Ferroelectric Electron Emission Research Articles

Violation of the conformity between the induction current and the emission current during the pyroelectric effect in a single crystal of lithium tantalate under vacuum conditions

A comparison of the induction current and the emission current during the pyroelectric effect under vacuum conditions with periodic variation in the temperature of a single crystal of lithium tantalate is presented. An increase in the variation frequency leads to suppression of the emission current, which prevents observing the effect of the optimal frequency with the maximum amplitude as in the case of the induction current. The conformity of both current forms is shown, except for the region of 2 mHz and less where an additional current wave is observed. It is established that this additional wave is initiated above a certain threshold of potential difference and leads to its stabilization. Keywords: pyroelectric effect, ferroelectric electron emission, pyroelectric accelerator, lithium tantalate.

Pyroelectric material property considerations for x-ray generation

The method of generating x-rays using the pyroelectric effect has garnered interest for applications that desire portability and low power consumption, particularly for real-time in-field and on-line analyses. However, the x-ray intensity produced by this type of x-ray generator is low and inconsistent compared to conventional x-ray tubes. The properties of several pyroelectric materials, including LiTaO3, LiNbO3, and PMN-xPT, were studied and subsequently tested on an in-house developed x-ray generator to explore their suitability for the application. The production of electrons to subsequently generate x-ray relies on the process of ferroelectric electron emission and field ionization to be dominant over charge compensation via the DC conductivity of the pyroelectric material. Given that the time of temperature change occurs faster than the material's charge relaxation time, it was found that the ratio of the pyroelectric coefficient to relative permittivity determined the performance of the x-ray generator. Thus, the x-ray count rates and end-point energies produced by LiTaO3 showed that it continues to be a strong candidate for such x-ray generation applications.

Effects of Thickness, Pulse Duration, and Size of Strip Electrode on Ferroelectric Electron Emission of Lead Zirconate Titanate Films

Sol–gel-derived lead zirconate titanate (PZT) thin-film emitters with thickness up to 9.8 μm have been prepared on Pt/TiO2/SiO2/Si wafer via chemical solution deposition with/without polyvinylpyrrolidone (PVP) modification, and the relationship between the film thickness and electron emission investigated. Notable electron emission was observed on application of a trigger voltage of 120 V for PZT film with thickness of 1.1 μm. Increasing the film thickness decreased the threshold field to initiate electron emission for non-PVP-modified films. In contrast, the electron emission behavior of PVP-modified films did not show significant dependence on film thickness, probably due to their porous structure. The emission current increased with decreasing strip width and space between strips. Furthermore, it was observed that increasing the duration of the applied pulse increased the magnitude of the emission current. The stray field on the PZT film thickness was also calculated and found to increase with increasing ferroelectric sample thickness. The PZT emitters were found to be fatigue free up to 105 emission cycles. Saturated emission current of around 25 mA to 30 mA was achieved for the electrode pattern used in this work.

High intensity electron emission from ferroelectric cathode induced by a pyroelectric crystal

A high voltage pulse generated by changing the temperature of a pyroelectric crystal was used to trigger a strong ferroelectric electron emission from a ferroelectric cathode. Different configurations such as a positive or negative pulse being applied to the front or back of the ferroelectric cathode were investigated. Negative pulse applied to the front of the cathode was found to generate the largest emission current and total charges. These differences in emission properties are interpreted using the mechanism of surface plasma assisted electron emission.

Effect of annealing temperature on ferroelectric electron emission of sol–gel PZT films

In this work, the influence of annealing temperature on the ferroelectric electron emission behaviors of 1.3-μm-thick sol–gel PbZr 0.52 Ti 0.48 O 3 (PZT) thin film emitters was investigated. The results revealed that the PZT films were crack-free in perovskite structure with columnar-like grains. Increasing annealing temperature led to the growth of the grains with improved ferroelectric and dielectric properties. The remnant polarization increased slightly from 35.3 to 39.6 μC/cm 2 and the coercive field decreased from the 56.4 to 54.6 kV/cm with increasing annealing temperature from 600 to 700 °C. The PZT film emitters exhibited remarkable ferroelectric electron emission behaviors at the threshold voltage above 95 V. The film annealed at 700 °C showed a relatively lower threshold voltage and higher emission current, which is related to the improved ferroelectric and dielectric properties at higher annealing temperature. The highest emission current achieved in this work was around 25 mA at the trigger voltage of 160 V.

Time-resolved properties of ferroelectric electron emission from [Pb(Mg1/3Nb2/3)O3]0.71[PbTiO3]0.29 single crystals

Ferroelectric electron emission (FEE) is an attractive and prospective application of ferroelectric thin film and bulk materials. Although extensive studies have shown that the emission is connected to a change of the ferroelectric polarization, the exact underlying emission process remained unclear to date. Here, FEE from ferroelectric relaxor [Pb(Mg1/3Nb2/3)O3]0.71[PbTiO3]0.29 (PMN-PT) single crystals was investigated by quantifying the amount of emitted electrons as a function of amplitude, pulse repetition rate, and pulse duration of the excitation voltage, hence clarifying the time-resolved emission process. It is demonstrated that FEE from PMN-PT can be described in the framework of a random field model, with the measured electron flux correlating with the amount of reversed polarization. Furthermore, our time-dependent analysis gives insight into the polarization switching and screening processes within PMN-PT. This allows us to draw general conclusions on the future applications of FEE.

Ultra-low voltage ferroelectric electron emission from lead zirconate titanate thin films with nanostructured top electrodes

Electron emission from thin ferroelectric Pb(Zr0.4Ti0.6)O3 films is demonstrated reaching emission current densities of up to 3×10-8 A cm-2 for pulsed excitation voltages of 60 V. Nevertheless, the emission process sets in at voltages as low as 10 V. Thin lead zirconate titanate (PZT) films were prepared with a structured top electrode, which exhibits nanometer-sized regularly arranged apertures. The emission current was measured under UHV conditions by both a single electron detector for small emission currents and an amperemeter for larger currents. The voltage dependent polarization state within the emission apertures was imaged using piezoresponse force microscopy and revealed that an increased fraction of the free surface area is switched by an increased applied voltage. This shows that the emission process is strongly correlated to the switching of ferroelectric polarization. Moreover, with the help of a metal grid in front of the detector, the maximum kinetic energy of emitted electrons was investigated and found to be limited by the excitation voltage, only.

Study on the characteristics of ferroelectric electron emission

Electron emission from ferroelectric cathodes 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, the electron emission properties of ferroelectric cathodes made of lanthanum-doped lead zirconate–titanate (PLZT) ceramic are studied. The electron beam spot shape was recorded via proximity-imaging techniques.

Technology of Ferroelectric Electron Emission

Electron emission from ferroelectric cathodes is commonly suggested as an electron source for different application due to its special characteristics such as high current density, easy treatment and operation, etc. The technology of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) ferroelectric cathode is introduced in this paper. Stable emission current is obtained from the PMN-PT ferroelectric cathode and the characteristic of ferroelectric electron emission is deal with as well.

Low-voltage pulse exciting electron emission from ferroelectric copolymer film cathode: Role of film thickness and emission stability

Ferroelectric copolymer thin films P(VDF-TrFE) are used as a ferroelectric cathode for investigation of their electron emission properties. This ferroelectric copolymer films with different thicknesses are deposited by spin-coating method, and then the annealing process is carried out to improve the crystallinities of as-deposited copolymer films. The measurement results of ferroelectric electron emission showed that the copolymer P(VDF-TrFE) films had a desired ferroelectric electron emission ability excited at low-voltage pulse, and its peak emission current can reach to be ∼1.3 μA when the pulse voltage is 280 V. In addition, the effect of film thickness on electron emission property and emission stability of copolymer thin film P(VDF-TrFE) are discussed.

Formation of Nanocrystalline Copolymer Thin Film PVDF-TrFE and Its Ferroelectric Electron Emission Property

Ferroelectric copolymer thin film PVDF-TrFE was deposited by spin coating method, and then annealed for the improved crystallization. The XRD and AFM measurements showed that as-formed PVDF-TrFE thin film was composed of the nanocrystallines with 50-80 nm in size and some amorphous phases. Meanwhile, as-formed PVDF-TrFE thin films also show a good polarization inversion property with a switch current of approximately 2.0 microA at a coercive field 40 MV/m. Electron emission testing results showed that under a continuous excitation of applied voltage pulses, PVDF-TrFE thin films exhibited an expected electron emission ability with emission current range of 0.08-0.52 microA, and the related electron emission mechanism was discussed.

Electron emission from ferroelectric thin films enhanced by the presence of 90° ferroelectric domains

In this work, a ferroelectric domain-enhanced electron emission mechanism is proposed. The polarization distribution near 90 degrees domain walls is calculated by solving a set of second order differential equations, including the Poisson's one and equations derived from an expansion of the free energy Phi(P) in power series of the polarization according to the Devonshire-Landau-Ginzburg theory. Domain walls intersecting the emitting surface cause sufficient electric fields and lower the potential barrier for electron emission. This induces centers of enhanced electron emission. Relaxing domain walls were found to excite trapped excess electrons in front of the wall.

Electron emission from ferroelectric copolymer thin films of vinylidene fluoride and trifluoroethylene

Electron emission from ferroelectric copolymer thin films consisting of vinylidene fluoride and trifluoroethylene (PVDF-TrFE) are reported. The ∼3μm thick copolymer thin films were deposited by spin coating and were then annealed to improve their crystallinity. The as-annealed films exhibited an electron emission capability, as anticipated; an emission charge within the range from 122to308pC∕cycle occurs at a positive excitation voltage with different excitation frequencies. It was found that the electron emission process of the PVDF-TrFE thin films differs from the conventional ferroelectric electron emission. A possible emission mechanism is proposed, which suggests that an amorphous phase in the polymer films plays an important role in trapping and emitting electrons.

Electron emission and phase transition of Zr-rich lead zirconate titanate ferroelectrics

This letter focuses on understanding the influences of antiferroelectric–ferroelectric (AFE–FE) phase transition on the ferroelectric electron emission process. The piezoelectric constant and electron emission current of un-prepoled PZT 96.5/3.5 ceramics as a function of emission times were studied. The hysteresis loops of PZT 96.5/3.5 ceramics before and after the electron emission process were presented. The results show that emission currents obtained from PZT 96.5/3.5 ferroelectrics in different phase states were similar. It was difficult to explain the experiment results using the fast AFE–FE phase transition model. Electron emission from PZT 96.5/3.5 ferroelectrics was independent of the AFE–FE phase transition.

Electron Emission from Barium Strontium Titanate Ceramics

This paper focuses on understanding the influence of materials' properties on the ferroelectric electron emission. Ferroelectric (x=1.0 and 0.8) and paraelectric (x=0.67 and 0.5) compositions of barium strontium titanate (BaxSr(1−x)TiO3) system were chosen for study based on their different ferroelectric and dielectric properties. Similar emission current waveforms were obtained from four compositions with negative triggering voltage applied to the rear electrode of the samples. It was difficult to explain the experimental results using the spontaneous polarization‐switching model. The mechanism of electron emission from BaxSr(1−x)TiO3 ceramics was ascertained to surface plasma emission.

Measurements of ion‐induced ferroelectric emission and surface charge dynamics on LiTaO3(0001) by time‐of‐flight scattering and recoiling spectrometry (TOF‐SARS)

AbstractWe have derived a special surface analysis method for studying surface charge dynamics on ferroelectrics from time‐of‐flight ion scattering and recoiling spectrometry (TOF‐SARS). In this method, shifts of the TOF‐SARS peaks of a ferroelectric crystal are measured as a function of sample temperature, and these spectral data are used to deduce changes in electrical potential on the sample surface. These changes are then converted to information on surface charge dynamics. In addition, the method is also applicable in extracting data regarding ion‐induced ferroelectric electron emission (FEE) from the TOF‐SARS spectra. In this work, we have tested the method with LiTaO3(0001) crystals having the nominal stoichiometry and single domain properties. Our results show that for temperature changes from 25 to ∼100 °C, the excess amount of surface charge induced by pyroelectricity, ion irradiation, and ion‐induced electron emission is drained mainly by surface conductivity. For temperature changes above 100 °C, the bulk ionic conductivity becomes an important charge drainage channel. Our measurements give an activation energy of 0.75 eV for the thermally activated ionic conductivity, and the result agrees well with the literature value previously obtained by d.c. conductivity measurements. Copyright © 2006 John Wiley & Sons, Ltd.

Energy-resolved analysis of ferroelectric electron emission from TGS using emission electron microscopy

Ferroelectric electron emission arises when the spontaneous polarization of a ferroelectric is switched due to the application of an electric field. In order to study the origin of emission and the related emission mechanism, space-resolved emission electron microscopy has been employed. The integral energy distribution of the emitted electrons from triglycine-sulfate surfaces has been investigated using a cylindrical sector analyzer and an imaging retarding field analyzer. Space-resolved emission photography and energy distribution measurements were obtained, revealing the effect of ferroelectric switching on the electric field distribution and hence on the emission process. Evidence of secondary electron emission from the metal electrodes has been found.

Visualization of field induced ferroelectric electron emission from TGS using emission electron microscopy

Field induced electron emission from triglycinesulfate (TGS) has been investigated using parallel imaging electron emission microscopy (EEM). The emission phenomenon has been induced by applying an ac electrical field up to 2 kV/mm to a single crystal of approximately 0.1 mm thickness. Emission patterns have been observed as a function of the applied field amplitude and of the crystal temperature. At voltages below the coercive field, no emission is visible. When approaching the Curie temperature, emission gradually disappears. This indicates an electron emission mechanism relying on the existence of a switchable ferroelectric phase. The information content of the images is discussed, an interpretation is given on the basis of existing theories.

C-Au-S Semiconducting Layers for PVDF Ferroelectric Electron Emission

Electron emission phenomena from PVDF (polyvinylidene fluoride) ferroelectric substance by polarization inversion were studied. However the electron emission was not observed. To discussion the reason, the electric field distribution on the substance was theoretically calculated using a charge simulation method. The field was distributed along the surface of ferroelectric substance between the teeth electrodes. It was supposed that the high surface insulating properties prevented electron flow and accumulation on the surface. Therefore C-Au-S layer was tried to use as semiconducting layer on PVDF surface to accumulate the electric charge. The ability of C-Au-S layer on the ferroelectric electron emitter was discussed.

Spectral measurements of gyrotron oscillator with ferroelectric electron gun

Since the discovery of the ferroelectric electron-emission effect, its implementation in microwave tubes has been impeded by various reasons and in particular by its relatively wide energy spread. Recently, a 1.5 kW microwave output from a gyrotron based on repetitive ferroelectric electron gun has been reported. This letter presents measurements of the spectral variations of the gyrotron output, and relates them to the electron-gun energy spread and to other inherent line-widening causes, such as the pulse length. The result shows that the contribution of the electron energy spread to the spectral content is not significantly larger than the other causes of line broadening.