No abstract

Using energy-filtered transmission electron microscopy we measured surface-plasmon resonances of gold nanoplatelets with different shapes and edge lengths at high spatial resolution. We find equidistant maxima of the energy-loss probability along the platelet edges. The plasmon dispersion of the different geometries is very similar, i.e., hardly dependent on specimen shape. The experimental results are verified by means of finite-difference time-domain calculations which reveal the presence of wedge-plasmon polaritons propagating along the platelet edges. At platelet corners, apart from radiative losses, wedge-plasmon polaritons are partially reflected or transmitted to neighboring edges. The interference of all these contributions leads to the observed plasmon resonance modes. This is an essential step towards a thorough understanding of plasmon eigenmodes in prismatic nanoplatelets.

No abstract

No abstract

The excellent mechanical properties of powder metallurgy (P/M) superalloys strongly depend on the microstructure, such as grain size, and morphology and size distribution of the ␥ Ј precipitates. The microstructure is, in turn, determined by the heat treatment, viz., solution annealing, quenching, and subsequent aging. To study the effect of the quenching process, two types of quenching methods were used to produce different quenched microstructures in a UDIMET 720LI (U720LI) alloy. One was a continuous quenching method, where samples were cooled along linearly controlled cooling profiles, each at a fixed cooling rate. This test studied the effect of cooling rate on the size of cooling ␥Ј precipitates (formed during quenching) and the consequent strengthening effect. The other test was the interrupted quenching test, which allowed tracking the growth of cooling ␥Ј precipitates with decreasing temperature during quenching at a given cooling rate. The strengthening response at each interrupt temperature was also studied. Results from the continuous cooling tests showed that the relationship between the size of the cooling ␥Ј precipitate and the cooling rate obeys a power law, with an exponential being about 0.35. The tensile strength was found to increase linearly with the cooling rate. Strengthening due to the subsequent aging treatment occurred regardless of cooling rates. The interrupted cooling tests showed that ␥ Ј growth is a linear function of decreasing temperature for a given cooling rate. A nonmonotonic degradation of tensile strength against interrupt temperature was discovered.