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Homogeneous face-centered cubic (fcc) polycrystalline CoCrFeNi films were deposited at room temperature on (0001)alpha-Al2O3 (c-sapphire). Phase and morphological stability of 200 to 670 nm thick films were investigated between 973 K and 1423 K. The fcc-phase persists while the original texture of 30-100 nm wide columnar grains evolves into ~10 or ~1000 micron wide grains. Only the grains having specific orientation relationships to the sapphire grow; as in the case of pure fcc metal (M) films 4 orientation relationships (OR) are found: OR1 (M(111)[1-10]//alpha-Al2O3 (0001)[1-100]) and OR2 (M(111)[1-10]//alpha-Al2O3 (0001)[11-20]) and their twin-related variants (OR1t and OR2t). Below 1000 K, the film microstructure stabilizes into 10 micron wide OR1 and OR1t twin grains independent of film thickness. Above 1000 K, the OR2 and OR2t grains expand to sizes exceeding more than a 1000 times the film thickness. Upon annealing, the films either retain their integrity or break-up depending on the competing kinetics of grain growth and grain boundary grooving. Triple junctions of the grain boundaries, the major actors in film stability, were tracked. Thinner films and higher temperatures favor film break-up by dewetting from the holes grooved at the triple junctions down to the substrate. The grain boundaries of the OR2 and OR2t grains migrate fast enough to overcome the nucleation of holes from which break-up could initiate. The growth of the OR2 and OR2t grains in this complex alloy is faster than in pure fcc metals at equivalent homologous annealing temperatures., 6 figures and 3 tables

The dynamics of solid state dewetting phenomena of a 50nm thick, mazed bicrystalline Al film on single crystalline α-Al2O3(sapphire) substrates was studied in-situ using an environmental scanning electron microscope (ESEM). The bicrystalline Al thin films served as a model system where the influence of grain boundaries and texture effects are well determined compared to polycrystalline films. The experiments were performed in controlled oxidizing and reducing atmospheres at 773K and 823K, respectively, to shed light on the differences in dewetting mechanisms and dynamics.While the reducing atmosphere led to spontaneous dewetting at 823K after an incubation time of a few minutes, a hierarchical dewetting process was observed for the sluggish dewetting under oxidizing conditions. Voids initiated at (substrate or surface) defects and expanded trying to maintain a hexagonal shape. Pinning and depinning processes led to a discontinuous void growth and irregular void shapes including finger instabilities. As a consequence, the void growth followed a variety of power law exponents between 0.10 and 0.55. A new microkink-flow mechanism was discovered at the terminating Al planes at the void.

Nano-crystalline Ni and Cu films deposited on the r-plane of sapphire (-Al 2 O 3) develop a fiber-texture upon annealing, in which grains grow up to 300 to 500 times larger than the film thickness. Most of the largest grains, which have grown at the expense of others, display one of four preferred orientation relationships (ORs) to the substrate. The four preferred ORs are OR1r = Me(111) //-Al 2 O 3 , OR2r = Me(111) //-Al 2 O 3 (Me = Ni or Cu), and their twins, which are rotated 60° about the axis perpendicular to the substrate. For these ORs, one of the densest atomic rows that lies within the Me {111} interfacial plane, aligns with the direction of the step edges that form at the intersection of the r-plane with one of its neighboring facets on the equilibrium shape of sapphire (i.e. the c-(0001), p-or s-planes). One of the ORs is most preferred when the steps at the interface are such that a {100}-type ledge of the Me {111} interfacial plane faces the ledge of the sapphire step. This observation provides a useful insight into the origin of the preferred ORs, and confirms the important role of surface steps in texture development. The evolution of Ni films of different thicknesses, ranging from 100 to 560 nm, was analyzed. Grain boundary grooving inhibits grain boundary motion and favors hole formation and dewetting in the thinnest films (100 nm). The crystals left behind after dewetting display ORs which may differ from the preferred ones. Large grains with the preferred ORs can grow at the expense of others when the film thickness is greater than 300 nm.

International audience; The bulk quaternary equiatomic CoCrFeNi alloy is studied extensively in literature. Under experimental conditions, it shows a single-phase fcc structure and its physical and mechanical properties are similar to those of the quinary equiatomic CoCrFeMnNi alloy. Many studies in literature have focused on the mechanical properties of bulk nanocrystalline high entropy alloys or compositionally complex alloys, and their microstructure evolution upon annealing. The thin film processing route offers an excellent alternative to form nanocrystalline alloys. Due to the high nucleation rate and high density of defects in thin films synthesized by sputtering, the kinetics of microstructure evolution is often accelerated compared to those taking place in the bulk. Here, thin films are used to study the phase evolution in nanocrystalline CoCrFeNi deposited on Si/SiO 2 and c-sapphire substrates by magnetron cosputtering from elemental sources. The phases and microstructure of the films are discussed in comparison to the bulk alloy. The main conclusion is that second phases can form even at room temperature provided there are sufficient nucleation sites.

International audience; The movement of grain boundaries in pure metals and alloys with a low concentration of dislocations has been historically proved to follow curvature flow behavior. This mechanism is typically known as grain growth (GG). However, recent 3D in-situ experimental results tend to question this global picture concerning the influence of the curvature on the kinetics of interface migration. This article explains, thanks to 2D anisotropic full-field simulations, how the torque effects can complicate these discussions. It is then illustrated that neglecting torque effects in full-field formulations can have a significant effect on the overall rate of GG, the shape of grains and grain boundaries as well as their local kinetics. The apparent reduced mobility can be much more complex than expected without necessarily questioning the influence of the curvature on the local kinetic equation.

The invention relates to a process for preparing single-crystal thin films of pure metals or alloys, by deposition and growth of grains on a (0001) sapphire having a miscut comprised between 0.2° and 5°, and oriented towards a specific plane. It also relates to a single-crystal thin film obtainable by such a process and uses thereof., L'invention concerne un procédé de préparation de films minces monocristallins de métaux ou d'alliages purs, par dépôt et croissance de grains sur un saphir (0001) présentant une mauvaise découpe comprise entre 0,2° et 5°, et orientés vers un plan spécifique. L'invention concerne également un film mince monocristallin pouvant être obtenu par un tel procédé et ses utilisations.

In this study, we report on face-centered cubic structured CoCrFeNi high-entropy alloy thin films with finely dispersed nano-oxide particles which are formed by internal oxidation. Analytical scanning transmission electron microscopy imaging found that the particles are Cr 2 O 3 . The oxide particles contribute to the hardening of the film increasing its hardness by 14% compared to that of the film without precipitates, through the Orowan-type strengthening mechanism. Our novel approach paves the way to design medium- and high-entropy alloys with high strength by making use of oxide phases.

Grain boundary (GB) and surface segregation have been studied by computer simulations in the so-called Cantor alloy: $\mathrm{C}{\mathrm{o}}_{20}\mathrm{N}{\mathrm{i}}_{20}\mathrm{C}{\mathrm{r}}_{20}\mathrm{F}{\mathrm{e}}_{20}\mathrm{M}{\mathrm{n}}_{20}$. Monte Carlo, molecular dynamics, as well as lattice statics methods, using second nearest-neighbor modified embedded atom method potentials, have been applied sequentially in order to equilibrate the alloy. Simulations of GB segregation showed that Cr segregates most strongly, and is accompanied by weak Mn segregation. In contrast, in the case of surface segregation, Mn segregates most strongly to the outermost surface atom plane. However, when adsorption is measured as the integrated excess of the components over a 4-atom-layer region adjacent to the surface, Cr again emerges as the dominant segregant. A mass balance model has also been applied to the results of the segregation behavior, in order to estimate the potential for depletion of the bulk alloy composition due to segregation at GBs. It is found that significant depletion of bulk composition can occur if the alloy grain size falls below about 100 nm.

International audience; A systematic variation in the orientation relationship (OR) of Ag films grown on Ni substrates previously discovered by a combinatorial approach is analyzed using concepts of grain boundaries, surface science and phase transformations. On roughly half of all Ni substrate orientations, Ag adopts a "special" OR that varies systematically from a twin OR, which develops on substrates lying along the (111)-(210) line of the standard stereographic triangle (SST), to the so-called oct-cube OR, which arises exclusively on (100) substrates. On the other half of Ni substrate orientations, Ag adopts the standard cube-on-cube OR. The special ORs are modeled by a) linear interpolation, b) 1D edge-to-edge matching and c) 2D transformation strains, using the twin relationship as a reference. The 1D model shows that the systematic variation in the special ORs can be understood in terms of a growth mechanism by attachment at steps and a lattice rotation due to the difference between the step heights in the substrate and the film. The 2D model explains why this mechanism does not apply to substrates on which Ag displays the cube-on-cube OR.

International audience; This paper compares two approaches for investigating the near-surface composition profile that results from surface segregation in the so-called Cantor alloy, an equi-molar alloy of CoCrFeMnNi. One approach consists of atomistic computer simulations by a combination of Monte Carlo, molecular dynamics and molecular statics techniques, and the other is a nearest neighbor analytical calculation performed in the regular solution approximation with a multilayer model, developed here for the first time for a N-component system and tested for the 5-component Cantor alloy. This type of comparison is useful because a typical computer simulation requires the use of ~100 parallel processors for 2 to 3 hours, whereas a similar calculation by means of the analytical model can be performed in a few seconds on a laptop machine. The results obtained show qualitatively good agreement between the two approaches. Thus, while the results of the computer simulations are presumably more reliable, and provide an atomic scale picture, if massive computations are required, for example, in order to optimize the composition of a multicomponent alloy, then an initial screening of the composition space by the analytical model could provide a highly useful means of narrowing the regions of interest, in the same way that the CALPHAD method allows rapid investigation of phase diagrams in complex multinary systems.

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}

International audience; Continuous thin films of Pt on A-plane 1 1 2 0 À Á sapphire substrates were dewetted to characterize the morphological evolution and dew-etting kinetics at 800 °C using an oxygen partial pressure of 10 À20 atm. Hole growth was studied, focusing on partially dewetted samples. Four different low-index orientation relationships were found between the Pt and sapphire substrate by electron backscattered diffraction combined with transmission electron diffraction patterns. Abnormal grains adjacent to the holes with a small deviation from one of the low-index orientation relationships were observed. The difference in the heights of the abnormal grains adjacent to the holes (rim-height) is influenced by the initial position of the hole, and the existence of grains with a low-energy interface orientation relationship, and not only by diffusivity rates dictated by surface orientation as described in existing edge-retraction models. The existence of low-index orientation relationships is seen as the driving force for abnormal grain growth in the vicinity of the holes, and is a dominant factor in controlling the dewetting rate of thin metal films on oxide surfaces.

International audience; Molecular dynamics simulations have been performed to compare the orientation relationships (ORs) that develop between Ag films/particles equilibrated with Ni, depending on whether the Ag is subjected to three-dimensional (3-D) confinement by being embedded in Ni, or to 2-D confinement by equilibration with a Ni substrate. Previous results of both simulations and experiments have shown that Ag films equilibrated with planar Ni substrates display a large number of different ORs; in particular, Ag equilibrated on Ni{100} displays an OR of Ag{111} // Ni{100} , often referred to as an oct-cube OR. Here it is shown that a Ag particle embedded in Ni displays an OR of Ag{111} // Ni{111} , i.e., a cube-on-cube OR. It has also been shown that as the confinement of a Ag particle is gradually increased from 2-D to 3-D, by equilibrating a Ag particle on Ni(100) substrates with progressively deeper dimples, a transition in OR occurs from oct-cube to cube-on-cube. This result contradicts the conventional notion which supposes that the ORs displayed in the presence of 3-D confinement (e.g., during phase transformations) will also tend to be displayed in epitaxy on a substrate.

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 equilibrium configuration of compound sessile drops has been calculated previously in the absence of gravity. Using the Laplace equations, we establish seven dimensionless parameters describing the axisymmetric configuration in the presence of gravity. The equilibrium axisymmetric configuration can be either stable or unstable depending on the fluid properties. A stability criterion is established by calculating forces on a perturbed Laplacian shape. In the zero Bond number limit, the stability criterion depends on the density ratio, two ratios of interfacial tensions, the volume ratio of the two drops, and the contact angle. We use Surface Evolver to examine the stability of compound sessile drops at small and large Bond numbers and compare with the zero Bond number approximation. Experimentally, we realize a stable axisymmetric compound sessile drop in air, where the buoyancy force exerted by the air is negligible. Finally, using a pair of fluids in which the density ratio can be tuned nearly independently of the interfacial tensions, the stability transition is verified for the axisymmetric configuration. Even though the perturbations are different for the theory, simulations and experiments, both simulations and experiments agree closely with the zero Bond number approximation, exhibiting a small discrepancy at large Bond number.

The crystal shape of Ni particles, dewetted in the solid state on sapphire substrates, was examined as a function of the partial pressure of oxygen (P(O 2)) and iron content using scanning and transmission electron microscopy. The chemical composition of the surface was characterized by atom-probe tomography. Unlike other face-centered cubic (fcc) equilibrium crystal shapes, the Ni crystals containing little or no impurities exhibited a faceted shape, indicating large surface anisotropy. In addition to the {1 1 1}, {1 0 0} and {1 1 0} facets, which are usually present in the equilibrium crystal shape of fcc metals, high-index facets were identified such as {1 3 5} and {1 3 8} at low P(O 2), and {0 1 2} and {0 1 3} at higher P(O 2). The presence of iron altered the crystal shape into a truncated sphere with only facets parallel to denser planes. The issue of particle equilibration is discussed specifically for the case of solid-state dewetting.

This article reports the monitoring of reversible displacement of a gallium droplet on a tungsten submicron wire deposited by focused ion beam from tungsten hexacarbonyl precursor. The authors demonstrate that by applying a voltage to the wire terminals, the internal electric field created along the wire produces the motion of the droplet. Since the matter involved in this displacement is conductive, the authors show that it is possible to build a submicron electrical switch. Contact can be switched on and off between two electrodes separated by a submicron gap, by electrical monitoring the position of the conductive droplet. In nanoscience, connections of nano-objects are needed to demonstrate the peculiar electrical properties of such objects. A lot of studies have been devoted to direct writing of high quality metallic wires by local decomposition of gaseous molecules induced by tightly focused ion or electron beams. 1–4 These techniques are particularly suitable to link the micron world optical lithography to the nanoworld. Cross beam systems coupling a focused ion beam FIB and a scanning electron microscope SEM equipped with a gas injection system have been widely used in microelectronic industry for integrated circuit rewiring at the submicron scale. The deposited materials are often contaminated by C and O coming from the decomposition of the ligands of the precursor molecules, usually organometallic or metal organic molecules. Furthermore, extra contamination of the deposited wires occurs by implantation of gallium atoms coming from the Ga + ion beam itself. Consequently, the metal wire resistivity is usually up to 100 times higher than the bulk one. Tungsten nanowires 200 nm wide by 80 nm thick have been fabricated by a focused ion beam induced deposition process 5,6 FIBID from the dissociation of WC0 6 molecules and studied in our cross beam system equipped with in situ electrical measurements. A current density above a threshold value 5,6 of 1.4 10 7 A / cm 2 induces a wire annealing by Joule effect which improves their electrical conductivity. The high current density induces the exudation of gallium out of the wire and its merging as several droplets Fig. 1. The exudation of gallium is closely related to the light 3% decrease of the wire resistance between 1.1 and 4 V Fig. 1. Droplet formation along the wire takes place when the voltage reaches about 2.5 V. This value increases with the initial value of the resistance of the wire to get the current density threshold required. Increasing the voltage up to 4 V drives all the droplets toward the lowest potential electrode, leading to the formation of a unique droplet of about 550 nm in diameter SEM image inserted in Fig. 1. For a voltage above 4 V, the resistance of the wire drops due to the nonreversible crys-tallization of the tungsten wire. 5,6 The value of the resistance after the first ramping can be ten times less than the value of the resistance of the as-deposited wire. The droplet contains about 90 at. % of gallium atoms and 10 at. % of oxygen atoms as observed by ex situ energy dispersive x-ray analysis. Most of the oxygen contained in the droplet is a consequence of the sample transfer through air from one SEM to the other. A gallium droplet, which has been formed at one extremity of a wire, as explained previously, 5,6 migrates toward the opposite terminal if the voltage is reversed. The droplet is always driven toward the lowest potential electrode when the voltage applied 2.5 V induces a current density of about 1.4 10 7 A / cm 2 through the tungsten wire. Droplet position change was followed in situ by SEM. Figure 2 displays three images grabbed from a SEM video, separated in time by 0.6 s between Figs. 2a and 2b and 0.4 s between Figs. 2b and 2c. We started with one drop-let nearby the left electrode and slowly increased the voltage. One can see that the left droplet diameter decreases slightly while the right one increases. It demonstrates that the gal-lium transfer occurs from the left electrode to the right one by changing the polarity of the voltage between the two electrodes. During the transfer, the W wire remains unchanged between the initial and final states. It should be stressed that instead of moving at once from one point of the wire to the other, the droplet diameter decreases while simultaneously a Electronic

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.

Biominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nanometers. Thus, the transition from imperfect crystallographic order at millimeter scale to nearly perfect single crystalline domains at nanometer scale is progressive. The concept of >mesocrystal> involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of >multilevel modularity.> This modularity has potential implications for the origin of complex biomineral shapes in nature. A multi-level modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they grow, This work has been supported by Centre National de la Recherche Scientifique (CNRS), Institut National des Sciences de l’Univers (INSU) through grants ECLIPSE 2005, INTERRVIE 2009, and by Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants to D.V.

Surface phase transitions at Ga-rich liquid surfaces have been investigated in Ga-Pb alloys with low lead content. In the region of the liquid-liquid miscibility gap, the Pb-rich liquid phase completely wets the surface of the Ga-rich phase at coexistence. Observations have been made of demixing and solidification of the Pb-rich liquid film. Ga-rich alloys, which are single-phase below the monotectic temperature, can be undercooled below the liquidus, as far as the metastable binodal line where the Pb-rich wetting liquid film forms and solidifies into thin {111} Pb crystals. These films completely redissolve upon reheating to the liquidus temperature. Freezing occurs at surfaces because of complete wetting of the liquid rich in the high melting point component and the hysteretic character of the solidification transformation. Such ''surface'' experiments allow assessment of the stable and metastable liquidus lines of the Ga-Pb phase diagram in the vicinity of the monotectic temperature.

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.

Wetting of single-crystal surfaces of metallic solids and oxides by liquid metals and alloys is anisotropic because of the anisotropy of the energies of solid surfaces and of their interfaces with liquids. To provide a basis for a discussion of wetting anisotropy, we review first the literature on surface and interfacial energies in metal-metal and metal-ceramic systems. We then summarize the relevant literature on the anisotropy of the energies of solid surfaces and of solid-liquid interfaces. These energies are then used in conjunction with the Young equation to estimate the expected anisotropy of wetting. Some serious discrepancies are found between these estimates and the experimental anisotropy of wetting. We show that under certain experimental conditions the wetting angles that have been determined are not Young contact angles.

The impingement and interdiffusion of adsorbed Pb and Bi layers spreading from separated 3D pure bulk sources on Cu(1 0 0) has been studied, at T = 513 K, by in situ scanning Auger microscopy. When the leading edges of the pure Pb and Bi diffusion profiles impinge, they both consist of low-coverage lattice gas surface alloyed phases. In these low-coverage phases, Pb displaces surface alloyed Bi and the point of intersection of the profiles drifts towards the Bi source. These features lead to the conclusion that Pb atoms are more strongly bound at surface alloyed sites in Cu(1 0 0) than Bi atoms. Once the total coverage (Pb + Bi) on the substrate reaches about one monolayer, Pb and Bi are dealloyed from the substrate, and the interdiffusion profiles become essentially symmetric. Pb and Bi mix in all proportions, with an interdiffusion coefficient of ∼10−13 m2/s. This is considerably smaller than the self-diffusion coefficients previously observed for pure Pb and Bi in their respective high-coverage phases, indicating that the mechanism of interdiffusion is different from that of self-diffusion. As interdiffusion proceeds, the point of intersection of the Pb and Bi profiles reverses its drift direction, leading to the conclusion that binding of Bi atoms to the Cu(1 0 0) substrate is stronger than that of Pb atoms in the highest-coverage surface dealloyed layers.

International audience; Molecular dynamics simulations of Ag films equilibrated on Ni have been performed for 12 different Ni substrate orientations. The results show that well-equilibrated films display several different orientation relationships (ORs) depending on the Ni substrate orientation: cube-on-cube, twin, oct-cube, and a series of special ORs that are a consequence of the oct-cube OR that develops on Ni(100). It is found that an important feature displayed by the observed ORs is the alignment of the step edges of the Ag film with those of the Ni substrate at the interface. Such alignment is initiated during film formation, but also tends to produce minimum energy interfaces between film and substrate. This feature of hetero-epitaxy and of the resulting ORs has not previously been emphasized.

International audience; The orientation relationships (ORs) that develop when Ag films are equilibrated on more than 200 different Ni substrate orientations distributed over the standard stereographic triangle have been determined by electron backscatter diffraction. Four different types of OR have been observed, including cube-on-cube, twin-related, oct-cube (that develops only on Ni(100)), as well as a family of more complex ORs (referred to as "special") that arise during the gradual transition from the oct-cube to the twin OR. A mechanism of OR development, based on the alignment of the step edges on the Ag side of the interface with those of the Ni substrate, has been validated by comparison with the results obtained on the large range of substrate orientations investigated in this study. The mechanism proposes that step alignment occurs in the early stages of film formation, but is also consistent with equilibrium ORs as it tends to produce minimum energy interfaces. This feature of hetero-epitaxy and of the resulting ORs has not previously been emphasized.

A recently developed model of grain boundary (GB) segregation, in terms of the five macroscopic parameters of GB orientation, has been exercised to explore the anisotropy of GB segregation. The five macroscopic GB orientation parameters are defined by means of the orientations of the two crystallographic planes that terminate the crystals on either side of the GB, and a twist angle. Some important conclusions include the following: (a) the composition of a boundary depends on all five parameters of GB orientation, (b) the segregation profile across a GB depends on the two planes which terminate the adjacent crystals, (c) the composition profile across GB’s terminated by identical crystallographic planes is symmetric, but is asymmetric when GB’s are terminated by different planes, and (d) the strength of the segregation on one side of a GB influences the extent of segregation on the other. Some experimental results on Nb-doped TiO2 are presented in order to verify above predicted trends. In addition, it is shown that the model predicts the possibility of anisotropic GB wetting transitions as two-phase coexistence is approached.

The wetting of lead on silicon wafers with regularly patterned holes, and covered by native silica, has been investigated at 610 K under ultrahigh vacuum conditions. The advancing and receding macroscopic contact angles have been measured by slowly compressing and stretching a liquid lead bridge between two identically patterned substrates. These angles are shown to depend on the distribution of the holes in the wafers and the continuity of the triple line.

Surface diffusion of Pb and Bi over Cu(1 0 0) surfaces has been studied by scanning Auger microscopy techniques. The diffusion profiles of Pb and Bi have been found to be quite different. The results show that three major factors control the shapes of the surface diffusion profiles: (a) First order phase transitions, which lead to phase coexistence over specified coverage ranges, tend to produce abrupt changes in coverage versus distance profiles; (b) profiles can be affected by the existence of significant differences in the diffusion coefficients of the various phases present, and by the possibility (c) of important changes in diffusivity within a given phase, as a function of coverage, due to interactions between the diffusing atoms. In addition, it has been shown that the strong connection between diffusion profile shapes and the 2D phase diagram allows certain features of the 2D phase diagram to be determined from diffusion profiles.

The equilibrium crystal shape (ECS) of Bi-saturated Cu at 1223 K has been studied, after quenching the material to room temperature, by a scanning electron microscopy investigation of the shapes of pores (or negative crystals) that are present on grain boundary fracture surfaces. Bi-saturation of Cu surfaces at 1223 K results in dramatic changes in the ECS compared to pure Cu. Whereas all possible surface orientations are stable in the case of pure Cu, only the {1 1 1}, {1 0 0}, {1 1 0}, and {3 2 0} orientations are stable in Bi-saturated Cu crystals. In addition, the weak maximum anisotropy of pure Cu of 2% is increased fourfold by Bi saturation of the surface.

The morphologies of α-Al2O3 single-crystal substrates, annealed in contact with Cu droplets ranging in size from 1 to 10 μm, are observed by high-resolution scanning electron microscopy. After 45 min at 1373 K in a He-5% H2 atmosphere, the alumina substrates display different shapes depending on their orientation and on the addition of small amounts of titanium to the copper. The alumina surface may remain flat, display a hollow of faceted spherical shape at the solid/liquid interface, or develop anisotropic ridges at the triple line. The shape changes result from the diffusion of the components of alumina that takes place to achieve a minimum interfacial energy of the drop–substrate system. Explanations of these features are proposed with a discussion of the conditions under which the Young equation can be used for characterizing wetting at high temperature.

The stability of a double-slab configuration of two-phase particles confined in a third phase is studied as a function of shape in two and three dimensions. The condition of stability against splitting one phase in the particle into two separate identical slabs is shown to be the sum of the wetting factor and the change in the interface area relative to the shape of the two-phase particle. It is found that the double-slab configuration can be stable for a wide range of wetting factors and shapes.

Nous testons par des experiences de mouillage sous ultra-vide, l'etat de l'interface entre le plomb liquide et differents solides metalliques (metaux purs: Al, Fe et Ni, et l'acier T91) a des temperatures en dessous de 400°C. L'objectif est de comprendre si les couches d'oxyde natif formees sur ces surfaces peuvent etre decollees au cours d'un contact prolonge avec le plomb liquide. Celui-ci est mis en contact intime avec les surfaces des substrats grâce a l'elaboration de gouttes de plomb in-situ. Les substrats utilises sont soit des polycristaux massifs, soit des films nanocristallins obtenus par evaporation sous ultra-vide. Les experiences de mouillage sont realisees par la methode de la goutte posee, et/ou celle du pont liquide. Cette derniere permet d'etudier le mouillage sur des surfaces solides fraiches ou des ex-interfaces solide/liquide en ecrasant et etirant des ponts liquides formes entre deux substrats paralleles horizontaux. Nous montrons que le plomb liquide delamine les couches d'oxyde natif formees sur les substrats. Nous en concluons que si des revetements sont necessaires pour proteger des solides metalliques d'une corrosion par le plomb liquide, il faut qu'ils soient renouvelables in-situ.

Surface energy measurements have been performed on liquid Ga-Sn binary and on Ga-Pb-Sn as well as Ga-Pb-Tl ternary alloys, by the sessile drop technique under ultrahigh vacuum conditions. The purpose of these measurements was to investigate the change in adsorption behavior of Pb in Garich alloys as a consequence of ternary additions. In order to aid in the interpretation of the results, a multilayer model of surface segregation was formulated in the regular solution approximation. The results show evidence of site competition effects between the two solutes, which reduce the surface concentration of Pb in relation to binary Ga-Pb alloys. The effects of Sn on previously studied wetting-related adsorption transitions in Ga-Pb were also investigated. It was concluded that Sn additions are likely to raise the wetting temperature of the Ga-Pb alloy.

Adsorption of Tl has been measured by Auger electron spectroscopy as a function of temperature at the surface of three liquid Ga–Tl alloys of compositions: 2×10−2, 2×10−3, and 5×10−4 at.% Tl. The temperature of the prewetting critical point is estimated to be 200±10 K, whereas the wetting temperature is estimated to lie below 145 K. Thus, it appears that the wetting transition in this system is first order rather than critical. This result is in contrast to previous measurements on the Ga–Pb system, where it was not possible to ascertain the nature of the wetting transition. Taken together, these results indicate that wetting transitions in binary metallic systems with short-range interactions occur at temperatures that are significantly lower in relation to the critical temperatures than is the case in organic liquid systems with long-range interactions.

We address the shape and distribution of two-phase systems embedded within a third phase. To motivate this work, we begin by describing transmission electron microscopy observations of the configurations adopted by the solid and vapor phases of lead when these are confined together within a silicon cavity. We then perform analytical calculations of the stability of various possible configurations of two-phase systems confined in a cubic-shaped cavity. The most stable configurations are a function of the volume ratio of the two phases in the cavity, and of a parameter describing the wetting behavior in the three-phase system. The wealth of configurations obtained for embedded solid/fluid or condensed/fluid phases within a solid cavity is presented. Wetting anisotropy on the walls of the cavity, and the faceted or isotropic character of the interface between the two embedded phases, are shown to be physical parameters that determine the number of possible stable configurations.

The wetting of Pb-Ni crystals on graphite has been observed at 558 K in a Scanning Auger Microprobe. Samples were prepared so as to produce 10 μm crystals of Pb with Ni contents increasing from 0 to 0.3 wt% along one axis of the graphite substrate. In the low Ni region, the contact angle was found to decrease slowly from 119° to 98° with increasing Ni content. In the region of high Ni content, a constant contact angle of 83° was measured. In between, crystals with contact angles of 98° and 83° were observed to coexist, near the limit of solubility of Ni in Pb, indicating the presence of a first order transition in contact angle. The continuous decrease in contact angle, in the low Ni region, is due to Ni adsorption at the Pb-graphite interface, which leads to a decrease in interfacial energy. The constant contact angle in the high Ni region is associated with the precipitation of a Ni-rich phase. Various hypotheses are advanced to account for the first order transition in contact angle as a function of Ni concentration.

In the present study, adsorption of Pb at the surface of single-phase liquid Ga–Pb alloys has been measured by Auger electron spectroscopy for four compositions ranging from 2×10 −4 to 5×10 −6 Pb bulk atom fraction, over the temperature range from 240 to 500 K. These measurements complement and extend those reported in the companion paper. The results have been used to obtain additional information on the extension of the prewetting line above the temperature of the prewetting critical point. Extrapolation of the results indicate that the prewetting critical point lies in the vicinity of 240 K, in reasonable agreement with the estimate obtained by surface-energy measurements in the companion paper. In addition, the results show that the wetting transition temperature also lies close to 240 K, which makes it difficult to ascertain whether the wetting transition is critical or first order.

Molecular dynamics simulations have been performed to study the interaction between a faceted pore and an anisotropic grain boundary (GB). Nickel was chosen as a convenient model system. In order to establish the equilibrium crystal shape (ECS) of the pore, studies were also conducted on isolated pores. Isolated pores were found to be subject to the nucleation inhibition of equilibration that has been predicted by Rohrer et al. (J Am Ceram Soc 2000;83:214, 2001;84: 2099). This work shows that configurations close to the ECS can be obtained if supersaturation within a pore is artificially increased by adding mobile adatoms to the internal surfaces of the pores. In the case of pores located at GBs, the nucleation energy barriers to facet displacement are not present for facets in contact with the GB at the triple line, but may still persist for facets that have no contact with the GB. This problem can be overcome by approaching the equilibrium shape from different initial configurations. The configuration of the GB in the vicinity of the pore has been found to be essentially planar, indicating that GB puckering in the vicinity of anisotropic pores is not generally necessary. The present calculations show that incompatibilities between misoriented pore facets that meet at the triple line with the GB are easily accommodated by local atomic rearrangements at the disordered region of intersection with the GB.

The wetting of Cu O and Au Cu O alloys on alumina single-crystals and the surface free energy of these liquids have been determined as a function of oxygen activity. The explored oxygen activity range is from 10 −10 to the value corresponding to the formation of the mixed oxide AlCuO 2 . The oxygen adsorption at the surface of a metallic liquid and its interface with an oxide are shown to mainly depend on the external phases in contact with the liquid (vapour or oxide respectively). The free energies of the surfaces show monotonic decreases with log a o above a critical value of a o . The free energies of the metal-oxide interfaces also show monotonic decreases and stepped decreases at low oxygen activity. These are interpreted as oxygen adsorption transitions corresponding to the formation of a 2D-interfacial phase. The independence of surface and interfacial oxygen adsorptions suggests that the wetting and adhesion of a liquid metal on an oxide are not systematically improved with increasing oxygen activity.

The existence of a liquid gallium film or droplets on the surface of a GaAs(s) single crystal at high temperature is analyzed using the thermodynamics of vaporization and interfaces in the AsGa system. The steady-state of vaporization is calculated by taking into account the congruent vaporization of the liquid phase, the vaporization of solid GaAs in equilibrium with the liquid phase and the congruent vaporization of the GaAs(s) crystal. The stability of a liquid film or droplets at the surface of a crystal is estimated by examining the surface and interfacial tensions of the liquid phase. The composition of the liquid depends on the vaporization steady-state and this is compared with independent free vaporization studies. Two temperature domains are determined: at high temperature (T > 905 K) gallium rich droplets are formed by arsenic excess vaporization and at low temperature (T < 905 K, which is the maximal temperature for congruent vaporization of the solid GaAs) the liquid droplets must disappear by gallium vaporization since the GaAs system tends to come back to the congruent vaporization of the pure crystal.

The maximum wetting hysteresis is measured using the tensiometric ‘immersion-emersion’ method and a new optical technique: the ‘sandwich drop’ method. Experiments are performed on model-systems: liquid Sn at 1173 K, either on stepped SiO 2 surfaces or on two-phased Si-SiO 2 surfaces, the geometric shape of the defects (of micrometric size) of which are strictly controlled. The three main results are: (1) the hysteresis exists only if the length of the defect overcomes the amplitude of the thermal wandering of the triple line; (2) the wetting hysteresis depends on the linear density of the defects as the chemical pinning of the triple line occurs in only (advancing or receding) spreading direction; (3) for a same shape and distribution of the defects, the width of the hysteresis changes when the chemistry of the substrate and the defect are exchanged.

International audience

Existing methods to rapidly compute interface-energy minimizing shapes with anisotropy are collected and clarified, and new methods are introduced. A description of freely available, platform-independent software for the computation and display of equilibrium geometries is provided. The software relies on a new computational method to rapidly find equilibrium geometries. It also features a graphical user interface and includes the 32 crystallographic point groups to simplify inputting interfacial energies and their associated orientations. When a particle is completely enclosed within a single interface (isolated), the software computes and provides visualization for Wulff shapes. When a particle is enclosed by two interfaces, such as a particle at a grain boundary, the software minimizes their collective interfacial energy; if one of the interfaces is planar, the computation reproduces the Winterbottom construction. When both interfaces are deformable, the software provides a new tool for calculating the particle shape and the distortions of boundaries that are attached to it, even for highly anisotropic interfaces. The properties of particles bounded by two deformable interfaces are discussed, and applications of the software are illustrated. In some cases, the software can be used as a method to infer values of relative interfacial energies from a microscopic observation.

Nanometer-thick films at interfaces and surfaces exist in various materials and can substantially influence their properties. Whether these films are an equilibrium or transient state is debated. To address this question, we equilibrated 1.2-nanometer-thick films at gold-sapphire interfaces in the presence of anorthite glass and measured the solid-solid interface energy. The equilibrated film significantly reduced the interfacial energy and could be described by the Gibbs adsorption isotherm expanded to include structure in addition to chemical excess. Unlike artificially made conventional thin films, these films do not break up during equilibration and offer an alternative design criterion for thin-film technology. These results demonstrate that nanometer-thick films at interfaces and surfaces can be an equilibrium state and included in phase diagrams with dedicated tie-lines.

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.