Ion beam sputtered surface dynamics investigated with two-time correlation functions : a model study

Ion beam sputtering is a widely used technique to obtain patterned surfaces. Despite the large use of this approach on different materials to create surface nanostructures, the theoretical model to explain the time evolution of the erosion process is still debated. We show with the help of simulations, that two-time correlation functions can serve to assess the validity of different models. These functions can be measured experimentally with the X-ray photon correlation spectroscopy technique

Ageing dynamics of ion bombardment induced self-organization processes

Instabilities caused during the erosion of a surface by an ion beam can lead to the formation of self-organized patterns of nanostructures. Understanding the self-organization process requires not only the in-situ characterization of ensemble averaged properties but also probing the dynamics. This can be done with the use of coherent X-rays and analyzing the temporal correlations of the scattered intensity. Here, we show that the dynamics of a semiconductor surface nanopatterned by normal incidence ion beam sputtering are age-dependent and slow down with sputtering time. This work provides a novel insight into the erosion dynamics and opens new perspectives for the understanding of self-organization mechanisms

Osmotic pressure induced tensile forces in tendon collagen

Water is an important component of collagen in tendons, but its role for the function of this load-carrying protein structure is poorly understood. Here we use a combination of multi-scale experimentation and computation to show that water is an integral part of the collagen molecule, which changes conformation upon water removal. The consequence is a shortening of the molecule that translates into tensile stresses in the range of several to almost 100 MPa, largely surpassing those of about 0.3 MPa generated by contractile muscles. Although a complete drying of collagen would be relevant for technical applications, such as the fabrication of leather or parchment, stresses comparable to muscle contraction already occur at small osmotic pressures common in biological environments. We suggest, therefore, that water-generated tensile stresses may play a role in living collagen-based materials such as tendon or bone.United States. Office of Naval Research. Presidential Early Career Award for Scientists and EngineersNational Institutes of Health (U.S.) (U01-EB016422

Micro-diffraction par rayons X des ilots SiGe/Si (001) individuels (au delà des propriétés des grands ensembles)

We show in this work a novel approach called scanning x-ray diffraction microscopy (SXDM) which enables to characterise a single SiGe/Si (001) island by combining the advantages of image microscopy with high resolution diffraction. The technique consists of focusing an x-ray beam to a spot small enough to illuminate one island and thereafter perform diffraction. SXDM further allows to image and identify the different islands in real space whereby their precise positions are obtained so that the islands can be translated individually in the beam focus and made to undergo diffraction. From different measurements on individual islands, we show clear evidence of variations in the structural properties from one island to another, yet grown on the same sample under similar conditions; this wou Id have not been possible if an unfocused x-ray beam was used. Through finite-element calculations (FEM), the different strain and composition profiles of the islands are determined thereby establishing a structure model for the islands. Eventually, we show that SXDM can be combined with local probe devices such as atomic force microscopy (AFM) to investigate possible interactions between the surface the AFM tip, for instance surface deformations. Key words: Quantum dots, SiGe islands, X-rays, X-ray diffraction, Characterisation, AFM.Dans ce travail, on montre une nouvelle technique appelée "scanning x-ray diffraction microscopy" (SXDM) qui permet de caractériser un îlot de SiGe/Si (001) en combinant les avantages de l'imagerie par microscopie et la diffraction par rayons x à haute résolution. L'approche consiste à concentrer un faisceau de rayons x en une tache suffisamment petit pour illuminer un seul îlot et par suite le soumettre à une mesure de diffraction. SXDM permet de faire une image dans l'espace réel de l'ensemble des îlots et ainsi déterminer les coordonnées de leurs positions respectives si bien qu'il est alors possible de translater chacun des îlots dans le faisceau de rayons x à tour de rôle et faire une mesure de diffraction. A travers de différentes mesures sur des îlots individuels, on met en évidence l'existence d'une variation des propriétés structurales entre les îlots bien qu'ils aient tous été fabriqués dans les mêmes conditions de croissance. Avec l'aide des calculs de éléments finis, le profil de composition chimique et de l'état de contrainte des différents îlots ont été effectués et a permis d'engendrer un modèle structural des îlots. En outre, on montre que le SXDM peut être combiné avec d'autres techniques de microscopie de champs proche telle que la microscopie à force atomique (AFM) pour établir des interactions possibles entre la pointe de l'AFM et la surface de l'îlot, par exemple des déformations surfaciques. Mots clés: Boîtes quantiques, îlots SiGe, Rayons X, Diffraction par rayons X, Caractérisation, AFM.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Self-Repair of a Biological Fiber Guided by an Ordered Elastic Framework

Incorporating sacrificial cross-links into polymers represents an exciting new avenue for the development of self-healing materials, but it is unclear to what extent their spatial arrangement is important for this functionality. In this respect, self-healing biological materials, such as mussel byssal threads, can provide important chemical and structural insights. In this study, we employ in situ small-angle X-ray scattering (SAXS) measurements during mechanical deformation to show that byssal threads consist of a partially crystalline protein framework capable of large reversible deformations via unfolding of tightly folded protein domains. The long-range structural order is destroyed by stretching the fiber but reappears rapidly after removal of load. Full mechanical recovery, however, proceeds more slowly, suggesting the presence of strong and slowly reversible sacrificial cross-links. One likely role of the highly ordered elastic framework is to bring sacrificial binding sites back into register upon stress release, facilitating bond reformation and self-repair

Versatile vacuum chamber for in situ surface X-ray scattering studies

A compact portable vacuum-compatible chamber designed for surface X-ray scattering measurements on beamline ID01 of the European Synchrotron Radiation Facility, Grenoble, is described. The chamber is versatile and can be used for in situ investigation of various systems, such as surfaces, nanostructures, thin films etc., using a variety of X-ray-based techniques such as reflectivity, grazing-incidence small-angle scattering and diffraction. It has been conceived for the study of morphology and structure of semiconductor surfaces during ion beam erosion, but it is also used for the study of surface oxidation or thin film growth under ultra-high-vacuum conditions. Coherent X-ray beam experiments are also possible. The chamber is described in detail, and examples of its use are given