Role Of Thermal Effects Research Articles

Intensive Structural Disorder Induces Electronic Delocalization: Amorphous Solid‐Liquid Transition in Ovonic Threshold Switching Materials

AbstractDisorder‐induced electronic localization is responsible for the OFF state of the Ovonic threshold switching (OTS) device, which is an indispensable component in the present 3D‐crossbar‐architecture phase‐change memory circuit. However, the atomic mechanism of the OTS device, especially the role of thermal effect, remains a long‐term open question. Recent researches suggest that the working current of the OTS ON‐state is often large enough to melt the adjacent phase‐change memory material in the OTS+PCM devices. Thus, Joule heating‐induced atomic/electronic structure transition in OTS materials must be seriously considered. Taking the typical OTS material GeSe as an example, first‐principles calculations reveal an unexpected electronic delocalization induced by the enhanced structural disorder upon solid‐liquid transition. Meanwhile, as the temperature rises, the band gap decreases or even closes, leading to an increase in carrier concentration. Therefore, the melting filament with high conductivity could be responsible for the holding‐ON state of OTS materials. The results in this study may provide possible explanations for some puzzles of OTS devices, such as the reasons for holding‐ON state and limited endurance.

Atomistic modeling of thermal effects in focused electron beam-induced deposition of Me$$_2$$Au(tfac)

The role of thermal effects in the focused electron beam induced deposition (FEBID) process of Me$_2$Au(tfac) is studied by means of irradiation-driven molecular dynamics simulations. The FEBID of Me$_2$Au(tfac), a commonly used precursor molecule for the fabrication of gold nanostructures, is simulated at different temperatures in the range of $300-450$ K. The deposit's structure, morphology, growth rate, and elemental composition at different temperatures are analyzed. The fragmentation cross section for Me$_2$Au(tfac) is evaluated on the basis of the cross sections for structurally similar molecules. Different fragmentation channels involving the dissociative ionization (DI) and dissociative electron attachment (DEA) mechanisms are considered. The conducted simulations of FEBID confirm experimental observations that deposits consist of small gold clusters embedded into a carbon-rich organic matrix. The simulation results indicate that accounting for both DEA- and DI-induced fragmentation of all the covalent bonds in Me$_2$Au(tfac) and increasing the amount of energy transferred to the system upon fragmentation increase the concentration of gold in the deposit. The simulations predict an increase in Au:C ratio in the deposit from 0.18 to 0.25 upon the temperature increase from 300 K to 450 K, being within the range of experimentally reported values.

Perspective of unstable solid electrolyte interphase induced lithium dendrite growth: Role of thermal effect

It is experimentally demonstrated recently that the complicated temperature dependence of lithium electrodeposition, which remains unclear and requires further exploration, may provide a regulatory strategy for suppressing dendrites. In order to explore the underlying physics of temperature-dependent performance of lithium metal batteries, we utilize a comprehensive model including the electrochemical process of lithium electrodeposition, the non-uniform solid electrolyte interface (SEI) evolution on the moving dendrite surface and their interaction with incorporating the thermal effects, where the temperature dependencies of the SEI formation, lithium electrodeposition and bulk diffusion kinetic are assumed to follow Arrhenius-type dependencies independently. On the basis of present work, we are able to evaluate the competition mechanisms of the interfacial reactions between SEI formation and lithium dendrite growth with a series of governing mechanisms including different ambient temperature, applied current density and surface geometric curvature. The results show that the inhomogeneity of SEI layer controlled by multiple factors finally determine whether or not the lithium dendrite can be suppressed at elevated temperature, which provide a new perspective into the underlying thermo-electro-chemical performance and may be instructive for the interfacial design of rechargeable batteries.

The Role of Thermal Effects in Plasma Medical Applications: Biological and Calorimetric Analysis

Plasma Medicine tools exploit the therapeutic effects of the exposure of living matter to plasma produced at atmospheric pressure. Since these plasmas are usually characterized by a non-thermal equilibrium (highly energetic electrons, low temperature ions), thermal effects on the substrate are usually considered negligible. Conversely, reactive oxygen and nitrogen species (RONS), UV radiation and metastables are thought to play a major role. In this contribution, we compare the presence of thermal effects in different operational regimes (corresponding to different power levels) of the Plasma Coagulation Controller (PCC), a plasma source specifically designed for accelerating blood coagulation. In particular, we analyze the application of PCC on human blood samples (in vitro) and male Wistar rats tissues (in vivo). Histological analysis points out, for the highest applied power regime, the onset of detrimental thermal effects such as red cell lysis in blood samples and tissues damages in in-vivo experiments. Calorimetric bench tests performed on metallic targets show that the current coupled by the plasma on the substrate induces most of measured thermal loads through a resistive coupling. Furthermore, the distance between the PCC nozzle and the target is found to strongly affect the total power.

Role of thermal effects in neon and argon constricted discharges

The paper is aimed at investigating the role of inhomogeneous heating of the neutral gas in a constricted glow discharge in neon and argon. It is shown that inhomogeneous heating is not the primary cause of constriction in specified gases at pressures of tens and hundreds Torr cm and reduced currents not exceeding 100–200 mA cm−1. Constriction of the positive column occurs even with an insignificant gas heating in a pulsed regime. An abrupt constriction is caused by the nonlinear dependence of the ionization number on the electron density. In mentioned discharge conditions the frequency of electron–electron collisions is comparable to the electron energy relaxation frequency due to elastic electron-atom collisions. Thermal effects play a secondary role in the formation of a constricted discharge. At the same time, inhomogeneous gas heating in argon is more notable than in neon. Unlike neon, stationary argon discharge loses spatial stability in a vertically oriented tube as the pressure and current increase and a buoyancy effect takes place in a horizontal orientation. Such difference in the behavior of constricted neon and argon discharges is mainly caused by the difference in shape of elastic electron-atom collision cross sections. Interferometric methods allowed to study the temperature field of neutral atoms, dynamics of both gas heating and ascent of constricted cord. Observed effects are interpreted on the basis of the heat equation and the Navier–Stokes equation. Comparison of experimental and theoretical results shows good agreement.

Joule overheating poisons the fractional ac Josephson effect in topological Josephson junctions

Topological Josephson junctions designed on the surface of a 3D-topological insulator harbor Majorana bound states among a continuum of conventional Andreev bound states. The distinct feature of these Majorana bound states lies in the 4π-periodicity of their energy-phase relation that yields a fractional ac Josephson effect and a suppression of odd Shapiro steps under radio-frequency irradiation. Yet, recent experiments showed that a few, or only the first, odd Shapiro steps are missing, casting doubts on the interpretation. Here we show that Josephson junctions tailored on the large bandgap 3D-topological insulator Bi2Se3 exhibit a fractional ac Josephson effect acting on the first Shapiro step only. With a modified resistively shunted junction model, we demonstrate that the resilience of higher order odd Shapiro steps can be accounted for by thermal poisoning driven by Joule overheating. Furthermore, we uncover a residual supercurrent at the nodes between Shapiro lobes, which provides a direct and novel signature of the current carried by the Majorana bound states. Our findings showcase the crucial role of thermal effects in topological Josephson junctions and lend support to the Majorana origin of the partial suppression of odd Shapiro steps.

Excitation of Surface Plasma Waves in Microwave Radiation Sources by Electron Beam with Allowance for Thermal Velocity Spread

Based on the hydrodynamic model, in the linear approximation, the problem of excitation by an electron beam of surface waves in electrodynamic systems of plasma relativistic microwave electronics has been considered with consideration of electron velocity spread. Complex instability increments have been determined for complex parameters of the beam-plasma system. Two instability regimes differing in the dynamics of beam plasma oscillations during instability development have been observed: Compton (singleparticle) and Raman (collective) instabilities. The role of thermal effects in an electron beam and its density in the formation of a particular mode of beam instability has been analyzed.

Abnormal lubricant aggregation on roughness features in a rolling–sliding elastohydrodynamic contact

Any practical surface has some roughness which tends to decrease film thickness in concentrated contacts and increase the risk of surface failures. Surface roughness is deformed but roughness also influences the lubrication process. Therefore, it is important to understand these constrains, to predict a real performance of rough surfaces. It was already reported that roughness tends to flatten inside the contact under rolling–sliding conditions. However, this paper presents experiments showing an abnormal effect inside point contact when the additional lubricant is aggregated on the roughness feature (ridge). Enhanced roughness deformation has a protecting function against direct asperities contacts. The relationship to lubricant speed changes inside the contact, a role of thermal effect and possibility of phase transitions are discussed.

Role of Thermal Effects on Magnetic Interactions in Stacked Magnetic Layers With Perpendicular Anisotropy

The role of thermally excited magnetization reversals on magnetic interactions in stacked magnetic layers with perpendicular anisotropy has been investigated by first-order reversal curves (FORC) and coercive squareness (S*). For this purpose, a study of the effect of systematic variation of exchange interaction in granular perpendicular magnetic anisotropy layers on FORC contours has been carried out along with S* and coercivity measurements at various timescales. The results indicate that the FORC contour peak height is a better parameter than S* to study the exchange interactions in systems such as magnetic recording media and is insensitive to thermal effects.

Thermal sensitivity of DASH interferometers: the role of thermal effects during the calibration of an Echelle DASH interferometer

The use of a Doppler asymmetric spatial heterodyne (DASH) interferometer with an Echelle grating provides the ability to simultaneously image the 558 and 630 nm emission lines (e.g., at grating orders of n=8 and n=7, respectively) of atomic oxygen in the thermosphere. By measuring the Doppler shifts of these lines (expected relative change in wavelength on the order of 10⁻⁸), we are able to determine the thermospheric winds. Because the expected wavelength changes due to the Doppler shift are so small, understanding, monitoring, and accounting for thermal effects is expected to be important. Previously, the thermal behavior of a temperature-compensated monolithic DASH interferometer was found to have a higher thermal sensitivity than predicted by a simple model [Opt. Express 18, 26430, 2010]. A follow-up study [Opt. Express 20, 9535, 2012] suggested that this is due to thermal distortion of the interferometer, which consists of materials with different coefficients of thermal expansion. In this work, we characterize the thermal drift of a nonmonolithic Echelle DASH interferometer and discuss the implications of these results on the use of only a single wavelength source during calibration. Furthermore, we perform a finite element analysis of the earlier monolithic interferometer in order to determine how distortion would affect the thermal sensitivity of that device. Incorporating that data into the model, we find good agreement between the modified model and the measured thermal sensitivities. These findings emphasize the fact that distortion needs to be considered for the design of thermally compensated, monolithic DASH interferometers.

Supercritical CO2 as a green solvent for eucalyptus and citrus essential oils processing: role of thermal effects upon mixing

The knowledge of thermodynamic properties such as the heat of mixing or the heat capacity is very important for the correct design and the optimisation of separation processes. This paper describes thermal effects associated with the supercritical carbon dioxide extraction and fractionation of eucalyptus and citrus essential oils. In particular, the excess molar enthalpies (HEm) for the binary mixtures CO2 + citral and the ternary mixtures CO2 + 1,8-cineole + limonene were measured at conditions of temperature and pressure typically used in these techniques. Values for both systems were exothermic over the entire range of composition, exhibiting a very exothermic minimum in the CO2-rich region due to the change of state of carbon dioxide from that of a low-density fluid to that of a liquid-mixture composition. Data were analysed in terms of phase equilibria and critical parameters as well as densities of pure components and their mixtures. Cubic equations of state were used to model data, values for the ternary mixtures were satisfactorily predicted using binary data for the three related binary systems. Thermal effects reported in this publication and in previous work for binary mixtures formed by supercritical CO2 and the key components of eucalyptus and citrus essential oils (1,8-cineole, limonene, linalool and citral) were compared and analysed in terms of CO2–terpene interactions. In the case of 1,8-cineole and limonene, values for the temperature increments due to their mixing with carbon dioxide were estimated and found to be of considerable magnitude.

On the breaking of a plasma wave in a thermal plasma. I. The structure of the density singularity

The structure of the singularity that is formed in a relativistically large amplitude plasma wave close to the wave breaking limit is found by using a simple waterbag electron distribution function. The electron density distribution in the breaking wave has a typical “peakon” form. The maximum value of the electric field in a thermal breaking plasma is obtained and compared to the cold plasma limit. The results of computer simulations for different initial electron distribution functions are in agreement with the theoretical conclusions. The after-wavebreak regime is then examined, and a semi-analytical model of the density evolution is constructed. Finally the results of two dimensional particle in cell simulations for different initial electron distribution functions are compared, and the role of thermal effects in enhancing particle injection is noted.

The role of thermal effect on mantle seismic anomalies under Laurentia and Fennoscandia from observations of Glacial Isostatic Adjustment

The role of thermal effect on mantle seismic anomalies under Laurentia and Fennoscandia from observations of Glacial Isostatic Adjustment

A non-Newtonian model based on Ree–Eyring theory and surface effect to predict friction in elastohydrodynamic lubrication

The traction behaviour of various lubricants is investigated in elastohydrodynamic regime using a tribometre that simultaneously allows the contact visualization and the friction measurement under controlled contact kinematics. First, the film formation capability is determined: although the base oil and the polymer, via their viscosity, govern the film thickness in EHL regime, the additives control the existence of a boundary film at low entrainment speed. Second, the relative role of the additives and of the base oil on the frictional behaviour is studied for various experimental conditions: this clearly demonstrates that the piezo-viscous response of the lubricant controls the Newtonian/non-Newtonian transition and the friction level. The role of thermal effects is discussed. A strong influence of the entrainment speed, over the frictional response is unexpectedly observed, even in full film regime. A rheological model based on Ree–Eyring theory supposing a heterogeneous flow due to adsorbed surface layers, is proposed to discuss the organization of the molecules within the contact and its effect on the frictional response of the contact.

Nonlinear absorption in Au films: Role of thermal effects

The effective nonlinear optical absorption coefficient ${\ensuremath{\beta}}_{\mathrm{eff}}$ is measured for $20\text{\ensuremath{-}}\mathrm{nm}$-thick Au films at $630\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ as a function of pulse width. The $z$-scan measurements show that ${\ensuremath{\beta}}_{\mathrm{eff}}$ increases from $6.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ to $6.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}\mathrm{cm}\phantom{\rule{0.2em}{0ex}}{\mathrm{W}}^{\ensuremath{-}1}$ as the pulse width is varied from $0.1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}5.8\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. To help interpret this $\ensuremath{\sim}100\ifmmode\times\else\texttimes\fi{}$ increase, differential transmission and reflectivity measurements are performed using $775\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ pump and $630\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ probe pulses. All experiments are simulated with a two-temperature model for electrons and lattice. The pulse width dependence of ${\ensuremath{\beta}}_{\mathrm{eff}}$ is consistent with thermal smearing of $d$-band to conduction-band transitions, with ${\ensuremath{\beta}}_{\mathrm{eff}}$ arising from changes in the linear $(\mathrm{Im}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\chi}}^{(1)})$ absorption coefficient.

On the Evolution of Carrier Distribution and Wavelength Switching in Asymmetric Multiple Quantum-Well Lasers

The evolution of the carrier distribution with current in two different asymmetric multiple quantum laser structures was studied experimentally through measurements of electroluminescence (EL). The EL was measured through the substrates of lasers and provided information about the carrier distributions. The carrier concentration was observed to increase with current both below and above threshold, presumably owing to the change of threshold conditions. The switch of the lasing wavelength from long to short wavelength was explained by inhomogeneous broadening of the gain of the wells and by incomplete clamping of the carrier concentration above threshold, as inferred from the measured EL and gain spectra. The role of thermal effects was investigated by comparing the laser performance under continuous-wave and pulsed operation

Cosmological phase transitions and radius stabilization in higher dimensions

Recently there has been considerable interest in field theories and string theories with large extra space-time dimensions. In this paper, we explore the role of such extra dimensions for cosmology, focusing on cosmological phase transitions in field theory and the Hagedorn transition and radius stabilization in string theory. In each case, we find that significant distinctions emerge from the usual case in which such large extra dimensions are absent. For example, for temperatures larger than the scale of the compactification radii, we show that the critical temperature above which symmetry restoration occurs is reduced relative to the usual four-dimensional case, and consequently cosmological phase transitions in extra dimensions are delayed. Furthermore, we argue that if phase transitions do occur at temperatures larger than the compactification scale, then they cannot be of first-order type. Extending our analysis to string theories with large internal dimensions, we focus on the Hagedorn transition and the new features that arise due to the presence of large internal dimensions. We also consider the role of thermal effects in establishing a potential for the radius of the compactified dimension, and we use this to propose a thermal mechanism for generating and stabilizing a large radius of compactification.

Damage production and self-annealing during molecular implantation analyzed by RBS and ellipsometry

Abstract The role of thermal effects in primary damage production during ion implantation, i.e., a so-called micro-and macrotemperature, will be outlined. It is suggested that a strict control of thermal conditions around the cascade(s) can be a key factor in implantation technology, especially, when properties of layers implanted in different machines are compared. The role of hot implantation as an annealing concept will be demonstrated for the case of implantation with bi-molecular ions.

MULTICOMPONENT NON-ISOTHERMAL ADSORPTION DYNAMICS

The present state of the theoretical basis of adsorption dynamics of multicomponent mixture with account for thermal effects accompanying adsorption is presented. Theoretical models for the non-isothermal kinetics and dynamics of adsorption in multicomponent mixtures are analyzed. A classification of these models is given, and model equations accounting for all major qualitative physicochemical features of heat and mass transfer through interfaces and in the intergranular space of porous media are presented. The following topics are considered: (1) Considerable role of thermal effects in the adsorption and desorption processes; (2) Considerable interaction of mixture components due to the non-linear nature of the adsorption isotherms of the mixture; (3) Considerable dependence of heat and mass transfer coefficients on concentration of mixture component and temperature; (4) Considerable effect of the mutual diffusion of the mixture component; (5) The role of the thermal diffusion effect (the Soret effect) and the diffusion-thermal effect (the Dufour effect) on heat and mass transfer when local concentration and temperature gradient inside the porous grains of the adsorbents are significant. The effect of slow heat and mass kinetics on the nature of distribution of concentration and temperature in the adsorber is considered. The qualitative differences between the equilibrium theory and non-equilibrium theory of multicomponent non-isothermal adsorption dynamics are shown. The coherent (steady) and incoherent (transient) patterns of concentration and thermal waves in the adsorber are analysed. The conditions of existence of the frontal patterns of mixture separation are found, and simple formulae estimating major parameters of frontal behavior in adsorption separation of mixture, which take into account of all basic qualitative features of interphase heat and mass transfer outlined in items (1) trough (5) above, are given

Pressure profiles, resonant Pfirsch–Schlüter currents, thermal instabilities, and magnetic island formation

A prescription for constructing the plasma pressure profile in the vicinity of an equilibrium magnetic island is derived by solving a sourced pressure diffusion equation near the island region. For pressure sources and sinks that are relatively constant in space, it is found that the plasma pressure profile is insensitive to pressure sources; thus the pressure profile can be constructed by assuming that the net pressure flux across any topologically toroidal magnetic surface is constant. This construction of the pressure profile is also valid for magnetic islands that are slowly evolving in time. By coupling the pressure evolution equation with the magnetostatic equilibrium equations, the theory is applied to the case of self-consistent construction of pressure-gradient-driven magnetic islands. In particular, the question of resonant Pfirsch–Schlüter current induced magnetic islands and the role of thermal effects on nonlinear magnetic islands is addressed.