U.S. patent application number 11/432909 was filed with the patent office on 2008-05-29 for deicing of radiation detectors in analytical instruments.
Invention is credited to James V. Howard, Tom Jacobs, Mark E. Misenheimer, David B. Rohde, Bruce R. Weber.
Application Number | 20080121801 11/432909 |
Document ID | / |
Family ID | 39402153 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080121801 |
Kind Code |
A1 |
Howard; James V. ; et
al. |
May 29, 2008 |
DEICING OF RADIATION DETECTORS IN ANALYTICAL INSTRUMENTS
Abstract
In an analytical instrument having a radiation detector, such as
an electron microscope with an X-ray detector, a thermoelectric
element (such as one or more Peltier junctions) is driven by a
cooling power supply to cool the detector and thereby decrease
measurement noise. Oil condensates and ice can then form on the
detector owing to residual water vapor and vacuum pump oil in the
analysis chamber, and these contaminants can interfere with
measurement accuracy. To assist in reducing this problem, the
thermoelectric element can be powered in the reverse of its cooling
mode, thereby heating the detector and evaporating the
contaminants. After the detector is cleared of contaminants, it may
again be cooled and measurements may resume. Preferably, the
thermoelectric element is heated by a power supply separate from
the one that provides the cooling power, though it can also be
possible to utilize a single power supply to provide both heating
and cooling modes.
Inventors: |
Howard; James V.; (Madison,
WI) ; Jacobs; Tom; (Madison, WI) ;
Misenheimer; Mark E.; (Middleton, WI) ; Rohde; David
B.; (Madison, WI) ; Weber; Bruce R.;
(Waunakee, WI) |
Correspondence
Address: |
THERMO FINNIGAN LLC
355 RIVER OAKS PARKWAY
SAN JOSE
CA
95134
US
|
Family ID: |
39402153 |
Appl. No.: |
11/432909 |
Filed: |
May 12, 2006 |
Current U.S.
Class: |
250/307 ;
250/311 |
Current CPC
Class: |
F25B 21/04 20130101;
H01J 2237/002 20130101; H01J 37/244 20130101; H01J 2237/182
20130101; H01J 37/26 20130101 |
Class at
Publication: |
250/307 ;
250/311 |
International
Class: |
H01J 37/21 20060101
H01J037/21 |
Claims
1. An analytical instrument comprising: a. a radiation detector; b.
a mount thermally coupled to the radiation detector; c. a
thermoelectric element coupled to the mount, wherein the
thermoelectric element comprises a cold side configured adjacent to
the mount and an opposing hot side to the mount; and d. a power
supply supplying current to the thermoelectric element sufficient
to heat the thermoelectric element so that the detector can be
conditioned in 15 minutes or less.
2. The analytical instrument of claim 1 further comprising a second
power supply capable of supplying current to the thermoelectric
element sufficient to cool the thermoelectric element.
3. The analytical instrument of claim 1 wherein the power supply is
reversible, whereby current may be supplied to the thermoelectric
element sufficient to cool the thermoelectric element.
4. The analytical instrument of claim 1 wherein the mount is at
least substantially formed of heat-conductive metal.
5. The electron microscope of claim 1 wherein the thermoelectric
element includes at least two stages therein.
6. The analytical instrument of claim 1 wherein: a. the mount is
elongated, with the radiation detector situated on an end of the
length of the mount; and b. the mount extends into an analysis
chamber, the analysis chamber being in communication with a vacuum
pump.
7. The analytical instrument of claim 6 further comprising a. an
electron beam source supplying an electron beam to the analysis
chamber, and b. a sample stage whereupon a specimen may be situated
for analysis.
8. The analytical instrument of claim 6 wherein the mount is
translatable within the analysis chamber.
9. The analytical instrument of claim 6 further comprising a heat
sink coupled to the thermoelectric element outside the analysis
chamber.
10. The analytical instrument of claim 6 wherein the mount bears a
solid window thereon, the window being situated between the
radiation detector and the analysis chamber.
11. A method of operating an analytical instrument which includes:
(1) a radiation detector; (2) a mount thermally coupled to the
radiation detector, and (3) a thermoelectric element coupled to the
mount, wherein the thermoelectric element comprises a cold side
configured adjacent to the mount and an opposing hot side to the
mount; and the method including the step of supplying current to
the thermoelectric element sufficient to heat the thermoelectric
element so that the detector can be conditioned in 15 minutes or
less.
12. The method of claim 11 followed by the step of supplying
current to the thermoelectric element sufficient to maintain the
thermoelectric element at a substantially constant temperature for
a predetermined period of time.
13. The method of claim 11 wherein the step of supplying current to
the thermoelectric element sufficient to heat the thermoelectric
element is preceded by the step of supplying current to the
thermoelectric element sufficient to cool the thermoelectric
element.
14. The method of claim 13 wherein the steps of: a. supplying
current to the thermoelectric element sufficient to heat the
thermoelectric element, and b. supplying current to the
thermoelectric element sufficient to cool the thermoelectric
element, are respectively performed by distinct power supplies.
15. The method of claim 11 further comprising the step of directing
electrons toward a specimen situated adjacent to the radiation
detector.
16. The method of claim 15 further comprising the step of
establishing a vacuum between the specimen and the radiation
detector.
17. A method of operating an analytical instrument which includes:
(1) an analysis chamber, (2) a radiation detector coupled to a
heat-conductive mount within the analysis chamber, and (3) a
thermoelectric element coupled to the mount, the method including
the steps of: a. at least substantially evacuating gas from the
analysis chamber; b. supplying current to the thermoelectric
element suitable to decrease the temperature of the radiation
detector to an operating temperature; c. subsequently supplying
current to the thermoelectric element to increase the temperature
of the radiation detector to a conditioning temperature which is
above the operating temperature; d. maintaining the temperature of
the radiation detector at or about the conditioning temperature for
a discrete conditioning period; and e. supplying current to the
thermoelectric element suitable to return the radiation detector to
a temperature at or about the operating temperature.
18. The method of claim 17 wherein the conditioning temperature is
above the ambient temperature as measured outside the analysis
chamber.
19. The method of claim 17 wherein the conditioning period is less
than or equal to 15 minutes.
20. The method of claim 17 further including the step of directing
an electron beam into the analysis chamber when the radiation
detector is at or about the operating temperature.
21. The method of claim 17 proceeded by the step of advancing the
mount into the analysis chamber.
Description
FIELD OF THE INVENTION
[0001] This document concerns an invention relating generally to
inhibiting or preventing ice formation on cooled (e.g.,
cryogenically chilled) sensors present in analytical instruments,
and more specifically to ice prevention/removal on cooled radiation
detectors such as those found in electron microscopes.
BACKGROUND OF THE INVENTION
[0002] Various instruments for analyzing the characteristics of
materials rely on sensors for at least a portion of their
measurement operations, with these sensors being chilled to low
temperatures to enhance measurement accuracy (e.g., by decreasing
electronic "noise"). As an example, electron microscopes often
include an X-ray detector (such as a silicon sensor) mounted at the
end of an elongated probe or other mount, often called a "cold
finger," which is situated next to a specimen to be analyzed. The
cold finger is chilled to cryogenic (ultralow) temperatures,
usually by a Dewar system utilizing liquid nitrogen coolant, though
some systems use a standard refrigeration cycle for cooling (i.e.,
evaporative cooling). Additionally, one provider (Thermo Electron,
Madison, Wis., USA) has long provided thermoelectric (Peltier)
cooling of detectors. During operation, as the specimen is
bombarded by electrons from the microscope's electron beam, it
emits X-rays which are picked up by the detector. The detector
measurements can be processed to provide information regarding the
specimen's material and other characteristics.
[0003] These arrangements suffer from the unfortunate disadvantage
that while cooling of the detector enhances measurement quality,
cooling also increases the possibility that the detector will be
fouled (and its measurements skewed) owing to water/oil
condensation, and ice formation, on the cooled detector. Moisture
and oil are often present in the analysis chamber wherein the
specimen and detector are located, with the oil originating from
the vacuum pumping system. While they can be diminished by steps
such as evacuating the analysis chamber so the specimen and
detector are in vacuum (a common step), ice and oil condensates
still tend to collect on the detector owing to factors such as
residual gas within the analysis chamber and moisture release from
the specimen. Some detectors and mounts are partially insulated
from the analysis chamber by a surrounding shell about the mount
and/or a window between the chamber and the detector; however, even
these arrangements tend to accumulate ice and oil on the shell
and/or window. Additionally, while windows help protect detectors
from contamination, they can also block lower-energy emissions that
could otherwise be usefully detected by the detector.
[0004] As discussed in U.S. Pat. Nos. 4,931,650 and 5,274,237, the
foregoing difficulties have led to the development of a variety of
corrective devices and methodologies. Both patents describe the use
of periodic warm-up cycles wherein the mount and detector are
allowed to warm up to drive off water. U.S. Pat. No. 4,931,650
assists such a procedure by incorporating a resistive heater for
warming the detector, and U.S. Pat. No. 5,274,237 has a portion of
the analysis chamber about the detector at a cooler temperature so
that the bulk of any ice will form away from the detector. However,
it would be useful to have further arrangements available for
avoiding detector ice contamination in electron microscopes and
other analytical instruments.
SUMMARY OF THE INVENTION
[0005] The invention involves arrangements which are intended to at
least partially address the aforementioned problems. A brief
summary of an exemplary version of the invention follows below in
order to give the reader a basic understanding of some of its
advantageous features, with reference being made to the
accompanying drawing, which schematically depicts the exemplary
version. Since this is merely a summary, it should be understood
that more details regarding preferred versions of the invention may
be found in the Detailed Description set forth elsewhere in this
document. The claims set forth at the end of this document then
define the various versions of the invention in which exclusive
rights are secured.
[0006] The invention is primarily intended for implementation in an
analytical instrument 100 having a radiation detector 102, such as
the electron microscope schematically depicted in the accompanying
FIGURE. In the electron microscope 100, a specimen 104 on a sample
stage 106 is subjected to an electron beam 108 from an electron
beam source 110, and a radiation detector 102 (here an X-ray
detector) receives radiation emitted from the specimen 104 to
provide information regarding the characteristics of the specimen
104. The foregoing components are situated within an analysis
chamber 112, which is evacuated by means of a vacuum pump 114.
[0007] The radiation detector 102 is coupled to a thermally
conductive mount 116 (e.g., a "cold finger" made of copper and/or
another conductive metal), which is shown as being slidably
connected to the analysis chamber 112 to allow the radiation
detector 102 to be advanced or retracted to a desired position
relative to the sample stage 106. The mount 116 is then coupled to
a thermoelectric element 118 such as one or more Peltier junctions,
with a multi-element "stack" being depicted in the FIGURE. The
thermoelectric element(s) 118 have a cold side 120 adjacent the
mount 116 and detector 102 and an opposing hot side 122. A heat
sink 124, here shown as a series of fins, is coupled to the hot
side 122 of the thermoelectric element(s) 118 to allow cooling of
the mount 116 when the element(s) 118 are supplied with power from
a cooling power supply 126. To deter ice formation and/or oil
condensation on the mount 116 and detector 102, the detector 102
may be isolated from the chamber interior by a shell 128
surrounding the mount 116, and by a window 130 situated on the
shell 128 between the sample stage 106 and the detector 102. In
addition, a housing 132 about the element(s) 118 is joined to the
chamber 112 via a bellows 134 which helps prevent air from leaking
into the chamber 112, with such leakage also being deterred by a
seal 136 in the walls of the chamber 112 about the mount 116. (or
about the shell 128 surrounding the mount 116).
[0008] In operation, the analysis chamber 112 is at least
substantially evacuated by the vacuum pump 114, and current is
supplied to the thermoelectric element(s) 118 by the cooling power
supply 126 to decrease the temperature of the mount 116 and the
radiation detector 102 to an operating temperature. The electron
beam source 110 is then activated, and the radiation detector 102
is used to take measurements from the specimen 104. If the mount
116 and detector 102 are maintained at low temperatures for an
extended period of time (as they often are), oil condensates and/or
ice can form on the detector 102 (or on the adjacent window 130, if
present), and thereby interfere with measurements. To reduce or
eliminate this problem, another power supply 138--one configured to
increase the temperature of the mount 116 and the radiation
detector 102 to a conditioning temperature sufficient to melt ice,
and evaporate oil/water condensates--can be provided in connection
with the thermoelectric element(s) 118 to heat them when desired.
(It is also possible to simply have a single power supply which is
reversible so as to provide both cooling and heating functions, but
since control and reversibility is expensive to achieve with
readily available power supplies, it is generally less expensive to
simply utilize separate power supplies for heating and cooling of
the same element(s) 118.) The heating power supply 138 can maintain
the temperature of the radiation detector 102 at or about the
conditioning temperature for a discrete conditioning period
sufficient to drive off water and oil, and can then be turned off.
The cooling power supply 126 can then be reactivated to supply
suitable current to the thermoelectric element(s) 118 to return the
radiation detector 102 to a temperature at or about the operating
temperature, at which point the radiation detector 102 may resume
taking measurements. (It is recommended that the detector 102 only
take measurements when at the operating temperature, and that it
not take measurements during the conditioning period, since the
heated detector 102 may exhibit substantial measurement noise.)
[0009] Beneficially, since the thermoelectric element(s) 118 can
actively heat the mount 116 and detector 102--that is, they can
raise the temperature of the detector 102 to a conditioning
temperature above the ambient temperature (as measured outside the
analysis chamber 112), rather than simply turning off so that the
mount 116 and detector 102 slowly warm from their operating
temperature to the ambient temperature--reconditioning of the
detector 102 (i.e., removal of oil and water/ice) can be very
quickly performed with conditioning periods of 15 minutes or less.
This is a significant advantage in comparison to prior arrangements
wherein reconditioning simply occurred by removing the cooling
source (e.g., by terminating the supply of liquid nitrogen or other
refrigerant), and hours were required for the detector 102 to
slowly return to ambient temperature and for water/oil to evaporate
off the detector 102.
[0010] Further advantages, features, and objects of the invention
will be apparent from the remainder of this document in conjunction
with the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of an exemplary preferred version
of the invention, showing a radiation detector 102 situated at the
end of a mount or "cold finger" 116 opposite a specimen 104 (which
receives an electron beam 108 from an electron source 110), and
wherein a stack of thermoelectric elements 118 can cool the mount
116 (and thus the detector 102) to an operating temperature via a
cooling power supply 126 so that the detector 102 may take
measurements from the specimen 104, and/or heat the mount 116 and
detector 102 to a conditioning temperature via a heating power
supply 138 to remove water/ice and oil condensates from the
detector 102.
DETAILED DESCRIPTION OF PREFERRED VERSIONS OF THE INVENTION
[0012] The analytical instrument 100 depicted in the FIGURE can be
readily constructed from existing electron microscopes, with
examples being the FEI (Hillsboro, Oreg., USA) Nova, Quanta,
Altura, Expida, Strata, Tecnai, and Titan series electron
microscopes, Carl Zeiss SMT (Thormwood, NY, USA) Supra, Ultra,
Libra, and CrossBeam series electron microscopes, Hitachi
(Pleasanton, Calif., USA) S and H series electron microscopes, and
JEOL (Tokyo, JP) JSM series electron microscopes. However, since
the instrument 100 is merely an exemplary preferred version of the
invention, it should be kept in mind that the invention, as claimed
below, can assume a variety of forms which drastically vary from
the one shown in the FIGURE. As examples, the vacuum chamber 112
may be shaped differently, the analytical instrument may be other
than an electron microscope 100 (and thus the electron beam source
110 may not be present), and the radiation detector 102 may measure
electromagnetic radiation in wavelength ranges other than or in
addition to X-rays (for example, in the infrared range). The mount
116 may have a configuration other than as an elongated "cold
finger," and while the mount 116 shown in the FIGURE is
translatably mounted to the analysis chamber 112 with respect to
the sample stage 106 via an O-ring or other seal 136, the mount 116
could instead be stationary, or could be made movable within the
chamber 112 by other arrangements. In addition, the nature,
configuration, and layout of the thermoelectric element(s) 118, the
cooling and heating power supplies 126 and 138, and the heat sink
124 may vary widely, since such components are available in a broad
range of different configurations.
[0013] As previously noted, the shell 128 and window 130, which
serve to isolate the mount 116 and detector 102 from the analysis
chamber 112 (and thus from condensation of water and oil from the
chamber 112 onto the detector 102), need not be present. If they
are present, in which case condensation and icing may occur on the
shell 128 and window 130 rather than on the mount 116 and detector
102, the shell 128 might be conductively coupled to the
thermoelectric element(s) 118 so that the shell 128 and window 130
can be efficiently heated. Alternatively, the shell 128 could be
coupled to a separate set of one or more thermoelectric elements
(and to a heating power supply), one not shown in the FIGURE, so
that it can be heated independently of any cooling of the mount 116
and detector 102.
[0014] In similar respects, one or more thermoelectric elements 118
(and a cooling power supply 126), and/or some other form of cooling
means, could be situated in the analysis chamber 112 at a location
spaced away from the mount 116 and detector 102, and these could be
activated when the mount 116 and detector 102 are warmed to the
conditioning temperature. In this manner, water and oil that have
condensed on the mount 116 and detector 102 can be driven off and
collected on the separate thermoelectric elements (and/or other
cooling means). Other arrangements, such as those noted in the
prior patents listed at the outset of this document, could also or
alternatively be used.
[0015] The use of a heating power supply 138 in conjunction with
thermoelectric heating elements is not limited to situations where
thermoelectric cooling is used. Thus, thermoelectric elements 118
could be used to heat a detector 102 to a conditioning temperature
in cases where conventional liquid nitrogen or other cryogenic
cooling systems are used.
[0016] Preferred versions of the invention have been described
above in order to illustrate how to make and use the invention. The
invention is not intended to be limited to these versions, but
rather is intended to be limited only by the claims set out below.
Thus, the invention encompasses all different versions that fall
literally or equivalently within the scope of these claims.
* * * * *