Process Characterization and Optimization of Roll-to-Roll Plasma Chemical Vapor Deposition for Graphene Growth

Large-scale production of graphene and other nanostructures remains a hindrance to their adoption in the semiconductor and materials manufacturing industries. The 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 ID/IG intensity ratio. Furthermore, in situ optical emission spectroscopy (OES) 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. Nevertheless, graphene quality measured from Raman spectroscopy declines significantly with increased Cu foil velocity (web speed) in the roll-to-roll process, inducing a critical limitation in current production rates for roll-to-roll CVD nonmanufacturing techniques. With the aid of heat transfer modeling of the moving foil, we show that the graphene quality decrease is primarily due to Cu foil temperature decline with increased web speed. The Cu foil temperature distribution is determined both experimentally and numerically during roll-to-roll graphene growth as a function of web speed, plasma power and plasma length. The maximum Cu foil temperature in the plasma rises with increased plasma power due to increased heating from the plasma. However, the maximum Cu foil temperature decreases with increased web speed caused by higher heat advection by the moving foil. In addition, shortening the plasma slit (by decreasing the electrodes length) cools the Cu foil temperature and diminishes its temperature uniformity in the plasma region. Consequently, graphene crystallization, identified using Raman spectroscopy, improves with higher Cu foil temperatures. As a result, an optimum condition is defined by raising the plasma power, lowering the web speed and increasing the plasma region length, which consistently produces high-quality graphene on Cu foil. The throughput of graphene production can be increased by utilizing Ni foil as a substrate since carbon solubility in Ni is higher than in Cu. Thus, the effects of web speed and plasma power on Ni foil temperature distribution are evaluated during graphene deposition in the roll-to-roll process. Furthermore, the Ni foil cooling rate, which strongly affects carbon atom segregation from Ni after the growth process, is derived from the heat transfer model. Plasma power has negligible effects on the cooling rate, whereas the web speed has a significant impact on the cooling rate. Consequently, graphene has comparable quality at different plasma powers, whereas web speed controls graphene quality, particularly with regards to uniformity and thickness. Our work highlights the benefits of using Ni foil in a roll-to-roll process for graphene deposition at higher web speeds and lower substrate temperatures, rather than using Cu foil, which requires significantly more substrate heating. 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 → a3Σg +), 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 (N2), oxygen (O2) and methane (CH4) gases on power dissipation and gas temperature in a hydrogen (H2) plasma are assessed. The rotational temperatures measured from the gas species have different values due to the non-equilibrium nature of the plasma. Of the gases measured, the rotational temperature of N2 + is most accurate in representing the translational gas temperature. These results improve the understanding and control of the thermochemical environment for carbon nanostructure growth in the plasma chemical vapor deposition processes. 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 rollto- 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 N2 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 (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The described large-scale graphite production can produce a graphite-Cugraphite structure or uniform thin graphite films for thermal management applications in electronics devices. Graphene growth optimization, substrate thermal analysis, and plasma characterizations are used to control graphene mass-production in a custom-built roll-to-roll plasma CVD system. These techniques are addressed to provide a route for nanomanufacturing of graphene and graphite on Cu and Ni foils. These methods aid in understanding the correlations between process conditions and graphene quality, as well as the interactions between the plasma and the substrate, to yield high-throughput production of high-quality graphene. The procedure outlined here can be applied to efficiently scale-up the production of other micro- and nanomaterials

New generation of electrochemical immunoassay based on polymeric nanoparticles for early detection of breast cancer

Screening and early diagnosis are the key factors for the reduction of mortality rate and treatment cost of cancer. Therefore, sensitive and selective methods that can reveal the low abundance of cancer biomarkers in a biological sample are always desired. Here, we report the development of a novel electrochemical biosensor for early detection of breast cancer by using bioconjugated self-assembled pH-responsive polymeric micelles. The micelles were loaded with ferrocene molecules as "tracers" to specifically target cell surface-associated epithelial mucin (MUC1), a biomarker for breast and other solid carcinoma. The synthesis of target-specific, ferrocene-loaded polymeric micelles was confirmed, and the resulting sensor was capable of detecting the presence of MUC1 in a sample containing about 10 cells/mL. Such a high sensitivity was achieved by maximizing the loading capacity of ferrocene inside the polymeric micelles. Every single event of binding between the antibody and antigen was represented by the signal of hundreds of thousands of ferrocene molecules that were released from the polymeric micelles. This resulted in a significant increase in the intensity of the ferrocene signal detected by cyclic voltammetry

A numerical investigation of quasi-static magnetoconvection with an imposed horizontal magnetic field

Quasi-static Rayleigh-B\'enard convection with an imposed horizontal magnetic field is investigated numerically for Chandrasekhar numbers up to $Q=10^6$ with stress free boundary conditions. Both $Q$ and the Rayleigh number ($Ra$) are varied to identify the various dynamical regimes that are present in this system. We find three primary regimes: (I) a two-dimensional (2D) regime in which the axes of the convection rolls are oriented parallel to the imposed magnetic field; (II) an anisotropic three-dimensional (3D) regime; and (III) a mean flow regime characterized by a large scale horizontal flow directed transverse to the imposed magnetic field. The transition to 3D dynamics is preceded by a series of 2D transitions in which the number of convective rolls decreases as $Ra$ is increased. For sufficiently large $Q$, there is an eventual transition to two rolls just prior to the 2D/3D transition. The 2D/3D transition occurs when inertial forces become comparable to the Lorentz force, i.e. when $\sqrt{Q}/Re = O(1)$; 2D, magnetically constrained states persist when $\sqrt{Q}/Re \gtrsim O(1)$. Within the 2D regime we find heat and momentum transport scalings that are consistent with the hydrodynamic asymptotic predictions of Chini and Cox [Phys. Fluids \textbf{21}, 083603 (2009)]: the Nusselt number ($Nu$) and Reynolds number ($Re$) scale as $Nu \sim Ra^{1/3}$ and $Re \sim Ra^{2/3}$, respectively. For $Q=10^6$, we find that the scaling behavior of $Nu$ and $Re$ breaks down at large values of $Ra$ due to a sequence of bifurcations and the eventual manifestation of mean flows.Comment: 31 pages, 9 figure

Optimization and Control of Production of Graphene

Graphene is a 2-dimensional element of high practical importance. Despite its exceptional properties, graphene’s real applications in industrial or commercial products have been limited. There are many methods to produce graphene, but none has been successful in commercializing its production. Roll-to-roll plasma chemical vapor deposition (CVD) is used to manufacture graphene at large scale. In this research, we present a Bayesian linear regression model to predict the roll-to-roll plasma system’s electrode voltage and current; given a particular set of inputs. The inputs of the plasma system are power, pressure and concentration of gases; hydrogen, methane, oxygen, nitrogen and argon. This voltage/current modeling will help in better understanding the plasma physics which is directly related to the quality of graphene produced. The above model is based on a dataset which was formed using 100 different input conditions and then measuring the electrode voltage/current corresponding to those inputs. Our model demonstrates the advantages of Bayesian approach that captures the epistemic uncertainty in the model parameters, which is important when dealing with small size data set. Our algorithm predicts the regression coefficients which are used to approximate the output voltage and current. The model presented in this research will give insights about the plasma physics and thus help in optimization of production of graphene

The Results of Applying the Principles of Corporate Governance in Corporations Listed on the First Market in the Amman Stock Exchange

This study aims to determine the extent of the application of the principles of corporate governance in corporations listed on the First Market in the Amman Stock Exchange, to fulfill the objectives of the study questioners were distributed to the 55 first market corporations in the ASE, the results showed that there is a strong application of corporate governance in corporations listed on the First Market in the Amman Stock Exchange, a lack in awareness of corporate officers in these corporations about the importance of corporate governance principles, in addition to lack of confidentiality when it comes to sharing information with external users of the financial systems, and an increase in non-occupancy of executive tasks by Board members

A model-based time-reversal of left ventricular motion improves cardiac motion analysis using tagged MRI data

<p>Abstract</p> <p>Background</p> <p>Myocardial motion is an important observable for the assessment of heart condition. Accurate estimates of ventricular (LV) wall motion are required for quantifying myocardial deformation and assessing local tissue function and viability. Harmonic Phase (HARP) analysis was developed for measuring regional LV motion using tagged magnetic resonance imaging (tMRI) data. With current computer-aided postprocessing tools including HARP analysis, large motions experienced by myocardial tissue are, however, often intractable to measure. This paper addresses this issue and provides a solution to make such measurements possible.</p> <p>Methods</p> <p>To improve the estimation performance of large cardiac motions while analyzing tMRI data sets, we propose a two-step solution. The first step involves constructing a model to describe average systolic motion of the LV wall within a subject group. The second step involves time-reversal of the model applied as a spatial coordinate transformation to digitally relax the contracted LV wall in the experimental data of a single subject to the beginning of systole. Cardiac tMRI scans were performed on four healthy rats and used for developing the forward LV model. Algorithms were implemented for preprocessing the tMRI data, optimizing the model parameters and performing the HARP analysis. Slices from the midventricular level were then analyzed for all systolic phases.</p> <p>Results</p> <p>The time-reversal operation derived from the LV model accounted for the bulk portion of the myocardial motion, which was the average motion experienced within the overall subject population. In analyzing the individual tMRI data sets, removing this average with the time-reversal operation left small magnitude residual motion unique to the case. This remaining residual portion of the motion was estimated robustly using the HARP analysis.</p> <p>Conclusion</p> <p>Utilizing a combination of the forward LV model and its time reversal improves the performance of motion estimation in evaluating the cardiac function.</p

Modeling of a Roll-to-roll Plasma CVD System for Graphene

Graphene 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

A Socio –Textual Analysis of Written Wedding Invitation in Jordanian Society

The present study examined the generic structure of wedding invitations in Jordanian society in order to find out what components people employ to articulate the communicative purpose of these invitations. It also investigated the effect of socio-cultural aspects on the generic structure of wedding invitations through focusing on the relationship between language and cultural representations within the discourse of this genre. The sample consisted of 55 invitation cards from a collection of 150 cards covering the periods from 1979 until 2006. These cards have been subjected to the model of analysis proposed by Holmes (1997) and a modified version of the model outlined by Clynes and Henry (2004). The results showed that this genre was built around six obligatory and two optional moves. These moves communicate a lot of information about the prevailing socio-cultural values in Jordanian society that are encoded in the rhetorical and organizational components of this genre

High-resolution magnetic resonance imaging and diffusion tensor imaging of the porcine temporomandibular joint disc

This is the published version. Copyright © 2014 The British Institute of RadiologyObjectives: Diffusion tensor imaging (DTI) is an MRI modality for characterizing the property, microstructural organization and function in tissues such as the brain and spinal cord. Prior to this investigation, DTI had not been adapted for studies of the temporomandibular joint (TMJ) disc. Objectives were to test the feasibility of DTI to evaluate the porcine TMJ disc and to use DTI to observe differences in magnitude of anisotropy of water diffusion between TMJ disc regions. Methods: Five adult pig TMJs were scanned on a 9.4 Tesla horizontal bore MRI scanner using an inductively coupled surface coil. High-resolution gradient-echo and diffusion-weighted spin-echo based images were obtained. The mean diffusivity and fractional anisotropy (FA) were computed in different regions of the disc. Two observers were calibrated to review the two-dimensional and three-dimensional images. Polarized light microscopy was used as the gold standard for collagen fibre orientation. Results: In the sagittal plane, the mean diffusivity was higher in the posterior (1.28±0.10×10−3 mm−2 s−1) and anterior (1.27±0.08×10−3 mm−2 s−1) bands compared with the intermediate zone (0.96±0.01×10−3 mm−2 s−1), and the FA index was also lowest in the intermediate zone. In the coronal plane, the mean diffusivity was higher in the medial (1.42±0.01×10−3 mm−2 s−1) and lateral (1.21±0.12×10−3 mm−2 s−1) aspects than in the centre (1.09±0.08×10−3 mm−2 s−1), and the FA index was also lowest in the centre. Conclusions: DTI is a useful method for non-invasively characterizing the structure/property relationships of the porcine TMJ disc

A systems thinking approach to address sustainability challenges to the energy sector

The energy sector is an intrinsically dynamic and complex system, and therefore its behaviour is not solely controlled by constituent components. Rather, it is a consequence of dynamic interactions among them. To properly manage such a system in a sustainable manner, it is necessary to understand the underlying dynamics of component interactions. Despite this, the interconnections between components of the energy sector in research and policy have received little attention. Here, we outline crucial limitations of previous efforts and emphasize the importance of using systems thinking in addressing the energy sector's sustainability challenges. We demonstrate this by a case study of the Australian energy sector, which has experienced emerging sustainability issues. Research findings show that current policies promoting energy development in the country are likely to be ‘fixes that fail’ that ultimately undermine sustainability. To achieve in building a sustainable energy sector, the policy must focus on implementing long-term solutions and avoid short-term quick fixes