Thermostimulated electron emission from polar cleavage of a triglycine sulfate crystal

This paper reports the results of experimental investigations into thermostimulated electron emission from the positive and negative cleavage surfaces of a ferroelectric triglycine sulfate crystal. It is shown that the current density j of emission from the negative surface is universally higher than that from the positive surface over the entire range from room temperature to the Curie point. The shape of the j(T) curves substantially depends on the degree of natural unipolarity of the studied samples. The results obtained are discussed in the framework of the mechanism of field electron emission from the surface electronic states.     

Thermally stimulated exoelectron emission of BeO: Excitation by low energy electron impact

The thermally stimulated exoelectron emission (TSEE) of oxide films on polycristalline Be substrates can be excited by extremely low energy electron bombardment (primary energies below 5 eV). The emission intensity as a function of primary energy is different for the two groups of high and low temperature glow peaks. A threshold of excitation for the glow maxima below 400°C cannot be measured down to excitation energies of 1 eV, whereas a resonance in the excitation function is found around 3.5 eV for the peaks above that temperature. These excitation functions are discussed in connection with the present emission concepts of BeO.     

Electron-beam induced reduction of carbon concentration on BeO and its effects on secondary electron emission

Electron-beam stimulated reduction of C concentration on BeO, which requires an oxygen ambient ～ 10^?7 torr, was studied using Auger spectroscopy. As the C Auger line decreases, those of Be and O increase, the secondary electron emission ratio δ increases, and the work function decreases. We have concluded that these effects stem from electron stimulated desorption of C. The desorption process is monomolecular, at least initially, with a cross-section of about 2.1 × 10^?20cm², from which we infer that the desorbing species is CO⁺. The adsorbed C, initially in the graphite form, can be converted to the carbide form by heat treatment as low as 450°C. This conversion is accompanied by a decrease in work function of 2.50 V from the value associated with the graphite C. The magnitude of the Auger electron signal from carbide C decreases under electron beam irradiation; however, in this case, the reduction in the magnitude of the C Auger line is not accompanied by any change in δ or yield curve. It is suggested that this decrease is not due to desorption of the carbide C, but rather to an electron-induced change in the C bonding state.     

Thermostimulated polariton emission of zinc selenide films on metal substrate

Angular dependences of the spectral radiance for bulk and surface polaritons in ZnSe films on an aluminium mirror have been investigated both experimentally and theoretically. A shift of a surface polariton branch to low frequencies has been observed. The difference between the surface polariton and the transverse optical phonon frequencies turned to be inversely proportional to the metal substrate conductivity. Theoretical results obtained are in good agreement with the experiment.     

Cryostat for low temperature x-irradiation and electron paramagnetic resonance

A cryostat for x-irradiation of solid samples at liquid air temperature is described. The design of the sample mount in the cryostat enables quick transfer of the sample after x-irradiation into EPR cavity to facilitate EPR study without warming the sample.     

Thermally stimulated exoelectron emission (TSEE) of BeO: Work function dependence

The TSEE of oxide films on Be foils has been investigated in ultrahigh vacuum with the facility of preparing clean oxide layers by argon sputtering and oxidation in situ. There is the possibility of monitoring the chemical state of the surfaces investigated by Auger spectroscopy via chemical effects in the Be-KVV line. Only surfaces oxidized in wet oxygen turn out to be TSEE-active and extremely stable emitters. Measurements of the thermionic work function demonstrate that low electron affinity values of the oxide surfaces are necessary to observe exoelectron emission. Clean oxide surfaces are found to be TSEE-inactive.Dedicated to Prof. Dr. Dr. Ing. E.h. W. Hanle on occasion of his 75th birthday.Part of thesis (D 26).     

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. PACS 68.37.-d; 77; 77.80.Fm; 77.80.-e     

Field electron emission improvement of ZnO nanorod arrays after Ar plasma treatment

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved after radio-frequency (rf) Ar plasma treatment. With Ar plasma treatment for 30 min, flat tops of the as-grown ZnO nanorods have been etched into sharp tips without damaging ZnO nanorod geometrical morphologies and crystallinity. After the Ar ion bombardment, the emission current density increases from 2 to 20 μA cm⁻² at 9.0 V μm⁻¹ with a decrease in turn-on voltage from 7.1 to 4.8 V μm⁻¹ at a current density of 1 μA cm⁻², which demonstrates that the field emission of the as-grown ZnO nanorods has been efficiently enhanced. The scanning electron microscopy (SEM) results, in conjunction with the results of transmission electron microscopy (TEM), Raman spectroscopy and photoluminescence observation, are used to investigate the mechanisms of the field emission enhancement. It is believed that the enhancements can be mainly attributed to the sharpening of rod tops, and the decrease of electrostatic screening effect.     

Upshifted electron cyclotron emission

The possibility of inferring the high energy part of the electron distribution function by means of its electron cyclotron emission is investigated. It is shown, with different set-ups, that the emission leaving the plasma perpendicular to the magnetic field cannot achieve this goal. A new configuration viewing the plasma from the low field side, oblique respect to the magnetic field -upshifted emission — is presented and its useful properties for localizing the electrons, responsible for the emission, in real and momentum space discussed.     

Theory of secondary electron emission

The fine structure in angle-resolved secondary electron spectra is shown to be related to the total reflectivity in low-energy electron diffraction (LEED). Theoretical results for tungsten are compared with experimental data. For non-normal emission, spin-orbit coupling is predicted to produce spin polarization of the emitted electrons.     

On low-field electron emission mechanisms

It is established by direct experiments that the main component of the stationary field-emission current in fields E<10⁵ V/cm is due to piezogeometric intensification (by a factor of 10³) of the electricfield at the end faces of piezoelectrically active films. An emission mechanism governed by electrons supplied by tunneling from the valence band of the piezoelectric is proposed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 823–827 (10 June 1997)     

Space-charge limitation of secondary electron emission

The paper deals with the calculation of the potential minimum due to the emission of true secondary electrons from a plane electrode. The results together with the corresponding limitation of the emission current are given in the form of graphs because an analytical solution of the problem is impossible.     

反铁电陶瓷的强电子发射特性研究

采用掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,研究了脉冲电压激励下陶瓷的电子发射特性.当激励电压为800V、抽取电压为0V时,得到1.27A/cm²的发射电流密度;当抽取电压增加到4kV时,获得1700A/cm²的发射电流密度.分析了发射电流随抽取电压的变化关系,讨论了反铁电陶瓷强电子发射的内在机理.结果表明：掺镧锆锡钛酸铅反铁电陶瓷能够在较低的激励电压(400V)下实现电子发射,发射电流远大于按照Child-Langmuir定律计算出的电流,三接点附近局域反铁电—铁电相变产生初始电子发射,初始电子电离中性粒子形成等离子体,增强了电子发射. 关键词： 铁电阴极 反铁电体 电子发射     

Test object for emission electron microscope

The resolution of emission electron microscopes approaches some nanometers, which leads to the need for new test objects. Microfields, which are almost always present at the sample surface, deform the trajectories of electrons forming the image. This leads to a distortion of the emission electron microscopy image and a decrease of lateral resolution. We propose a test object, where the influence of microfields conditioned by contact potential differences is compensated by a specially shaped relief of the sample surface.     

Field electron emission in graphite-like films

Results of investigation of carbon films deposited with the use of gas-phase chemical reactions in the plasma of a dc discharge are presented. Films obtained at different parameters of the deposition process varied widely in their structure and phase composition, from polycrystalline diamond to graphite-like material. Comparative study of the structure and phase composition of the films using Raman spectroscopy, cathodoluminescence, electron microscopy, and diffractometry, as well as the obtained field electron emission characteristics, have shown that the threshold value of the electric field strength for electron emission decreases with a decrease in the size of diamond crystallites and growth of the fraction of non-diamond carbon. The lowest threshold fields (less than 1.5 V/μm) are obtained for films consisting mainly of graphite-like material. A model based on the experimental data is proposed, which explains the mechanism of field electron emission in carbon materials.     

Shunting effect in explosive electron emission

An explanation is given to the results of an experiment on studying the explosive electron emission in a wire-cathode diode where a strongly nonuniform energy deposition into the wire material was observed using an X pinch as a radiation source for projection x-ray imaging. The specific input energy, contrary to the well-known observations, was not a maximum at the wire end, i.e., in the region of the strongest electric field, and the wire explosion occurred in the bulk, distant from the end. This is accounted for by the contribution of the wire side surface to explosive electron emission and by the gas desorption from the wire intensely heated by a current of density 10⁸ A/cm². Thus, the space between anode and cathode (wire end) is bridged by two plasmas: one generated due to the explosive electron emission from the wire side surface and the other produced from the desorbed gas.     

Ion-induced electron emission from clean metals

We report recent experimental work on electron emission from clean polycrystalline metal surfaces under ion bombardment. We critically discuss existing theories and point out the presently unsolved problems.     

Auger electron emission from fixed-in-space CO

We have measured the angular distribution of carbon K-Auger electrons from fixed in space, core-ionized, CO molecules in coincidence with the kinetic energy release of the C+ and O+ fragments. We find a very narrow ejection of Auger electrons in the direction of the oxygen and an oscillatory diffraction pattern. Even for similar electron energies, the angular distribution strongly depends on the symmetry of the final state.     

Diffraction effects in low-energy electron emission

The origin of diffraction peaks in the energy distribution of intensity of low-energy (< 1000 eV) electron emission from crystals is discussed from the standpoint of the dynamical theory of diffraction. The emitted electrons are considered to originate at relatively incoherent point sources in the crystal. The two-beam approximation of dynamical theory is used. The theory accounts for the chief regularities of diffraction peaks: temperature-dependence of peak intensities like that for low-energy electron diffraction (LEED) peaks, correlation of peak energies with X-ray absorption fine structure, and correlation of peak energies with the energies of normal-incidence LEED peaks in specular reflection. It is shown that the conditions for diffraction peaks coincide with the conditions for emergence of Kikuchi lines. It is predicted that for energies just above those of diffraction peaks, such emergences should be observable in the angular distribution of emission as intensity minima for emission along low-index crystal axes. Theory of Kikuchi band profiles is developed in an Appendix.