Synthesis, Characterization, and Device Applications of Two-Dimensional Materials

Two-dimensional (2D) materials have attracted tremendous research interest, as they offer novel physics, facile visualization by electron and scanning probe microscopy, and the potential to become next-generation electronic materials, all due to reduced dimensionality. Large-area 2D single crystals are needed for both fundamental scientific experiments and electronic device applications. New methods need to be developed to exploit state-of-the-art microscopy in the scientific investigation of 2D materials. Mechanisms behind the behavior of 2D-material based devices need to be resolved and new device concepts and applications need to be explored. This dissertation addresses these three aspects of 2D materials research.Using chemical vapor deposition growth of graphene on copper as a platform, the first part of my research in this thesis demonstrates a facile method involving a simple in-situ treatment of the copper catalytic substrate right before the growth that results in mm-sized graphene single crystals, elucidating the key factors of achieving large-area 2D single crystals.The second part of this work developed experimental methods to resolve important issues in 2D materials research by employing modern transmission electron microscopy. Here, a method has been developed to determine the edge orientation and termination without imaging the edge down to the atomic scale of monolayer hexagonal boron nitride (h-BN), enabling a direct comparison to theoretical predictions. Another important issue in 2D materials research is the determination of the layer count and its lateral spatial uniformity. In this work, a method is developed to map the layer count of a 2D material at nanometer-scale lateral resolution over extended areas, utilizing a combination of mass-thickness mapping offered by STEM and element-specific quantization afforded by electron energy loss spectrum (EELS) mapping.The last part of this thesis work unravels the multiple mechanisms behind the behavior of field effect transistors (FETs) based on PdSe2. The change in device behavior in early reports from ambipolar to n channel was puzzling. As commonly encountered in device research, many factors, including channel material properties, defects, contaminants, and contact effects, are almost always entangled. Here, I use multiple control devices to unravel various mechanisms and provide consistent explanations for device behvior variations

Simulation of product transportation in open pit mines

A research report submitted to the Faculty of Engineering and Built Environment, University of Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Masters of Science in Engineering Johannesburg, 2015Open pit mines account for more than 60 percent of all surface mines, and haulage costs account for almost 60 percent of total operating costs for these mines. It necessitates maintaining an efficient haulage system where all fleet equipment performs effectively to achieve the mine’s objectives. Discrete event simulation supported by animation offers a powerful method for evaluating such systems. This research has developed a simulation software program using Visual Basic for Application (VBA), GPSS/H (General Purpose Simulation System), and PROOF 5 animation. Remaining within the defined assumptions and boundary conditions, the research combines the powers of three software languages to build a general-purpose, data-driven, and user-friendly simulation program. The research focuses on the study and simulation of some of the important complexities of the truck haulage system. These include uncertainty or system randomness, fleet heterogeneity, multi-loader multi-dump sites, bunching of haulers, and hauler dispatching. In the developed simulation program, the user is required to provide the inputs in the user-friendly environment of VBA. The simulation program arranges the inputs in a pre-arranged format and then sends them to GPSS/H. The simulation language generates a discrete event simulation model based on the receiving structural and operational data. After simulating the system, the model generates the simulation outputs and animation commands in separate files. VBA displays a summary of the simulation results, and PROOF 5 demonstrates the results in a 2-dimensional graphical animation along with detailed information. This research also includes three case studies based on hypothetical mines for the analysis of simulation results. It establishes comparisons between the dispatching policies of fixed allocation and variable allocation of Minimize Production Requirements (MPR), and shows that the MPR policy is more suitable to achieve the quality control objectives. The developed simulation program contributes by demonstrating the powers of simulation to analyse open pit haulage systems. It also shows how simulation can be utilized as a useful technique to answer many ‘what-if?’ questions and scenarios

Ngoc Efforts Towards The Creation Of A Regional Human Rights Arrangement In The Asia-Pacific Region

I feel honored to be given an opportunity to speak at this panel on an issue which has a lot to do with a part of the world I belong to. NGOs in Asia and the Pacific have been crucial to the struggle for a regional human rights arrangement. Indeed it is they who have kept both the debate over and the struggle for an Asian human rights system alive

Impact of board structure and firm performance on chief executive's compensation / Mohsin Ali Patel

The corporate board usually influences all important decisions of a firm including setting of its long-term goals, developing a corporate strategic policy, as well as hiring and setting the compensation of the chief executive. Moreover, the organization of the board may have a significant effect on the monitoring and governance of the company. This paper analyses the impact of structure of the board and firm performance on chief executive compensation, in an emerging economy context specifically, Pakistan. Chief executive compensation is one of the controversial and sought after topics in research nowadays. Interestingly, the exploration into the topic has found that there is a significant and positive impact of the non-executive directors serving on the corporate boards on the compensation of chief executive. Furthermore, the size of the board has also showed to have a significant and positive impact on the chief executive’s compensation which logically means that the companies in which the boards are larger than the mean size will relatively pay higher to their chief executives. Also it was found that the performance of the firm does not have a statistically significant impact on chief executive compensation. These results have policy implications and are important to corporate stakeholders

On the Factor Refinement Principle and its Implementation on Multicore Architectures

The factor refinement principle turns a partial factorization of integers (or polynomi­ als) into a more complete factorization represented by basis elements and exponents, with basis elements that are pairwise coprime. There are lots of applications of this refinement technique such as simplifying systems of polynomial inequations and, more generally, speeding up certain algebraic algorithms by eliminating redundant expressions that may occur during intermediate computations. Successive GCD computations and divisions are used to accomplish this task until all the basis elements are pairwise coprime. Moreover, square-free factorization (which is the first step of many factorization algorithms) is used to remove the repeated patterns from each input element. Differentiation, division and GCD calculation op­ erations are required to complete this pre-processing step. Both factor refinement and square-free factorization often rely on plain (quadratic) algorithms for multipli­ cation but can be substantially improved with asymptotically fast multiplication on sufficiently large input. In this work, we review the working principles and complexity estimates of the factor refinement, in case of plain arithmetic, as well as asymptotically fast arithmetic. Following this review process, we design, analyze and implement parallel adaptations of these factor refinement algorithms. We consider several algorithm optimization techniques such as data locality analysis, balancing subproblems, etc. to fully exploit modern multicore architectures. The Cilk++ implementation of our parallel algorithm based on the augment refinement principle of Bach, Driscoll and Shallit achieves linear speedup for input data of sufficiently large size

Investigating the Performance of Smote for Class Imbalanced Learning: A Case Study of Credit Scoring Datasets

Classification of datasets is one of the major issues encountered by the data mining community. This problem heightens when the real world datasets is also imbalanced in nature. A dataset happens to be imbalanced when the numbers of observations belonging to rare class are greatly outnumbered by the observations of another class. Class with greater number of observation is called the majority or the negative class, while the other with rare observations is referred to as the minority or the positive class. Literature represents number of resampling techniques that address the problem of class imbalance. One of the most important strategies is to resample the datasets that aim to balance the number of minority or majority observations by over-sampling or under-sampling respectively. This paper aims to investigates and analyze the performance of most widely used oversampling procedure Synthetic Minority Oversampling Technique (SMOTE) for different thresholds of oversampling using four classifiers for three credit scoring datasets

The relationship between Islamic bank products, client attraction and business expansion: Evidence from Pakistani banking industry

This research article investigates the relationship between Islamic bank products, client attraction, and business expansion in the Pakistani industry. The study utilizes a survey of Islamic bank customers and employs structural equation modeling to test the proposed relationships. The results indicate that Islamic bank products have a positive relationship with both client attraction and business expansion, and that client attraction mediates the relationship between Islamic bank products and business expansion. The implications of these findings for the Islamic banking industry in Pakistan and beyond are discussed, as well as limitations and potential avenues for future research

MAXIMIZING THE ELECTROCATALYTIC ACTIVITIES OF NON-NOBLE TRANSITION METAL???S COMPOUNDS FOR WATER ELECTROLYSIS

Department of Chemical EngineeringThe rapid growth in population and advancement in heavy industry, has badly influenced world economy due to sharp rise in cost of oil prices. Currently, about 80% of energy is produced from fossil fuels, which adds greenhouse gases (CO2, SOx & NOx) to the environment by increasing global temperature and environmental pollution. Therefore, development of sustainable, environmentally friendly and alternatives energy sources to fossil fuels attracts much attentions in recent decades. Among the various alternative advanced clean energy technologies, the fuel cells, CO and CO2 to liquid fuel conversions, water electrolysis, solar, wind, marine energy, electrochemical energy storage (EES) devices including various types of batteries and supercapacitors (SCs) have been attracted much attention in recent years. Although, many efforts have been exercised to improve these technologies but they are still facing many challenges like high cost, durability, reliability, efficiency and maintenance to commercialize at public sectors. The hydrogen (H2) is the only alternative clean fuel which can mitigate energy and environmental related issues. Among the various alternative energy technologies, for example fuel cells, CO2 conversions and water electrolysis uses hydrogen as the primary energy carrier. Currently, about 95% of total hydrogen is produced by using conventional technologies like steam methane reforming (SMR) and coal gasification (CG). Evidently, these methods are adding more greenhouse gases to the environment and the quality of hydrogen is also poor. The pure hydrogen is generated by water electrolysis which is usually conducted either photochemically and photoelectrochemically or electrochemically. Amongst all water electrolysis processes, the electrochemical water splitting is the only available greener, sustainable and rapid route of generating highly pure H2 at commercial scale. Transition metal compounds (TMCs) such as phosphides, carbides and chalcogenides have attracted massive attention as alternatives of noble metals (Pt, Ru or Ir) since last few years due to their superior electrical conductivity, mechanical strength, and chemical stability. In spite of the success, there are still many challenges like poor performance, stability in wide pH range, expensive and poisonous starting precursors, environmentally unsafe synthetic procedures, lack of in-depth mechanistic knowledge and so on which are creating hurdles for sustainable hydrogen production with both economic and environmental advantage. Here, simple, economical, ecofriendly and commercially adoptable synthesis procedures are developed to increase the number of active sites and intrinsic catalytic activity of transition metals carbides, phosphides and sulfides through heteroatom doping. Moreover, these nanostructures are grafted on conductive substrates (like doped-graphene, carbon cloth, nickel foam etc.) for electrochemical water splitting applications. The electrochemical properties of molybdenum carbides are tuned either by encapsulating or imbedding them in boron (B) and nitrogen (N) co-doped carbon network (BCN) via a unique organometallic complex-assisted approach. Due to the synergic effect of BCN network, the molybdenum carbides show a remarkable electrocatalytic hydrogen evolution (HER), oxygen evolution (OER) and oxygen reduction (ORR) performances and excellent durability in both acidic and basic aqueous defeating the most of earlier reported molybdenum carbides based electrocatalyst in the literature. The mechanistic study for water electrolysis and the synergic effect BCN network at electrochemical performance of molybdenum carbides is also discussed in detail. The intrinsic catalytic activity stability of molybdenum phosphides nanocrystallite (MoP) are modulated by dual-doping of S and N into its structure via a unique, inexpensive and environmental-friendly thiourea-phosphate-assisted rout. The number of active sites are also increased by controlling the shape of nanoparticles and loading them on S, N self-doped graphene. The obtained MoP/SNG catalysts displays extraordinary hydrogen evolution (HER) performance in both acidic and alkaline media. Similarly, the sulfur-doped CoP (S:CoP) and Co2P (S:Co2P) nanoparticles are also synthesized as a noble metal-free electrocatalyst via above indigenously developed thiourea-phosphate-assisted route. The S-doped Co-phosphide based electrode exhibits excellent activity and stability for overall water splitting defeating noble mental-based Pt/C, IrO2, and reported non-noble metal-based electrocatalysts. Density functional theory calculations reveal that the excellent activity is attributable to the modified electronic structures of Co-phosphides which favor the overall water splitting at both S:CoP and S:Co2P electrodes. The S-doping also increases the number of exposed active sites especially on the conductive substrates which works as the excellent alkaline electrolyzers for overall water splitting. The electroctalytic hydrogen evolution reaction (HER) activity of MoS2 increases when it possesses multifunctional active sites including structural defects, Mo-exposed edges, S-vacancies, 1T-phase and expanded interlayer distances. Previous reports on MoS2-based catalysts targeted only a single or few of these active sites, the all-in-one MoS2 electrocatalyst synthesized herein contains all of the above characteristics by using a supramolecular structure of melamine-phosphomolybdate (MA-PMo12) and a weakly reducing thiourea. During preparation, the in-situ produced NH3 gas acts as interculants between MoS2 sheets and makes expanded interlayers spacing ammoniated 1-T MoS2 (A-MoS2). After reduction of guest NH3 into interlayer-expanded MoS2 in hydrogen leads to form an MoS2 with multiple active sites described above (R-MoS2) which exhibits surprisingly high hydrogen evolution reaction (HER) activity in alkaline media outperforms to all earlier reported MoS2-based electrocatalysts.ope