Papers by Keyword: Characterization

Abstract: Synchrotron monochromatic beam X-ray topography (SMBXT), synchrotron white beam X-ray topography (SWBXT) and high-resolution X-ray topography (HRXRT) were used to characterize a series of wafers sliced from two PVT-grown 4H-SiC boules under similar growth conditions. A unique spoke-shaped distribution of the threading screw/mixed dislocations (TSDs/TMDs) density map can be observed from wafers sliced from later stages of growth of both boules. Systematic sequential analysis of the SMBXT grazing incidence images and HRXRT reflection images of the wafers reveals the spoke patterns are formed due to continuous deflection process of TSDs/TMDs by thin layer of polytypes that propagate along step flow direction and expand vertically, leading to TSD density difference across the wafer. Regions with high TSD densities have higher growth rate, resulting in a ridge and valley structure. Generation of macrosteps in the valley regions due to regular step structure deflect more TSDs/TMDs that then form mixed type (Shockley+Frank) stacking faults.

Abstract: The performance and reliability of silicon carbide (SiC) devices are critically dependent on the quality of epitaxial layers which in turn are influenced by substrate properties. The accurate classification of epitaxial defects coming from substrate crystal defects and surface defects is critical since these can adversely affect device performance. In this paper, two new methods of defect characterization in substrates and epitaxial layers are presented utilizing photoluminescence (PL) spectrum and carrier lifetime. These methods can be used to study the evolution of defects from substrates to epi and to better predict Epi yields.

Abstract: This paper investigates the effect of DLTS measurement parameters on characterizing deep level defects in 4H-SiC Schottky barrier diode (SBD). By adjusting parameters such as the time window (t_W), pulse time (t_P), reverse voltage (U_R), and pulse voltage (U_P), the underlying mechanisms influencing defect peak positions, signal amplitudes, and peak broadening are analyzed. Experimental results reveal three deep level defects identified in 4H-SiC SBD: majority carrier traps T1 (E_C - 0.66 eV) and T2 (E_C - 1.0 eV), along with minority carrier trap T3 (E_V + 1.1 eV). Parameter settings not only influence defect characterization sensitivity and concentration calculations but also reveal the dynamics of carrier capture and emission. Through the thorough analysis of the DLTS signal and behavior under different DLTS measurement conditions, the electronic properties and concentration profiles of deep level defects in 4H-SiC epitaxial layers are determined.

Abstract: This work relates initially to the application of various chemical formulations on leather surfaces to function as water repellents. Efforts have been made to search for a nonfluorinated formulation because of the damaging health effects of fluorinated water repellents. The metal complex stearato chromic chloride, which was prepared in the laboratory, is the most suitable. A complete synthesis protocol is developed first. Characterization tests (ATR-FTIR, XRD) of the chemical were performed to confirm that the intended product was properly synthesized. Microscopic examination of the leather revealed that it was not damaged by the application of the formulation and retained its softness and ability to feel. The methods of application to leather are then described. Finally, the necessary tests of performance are completed. For the different types of leathers that are evaluated, stearato chromic chloride can be easily applied and used as a compatible, durable and permanent water repellent. When synthesized according to a given protocol, minimal repellent chemicals are present in the exhaust solution, thus safeguarding the environment against chromium toxicity.

Abstract: Under the current research project, the feasibility of reducing the carbon footprint of masonry restoration mortars was investigated, by means of replacing a part of cement with emery. A two-fold advantage is offered by following this strategy: (i) to develop more sustainable restoration mortars and (ii) to validate the use of a rock that can potentially offer greater resistance to depletion/ weathering. Emery, a naturally occurring rock was characterized via X-ray fluorescence and stereo microscopy. The reference mortar was prepared according to EN 196-1:2016, with a CEMII/B-M(P-LL)42.5R cement targeting a flow table spread of 12-16±1 mm (in accordance with EN1015-3:1999+A1). Consequently, (i) a 20% and (ii) a 50% CEMII replacement with corundum powder was materialized. The mean compressive strength was reduced, as originally intended, by approximately 50% for the 50% replacement, allowing the mortar to be used for restoration purposes, where natural, low strength materials are preferred, which not exceeding the strength of masonry stones. Interestingly, flexural strength did not fall drastically. A number of complications arise on setting the flow spread as the basic design parameter and discussion on mix design is elaborated upon and correlated with the 7-and 28-day strength tests (in accordance with EN1015-11:1999+A1). Furthermore, the pore structure of the surface of the specimens was investigated via stereo microscopy and interesting observations pave the way for more sustainable mortar design.

Abstract: The research consists of incorporating CTAB into the layers of the the bentonite structure, integrating acid-treated bentonite with cetyltrimethylammonium bromide (CTAB), and obtaining an organic material adsorbent. The physical and chemical properties of the sample modifications are identified by employing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric/thermal analysis (TGA/DTA). The bentonite used in this study was recovered from the Trebia deposit, located on the north-western flank of the Tidiennit massif in the Nador region (northeast Morocco). The composite developed in the present study is a practical adsorbent for the treatment of industrial wastewater. CTAB was successfully inserted into acid-activated bentonite, demonstrating intercalation processes through X-ray diffraction, FTIR, SEM, and TGA/DTA. The modified Bentonite structure showed increased interlayer space due to the introduction of molecules or ions. The TGA/DTA graphs confirmed the hydrophobic alteration of Bentonite, with reduced clay dehydration and a surfactant decomposing on the surface and interlayer spaces. Morphologically, CTAB formed large particles and cavities.

Abstract: Axial sliced samples from 4H-SiC boules grown by PVT method were characterized by lab-based X-ray topography systems. Valuable information about dislocation behaviors during crystal growth was revealed. TSD/TMD propagation during PVT growth was studied. The different TSD/TMD propagation directions inside and outside the facet region were identified as the direct cause of the reduced TSD/TMD density at the facet boundary on some c-plane wafers. A defect reduction mechanism was proposed based on this discovery. It was observed that TSDs/TMDs were emitted by a void structure formed during crystal growth, which explained the elevated TSD/TMD density in the center regions of some wafers. The formation mechanism of such defect is different from the previous studies and remains under investigation.

Abstract: Cellulose is an important structural material found naturally within the cell walls of plants that has recently been researched as a biodegradable, renewable, and non-toxic reinforcing agent used to improve properties for a variety of composite systems. Cellulose is usually derived from wood sources via acid hydrolysis. Bacterial cellulose (BC) is produced by bacteria proliferation using nitrogen, carbon, and oxygen sources, and is similar chemically to plant extracted cellulose. Compared to commercially available cellulose, BC has higher purity and increased hydrophilicity. In this work, banana peels are used as a carbon source for bacterial cellulose growth. The peels were heat treated to maximize sugar and carbon contents. In addition, BC derived from the banana peels doesn’t require any bleaching or chemical post-processing. In this research, BC derived from banana peels is synthesized, characterized, and analyzed for its physical, mechanical, and thermomechanical properties, as compared to commercial nanocellulose.

Abstract: Geopolymers offer a sustainable alternative to reduce reliance on Portland cement in construction. This study examines coal fly ash and rice husk ash as potential substitutes in geopolymer formulations. Microstructural tests, including chemical composition analysis (SNI 2049-3-2022), Density (SNI 1964-2008), FTIR, and SEM-EDS, were conducted to evaluate their properties. Chemical analysis showed that coal fly ash contains 90.55% silica (SiO₂) and less than 10% calcium oxide (CaO), categorizing it as Class F fly ash, while rice husk ash has 50.86% SiO₂ and 38.41% CaO, both comparable to cement. FTIR confirmed hydroxyl group presence through O-H stretching, while SEM-EDS revealed elements like silicon, aluminum, calcium, and metallic oxides, consistent with their surface morphology. The results demonstrate that coal fly ash and rice husk ash meet the pozzolanic element requirements necessary for geopolymer formation. Their chemical composition, supported by FTIR and SEM-EDS findings, highlights their potential as alternative cement substitutes in sustainable construction.

Abstract: This study explored eggshells as an eco-friendly and cost-effective material for synthesizing hydroxyapatite. The phase compositions and morphological structure of polylactic acid composite with and without co-doped hydroxyapatite addition via a melt blending approach were evaluated. Furthermore, the biodegradation profile of the polylactic acid composite in phosphate buffer solution was studied. The concentrations of PLA/HAp, PLA/7.5MgO-7.5ZnO, and PLA/12.5MgO-2.5ZnO samples, respectively, were examined in this study. The results of morphological evaluation showed a well-distributed irregular spherical phase of hydroxyapatite. Meanwhile, the co-doped hydroxyapatite phases have variations in sizes and shapes. The polylactic acid composites showed fractured, rough, and honeycomb surfaces with interconnected pores suitable for cell propagation and enhancement, and the elemental composition proved precipitation of apatite formation. Characteristics of absorption bands of the hydroxyapatite, magnesium, zinc, and polylactic acid were present, respectively. The XRD spectra confirmed the presence of crystalline and semi-crystalline structures with percent crystallinity of 48.57%, 56.64%, and 60.08%, respectively. Meanwhile, the addition of the co-doped hydroxyapatite results in shifts in the 2θ angles of the crystal phases. The biodegradation study revealed the beneficial role of reinforcing polylactic acid composite with biogenic hydroxyapatite and hybrid doped hydroxyapatite as fillers and their synergetic effect with the pH of 7.08±0.21, 6.63±0.46, & 7.28±0.44, the porosity of 52.26±7.29, 48.57±6.74, & 43.72±5.07 %, and the degradation rate (weight loss) of 51.83±7.03, 48.16±6.85, & 43.66±5.46, respectively. Findings revealed that the current study aligns with the sustainable biodegradable composite used in bone tissue repair and hence contributed towards sustainable material without polluting the environment.