Emission, plasma formation, and brightness of a PZT ferroelectric cathode

Abstract

This h a preprint of a p a~i n~n d e d forpubliotion in a jotun?l or proceeding. Since changes may be nude before pnbliotion, this preprint is made available with the understanding ttut it will not be ated or reproduced without the permhion of the author. We have measured an 36-A-~m-~ current emission density over the surface area of an 11.4-cm2-area Lead-Titanate-Zmonate @T) ferroelectric cathode with a pulsed andcathode (A-K) potential of 50 kV. We have also observed currents above those pfedicted by classical Child-Langmuir formula for a wide variety of cases. Since a plasma within the A-K gap could also lead to increase current emission we are attempting to measure the properties of the plasma near the cathode surface at emission time. In other measurements, we have observed strong gap currents in the absence of an A-K potenrial. Further, we continue to make brightness measurements of the emitted beam and observe spatially non-uniform emission and large shot-to-shot variation. Measurements show individual beamlets with a brightness as high 10lr Am-2rad-2. 7 DISCLAIMER

Features and technology of ferroelectric electron emission

“…Equation (4) may explain the two orders of magnitude increase of emitted current density compared with the Langmuir-Child current density. Such an enhancement of emitted current density can be observed, if an extraction field is applied and if the plasma density n e is sufficiently high (as for example reported in [15], [16], [18], [19]). The enhancement effect of the surface plasma can also be recognized in FE self-emission mode (for example in Fig.…”

“…[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.…”

“…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].…”

“…In Refs. [12][13][14][15][16][17][18][19] PZT material with a Zr/Ti composition around 52/48, produced industrially for piezoelectric applications, has been used often for emission experiments with reverse field direction. Industrially available materials of this type are mostly doped with a few percent of Nb or Nd.…”

“…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].…”