US3617741A

US3617741A - Electron spectroscopy system with a multiple electrode electron lens

Info

Publication number: US3617741A
Application number: US854437A
Authority: US
Inventors: Kai M B Siegbahn; Edward F Barnett
Original assignee: Hewlett Packard Co
Current assignee: SURFACE SCIENCE LABORATORIES Inc; HP Inc
Priority date: 1969-09-02
Filing date: 1969-09-02
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: JPS5113435B1; DE2043323A1; GB1276400A; DE2043323B2; DE2043323C3; FR2060766A5; DE7032595U

Abstract

A source of X-radiation and a target under study are mounted on the Rowland circle of a crystal monochromator employed to focus a characteristic line of the X-radiation on the target. An electron lens with four electrodes for providing three independently variable electrical parameters is mounted in the photoelectron path between the target and an electron spectrometer adjusted to focus photoelectrons within a fixed energy range on a detector. The electrical parameters of this electron lens are adjusted to provide a target image of constant size and position at the entrance of the electron spectrometer while accelerating or decelerating photoelectrons from the target into the energy range for which the electron spectrometer is adjusted.

Description

United States Patent [54] ELECTRON SPECTROSCOPY SYSTEM WITH A MULTIPLE ELECTRODE ELECTRON LENS 23 Claims, 6 Drawing Figs.

[52] US. Cl ..250/49.5 AE, 250/419 ME, 250/49.5 A, 250/495 P [5 l] Int. Cl.. l-l0lj 37/00, GOln 23/00 [50] Field of Search 250/419 SE, 4l.9 ME, 49.5 A, 49.5 C, 49.5 Pl

[ 56] References Cited UNITED STATES PATENTS 3,084,249 4/1963 Enge 250/419 36 DETEC OR OTHER REFERENCES Photon Impact Studies of Molecules Using A Mass Spectrometer" By H. Hurzeler et al. from The Journal of Chemical Physics, Vol. 28, No. LJan. 1958, pp. 76- 82.

The Esca Method Using Monochomatic X-rays and A Permanent Magnet Spectrograph By A. Fahlman et al. From Arkiv For Fysik, Vol. 32, Paper 7, 1966, pp. 111- 129.

lon Microprobe Mass Analyser By H. Liebl from the Journal Of Applied Physics, Vol. 38, No.- l3, Dec. I967, pp. 5277- 5283.

Primary Examiner-William Fv Lindquist Attorney-Roland l. Griffin ABSTRACT: A source of X-radiation and a target under study are mounted on the Rowland circle of a crystal monochromator employed to focus a characteristic line of the X-radiation on the target. An electron lens with four electrodes for providing three independently variable electrical parameters is mounted in the photoelectron path between the target and an electron spectrometer adjusted to focus photoelectrons within a fixed energy range on a detector. The electrical parameters of this electron lens are adjusted to provide a target image of constant size and position at the entrance of the electron spectrometer while accelerating or decelerating photoelectrons from the target into the energy range for which the electron spectrometer is adjusted.

CRYSTAL MONOCHROMATOR ROWLAND CIRCLE PATENTEUNDV 2 SHEET 10F 2 ELECTRON SPECTROMETER CRYSTAL MON OCHROMATOR ROWLAND CIRCLE DETECTOR igure 1 LECTRON LENS INVENTORS KAI MB. STEGBAHN EDWARD F. BARNETT ATTORNEY ELECTRON SPECTROMETER PATENTEUNUV 2 SHEET 2 BF 2 ELEcTRD LENS PLANE OF RowLAND CIRCLE 2o ELECTRON SPECTROMETER w TARGET igure 5 ELECTRON SPECTROMETER S R O T N E V N ELECTRON LENS KAI MB.SIEGBAHN EDWARD F. BARNETT BY W ATTORNEY ELECTRON SPECTROSCOPY SYSTEM WITH A MULTIPLE ELECTRODE'ELECTRON LENS BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to electron spectroscopy for chemical analysis (hereinafter referred to asESCA) and, more particularly, to improved ESCA systems employing multiple electrode electron lenses.

Typically, the main contributions to the width of an electron line in an ESCA spectrum are the inherent width of the characteristicX-ray line used to excite the electron emission and the inherent width of the atomic level under study. In order to obtainuseful information about atoms and molecules from ESCA, the width of the electronline should reflect only the inherent width of the atomic level under study. An ESCA system in which the width of the X-ray line used to excite the electron emission is prevented from contributing to the width 1 or 2. The angular spread with which photoelectrons enter the electron spectrometer in the circumferential direction is limited in systems employing multiple electrode electron lenses of the type described aboveby the aperturing effect of the lens electrodes. Accordingly, it is another object of this invention to provide an improved ESCA system of that type in which the acceptance angle of the photoelectronsmay be increased in the circumferential direction by as much as a factor of ten, thereby significantly increasing the sensitivity of the system without impairing its resolution.

' This object is accomplished according to another preferred embodiment of this invention by employing a modified hemispherical electrode spectrometer with a conical entrance end having an axis of symmetry that passesthrough the center of the hemispherical electrodes and by employing an electron lens having four pairs of conical fan-shaped electrodes with of the electron line in the ESCA spectrum is described and claimed in copending US Pat. application, Ser. No. .765,l40 entitled ELECTRON SPECTROSCOPY SYSTEM WITH DISPERSION COMPENSATION, filed on Oct. 4, 1968, by Kai Siegbahn, issued as,U.S. Pat. No. 3,567,926 on Mar. 2, I97 I and assigned to the same assignee as this patent application. In that system the dispersion of a crystal, monochromator used to focus a characteristic X-ray line on a target is made equal to that of an electron spectrometer used to focus photoelectrons emerging from the irradiated target on to a detector. The geometry of the system is arranged so that the dispersion of the electron spectrometer compensates for the dispersion of the crystal monochromator and thereby prevents the width of the X-ray line focusedon the target from adding to the width of the electron line focused on the detector. However, this can only be accomplished for a relatively narrow electron energy range of about to percent of the op,- timum electron energy for dispersion compensation in such a system. Accordingly, it is an object of this invention to provide an improved ESCA system in which dispersion compensation may be employed for a much wider energy range to prevent the width of the X-ray line from adding to the width of the electron line. I

This object is accomplished according to a preferred embodiment of this invention by employing an electron lens comprising four conical ring-shaped electrodes having a common axis of symmetry in the photoelectron path between the target and the electron spectrometer. These electrodes are electrically insulated from each other to provide three independently variable electrical parameters. The focusing action of this electron lens produces an image of the target at the entrance of the spectrometer. By adjusting the electrical parameters of the electron lens the size and position of this image may be maintained constant while accelerating or decelerating photoelectrons from the target into the energy range for which the electron spectrometer is adjusted. This substantially increases the energy range over which dispersion compensation may be employed to prevent the width of the X-ray line focused on the target from adding to the width of the electron line focused on the detector.

ln ESCA systems employing electrostatic electron spectrometers with hemispherically shaped electrodes, greater sensitivity may be achieved for a given absolute resolution by increasing the solid angle at which photoelectrons from the target enter the electron spectrometer. This solid angle is hereinafter referred to as the acceptance angle. It is approximately proportional to the product of the angular spread of the photoelectrons entering the electron spectrometer in the radial direction (the direction in which the'photoelectrons are subsequently deflected and dispersed by the spectrometer) and the angular spread of the photoelectrons entering the electron spectrometer in the circumferential direction (the direction normal to the radial direction). Because of aberrations in the electron spectrometer, the angular spread with which photoelectrons enter the electron spectrometer in the radial direction must be kept very small, on the order of about the same axis of symmetry as'the conical-entrance end of the hemispherical electrode spectrometer. These pairs of electrodes are positioned so that their apertures are narrowest in the radial direction and broadest in the circumferential direction. The focusing action of'the electron lens therefore occurs mainly, or entirely, in the radialdirection, thereby increasing the acceptance angle in the circumferential direction and providing greater sensitivity fora given absolute resolution. Each of these pairs of electrodes is electrically insulated from the others to provide three independently variableelectrical parameters for controlling the size and position of the target image and the kinetic energy of the photoelectrons entering the electron spectrometer.

BRIEF DESCRIPTION OF THE DRAWING tron lens having its axis of symmetry oriented at a finite angle 1 with respect to the plane of the Rowland circle.

FIG. 5 is a sectional elevational representation of an electron lens and spectrometer that may be used to provide an improved dispersion-compensated ESCA system according to another preferred embodiment of this invention.

FIG. 6 is an elevational representation of the electron lens and spectrometer of FIG. 5 as viewed in a plane perpendicular to the plane of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a dispersion-compensated ESCA system for use in studying the chemical composition of a selected target 10. This system includes a fixedly mounted source 12 for emitting a beam of X-radiation 14 along a first axis 16. Source 12 may be constructed, for example, as described on pages 178-179 of the book ESCAwritten by Kai Siegbahn et al. and published in Dec. 1967, by Almqvist andWicksells Boktryckeri AB (hereinafter referred to as the book ESCA). A dispersing crystal 18 of a crystal monochromator isfixedly mounted on the first axis 16 in the path of the X-radiation l4. Dispersing crystal 18 is provided with a curved surface so that the atomic layers have a radius equal to the diameter of the Rowland circle 20. The dispersion of the crystal monochromator (caused by Bragg reflection within dispersing crystal 18) produces a spectrum of the X- radiation 14. A characteristic line 22 of this X-ray spectrum is focused by the crystal monochromator along a second axis 24 making an angle B of about 22 with the first axis 16. Target 10 is removably mounted on the second axis 24 in thepath of this characteristic X-ray line 22. Both target 10 and source 12 are mounted on the Rowland circle 20 of the crystal monochromator.

The irradiation of target 10 by the characteristic X-ray line 22 causes photoelectrons to emerge from the target along a third axis 26 making an angle +'y 1 (see FIG. 3) of about 75 with the second axis 24. Due to the dispersion of the crystal ty and resolution of the system. By adjusting the potential difference V V between

lens electrodes

40 and 42 and the potential difference V V between

lens electrodes

40 and 44, the size and position of image 48 may be selected and, in addice lerated or decelerated into the range for which electron spectrometer 28 is adjusted.

An image 48 of target is produced at the entrance end of electron spectrometer 28 by the focusing action of electron monochromator, the characteristic X-ray line 22 has a finite 5 tion, maintained constant to provide the system with maxline width that causes photoelectrons from the same energy imum sensitivity and resolution irrespective of the initial level but different parts of the target to emerge with different kinetic energy of the photoelectrons being decelerated or acenergies. For example, as indicated in FIG. 1, a higher energy celerated into the energy range for which spectrometer 28 is photon strikes target 10 to the right (as viewed in the beam adjusted. direction of the characteristic X-ray line) of a lower energy 10 In order to preventthe width of the characteristic X-ray line photon and produces photoelectrons of higher energy (E,+A 22 from adding to the width of the electron line focused on de- E) than the photoelectrons of energy (E,AE) produced by tector 36, the overall dispersion of electron lens 38 and electhe lower energy photon. tron spectrometer 28 is made to cancel the dispersion of the As shown in FIGS. 1 and 2, an elec ron disp r ng device, crystal monochromator. This is achieved by arranging the such as an electron spectrometer 28 fixedly mounted with iIS geometry of the system and choosing the electrical parameters entrance end on the third axis 26, is employed for analyzing so th t; photoelectrons from the irradiated target 10. Electron specp sin a Sin E trometer 28 may comprise, for example, an electrostatic spec- 7 tan 0 trometer with

hemispherical electrodes

32 and 34, such as the i 7 one represented in FIGS- 1 and or a semicircular magnetic "hi this equation (as indicated with the air of FIGS. land 3); spectrometer, such as the one shown and described in connecp equals the mean radius f Spectrometer 2 tion with Section Vlll:3 on pages 182 et seq. of the book Requals the radius fR l d circle 0; ESCA. In any case, electron spectrometer 28 is adjusted such M equa15the magnification ofejectt-oh lens as by operating its

electrodes

32 and 34 at selected potentials 6 equals the Bragg angle (the angle between the second axis V and V respectively, to focus a fixed and relatively narrow 24 and a tangent to the Rowland circle 20 at a point ihtep energy range of the photoelectrons (for example, about lOev. sected by this Second axis); out of about 1,500ev.) onto a detector 36 mounted at the exlt q) equals the angle between the third axis 26 and the end of the electron spectrometer. Detector 36 may comprise a radiated surface of target 10; fixedly'moumed phfnomumpher tube or a removably -y equals the angle between the irradiated surface of target g photograph: plate as represemed Schemaucany m 10 and a tangent to the Rowland circle 20 at a point inter- An electron lens 38 is fixedly mounted along the third axis zzz g zggii f Second axls 24 and the "radiated Sur 26 between target 10 and the entrance end of electron spec- E equals the kinetic energy of the central electron my in trometer 28 to accelerate or decelerate photoelectrons from Spectrometer and the target into the energy range for which the electron spec- E equals the mean e'hergy of the photons in the charac trometer is adjusted. Electron lens 38 comprises four conical teristic X ray he 22 ring-Shaped electrodes 46 symmeiricauy posi' From the above equation it may be seen that for a given tloned about and spaced along the third axls 26 with the smalgeometry and ratio of E8 to El dispersion compensation aperture adjacent to target 10 and a larger apenure 40 re uires that the ma nification M of electron lens 38 and jacent to the entrance end of electron spectrometer 28. These twice the Size of g at mm 48 be k t t t th four

electrodes

40, 42, 44, and 46 are electrically insulated g g6 eP as from each other and o erated at inde endentl controllable range of mmal. photoeiectrmi .energies be w p p d. As described above thls ls accom llshed b ad ustln potentials V V V and V so that the potentlal dlfference l d J V -V between

electrodes

40 and 42, the potential difference 5 t e q i gig I erencetsl 5 i V -,V; between

electrodes

40 and 44, and the potential dif- Rotenua l Hence 315.3 Juste to varyt e range 0 mlference V V between

electrodes

40 and 46 ma be inde enphoioeleqmn energles bemg analyzed 3 y p A dlsperslon-compensated ESCA system of the type dently varled. The potentials V and V of the

spectrometer d d b h b h h f electrodes

32 and 34, respectively, should be chosen so that 8 We as been Wm t e lmenslons Set on m the central ray of the electrons passing through the spectrome- 50 h table (the a fa nd represent, the ter follows an equipotential surface of the same potential V as gnudma] dlmenslons and dlameiersf respecnvely of the closest lens electrode 46, This condition determines a electronic as shown for greaterclamym H04): positive value for the potential difference V,\/ between the inner spectrometer electrode 32 and the closest lens electrode (p 5.0"; b= 0.5" r,=l .0" 46 and a negative value for the potential difference V V 55 Pa c= r,=2.0:: between the outer spectrometer electrode 34 and the closest 3; 3: 2:8,, lens electrode 46. The potential difference V -V between the electrode 40 closest to target 10, which is operated at the =30 same potential V; as electrode 40 and the electrode 46 closest to the entrance end of electron spectrometer 28 controls the 5 5 5 ratio of the final to the initial kinetic energy of photoelectrons emerging from the target 10 and passing through the electron Dispersion compensation has been achieved in this system spectrometer 28. By adjusting this potential difference V.,V at deceleration ratios E,/E, of, for example, one-third and onephotoelectrons having initial kinetic energies over a wide sixth, by operating the electron spectrometer and lens elec- E../E,, Vi. v. \z, v. V v. \4. v. \'5, v. v. Ei. w. E... w.

1/3 -264 402 0 680 -355 -34li 510 170 1/6 774 -lll-. (I 1,000 -770 850 1,020 17" range (for example, about 300 to 1,500 ev.) can be ac- 7O trodes at the potehtials set forth in the table below (where E, is

the mean kinetic energy of those photoelectrons, as they leave the target, that pass through the spectrometer):

The electron lens 38 employed in the system of FIG. 1 may be entirely electrostatic or it may have both electrostatic and lens 3 8.Th e size and po sition ofimage affect the sensitivi magnetic components. Moreover, the electron lens 38 may be mounted so that its axis of symmetry is positioned in the plane of the Rowland circle 20 or, as indicated in FIG. I, at a finite angle with respect to the plane of the Rowland circle 20, as indicated by dashed lines in FIG. 4. The latter alternativemay be used to advantage in systems where the electronlens 38 would otherwise absorb large amounts of the X-radiation 14 before it reaches the target 10.

For greatest sensitivity the acceptance angle of electron spectrometer 28 should be centered on the axis along which the highest photoelectron emission per unit solid angle with the least loss of monochromatization is achieved. This axis is perpendicular to the plane of the Rowland circle for a gaseous target in which photoelectrons may be produced throughout the entire region along the arc of the Rowland circle subtended by the characteristic X-ray line 22. For such a gaseous target it is therefore especially advantageous to mount the electron lens 38 and spectrometer 28 so that the central ray, of the photoelectrons 30 accepted'thereby isperpendicular to the plane of the Rowland circle 20, as indicated by solid lines in FIG. 4. These same considerations are equally applicableto the use of electron spectrometer 28 in an ESCA system not employing an electron lens 38.

Electron lens 52 comprises four pairs of conical fan-shaped

A electrodes

62, 64, 66, and having the same axisof symmetry 60 as the conical entrance end 58 of electron spectrometer 50. These pairs of

electrodes

62, 64, 66, and 68 are electrically insulated from each other and operated at independently adjustable potentials V V V and V respective ly, to provide three independently variable potential dif ferences V,-V between the first and second pairs 62 and.64, V V between the first and

third pairs

62 and 66, and V V.

between the first and

fourth pairs

62 and 68. By adjusting,

these three independently variable potential differences the size and position of the target image and the kinetic energy of the photoelectrons entering electron spectrometer 50 may be controlled to provide dispersion compensation for an extended energy range as described above in connection with FIG. 1.

Electron lens 52 is fixedly mounted with its smallest conical aperture adjacent to target 10 and with its largest conical aperture adjacent to the conical entrance end 58 of electron spectrometer 50. The conical apertures of electron lens 52 are narrowest in the radial direction and broadest in the circumferential direction so that the focusing action of the electron lens occurs mainly, or entirely, in the radial direction and only slightly, if at all, in the circumferential direction. This has the effect of increasing the acceptance angle in the circumferential direction, thereby providing greater spectrometer sensitivity for a given absolute resolution.

ideally, the target 10 should lie on a conical surface thatintersects the adjacent surfaces of electrode pair 62 at right angles and that passes through, or is near to, .the axis of symmetry 60 of electron lens 52. The closer target 10 is to theaxis of symmetry 60 of electron lens 52, the greater the reduction in aberrations that may be achieved. All of the rays of the photoelectrons accepted by electron lens 52 are nearly normal to the conical surfaces forming the edges of the lens apertures and the entrance end 58 of the electron spectrometer 50. This also helps to reduce aberrations. Electron lens 52 produces an image of the accepted rays in a cone 70 passing through the center C of the

hemispherical electrodes

54 and 56.

We claim:

I. An electron spectroscopy system comprising:

a source for producing a beam of electromagnetic radiation along a first axis; v

a monochromator including a dispersing element positioned on the first axis in the path of said electromagneticradiation, said monochromator focusing a portion of this.electromagnetic radiation along a second axis onto a target positioned on the second axis and substantially on the Rowland circle of the monochromator thereby producing electron emission fromthe irradiated target along a third axis;

a detector;

an electron dispersing device positioned on the third axis in the path of this electron emission, said electron dispersing device focusing electrons from the irradiated targetonto the detector; and

an electron lens forming an image of the irradiated target with the electrons ,from this imagepassing through the electron dispersing device, said electronlens including at least-four'focusing elements positioned along the third axis in the electron path between the target and the electron dispersing device to provide at leastthree independently variable electrical parameters for controlling the size and position of the image and thedifference between the initial and final kinetic energies of the electrons passingthrough the electron lens.

2. An electron spectroscopy system as in claim I wherein said focusing elements comprise generally conical, ringshaped electrodes electrically insulated from each other and independently operable at different electrical potentials, said electrodes being symmetrically positioned about and spaced along the third axis with their narrowest aperture positioned adjacent to the target and a larger aperture positioned adjacent to the electron dispersing device.

3. An electron spectroscopy system asinclaim 2 wherein:

said source is positioned substantially on the Rowland circle of the monochromator;

said electromagnetic radiation is X-radiation, the portion of said electromagnetic radiation beingfocused onto the target comprising a characteristic line of this X-radiation; and

the overall dispersion of the electron lens and the electron dispersing device is made to cancel the dispersion of the monochromator to reduce the contribution of the characteristic X-ray line width to the line width of the electrons focused onto the detector.

4. An electron spectroscopy system as in claim lwherein:

said electron dispersing device comprises an electronspectrometer having apair of hemispherical electrodes electrically insulated from each other and operable at dif ferent electrical potentials, said electron spectrometer having agenerally conical-shaped entrance end with. an axis of symmetry passing through the-center of the hemispherical electrodes; and

said focusing elements comprise four pairs of generally conical, fan-shaped electrodes electrically insulated from each other and independently operable at differentelectrical potentials, said pairs of fan-shaped electrodes having the same axis of symmetry as the conically-shaped entrance end of the spectrometer and being spaced apart with their smallest conical aperture positioned adjacent to the target and their largest conical aperture positioned adjacent to the conically-shaped entrance end of the electron spectrometer.

5. An electron spectroscopy system as in claim- 4. wherein the image of the irradiated target is formed by the electron lens at the conically shaped entrance end of the electron spectrometer in a cone having its apex located at the center of the hemispherical electrodes.

6. An electron spectroscopy system as in claim 5 wherein:

said source is positionedsubstantially on the Rowland circle of the monochromator;

said electromagnetic radiation is X-radiation, the portion of said electromagnetic radiation being focused onto the target comprising a characteristic line of this X-radiation; and

the overall dispersion of the electron lens and the electron spectrometer is made to cancel the dispersion of the monochromator to reduce the contribution of the characteristic X-ray line width to the line width of the electrons focused onto the detector.

7. An electron spectroscopy system as in claim 1 wherein the electron lens has an axis of symmetry positioned in the plane of the Rowland circle of the monochromator.

8. An electron spectroscopy system as in claim 1 wherein the electron lens has an axis of symmetry positioned at a finite angle with respect to the plane of the Rowland circle of the monochromator. v

9. An electron spectroscopy system as in claim 8 wherein the axis of symmetry of the electron lens is positioned perpendicular to the plane of the Rowland'circle of the monochroma- {OR 10. An electron spectroscopy system as in claim 1 wherein the overall dispersion of the electron lens and the electron dispersing device cancels out the dispersion of the monochromator.

11. An electron spectroscopy system as in claim 1 wherein said focusing elements comprise at least four electrodes electrically insulated from each other and independently operable at different electrical potentials with the potential differences between a first and a second, the first and a third, and the first and a fourth of these electrodes being adjustable to control the size and position of the image of the irradiated target and the ratio of the final to the initial kinetic energy of the electrons emitted from the irradiated target and passing through the electron dispersing device.

12. An electron spectroscopy system as in claim 1 wherein:

said electromagnetic radiation is X-radiation, the portion of said electromagnetic radiationbeing focused onto the target comprising a characteristic line of this X-racliation; and

the overall dispersion of the electron lens and the electron dispersing device is made equal in magnitude to and opposite in sign from the dispersion of the monochromator so that these dispersions cancel.

13. An electron spectroscopy system as in claim 12 wherein:

said electron dispersing device comprises an electron spectrometer having a pair of hemispherical electrodes electrically insulated from each other for operation at different electrical potentials;

said source, monochromator, target, electron spectrometer,

and electron lens are arranged so that p SinOSinrbE,

tan 0, where p equals the mean radius of the hemispherical electrodes of the electron spectrometer, R equals the radius of the Rowland circle of the monochromator, M equals the magnification of the electron lens, equals the angle between the second axis and a tangent to the Rowland circle at a point intersected by the second axis and by the irradiated surface of the target, 1 equals the angle between the third axis and the irradiated surface of the target, 7 equals the angle between the irradiated surface of the target and a tangent to the Rowland circle of the monochromator at a point intersected by the second axis and by the irradiated surface of the target, E, equals the kinetic energy of the central electron ray in the electron spectrometer, and E equals the mean energy of the photons in the characteristic line of the X radiation.

14. An electron spectroscopy system as in claim 12 wherein said focusing elements comprise at least four electrodes electrically insulated from each other and independently operable at different electrical potentials with the potential differences between a first and a second, the first and a third, and the first and a fourth of these electrodes being adjustable to control the size and position of the image of the target and the ratio of the final to the initial kinetic energy of the electrons emitted from the irradiated target and passing through the electron spectrometer.

15. An electron spectroscopy system as in claim 12 wherein said focusing elements comprise at least four generally ringshaped electrodes spaced along the third axis and electrically insulated from each other for operation at independently adjustable electrical potentials.

16. An electron spectroscopy system as in claim 12 wherein:

said electron dispersing device comprises an electron spectrometer operated to focus electrons within a selected energy range onto the detector; and

said focusing elements comprise at least four electrodes spaced along the third axis and operated at independently adjustable electrical potentials to maintain the size and position of the image of the irradiated target constant while accelerating or decelerating electrons from the irradiated target into the selected energy range of the electron spectrometer.

17. An electron spectroscopy system as in claim 16 wherein said electron spectrometer comprises a pair of hemispherical electrodes operated at independently adjustable electrical potentials to focus electrons within the selected energy range onto the detector.

18. An electron spectroscopy system comprising:

a source for producing a beam of electromagnetic radiation along a first axis;

a monochromator including a dispersing element positioned along the first axis in the path of this electromagnetic radiation to project a portion thereof along a second axis onto a target positioned along the second axis and substantially on the Rowland circle of the monochromator and thereby produce electron emission from the irradiated target along a third axis;

a detector;

an electron dispersing device positioned along the third axis in the path of this electron emission to focus electrons from the irradiated target onto the detector; and

an electron lens positioned along the third axis between the irradiated target and the electron dispersing device in the path of this electron emission to form an image of the irradiated target adjacent to the electron dispersing device with the electrons from this image passing through the electron dispersing device, said electron lens including means for adjusting the size and position of the image of the irradiated target and means for independently adjusting the ratio of the final to the initial kinetic energy of the electrons emitted from the irradiated target and passing through the electron dispersing device.

19. An electron spectroscopy system as in claim 18 wherein said means comprise at least four electrodes positioned along the third axis between the irradiated target and the electron dispersing device in the path of the electron emission, said electrodes being electrically insulated from each other for operation at independently adjustable electrical potentials.

20. An electron spectroscopy system as in claim 19 wherein:

said electrodes are operable at different electrical potentials; and

the potential differences between a first and a second, the

first and a third, and the first and a fourth of said electrodes are adjusted to control the size and position of the image of the irradiated target and the ratio of the initial to the final kinetic energy of the electrons emitted from the irradiated target and passing through the electron dispersing device.

21. An electron spectroscopy system as in claim 20 wherein:

said source comprises a source of X-radiation positioned substantially on the Rowland circle of the monochromator;

said electromagnetic radiation comprises X-radiation with the portion projected onto the target comprising a characteristic line thereof;

said electron dispersing device comprises an electron spectrometer; and

the potential differences between the first and the second, the first and the third, and the first and the fourth of said electrodes are adjusted to make the overall dispersion of the electron lens and the electron spectrometer substantially equal in magnitude to and opposite in sign from the dispersion of the monochromator so that these dispersions cancel and thereby reduce the contribution of the characteristic X-ray line width to the line width of the electrons focused onto the detector. 22. An electron spectroscopy system as in claim 1 wherein: said electron spectrometer is operated to focus electrons within a selected energy range onto the detector; and

said electrodes are independently adjustably operated to maintain the size and position of the image of the irradiated target constant while accelerating or decelerating electrons from the irradiated target into the selected energy range of the electron spectrometer.

23. An electron spectroscopy system as in claim 18 wherein said electron lens and said electron spectrometer have an overall dispersion adjusted to cancel the dispersion of the monochromator.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,617 741 Dated Ngyembe: 2 122],

Inv n (s) lggi 14,5, fiiegbghn and Edyard FLBarnett It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 3, "75 should read 70 Column 4, line 21, "air" should read aid line 67, "E /E should read E /E lines 67-69, the table listed should be placed immediately below line 73;

Column 5, line 19, cancel "30";

Column 9, line 10, "1'' should read 21 Signed and sealed this 2nd day of Ma 1972.

r SEAL) Attest:

EDWARD M.'FLETCHER,JR. ROBERT GOTTSCHALK attesting Officer Commissioner of Patents DRM PO-IOSO (10-59) USCOMM-DC 60375-P59 fl US, GOVERNMINT PRINTING OFFICE H69 0-366-"4 160010

Claims

1. An electron spectroscopy system comprising: a source for producing a beam of electromagnetic radiation along a first axis; a monochromator including a dispersing element positioned on the first axis in the path of said electromagnetic radiation, said monochromator focusing a portion of this electromagnetic radiation along a second axis onto a target positioned on the second axis and substantially on the Rowland circle of the monochromator thereby producing electron emission from the irradiated target along a third axis; a detector; an electron dispersing device positioned on the third axis in the path of this electron emission, said electron dispersing device focusing electrons from the irradiated target onto the detector; and an electron lens forming an image of the irradiated target with the electrons from this image passing through the electron dispersing device, said electron lens including at least four focusing elements positioned along the third axis in the electron path between the target and the electron dispersing device to provide at least three independently variablE electrical parameters for controlling the size and position of the image and the difference between the initial and final kinetic energies of the electrons passing through the electron lens.

2. An electron spectroscopy system as in claim 1 wherein said focusing elements comprise generally conical, ring-shaped electrodes electrically insulated from each other and independently operable at different electrical potentials, said electrodes being symmetrically positioned about and spaced along the third axis with their narrowest aperture positioned adjacent to the target and a larger aperture positioned adjacent to the electron dispersing device.

3. An electron spectroscopy system as in claim 2 wherein: said source is positioned substantially on the Rowland circle of the monochromator; said electromagnetic radiation is X-radiation, the portion of said electromagnetic radiation being focused onto the target comprising a characteristic line of this X-radiation; and the overall dispersion of the electron lens and the electron dispersing device is made to cancel the dispersion of the monochromator to reduce the contribution of the characteristic X-ray line width to the line width of the electrons focused onto the detector.

4. An electron spectroscopy system as in claim 1 wherein: said electron dispersing device comprises an electron spectrometer having a pair of hemispherical electrodes electrically insulated from each other and operable at different electrical potentials, said electron spectrometer having a generally conical-shaped entrance end with an axis of symmetry passing through the center of the hemispherical electrodes; and said focusing elements comprise four pairs of generally conical, fan-shaped electrodes electrically insulated from each other and independently operable at different electrical potentials, said pairs of fan-shaped electrodes having the same axis of symmetry as the conically-shaped entrance end of the spectrometer and being spaced apart with their smallest conical aperture positioned adjacent to the target and their largest conical aperture positioned adjacent to the conically-shaped entrance end of the electron spectrometer.

5. An electron spectroscopy system as in claim 4 wherein the image of the irradiated target is formed by the electron lens at the conically shaped entrance end of the electron spectrometer in a cone having its apex located at the center of the hemispherical electrodes.

6. An electron spectroscopy system as in claim 5 wherein: said source is positioned substantially on the Rowland circle of the monochromator; said electromagnetic radiation is X-radiation, the portion of said electromagnetic radiation being focused onto the target comprising a characteristic line of this X-radiation; and the overall dispersion of the electron lens and the electron spectrometer is made to cancel the dispersion of the monochromator to reduce the contribution of the characteristic X-ray line width to the line width of the electrons focused onto the detector.

8. An electron spectroscopy system as in claim 1 wherein the electron lens has an axis of symmetry positioned at a finite angle with respect to the plane of the Rowland circle of the monochromator.

9. An electron spectroscopy system as in claim 8 wherein the axis of symmetry of the electron lens is positioned perpendicular to the plane of the Rowland circle of the monochromator.

10. An electron spectroscopy system as in claim 1 wherein the overall dispersion of the electron lens and the electron dispersing device cancels out the dispersion of the monochromator.

12. An electron spectroscopy system as in claim 1 wherein: said source is positioned substantially on the Rowland circle of the monochromator; said electromagnetic radiation is X-radiation, the portion of said electromagnetic radiation being focused onto the target comprising a characteristic line of this X-radiation; and the overall dispersion of the electron lens and the electron dispersing device is made equal in magnitude to and opposite in sign from the dispersion of the monochromator so that these dispersions cancel.

13. An electron spectroscopy system as in claim 12 wherein: said electron dispersing device comprises an electron spectrometer having a pair of hemispherical electrodes electrically insulated from each other for operation at different electrical potentials; said source, monochromator, target, electron spectrometer, and electron lens are arranged so that Rho equals the mean radius of the hemispherical electrodes of the electron spectrometer, R equals the radius of the Rowland circle of the monochromator, M equals the magnification of the electron lens, theta equals the angle between the second axis and a tangent to the Rowland circle at a point intersected by the second axis and by the irradiated surface of the target, phi equals the angle between the third axis and the irradiated surface of the target, gamma equals the angle between the irradiated surface of the target and a tangent to the Rowland circle of the monochromator at a point intersected by the second axis and by the irradiated surface of the target, Es equals the kinetic energy of the central electron ray in the electron spectrometer, and EP equals the mean energy of the photons in the characteristic line of the X radiation.

15. An electron spectroscopy system as in claim 12 wherein said focusing elements comprise at least four generally ring-shaped electrodes spaced along the third axis and electrically insulated from each other for operation at independently adjustable electrical potentials.

16. An electron spectroscopy system as in claim 12 wherein: said electron dispersing device comprises an electron spectrometer operated to focus electrons within a selected energy range onto the detector; and said focusing elements comprise at least four electrodes spaced along the third axis and operated at independently adjustable electrical potentials to maintain the size and position of the image of the irradiated target constant while accelerating or decelerating electrons from the irradiated target into the selected energy range of the electron spectrometer.

18. An electron spectroscopy system comprising: a sourcE for producing a beam of electromagnetic radiation along a first axis; a monochromator including a dispersing element positioned along the first axis in the path of this electromagnetic radiation to project a portion thereof along a second axis onto a target positioned along the second axis and substantially on the Rowland circle of the monochromator and thereby produce electron emission from the irradiated target along a third axis; a detector; an electron dispersing device positioned along the third axis in the path of this electron emission to focus electrons from the irradiated target onto the detector; and an electron lens positioned along the third axis between the irradiated target and the electron dispersing device in the path of this electron emission to form an image of the irradiated target adjacent to the electron dispersing device with the electrons from this image passing through the electron dispersing device, said electron lens including means for adjusting the size and position of the image of the irradiated target and means for independently adjusting the ratio of the final to the initial kinetic energy of the electrons emitted from the irradiated target and passing through the electron dispersing device.

20. An electron spectroscopy system as in claim 19 wherein: said electrodes are operable at different electrical potentials; and the potential differences between a first and a second, the first and a third, and the first and a fourth of said electrodes are adjusted to control the size and position of the image of the irradiated target and the ratio of the initial to the final kinetic energy of the electrons emitted from the irradiated target and passing through the electron dispersing device.

21. An electron spectroscopy system as in claim 20 wherein: said source comprises a source of X-radiation positioned substantially on the Rowland circle of the monochromator; said electromagnetic radiation comprises X-radiation with the portion projected onto the target comprising a characteristic line thereof; said electron dispersing device comprises an electron spectrometer; and the potential differences between the first and the second, the first and the third, and the first and the fourth of said electrodes are adjusted to make the overall dispersion of the electron lens and the electron spectrometer substantially equal in magnitude to and opposite in sign from the dispersion of the monochromator so that these dispersions cancel and thereby reduce the contribution of the characteristic X-ray line width to the line width of the electrons focused onto the detector.

22. An electron spectroscopy system as in claim 1 wherein: said electron spectrometer is operated to focus electrons within a selected energy range onto the detector; and said electrodes are independently adjustably operated to maintain the size and position of the image of the irradiated target constant while accelerating or decelerating electrons from the irradiated target into the selected energy range of the electron spectrometer.