Melting Of Thin Films Research Articles

New plasmonic platform for enhanced luminescence of Valrubicin

Luminescence enhanced by new structure of plasmonic platform with aluminum oxide (Al2O3) buffer layer deposited on gold nanostructures is investigated. Regularly distributed gold nanostructures of average dimension of 50 nm formed the active part of plasmonic platforms. They were manufactured on Corning 1737 glass substrate by melting of gold thin film. The nanostructures were coated by dielectric Al2O3 thin film with thickness of 6 nm deposited by atomic layer deposition (ALD) method. Thin film of Valrubicin as a luminescence material was deposited on prepared substrates by spin-coating technique. Luminescence spectra show that designed plasmonic platform with Al2O3 thin film between gold nanostructures and Valrubicin enhanced fluorescence intensity by about 4.5 times.

Generating liquid nanojets from copper by dual laser irradiation for ultra-high resolution printing.

When the energy of a short laser pulse is localized in a fluid material, a flow motion is induced that can lead to the generation of free-surface jets. This nozzle-free jetting process is exploited to print conductive materials, typically metal nanoparticle inks, but this approach remains limited to the transfer of low viscosity fluids with a minimum feature size of few micrometers. We introduce a dual-laser method to achieve reproducible high-aspect-ratio jets from thin solid films. A first laser irradiation induces the melting of copper thin films and a second synchronized short pulse irradiation initiates the jetting process. Using time-resolved microscopy, we investigate the influence of the film thickness on the flow motion mechanisms and the ejection dynamics. For a wide range of laser fluences, we present observations similar to those obtained when the jets are generated by a single laser pulse from liquid donor films. The use of a solid film allows reducing the film thickness and then the volume of transferred material. Finally, we analyze these results in the perspective of using this double pulse LIFT technique for additive manufacturing of nano-micro-structures. Stable jets are formed from the copper films over distances exceeding 50-μm and are exploited to demonstrate periodic printing of 1.5-μm diameter droplets.

Development of 2000 K Class High Temperature In Situ Transmission Electron Microscopy of Nanostructured Materials via Resistive Heating

We report the development of a new type of a 2000 K class high temperature stage for transmission electron microscopy (TEM) of various shaped nanostructured materials, i.e., nanometer-sized isolated nanostructures, such as particles, fibers, and thin films, and nanocrystalline bulk materials. The maximum temperature of the heating stage was 300–700 K higher than that of prevailing heating stages. In addition, we found that since the structure of the developed heating stage is simple, the stage can be applied to most of transmission electron microscopes without any additional modification. The stability of the heating stage was confirmed by In Situ high-resolution observation of the lattice fringes of the zirconium dioxide nanoparticles heated at 1183 K. We observed In Situ the nanoscale structural variation of titanium plate surfaces around 900 K and the melting of nanocrystalline iron thin films around 1808 K by this method. It was demonstrated that the heating stage is useful for the analysis of high temperature structural dynamics of various shaped nanostructured materials.

Kinetics of powder layer shrinkage during electron-beam treatment

When layerwise synthesis of new material occurs, only thin surface area, thin melt film or thin powder layer undergo essential changes. To describe the behaviour of thin layer where temperature and composition change, a model similar to shallow-water theory is suggested. The equations for thin layer behaviour are deduced for the Maxwell model of viscoelastic body in the approximation of incompressibility. The hydrodynamic part of the problem is coupled with thermal-kinetical one.

A new criterion for melting of nanostructures of arbitrary shapes

We introduce a new and general criterion for melting as an alternative to the commonly used Lindemann criterion. Nanostructures are modeled using a zipper model and the melting process is assumed to start from the outer layer and develop towards the center layer. Melting occurs when the logarithm of the partition function per number of layers is zero. The equation shows good consistency with experimental data for the melting of thin films, nanoparticles, and nanowires. We also introduce a degree-of-freedom parameter which seems to be universal for most metals.

Zipper model for the melting of thin films

We propose an alternative model to Lindemann’s criterion for melting that explains the melting of thin films on the basis of a molecular zipper-like mechanism. Using this model, a unique criterion for melting is obtained. We compared the results of the proposed model with experimental data of melting points and heat of fusion for many materials and obtained interesting results. The interesting thing reported here is how complex physics problems can sometimes be modeled with simple objects around us that seemed to have no correlation. This kind of approach is sometimes very important in physics education and should always be taught to undergraduate or graduate students.

Thermodynamic model of the melting of thin metal films

The size dependence of the melting temperature Tm of nanoscale metal (Sn, Cu) films on solid substrates made of another high-melting metal and carbon is studied. It is established that an increase in the melting temperature must be observed for metal films on C substrates as the film thicknesses decrease. For a system consisting of a metal film on the surface of another metal, the dependence of the melting temperature on the film thickness is less pronounced and corresponds to a decrease in Tm with decreasing h (h is the film thickness).

Effect of grain size on the melting point of confined thin aluminum films

The melting of aluminum thin film was studied by a molecular dynamics (MD) simulation technique. The effect of the grain size and type of confinement was investigated for aluminum film with a constant thickness of 4 nm. The results show that coherent intercrystalline interface suppress the transition of solid aluminum into liquid, while free-surface gives melting point depression. The mechanism of melting of polycrystalline aluminum thin film was investigated. It was found that melting starts at grain boundaries and propagates to grain interiors. The melting point was calculated from the Lindemann index criterion, taking into account only atoms near to grain boundaries. This made it possible to extend melting point calculations to bigger grains, which require a long time (in the MD scale) to be fully molten. The results show that 4 nm thick film of aluminum melts at a temperature lower than the melting point of bulk aluminum (933 K) only when the grain size is reduced to 6 nm.

Capturing Dynamics of Pulsed Laser Induced Melting and Rapid Solidification in Aluminum Polycrystals with Nanoscale Temporal Resolution In-situ TEM

The unprecedented spatiotemporal resolution offered by the dynamic transmission electron microscope (DTEM) facilitates unique studies of irreversible transitions in condensed matter [1]. In prior work we utilized the DTEM for single-shot nano-second temporal resolution bright field imaging and diffraction studies of rapid solidification (RS) in Al, Cu, Ag and Al-Cu alloy thin films [2-5]. Recent upgrades to the DTEM instrument enable single-pump/multiple-image-acquisition experiments (image series), which hold prospect to greatly reduce quantitative uncertainties in measurements, e.g. transformation front velocity, during RS, and increase by about one order of magnitude the data density obtained from direct observations of the dynamics of the irreversible transformation processes [6]. Here we report and discuss first results of in-situ TEM investigations of the dynamics of pulsed-laser induced melting and RS in Al thin films performed with the upgraded DTEM. Thin Al films, 80nm-160nm thick, were deposited by e-beam evaporation on square windowed TEM grids with 50 nm thick amorphous Si3N4 membranes and melted with a single 15 ns, 1064 nm laser pulse, defining time t0 (Fig. 1). Image series comprised of nine frames have been acquired with preselected 20ns exposures per frame and 0.2s time steps between frames and also for 50ns exposures and inter-frame time steps of 2s. The resulting image series spanning at least ~1.8s (e.g. Fig. 1) and up to ~20.4s have been acquired for systematically varied pre-delay times, t, in the range of -0.2s to 40μs. Dynamics of the morphological and structural changes in the nano-crystalline Al thin films and the kinetics during the pulsed laser induced sequences of melting and subsequent RS have been determined from direct observations. Bright field imaging showed (e.g. Fig. 2) that the laser pulse induced irreversible transformation involves the preferential melting along grain boundaries and development of a ‘mushy’ two-phase region during the melting sequence. Subsequently solidification initiates with a transformation interface that is rough on the scale of the adjacent crystalline grains. Driven by the thermal gradient the solidification interface transitions to a planar morphology, which supports growth of columnar crystals to the center of the melt pool. Effects from the Si frame support of the TEM transparent square windows, which represents a heat sink, on the solidification velocity measurements in the DTEM have been studied systematically. Kinetic details of the Al thin film melting and the solidification sequences under the driven conditions are analyzed quantitatively and discussed. Post-mortem TEM analysis have been performed to evaluate crystallographic details of the directional solidified Al grains relative to the original film.

Melting of crystalline silicon thin films

Melting of crystalline silicon thin films is studied by molecular dynamics (MD) simulations using Stillinger–Weber potential. Models are heated up from a crystalline to a normal liquid state. Temperature dependence of total energy and the Lindemann ratio exhibits a first-order-like behavior of the transition at a melting point. Heat capacity of the system exhibits a single peak at around the melting point. Atomic mechanism of melting is analyzed via monitoring spatio-temporal arrangements of the liquidlike atoms occurred during heating process. We find the formation of a quasi-liquid surface layer containing both solidlike and liquidlike atoms, i.e. at temperature around the melting point (Tm), there is a mixed phase of the solidlike and liquidlike atoms in the surface layer. The mechanism of melting of crystalline silicon is different from that of Lennard–Jones crystals and monatomic glass with free surfaces due to the potentials used in simulation and due to sizes of models.

Erratum to “Melting of thin films of alkanes on magnesium oxide”

In the above article the name of one of the authors has been mistyped. The correct name of the author is D. Fernandez-Canoto.

Electric Current-Induced Mass Flow in Very Thin Infinite Metallic Films

This paper reports on the mass transport behavior of infinitely extended, continuous, and very thin metallic films under the influence of electric current. Application of direct current of high densities (> 108 A/m2) results in visible melting of thin film at only one of the electrodes, and the melt then flows towards the other electrode in a circularly symmetric fashion forming a microscale ring pattern. For the two tested thin film systems, namely Cr and Al, of thicknesses ranging from 4 to 20 nm, the above directional flow consistently occurred from cathode to anode and anode to cathode, respectively. Furthermore, application of alternating electric current results in flow of the liquid material from both the electrodes. The dependence of critical flow behavior parameters, such as flow direction, flow velocity, and evolution of the ring diameter, are experimentally determined. Analytical models based on the principles of electromigration in liquid-phase materials are developed to explain the experimental observations.

Morphological varieties and kinetic behaviors of poly(3-hydroxybutyrate) (PHB) spherulites crystallized isothermally from thin melt film

The spherulitic morphologies of poly(3-hydroxybutyrate) (PHB) crystallized isothermally from thin melt film with different crystallization temperatures were observed by means of polarized optical microscopy, optical microscopy, SEM, and atomic force microscopy techniques, and the kinetic behaviors were analyzed carefully in this work. It was found that the nonbanded spherulites could be observed at lower and higher crystallization temperatures, and the banded spherulites were formed usually at an intermediate range within experimental crystallization temperatures. The competition of the crystallization rate (vc) and the diffusion rate (vd) of melt molecules was employed to explain the transition of the spherulitic morphologies. It was considered that the change of the ratio of vd and vc would result in the transition of the spherulitic morphologies. The formation and development of the banded structure were discussed in detail. It was found that the band spacing was proportional to diffusion length of melt molecules and increased with increasing of crystallization temperature. The kinetic behaviors of PHB spherulites formed from the thin melt film with different crystallization temperatures were also discussed in this work.

Thermodynamic Theory of Two Rough Surfaces Friction in the Boundary Lubrication Mode

The thermodynamic theory of thin lubricant film melting, confined between two hard rough solid surfaces, is built using the Landau phase transition approach. For the description of a melting condition, the order parameter is introduced which is a periodical part of microscopic medium density function. The shear modulus of lubricant is proportional to the order parameter squared. The thermodynamic and shear melting are described consistently. A mechanical analogue of a tribological system in the boundary friction mode is studied. The time dependencies of the friction force, the relative velocity of the interacting surfaces, and the elastic component of the shear stresses appearing in the lubricant are obtained. It is shown that the shear modulus of the lubricant and the elastic stresses become zero in the liquid-like state. The irregular stick-slip mode of melting is described, which is observed in experiments. It is shown that the frequency of stiction spikes in the irregular mode increases with growth of the shear velocity. Comparison of the obtained results with experimental data is carried out.

Ultrafast solid-liquid-vapor phase change of a thin gold film irradiated by femtosecond laser pulses and pulse trains

Effects of different parameters on the melting, vaporization and resolidification processes of thin gold film irradiated by femtosecond pulses and pulse train were systematically studied. The classical two-temperature model was adopted to depict the non-equilibrium heat transfer in electrons and lattice. The melting and resolidification processes, which was characterized by the solid-liquid interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, was obtained by considering the interfacial energy balance and nucleation dynamics. Vaporization process which leads to ablation was described by tracking the location of liquid-vapor interface with an iterative procedure based on energy balance and gas kinetics law. The parameters in discussion included film thickness, laser fluence, pulse duration, pulse number, repetition rate, pulse train number, etc. Their effects on the maximum lattice temperature, melting depth and ablation depth were discussed based on the simulation results.

Melting and solidification behavior of laser-crystallized silicon thin-films studied by transient conductance measurements

In this paper we report on transient conductance measurements during melting and solidification of thin silicon films on foreign substrates, which were irradiated with an excimer laser. The silicon films were deposited on borosilicate float glass or single crystal silicon wafers that were coated with different intermediate layers. Our results show that the laser fluence required to melt the entire Si layer is mainly determined by the silicon–substrate interfacial thermal resistance and not by the heat conductivity of the bulk substrate. The solidification velocity, on the other hand, is strongly influenced by the heat conductivity of the bulk substrate and reaches a maximum value of 0.95m/s for c-Si compared to 2.19m/s for borosilicate float glass.

Dynamics of solidification in Al thin films measured using a nanocalorimeter

We demonstrate how a nanocalorimeter can be used to measure the dynamics of thin film melting and solidification using aluminum as a model system. Recalescence, a rise in temperature due to enthalpy release on solidification, is observed when the rate of heat release is faster than the rate of heat extraction. For thin films, with a large density of nucleation centers at the interface, recalescence effects are observed at high cooling rates where direct measurements of heat capacities and enthalpy changes are challenging. Temperature rates of 104 K/s were applied using nanocalorimeter chips; the nanocalorimeter allows direct measurement of the under cooling, temperature rise during solidification, and the associated changes in enthalpy. This work highlights some of the challenges recalescence causes in physical measurements and provides a numerical strategy to evaluate enthalpy changes during rapid solidification.

Cellular Crystallization in Thin Melt Film of it-Poly(butene-1): An Implication to Spherulitic Growth from Bulk Melt

Crystallization of it-polybutene-1 (iPB-1) in form 2 from thin films of several tens of nanometers thick evolves a cellular structure composed of single-layered lamellar crystals. The dependences on thickness and crystallization temperature of the structure, namely of the cell width corresponding to the lamellar width, have been examined quantitatively. Temperature dependence of the cell width well agrees with the width of lamellar crystals grown from bulk melt, for the thin films with thickness in the same order in magnitude as the long spacing of crystal-melt stacks in the bulk melt. Crystallization from thin films is self-evidently controlled by mass transport under possible influence of compositions. The correspondence of the growth structures from thin films and from bulk melt therefore suggests the essential role of the gradient field of mass transport for lamellar branching in bulk melt, which eventually evolves polymer spherulites. The dependence of cell width on film thickness reflects the facility of mass transport in thicker melt films and the overgrowth on the single-layered lamellar crystals.

Trace-element microanalysis by LA-ICP-MS: The quest for comprehensive chemical characterisation of single, sub-10 μm volcanic glass shards

Recent developments in laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) have enabled improvements in spatial resolution and analytical detection limits. Here, the analysis of individual glass shards from tephra deposits using a 193 nm Excimer laser (producing ablation craters as small as 4 μm diameter), coupled to a magnetic sector ICP-MS, is described. Analyses of individual glass shards with crater diameters of 20 μm and 10 μm is essentially routine, and when element fractionation is corrected for, good accuracy is achieved. Analytical precision is good, being around ±15–30% at 1 ppm and around ±2–3% at 500 ppm from 10 μm diameter ablation craters, and lower limits of detection (LLD) are <1 ppm for most elements from 10 μm craters, when 25–28 trace elements are determined in a ∼20 s analysis. Neither 44Ca nor 43Ca can be used reliably as the internal standard for the analysis of rhyolites from 10 μm ablation craters, because CaO is close to the lower limit of quantitation (LLQ); thus 29Si must be used, although either could be used in the analysis of basaltic glasses at 10 μm. With analyses at 6 μm or 4 μm, many trace elements in rhyolites (e.g. Zr, Ba, LREE, Y, Rb, U, Th) remain above the LLQ, but at this resolution, only Si can be used as an internal standard for glass analysis. Element fractionation is an issue for all analyses <20 μm in diameter, resulting from the formation of a thin melt film on the ablation crater walls. This melt film becomes an increasingly larger proportion of the volume of ablated material as crater diameters become smaller, because the surface area/volume ratio increases. Element retention or volatility from this melt film appears to cause much of the fractionation. For larger craters (20 μm) this fractionation appears to affect all compositions similarly. For many elements determined from smaller craters (10 μm–4 μm) there is a systematic variation in the degree of fractionation with the glass (and thus melt film) composition. This relates to a change in the degree of polymerisation of the glass, with, for example, the REE being the most fractionated in polymerised rhyolitic samples at the smallest crater diameters (4 μm). This systematic behaviour, however, offers some hope for the analysis of a selection of abundant trace elements in individual shards of glass using ablation craters of 6 μm and 4 μm in diameter.

Dynamical resolidification behavior of silicon thin films during frontside and backside excimer laser annealing

Abstract Excimer laser annealing (ELA) is frequently employed to fabricate low-temperature polycrystalline silicon films on glass substrate. The grain size and crystallinity of polycrystalline silicon films are significantly affected by the resolidification behavior during ELA. A real-time in situ time-resolved optical measurement system is developed to record the rapid phase transformation process during ELA. The average solidification velocity of liquid-Si is calculated from these optical spectra using MATLAB and Excel softwares. Field emission scanning electron microscopy images reveal maximum grain size of poly-Si films with a diameter of 1 μm, which is obtained in the complete melting regime of both frontside ELA and backside ELA. Recrystallization mechanisms of complete melting of Si thin films in frontside ELA and backside ELA are demonstrated. Resolidification scenarios of partial melting, near-complete melting and complete melting in frontside ELA and backside ELA are proposed.