R.M.C. de Almeida

Reaction-diffusion in high-k dielectrics on Si

Abstract Thinning of the gate dielectric as required by scaling rules is currently inhibiting the so far outstanding evolution of the silicon age, owing to unacceptably high gate current (leakage current) arising from electron tunneling through the gate dielectric ultrathin layer. One possible solution is to use an alternative material to SiO2, which would interrupt more than 40 years of successful microelectronics technology based on Si and SiO2. This article discusses atomic scale investigation on the underlying difficulties of introducing ultrathin films of metal oxides, silicates, and oxynitrosilicates having dielectric constants much higher than that of SiO2—called high-k dielectrics—as gate dielectrics in advanced, Si-based metal-oxide–semiconductor field-effect transistor (MOSFET) fabrication. More specifically, we address atomic transport and chemical reaction processes generating instabilities in high-k dielectric films during different thermal processing fabrication steps following their deposition on (i) single-crystalline Si substrates or (ii) single-crystalline Si substrates on which SiO2, SiNx, or SiOxNy ultrathin films were either unintentionally formed during deposition or intentionally grown previously to high-k film deposition. A most typical reaction–diffusion situation is established in near-surface, bulk, and near-interface regions of this large family of amorphous ultrathin films deposited on Si, whose phenomenology, mathematical modeling, and atomic scale understanding constitute the subject of this article.

Dynamics of thermal growth of silicon oxide films on Si

Thermal growth of silicon oxide films on Si in dry

Theoretical approach to biological aging

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Entropy and equilibrium state of free market models

is modeled as a dynamical system, assuming that it is basically a reaction-diffusion phenomenon. Relevant findings of the last decade are incorporated, as structure and composition of the oxide/Si interface and

A dynamical model for the immune repertoire

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Bursts and cavity formation in Hydra cells aggregates: experiments and simulations

transport and reaction at initial stages of growth. The present model departs from the well-established Deal and Grove framework [B. E. Deal and A. S. Grove, J. Appl. Phys. 36, 3770 (1965)] indicating that its basic assumptions, steady-state regime, and reaction between

Stretched exponential relaxation on the hypercube and the glass transition

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Thermal growth of silicon oxynitride films on Si : a reaction-diffusion approach

and Si at a sharp oxide/Si interface are only attained asymptotically. Scaling properties of these model equations are explored, and experimental growth kinetics, obtained for a wide range of growth parameters including the small thickness range, are shown to be well described by the model.

SCALING IN A CONTINUOUS TIME MODEL FOR BIOLOGICAL AGING

We present a model for biological aging that considers the number of individuals whose (inherited) genotype determines the maximum age for death: each individual may die before that age due to some external factor, but never after that limit. The genotype of the offspring is inherited from the parent with some mutations, described by a transition matrix. The model can describe different strategies of reproduction and it is exactly soluble. We applied our method to the bit-string model for aging and the results are in perfect agreement with numerical simulations.

Dynamics of complex systems above the glass temperature

AbstractMany recent models of trade dynamics use the simple idea of wealth exchanges amongneconomic agents in order to obtain a stable or equilibrium distribution of wealth amongnthe agents. In particular, a plain analogy compares the wealth in a society with thenenergy in a physical system, and the trade between agents to the energy exchange betweennmolecules during collisions. In physical systems, the energy exchange among moleculesnleads to a state of equipartition of the energy and to an equilibriumnsituation where the entropy is a maximum. On the other hand, in a large class of exchangenmodels, the system converges to a very unequal condensed state, where onenor a few agents concentrate all the wealth of the society while the wide majority ofnagents shares zero or almost zero fraction of the wealth. So, in those economic systems anminimum entropy state is attained. We propose here an analytical model where weninvestigate the effects of a particular class of economic exchanges that minimize thenentropy. By solving the model we discuss the conditions that can drive the system to anstate of minimum entropy, as well as the mechanisms to recover a kind of equipartition ofnwealth.