Ponencias (Física Aplicada I)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10851

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A semiclassical model for charge transfer along ion chains in silicates
(IOP Publishing, 2024) Archilla, Juan F. R.; Bajārs, Jānis; Doi, Yusuke; Kimura, Masayuki; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; University of Latvia; Universidad de Sevilla. FQM280: Física no Lineal
It has been observed in fossil tracks and experiments in the layered silicate mica muscovite the transport of charge through the cation layers sandwiched between the layers of tetrahedra-octahedra-tetrahedra. A classical model for the propagation of anharmonic vibrations along the cation chains has been proposed based on first principles and empirical functions. In that model, several propagating entities have been found as kinks or crowdions and breathers, both with or without wings, the latter for specific velocities and energies. Crowdions are equivalent to moving interstitials and transport electric charge if the moving particle is an ion, but they also imply the movement of mass, which was not observed in the experiments. Breathers, being just vibrational entities, do not transport charge. In this work, we present a semiclassical model obtained by adding a quantum particle, electron or hole to the previous model. We present the construction of the model based on the physics of the system. In particular, the strongly nonlinear vibronic interaction between the nuclei and the extra electron or hole is essential to explain the localized charge transport, which is not compatible with the adiabatic approximation. The formation of vibrational localized charge carriers breaks the lattice symmetry group in a similar fashion to the Jahn-Teller Effect, providing a new stable dynamical state. We study the properties and the coherence of the model through numerical simulations from initial conditions obtained by tail analysis and other means. We observe that although the charge spreads from an initial localization in a lattice at equilibrium, it can be confined basically to a single particle when coupled to a chaotic quasiperiodic breather. This is coherent with the observation that experiments imply that a population of charge is formed due to the decay of potassium unstable isotopes.
Multiple Time Stepping Methods for Numerical Simulation of Charge Transfer by Mobile Discrete Breathers
(American Institute of Physics, 2024-06-07) Bajārs, Jānis; Archilla, Juan F. R.; Universidad de Sevilla. Departamento de Física Aplicada I; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; Junta de Andalucía; Universidad de Sevilla. FQM280: Física No Lineal
In this work we propose new structure-preserving multiple time stepping methods for numerical simulation of charge transfer by intrinsic localized modes in nonlinear crystal lattice models. We consider, without loss of generality, one-dimensional crystal lattice models described by classical Hamiltonian dynamics, whereas charge (electron or hole) is modeled as a quantum particle within the tight-binding approximation. Proposed multiple time stepping schemes are based on symplecticity-preserving symmetric splitting methods recently developed by the authors. Originally developed explicit splitting methods do not exactly conserve total charge probability, thus, to improve charge probability conservation and to better resolve high frequency oscillations of the charge in numerical simulations with large time steps we incorporate multiple time stepping approach when solving split charge equations. Improved numerical results with multiple time stepping methods of charge transfer by mobile discrete breathers are demonstrated in a crystal lattice model example.
Quodons in tokamak fusion reactors
(IEICE Digital Library, 2023) Russell, F. Michael; Archilla, Juan F. R.; Universidad de Sevilla. Departamento de Física Aplicada I
Experiments have shown that alpha particles incident on different materials bring about the generation of quodons, that is packets of localized energy that can bind to an electric charge and transport it without the presence of an electric field, a phenomenon called hyperconductivity. Tokamak fusion reactors produce a huge amount of alpha particles, transporting energy and charge trough insulators and metals at much more speed that ohmic conduction and heat conductivity. The consequences are still unclear but should be studied and incorporated in reactor designs.
Spectrum of polarobreathers in a model for layered silicates
(IEICE Digital Library, 2023) Archilla, Juan F. R.; Bajars, Janis; Doi, Yusuke; Kimura, Masayuki; Universidad de Sevilla. Departamento de Física Aplicada I
Experiments in layered silicated have shown the capability of nonlinear excitations to couple with electric charge and transport it without the presence of an electric field, a phenomenon called hyperconductivity. We have constructed a model for these excitations and using the theory of exact breathers in their moving frame, obtained breathers coupled to a charge that travel carried by a nonlinear localized wave.
Ballistic charge transport by polarokinks and polarobreathers
(IEICE Digital Library, 2022) Archilla, Juan F. R.; Bajars, Janis; Doi, Yusuke; Kimura, Masayuki
Some materials of the mica group experience hyperconductivity, the transport of electric charge without an electric field. The charge transport is stimulated by ion bombardment that produces nonlinear waves that transport charge. We have developed a semiclassical model using physical principles and empiric potentials and found nonlinear waves that are able to transport charge.
Geometric numerical integration of semi-classical Hamiltonain lattice dynamics
(IEICE Digital Library, 2022) Bajars, Janis; Archilla, Juan F. R.; Universidad de Sevilla. Departamento de Física Aplicada I
In this work we provide a brief overview of recently proposed symplecticity-preserving symmetric splitting methods for semi-classical Hamiltonian dynamics of charge transfer by intrinsic localized modes in nonlinear crystal lattice models [1]. Without loss of generality, we consider one-dimensional crystal lattice models described by classical Hamiltonian dynamics, whereas charge particle is modeled as quantum particle within the tight-binding approximation. Canonical Hamiltonian equations for the coupled lattice-charge dynamics are derived. Structurepreserving splitting methods are constructed by splitting the total Hamiltonian into the sum of Hamiltonians which individual dynamics can be solved exactly. Exactly charge conserving symplectic splitting methods are also proposed which require only one solution of a linear system of equations per time step. Developed computationally efficient non-dissipative methods provide new means for long-time simulations of charge transfer by nonlinear lattice excitations.
Supratransmission-induced discrete rogue wave in nonlinear chain
(IEICE Digital Library, 2022) Togueu Motcheyo, Alain B.; Kimura, Masayuki; Doi, Yusuke; Archilla, Juan F. R.; Universidad de Sevilla. Departamento de Física Aplicada I
We numerically generate a discrete rogue wave in a chain of a nonlinear pendulum using the nonlinear supratransmission way and the instability of shaken pendulum. This could open the way for the application of discrete rogue waves within simple devices.
A tight-binding model for charge transport in silicate layers
(IEICE Digital Library, 2020) Archilla, Juan F. R.; Doi, Yusuke; Kimura, Masayuki; Universidad de Sevilla. Departamento de Física Aplicada I
Observations and experiments in silicates of the mica group show the transport of electric charge along the cation layers in absence of an electric field, a phenomenon called hyperconductivity. The transport of charge is achieved when a nonlinear vibration brings about that the ions become close enough for the transfer of an electron or hole. A model is developed in detail, approximations of different order for smaller vibration are considered so as to obtain approximate solutions. The full equations are integrated numerically with several approaches to overcome the problem caused by the different time scales of ion and electron movements. Localized solution showing the transport of charge coupled to nonlinear excitations are observed and described.
One-dimensional models for liquid columns subjected to electric fields
(IEEE, 1994-10) Castellanos Mata, Antonio; García García, Francisco Javier; González García, Heliodoro; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada III; Dirección General Interministerial de Ciencia y Tecnología (DGICYT). España
An analysis of slender axisymmetric liquid columns is performed on the basis of one-dimensional models, recently derived and generalized here to include the effect of dielectric forces at the interface. The natural frequencies and stability criteria in the absence of gravity are obtained. Results are compared with the known exact linear solutions of the corresponding three-dimensional problems.
3-D and 1-D dynamics of slender liquid jets: linear analysis with electric field and accuracy of 1-D models near the breakup
(IEEE Xplore, 1999-10) García García, Francisco Javier; Castellanos, Antonio; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Universidad de Sevilla. Departamento de Física Aplicada I
In a previous paper [Phys. Fluids, vol. 6, 2676 (1994)], the authors derived four 1-D models (Lee, Cosserat, averaged, and parabolic models) for slender axisymmetric liquid jets from the Navier-Stokes equations. The error of these 1-D models was calculated for small perturbations, in the absence of electric field. Here, we extend the linear error analysis to both perfectly insulating liquid jets in a tangential electric field and perfectly conducting liquid jets in a radial electric field. The accuracy of these models for studying the breakup, when nonlinear effects are no longer negligible, is also tested in the absence of electric field. A comparison of numerical 3-D solutions with results from 1-D models is made. A formulation of the energy conservation in 1-D models allows identifying and correcting a numerical instability of the averaged model near the breakup. It also explains why the Cosserat model overestimates the breakup time for moderate or large viscosity. Good agreement between 1-D and 3-D numerical results is found.
Perpendicular-field EHD instabilities visualized in a tip-plane configuration
(IEEE Xplore, 2002-10) Vega, F.; Pérez Izquierdo, Alberto Tomás; García García, Francisco Javier; Castellanos, Antonio; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia y Tecnología (MCYT). España
EHD interfacial instabilities can be induced by corona discharge from a tip electrode onto a liquid-air interface. The corona current charges the liquid surface and instabilities may appear depending on the applied voltage and the liquid properties. We present a technique to detect the onset of instability based on image processing. To establish the instability threshold we apply an edge-detection algorithm to images of the liquid surface acquired through a videa camera.
Dynamics and deformation of a drop in a DC electric field
(IEEE Xplore, 2003-10) Khayari, Abdelmounim; Pérez Izquierdo, Alberto Tomás; García García, Francisco Javier; Castellanos, Antonio; Universidad de Sevilla. Departamento de Física Aplicada I; Universidad de Sevilla. Departamento de Electrónica y Electromagnetismo; Ministerio de Ciencia Y Tecnología (MCYT). España
We consider a single conducting drop in suspension in a poorly conducting liquid between two horizontal electrodes. When a DC field is applied to the electrodes, the drop charges and rises within the'liquid, then falls down as its charge leaks away, due to the finite elechic relaxation time of the liquid. The drop keepsbouncing as long as the high voltage applied remains above a minimum threshold. We focus our study on the dynamics and the deformation of a water drop before the lift-off and during its motion. Electrodes of different materials are used in order to illustrate the role of interfacial energy between the electrode and the water.
In situ mechanical, temperature and gas exposure treatments of materials combined with variable energy positron beam techniques
(ScienceDirect, 2002-06-21) Schut, Henk; Veen, A. van; Rivera, A.; Huis, M.A van; Alba García, A.; Escobar-Galindo, Ramón; Universidad de Sevilla. Departamento de Física Aplicada I
An overview is given of the extension of the Delft variable energy positron (VEP) beam facility with equipment for in situ heating, cooling, 4-point bending, hydrogen permeation and gas ad- and absorption of bulk materials, surfaces and interfaces.
The design of an electrostatic variable energy positron beam for studies of defects in ceramic coatings and polymer films
(ScienceDirect, 2002-06-22) Abadjieva, E.; Schut, Henk; Alba García, A.; Escobar-Galindo, Ramón; Veen, A. van; Pimblott, S.M.; Universidad de Sevilla. Departamento de Física Aplicada I
An electrostatic variable energy positron beam for studying defects in ceramic coatings, polymer films and MOS-devices is developed for operation in Doppler-broadening (DB) and positron annihilation lifetime (PAL) modes. In DB mode the implantation energy can be varied between 3 and 30 keV with a beam diameter on the target ranging from 0.4 to 0.5 mm FWHM. In PAL mode the start-signal is given by secondary electron emission from a 25 nm thin carbon foil placed in front of the target. After passing the foil the positron beam is focused on the target with a spot size of 2 mm FWHM at 1 keV down to 0.6 mm FWHM at 30 keV. The target chamber is equipped with an in situ four-point bending device for studying defects introduced by tensile and compressive stresses.
Nano-porosity in silica reinforced methyltrimethoxysilane coatings studied by positron beam analysis
(ScienceDirect, 2003-06) Escobar-Galindo, Ramón; Veen, A. van; Schut, Henk; Falub, Claudiu V.; Balkenende, A.R.; With, Govert de; Hosson, J.Th.M. de; Universidad de Sevilla. Departamento de Física Aplicada I
The porosity in particle reinforced sol-gel coatings has been studied. Silica particles (Ludox-TM40) are introduced into methyl silicate coatings to increase the hardness, the elastic modulus and the fracture toughness. The methyl silicate has a relatively low density (about 1.2 g/cm2), while the silica particles are known to be porous. However, the porosity of the silica particles is not accurately known. For model calculations on mechanical properties like the E-modulus this porosity should be known. Positron Beam Analysis (PBA), using the Doppler Broadening (DB) and 2D-Angular Correlation of Annihilation Radiation (2D-ACAR) techniques, was therefore performed for analysis of the porosity. Samples with different weight fractions (0, 20 and 63 wt.%) of silica particles of typically 40 nm in diameter and treated at different curing temperatures (623 and 723 K) were measured. With increasing filler content we observed a decrease in the positron annihilation S-parameter and a broadening of the para-positronium (p-Ps) fraction. By neglecting positron diffusion we can separate porosity in the matrix from that in the particles. This assumption is valid as long as the expected positron diffusion length is short compared to the size of the filler particles, as in the present case. A more detailed description takes into account the local environment of the filler particles affecting their adhesion to the matrix. It is concluded that the density of the silica particles is about 1.4 g/cm2.
Systematic positron study of hydrophilicity of the internal pore surface in ordered low-k silica thin films
(ScienceDirect, 2003-09-15) Escobar-Galindo, Ramón; Veen, A. van; Schut, Henk; Eijt, S.W.H.; Falub, Claudiu V.; Balkenende, A.R.; Theije, Fremke de; Universidad de Sevilla. Departamento de Física Aplicada I
Non-destructive Doppler Broadening (DB), Positronium fraction (f-Ps) and Two Dimensional Angular Correlation of Annihilation Radiation (2D-ACAR), Positron Beam Analysis (PBA) techniques have been used to study well-ordered mesoporous silica thin films with hydrophobic or hydrophilic character. The DB results, characterized by the S and W parameters, are related to both the open volume and the chemical environment at the positron annihilation site. The f-Ps and 2D-ACAR techniques are very sensitive probes to determine the type of porosity (open or closed in terms of positronium escape) in thin film materials. Samples with varying pore size (well-controlled at 2, 3 and 4.5 nm, or incorporating microporosity in the silica), pore fraction (from 4 to 57%) and extent of hydrophilicity have been studied. In the hydrophilic samples with small pore size the S-parameter increases with the porosity while the Ps-fraction remains almost unchanged. Increasing the pore size leads to smaller changes in S with increasing porosity. However, an abrupt change in the Ps-fraction is observed for samples with porosity higher than 45%, indicating a positronium percolation threshold for samples with 2D ordering structure. On the other hand, for hydrophobic samples with high porosity (57%) the highest S parameter and Ps-fraction were obtained for the three pore sizes studied. 2D-ACAR is used to determine the fraction and velocity of Ps escaping from some of the latter samples exhibiting positronium percolation. The relationship between these observations and porosity will be discussed in terms of branching of the positron annihilation channels inside the mesoporous films.
Depth-selective 2D-ACAR studies on low-k dielectric thin films
(ScienceDirect, 2003) Eijt, S.W.H.; Veen, A. van; Falub, Claudiu V.; Escobar-Galindo, Ramón; Schut, Henk; Mijnarends, P.E.; Theije, Fremke de; Balkenende, A.R.; Universidad de Sevilla. Departamento de Física Aplicada I
Depth-selective 2D-ACAR investigations on ordered mesoporous silica thin films provide direct evidence that para-positronium (p-Ps) created deep in the films can escape through a network of interconnected pores. The depth dependence of the escape fraction and of the average kinetic energy of non-thermally excited p-Ps is in quantitative agreement with Monte Carlo modeling, assuming classical collisions of p-Ps with the pore walls. The model provides insight in the shape of the angular correlation distributions and their sensitivity to, e.g., the effective wall mass Ms and pore dimensions.
Thermally induced delamination of amorphous hydrogenated carbon coatings monitored by positron beam analysis
(ScienceDirect, 2004-03) Escobar-Galindo, Ramón; Veen, A. van; Schut, Henk; Rabbani, F.; Janssen, G.C.A.M.; Hosson, J.Th.M. de; Universidad de Sevilla. Departamento de Física Aplicada I
In this work we have studied the adhesion of PVD amorphous hydrogenated carbon (a-C:H) thin coatings (<200 nm) on crystalline silicon by means of positron beam analysis (PBA). PBA allows the study of the a-C:H layer and the interface by monitoring changes on the Doppler broadening parameters S and W. Depending on the deposition condition, using PBA some samples were found to be delaminated after deposition. Annealing experiments were performed on samples that did not show signs of delamination after deposition. Some of these samples were distinguished by the fact that nitrogen was used in the manufacturing process. Samples were annealed for 30 min in vacuum up to 600 °C in order to remove gases absorbed at the interface. PBA experiments were performed after each annealing step. For the sample without N2 there are no S–W changes either in the coating or at the interface until 600 °C is reached. On the other hand, for the sample containing N2, there is a gradual change in these parameters with temperature. In this coating, after annealing to 500 °C, the increase in W is related to release of H2 and consequent restructuring of the layer. The decrease in the value of S between 500 and 600 °C indicates the formation of graphitic crystallites. There is open volume at the coating/substrate interface since the S parameter gradually increases while W remains constant until 400 °C. This behaviour in S–W is related to the removal of physisorbed hydrogen. At approximately 400 °C the H bonded to C at tetrahedral sites is also released which leads to an internal restructuring of the ‘lattice’, hence a decrease in the value of S is observed. Finally, at 600 °C both coatings delaminate, as the interface parameters tend towards the same values as those of the sample which had delaminated after deposition.
Compositional depth profiling analysis of thin and ultrathin multilayer coatings by radio-frequency glow discharge optical emission spectroscopy
(ScienceDirect, 2006-06-20) Escobar-Galindo, Ramón; Forniés, E.; Albella Martín, José María; Universidad de Sevilla. Departamento de Física Aplicada I
In most of the industrial applications of multilayer coatings, a detailed knowledge of the interlayer structure and the interfaces is needed. In comparison with standard surface analysis techniques (SIMS, XPS, AES, etc.), depth profiling by radio-frequency glow discharge optical emission spectroscopy (rf-GDOES) provides rapid information, with a high depth resolution, about the multilayer composition. In rf-GDOES analysis, the depth resolution mainly depends on the roughening induced during the sputtering, the resulting crater geometry and sputtering of material re-deposited on the crater wall. In this work, we have isolated the contribution of these effects in the depth resolution of metal and metal nitride multilayer coatings. The importance of these effects has been firstly tested on multilayer stacks consisting of three alternating metal or nitride layers, typically of 500 nm each. The profiles of materials with high sputtering rate become less affected than material with low sputtering rate due to lower mixing of the layers. The contribution of these factors increased during the analysis of thinner multilayer coatings (∼ 100 nm). After reversing the order of the layer elements, completely different profiles were measured, confirming the role of the differences in sputtering rate and crater shape. Finally, in order to evaluate the depth resolution function of the GDOES technique, ultrathin metal chromium and aluminium nitride layers of 5 nm have been buried at different depths in a metal titanium and chromium nitride matrix, respectively, up to a thickness of 2 μm. The markers were properly resolved both near the surface and deeply embedded in the matrix, demonstrating the excellent capabilities of the GDOES technique to detect very thin films in the nanometric range.
Biocompatible Silver-containing a-C:H and a-C coatings: A Comparative Study
(SpirngerLink, 2007-04-18) Endrino, José Luis; Allen, Matthew; Escobar-Galindo, Ramón; Zhang, Hanshen; Anders, André; Albella Martín, José María; Universidad de Sevilla. Departamento de Física Aplicada I
Hydrogenated diamond-like-carbon (a-C:H) and hydrogen-free amorphous carbon (a-C) coatings are known to be biocompatible and have good chemical inertness. For this reason, both of these materials are strong candidates to be used as a matrix that embeds metallic elements with antimicrobial effect. In this comparative study, we have incorporated silver into standard diamond-like carbon (DLC) coatings by plasma ion implantation and deposition (PIII&D) using methane (CH4) plasma and simultaneously depositing Ag from a pulsed cathodic arc source. In addition, we have grown amorphous carbon – silver composite coatings using a dual-cathode pulsed filtered cathodic-arc (FCA) source. The silver atomic content of the deposited samples was analyzed using glow discharge optical spectroscopy (GDOES). In both cases, the arc pulse frequency of the silver cathode was adjusted in order to obtain samples with approximately 5 at.% of Ag. Surface hardness of the deposited films was analyzed using the nanoindentation technique. Cell viability for both a-C:H/Ag and a-C:/Ag samples deposited on 24-well tissue culture plates has been evaluated.

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