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The fabrication of ordered macroporous silicon is obtained by exploiting the self-assembly properties of polymer nanospheres. Here, we demonstrate the method by using nanospheres of 200 nm and 500 nm. These self-assemble in monolayers of ordered hexagonal close-packed nanospheres. A controlled reactive ion etch of the assembled nanospheres, subsequent evaporation of metal, followed by 'lift-off' of the polymer nanospheres, provides a mask suitable for a further reactive ion etch step to provide macroporous polysilicon. This methodology provides a novel approach for the fabrication of highly ordered macroporous polysilicon; porous silicon substrates with pores of this size (50-500 nm) were previously only fabricated using rather difficult processing methods. The method reported here is straightforward and achieved using fabrication methods that are compatible with those currently used for microelectromechanical systems (MEMS), photonic devices and nanostructured surfaces.

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The question of obtaining information on the band structure of solids using quasielastic knock-out of an electron by an electron from a very thin crystalline film is discussed. It has been found that Van Hove singularities practically have no effect on the quasielastic knock-

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