C-Ti multilayer nanostructures were deposed by Thermionic Vacuum Arc (TVA) technology. The layers consisting of about 100nm Carbon base layer and seven 40nm alternatively T i and C layers were deposed on Silicon substrates. The thickness of such a multilayer structure was up to 500nm. On the other hand, in order to obtain C-Ti multilayer structures with variable thickness and different percentages in C and T i of layers, a 20nm thick C layer was first deposed on Si substrate and then seven T i-C layers, each of these having different thickness of up to 40nm were deposed. To perform the successively layers with various thickness were changed the discharge parameters for C and T i plasma sources to obtain the desirable thickness. By changing of substrate temperature between room temperature and 300°C and on the other hand the bias voltage up to −700V , different batches of samples were obtained for this study. To characterize microstructure properties of as prepared C-Ti multilayer structures were used Electron Microscopy techniques (TEM, SEM, STEM), X-Ray Photoelectron Spectroscopy, Raman Spectroscopy and RBS techniques. The measurements reveal the content of diamond-like sp<sup>3</sup> and graphite-like sp<sup>2</sup> ; the ratio sp<sup>3</sup>/sp<sup>2</sup> increases when the bias voltage increases. Also, HRTEM and SAED patterns reveal an increase of amount and size of TiC nanocrystals with the increase of energy of Ti and C ions determined by increase of anode potential. For providing reliable quantitative information regarding the composition and the elements depth profile, RBS studies were performed using the 3MV Tandem Accelerator with specialized RBS spectrum simulation program SIRMA. Raman measurement reveal that peaks appear at around 250, 340, 420, 610, 740, 1340 and 1530−1567cm<sup>−1</sup> , suggesting mixtures of TiC, Ti<sub>3</sub>C<sub>2</sub>O<sub>2</sub> and Ti<sub>3</sub>C<sub>2</sub> and at 1340, 1560cm<sup>−1</sup> , the characteristic D an G peaks of disordered carbon. The characterstic peaks of Ti<sub>3</sub>C<sub>2</sub>O<sub>2</sub> and Ti<sub>3</sub>C<sub>2</sub> have vibrational modes at 347, 730 and 621cm<sup>−1</sup> respectively, peaks at 260 and 420cm<sup>−1</sup> correspond to TiC. The shift shown in the spectra of the samples may occurs owing to the mechanical stress. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured, and then the electrical conductivity. Using the Wiedeman-Frantz law was calculated the thermal conductivity, which increase with increase of the temperature, according to the decrease in the proportion of TiC phase.
Carbon-Titan (C-Ti) multilayer films were deposited on silicon substrates by means of Thermionic Vacuum Arc (TVA) method. The final thickness of the multilayer structures was up to 400nm. The coated layers consisted of a base layer of about 100nm of Carbon deposited at low evaporation rates in order to ensure its stability on the substrate. Subsequently, seven Carbon and Titanium layers were deposited alternatively on top of Carbon base layer, each of them has a final thickness up to 40nm. For this study we obtained different batches of samples by variation of the substrate temperature between 0°C and 400°C, and the ion acceleration voltage applying a negative substrate bias voltage up to -700V . A low deposition rate 0.14nm/s for C and 0.18nm/s for Ti respectively was used in order to obtain the precise thickness. <p> </p>The characterization of microstructure properties of as prepared C-Ti multilayer structures were done using Electron Microscopy techniques (TEM, SEM, STEM), and Raman Spectroscopy. TEM and STEM studies were performed on Philips Tecnai F30G2 at 300kV setup. Identification of the structure of the material was based on the data obtained from diffraction pattern with a Philips CM120ST using CRISP2 application, with crystalline material module (ELD). The morphology and thickness of the samples were also determined by SEM techniques with Quanta FEG450 setup. The thickness thus measured are between 155.4nm and 393.9nm. Raman spectra were measured at room temperature on a Jobin Yvon T6400 spectrometer using 514.5nm line of an Ar+ laser as the excitation source. The measurements reveal the content of diamond-like <i>sp</i><sup>3</sup> and graphite-like <i>sp</i><sup>2</sup>; the ratio <i>sp</i><sup>3</sup>/<i>sp</i><sup>2</sup> increases when the bias voltage increases. For tribological characteristics determination, systematic measurements were performed using a ball-on-disk tribometer made by CSM Switzerland with normal force of 0.5, 1, 2, 3N respectively. The coefficient of friction depends on the substrate temperature and on the bias voltage. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured using drop voltage between two ohmic contacts on the sample and drop voltage on a standard resistance in a constant current regime. Owing to metallic layer of titanium in multilayer films, mechanical and electrical properties can be improved.
Protective nitrogen doped Si-C multilayer coatings on carbon, used to improve the oxidation resistance of carbon, were obtained by Thermionic Vacuum Arc (TVA) method. The initial carbon layer having a thickness of 100nm has been deposed on a silicon substrate in the absence of nitrogen, and then a 3nm Si thin film to cover carbon layer was deposed. Further, seven Si and C layers were alternatively deposed in the presence of nitrogen ions, each having a thickness of 40nm. In order to form silicon carbide at the interface between silicon and carbon layers, all carbon, silicon and nitrogen ions energy has increased up to 150eV . The characterization of microstructure and electrical properties of as-prepared N-Si-C multilayer structures were done using Transmission Electron Microscopy (TEM, STEM) techniques, Thermal Desorption Spectroscopy (TDS) and electrical measurements. Oxidation protection of carbon is based on the reaction between oxygen and silicon carbide, resulting in SiO<sub>2</sub>, SiO and CO<sub>2</sub>, and also by reaction involving N, O and Si, resulting in silicon oxynitride (SiN<sub>x</sub>O<sub>y</sub>) with a continuously variable composition, and on the other hand, since nitrogen acts as a trapping barrier for oxygen. To perform electrical measurements, 80% silver filled two-component epoxy-based glue ohmic contacts were attached on the N-Si-C samples. Electrical conductivity was measured in constant current mode. The experimental data show the increase of conductivity with the increase of the nitrogen content. To explain the temperature behavior of electrical conductivity we assumed a thermally activated electric transport mechanism.
Ionized nitrogen doped Si-C multi-layer thin films used to increase the oxidation resistance of carbon have been obtained by Thermionic Vacuum Arc (TVA) method. The 100 nm thickness carbon thin films were deposed on silicon or glass substrates and then seven N doped Si-C successively layers on carbon were deposed. To characterize the microstructure, tribological and electrical properties of as prepared N-SiC multi-layer films, Transmission Electron Microscopy (TEM, STEM), Energy Dispersive X-Ray Spectroscopy (EDXS), electrical and tribological techniques were achieved. Samples containing multi-layer N doped Si-C coating on carbon were investigated up to 1000°C. Oxidation protection is based on the reaction between SiC and elemental oxygen, resulting SiO<sub>2</sub> and CO<sub>2</sub>, and also on the reaction involving N, O and Si-C, resulting silicon oxynitride (SiN<sub>x</sub>O<sub>y</sub>) with a continuously vary composition, and because nitrogen can acts as a trapping barrier for oxygen. The tribological properties of structures were studied using a tribometer with ball-on-disk configuration from CSM device with sapphire ball. The measurements show that the friction coefficient on the N-SiC is smaller than friction coefficient on uncoated carbon layer. Electrical conductivity at different temperatures was measured in constant current mode. The results confirm the fact that conductivity is greater when nitrogen content is greater. To justify the temperature dependence of conductivity we assume a thermally activated electrical transport mechanism.
Ionized nitrogen doped Si-C thin films at 200°C substrate temperature were obtained by Thermionic Vacuum Arc (TVA) method. To increase the energy of N, C and Si ions, -400V, -600V and -1000V negative bias voltages was applied on the substrate. The 400nm, 600nm and 1000nm N-SiC coatings on glass was deposed. To characterize the structure of as-prepared N-SiC coatings, Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), X-Ray and Photoelectron Spectroscopy (XPS) techniques was performed. Electrical conductivity was measured comparing the potential drop on the structure with the potential drop on a series standard resistance in a constant current mode. To justify the dependence of measured electrical conductivity by the temperature, we assume a thermally activated electrical transport mechanism.
Crystalline Si-C thin films were prepared at substrate temperature between 200°C and 1000°C using Thermionic
Vacuum Arc (TVA) method. To increase the acceleration potential drop a negative bias voltage up to -1000V was
applied on the substrate. The 200nm thickness carbon thin films was deposed on glass and Si substrate and then 200-500
nm thickness Si-C layer on carbon thin films was deposed. Transmission Electron Microscopy (TEM), High Resolution
Transmission Electron Microscopy (HRTEM), X-Ray Photoelectron Spectroscopy (XPS), and electrical conductivity
measurement technique characterized the structure and physical characteristics of as-prepared SiC coating.
At a constant acceleration potential drop, the electrical conductivity of the Si-C films deposed on C, increase with
increasing of substrate temperature. On the other part, significant increases in the acceleration potential drop at constant
substrate temperature lead to a variation of the crystallinity and electrical conductivity of the SiC coatings
XPS analysis was performed using a Quantera SXM equipment, with monochromatic AlKα radiation at 1486.6eV.
Electrical conductivity of the Si-C coating on carbon at different temperatures was measured comparing the potential
drop on the sample with the potential drop on a series standard resistance in constant mode.
SiC single-layer or multi-layer on C used to improve the oxidation resistance and tribological properties of C have been obtained by Thermionic Vacuum Arc (TVA) method. The 200nm thickness carbon thin films was deposed on glass or Si substrate and then 100÷500 nm thickness SiC successively layers on carbon thin film was deposed. The microstructure and mechanical characteristics of as-prepared SiC coating were investigated by Transmission Electron Microscopy (TEM, STEM), Energy Dispersive X-Ray Spectroscopy (EDS), Electron Scattering Chemical Analysis (ESCA) and tribological techniques. Samples containing SiC single-layer or multi-layer coating on carbon were investigated up to 1000°C. The results of thermal treatments reveals the increase of oxidation resistance with increase of the number of SiC layers. The mechanism of oxidation protection is based on the reaction between SiC and elemental oxygen resulting SiO<sub>2</sub> and CO. The tribological behavior of SiC coatings was evaluated with a tribometer with ball-on-disk configuration from CSM device with 6mm diameter sapphire ball, sliding speed in dry conditions being 0.2m/s, with normal contact loads of 0.5N, 1N, 1.5N and 2N, under unlubricated conditions. The friction coefficient on SiC was compared with the friction coefficient on uncoated carbon layer. Electrical surface resistance of SiC coating on carbon at different temperatures was measured comparing the potential drop on the sample with the potential drop on a series standard resistance in constant mode.