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Nat Mater ; 11(7): 585-9, 2012 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-22561901


A complicating factor in unravelling the theory of high-temperature (high-T(c)) superconductivity is the presence of a 'pseudogap' in the density of states, the origin of which has been debated since its discovery. Some believe the pseudogap is a broken symmetry state distinct from superconductivity, whereas others believe it arises from short-range correlations without symmetry breaking. A number of broken symmetries have been imaged and identified with the pseudogap state, but it remains crucial to disentangle any electronic symmetry breaking from the pre-existing structural symmetry of the crystal. We use scanning tunnelling microscopy to observe an orthorhombic structural distortion across the cuprate superconducting Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4+x) (BSCCO) family tree, which breaks two-dimensional inversion symmetry in the surface BiO layer. Although this inversion-symmetry-breaking structure can impact electronic measurements, we show from its insensitivity to temperature, magnetic field and doping, that it cannot be the long-sought pseudogap state. To detect this picometre-scale variation in lattice structure, we have implemented a new algorithm that will serve as a powerful tool in the search for broken symmetry electronic states in cuprates, as well as in other materials.

Nanotechnology ; 22(36): 365708, 2011 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-21844643


A nanomechanical testing set-up is developed by integrating an atomic force microscope (AFM) for force measurements with a scanning electron microscope (SEM) to provide imaging capabilities. Electrospun nanofibers of polyvinyl alcohol (PVA), nylon-6 and biological mineralized collagen fibrils (MCFs) from antler bone were manipulated and tensile-tested using the AFM-SEM set-up. The complete stress-strain behavior to failure of individual nanofibers was recorded and a diversity of mechanical properties observed, highlighting how this technique is able to elucidate mechanical behavior due to structural composition at nanometer length scales.

Teste de Materiais/métodos , Microscopia de Força Atômica/métodos , Nanofibras/química , Resistência à Tração , Animais , Caprolactama/análogos & derivados , Caprolactama/química , Cervos , Colágenos Fibrilares/química , Colágenos Fibrilares/ultraestrutura , Interferometria , Lasers , Microscopia Eletrônica de Varredura , Nanofibras/ultraestrutura , Polímeros/química , Álcool de Polivinil/química