with a defined orientation and covering a large area have been fabricated by ion beam sputtering. The density of the Si cones is as high as 6 x 10⁸ cm^–2. A silicide tip was found on top of each Si cone. The Si cone arrays have a relatively low turn-on field, which may be useful for applications of these arrays in electronic vacuum devices. (S. T. Lee et al., September 16, Adv. Mater. 2002, 14, 1308-1311)