Physical principles of memory and logic devices based on nanostructured Dirac materials

During the las decades, the silicon-based semiconductor industry has enabled higher performance per cost of integrated circuits due to the ability of nearly doubling the amount of transistors per chip every two years, however, this has resulted in overheating issues and fundamental manufacturing problems that are very di¿cult to solve. Therefore, Dirac materials (DMs), such as graphene and topological insulators (TIs), are being extensively investigated as possible candidates for replacing silicon-channel devices in the next-generation integrated circuits, due to their attractive ultrahigh carrier mobility and possibility of quantum e¿ects that may be useful for electronic applications. This requires to study the physical principles of such nanostructures to e¿ectivelypredictthequantumtransportbehaviorofpossibledevices. Theaimofthis work is to explore the physical properties of Dirac material-based nanostructures that could be used for novel memory and logic devices, by using tight-binding (TB) and density function theory (DFT) methods combined with the non-equilibrium function (NEGF) formulationDoctoradoDOCTOR(A) EN INGENIERÍA ELECTRICA Y ELECTRÓNIC

Characterizing real-life graphene through the latest first-principles methodological developments

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica de la Materia Condensada. Fecha de lectura: 15-04-2016Esta tesis tiene embargado el acceso al texto completo hasta el 15-10-201

CARBON-BASED COMPLEX STRUCTURE AND MODEL DEVELOPMENT

Growing concerns about the environment and energy crisis prompt a search for effective carbon-based materials due to their low cost, renewability, sustainability, easy accessibility and excellent properties. We study the model development, structure and properties of graphene oxide, cellulose and their nanocomposites in order to obtain a better fundamental understanding of carbon complex materials and construct a structure-property relationship via reactive molecular dynamics simulations. In chapter 3, the model development of GO is studied. Theoretical GO models developed so far present a good description of its chemical structure. However, when it comes to the structural properties, such as the size and distribution of vacancy defects, the curvature (or roughness), there exist significant gaps between computational models and experimentally synthesized GO materials. We carry out reactive molecular dynamics simulations and use experimental characteristics to fine tune theoretical GO models. Attentions have been paid to the vacancy defects, the distribution and hybridization of carbon atoms, and the overall C/O ratio of GO. The GO models proposed in this work have been significantly improved to represent quantitative structural details of GO materials synthesized via the modified Hummers method. The temperature-programmed protocol and the computational post analyses of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, vacancy size and curvature distribution, are of general interest to a broad audience working on GO structures from other synthesis methods and other two-dimensional materials and their composites. In Chapter 4, we outline the state-of-the-art understanding of cellulose structures, and discuss in details cellulose interactions, dissolutions and decompositions via computational methods of molecular dynamics (MD) and reactive molecular dynamics (RxMD) simulations. In addition, cellulose characterizations, beneficial to validate and support computational results, are also briefly summarized. Such a state-of-the-art account of atomistic computational studies could inspire interdisciplinary collaborations, optimize process design, promote cellulose-based materials for emerging important applications and shed a light on fundamental understandings of similar systems of biomolecules, polymers and surfactants. In Chapter 5, we investigate the fundamental mechanism of how cellulose structure transforms under pyrolysis conditions and the practical guideline of how cellulose properties are fined tuned accordingly. A series of reactive molecular dynamics calculations has been designed to reveal the structural evolution of crystalline cellulose under pyrolysis treatments. Through the detailed analysis of cellulose configuration change, hydrogen bonding network variation, reaction and redistribution of carbon, oxygen and hydrogen elements, and Young’s modulus, a molecule level insight of crystalline cellulose and its structural evolution under pyrolysis conditions has been constructed via reactive molecular dynamics simulations. We anticipate those theoretical results could effectively promote the design, the manufacture, and the optimization of cellulose based materials for relevant emerging applications. In Chapter 6, we combined the results from previous chapters and explore a new composite material that incorporating amorphous cellulose chains on GO surface, which is barely reported by recent publications. A series of RxMD simulations have been carried out to reveal the mechanical properties of pure GO and cellulose-GO nanocomposites. Two different cellulose-GO composites are constructed, namely, cellulose (monolayer)-GO model and cellulose (multilayer)-GO model. The tensile deformation, Young’s modulus and mechanical strength of GO and cellulose-GO composites have been recorded and calculated under the temperature of 300, 500 800 K, with two strain rates of 10-4/fs and 10-5/fs. We hope the GO model with the simultaneously description to both structural and chemical properties can provide a new fundamental understanding of the mechanical performance of GO and cellulose-GO composites, and could add some advancement to existing knowledge of carbon-based materials

Electrical characterization of single-walled carbon nanotubes : leading toward electronic devices

This thesis presents research involving the electrical characterization of single-walled carbon nanotubes produced by the pulsed-laser vaporization technique. Carbon nanotubes were suspended in organic solvents and separated using ultrasonic excitation. The dispersed nanotubes were either physically deposited or spin-deposited onto electrode structures that were prefabricated using standard electron-beam lithography. Atomic force microscopy was used to locate and measure nanotubes that spanned across metal electrodes. Two-probe charge transport measurements were then made on these nanotube samples. The first sample exhibited current rectification, while many other carbon nanotubes were damaged by electrical breakdown. The effect of manipulating a nanotube at the electrode junction is also demonstrated. It was found that a potential barrier could be introduced, changing the I-V response of the nanotube device. Then, p-channel field-effect transistor behavior is shown for an individual single-walled carbon nanotube. Finally, an electrodeposition technique is presented for reducing the large contact resistance between a nanotube and the metal electrodes. This technique decreased the electrode-nanotube contact resistance by a factor of more than six, and maintained the semiconducting behavior of the nanotube. Energy band diagram models are used to try to explain some of the observed electronic properties

On Folding: Towards a New Field of Interdisciplinary Research

It is only recently, with the increasing interest in origami and folding in natural sciences and the humanities, that the fold as a new conception in a whole range of disciplines has begun to be conceived in a broader way. Folding as a material and structural process offers a new methodology to think about the close relationship of matter, form and code. It henceforth crosses out old dichotomies, such as the organic and the inorganic or nature and technology, and blurs the boundaries between experimental, conceptual and historical approaches. This anthology aims to unfold this new interdisciplinary field and its disciplinary impact, ranging from materials science, biology, architecture, and mathematics to literature and philosophy

Nonlinear Partial Differential Equations on Graphs

One-dimensional metric graphs in two and three-dimensional spaces play an important role in emerging areas of modern science such as nano-technology, quantum physics, and biological networks. The workshop focused on the analysis of nonlinear partial differential equations on metric graphs, especially on the bifurcation and stability of nonlinear waves on complex graphs, on the justification of Kirchhoff boundary conditions, on spectral properties and the validity of amplitude equations for periodic graphs, and the existence of ground states for the NLS equation with and without potential

Combustion generated fine carbonaceous particles

Soot is of importance for its contribution to atmospheric particles with their adverse health impacts and for its contributions to heat transfer in furnaces and combustors, to luminosity from candles, and to smoke that hinders escape from buildings during fires and that impacts global warming or cooling. The different chapters of the book adress comprehensively the different aspects from fundamental approaches to applications in technical combustion devices

Putting Chinese natural knowledge to work in an eighteenth-century Swiss canton: the case of Dr Laurent Garcin

Symposium: S048 - Putting Chinese natural knowledge to work in the long eighteenth centuryThis paper takes as a case study the experience of the eighteenth-century Swiss physician, Laurent Garcin (1683-1752), with Chinese medical and pharmacological knowledge. A Neuchâtel bourgeois of Huguenot origin, who studied in Leiden with Hermann Boerhaave, Garcin spent nine years (1720-1729) in South and Southeast Asia as a surgeon in the service of the Dutch East India Company. Upon his return to Neuchâtel in 1739 he became primus inter pares in the small local community of physician-botanists, introducing them to the artificial sexual system of classification. He practiced medicine, incorporating treatments acquired during his travels. taught botany, collected rare plants for major botanical gardens, and contributed to the Journal Helvetique on a range of topics; he was elected a Fellow of the Royal Society of London, where two of his papers were read in translation and published in the Philosophical Transactions; one of these concerned the mangosteen (Garcinia mangostana), leading Linnaeus to name the genus Garcinia after Garcin. He was likewise consulted as an expert on the East Indies, exotic flora, and medicines, and contributed to important publications on these topics. During his time with the Dutch East India Company Garcin encountered Chinese medical practitioners whose work he evaluated favourably as being on a par with that of the Brahmin physicians, whom he particularly esteemed. Yet Garcin never went to China, basing his entire experience of Chinese medical practice on what he witnessed in the Chinese diaspora in Southeast Asia (the ‘East Indies’). This case demonstrates that there were myriad routes to Europeans developing an understanding of Chinese natural knowledge; the Chinese diaspora also afforded a valuable opportunity for comparisons of its knowledge and practice with other non-European bodies of medical and natural (e.g. pharmacological) knowledge.postprin