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The propagation of frost in an assembly of supercooled dew droplets takes place by the formation of ice protrusions that bridge ice particles and still-liquid droplets. In this work, we develop a Kinetic Monte Carlo (KMC) model to study the formation kinetics of the ice protrusions. The KMC simulations reproduce well the experimental results reported in the literature. The elongation speed of the ice protrusions does not depend on the droplet size but increases when the interdroplet distance decreases, the temperature increases, or the substrate wettability increases. While 2D diffusion of the water molecules on the substrate surface is sufficient to explain the process kinetics, high 3D (vapor) water-molecule concentration can lead to the development of 3D lateral branches on the ice protrusions. A 1D analytical model based on the water-molecule concentration gradient between a droplet and a nearby ice particle reproduces well the simulation results and highlights the relation between the protrusion elongation kinetics and parameters like the interdroplet distance, the water diffusivity, and the concentration gradient. The bridge-formation time has a quadratic dependence on the droplet-ice distance. Comparing the simulations, the analytical model, and the experimental results of the literature, we conclude that the propagation of frost on a flat substrate in an assembly of supercooled dew droplets with interdroplet spacing larger than about 1 μm is limited by water-molecule diffusivity.

International audience; Second-harmonic generation (SHG) is a nonlinear optical method allowing the study of the local structure, symmetry, and ferroic order in noncentrosymmetric materials such as ferroelectrics. The combination of SHG microscopy with local polarization analysis is particularly efficient for deriving the local polarization orientation. This, however, entails the use of tedious and time-consuming modeling methods of nonlinear optical emission. Moreover, extracting the complex domain structures often observed in thin films requires a pixel-by-pixel analysis and the fitting of numerous polar plots to ascribe a polarization angle to each pixel. Here, the domain structure of GeTe films is studied using SHG polarimetry assisted by machine learning. The method is applied to two film thicknesses: A thick film containing large domains visible in SHG images, and a thin film in which the domains' size is below the SHG resolution limit. Machine learning-assisted methods show that both samples exhibit four domain variants of the same type. This result is confirmed in the case of the thick film, both by the manual pixel-by-pixel analysis and by using piezoresponse force microscopy. The proposed approach foreshows new prospects for optical studies by enabling enhanced sensitivity and high throughput analysis.

Vacancies at interfaces between a film and a substrate can affect material properties and could play a role in solid state dewetting. Using kinetic Monte Carlo simulations, we show that interfacial mono-vacancies diffuse and coalesce to form vacancy clusters and voids. The film/substrate excess energy ES, which is related to the apparent contact angle, controls the mechanisms of coalescence. Depending on ES, voids emerging at the film surface form a hole that can be filled by the film or can lead to dewetting of the film from the substrate.

International audience; In the quest for materials for ferroelectrics-based spintronics with a large spin-orbit coupling, it is essential to carefully control the ferroelectric domains structure, their spatial organization and the domain wall type. Here, we perform the growth of GeTe thin lms on Si by molecular beam epitaxy in a large thickness range. We show that the volume fraction along with the size of the ferroelectric nanodomains can be controlled by nely adjusting the deposition thickness and temperature. We evidence the formation of 71 •-type domain walls and in situ measurements during thermal cycling show the hysteretic appearance and decay of ferroelectric domains. In combination with a detailed analysis of the GeTe/Si interface, we demonstrate that the interfacial mist dislocations formed during the growth plays a key role in the stability of the ferroelectric nanodomains.

International audience; Au deposition on Si(110) at temperature higher than 633 K leads to the formation of elongated liquid nano-droplets. In this work we show that under an electric eld, the droplets move along the [1-10] axis towards the positive electrode by electromigration. During the motion, they dissolve the substrate forming a hole underneath and a nanowire behind them. We develop a model highlighting that the driving force of these processes is bound to the respect (i) of the Au-Si bulk chemical equilibrium and (ii) of the correct balance of surface/interfacial energies. The motion takes place by means of sudden jumps with length of the order of a few µm and by small readjustments of the order of some nm of the droplet front and back edges. With respect to experiments without electric eld, electromigration changes the droplet motion by widening the droplet dissolution front and by facilitating droplet jumps.

The passage of an electric current in a material can cause a biased mass transport at its surface. This migration phenomenon is intimately related to the microscopic details of atomic processes of diffusion and attachment/detachment at step edges. Using low-energy electron microscopy, we have examined in operando under an electric current the migration of $\mathrm{Si}(111)\text{\ensuremath{-}}1\ifmmode\times\else\texttimes\fi{}1$ advacancy islands confined on $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ terraces. The islands move opposite to the current direction, with velocity increasing with the radius. The effective valence of Si adatoms is $2.8\ifmmode\pm\else\textpm\fi{}0.5$ and the kinetic length of attachment-detachment is about 500 nm. The analysis of the island's shape reveals that the electric current significantly biases the kinetic rate of mass transfers at step edges modifying the overall island's shape.

We report on the observation of a coupling between the dewetting of a Si layer on $$\hbox {SiO}_{{2}}$$ induced by surface/interface energy minimization and the etching between both materials due to the $$\hbox {Si}+\hbox {SiO}_{2}\longrightarrow 2$$ $$\hbox {SiO}^\uparrow _g$$ reaction. In the limit of a thin $$\hbox {SiO}_{{2}}$$ layer ( $$\le 10 \,\hbox {nm}$$ ) sandwiched between a Si layer and a Si handle wafer, the front of Si dewetting and the front of $$\hbox {SiO}_{{2}}$$ etching coexist in a narrow region. The interplay between both phenomena gives rise to specific morphologies. We show that extended Si fingers formed by dewetting are stabilized with respect to Rayleigh–Plateau-type instability over tenth of microns thanks to a localized etching of the $$\hbox {SiO}_{{2}}$$ layer. The breakup of this structure occurs abruptly by an unzipping process combining dewetting and etching phenomena. We also put in evidence that Si rings are created with a thin $$\hbox {SiO}_{{2}}$$ layer in the center. These processes are thermally activated with an activation energy of $$2.4\pm 0.5 \,\hbox {eV}$$ and $$4.0\pm 0.5 \,\hbox {eV}$$ , respectively, for dewetting and the etching reaction. All these results highlight the respective roles of wetting and etching in Si/ $$\hbox {SiO}_{{2}}$$ /Si system dynamics and could be a stepping stone for the development of advanced processes based on Silicon-On-Insulator technology.

Nucleation, growth and coalescence of 3D Au-Ge droplets on Ge(1 1 1) surface have been studied in real time by low energy electron microscopy. The surface diffusion energy barrier of Au on Ge(1 1 1) is estimated as 1.8 ± 0.2 eV from the dependence of the number of droplets per surface unit with temperature and Au deposition rate. At long time scale it is also shown that the droplets have a diffusive motion that results in dynamic coalescence events. From the decrease of the droplet number, the size-dependence of the diffusion coefficient of the droplets is shown to decay as R - 1.9 ± 0.5 where R is the droplet radius. This result indicates that the spontaneous motion of the droplets is controlled by an interfacial mass-transport phenomenon.

International audience; Nanostructures on surfaces can be displaced by applying an electric eld or electric currents through a material. This induced mass transport is referred to as electromigration. In this article we show that the anisotropy of diusion may control the direction of motion of electromigrating nanostructures. For this purpose we study in situ and in real time, by Low Energy Electron Microscopy, the motion of 2D one-atom thick islands or one-atom deep holes on a highly anisotropic surface (reconstructed Si(100)). Based on experiments and Kinetic Monte Carlo simulations, we propose a simple analytical model that explains most of the observations. In particular, the direction of motion of the nanostructures depends on the diusion anisotropy and does not necessarily coincide with the electric eld direction. This work opens a way for the manipulation of 2D nanostructures by means of an electric eld on anisotropic surfaces.

The deposition of Au on Ge(111)-$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-Au above the eutectic temperature results in the formation of AuGe liquid droplets that reach the liquidus composition by digging a hole in the Ge substrate. The combination of low-energy electron microscopy and atomic force microscopy measurements shows that AuGe droplets randomly migrate or electromigrate under an applied electric current dragging their underneath hole. The droplet motion is due to a mass transport phenomenon based on Ge dissolution at the droplet front and Ge crystallization at its rear. At high temperature the mass transport is limited by attachment or detachment at the solid-liquid interface and the activation energy is $1.05\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{ }\mathrm{eV}$. At low temperature the effective activation energy increases as a function of the droplet radius. This behavior is attributed to the nucleation of 2D layers at the faceted liquid-solid interface.

A1. Interfaces A1. Orientation relationship A1. Electron backscatter diffraction A3. Solid phase epitaxy A3 Polycrystalline deposition B1 Sapphire abstract Copper!lms deposited on m- and r-plane sapphire substrates have been dewetted in either the solid or the liquid state, and equilibrated at 1253 K. The orientation relationships (ORs) between the dewetted copper crystals and the sapphire substrates have been investigated by electron backscatter diffraction. In addition, the shape of the copper/sapphire interface has been studied by scanning electron microscopy. Although the as-deposited!lms develop {1 1 1} surfaces parallel to both substrates, after solid state dewetting the copper crystals on the m-plane substrate are found to change their interface plane from Cu{1 1 1}||Al 2 O 3 (m-plane) to Cu{1 1 1}||Al 2 O 3 (a-plane), and after liquid state dewetting the preferred OR of copper on both m- and r-plane substrates may be expressed as: Cu{1 1 1}! 110 "||Al 2 O 3 {1 1 2 ! 0}

Fundamental interest for 2D electron gas (2DEG) systems has been recently renewed with the advent of 2D materials and their potential high-impact applications in optoelectronics. Here, we investigate a 2DEG created by the electron transfer from a Ag adatom gas deposited on a Si(111) $$\sqrt{{\bf{3}}}{\boldsymbol{\times }}\sqrt{{\bf{3}}}$$ 3 × 3 -Ag surface to an electronic surface state. Using low-energy electron microscopy (LEEM), we measure the Ag adatom gas concentration and the 2DEG-induced charge transfer. We demonstrate a linear dependence of the surface work function change on the Ag adatom gas concentration. A breakdown of the linear relationship is induced by the occurrence of the Ag adatom gas superstructure identified as Si(111) $$\sqrt{{\bf{21}}}{\boldsymbol{\times }}\sqrt{{\bf{21}}}$$ 21 × 21 -Ag only observed below room temperature. We evidence below room temperature a confinement of the 2DEG on atomic terraces characterised by spatial inhomogeneities of the 2DEG-induced charge transfer along with temporal fluctuations. These variations mirror the Ag adatom gas concentration changes induced by the growth of 3D Ag islands and the occurrence of an Ehrlich-Schwoebel diffusion barrier of 155 ± 10 meV.

International audience; Owing to its ability to produce an assembly of nanoislands with controllable size and locations, the solid state dewetting of patterned films has recently received great attention. A simple Kinetic Monte Carlo model based on two reduced energetic parameters allows one to reproduce experimental observations of the dewetting morphological evolution of patterned films of Si(001) on SiO2 (or SOI for Silicon-on-Insulator) with various pattern designs. Thus, it is now possible to use KMC to drive further experiments and to optimize the pattern shapes to reach a desired dewetted structure. Comparisons between KMC simulations and dewetting experiments, at least for wire-shaped patterns, show that the prevailing dewetting mechanism depends on the wire width.

The orientation relationships (ORs) of copper crystals on a $$ (11\bar{2}0) $$ sapphire substrate equilibrated at 1253 K are presented. They barely depend on the procedures used in sample preparation, i.e. dewetting of a copper film in the liquid state or in the solid state. The most frequent OR found is Cu(111) || Al2O3 $$ (11\bar{2}0) $$ and Cu $$ [1\bar{1}0] $$ within few degrees from Al2O3[0001]. A secondary, lower frequency OR is also observed: Cu(001) || Al2O3 $$ (11\bar{2}0) $$ with Cu $$ [1\bar{1}0] $$ within a few degrees from either Al2O3 $$ [1\bar{1}00] $$ or Al2O3[0001]. These ORs do not follow the Fecht and Gleiter model which proposes that dense directions of the metal should align with dense directions of the oxide. On annealing, even at a temperature about half of the melting point of sapphire, fast diffusion of sapphire at the copper/sapphire interface is observed: the copper particles tend to achieve their interfacial equilibrium shapes by sinking into the substrate, and sapphire ridges form at the triple line. Finally, it is shown that the Cu(111) || Al2O3 $$ (11\bar{2}0) $$ interface remains flat at the atomic scale, and is therefore part of the copper/sapphire equilibrium interfacial shape.

International audience; The thermal decomposition of Si dioxide layers formed by wet chemical treatment on Si(001) has been studied by low-energy electron microscopy. Independent nucleations of voids occur into the Si oxide layers that open by reaction at the void periphery. Depending on the voids, the reaction rates exhibit large differences via the occurrence of a nonlinear growth of the void radius. This non-steady state regime is attributed to the accumulation of defects and silicon hydroxyl species at the SiO2/Si interface that enhances the silicon oxide decomposition at the void periphery. (C) 2016 AIP Publishing LLC.

Alloys displaying positive enthalpy of mixing demix below a critical temperature. In Co-Cu and related ternaries the miscibility gap is metastable, i.e. it occurs at temperatures lower than the liquidus. In order to study the liquid phase separation high melt undercooling is necessary. This was obtained via rapid solidification techniques using melt spinning and casting in moulding devices, as well as high temperature DSC experiments with samples embedded in a flux. Results are given for Co-Cu, Co-Cu-Fe and Co-Cu-Ni systems. Phase diagrams were optimised using the DSC data. The mechanism of phase separation was investigated by comparing samples produced under different cooling conditions. The hierarchy of microstructures obtained was interpreted accounting for the processing technique and the phase diagram. They constitute a database useful for the interpretation of the thermal history of samples processed in microgravity.

Surface and bulk liquid phase transitions are measured by a unique method currently used to determine surface and interfacial tension of liquid alloys. Focusing on the Al–In system, the location of the liquid miscibility gap was determined from the critical to the monotectic temperatures. The surface tensions of nine liquid alloys, the interfacial tension between coexisting liquids and their densities were measured as a function of temperature. Implementing the bulk data extracted from the asymmetric miscibility gap into a sub-regular model reproduced the experimental surface and interfacial tensions. The wetting temperature was estimated to lie well below the monotectic temperature. The micrometer thickness of the In-rich films which wet the surface of the Al-rich liquid phase after solidification is suggested to be due to the growth of the equilibrium wetting film by diffusion from the Al-rich phase during cooling.

This paper reports that monitoring the composition of the c (0 0 0 1), a (11–20) and m (10–10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in Ar H 2 or Ar O 2 atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c -surface of sapphire both under Ar O 2 and Ar H 2 . (ii) Potassium adsorption enhances the kinetics of step-bunching on the c -surface under Ar O 2 . (iii) The step edges on the a -surface may develop a comb-like morphology made of parallel strips along the [10–10] direction. (iv) At 1253 K, clean m -surfaces may be stable. (v) Under Ar H 2 , alumina surface diffusion is much slower than under Ar O 2 for all surface orientations, the surface concentration of impurities is low, and the Al–O ratio of the AES signals at the surface is significantly larger.

CuCoNi rapidly solidified alloys are interesting because they display giant magnetoresistance (GMR). In the present work a Cu 85 Co 10 Ni 5 alloy has been synthesized by melt spinning and analysed for GMR. The ribbons obtained have been annealed at different temperatures and the evolution of the crystal structure with annealing has been studied by X-ray diffraction. The fine microstructure has been observed by TEM and related to the magnetic properties, investigated in a vibrating sample magnetometer. In the studied composition the magnetoresistance was found to be lower than in binary CuCo alloys without Ni addition.

Six highly alloyed Cu-Fe-Ni alloys have been processed with different heat treatments and studied by means of electron microprobe and differential thermal analyses. The results are discussed in comparison with an equilibrium phase diagram calculation performed using the CALPHAD (CALculation of PHAse Diagrams) method. An unexpected temperature window for homogenization has been found in the middle of the composition range.

This work deals with the effect of Ni addition on the liquid–liquid phase separation in the Cu–Co system which displays a liquid metastable miscibility gap. Cu–Co–Ni samples with different compositions have been processed by differential scanning calorimetry using a fluxing technique to precisely determine transformation temperatures. The ternary phase diagram has been evaluated by Calphad, extrapolating the binary systems and optimizing ternary parameters using the experimental results of the present work. Ni additions reduce the demixing temperature, bringing the binodal line below the peritectic. The mechanisms of demixing and formation of microstructures have been clarified for low and high Ni content.

Some Cu-based alloys, like Cu–Co, Cu–Fe and Cu–Co–Fe, display a liquid metastable miscibility gap. When the melt is undercooled below a certain temperature depending on the alloy composition, they present a separation in two liquid phases, followed by coagulation before dendritic solidification. In order to predict the phase equilibria and the mechanisms of microstructure formation, a determination of the metastable monotectics in the phase diagrams is essential. This paper focuses on the up-to-date findings on the Cu–Co, Cu–Fe and Cu–Co–Fe metastable miscibility gap in the liquid phase. Furthermore, the knowledge on the phase equilibria in the three systems is extended by presenting new results obtained by differential scanning calorimetry (DSC) and comparing them with the calculated phase diagrams.

This paper deals with Co42Cu58 (at.%) alloy processed to obtain a cooling rate gradient during solidification. The Co–Cu system displays a metastable miscibility gap in the liquid state. Undercooling of the melt beyond a certain limit results in liquid separation and formation of droplets of the minority phase in a matrix of the dominant phase. The material was melted and cast in a wedge shaped copper mould to obtain a gradient of cooling rates. The cooling history of the alloy during the solidification was monitored by insertion of thermocouples at different positions in the mould. During cooling, the melt separated into droplets of Co-rich and Cu-rich phases. The Co-rich droplets are mainly coagulated along the major axis of the samples and an explanation of this segregation mechanism is proposed. The distribution of the size of the Co-rich particles was measured in various areas along the sample and correlated to the cooling rate.

We report on a new mechanism of nanowire formation: during Au deposition on Si(110) substrates, Au–Si droplets grow, move spontaneously, and fabricate a Si nanowire behind them in the absence of Si external flux. Nanowires are formed by Si dissolved from the substrate at the advancing front of the droplets and transported backward to the crystallization front. The droplet shape is determined by the Si etching anisotropy. The nanowire formation can be tuned by changing experimental parameters like substrate temperature and Au deposition rate.

International audience

This article deals with the metastable liquid-liquid separation in the Cu-Co system. Several samples with different compositions were investigated by differential scanning calorimetry. High undercooling with respect to the liquidus was reached by means of the glass fluxing technique. The alloys were cycled with several heating and cooling runs in order to determine the temperature of the liquid-liquid separation and of the remixing. For each composition, demixing and remixing temperatures were found to be equal. Nucleation rate calculations of the liquid phase separation were carried out to explain the experimental results. The liquid-liquid separation in the Cu-Co system was found to be a nucleation process occurring with no detectable undercooling below the binodal line.

International audience; Since a few years there have been many efforts for studying solid state dewetting that means the spontaneous agglomeration of a metastable film into an assembly of 3D crystallites [1–3]. Since the size of the so-formed 3D crystallites depends on the initial thickness of the film [3–6], solid state dewetting of ultra-thin films is a promising method for producing nanodots [7, 8]. Many studies thus focused on the effect of the film thickness on the dewetting morphologies. Generally thicker films dewet by void nucleation and opening process forming then well-organized 3D islands [1–3]. In contrast to this thinner films tend to form more complex structures [9–14]. For instance Kinetic Monte Carlo simulations have shown that a 3 ML-thick film dewets by void nucleation whereas a 1 ML-thick film dewets by forming a labyrinthine pattern of bilayer islands [10, 11]. In the literature the specific behavior of the thinner films has been attributed to barrierless void nucleation [15], spinodal dewetting (enhanced sensitivity to thickness or thermal fluctuations) [16], short range effect of the wetting potential [17, 18] or local stresses [14, 19]. Recently we investigated dewetting properties of Silicon-on-Insulator (SOI) samples capped by a chemically-prepared oxide layer. We thus reported that films thicker than 8 nm dewet in four steps and break down into self-organized 3D crystals whereas films thinner than 6 nm dewet by labyrinthine formation [9]. In this paper we show that this thin film effect is actually due to a subtle interplay between film deoxidation and film dewetting. Indeed the temperature at which a film dewets (T dew (h)) depends on its thickness h whereas the deoxidation temperature (T deox) is a constant. We thus show that if T dew (h) > T deox SOI dewetting occurs by void opening and leads to 3D crystals whereas if T dew (h) < T deox SOI dewetting leads to labyrinthine morphologies. In other words, the dewetting of the thicker films does not depend on the oxide cap (that decomposes before dewetting and thus only depends on the surface energy gain due to the disappearance of the Si surface with respect to the uncovered bare substrate) while the dewetting of the thinner films depends on the deoxidation (since only the clean deoxidized parts of the silicon film can dewet). We use LEEM to investigate in-situ and in real time the decomposition of the oxide as well as the dewetting of the SOI films. We define the deoxidation temperature T deox as the temperature at which LEEM enables to see void opening in the oxide cap layer with subsequent silicon film appearance. In a similar manner, the dewet-ting temperature T dew is defined as the temperature at which the amorphous SiO 2 substrate starts becoming visible by retraction of the silicon film. Obviously both temperatures T deox and T dew do not correspond to phase transitions and thus depend on the observation means. However since measured in the same experimental conditions they can be compared without any ambiguity. The SOI samples used in the experiments (12 nm Si on top of 25 nm SiO 2) were prepared as described elsewhere [20]. By means of repeated etching and oxidation cycles a stepwise thinning of the samples is possible to produce films of a certain thickness with a very high accuracy ending with a final oxidation step. Since this protective oxide layer is produced with the same wet chemical oxidation for each Si film thickness the thickness of the oxide is the same for all samples. Ellipsometry measurements have proven that the oxide thickness is constant with approximately 1 nm. FIG. 1. Temperature at which the initial deoxidation (black) and dewetting (red) was observed depending on the Si film thickness. Dewetting velocities are in the range of 1 to 8 nm s. The data point at 21.6 nm was obtained using a SOI sample of 22 nm Si on top of 150 nm SiO2. In Figure 1 are thus reported T deox and T dew as a function of the Silicon film thickness. As expected, the decomposition temperature of the capping oxide does not depend on the thickness of the silicon film and is rather constant at T deox =760 • C whereas T dew decreases as h n with n = 0.08 ± 0.01 comparable to [21, 22] where exponents n = 0.15 ± 0.01 have been reported. In the following we will report dewetting morphologies

We report that solid state dewetting of Si thin film on SiO2 can be reversibly inhibited by exposing the Si surface to a partial pressure of dioxygen (∼10−7Torr) at high temperature (∼1100K). Coupling in situ Low-Energy Electron Microscopy and ex situ atomic force microscopy we propose that the pinning of the contact line induced by the presence of small amounts of silicon oxide is the main physical process that inhibits the dewetting.

Copper particles have been grown on sapphire (0 0 0 1) substrates by dewetting a copper film either in the solid or the liquid state. After equilibration the particles adopt different orientation relationships (ORs). Solid state dewetting produces a single OR: Cu(1 1 1) [ 1 1 ¯ 0 ] ||Al2O3(0 0 0 1) [ 1 0 1 ¯ 0 ] . In contrast, dewetting in the liquid state (followed by solid state equilibration) produces four additional ORs, Cu(1 1 1) [ 1 1 ¯ 0 ] ||Al2O3(0 0 0 1) [ 2 1 ¯ 1 ¯ 0 ] , Cu(1 1 0) [ 1 1 ¯ 0 ] ||Al2O3(0 0 0 1) [ 2 1 ¯ 1 ¯ 0 ] , Cu(3 1 1) [ 0 1 1 ¯ ] ||Al2O3(0 0 0 1) [ 2 1 ¯ 1 ¯ 0 ] and Cu(2 1 0)[0 0 1]||Al2O3(0 0 0 1) [ 2 1 ¯ 1 ¯ 0 ] , which have been found to have a similar interfacial energy. All of the ORs observed in this study are consistent with the Fecht and Gleiter lock-in model, from which one would expect that densely packed directions in the interface plane of the metal crystals will tend to align with relatively dense directions in the substrate surface. The 30° change in alignment direction on the c-sapphire side of the interface, from Al2O3 [ 1 0 1 ¯ 0 ] for solid state dewetted samples to Al2O3 [ 2 1 ¯ 1 ¯ 0 ] for samples dewetted in the liquid state, appears to be related to a reconstruction of the copper–c-sapphire interface that occurs at a temperature between those at which the two types of samples are processed.

A model of O-adsorption at liquid metal surfaces has been constructed, using liquid Cu as an example. The modeling approach used is similar to the regular solution scheme previously used successfully for modeling the adsorption/segregation behavior of metal alloys, in that the internal energy of the system is evaluated by nearest neighbor bond energies. In the model, the adsorption of oxygen in the near-surface region is allowed to occur at both surface and sub-surface sites. The model predicts a variety of possible adsorption characteristics, including the possibility of first order adsorption transitions which involve the formation of a 2-dimensional surface oxide, and different sequences for the occupancy of surface and sub-surface adsorption sites. In particular, by fitting the model to the experimental dependence of Cu surface energy on O-partial pressure, it is possible to conclude that O-adsorption in that case most likely occurs by the occupancy of sub-surface sites.

The contact angle of liquid Cu on monocrystalline and polycrystalline Co surfaces is found to be close to zero, and some of the grain boundaries of the Co polycrystal are completely wetted by liquid Cu. The consistency of these results is discussed in terms of interfacial, grain boundary and surface energies in the Co–Cu system. The Co solid/Cu liquid interfacial energy is found to be equal to or smaller than 390 mJ m−2 at 1383 K.

Cu–Co–Fe alloys undercooled below a certain temperature display demixing of the liquid, followed by coagulation before dendritic solidification. In this article high temperature phase equilibria in Cu–Co–Fe samples have been precisely determined by DSC. Special attention has been paid to the liquid–liquid phase separation and on its effect on the formation of microstructures. The measured transformation temperatures have also been used to update the description of the ternary phase diagram.

Since the beginning of materials science research under microgravity conditions immiscible alloys have been an interesting subject. New possibilities to investigate such systems are offered by containerless processing techniques. Of particular interest is the ternary system Cu-Fe-Co, and its limiting binaries, Cu-Co and Cu-Fe. They all show a metastable miscibility gap in the regime of the undercooled melt. Within the ESA-MAP project "CoolCop", different aspects of this alloy have been investigated; results obtained so far are reported here.

We study the nano-pits formed during the etching of a SiO2 film by reactive Si islands at T≈1000 °C. Combining low energy electron microscopy, atomic force microscopy, kinetic Monte Carlo simulations, and an analytic model based on reaction and diffusion at the solid interface, we show that the shape of the nanopits depend on the ratio R/xs with R the Si island radius and xs the oxygen diffusion-length at the Si/SiO2 interface. For small R/xs, nanopits exhibit a single-well V-shape, while a double-well W-shape is found for larger R/xs. The analysis of the transition reveals that xs∼60 nm at T≈1000 °C.

The binary Co–Cu and the ternary Co–Cu–Fe systems have been optimized using the CALPHAD approach. Experimental data that have appeared recently in the literature have been used to improve the description of the metastable miscibility gap on both binary and ternary liquid phases. In the Co–Cu–Fe system, ternary parameters have been obtained to properly describe the miscibility gap. A significant improvement with respect to previous thermodynamic descriptions has been achieved. A set of model parameters for the liquid, f.c.c., and b.c.c. phases is given.

This paper deals with rapidly solidified binary Fe–C alloys containing 3.8 wt% and 4.3 wt% C. Their microstructure reveals that, as an effect of undercooling, the conventional eutectics have been suppressed and there is occurrence of the ferrite–cementite eutectic. Both phases are metastable: ferrite is supersaturated in C and cementite has a C deficiency. This is demonstrated by means of determination of phase fractions in metallographic sections and of lattice parameters via Rietveld refinement of X-ray diffraction patterns. A major consequence of non-stoichiometricity of cementite is the reduced value of the Curie temperature (up to 17 °C) with respect to that of the equilibrium compound. The maximum C deficiency in Fe3C1−x is estimated as x = 0.02. The free energy of defective cementite has been computed by means of the two sublattice model and compared with that of ferrite and austenite obtained from an assessed phase diagram. It is shown that the non-stoichiometric phase is close in energy to the equilibrium one for a composition range of several atomic per cent. It is suggested that this helps in explaining the mechanism of cementite dissolution by heavy deformation of ferrous alloys, and the ease of cementite nucleation in castings.