Electron emission from ferroelectric/antiferroelectric cathodes excited by short high-voltage pulses

Abstract

Un-prepoled Lead Zirconate Titanate Lanthanum doped-PLZT ferroelectric cathodes have emitted intense current pulses under the action of a high voltage pulse of typically 8 kV/cm for PLZT of 8/65/35 composition and 25 kV/cm for PLZT of 4/95/5 composition. In the experiments described in this paper, the exciting electric field applied to the sample is directed from the rear surface towards the emitting surface. The resulting emission is due to an initial field emission from the metal of the grid deposited over the emitting surface with the consequent plasma formation and the switching of ferroelectric domains. These electrons may be emitted directly from the crystal or from the plasma. This emission requires the material in ferroelectric phase. In fact, PLZT cathodes of the 8/65/35 type, that is with high Titanium content, showing ferroelectric-paraelectric phase sequence, emit at room temperature, while PLZT cathodes of the 4/95/5 type, that is with low Titanium content, having antiferro-ferro-paraelectric phase sequence, emit strongly at a temperature higher than 130°C.

Features and technology of ferroelectric electron emission

“…[14][15][16][17][18][19][20][21][22], initiates P s -switching at the same threshold field level. However, the sequence of processes following the switching, including plasma formation and electron extraction by external field, may widely differ from the FE self-emission described above.…”

“…However, the emission intensities and the kinetic electron energies are differently influenced in both cases by the cathode surface potential distributions and by the plasma, which had formed earlier by P sswitching during the rise time of the excitation pulse. Emitted charge (top), current (middle) and HV waveforms (bottom) measured under electric field excitation with field direction from RE to GE and under the influence of an external extraction potential V ext [21].…”

“…The strong electrically-induced emission from FE samples covered with metallic grid electrodes is very efficient, but weak FE emission has also been observed from a bare FE surface without any electrode or conducting material (for example, [3,5,26]). The latter type of electron emission cannot be induced with any of the alternative emission methods [14][15][16][17][18][19][20][21][22] using reverse field excitation, which rely on the field emission of electrons from the FE-metal interfaces of the GE grid electrode [27].…”

“…Fig. 7) and when it is pulsed with reverse-field direction (positive HV pulse to the rear electrode RE [21]). The reversed field switching generates a polarization field pattern which is characterized by identical strength, but by a reversed direction compared to the excitation of FE emission with negative HV pulses to RE.…”

“…Later on different methods were studied in other laboratories to extract intense electron beams from FE cathodes (for example, Refs. [14][15][16][17][18][19][20][21][22]), and confusion arose about what is meant by 'ferroelectric electron emission'. The phenomenological appearance and some of the basic processes differ in these latter cases from those in the original 'strong FE emission mode' [4][5][6][7][8][9][10][11][12][13].…”