University of California, Santa Barbara

About: University of California, Santa Barbara is a education organization based out in Santa Barbara, California, United States. It is known for research contribution in the topics: Population & Laser. The organization has 30281 authors who have published 80852 publications receiving 4626827 citations. The organization is also known as: UC Santa Barbara & UCSB.

Metallic transport in polyaniline

Abstract: Most plastics are good insulators. But conducting polymers also form the basis of a new field of ‘plastic electronics’. Some of these materials show exceptionally high conductivities, almost as high as metals. But their properties deviate from true metallic behaviour in several important ways. Now a conducting plastic with resistivity properties much more like those of true metals has been synthesized. The properties of this polyaniline compound may bring practical plastic electronics a little closer. True metallic conductivity in a much-studied conducting polymer (polyaniline) is demonstrated, but synthesized by a route that minimizes the density of structural defects believed responsible for the earlier deviations from classical metallic behaviour. Despite nearly three decades of materials development, the transport properties in the ‘metallic state’ of the so-called conducting polymers are still not typical of conventional metals1,2,3,4,5,6,7. The hallmark of metallic resistivity—a monotonic decrease in resistivity with temperature—has not been obtained at temperatures over the full range below room temperature; and a frequency dependent conductivity, σ(ω), typical of metals has also not been observed. In contrast, the low-temperature behaviour of ‘metallic’ polymers has, in all previous cases, exhibited an increase in resistivity as temperature is further decreased, as a result of disorder-induced localization of the charge carriers1,2,3,4. This disorder-induced localization also changes the infrared response such that σ(ω) deviates from the prediction of Drude theory5,6,7. Here we report classic metallic transport data obtained from truly metallic polymers. With polyaniline samples prepared using self-stabilized dispersion polymerization8, we find that for samples having room-temperature conductivities in excess of 1,000 S cm-1, the resistivity decreases monotonically as the temperature is lowered down to 5 K, and that the infrared spectra are characteristic of the conventional Drude model even at the lowest frequencies measured.

Evidence for quantum annealing with more than one hundred qubits

Abstract: Quantum annealing is expected to solve certain optimization problems more efficiently, but there are still open questions regarding the functioning of devices such as D-Wave One. A numerical and experimental investigation of its performance shows evidence for quantum annealing with 108 qubits.

Direct imaging of the pores and cages of three-dimensional mesoporous materials

Abstract: Mesostructured composite materials, with features ranging from 20 to 500 A in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (> 10 microm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure.