SU1534550A1 - Electronic spectrometer - Google Patents

Abstract

The invention relates to electron spectroscopy technique used to study atoms, molecules of a solid, surface. The aim of the invention is to enhance the functionality of a prism type spectrometer, increasing its sensitivity and resolution. To achieve the goal, a switch of 6 modes of operation is introduced into the electronic spectrometer, with curvilinear gap gaps made along arcs of second-order curves, and the electrodes of the energy analyzer connected to an adjustable power supply 3. The drawing also shows a series of ionization sources 1, a receiver 2 electrons, a control system 4, an electrostatic energy analyzer 5. In the spectrometer it is possible to change the position and shape of the slit gaps of the lens and thereby increase its sensitivity and resolution. 7 il.

Description

The invention relates to techniques for electronic spectroscopy used to study atoms, molecules, solids, surfaces.

The purpose of the invention is the expansion of the analytical capabilities of the prism type spectrometer, an increase in its sensitivity and resolution.

The essence of the invention lies in the fact that when using systems that are free of transaxial symmetry, ed and in the collimator and fixing lenses of the spectrometer, thereby removing the restrictions imposed by the law of conservation of the azimuthal component of the particle momentum, the possibility is obtained, first of all, by changing when calculating spectrometer position and shape of the slit gaps of the lens, optimize its design according to various parameters and thereby increase the sensitivity and resolution of the spectrometer, and On the other hand, changing the potential ratios at the analyzer electrodes with the help of a switch, it is possible to quickly change, within a wide range of design parameters, the main characteristics of the spectrometer and thereby significantly expand its analytical capabilities in comparison with the known spectrometer.

The implementation in the energy analyzer of the well-known gap-gap spectrometer along arcs, which are second-order curves with spaced centers of curvature or evolutions, is necessary to reduce the spectrometer aberrations, to inform the spectrometer of the ability to work at various degrees of particle deceleration in the lenses, at different values and their cardinal positions elements, which provides an increase in the resolution and sensitivity of the spectrometer, its operation in modes with different ionization sources, with high aperture or with an expanded field of view. The switch of operating modes is necessary for the operational change of potential relations on the analyzer electrodes and thereby the transition from one spectrometer operating mode to another.

Figure 1 shows a block diagram of an electronic spectrometer; figure 2 and 3 is an electrostatic prism energy analyzer in projections on the horizontal and vertical plane (in addition, figure 2 shows the electric power supply circuit of the energy analyzer) *, figure 4 is a diagram illustrating the process of optimizing the design of the energy analyzer of the spectrometer for various parameters.

The spectrometer (Fig. D) contains a number of sources of ionization AI ^, AI II _P , 2 electron receiver, adjustable. source 3 of electric, power, control system 4, information collection and processing and electrostatic energy analyzer 5. The electrodes of the energy analyzer are connected to the power source through a switch 6 operating modes. The vacuum system of the spectrometer in figure 1 is not shown.

Fig. 2 schematically shows the projection of the electrode system of the energy analyzer on its longitudinal (horizontal) plane, and in Fig. 3, on a vertical plane, which is parallel to ON in section I, in section II - NN * and in section III No. ', i.e. . is the plane of the axial section of the beam. The cross section of an electron beam exiting from the central point of the entrance slit 7 (object), electrodes 8-10 of the prism, electrodes 11-14 of the collimator lens and electrodes 15-18 of the focusing lens, and slit 19 of the electron receiver are also shown. The points O »and 0 _O show the calculated positions of the centers of curvature of the gap gaps between the electrodes 14, 13 and 12, II, made along arcs of circles with radii r ₄ and R _? and dashed lines E ₂ and E _{4 the} position and shape evolute gap gaps between the electrodes 13, 12 and 11, 10, made along arcs, which are curves of the second order of variable curvature. The curvature of each gap gap is determined by the curvature perpendicular to the horizontal plane of the cylindrical surface, dividing this gap in half, and its width is selected for reasons of ensuring the electric strength of the structure and has the same value throughout. Therefore, the edges of the electrodes, limiting one slot, have a common evolute and, in particular, with a circular shape of the gap, the common center of curvature In a particular design, the shape of the gaps and their number is determined by calculation based on the optimization of the analytical capabilities of the device and its dimensions.

The voltage divider 20 of the regulated electric power source is selected from resistances 21 connected to the switch 22 of the spectrometer operation modes.

The spectrometer works as follows.

Electrons emitted from the sample enter the analyzer through an input slit 7 located in the front focal plane of the analyzer. A diverging beam with a solution defined by the opening of the aperture diaphragm comes out from each point of the slit. Using a collimator lens, the beam is formed in such a way that in the projection onto the horizontal plane it turns into a parallel one (Fig. 2). An electron prism decomposes this beam into a series of fragments, each of which is a parallel beam corresponding to electrons of a certain energy. Images of the entrance slit corresponding to different particle energies are formed by a focusing lens in the rear focal plane of the analyzer. Slit 19 of the electron receiver is installed in this plane on the electron-optical axis of the device, and the spectrum is taken by measuring the magnitude of the recorded electron current when the potentials on its electrodes

In the vertical plane (FIG. 3), a series of intermediate linear electronic images of the entrance slit 7 are formed in the analyzer.

Switching the spectrometer to various operating modes is accomplished by switching potentials on the analyzer electrodes using the 22 mode switch. Figure 2 shows the electrical circuit of the switch and voltage divider 20, corresponding to the given specific example. The voltage U of the regulated power source is related to the energy Ej of the analyzed particles, to which the device is tuned, by known ratios. If particles are on different sections of the path in the analyzer acquisition. Ί.534550 6 melt energy as large E _о , and less E _fl , then

U = E · (V - V) (Г woke * min '”if the energy E of the particles is not less than Е _о , then ^u = ^E ” < ^v ““ _t -'> · (la) of the path

If all the way ΕέΕ, then (1c)

In expressions (1a) - (1c), V _{MaKC is the} maximum, and V _Min is the minimum of all possible potential values on the analyzer electrodes, measured in units of E _о .

The magnitude and type of resistance of the divider 20 are selected from the requirements for stability and other parameters of the power source. Switch 22 connects each electrode in a given analyzer operation mode to a divider point corresponding to voltage ^U i, j = - О, (2) where the symbols i and j denote electrodes and modes;

V; j is the potential at the electrode, also measured in units of E _о „

I

When the operating mode of the prism analyzer is switched, the positions of its focal planes remain unchanged, and the focal lengths of the collimator and focusing lenses change. This ensures that the analyzer gives new values of linear dispersion, resolution, aperture, and field of view.

In the process of calculating the electron-optical scheme of the energy analyzer, by varying the shape (within the family of second-order curves) of the curvilinear gap gaps and their position, as well as the potentials on the electrodes, it is possible to increase the sensitivity and resolution of the spectrometer already in the paraxial approximation. In addition, the analyzer of the proposed spectrometer provides an increase in sensitivity and resolution compared to the known one due to the reduction of spherical aberrations. The analyzer aberrations are determined mainly by the '1534550' third-order spherical aberrations of the smallness of the collimator and focusing lenses = C, cZp ² + С _г ού \ (3)

- aberrational broadening of the image of the source gap in a direction parallel to the longitudinal plane;

- aperture angles in the longitudinal and transverse planes, respectively;

C ^ and C ^ -. aberration coefficients.

The use of lenses that do not have rotational symmetry in the present invention can significantly reduce or even reduce to zero the coefficients C <and C ₂ . So, the coefficient. C (reduces to zero even when using the gaps between the electrodes cut along the arcs of circles, by a special selection of the radii of these circles and the positions of their centers of curvature. In order to reduce both coefficients to zero, it is necessary to use electrodes cut along arcs of specially selected non-circular shape and spaced evolute solution of such problems in the construction ^svetoop-;.! cal systems achieved relatively simply, for example, the spherical aberration of the glass lenses can be reduced to zero if.. ezhdu radii R ₄ and R ₂ surfaces bounding the lens, its thickness Di ^ relative refractive index ratio η of glass is provided

Rl - R <_ (η ² - 1) (η + 2) h. —I ------ '

It is possible to make the lens devoid of spherical aberration if, for example, the surface facing the image is made along a sphere with a radius R equal to the focal length f of the lens *; and the second surface - along an ellipsoid with eccentricity ξ and the main semiaxis a, the requirements ε = ι, a30 satisfying __fn η + ί (5) (5) are written

Expressions (4) and for the case of location: the subject at infinity;

As an example, we give the calculation results obtained in the development of a specific electronic spectrometer designed to study surface phenomena in several modes, corresponding to the excitation of the sample by X-ray, ultraviolet radiation, electron impact, as well as in modes with increased aperture at a moderate size of field of view and with an expanded field vision with moderate aperture. In the energy range of 1003000 eV (when using an x-ray or electron gun as the ionization source), the relative resolution of the spectrometer should be no worse than 0.1% with the width of the investigated surface of the sample 1 mm.

When reducing the width of 0.1 mm resolution should be better than 0.03% in the low energy region (for _n sample ultraviolet ray excitation) 'absolute resolution should be better than 30 mV at an energy of _about 10 eV maximum aperture analyzer better than 1 % of 2ΐ “, and the area of the analyzed surface of the sample. up to 4 mm ² about

The type of prism (decelerating or accelerating) of the energy analyzer, the angle at its apex, the angle of incidence on the prism, the distance between the prism and the collimator and focusing lenses, the degree of deceleration or acceleration of particles in the lenses are selected from the considerations of ensuring the required energy dispersion, given dimensions, capabilities · the implementation of electrical power, the exclusion of mutual overlap. fields of a prism and lenses in the same way as was done in the well-known spectrometer.

The design of the energy analyzer is symmetric with respect to the plane PP (figure 2). The angle at the apex of the prism is J = 40, and the angle of incidence of the beam on the prism is Θι = 70 °. Removing the point of intersection of the axial trajectory with the PP plane from the gap between the electrodes 8 and 9 4.9d, where d is the distance between the plates of one electrode. The width of the electrode is 9 2.13d. The length of the electrode 10 common to the prism and lenses, counted along the ON axis, is 12.5d. The exit slit 7 is 8d away from the nearest curved lens slit.

To work in the energy range of 100-3000 eV, it is proposed to use a 16-times slowing collimator and 16-times accelerating focusing lens. In the energy region below 20 eV, it is proposed to use a single lens.

The potential V _c at the intermediate electrode of the three-electrode lens can be of an intermediate value in comparison with the potentials at the extreme electrodes or exceed them. The cases when V _{c is} less than the potentials at the extreme electrodes have no practical value due to large distortions of the beam formed in this mode.

The ability to independently select the curvature of the gap gaps allows using two unified three-electrode lens design to provide two modes of operation of the spectrometer. This feature is illustrated by the graphs of FIG. 4. Here are the results of calculating a collimator lens consistent with the described prism. The abscissa shows the radius of curvature of the second slit of the lens. Curves 1a and Gb show the curvature of the first slit at which the desired focus mode is implemented. Curves 2-a and 2-6 show the potential values V _c necessary for this mode, measured in units of potential V _o at the entrance to the lens.

Curves 3a and 3b are the maximum effective slit height determined by the analyzer's field of view. .

The data of the graphs in Fig. 4 were obtained for a lens slowing down electrons by 16 times and with a constant width of the intermediate electrode S = 6, Id. The graphs show that for each R ^ there are two values of R ₍ which, with the corresponding value of V _c, provide the required focus.

Moreover, the point M of intersection of curves 1-a and 1-6 defines a single three-electrode system that allows only some change in potential V _c to switch from one mode to another. One of them, as can be seen from figure 4, provides a larger field of view, but the second, as will be shown, a larger aperture. Note that the contribution of lens aberrations to the resolution of the spectrometer in both

1534550 Yu modes is small. The broadening of the instrument line, due to the coefficients C (and, in both modes, less than 0.02%.

Thus, the graphs of $ 4 illustrate the process of optimizing the design of the lens in order to provide a single three-electrode lens system of two different modes of operation of the ed spectrometer.

Similar calculations were performed for a number of lens families with constant S. For each family, as in FIG. 4, point M was found. The analyzer parameters corresponding to this point are shown in FIG. 5. Here, it is shown how, with a change in 8, the analyzer luminosity Q (curves 1-a and 1-6) changes, the limiting effective height of the electron-optical object h _n (curves 2-a and 2-6) and the contribution of AR aberrations of the collimator and focusing lenses to the resolution of the spectrometer (curves 3-a and 3-b). The curves show that for

S = 6, Id, in one of the modes, the maximum aperture of the analyzer is observed, although the value of h _n is small. With the same S in the second mode, a significant height of pre30 meta-O, 35d is provided. If, as in the well-known spectrometer, d = 12 mm is chosen, then this value of h _n satisfies the requirements set in the calculation of the analyzer. Thus, two analyzer operation modes were determined35. A lens with an intermediate electrode width of S = 6, Id was chosen, which ensures the optimum value of aperture in one of the modes, and in the other, the height of the electron-optical object h _n that meets the set requirements. The radii of curvature of the slits of this lens are 5.60d and 9.95d. It provides two modes of operation of the analyzer at two values of V _c = 0.273 V _Q and V _c = = O, 178V _o .

The mode with the highest aperture of the analyzer is realized when a potential is applied to the intermediate electrode of the lens greater than the potentials at the extreme electrodes. This lens uses one of the slits already found, namely, a slit with a radius of curvature of 5.60 d. By changing the width S of its intermediate electrode and choosing the curvature of its second slot and the potential that provide the required focusing of the analyzer, it is possible to show light siphon S = ¹ e like 5, as it was in FIG. 5, that the maximum analyzer la is achieved = l, 5d. At the same time, -52 ~ 1.4% of 2'8

At _c = 3.8 V _o , and the effective height of the electron-optical object h _n = 0.025d. The radius of curvature of the second slit of this lens was 6 _t 96d. Thus, the lens design was found to provide maximum spectrometer luminosity ”

Similar calculations were performed to find a single lens. As its first slit, the previously found slit with a radius of curvature of 9.95d was used. In a single lens, spherical aberrations are significant. Therefore, its calculation was set so as to minimize these aberrations. Fig. 6 shows the results of the calculations. The abscissa shows the width S of the intermediate electrode of a single lens. · Curve 1 describes the radius of curvature of the second slit of this lens, and curve 2 describes the potential on its intermediate electrode, which provides the required focus. Curve 3 characterizes the change in the aberration coefficient C <, and curve 4 of the coefficient changes Si

In accordance with the data of FIG. 6, a lens with 8 = 2.5d was selected as a single lens, for which C ₄ = 0 (with ₂ , S changes little with a change in S, and its contribution to resolution is small). The potential V _c for such a lens was V- _c = 4.50 V _a . The radius of curvature of the second slit is 7.28d. The aperture ratio of the analyzer in this mode is 0.2% of 2 ^, and the maximum height of the electron-optical object is 0.33d „

Thus, the choice of the geometric dimensions of the elements of the energy analyzer was completed. Following the notation of FIG. 2, we present these dimensions. The length of the lens electrodes counted along the electron-optical axis: electrode 4 - 2.5d, 5 - 4.60d, 6 - l, 5d. The radii of curvature of the gap between the electrodes: 7 and 6 - 5.60 d, 6 and 5-6.69 d, 5n4 - 9.950.4 and 3-7.7 d. All centers of curvature of the collimating electrodes are located between the gap 8 and the corresponding gap. Focusing. The shoulder of the spectrometer has similar dimensions. Potentials V "on the analyzer electrodes, assigned to 10

1534550 12 potential U _? at its output and input are given for all modes. Note that, as usual, the potential of that point in space at which the kinetic energy of the particles is equal to zero is considered equal to zero. ”The electrodes 7 and 7a are assumed to be connected to the source of the analyzed particles, ie potential V _{7 is} numerically equal to the energy of these particles E £.

Finally, we show another possibility of using the invention to control the parameters of the spectrometer 15 without changing its design. The described embodiment with a three-electrode lens potential V _from the intermediate electrode potential exceeding the largest on the outer lens electrodes provides a large aperture value spectrometer, but the field of view of the analyzer with small.

Using the calculated lens as a multi-electrode, one can significantly increase the effective size of the electron-optical object. This possibility is shown by the calculation results shown in Fig.7.

I

Here, the abscissa shows the potential Ud on the electrode 4. (according to the notation of Fig.2), and the graphs show how, depending on the Ud, the potentials Vg (curve 1) and V _s (curve 2) on the electrodes 6 and 5, respectively, to maintain focus. From curve 3, which describes the change in the aperture of the device, it can be seen that the aperture with a change in Yp varies slightly. Also, the contribution of AR lens aberrations to the resolution of the device changes slightly (curve 5) »A effective height h _{n of the} object. (Curve 4) when U / V _m changes from 0.0625, which corresponds to a three-electrode lens operation mode, up to 0.1 1 to increase h _{r |} from 0.025d to 0.08d, i.e. more than 3 times ”Thus, one more mode of operation of the spectrometer with a large aperture and relatively large size of the electron-optical object can be recommended for use, namely, the mode corresponding to the data of Fig. 7 at U / V ₇ = 0.110. It is not possible to further increase the dimensions in this way in this design, since an increase in Y ₄ / Y _{7 of} more than 0.12 leads to uncorrectable detuning of the lens.

We also note that in all modes calculated for the spectrometer to operate in the high-energy region, the contribution of aberrations to the resolution did not exceed 0.01% for modes 2.3, and 5 and 0.02% for mode 1. That is, In the calculated spectrometer, with a corresponding decrease in the slit width of the source and receiver of particles, an ultrahigh resolution is achieved - up to 0.02%, which also agrees with the set requirements. fifteen

To implement all operating modes, the switch must provide switching according to the circuit depicted in Fig.2.

In this case, the resistances entering 20 into the voltage divider (DN), calculated in accordance with the requirements of (1a) and (2), must have the value

r = l, 937'10 * ³ R, r ₂ = 3.205'10 '^ R, r ₃ = l, 202'10 ~ ³ R, r ₄ = 9.082 · 10 R, 25 r ₅ = 1.269 · 10 ~ * R, g _b = 2,658 · 10 '* R, g ₇ = 7,052 · 10' * R, r _g = 1,028-10 ' ¹ R, g = 2,711-10 ^_1 R, r ₄₀ = 2,671 10 R, r' = 9.082'10 'R, 4.074 -10' ¹ R, where R is the impedance of the DN ₀ 30

Claims (1)

Claim An electronic spectrometer containing an adjustable power source, ionization sources located at the input of an electrostatic prism-type Egergo * analyzer with a dispersing part made in the form of an electronic prism and collimating and focusing parts made in the form of electronic lenses formed by electrodes made in the form sequentially arranged pairs of flat plates parallel to one another, symmetrical with respect to the longitudinal plane of the energy analyzer, separated by a curved gap mi, and an electron receiver with gap gaps located at the output of the electrostatic energy analyzer, characterized in that, in order to expand the analytical capabilities of the spectrometer, increase its sensitivity and resolution, a mode switch is introduced into it, and curved gap gaps are made in arcs, representing second-order curves, the centers of curvature or evolutes of which are spaced relative to each other along the electron-optical axis, and the electrodes of the energy analyzer are connected cheny to a regulated source of electrical 'power supply via the mode switch deaboty spectrometer. FIG. 5 ^Qoz V ^, ° · '° FIG. 7