U.S. patent number 3,758,777 [Application Number 05/195,522] was granted by the patent office on 1973-09-11 for ion source for vaporizing and ionizing solid substances.
This patent grant is currently assigned to Varian Mat GmbH. Invention is credited to Curt Brunnee, Ludolf Jenckel.
United States Patent |
3,758,777 |
Brunnee , et al. |
September 11, 1973 |
ION SOURCE FOR VAPORIZING AND IONIZING SOLID SUBSTANCES
Abstract
High vacuum ion source for use with a mass spectro-meter to
analyze solid substances. A thermally conductive body having the
substance to be analyzed supported on a surface thereof is disposed
in the ionization chamber with the substance supporting surface
facing the ionization region of the chamber. A heat source, such as
an electron emitting device, is directed toward the opposite
surface of the body to heat the body and cause the substance to
vaporize. The heating of the body in turn heats the chamber
surfaces to prevent condensation of the vaporized substance. The
vaporized substance can be ionized by particle bombardment or field
emission. The body may take the form of a flat plate or a
cylindrical or other box-like structure.
Inventors: |
Brunnee; Curt (Platjenwerbe,
DT), Jenckel; Ludolf (Bremen-St. Magnus,
DT) |
Assignee: |
Varian Mat GmbH (Bremen,
DT)
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Family
ID: |
5721853 |
Appl.
No.: |
05/195,522 |
Filed: |
November 3, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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888320 |
Dec 29, 1969 |
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Foreign Application Priority Data
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Jan 7, 1969 [DT] |
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P 19 00 569.7 |
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Current U.S.
Class: |
250/425; 250/427;
250/288; 313/362.1 |
Current CPC
Class: |
H01J
49/14 (20130101); H01J 27/20 (20130101) |
Current International
Class: |
H01J
27/20 (20060101); H01J 49/14 (20060101); H01J
27/02 (20060101); H01J 49/10 (20060101); H01j
039/34 () |
Field of
Search: |
;250/41.9SB,41.9SE,41.9S
;313/63,230 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lindquist; William F.
Parent Case Text
This is a continuation, of U.S. Pat. application Ser. No. 888,320
filed Dec. 29, 1969, now abandoned.
Claims
We claim:
1. In a high vacuum ion source having means defining an ionization
chamber for containing therein a solid substance that is to be
vaporized and means for ionization of the vaporized solid
substances to form an ionization zone within the ionization
chamber, the improvement comprising:
a thermally conductive body disposed within the ionization chamber
having a heating surface facing said ionization zone,
said heating surface serving as a support means for a layer of the
substance to be vaporized,
means for supporting said body within the ionization chamber,
wherein the distance from the heating surface to the ionization
zone is less than the distance from other surfaces defining the
ionization chamber to the ionization zone,
said heating surface having a greater area than the facing area of
the ionization zone,
and a heat source directed toward a surface of said body opposite
the surface supporting the substance to be vaporized for maintaing
the heating surface and in turn the surfaces defining the
ionization chamber at a temperature sufficient to cause evaporation
of the solid substance to avoid condensation of the vaporized
substance at the surfaces defining the ionization chamber.
2. The apparatus of claim 1 wherein an even layer of the solid
substance that is to be vaporized is disposed on the heating
surface of the body.
3. The apparatus of claim 2 wherein said heating surface is
essentially flat and serves as a support for the even layer of the
substance to be vaporized.
4. The apparatus of claim 3 wherein said body is formed by a
plate.
5. The apparatus of claim 2 wherein said body has the shape of a
shell arranged parallel to said ionization zone and with its
concave surface turned towards the ionization zone.
6. The apparatus of claim 1 wherein said ionization chamber is a
box structure.
7. The apparatus of claim 1 wherein said body comprises a box
surrounding the ionization zone.
8. The apparatus of claim 7 wherein the inside of said box is
arranged concentrically to said ionization zone.
9. The apparatus of claim 1 wherein said heating surface is
composed of gold.
10. The apparatus of claim 1 further comprising means for moving
said body through a charging channel into and out of the vacuum
chamber.
11. The apparatus of claim 1 wherein the ionization is effected by
means of particle bombardment.
12. The apparatus of claim 1 wherein the ionization is effected by
means of field ion emission.
13. The apparatus of claim 1 and further comprising a cooling
device to cool the edges of said body and wherein said heat source
is directed toward a central area of the body.
14. The apparatus of claim 13 wherein said cooling device is
connected to said body by electrical insulators consisting of a
material of high thermal conductivity.
15. The apparatus of claim 1 wherein said body comprises a plate
having opposite facing surfaces of larger square area than any
other surfaces defining the plate, said heat source being directed
toward one of said opposite facing surfaces, the other of said
opposite facing surfaces being directed toward and disposed in
proximity to said ionization zone.
16. The apparatus of claim 15 comprising a cooling means coupled to
said one of said opposite faces at the edges thereof.
17. The apparatus of claim 16 wherein said plate is heated by said
heat source at the central area thereof and said cooling means
includes a thermally conductive means disposed at the edge area of
said plate.
18. The apparatus of claim 15 wherein said heating surface is
arranged essentially parallel to said ionization zone.
19. In a high vacuum ion source having means defining an ionization
chamber for containing a solid substance that is to be vaporized
and means for ionization of the vaporized solid substances to form
an ionization zone within the ionization chamber, the improvement
comprising:
a thermally conductive body disposed within the ionization chamber
having a heating surface facing said ionization zone,
said heating surface serving as a support means for a layer of the
substance to be vaporized,
means for supporting said body within the ionization chamber,
said heating surface having a greater area than the facing area of
the ionization zone,
and a heat source for maintaining the heating surface and in turn
the surfaces defining the ionization chamber at a temperature
sufficient to cause evaporation of the solid substance to avoid
condensation of the vaporized substance at the surfaces defining
the ionization chamber,
said body comprising a plate having opposite facing surfaces of
larger square area than any other surfaces defining the plate,
said heat source being directed toward one of said opposite facing
surfaces, the other of said opposite facing surfaces being directed
toward and disposed in proximity to said ionization zone and
supporting the substance to be vaporized.
Description
The invention relates to an ion source and a method for obtaining
ions from solid substances comprising an oven for vaporization of
said solid substances and means for ionization of the vaporized
solid substances within an ionization zone of a high vaccuum
chamber.
It is known to use an oven in the form of a heated crucible which
is positioned adjacent a sample window of the ionization chamber.
In order to obtain a high ionization efficiency the wall of the
ionization chamber at the side of the crucible has been curved
towards the ionization zone, so that the sample window for the
inlet of the vapor is brought close to the ionization zone.
However, even then the probability of ionization of the vaporized
solid substances is yet unsatisfying because a considerable portion
of the vaporized substances does not reach the ionization zone but
fails to enter the ionization zone and condenses at the cooler
walls of the ionization chamber and of the vaccuum chamber. It is
an object of the present invention to improve the ion yield from
solid samples with an ion source and method of the above mentioned
art.
This problem has been solved by that using an ion source as defined
above said ion source is provided with a heating surface which is
turned towards said ionization zone and which is maintained at an
even high temperature over its whole extend high enough to
evaporize said solid substances to avoid condensation of said
vaporized substances within the ionization chamber. Using such a
heated surface forming the sole close by surface facing the
ionization zone has the important advantage that optimum conditions
for vaporization are obtained and that losses of material by
condensation are avoided.
The heating surface preferably is made from a material of high
thermal conductivity e.g. gold. Thereby an even high volatilization
temperature is ensured all over the heating surface by using
heating means of simple construction.
Preferably the heating surface is arranged parallel to said
ionization zone and is made large compared to the extend of the
ionization zone.
Advantageously the large heating surface is used as a support for
an even layer of the substances to be vaporized.
The heating surface may be formed by one surface of a plate or
tablet which is turned towards the ionization zone. Said tablet may
have the shape of a shell arranged parallel to the ionization zone
and with its concave surface concentrical to the ionization
zones.
The heating surface may preferably be constituted by the inside of
a box surrounding the ionization zone. By that means the inside
wall of the entire ionization space is maintained at even high
temperature and all substances which are captured within the
ionization space have no chance to condense once having been
vaporized. Thus a high ionization efficiency is ensured. If the ion
source is provided with an elongated straight-lined ionization zone
then the heating surface may consist of the inside of a hollow
circular cylinder which is provided with an ion exit slit on a
generatix and a window in one of its front sides as entrance for
particle bombardment.
In a known manner the heating surface may be shiftable through a
charging valve into and out of the vaccuum chamber.
The drawing shows several embodiments of the invention. In the
drawing is
FIG. 1 an ion source with ionization by particle bombardment,
FIG. 2 a cross section along line II--II of FIG. 1,
FIG. 3 another embodiment of an ion source with ionization by
particle bombardment like FIG. 1,
FIG. 4 an ion source with field ion emission,
FIG. 5 an ion source like FIG. 2 which is provided with a cooling
device, and
FIG. 6 an ion source like FIG. 3 which also is provided with a
cooling device.
The ion source as shown in FIG. 1 consists in a conventional manner
of an ionization chamber 1 which is enclosed by a litlle metal box
2 connected by a joint 3 to a potential of e.g. + 3 kV. The
ionization is effected by electron bombardment. To this end the
metal box 2 is provided with an entry window 4 through which
electrons from a cathode 6 by means of an accelerator electrode 7
are bombarded along an electron beam 5. The electron beam is
concentrated on a band-shaped inization zone 8 by means of a magnet
(not shown in the drawing), leaves the ionization chamber 1 through
an exit window 9 and is collected by an anode electrode 10. The
cathode 6 is connected to a joint 11 with a potential of 3,1 kV.
The required inlet velocity of the electrons is effected by a
potential difference of 100 V between the accelerator electrode 7
and the metal box 2.
The ions produced within the ionization zone 8 by electron
bombardment from the gaseous or vaporous substances to be analyzed
by means of a drain electrode 14 connected to a potential of e.g.
2,9 kV are extracted through an exit slit 12 arranged parallel to
the ionization zone 8 and are emitted in the form of an ion beam 15
which in a conventional manner is subjected to a mass separation
within a separator tube by a magnetic sector field. The separator
tube 16 encloses part of the vaccuum space 17 including the ion
source.
The substance to be analyzed is vaporized by an evaporator oven 18
which is arranged within the ionization chamber 1. The solid
substance is applied in the form of a thin layer 19 upon a large
metallic heating surface 20 which is turned towards the ionization
zone 8. This heating surface 20 is formed by that side of a body
made of material of a high thermal conductivity which is turned
towards the ionization zone 8.
In the first embodiment shown in FIG. 1 and 2 the heating body
exists of a tablet 21 in the form of a rectangular plane metal
plate which is shiftable by a valve rod 23 of a conventional
charging valve with channel 22 into or out of the vacuum space 17.
For this purpose a window 24 is arranged in that side wall of the
box 2 turned towards the charging valve is large enough to let
through said tablet. The tablet 21 is maintained at the same
potential as the box 2 by a flexible line or by a contact 25.
A suitable heating means is provieed to maintain the heating
surface 20 at or above the required volatilization temperature.
Conventional means may be used for this heating purpose. Heating is
effected by electron bombardment in the embodiments shown in the
drawing. The electron bombardment is effected by cathodes 26 in
front of an electron entry slit 27 in the backside of the tablet.
In order to obtain an essentially even volatilization temperature
all over the heating surface an array of heating cathodes 26 may be
provided as is shown in FIG. 2. The tablet 21 is made of gold in
order to ensure said even volatilization temperature even with an
uneven distribution of electron bombardment.
The heating surface 20 of the tablet 21 is arranged with a small
distance d parallel to and at that side of the ionization zone 8
which is opposite the ion exit slit 12.
Preferably the ionization box 2 is maintained at a temperature
which is higher than the volatilization temperature in order to
avoid a condensation of vaporized substance at the inside of the
box.
FIG. 3 shows an embodiment in which the ionization box 2 itself is
formed as evaporator oven. This box has the shape of a circular
cylinder 29 with the ionization zone 8 extending along the axis of
the cylindrical inside surface whereas an ion exit slit 12 is
arranged along a generatrix and an electron entry window 4 and
electron exit window 9 are arranged in the opposite front sides.
The box 29 is made of gold and is heated by electron bombardment
from cathodes 26 through accelerator electrodes 30.
FIG. 4 shows the application of the invention in connection with
means for field ion emission. A very thin Wolaston-wire as emitter
31 is connected to a voltage of e.g. + 3 kV and is arranged
opposite a drain-electrode 32 with a potential of -10 kV which is
followed by additional slit electrodes 33 destinated to form the
required ion beam 15 for mass spectrometry.
In the shown embodiment the drain-electrode 32 forms part of the
evaporator oven 18 and has the shape of a shell the concave inside
of which is concentrical to the emitter 31 and which is completed
by a flat back wall to a box thus enclosing completely the whole
ionization chamber 1. The ions formed within the ionization source
are extracted out of the box through an exit slit 12. A slit 34 is
provided in the back wall to form a passage for the emitter 31
which is supported by an arm swingable around an axle 35.
Just as in the foregoing described embodiments the solid substance
to be vaporized also in FIG. 4 is applied to the inside heating
surface of the box 32 which is heated by electron bombardment from
cathodes 26 through accelerator electrodes 30.
It is important for the utility of the described ion sources that
after measurement the substance to be analyzed is rapidly cooled
below the volatilization temperature. FIG. 5 and 6 are showing
embodiments of the ion source like FIG. 2 and 3 which is provided
with a special device for rapid cooling. In the embodiment of FIG.
5 the tablet 21 supporting the sample 19 is heated by electron
bombardment from cathodes 26 and is connected to a cooling device
at it both ends. This cooling device consists of two electric
insulators 36,37 which consists of mzterial material high thermal
conductivity and which are connected at one end to the tablet 21
and at the other end to cooling coils 38,39. By this arrangement
the tablet 21 consisting of material of high thermal conductivity
is rapidly brought to the desired volatilization temperature by the
heating means and after switching out the heating means is very
rapidly cooled below the volatilization temperature by leading of
the heat through the insulators 36 and 37.
FIG. 6 is showing an embodiment in which a cylindrical box 29 at
both ends is connected to ring shaped electrical insulators 40,41
made of material of high thermal conductivity which at their free
outside are connected to cooling coils 42,43.
It will be understood that other applications of the invention are
possible and the embodiments disclosed may be subjected to various
changes, modifications and substitutions without necessarily
departing from the spirit of the invention. Thus, in conventional
ion sources with electron bombardment within an ionization box this
box could be heated entirely to an even volatilization temperature.
Of course, the substance to be vaporized must be brought into the
ionization box e.g. by applying a layer of the substance on the
inner surface of the box. If the ionization chamber is completely
enclosed by the heating surface, then the substance could be
brought within the ionization chamber in concentrated form e.g. in
the shape of a little lump although the distribution of the
substance all over the heating surface may be preferred on account
of a more intensive vaporization and a higher ion yield.
The invention is not restricted to ion sources with electron
bombardment but could be applied generally in ion sources in which
ionization is effected by particle bombardment. Furthermore it may
be applied to ion sources in which ionization is effected by
exposure of substances to radiation e.g. to ultraviolet light.
Finally the substances to be ionized could be entered in vaporous
or gaseous form from a primary oven outside the ionization chamber
through a heated channel into the heated ion source.
In any case it is important that all close by surfaces are heated
which are facing the ionization zone.
* * * * *