Papers by Keyword: Thermal Oxidation

Abstract: The synthesis and characterization of porous ZnO films using a two stage process by thermal oxidation using a bilayer precursor film (ZnO/Zn) consisting of a Zn film covered with a ZnO nanofilm formed on quartz substrates is reported. The Zn films of 50 nm were grown by DC sputtering method at 300K. In the first stage bilayer precursor films (BPF) of ZnO/Zn were produced by growing a ZnO nanofilm on Zn films by thermal oxidation at 350 °C by 30 min in N₂ atmosphere containing 5 ppm of O₂, and in the second stage the BPFs were oxidized at 800 °C for one hour either in dry N₂, dry or wet air with 42% of humidity. The produced porous ZnO films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectroscopy measurements. The results revealed the role of the oxygen content and the relevance of the humidity content in the processing atmosphere. When the BPF was oxidized in N₂ with low oxygen content nanoporous ZnO films of wurtzite phase with its c-axis perpendicular to the plane of the substrate were produced. When rich oxygen content oxidation atmospheres were used, either in dry or wet air, nanoporous ZnO films with three main crystallite orientations (100), (002) and (101), were produced. The optical transmittance characteristics at the band edge region were strongly influenced by the humidity content but induce the formation of reproducible nanoporous ZnO films with sizes of ≈ 10 nm.

Abstract: We reported that high oxidation temperature is attributed to break Si-C bond and release nitrogen gas to nitrogen ions over 1350°C. The capacitance-voltage characteristics of SiO₂/4H-SiC (0001) MOS capacitors fabricated under different thermal oxidation conditions are compared. The dependence of oxidation temperature on device characteristics (such as V_FB and ΔV_FB) is also analyzed. After a high temperature oxidation, the device reliability of SiC MOS is improved. Such behavior can be attributed to the reduction of the interface traps during high temperature oxidation.

Abstract: ZnO Nano and microstructures were obtained by thermal oxidation using Zn powders as source. To achieve those structures, the Zn powders were annealed at 650°C and 750°C under oxygen environment and atmospheric pressure. SEM results show that these experimental conditions promote the formation of hollow spherical microstructures with nanowires and nano-swords in each sphere. As was observed, the nanostructures start growing from the bottom surface of the spheres unlike those that were reported recently. The EDS results clearly show that those hollow spheres in the deep part make a compound with Zn and the top surface is mainly composed of ZnO. CL emission spectra show a main green emission that belongs to the sphere’s bottom surface; this emission is correlated to the existing defects that are presented. These results could allow the prediction of a possible growth mechanism under specific conditions.

Abstract: Cobalt (Co) nanowires were synthesized via electroless deposition in ethylene glycol under an external magnetic field then oxidized in air via thermal oxidation at 250 to 300 °C. The nanowires have lengths in the range of 10 to 14 µm while the diameter increases with oxidation temperature. This can be attributed to the partial melting of the nanowires during oxidation, resulting to sintering. The peaks in the XRD patterns show complete oxidation of Co nanowires, producing a mixture of Co₃O₄ and CoO. It was observed that Co₃O₄ and CoO peaks were more intense at 270 °C. There is a decrease in specific capacitance (F/g) with increase in scan rate due to poor electron exchange between active material electrode and electrolyte. Highest calculated specific capacitance was 339.28 F/g using nanowires oxidized at 270 °C at 1 mV/s scan rate.

Abstract: In this study, hematite (α-Fe₂O₃) nanostructures were synthesized via thermal oxidation of Fe sheet in dry air and in water vapor. SEM images show nanoblades and nanowires growing on the surface of the sheet. Samples synthesized in water vapor generally produced larger nanostructures while samples oxidized in higher temperatures formed taller and slender nanostructures. The α-Fe₂O₃ nanostructures were used as adsorbent for Cr (VI) in acidic medium. Chromium removal was highest with the samples synthesized at 650°C in water vapor with 95% efficiency. Kinetic and thermodynamic studies revealed that the adsorption process strongly followed pseudo-second order kinetics model and is endothermic. The process also follows the Langmuir adsorption isotherm model, suggesting that the process is described by homogeneous, monolayer adsorption. Adsorption of Cr (VI) onto hematite may be attributed to the electrostatic reaction between the positively charged hematite adsorbent and negative chromium ion.

Abstract: In this paper, the application of a high temperature thermal oxidation and annealing process to 4H-SiC PiN diodes with 35 μm thick drift regions is explored, the aim of which was to increase the carrier lifetime in the 4H-SiC. Diodes were fabricated using 4H-SiC material and underwent a thermal oxidation in dry pure O₂ at 1550^◦C followed by an argon anneal at the same temperature. Reverse recovery tests indicated a carrier lifetime increase of around 42% which is due to increase of excessive minority carriers in the drift region. The switching results illustrate that the use of this process is a highly effective and efficient way of enhancing the electrical characteristics of high voltage 4H-SiC bipolar devices.

Abstract: Iron oxide nanowires were synthesized on stainless steel mesh substrate using the thermal oxidation process at the varying temperature of 750°C for 60 min. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern showed that the iron oxide nanowires exhibited the structure of alpha-Fe₂O₃ (hematite). SEM images indicated that the diameter and the length of the nanowires were 80 to 285 nm and more than 5 μm, respectively. The dye-sensitized solar cell (DSC) properties based on the nanowires substrate was also studied. It was found that the power conversion efficiency (η) of the device was 0.11%.

Abstract: Surface modification of metallic implants is often required to facilitate positive interaction between the implant and the surrounding hard tissue. In the present study, an oxide layer (Cr₂O₃) was successfully created on a Co-Cr-Mo alloys substrate by using thermal oxidation technique in atmospheric condition. The effect of different carbon content (0.03% and 0.24%) of oxidized Co-Cr-Mo alloys was investigated in terms of its corrosion behavior using electrochemical impedance spectroscopy techniques that immersed in simulated body fluid. The corrosion tests were repeated for five times for each of sample condition. The results demonstrated that thermal oxidation and carbon content have correlation in influencing the corrosion performance in Co-Cr-Mo alloys. A high carbon content sample generates a lower corrosion-rate compared to low carbon content sample even though all samples were treated at similar oxidation temperature and time duration. Observation also showed that less diffusion of cobalt released in high carbon sample which is believed has effects in creating the uniformity and dense oxide layer without any presence of microcracks and delamination. This phenomenon can be concluded that carbon content in Co-Cr-Mo alloy have influenced in controlling the reaction of metal elements during thermal oxidation which is beneficial in formation of oxide layer. The uniformity and compact oxide layer substantially have enhanced the corrosion resistance of high carbon Co-Cr-Mo alloy.

Abstract: Ti-6Al-7Nb (Ti67) alloy has recently been developed to replace the commercial Ti6Al4V (Ti64) alloy because of the reported cytoxicity of vanadium. Surface modification by thermal oxidation is used to enhance the hardness and wear resistance of such titanium alloys. Since Ti67 alloy contains Nb as β phase stabilizer instead of V in Ti64, it is expected to behave differently upon processing by thermal oxidation. Therefore, it is of interest to compare the response of the two alloys to thermal oxidation in terms of hardness and wear resistance. Forged and cast samples were used to study the influence of the microstructure on the surface properties after oxidation. The forged samples with their equiaxed microstructure showed a well developed sub-surface hard layer (α-case) compared to the cast structure for the two alloys. The thickness of this case in Ti64 after oxidation at (900-1100 °C) was greater than in Ti67. This resulted in higher wear resistance of the Ti64 alloy relative to Ti67. These results are worth considering when designing implants for joints replacement.

Abstract: Tuning high density nanostructures by simple and economic method may contribute towards the development of solid oxide fuel cells. Copper oxide nanowires grown on Cu foil by thermal oxidation at relative low operating temperature from 400°C are characterized by using x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), atomic force morphology (AFM), conductive-AFM (C-AFM), and field emission scanning electron microscopy (FESEM). The role of oxidizing temperature and time on structural and electrical properties are studied. The formation of nanowires is confirmed by X-Ray diffraction pattern with the presence of copper oxide. The electrical conductivity of the nanowires was ranging from 0.2x10⁵ S m^-1 to 0.8x10⁵ S m^-1are determined from conductive atomic force microscopy. The oxidation time strongly influence the morphology and chemical composition of the nanowires. Field emission scanning electron microscopy reveals the growth mechanism of copper nanowires formation is based on vapour-solid (VS) mechanism. Herein, the successfully growth of CuO nanowire are directly from Cu foil to overcome the mismatching stress between the substrate and the oxide layer. Optimum parameters are studied to make better electrolyte performance in the applications of solid oxide fuel cell (SOFC).