Papers by Keyword: TEM

Abstract: The fabrication of high-quality 4H-SiC epitaxial layers for power semiconductor devices involves complex processes including bulk crystal growth, wafer slicing, polishing, and chemical vapor deposition (CVD) epitaxy with precise step-flow control on slightly off-cut Si-face substrates. Despite advances, intrinsic crystallographic defects such as threading dislocations, basal plane dislocations, and stacking faults remain significant challenges, propagating into epitaxial layers and degrading device performance and reliability. This study examines defect types and their impact on 4H-SiC wafers, emphasizing the transition from 150 mm to 200 mm substrates, which introduces increased defect densities and polytype inclusions. Comprehensive defect characterization using advanced microscopy, molten KOH etching, and electrical wafer sorting reveals strong correlations between physical defects—such as micropipes, carrot-like stacking faults, and triangular 3C-SiC inclusions—and device failures, particularly under reliability stress tests like High Temperature Reverse Bias (HTRB). The findings highlight the critical role of substrate quality, epitaxial growth conditions, and defect mapping in improving yield and device robustness. This work underscores the necessity of integrating multi-scale defect inspection and targeted reliability assessments to optimize 4H-SiC power device manufacturing and performance.

Abstract: It is well known that the work hardening process of low-carbon steels is highly dependent on the movement and accumulation of dislocations in the crystal grains, which affect the stress and strain magnitudes and their distribution. The aim of this paper is to explain the importance of dislocation movement and density on the temperature, i.e. stress and strain changes during cold plastic deformation of low-carbon steels. Therefore, tests were carried out in this paper using the methods of static tensile testing, thermography, digital image correlation (DIC) and microstructural analysis. The microstructure analysis was carried out using a light and transmission electron microscope (TEM). The transmission electron microscope analysis was performed in two different modes, the TEM and scanning TEM (STEM). The results of static tensile testing, thermography and digital image correlation (DIC) are related to the microstructural changes that occur during the work hardening process of low-carbon steel. At the moment of maximum work hardening (immediately before fracture), significant grain elongation and high dislocation density of low-carbon steel were observed.

Abstract: Austenitic stainless steels (ASSs) are characteristic with a combination of good mechanical and corrosion properties. Therefore, they are used in the primary circuits of nuclear power plants. Under the influence of a corrosive environment containing chloride ions and mechanical loading, the phenomenon of stress corrosion cracking occurs in ASSs. SCC can also be initiated by the surface condition of ASSs. Machining is usually the last stage of production, during which a significant deformed zone with high residual tensile stresses can be created, which can accelerate the initiation of stress corrosion cracking. Research is focused on analyzing the influence of final turning on microstructural changes of the surface-machined layer caused by various turning parameters (e.g.: cutting speed, feed, depth of cut, cutting tool geometry). No significant microstructure changes were observed between the samples by light microscopy, so we focused on transmission electron microscopy (TEM) on thin lamellas prepared using the focus ion beam (FIB) technique. TEM observation confirmed the presence of a deformed zone and a passivation layer. In the case of the sample that was turned with a higher feed and cutting speed, the passivation layer was discontinuous. Such a microstructural change can significantly affect the corrosion resistance of ASS.

Abstract: To generate both two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) at will in SiC polytype heterojunctions, simultaneous lateral epitaxy (SLE) method has been extended to form epilayers of alternating stacks of 4H-and 3C-SiC, which includes the first formation of single-domain 4H-SiC on 3C-SiC. The process starts with a spontaneous generation of mononuclear 3C-SiC on the atomically flat wide terrace on 4H-SiC, which expands parallel to the basal plane to form a single-domain 3C-SiC layer having the coherent interface with the underlying 4H-SiC layer. Step-controlled epitaxy is then applied using the adjacent 4H-SiC steps to grow an alternative 4H-SiC layer on top of the 3C-SiC surface, forming another coherent interface. The crystal structure, the interface structure, and the carrier distribution of this stacked epilayers was analyzed. Finally, it is demonstrated that 2DEG occurs at the coherent interface between the 3C-SiC Si-and 4H-SiC C-faces and 2DHG at the 3C-SiC C-and 4H-SiC Si-faces.

Abstract: The lightweight composition, non-magnetic nature, and machinability of aluminum alloy A356 make it an important material in many industries due to its significant mechanical properties such as strength, ductility, fatigue resistance, and castability. Aluminium alloy forms an oxide layer when exposed to air. The microstructure of this alloy plays a critical role in determining its mechanical behavior. This study utilized aluminum alloy A356, composed of 92.05% aluminum, 7% silicon, 0.35% magnesium, 0.20% copper, 0.10% manganese, and 0.10% zinc. This alloy exhibits extremely high corrosion resistance, similar to stainless steel, with a melting point of 650°C. The study examines multi- component (mainly Al with Si) A356 containing small amounts of Mg, Cu, Mn, and Zn for their complex microstructural behavior. It includes observations using techniques such as optical microscopy and X-ray diffraction (XRD). This research was carried out to investigate different areas of the same metal’s microstructure and to discover the influence of cooling rates during the solidification process. The findings revealed that there are dissimilarities between the central parts and outer areas, as well as similarities between the two side portions. Also, this study highlights processing conditions’ impact on the material response while looking at heat transfer rate effects during solid-state transformation. The findings of this study highlight the presence of distinct microstructures (dendritic and equiaxed structures) across different sections of the cast Aluminum alloy A356. These findings contribute to a better understanding of the microstructure-property relationship of Aluminum alloy A356, assisting in improvising design and manufacturing processes for enhanced performance.

Abstract: Analysis of forward bias degradation reduction of 4H-Silicon Carbide (4H-SiC) PiN diodes on bonded substrates was performed. In the analysis, cathodoluminescence (CL), photoluminescence imaging (PL imaging), and transmission electron microscope (TEM) were used. Under high forward bias stress, the Shockley-type stacking fault (SSF) does not expand into the transferred layer of the bonded substrate, while in the monocrystalline substrate, the SSF expands below the epilayer/substrate interface. The basal plane dislocation (BPD) within the transferred layer does not expand to the SSF. The transferred layer has the effect of suppressing the expansion of SSFs. This effect can be caused by hydrogen implantation for wafer splitting to produce bonded SiC substrates.

Abstract: The composites based on reactive metals (Zr, Ta, Nb, Ti) sheets explosively welded to stainless steel plates were investigated using X-ray synchrotron radiation, TEM and SEM to characterize phase transformations in near-the-interface layers. SEM and TEM investigations of the solidified melt regions unveiled amorphous and nanocrystalline non-equilibrium phases of variable chemical compositions, incorporating elements from the joined components. Phase analysis in layers near the interface carried out using high-resolution synchrotron radiation show predominantly reflections coming from the main elements of parent sheets/plates. Nevertheless, a closer look at the diffraction patterns shows the presence of reflections coming from the phases based on the two-component equilibrium phase diagrams. The measurements performed at the interface, but including only the steel plate, revealed significant amounts of α-Fe, γ-Fe and ε-Fe phases. Their appearance was attributed to the high pressure and fast cooling rates, which promoted a martensitic transformation in steel.

Abstract: In this study, a catalyst based on Montmorillonite clay was implemented for carbon nanotubes (CNTs) synthesizing. The kaolinite clay was used as a supporting material for iron-cobalt bimetallic catalytic nanoparticles. The CNTs have been synthesized by using atmospheric chemical vapor deposition (APCVD). To assess the quality of preparation both the catalyst and CNTs have been characterized by different techniques. The chemical bonding and interactions were verified by FT-IR. The general overview of microstructure was examined using SEM, while, the detailed structure and morphology were examined by HR-TEM, in addition to thermal analysis (DTA); surface area (BET); X-ray fluorescence (XRF), Raman spectroscopy, and XRD analysis. The results revealed that; Fe₂O₃ and Co₃O₄ NPs were uniformly assembled on the clay nanoplatelets. The specific BET surface area of the clay and catalyst was determined to be 46.12 and 57.06 m²/g respectively. Also, from XRD, the peaks at 26° and 42.7° confirm the presence of CNTs. The FTIR absorption bands, D, G, and G^\ bands from the Raman spectrum confirm the hexagonal structure of the CNTs. The obtained results prove the high quality of CNTs preparation.

Abstract: At room temperature, zinc oxide (ZnO) nanoparticles co-doped with praseodymium (Pr) and copper (Cu) using a low-cost chemical co-precipitation method. As a capping agent, polyvinylpyrrolidone (PVP) was used for synthesizing the nanosamples, and a pH of 9 was maintained. The synthesis of nanosamples was then characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and photoluminescence (PL). X-ray diffraction studies revealed the wurtzite hexagonal structure of ZnO, and no impurity peaks were found. The particle size obtained from XRD studies was 32 to 46 nm and is well supported by TEM. SEM micrographs demonstrated the surface morphology of the samples. With Cu dopant concentration, Pr-doped ZnO nanosamples exhibited enhanced luminescence properties.

Abstract: The challenge in this research is the producing of nanoparticle superconductor compound. The benefit of nanoparticle is making the improving of the superconductor compound. The Bi₂Sr₂Ca₂Cu₃O₁₀ (Bi-2223) compound prepared by Co-precipitation method at different sintering temperatures (600, 700, 850 °C) (20 hrs) with pH value (7). The electric resistivity of samples measured under liquid helium closed cycle cryogenic system. The TEM estimation of sample prepared by Co-precipitation recognized the range of particles size is about (22 - 48nm) at sintering temperature (600 °C). The range of nanoparticles size is in about (65-112 nm) at sintering temperature (700 °C) and (80-124) nm at sintering temperatures (850°C). The critical temperature of sample at sintering temperatures (700, 850 °C) was about (109 ,112) K respectively The crystal structure confirmed by using X-ray diffraction, these peaks were found to be well indexed by the tetragonal phase of Bi-2223. It was defined the successful of this method is a function to presence of full properties for superconductor compound like Bi-2223 system. .