Thin Film Of Liquid Metal Research Articles

Breakup-Free and Colorful Liquid Metal Thin Films via Electrochemical Oxidation.

Thin-film metal conductors featuring high conductivity and stretchability are basic building blocks for high-performance conformable electronics. Gallium-based liquid metals are attractive candidates for thin-film conductors due to their intrinsic stretchability and ease of processing. Moreover, the phase change nature of liquid metal provides an opportunity to create conformal electronics in a substrate-free manner. However, thin liquid metal films tend to break during the solid-to-liquid transition due to the high surface tension of liquid metal. Here, we created breakup-free liquid metal thin films by the electrochemical oxidation of solid gallium films. We show that electrochemical oxidation can enhance the mechanical strength of the gallium oxide layer and its interfacial adhesion to the gallium core. When heated to the liquid state, the oxidized gallium films can maintain their structural integrity on various solid substrates, hydrogels, and even the water surface. The solid-liquid phase change-induced stiffness decrease allowed the gallium films to be conformably attached to various nonplanar surfaces upon heating or water transfer printing. Moreover, we also found that enhanced electrochemical oxidation can result in the formation of structure color due to nanoporous structures on the film surface. We also demonstrate the applications of oxidized liquid metal films in functional electronics, electrophysiological monitoring, and tattoo art.

Electrodeposition of Crystalline Germanium on Glass

The research objective of this work is to test the hypothesis that crystalline germanium can be deposited on insulating substrates through electrochemical-liquid phase epitaxy (ec-LPE). In doing so, this work establishes a new method of semiconductor-on-insulator fabrication. Semiconductor-on-insulator device constructs are at the heart of all modern electronics. Methods that simplify fabrication by lowering the thermal budget and eliminating hazardous precursors are highly desirable. Recently, a new method for the direct preparation of covalent semiconductor crystals at ambient conditions, ec-LPE, was demonstrated by our group. This method utilizes thin liquid metal films simultaneously to perform electrochemical reduction of precursors and to direct heterogeneous nucleation at an underlying substrate of interest. In this work, the fabrication of germanium-on-glass using ec-LPE is demonstrated for the first time. Amperometry, microscopy, and Raman spectroscopy will be presented to demonstrate the proof of principle, i.e. the growth of Ge crystals electrochemically on insulating glass. The surface chemistry of glass substrates will be discussed, including glass functionalized with (3-Aminopropyl)triethoxysilane (APTES), and N-(Trimethoxysilylpropyl)ethylene-diamine triacetic acid (EDTA–TMS). Surfaces with a higher chelating group density improved the efficacy of Ge ec-LPE. These results set the groundwork for semiconductor-on-insulator process development based on ec-LPE.

On thermal axisymmetric liquid-metal divertors

Abstract Motivated by liquid-metal divertor concepts, we consider a detailed model of a thin liquid-metal film flowing down a toroidally-symmetric solid substrate, driven by gravity as well as thermal and mechanical interaction with the SOL. In the relevant physical limit where the film is thin relative to the divertor extent, and the induced magnetic field is weaker than the applied field, the governing equations may be approximated asymptotically to yield tractable reduced-order dynamics. The analysis incorporates gravitational, thermocapillary and thermoelectric forces, and reveals several nontrivial findings. Firstly, we find that the influence on the liquid metal flow of the toroidal component of the applied field is negligible compared to that of the poloidal component. This has important ramifications for the behaviour of the liquid metal. Secondly, we identify a “spiral-type flow” due to a flow component in the toroidal direction. This flow has been previously reported in the literature in the isothermal case when using extreme parameters. Our analysis explains why these extreme parameter choices were required to observe the isothermal flow, and reveals that, for typical parameters in the thermal case, the flow becomes significant due to thermoelectric forces. Thirdly, we deduce full dimensional velocity scalings. Finally, we present a case study that employs the reduced-order model to explore the effects of sweeping the plasma strike point up and down the divertor. We simulate fully transient dynamics within the divertor and demonstrate how, in some regions of parameter space, the sweeping might promote dry-out or droplet ejection of the liquid metal. We discuss how the case study can inform both divertor material choice as well as tokamak operating parameters.

Electrodeposition of Grop Ⅳ Semiconductor Thin Film

This presentation describes our latest work in the growth of Si films by electrochemical liquid phase epitaxy (ec-LPE). This method is an advanced form of the electrochemical liquid-liquid-solid crystal growth process, where a liquid metal serves both as a cathode for electrodeposition and as a solvent for crystal growth. Using tailored thin liquid metal film electrodes and non-aqueous electrolytes, it is possible to electrodeposit crystalline Si at unusually low temperatures. Data will first be presented that describes suitable electrolytes for Si ec-LPE. Results will then be presented that describe how the liquid metal identity impacts material quality. Finally, the attainable material quality and the requirements for solar grade crystalline Si will be discussed.

Numerical and Experimental Study of Plastic Deformation During Flash Butt Welding of X65 Pipeline Steel

AbstractThe plastic deformation during flash-butt welding (FBW) and its effects on weld quality are investigated by using numerical and experimental methods. The electro-thermo-mechanical coupling model of FBW is validated by comparing the calculated temperature and plastic deformation to measured one, obtaining reasonable agreement. The calculation results reveal that a thin liquid metal film forms at the contact interface during accelerating flash stage to provide temperature conditions for upsetting. The length of liquid metal (including burning and expelled losses) is 29.7 mm for one piece pipeline tube under the given condition. The stress and strain at contact surface are both almost zero at the initial stage of upsetting due to the thin liquid metal film existing at the contact interface, and they rapidly increase to 58.0 MPa and 17.7, respectively, while the liquid metal are excluded from the contact interface between two tubes to be welded. The maximum plastic deformation is 18.1 mm at the given condition under the action of upsetting force. The experimental results illustrate that the microstructure of X65 FBW joints consists of massive ferrite, grain boundary pre-eutectic ferrite, pearlite, and widmannstatten, while the microstructure in heat-affected zone is fine ferrite and pearlite. The coarse grain size and gray spots in the butt joint severely decrease the tension strength and impact toughness.

Flow of a thin liquid-metal film in a toroidal magnetic field

We investigate the gravity-driven flow of a thin film of liquid metal on a conducting conical substrate in the presence of a strong toroidal magnetic field (transverse to the flow and parallel to the substrate). We solve the leading-order governing equations in a physically relevant asymptotic limit to find the free-surface profile. We find that the leading-order fluid flow rate is a non-monotonic bounded function of the film height, and this can lead to singularities in the free-surface profile. We perform a detailed stability analysis and identify values of the relevant geometric, hydrodynamic and magnetic parameters such that the flow is stable.

Liquid electromigration in gallium-based biphasic thin films

Liquid metals have recently gained interest as a material of choice for soft and stretchable electronic circuits, thanks to their virtually infinite mechanical failure strain and high electrical conductivity. Gallium-based thin films are obtained by depositing gallium in the vapor phase to form a class of liquid metal conductors. The films, with an average thickness below 1 µm, withstand mechanical strain in excess of 400%. However, modes of failure other than mechanical ones have not yet been thoroughly investigated. In particular, electromigration, a well-known cause of failure in solid thin film traces for integrated circuits, also occurs in bulk liquid metals. In this work, microscopic observation of the thin conductive traces reveals that gallium is displaced from the anode terminal toward the cathode terminal after direct current stressing. This results in a catastrophic increase in the trace resistance and electrical failure. The mean time to failure decreases with increasing current density, following Black’s equation, an empirical mathematical model originally developed to describe failure in solid metal thin-film tracks due to electromigration. We show that using alternating current, e.g., symmetric square wave, rather than direct current can extend the lifetime of the thin liquid metal film conductor by several orders of magnitude. These results may help stretchable circuit designers who select liquid metal thin-film conductors as the stretchable interconnect technology to predict devices’ lifetime and implement mitigation strategies at the system level or at the material level.

Micropatterning of Liquid Metal by Dewetting

Although gallium-based liquid metals are attracting growing interest thanks to its potential applications in deformable, flexible electronic devices, challenges in fabrication associated with the high surface tension and oxide skin remain to be overcome. We report a novel fabrication technique for liquid metal circuits using dewetting. An excessively thin liquid film spontaneously shrinks on a substrate to reduce surface free energy. In the case of a thin liquid metal film on a substrate with microgrooves, the oxide on the microgroove wall and the additional viscous resistance delay the shrinkage in the grooves, which separates the liquid volume inside the microgrooves from the external volume. Utilizing this mechanism, we successfully produced 20- $\mu \text{m}$ -thick conductive lines of eutectic gallium indium (EGaIn) on polydimethylsiloxane. This fabrication technique is simple, fast, and cost-effective and requires no top covering layer. The resultant metal lines show potentially applicable electrical resistance to flexible and stretchable electronic devices. [2017-0082]

Gravitational flow of a thin film of liquid metal in a strong magnetic field

The influence of a poloidal magnetic field of the spherical Tokamak on super thin (h≈0.1mm) film flow of liquid metal driven by gravity over the surface of the cooled divertor plate is addressed. The experimental setup developed at the Institute of Physics, University of Latvia (IPUL) is described, which makes it possible to drive and visualize such liquid metal flows in the solenoid of the superconducting magnet “Magdalena”. As applied to the above setup, the magnetic field effect on the operation of the capillary system of liquid metal flow distribution (CSFD) is evaluated by using molten metal (lithium or eutectic InGaSn alloy) with a very small linear flowrate q≤1mm2/s, spread uniformly across the substrate. The magnetic field effect on the main parameters of the fully developed film flow is estimated for the above-mentioned liquid metals.An approximation technique has been proposed to calculate the development of the gravitational film flow. A non-linear differential second order equation has been derived, which describes the variation of the film flow thickness over the substrate length versus the flowrate q, magnetic field B and the substrate sloping α.Results of InGaSn film flow observations in a strong (B=4T) poloidal magnetic field are presented. Analysis of the video records evidences of experimental realization of a stable stationary film flow at width-uniform supply of InGaSn.

Film thickness mediated transition in the kinetics of electric current induced flow of thin liquid metal films

Application of high electric-field between two points in a thin metallic film results in liquefaction and subsequent flow of the liquid-film from one electrode to another in a radially symmetric fashion. Here, we report the transition of the flow kinetics driven by the liquid film thickness varying from 3 to 100 nm. The mechanism of the flow behavior is observed to be independent of the film thickness; however, the kinetics of the flow depends on the film thickness and the applied voltage. An analytical model, incorporating viscosity and varying electrical resistivity with film thickness, is developed to explain the experimental observations.

Self-organization in a chromium thin film under laser irradiation

Self-organization of chromium on glass was observed during laser ablation of the metal film with partially overlapping laser pulses. The beam of a nanosecond pulse laser tightly focused to a line was applied to the back-side ablation of the chromium thin film on a glass substrate. While the line ablated with a single laser pulse had sharp edges on both sides with ridges of the melted metal, the use of partially overlapping pulses formed a complicated structure made of the metal remaining from the ridges. Regular structures of ripples were developed in a certain range of laser fluence and pulse overlap. The ripple period could be controlled from 2.5 to 4 μm by variation of the processing parameters. Various experimental techniques were applied to test the structures, and different models of the ripple formation in the thin metal film were considered. The initial quasi-periodical formation started because of dewetting of thin liquid metal films on the glass substrate after its melting. Similar to the evaporation of liquid films, the small perturbation in the ridge thickness was able to induce instability in evaporation of the thin melted metal film. Freezing of the nonequilibrium state between laser pulses was one of the stabilizing factors in self-organization of the metal.

Neutron and gamma ray heating in the grazing incident liquid metal mirrors for laser inertial fusion energy power plants

A thin film of liquid metal can serve as final optics of a laser inertial fusion energy (IFE) power plant. Calculations of pulsed neutron and gamma-ray heating are presented for a grazing incident liquid metal mirror (GILMM) used for robust final optics of a laser IFE power plant. Different liquid films (Li, Na, Mg, Al, Si, K, Ga, Ag, Au, Pb, Bi and Flibe “Li 2BeF 4”) are considered at a distance of 30 m from a nominal 1 GJ fusion source as well as different substrate materials (SS-304 and SiC). The effect of neutron heating both in the liquid metal film as well as in the subsrate material will be by around three to four orders of magnitude lower than the laser heating limit. Hence the nuclear heating will not be a limiting factor for grazing incident liquid metal mirror (GILMM) of a laser IFE power plant.

Grazing incidence liquid metal mirrors (GILMM) for radiation hardened final optics for laser inertial fusion energy power plants

A thin film of liquid metal is suggested as a grazing incident mirror for robust final optics in a laser inertial fusion energy (IFE) power plant. The amount of laser light the grazing incidence liquid metal mirror (GILMM) can withstand, called the damage limit is limited by the surface disturbances initiated by rapid laser heating. For 0.35-μm light, the damage limit for a sodium film 85° from normal is calculated to be 57 J/cm 2 normal to the beam for a 20 ns pulse and 1.3 J/cm 2 for a 10-ps pulse (2 and 90 m 2 of mirror area per 100 kJ of laser energy at 20 ns and 10 ps, respectively). Feasibility relies on keeping the liquid surface flat to the required accuracy by a combination of polished substrate, adaptive (deformable) optics, surface tension and low Reynolds number, laminar flow in the film. The film's substrate must be polished to ±0.015 μm. Then surface tension keeps the surface smooth over short distances (<10 mm) and low Reynolds number laminar flow keeps the surface smooth (disturbances less than ±0.01 μm) over long distances (>10 mm). Adaptive optics techniques keep the substrate flat to within ±0.06 μm over 100-mm distance and ±0.6 μm over 1000 mm distances, even after 30 years of cumulative damage via neutron irradiation. The mirror can stand the X-ray pulse when located 30 m away from the microexplosions of nominal yield of 400 MJ (50 MJ of X-rays) when Li is used, but for higher atomic number liquids like Na there may be a significant rise in temperature, forcing the use of other X-ray attenuation methods such as attenuation by xenon gas. The GILMM should be applicable to both direct and indirect drive and pulse lengths appropriate to slow compression (∼20 ns) or fast ignition (∼10 ps). For direct-drive laser beams near the poles (70°, where 90° is vertical), stable thin films become more challenging. Proof of the concept experiments are needed to verify the predicted damage limit and required smoothness.

X-ray reflectivity studies of liquid metal and alloy surfaces

Surface-induced atomic layering at the liquid/vapor interface in liquid metals has been observed using x-ray reflectivity on sputtered clean surfaces under ultrahigh vacuum conditions. A well-defined quasi-Bragg peak is obtained for surfaces of elemental Ga and a Ga-In alloy at large wave vectors qz;2.3‐2.5 A 21 . These results are an unambiguous indication of atomic layering with an interlayer spacing d;2p/qz52.5‐2.7 A. For liquid Ga, the amplitude of the electron-density oscillations, which is significantly underestimated by existing theory and molecular simulation, decays with a characteristic length of 6 A, which is twice that of Hg. Results on the alloy show a clear enrichment of indium at the topmost surface layer, consistent with the Gibbs adsorption rule. The enrichment consists of a single monolayer, with subsequent layers at the bulk eutectic composition. In order to suppress mechanically excited surface waves, the measurements were performed on thin liquid metal films (,0.5 mm deep!, which leads to a macroscopically curved surface due to the large surface tensions in liquid metals. The experimental challenges posed by measurements on curved surfaces and the techniques that were developed are discussed in detail. @S0163-1829~97!01324-6#

Dewetting Modes of Thin Metallic Films: Nucleation of Holes and Spinodal Dewetting.

We have studied the dewetting of thin liquid metal films (Au, Cu, Ni) on fused silica substrates which occurs after melting with a Q-switched laser pulse. Optical microscopy, scanning electron microscopy, and scanning near field acoustic microscopy reveal two distinctly different modes of the dewetting process: On one hand, we observe heterogeneous nucleation of ``dry'' circular patches, which grow in diameter during the melting period. On the other hand, an instability of the liquid film against the growth in amplitude of surface waves with a characteristic wavelength is observed, which we believe is the first observation of spinodal dewetting. In contrast, the final structure of the ruptured film depends on whether nucleation or spinodal dewetting is dominant.

Field emission from thin liquid metal films

Field emission from liquid metal surfaces occurs with different mechanisms such as from liquid metal vapor arc cathode spots and liquid metal electron sources. At rather bulk liquid metal coverages, in both cases the emission performance likewise is affected by hydrodynamic and electrohydrodynamic effects, respectively. Reducing the liquid metal coverage to a relatively thin liquid metal film, the field-induced microstructure, as well as the intrinsic microstructure of the liquid metal film on a solid substrate dominates, and new emission modes appear. Representative examples for that are the film emission mode of liquid metal film cathodes (LMFC) and the stationary emission mode of microstructured liquid metal electron sources (MILMES). Both field emission from a cathode spot as well as from a field emitter in vacuum is examined in the scope of the dynamic field (DF) emission model which has been adapted for this purpose, considering especially emission stability. Finally, experimental results obtained with a mercury film cathode, and different types of cesium liquid metal electron sources are analyzed and compared with theoretical aspects of the DF emission model.

Estimates of the effect of a plasma momentum flux on the free surface of a thin film of liquid metal

Estimates of the effect of a plasma momentum flux on the free surface of a thin film of liquid metal

Estimates of the effect of a plasma momentum flux on the free surface of a thin film of liquid metal

The use of a thin film of liquid metal (LM) to protect a divertor surface requires that the LM film be able to withstand the flux of momentum carried by the energetic plasma exhaust flow. This momentum flux was estimated from edge modeling results of an ITER conceptual design activity (CDA) type divertor, and was found to be comparable with the hydrostatic pressure of a typical LM film of the order of millimeters in height. A two-dimensional, free boundary fluid code, RIPPLE, was modified to account for this flux and used to give an initial estimate of the seriousness of this effect. Lithium films are dramatically affected, to such a degree that their use in an LM divertor is seriously questioned. Gallium films withstand the momentum flux much better, with speeds of around 1 m s −1 giving adequate performance in a realistic CDA divertor momentum flux profile. The inclusion of magnetohydrodynamic forces, not present in this initial estimation, is required to describe fully the LM film response.

Analysis of Thin Film Liquid Metal Protection of Fusion Reactor Limtter/Divertor Surfaces

In an effort to prolong the lifetime of impurity control components, the idea of protecting the contact surface from erosion and radiation damage with a thin film of liquid metal has been advanced. This flowing, liquid metal film could also be used to remove the high heat fluxes incident on limiter or divertor surfaces, thus eliminating problems with thermal stresses in the components as well. In order to determine the attractiveness and feasibility of such a concept, the heat transfer characteristics of a thin film of liquid metal are examined when the film is exposed to a large, one-sided heat flux incident on the free surface. The method developed yields the temperature at any location in the film and is used to determine, for a given design and space-dependant heat flux, the film velocity required to keep the maximum film temperature below whatever Tmax limit is imposed. In addition, the behavior of the film flow at the required velocity is examined in order to determine if such a flow is possible. This analysis is accomplished by using a one-dimensional model of the film height, developed from the basic set of MHD equations, to show the design conditions that allow for a stable film. The analytical method is applied to ITER-type limiter and divertor configurations, resulting in required film velocities (v < 5 m/s for the cases examined) and allowable values of the design parameters (channel size, wall conductivity, and substrate angle) that yield a stable film, capable of removing all incident heat.

Electrohydrodynamical study of the instability of a thin liquid metal film: Application to planar liquid metal ion sources

Liquid metal ion sources are of interest in diverse areas of technology since they provide a high brightness, quasipoint source of ions and droplets for microfabrication, surface analysis, ultrathin film deposition, and other potential applications. N. M. Miskovsky, M. Chung, P. H. Cutler, T. E. Feuchtwang, and E. Kazes [J. Vac. Sci. Technol. A 6, 2992 (1988)] have developed an electrohydrodynamic capillary wave theory for ion and droplet emission in electrically stressed conducting viscous fluids based on a mathematical formalism introduced by J. R. Melcher and C. V. Smith [Phys. Fluids 12, 778 (1969)] and S. Grossmann and A. Muller [Z. Phys. B 57, 161 (1984)]. As the simplest analytical application of this theory they chose a model consisting of a planar fluid of thickness ‘‘a’’ supported on a rigid electrode. A parallel planar counter electrode is at a distance ‘‘b’’ from the unperturbed surface. The Navier–Stokes equation was solved subject to a dynamical Laplace–Young stress boundary condition (which includes the frictional tensor) to obtain the dispersion relation used to investigate the stability of the system. In earlier work the effect of viscosity and gravity on the spectrum of unstable wavelengths for the case of a thick film (i.e., λ≫a) was investigated within the planar surface capillary wave model. In this limit, it was found that viscosity plays a significant role in determining the growth rate and the dominant mode, suggesting that it should be included in studies of the instabilities in liquid metal ion sources. It was also found that the local electric field is much larger than the average field of the perturbed fluid surface, implying that nonlinear effects can be important. In the present study the same formalism is used to investigate the case of a thin (i.e., λ&amp;lt;a) liquid metal film. For thin films, that is, &amp;lt;1 μm, the effect of the boundary conditions at the supporting electrode can produce significant changes in the maximum growth rate (∼20%), the dominant mode (∼10%), and the maximum value of Re(ω2) (∼40%). For both the thick- and thin-film regimes viscous damping is found to have an important role increasing the stability of the fluid film. In addition, an increase in viscosity shifts the most unstable mode to longer wavelengths. This shift competes with the effect of decreasing the film thickness.