436. Mechanisms of photostimulated electron emission and emission centre generation processes in ionic crystals

Classified

abstracts

431-443 18

431. Secondary electron crystals. (USSR)

emission

of the

(111)

face

of tungsten

single

The secondary electron emission of the (I I I) fact of tungsten single crystals was studied in ultrahigh vacuum. The influence of the primary electron energy on the secondary electron coefflcicnt, the true secondary electron cocficient, and the inelastically rcflectcd electron cocficient were accurately measured, in the range 200-3000 cV. The tint structure on these curves was more pronounced with the tungsten crystal at liquid nitrogen tempcraturc than at room tcmperature. M V Gomoyunova and B Z Aliev, Fiz Twrd Tela, 11 (II), L)ec 1969. 3619-3621 (;,I R~sirr/r). I8 432. Energy spectrum of surface layers. (USSR)

ion-electron

emission

from

single

crystal

Mechanisms of electron emission from single crystal surface layers due to ion bombardment are analyzed, taking into account diffusion, retardation, and absorption of electrons generated in ion collisions with layer atoms. Calculation of the energy spectrum of emitted electrons from single crystal surfaces due to ion bombardment is based on the diffusion model of electron release. Calculations agree with experimental data. A S Dolgov, FL Tverd Tela, I1 ( IO), Ocr 1969, 28 I O-28 I2 (irr R~sirr~r). 18 433. Thickness of the surface stimulated emission in a CsBr

layer crystal

participating phosphor.

in electron (USSR)

thermo-

Rassiatr).

I8 Interaction graphite.

of lanthanum

hexaboride

with

molybdenum,

tantalum

(USSR) Lanthanum hexaboride is used as a vacuum thermionic emitter with low work function, which is resistant to air exposure. The interaction of lanthanum hexaboride with molybdenum, tantalum and graphite substrates is investigated over a broad temperature range. L M Cert et al, fzv Akad Naak SSSR Neog Mater, 5 (12). Dee 1969, 2198-2 I99 (in Rassiarr). 18 : 31 435. Field electron emission transition in a vacuum arc. (USSR) Disturbances in a field electron emitter caused by a vacuum arc were investigated. Pre-breakdown currents from the tungsten tip were measured and analyzed in a vacuum of IO-s to 10-O torr. The fluctuating character of the charge carrier motion in the vacuum gap was observed. G N Fursey and G K Kartsev, Z/I Tekh Fiz, 39 (I 0), Ocf 1969, 1917I9 I9 (in Russian). I8 436. Mechanisms centre generation

of photostimulated processes in ionic

electron crystals.

emission (USSR)

and

distribution crystals.

of electrons

originating

due

to interaction

of

(USSR) Experimental results arc presented for the ion-electron emission arising from Ar ion interaction with atomically clean copper, aluminium and silicon surfaces. It is shown that maxima in the energy spectra of cmittcd electrons are found for aluminium and copper. These maxima arc related to surface or bulk plasma oscillations in the crystal. Coefficients of ion-electron and ion-ion emission are measured in the energy interval 30-70 keV of the bombarding ions. V I Krotov et al, Radiorekh Elekirotr, I4 ( 12). Dee 1969, 22462249 (in Rmsiau).

18 439. small

Secondary energies

electron of primary

emission electrons.

of efficient

semiconductor

emitters

at

(USSR) Secondary electron emission properties of K,Te, Rb,Te, Cs,Te, Cs:,Sb and (Cs)Na,KSb efficient semiconductors emitters are investigated in the region of primary electron energies of I to 20 eV. Threshold energies for secondary electron emission are given. High values of the coefficient of elastically reflected electrons (0.7 to 0.8) at primary electron energies of I to 2 eV and small values of the first critical potential (4 to 6 eV) are explained, as in the case of dielectrics, as manifestation of the predominant role of slow electron scattering on phonons. L F Afonina

Radio/eklr

et al,

Elekrmrr,

14 (I 2). Dee 1969,

2237-2241

(iu Russian). I8

The thickness of the surface layer participating in electron thermostimulated emission in vacuum from the crystal phosphor, CsBr. is experimentally determined. It is found that this thickness corresponds to the penetration depth of electrons with energy of 3 keV in this crystal and amounts to 3 IO” A. The experimental results are discussed. A A Persinen et al, Fiz Tverd Tela, 11 (IO), Ocl 1969, 2902-2905 (irr 434. and

I8 438. Energy Ar ions with

emission

It is found that photoelectron emission from colour centres in ionic crystals, the so-called “photostimulated” emission, can arise as combined photo-thermionic emission (inner photoeffect connected with thermionic electron emission from the conduction band) besides the mechanism of normal photoemission. It is concluded that F centres are the main photostimulated emission centres in alkali halide crystals. Experimental results show that photostimulated emission can be successfully applied to the investigation of colour centres formation in thin surface layers. Kh F Kyaembre et al, RadiotekA Elektron, 14 (12). Dee 1969, 2216222 I (in Rassian). I8 437. Photoelectron emission of some polymers. (USSR) The work function of several polymers was measured by a photoelectron emission method. Polarization diminution of the ionization potential of isolated molecules was also determined. The experimental results are discussed. F I Vilesov et al, Fiz Tverd Tela, 11 (II), Nor, 1969, 3409-3410 (in

440. Some regularities in variations of the dielectric electron emission coefficient on electron bombardment.

layer

secondary

(USSR) Dependences of the secondary electron emission coefficients on the bombardment time and on the primary current density are investigated for beryllium, magnesium and barium oxide layers and also for sodium chloride layers. It is shown that observed changes of the secondary electron emission coefficient are due to formation of colour centres. Their recombination obey the monomolecular law. Parameters are evaluated which determine the secondary emission variation. A M

Tyutikov

and

1969, 223 l-2236

M

N Toiseva,

Rudiorekh

Elektron,

14 (12).

Dee

(in Russiaa).

I8 441. diode

Determination with spherical

of conditions electrodes.

for

virtual

cathode

formation

in

a

(USSR) The behaviour of vacuum diodes with spherical electrodes is investigated. The solution of the Poisson equation is used to determine the conditions for virtual cathode formation. A table including all of the practical range of potentials and electrode diameters is presented, which allows determination of the critical parameters. It is found that two possible values of the relation between electrode diameters correspond to each set of the potential and the critical current, as opposed to a plane diode, in which only one interelectrode distance corresponds to each set of the potential and the critical current. B V Eliseev and Yu P Mordinov, Z/I Tekh Fiz, 39 (l2), Dee 1969, 2169-2172 (in Russian). I8 442. Surface ionization threshold temperatures.

of readily

ionized

atoms

in the

region

of the

(USSR) On surface ionization of readily ionized atoms in uniform surfaces, the low temperature thresholds are observed, at which the ionization coefficient rapidly changes, from a value close to unity, towards zero. Investigation of the threshold temperatures as functions of the vapour pressure of the ionized elements and the electric field intensity at the adsorbent surface enables experimental determination of the desorption temperatures of adatoms in an ionized state as well as other desorption characteristics. The surface ionization of caesium on tungsten is examined. It is found that the surface ionization in this case is determined by the dependence of the ion and atom desorption temperatures on the surface coverage. Analysis of the experimental data affords characteristics of the atomic interaction with the adsorbent surface. N I Ionov et al, Z/I Tekh Fiz, 39 (lo), Ocf 1969, 1893-1904 (in Russian). 18 443. Investigation ultrasoft X-rays.

of some (USSR)

characteristics

of

electron

excitation

by

Photoelectron emission in vacuum due to ultrasoft X-rays was investigated for a number of photocathodes, prepared by vacuum evaporation on a stainless steel substrate. Using an electron multi219