Thin-film gated photocathodes for electron-beam lithography

Photoemission has often been proposed as a promising approach for achieving arrays of independently modulated photocathodes for electron-beam lithography applications. In most such proposals the modulation of the photocurrent is assumed to be achieved by controlling the incident light energy reaching each photocathode. For many applications, however, the optical complexity of such a scheme limits the attractiveness of the photocathode approach. In this article we propose a novel gated photocathode structure which resolves this concern. It allows stable and reproducible electrical modulation of the photocurrent from each photocathode in a thin-film array under continuous optical illumination. In addition, by using illumination of the photocathodes through a transparent substrate, the position, the size, and the shape of each photocathode can be accurately determined during fabrication rather than being determined by the size of the optical illumination spot on the photocathode material. A number of structures with different geometry have been fabricated and tested, and found to exhibit behavior consistent with theoretical expectations. It is found that even in accelerating fields as high as 105 volts per cm, photocurrent can be extinguished by applying only a few volts to the gate of such structures.