91 research outputs found
Process Characterization and Optimization of Roll-to-roll Plasma Chemical Vapor Deposition for Graphene Growth
Get PDFThe main purpose of this thesis is to develop an efficient and scalable technique for depositing graphene on various flexible substrates. Hence, a custom-built roll-to-roll capacitively coupled plasma chemical vapor system for deposition of graphene on flexible substrates is thoroughly described in this work. Graphene quality on Cu foil has been optimized for a roll-to-roll process using statistical optimization methods. Since graphene quality and uniformity depend on plasma input parameters, such as plasma power, gas pressure, and the gas mixture used, effects of input parameters have been explored to maximize graphene quality, as quantified by Raman spectroscopy using the I D/IG intensity ratio. Furthermore, in situ optical emission spectroscopy has been developed and utilized to determine the effects of several plasma species on graphene growth and quality. OES results demonstrate that graphene quality on Cu foil increases with CH radical emission; however, O and H atoms, C2 and CN radicals, and Ar + ion all negatively correlate to graphene quality. Results aid in developing a conceptual model for a graphene growth mechanism that indicates the adverse impact of ion bombardment on graphene quality in the low-frequency capacitively coupled plasma. However, the existence of active carbon species in the plasma, such as CH radical, accelerates the growth process and leads to moderate-quality graphene deposition on Cu foil at web speeds reaching as high as 1 m/min. Plasma plays a crucial role in heating the foil for graphene deposition in the roll-to-roll process, without the need of a supplemental heating source. Thus, accurate measurement of the translational gas temperature in the plasma is vital, since gas temperature strongly influences the foil temperature distribution, which, in turn, affects graphene growth kinetics. Optical emission spectroscopy (OES) is used to measure the rotational temperatures of N2+ (B-X), CN (B-X) and H2 (d3Πu → a3 Σg+), and to determine accurate translational gas temperatures. Power dissipation in the plasma is also measured to understand gas temperature variation for the experimental input conditions. Thus, the effects of plasma power, gas pressure and the addition of nitrogen, oxygen and methane gases on power dissipation and gas temperature in a hydrogen plasma are assessed. The rotational temperatures measured from the gas species have different values due to the non-equilibrium nature of the plasma. Graphene quality significantly depends on gas pressure since our plasma roll-to-roll system is sustained by a capacitively coupled plasma that operates in two modes, depending on the gas pressure and discharge gap. The modes are identified as alpha and gamma modes, and are sustained by volume ionization and secondary electron emission processes, respectively. Up to our knowledge, the presence of both modes at 80 kHz plasma frequency has not previously been reported. Thus, a detailed characterization of argon plasma is attempted to determine the underlying plasma physics of the low-frequency plasma. Due to strong ion bombardment on the electrodes, the gamma mode coexists with the alpha mode, resulting in a hybrid mode. The voltage square waveform is found to play an important role in sustaining this hybrid mode. The hybrid mode exists at low gas pressures of 5.5 and 9.5 mbar in the plasma set power ranges from 300 to 1100 W. However, the plasma at 13.8 mbar gas pressure transforms from hybrid to gamma mode when the plasma set power is beyond 750 W due to increased secondary electron emission processes. The emission spectra measured from optical emission spectroscopy reveal the presence of non-Ar species in the gamma mode, such as H, CH, and C2. These species are sputtered from the graphite electrodes by ion bombardment to produce secondary electrons that sustain the gamma discharge. Results show the possibility of sustaining the hybrid mode at a low plasma frequency using a tailored waveform. As a results of these plasma characterization tools, we report a continuous and rapid roll-to-roll deposition of thin graphite film on Cu foil. The composition of the Ar/H2/CH4/N2/O2 plasma plays significant role in the successful direct growth of the thin graphite film on copper foil. Optical emission spectroscopy is used to characterize the plasma during graphite synthesis and show that the addition of N 2 enhances the plasma reactivity, and O2 was found to increase the deposition rate of the graphite film. The film was characterized by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The described large-scale graphite production can produce a graphite-Cu-graphite structure or uniform thin graphite films for thermal management applications in electronics devices. (Abstract shortened by ProQuest.
Enhanced Performance of a Thermoelectric Module with Heat Pipes for Refrigeration Applications
No full textThermoelectric module (TEM)-based coolers are gaining traction as compact, portable refrigeration solutions for storing medicine, beverages, and food. However, their adoption has been limited by relatively low cooling power and efficiency. This study demonstrates the importance of heat transfer in enhancing the coefficient of performance (COP) of TEMs through optimizing their boundary conditions. Among the three boundary conditions evaluated, the most effective involved integrating heat pipes (HPs) with a cooling fan on both sides of the TEM. This configuration significantly improved thermal management, enabling the system to achieve a COP of 0.53, with a cooling rate of 26.26 W and a cold-side temperature of 278.5 K. The enhanced heat extraction from the hot side, reaching 61.94 W, reduced the hot-side temperature to 305.6 K and decreased the overall thermal resistance, confirming the critical role of active heat dissipation. Moreover, placing a cooling fan on the HPs is crucial for facilitating efficient heat transfer from the hot side with a lower thermal resistance, as confirmed via thermal resistance analysis. Furthermore, a prototype refrigerator based on the TEM with HPs was built and tested indoors and outdoors with a COP of 0.45, a cooling rate of 21.97 W, and a cold-side temperature of 271.0 K. This study shows that the COP of TEMs can be increased by applying HPs to reduce the total thermal resistance of the TEM sides. Further optimization of TEM-based refrigerators holds promise for improving their performance in sustainable, small-scale cooling applications
Analisis Makna dan Jenis Makna dalam Cerita Pendek “الصندوق” Karya Majed Sulaiman
Get PDFThis study analyzes the meanings in the short story “الصندوق” (The Box) by Majed Sulaiman using a semantic approach. The research applies a descriptive qualitative method based on the theories of Leech, Palmer, and Chaer, focusing on lexical, denotative, connotative, and contextual meanings. The results show that each word in the story carries deep meaning. The word “صندوق” (box), for example, literally means a container but symbolically represents love, memory, and family bonds. The author delivers moral values through simple yet meaningful language. This study concludes that semantic analysis helps reveal the moral and emotional messages in Arabic literary works, especially in children’s stories
Mid-IR Absorption Cross-Section Measurements of Hydrocarbons
No full textLaser diagnostics are fast-response, non-intrusive and species-specific tools perfectly applicable for studying combustion processes. Quantitative measurements of species concentration and temperature require spectroscopic data to be well-known at combustion-relevant conditions. Absorption cross-section is an important spectroscopic quantity and has direct relation to the species concentration. In this work, the absorption cross-sections of basic hydrocarbons are measured using Fourier Transform Infrared (FTIR) spectrometer, tunable Difference Frequency Generation laser and fixed wavelength helium-neon laser. The studied species are methane, methanol, acetylene, ethylene, ethane, ethanol, propylene, propane, 1-butene, n-butane, n-pentane, n-hexane, and n-heptane.
The Fourier Transform Infrared (FTIR) spectrometer is used for the measurements of the absorption cross-sections and the integrated band intensities of the 13 hydrocarbons. The spectral region of the spectra is 2800 – 3400 cm-1 (2.9 – 3.6 μm) and the temperature range is 673 – 1100 K. These valuable data provide huge opportunities to select interference-free wavelengths for measuring time-histories of a specific species in a shock tube or other combustion systems. Such measurements can allow
developing/improving chemical kinetics mechanisms by experimentally determining reaction rates.
The Difference Frequency Generation (DFG) laser is a narrow line-width, tunable laser in the 3.35 – 3.53 μm wavelength region which contains strong absorption features for most hydrocarbons due to the fundamental C-H vibrating stretch. The absorption cross-sections of propylene are measured at seven different wavelengths using the DFG laser. The temperature range is 296 – 460 K which is reached using a Reflex Cell. The DFG laser is very attractive for kinetic studies in the shock tube because of its fast time response and the potential possibility of making species-specific measurements.
The Fixed wavelength helium-neon (HeNe) laser at 3.39 μm is used to measure the absorption cross-section of the fuels mentioned above. The dependence on temperature, pressure and bath gas (helium, argon and nitrogen) is also examined. The temperature and pressure ranges of this study are 296 – 800 K and 250 – 1000 Torr, respectively. These are the first measured cross-sections at HeNe laser wavelength that are applicable at combustion-relevant conditions
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A Heat Transfer Model for Graphene Deposition on Ni and Cu Foils in a Roll-to-Roll Plasma Chemical Vapor Deposition System
Get PDFAbstract
High-throughput production is a major bottleneck for integration of graphene-based technologies in existing and future applications. Here, a semi-empirical heat transfer model is developed to optimize large-scale deposition of graphene on Ni and Cu foils in a roll-to-roll (R2R) plasma chemical vapor deposition (CVD) system. Temperature distributions in Ni and Cu foils during deposition are recorded with in situ temperature measurements using near-IR optical emission spectroscopy. The model indicates that foil movement significantly affects the temperature distribution and the cooling rate of the foil. Consequently, graphene growth on Cu is limited to lower web speeds for which the foil temperature is higher, and the residence time in the plasma is longer. On the other hand, graphene can be deposited on Ni at relatively higher web speeds due to moderately high diffusion rate of carbon in Ni and increased cooling rates up to 20 K/s with higher web speed. Critical limitations in the production rates of graphene using R2R CVD process exist due to significant effects of web speed on the temperature distribution of the substrate. The thermal analysis approach reported here is expected to aid in enhancing the throughput of graphene production in R2R CVD systems
A Heat Transfer Model for Graphene Deposition on Ni and Cu Foils in a Roll-to-Roll Plasma Chemical Vapor Deposition System
No full textTHERMAL ANALYSIS AND OPTIMIZATION OF GRAPHENE DEPOSITION IN A ROLL-TO-ROLL PLASMA CVD PROCESS
No full textCorrection to:PTH1 receptor agonists for fracture risk: a systematic review and network meta-analysis (Osteoporosis International, (2025), 10.1007/s00198-025-07440-1)
Get PDFThe original online version of this article was revised: In this article, the author Olivier Bruyère's name was missing; the order in which the authors appeared in the author list was incorrectly given as: Charlotte Beaudart 1,2 · Nicola Veronese 1,3 · Jonathan Douxfils 4,5,6 · Jotheeswaran Amuthavalli Thiyagarajan 7 · Francesco Bolzetta 8 · Paolo Albanese 8 · Gianpaolo Voltan 8 · Majed Alokail 9 · Nicholas C. Harvey 1,10 · Nicholas R. Fuggle 1,10 · René Rizzoli 1,11 · Jean‑Yves Reginster 1,9 where it should have been: Charlotte Beaudart 1,2, Nicola Veronese 1,3, Jonathan Douxfils 4,5,6, Jotheeswaran Amuthavalli Thiyagarajan 7, Francesco Bolzetta 8, Paolo Albanese 8, Gianpaolo Voltan 8, Majed Alokail 9, Nicholas C. Harvey 1,10, Nicholas R. Fuggle 1,10, Olivier Bruyère 1,11, René Rizzoli 1,12, Jean-Yves Reginster 1,9 In this article, the affiliation “Research Unit in Public Health, Epidemiology and Health Economics, University of Liege, Liege, Belgium” for Olivier Bruyère was missing. The original article has been corrected.</p
Studies on the reproductive, cytological and biochemical toxicity of Ginkgo biloba in Swiss albino mice
No full textTitle: Studies on the reproductive, cytological and biochemical toxicity of Ginkgo biloba in Swiss albino mice
Author(s): Al-Yahya AA (Al-Yahya, Abdulaziz A.), Al-Majed AA (Al-Majed, Abdulhakeem A.), Al-Bekairi AM (Al-Bekairi, A. M.), Al-Shabanah OA (Al-Shabanah, O. A.), Qureshi S (Qureshi, S.)
Source: JOURNAL OF ETHNOPHARMACOLOGY Volume: 107 Issue: 2 Pages: 222-228 Published: SEP 19 2006
Department: Pharmacology and Toxicology
Abstract: Ginkgo biloba (an herbal product), used as a folkloric medicine in the treatment of dementia, was evaluated for its effects on reproductive, cytological and biochemical toxicity in male Swiss albino mice. The mice were treated with different doses (25, 50 and 100 mg/kg/day) of the aqueous suspension of Ginkgo biloba for 90 days by oral gavage. The following parameters were evaluated: (1) reproductive organ weight; (2) motility and content of sperms; (3) spermatozoa morphology; (4) cytology of the testes chromosomes; (5) study on reproduction; (6) biochemical study on proteins, nucleic acids, malondialdehyde (MDA) and nonprotein sulfhydryl (NP-SH). The treatment caused significant changes in the weight of caudae epididymis, prostate, chromosomal aberrations, rate of pregnancy and pre-implantation loss. However, the percent motility, sperm count and morphology of spermatozoa were not affected. Our study on biochemical parameters showed depletion of nucleic acids, NP-SH and increase of MDA, which elucidated the role of free radical species in the induced changes in testis chromosomes and the reproductive function. The exact mechanism is not known, however, the activation of GABA, glycine and glutamate under the influence of Ginkgo biloba and its constituents might have generated free radicals and depleted cellular glutathione by calcium influx and membrane depolarization. The observed toxicity is attributed to the toxic constituents (ginkgolic acids, biflavones, cardanols, cardols, bilobalides and quercetin) of Ginkgo biloba. Our results warrant careful use of Ginkgo biloba as a remedy for impotence and/or erectile dysfunction. (c) 2006 Elsevier Ireland Ltd. All rights reserved
Modeling of a Roll-to-roll Plasma CVD System for Graphene
Get PDFGraphene is a 2D carbon material that has extraordinary physical properties relevant to many industrial applications such as electronics, oxidation barrier and biosensors. Roll-to-roll plasma chemical vapor deposition (CVD) has been developed to manufacture graphene at large scale. In a plasma CVD chamber, graphene is grown on a copper foil as it passes through a high-temperature plasma region. The temperatures of the gas and the copper foil play important roles in the growth of graphene. Consequently, there is a need to understand the temperature and gas velocity distributions in the system. The heat generated in the plasma creates a thermal field that enhances natural convection inside the system enclosure. The analysis of temperature and fluid flow of hydrogen was carried out numerically using FLUENT, a commercial computational fluid dynamics package. A three-dimensional model has been built including the heat source from the plasma, natural convection, radiation and simple gas reactions. The plasma is generated between two rectangular parallel plates whose major axis can be oriented either vertically or horizontally. The temperature and flow for the vertical plasma electrodes configuration exhibit higher values than the horizontal configuration due to increased interactions of the heated plates with the buoyancy-driven flow. Furthermore, the presence of the copper foil that is used as the substrate for graphene deposition decreases the temperature and velocity in the adjacent regions because the copper foil acts as a fin and impedes fluid flow, respectively. Finally, adding methane as a mixture with hydrogen increases the gas temperature in the plasma region due to the lower thermal conductivity of methane. The numerical results help in understanding the temperature and the flow in the roll-to-roll CVD plasma system that makes it suitable for modeling graphene production for the purpose of optimizing manufacturing process conditions
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