SU1485086A1 - Method of analysing excitation parameters of solid body surface - Google Patents

Description

The invention relates to the field of physical methods for studying the characteristics of the surface of a solid

The invention relates to physical methods for studying the characteristics of a solid surface.

The purpose of the invention is to provide the possibility of determining the cross section for the excitation of electron-stimulated desorption of ions on the surface of solids.

The method is as follows.

A submonolayer film of adsorbate containing at least two isotopes is applied on the surface of the sample under investigation in a vacuum of 10 10 Torr. Then the sample is irradiated with electrons with an energy not lower than the threshold excitation energy of electron-stimulated desorption of ions; measure the current of secondary particles, obra2

body. The purpose of the invention - Collateral ^- determination of possible cross sections of excitation of electron-stimulated desorption of ions from solid surfaces. To do this, a submonolayer film of adsorbate containing at least two isotopes is applied to the sample under test, the sample is irradiated with electrons, the work function is measured, * which determines the concentration of adsorbate on the sample surface, the relative content of adsorbate isotopes in the film is measured, the currents of desorbed ions of each adsorbate isotope are measured and According to the data obtained, the excitation cross section of electron-stimulated desorption is determined. 2 hp f-ly. ''

measured by one of the known methods of the work of the surface output with the applied film, determines the concentration M _{o of the} adsorbate on the sample surface, measures the relative content of K two adsorbate isotopes in a submonolayer film, measures the currents and ϊ desorbing ions of each adsorbate isotope and the measured values determine the cross-section of the process of excitation of electron-stimulated desorption of ions from the sample surface.

Depending on the nature of the adsorbate, there may be two cases.

When an adsorbate forms a predominantly ionic bond with the sample surface, the energy of the primary

"_5Ц. n "1485086 A1

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electrons choose no less than the threshold energy of Auger ionization of atoms of the sample surface.

When an adsorbate forms a bond of a predominantly covalent type with the sample surface, the energy of the primary electrons is chosen to be no less than the threshold energy of excitation or ionization of the valence electrons of the complex from the adsorbed particle and the atoms of the sample surface associated with it.

Based on the described set of operations, it is possible to determine the excitation cross section 0 of electron-stimulated desorption. To do this, use the following analytical expression:

15

+. +

Ω = sm, / h

20

·)

where = e [t7 / pts / (4ga ^ / t _g - 1);

mass of adsorbate isotopes;

the concentration of isotope .5 PA adsorbate with a mass of u,,

primary electron current;

relative ion yield of adsorbate isotopes.

“E

thirty

All operations of the method are carried out in vacuum ^ 10 ~ '° Torr.

Example. The method is performed in a high-vacuum chamber, where the pressure of the residual gases is reduced to P = 2 * 10 ' ^and torr with the help of a sorption orbitron pump. The substrate used dd tungsten textured tape 20x1h h0,01 size ³ mm with preferential access to the surface of the face (100)., Oxidized by exposure to oxygen. (6'10 ^'4 torr with ^"1) to form on the surface of the oxide layer 45 at T = 1300 K, free from residual gas impurities. The oxygen inlet is performed by thermal decomposition of barium peroxide. Then oxygen was evacuated and the surface is cooled to a temperature T = 300 K for application of the adsorbate (lithium t ₍₌ 6a, e., M _d = 7a, e.). Lithium deposited on the substrate is carried out filamentary evaporators by thermal decomposition hromatita lithium.

The amount of adsorbate deposited is controlled by the magnitude of the work function of the system, measured by the method of contact potential difference. The concentration of the adsorbate Ν _ο = 5-K? ** at / cm ^{2 is} chosen in the region of the sharpest concentration dependence of the work function. The relative content of isotopes K in the adsorbate film K = 1/20, it is measured by the method of thermal desorption spectrometry. The source of electrons is a tungsten filament with a diameter of 0.01 mm, placed parallel to the sample surface at a distance of 4 mm. The electron current density on the sample is 0.5 · 10 ' ⁶ A / cm ² , which excludes the possibility of thermal desorption from the surface.

The electron energy is set by the potential difference between the filament and the sample and is chosen equal to E = 100 eV, i.e. above the threshold. Such a choice of the energy of the bombarding electrons is due to the fact that near the threshold the current of the desorbed ions is small and lies on the border of the sensitivity of the recording equipment. At high energies of primary electrons, a sharp increase in the yield of ions is observed, and at energies above 80 eV, the dependence of the ion current on the energy of the incident electrons; goes to saturation. Therefore, the choice of the energy of primary electrons in the region of 100 eV reduces the error in measuring the magnitude of the ion current, eliminating the effect of fluctuations in the accelerating voltage.

I

An increase in the accelerating voltage above 150 V is impractical because it can lead to thermal desorption of ions due to the heating of the surface with a high-energy electron beam. The current of the desorbed lithium ions passes through a static magnetic mass spectrometer (resolution 200), which carries out the mass separation of the desorbed lithium ions by mass. Then the ions are fed to a channel electron multiplier (WES-b) with a gain of 10 ⁷ and further to an AI-1024 analyzer operating in the counting mode of individual pulses. The measurement error of the corresponding currents does not exceed 5% when the analyzer is operating in the signal accumulation mode. Under these conditions, the experimentally determined currents are as follows:

X, = (2.5 + 0.2). 1TG ' ⁴ A,

= (4.0 + 0.3) · 10 ^FROM A.

five

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The relative ion yield of lithium isotopes (5 = (1.2 + 0.1). Calculation of the cross section (cm ^) of the excitation of electron-stimulated desorption of ions by _

I ’e

the proposed formula gives the value

9 * · = (5.7 + 0.7) - Yu " ²¹ .

Claims (3)

Claim ten 1. A method for determining the excitation parameters of a solid surface, consisting in irradiating the surface of a sample with primary electrons with an energy not lower than the threshold excitation energy 15, measuring the current of secondary ions and calculating the desired excitation parameter using an analytical relationship that differs from The goal is to ensure that it is possible to determine the cross section for the excitation of electron-stimulated desorption of ions from the surface of solids; ynuyu film adsorbate comprising at least * two isotopes measured work function is determined by its largest concentration Ν _β adsorbate is measured relative zo K content two adsorbate isotopes • that on the sample surface is measured currents ίζ, and desorbing ions of each isotope adsorbate moreover, all these operations are performed in a vacuum ^ 10 ~ ^<o Torr, the measured values of determine the section C} * ^{- the} excitation of electron-stimulated desorption by the formula where oC - -4ga, 7sh _g 7 C-> | ha, / t _a '-1) _x w, and - the mass of the adsorbate isotopes, 'Ν „= Ν ^ Κ / (К + 1) is the concentration of the isotope with mass w <; ίβ is the current of primary electrons (5. / * / К "" - relative ion yield ' ¹ adsorbate isotopes. 2. The method according to claim 1, characterized in that an adsorbate film is applied to the surface of the sample, which forms a predominantly ionic bond with the surface, and the energy of the primary electrons is chosen to be no less than the threshold energy of Auger ionization of the surface atoms of the sample. 3. Pop method 1, characterized in that an adsorbate film is applied to the surface of the sample, forming a predominantly covalent type bond with the surface, and the energy of the primary electrons is chosen not less than the threshold energy of excitation or ionization of the valence electrons of the complex of the adsorbed particle and the surface atoms associated with it sample.