L. M. Gaggero-Sager

Design of graphene electronic devices using nanoribbons of different widths

We present a simple design of a field effect transistor based on graphene nanoribbons, taking advantage of the metallic and semiconductor nature of nanoribbons with different widths. Such device could be constructed by using lithography techniques. The conductance of the proposed device is obtained by using the Kubo formula, assuming a strong damping due to the substrate and imperfections of the lattice. By removing the control electrodes, the design could also be used as an electrical resistance.

Transport and Electronic Properties of Two Dimensional Electron Gas in Delta-Migfet in GaAs

The objective of this work is to analyze electronic transport phenomena, due to ionized impurity scattering in δ-MIGFET (Delta-Multiple Independent Gate Field Effect Transistor). In this work, we report theoretical results for electronic transport in a delta-MIGFET using the device electronic structure and analytical expression of mobility and conductivity. The results show that the analytical mobility and conductivity are a good way to analyze Received 13 August 2010, Accepted 14 October 2010, Scheduled 10 November 2010 Corresponding author: Outmane Oubram (oubram@uaem.mx). † Also with Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, Mexico D.F 04510, Mexico.

Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene

AbstractWe investigate the transmission properties of quasiperiodic or aperiodic structures based on graphene arranged according to the Cantor sequence. In particular, we have found self-similar behaviour in the transmission spectra, and most importantly, we have calculated the scalability of the spectra. To do this, we implement and propose scaling rules for each one of the fundamental parameters: generation number, height of the barriers and length of the system. With this in mind we have been able to reproduce the reference transmission spectrum, applying the appropriate scaling rule, by means of the scaled transmission spectrum. These scaling rules are valid for both normal and oblique incidence, and as far as we can see the basic ingredients to obtain self-similar characteristics are: relativistic Dirac electrons, a self-similar structure and the non-conservation of the pseudo-spin.

TRANSPORT PROPERTIES OF DELTA DOPED FIELD EFFECT TRANSISTOR

The first calculation of mobility and conductivity between source and drain as function of gate voltage in a δ-doped Field Effect Transistor is presented. The calculation was performed with a model for the δ-FET that was shown in (1). The mobility was calculated using a phenomenological expression that was presented in (2). That expression does not have empirical form, neither empirical parameter. For the first time a phenomenological expression of the conductivity is presented, which is derived from the mobility expression. The conductivity shows three different regions: a parabolic region and two linear regions. The parabolic region represents the region at which the conduction channel begins to close. On the other hand, the mobility shows a more different behavior. In the mobility there are four regions. These regions correspond to the disappearance of the different conduction channels that form the subbands of the delta- doped quantum well. The different behavior between mobility and conductivity relies on the depletion of the delta-doped quantum well as the gate potential grows.

TRANSPORT AND ELECTRONIC PROPERTIES OF THE GaAs ALD-FET

According to the scaling-down theory, the ALD-FET (Atomic Layer Doping-Field Efiect Transistor) structure has attracted a lot of attention in view of its uses for developing devices with very short channels and for achieving very-high-speed operation. Therefore, there is a strong need to obtain an accurate understanding of carrier transport (mobility and conductivity) in such devices. In this work, we report the carrier transport based on the electronic structure of devices. Our results include analytical expressions of both mobility and conductivity. Our analytical expressions for the mobility and conductivity allow us to analyze transport in ALD-FET. We report regions where this device operates in digital and analogue mode. These regions are delimited in terms of intrinsic and extrinsic parameters of the system. The width of the Ohmic region as well as the NDR (Negative Difierential Resistance) properties of the system are also characterized.

Effect of the hydrostatic pressure on the electron mobility in delta-doped systems

The influence of hydrostatic pressure on the electron states and low-temperature mobility in n-type GaAs δ-doped single quantum wells is studied. Values of hydrostatic pressure consider are below the so-called Γ-X crossover, keeping all attention in the electronic properties at the Brillouin zone center. The effect of the pressure on the electron mobility is described via a relative quantity that is proportional to the ratio between P ≠ 0 and zero pressure results. Calculation is performed using an analytical description of the potential energy function profile, based on the Thomas-Fermi approach, taking explicitly into account the dependence upon P of the main input parameters: effective masses and dielectric constant. The relative mobility increases for higher values of P. The cases of zero and finite -although small- temperature are studied, showing that the influence of T is mainly to lower the values of the relative mobility in the entire range of P considered. Numerical results are reported for a two-dimensional density of ionized impurities equals to 7.5 × 1012 cm-2.

Self-similar conductance patterns in graphene Cantor-like structures

Graphene has proven to be an ideal system for exotic transport phenomena. In this work, we report another exotic characteristic of the electron transport in graphene. Namely, we show that the linear-regime conductance can present self-similar patterns with well-defined scaling rules, once the graphene sheet is subjected to Cantor-like nanostructuring. As far as we know the mentioned system is one of the few in which a self-similar structure produces self-similar patterns on a physical property. These patterns are analysed quantitatively, by obtaining the scaling rules that underlie them. It is worth noting that the transport properties are an average of the dispersion channels, which makes the existence of scale factors quite surprising. In addition, that self-similarity be manifested in the conductance opens an excellent opportunity to test this fundamental property experimentally.

Angle-dependent bandgap engineering in gated graphene superlattices

Graphene Superlattices (GSs) have attracted a lot of attention due to its peculiar properties as well as its possible technological implications. Among these characteristics we can mention: the extra Dirac points in the dispersion relation and the highly anisotropic propagation of the charge carriers. However, despite the intense research that is carried out in GSs, so far there is no report about the angular dependence of the Transmission Gap (TG) in GSs. Here, we report the dependence of TG as a function of the angle of the incident Dirac electrons in a rather simple Electrostatic GS (EGS). Our results show that the angular dependence of the TG is intricate, since for moderated angles the dependence is parabolic, while for large angles an exponential dependence is registered. We also find that the TG can be modulated from meV to eV, by changing the structural parameters of the GS. These characteristics open the possibility for an angle-dependent bandgap engineering in graphene.

Infinite Ergodic Theory and Non-extensive Entropies

We recapitulate results from the infinite ergodic theory that are relevant to the theory of non-extensive entropies. In particular, we recall that the Lyapunov exponent of the corresponding systems is zero and that the deviation between neighboring trajectories does not necessarily grow polynomially. Nonetheless, as we show, no single quantity can describe this subexponential growth, the generalized q-exponential expq being, in particular, ruled out. We also revisit a number of dynamical systems preserving nonfinite ergodic measure.

A physical model for dementia

Aging associated brain decline often result in some kind of dementia. Even when this is a complex brain disorder a physical model can be used in order to describe its general behavior. A probabilistic model for the development of dementia is obtained and fitted to some experimental data obtained from the Alzheimers Disease Neuroimaging Initiative. It is explained how dementia appears as a consequence of aging and why it is irreversible.