Modelling of plasmodic and graphene nanodevices

Resum

Due to the experimental developments and the deeper understanding of the behaviour of matter at the nanometre scale, nanoscience and nanotechnology have experienced a huge boost over the past few decades, becoming a major research topic in multiple fields of science. A non-exhaustive list of the latter includes material science, optics, chemistry, biology and biomedicine. One of the research areas where nanoscience has had a fast and ground-breaking impact is the field of Information Technology. The constant reduction in the size of components in the semiconductor industry has smoothly led it to the nanoscale. However, most of the properties of bulk matter are greatly affected by this shrinking of the dimensions. This has led to difficult technological challenges which compromise future advances. Most of the investment is directed towards overcoming this problems without changing the base technology. However, there is also a need for the so-called blue sky research, that is, research which involves a change of paradigms with respect to the ones in use nowadays. It is the goal of the present work to show the results obtained in some of this new research directions. Objectives and outline: In the first part of this Thesis, graphene is presented as a base material to build transistors and spintronic devices. They take advantage of the quantum nature of charge carriers, which supersedes the usual classical description as the systems scale down. In chapter 1, some electronic properties of graphene and graphene nanoribbons are obtained using a Tight Binding (TB) description. In addition to it, key concepts of coherent electronic transport are presented, in order to understand the following original results: • In chapter 2, interference effects of electrons are used to test the possibility of building a QID based on a graphene nanoring. • In chapter 3, the previous device is extended to provide control over the spin polarization. This is accomplished by means of a ferromagnetic insulator placed close to the arms of the ring, resulting in a tunable source of polarized electrons. • In chapter 4, a set of ferromagnetic strips on top of a graphene nanoribbon are shown to produce an I − V characteristic with spin-dependent NDR, which could be of great importance for non-linear electronic applications in spintronics. In appendix A, the numerical method used to calculate the transmission through the studied samples is presented. The second part of this Thesis deals with the integration of electro-optical systems in the nanometre scale, and comprises two main results: In chapter 5, localized surface plasmons in MNPs are employed to modify the properties of incoming plane waves and engineer radiating patterns, thus building up a nano-antenna. • In chapter 6, the dynamics of a SQD in close proximity to an interface is studied. It is shown that a back gate allows the inner state of the SQD to be controlled. The two aforementioned results are accompanied by the numerical method in which they rely, which calculates the effect of interfaces in the emission of neighbouring systems, accomplished using Sommerfeld integrals. This is detailed in appendix B. Finally, the main results and conclusions will be summarized, and some new possible research directions motivated by the present work. Note that a summary with the main points of this Thesis is also available in Spanish, before the appendices.