Lasing in metal-insulator-metal sub-wavelength plasmonic waveguidesHill, M.T.; Marell, M.J.H.; Leong, E.S.P.; Smalbrugge, E.; Zhu, Y.C.; Sun, Minghua; Veldhoven, van, P.J.; Geluk, E.J.; Karouta, F.; Oei, Y.S.; Nötzel, R.; Ning, C.Z.; Smit, M.K.

By controlling local substrate temperature in a chemical vapor deposition system, we have successfully achieved spatial composition grading covering the complete composition range of ternary alloy CdSSe nanowires on a single substrate of 1.2 cm in length. Spatial photoluminescence scan along the substrate length shows peak wavelength changes continuously from approximately 500 to approximately 700 nm. Furthermore, we show that under strong optical pumping, every spot along the substrate length displays lasing behavior. Thus our nanowire chip provides a spatially continuously tunable laser with a superbroad wavelength tuning range, unmatched by any other available semiconductor-based technology.

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We report the formation of a stable superhydrophobic surface via aligned carbon nanotubes (CNTs) coated with a zinc oxide (ZnO) thin film. The CNT template was synthesized by chemical vapor deposition on an Fe-N catalyst layer. The ZnO film, with a low surface energy, was deposited on the CNT template by the filtered cathodic vacuum arc technique. Contact angle measurement reveals that the surface of the ZnO-coated CNTs is superhydrophobic with water contact angle of 159 degrees . Unlike the uncoated CNTs surface, the ZnO-coated CNTs surface shows no sign of water seepage even after a prolonged period of time. The wettability of the surface can be reversibly changed from superhydrophobicity to hydrophilicity by alternation of ultraviolet (UV) irradiation and dark storage.

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This paper examines the three categories of permeability functions for unsaturated soils, including empirical macroscopic, and statistical models. The theoretical backgrounds and performance of each category are examined against various experimental data. The paper also shows that it is possible to degenerate statistical models to macroscopic models and then to empirical models. A new empirical equation for the permeability function is suggested. The statistical model demonstrates good performance and can be readily applied. In some cases the performance of the statistical model can be further improved with the i n d u c t i o n of a correction factor. INTRODUCTION Many GeotechnicaI and geoenvironmental problems involve water flow through unsaturated soils. Water coefficient of permeability in an unsaturated soil is a function of pore-water pressure or water content. Direct measurements of permeability in the laboratory can be time-consuming. especially for low water content conditions. Indirect measurements of permeability are commonly performed by establishing permeability functions through the use of the relationship between water content and pore-water pressure (i.e., soil-water characteristic curve). There are numerous permeability functions available for unsaturated soils. In general, the various permeability functions can be categorized into three groups: empirical macroscopic, and statistical models. It is important that the assumptions and theoretical backgrounds associated with each category of function be known prior to its use in application. A review of these backgrounds is presented in the Paper. The performance Of each Category of function is also examined against various experimental data. Advantages and limitations associated with each model are illustrated in the paper. PERMEABILITY OF UNSATURATED SOILS Permeability of saturated soils is a function of void ratio e only. For unsaturated soils, the coefficient of permeability with respect to water i s a function of both void ratio e and water content w. Since void ratio e, water content w, and degree of saturation S are interrelated, can be expressed as a function of any two of the three parameters. i.e. measure such a wide range of permeability values efficiently. permeability measurements can be performed either in the field or in the laboratory. However, field measurements are usually more. variable due partly to macroscopic features and partly from the assumptions made. In this paper only laboratory measurements are discussed In direct measurement there are steady-state and unsteadystate methods (Fredlund and Rahardjo 1993). In the steadystate method, a matric suction is first imposed on a soil specimen using the axis-translation technique (Hilf 1956). at equilibrium, denoted by a constant water content, a hydraulic gradient is then imposed across the soil specimen The flow rate is measured and the permeability is obtained via Darcy's law. using the unsteady-state method or instantaneous profile method, a cylindrical soil specimen is subjected...

This paper reports an effective method to enhance the surface plasmon resonance (SPR) on Ag films by using a thin Ni seed layer assisted deposition. Ag films with a thickness of about 50 nm were deposited by electron beam evaporation above an ultrathin Ni seed layer of approximately 2 nm on both silicon and quartz substrates. The root-mean-square (rms) surface roughness and the correlation length have been reduced from >4 nm and 28 nm for a pure Ag film to approximately 1.3 and 19 nm for Ag/Ni films, respectively. Both experimental and simulation results show that the Ag/Ni films exhibit an enhanced SPR over the pure Ag film with a narrower full width at half-maximum. Ag films with a Ge seed layer have also been prepared under the same conditions. The surface roughness can be reduced to less than 0.7 nm, but narrowing of the SPR curve is not observed due to increased absorptive damping in the Ge seed layer. Our results show that Ni acts as a roughness-diminishing growth layer for the Ag film while at the same time maintaining and enhancing the plasmonic properties of the combined structures. This points toward its use for low-loss plasmonic devices and optical metamaterials applications.

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