Papers by Keyword: SEM

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 has been studied how SiO₂ nanoparticles affect the mechanical and electrical properties of low-density polyethylene (LDPE). The tensile strength, microstructural features, and AC breakdown characteristics of LDPE containing silicon dioxide (SiO₂) nanoparticles were investigated in this work. The concentrations of filler were adjusted to 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 3.0 wt%, and 4.0 wt%. The samples were prepared by using Haake machine and shaped by compression moulding, and a sphere to sphere electrode arrangement was used for AC breakdown testing. The breakdown reliability was assessed using the Weibull distribution. Molecular interaction and nanoparticle dispersion were analysed using Raman spectroscopy and scanning electron microscopy (SEM), respectively. The findings demonstrated that mechanical strength and breakdown voltage increases with filler concentration, reaching a maximum at 2.0 wt% SiO₂. When compared to pure LDPE, the AC breakdown voltage increased by 27.54% at this concentration. SEM pictures showed a homogeneous dispersion of nanoparticles, while Raman spectra verified improved interfacial bonding. AC breakdown voltage above 2.0 wt% shows decrease value due to agglomeration of nanoparticles. According to this study, LDPE insulation performance is best enhanced by 2.0 wt% SiO₂.

Abstract: Aluminum 7075 alloy has excellent mechanical properties and exhibits good ductility, strength, toughness, and fatigue resistance. The addition of oxide additives to cast Al7075 has also enhanced tribological properties apart from these properties. In this study, the tribological properties of cast Al7075 with the addition of 2.5% zirconium oxide (Zirconia) and titanium oxide (Titania), produced in a resistance melting furnace followed by die casting, were investigated. The wear test is conducted using a pin-on-disc wear testing machine, as specified by ASTM G99. The comparison is based on two independent process variables: a fixed sliding distance of 1000 m for all samples and applied load variations are 10, 20, 30, and 50 N with 500, 700, and 1000 revolution speeds. Using a scanning electron microscope (SEM), the wear surface morphology of the samples was analyzed, and the wear test results were compared. Further, it was found that oxides added samples showed less wear loss compared to as-cast Al7075 samples. The abrasion mechanism for as-cast Al7075 samples is identified as ploughing and deep wear tracks, while for Al7075 samples with Zirconia and Titania addition, it is characterized by delamination and shallow wear marks that show less wear.

Abstract: Fatigue damage is one of the key degradation mechanisms affecting the service life and reliability of aluminum alloys in a wide range of technical applications. The present study focuses on the fracture mechanisms of aluminum alloys under cyclic loading, with a view to the initiation and analysis of fatigue crack propagation in the context of the microstructural characteristics of the material. Special attention was paid to the influence of grain morphology, distribution and type of intermetallic phases, as well as the presence of casting defects on the initiation and development of cracks. Fatigue experiments were performed on a selected Al-Mg alloy of the EN AC 51200 type for the use of three-point bending loading. The results show that the key factors affecting the fatigue behavior are the size and distribution of precipitates, the nature of the interfaces between the phases and the occurrence of microcracks initiated mainly in areas of stress concentration. The knowledge gained contributes to a deeper understanding of fatigue mechanisms in aluminum alloys and provides a basis for their optimization in terms of composition and technological processing in order to increase their resistance to fatigue failures.

Abstract: This study investigates the effect of nano-TiO₂ (nTiO₂) reinforcement on the corrosion behaviour of cold work aluminium composites in a 0.3M H₂SO₄ environment. Al-nTiO₂ composites were fabricated with 0%, 1%, 2%, 3%, and 5% weight fractions of nano-TiO₂ using stir casting. The corrosion performance was evaluated using potentiodynamic polarization (PDP), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The results show that increased TiO₂ content enhances corrosion resistance up to 5%, particularly at lower cold-working loads. Sample J (5% TiO₂, 2 kg load) exhibited the lowest corrosion rate (0.09474 mm/yr) and highest polarization resistance (809.58 Ω). SEM/EDX analysis revealed denser passive layers and reduced sulfur compound deposits in higher TiO₂ composites. This work highlights the effectiveness of nano-TiO₂ in improving electrochemical stability and corrosion morphology of aluminium composites in acidic environments.

Abstract: Machining of extremely hard materials with complex shapes are very difficult in traditional processes due to which Electro Discharge Machining (EDM) is being used in many industries mainly aerospace, medical, automotive etc. EDM uses a series of sparks generated between tool-electrode and workpiece-anode to erode materials. These sparks are generated continuously inside the dielectric fluid and produce extreme heat which melt and vaporize the material. Pumping action of the dielectric fluid helps in removing excess material from machined surface. In this experimental work, the impact of input parameters namely current, pulse on time and voltage on two performance features like material removal rate (MRR) and surface roughness (Ra) have been investigated. Incoloy 800HT is used as work-piece and copper as tool material. Incoloy 800HT is an iron-nickel-chromium-based superalloy known for its ability to retain mechanical properties at high temperatures and its exceptional resistance to oxidation, carburization, and corrosion. Taguchi based grey analysis is used the multi-criterion decision-making (MCDM) method for optimization. From the analysis it is revealed that current has the most significant influence on both material removal rate (MRR) and surface roughness (SR), with higher current increasing MRR but deteriorating Ra. Micrograph analysis of machined surface is performed using scanning electron microscope (SEM).

Abstract: Recently, there has been a growing interest in replacing synthetic fibres with natural fibres in polymer composites due to environmental concerns. This study examined the fibres from the Newbouldia laevis plant for their potential use in lightweight polymer composites, particularly in applications sensitive to strength and temperature. The fibres were extracted from the plant's stem, and various properties such as density, moisture content, moisture regain, and diameter were measured. Chemical analysis revealed the percentages of cellulose, hemicellulose, lignin, extractives, and ash present in the fibres. Furthermore, Fourier transform infrared analysis confirmed the presence of these essential components. Scanning electron microscopy images showed the rough surfaces of the fibres, which enhance the adhesion between the fibre and matrix during the production of polymer composites. Energy dispersive X-ray analysis identified carbon and oxygen as the main elements in the fibres. Thermal analysis provided insights into the thermal stability and maximum degradation temperatures of the fibres. Lastly, a single fibre tensile test was performed to evaluate the tensile strength, elastic modulus, and elongation at break of the fibres using Weibull distribution statistical analysis. The results of this study indicate that Newbouldia laevis fibres could be a promising reinforcement for lightweight polymer composites in strength and temperature-sensitive applications.

Abstract: Cu₃SnS₄ films were grown on glass substrates via method of spin coating, followed by annealing at 550 °C in a furnace under H₂S:Ar (1:9) sulfur rates of 30 and 40 sccm for 15, 30, and 60 minutes. The effect of the sulfur rate and annealing time on the structural, morphological, and optical behaviors of the samples was systematically investigated using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), photoluminescence (PL), Hall effect, and UV-Vis spectroscopy. The XRD patterns revealed that all the Cu₃SnS₄ samples had a polycrystalline structure. The crystallite size, dislocation density, interplaner distance, micro-strain, and crystallite number of the Cu₃SnS₄ samples were calculated from the XRD spectra. Among all the samples, the CTS sample annealed for 15 minutes under a 30 sccm H₂S:Ar (1:9) gas flow showed the best crystalline structure. The surface morphology of the samples showed spherical micro-crystal formations. Analysis of the Cu₃SnS₄ samples indicated that the surfaces were composed of valley and peak regions. The valley regions appeared relatively smooth, while the peak regions displayed a crystal structure with specific orientations. When examining the energy band gap values, it is observed that the energy band gap of the films increases significantly with the increase in sulfur flow rate. PL analysis revealed emission peaks at approximately 1.41 eV and 1.80 eV, along with broad emission bands at 549 nm, 567 nm, 689.42 nm, and 882.6 nm. An increase in sulfur content led to a reduction in peak intensity, which is attributed to conduction band fluctuations and the formation of structural defects. The carrier concentration of the samples is found to be on the order of 10¹⁷ cm⁻³ and 10¹⁸ cm⁻³, which is more appropriate for thin-film solar cells (TFCSs).

Abstract: This paper focuses on the deposition and characterization of tungsten carbide (WC) hard thin films using the plasma jet deposition technique, with special emphasis on their hydroabrasive wear behavior. Tungsten carbide coatings are recognized for their exceptional properties such as high hardness, excellent wear and corrosion resistance, and chemical and thermal stability. The plasma jet deposition technology allows the formation of dense layers, well adhered to the substrate, with precise control over the thickness and microstructure of the deposited layer. The study analyzed process parameters, such as spray distance and particle velocity, which influence the microstructure and performance of the deposited layers. The characterization of the layers was carried out by methods such as scanning electron microscopy (SEM) and the composition was determined with the help of the EDX probe. The tribological properties of the WC layer were also investigated.

Abstract: This study explores the potential of self-healing concrete with bacteria encapsulated in calcium lactate and expanded clay (LECA) to enhance the durability and strength of concrete structures. The effect of encapsulating Lysinibacillus sphaericus bacteria in LECA on the mechanical properties of concrete was investigated, including compressive and tensile strength. Calcium lactate acts as a precursor and nutrient source for the biomineralization process through Microbially Induced Calcium Carbonate Precipitation (MICP). Experimental results demonstrate that concrete with bacteria encapsulated in LECA exhibits a significant increase in compressive strength compared to conventional concrete and concrete containing non-encapsulated bacteria. This increase is attributed to the protection provided by LECA to the bacteria and calcium lactate, promoting their self-healing activity and improving the concrete's ability to withstand loads. An increase in compressive load was observed for design DR-5 compared to DR-0 (control), with increments of 3.40%, 0.21%, and 6.92% on days 7, 14, and 28, respectively. However, challenges were identified regarding tensile strength, as design DR-5 was initially lower than design DR-0 by 24.25% and 19.51% on days 7 and 14, respectively. Nonetheless, on day 28, design DR-5 surpassed the control design by 1.45%. This study concludes that the encapsulation of bacteria in LECA, along with calcium lactate as a nutrient source, is a promising strategy for enhancing the performance of self-healing concrete, opening new avenues for research and applications in sustainable construction.