We fabricate and characterize large-area plasmonic substrates that feature asymmetric periodic nanostructures made of aluminum. Strong coupling between localized and propagating plasmon resonances leads to characteristic Fano line shapes with tunable spectral positions and widths. Distinctive colors spanning the entire visible spectrum are generated by tuning the system parameters, such as the period and the length of the aluminum structures. Moreover, the asymmetry of the aluminum structures gives rise to a strong symmetry broken color rendering effect, for which colors are observed only from one side of the surface normal. Using a combination of immersed laser interference lithography and nanoimprint lithography, our color rendering structures can be fabricated on areas many inches in size. We foresee applications in anticounterfeiting, photovoltaics, sensing, displays, and optical security.

An in-situ study on the directional solidification of an inoculated Al-20 wt%Cu alloy under well-controlled constant cooling rates and temperature gradients has been carried out using a microfocus X-radiography set-up. The influences of temperature gradient and cooling rate on the heterogeneous nucleation rate and growth kinetics of equiaxed grains have been studied quantitatively. It is shown that under the same cooling rate, the nucleation rate of grains decreases with increasing temperature gradient. A high temperature gradient also promotes preferential growth of dendrite arms along the temperature gradient direction, and therefore the formation of elongated grains.However, the temperature gradient effects on nucleation and grain growth decrease with increasing cooling rate. It is revealed that the propagation velocity of the nucleation front in directional solidification castings is approximately equal to the ratio between cooling rate Ṫ and temperature gradient . Based on the experimental observations, a novel numerical grain size prediction model has been proposed, in which the temperature gradient effect on the nucleation kinetics was rigorously treated by introducing two new concepts termed as 'inhibited nucleation zone'(INZ) and 'active nucleation zone'(ANZ). The model has been applied to simulate the present insitu solidification experiments. A good agreement was achieved between the predicted grain number density and the experimental measurements, showing the importance of including the temperature gradient effect on heterogeneous nucleation. Furthermore, the present model also has the capability to predict the temperature gradient necessary for the transition from equiaxed to columnar grain growth.

A comprehensive study on the heterogeneous nucleation and grain growth of Al-10wt.%Cu alloys inoculated with Al-5Ti-1B was carried out. To further reveal the solute segregation stifling mechanism, in-situ near-isothermal melt solidification experiments with constant cooling rates and greatly suppressed melt convection were realized by in-situ microfocus X-radiography study. The kinetics of heterogeneous nucleation and grain growth under the isolated influence of cooling rate and addition level of inoculant particles has been quantitatively studied. Moreover, novel image processing and analysis approaches have been proposed, to determine the maximum

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