Computational modeling of defects in nanoscale device materials

This PhD thesis concerns the computational modeling of the electronic and atomic structure of point defects in technologically relevant materials. Identifying the atomistic origin of defects observed in the electrical characteristics of electronic devices has been a long-term goal of first-principles methods. First principles simulations are performed in this thesis, consisting of density functional theory (DFT) supplemented with many body perturbation theory (MBPT) methods, of native defects in bulk and slab models of In0.53Ga0.47As. The latter consist of (100) - oriented surfaces passivated with A12O3. Our results indicate that the experimentally extracted midgap interface state density (Dit) peaks are not the result of defects directly at the semiconductor/oxide interface, but originate from defects in a more bulk-like chemical environment. This conclusion is reached by considering the energy of charge transition levels for defects at the interface as a function of distance from the oxide. Our work provides insight into the types of defects responsible for the observed departure from ideal electrical behaviour in III-V metal-oxidesemiconductor (MOS) capacitors. In addition, the formation energetics and electron scattering properties of point defects in carbon nanotubes (CNTs) are studied using DFT in conjunction with Green’s function based techniques. The latter are applied to evaluate the low-temperature, low-bias Landauer conductance spectrum from which mesoscopic transport properties such as the elastic mean free path and localization length of technologically relevant CNT sizes can be estimated from computationally tractable CNT models. Our calculations show that at CNT diameters pertinent to interconnect applications, the 555777 divacancy defect results in increased scattering and hence higher electrical resistance for electron transport near the Fermi level.

'Muchos Méxicos': widening the lens in Rulfo's cinematic texts

It is difficult to overstate the importance of Juan Rulfo’s two major pieces of fictional narrative work—his haunting, enigmatic novel Pedro Páramo (1955) and his unrelenting depictions of the failures of post-revolutionary Mexico in his short story collection El Llano en llamas (1953). In her foreword to the Margaret Sayers Peden English translation, Susan Sontag hails Pedro Páramo as ‘not only one of the masterpieces of 20th Century world literature, but one of the most influential of the century’s books’. García Márquez has compared the influence of Rulfo on 20th Century world literature to that of Sophocles: ‘No son más de 300 páginas, pero son casi tantas y creo tan perdurables como las que conocemos de Sófocles’ and, completing this oftrepeated triumvirate of recommendations, Jorge Luis Borges has referred to Pedro Páramo as: ‘una de las mejores novelas de las literaturas de lengua hispánica, y aun de la literatura.’ Despite the praise heaped upon Rulfo’s two most famous books, when his third book of fiction, El gallo de oro y otros textos para cine, was finally published in 1980, just six years before his death, it was greeted with almost critical silence. It is precisely this publication that provides the focus of this investigation. The collection contains three texts—El despojo, La fórmula secreta and El gallo de oro. Constituting a third of the fictional work he published in his lifetime, expanding upon themes present in El Llano en llamas and Pedro Páramo while, at the same time, examining new ground, no thematic discussion of Rulfo’s written output is complete without including these texts. Yet they are frequently dismissed. In this way this investigation attempts to go some way towards filling this critical gap in the work of one of the most influential writers of the twentieth century