Abstract. Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filam... more Abstract. Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemical Vapor Deposition reactor (HFCVD) using CH4/H2 gas mixtures. A series of experiments varying the levels of boron doping from 5000 to 25000 ppm were performed. Morphological, structural and electrochemical studies were conducted whose aim was the understanding about the film properties. The morphological and structural characterizations of these materials were made by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The evaluation of the electrodes was performed using cyclic voltammetry. The electrochemical response showed the influence of boron content in the work potential window. The doped diamond films produced and characterized in this work are efficient as an electrode for environmental applications.
Abstract Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and ... more Abstract Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125 W. After deposition, the films were submitted to SF6-plasma treatment for 5 minutes. SF6 plasmas were generated at a pressure of 13.3 Pa by a RF power supply operating at 13.56 MHz with the output fixed at 70 W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF6 plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF6 plasmas with surface species was responsible for the decrease of the film thickness...
Thin �lms of uorinated hydrogenated amorphous carbon (a-C:H:F) were synthesized by radiofrequency... more Thin �lms of uorinated hydrogenated amorphous carbon (a-C:H:F) were synthesized by radiofrequency plasma enhanced chemical vapor deposition on glass and silicon substrates using acetylene, argon, and sulfur hexa uoride mixtures as precursors. The radiofrequency signal was applied to the lower electrode whereas the upper one was grounded. The deposition time was 5 minutes at a pressure of 9:5Pa and the power varied from 5 to 125W. Raman spectroscopy and X-ray photoelectron spectroscopy were employed to investigate the molecular structures and chemical compositions of the a-C:H:F �lms. The Raman spectra indicated that the �lms had polymer-like structure, for lower power (5 to 25W), graphitic structure, for intermediate power (50 to 75W), and higher sp3 hybridization, for higher power (100 and 125W). The XPS analysis showed the presence of C-C, C-H, C-O, C-CF, C=O, and C-F chemical bonds. The thicknesses of the �lms were between 55 and 32 nm for RF power varying from 5 to 125W. The wet...
This work presents an investigation about the influence of ion implantation on amorphous hydrogen... more This work presents an investigation about the influence of ion implantation on amorphous hydrogenate carbon (a-C:H) films. These films were synthesized by Plasma Enhanced Chemical Vapor Deposition (PECVD) from low pressure acetylene (C 2 H 2 ) and argon (Ar) mixture, using a 13.56 MHz radiofrequency (RF) discharge. Plasma Immersion Ion Implantation (PIII) was employed as post-treatment technique, using a helium (He) plasma and high voltage negative pulses at different exposition time. The films were characterized by their chemical composition, surface hardness and wettability. Results revealed the increase of sp 3 hybridization and hardness, drop of contact angle and rise of surface energy, as the implantation time increased. These results are attributed to the growth of the insaturation and crosslinking degree promoted by ion bombardment.
ABSTRACT Pesticide removal by the electrochemical oxidation was investigated with commercial Carb... more ABSTRACT Pesticide removal by the electrochemical oxidation was investigated with commercial Carbofuran with an electrolyte containing aqueous solutions K 2 SO 4 0.1 mol L -1 or H 2 SO 4 0.1 mol L -1 thermo stated at 20ºC, in a flow reactor with recirculation system. The degradation reactions were performed at constant applied current densities in the range 10 to 200 mAcm -2 , flow rates of 50 and 300 Lh -1 for a total of 5 hours. The electrochemical oxidation of carbofuran pesticides has been carried using as anode four Ti/BDD electrodes, produced by Hot Filament Chemical Vapor Deposition reactor. The morphological and structural characterizations of the electrodes were evaluated by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The electrochemical of Ti/BDD electrodes was performed by Cyclic Voltammetry in presence of the electrolytes. The effect of pH of the electrolyte in the electrochemical degradation of carbofuran was monitored by UV–Vis Spectrophotometry, Total Organic Carbon and High Performance Liquid Chromatography. The reducing the TOC concentration promoted the mineralization of pesticide contributing to the formation of carbofuran intermediates resulting from the reaction of oxidation. A completely degraded of the pesticide was obtained under an acid pH and current densities of 200 mAcm 2 .
Diamond-like carbon (DLC) films were grown from radiofrequency plasmas of acetylene-argon mixture... more Diamond-like carbon (DLC) films were grown from radiofrequency plasmas of acetylene-argon mixtures, at different excitation powers, P . The effects of this parameter on the plasma potential, electron density, electron temperature, and plasma activity were investigated using a Langmuir probe. The mean electron temperature increased from about 0.5 to about 7.0 eV while the mean electron density decreased from about 1.2 × 10 9 to about 0.2 × 10 9 cm −3 as P was increased from 25 to 150 W. Both the plasma potential and the plasma activity were found to increase with increasing P . Through actinometric optical emission spectrometry, the relative concentrations of CH, [CH], and H, [H], in the discharge were mapped as a function of the applied power. A rise in [H] and a fall in [CH] with increasing P were observed and are discussed in relation to the plasma characteristics and the subimplantation model. The optical properties of the films were calculated from ultraviolet-visible spectroscopic data; the surface resistivity was measured by the two-point probe method. The optical gap, E G , and the surface resistivity, ρ s , fall with increasing P . E G and ρ s are in the ranges of about 2.0-1.3 eV and 10 14 -10 16 /ᮀ, respectively. The plasma power also influences the film self-bias, V b , via a linear dependence, and the effect of V b on ion bombardment during growth is addressed together with variation in the relative densities of sp 2 and sp 3 bonds in the films as determined by Raman spectroscopy.
The great versatility of polymers has promoted their application in a series of ordinary situatio... more The great versatility of polymers has promoted their application in a series of ordinary situations. The development of specific devices from polymers, however, requires modifications to fit specific stipulations. In this work the surface properties of thin films grown onto polyvinylchloride (PVC) were investigated. Hydrogenated amorphous carbon films were deposited onto commercial PVC plates from acetylene and argon plasmas excited by radiofrequency (13.56 MHz, 70 W) power. The proportion of acetylene in the gas feed was varied against that of argon, keeping the total pressure constant at 2.5 Pa. Deposition time was 1800 s. Film elemental composition was analyzed by X-ray photoelectron spectroscopy, XPS. Water contact angle measurements were performed using the sessile drop technique. The root mean squared roughness was derived from 50 × 50 µm 2 surface topographic images, acquired by scanning probe microscopy. Nanoindentation and pin-on-disk techniques were employed on the determination of film hardness and sliding wear, respectively. Oxidation resistance was obtained through the etching rate of the samples in oxygen radiofrequency (1.3 Pa, 50 W) plasmas. From XPS analysis it was detected oxygen and nitrogen contamination in all the samples. It was also found that sp 3 /sp 2 ratio depends on the proportion of argon in the plasma. At lower argon concentrations, hardness, wear and oxidation resistances were all improved with respect to the uncoated PVC. In such conditions, the surface wettability is low indicating a moderate receptivity to water. This combination of properties, ascribed to a balance between the ion bombardment and deposition processes, is suitable for materials exposed to rigorous weathering conditions.
Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished ... more Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125 W. After deposition, the films were submitted to SF 6 -plasma treatment for 5 minutes. SF 6 plasmas were generated at a pressure of 13.3 Pa by a RF power supply operating at 13.56 MHz with the output fixed at 70 W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF 6 plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF 6 plasmas with surface species was responsible for the decrease of the film thickness and surface energy, and for the increase of the film roughness and hydrophobicity.
Journal of Superconductivity and Novel Magnetism, 2013
a-C:H films were grown by plasma-enhanced chemical vapor deposition in atmospheres composed by 30... more a-C:H films were grown by plasma-enhanced chemical vapor deposition in atmospheres composed by 30 % of acetylene and 70 % of argon. Radiofrequency signal (RF) was supplied to the sample holder to generate the depositing plasmas. Deposition time and pressure were chosen 300 s and 9.5 Pa, respectively, while the excitation power changed from 5 to 125 W. The films were exposed to a post-deposition treatment during 300 s in RF-plasmas (13.56 MHz, 70 W) excited from 13.33 Pa of SF 6 . Raman and X-ray photoelectron spectroscopy were used to evaluate the microstructure and chemical composition of the films. The thickness was measured by perfilometry. Hardness and friction coefficient were determined from nanoindentation and risk tests, respectively. With increasing power, the film thickness reduced, but a further shrinkage occurred upon the fluorination process. After that, the molecular structure was observed to vary with deposition power. Fluorine was detected in all samples replacing H atoms. Consistently with the elevation in the proportion of C atoms with sp 3 hybridization, hardness increased from 2 to 18 GPa. Friction coefficient also increased with power due to the generation of dangling bonds during the fluorination process.
This work was performed to verify the chemical structure, mechanical and hydrophilic properties o... more This work was performed to verify the chemical structure, mechanical and hydrophilic properties of amorphous hydrogenated carbon films prepared by plasma enhanced chemical vapor deposition, using acetylene/argon mixture as monomer. Films were prepared in a cylindrical quartz reactor, fed by 13.56 MHz radiofrequency. The films were grown during 5 min, for power varying from 25 to 125 W at a fixed pressure of 9.5 Pa. After deposition, all samples were treated by SF 6 plasma with the aim of changing their hydrophilic character. Film chemical structure investigated by Raman spectroscopy, revealed the increase of sp 3 hybridized carbon bonds as the plasma power increases. Hardness measurements performed by the nanoindentation technique showed an improvement from 5 GPa to 14 GPa following the increase discharge power. The untreated films presented a hydrophilic character, which slightly diminished after SF 6 plasma treatment.
Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemic... more Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemical Vapor Deposition reactor (HFCVD) using CH 4 /H 2 gas mixtures. A series of experiments varying the levels of boron doping from 5000 to 25000 ppm were performed. Morphological, structural and electrochemical studies were conducted whose aim was the understanding about the film properties. The morphological and structural characterizations of these materials were made by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The evaluation of the electrodes was performed using cyclic voltammetry. The electrochemical response showed the influence of boron content in the work potential window. The doped diamond films produced and characterized in this work are efficient as an electrode for environmental applications.
In many applications, polymers have progressively substituted traditional materials such as ceram... more In many applications, polymers have progressively substituted traditional materials such as ceramics, glasses, and metals. Nevertheless, the use of polymeric materials is still limited by their surface properties. Frequently, selective modifications are necessary to suit the surface to a given application. Amongst the most common treatments, plasma immersion ion implantation (PIII) has attracted the attention of many researchers owing to its versatility and practicality. This method, however, requires a power supply to provide high voltage (tens of kV) negative pulses, with a controlled duty cycle, width and frequency. Owing to this, the implementation of PIII on the industrial scale can become economically inviable. In this work, an alternative plasma treatment that enables low energy ion bombardment without the need of a high voltage pulse generator is presented. To evaluate the efficiency of the treatment of polymers, polyvinylchloride, PVC, specimens were exposed to 5 Pa argon plasmas for 3600 s, at excitation powers, P, of between 10 and 125 W. Through contact angle and atomic force microscopy data, the influence of P on the wettability, surface free energy and roughness of the samples was studied. Surface chemical composition was measured by X-ray photoelectron spectroscopy, XPS. To evaluate the effect of aging under atmospheric conditions, contact angle and XPS measurements were performed one and 1334 days after the treatment. The plasma potential and ion density around the driven electrode were determined from Langmuir probe measurements while the self-bias potential was derived with the aid of an oscilloscope. From these data it was possible to estimate the mean energy of ions bombarding the PVC surface. Chlorine, carbon and oxygen contamination were detected on the surface of the as-received PVC. Upon exposure to the plasma, the proportion of chlorine was observed to decrease while that of oxygen increased. Consequently, the wettability and surface energy increased after the treatment but such modifications were not stable after aging: the contact angle increased for all the samples, modifying the initially hydrophilic surface into a highly hydrophobic one. Consistently, the surface composition also changed after aging: there was carbon enrichment due to further losses of oxygen and chlorine. Another relevant factor for the elevation of  was the change in morphology induced by the treatment. At greater powers, the uniform matrix of the PVC was transformed into a columnar structure containing randomly distributed sharp pillars. Interpretation of such results is proposed in terms of the total energy deposited in the solid by ionic collisions.
Palavras-chave: filme polimérico; carbono amorfo; polimerização a plasma. * [email protected]... more Palavras-chave: filme polimérico; carbono amorfo; polimerização a plasma. * [email protected] RESUMO Filmes finos polimerizados a plasma apresentam estruturas amorfas, reticulados, que os tornam resistentes a ataques químicos em meios ácidos ou básicos, além de serem aderentes aos mais diversos tipos de substratos. Tais propriedades são interessantes para diversas aplicações tecnológicas, mas são fortemente dependentes dos parâmetros do processo, tais como: tipo de reator, potência e pressão da descarga, tipo de monômero, temperatura do substrato, etc. Neste trabalho, os filmes foram produzidos a partir de uma mistura de benzeno e argônio, sendo o porta-substrato aquecido resistivamente a 280 °C. Os parâmetros de deposição foram radiofreqüência de 13,56 MHz, potência de 50 W e pressão de 5 a 18 Pa. A estrutura molecular dos filmes foi investigada por espectroscopia no infravermelho, entre 4000 e 1000 cm -1 . A molhabilidade e energia de superfície foram avaliadas através de medidas de ângulo de contato, usando um goniômetro Ramé-Hart 100-00.
Os filmes de carbono amorfo hidrogenado (a-C:H) possuem propriedades interessantes para aplicaçõe... more Os filmes de carbono amorfo hidrogenado (a-C:H) possuem propriedades interessantes para aplicações tecnológicas, tais como alta dureza, resistência ao desgaste, baixo coeficiente de atrito e biocompatibilidade. Neste trabalho, os filmes foram depositados a plasma por radiofrequência a partir de uma mistura de acetileno (C 2 H 2 ) e argônio (Ar), buscando investigar a influência da potência (P) na composição química de filmes depositados através do processo PECVD (Plasma Enhanced Chemical Vapor Deposition). Os parâmetros de deposição foram: radiofreqüência de 13,56 MHz, potência variando de 5 a 125 W e pressão de 9,5 Pa. A estrutura molecular dos filmes foi investigada por espectroscopia Raman e espectroscopia de fotoelétrons excitados por raios X (XPS).
Abstract. Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filam... more Abstract. Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemical Vapor Deposition reactor (HFCVD) using CH4/H2 gas mixtures. A series of experiments varying the levels of boron doping from 5000 to 25000 ppm were performed. Morphological, structural and electrochemical studies were conducted whose aim was the understanding about the film properties. The morphological and structural characterizations of these materials were made by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The evaluation of the electrodes was performed using cyclic voltammetry. The electrochemical response showed the influence of boron content in the work potential window. The doped diamond films produced and characterized in this work are efficient as an electrode for environmental applications.
Abstract Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and ... more Abstract Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125 W. After deposition, the films were submitted to SF6-plasma treatment for 5 minutes. SF6 plasmas were generated at a pressure of 13.3 Pa by a RF power supply operating at 13.56 MHz with the output fixed at 70 W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF6 plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF6 plasmas with surface species was responsible for the decrease of the film thickness...
Thin �lms of uorinated hydrogenated amorphous carbon (a-C:H:F) were synthesized by radiofrequency... more Thin �lms of uorinated hydrogenated amorphous carbon (a-C:H:F) were synthesized by radiofrequency plasma enhanced chemical vapor deposition on glass and silicon substrates using acetylene, argon, and sulfur hexa uoride mixtures as precursors. The radiofrequency signal was applied to the lower electrode whereas the upper one was grounded. The deposition time was 5 minutes at a pressure of 9:5Pa and the power varied from 5 to 125W. Raman spectroscopy and X-ray photoelectron spectroscopy were employed to investigate the molecular structures and chemical compositions of the a-C:H:F �lms. The Raman spectra indicated that the �lms had polymer-like structure, for lower power (5 to 25W), graphitic structure, for intermediate power (50 to 75W), and higher sp3 hybridization, for higher power (100 and 125W). The XPS analysis showed the presence of C-C, C-H, C-O, C-CF, C=O, and C-F chemical bonds. The thicknesses of the �lms were between 55 and 32 nm for RF power varying from 5 to 125W. The wet...
This work presents an investigation about the influence of ion implantation on amorphous hydrogen... more This work presents an investigation about the influence of ion implantation on amorphous hydrogenate carbon (a-C:H) films. These films were synthesized by Plasma Enhanced Chemical Vapor Deposition (PECVD) from low pressure acetylene (C 2 H 2 ) and argon (Ar) mixture, using a 13.56 MHz radiofrequency (RF) discharge. Plasma Immersion Ion Implantation (PIII) was employed as post-treatment technique, using a helium (He) plasma and high voltage negative pulses at different exposition time. The films were characterized by their chemical composition, surface hardness and wettability. Results revealed the increase of sp 3 hybridization and hardness, drop of contact angle and rise of surface energy, as the implantation time increased. These results are attributed to the growth of the insaturation and crosslinking degree promoted by ion bombardment.
ABSTRACT Pesticide removal by the electrochemical oxidation was investigated with commercial Carb... more ABSTRACT Pesticide removal by the electrochemical oxidation was investigated with commercial Carbofuran with an electrolyte containing aqueous solutions K 2 SO 4 0.1 mol L -1 or H 2 SO 4 0.1 mol L -1 thermo stated at 20ºC, in a flow reactor with recirculation system. The degradation reactions were performed at constant applied current densities in the range 10 to 200 mAcm -2 , flow rates of 50 and 300 Lh -1 for a total of 5 hours. The electrochemical oxidation of carbofuran pesticides has been carried using as anode four Ti/BDD electrodes, produced by Hot Filament Chemical Vapor Deposition reactor. The morphological and structural characterizations of the electrodes were evaluated by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The electrochemical of Ti/BDD electrodes was performed by Cyclic Voltammetry in presence of the electrolytes. The effect of pH of the electrolyte in the electrochemical degradation of carbofuran was monitored by UV–Vis Spectrophotometry, Total Organic Carbon and High Performance Liquid Chromatography. The reducing the TOC concentration promoted the mineralization of pesticide contributing to the formation of carbofuran intermediates resulting from the reaction of oxidation. A completely degraded of the pesticide was obtained under an acid pH and current densities of 200 mAcm 2 .
Diamond-like carbon (DLC) films were grown from radiofrequency plasmas of acetylene-argon mixture... more Diamond-like carbon (DLC) films were grown from radiofrequency plasmas of acetylene-argon mixtures, at different excitation powers, P . The effects of this parameter on the plasma potential, electron density, electron temperature, and plasma activity were investigated using a Langmuir probe. The mean electron temperature increased from about 0.5 to about 7.0 eV while the mean electron density decreased from about 1.2 × 10 9 to about 0.2 × 10 9 cm −3 as P was increased from 25 to 150 W. Both the plasma potential and the plasma activity were found to increase with increasing P . Through actinometric optical emission spectrometry, the relative concentrations of CH, [CH], and H, [H], in the discharge were mapped as a function of the applied power. A rise in [H] and a fall in [CH] with increasing P were observed and are discussed in relation to the plasma characteristics and the subimplantation model. The optical properties of the films were calculated from ultraviolet-visible spectroscopic data; the surface resistivity was measured by the two-point probe method. The optical gap, E G , and the surface resistivity, ρ s , fall with increasing P . E G and ρ s are in the ranges of about 2.0-1.3 eV and 10 14 -10 16 /ᮀ, respectively. The plasma power also influences the film self-bias, V b , via a linear dependence, and the effect of V b on ion bombardment during growth is addressed together with variation in the relative densities of sp 2 and sp 3 bonds in the films as determined by Raman spectroscopy.
The great versatility of polymers has promoted their application in a series of ordinary situatio... more The great versatility of polymers has promoted their application in a series of ordinary situations. The development of specific devices from polymers, however, requires modifications to fit specific stipulations. In this work the surface properties of thin films grown onto polyvinylchloride (PVC) were investigated. Hydrogenated amorphous carbon films were deposited onto commercial PVC plates from acetylene and argon plasmas excited by radiofrequency (13.56 MHz, 70 W) power. The proportion of acetylene in the gas feed was varied against that of argon, keeping the total pressure constant at 2.5 Pa. Deposition time was 1800 s. Film elemental composition was analyzed by X-ray photoelectron spectroscopy, XPS. Water contact angle measurements were performed using the sessile drop technique. The root mean squared roughness was derived from 50 × 50 µm 2 surface topographic images, acquired by scanning probe microscopy. Nanoindentation and pin-on-disk techniques were employed on the determination of film hardness and sliding wear, respectively. Oxidation resistance was obtained through the etching rate of the samples in oxygen radiofrequency (1.3 Pa, 50 W) plasmas. From XPS analysis it was detected oxygen and nitrogen contamination in all the samples. It was also found that sp 3 /sp 2 ratio depends on the proportion of argon in the plasma. At lower argon concentrations, hardness, wear and oxidation resistances were all improved with respect to the uncoated PVC. In such conditions, the surface wettability is low indicating a moderate receptivity to water. This combination of properties, ascribed to a balance between the ion bombardment and deposition processes, is suitable for materials exposed to rigorous weathering conditions.
Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished ... more Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125 W. After deposition, the films were submitted to SF 6 -plasma treatment for 5 minutes. SF 6 plasmas were generated at a pressure of 13.3 Pa by a RF power supply operating at 13.56 MHz with the output fixed at 70 W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF 6 plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF 6 plasmas with surface species was responsible for the decrease of the film thickness and surface energy, and for the increase of the film roughness and hydrophobicity.
Journal of Superconductivity and Novel Magnetism, 2013
a-C:H films were grown by plasma-enhanced chemical vapor deposition in atmospheres composed by 30... more a-C:H films were grown by plasma-enhanced chemical vapor deposition in atmospheres composed by 30 % of acetylene and 70 % of argon. Radiofrequency signal (RF) was supplied to the sample holder to generate the depositing plasmas. Deposition time and pressure were chosen 300 s and 9.5 Pa, respectively, while the excitation power changed from 5 to 125 W. The films were exposed to a post-deposition treatment during 300 s in RF-plasmas (13.56 MHz, 70 W) excited from 13.33 Pa of SF 6 . Raman and X-ray photoelectron spectroscopy were used to evaluate the microstructure and chemical composition of the films. The thickness was measured by perfilometry. Hardness and friction coefficient were determined from nanoindentation and risk tests, respectively. With increasing power, the film thickness reduced, but a further shrinkage occurred upon the fluorination process. After that, the molecular structure was observed to vary with deposition power. Fluorine was detected in all samples replacing H atoms. Consistently with the elevation in the proportion of C atoms with sp 3 hybridization, hardness increased from 2 to 18 GPa. Friction coefficient also increased with power due to the generation of dangling bonds during the fluorination process.
This work was performed to verify the chemical structure, mechanical and hydrophilic properties o... more This work was performed to verify the chemical structure, mechanical and hydrophilic properties of amorphous hydrogenated carbon films prepared by plasma enhanced chemical vapor deposition, using acetylene/argon mixture as monomer. Films were prepared in a cylindrical quartz reactor, fed by 13.56 MHz radiofrequency. The films were grown during 5 min, for power varying from 25 to 125 W at a fixed pressure of 9.5 Pa. After deposition, all samples were treated by SF 6 plasma with the aim of changing their hydrophilic character. Film chemical structure investigated by Raman spectroscopy, revealed the increase of sp 3 hybridized carbon bonds as the plasma power increases. Hardness measurements performed by the nanoindentation technique showed an improvement from 5 GPa to 14 GPa following the increase discharge power. The untreated films presented a hydrophilic character, which slightly diminished after SF 6 plasma treatment.
Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemic... more Boron-Doped Diamond electrodes were produced on silicon substrate (BDD/Si) by Hot Filament Chemical Vapor Deposition reactor (HFCVD) using CH 4 /H 2 gas mixtures. A series of experiments varying the levels of boron doping from 5000 to 25000 ppm were performed. Morphological, structural and electrochemical studies were conducted whose aim was the understanding about the film properties. The morphological and structural characterizations of these materials were made by Scanning Electron Microscopy and by Raman Scattering Spectroscopy techniques. The evaluation of the electrodes was performed using cyclic voltammetry. The electrochemical response showed the influence of boron content in the work potential window. The doped diamond films produced and characterized in this work are efficient as an electrode for environmental applications.
In many applications, polymers have progressively substituted traditional materials such as ceram... more In many applications, polymers have progressively substituted traditional materials such as ceramics, glasses, and metals. Nevertheless, the use of polymeric materials is still limited by their surface properties. Frequently, selective modifications are necessary to suit the surface to a given application. Amongst the most common treatments, plasma immersion ion implantation (PIII) has attracted the attention of many researchers owing to its versatility and practicality. This method, however, requires a power supply to provide high voltage (tens of kV) negative pulses, with a controlled duty cycle, width and frequency. Owing to this, the implementation of PIII on the industrial scale can become economically inviable. In this work, an alternative plasma treatment that enables low energy ion bombardment without the need of a high voltage pulse generator is presented. To evaluate the efficiency of the treatment of polymers, polyvinylchloride, PVC, specimens were exposed to 5 Pa argon plasmas for 3600 s, at excitation powers, P, of between 10 and 125 W. Through contact angle and atomic force microscopy data, the influence of P on the wettability, surface free energy and roughness of the samples was studied. Surface chemical composition was measured by X-ray photoelectron spectroscopy, XPS. To evaluate the effect of aging under atmospheric conditions, contact angle and XPS measurements were performed one and 1334 days after the treatment. The plasma potential and ion density around the driven electrode were determined from Langmuir probe measurements while the self-bias potential was derived with the aid of an oscilloscope. From these data it was possible to estimate the mean energy of ions bombarding the PVC surface. Chlorine, carbon and oxygen contamination were detected on the surface of the as-received PVC. Upon exposure to the plasma, the proportion of chlorine was observed to decrease while that of oxygen increased. Consequently, the wettability and surface energy increased after the treatment but such modifications were not stable after aging: the contact angle increased for all the samples, modifying the initially hydrophilic surface into a highly hydrophobic one. Consistently, the surface composition also changed after aging: there was carbon enrichment due to further losses of oxygen and chlorine. Another relevant factor for the elevation of  was the change in morphology induced by the treatment. At greater powers, the uniform matrix of the PVC was transformed into a columnar structure containing randomly distributed sharp pillars. Interpretation of such results is proposed in terms of the total energy deposited in the solid by ionic collisions.
Palavras-chave: filme polimérico; carbono amorfo; polimerização a plasma. * [email protected]... more Palavras-chave: filme polimérico; carbono amorfo; polimerização a plasma. * [email protected] RESUMO Filmes finos polimerizados a plasma apresentam estruturas amorfas, reticulados, que os tornam resistentes a ataques químicos em meios ácidos ou básicos, além de serem aderentes aos mais diversos tipos de substratos. Tais propriedades são interessantes para diversas aplicações tecnológicas, mas são fortemente dependentes dos parâmetros do processo, tais como: tipo de reator, potência e pressão da descarga, tipo de monômero, temperatura do substrato, etc. Neste trabalho, os filmes foram produzidos a partir de uma mistura de benzeno e argônio, sendo o porta-substrato aquecido resistivamente a 280 °C. Os parâmetros de deposição foram radiofreqüência de 13,56 MHz, potência de 50 W e pressão de 5 a 18 Pa. A estrutura molecular dos filmes foi investigada por espectroscopia no infravermelho, entre 4000 e 1000 cm -1 . A molhabilidade e energia de superfície foram avaliadas através de medidas de ângulo de contato, usando um goniômetro Ramé-Hart 100-00.
Os filmes de carbono amorfo hidrogenado (a-C:H) possuem propriedades interessantes para aplicaçõe... more Os filmes de carbono amorfo hidrogenado (a-C:H) possuem propriedades interessantes para aplicações tecnológicas, tais como alta dureza, resistência ao desgaste, baixo coeficiente de atrito e biocompatibilidade. Neste trabalho, os filmes foram depositados a plasma por radiofrequência a partir de uma mistura de acetileno (C 2 H 2 ) e argônio (Ar), buscando investigar a influência da potência (P) na composição química de filmes depositados através do processo PECVD (Plasma Enhanced Chemical Vapor Deposition). Os parâmetros de deposição foram: radiofreqüência de 13,56 MHz, potência variando de 5 a 125 W e pressão de 9,5 Pa. A estrutura molecular dos filmes foi investigada por espectroscopia Raman e espectroscopia de fotoelétrons excitados por raios X (XPS).
Filmes Protetivos contra corrosão de Materiais Metálicos, 2016
Os reatores usados na planta-piloto de geração do bioetanol são submetidos a situações drásticas ... more Os reatores usados na planta-piloto de geração do bioetanol são submetidos a situações drásticas de funcionamento (alta temperatura, meio químico agressivo), logo o tratamento de superfície, através da deposição de filmes em condições adequadas, diminui a corrosão e aumenta a dureza do material que é utilizado na confecção desses reatores. Para aumentar as propriedades de barreira do aço AISI 304, material usado para confecção dos reatores, foram preparados filmes de hexametildisiloxano (HMDSO) por radiofrequência através do método de Deposição de Vapor Químico Assistido a Plasma (Plasma-Enhanced Chemical Vapor Deposition, RF-PECVD) a partir das misturas de HMDSO/oxigênio (O2) e HMDSO, O2 e argônio (Ar). Para melhorar as propriedades mecânicas do aço AISI 304 foram depositados filmes de carbono amorfo hidrogenado (a-C:H), a partir da mistura de metano e argônio, utilizando a técnica de deposição e implantação iônica por imersão a plasma (IIIP&D). A qualidade e as propriedades do aço AISI 304 revestido com os filmes foram analisadas através das técnicas de XPS, Espectroscopia Raman, Espectroscopia de Infravermelho, Ângulo de Contato, Perfilometria, Espectroscopia de Impedância Eletroquímica (EIE), Microscopia Eletrônica de Varredura (MEV), Microscopia de Absorção atômica (AFM) e Nanoindentação. Os resultados revelam que a natureza orgânica (tipo polimérica) ou inorgânica (tipo sílica) dos filmes depende significativamente da proporção de HMDSO na mistura. E que as propriedades químicas, mecânicas e de superfície são significativamente dependentes dos parâmetros utilizados no processo de produção desses filmes. Os filmes apresentaram excelentes propriedades de barreira, aumentando o caráter protetivo do aço em 5 ordens de grandeza, em meio salino, ácido e básico.
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Papers by Nazir M Santos