal stress of the films was obtained by profilometry and a relationship with their structure was found. The results are compared with those corresponding to metal-free (pure) a-C:H films.

A full monolithic inorganic electrochromic device was deposited by means of plasma assisted physical vapor deposition. The layer stack was evaporated under different conditions that optimized the performance of each individual layer. Optical and electrochemical characterizations were carried out on the EC-device in order to establish its performance. Electro-optical data were registered over more than 6000 cycles of mixed chronoamperometric and voltammetric cycles. Degradation of the electro-optical characteristics of the device was observed during the test, probably due to atmospheric interaction.

Thin films of Ta2O5 were deposited at room temperature by RF-magnetron reactive sputtering from a tantalum oxide target. Fused silica, aluminised glasses and bilayered WO3/ITO structures on glass were used as substrates. The deposition parameters considered were RF power, oxygen ratio and the total pressure inside the reactor. The samples with fused silica were optically characterized with a UV–visible spectrophotometer (190–900 nm). From the transmittance spectra, exceeding 90%, we obtained the refractive index, the optical gap, the absorption and the film thickness. Electro-optical measurements were performed by applying cyclic voltammetries to the samples, including the electrochromic layer of WO3, in an electrochemical cell compatible with light transmission and therefore for in-situ optical analysis. The transferred charge, which reached up to 70 mC/cm2, provides an approach for quantifying the ionic conductivity of the deposited material, and its probable correlation with porosity. Comparing these structural characteristics to the related optics, a relationship between ion conduction and porosity was found. Variation of process parameters to achieve optimal performance offers the industry new possibilities to use these films as solid electrolytes for electrochromic devices built on glass substrates or polymers.

Cerium oxide (CeO 2 ) thin films were deposited by e-beam PVD on various substrates, such as glass, ITO-coated glass, Si wafers and fused silica. Substrate temperature was kept constant at 125 °C for all samples. The technological parameters of interest were oxygen partial pressure and plasma assistance during the deposition process. The basic structural properties of these films were studied by XRD, transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Composition of the samples was evaluated by X-ray photoelectron spectroscopy (XPS) and infrared transmittance (FTIR). The samples were optically characterized in the Ultraviolet–visible (UV–VIS) range (190–900 nm). The electrochromic properties of CeO 2 were characterized using a lithium-based electrolyte. This paper assesses the feasibility of using pure CeO 2 thin films as ion-storage layers in all-solid inorganic electrochromic devices.

We report the preparation of hydrogenated amorphous carbon (a-C:H) films from asymmetrical bipolar pulsed d.c. methane discharges. The films were deposited at 10 Pa of pressure on c-Si substrates placed onto an electrode powered by a pulsed d.c. generator. The asymmetrical bipolar pulsed d.c. voltage waveform consisted of a fixed positive pulse amplitude of 40 V followed by a variable negative pulse whose peak amplitude was varied from −400 up to −1400 V. Pulse frequencies of 100, 125, 150 and 200 kHz were used at a constant positive pulse time of 2 μs. In addition, a series of a-C:H samples were grown from r.f. capacitive discharges at bias voltages from −200 to −800 V. Pulsed d.c. a-C:H films 1-μm-thick were deposited at growth rates up to 60 nm/min and with internal compressive stress values between 1 and 1.5 GPa. Fourier transform-infrared and Raman analyses revealed the diamond-like character of the films. The effects of pulse parameters on the growth and structural properties of the films are discussed and compared to those of films obtained by conventional r.f. plasma-enhanced chemical vapour deposition.

We discuss the effects of both the electrical power supplied to an r.f. magnetron discharge and the Ar gas pressure on the growth of amorphous carbon (a-C) films on silicon substrates by sputtering of a graphite target. The power applied to the magnetron cathode was provided in a continuous wave mode as well as in a pulsed mode where the amplitude of the r.f. signal was square-wave modulated. In the continuous wave deposition mode the power was varied from 100 to 300 W at a fixed pressure of 0.2 Pa, and the pressure from 0.2 to 2 Pa at a constant power of 300 W. The pulsed mode processes were performed by varying the r.f. peak power from 200 to 400 W at 100 Hz of modulating frequency and 20% of duty cycle. At 0.2 Pa pressure the deposition rate increased from 1 to 6 nm/min with increasing power, and decreased to 2 nm/min as pressure was increased up to 2 Pa. The compressive stress was approximately 3 GPa for films grown at low pressure and low power, and decreased below 1 GPa at higher pressure or power. Raman analysis revealed that increasing pressure favours the growth of a-C films with more disordered sp 2 domains, whereas the increase in r.f. power first leads to a reduction and then to an increase in the number and clustering of sp 2 sites into ordered rings. The friction coefficient measured using a ball-on-disk tribometer ranged between 0.1 and 0.2, being the films deposited at higher power levels that possessed the lowest values. These results were discussed in terms of the effects induced by pressure and power on the energy and flux of the species impinging the film-growing surface.

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Here we approximate the plasma kinetics responsible for diamondlike carbon (DLC) depositions that result from pulsed-dc discharges. The DLC films were deposited at room temperature by plasma-enhanced chemical vapor deposition (PECVD) in a methane (CH4) atmosphere at 10 Pa. We compared the plasma characteristics of asymmetric bipolar pulsed-dc discharges at 100 kHz to those produced by a radio frequency (rf) source. The electrical discharges were monitored by a computer-controlled Langmuir probe operating in time-resolved mode. The acquisition system provided the intensity-voltage (I-V) characteristics with a time resolution of 1 μs. This facilitated the discussion of the variation in plasma parameters within a pulse cycle as a function of the pulse waveform and the peak voltage. The electron distribution was clearly divided into high- and low-energy Maxwellian populations of electrons (a bi-Maxwellian population) at the beginning of the negative voltage region of the pulse. We ascribe this to intense stoc...

The effects of environmental conditions and fluorine content on friction of diamond-like carbon (DLC) films are determined and discussed. Relative humidity (RH) has a considerable effect on friction values, modifying them up to a factor 2. Two regions of RH are found, depending on its effect over friction. From 20% to 60% of RH, friction decreases probably due to a better substitution of superficial atoms by hydrogen. From 60% to 80% friction remains stable and equal for almost all samples. A possible explanation would be the formation of a physisorbed layer of water on the surface, which would mask the relatively small chemical and structural variations of the films. Moreover, the different components of surface free energy (SFE) are determined using Van Oss–Chaudury–Good model. The results clearly indicate the importance of Lifshitz–Van der Waals component on SFE and the small correction that supposes acid-base interactions. According to this model, the studied DLC is a monopolar basic material. The basic component is reduced when F content is increased.

The ion fluxes and ion energy distributions (IED) corresponding to discharges in methane (CH4) were measured in time-averaged mode with a compact retarding field energy analyser (RFEA). The RFEA was placed on a biased electrode at room temperature, which was powered by either radiofrequency (13.56 MHz) or asymmetric bipolar pulsed-dc (250 kHz) signals. The shape of the resulting IED showed the relevant populations of ions bombarding the cathode at discharge parameters typical in the material processing technology: working pressures ranging from 1 to 10 Pa and cathode bias voltages between 100 and 200 V. High-energy peaks in the IED were detected at low pressures, whereas low-energy populations became progressively dominant at higher pressures. This effect is attributed to the transition from collisionless to collisional regimes of the cathode sheath as the pressure increases. On the other hand, pulsed-dc plasmas showed broader IED than RF discharges. This fact is connected to the different working frequencies and the intense peak voltages (up to 450 V) driven by the pulsed power supply. This work improves our understanding in plasma processes at the cathode level, which are of crucial importance for the growth and processing of materials requiring controlled ion bombardment. Examples of industrial applications with these requirements are plasma cleaning, ion etching processes during fabrication of microelectronic devices and plasma-enhanced chemical vapour deposition of hard coatings (diamond-like carbon, carbides and nitrides).

We report the spontaneous formation of multilayer structures with nanometric periodicity during Ti–C thin-film growth by reactive magnetron sputtering. Their characterization was performed by transmission electron microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and secondary ion mass spectrometry. We discuss film structure and morphology as a function of metal content, and propose surface-directed spinodal decomposition as the mechanism responsible for the segregation of species in separated layers by up-hill diffusion.