Preparation of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films by electron beam evaporation

Abstract

The pseudospark, a transient, low-pressure gas discharge, emits a short-duration, pinched, intense electron beam during the breakdown phase. At a voltage of typically 20 kV approximately 10% to 20% of the total discharges current appears as an electron beam current of typically 20-ns duration. In general it is possible to run the pseudopark from charging voltages of some kilovolts up to approximately 100 kV with corresponding beam currents between amperes and several kiloamperes. The optimization of electron production and beam formation in such a gas discharge has led to the development of a special discharge geometry. A pair of plane parallel electrodes with circular holes on a common symmetry axis is held in place by an insulator ring. When operated on the left-hand side of the corresponding Paschen curve, the breakdown occurs along the longest possible path, which is located on the symmetry axis of the cathode hole. Such a system is called a two-electrode pseudospark chamber. A simple stack of electrode and insulator disks, a so-called multielectrode system, shows improved performance as an electron beam source. A very promising application, the production of thin films of high-temperature superconductors on single crystalline SrTiO/sub 3/ substrates, is described. >