The structural and electrical properties of thermally grown TiO2 thin films

We studied the structural and electrical properties of TiO2 thin films grown by thermal oxidation of e-beam evaporated Ti layers on Si substrates. Time of flight secondary ion mass spectroscopy (TOF-SIMS) was used to analyse the interfacial and chemical composition of the TiO2 thin films. Metal oxide semiconductor (MOS) capacitors with Pt or Al as the top electrode were fabricated to analyse electrical properties of the TiO2 thin films. We show that the reactivity of the Al top contact affects electrical properties of the oxide layers. The current transport mechanism in the TiO2 thin films is shown to be Poole–Frenkel (P–F) emission at room temperature. At 84 K, Fowler– Nordheim (F–N) tunnelling and trap-assisted tunnelling are observed. By comparing the electrical characteristics of thermally grown TiO2 thin films with the properties of those grown by other techniques reported in the literature, we suggest that, irrespective of the deposition technique, annealing of as-deposited TiO2 in O2 is a similar process to thermal oxidation of Ti thin films

Relativistic Kinetic Equations for Finite Domains and Freeze-out Problem

The relativistic kinetic equations for the two domains separated by the hypersurface with both space- and time-like parts are derived. The particle exchange between the domains separated by the time-like boundaries generates source terms and modifies the collision term of the kinetic equation. The correct hydrodynamic equations for the ``hydro+cascade'' models are obtained and their differences from existing freeze-out models of the hadronic matter are discussed

Scattering Theory of Charge-Current Induced Magnetization Dynamics

In ferromagnets, charge currents can excite magnons via the spin-orbit coupling. We develop a novel and general scattering theory of charge current induced macrospin magnetization torques in normal metal$|$ferromagnet$|$normal metal layers. We apply the formalism to a dirty GaAs$|$(Ga,Mn)As$|$GaAs system. By computing the charge current induced magnetization torques and solving the Landau-Lifshitz-Gilbert equation, we find magnetization switching for current densities as low as $5\times 10^{6}$~A/cm$^2$. Our results are in agreement with a recent experimental observation of charge-current induced magnetization switching in (Ga,Mn)As.Comment: Final version accepted by EP

Dissipative hydrodynamics in 2+1 dimension

In 2+1 dimension, we have simulated the hydrodynamic evolution of QGP fluid with dissipation due to shear viscosity. Comparison of evolution of ideal and viscous fluid, both initialised under the same conditions e.g. same equilibration time, energy density and velocity profile, reveal that the dissipative fluid evolves slowly, cooling at a slower rate. Cooling get still slower for higher viscosity. The fluid velocities on the otherhand evolve faster in a dissipative fluid than in an ideal fluid. The transverse expansion is also enhanced in dissipative evolution. For the same decoupling temperature, freeze-out surface for a dissipative fluid is more extended than an ideal fluid. Dissipation produces entropy as a result of which particle production is increased. Particle production is increased due to (i) extension of the freeze-out surface and (ii) change of the equilibrium distribution function to a non-equilibrium one, the last effect being prominent at large transverse momentum. Compared to ideal fluid, transverse momentum distribution of pion production is considerably enhanced. Enhancement is more at high $p_T$ than at low $p_T$. Pion production also increases with viscosity, larger the viscosity, more is the pion production. Dissipation also modifies the elliptic flow. Elliptic flow is reduced in viscous dynamics. Also, contrary to ideal dynamics where elliptic flow continues to increase with transverse momentum, in viscous dynamics, elliptic flow tends to saturate at large transverse momentum. The analysis suggest that initial conditions of the hot, dense matter produced in Au+Au collisions at RHIC, as extracted from ideal fluid analysis can be changed significantly if the QGP fluid is viscous.Comment: 11 pages, 10 figures (revised). In the revised version, calculations are redone with ADS/CFT and perurbative estimate of viscosity. Comments on the unphysical effects like early reheating of the fluid, in 1st order dissipative theories are added. The particle spectra calculations are redone with modified programm

Transport in a highly asymmetric binary fluid mixture

We present molecular dynamics calculations of the thermal conductivity and viscosities of a model colloidal suspension with colloidal particles roughly one order of magnitude larger than the suspending liquid molecules. The results are compared with estimates based on the Enskog transport theory and effective medium theories (EMT) for thermal and viscous transport. We find, in particular, that EMT remains well applicable for predicting both the shear viscosity and thermal conductivity of such suspensions when the colloidal particles have a ``typical'' mass, i.e. much larger than the liquid molecules. Very light colloidal particles on the other hand yield higher thermal conductivities, in disagreement with EMT. We also discuss the consequences of these results to some proposed mechanisms for thermal conduction in nanocolloidal suspensions.Comment: 13 pages, 6 figures, to appear in Physical Review E (2007

Momentum of an electromagnetic wave in dielectric media

Almost a hundred years ago, two different expressions were proposed for the energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical arguments were advanced in favour of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy--momentum tensor is complete on its own. When the appropriate accompanying energy--momentum tensor for the material medium is also considered, experimental predictions of all the various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0 from Eq.(44

Isotropic cosmological singularities: other matter models

Isotropic cosmological singularities are singularities which can be removed by rescaling the metric. In some cases already studied (gr-qc/9903008, gr-qc/9903009, gr-qc/9903018) existence and uniqueness of cosmological models with data at the singularity has been established. These were cosmologies with, as source, either perfect fluids with linear equations of state or massless, collisionless particles. In this article we consider how to extend these results to a variety of other matter models. These are scalar fields, massive collisionless matter, the Yang-Mills plasma of Choquet-Bruhat, or matter satisfying the Einstein-Boltzmann equation.Comment: LaTeX, 19 pages, no figure

Density dynamics from current auto-correlations at finite time- and length-scales

We consider the increase of the spatial variance of some inhomogeneous, non-equilibrium density (particles, energy, etc.) in a periodic quantum system of condensed matter-type. This is done for a certain class of initial quantum states which is supported by static linear response and typicality arguments. We directly relate the broadening to some current auto-correlation function at finite times. Our result is not limited to diffusive behavior, however, in that case it yields a generalized Einstein relation. These findings facilitate the approximation of diffusion constants/conductivities on the basis of current auto-correlation functions at finite times for finite systems. Pursuing this, we quantitatively confirm the magnetization diffusion constant in a spin chain which was recently found from non-equilibrium bath scenarios.Comment: 4 pages, 1 figure, accepted for publication in Europhys. Let

The role of Joule heating in the formation of nanogaps by electromigration

We investigate the formation of nanogaps in gold wires due to electromigration. We show that the breaking process will not start until a local temperature of typically 400 K is reached by Joule heating. This value is rather independent of the temperature of the sample environment (4.2-295 K). Furthermore, we demonstrate that the breaking dynamics can be controlled by minimizing the total series resistance of the system. In this way, the local temperature rise just before break down is limited and melting effects are prevented. Hence, electrodes with gaps < 2 nm are easily made, without the need of active feedback. For optimized samples, we observe quantized conductance steps prior the gap formation.Comment: including 7 figure