Abstract—The miniature cold field emitters are very attractive for utilization in low-power gyrotrons operating in range of short millimeter and terahertz waves. But such emitters are usually nondurable when exploiting in technical vacuum. Multi-tip field emitters with protective coatings developed and investigated by the authors are promising for use in short-wave gyrotrons operating in a technical vacuum. I. INTRODUCTION AND BACKGROUND old field emitters are very attractive for use in many type of electron devices, including microwave ones, but difficulties in achievement of high durability at technical vacuum conditions and obtainment of high enough currents preclude the application of field emitters in high voltage facilities operating in technical vacuum conditions. During the last years the interest to the use of cold field emitters has increased significantly in connection with appearance and development of comparatively low-power gyrotrons operating in range of short millimeter and terahertz waves. Such gyrotrons can be used for different type of diagnostics. The miniature cold field emitters are much better suited for such devices, than thermionic ones. The authors searched for methods to create the durable and high current field emitters for microwave devices operating in technical vacuum. Multi-tip cathodes with special protective coatings of new type developed by the authors from St. Petersburg State Polytechnical University are very perspective for such application. The multi-tip silicon cathodes that we are investigating now have generally a low conductivity and can provide even moderate currents only in conditions when their conductivity is enhanced by heating to 200 - 400 C. Besides, such cathodes are not strong enough and usually are destroyed under the action of ponderomotive forces at small enough fields. In addition, silicon cathodes are easily damaged in the presence of an intense ion bombardment. So, to solve the problem of silicon cathodes practical use we need to find ways to increase their conductivity, strength to the action of the ponderomotive forces and to the ion bombardment. Previously performed our investigations [1- 4] showed that special coating by the molecules of fullerene C 60 can be used to protect the tip field emitters from the destructive action of the ion bombardment. For the first time, the protective role of fullerene coatings was exhibited for single tungsten field emitters. Fullerene coatings have high work function (eϕ∼5.3- 5.4 eV). However, formation of a structure including a generous amount of roughly equal in size protrusions on its surface [2] allowed emitters with fullerene coatings to operate at moderate voltages. Additional reduction of the operating voltages was achieved in the result of activating of the fullerene coating by a flow of slow (40-80 eV) potassium ions [3,4]. Revealed mechanism of fullerene coating self- reproduction in presence of intensive ion bombardment explains the stable operation of such emitters at technical vacuum conditions. By now, the method of deposition of activated fullerene coatings on the surface of silicon multi-tip cathodes was worked out. This coating increased the durability of the emitter, but does not substantially changed its conductivity and strength. We have shown that all three above-mentioned problems can be solved simultaneously if we used a two-layer metal - fullerene coatings. Methods for creating of the tip field emitters with protective coating, as well as the results of their investigation are described in this paper. II. EXPERIMENTAL METHODS AND RESULTS OF MEASUREMENTS Silicon tips were grown on the end surface of a cylindrical silicon rod with diameter 1 mm. Quantity of tips on this surface for the investigated cathodes was varied approximately from 50 to 350. The surface morphology of the field emitters was controlled by using the scanning electron microscope Supra 45 WDXS before installation into an experimental device and after the experiments. Fig. 1 shows the typical image of a small area of the silicon multi-tip emitter obtained with the scanning electron microscope. Radius R of the top of silicon tips varied for different samples in the range of about 5 to 25 nm. The height h of the tips varied approximately from 5 to 40 μm. The distance l G.G. Sominski 1 , E.P. Taradaev 1 , T.A. Tumareva 1 , M.V. Mishin 1 , and A.N. Stepanova 2 1 Saint-Petersburg State Polytechnical University, 195251, Russia 2 Institute of Crystallography RAS, Moskow, 119333, Russia Multi-tip Field Emitters for Electron Devices Operating in Technical Vacuum С Fig.1. Image of multi-tip cathode obtained in scanning electron microscope.