U.S. patent number 3,596,087 [Application Number 04/624,592] was granted by the patent office on 1971-07-27 for spark source mass spectrometers and sample insertion probe therefor.
This patent grant is currently assigned to Associated Electrical Industries Limited. Invention is credited to John Stewart Heath.
United States Patent |
3,596,087 |
Heath |
July 27, 1971 |
SPARK SOURCE MASS SPECTROMETERS AND SAMPLE INSERTION PROBE
THEREFOR
Abstract
A mass spectrometer with an insertion probe for holding and
inserting a sample through a vacuum lock. Means are provided for
cleaning the samples.
Inventors: |
Heath; John Stewart (Sale,
EN) |
Assignee: |
Associated Electrical Industries
Limited (London, EN)
|
Family
ID: |
10003317 |
Appl.
No.: |
04/624,592 |
Filed: |
March 20, 1967 |
Foreign Application Priority Data
|
|
|
|
|
Mar 21, 1966 [GB] |
|
|
12,371/66 |
|
Current U.S.
Class: |
250/426; 250/431;
250/288 |
Current CPC
Class: |
H01J
49/18 (20130101); H01J 49/0495 (20130101) |
Current International
Class: |
H01J
49/10 (20060101); H01J 49/18 (20060101); H01j
039/34 () |
Field of
Search: |
;250/41.9S,49.5,41.9SA
;314/1 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3368101 |
February 1968 |
Romand et al. |
|
Primary Examiner: Borchelt; Archie R.
Assistant Examiner: Birch; A. L.
Claims
I claim:
1. In an ion source for a mass spectrometer the improved
combination comprising:
a. structure defining an evacuable ionization chamber and a
cleaning station in the chamber,
b. an insertion probe for introducing at least one sample to be
analyzed into the ionization chamber while it is in an evacuated
state;
c. a valve connected to the structure and having a closed position
for maintaining a vacuum in the evacuable chamber; though also
having an open position for admitting the insertion probe;
d. cleaning means connected to the structure and adapted to clean a
sample when in the sample cleaning station;
e. ionization means carried in the chamber and defining an
ionization station; and,
f. said probe being insertable through the valve to position a
sample carried by it selectively and one at a time in the cleaning
and ionization stations.
2. The device of claim 1 wherein the cleaning means is within the
chamber.
3. The device of claim 2 wherein the cleaning means is a first
electrode means which cleans the sample by etching through ion
bombardment.
4. The apparatus of claim 3 wherein the first electrode means
comprises an annular electrode adapted to partially surround the
sample and clean the sample by ion bombardment.
5. The apparatus of claim 1 wherein the ionization means is a laser
generator positioned to direct a laser beam at the sample.
6. The apparatus of claim 1 wherein the insertion probe
comprises:
i. a tube;
ii. a rod axially movable within the tube; and,
iii. at least one demountable sample holder connected at one end of
the insertion probe.
7. The apparatus of claim 1 wherein the ionization means includes
at least one electrode assembly including movable sample mounting
means for holding the sample.
8. In a mass spectrometer of the spark source type, the combination
of:
a. structure defining an evacuable ionization chamber;
b. an insertion probe for introducing at least one sample of
material to be analyzed and a paired member into the chamber, the
insertion probe including means for demountably securing such
sample and paired member thereto;
c. valve means connected to the structure and having a closed
position for maintaining a vacuum in the evacuable chamber and an
open position for admitting the insertion probe;
d. electrode structure within the chamber for receiving the sample
and the paired member in an analyzing position; and,
e. said combination including a sample positioning means actuatable
from outside of the ionization chamber for transferring the sample
and the paired member from the probe to the electrode
structure.
9. The apparatus of claim 8 wherein the sample positioning means is
part of the insertion probe and wherein the probe comprises:
i. a tube;
ii. a control rod movable within the tube;
iii. a sealing member disposed in the tube and connected to the
control rod;
iv. a plate connected to the end of the tube;
v. a pair of sample holders pivotally mounted on opposite sides of
the plate;
vi. the sealing member including projecting elements each overlying
a side of the plate for rotating the sample holders; and,
vii. the rod being retractable relative to the tube to retract the
projecting elements so that the sample may be removed.
10. In a mass spectrometer of the spark source type including
source structure defining an evacuable ionization chamber, the
improvement which comprises:
a. an insertion lock connected to the source structure;
b. said lock having internal surfaces defining a passageway
communicating with the chamber and a valve for selectively opening
and closing the passageway;
c. the internal surfaces including a sealing portion, the valve
being positioned between the sealing portion and the chamber;
d. an insertion probe including an external sealing surface of the
contour of the sealing portion and adapted for sliding movement
through said sealing portion while maintaining vacuum sealing
engagement therewith;
e. said probe including means for carrying a sample and a paired
member near one end thereof whereby to position the sample and
paired member in the chamber when the probe projects through the
passage;
f. said valve including an opening sized to receive the probe when
the probe positions the sample and paired member in the
chamber;
g. said probe including structure effecting a seal within the
contour generated by said sealing surface whereby to prevent the
admission of gases through said probe into said chamber when the
probe is in the passageway; and,
h. spark means associated with said chamber for establishing a
spark between the sample and the paired member when the two are in
the ionization chamber.
11. The spectrometer of claim 10 wherein the paired member is a
second sample.
12. The spectrometer of claim 10 wherein the paired member is a
counter electrode.
13. The mass spectrometer of claim 10 wherein the spark means
includes a pair of electrode members in the chamber and wherein
said probe includes manipulating means for positioning each of the
samples and the paired member in a different one of the electrode
members.
14. The method of operating a spark source mass spectrometer
comprising the steps of:
a. positioning a sample on an insertion probe;
b. passing the probe through an insertion lock to position the
sample in an evacuated vacuum chamber while the vacuum is
maintained in the chamber;
c. cleaning the sample while in the chamber;
d. bringing the sample into contact with an electrode structure and
into an analyzing position in the chamber while still maintaining
the vacuum; and,
e. establishing a spark between the sample and a paired member in
the chamber.
15. The method of claim 14 wherein the step of bringing the sample
into contact with an electrode and into an analyzing position
includes the step of transferring the sample from the probe to the
electrode structure.
16. The method of claim 15 wherein the step of transferring the
sample to the electrode structure includes the step of rotating a
sample holder from a position longitudinal of the insertion probe
to a position transverse with respect to the axis of the insertion
probe.
17. The method of claim 15 wherein the probe is partially withdrawn
before a spark is established between the sample and a paired
member.
18. The method of claim 14 wherein the step of cleaning the sample
includes admitting a purging flow of inert gas into the chamber and
thereafter reestablishing the vacuum.
19. The method of claim 18 wherein the inert gas is argon.
20. The apparatus of claim 19 wherein the sample positioning means
is part of the insertion probe and wherein the probe comprises:
i. a tubular body;
ii. a control element disposed within the body and movable
longitudinally and rotatably relative to the body while in sealing
relationship therewith;
iii. said body having a central longitudinally extending member at
one end thereof;
iv. a sample holder mounted on said member; and,
v. means on an end of the control element adapted to contact and
manipulate the sample holder on movement of said control element to
shift the sample holder from a position longitudinal of the probe
to a position transverse
of the probe. 20. The method of claim 14 wherein the sample is
cleaned with an electrode and the cleaning is accomplished by
etching through ion
bombardment. 22. The method of claim 21 wherein the electrode is an
annular electrode and the sample is positioned at least partially
within
the annular electrode when it is cleaned. 23. In a mass
spectrometers of the spark source type, the combination of:
a. structure defining an evacuable ionization chamber;
b. an insertion probe for introducing at least one sample of
material to be analyzed into the evacuated chamber, the insertion
probe including means for demountably securing such sample
thereto;
c. valve means connected to the structure and having a closed
position for maintaining a vacuum in the evacuable chamber and an
open position for admitting the insertion prove;
d. electrode structure within the chamber for receiving the sample
in an analyzing position;
e. said combination including a sample positioning means actuable
from outside of the ionization chamber for transferring the sample
from the probe to the electrode structure;
f. said sample positioning means including structure in the probe
for maintaining a sample carried by the probe disposed
substantially longitudinally of the probe during insertion and for
moving the sample support to a position transverse of the probe
after insertion; and,
g. said sample positioning means also includes movable portions of
said
electrode structure adapted to transfer a sample from the probe.
24. The combination of claim 23 wherein the sample support is moved
from its longitudinal to its transverse position by rotation of the
sample support
member. 25. The method of operating a spark source mass
spectrometer comprising the steps of:
a. positioning a sample on an insertion probe;
b. passing the probe through an lock to position the sample in an
evacuated vacuum chamber while the vacuum is maintained in the
chamber;
c. rotating a sample holder from a position longitudinal of the
insertion probe to position transverse with respect to the as of
the insertion probe and bringing the sample into contact with an
electrode structure and into an analyzing position in the chamber
while still maintaining the vacuum; and,
d. establishing a spark between the sample and a paired member in
the
chamber. 26. In a mass spectrometer, the improved combination
comprising:
a. structure establishing an evacuable chamber and a sample
insertion passage communicating with the chamber;
b. ionization means establishing a sample ionization stain within
the chamber and including means to ionize a sample positioned at
the ionization station;
c. valve means connected to the structure for selectively closing
said passage to maintain a vacuum within the space;
d. said structure establishing a path of sample travel from
external of said structure through said valve means to said
ionization station;
e. an insertion probe adapted to transport a sample from a position
external of said structure along said path to said ionization
station; and,
f. cleaning means along said path and within said chamber for
cleaning a sample within said chamber after it has been moved along
said path past
said valve means by the insertion probe. 27. The mass spectrometer
of claim 26 wherein said cleaning means establishes a cleaning
station
between the valve means and the ionization station. 28. The
combination of claim 26 wherein said cleaning means includes means
to admit a purging
flow of gas after a sample has been cleaned. 29. The combination of
claim 26 wherein the cleaning means includes an electrode adapted
to clean a
sample by ion bombardment. 30. The device of claim 29 wherein the
electrode is an annular electrode adapted to partially surround the
sample
and clean the sample by ion bombardment. 31. The method of
positioning a sample in a spark source mass spectrometer comprising
the steps of:
a. mounting a sample and a paired member on a single insertion
probe;
b. inserting a probe into an insertion lock to establish a vacuum
seal therebetween;
c. opening a valve in the insertion lock and thereafter inserting
the sample and paired member into an evacuated ionization chamber
by passing the insertion probe through the valve, and,
d. thereafter establishing a spark between the sample and the
paired member
to ionize portions of the sample. 32. The method of claim 31
including the step of transferring the sample and paired member
from the probe to electrode structures within the evacuated chamber
prior to establishing a
spark. 33. The method of claim 31 wherein the paired member is a
second
sample. 34. An insertion probe comprising:
a. a tube;
b. a control rod movable within the tube;
c. a sealing member disposed in the tube and connected to the
control rod;
d. a plate connected to the end of the tube;
e. a pair of sample holders pivotally mounted on opposite sides of
the plate;
f. the sealing member including projecting elements each overlaying
a side of the plate for rotating the sample holders; and
g. the rod being retractable relative to the tube to retract the
projecting
elements so that the sample may be removed. 35. An insertion probe
comprising:
a. a tubular body;
b. a control element disposed within the body and movable
longitudinally and rotatably relative to the body while in sealing
relationship therewith;
c. said body having a central longitudinally extending member at
one end thereof;
d. a sample holder mounted on said member; and,
e. means on an end of the control element adapted to contact and
manipulate the sample holder on movement of said control element to
shift the sample holder from a position longitudinal of the probe
to a position transverse of the probe.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
1. Application Ser. No. 460,392, entitled "Mass Spectrometer sealed
Vacuum Lock," now U.S. Pat. No. 3,440,417, issued Apr. 22, 1969
invented by John Stewart Heath.
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates to ionization sources for mass spectrometers
and more particularly to a novel insertion probe, novel cooperating
structure for causing ionization of material, and to a novel method
of operating a mass spectrometer.
2. Description of the Prior Art
In mass spectrometers of the type in which ionization is
accomplished with an electron beam, devices have existed for
introducing samples into an ion source chamber for analysis without
destroying the vacuum in the ionization chamber. Thus, the
desirability of causing as little disturbance as possible to the
high vacuum existing within the ion chamber has been recognized.
One system for maintaining vacuum in an electron beam type mass
spectrometer is described and claimed in U.S. Pat. No. 3,158,740
issued Nov. 24, 1964 to R. D. Craig et al. under the title Mass
Spectrometer Sample Insertion Devices. While the problems attendant
to destroying the source vacuum have been met and solved Sealed
mass spectrometers with electron beam sources, with prior
spark-type ion sources, when the solid sample is placed in an ion
source chamber, the chamber is opened to the atmosphere and air is
permitted to enter the chamber.
When a chamber is opened to the atmosphere, in addition to the
relatively apparent problem of destroying the existing vacuum,
other undesirable conditions are produced within the chamber. One
undesirable condition is that contaminating molecules of such
materials as certain gases and water become attached to the
surfaces within the chamber by a process known as adsorption. When
the vacuum is reestablished, these contaminating molecules are
released to a certain extent and limit the vacuum that can
thereafter be attained. Removal of these contaminating molecules
and consequent reduction in their partial pressure can be achieved
only by pumping for long periods or by raising the temperature of
the chamber enclosure.
A reduction in the partial pressure of the contaminating molecules
of foreign matter has been found to be necessary for at least two
reasons. First, it is necessary to have a low partial pressure of
residual gases in the analyzer portion of the mass spectrometer to
permit the unobstructed passage of ions without collision with
gaseous contaminating foreign molecules. These collisions are
undesirable since they tend to scatter the ions and thus reduce the
resolving power and accuracy of the instrument. Second, a low
partial pressure of contaminating foreign molecules of oxygen and
water vapor is necessary in the ion source chamber in order that
ions of oxygen originating from the sample material will not be
masked by ions of oxygen originating from stray molecules of
residual foreign gases. It is often desirable to detect small
traces of oxygen in solid material since it is known that the
properties of many materials are sensitive to concentrations of
oxygen of less than one part in one million.
Another problem with prior mass spectrometers is that the solid
samples often become contaminated before being introduced into the
ion source chamber. Normally, decontamination of the surfaces of
the samples is carried out in a separate vacuum vessel and during
transfer from the vacuum vessel to the ion source chamber the
samples are often unavoidably contaminated both through handling
and by the reformation of surface oxide layers resulting from
contact with atmospheric oxygen.
SUMMARY OF THE INVENTION
With the present invention, a mass spectrometer has the usual
evacuable ionization chamber. A probe is provided for introducing a
sample or samples for analysis into the evacuated chamber. Samples
are introduced through a vacuum lock which permits insertion of the
probe while maintaining a high vacuum within the ionization
chamber. The probe positions each sample selectively and one at a
time at cleaning and analyzing positions within the chamber.
As will become more apparent, the probe can be used to insert
either one sample or a pair of samples simultaneously. For purposes
of explanation, the use of two samples will be discussed, yet it
should be understood that a single sample can be used. This permits
use of the known techniques of either (1) establishing an arc
between two samples of the same material or, (2) when desired, as
when arcing is difficult because the sample is a crystal or the
like, using a counter electrode of gold or other relatively stable
metal material and a single sample.
A cleaning electrode is mounted within the chamber for use when the
samples are mounted on the probe in its cleaning position. The
cleaning electrode is about the samples so that the samples may be
etched and thereby cleaned by ion bombardment. There is also an
access to the chamber for introducing a continuous flow of an inert
gas into the chamber during the etching of the samples and for
removing the gas and evacuating the chamber subsequent to etching
and prior to ionization of the samples.
After the samples have been cleaned, the probe is movable to the
analyzing position. There the samples are positioned in electrode
supports at which time the samples are in their analyzing position.
After the probe has positioned the samples in their analyzing
positions the probe is removed and a spark may be drawn between the
sample and a counter electrode or between the samples to ionize the
sample material. Alternatively, a laser generator mounted
externally of the chamber may be used to ionize the sample material
in which case the probe need not position the samples in the
electrode nor does it need to be withdrawn.
The above-referenced U.S. Pat. No. 3,440,417 discloses an insertion
lock including a plug for opening and closing a passageway and for
providing communication via this passageway between an exhaust port
and an ion source chamber. An insertion probe can be moved axially
in the passageway to introduce the sample into the chamber.
With the insertion probe bearing a sample initially placed in the
passageway, the valve may be opened and a vacuum maintained within
the chamber since the probe seals off the passageway. After the
sample has been positioned in the chamber, the probe may be
withdrawn past the plug but yet sealing off the passageway. After
the plug is closed, the probe may be fully withdrawn from the
passageway without materially affecting the vacuum in the
chamber.
In one form of the invention, the insertion probe includes a tube
having a plate connected at one end. The plate is connected to the
inner sides of the tube so as to be aligned with the central axis
of the tube and extends outwardly from the end of the tube. A
control rod extends through the length of the tube and has a
pistonlike sealing member connected at the end of the control rod
adjacent the plate forming a fluidtight seal with the inner surface
of the tube. A pair of sample positioners are connected to the
pistonlike sealing member. The positioners are arranged in
staggered fashion on opposite sides of the plate and extending
outwardly from the tube opening parallel to the axis of the tube. A
pair of pins are mounted in staggered fashion on opposite sides of
the plate adjacent and on opposite sides of the sample positioners.
Each sample holder has a slot in its side. The pins are each
disposed in an associated one of the slots with the slots facing in
opposite directions away from the adjacent and associated one of
the sample positioners. Samples are mounted on the ends of the
sample holders which ends are the ends furthest from the tube.
At the end of the control rod remote from the samples, a portion of
the control rod extends from the tube so that the rod may be
rotated manually or otherwise. The tube has a control slot formed
near this end of the tube and a key connected to the control rod is
adapted to travel in the control slot for guiding the movement of
the sample positioners. The control slot has a portion aligned
parallel to the axis of the tube, a second portion aligned somewhat
transverse to the axis, and another portion aligned parallel to the
axis of the tube and extending in an opposite direction from the
other parallel portion.
In the form of the invention wherein the sample is ionized by a
laser beam, the sample remains mounted at the end of the insertion
probe and the laser beam originates from a laser generator external
of the ionization chamber.
Accordingly, the principal objects of the present invention are to
provide a novel and improved mass spectrometer including structure
for maintaining a vacuum in the source when a sample is inserted,
novel structure for cleaning a sample in an evacuated chamber, a
novel sample insertion device, and a novel method of operating a
mass spectrometer.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a novel spark-type ion source in cross section;
FIG. 2 is a detailed view of the end of the insertion probe for
holding the samples;
FIG. 3 is a view of the right side of the end of the insertion
probe shown in FIG. 2;
FIG. 4 is a view of a sample holder in rotated position and an
accompanying sample positioner; and,
FIG. 5 is a cross-sectional view of an alternative form of the
novel ion source with laser ionization.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, an ion source is shown generally at 10. The
ion source 10 has an enclosure wall 14 which defines an ionization
chamber 16. An insertion lock 12 is connected to the enclosure wall
14. The insertion lock 12 is provided with a passage 17 which
communicates with the ionization chamber 16. An insertion probe 18
is shown inserted in the passage 17 in slidable engagement with the
interior members of the insertion lock 12.
The ion source 10 includes movable mountings 19, 20 in the form of
bellows secured to openings on opposite sides of the enclosure wall
14. A pair of insulating supports 26, 28 composed of an insulating
material are connected to the movable mountings 19, 20 respectively
and are located within the ionization chamber 16. The insulating
supports 26, 28 are respectively connected to a pair of
manipulators 22, 24 located outside the ionization chamber 16 and
to a pair of slotted electrode mounts 30, 32 composed of
electrically conductive material located opposite one another
within the ionization chamber 16.
A source terminal mounting 34 composed of insulating material is
mounted in an aperture in the enclosure wall 14. A pair of source
terminals 36, 38 project through the mounting 34 and are adapted to
be connected to an external high-voltage source. A pair of source
leads 40, 42 are connected between interior ends of the source
terminals 36, 38 respectively and to the electrode mounts 30, 32
respectively to provide high voltage to the electrode mounts 30, 32
for establishing an ionizing spark when samples are carried by
them.
A cleaning electrode terminal mounting 44 composed of insulating
material projects through an aperture in the enclosure wall 14 near
the passage 17. A cleaning electrode terminal 46 projects through
the cleaning electrode mounting 44 into the chamber 16. A lead 48
for supplying a high-positive potential is connected to the outer
end of the electrode terminal 46 and a cleaning electrode 50 is
mounted on the opposite end of the electrode terminal 46 within the
ionization chamber 16 adjacent the inner end of the passage 17. The
cleaning electrode 50 is preferably annular and has its center
aligned along the longitudinal axis of the passage 17 for at least
partially surrounding a sample or samples inserted in the chamber
and thereby permitting a uniformly cleaned sample to be obtained.
Cleaning is accomplished by applying 2kv. to the electrode 50 in
the presence of argon so that a sample surface is bombarded by
argon ions which removes surface atoms.
The insertion lock 12 includes a body 52, an end block 54 connected
at the outer end of the body 52, and a flanged, tubular mounting
member 56 connected to the inner end of the body 52. The mounting
member 56 is connected to the enclosure wall 14. The passage 17
extends through the end block 54, the body 52, and the mounting
member 56 and is defined by the inner structure of the insertion
lock 12.
A pair of tubes 59, 61 are connected to the side of the body 52 and
define ports 60, 62 respectively, each of which communicates with
the passage 17. The tubes 59, 61 may be connected to vacuum pumps.
A valve plug 64 is located within the passage 17 and is preferably
in the form of a rotary ball. A valve shaft 66 is positioned
radially outwardly from the passage 17, and is connected to the
valve plug 64. The shaft 66 passes through a mounting cup 68 which
carries seal structure to be described presently. On its opposite
side, the plug 64 engages an annular bearing end seal 70.
The plug 64 has a bore 72 which, in the open position shown in FIG.
1, communicates with and forms a part of the passage 17. The plug
64 has a transverse bore 74 connecting the port 62 to the bore 72
to provide a path for withdrawing gases through the passage 17.
The insertion lock 12 includes a number of seals some of which are
constructed to slidably engage the outer surface of the insertion
probe 18 so that a high vacuum can be maintained in the ionization
chamber 16 while the insertion probe seals off the passage 17.
The plug 64 is clamped between two plug seals 76, 78 each of which
is provided with an opening for admitting the insertion probe 18.
The plug seal 78 engages a seal wedge 80 at the side of the plug 64
toward the chamber 16. A disc spring 82 located between the
mounting member 56 and the seal wedge 80 biases the seal wedge 80
against the plug seal 78. This biases the plug seal 78 against the
inner walls of the body 52 and against the plug 64. Another plug
seal 84 surrounds the shaft 66 and engages the shaft side of the
plug 64. A seal wedge 86 is biased against the plug seal 84 by a
disc spring 88 located between the seal wedge 86 and the cup 68.
This biases the plug seal 84 against the inner walls of the body 52
and against the plug 64.
A sliding seal 102 including a flange 103 is positioned near the
outer end of the passage 17 and around the insertion probe 18. The
sliding seal may be formed of Polytetrafluoroethylene sold under
the trademark "Flourosint" by Polypenco Limited, Welwyn Garden
City, Herts, England. The sliding seal 102 has radially extending
flange 103 which abuts the inner end of the block 54. The sliding
seal 102 is identified as a sliding seal because, while it remains
stationary relative to the insertion lock 12, it provides a seal
against the outer surface of the insertion probe 18 as it is
shifted axially in the passage 17. This permits a vacuum to be
maintained in the ionization chamber 16 and only the insertion
probe 12 blocking the passage 17.
An annular seal wedge 100 is positioned next to the sliding seal
102 and a seal wedge 96 engages the seal wedge 100. A spacing tube
92 is provided which has an opening 75 at one side communicating
with the port 60. The spacing tube is biased against a seal wedge
90 by a disc spring 98 which also biases the seal wedge 96 against
the seal wedge 100. The bias on the seal wedge 100 clamps the
flange 103 of the sliding seal 102 against portions of the end
block 54, thus holding the sliding seal 102 in place. The bias on
the seal wedge 90 is applied against the seal 74 to urge it into
engagement with the plug 64 and the body 52.
At the exterior of the insertion lock 12, a handle 104 is connected
to the shaft 66 for rotating the plug 64. The plug 64 is shown in
an open position in FIG. 1 for admitting the insertion probe 12.
The handle 104 may be locked in this open position by a locking bar
108 which is rotatably mounted on the end block 54. A collar 110
surrounds and is secured to an end of the locking bar 108 which
passes through the end block 54 and a pin 113 is connected to the
collar 110. The pin 113 engages a ring 116 mounted on the handle
104. A spring 112 biases the pin 114 against the ring 116 in the
position shown. By rotating the locking bar 108, the pin 113 will
be moved clear of the ring 116 and the handle 104 may be rotated to
close the plug 64.
Referring to FIGS. 2 and 3, the sample mounting arrangement and
control mechanism of the insertion probe 18 is shown in greater
detail. The insertion probe 18 includes a housing tube 114 ground
on its outer surface to very fine cylindrical finish and has a
through bore 115 along its length. A plate 118 includes a portion
disposed in the bore 115 and connected to the interior of the tube
114 at its end adapted to be inserted within the ionization chamber
16. The plate 118 also has a portion projecting from the bore 115
at the same end of the tube 114, and the plate 118 is preferably
aligned along the central axis of the tube 114. Pivot pins 130,
131, arranged in a staggered fashion, project from opposite sides
of the exposed portion of the plate 118. A sample holder 133 having
a transverse slot 134 for receiving the pin 130 is pivotally
mounted on the pin 130 adjacent one side of the plate 118.
Similarly, a sample holder 135 (FIG. 3) having a transverse slot
134' is pivotally mounted on the pin 131 adjacent the other side of
the plate 118. Before removal, the sample holders 133, 135 are
aligned somewhat parallel to the longitudinal axis of the tube 114
and the open ends of the slots 134, 134' face in opposite
directions. Samples 136, 137 are respectively mounted in ends of
the sample holders 133, 135 and are secured thereto by screws 138,
138'. It is known in the art to use one sample and a counter
electrode in a spark source mass spectrometer. While the members
136, 137 are described as samples throughout the specification, it
should be recognized that in practice one will use one sample and a
paired member. The paired member will be either a second sample or
a counter electrode.
A rodlike control member 139 is positioned in the bore 115 of the
tube 114 and extends substantially the entire length of the tube
114. A portion of the control member 139 projects from one end of
the tube 114 and the plate 118 projects from the opposite end. A
pistonlike sealing member 140 is connected to the control member
139 at its inner end adjacent the plate 118. The sealing member 140
slidably engages the inner surface of the tube 114 to provide a
fluidtight seal and thereby prevent contaminating molecules from
entering the ionization chamber 16 through the tube 114.
With reference to FIG. 1, the tube 114 has a control slot S at its
outer end. The control slot has offset portions 142, 143 aligned
somewhat parallel with the longitudinal axis of the tube 114 and a
transverse connecting portion 114. A key K is connected to the
control member 139 and its movement is guided by the slot S.
A pair of sample positioners 145, 146 are connected to the inner
side of the sealing member 140 adjacent the plate 118 and are
arranged on opposite sides of the plate 118 for engagement with and
control of the sample holders 133, 135 respectively. The sample
positioners 145, 146 are aligned somewhat parallel to the
longitudinal axis of the tube 114 and are located adjacent sides of
the sample holders 133, 135 respectively facing away from the open
ends of the slots 134, 134', respectively.
The insertion probe 18 has a locating collar 160 around and secured
to the base of the tube 114. A pair of locating pins 161 are
carried in bores 162 in the collar 160. Springs 163 normally bias
the locating pins 161 outwardly against annular retaining caps
164.
The locating pins, when brought into engagement with end surface
170 of the block 54, locate the probe 18 in its analyzing position
as shown in FIG. 1.
The procedure for inserting the insertion probe 18 into the
insertion lock 12 and ultimately within the ionization chamber 16
will now be described. The locking bar 108 is rotated to release
the handle 104 so that the plug 64 may be rotated and closed. With
the plug 64 in closed position, a vacuum is established within the
ionization chamber 16. The sample holders and samples are mounted
on the plate 118 axially in line with the tube 114, and the
insertion probe 18 is partially inserted into the passage 58 of the
insertion lock 12 until a seal is established with the sliding seal
102. Next, the plug 64 is rotated to an open position and the pin
113 is engaged with the ring 116 to hold the plug in its open
position. With the plug 64 in open position, the insertion probe 18
is advanced to the cleaning position adjacent the electrode 50. In
this position the samples are in the ionization chamber 16 and
surrounded by the cleaning electrode 50 shown in phantom in FIG.
1.
A purge flow of argon is then caused to flow through tube 175 and
space 17 into the source region giving a pressure of about 0.02
torr. A high positive voltage is applied to the electrode 50 to
produce a high-voltage discharge. Ions produced in the discharge
bombard the surface of the samples 136, 137, thus etching or
eroding the surface of the samples by a process referred to as
sputtering. This erosion occurs equally over the surface of the
samples 136, 137 to clear off foreign matter and any oxidized
surface which may be present.
The purge flow of argon is then stopped allowing the pressure in
the ionization chamber 16 to fall as the vacuum is reestablished.
The insertion probe 18 is then advanced to the analyzing position,
which is the position of the probe shown in FIG. 1, so that the
sample holders are adjacent the electrode mounts 30, 32. At this
time the samples are in the position shown in FIGS. 2 and 3. The
key K is at the upper end of the slot portion 142 so that the
positioners 145, 146 maintain the samples in that position.
The samples are then positioned in the electrode mounts 30, 32. To
accomplish this, the control member 139 is withdrawn axially until
the key K is at the juncture of slot portions 142, 144. At this
time the sample holders 133, 135 are free to rotate approximately
90.degree. about the pins 130, 131 since the sample positioners
145, 146 and the sealing member 140 are retracted to a position
indicated in the dotted lines in FIG. 2.
The control member 139 is then rotated to a position in which the
key K is at the juncture of the slot portions 143, 144. This
rotation causes the positioners 145, 146 to engage and rotate the
sample holders 133, 135 approximately 90.degree. from their initial
axially aligned position. The sample positioners 145, 146, the
sample holders 133, 135 and the samples 136, 137 are then in the
positions of FIGS. 1 and 4 with the samples 136, 137 aligned
parallel and projecting in opposite directions. At this time, the
sample holders 133, 135 are supported by the sample positioners
145, 146 respectively, as indicated in FIG. 1 and by the solid line
in FIG. 4. The manipulators 22, 24 are then moved toward the sample
holders 133, 135 to a position at which the slots in the electrode
mounts 30, 32 may receive the sample holders 133, 135 respectively
and secure them by friction, or other means. The control member 139
is then retracted to a position in which the key is at the lower
end of the slot portion 143 and the sample positioner 145 is at the
position shown in phantom in FIG. 4.
The probe is next shifted axially inwardly depressing the plungers
161 in the bores 162 against the action of the springs 163 until
the collar abuts the end surface 170. This axial shifting of the
probe removes the pins 130, 131 from the slots 134, 134'. The
sample holders 133, 135 are then moved by operating the
manipulators 22, 24 a sufficient amount to allow the insertion
probe 18 to be withdrawn. The probe is partially withdrawn to allow
closing of the plug 64 while the probe still seals the passage 17.
The plug 64 is then closed, and the insertion probe 18 is removed
from the insertion lock 12.
The ionization chamber 16 is continuously vacuum pumped while the
samples are in the analyzing position. With the samples 136, 137
held in the electrode mounts 30, 32, an arc is produced between the
samples 136, 137. The arc may be produced by any one of the three
following method:
1. A high-radio frequency voltage;
2. A high-voltage pulse followed by a low-voltage DC arc; or,
3. A mechanical vibration arranged to cause intermittent contact
between the electrodes supplied from an inductive low-voltage power
supply. The electrodes are maintained at a DC voltage such as 20
kilovolts positive with respect to ground and the ions formed in
the arc are accelerated by this voltage to a plate (not shown)
maintained at ground potential. Ions pass through a hole in this
plate for analysis by the mass spectrometer.
An alternative ion source arrangement is shown in FIG. 5. In this
arrangement, the tube 114' holds an insulator support 150. A single
sample 152 is mounted on the insulator support 150. An inset
structure 154 is connected to the enclosure wall 14' and includes a
window 156 at one end. A laser beam 157 is projected from an
externally positioned laser generator 158 through a lens 159 and
through the window 156 upon the sample 152. Procedure for using
this arrangement differs from the above-described procedure in that
the tube 114' remains within the ionization chamber 16' during
ionization of a single sample 152 by the laser beam 157.
Although the invention has been described in its preferred form
with a certain degree of particularity, it is understood that the
present disclosure of the preferred form has been made only by way
of example and that numerous changes in the details of construction
and the combination and arrangement of parts may be resorted to
without departing from the spirit and the scope of the invention as
hereinafter claimed.
* * * * *