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Nanosensor Laboratory
Published in Vinod Kumar Khanna, Nanosensors, 2021
Photolithography is the process of transferring geometric shapes or patterns on a mask to the surface of a silicon wafer coated with a photoresist. What is a photoresist? It is a light-sensitive material performing two basic functions, namely precise pattern formation and protection of the substrate from chemical attack during the etching process. Photolithography is the means by which the small-scale features of integrated circuits are created. The steps involved in the photolithographic process are wafer cleaning, barrier layer formation, photoresist application, soft baking (the step during which the solvents are removed from the photoresist), mask alignment, exposure and development, and hard baking (the step to harden the photoresist and improve adhesion of the photoresist to the wafer surface). A diffusion barrier layer is a layer of thermally grown silicon dioxide that blocks the entry of dopant impurities, like phosphorus and boron, into the silicon wafer so that these impurities enter only through the windows in the oxide layer etched after the photolithographic operation.
Electronic Packaging Approaches for High-Temperature Environments
Published in John D. Cressler, H. Alan Mantooth, Extreme Environment Electronics, 2017
Thin film substrates are fabricated by sequential vacuum deposition (evaporation or sputtering) of conductive, resistive, and dielectric layers on to a base substrate and patterning by photolithography. Plating may be used to increase the thickness of conductors. As with thick film, Al2O3 is the most common base substrate, but AlN and Si3N4 have been used. Thin film metallization is typically a three-layer stack: (1) adhesion layer, (2) diffusion barrier, and (3) conductor layer. Cr and Ti are common adhesion layers. Ni, NiCr, and TiW are often used for the diffusion barrier. For high-temperature applications, Au is generally used as the conductor layer. At temperatures above 300°C, Ni will diffuse through the Au layer with long-term exposure and is not an effective diffusion barrier. TiW has recently been demonstrated as an effective diffusion barrier in a Ti/TiW/Au metallization on AlN substrates at 300°C [11]. Without the TiW diffusion barrier, the Ti would diffuse into the Au layer, increasing the electrical resistivity due to increased electron scattering caused by the impurity (Ti).
Power Connectors
Published in Paul G. Slade, Electrical Contacts, 2017
According to the available data, nickel appears to be the most practical coating material from the point of view both of its cost and the significant improvements to the metallurgical and contact properties of electrical connectors. The resistance of nickel to form intermetallic phases with copper, aluminum, and other metals, makes it as a very effective diffusion barrier in a variety of electrical and electronic devices where diffusion between the coating and substrate base represents a significant problem. In recent years, nickel was successfully employed for coating aluminum conductors and power connectors. However, nickel does not protect aluminum galvanically and presents subsurface corrosion problems when plated over aluminum. Furthermore, fretting produces considerable degradation of the contact zones in nickel-coated aluminum contacts. Lubrication and higher loads are found to mitigate these adverse effects. Despite these disadvantages, nickel-plating is still becoming more attractive for contact applications in electric power applications.
From titanium ore extraction and processing to its applications in the transportation industry — an overview
Published in CIM Journal, 2023
C. Siemers, F. Haase, L. Klinge
Considerable efforts have been made since the late 1980s to improve the oxidation and creep resistance at elevated temperatures of both conventional Ti alloys and Ti aluminides (e.g., Tsuyama, Mitao, & Minakawa, 1992). The two most compelling elements are Si and Nb (Maki, Shioda, Sayashi, Shimizu, & Isobe, 1992). The formation of a thin SiO2 layer at the metal-oxide interface forms a diffusion barrier for oxygen penetration and thus reduces further oxidation. In addition, the precipitation of Ti3Si or Ti5Si3 intermetallic phase at the grain boundaries decelerate grain boundary oxidation (Maki et al., 1992). The mechanisms by which Nb additions improve the oxidation resistance of Ti alloys have been intensively discussed for several years. They include diffusion of Nb5+ ions into the oxide layer and formation of an Nb-enriched layer at the subsurface of Nb-containing Ti alloys, which hinders oxygen diffusion into the subsurface (Tegner, Zhu, Siemers, Saksl, & Ackland, 2015).
Effect of heating rates on the energy release application of Al/MLG/Fe2O3 nanothermite
Published in Philosophical Magazine, 2023
Priya Thakur, Vimal Sharma, Nagesh Thakur
On the other hand, another model proposed by Levitas et al. [19] explains the oxidation mechanism of nanoscale aluminium at high heating rates (>10°C/min). The current model describes heating, phase change and rapid pressure developed within the fuel (nano-Al) particle core. The mechanism has been called the melt dispersion mechanism (MDM) because it results in a burst-like dispersion of molten fuel. As per this model, the shell is subjected to tensile stress, whilst the molten aluminium core is under compression. Small clusters of just a few nanometres in diameter of molten aluminium are released when the internal tension of the aluminium oxide surpasses its yield strength. This quick exposure to the metal oxide shows no diffusion barrier and therefore the reaction is completely controlled by kinetically. The rapid reaction is thought to be caused by the less diffusion distance at the nanoscale and the immediate exposure of fuel and oxidiser without a diffusion barrier.
Flow accelerated corrosion of carbon steel containing chromium under water chemistry conditions of boiling water reactor applying mitigation techniques of corrosive environment
Published in Journal of Nuclear Science and Technology, 2022
Kazushige Ishida, Yoichi Wada, Takayuki Shimaoka, Ryosuke Shimizu
The cause of FAC suppression by adding 0.052 wt% Cr under LDO was investigated from the results of cross-sectional SEM observations and EDX mappings. The cross-sectional SEM observations indicated the oxide film thickness increased as the chromium content increased. Furthermore, from both SEM observations and EDX mappings, the base metal was seen to be covered with a porous oxide film for the chromium content of 0.015 wt% and 0.052 wt%, but the side close to the base metal was covered with a dense oxide film for the chromium content of 0.13 wt% or more. The 0.13 wt% Cr specimen was covered with a dense oxide and had a porous oxide film on the outside. The observation results regarding the increase in the oxide film thickness and the densification of the oxide film with the increase in the chromium content were in agreement with Reference [19]. When the thickness of the oxide film increased and the oxide film was densified, it seemed to become a diffusion barrier for iron ions between the base metal and the test water, so that the thinning rate decreased as the chromium content increased.