Among near field microscopes, the atomic force microscope appears as a powerful and versatile tool for investigating local mechanical properties. In addition, we can take advantage of the tip sample interaction, to perturb, and in turn modify the surface of soft samples. Here we report an attempt to modify the structure of a substituted polyacetylene film spread on a surface. Regular periodic patterns are obtained, and we show that scan frequency and applied load are the pertinent parameters that control the period. These results can be described as bundle formation via a peeling process.Atomic force microscopy (AFM) in contact mode has opened a wide range of investigation: adhesive properties, tribology, and rheology at submicromic scale.Because of the contact mode, it turns out that the elastic properties of the sample become of primary importance. Particularly for soft samples, this leads to images that involve surface roughness and elastic response of the sample, thus also imaging the mechanical properties [1]. Moreover, for soft materials, one may
Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid-solid phase transition of an incommensurate host-guest system: the channel inclusion compound of nonadecane/urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other-an internal variable available only in superspace. This unanticipated pathway for degrees of freedom to rearrange leads to a second phase transition, which again is controlled by the higher dimensionality of superspace. These results reveal nature's capacity to explore the increased number of phases allowed in aperiodic crystals.
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