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International audience; Face-centered cubic/body centered cubic (FCC/BCC) nanolaminates prepared by Accumulative Roll Bonding (ARB) have been extensively studied because of their unique mechanical properties. Recently, micro-beam bending experiments, performed on Cu/Nb ARB samples, have shown an anisotropic interface sliding behavior linked to the strong in-plane texture. To test interface sliding on a macroscale we have developed a shear test based upon a specific sample geometry and on in situ tensile loading on an X-ray synchrotron beamline. As received nanolaminate samples exhibit a very anisotropic crystallographic texture as expected from the fabrication process. In situ X-ray diffraction in the sheared zone during mechanical loading yields strains in Cu and Nb. Early brittle failure prevents investigating further the sliding at interfaces. This is probably caused by crack initiation from the inner surfaces of the notches used to induce shear.

International audience; A system composed of two cubic nonlinear oscillators with close natural frequencies, and thus displaying a 1:1 internal resonance, is studied both theoretically and experimentally, with a special emphasis on the free oscillations and the backbone curves. The instability regions of uncoupled solutions are derived and the bifurcation scenario as a function of the parameters of the problem is established, showing in an exhaustive manner all possible solutions. The backbone curves are then experimentally measured on a circular plate, where the asymmetric modes are known to display companion configurations with close eigenfrequencies. A control system based on a Phase-Locked Loop (PLL) is used to measure the backbone curves and also the frequency response function in the forced and damped case, including unstable branches. The model is used for a complete identification of the unknown parameters and an excellent comparison is drawn out between theoretical prediction and measurements.

An experimental proof of concept of a new semi-passive nonlinear piezoelectric shunt absorber, introduced theoretically in a companion article, is presented in this work. This absorber is obtained by connecting, through a piezoelectric transducer, an elastic structure to a resonant circuit that includes a quadratic nonlinearity. This nonlinearity is obtained by including in the circuit a voltage source proportional to the square of the voltage across the piezoelectric transducer, thanks to an analog multiplier circuit. Then, by tuning the electric resonance of the circuit to half the value of one of the resonances of the elastic structure, a two-to-one internal resonance is at hand. As a result, a strong energy transfer occurs from the mechanical mode to be attenuated to the electrical mode of the shunt, leading to two essential features: a nonlinear antiresonance in place of the mechanical resonance and an amplitude saturation. Namely, the amplitude of the elastic structure oscillations at the antiresonance becomes, above a given threshold, independent of the forcing level, contrary to a classical linear resonant shunt. This paper presents the experimental setup, the designed nonlinear shunt circuit and the main experimental results.

Centrifugal pendulum vibration absorbers (CPVA) are used in the automobile industry to reduce the vibrations of the transmission system. These passive devices are made of several masses oscillating along a given trajectory relative to the rotor. In this paper, the dynamic stability of a new class of CPVA is investigated. The particularity of this new class is that masses now admit a significant rotation motion relative to the rotor, in addition to the traditional translation motion. The efficiency of such devices is optimal for a perfect synchronous motion of the oscillating masses. However, masses unison can be broken for the benefit of energy localisation on a given absorber, leading to a loss of mitigation performances. To assess the stability of such devices, a dynamical model based on an analytic perturbation method is established. The aim of this model is to predict analytically localisation and jumps of the response. The validity of the model is confirmed through a comparison with both a numerical resolution of the system’s dynamics and an experimental study.

International audience; This article proposes a novel mean for tuning the natural frequency of an electromagnetic resonant shunt, using a pulse-width modulation (PWM) circuit. It is used to modulate the value of the capacitance of the shunt, and the electrical frequency is shown to be proportional to the command parameter of the PWM, the duty cycle. An easy and efficient strategy to tune the resonant shunt in real time is then proposed, thus obtaining a low powered and always stable vibration control device. The article proposes the theory of PWM, giving a robust method to predict the dynamics of the system. Then, an accurate multi-mode theoretical model of the tunable resonant shunt coupled to an elastic structure is proposed and experimentally validated on an elastic multi-mode structure, in the case of two different control strategies. The first one is a standard resonant shunt with both the electrical frequency and damping optimized to reduce a given resonance peak. The second one is based on a resonant shunt with the electrical damping as low as possible, which creates an antiresonance and a “notch” type mechanical response at the driving frequency. Both strategies are experimentally validated with real time variation and adaptation of the electrical frequency, obtaining an efficient vibration control device, able to reduce by a factor 40 the vibration level.

International audience; Hybrid bonding is a very promising 3D packaging technology which allows extremely high interconnect density between electronic chips. In its most advanced interconnect pitch, Cu pads as small as 300 nm may be used. Successful bonding relies directly on the thermomechanical displacement of Cu above the oxide matrix. Hence, the control of this technology relies on a profound understanding of the thermomechanical behavior of 300 nm Cu pads. To achieve this goal, X-ray synchrotron Laue micro-diffraction is used to monitor the strain state and orientation of individual Cu pads in situ during heat treatment. The experimental findings are completed with Finite Element Modeling simulations including elastic anisotropy and plastic behavior. The 300 nm Cu pads are found monocrystalline with random lattice orientations. The thermomechanical behavior of each pad is found highly driven by its crystal orientation in accordance with the elastic and plastic anisotropy of copper. Very good agreement is found with simulations offering profound understanding of the single nanocrystalline Cu grains properties and providing solid conclusions for a successful hybrid bonding at sub-micrometric pitch level.

To passivate Si-SiO2 dangling bonds, metal–oxide–semiconductor field-effect transistor devices are usually treated with hydrogen. Herein, the effects of such a treatment on the crystallization behavior on N-doped, Ge-rich Ge2Sb2Te5 phase-change materials for memory applications are investigated using synchrotron X-ray diffraction (XRD) in situ during heat treatment. Uniform thin films, and laterally confined, metallized ones (simulating devices of different complexity) of initially amorphous N-doped GGST are investigated. The specimens are heated up to 450–500 °C at a rate of 2 °C/min. Some of the specimens are treated with H/D; the equivalent untreated specimen is investigated for each of them. Crystallization onsets are estimated by quantification of the crystallized quantity during material transformation from the XRD patterns. In thin films, the hydrogen treatment results in lowered crystallization temperatures of the emerging cubic, metastable Ge2Sb2Te5 phase. Its trigonal, thermodynamically stable polymorph always forms, but its crystallization temperature is unchanged. Patterned and metallized samples show less differences, are strongly textured, and no trigonal phase is observed. It is shown that certain questions might only be answered at large-scale facilities where high energy photons are available at high flux, allowing data acquisition during the annealing process with a temperature resolution sufficient for a fine description of the sample transformation.

International audience; This paper addresses the design of the elastic structure of artificial wings to optimize their dynamical behaviour to reproduce insect wings kinematics. Our bioinspired kinematics is based on the original concept of using the resonant properties of the wing structure in order to combine the motion of two vibration modes, a flapping and a twisting mode, in a quadrature phase shift. Oneway of achieving this particular combination is to optimize the geometry and elastic characteristics of the flexible structure such that the two modes are successive in the eigenspectrum and close in frequency. This paper first proposes a semi-analytical model, based on assembled Euler-Bernoulli beams, to understand, compute and optimize the artificial wing dynamic vibrations. Then, using this model, it is shown that it is possible to obtain several artificial wing structures with a flapping and a twisting mode close in frequency. Finally, experimental validations are performed on micromachined insect-sized prototypes to validatethe model and the concept.

International audience; In this work we study the nonlinear coupling between the transverse modes of nanoresonators such as nanotubes or nanowires in a singly clamped configuration. We previously showed that at high driving, this coupling could result in a transition from independent planar modes to a locked elliptical motion, with important modifications of the resonance curves. Here we clarify the physical origins, associated to a 1:1 internal resonance, and study in depth this transition as a function of the relevant parameters. We present simple formulae that permit to predict the appearance of this transition as a function of the frequency difference between the polarizations and the nonlinear coefficients and give the "backbone curves" corresponding to the elliptical regime. We also show that the elliptical regime is associated with the emergence of a new set of solutions of which one branch is stable. Finally we compare single and double clamped configurations and explain why the elliptical transition appears on different polarizations.

International audience; [FeII(Htrz)2(trz)](BF4) spin crossover particles of 85 nm mean size are dispersed in an SU‐8 polymer matrix and spray‐coated onto silicon microcantilevers. The subsequent photothermal treatment of the polymer resist leads to micrometer thick, smooth, and homogeneous coatings, which exhibit well‐reproducible actuation upon the thermally induced spin transition. The actuation amplitude as a function of temperature is accurately determined by combining integrated piezoresistive detection with external optical interferometry, which allows for the assessment of the associated actuation force (9.4 mN), stress (28 MPa), strain (1.0%), and work density (140 mJ cm−3) through a stratified beam model. The dynamical mechanical characterization of the films evidences an increase of the resonance frequency and a concomitant decrease of the damping in the high‐temperature phase, which arises due to a combined effect of the thickness and mechanical property changes. The spray‐coating approach is also successfully extended to scale up the actuators for the centimeter range on a polymer substrate providing perspectives for biomimetic soft actuators.

ZnO thin films are interesting for applications in several technological fields, including optoelectronics and renewable energies. Nanodevice applications require controlled synthesis of ZnO structures at nanometer scale, which can be achieved via atomic layer deposition (ALD). However, the mechanisms governing the initial stages of ALD had not been addressed until very recently. Investigations into the initial nucleation and growth as well as the atomic structure of the heterointerface are crucial to optimize the ALD process and understand the structure–property relationships for ZnO. We have used a complementary suite of in situ synchrotron x-ray techniques to investigate both the structural and chemical evolution during ZnO growth by ALD on two different substrates, i.e., SiO2 and Al2O3, which led us to formulate an atomistic model of the incipient growth of ZnO. The model relies on the formation of nanoscale islands of different size and aspect ratio and consequent disorder induced in the Zn neighbors’ distribution. However, endorsement of our model requires testing and discussion of possible alternative models which could account for the experimental results. In this work, we review, test, and rule out several alternative models; the results confirm our view of the atomistic mechanisms at play, which influence the overall microstructure and resulting properties of the final thin film.

International audience; The monochromatic and geometrically anisotropic acoustic field generated by 400 nm and 120 nm diameter copper nanowires simply dropped on a 10 µm silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both side of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite Difference Time Domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced.

International audience; The growth of zinc oxide thin films by atomic layer deposition is believed to proceed through an embryonic step in which three-dimensional nanoislands form and then coalesce to trigger a layer-by-layer growth mode. This transient initial state is characterized by a poorly ordered atomic structure, which may be inaccessible by X-ray diffraction techniques. In this work, we apply X-ray absorption spectroscopy in situ to address the local structure of Zn after each atomic layer deposition cycle, using a custom-built reactor mounted at a synchrotron beamline, and we shed light on the atomistic mechanisms taking place during the first stages of the growth. We find that such mechanisms are surprisingly different for zinc oxide growth on amorphous (silica) and crystalline (sapphire) substrate. Ab initio simulations and quantitative data analysis allow the formulation of a comprehensive growth model, based on the different effects of surface atoms and grain boundaries in the nanoscale islands, and the consequent induced local disorder. From a comparison of these specttoscopy results with those from X-ray diffraction reported recently, we observe that the final structure of the zinc oxide nanolayers depends strongly on the mechanisms taking place during the initial stages of growth. The approach followed here for the case of zinc oxide will be of general interest for characterizing and optimizing the growth and properties of more complex nanostructures.

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International audience; This paper deals with vibration control by means of piezoelectric patches shunted with electrical impedances made up by a resistance and a negative capacitance. The paper analyses most of the possible layouts by which a negative capacitance can be built and shows that a common mathematical description is possible. This allows closed formulations to be found in order to optimise the electrical network for mono- and multi-mode control. General analytical formulations are obtained to estimate the performance of the shunt in terms of vibration reduction. In particular, it is highlighted that the main effect of a negative capacitance is to artificially enhance the electromechanical coupling factor, which is the basis of performance estimation. Stability issues relating to the use of negative capacitances are especially addressed using refined models for the piezoelectric patch capacitance. Furthermore, a new circuit based on a couple of negative capacitances is proposed and tested, showing better performances than those provided by the usual layouts with a single negative capacitance. Finally, guidelines and analytical formulations to deal with the practical implementation of negative capacitance circuitsare provided.

Passive structural vibration reduction by means of shunted piezoelectric patches is addressed in this paper. We present a strategy to optimize, in terms of damping efficiency, the geometry of piezoelectric patches as well as their placement on the host elastic structure. This procedure is based on the maximization of the modal electro-mechanical coupling factor (MEMCF) of the mechanical vibration mode to which the shunt is tuned. To illustrate the method, a general analytical model of a laminated beam is proposed. Two particular configurations are investigated: (i) a beam with two collocated piezoelectric patches connected in series or in parallel to the shunt and (ii) a cantilever beam with one patch. After a modal expansion, original closed-form solutions of the MEMCF are exhibited, which enables to compute optimal values for the placement, length and thickness of the piezoelectric patches that maximize the MEMCF. A dimensionless model is used so that this study can be used to design any smart beam, whatever be its dimensions. More general results about the coupling mechanisms between the piezoelectric patches and the host structure are also raised. In particular, it is found that the patches thickness is an essential parameter and that several configurations are possible, depending on the considered vibration mode. Experiments are also proposed to validate the model.

International audience; We present a study of nickel-silicides ordered alloys by means of first-principles calculations. Emphasis was put on the phases (low and high temperatures) identified in the binary phase diagram, namely: Ni3Si-β1, -β2, and -β3, Ni31Si12-γ, Ni2Si-δ, -θ, Ni3Si2-ɛ, NiSi-MnP and NiSi2-α. In addition, some common structures are computed for information: L12, D03 and D022. The simulations reproduce with a high accuracy lattice parameters and formation energies of main experimental structures, except for β2 and β3. Our results clarify the crystallographic nature of the γ structure, and the comparison of experimental Raman spectra and vibrational calculations will help experimentalists to identify without ambiguity NiSi3 structures.

The periodic strain induced in mono-crystalline Si lines isolated by the Shallow Trench Isolation process is investigated by High-Resolution X-ray diffraction which is very sensitive to local strain and is non-destructive. The array periodicity gives rise to satellites in the reciprocal space around the Si Bragg peak, their envelope being directly linked to the local strain field. In the particular case of sub-micrometric arrays, the reciprocal space maps present a secondary diffraction peak caused by a homogeneous strain area in the middle of the Si lines. The secondary intensity relative position can be translated in transverse and perpendicular strain values, which allows a quantitative comparison of samples. We first compare two process flows to show the effect of top-layer deposition on Si strain. Then, the influence of geometrical variations is studied for the softer process. When considering a fixed period, the strain is getting higher for a lower Si line/SiO2 trench width ratio. The trenches depths variation shows a few effects on the strain values; the decrease in strain with decrease in depth is only noticeable for the transverse value. Finally, the homogeneous strain values increase with decrease in period from 580 nm down to 200 nm. All these results confirm that most of the stress is applied to the Si-active areas by the trenches filled with SiO2.

International audience; This study is devoted to the derivation of some properties of the von Kármán equations for geometrically nonlinear models of plates, with a boundary of arbitrary shape, for applications to nonlinear vibration and buckling. An intrinsic formulation of the local partial differential equations in terms of the transverse displacement and an Airy stress function as unknowns is provided. Classical homogeneous boundary conditions-with vanishing prescribed forces and displacements-are derived in terms of the Airy stress function in the case of a boundary of arbitrary geometry. A special property of this operator, crucial for some energy-conserving numerical schemes and called "triple self-adjointness", is derived in the case of an edge of arbitrary shape. It is shown that this property takes a simple form for some classical boundary conditions, so that the calculations in some practical cases are also simplified. The applications of this work are either semi-analytical methods of solution, using an expansion of the solution onto an eigenmode basis of the associated linear problem, or special energy-conserving numerical methods.

Nickel based silicide films were prepared by annealing nickel-platinum layers deposited on n-doped Si substrates. We report on the evolution of the crystallography, the phase formation and the redistribution of contaminants on blanket wafers during silicide formation as a function of the silicon surface preparation prior to Ni(Pt) deposition. In situ argon sputtering etch creates a contamination layer which modifies phase texture during the formation of the first Ni silicide phases. Using remote pre-clean results in a predominant Ni"2Si phase with preferential grain orientation after a first anneal. After a second anneal, the monosilicide forms, regardless of what nickel rich silicide phase was initially formed and regardless of the surface preparation prior to metal deposition.

International audience; Interfaces between polarity domains in nitride semiconductors, the so-called Inversion Domain Boundaries (IDB), have been widely described, both theoretically and experimentally, as perfect interfaces (without dislocations and vacancies). Although ideal planar IDBs are well documented, the understanding of their configurations and interactions inside crystals relies on perfect-interface assumptions. Here, we report on the microscopic configuration of IDBs inside n-doped gallium nitride wires revealed by coherent X-ray Bragg imaging. Complex IDB configurations are evidenced with 6 nm resolution and the absolute polarity of each domain is unambiguously identified. Picoscale displacements along and across the wire are directly extracted from several Bragg reflections using phase retrieval algorithms, revealing rigid relative displacements of the domains and the absence of microscopic strain away from the IDBs. More generally, this method offers an accurate inner view of the displacements and strain of interacting defects inside small crystals that may alter optoelectronic properties of semiconductor devices.

Thermo-mechanical stress is a major concern in the frame of 2.5D integration. Passive stress sensors were integrated in a silicon interposer test vehicle to quantify stress at critical locations. The sensors were integrated in a rosette-shape consisting of eight oriented copper serpentines acting like strain gauges. This innovative design allows the calculation of a partial stress tensor, including three planar and one out-of-plane components. Electrical measurements at wafer level, combined with FIB/SEM cross-sections, revealed a strong impact of elaboration processes on the structures electrical characteristics. Numerical simulations using finite element analysis were built to evaluate the sensitivity of copper serpentines to mechanical stress. Finally a dedicated four-point bending tool coupled with a four-terminal resistance measurement setup was fabricated to experimentally extract the values of sensors sensitivity factors. Preliminary results depicted in this paper highlight a sensitivity to stress of distinctly oriented resistors. Several identified sources of data dispersion are inherent to the present measurement configuration. Added-value and limitations of such sensors were underlined, and recommendations regarding the testing strategy were drawn to allow a reliable estimation of the stress fields.

X-ray diffraction was recognized from the early days as highly sensitive to atomic displacements. Indeed structural crystallography has been very successful in locating with great precision the position of atoms within an individual unit cell. In disordered systems, it is the average structure and fluctuations about it that may be determined. In the field of mechanics, diffraction may thus be used to evaluate elastic displacement fields. In this short overview, we give examples from recent work where X-ray diffraction has been used to investigate average strains in lines, films or multilayers. In small objects, the proximity of surfaces or interfaces may create very inhomogeneous displacement fields. X-ray scattering is again one of the best methods to determine such distributions. The need to characterize displacement fields in nano-structures together with the advent of third generation synchrotron radiation sources has generated new and powerful methods (anomalous diffraction, coherent diffraction, micro-diffraction, etc.). We review some of the recent and promising results in the field of strain measurements in small dimensions via X-ray diffraction.

International audience; This paper is devoted to the derivation and the analysis of vibrations of shallow spherical shell subjected to large amplitude transverse displacement. The analog for thin shallow shells of von Kármán's theory for large deflection of plates is used. The validity range of the approximations is assessed by comparing the analytical modal analysis with a numerical solution. The specific case of a free edge is considered. The governing partial differential equations are expanded onto the natural modes of vibration of the shell. The problem is replaced by an infinite set of coupled second-order differential equations with quadratic and cubic non-linear terms. Analytical expressions of the non-linear coefficients are derived and a number of them are found to vanish, as a consequence of the symmetry of revolution of the structure. Then, for all the possible internal resonances, a number of rules are deduced, thus predicting the activation of the energy exchanges between the involved modes. Finally, a specific mode coupling due to a 1:1:2 internal resonance between two companion modes and an axisymmetric mode is studied. © 2004 Elsevier Ltd. All rights reserved.

Thin metal films react with silicon substrates to form various metal silicides. The sequence and kinetics of phase formation are still an area of intense research. Comparatively much less work has been done on the issue of stress development caused by the appearance of these new phases. A detailed review of the subject has been done ten years ago. We present here recent results obtained on Pd-Si, Co-Si, Ni-Si and discuss them in the light of what is known today on the elastic and plastic properties of thin films. A simple model published by S. - L. Zhang and F. M. d’Heurle takes into account the simultaneous stress formation due to the reaction and the relaxation of these stresses. It provides a qualitatively satisfying picture of stress evolution at least for the first phase which forms. The model relies on two basic elements: 1) stress formation due to the formation of a new phase, and 2) the stress relaxation mechanism at work in the growing silicide film. The sign of the stress can be understood from the variation in volume that occurs at the growing interface(s). The stress relaxation mechanisms at work in a growing film are complex. They are highly dependent on the microstructure (as we have shown when comparing Pd/Si(001) and Pd/Si (111)) but should be also highly size dependent (e.g. dislocation glide is more difficult in small scale structures). Inhomogeneous plastic relaxation in polycrystalline silicide films may be an important issue.

We propose a new approach to follow stress development during solid state reaction between a Ni thin film and Si (0 0 1). Substrate curvature measurements were performed simultaneously with X-ray diffraction at LURE synchrotron radiation facility. The measured curvature yields the average force whereas X-ray diffraction yields the different phases that form as well as the strain variation undergone by these phases. During annealing with a constant heating rate of 2 °C/min, Ni grain growth is first observed, followed by the formation of Ni 2 Si, Ni 3 Si 2 and then NiSi. The Ni 2 Si formation is correlated with a rapid increase in compressive force. At the end of Ni consumption, the force evolves in tension until NiSi formation, which is accompanied by an additional increase in compressive force and then a final force relaxation at higher temperature. It is interesting to note that the NiSi phase appears at the expense of Ni 3 Si 2 , and surprisingly, at the benefit of Ni 2 Si until the Ni 3 Si 2 is completely consumed. Strain buildup during Ni 2 Si and Ni 3 Si 2 formation exhibit clear differences. Both Ni 3 Si 2 and Ni 2 Si phases exhibit a bell shape behavior of the strain evolution versus temperature at variance with predictions from the Zhang and d’Heurle model [Thin Solid Films. 213, 1992, 34].

Understanding and quantifying stress buildup during silicide formation from metal-silicon reaction is crucial for a proper modeling of stress fields in active areas. In this work we have performed in situ wafer curvature measurements and ex situ X-ray diffraction during the reaction of a Ni thin film with Si(001). Wafer curvature exhibits marked extrema at temperatures depending on the heating rate. Such behavior is indicative of kinetically limited processes. Isothermal annealings at 230 ^oC show features similar to those found in ramp heating. Ex situ X-ray diffraction on cooled down samples reveal that the changes in F/w are correlated with the phase formation sequence Ni"2Si, Ni"3Si"2 and NiSi. The F/w trends are explained on the basis of the volume expansion undergone by the different phases during reactions.

The structural evolution in fiber-textured Ti/Si thin films was investigated by in-situ X-ray diffraction in the temperature range preceding the formation of silicide compounds. Abnormal thermal behaviour of both 002 and 101 diffraction profiles was observed at 360 and 450 °C, which could be understood in terms of Si diffusion, first in Ti grain boundaries, then into the grains. By combining ex-situ strain studies with analysis of the Si local environment in the whole Ti silicide family from Ti5Si3 to TiSi2, it was possible to determine the stress-free lattice parameters of annealed films. They are significantly higher than the bulk parameters, and indicate that nearly 4.5 at.% Si is present in the Ti grains.

Using X-ray diffraction experiments and curvature measurements, in-situ real-time measurements of stress are performed during solid state reaction of a palladium thin film with Si(001). From X-ray diffraction measurements and using the sin2ψ method, we found out that the stress in the metal and in the silicide is compressive. This stress decreases all along the solid-state reaction for the silicide. We then compared our results with the qualitative model proposed by Zhang and d'Heurle. This model suggests the development of a high compressive stress (-2.4 GPa) in the silicide.

International audience; This article is devoted to an experimental validation of a theoretical model presented in an earlier contribution by the same authors. The non-linear forced vibrations of circular plates, with the excitation frequency close to the natural frequency of an asymmetric mode, are investigated. The experimental set-up, which allows one to perform precise measurements of the vibration amplitudes of the two preferential configurations, is presented. Experimental resonance curves showing the amplitude and the phase of each configuration as functions of the driving frequency are compared to the theoretical ones, leading to a quantitative validation of the predictions given by the model. Finally, all the approximations used are systematically discussed, in order to show the scope and relevance of the approach. © 2003 Elsevier Science Ltd. All rights reserved.

The diffraction of X-rays by a thin layer (of the order of a few nanometres) with a gradient in interplanar spacings is considered. It is shown that optical coherence over the film thickness leads to diffraction peak positions that no longer obey Bragg's law. Although a fitting of the diffracted intensity is indeed still possible, this has direct consequences on the applicability of more straightforward analysis methods, such as the sin2ψ method, which rely on diffraction peak positions. The intensity and peak position calculations are supported by a comparison with experimental data from a (001) Fe/GaAs thin (3 nm) epitaxic film.

Stress development and relaxation are important issues for the reliability of integrated circuits. In this article we report on the stress evolution during solid state reaction, which occurs in Ti/Al bilayers. Whereas the formation of TiAl3 is expected to induce large tensile stress because of a global volume decrease of 6-8%, our in-situ X-ray diffraction measurements during annealing at 465 °C indicate the formation of a compressive compound. Furthermore, an increase in the lattice parameter of Ti is evidenced by X-ray diffraction. A plausible explanation for this expansion is the incorporation of O in solution from a reaction with the underlying SiO2 layer.

In-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible planar Kirchhoff elastic rod under large displacements and rotations. Equilibrium configurations and vibrations around these configurations are computed analytically in the incipient post-buckling regime. Of particular interest is the variation of the first mode frequency as the load is increased through the buckling threshold. The loading type is found to have a crucial importance as the first mode frequency is shown to behave singularly in the zero thickness limit in the case of prescribed axial displacement, whereas a regular behavior is found in the case of prescribed axial load. This publication is based in part upon work supported by Award no. KUK-C1-013-04, made by King Abdullah University of Science and Technology (KAUST) (A.G.). A.G. is a Wolfson/Royal Society Merit Award holder. Support from the Royal Society, through the International Exchanges Scheme (Grant IE120203), is also acknowledged

This study concerns the analysis of elastic strains in Au/Ni multilayers whose periods lie in the range 1–5 nm. Lattice parameter measurements have been performed by x-ray diffraction in various directions. The results are interpreted in terms of elastic strain and interfacial mixing. It is shown that considerable strains (several percent) are encountered within these very thin layers. In the Au sublayers, coherence is never observed with the underlying Ni film and the residual strain relaxes progressively as the Au film thickens. In the Ni sublayers, interfacial mixing controls the lattice parameter and the elastic strain is a function of this mixing. Out of equilibrium mixing of Au into Ni is ascribed to dynamic segregation during the growth of Ni on Au. All these results bring new insights on the still open question of stress relaxation mechanisms in ultrathin films.

International audience; This work presents a Non-Volatile SRAM (NV-SRAM) cell, resilient to information loss. The cell features fast storage (20ns) for the operating voltage of 1.0V. The information is backed-up during POWER-DOWN/ RECOVERY cycle in two bipolar Oxide Resistive RAMs (OxRRAMs). The proposed NV-SRAM is designed with an 8T2R structure using 22nm FDSOI technology and resistive memory devices based on HfO 2. The stability and the reliability of the NV-SRAM cell is investigated by taking into account the variability of the transistors. It is shown that high R OFF /R ON is necessary to ensure reliable RECOVERY operation and high SRAM yield under cell area and power consumption constraints.

The growth of higher manganese silicide (HMS) films on monocrystalline silicon (100) has been investigated. This growth was performed by solid-state reaction. Using electron beam evaporation a single layer of manganese was deposited on a silicon substrate. The samples so prepared were heat treated in a classical furnace under vacuum. A highly textured film was obtained after treatment at 890°C for 18 h. The obtained HMS was identified as Mn15Si26. The texture relationship is (105) [100] Mn15Si26 ∥ (100) [100] Si. Mn15Si26 has a tetragonal cell; hence, the angle between the c-axis and the normal of the sample surface is 60°. Since this value is far from 0° and 90°, a large transverse thermoelectric effect is expected in these samples. As a consequence the HMS films could be used in anisotropic electromotive force-thermogenerators.

We measured the transverse magnetoresistance Δϱ ϱ of good quality TiSi2 single crystals at low temperatures (4.2≤T≤112 K) in magnetic fields up to 7.8 Tesla. Single crystals were produced by a modified Czochralski pulling technique and they have low residual resistivity (typically ϱ(4.2 K ) = 0.15 μΩ· cm ) and high residual resistance ratio (typically RRR > 50). The angular dependence of magnetoresistance shows either minima or maxima when the magnetic field is parallel to the principal crystallographic axes. At high fields (B > 1 T). we found that the magnetoresistance has a magnetic field dependence weaker than the B2 law expected for compensated metals. At 7.8 T, the values of ωcτ obtained are of the order of unity. The Kohler scaling rule is observed within three orders of magnitude of the reduced parameter B ϱ (where ϱ is the zero field resistivity measured between 4.2 and 112 K).

X-ray scattering experiments on coherent CuNi multilayers are performed at various annealing temperatures. First, we show that the classical thermoelasticity theory can be applied in such nanosamples to link composition and strain fields at intermediate temperature. Second, when interdiffusion takes place at higher temperature, the satellite peaks measured at different annealing times indicate the presence of a layer-by-layer interdiffusion mode controlled by the asymmetry of the atomic mobilities in this system.

International audience; This work addresses passive reduction of structural vibration by means of shunted piezoelectric patches. The two classical resistive and resonant shunt solutions are considered. The main goal of this paper is to give closed-form solutions to systematically estimate the damping performances of the shunts, in the two cases of free and forced vibrations, whatever the elastic host structure is. Then it is carefully demonstrated that the performance of the shunt, in terms of vibration reduction, depends on only one free parameter: the so-called modal electromechanical coupling factor (MEMCF) of the mechanical vibration mode to which the shunts are tuned. Experiments are proposed and an excellent agreement with the model is obtained, thus validating it.

The usual Si dopants, B, P, As, and Sb, plus Ge were implanted into thick (400 nm) TiSi 2 layers deposited in an amorphous state by sputtering from a compound target. Samples with the various implants were annealed at temperatures from 300 to 700°C and analyzed both by transmission electron microscopy and secondary ion spectroscopy. The annealed samples display a very large grain size, which complicates the interpretation of the concentration profiles obtained by SIMS. In the case of a high dose of B (1 × 10 16 atoms/cm 2 at least), there is an indication of grain boundary transport occurring mostly in the initial stage of the heat treatments, followed by phenomena dominated by a reduced solubility in the terminal large-grained matrix. With all elements, except Sb, evidence of diffusion is obtained at 400°C. Germanium diffusion is even observed at 300°C.

The disilicides of vanadium, niobium and tantalum are isoelectronic. They crystallize in the same hexagonal structure (type C40 space group P6222) with lattice parameters increasing by about 4% from the vanadium to the tantalum compound. We report specific heat measurements for the three compounds in the temperature range from 100 mK to 7.5 K. We used a transient heat pulse technique and low temperatures were achieved with a dilution refrigerator. From the results we determined the electronic contribution to the specific heat γT as well as the phonon contribution βT3. γ is twice larger for VSi2 than for the other two compounds and the density of states at the Fermi level, D(EF), determined from γ is in rather good agreement with the theoretical calculations of the band structures from the literature. The Debye temperature θD deduced from β varies as M-1/2 where M is the molar mass.

Electrical transport and optical properties of transition-metal silicides are reviewed. They are integrated with thermal properties of single-crystal silicides. Most of these compounds behave as metals while some of them behave as semiconductors. The former show an increasing electrical resistivity ρ with increasing temperature. Several of them show a non-classical deviation of ρ(T) from linearity in the high-temperature limit. This deviation, related to intrinsic properties of the compound, can be affected both in sign and in amount by the presence of foreign atoms (impurities) and structural defects. Moreover, defects dominate the electrical transport at low temperatures both in metallic and semiconducting compounds. Therefore, the interpretation of the electrical properties measured as a function of temperature may give a non-realistic description of silicide intrinsic properties. Since also other physical properties, like thermal and optical ones, can be strongly affected by impurities and defects, results about single-crystal silicides will be first illustrated. Single-crystal preparation and structural characterization are described in detail, with emphasis on crystalline quality in terms of residual resistivity ratio. The electrical quantities, resistivity and magnetoresistance, are measured as a function of temperature and along the main crystallographic directions. The effect of impurities and defects on the transport properties is then evaluated by examining the electrical transport of polycrystalline thin-film silicides. The different contributions to the total resistivity are measured by changing: (i) film stoichiometry, (ii) impurity concentration, (iii) texture growth and (iv) film thickness. Hall-coefficient measurements are briefly discussed with the main purpose to evidence that great caution is necessary when deducing mobility and charge-carrier density values from these data. The theoretical models currently used to interpret the low- and high-temperature resistivity behavior of the metallic silicides are presented and used to fit the experimental resistivity curves. The results of these studies reveal that in several cases there are well-defined temperature ranges in which a specific electron—phonon scattering mechanism dominates. This allows a more detailed study of the microscopic processes. The optical functions from the far-infrared to the vacuum ultraviolet, derived from Kramers—Kronig analysis of reflectance spectra or directly measured by spectroscopic ellipsometry, are presented and discussed for some significant metallic disilicides, both single crystals and polycrystalline films. Different physical phenomena are distinguished in the spectra: intraband transitions at the lowest photon energies, interband transitions at higher energies, and collective oscillations. In particular, the free-carrier response derived from this analysis is compared with the transport results. The interpretation of the experimental spectra is based on the calculated electronic structures or optical functions. Moreover, it is shown how the optical studies contribute to assess definitively the semiconducting character of some disilicides. Specific-heat measurements on single crystals between 0.1 and 8 K are reported. The Debye temperature and the density of electronics states at the Fermi surface are deduced from the lattice and electronic contributions, respectively. Some silicides have been found superconductors with small electron—phonon coupling constants. Emphasis is given to the comparison between the properties deduced from these studies and those obtained from the analysis of electrical transport data. The final part of this review is devoted to the calculation of some microscopic physical quantities, as for example the electron mean free path, the charge-carrier density, the Fermi velocity. The parameters of the best fit to the experimental resistivity curves, the free-carrier parameters obtained from infrared spectra and the density of electronic states at the Fermi surface determined from specific-heat measurements were used in such evaluations.

International audience; Post Si(C)N hillocks are characterized on Cu interconnects networks. Each network is compounded by standard damascene process electroplated Cu lines with given width and local line density. AFM results show that total volume per area of post Si(C)N hillocks both on narrow and large lines increases linearly with local Cu line density. Two trends of hillocks nucleation and growth are highlighted depending on line width. For line widths inferior to 4 pun, hillocks are located at the line edge. As line density increases, the number of hillocks remains constant but their mean volume proportionally increases. For wider lines, hillocks preferentially nucleate at the center of the line. The number of hillocks proportionally increases as line density increases, but hillock mean volume remains constant. Post Si(C)N hillocks density is found to be proportional to post CMP Cu grain surface boundary density before capping. It is proposed that hillocks growth could be controlled by Cu/Ta interface diffusion on narrowest lines and by grain boundary diffusion on wider ones. (C) 2009 Elsevier B.V. All rights reserved.