Our drive towards ever smaller, ever faster electronic devices is possibly leading us to the end of the silicon era. We are now entering the realm of nanoscience and technology where one is forced to look at the world from a completely different perspective. Systems as small as a dozen atoms could perform the same tasks that are today performed by sub-micrometer scale silicon-based devices. However, underlying mechanisms, at this length scales, is completely different. Thus, in the same way that nanoscale systems present tantalizing possibilities, they also present great challenges.

We believe carbon-based materials could be the underlying framework of tomorrow’s electronics. The many allotropic forms of carbon can be organized in variety of ways to suit the needs of a needed device/effect.

Within that class of materials one can find carbon nanotubes, graphene and graphene-nanoribbons, organic molecules, and last but not least biological molecules; such as DNA and petides.

Graphene has emerged as a material with tantalizing properties, which in turn can lead to a plethora of applications. The fact that it is the thinnest possible membrane - only a single atom thick - combined with its high mobility can lead a large number of different types of electronic devices. In particular it can be employed in third-generation DNA sequencing.

In this project we use a combination of Density Functional Theory, Classical Molecular Dynamics simulations and Non-equilibrium Green's functions to simulate the electronic and transport properties of a DNA strand as it passes through a pore drilled in the graphene sheet. Proposal is that the transverse current passing on the graphene sheet - and around the pore - will be altered by the present of the basis. It will lead to different tunneling probabilities for electrons crossing the pore. Depending on the type of basis one would have different values for the current and consequently could differentiate between them.
Here we include the effects of the solvent and other DNA basis outside the pore by means of a classical electrostatic potential. This potential enters as an external potential in the Kohn-Sham equation for the Quantum Mechanical system. Once the Hamiltonian for this system has been obtained we are able to calculate the transport properties of the system.

Following the need for new - and renewable - sources of energy worldwide, fuel cells using electrocatalysts can be thought of as a viable option. Understanding the local structure of water molecules at the interfaces of the metallic electrodes is a key problem, which involves a detailed study of the nature of the interactions between water-water and water-substrate Notably the system is under an external potential bias, which makes the task of simulating this setup difficult.

A first principle description of all components of the system is the most appropriate methodology in order to advance understanding of electrochemical processes. There, the metal is usually charged. To correctly compute the effect of an external bias potential applied to electrodes, we combine density functional theory (DFT) and non-equilibrium Green's functions methods (NEGF), with and without van der Waals interactions, thus simulating a realistic out-of-equilibrium open system. We analyze in detail the structural, dynamic and energetic properties of liquid-water interacting metal surfaces at ambient temperature, using first principles molecular dynamics, both in the presence and absence of an external bias potential applied to the electrodes

This work is carried out in collaboration with Prof. Luana Pedroza from Universidade Federal do ABC, São Paulo, Brazil

Semiconductor heterostructures constitute the main building block for several technological applications, since they enable the possibility of tailoring the device's properties by taking advantage of the individual materials' characteristics. With the advent of reduced-dimensionality (1D and 2D) semiconductors and their variety of electronic and optical properties, the route towards a new generation of optoelectronic devices based on nanometer-thick materials seem to be paved. Since the operating principle of several emerging technologies including photovoltaics are based on complex processes that take place at the interfaces between different materials, the correct understanding of their physics at atomistic scales is crucial to predict the viavility of using these materials as platforms for practical applications in nanoelectronics and optoelectronic.

In this sense, we investigate the electronic and optical properties of heterostructures' interfaces. For this purpose, we use a methodology based on many-body density functional theory within the GW approximation and Bethe-salpeter equation to better describe the exchange and correlation potential as well as excited-states. This way, we are able to propose optimal heterostructures with potential for photovoltaic applications.

Defects in nanotubes can significantly alter their electronic and transport properties (as well as its mechanical properties). Such defects could be produced by ion irradiation and could be using for tailoring the electrical conductivity of multi-wall carbon nanotubes.

We study the electronic transport properties of double-wall carbon nanotubes with and without defects to infer the changes in the transmission coefficients of these devices. The main effect we are interested in is the influence of the links between the tubes on the transport.

One of the possible applications of carbon nanotubes is in the field of sensors. The electronic transport properties of CNTs might be severely altered in the presence of a foreign species. Traditional simulations usually don’t take into consideration the fact that a realistic nanotube consists of binding sites which

In this research topic we aim to combine the power of ab initio simulations with recursive Green’s function methods to atomistically simulate the properties of long one-dimensional sensors. Currently we are also interested in the same effect in bundles of nanotubes which could pave the way to simulating a real device and thus provide experimentalists with quantitative predictions.

Instead of using the charge of the electron, one might consider using another of its intrinsic properties, namely the spin. The so called field of spintronics started with the discovery of the giantmagnetoresistance effect in 1988 and has progressed to become a major research area in science.

Today we can envision the production of nanoscopic devices that can perform new and tantalizing tasks in this field. Carbon-based materials, due to the small spin-orbit coupling could be the perfect material for building such systems. Both small organic molecules and more recently graphene could be the underlying framework for spintronics devices. In this field e aim to study the electronic and transport properties of spintronics devices using a combination of out-of-equilibrium Green’s functions and density functional theory. We interested in effects such as GMR in molecules attached to magnetic electrodes as well as spin filtering effects.

The potential medical applications of nanoscience and nanotechnology are a major driving force in the field’s research effort. Although carbon nanotubes present interesting properties, its toxicity prevents its widespread use in medicine. Thus, researchers have initiated a search for other one-dimensional systems that can be biologically compatible. In that aspect peptide nanotubes could provide us with a possible route. Its properties, including the effects of water In the structure, however, are little known.

In this research project our aim is to determine, using a combination of ab initio density functional theory as well as tight-binding DFT, the electronic struture of peptide nanotubes in the presence of water. Most importantly, we are interested in the importance of the water molecules on the overall stability of the nanotube.