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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.

In socio-ecosystems, human activities are structured in time and space by interactions between different regulatory systems with different collective goals. These regulatory systems are modeled by institutions and organizations, and the regulatory mechanisms by norms applied to agents in Multi-Agent Systems (MAS). However, little is said about sharing resources, space and time. In particular, temporal and spatial expressivity is often limited in MAS for institutions and norms. This research proposes an institutional MAS model capable of representing multiple institutions and norms in the socio-ecosystem, in order to account for the multiplicity of interactions through agents, resources, space and time. We propose an extension of Descriptive Logic for the description of institutions and norms, and use Allen's algebra and the RCC8 to represent time and space. The resulting model allows us to know the norms applicable to an agent located socially, spatially and temporally.

International audience; The Burton, Cabrera and Frank (BCF) theory plays a key conceptual role in understanding and modeling the crystal growth of vicinal surfaces. In BCF theory the adatom concentration on a vicinal surface obeys to a diffusion equation, generally solved within quasi-static approximation where the adatom concentration at a given distance x from a step has a steady state value) (x n. Recently, we show that going beyond this approximation [B. Ranguelov and S. Stoyanov, Phys. Rev.B, 76, 035443 (2007)], for fast surface diffusion and slow attachment/detachment kinetics of adatoms at the steps, a train of fast-moving steps is unstable against the formation of steps density waves. More precisely, the step density waves are generated if the step velocity exceeds a critical value related to the strength of the step-step repulsion. This theoretical treatment corresponds to the case when the time to reach a steady state concentration of adatoms on a given terrace is 2 comparable to the time for a non-negligible change of the step configuration leading to a terrace adatom concentration) , (t x n that depends not only on the terrace width, but also on its " past width ". This formation of step density waves originates from the high velocity of step motion and has nothing to do with usual kinetic instabilities of step bunching induced by Ehrlich-Schwoebel effect, surface electromigration and/or the impact of impurities on the step rate. The so-predicted formation of step density waves is illustrated by numerical integration of the equations for step motion. In order to complete our previous theoretical treatment of the non-stationary BCF problem, we perform an in-situ reflection electron microscopy experiment at specific temperature interval and direction of the heating current, in which, for the first time, the step density waves instability is evidenced on Si(111) surface during high Si adatoms deposition rates.

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; The Fully-Depleted Silicon-on-Insulator (FD-SOI) technology for advanced CMOS devices is based on SOI substrates formed by an ultra-thin Si or SiGe film on a thick insulator. A reduction of parasitic resistances of such CMOS components is obtained with the Raised Source and Drain (RSD) technology. In this work we show that modifying the Siconi TM plasma-based etching process widely used in microelectronic and/or combining it to wet-etching methods allows to improve the principal steps of fabrication of RSD FD-SOI CMOS devices. More precisely, using sampling areas on 300 mm wafers that simulate the principal stages of FD-SOI building, (i) we show that a modified SiCoNi process may be used to increase the etching selectivity necessary to dissolve the oxide layer while maintaining a low-k spacer of high quality, (ii) we propose a combination of optimized SiCoNi-dry and wet etching that reduces the post-etching roughness and the contamination level of the channel surface before the subsequent epitaxy.

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.

Spontaneous dewetting of solid thin films proceeds by edge retraction of film edges and/or by heterogeneous void growth. Classical 1D and 2D continuous models of the evolution of a dewetting film, based on surface diffusion mechanisms, predict that in the long-time limit dewetting obeys universal scaling laws. In this paper, we review 1D and 2D predictions and recent experimental results. For this purpose, using Si(001)/SiO2 and Ge(001)/SiO2 single-crystalline thin films in different geometries, we have been able to compare theoretical predictions to experimental results obtained by combining in situ LEEM and ex situ AFM measurements. For dewetting from film edges, experimental results partially differ from continuous models predictions. More precisely, because of the crystallographic anisotropy: (i) the facetted edges remain stable during dewetting (they simply recede at constant shape) while poorly or un-facetted edges are unstable (they recede by finger formation); (ii) rim formation, induced by mass-conservation condition, proceeds in a layer-by-layer mode and is limited by 2D nucleation properties on the top of the rim; (iii) the island generation mechanism differs from the mass shedding behaviour predicted by 1D models. For dewetting mechanisms involving void growth, different behaviours are reported and discussed. For thin Si(001)/SiO2 films, the corners of the opening square-shaped voids lead to a local destabilisation of the growing voids. For thin Ge(001)/SiO2 films, the side of the voids invariably turns instable and forms tip dendrites whose branch density depends on the temperature and the initial film thickness. Finally, ultra-thin films, more sensitive to local fluctuations, dewet in a fractal geometry.

In semiconductor industry, the continuous scaling reduction of CMOS components improves devices performances and reduces manufacturing cost. However, the electrostatic control of the channel must be very accurate. To address this requirement, Fully-Depleted Silicon-On-Insulator (FD-SOI) technology, relying on the use of ultra-thin SOI films (less than 10 nm), is a promising option for the technical nodes beyond 14nm. This option requires the realization of Raised Source & Drain (RSD) by epitaxial Chemical-Vapor Deposition (CVD) of silicon alloys [1, 2]. The quality of the RSD epitaxy depends on the cleanliness of the surface before the deposition. For standard SOI technology, the state of the art generally consists in a high temperature treatment of the surface (>1000°C) in presence of hydrogen. However, such a thermal budget cannot be used for ultra-thin SOI films that dewets and agglomerates into 3D islands in this temperature range [3, 4]. Therefore, for ultra-thin SOI films, an efficient low temperature surface preparation process is required to avoid improper growth of Si or SiGe:B ( resp. SiC:P) layers, used as RSD material for pFET (resp. nFET). This works focus on the surface preparation prior to the low-temperature epitaxy of Si0.7Ge0.3:B layers on full-sheet and patterned wafers. In a first stage different processes of surface preparations are evaluated including standard wet cleans (HF-last, HF-RCA), plasma-based clean (SiCoNiTM setup [5, 6]) and their combination. For SiGe channels, the so-called HFRCA + SiCoNi process without any subsequent baking is recommended to reach clean surfaces [7]. In a second stage, we show that the Si1-xGex growth rate increases linearly when increasing the B2H6 boron-precursor gas flow. However the quality of the SiGe:B epitaxial films is degraded for high boron doping (≈1021at.cm-3) with B accumulation at the interface (Fig. 1). We report on the conditions necessary to reach high boron concentrations while maintaining a uniform boron concentration by incorporating carbon (≈1%) in the RSD deposition step. A wide set of characterization tools are used to assess the sample quality in terms of defect density, chemical analysis, roughness and surface morphology: AFM, SEM, TEM, Spectrometric Ellipsometry (SE), EDX, XPS, Secondary Ion Mass Spectroscopy (SIMS), Model Based Infrared Reflectometry (MBIR), Atom Probe Tomography (APT), Spectroscopy Infrared Reflectometry (SIR) and Low-Energy Electron Microscopy (LEEM). Keywords: Si, SiGe, SiCoNiTM Preclean, FD-SOI, SiGe:B, WET clean, RSD References: [1] N. Loubet et al. Ultra-Low resisitivity in-situ phosphorus doped Si and SiC epitaxy for source/drain formation in advanced 20 nm n-type field effect transistor devices, Thin Solid Films 520 (2012) 3149-3159. [2] J.M et al. Very Low Temperature (Cyclic) Deposition / Etch of In Situ Boron-doped SiGe Raised Sources and Drains. ECS Journal of Solid State Science and Technology, 3 (11) P382-P390 (2014). [3] F.Cheynis et al. Dynamics and instability of solid-state dewetting. Comptes Rendus Physique 14 578-589 (2013). [4] D.Dutartre et al. Defect free Stranski Krastanov growth of strained Si1-xGex layers on Si, Journal of Crystal Growth 142, p. 78-86 (1994). [5] H Yang, X Lu, CT Kao, M Chang - US Patent 7,780,793, (2010). [6] R Arghavani, CT Kao, X Lu - US Patent 7,955,510, (2011). [7] M.Labrot et al. Low thermal budget for Si and SiGe surface preparation for FD-SOI technology. Applied Surface Science 371, p. 436–446 (2016). Figure 1

International audience; Carbon is an important determinant of the sustainability of West African farming systems and of the atmospheric greenhouse effect. Given the complexity of C dynamics, various simulation models have been developed. Few include socioeconomic factors or handle system heterogeneity. This study pro- poses a generic, multi-agent model for the analysis of C dynamics at village level. It assumes that a better analysis of carbon dynamics at village level requires account to be taken of social, economic, physical and biological factors as well as of the actions of individuals and their interdependence. The Carbon of Territory Multi-Agent Simulator (CaTMAS) model is based on the Organization-Role-Entity-Aspect (OREA) meta-model and the Multi-Agent Systems (MAS) approach. OREA enables C dynamics to be studied from various points of view through the roles played by entities within organizations and also allows various entities to play the same role in various ways through the notion of aspects. The model was coupled with the Century model and a geographical information system to provide a realistic representation of C dynamics. CaTMAS provides not only a framework for the explicit description of the carbon dynamics of farming systems but can also be used to assess the viability of farming systems using various socioeconomic and biophysical scenarios. The model includes interactions between human activities and the environment. Simple simulations involving two cropping systems and focusing on the impact of population growth and different climate regimes on the C dynamics indicate that CaTMAS accounts realistically for the relationships between population, agriculture, climate and SOC dynamics. In simulation, population growth, which drives food demand, leads to agricultural expansion, land scarcity and decrease in fallow duration. These effects are accentuated by increasing temperature and decreasing rainfall which affect the SOC dynamics controlling soil fertility and thus crop production. Improvements to the model should make it possible to extend the scale of the simulation of C dynamics and include refinements such as the inclusion of the trading of carbon credits.

La determination des regles de transition moyennes, vers lesquelles tendent les pratiques de successions culturales des agriculteurs apres le defrichement de la foret, est essentielle pour decider d’une strategie de conservation. La lisiere du couloir forestier est malgache se caracterise par une mosaique paysagere heterogene. Parmi les six etats d’occupation du sol que peut prendre une parcelle – foret, culture, jachere, herbe, plantation et riziere – nous justifions le choix des quatre premiers pour modeliser les dynamiques ecologiques et les successions culturales. Les transitions entre ces etats, gouvernees par des regles recueillies aupres des agriculteurs riverains de la foret, sont representees par un modele d’automate temporise parametre par les durees de sejour en culture, jachere, herbe et par le nombre de cycles culturaux depuis le premier defrichement de la foret. L’objectif est de calibrer et valider l’automate temporise a l’aide d’un modele markovien selon la metrique de χ 2, a partir de deux jeux d’historiques d’occupation du sol de parcelles en lisiere, initialement en foret, independantes et non spatialisees. L’automate temporise est calibre par simulation, sur le premier jeu de donnees de 34 ans, puis valide sur le second jeu de donnees de 22 ans depuis le premier defrichement, de maniere a minimiser la distance entre deux matrices markoviennes – celle qui resume la dynamique simulee et celle qui agrege la dynamique observee. Selon les tests de χ 2, les parametres ajustes du modele sont acceptables et conformes en moyenne aux pratiques des agriculteurs. Des scenarios de disparition de la foret sont construits avec le modele valide.

Plague remains endemic in many countries in the world and Madagascar is currently the country where the highest number of human plague cases is reported every year. The investigation of causal factors, which command the disease dynamics in rodent populations, is a crucial step to forecast, control and anticipate the infection extension to humans. This paper presents simulation results obtained from an epidemic model, SIMPEST, designed to simulate bubonic plague in a rodent population at a high level of spatial and temporal resolution. We developed a structurally realistic individual-based model, mobilizing knowledge about fleas and rats behaviour, inter-individual plague transmission, and disease evolution in individual organisms, so that the model reflects the way the real system operates and to generate spatial and temporal patterns of disease spread. To assess the structural validity of our simulations, we perform sensitivity analyses on the initial population size and spatial distribution, and compare our results with theoretical statements, garnered from both previous modelling experiences and repeated field observations. We show our results are consistent with referents about population size conditions for a disease to invade and persist and the effect of the contact network on disease dynamics.

The purpose of this paper is to review some elasticity effects in epitaxial growth. We start by a description of the main ingredients needed to describe elasticity effects (elastic interactions, surface stress, bulk and surface elasticity, thermodynamics of stressed solids). Then we describe how bulk and surface elasticity affect growth mode and surface morphology by means of stress-driven instability. At last stress-strain evolution during crystal growth is reported., 12 pages

Elastically mediated interactions between surface domains are classically described in terms of point forces. Such point forces lead to local strain divergences that are usually avoided by introducing a poorly defined cut-off length. In this work, we develop a selfconsistent approach in which the strain field induced by the surface domains is expressed as the solution of an integral equation that contains surface elastic constants, Sij. For surfaces with positive Sij the new approach avoids the introduction of a cut-off length. The classical and the new approaches are compared in case of 1-D periodic ribbons. Fil: Fuhr, Javier Daniel. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Müller, Pierre. Aix Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia

International audience; We identify three different visions of complexity with the aim to clarify the research field on complex systems. We use Laplace’s demon as a reference for formulating these visions. Vision 1 breaks Laplace’s dream by exhibiting fundamental difficulties in mathematics, physics and computer sciences hampering to derive systemic properties from the knowledge of components characteristics and their interactions rules. Vision 2 reactivates Laplace’s dream, with new demons based on increased computation power and big data availability, yet subject to the limitation identified by vision 1. Finally, vision 3 challenges Laplace’s demon to simulate subjectivity, counterfactuals, empathy and their cascading collective effects.; Nous distinguons trois visions de la complexité afin de clarifier les contours de la recherche dans ce domaine. Nous utilisons le démon de Laplace comme référence pour présenter ces visions. La vision 1 brise le rêve du démon de Laplace en identifiant des systèmes particuliers qui lui résistent en mathématiques, physique et informatique. La vision 2 propose une nouvelle version du rêve de Laplace fondée sur la disponibilité récente de grandes quantités de données et de nouvelles technologies de programmation, de stockage et de calcul. La vision 3 met le démon face au défi de simuler la subjectivité et ses effets collectifs.

Experimental determination of absolute surface energies remains a challenge. We propose a simple method based on two independent measurements on 3D and 2D equilibrium shapes completed by the analysis of the thermal fluctuation of an isolated step. Using then basic equations (Wulff' theorem, Gibbs-Thomson equation, thermodynamics fluctuation of an isolated step) allows us to extract the absolute surface free energy of a singular face. The so-proposed method can be applied when (i) all orientations exists on the equilibrium shape, (ii) the surface stress is isotropic. This procedure is applied to the case of Si(111) where we find a value between 0.59 Jm-2 and 0.83 Jm-2 at 1373 K., 13 pages, 7 figures

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

Some aspects of the thermodynamics and mechanics of solid surfaces, in particular with respect to surface stress and surface energy, are reviewed. The purpose is to enlighten the deep differences between these two physical quantities. We consider successively the case of atomic flat surfaces and the case of vicinal surfaces characterized by surface stress discontinuities. Finally, experimental examples, concerning Si surfaces, are described.

We report on the observation of the random walk of solid-state silicon islands on SiO2 substrates during annealing at high temperatures. The mean square displacement (MSD) of the islands exhibits three regimes. At short times, the islands undergo equilibrium diffusion and begin to etch the surface thereby creating ringlike trenches. Then, an unusual size independent diffusionlike behavior is observed with a linear increase of the MSD. This behavior is attributed to a pinning instability of the triple line. Finally, as etching proceeds pits are formed in the substrate, and the MSD saturates as the islands are self-trapped in their own pits. Kinetic Monte Carlo simulations reproduce the main features of the three regimes, and provide a consistent picture of the microscopic reaction mechanisms at play in the experiments.

International audience; Companion Modelling (ComMod) is an iterative approach of modelling in interaction with local stakeholders. KatAWARE is a multi-agent model constructed through a ComMod process with the Water User Association of the Kat River Valley, Eastern Cape, South Africa. By describing the construction of the KatAWARE model, the aim of this paper is to propose a detailed methodology to formalize and to systematize the modelling phases of Companion Modelling. The Kat River catchment will serve as case study for the application of the proposed methodology. This methodology is composed of four steps: (1) the specification of the structure of the system, its dynamics and the indicators one wants to monitor, (2) the description of the initial state of the simulation, (3) the implementation of the model which can take the form of a computer program or of a role-playing game, (4) the reflection step to criticize the model and to propose further improvements. For the first two steps, we propose to use a representation based on the Unified Modelling Language.

International audience; Using low-energy electron microscopy (LEEM), we investigate the ultrahigh vacuum annealing of silicon-on-insulator (SOI) samples capped by a chemically-prepared oxide layer. Consistent with previous reports: (1) for T > 750 • C, the capping-oxide decomposes by void nucleation and growth, then (2) for T > 850 • C, the Si thin-film dewets from the SiO2 substrate. Here, we show that the morphological evolution of the surface during the dewetting process is dependent on the preparation of the SOI surface. Two dewetting pathways are evident in recent literature, we find that one evolution is characteristic of clean Si(100)-2 × 1 surfaces, while the other is correlated with surface contamination. Silicon thin-films, capped by ultra-thin oxide layers, are the basic building blocks of microelectronics. Microelectronic device fabrication requires thermal annealing steps, which may induce drastic morphological changes in these building blocks. Here, we explore the annealing behavior of oxide-capped silicon-on-insulator (SOI) films. During annealing at T > 750 • C, the oxide capping layer decomposes (Fig. 1(a)) by void nucleation and growth. Then at T > 850 • C, the Si thin film spontaneously dewets (Fig. 1(b)), forming an assembly of three dimensional Si nanocrystals. Previous works [1, 2, 3, 4, 5] have explored the thermal decomposition of ultrathin Si-oxide, and the subsequent dewetting of the Si (SOI) layer [6, 7]. Here, we report two results which, to our knowledge, have not been reported previously. During thermal decomposition of the capping oxide layer, the radii of the initial isolated voids obeys a r ∝ t 1/3 law. This exponent suggests that void growth is governed by diffusion of the decomposition product (SiO molecules) on the oxide outside the voids. The decomposition of the oxide exposes a 2 × 1 reconstructed surface, characteristic of clean Si(100), ideal for studying the mechanisms of the SOI dewetting process. The dewetting proceeds by the opening of square, crystallographically oriented holes, followed by a finger instability that leads to the formation of self-organized

Six former students with close remaining ties to UZH have provided short profiles of their experience at UZH and in their later careers. Since their time at UZH, they have become professors, founders of companies, heads of industrial research in leading chemical companies, patent attorneys, among other careers. They clearly illustrate how personally beneficial a UZH training can be.

By introducing finite size surface and interfacial excess quantities, interactions between interfaces are shown to modify the usual surface premelting phenomenon. It is the case of surface melting of a thin solid film s deposited on a planar solid substrate S. More precisely to the usual wetting condition of the solid s by its own melt l, necessary for premelting (wetting factor F0 this interface attraction boosts the premelting so that a two stage boosted surface premelting is foreseen: a continuous premelting, up to roughly half the deposited film, is followed by an abrupt first order premelting. When G, 65 pages, 16 figures

Using recently proposed improvements of Reflection Electron Microsopy (REM) we study in perfectly controlled thermodynamics conditions spiral shapes and spirals on Si(111) surface. It is shown that the new method named low distortion reflection electron microscopy (LODREM) is a powerful instrument, resolving in much more details (compared with REM) growth or evaporation spirals at the crystal surface. More precisely, we examine the distance between two successive steps of a spiral at growth (or evaporation) with respect to the supersaturation (or undersaturation). It is found that this distance scales with an exponent close to -1/2. This result, which deviates from the BCF theory originates from a non local behavior with a slow kinetic of attachment of the adatoms at the steps., 21 pages, 8 figures

Modeling is the shared activity for both modeling and simulation, and knowledge representation. At the same time, the objectives of these two domains are not the same and both seem necessary when dealing with modeling highly structured and complex systems. To face the complexity of the systems we are trying to model and to simulate nowadays, the challenge addressed in this paper is to mix both approaches in a common framework. We first describe separately the recent advances made in the modeling and simulation community as well as in the knowledge representation community. We show that, despite the same goal to describe a reality, or at least a part of it, it results in very different, although related concepts. This difference is due to the focus taken by these communities. The first community is centered on dynamics, and the second one on static descriptions. From the analysis of the differences and similarities, we propose an architecture which is being tested in a modeling and simulation platform: Mimosa. The outcome is a formal way to pave the path from conceptual to running models which is sketched in this paper. The achievements and the perspectives are discussed in the conclusion.

A generalised Wulf-Kaishew theorem is given describing the equilibrium shape (ES) of an isolated 3D crystal A deposited coherently onto a lattice mismatched planar substrate. For this purpose a free polyhedral crystal is formed then homogeneously strained to be accommodated onto the lattice mismatched substrate. During its elastic inhomogeneous relaxation the epitaxial contact remains coherent so that the 3D crystal drags the atoms of the contact area and produces a strain field in the substrate. The ES of the deposit is obtained by minimising at constant volume the total energy (bulk and surface energies) taking into account the bulk elastic relaxation. Our main results are: (1) Epitaxial strain acts against wetting (adhesion) so that globally it leads to a thickening of the ES. (2) Owing to strain the ES changes with size. More precisely the various facets extension changes, some facets decreasing, some others increasing. (3) Each dislocation entrance, necessary for relaxing plastically too large crystals abruptly modifies the ES and thus the different facets extension in a jerky way. (4) In all cases the usual self-similarity with size is lost when misfit is considered. We illustrate these points in case of box shaped and truncated pyramidal crystals. Some experimental evidences are discussed., Comment: 57 pages, 9 figures

L'essor de l'informatique reactive les debats sur la nature des activites de modelisation et de simulation. Ce forum reunit des mathematiciens et des informaticiens a propos de la place respective des mathematiques et de l'informatique dans les modeles. La premiere partie propose deux exemples d'implication des mathematiques dans les sciences de la vie, et traite ensuite de la distinction entre deux formes de modelisation d'une meme realite, par une mise en equation ou une mise en programme, en soulignant la necessite de theoriser les modeles informatiques. La seconde partie presente les apports complementaires, a trois niveaux, des mathematiques et de l'informatique dans le cas des modeles a base d'agents. Le debat a plusieurs voix revient ensuite sur le choix du type de modelisation face au probleme pose, les differences entre equations et programmes, les verites issues des theoremes ou des simulations, le role de l'experimentation.

This paper investigates faceting mechanisms induced by electromigration in the regime where atomic steps are transparent. For this purpose we study several vicinal orientations by means of in-situ (optical diffraction, electronic microscopy) as well as ex-situ (AFM, microprofilometry) visualization techniques. The data show that faceting proceeds in two stages. The first stage is short and leads to the appearance of a step density wave, with a wavelength roughly independent of the surface orientation. The second stage is much slower, and leads to the formation of a hill-and-valley structure, the period of which depends on the initial surface orientation. A simple continuum model enables us to point out why the wavelength of the step density wave does not depend on the microscale details of the surface. The final wavelength is controlled by the competition between elastic step-step interaction and facet edge energy cost. Finally, the surface stress angular dependence is shown to emerge as a coarsed-grained picture from the step model., Comment: 26 pages, 9 figures

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.

While measurements of the polar dependence of the surface free energy are easily available, measurements of the whole polar dependence of the surface stress of a crystal do not exist. In this paper is presented a new procedure that allows, for the first time, the experimental determination of the surface stress polar dependence of a crystal. For this purpose (1) electromigration is used to control the kinetic faceting of surface orientations that belong to the equilibrium shape of the crystal and (2) for each destabilised surface, the period of faceting as well as the crystallographic angles of the appearing facets are measured by AFM. The so-obtained data lead to a set of equations whose mathematical solution, compatible with physical constraints, gives access to the surface stress polar dependence of the whole crystal and thus to a better understanding of surface stress properties., Comment: 8 pages, 6 Figures

From a macroscopic point of view phase transitions as surface melting or two dimensional (2D) towards three dimensional (3D) growth mode (Stranski-Krastanov transition) can be described in terms of Gibbs excess quantity duly amended by size effects (since usual Gibbs excess quantities are only well defined for semi-infinite systems). The aim of this study is to consider such amended quantities to describe surface melting and Stranski-Krastanov transition of epitaxial layers. the so-introduced size effects allows us to predict the equilibrium thickness of the wetting layer of the Stranski-Krastanov growth mode and to describe and classify two different melting cases: the incomplete melting relayed by a first order transition and the continuous premelting relayed by continuous overheating, Comment: 20 pages 6 figures

International audience; energy (surface tension, interface tension, angle of contact, etc.) PACS.68.10.Gw-Interface activity, spreading PACS.68.55.-a-Thin film structure and morphology Abstract. 2014 When wetting is complete, coherent epitaxies on a thick planar substrate B build up z continuous pseudomorphous layers A which are fully strained according to their natural misfit m. The so-accumulated strain energy density is responsible for some remarkable facts: 1) Each layer is formed at precise undersaturation. At saturation there is a specific number of wetting layers z0. 2) Such layers accumulate strain energy and then may relax plastically by interfacial dislocations at a critical thickness zd1. 3) At some other critical thickness zSK, (z0 zSK zd1), the monolayer growth becomes less stable than layer thickening, what leads to three-dimensional (3D) islanding on the zsk wetting layers, called Stranski-Krastanov (SK) growth. Such islands laterally relax and, since coherent with their substrate, drag the substrate which relaxes too. 4) If the equilibrium shape ratio r of non misfitted 3D deposit (m = 0) depends on the wetting, for a misfitted (m ~ 0) and relaxed crystal, the strain opposes to wetting, so that the higher the elastic energy, the greater the shape ratio rm. 5) Since the equilibrium shape of a 3D crystal depends upon strain, at each dislocation entrance the shape ratio of the crystal varies in a sudden way.

Using low-energy electron microscopy movies, we have measured the dewetting dynamics of single-crystal Si(001) thin films on SiO2 substrates. During annealing (T > 700 degrees C), voids open in the Si, exposing the oxide. The voids grow, evolving Si fingers that subsequently break apart into self-organized three-dimensional (3D) Si nanocrystals. A kinetic Monte Carlo model incorporating surface and interfacial free energies reproduces all the salient features of the morphological evolution. The dewetting dynamics is described using an analytic surface-diffusion-based model. We demonstrate quantitatively that Si dewetting from SiO2 is mediated by surface-diffusion driven by surface free-energy minimization.

Thermostimulated luminescence (TSL) of vitreous silica (tetrasil SE) irradiated with alpha particles has revealed a correlation between the effects of alpha irradiation and a change in thermally stimulated luminescence. The defect centers producing some components in the TSL and ESR spectra are E′ centers. After the sample was annealed at 623 K a new signal was detected in the ESR spectra. It was detected in the oxygen-deficient regions of the sample. The radiation damage in the samples was determined by measuring the changes in the TSL produced by alpha irradiation (2.4 × 105 Gy). The creation of new defects was correlated with the formation of oxygen vacancies. These defects created by alpha particles were partially reversible by thermal treatments.

We would like to note that most of the results published in Li et al 2008 New J. Phys. 10 043007 agree with the results of Muller and Kern 1996 Appl. Surf. Sci. 102 6 that do not appear to be widely known.

Investigations of free-standing liquid films enjoy an increasing popularity due to their relevance for many fundamental and applied scientific problems. They constitute soap bubbles and foams, serve as membranes for gas transport or as model membranes in biophysics. More generally, they provide a convenient tool for the investigation of numerous fundamental questions related to interface-and confinement-driven effects in soft matter science. Several approaches and devices have been developed in the past to characterise reliably the thinning and stability of such films, which were commonly created from low-viscosity, aqueous solutions/dispersions. With an increasing interest in the investigation of films made from strongly viscoelastic and complex fluids that may also solidify, the development of a new generation of devices is required to manage reliably the constraints imposed by these formulations. We therefore propose here a microfluidic chip design which allows for the reliable creation, control and characterisation of free-standing films of complex fluids. We provide all technical details and we demonstrate the device functioning for a larger range of systems via a selection of illustrative examples, including films of polymer melts and gelling hydrogels., Lab on a Chip, Royal Society of Chemistry, In press

International audience; Study of thermo-stimulated luminescence of an a irradiated natural glass has revealed the formation of a structural defect that cannot be annealed thermally and is therefore cumulative. This phenomenon was again encountered and analysed in synthetic borosilicate glass to be used as radionuclear waste glass. To detect this structural modification, the thermoluminescence signal of an a irradiated sample is traced under certain conditions, Two peak characteristics of a previous a irradiation appear at 230 °C and 320 °C. Their intensity increases at each new experiment, although the a irradiation dose administered remains constant. In other words, despite the successive thermal emptyings, the glass keeps the trace of previous irradiations and consequently gives an increasing signal for constant doses. This study deals with a description of a physical phenomenon concerning the formation of defects within a irradiated glass matrices. This phenomenon was detected after a thermoluminescence (TL) analysis induced by a particles in natural glass (1,2) and it was systematically detected in synthetic horosili-care glass to be used as radionuclear waste glass. It should be remembered that during the fission reaction of uranium 235 in the centre of a nuclear plant, new nuclei and transuranic elements (neptu-nium, plutonium, americium) are generated. The former constitute the major part of nuclear waste, while the latter are long-life a emitters. After waste recycling to extract the uranium and plutonium (which is fissile and can be reused, mainly in fast-breeder reactors), a nitric solution remains containing 99.9% of fission products, 0.5% of generated plutonium and most of the neptunium and americium. Being con

The Malagasy local communities managing forest resources have difficulties in assessing the impacts of the management plans they decide upon. To help them, we have designed an integrated model with the ecological processes, the various regulations (zoning, quota, etc..) and the resulting inhabitants behavior in order to explore the impacts of scenarios. The model MIRANA has been designed using the MIMOSA framework in which one must design a conceptual model using ontologies, annotate the conceptual model with the necessary processes, and design a concrete model from which to generate the simulation model. In MIRANA, the conceptual model is made of the set of ontologies describing the actors of the system (households, communities, etc.), the objects they are acting on (lands, animal and vegetal species, etc.), the actions carried out by the actors on the objects (hunting, cultivation, etc.) and the regulations on the actions. The actors are provided with needs (food, money, etc.) or objectives (conservation, production, etc.) and planning mechanisms. The objects are provided with spontaneous processes (fertility dynamics, growth of biomass, etc.). This paper is focused on the representation and use of a multiplicity of normative structures for the regulation of the interactions with the environment.