Electron-emissive materials are poised to improve device performance when physical size, weight, power consumption, beam current, and/or high pulse repetition frequencies are an important issue for competitive performance. Cold cathodes offer potential property improvements over conventional thermionic sources - instant on/off performance, high brightness, high-current density, large transconductance-to-capacitance ratio, or low-voltage operation characteristics. Many extraordinary technologies are developing, some well known, and some new to the electron sources scene. Flat-panel displays...