D. Shur

Electron emission from ferroelectrics

Electron emission from ferroelectrics (FEE) is an unconventional electron emission effect. Methods of FEE excitation are quite different compared to classic electron emission from solids. Two kinds of FEE have been observed, “weak” and “strong.” “Weak” electron emission (current density 10−12–10−7 A/cm2) occurs from polar surfaces of ferroelectric materials in the ferroelectric phase only. A source of the electric field for “weak” FEE excitation is an uncompensated charge, generated by a deviation of macroscopic spontaneous polarization from its equilibrium state under a pyroelectric effect, piezoelectric effect, or polarization switching. The FEE is a tunneling emission current which screens uncompensated polarization charges. It is shown that the FEE is an effective tool for direct domain imaging and studies of electronic properties of ferroelectrics. “Strong” FEE, which is 10–12 orders of magnitude higher than “weak” FEE, achieves 100 A/cm2 and is plasma-assisted electron emission. Two modes of the sur...

Plasma‐assisted electron emission from (Pb,La)(Zr,Ti)O3 ceramic cathodes

Strong pulsed electron emission has been observed from 12/65/35 lead lanthanum zirconate titanate ceramic composition in two different nonswitched phases at room temperature and at the temperature 100 °C. The electron emission parameters of this composition appear to be independent of phase for the two phases investigated. Fast photography and direct observation show that the strong electron emission occurs from the surface discharge plasma. The new experimental data make it possible to demonstrate the validity of the Child–Langmuir law for this electron emitter. A pulsed plasma lead lanthanum zirconate titanate ceramic cathode with burst frequency up to 100 kHz and collector current density up to 10 A/cm2 is developed.

Polarization switching in ferroelectric cathodes

A new mechanism of polarization switching and electron emission in ferroelectric cathodes is proposed. Surface flashover plasma of a ferroelectric origin was observed on a polar ferroelectric surface [D. Shur, G. Rosenman, and Ya. E. Krasik, Appl. Phys. Lett. 70, 574 (1997)]. Simultaneous measurements of switched charge and plasma density show that expanding surface plasma represents a dynamic switching electrode. Direct measurements of ion/electron emission currents and surface analysis implemented by different analytic tools indicate that electrons and ions from the surface plasma contribute to spontaneous polarization screening. The high energy of charged particles emitted from the surface plasma is ascribed to a high surface potential during polarization switching.

Surface discharge plasma induced by spontaneous polarization switching

A flashover plasma has been induced by spontaneous polarization switching on a polar surface of the ferroelectric crystal triglycine sulphate (TGS). The effect has not been observed in the paraelectric phase. The threshold switching voltage for a surface flashover ignition was as low as 100 V for pulsed and ac voltage. A mechanism of plasma initiation on a ferroelectric surface is proposed. It is assumed that the plasma is ignited by electron emission initiated by polarization switching. Subsequent electron avalanching occurs as a result of the high potential gradient along the ferroelectric surface caused by inhomogeneous polarization switching. Electrons and ions with energies up to several hundreds of eV were been recorded due to a high surface potential of the switched ferroelectric.

Copious electron emission from triglycine sulfate ferroelectric crystals

It is shown experimentally that the electron charge emitted from triglycine sulfate pulse ferroelectric cathodes can be as large as 129 μC/cm2. This charge considerably exceeds the measured value of spontaneous polarization, Ps=2.8 μC/cm2. A bipolar voltage is found to facilitate the appearance of the electron emission. It is proposed that the source of the emission current is the plasma of uncompleted surface discharges. This plasma is initiated at the metal‐vacuum‐dielectric triple points both by the field electron emission and the electron emission stimulated by polarization switching.

A high-perveance ferroelectric cathode with a narrowed electron energy spread

A pulsed ferroelectric electron cathode with a current density of up to 45 A based on ceramic is presented. The experimental set-up for the cathode triggering allowed us to achieve a perveance of more than P and an energy spread in the generated electron beam as low as 100 eV (FWHM).

Ferroelectric electron emission flat panel display

Ferroelectric electron emission observed under periodic spontaneous polarization switching is the basis for the development of a new type of flat panel display. Electron emission occurs from individually operated ferroelectric domains. It is shown that ferroelectric displays may be fabricated in ‘‘plane‐to‐plane’’ geometry which is not possible for field emission displays.

Lifetime of ferroelectric Pb(Zr, Ti)O3 ceramic cathodes with high current density

Electron emission from ferroelectric cathodes is investigated, it is commonly suggested as an electron source for different applications due to its special characteristics such as high current density, easy treatment, and operation. In this experimental research, a lifetime of lead zirconate-titanate ceramic cathode with composition related to a ferroelectric phase was studied. The strong plasma emission from the cathode was excited in a nonreversal (nonswitching) mode by application of unipolar high stress. Severe damage to the cathodes was observed, especially in a high repetition rate. An upper limit of the lifetime of the ferroelectric cathode with plasma-induced emission was estimated at about ∼106 pulses of ∼200 ns each at ∼100 Hz repetition rate. Possible applications of the limited lifetime ferroelectric cathode are discussed.

Figures of merit for ferroelectric electron emission cathodes

Pyroelectrically induced electron emission from different ferroelectric single crystals and ceramics is studied. It is observed that (Pb,La)(Zr,Ti)O3 ceramics generate rather low ferroelectric electron emission (FEE) current compared with single crystals such as triglycine sulphate and lithium niobate. Figures of merit for FEE cathodes in the pyroelectric excitation mode are derived. It is shown that a physical origin and consequently figures of merit are quite different for FEE cathodes and conventional field electron cathodes.

Diffusion-induced domain inversion in ferroelectrics

Abstract The basic property of ferroelectric crystals is switching of the direction of the macroscopic electric dipole moment under applying of an external electric field. Recently the polarization reversal effect without the external electric field has been discovered. It occurs under some treatments, namely, during proton-exchange. Ti,Rh-indiffusion in LiNbO3, out(in)-diffusion in LiNbO4, and LiTaO3, under Rb ionexchange and out(in)-diffusion at elevated temperature in KTiOPO4. The effect takes place at any polar surface and it is observed both far and near the Curie temperature. As a result a bidomain structure is formed. The diffusion-induced polarization reversal in ferroelectrics represents a new physical phenomenon and it is widely used in modern electronics and nonlinear optics. The studies of the effect are based on several traditional and new methods providing necessary data about the spontaneous polarization distribution and electrical parameters of these structures. In this paper, we review re...