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RESISTIVITY INDUCED BY ELECTRON SCATTERING FROM DISORDERED GRAIN BOUNDARIES IN THIN GOLD FILMS Imprimir
Raul Muñoz
Departamento de Física, DFI
FCFM, Universidad de Chile

Viernes 7 de agosto, 16:15
Departamento de Física, Sala F12
Av Blanco Encalada 2008

En este trabajo se presenta un resumen de los experimentos que han permitido medir los efectos de tamaño que gobiernan el transporte de carga en películas metálicas delgadas. En particular, hemos podido discriminar (experimentalmente) entre una resistividad inducida por  dispersión de electrones por una superficie rugosa, y una resistividad inducida por  dispersión de electrones por bordes de grano.

Se presenta también la primera  teoría cuántica de scattering electrón-borde de grano, donde el comportamiento del gas  de electrones se describe empleando la solución exacta de la ecuación de  Schrodinguer en un potencial periodico de Kronig-Penney, donde los bordes de grano son representados por una  serie de deltas de Dirac espaciadas por una distancia D. Este trabajo corresponde a la investigación doctoral  desarrollada por el Sr. Claudio Arenas en el area de Física Aplicada. El resultado notable  de este modelo cuántico, es el cambio drástico de paradigma referente a los  mecanismos que dan origen a la resistividad en nanoestructuras metálicas constituídas por granos  cuyo diamtero D es inferior al camino libre medio electrónico en el material  cristalino a temperatura ambiente (39 nm en Cu, 38 nm en Au).

Esta condición debiera ser satisfecha por las interconexiones de Cu en los circuitos integrados previstos por la ITRS para la próxima década. En películas de Au donde D es del orden de 11 nm, la resistividad de la película resulta controlada por localización (debil) de  Anderson, inducida por scattering de electrones en un conjunto de granos desordenados, lo que da origen a una longitud de localización de alrededor de 110  nm. Se espera que interconexiones de Cu exhiban un comportamiento similar, con una  resistividad controlada también por localización de Anderson inducida por scattering electrónico en un conjunto de granos desordenados.
 

Seminarios Anteriores

Thermally induced fluctuations in plasmas and its relation to "turbulence" in plasma? Imprimir
Alejandro Valdivia
Departamento de Física, DFC
Facultad de Ciencias, U. de Chile

Viernes 31 de julio, 16:15
Departamento de Física, Sala F12
Av Blanco Encalada 2008

Recently, there has been quite a lot of discussion about the relevance of thermally induced magnetic fluctuations in plasma, particularly in laboratory and solar wind plasmas. These fluctuations are produced by the random motion of particles in the plasma so that their understanding requires a kinetic treatment that relies on an extension of the fluctuation-dissipation theorem. In the solar wind, this treatment has been able to quantitatively describe their relevance to the observed magnetic fluctuations for anisotropic plasmas.
 
Living in the boundary Imprimir
Rodrigo Aros
Departamento de Ciencias Físicas
Universidad Andrés Bello

Viernes 10 de julio, 16:15
Departamento de Física, Sala F12
Av Blanco Encalada 2008

During the last decades the AdS/CFT conjecture took a central role in gravitation and high energy physics as it can open a connection with other areas of physics such as solid state, particle and fluid physics. In fact this conjecture may well lay on the idea that our reality could have more than a single description. In this talk this will be discussed  and some new ideas concerning a potential duality between AdS gravity and Conformal gravity.
 
Crystallization fronts in supercooled liquids: how rapid fronts can lead to disordered glassy solids Imprimir
Edgar Knobloch
Professor of Physics
University of California at Berkeley

Viernes 19 de junio, 16:15
Departamento de Física, Sala F12
Av Blanco Encalada 2008

Resumen:

We determine the speed of a crystallization front as it advances into the uniform liquid phase after the system has been quenched into the crystalline region of the phase diagram. There are two mechanisms by which the front can advance, depending on whether the liquid state is linearly stable or not. When the liquid is linearly unstable, the front speed can be calculated by applying a marginal stability criterion. As the crystallization front advances into the unstable liquid phase, the density profile behind the advancing front develops density modulations and the wavelength of these modulations is a dynamically chosen quantity. For shallow quenches, the selected wavelength is close to that of the crystalline phase and so well-ordered crystalline states are formed. However, when the system is deeply quenched, we find that this wavelength can be quite different from that of the equilibrium crystal, so the crystallization front naturally generates disorder in the system. Significant rearrangement and ageing must subsequently occur for the system to form the regular well-ordered crystal that corresponds to the free energy minimum. Additional disorder is introduced whenever a front develops from random initial conditions. We illustrate these findings using two different models of a fluid of soft, purely repulsive particles in solution.
 
Bio-inspired microfluidics: The case of the velvet worm Imprimir
Andrés Concha
Escuela de Ingeniería y Ciencias
Universidad Adolfo Ibañez

Viernes 12 de junio, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

The rapid squirt of a proteinaceous slime jet endows the ancient velvet worms (Onychophora) with a unique mechanism for defense from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date neither qualitative nor quantitative descriptions have been provided for this unique adaptation. We have investigated the mechanism that allows velvet worms the fast oscillatory motion of their oral papillae and the exiting liquid jet that oscillates with frequencies f ∼ 30 − 60 Hz. Using anatomical images and high speed videography, we show that even without fast muscular action of the papilla, a strong contraction of the slime reservoir and the geometry of the reservoir-papilla system suffices to accelerate the slime to speeds up to v ∼ 5 m/s in about ∆t ∼ 60 ms. A theoretical analysis and a physical simulacrum allow us to infer that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. We propose several applications that can be implemented using this instability, ranging from high-throughput droplet production, printing, and micro-nanofiber production among others.
 
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