Soft wetting: surface effects in highly deformable amorphous materials
Bruno Andreotti
Université Paris Diderot Paris-VII, Paris, France
andreotti@pmmh.espci.fr
As largely demonstrated in the last two decades, elasticity plays an important role in surface physics. Phenomena such as surface reconstruction, surface segregation, surface adsorption, elastic instabilities, self assembly, and nano-structuration of crystalline solids are directly induced by surface stresses. However, it is only recently that the soft condensed matter community has discovered this field of physics and started to extend concepts to soft amorphous solids. I will review the important thermodynamic results of solid surface physics, which make the distinction between two quantities that turn out to be equal in an incompressible liquid: surface energy and surface stress. I will then show that important qualitative phenomena are not correctly described by macroscopic theories and require a treatment were nanoscopic aspects are explicitely introduced. These concepts will be illustrated by recent experimental results obtained on gels and elastomers, answering qualitative questions like: Why is the spreading of a drop much slower on an soft solid than on a rigid substrate? Does elasticity modifies the contact angle made by a drop on a soft solid? How does a drop deform a soft solid? To conclude, I will open perspectives on the functionalisation of soft solids.
Thin-Film Alchemy: Creating Astonishing Properties in Oxide Nanosandwiches
Darrell G. Schlom
Department of Materials Science and Engineering and
Kavli Institute at Cornell for Nanoscale Science
Cornell University, Ithaca,USA
schlom@cornell.edu
Thin-film synthesis has played a critical role in the development of conventional semiconductor devices, as well as in shaping the current landscape of fundamental science and technology at the nanoscale. Techniques like molecular-beam epitaxy, which is famous for its ability to customize the layering of semiconductors with atomic-layer precision, can also be applied to the growth of thin films of multicomponent oxide materials. With their wider assortment of functional properties, creating oxide nanosandwiches and applying thin film tricks to enhance their properties has tremendous potential. Using epitaxy and the misfit strain imposed by an underlying substrate, it is possible to strain oxide thin films to percent levels—far beyond where they would crack or plastically deform in bulk. Under such strains, the properties of oxides can be dramatically altered. For example, materials that are not ferroelectric or ferromagnetic in their unstrained state can be transmuted into ferroelectrics, ferromagnets, or materials that are both at the same time. Results of fundamental scientific importance as well as revealing the tremendous potential of utilizing multicomponent oxide thin films to create devices with enhanced performance will be shown.
Photonic Topological Insulators
Mordechai (Moti) Segev
Technion, Israel Institute of Technology, Haifa, Israel
msegev@techunix.technion.ac.il
Photonic systems are naturally an excellent avenue to study fundamental concepts of waves' interactions, and many times lead to new discoveries. In this context, the recent breakthroughs on photonic topological insulators will be discussed, with an emphasis on fundamental aspects that are universal to many waves systems in nature.