Tuning the Dirac Cone of Bilayer and Bulk Structure Graphene by Intercalating First Row Transition Metals using First Principles Calculations

Modern nanoscience has focused on two-dimensional (2D) layer structure materials which have garnered tremendous attention due to their unique physical, chemical and electronic properties since the discovery of graphene in 2004. Recent advancement in graphene nanotechnology opens a new avenue of creating 2D bilayer graphene (BLG) intercalates. Using first-principles DFT techniques, we have designed 20 new materials \textit{in-silico} by intercalating first row transition metals (TMs) with BLG, i.e. 10 layered structure and 10 bulk crystal structures of TM intercalated in BLG. We investigated the equilibrium structure and electronic properties of layered and bulk structure BLG intercalated with first row TMs (Sc-Zn). The present DFT calculations show that the 2$p_z$ sub-shells of C atoms in graphene and the 3$d_{yz}$ sub-shells of the TM atoms provide the electron density near the Fermi level controlling the material properties of the BLG-intercalated materials. This article highlights how the Dirac point moves in both the BLG and bulk-BLG given a different TM intercalated materials. The implications of controllable electronic structure and properties of intercalated BLG-TM for future device applications are discussed. This work opens up new avenues for the efficient production of two-dimensional and three-dimensional carbon-based intercalated materials with promising future applications in nanomaterial science.Comment: 60 pages, 9 figures. arXiv admin note: text overlap with arXiv:1701.03936 by other author

Towards the formation and measurement of ethnic price perception

This research is the outcome of a preeminent interest in the topic of price perception. Pointedly, the perception of prices is part of the purchasing process, the same willingness to pay and the actual purchase behaviour, and is indubitably a perceptual construct. As such, perception is problematic to measure as it does not relate to an observable behaviour. On the other hand, pricing is regarded as an important variable in the marketing mix. This research contributes to theory by augmenting the current knowledge on the perception of prices including the methods used in the measurement of such perception. Moreover, this research addresses a gap in the understanding of how diverse ethnic groups perceive prices. The relationship set in this study between ethnicity and price perception is thought-provoking as it contributes to the current discussion around diversity in the marketplace. For example, the literature shows advances in areas such as multicultural and ethnic marketing and this research makes a significant contribution to these areas from price perception. Accordingly, this study involved a systematic review of the literature and presented a framework that suggested that the formation of price perception is affected by external factors such as culture and ethnicity. Furthermore, a qualitative study examined the formation of price perception around ethnic groups. Next, this research used a quantitative study that sought differences in price perception among ethnic groups. Thus, the quantitative study used a price perception scale (Lichtenstein et al., 1993) and a choice-based conjoint analysis. Also, the study adopted structural equation modelling (SEM) to measure differences among scales and the multinomial logit model to analyse the choice-based conjoint analysis. The findings of both the quantitative and the qualitative studies link to the systematic review and support the framework for the formation and measurement of price perception originally proposed

Iron Intercalation in Covalent-Organic Frameworks: A Promising Approach for Semiconductors

Covalent-organic frameworks (COFs) are intriguing platforms for designing functional molecular materials. Here, we present a computational study based on van der Waals dispersion-corrected hybrid density functional theory (DFT-D) to design boroxine-linked and triazine-linked COFs intercalated with Fe. Keeping the original $P-6m2$ symmetry of the pristine COF (COF-Fe-0), we have computationally designed seven new COFs by intercalating Fe atoms between two organic layers. The equilibrium structures and electronic properties of both the pristine and Fe-intercalated COF materials are investigated here. We predict that the electronic properties of COFs can be fine tuned by adding Fe atoms between two organic layers in their structures. Our calculations show that these new intercalated-COFs are promising semiconductors. The effect of Fe atoms on the electronic band structures and density of states (DOSs) has also been investigated using the aforementioned DFT-D method. The contribution of the $d$-subshell electron density of the Fe atoms plays an important role in improving the semiconductor properties of these new materials. These intercalated-COFs provide a new strategy to create semi-conducting materials within a rigid porous network in a highly controlled and predictable manner.Comment: 39 pages. arXiv admin note: text overlap with arXiv:1703.0261

Failing and Merging as Competing Alternatives during Times of Financial Distress: Evidence from the Colombian Financial Crisis

This paper studies the determinants of individual bank failures and M&A processes in Colombia during the financial crisis of the late 1990s. Using bank-specific data we estimate competing risk hazards models and find that while profitability and capitalization are the most important determinants of the probability of failing, bank´s size, efficiency and capitalization are the main determinants of the probability of participating in an integration process. All else constant, an increase in capitalization reduces the probability of disappearing, whether due to the occurrence of bankruptcy, a merge or an acquisition. However, a marginal increase in capitalization reduces significantly more the probability of bankruptcy than the probability of integration. This study is the first to present a competing risks hazard model to identify covariates that excerpt significant influence on the probability of failing or merging for banks of an emerging economy.Survival analysis; Competing risk models; Colombia. Classification JEL: G21; G33; G33; C25

Laser printing of passive electrical components

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2018, Tutor: J.M. Fernández-PradasLaser Induced Forward Transfer (LIFT) is used as a useful alternative to other ink printing techniques. Printing conductive materials with any geometry as desired gives us a degree of freedom in many fields of needs, such as microelectronics design. In this work silver nanoparticles ink is used and its resistivity is measured. First of all, the adequate scanning speed to get conductive lines must be known. In order to do that, a first printing with several speeds is done. It is observed that if the scanning velocity is fast enough, individual droplets are formed. However, by diminishing the velocity, the droplets get closer and closer until they form a straight line. Moreover, if the speed continues reducing, agglomerated material is formed. Next step is to determine the appropriate energy for printing. In order to get this, several droplets with different energies are printed. It is observed that, as the energy increases, the droplets lose their regular geometry and show as a splash. Furthermore, several lines are printed with different energies and their resistance have been measured, expecting a decreasing linear dependence, as more conductive material is added. Nevertheless, a much more complex dependence is obtained. Finally, once the parameters have been optimized, a fourth and last one printing of a maze pattern with many electrodes is done, with the objective to study the length-resistance dependence. Although a non-uniformity printing effect appears along the sample, the resistance increases linearly with length

Assessment of Grain Safety in Developing Nations

Grains are the most widely consumed foods worldwide, with maize (Zea mays) being frequently consumed in developing countries where it feeds approximately 900 million people under the poverty line of 2 USD per day. While grain handling practices are acceptable in most developed nations, many developing nations still face challenges such as inadequate field management, drying, and storage. Faulty grain handling along with unavoidably humid climates result in recurrent fungal growth and spoilage, which compromises both the end-quality and safety of the harvest. This becomes particularly problematic where there is little awareness about health risks associated with poor quality grain. Fungi are contaminants of maize and some can produce toxins, known as mycotoxins, that both devalue crop marketability and have detrimental health effects, especially to those malnourished. As some households depend on their harvest for self-consumption, losses due to fungi endanger their food security. To abate the threat posed by mycotoxigenic fungi on maize among developing nations, this research was conducted as a compilation of works in several countries. More specifically, it describes agricultural practices currently in use in developing nations, provides an overview of mycotoxin prevalence and approaches that can be used to improve grain safety post-harvest through proper storage. Additionally, it provides a platform to evaluate the economic feasibility of storage technologies for maize storage at household level. While the countries of focus were Guatemala, Honduras and Nepal, findings presented can lead to improved decision-making within any maize production chain to safeguard consumers throughout the developing world. Advisor: Andréia Bianchin

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