J.L. újar

Bio: J.L. újar is an academic researcher from University of Barcelona. The author has contributed to research in topics: Ceramic & X-ray photoelectron spectroscopy. The author has an hindex of 2, co-authored 2 publications receiving 21 citations.

Nanometric powder of stoichiometric silicon carbide produced in square-wave modulated RF glow discharges

Abstract: SiC nanometric powder has been obtained in square-wave modulated radiofrequency glow discharges from CH 4 and SiH 4 gas mixtures. Chemical and structural characterization revealed that the as-deposited SiC:H powder underwent spontaneous oxidation when exposed to atmosphere. To stabilise the powder chemically, we carried out a thermal treatment under vacuum (10 −4 Pa) consisting of heating to 800°C (20°C/min). The effects on the structure of the powder were examined by FTIR, EA, XPS and from optical transmittance measurements. They can be summarized as follows: dehydrogenation of the powder that induces the formation of a SiC carbidic network and chemical stability under atmospheric conditions, further confirmed by exposure to air for more than 6 months. In addition, TEM images showed that the annealed powder presented a short-range order in β -SiC units, but there was no evidence of size changes due to sinterization or compactaction phenomena.

Synthesis of nanosize si-c-n powder in low pressure plasmas

Abstract: Multicomponent powders based on the B–C–N–Si system are of great interest as starting materials for sintering advanced ceramics and composites with improved properties. The square-wave modulation of the electrical power supplied to low pressure (

Microwave Plasma Synthesis of Materials—From Physics and Chemistry to Nanoparticles: A Materials Scientist’s Viewpoint

Abstract: In this review, microwave plasma gas-phase synthesis of inorganic materials and material groups is discussed from the application-oriented perspective of a materials scientist: why and how microwave plasmas are applied for the synthesis of materials? First, key players in this research field will be identified, and a brief overview on publication history on this topic is given. The fundamental basics, necessary to understand the processes ongoing in particle synthesis—one of the main applications of microwave plasma processes—and the influence of the relevant experimental parameters on the resulting particles and their properties will be addressed. The benefit of using microwave plasma instead of conventional gas phase processes with respect to chemical reactivity and crystallite nucleation will be reviewed. The criteria, how to choose an appropriate precursor to synthesize a specific material with an intended application is discussed. A tabular overview on all type of materials synthesized in microwave plasmas and other plasma methods will be given, including relevant citations. Finally, property examples of three groups of nanomaterials synthesized with microwave plasma methods, bare Fe2O3 nanoparticles, different core/shell ceramic/organic shell nanoparticles, and Sn-based nanocomposites, will be described exemplarily, comprising perspectives of applications.

Hard silicon carbonitride films obtained by RF-plasma-enhanced chemical vapour deposition using the single-source precursor bis(trimethylsilyl)carbodiimide

Abstract: Amorphous silicon carbon nitride (Si/C/N) coatings were prepared on steel substrates by RF plasma-enhanced chemical vapour deposition (RF-PECVD) from the single-source precursor bis(trimethylsilyl)carbodiimide (BTSC). The films were characterised by X-ray diffraction (XRD), ellipsometry, FTIR, glow discharge optical emission spectroscopy (GDOES), optical microscopy, AFM, hardness measurements, scratch-, tribological- and corrosion-tests. The results of these studies show that the coatings obtained on the RF-powered electrode (cathode) were black, thick (>20 μm) and hard (21–29 GPa), while those grown on the grounded electrode (anode) were yellow, thin (<4 μm) and soft (∼5 GPa). Coatings on the anode contained around 19 at.% oxygen and exhibited silicon predominantly bonded to oxygen. In contrast, the oxygen content of the films deposited on the cathode was below 2 at.%. Silicon atoms in these coatings are co-ordinated predominantly to nitrogen and carbon. The surface of all coatings was very smooth with a maximum rms roughness between 2 nm and 5 nm for an area of 5 μm × 5 μm. Scratch and tribological tests reveal a brittle nature of the cathode-coatings and rather weak adhesion to the metal substrates. Salt-spray tests indicate an excellent corrosion resistance of the material.

Synthesis and characterization of submicron silicon carbide powders with silicon and phenolic resin

Abstract: A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid–solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders.

Electrical instability of low-dielectric constant diffusion barrier film (a-SiC:H) for copper interconnect

Abstract: An a-SiC:H deposited by CVD system is the most promising dielectric diffusion barrier to replace silicon nitride in the Cu-interconnect structure due to its low dielectric constant, good Cu barrier ability, and low moisture uptake. In this paper, electrical instabilities of a-SiC:H film under electric field were reported for the first time. At electric field higher than 1.8 MV/cm and independent of the polarity, charges will be built up in the SiC film even at room temperature. A dielectric polarization model was proposed to explain this high field instability. The formation of molecular dipole is attributed to the incorporated nitrogen atoms, which distort the symmetric tetrahedral SiC molecule. The dielectric polarization is further verified by the increase of dielectric constant at high temperature and low frequency. At elevated temperature, film instability can be observed at electric field as low as 0.4 MV/cm. A carrier injection model combined with the polarization was proposed to explain the low-field instability. It is assumed that slight polarization occurs at such a low electric field because of high temperature. The dominant mechanism is electron injection from metal gate into SiC film via the Schottky emission process. It is thus recommended that the incorporation of nitrogen must be minimized and the film stability must be carefully evaluated at real circuit level.

Surface analysis of nanostructured ceramic coatings containing silicon carbide nanoparticles produced by plasma modulation chemical vapour deposition

Abstract: Ceramic nanometric multilayer structures of nanostructured particles of SiCx:H layers and amorphous Si films were obtained by chemical vapour deposition using modulated rf plasma This technology has been extensively used for producing ceramic Si-based nanoparticles (SiCxNy) with unique characteristics including spherical morphology, composition and controlled ultrafine particle size in the range 2–100 nm Hybrid multilayer nanostructures of ceramic coatings containing Si and SiC were produced to study their structural, mechanical and surface properties Low densities of crystalline nanoparticles were embedded in a-Si matrix during the growth of these structures and they were intercalated between amorphous Si layers The phase structure, microstructure and morphology of the hybrid multilayered films were examined by transmission electron microscopy and selected area electron diffraction, which revealed the presence and distribution of the nanoparticles in the multilayered structure of the films The hardness and Young's modulus were measured by the nanoindentation technique, and the wear properties were evaluated using an improved pin-on-disc system These results showed that the mechanical properties of the films (hardness, friction, propagation of cracks and wear resistance) were notably enhanced by the presence of the nanoparticles Potential applications of these coatings based on ceramic multilayers include the production of tough and hard coatings, protective and wear-resistant coatings for mechanical tools, gears and mechanical parts, optical surfaces and fibres, corrosion and high temperature-resistant coatings, as well as inorganic membranes, buffer layers for heterogeneous coatings, and coatings with anisotropic properties