U.S. patent number 3,787,692 [Application Number 05/144,106] was granted by the patent office on 1974-01-22 for induced electron emission spectrometer using plural radiation sources.
This patent grant is currently assigned to Varian Associates. Invention is credited to Weston A. Anderson.
United States Patent |
3,787,692 |
Anderson |
January 22, 1974 |
INDUCED ELECTRON EMISSION SPECTROMETER USING PLURAL RADIATION
SOURCES
Abstract
An induced electron emission spectrometer wherein different
sources are employed to irradiate the sample from different energy
sources to permit the operator to distinguish the photoelectron
emission lines from the Auger electron emission lines. In one
embodiment, the X-ray source employs two different X-ray energy
emitting materials with means for selectively energizing one or the
other of said materials to irradiate the sample under investigation
with selective X-ray energies. In another embodiment the sample is
first irradiated with X-rays and thereafter irradiated with
electrons. In another embodiment, an X-ray source and then an
ultraviolet radiation source are used.
Inventors: |
Anderson; Weston A. (Palo Alto,
CA) |
Assignee: |
Varian Associates (Palo Alto,
CA)
|
Family
ID: |
22507062 |
Appl.
No.: |
05/144,106 |
Filed: |
May 17, 1971 |
Current U.S.
Class: |
250/305;
378/124 |
Current CPC
Class: |
H01J
49/484 (20130101) |
Current International
Class: |
H01J
49/00 (20060101); H01J 49/48 (20060101); H01j
037/26 () |
Field of
Search: |
;250/49.5AE,49.5PE,49.5A
;313/56 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"An Apparatus for the ESCA Method" by Fahlman et al., ARKIV FYSIK,
Jan. 1966, pp. 479-489. .
The Auger Effect and Other Radiationless Transistions by Burhop,
1952, pp. 24-25..
|
Primary Examiner: Lawrence; James W.
Assistant Examiner: Nelms; D. C.
Attorney, Agent or Firm: Cole; Stanley Z. Berbert; Leon F.
Morrissey; John J.
Claims
1. In an induced electron emission spectrometer wherein cathode
means are provided for producing electrons and anode means are
bombarded by said electrons to produce X-rays for irradiating a
sample to be analyzed, said sample emitting charged particles, a
charged particle detector, and energy selecting means for directing
charged particles of selected energy onto said charged particle
detector, the improvement comprising anode means comprising at
least two different X-ray irradiating materials and cathode means
for selectively bombarding one or the other of said irradiating
2. The spectrometer of claim 1 wherein said two different X-ray
irradiating
3. The spectrometer of claim 1 wherein said anode comprises at
least two sections and wherein said cathode means comprises a
portion for each anode
4. The spectrometer of claim 3 wherein said two different x-ray
irradiating
5. The spectrometer of claim 3 wherein said anode is annular
shaped, with each section in the form of a half-circle, and wherein
said cathode is in two half-circle sections, one for each anode
section, and means for
6. The spectrometer of claim 5 wherein said two different X-ray
irradiating
7. The spectrometer of claim 1 wherein said anode comprises at
least two sections and wherein means are provided for selectively
directing the electrons from said cathode onto one or the other of
said anode sections.
8. The spectromter of claim 7 wherein said two different X-ray
irradiating
9. The spectrometer of claim 7 wherein said anode sections are
concentric annular anodes and wherein said cathode is annular
shaped and concentric with said two anode sections, said latter
means selectively directing electrons from the cathode onto one or
the other of said anode sections.
10. The spectrometer of claim 9 wherein said two different
X-ray
11. In an induced electron emission spectrometer wherein a sample
under analysis emits electrons upon being irradiated with X-ray
radiation, means for selectively bombarding with electrons a first
target to produce X-rays having a first energy and a second target
to produce X-rays having a second energy, said second energy being
different from said first energy, means for irradiating said sample
with said X-rays of said first energy to produce a first induced
electron emission spectrum from said sample and means for
irradiating said sample with X-rays of said second energy to
produce a second induced electron emission spectrum from said
sample, detector means for detecting said electrons emitted from
said sample, and energy selecting means for directing emitted
electrons of selected energies onto said detector means, THE
IMPROVEMENT WHEREIN said means for selectively bombarding with
electrons said first and second targets comprises a focusing
electrode whereby said bombarding electrons can be selectively
focused to bombard either of said targets.
Description
BACKGROUND OF THE INVENTION
Induced electron emission spectrometers are presently utilized to
perform non-destructive, direct qualitative and quantitative
analysis of samples, including chemical analysis, measurement of
electron binding energies, and structure determinations. One
typical form of IEE spectrometer is shown and described in United
States Patent Applications Ser. No. 763,691 entitled Apparatus For
Performing Chemical Analysis By Electron Emission Spectroscopy
filed on Sept. 30, 1968 by J.C. Helmer et al and Ser. No. 825,680
entitled Induced Electron Emission Spectrometer Having A
Unipotential Sample Chamber filed on May 19, 1969 by J.C. Helmer et
al, both of which are assigned to the assignee of this application,
and also in the Journal of Applied Physics Letters, Vol. 13, Pages
226 - 268, (1968).
In operation, electrons emitted from a thermionic cathode are
directed onto the surface of an anode of a suitable material such
as aluminum or magnesium to produce soft X-rays therefrom. The
X-rays, which are of a precisely known energy (e.g. 1486eV for
aluminum and 1353eV for magnesium), irradiate the surface of the
sample under analysis to produce photoelectrons therefrom. The
photoelectrons pass through an analyzer section where the energy
range of the photoelectron emission is determined, the
photoelectrons being counted in an electron multiplier detector as
the energy range is scanned. The photoelectron energy lines are
recorded on an X-Y plotter or the like as the IEE spectrum. The
energy range is a function of the element under analysis, and the
photoelectron energy is also a function of the chemical environment
of the particular atom.
In addition to the photoelectrons of interest, the X-ray
irradiation results in Auger electrons being emitted from the
sample due to the well known Auger effect, and these electrons are
also counted and appear as Auger lines in the IEE spectrum. An
experienced operator is able to distinguish the Auger lines from
the photoelectron lines by their relative positions in the
spectrum. However, less experienced operators often confuse the
Auger lines with the photoelectron lines of interest and the
spectrum is misinterpreted.
Auger electrons may also be produced from the sample by irradiating
the sample by electron bombardment, and Auger electron analysis is
often performed in this manner.
BRIEF SUMMARY OF THE PRESENT INVENTION
The present invention provides a fast and simple method and
apparatus for distinguishing energy lines due to photo-electrons
from energy lines due to Auger electrons in an IEE spectrum.
In one embodiment of the invention, two sources of X-rays are
provided in the X-ray source section of the spectrometer, these
sources being made of different materials emitting X-rays of
different energies, for example aluminum and magnesium. The
photoelectron line positions in the spectrum are dependent on the
energy of the particular impinging X-ray, i.e. the photoelectrons
have a kinetic energy E equal to the photon energy hv minus the
binding energy .phi. of the electrons of the element in the sample.
Therefore the detected photoelectron line positions obtained with
one X-ray material will be shifted relative to the photoelectron
line positions obtained using the other X-ray material. However,
the Auger electron lines are independent of the X-ray energy and
their positions will remain the same for the two different X-ray
sources.
Therefore, by employing two successive analyzer scans using the two
different X-ray sources, a shift in any observed spectrum line will
immediately signify to the operator that the particular detected
line is a photoelectron energy line whereas a non-shifted position
line can be interpreted as an Auger electron line.
In one form of the invention, the anode which emits the X-rays in
response to the electron bombardment is made in annular form with
two half-circle sections, one half-circle section having an X-ray
emitting surface of one material, e.g. aluminum, and the other
half-circle section having an X-ray emitting surface of a different
material, e.g. magnesium. One thermionic filament is positioned to
direct electrons onto one of said anode sections and a seperate
thermionic filament is positioned to direct electrons onto the
other anode section. By selectively energizing the two different
filaments, the operator may select X-rays of either of the two
energy levels.
In another form of the invention, two annular, concentrically
positioned anodes are utilized, each of a different X-ray emitting
material. A single thermonic filament is utilized to provide
electrons for bombarding the annular shaped anodes, with means for
selectively directing the electrons onto one or the other of the
two anodes to obtain X-rays of one or the other energy levels.
In another embodiment of the invention, the sample is irradiated
with X-rays to produce photoelectrons and Auger electrons
therefrom. The sample is then irradiated with electrons so that
only Auger electrons are emitted from the sample. The absense of
the photoelectron lines will serve the operator in distinguishing
the photoelectron emission lines from the Auger emission lines.
In another embodiment, a source of ultraviolet radiation is used in
conjunction with an X-ray source, the photoelectron lines from the
ultraviolet radiation being shifted relative to the X-ray induced
lines to thereby distinguish the Auger lines.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an induced electron emission
spectrometer employing the present invention.
FIG. 2 is a face view of one form of X-ray source having two
half-circle anode sections, each with a different X-ray material
surface.
FIG. 3 is a face view of another form of X-ray source employing two
concentric anode sections.
FIG. 4 is a schematic view of still another form of X-ray and
electron beam source for practising the present invention.
FIG. 5 is a face view of the structure of FIG. 4.
FIG. 6 is a schematic diagram showing an ultraviolet radiation
source used with an X-ray source.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, the induced electron emission spectrometer
comprises an X-ray source including an annular anode 11 provided
with a surface 12 of good X-ray emitting material, for example
aluminum or magnesium, and a thermionic cathode 13 and focus
electrode 14 encircling the anode 11 and adapted to provide an
annular shaped stream of electrons 13' bombarding the anode surface
12. The anode 11 is provided with a central channel 15 for cooling
by water flow.
The X-rays emitted from the anode surface 12 are directed onto the
sample 16 to be analyzed, and the photoelectrons emitted from the
sample due to this irradiation pass into the analyzer section
including the spherical-shaped condenser structure 17, focus
control electrodes 18, cylindrical condenser 19, and electron
multiplier unit 21. A sweep potential applied between the sample
and the analyzer entrance permits energy selection of the emitted
photoelectron admitted into the analyzer. The photoelectron count
registered by the electron multiplier 21 may be plotted on an X-Y
recorder 22 as a function of the analyzing energies.
Since Auger electrons emitted from the sample 16 will be focused on
and counted by the electron multiplier 21 as well as the
photoelectrons, lines will appear in the IEE spectrum due to the
Auger electrons. From the relative positions of these lines in the
spectrum, an experienced operator is able to distinguish the Auger
electron lines from the photoelectron lines. Less experienced
operators are easily confused by the lines.
To provide the operator with a simple, fast technique for line
distinction, the X-ray anode 11 is provided in two half-circle
sections 23 and 24 as shown in FIG. 2, with one half section 23
having a surface of one X-ray material, e.g. aluminum, and the
other half section 24 having a surface of another X-ray material,
e.g. magnesium. The thermionic filament cathode 13 is provided in
two half-circle sections 25 and 26, one for each anode section. A
simple switch 27 permits the operator to energize either of the
cathode sections 25 or 26, thus selectively bombarding one or the
other of the anode surfaces 23 or 24 to provide one or the other of
the two values of X-ray energy irradiating the sample. The
photoelectron lines in the spectrum will be shifted for the two
different X-ray energies, whereas the Auger electron lines will
remain unchanged. One sweep of the analyzer with one X-ray source
energized, followed by a second sweep using the other X-ray source
will quickly inform the operator whether a particular line is one
due to photoelectrons or to Auger electrons.
Although a cylincrical sample is shown, other shapes such as a flat
sample can be employed. The sample can also be rotated so the same
surface of the sample is irradiated by both X-ray energies.
FIG. 3 shows another embodiment of the present invention wherein
the anode portion of the X-ray source includes two concentric
annular members 27 and 28, each having a different X-ray material
on its face surface. A single thermionic cathode 29 is provided
encircling the two anode sections. The operator, by selecting the
potential applied to the focus electrode 14 positioned between the
cathode 29 and the two anodes, can direct the electrons to bombard
the X-ray emitting surface of one or the other of the anodes 27 and
28, and thus chose the X-ray energy as with the X-ray source
described above with reference to FIG. 2.
It should be understood that the X-ray source may take other forms
and that the X-ray materials may be those other than aluminum and
magnesium without departing from the scope of this invention.
Referring now to FIGS. 4 and 5 there is shown a source of X-rays
for bombarding the sample which comprises a semicircular shaped
anode 31 of X-ray emitting material, and semicircular shaped
thermionic cathode 32 and focus electrode 33 for providing a beam
of electrons to bombard the anode and produce the X-rays as
described above. An apparatus is provided for producing a
semicircular beam of electrons for bombarding the sample 16 which
comprises a thermionic cathode 34, repeller electrode 35 and focus
electrode 36.
When cathode 32 is energized, the sample 16 is irradiated with
X-rays and, during the scan by the analyzer, both photoelectron and
Auger electron lines are observed. When the cathode 34 is energized
in lieu of cathode 32, a beam of electrons is provided from the
electron beam source comprising cathode 32 and electrodes 35, 36 to
irradiate the surface of the sample to thereby emit Auger electrons
therefrom but not photoelectrons. The Auger electron lines obtained
may be utilized to distinguish the photoelectron lines from the
Auger electron lines obtained with the X-ray irradiation.
As shown in FIG. 6, a source of ultraviolet radiation 37 may be
used with the source of X-rays 38 so that the operator can switch
from one to the other. The photoelectron lines emitted due to the
ultraviolet radiation are shifted substantially relative to the
X-ray induced line, so that the Auger lines may be readily
recognized.
* * * * *