MEETINGS AND CONFERENCES

CONFERENCE ON CATHODE ELECTRONICS

From November 25 to 29, 1955, a conference on cathode electronics was held in Kiev, at the Institute of Physics of the Academy of Sciences of the Ukrainian SSR, convened by the Council on Radiophysics and the Department of Physico-Mathematical Sciences of the Academy of Sciences of the USSR and by the Academy of Sciences of the Ukrainian SSR.

Representatives of research institutions of the Academy of Sciences of the USSR, the Academy of Sciences of the Ukrainian SSR, the Academy of Sciences of the Uzbek SSR, research institutes and industrial plants, and higher educational institutions took part in the work of the conference. The papers that were heard and the discussions testify to the considerable successes achieved by Soviet scientists and industrial workers in the field of physical and technical cathode electronics. The conference directed the attention of workers in science and technology toward the solution of a number of new problems of importance to the national economy.

Academician A. A. Lebedev opened the conference with an introductory address. N. D. Morgulis delivered a paper entitled “Some Results and Problems of Research in the Field of Physical Cathode Electronics.” The paper examined the principal questions, the present state, and the prospects of work on cathode electronics. In the field of the investigation of thermionic emission, major successes were noted, achieved in recent years in a large number of experimental studies and in the development of new types of cathodes. Attention was drawn to the wholly insufficient number of theoretical works and to the urgent necessity of generalizing the large number of experimental investigations devoted to the oxide cathode and of creating a theory of the real oxide cathode.

Much attention was devoted to investigations of metal-film systems aimed at creating cathodes with controllable electronic and adsorption parameters, and of new emission systems—above all, pulsed heated metals.

In the field of investigations devoted to autoelectronic emission, major successes achieved in recent times were also noted, as well as the topical importance of this question, connected with the following directions: a) the production of high emission densities and the first attempts to create devices of autoelectronic action; b) the development of electron and ion projectors and the investigation of the nature of the image given by them; c) the application of autoelectronic projectors to the study of surface phenomena; d) questions of autoelectronic emission in a gas discharge. The comparatively great prospects for the development of this field and the relatively small attention that has been devoted to it up to now were emphasized.

In the field of investigations of photoelectronic emission, a number of interesting experimental results were noted, especially important for the study of the energy structure of solids and of the exciton mechanism of the photoeffect. Attention was drawn to the necessity of a theoretical generalization.

of the results obtained. At the same time, the lag in the improvement of old and the creation of new effective cathodes, especially for the long-wavelength region of the spectrum, is emphasized. Some successes have been achieved in studying the simplest antimony-cesium cathode; however, the results obtained here also require theoretical generalization.

In the field of research on secondary electron emission, interesting results obtained recently were noted. Attention was drawn to the fact that the question of the relative role of electron excitation and of the kinetics of their motion in the phenomenon of secondary emission has still not been clarified. The great importance and prospects were emphasized of studies of discrete losses in solids, charge and induced conductivity of dielectrics, in particular in connection with the question of the direct conversion of the energy of radioactive radiation into electrical energy.

In the field of phenomena occurring when heavy particles strike a surface, the lag in research on the process of cathode sputtering and in the theory of this phenomenon was noted. Attention was drawn to the necessity of creating surfaces with an increased work function in order to expand the number of thermally ionizing elements, and to a number of interesting works in the field of secondary ion-electron emission, some of which have been carried out at a very high experimental level.

In conclusion, the necessity was noted of comprehensively accelerating work in the field of physical cathode electronics, of closely linking it with the work of the electrovacuum industry, and of conducting it using all modern methods of research and with the indispensable participation of theoretical physicists.

The reports and communications heard at the conference may be provisionally grouped according to the following problems:

THERMIONIC EMISSION

The survey report on this problem was given by B. M. Tsarev. The report analyzed the requirements imposed on thermionic cathodes in modern electrovacuum devices. The modern classification of thermionic cathodes and the degree to which the requirements placed on them when operating in various electrovacuum devices are met were considered. Criteria were given for evaluating the quality of cathodes. Considerable attention was devoted to analyzing further ways of improving old and creating new thermionic cathodes. The most promising directions were noted: a) creation of new design variants of existing cathodes (hollow cathodes, cathodes with a focusing beam of higher density using cathode optics). b) Development of film cathodes both on the basis of barium and of thorium (porous-film cathodes, cathodes with diffusion of the activator through the metal). c) Creation of cathodes based on borides. d) Development of complex cathodes (impregnated, pressed, sintered). Increasing the operating temperature of cathodes by replacing oxides with less volatile salts. e) Clarification of the possibility of creating cathodes based on cesium for operation in high-vacuum devices.

N. D. Morgulis reported the work “On the Physics of Porous Metal-Film Cathodes,” in which the results were presented of a comprehensive investigation of various physical properties of cathodes of this type with purely carbonate filling. An equation was derived for the diffusion rate of Ba through the pores of the cathode, assuming that the latter proceeds both by Knudsen effusion and by migration along the pore walls. The magnitude of the rate of evaporation of Ba and of the pressure drop in the depth of the cathode was estimated. An experimental determination of the elasticity of Ba and Sr vapors was carried out both over cathodes with different degrees of porosity and over free-

nium barium compound. On the basis of the results obtained, as well as of data from the literature, it may be concluded that the loss of Ba from the cathode occurs chiefly by Knudsen effusion through pores.

A mass-spectrometric determination was made of the composition of the residual gases during 100 hours of operation of the cathode in a laboratory apparatus, both in the emission-free and in the emission regimes. It was shown that the poisoning action of the residual gases and the splitting of the active barium film by ionic bombardment can exert a substantial influence on cathode emission. The paper also gives a calculation of the effective emission zone on the grains of the cathode surface, which leads to the conclusion that the distribution of cathode emission over the surface must be highly nonuniform. From consideration of the kinetics of the thermochemical reactions of BaCO₃ and of the products of its decomposition with tungsten and molybdenum, it is concluded that such a cathode must constitute a system: metal—semiconductor layer—film of Ba adatoms. This is confirmed both by electronographic analysis of the cathode surface and by the pronounced tendency of these cathodes to sparking.

In Ya. P. Zingerman’s report, “Electron emission of porous metal-film cathodes,” an experimental study was communicated of the thermionic emission of porous metal-film cathodes of end type with carbonate filling. The current-voltage characteristics of the cathode were studied in accelerating and retarding electric fields, measured both at very low (600–900° K) and at operating temperatures (1300–1500° K). At low temperatures the characteristics in the retarding field on the scale $\lg I_a = f(v)$ give a strictly linear dependence over a very wide interval of variation of the anode current (6–7 orders of magnitude). The electron temperature measured from these characteristics proved to be in good agreement with the cathode temperature. The characteristics in the accelerating field made it possible to establish the presence of spots in the distribution of work function over the cathode surface, with spot sizes of the order of $10^{-4}$ cm and with an amplitude of variation of the work function $\approx 0.3$–$0.5$ eV. The mean (2.1 eV) and minimum (1.75 eV) work functions of the cathode were measured. At operating temperatures it was experimentally shown that the cause of the anomalous saturation of the characteristic is the gradual saturation of emission from a cathode surface nonuniform in work function. A method was proposed for analyzing the characteristic which makes it possible to obtain the distribution curve of the saturation-current density over the cathode surface.

The subject “Influence of adsorbed films of dipole molecules on the work function of an electron from a metal” was treated in the report by N. D. Morgulis and V. M. Gavrilyuk. In the work the influence of an adsorbed CsCl film on the work function of W was studied experimentally. The experiments were carried out in a vacuum of $\sim 10^{-9}$ mm, using radioactive Cs¹³⁴ to determine the concentration of molecules in the film. The dependence of the work function $W$ on the concentration of CsCl molecules was determined. The fact that dipole CsCl molecules lower the work function of tungsten is interpreted as an indication of the presence at the metal surface of an orienting electric field. It is shown that the intensity of this field lies within the limits $10^6$–$10^7$ V/cm. The possibility is also suggested of an electronic exchange interaction of the molecule with the metal, which may lead to the appearance of an additional surface charge.

I. M. Dykman spoke on the communication “Change in the work function upon adsorption of dipole molecules on a metal surface.” The author carried out a theoretical generalization of the concepts of the adsorption of dipole molecules on a metal surface set forth in the preceding report. He showed that, in physical adsorption, the decrease in the work function

may be explained by the predominant orientation of the molecular dipoles by the electric field \(E\) acting at the metal surface and directed from the metal into the vacuum. The potential energy of a system of \(n\) dipoles adsorbed on a metal surface is calculated by the author with the aid of an effective electric field which, on the average, acts on each dipole. Its magnitude is determined both by the field \(E\) and by the field produced by all the dipoles. It is shown that the dependence of \(\Delta \varphi\) on \(\eta\) is always a function with a maximum. Several limiting cases are considered, making it possible to simplify considerably the formulas obtained. A comparison of the theory with the experimental data of N. D. Morgulis and V. M. Gavrilyuk (the CsCl—W system) and V. M. Gavrilyuk (the BaO—W system) is given. The values of \(E\) obtained in this way for these cases agree well with one another.

V. M. Gavrilyuk reported on the work “The influence of barium and barium oxide films on the work function of tungsten, gold, and germanium.” The author established the limits of variation of the work function for the above-mentioned systems and determined the dependences of the work function on the concentration of atoms or molecules in the film. Conclusions were drawn concerning possible mechanisms of the action of BaO films on the work function of metals in the spirit of the preceding reports. It was shown that, in order to explain the suppressing action of gold coatings on thermionic emission, the generally accepted notions of the removal of active barium from the surface of gold are insufficient. For this purpose the monotonic dependence of the work function of gold on the concentration of Ba atoms, established in the work, is absolutely necessary. It is shown that the effect of a BaO film on the work function of a semiconductor (germanium) is considerably smaller than in the case of a metal (\(\Delta \varphi = 1.2\) ev) and than in the case of a barium film on germanium (\(\Delta \varphi = 2.4\) ev). The dependence of the work function of a germanium film on a metal on its thickness was investigated.

The speaker K. B. Tolpygo noted in the debate that the thickness dependences of the work function of semiconductors in the absence and in the presence of surface levels will differ sharply. Therefore, investigations of these dependences can shed light on the question of the surface states of a semiconductor.

In the report by G. N. Shuppe, E. P. Sytogo, and R. M. Kadyrova, “Positive surface ionization of sodium and the work function of the (110) face of a tungsten single crystal,” the results were presented of an interesting investigation of thermionic emission and the emission of Na ions obtained by thermal ionization from different faces of a single-crystal tungsten wire. The value of the work function of the (110) face, determined from thermionic emission, proved to be \(4.8 \pm 0.1\) ev, whereas by the Saha—Langmuir formula this value is equal to \(5.3 \pm 0.1\) ev. Thus the work function of the (110) face of a tungsten single crystal is \(5.3\) ev.

V. G. Bolshov, in the work “Investigation of thermoelectronic and secondary emission at the melting point,” set himself the aim of measuring thermoelectronic and secondary emission at the melting point of Si and Ge. The author showed that thermionic emission does not undergo a jump at the melting point; however, in the case of Ge the work function changes with temperature from 2.5 to 3.5 ev. A different behavior is observed for secondary emission. The coefficient of secondary emission at the melting point of the above-mentioned substances changes discontinuously. The magnitude and direction of the jump depend on the nature of the substance.

Concerning the very small value of the work function of germanium presented in the report, P. G. Borzyak, N. D. Morgulis, K. B. Tolpygo, and others expressed a number of critical comments. The author asserted that the obtained value of the work function is connected with the high purity of the germanium he used.

D. G. Bulyginsky delivered a report on the topic: “Investigation of the distribution of the work function over the surface of an oxide cathode.” The speaker reported on a method that makes it possible to determine the distribution function of the area of an inhomogeneous cathode according to work function \( \beta(\varphi) \). The method is based on the assumption that the deviation of the delay curve, on a semilogarithmic scale, from a straight line in the region of transition to the saturation current is due to the gradual saturation of the emission current from cathode areas having different work functions. The author paid attention to the analysis and elimination of various factors that can cause distortions of the delay curve. The method was applied by the author to an oxide cathode on a core of silicon nickel. He obtained curves \( \beta(\varphi) \) for various states of activation and cathode temperatures, and concluded that each of the local work functions has a positive temperature coefficient, the larger the greater the work function. This conclusion agrees well with the ideas concerning the work function of a donor semiconductor.

Those who spoke in the discussion—K. B. Tolpygo, S. I. Pekar, and N. D. Morgulis—expressed critical comments regarding the speaker’s method, and also pointed out that this question had been investigated in 1952 by Ya. P. Zingerman.

In the work of Yu. G. Ptushinsky, “Investigation of the dynamics of formation of the blocking layer of an oxide cathode by the method of radioactive isotopes,” the dynamics of growth of the intermediate layer \(\mathrm{Ba_3WO_6}\), arising at the contact between the oxide coating of the cathode and a core of the alloy \(\mathrm{Ni-W}\) with an admixture of \(\mathrm{W}^{185}\), was studied. The author showed that the growth of this layer, i.e., the entry of tungsten from the core, ceases after the first 100–150 hours of cathode operation. The concentration of excess barium, released in the process of the reaction between \(\mathrm{BaO}\) and \(\mathrm{W}\) at the operating temperature, remains sufficient for normal operation of the cathode for thousands of hours, which may explain the long service life of such cathodes. The tungsten impurity in the oxide coating at \(1000^\circ\mathrm{C}\) over 200 hours does not migrate a distance greater than \(5\,\mu\).

D. P. Vinogradov reported the work “On the interpretation of the electron-optical image of an oxide cathode,” in which it is shown that the sharply inhomogeneous character of the electron emission of an oxide cathode observed in an emission microscope is caused by irregularities of the cathode surface. These irregularities create microlenses that collect electrons into beams, the size and shape of which depend on the geometry of the cathode surface. Thus, the cause of the nonuniform electron density in the plane of the image is established, but the existence in the oxide cathode of emission centers whose dimensions are much smaller than the magnitude of the surface irregularities of the oxide cathode is not denied.

E. P. Ostapchenko reported the results of X-ray structural investigations of systems of double and triple carbonates. The author’s previously published data on the crystal structure of the double and triple carbonates of Ba, Sr, and Ca are summarized. The regions of formation of various phases have been established, and a state diagram of the triple carbonates has been constructed. The speaker reported that the oxides Ba and Sr, when calcined together, form mixed crystals; the same picture is observed for the oxides Sr and Ca, whereas the oxides Ba and Ca do not give mixed crystals. When \(\mathrm{BaO}\), \(\mathrm{SrO}\), and \(\mathrm{CaO}\) are calcined together, the formation of mixed crystals is observed; however, if in a certain region a single-phase solid solution is formed, then at other ratios of the components two phases of the solid solution are formed. The formation of mixed crystals leads to a decrease in the work function. Data are presented on the process of decomposition of double and triple carbonates.

In the report by V. S. Parkhomenko, M. A. Chistyakova, G. A. Vostrova, and G. M. Kudryashova, “Investigation of the Emission Properties of Oxide Cathodes with Cores Made of New Nickel Alloys,” the results were presented of a comprehensive study of the emission properties of oxide cathodes with various cores, both in experimental diodes and in industrial tubes.

FIELD EMISSION

D. V. Zernov presented the survey report “Field Emission (State and Prospects).” The report considered the principal stages in the development and the present state of work in the field of theoretical and experimental study of the mechanism of field emission from pure metals and semiconductors, and discussed the prospects for using field-emission cathodes in technical electronic devices. The speaker devoted greatest attention to investigations carried out in recent years on thermofield emission of metals, field emission of metals at high current densities, and also to the latest theoretical works devoted to field emission from semiconductors. The potential advantages of the field-emission cathode in comparison with the thermionic cathode were indicated, as well as the shortcomings that at present hinder the introduction of this cathode into technical and electronic devices. Possible ways of eliminating these shortcomings were outlined. On the basis of a review of the published investigations, the speaker showed that the present state of work in the field of field emission is characterized by: 1) a quantum-mechanical theory of field emission from metals, essentially completed in its general outlines and having withstood comprehensive experimental verification; 2) a fairly well-developed theory of field emission from semiconductors, with a still insufficient number of experimental works in this field; 3) a comparatively good (though not yet fully perfected) technique for obtaining relatively stable, reproducible, and long-lived field-emission cathodes, the state of which makes realistic, in the more or less near future, the use of field emission in certain technical electronic devices.

In the report by A. P. Komar and Yu. N. Talanin, “Experiments with Electron and Ion Projectors,” certain results were presented that were obtained in working with an electron projector with a tungsten tip under conditions of a relatively poor vacuum ($10^{-7}$–$10^{-8}$ mm Hg). It was shown that the form of the tip in the authors’ experiments was the same as in experiments under a very high vacuum. The authors often observed the pattern of a so-called “ribbed” tip, or one “contaminated with carbon.” It is very stable and does not change even under high-temperature heating. The conclusion was drawn that, in the case of a “ribbed” tip, the authors are dealing with the form of a single crystal that is closest to equilibrium. Such a form of the single crystal can almost never be obtained under conditions of a very high vacuum; however, it is easily obtained if the tip is contaminated with carbon, which promotes the formation of an equilibrium structure. With strong contamination, the formation of tungsten carbide was observed. The surface of the tip is also contaminated by residual gases and by their compounds with carbon, which form readily mobile films observed in the projector. In this case the contaminants are two-dimensional crystals, which upon heating turn into a two-dimensional liquid. In the case of especially large contaminations during heating, it can be observed how the films descend from the tip one after another. As the surface is cleaned, the motion of the films slows down and then ceases altogether.

I. L. Sokolskaya reported on the work “Surface Migration in an Electric Field and the Bond Energy of Tungsten Atoms,” in which the process of surface migration of tungsten atoms on their own lattice in an electric field was studied with the aid of an electron projector. The speaker showed that the magnitude of the field-emission current at a fixed voltage can serve as a quantitative characteristic of the processes of change in the shape of a tip when it is heated in an electric field or without a field. It was also shown that the process of “restructuring” proceeds at the same rate independently of the direction of the field at the tip. The temperature dependence of the rate of restructuring in a retarding electric field was measured, which made it possible to protect the tip from ion bombardment and to carry out experiments in very strong fields without the risk of melting the tip by the electron current. The activation energies of the processes of restructuring and smoothing were also determined (2.36 and 3.2 eV, respectively). Interpretation of the results obtained on the basis of the ideas of Stranks and Frenkel enabled the author to calculate the interaction energy of two nearest neighbors in the tungsten lattice.

SECONDARY ELECTRON EMISSION

L. N. Dobretsov presented the review lecture “Secondary Electron Emission (State and Prospects).”

The phenomenon of secondary electron emission may be regarded as consisting of three consecutive processes: a) excitation of secondary electrons, b) their motion to the surface of the emitter, and c) escape of the excited electrons through the boundary of the body to the outside. Analysis of existing ideas about the mechanism of excitation of secondary electrons leads the author to the conclusion that the principal process determining the form of the law of energy loss by a primary electron and, consequently, the excitation of secondary electrons in a metal, is internal transitions of free electrons, while the number of interband transitions is small. In dielectrics only interband transitions and excitation of excitons are possible. Consideration of the motion of excited electrons toward the surface makes it possible to conclude that the principal type of interaction in metals determining the probability of electron escape to the surface is interaction with conduction electrons. Such consideration makes it possible to justify the form of the function for the probability of escape of secondary electrons to the surface, frequently used in semiphenomenological theories leading to the well-known “similarity law.” Using the expression he proposed for the law of losses in a metal, the author obtains a modification of the “similarity law” that agrees better with experiments. The speaker further considered the mechanism of escape of secondary electrons to the surface in dielectrics, as well as the question of the escape of secondary electrons through the boundary of a solid to the outside.

In the discussion, I. M. Dykman, N. D. Morgulis, P. V. Timofeev, A. I. Pyatnitskii, and others made a number of critical remarks. N. G. Nakhodkin presented data characterizing secondary emission from metals as occurring mainly at the expense of bound electrons. N. L. Yakopol’skii expressed the wish that work directed toward determining the type of loss law be developed.

V. G. Tel’kovskii delivered a report “Secondary Electron Emission of Metals under the Action of Ions and Neutral Particles.” The work presents the results of an experimental study of the secondary electron emission of pure metals (Mo, Zr, Ni, Ta, Cu) and graphite under bombardment of their surfaces by ions of hydrogen, helium, nitrogen, neon, argon, and molybdenum and by neutral atoms of inert gases with energies from several keV to 120 keV. The experiments were carried out on an appara—

novke of a new type, a large mass spectrometer with an ion arc source with a longitudinal magnetic field. The pressure of residual gases in the target region during the measurements did not exceed \(3\cdot 10^{-8}\) mm Hg. The temperature of the targets during the measurements was in most cases of the order of 1300–1500° C. Neutral particles were obtained by the method of resonant charge exchange. The author showed that, with negligible contamination of the target surface, the coefficient of secondary emission \(\gamma\) depends substantially on the flux density of ions or neutral particles. The work established that \(\gamma\) for all ions investigated in the target linearly increases up to velocities \(2\cdot 10^8\) cm/sec. For higher velocities (for protons) a broad maximum is observed (\(2.5\cdot 10^8\) cm/sec). The threshold of secondary emission is clearly expressed, and the values of the threshold velocities depend only weakly on the target material and on the kind of ions. The velocity distribution of secondary electrons is Maxwellian; the “temperature” of the electrons does not depend on the energy of the incident ions and lies within 5000–8000°. \(\gamma\) is strictly proportional to the number of particles entering the molecular ion. The magnitude of the ion charge does not change \(\gamma\), and secondary emission under the action of neutral atoms coincides with emission under the action of ions. Consequently, secondary electron emission is determined only by the energy of the incident particle, and not by its charge. The author concludes that the generally accepted autoelectronic theory of secondary electron emission does not correspond to reality.

A. R. Shulman reported the paper “Secondary Electron Emission of Dielectrics,” in which he set forth the results of an experimental investigation, by means of a pulsed technique, of the secondary electron emission of \(\mathrm{Al_2O_3}\), \(\mathrm{ThO_2}\), alkali-halide compounds, and a number of other substances. The author showed that the principal characteristic of secondary emission—the curve of the dependence of the yield on the energy of the primary electrons—for dielectrics has a form different from that for metals. In many cases there is a rather wide range of energies in which the coefficient of secondary emission does not depend on the energy of the primary electrons. The velocity distribution curves of secondary electrons also testify to a mechanism of secondary emission in dielectrics different from that in metals. The author measured the temperature dependences of the coefficient of secondary emission for a number of alkali-halide compounds. The speaker interpreted the data obtained on the basis of theoretical ideas about the mechanism of electron interaction in matter.

In another report by A. R. Shulman, “Inelastic Scattering of Electrons in Solids,” results were presented of an experimental investigation of the regularities of inelastic scattering of electrons by solids. The author paid special attention to the cleanliness of the surface of the substance. For this purpose a rapid method was developed for obtaining data on the energy distribution of electrons scattered by a solid. The speaker reported that the spectrum of inelastic scattering of electrons is a superposition of continuous and discrete spectra, while the characteristic spectrum of inelastically scattered electrons may be described in an approximation of weakly bound electrons.

D. A. Gorodetskii, in the report “Reflection of Slow Electrons from the Surface of a Pure Metal and of a Metal Covered with Adsorbed Films,” reported that he had carried out a study of the reflection coefficient of electrons with energies in the range from 2 to 10 eV from surfaces of polycrystalline and single-crystal tungsten, both clean and covered with adsorbed films of barium and oxygen, and also from surfaces of barium and silver. The measurements were carried out at a total pressure of the order of \(3\cdot 10^{-9}\) mm Hg and a pressure of the condensing component of \(10^{-10}\) mm Hg. The author showed that the coefficient of reflection of electrons depends much more strongly on the cleanliness of the metal surface-

tially, than the work function. The dependence of the reflection coefficient on energy for tungsten does not coincide with the course of the theoretical curve: an increase of this coefficient with increasing electron energy is observed. For thick layers of silver and barium deposited on tungsten, the normal course of the reflection coefficient is observed—a decrease in reflection with increasing energy. An adsorbed Ba film, simultaneously with a decrease in the work function, sharply increases reflection in the region of low energies. The reflection coefficient in this region passes through a maximum as the concentration of adsorbed atoms in the film is increased. The maximum corresponds to an optimal coating. This is in qualitative agreement with ideas concerning the formation of a maximum of the potential barrier upon deposition of an active film. A silver film on tungsten increases reflection without changing the course of the curve. A correlation has been established between the threshold of inelastic reflection and the work function of the metal.

U. A. Arifov reported on work carried out jointly with A. Kh. Ayukhanov on the topic “Some results of an investigation of the secondary emission of metals under ion bombardment, obtained by the oscillographic method of double modulation,” in which, using the double-modulation method developed by the authors jointly with S. V. Starodubtsev, a study was made of the energy distribution of secondary currents and of the coefficient of secondary emission as functions of the mass of the atoms and the temperature of the target, the density of atoms in adsorbed films, and the energy of the primary ions and other physical parameters when targets of W, Ta, Mo, and Ni and films of alkali metals were bombarded with positive ions Li, Na, K, Rb, Cs, and Ba. It was shown that, in the absence of contamination on the surface, the secondary-emission coefficient for these metals is very small \((\gamma < 1\%)\).

The report by V. N. Lepeshinskaya was devoted to the question “On certain anomalies characteristic of the secondary electron emission of magnesium alloys.” The speaker reported that the retarding-potential curves for secondary electrons when working with activated magnesium alloys possessing large coefficients of secondary emission have an anomalous character: saturation sets in at considerable positive potentials. Comparative measurements by various methods (static methods, as well as methods of single periodic pulses) showed that these methods give identical results. Only when the target is heated at the moment of measurement to a temperature of the order of \(400^\circ\)C does saturation of the retarding curve occur at about \(+1\) V. The author made an attempt to interpret the results obtained.

At the meeting a report by V. S. Kulvarskaya, “Alloyed nickel secondary cathodes,” was also heard.

PHOTOELECTRON EMISSION

P. V. Timofeev presented a survey report, “Electron emission from complex surfaces (state and prospects).”

The quantitative theory of complex emitters consisting of alkali or alkaline-earth metals and their compounds with oxygen or other substances is in an embryonic state. Experimental studies have shown that the magnitude of electron emission depends on the structure of the surface layer of the emitter and, in particular, on the amount of free alkali and alkaline-earth metal contained in it. Under appropriate conditions, positive charges arise on the surfaces of complex emitters in the course of irradiation by electrons; in the author’s opinion, these charges exert a substantial influence on the emission of electrons. As a result, large secondary-emission coefficients arise, and anomalous phenomena are observed, ...

...occurring in autoelectronic emission from oxygen–cesium photocathodes, and similar processes, for example, the fatigue of oxygen–cesium photocathodes. The distribution of electron energy levels in the surface layer differs substantially from the distribution of these levels in the bulk of the emitter. The thickness of the surface layer from which electron emission occurs in most cases does not exceed \(10^{-6}\) cm, and, consequently, electron emission must be determined by surface levels.

The author notes that for this reason one cannot agree with conceptions of the emission mechanism based on an energy scheme valid for the internal layers, and, in particular, with certain conclusions about emission properties drawn on the basis of measuring conductivity. In conclusion, the author repeats that emitters of the oxygen–cesium type at large gradients of the electric field at their surface and at a temperature of \(20^\circ\)C can emit positive ions.

In the work of P. G. Borzyak, V. F. Bibik, and G. S. Kramarenko, “Features of the photoeffect of silver–oxygen–cesium cathodes,” the authors attempted to elucidate the role, in the properties of the silver–oxygen–cesium photocathode, of its structural components: cesium oxide and silver crystallites. On the basis of a study of certain optical and photoelectric properties, first separately of dispersed silver films with reduced work function and oxygen–cesium films, and then of oxygen–cesium films with silver introduced into them, the authors came to the conclusion that the silver–oxygen–cesium photocathode cannot be regarded simply as a film of an impurity semiconductor whose photoelectric properties are determined by the atomic impurity of cesium and silver. In their opinion, the silver–oxygen–cesium cathode is a composite one, consisting of two parts: a semiconducting oxygen–cesium part, which determines the sensitivity of the composite cathode in the ultraviolet region, and a dispersed-metallic part, which determines the sensitivity of the composite cathode in the long-wavelength region.

Yu. A. Shuba presented the paper “The external photoeffect from cadmium sulfide.” Measurements made by the author of photoelectron emission from cadmium sulfide show that the distribution of photoelectrons by energies does not depend on the energies of the exciting quanta in the range from 2500 to 1900 Å. The characteristics of the external photoeffect in this spectral region change appreciably under simultaneous irradiation with visible light. Illumination in the region of the main optical absorption of cadmium sulfide decreases by several tenths of an electron-volt the thermoelectronic work function and the red boundary of the photoeffect and increases the quantum yield (by several orders of magnitude near the red boundary of the photoeffect). Opposite changes in the spectral and volt-ampere characteristics occur under longer-wavelength illumination. These changes in emission are apparently due to an internal photoeffect taking place under the action of the illumination. They are also observed in emitters of artificial cadmium sulfide layers. The author believes that a possible explanation of the character of the distribution of electrons by energies consists in exciton excitation of electrons.

In the report delivered on behalf of L. N. Bykhovskaya, “The influence of electron bombardment on the photoelectric emission of composite photocathodes,” it was shown that bombardment of the surface of oxygen–cesium translucent cathodes with integral sensitivity less than 20 \(\mu\)A/lm leads to a strong increase of photoemission in the long-wavelength region of the spectrum (\(\lambda > 600\) m\(\mu\)). The increase in photocurrent after bombardment is characterized by a sharp maximum (emission increases by a factor of 30–40) in the region of 950–1150 m\(\mu\) and a small maximum near 700 m\(\mu\). The increase in the sensitivity of cathodes grows with increasing current density...

of the bombarding electrons, and also with increasing bombardment time; it is proportional to the amount of electric charge received by the cathode during bombardment. The return of the sensitivity to its initial value upon illuminating the cathode with long-wavelength light occurs in several hours, while under the action of light with $\lambda < 500\ m\mu$ it occurs in several seconds. Bombardment of cathodes with an integral sensitivity greater than $20\ \mu\text{A}/\text{lm}$ causes a slight decrease in sensitivity in the long-wavelength region. It is shown that the increase in emission of these cathodes under bombardment is connected with the presence of cesium oxide on their surface. The sensitivity of cesium-antimony cathodes does not increase as a result of electron bombardment. It is concluded that the existing ideas about the mechanism of photoemission of complex cathodes do not at present give a complete explanation of the observed phenomena.

B. I. Dyatlovitskaya delivered a report, “The Photoeffect of Antimony-Cesium Cathodes Sensitized with Oxygen,” in which she presented the results of investigations of the optical and photoelectric properties of antimony-cesium cathodes sensitized with oxygen. The speaker established that sensitization: 1) does not appreciably affect the optical properties of antimony-cesium layers, 2) leads to a significant increase in photoemission throughout the investigated spectral interval $(400—730\ m\mu)$. These results are regarded as evidence that sensitization leads to a lowering of the potential barrier $\Delta = 0.1\ \text{eV}$. The latter, by virtue of the intrinsic character of the photoeffect, leads to a significant increase in photoemission. When the cathode is treated with oxygen in an amount considerably greater than that necessary for optimal sensitization (poisoning), a change is observed in the optical characteristics of the cathode, i.e., a change occurs in the structure of the cathode.

In the work of V. M. Gavrilyuk, “The Influence of Adsorption of Dipolar Barium Oxide Molecules on the Photoemission of an Antimony-Cesium Cathode,” an attempt was made to control the work function and the photoemission of a semiconducting antimony-cesium cathode by adsorbing dipolar barium oxide molecules on its surface. The author established that adsorption of barium oxide molecules at the optimum leads to a decrease in the work function of the cathode by approximately $0.1\ \text{eV}$ and to an increase in the photocurrent by approximately a factor of $1.5$. Comparison of the results of the work with the data of B. I. Dyatlovitskaya (the preceding report) allowed the author, following G. A. Morozov and B. I. Dyatlovitskaya, to conclude that the mechanism of sensitization of the antimony-cesium cathode by oxygen consists in the formation, on the cathode surface, of dipolar cesium oxide molecules.

N. M. Politova delivered a report, “Investigation of the Kinetics of Photoelectrons from an Antimony-Cesium Cathode.” The speaker pointed out a discrepancy between the values of the work function calculated from Einstein’s equation and the photoelectric work function determined from the red boundary of the photoeffect for an antimony-cesium cathode. The first value is appreciably smaller than the latter and increases with increasing quantum energy. This shows that the value of the maximum energy of the photoelectrons does not correspond to the usual ideas about the mechanism of the photoeffect from an antimony-cesium cathode.

OPERATION OF THE CATHODE UNDER CONDITIONS OF ION BOMBARDMENT AND GAS DISCHARGE

G. V. Spivak, I. N. Prilezhaeva, and V. E. Yurasov presented a report, “On Processes on a Metal Surface during Cathode Sputtering,” in which the results of investigations of the microrelief arising on the metal surface during cathode sputtering were presented. The authors showed that, in this case, as a result of increased migra-

tion, as well as condensation on the metal surface, terraces arise bounded by equilibrium planes, which is in agreement with the theory of crystal growth. The possibility was shown of using cathodic sputtering to reveal the structure of a metal, including at elevated specimen temperatures. The influence of gas purity on the process of ionic etching was also investigated.

N. D. Morgulis and V. D. Tishchenko, in the report “Cathodic Sputtering in the Near-Threshold Region,” described their use of the labeled-atom method to investigate the threshold of cathodic sputtering of a whole series of metals by Ar and Ne ions. The work showed that the threshold energies have very small values (3–20 eV), much smaller than the corresponding values cited recently in the literature. A correlation was established between the magnitude of the threshold energy and the melting point of the sputtered metal. The authors also obtained data indicating a dependence of the threshold energy on the mass of the sputtering ion and its independence of the mass of the atoms of the sputtered metal.

E. M. Belavtseva reported on work carried out jointly with A. I. Frimer and A. M. Gerasimova, “Electron-Microscopic Study of the Structure of Photocathodes Exposed to Gas Discharge.” The authors showed that, under the action of a self-sustained gas discharge, oxygen–cesium and antimony–cesium cathodes exhibit insignificant changes in structure and a change in sensitivity. A glow discharge strongly destroys the surface of cathodes and causes a complete loss of sensitivity. After exposure to this discharge, the surface of an antimony–cesium cathode has a clearly expressed dispersed structure of an unfinished cathode. Thick bismuth–cesium cathodes exhibit deep structural changes and an increase in sensitivity. A self-sustained discharge causes comminution of crystallites. A glow discharge causes the appearance of structure and the spalling of crystals. The illuminated areas are destroyed more strongly than the unilluminated ones. Particles of the sputtered material form a photocathode with a fairly high sensitivity and a highly dispersed structure.

In the report by E. M. Reikhrudel and A. G. Zimelev, “Properties of a Cathode with an Ignition Device in a Pulsed Discharge at Low Pressures,” some results were presented of an investigation of the emission and electron-optical properties of a cold cathode with an ignition device, and the possibilities of its application in pulsed electronics were indicated. A cold cathode with an ignition device in high-voltage electron devices makes it possible, in a microsecond pulsed regime, to obtain currents of the order of 1000 A. The current density reaches \(10^{4}\ \mathrm{A}\cdot\mathrm{cm}^{-2}\). The cathode can operate in a high vacuum and over a wide range of gas pressures (from \(10^{-6}\) to \(10^{-1}\) mm Hg). The authors showed the possibility of controlling, in the initial phase of discharge development, an intense electron beam by means of fields acting near the cathode surface, and proposed a method for calculating the beam diameter. The cathode was used to create powerful pulsed sharply focused X-ray tubes, and also in a pulsed gas-discharge ion source. A cathode in the form of a molybdenum disk 3 mm in diameter operated for a long time, withstanding more than 300,000 pulses.

At the Conference there was also heard a report by V. G. Granovskii and N. B. Rozanova, “Phenomena at Electrodes during Powerful High-Vacuum Breakdown.”

In conclusion of its work, the Conference adopted a detailed resolution outlining the principal tasks of workers in science and technology in the field of cathode electronics.

V. M. Gavrilov