Enhanced Field Emission from Metallic Surfaces and Nanowires

The role of material properties, surface preparation and cleaning techniques on Nb and Cu was studied for EFE , which is disastrous for high field vacuum devices. Dry ice cleaning is found to suppress EFE from the metallic surfaces very efficiently. High purity single crystal and large grain Nb samples showed the onset of FE at high fields (120 ? 200 MV/m). For the first time, the grain boundary assisted field emission was observed for Nb. A correlationbetween size of emitters and onset fields is obtained, which sets a threshold for the tolerable defect size to achieve the envisaged accelerating gradients in cavities reliably. Additionaly, the systematic study performed on electrochemically deposited Cu, Ni and Au nanowires of different aspect ratios and spatial distribution for cold cathode applications. In our findings, Au coating on Ni nanowires provided improved FE properties. Further, in Au Nanowires up to 40 % percentage of the wires were emitting. Achieving much larger emitter number densities ~10^5 cm^?2 at 6 V/µm compared to CNT cathodes with respect to the number of deposited nanostructures, makes Au NWs interesting for cold cathode applications.