Virginia Dinca

Growth and characteristics of tantalum oxide thin films deposited using thermionic vacuum arc technology

Tantalum pentoxide (Ta2O5) thin films were synthesized using thermionic vacuum arc (TVA) technology. TVA is an original deposition method using a combination of anodic arc and electron gun system for the growth of thin films from solid precursors under vacuum of 10−6 Torr. The properties of the deposited Ta2O5 thin films were investigated in terms of wettability, refractive index, morphology, and structure. The surface free energy was determined by means of surface energy evaluation system indicating a hydrophilic character and the refractive index was measured by Filmetrics F20 device. The morphology was determined from bright field transmission electron microscopy (TEM) image performed by Philips CM 120 ST TEM system. It exhibits nanoparticles of 3–6 nm diameter smoothly distributed. Selected area electron diffraction pattern revealed the contrast fringes given by complex polycrystalline particles included in the amorphous film. The measured fringes could be indexed using monoclinic structure of Ta2O5.

Binary C-Ag Plasma Breakdown and Structural Characterization of the Deposited Thin Films by Thermionic Vacuum Arc Method

Binary elemental plasma of carbon and silver was synthesized using the thermionic vacuum arc technology for the first time in this configuration. The structural investigations of the deposited silver/amorphous carbon (Ag/a-C) nanocomposites thin film on different materials, such as Si, glass, and stainless steel OLC 45 substrates performed by high-resolution transmission electron microscopy were reported, as well as the modification of the properties at the nanometer level.

Nitrogen doped silicon-carbon multilayer protective coatings on carbon obtained by thermionic vacuum arc (TVA) method

To obtain protective nitrogen doped Si-C multilayer coatings on carbon, used to improve the oxidation resistance of carbon, was used TVA method. The initial carbon layer has been deposed on a silic...

Nanostructured carbon-titanium multilayer films obtained by thermionic vacuum arc method

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. 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 sp3 and graphite-like sp2; the ratio sp3/sp2 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.

Nitrogen doped silicon-carbon multilayer protective coatings on carbon obtained by TVA method

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 SiO2, SiO and CO2, and also by reaction involving N, O and Si, resulting in silicon oxynitride (SiNxOy) 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.

Characterization of nitrogen doped silicon-carbon multi-layer nanostructures obtained by TVA method

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 SiO2 and CO2, and also on the reaction involving N, O and Si-C, resulting silicon oxynitride (SiNxOy) 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.

Structural and electrical properties of N doped SiC nanostructures obtained by TVA method

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.

The effect of the substrate temperature and the acceleration potential drop on the structural and physical properties of SiC thin filmsdeposed by TVA method

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.

Growth and Characterization of the High Purity C-Mg Thin Films Obtained by Thermionic Vacuum Arc (TVA) Technology

We investigated the growth and structure properties of C-Mg thin films obtained for the first time by Thermionic Vacuum Arc (TVA) deposition. The TVA technology is suitable for producing nanostructured materials because of the high power density of the vapor plasma generated by accelerated electron flux from the cathode and high energy of the ions incident on the depositing film, both these properties ensuring a high dispersion of the evaporated material. The properties of the deposited C-Mg thin films were investigated in terms of wettability and morphology. The surface free energy (SFE) was determined by means of Surface Energy Evaluation System (See System) indicating a hydrophobic character and the morphology were determined from BF-TEM image performed by Philips CM 120 ST TEM system.

Surface Activation of the Polycarbonate in Atmospheric Pressure Plasma Generated in Air and Helium by Surface Dielectric Barrier Discharge (SDBD)

Surface Dielectric Barrier Discharges (SDBD) plasma treatment has been performed to produce uniform atmospheric plasmas in He and in open air in order to functionalize the polycarbonate surface. SDBD is used for different application, processing especially of low-cost polymeric materials, combining the advantages of non-equilibrium plasma properties with the ease of atmospheric-pressure operation. Contact angle measurements were used to record the short-and long - term variations in wettability of treated and untreated polycarbonate sheets. The modification process was determined with hydrophilic measurements evaluated by means of the SEE system drop test.