Papers by Keyword: Annealing

Abstract: Green light-emitting YPO₄:Tb³⁺ and YPO₄:Tb³⁺: Ce³⁺ nanoparticles were synthesised at low temperatures using the polyol method. The phase purity, micromorphology and luminescence characteristics were studied using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transfer Infrared absorption spectroscopy (FT-IR) and Photoluminescence spectroscopy (PL). Combined XRD and TEM analysis showed that the YPO₄ nanoparticles crystallised into a single phase of tetragonal (I41/amd) structure. For all samples, the emission intensity at λ_em=543 nm assigned to ⁵D₄→⁷F₅ is more prominent than ⁵D₄→⁷F₆ with a maximum at λ_em=488 nm, and the asymmetric ratio was calculated and analysed. The asymmetric ratio is strongly correlated with the symmetry around the local environment of Tb³⁺ ions. A significant increase in the asymmetric ratio is observed with an increase in annealing temperature. The energy transfer from Ce³⁺ ions to Tb³⁺ ions was tested by studying the photoluminescence properties of YPO₄:Tb³⁺ and YPO₄:Tb³⁺: Ce³⁺ nanoparticles and how it results in the improvement of the luminescence intensity. The Ce³⁺ 5d−4f and Tb^{3+ 5}D₄→⁷F_J (J = 6 − 3) transitions were observed.

Abstract: Dislocation behaviors after post-growth thermal treatment were investigated by X-ray topography and KOH etching. Generation of prismatic dislocations were observed in X-ray topography, and density of basal plane dislocations (BPDs) increases with annealing temperature and radial temperature gradient. Distribution of newly generated BPDs in the wafer after thermal treatment is correlated to the resolved shear stress arising from radial temperature gradient.

Abstract: Semiconductor devices rely on the incorporation of donor and acceptor atoms into the crystal lattice to form locally doped regions. For dopant atoms incorporated into SiC by ion implantation, a high-temperature annealing step is required to achieve electrical activation. This annealing step is accompanied by redistribution of the implanted atoms. The influence of the annealing parameters on dopant redistribution is crucial when aiming for ever smaller device dimensions. In this work, we present a consistent analysis of the diffusion of Al implanted in 4H-SiC after high-temperature annealing at 1650 °C and 1800 °C for different annealing times. We identify the equilibrium diffusion coefficient at long annealing times from Al profiles obtained by SIMS analyses for both annealing temperatures. The temperature dependence is determined using an Arrhenius representation. This allows to quantify the equilibrium diffusion lengths for the actual temperature profiles, including heating and cooling rates. We find that the measured diffusion lengths for short annealing times are larger than expected from equilibrium diffusion and attribute the excess length to transient enhanced diffusion. Comparing the transient diffusion lengths of room-temperature and 500 °C-implanted samples, we conclude that the transient behavior is likely related to residual crystal damage induced during the implantation process.

Abstract: The problem of crystal damage recovery and of impurity substitution in implanted semiconductors is considered from a statistical mechanical viewpoint. This is done by resorting to a thermodynamic pseudo-potential originally developed for cooperative structural rearrangements in disordered systems close to their glass transition. The dependence of the substitutional fraction φ on the post-implantation annealing temperature T_ann in Al/4H-SiC systems is discussed in the light of these ideas. After completion of the annealing process, an Arrhenius plot of φ(T_ann) shows a slope in the order of 1 eV or less, depending on the amount of lattice damage initially produced by the implantation. Slopes ∼4 eV are found after incomplete annealing, indicating that substitution occurs mainly in damaged crystal cells. These concepts are suggested to be used for optimization of the doping procedure by ion implantation.

Abstract: In conventional machining of SiC wafers, material loss and sub-surface damage (SSD) of both the front and back surfaces are major issues. In this study, we focused on Dynamic AGE-ing^® (DA), which is a sublimation-controlled process, and applied it to the total wafering process without any mechanical contact of both the front and back surfaces to explore the possibilities to reach the CMP-equivalent quality. DA process enables material lossless planarization of SiC wafers by applying a temperature gradient to achieve simultaneous etching and growth at the same rate on one and the other surfaces, respectively. To drive the planarization function for a multi-wire saw finished as-sliced wafer, as an example, a high-temperature regime above 2000 °C under an Ar background pressure higher than 1 kPa to suppress etching and growth rates was employed as the first step in the DA treatment. In this step, an effective annealing function arises where sublimation and recrystallization occur simultaneously through a sub-surface region on both sides of the wafer. Due to the active interchange of the surface and subsurface layer, a self-organizing planarization effect occurs on a macroscopic scale on both surfaces with the removal of SSD. The conventional DA processes were employed for the following microscopic flatness control. As a result, the roughness of the 6-inch as-sliced wafer was reduced to 0.7 nm on the Si-face and 2.0 nm on the C-face while maintaining the wafer thickness. This is the first promising result exhibiting the potential of thermal contactless treatment for next-generation wafer manufacturing by improving quality and cost.

Abstract: This work reports on the high-temperature reorganization behavior of single-crystalline porous 4H-silicon carbide (4H-SiC) thin foils. Porous 4H-SiC thin foils are realized via state-of-the-art photoelectrochemical etching in hydrofluoric (HF) acid solution enabling for the first time a released foil with a diameter of 2 inches. Subsequent annealing under inert gas atmosphere and comparison between samples suggests that a temperature of 1500 °C allows for various degrees of compactification across the foil surface, whereas at 1600 °C single crystallinity can be preserved.

Abstract: Wire arc additive manufacturing (WAAM) has gained significant attention in recent years as a cost-effective and efficient method for fabricating complex geometries. This study investigates the effects of cold forging and annealing on mechanical properties of AISI 308LSi wall fabricated using an automatically controlled gas metal arc welding on a CNC machine. The multilayer WAAM wall manufactured at an optimized parameters was first machined to a fairly smooth surface. Thereafter, the wall samples were differently subjected to annealing at 930°C and cold forging processes to improve the mechanical properties. Microstructural characterization of the post-processed and as-deposited samples were performed using optical and scanning electron microscopy while the tensile and hardness properties were investigated using Instron universal testing machine and Vickers hardness tester respectively. Annealing process was found to improve the tensile properties while the cold forging improved hardness of the deposited WAAM wall. These findings offer valuable insights into optimizing post-processing techniques for WAAM parts, especially 308LSi stainless steel and contribute to the advancement of this technology for industrial applications.

Abstract: SACM 645 nitriding steel is a commercial Cr-M0-Al medium carbon low alloy steel. Due to its good balance of strength, toughness and wear resistance the steel has been widely used for several general-purpose parts. Hot forging is a heat treatment method commonly used to increase the hardness of steel. The temperature and strain rate used in hot forging of steel results in changes in grain shape and size through a mechanism known as recovery, recrystallization and grain growth. There are common problems such as defect, net shape and cracked. The designer lacked of knowledge and understanding of the behavior of materials in hot forging process. This research aimed to study material properties under Hot forging at high temperature and effect of times annealing. Experiment, it was found that at 5 temperature levels, which were 850, 950, 1,050, 1,150 and 1,200 °C and annealing test in furnace temperature constant 800°C, holding time in furnace for 6 different times (1-6 hour). Therefore hot forging and the annealing test after hot forging concluded low temperatures, annealing time less result in small grain sizes and high hardness values. On the other hand, the higher temperature, annealing time long the larger the grain size and the lower the hardness. Consequently, the designer can use the information to improve the hot forging process, annealing determines the material properties of the finished products to the design of the part fabrication process.

Abstract: Zinc sol deposited via dip coating on Fluorine-doped Tin Oxide (FTO) coated glasses were annealed at 450 °C in normal ambient to form ZnO layers. The effect of annealing durations, i.e. 30, 60, 90, and 120 min on their surface morphology, crystallinity, optical, electrical and Dye-Sensitized Solar Cells (DSSCs) performance were studied. The XRD analyses indicated the formation of wurtzite ZnO after 60 min of annealing. It is noted that the ZnO layers annealed at 60-120 min showed good crystal quality attributed to its sharp, narrow and strong diffraction peaks. Generally, ZnO layers with uniform thickness have been deposited on the FTO coated glasses. The thickness of ZnO layers decreased from 0.88, 0.78, 0.76, and 0.73 mm when the annealing duration increased from 30 to 120 min due to removal of hydrocarbons from the zinc sol. The O at. % increased with annealing duration, indicating that more oxygen reacted with zinc to form ZnO. The ZnO thin film annealed at 60 min had relatively low sheet resistance (9.6 W) with optical bandgap of 3.04 eV. This suggests that ZnO layers annealed at 60 min have the largest amount of oxygen vacancies that contributed electrons for charges transportation in the layers. Besides, the Room Temperature Photoluminescence (RTPL) analyses showed that the ZnO thin film annealed for 60 min showed I_UV/I_Vis ratio = 0.89, suggesting better crystal quality compared to shorter annealing duration.

Abstract: This study is concerned with the post-heat treatment of rotational friction welds. AISI 1030 carbon steel parts are welded by rotational friction welding (RFW). The welding process parameters include friction pressure (P1), friction time (T1); Forging pressure (P2), forging time (T2). During the friction phase, the rotational speed is 1450 rpm; after that, the welding parts is stopped immediately and pressed together. The weld samples will be annealed at 650 °C for 4 hours. The change in the properties of the material of a RFW weld joint such as hardness, tensile strength, bending strength as well as grain size when undergone a heat treatment process was investigated. The obtained results show that the annealing process strongly changes the mechanical properties through altering the microstructure of the weld. Particularly, the weld hardness and tensile strength decrease significantly while the bending strength and elongation increase as a result of the increase in grain size and uniformity of the phase distribution. The annealed weld has a hardness reduction of nearly 20% and a tensile strength reduction of about 24% compared to the original weld. The elongation in the tensile test increases from 1.1% for weld specimens to 2.54% for post-heat-treated welds. In the bending test, the maximum load before the appearance of cracks on the specimen increased by about 42% when comparing the post-heat and original weld specimens.