Papers by Keyword: Oxidation

Abstract: The oxidation behaviour of developed Fe₈₀Cr₂₀ alloy and commercial ferritic steel at 1173 - 1373 K in air is studied. Effects of crystallite size and titanium implantation on the oxidation behaviour of specimens were analyzed based on oxide morphologies and microstructures. Oxide scales characterisations of specimen after oxidized were identified by X-ray diffraction (XRD). The surface morphology of oxide scales were examined with scanning electronic microscope (SEM) and energy dispersive X-ray analysis (EDX). The rate constant of oxidation were determined using Wagner method. The results show that crystallite size and titanium implantation has remarkably enhanced the oxidation resistance. The oxidation kinetics indicate that the developed Fe₈₀Cr₂₀ as the finer crystallite size both unimplanted and implanted specimens show better performance.

Abstract: Trenched implanted vertical JFETs (TI-VJFETs) with self-aligned gate and source contacts were fabricated on commercial 4H-SiC epitaxial wafers. Gate regions were formed by aluminium implantation through the same silicon oxide mask which was used for etching mesa-structures. Self-aligned nickel silicide source and gate contacts were formed using a silicon oxide spacer formed on mesa-structure sidewalls by anisotropic thermal oxidation of silicon carbide followed by anisotropic reactive ion etching of oxide. Fabricated normally-on 4H-SiC TI-VJFETs demonstrated low gate leakage currents and blocking voltages exceeding 200 V.

Abstract: Rapid Thermal Processing (RTP) has been evaluated as an alternative to the conventional furnace process for the gate oxide formation of SiC lateral MOSFETs. We show that this innovative oxidation method has not only the advantage to significantly reduce the thermal budget compared to classical oxidation, but also produces a significant improvement of MOSFET performance when using N2O as oxidizing gas. Studying different surface preparation before gate oxidation, we demonstrate that in-situ surface preparation by H2 annealing increases considerably the channel mobility and also the electrical stability with respect to constant bias stress at low-field.

Abstract: To understand the structure of SiC–oxide interface more in detail, we propose a profiling theory of Si and C emission into SiC layer during oxidation. Simulations of the depth profiles of Si and C interstitials results in the structures analogous with those observed from a spectroscopic ellipsometry. To determine the diffusivities of Si and C interstitials, we performed capacitance–voltage measurements for examining the re-distribution profiles of nitrogen after oxidation and compared between observed and calculated profile. The calculated nitrogen profiles showed good fits to the observed ones in the case of self-diffusivity of C interstitials magnified by several 10 times for literature value. Finally, we discuss the validity of the proposed theory.

Abstract: We report a strong reduction in the density of near-interface traps (NITs) at the SiO2/4H-SiC interface after dry oxidation in the presence of potassium. This is accompanied by a significant enhancement of the oxidation rate. The results are in line with recent investigations of the effect of sodium on oxidation of 4H-SiC. It is evident that both alkali metals enhance the oxidation rate of SiC and strongly influence the energy distribution of interface states.

Abstract: The catalytic properties of the Pt3Ni(111) surface with Pt-skin [denoted as Pt-skin Pt3Ni(111)] are investigated through the adsorption and oxidation properties of CO on the Pt-skin Pt3Ni(111). It is found that, on the Pt-skin Pt3Ni(111), the adsorption of CO and O is weaker than that on the Pt(111) due to alloying with Ni. The CO reacts with the coadsorbed O atom and forms a CO2 species which binds weakly to the surface and can easily desorb from the surface, indicating that the CO can be oxidized directly on the Pt-skin Pt3Ni(111).

Abstract: Atomic force microscopy measurements are carried out on the surface and interface of SiO2 thermally grown on an atomically flat Si surface, and the uniformity of thickness on an atomic scale is investigated. Protuberances on the surface of SiO2 grown at 800 °C in 3.8 % O2 diluted by argon at the atmospheric pressure are generated in the initial stage of oxidation and subsequently increases in height at the same positions. The surface RMS value of SiO2 linearly increases up to the thickness of approximately 5 nm, which almost corresponds to what was called the initial oxidation thickness. This fact indicates that the roughness increase is related to the re-oxidation of SiO emitted from the Si/SiO2 interface during the initial oxidation. Additionally, the surface RMS value is saturated at a value of approximately 0.13 nm. A correspondence between the position of the dimples on the surface and the positions of the protuberances at the interface is also clear. The fact is the direct evidence of the local thinning of the thermally grown SiO2 films. Based on these results, an atomic scale thermal oxidation mechanism is discussed.

Abstract: ZrC-Zr2Si coating was prepared on carbon fiber reinforced silicon carbide matrix composites (C/SiC) by pack cementation method to prevent these composites from oxidation. SEM, EDS and XRD were applied to analyze the surface and cross-section morphologies, element distribution and phase composition of the coating, respectively. The results show that the coating made by the technique exhibits excellent oxidation resistance. The optimizing infiltration composition and process was: 60wt.%Zr-Si, 30wt.%PCS-DVB, 10wt.%Al2O3, holding 8 hours at 1400°C in Ar protecting atmosphere, ZrC-Zr2Si coating is obtained, homogeneous and density. The weight loss percentage of the coated C/SiC is only 1.52％after oxidation in air at 1500°Cfor 30min.

Abstract: The isothermal initial oxidation kinetics of Zr55Cu30Al10Ni5 bulk metallic glass in glassy state (lower than Tg = 685K) and in surpercooled liquid state (Tg = 685 K < T < Tx=774 K) is investigated under dry air by thermogravimetric method in short-term stage (for 1.5 hours). A protective parabolic law is followed in glassy state, except at 573 K where a linear law is followed. The self-limiting oxidation kinetics evolves from a short linear stage to a steady mild growth stage in supercooled liquid state at 723 K, which is induced mainly by crystallization and by the fast growth of dense scale. The growth of the scale is dominated by the formation of tetragonal-ZrO2 (t- ZrO2) in the range of 623 K - 673 K in glassy state for 1.5 hours. The activation energy of oxidation is mainly piloted by the diffusion of oxygen ions.

Abstract: Oxidation kinetic of a Zr55Cu30Al10Ni5 bulk metallic glass (BMG) and its crystalline counterpart were studied under dry artificial air (20% of O2 and 80% of N2) at 673 K by thermogravimetry analysis (TGA) method. According to TGA profiles, the oxidation kinetic in both amorphous and crystalline states followed a protective parabolic law. However, the oxidation rates for the amorphous alloy were obviously higher than those for the crystalline alloy. Pseudo-grazing incident X-Ray diffraction (GIXRD) has been carried out to identify the oxides nature and their crystalline structure. Tetragonal-ZrO2 dominated the oxide scale formed on both alloys (BMG and crystalline) at T = 673 K; meanwhile, a slight amount of Cu was detected on the oxide surface of studied BMG alloy. The atomic diffusion mechanism was investigated using a two-stage oxidation treatment to study oxide scale growth kinetics. The studied specimens were oxidized firstly under dry artificial air and then under 18O2 isotopic tracer gas for 1.5 hours respectively at 673 K. The evident solute penetration zone and ion diffusion characteristic through the oxide scale were determined by Cs+ secondary ion mass spectrometry (SIMS) depth profile. The results showed the mechanism of the oxide layer formation of both alloys was not only due to Oxygen ions diffusion from oxide surface to interior scale, but also to an outward diffusion of Zirconium ions from substrate to oxide layer and the ZrO2 oxide growth seemed to occur at the oxide/gas interface in our studied case.