Field emitter polymer arrays technology for vacuum electronics

The low electron affinity and excellent transport properties of some conducting organic polymers suggest that they might also provide good unheated cathode materials. It is demonstrated here that this is true also for some non-conjugated, undoped polymers deposited on flat metallic electrodes. The idea to use non-conjugated polymers as field-emission materials came from experimental results where they exhibit high conductivity properties in Metal-Polymer-Metal structures and supercurrents in Superconductor-Polymer-Superconductor structures. The following were used in this experiment: i) imid-siloxane copolymer; ii) aryl-polycarbonate; iii) nylon-60. Polymer films were prepared by deposition of a droplet of 5 % wt. solution on the polished Mo or Nb electrodes with 5 mm in diameter. The films were then heated in air for 1 h at a constant temperature of 370-400 K to remove the major part of the polymer solvent. The field emission was studied in a vacuum of 10 Torr. A stable field emission from polymer-coated cathodes at 4 kV/mm was obtained. However for initial activation of the cathode the threshold field should be 2.5-3 times more than 4 kV/mm. The field emission from polished metals was not observed up to 25 kV/mm. The current-voltage characteristics (CVC) of the cathodes were measured in both forward and reverse directions by high-voltage scanning at a frequency of 50 Hz. At relatively low bias voltages CVC agrees with the Fowler-Nordheim theory. The surface topography and the current distribution of the polymer film was simultaneously investigated by atomic force microscopy (AFM) before and after the action of electric field at room temperature. The CVC at different points of polymer surface was also investigated. Initially, polymers had smooth surfaces without conductivity but after a threshold field emission the surfaces were strongly modified: conductive arrays were formed up to 400 nm high. The current topography of the polymer film surfaces was visualized the appearance of thin conductive channels distributed evenly enough on the polymer surface. This nanoscale modification of polymer surface in a strong electric field can be explained by local electrification due to self-injection of charge carriers from the metal electrode into a relatively elastic polymer matrix. Low temperature conductivity investigations on Metal(Superconductor)/Polymer film (with arrays)/Metal (Superconductor) structures have been done to understand the nature of conductive arrays.