Papers by Keyword: Oxide

Abstract: Oxide particles of Fe-77Ni alloy scraps were reduced by hydrogen gas on the effect of temperature and time. The chemical composition of metallic powder was examined by X-ray diffraction (XRD) and FeNi₃ alloy was finally obtained with a mean particle size of 10μm.

Abstract: Ion implantation in silicon carbide (SiC) induces defects during the process. Implantation free processing can eliminate these problems. The junction termination extension (JTE) can also be formed without ion implantation in SiC bipolar junction transistor (BJT) using a well-controlled etching into the epitaxial base layer. The fixed charges at the SiC/SiO₂ interface modify the effective dose of the JTEs, leakage current, and breakdown voltage. In this paper the influence of fixed charges (positive and negative) and also interface trap density at the SiC/SiO₂ interface on the breakdown voltage in 4.5 kV 4H-SiC non-ion implanted BJT have been simulated. SiO₂ as a surface passivation layer including interface traps and fixed charges has been considered in the analysis. Simulation result shows that the fixed charges influence the breakdown voltage significantly more than the interface traps. It also shows that the positive fixed charges reduce the breakdown voltage more than the negative fixed charges. The combination of interface traps and fixed charges must be considered when optimizing the breakdown voltage.

Abstract: The electrical properties of metal-oxide-semiconductor (MOS) devices fabricated using dry oxidation on phosphorus-implanted n-type 4H-SiC (0001) epilayers have been investigated. MOS structures were compared in terms of interface traps and reliability with reference sample which was produced by dry oxidation under the same conditions. The notably lower interface traps density measured in MOS capacitor with phosphorus concentration exceeding 10¹⁸ cm^-3 at the SiO₂/SiC interface was attributed to interface traps passivation by incorporated phosphorus ions.

Abstract: HfAlO_x based RRAM devices were fabricated using atomic layer deposition by modulating deposition cycles for HfO₂ and Al₂O₃. The effect of rapid thermal annealing (RTA) on the resistive switching uniformity of HfAlOx based RRAM devices was investigated. Compared to the as-deposited devices, the resistive switching uniformity of HfAlO_x based RRAM devices after RTA treatment are remarkably improved. The uniformity improvement of HfAlO_x based RRAM after RTA treatment is related to microstructure change in the resistive switching film.

Abstract: The Glass Ionomers Cements (GICs) are materials widely used in dentistry, have advantages such as fluoride release and chemical adhesion to the dental substrate. They are recommended as a restorative material, luting agent in prosthetic dentistry and also in medicine. However, there is need for developing new bone cements as an alternative or replacement to the current polymethylmethacrylate cements, therefore, the objective of this research was to develop an experimental GIC and characterization regarding morphology, chemical composition and crystallinity. This composite was characterized by X-ray diffraction (XRD), Infrared Spectroscopy Fourier Transform (FTIR) and optical microscopy (OM). For comparative study, was used the GIC Vidrion R (SS White) in the control group. These cements are presented in semi-crystalline diffraction patterns, the FTIR spectra observed characteristic bands of these materials and microstructural study of the cements showed homogeneous distribution of filler in the polymer matrix, corroborating with the literature.

Abstract: Micromechanical simulations of polycrystalline zirconia using the finite element method are performed in order to obtain the stresses at the grain scale of a zirconium oxide layer, since these microstresses are important for damage prediction of the layer and then oxidation kinetics. The crystallographic texture of the layer of monoclinic zirconia is taken into account. The results show that even under high compressive macroscopic stresses, the microstresses can contribute to lateral cracking promoted by the presence of tetragonal zirconia.

Abstract: Twin roll casting (TRC) has been demonstrated to be an effective route for producing Al sheet at a reduced cost. However, the quality of the Al alloys sheets produced by the TRC process is limited by the formation of centreline segregation, which hampers the downstream processing, degrade the mechanical performance of the final rolled products, limit TRC to dilute alloys with a narrow freezing range, and hence prevent its application in a wide range of engineering sectors. To improve the quality of the TRC strips, a new technology, melt conditioning twin roll casting (MC-TRC) has been developed. It has been demonstrated that the MC-TRC process is capable of producing Al-alloy strips with minimal centerline segregation which is attributed to enhanced nucleation by well dispersed naturally occurring oxides in liquid Al alloys. This work aims to investigate the upper composition limit allowed for the MC-TRC process using the binary Al-Mg alloys as model alloys. The results showed that melt conditioning increases the range of alloys (solute content up to 7%) that can be twin roll cast without severe segregation.

Abstract: In this study, grain refinement efficiency of a new oxide master alloy based on MgAl₂O₄ was demonstrated on an A357 alloy. The grain size of the reference alloy was reduced by 50-60% with the addition of the master alloy and introduction of ultrasonic cavitation. A higher addition of master alloy was found to be not benificial in further reducing the grain size.

Abstract: This paper reports the preparation of Fe_xTi alloys from natural ilmenite by electro-reduction in molten CaCl₂. The electro-reduction experiment was carried out at 1000 °C and potential of 3.8 V, and an inert solid oxide oxygen-ion-conducting membrane (SOM) anode system was used to control the electrochemical experiment. The phase composition and morphology of the final product were investigated. The reaction mechanism involved in the electro-reduction process is discussed based on our experimental results and thermodynamic analysis. It is suggested that Fe_xTi alloys powder with different Fe contents (Fe_xTi, 0 ≤ x ≤ 2) and particle sizes can be obtained by controlling electrolysis conditions strictly. The result implies that the SOM process is a promising green method for the preparation of ferrotitanium alloys direct from natural ilmenite.

Abstract: A theoretical model for radiation effect in a metal-ferroelectric-semiconductor (MFS) field-effect transistor was proposed by considering the fixed charges (Q_fx) and interface charges (Q_it) induced by ionizing radiation. In this model, the energy band-bending and surface charge in Si at a given gate bias were calculated systematically as a function of fixed charges (Q_fx) and interface charges (Q_it). The drain-source current (I_D) was derived in an exact form without any approximation. All modeling done in this work was generalized to both n and p type Si substrates with an easy sign of the Fermi level potential in the formalism. The derived results demonstrate that the symmetry of polarization versus gate voltage curve of the MFS structure degrades when Q_fx and Q_it increase, which can explain the imprint behavior successfully. Additionally, the residual polarization in the ferroelectric field-effect transistor decreases with increasing Q_fx and Q_it, which can account for the polarization reduction. As expected, the calculated transfer characteristic of the ferroelectric FET shows that the subthreshold voltage is significantly affected by Q_fx and Q_it. This investigation may provide some useful insights for the space applications of ferroelectric FET’s.