Multilayer field emitters on a thin metal substrate

The purpose of this work is to determine the ability of creating multilayer cathodes from contacted materials with different work functions $e\varphi$ on thin metal substrates, as well as the practical use of such cathodes for the formation of intense sheet and annular in cross sections electron flows in miniature but high-voltage devices. Methods. Layers of hafnium ($e\varphi\sim$3.5 eV) and platinum ($e\varphi\sim5.3$ eV) with a thickness of 10 nm and 2 nm, respectively, were sequentially deposited on the side surface of the metal foil substrates using a fairly simple and efficient method of magnetron sputtering. Cathodes made from a foil with a multilayer coating, emitted sheet and annular in the cross section electron flows. Experimental measurements of the emission characteristics of multilayer cathodes and formed by them electron flows were carried out in triode electron-optical systems (EOS), consisted of a cathode, a control electrode (anode), and an electron collector in the form of a Faraday cup. The measurements were carried out in a technical vacuum of $10^{-7}$...$10^{-8}$ Torr. Results. The characteristics of sheet and annular in cross sections electron flows formed by triode EOSs with multilayer cathodes on thin substrates of aluminum (9 $\mu$m) and tantalum (10 $\mu$m) were experimentally determined. The dependences of the current from the cathode on the voltage between the cathode and the control electrode (current-voltage characteristics), as well as the changes in time of the electron current of electron flows generated by EOS, were measured. Conclusion. In this work, the possibility of forming sheet and annular in cross sections electron flows with currents of up to several tens of milliamperes at extremely large average field emission current densities of up to 300...400 A/cm$^2$ by using of multilayer cathodes on a thin metal substrate was demonstrated. The possibility of the stable operation of the studied cathodes during the high field emission in a technical vacuum is shown.