U.S. patent application number 12/200839 was filed with the patent office on 2009-03-19 for gas sorption tester for rapid screening of multiple samples.
Invention is credited to Karl J. Gross.
Application Number | 20090074612 12/200839 |
Document ID | / |
Family ID | 40453060 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090074612 |
Kind Code |
A1 |
Gross; Karl J. |
March 19, 2009 |
Gas Sorption Tester For Rapid Screening of Multiple Samples
Abstract
An apparatus determines gas sorption properties of a large
number of material samples simultaneously. The apparatus includes a
switchable manifold of low-volume conduits and an array of sensors,
where each low-volume conduit fluidly couples a single sample of
gas-sorbing material to a dedicated detector. The switchable
manifold is also configured to fluidly couple the samples to a
vacuum source or a dosing gas source. Because of the very low
internal volume of the conduits, essentially all gas released from
a particular sample is accurately detected by the corresponding
detector, either through sorption of the released gas, by measuring
pressure, or by other means. In this way, a very accurate
measurement of the quantity of gas released by the sample is made.
In one embodiment, the array of sensors includes hydride-based
sensors, which contain a material that forms an optically and/or
electrically responsive hydride upon exposure to
hydrogen-containing gas.
Inventors: |
Gross; Karl J.; (Fremont,
CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, L.L.P.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
40453060 |
Appl. No.: |
12/200839 |
Filed: |
August 28, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60973248 |
Sep 18, 2007 |
|
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|
Current U.S.
Class: |
422/400 |
Current CPC
Class: |
G01N 7/02 20130101 |
Class at
Publication: |
422/56 |
International
Class: |
G01N 7/02 20060101
G01N007/02 |
Claims
1. A gas sensing system, comprising: a hydride-forming material; an
optical sensor directed at the hydride-forming material; a fluid
conduit configured to transport a test gas to the hydride-forming
material; and a palladium orifice configured to fluidly isolate the
hydride-forming material from the fluid conduit, wherein the
optical sensor is configured to detect a change in the
hydride-forming material upon exposure to the test gas.
2. The gas sensing system of claim 1, wherein the hydride-forming
material comprises a material selected from the group consisting of
yttrium (Y), lanthanum (La), magnesium-titanium (Mg--Ti),
magnesium-nickel (Mg--Ni), and palladium (Pa).
3. The gas sensing system of claim 1, the hydride-forming material
is disposed within a sample library.
4. The gas sensing system of claim 3, wherein the sample library
comprises an optically transparent substrate.
5. The gas sensing system of claim 3, further comprising: a second
fluid conduit configured to transport the test gas to the
hydride-forming material; and a second palladium orifice configured
to fluidly isolate the hydride-forming material from the second
fluid conduit.
6. The gas sensing system of claim 5, further comprising a
switchable manifold fluidly coupled to the first and second fluid
conduits.
7. The gas sensing system of claim 1, wherein the hydride-forming
material comprises a material that is optically responsive in the
presence of hydrogen.
8. A gas sensing system, comprising: a hydride-forming material
configured to form at least one sensor; a first fluid conduit
configured to fluidly couple the hydride-forming material to a
first sample; and a second fluid conduit configured to fluidly
couple the hydride-forming material to a second sample, wherein the
first and second fluid conduits have an inner diameter no greater
than 2 mm.
9. The gas sensing system of claim 8, further comprising a
switchable manifold fluidly coupled to the first and second fluid
conduits.
10. The gas sensing system of claim 9, wherein the switchable
manifold is configured to fluidly couple the first conduit to a
first sample and the second fluid conduit to a second sample.
11. The gas sensing system of claim 9, wherein the switchable
manifold is configured to fluidly couple the first and second
conduits to the hydride-forming material.
12. The gas sensing system of claim 9, wherein the switchable
manifold is configured to fluidly couple the first and second fluid
conduits to a dosing gas source.
13. The gas sensing system of claim 9, wherein the switchable
manifold is configured to fluidly couple the first and second fluid
conduits to a vacuum source.
14. The gas sensing system of claim 9, wherein a portion of each of
the first and second fluid conduits comprises holes formed in a
body portion of the switchable manifold.
14. The gas sensing system of claim 8, wherein the hydride-forming
material comprises a material that is optically responsive in the
presence of a dosing gas.
15. The gas sensing system of claim 15, further comprising an
optical sensor directed at the hydride-forming material.
16. The gas sensing system of claim 15, wherein the dosing gas is
hydrogen.
17. The gas sensing system of claim 8, wherein the hydride-forming
material comprises a material that is electrically responsive in
the presence of a dosing gas.
18. The gas sensing system of claim 18, further comprising a
conductor electrically coupling the material to a data collection
system.
20. The gas sensing system of claim 8, wherein the hydride-forming
material is deposited on a substrate.
21. The gas sensing system of claim 8, wherein the hydride-forming
material forms at least two sensors, wherein a first sensor is
fluidly coupled to the first sample via the first fluid conduit,
and a second sensor is fluidly coupled to the second sample via the
second fluid conduit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of the U.S.
Provisional Patent Application titled, "METHODS AND APPARATUS FOR
COMBINATORIAL DETERMINATION OF SORPTION PROPERTIES," filed on Sep.
18, 2007 and having Ser. No. 60/973,248. The subject matter of this
related application is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention relate generally to
devices for performing measurements on small quantities of gases or
liquids, and particularly to an apparatus for performing gas
sorption measurements on multiple samples of gas-sorbing
materials.
[0004] 2. Description of the Related Art
[0005] Synthesis of materials using combinatorial chemistry has
been used effectively to produce new materials having small
variations in composition and/or structure numbering in the 10s,
100s or 1000s at a time. Such materials processing methods have led
to the discovery of new and improved chemicals, pharmaceuticals,
semiconductor materials and devices. However, due to the large
numbers of different materials involved, combinatorial methods can
only lead to timely material discovery when rapid screening of the
physical characteristics of the many types of new materials
produced thereby is available.
[0006] In the case of gas sorption materials, the gas sorption
properties of each new material must be tested, i.e., the
absorption, adsorption, desorption, physisorption, and/or
chemisorption properties, and such testing for even a single sample
is a lengthy and labor-intensive process. Such tests include
establishing pressure-composition-temperature (PCT) curves for
materials, and performing isothermal kinetics and capacity
measurements, thermodynamic measurements (van't Hoff curves) and
temperature-programmed desorption (TPD) measurements.
[0007] The sorption tests for establishing each PCT curve are
time-consuming and require very sensitive instrumentation, such as
high-accuracy pressure transducers. In addition, collecting
information regarding the kinetic sorption properties and
thermodynamic stability of gas-sorbing materials typically requires
further time-consuming testing of each sample. Thus, characterizing
the sorption properties of a new material is a relatively expensive
and lengthy process, especially since current testing techniques do
not allow rapid screening or testing across multiple samples. In
light of the expanding need for characterizing large numbers of new
materials, current techniques simply cannot be used to efficiently
or cost effectively analyze the large numbers of different
materials to be tested, particularly those developed using
combinatorial techniques.
[0008] Accordingly, there is a need in the art for an apparatus and
technique for the rapid screening of multiple gas-sorbing
samples.
SUMMARY OF THE INVENTION
[0009] One embodiment of the present invention sets forth an
apparatus that can determine the gas sorption properties of a large
number of material samples simultaneously. The apparatus includes a
switchable manifold configured to fluidly couple an array of
sensors and an array of samples to a vacuum source, a dosing gas
source, and each other. The array of sensors may include pressure
transducers, conventional gas detectors, resistivity sensors, and
hydrogen-induced phase-change materials including hydride-based
sensors.
[0010] One advantage of the disclosed apparatus is that can be used
to efficiently determine gas sorption properties of a large number
of material samples simultaneously and with high accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0012] FIG. 1 is a schematic diagram of a gas sorption apparatus
configured to perform tests on multiple samples simultaneously,
according to an embodiment of the invention.
[0013] FIGS. 2A-G schematically illustrate different operations
performed by a gas sorption apparatus in the course of sorption
testing, according to embodiments of the invention.
[0014] FIG. 3 is a schematic illustration of a sample library,
according to an embodiment of the invention.
[0015] FIGS. 4A, B illustrate schematic side views of one
embodiment of the isolation of each sample area of a sample library
from adjacent sample areas.
[0016] FIG. 5 is a schematic side view of a sensor array containing
an electrically responsive material, according to an embodiment of
the invention.
[0017] FIG. 6 is a schematic side view of a sensor array containing
an optically responsive material, according to an embodiment of the
invention.
[0018] FIG. 7 is a schematic side view of another embodiment of a
sensor that includes an optically responsive material and may be
contained in a sensor array.
[0019] FIG. 8 illustrates a schematic top view of a sensor array
containing a plurality of sensors after sorption testing.
[0020] For clarity, identical reference numbers have been used,
where applicable, to designate identical elements that are common
between figures. It is contemplated that features of one embodiment
may be incorporated in other embodiments without further
recitation.
DETAILED DESCRIPTION
[0021] Embodiments of the invention contemplate an apparatus that
determines gas sorption properties of a large number of material
samples simultaneously. The apparatus includes a switchable
manifold of low-volume conduits and an array of sensors, where each
low-volume conduit fluidly couples a single sample of gas-sorbing
material to a dedicated detector. The switchable manifold is also
configured to fluidly couple the samples and/or sensors to a vacuum
source and a dosing gas source. Because of the very low internal
volume of the conduits, essentially all gas released from a
particular sample is accurately detected by the corresponding
detector, either through sorption of the released gas, by measuring
pressure, or by other means. In this way, a very accurate
measurement of the quantity of gas released by the sample is made.
Alternatively, essentially all of the gas in the very low internal
volume of the conduits may be absorbed by the sample, the quantity
of gas adsorbed or absorbed being measured by the corresponding
detector, either through sorption of the released gas, by measuring
pressure, or by other means. In one embodiment, the array of
sensors includes hydride-based sensors, which contain a material
that forms an optically and/or electrically responsive hydride upon
exposure to hydrogen-containing gas.
[0022] FIG. 1 is a schematic diagram of a gas sorption apparatus
100 configured to perform tests on multiple samples simultaneously,
according to an embodiment of the invention. The principle
components of gas sorption apparatus 100 include a switchable
manifold 101, an array 102 of sensors 102A-D, a plurality of
samples 103A-D, a dosing gas source 104 and a vacuum source 105.
For improved performance, gas sorption apparatus 100 may also
include a controller 110 coupled to a valve controller 111, a
pressure controller 112, a temperature controller 113, a heater
assembly 115, and a data collection system 114. Controller 110 is
an electronic controller, such as a microprocessor, and is
configured to control the operation of gas sorption apparatus 100,
e.g., valve operation, pressure control, vacuum control, electronic
data collection, temperature control and/or dosing quantity and
frequency.
[0023] Switchable manifold 101 is configured to fluidly couple
samples 103A-D to detectors 102A-D by means of a low volume path.
To that end, switchable manifold 101 includes low-volume conduits
106. For improved accuracy of gas sorption tests performed by gas
sorption apparatus 100, the internal volume of low-volume conduits
106 is advantageously minimized. In one embodiment, low-volume
conduits 106 comprise small-diameter electro-polished stainless
steel tubing, having an internal diameter of 2 mm or less. In an
alternative embodiment, low-volume conduits 106 may be
small-diameter holes formed through the body of switchable manifold
101, e.g., by laser drilling, chemical growth, chemical etching, or
other techniques. In such an embodiment, low-volume conduits 106
may have outer diameters as small as 1 micron. Thus, the total free
volume between a given sample and corresponding sensor may be 0.1
ml or less.
[0024] The material in which low-volume conduits 106 are formed
preferably is characterized by low gas-permeability and
out-gassing, such as stainless steel, glass, ceramic materials,
alumina, Macor.TM., and other ultra-high vacuum (UHV) compatible
materials. In one embodiment, low-volume conduits 106 may be
configured to thermally isolate sensors 102A-D from samples 103A-D,
so that each sensor may be maintained at a substantially different
temperature than its corresponding sample. For example, low-volume
conduits 106 may be formed from small-diameter tubing that conduct
very little heat. Alternatively, low-volume conduits may be drilled
or formed through a solid block of thermally insulative material,
e.g., alumina. In this way, the samples and sensors are thermally
decoupled, allowing greater flexibility in the type of sorption
tests performed by gas sorption apparatus 100.
[0025] Switchable manifold 101 also includes one or more very
low-displacement valves, such as such as rotating valves and/or
sliding valves, for fluidly coupling and decoupling sensors 102A-D
from samples 103A-D, respectively as well as for fluidly coupling
sensors 102A-D from samples 103A-D from dosing gas source 104 or
vacuum source 105. Very low-displacement valves are known in the
art, and are well suited for applications in which conduits formed
through a solid material need to be sealed. For example, a very
low-displacement valve or valves may be incorporated into the body
of the Switchable manifold 101 as a system of rotating or sliding
plates with fluid coupling holes and grooves between sealing
gaskets. In addition, use of very low-displacement valves may
substantially reduce error in pressure- and volume-dependent
measurements, such as PCT measurements. An example of the
mechanical organization and operation of a sliding valve 406 is
described below in conjunction with FIG. 4A.
[0026] Array 102 includes a plurality of sensors 102A-D, each of
which is fluidly coupled to a single low-volume conduit 106.
Sensors 102A-D may be individually positioned in fluid contact with
low-volume conduits 106, as shown in FIG. 1. Alternatively, sensors
102A-D may be configured as a single assembly or sensor array, as
described below in conjunction with FIGS. 5-7. It is contemplated
that sensors 102A-D may be selected from a wide variety of possible
sensor types, depending on the particular dosing gas used and
specific test being performed. Sensors that may be used in array
102 include pressure transducers and conventional gas detectors. In
one embodiment, when the dosing gas is a hydrogen-containing gas,
array 102 may include hydride-based sensors, which contain a
material that forms an optically and/or electrically responsive
hydride upon exposure to hydrogen-containing gas. For clarity, gas
sorption apparatus 100 is illustrated in FIG. 1 with only four
sensors 102A-D, and array 102 is depicted as a linear array.
However, embodiments of the invention contemplate array 102
containing a large number of sensors, e.g., 10s or 100s of sensors.
Further, the sensors making up array 102 may be arranged in a
two-dimensional array, as illustrated below in FIG. 8, the
two-dimensional array having a means to fluidly separate each
detector one-from-another. The sensors or sensor arrays may be
replaceable to allow sensor types to be changed depending on the
experimental conditions, or easily replaced when contaminated or
not functioning.
[0027] As noted above, sensors A-D of array 102 may be pressure
transducers, which are high-accuracy pressure measuring device
capable of detecting changes in relative or absolute pressure in
each of low-volume conduits 106 to the degree necessary for
performing gas sorption tests. For example, types of pressure
transducers suitable for use in array 102 include a strain-gauge
pressure transducer, a piezoelectric pressure transducer, or a
capacitance manometer, such as a Model 870B Micro-Baratron.RTM. or
chip-based micro-pressure-sensors. In one embodiment, each sensor
in array 102 may include an array of multiple pressure transducers,
each having a different operating pressure range.
[0028] When array 102 includes pressure transducers, gas sorption
apparatus 100 may be used as a Sievert's device to perform a PCT
measurement or a TPD measurement of specific gases as they are
absorbed or desorbed from each of samples 103A-D. In this
embodiment, each of sensors 102A-D may also include a temperature
sensor. In this way, the temperature and pressure of the dosing gas
being tested are both known. As noted above, during testing,
sensors 102A-D are fluidly coupled to samples 103A-D, respectively,
via low-volume conduits 106. Because the internal volume of
low-volume conduits 106 is a small and accurately known volume, the
pressure changes that occur in the volume between sensors 102A-D
and samples 103 due to sorption or desorption of a dosing gas are
compounded. Therefore, the mass of dosing gas that flows into or
out of each material sample can be very accurately determined.
[0029] Array 102 may include conventional gas sensors known in the
art, such as flammable gas detectors or other gas sensors. In this
embodiment, sensors 102A-D may be used to quantify the amount of
dosing gas released from or absorbed by samples 103A-D based on a
property change of a reactive material contained in the sensor,
such as resistivity change. Because the resistivity of the reactive
material may be function of how much dosing gas is present, the
quantity of desorbed dosing gas is easily measured. Alternatively,
array 102 may include fuel cell-based sensors, which are designed
to produce a voltage upon reaction with a dosing gas, particularly
hydrogen-containing gases. In yet another alternative embodiment,
array 102 may include thermal conductivity or gas resistivity
sensors that measure the density of gas within the low-volume
conduits 106. It is noted that the accuracy of measurements based
on sensor reaction with the dosing gas may be enhanced by the
configuration of gas sorption apparatus 100 since the internal
volume of low-volume conduits 106 is a small, known volume. An
exemplary embodiment of a sensor using an electrically responsive
material is described below in conjunction with FIG. 5.
[0030] In one embodiment, array 102 may include hydride-based
sensors, which contain a material that forms an optically and/or
electrically responsive hydride upon exposure to
hydrogen-containing gas. Hydride-forming materials, as defined
herein, include any material that changes physical properties on
contact with hydrogen, and is not meant to necessarily imply the
formation of a stoichiometric hydride compound. Hydride-forming
materials that may be used in hydride-based sensors include yttrium
(Y), lanthanum (La), magnesium-titanium (Mg--Ti) alloys,
magnesium-nickel (Mg--Ni) alloys, and various palladium (Pa)
alloys. In fact, most hydrides undergo some optical transformations
and/or electrical property changes during formation from a
non-hydrided material. Therefore, many other possible
hydride-forming materials may also be used to some effect in such
sensors. Again, the low internal volume of low-volume conduits 106
is beneficial for improved accuracy of measurements. An exemplary
implementation of an optically responsive hydride-based sensor is
described below in conjunction with FIGS. 6 and 7.
[0031] Yttrium is one example of an optically responsive material
that may be used in a hydride-based sensor, according to an
embodiment of the invention. Yttrium is highly reflective at
visible wavelengths, and forms hydrides (YH.sub.2 and YH.sub.3)
that each have different reflectivities. YH.sub.2 is slightly less
reflective than yttrium, and YH.sub.3 is nearly transparent.
Therefore, when hydrogen gas is brought in contact with yttrium, an
optical detector will register less light reflected from the
surface of the yttrium as more hydrogen is absorbed by the yttrium.
A correlation between the quantity of hydrogen gas absorbed and the
intensity of light registered by the optical detector can be
constructed, so that the reflectance of the sensor indicates the
quantity of gas that has been absorbed by the detector and,
therefore, released by the sample. Such processes are most
advantageous when the detector material is reversible under typical
operating conditions, however it is contemplated that one-time-use
only detectors may be used. Some materials, such as yttrium, may
require an active, gas-transparent coating, such as a palladium cap
to prevent oxidation of the yttrium and possibly also act as a
catalyst for dissociation of the active gas such as hydrogen.
[0032] Each of samples 103A-D includes a material sample prepared
for sorption testing. Hence, each material sample is isolated from
the ambient environment in an gas-tight fashion and held in a
small-volume chamber. Each material sample may be a thin-film
material deposited on a substrate, a bulk sample, or any other
morphology conducive to sorption testing, such as a bulk sample
that has been pulverized. In one embodiment, a filter may be
disposed between each sample and the low-volume conduit 106 fluidly
coupled thereto, to prevent contamination and fouling of the
low-volume conduit 106 by the sample material. As described above
regarding sensors 102A-D, each of samples 103A-D may be
individually positioned in fluid contact with low-volume conduits
106, as shown in FIG. 1. Alternatively, samples 103A-D may be
configured as a single assembly, such as a sample library. Sample
libraries, according to embodiments of the invention, are described
below in conjunction with FIG. 3.
[0033] Valve controller 111 operates pressure controller 112 and
the very low-displacement valves contained in switchable manifold
101, thereby establishing the connections between dosing gas source
104, vacuum source 105, samples 103A-D, and sensors 102A-D.
Pressure controller 112 controls the pressure of gas introduced
into switchable manifold 101 from dosing gas source 104, which is
beneficial for certain sorption measurements. The control valve may
consist of a manual or software-controlled pressure regulator, a
flow control device, or needle valve. Temperature controller 113
controls the individual heaters 116 that make up heater assembly
115, to maintain each of samples 103A-D and sensors 102A-D at a
prescribed temperature or temperature history, such as a controlled
temperature ramping rate. As shown in FIG. 1, an individual heater
116 may be positioned in proximity to each of samples 103A-D and/or
sensors 102A-D. Controlling the sample and detector temperature
aids in performing certain sorption measurements. Data collection
system 114 is configured to obtain information from each of sensors
102A-D. The information may be obtained, for example, by an
electrical connection, an optical connection, or though an optical
system that images the sensors.
[0034] In operation, gas sorption apparatus 100 is configured to
perform one or more sorption tests simultaneously on a plurality of
samples. Depending on the type of sensors in array 102, gas
sorption apparatus 100 may perform PCT and TPD tests on samples
103A-D and generate kinetic and thermodynamic stability information
about the samples. In the course of such testing, switchable
manifold 101 fluidly couples samples 103A-D and/or sensors 102A-D,
to dosing gas source 104, and to vacuum source 105, as well as to
each other. FIGS. 2A-G schematically illustrate various operations
performed by gas sorption apparatus 100 in the course of such
sorption testing, according to different embodiments of the
invention.
[0035] FIG. 2A schematically illustrates gas sorption apparatus 100
with switchable manifold 101 positioned to fluidly couple samples
103A-D and sensors 102A-D to vacuum source 105 for evacuation of
any gases contained therein. Evacuation may be performed as part of
a preparation process for testing of samples 103A-D. FIG. 2B
schematically illustrates gas sorption apparatus 100 with
switchable manifold 101 disposed to fluidly couple samples 103A-D
to dosing gas source 104 for fully charging samples 103A-D and
sensors 102A-D in preparation for desorption PCT dosing
measurements. FIG. 2C schematically illustrates gas sorption
apparatus 100 with switchable manifold 101 positioned to fluidly
couple each of samples 103A-D to a corresponding sensor 102A, 102B,
102C, or 102D. In this configuration, each of sensors 102A-D are in
direct "gas contact" to a corresponding sample by means of a fluid
path that has very little, if any, free volume, i.e., a low-volume
conduit 106. FIG. 2D schematically illustrates gas sorption
apparatus 100 with switchable manifold 101 positioned to fluidly
couple each of sensors 102A-D to vacuum source 105, to pump-down
sensors 102A-D. FIG. 2E schematically illustrates gas sorption
apparatus 100 with switchable manifold 101 positioned to fluidly
couple each of samples 103A-D to vacuum source 105, to pump-down
samples 103A-D. FIG. 2F schematically illustrates gas sorption
apparatus 100 with switchable manifold 101 positioned to fluidly
couple each of sensors 102A-D to dosing gas source 104, to charge
sensors 102A-D with a dosing gas. FIG. 2G schematically illustrates
gas sorption apparatus 100 with switchable manifold 101 positioned
to fluidly couple each of samples 103A-D to dosing gas source 104,
to charge samples 103A-D with a dosing gas.
[0036] In FIGS. 2A-G, the fluid coupling and decoupling of sensors
102A-D and samples 103A-D to dosing gas source 104, vacuum source
105, as well as to each other, are shown schematically. One skilled
in the art will readily understand how to configure low-volume
conduits 106 and sliding and/or rotating valves to allow such fluid
coupling to take place, as is described herein. Further, while
fluidly coupling samples 103A-D or sensors 102A-D to dosing gas
source 104, vacuum source 105, and/or to each other, simultaneously
may be advantageous, individually controlling the fluid coupling of
each of samples 103A-D and/or sensors 102A-D by switchable manifold
101 also falls within the scope of the present invention. Although
more complex, one of skill in the art will readily understand how
to configure a system of sliding and/or rotating valves that allows
such individual connection of samples 103A-D or sensors 102A-D, as
needed.
[0037] By way of example, an absorption PCT measurement procedure
is described with respect to the different configurations of gas
sorption apparatus 100 illustrated in FIGS. 2A-G. First, sensors
102A-D and samples 103A-D are evacuated, as shown in FIG. 2A. Next,
samples 103A-D are isolated and dosing gas is introduced to sensors
102A-D, as illustrated in FIG. 2F. Sensors 102A-D are then fluidly
coupled to samples 103A-D as illustrated in FIG. 2C, and the change
in gas concentration in each of sensors 102A-D and corresponding
low-volume conduits 106 is measured as each of samples 103A-D
absorb the dosing gas. The quantity of gas change in each of
sensors 102A-D and low-volume conduits 106 is used to calculate the
quantity of gas absorbed by each of samples 103A-D, and a point on
the PCT curve for each sample is plotted. This procedure is then
repeated at increasingly higher pressures to generate additional
points and thereby construct a full PCT curve for each of samples
103A-D. Desorption PCT curves may be performed in the same manner,
except that one would start by fully charging the sample and
detectors at the highest pressure by exposing both samples 103A-D
and sensors 102A-D to the gas source at highest pressure and then
dosing gas out of each sample by decreasing the pressure in the
sensor and conduit in steps as above.
[0038] It is noted that in principal one would really need each of
sensors 102A-D to be pressure sensors rather than concentration
sensors to construct true equilibrium PCT curves, since the final
equilibrium pressure should be known at each dose and because
concentration can be determined in the classic Sieverts method by
knowing the volume, gas temperature and pressure change. Due to the
difficulty in making an array of highly accurate, separate pressure
sensors, it is contemplated that, in one embodiment, gas sorption
apparatus 100 may perform such measurements in an easier but less
accurate way. To wit, a concentration sensor, such as the
metal-hydride optical sensors described below in conjunction with
FIGS. 6 and 7, measures only the concentration change with each
dose. This concentration change may be plotted versus the applied
dosing pressure, which may be taken from a single pressure sensor
at the dosing gas supply line. In this way the storage capacity of
each of samples 102A-D is quantified and an approximate PCT plot
constructed. By taking very regular steps in dosing gas pressure,
or at least knowing the difference in source pressure between steps
and measuring the concentration change, it is possible to back
calculate the equilibrium pressure for each sample to construct the
true PCT curve.
[0039] Kinetics and TPD measurements can also be performed by gas
sorption apparatus 100, by configuring gas sorption apparatus 100
as illustrated in FIGS. 2A-G. Since such measurements are
concentration vs. time and concentration vs. temperature, it is not
necessary to have individual pressure sensors for each sample for
these measurements.
[0040] In one embodiment, samples 103A-D are arranged in a sample
library, which is positioned in fluid contact with low-volume
conduits 106 prior to sorption testing. FIG. 3 is a schematic
illustration of a sample library 300, according to an embodiment of
the invention. Sample library includes a plurality of sample areas
s, each surrounded by a border b. Sample areas s are discretized
regions on the surface of a substrate, such as a glass substrate,
metal substrate, or silicon wafer. Each of sample areas s may
include a different material composition. The plurality of material
compositions contained in sample library 300 may be formed thereon
by any known combinatorial techniques or other technically feasible
approaches including discrete or continuous deposition techniques.
For example, a continuous spectrum of material compositions of
continuously varying mixtures may be formed over the substrate of
sample library 300 using co-deposition of different materials on
the substrate. The sample areas s then discretize the continuously
varying mixtures on the substrate, dividing the substrate into
small areas of approximately constant composition. In this way, a
large number of samples of different compositions can be quickly
prepared and simultaneously measured using gas sorption apparatus
100. In one embodiment, one or more sample areas s in sample
library 300 contain material compositions of known sorption
properties, to be used for reference or calibration purposes.
[0041] The size of each sample area s may be relatively small, so
that a large number of different material compositions, e.g., 10s
or 100s, can be contained in a single sample library and tested
simultaneously by gas sorption apparatus 100. The minimum area of
each sample area s is only limited by the practical limitations of
the minimum width of border b and the accuracy desired for a given
sorption test. Since smaller sample areas s are capable of
absorbing and desorbing less total gas, the accuracy of any
sorption test can be adversely affected as the area of each sample
area s is reduced and as the thickness of each sample area s is
reduced.
[0042] The material of border b is selected to form a gas or liquid
barrier between the samples, so that each sample area s may be
completely isolated from adjacent sample areas during sorption
testing. In one embodiment, border b is simply a region of sample
library 300 in which no sample material has been deposited. In
another embodiment, border b includes an isolation member. The
isolation member may be a raised sealing material used to establish
a gas-tight seal with low-volume conduits 106. In this embodiment,
the surface of switchable manifold 101 may be a smooth, polished
surface against which the isolation member is pressed, thereby
isolating each sample area s from adjacent sample areas while
fluidly coupling each sample area s to a corresponding low-volume
conduit 106.
[0043] Because the quantities of gas that are sorbed and desorbed
from thin-film samples are extremely small, even a small quantity
of gas outgassing from the isolation member can adversely affect
the accuracy of a sorption test. Consequently, it is contemplated
that the isolation member may be formed from a material that is
subject to essentially no outgassing or gas permeability over the
wide range of temperatures and pressures associated with sorption
tests. Many UHV-compatible materials may be used for this purpose
and are well-known, such as a O-rings or UHV high-temperature
epoxy. In another example, the isolation member may be a grid
deposited in border s, the grid being formed from a relatively soft
metal, such as nickel or copper. In another embodiment, the
isolation member is incorporated into a surface of switchable
manifold 101, as described below in conjunction with FIGS. 4A,
B.
[0044] FIGS. 4A, B illustrate schematic side views of one
embodiment of the isolation of each sample area s of sample library
300 from adjacent sample areas. In FIG. 4A, sample library 300 is
positioned proximate to a sample receiver 402 in preparation for
mounting thereon. In FIG. 4B, sample library 300 is shown mounted
on sample receiver 402 and ready for sorption testing by gas
sorption apparatus 100. In this embodiment, each sample area s is
fluidly coupled to a dedicated low-volume conduit 106, and is
fluidly isolated from adjacent sample areas s when sample library
300 is mounted on sample receiver 402. Sample receiver 402 is
configured with an array of knife edges 401 that are aligned with
isolation members 405, which are disposed on sample library 300. In
this embodiment, isolation members 405 may be formed from a
relatively soft material, such as copper, nickel, or a
UHV-compatible polymer, and knife edges 401 may be a relatively
hard material, such as stainless steel. Thus, when sample library
300 is mounted on sample receiver 402, knife edges 401 engage with
isolation members 405 to fluidly isolate each of sample areas s.
Alternatively, sample receiver 402 may not be configured with knife
edges 401 and instead engages isolation members 405 with a
substantially flat, polished surface to form the gas-tight seal. In
another alternative embodiment, the surface of switchable manifold
101 may consist of an array of isolating rings, or squares of
knife-edge raised material that press into isolation members 405,
thereby isolating each sample area s from adjacent sample areas
while fluidly coupling each sample area s to a corresponding
low-volume conduit 106. In yet another embodiment, the entire
substrate of the sample library 300 is composed of material softer
than the knife-edge material 401, such that the knife-edge material
is pressed into the substrate between the discretized sample areas
s or through a non-discretized continuous sample s, thereby
isolating each sample area s from adjacent sample areas while
fluidly coupling each sample area s to a corresponding low-volume
conduit 106. Sample receiver 402 also includes low-volume conduits
106 positioned between knife edges 401, and is fluidly coupled and
decoupled from switchable manifold 101 by a sliding valve 406.
Sliding valve 406 actuates to fluidly couple and decouple sample
receiver 402 and any sample library mounted thereon by translating
horizontally as indicated by arrow 407.
[0045] In one embodiment, array 102 in FIG. 1 includes sensors with
an electrically responsive material to quantify the quantity of gas
released from sample materials during sorption testing. As noted
above, such sensors may include hydride-based sensors or more
conventional gas detectors. In either case, exposure to and
reaction with the dosing gas causes the electrically responsive
material contained in the sensor to undergo a change in one or more
electrical properties, such as resistivity or electrochemical
potential. This change in electrical properties can then be used to
quantify either the amount of dosing gas that has reacted with the
electrically responsive material, or the concentration of dosing
gas that is in fluid contact with the electrically responsive
material. In either case, the quantity of gas released by a sample
can be easily calculated.
[0046] FIG. 5 is a schematic side view of a sensor array 500
containing an electrically responsive material 501, according to an
embodiment of the invention. Sensor array 500 is one embodiment of
array 102, and includes a plurality of sensors d, which are each
fluidly coupled to a corresponding sample (not shown) via
low-volume conduits 106 and a sliding valve 406. Each sensor d has
a conductor that provides a signal back to data collection system
114.
[0047] In one embodiment, array 102 in FIG. 1 includes sensors with
an optically responsive material to quantify the quantity of gas
released from samples material during sorption testing. As noted
above, such sensors may include hydride-based sensors, where
exposure to and reaction with hydrogen gas causes the optically
responsive material contained in the sensor to undergo a change in
one or more optical properties, such as reflectivity and/or
transmissivity of visible light.
[0048] FIG. 6 is a schematic side view of a sensor array 600
containing an optically responsive material 601, according to an
embodiment of the invention. Sensor array 600 is one embodiment of
array 102, and includes a plurality of sensors 602, which are each
fluidly coupled to a corresponding sample (not shown) via
low-volume conduits 106 and a sliding valve 406. In operation,
illumination 605 from a light source is directed on sensors 602,
and light 606 reflected from sensors 602 is collected by an optical
detector 608. Optical detector 608 may be a digital camera that
captures the condition of multiple sensors 602 with one or more
images. The images are then stored in and/or processed by data
collection system 114 in FIG. 1. Alternatively, optical detector
608 may include a plurality of light sensors, such as photocells,
so that each sensor 602 has a corresponding and dedicated light
sensor. Thus, the optical response from each sensor may be gathered
either simultaneously or individually. As noted above, exposure to
the dosing gas produces a change in the reflectivity and/or
transmissivity of the optically responsive material, which is
measured by optical detector 608 or detectors as described
herein.
[0049] FIG. 7 is a schematic side view of a sensor that includes an
optically responsive material 701 and may be included in array 102,
according to an alternative embodiment of the invention. Similar to
sensors 602, exposure of dosing gas to sensor 700 produces an
optical response in optically responsive material 701 that can be
detected and/or recorded by an optical detector. In sensor 700,
however, optically responsive material 701 undergoes a distinct
color, transparency and/or reflectivity change upon absorption of
the dosing gas, rather than a gradual change in reflectivity or
transmissivity as more dosing gas is absorbed. In this fashion, a
clearly defined region of optically responsive material 701 changes
color when sensor 700 is exposed to a dosing gas of the appropriate
chemistry. For example, when the dosing gas being measured by
sensor 700 is hydrogen, optically responsive material 701 may be a
yttrium- or lanthanum-based compound. As is known in the art, such
compounds can produce the distinct reflectivity change necessary
for sensor 700 to function as contemplated herein.
[0050] To isolate optically responsive material 701 from ambient
hydrogen and other contamination that may result in unwanted
optical changes or passivation, sensor 700 includes a protective
layer 705 that isolates optically responsive material 701. Layer
705 may be the native yttrium-oxide or a secondary deposited metal
oxide or impermeable metal or polymer layer, which is known to
prevent diffusion of hydrogen therethrough. Sensor 700 also
includes a palladium orifice or window 702 deposited in and sealing
opening 707 of protective layer 705, as shown. Thus, palladium
orifice 702 prevents fluid contact between gases present in
low-volume conduit 106 and optically responsive material 701
preventing oxidation or passivation of the responsive material 701
in sealing opening 707. However, since hydrogen readily diffuses
through palladium, optically responsive material 701 should only be
exposed to hydrogen that is introduced via low-volume conduit 106
and the palladium orifice 702. Sensor 700 responds to exposure to
hydrogen by forming a circular reacted region of different color,
transparency, or reflectivity centered over opening 707, where the
diameter of the reacted region can be readily correlated to a
quantity of hydrogen gas absorbed by sensor 700. The diameter of
the reacted region in sensor 700 and the diameters of the reacted
regions in all other sensors in the same sample library can then be
recorded simultaneously by an optical detector, such as a digital
camera. In this fashion, hydrogen released by a plurality of
samples in sample library 300 can be simultaneously quantified,
greatly speeding the screening process.
[0051] FIG. 8 illustrates a schematic top view of a sensor array
800 containing a plurality of sensors 700 after sorption testing.
As shown, circular regions 801 are visible and the diameters
thereof are easily measured. Thus, desorbed gas concentrations of
each sample may be correlated to gas over-pressure and temperature
of each sample in a single or series of measurements.
[0052] In an alternative embodiment, the sensor array 800 may be
pre-charged with gas to the fully absorbed state and then exposed
to the sample array with each sensor acting as a gas source. The
concentration of gas absorbed by each sample can be measured
quantitatively by the diameter of the desorbed circular regions 801
of the sensor array 800. Additionally, measured increases (sample
desorption) or decreases (sample absorption) of the diameter of the
circular regions 801 with time may provide a measurement of the
individual kinetics of gas desorption or sorption of the array of
samples at a given temperature or with a controlled temperature
ramping.
[0053] In one embodiment, a sensor array containing sensors d in
FIG. 5, sensors 602 in FIG. 6, and/or sensor 700 in FIG. 7 may be
formed on a silicon substrate or an optically transparent substrate
such as glass. Deposition and etching processing techniques are
well suited to efficiently fabricating a large number of very small
sensors on a single substrate, thereby facilitating the screening
of large numbers of different material compositions. Sensors
containing either electrically and/or optically responsive
material, can be formed in this manner.
[0054] In one embodiment, a sensor array, such as sensor array 102,
may be mounted to switchable manifold 101 in FIG. 1 using the same
techniques described above for sample library 300, so that each
sensor is fluidly isolated from each adjacent sensor, but is
fluidly coupled to a corresponding sample material.
[0055] In one embodiment, hydride-based sensors may be used as
mini-reservoirs of hydrogen gas and can therefore be used as
"mini-dosers." For example, sensor array 800 can be dosed with
hydrogen such that each sensor 700 contains a known quantity of
hydrogen gas. Sample materials in a sample library can then be
fluidly coupled to vacuum source 105 of FIG. 1 and/or heated, as
necessary, to release the hydrogen or contaminants contained in
each sample material. Sensors 700 are fluidly coupled to the sample
library and heated, as required, to release hydrogen therefrom.
Sorption of hydrogen into each sample can then be readily
quantified by comparing the quantity of hydrogen actually released
by each sensor 700. Because the hydrogen content of each sensor 700
is measured optically, which, again, can be done quickly and
accurately, measurements of the hydrogen content of the sensors 700
can be performed multiple times throughout the life of a given
test. This approach allows the simultaneous collection of kinetic
and thermodynamic stability information for a large number of
material samples simultaneously. In one embodiment, one or more of
the samples so tested may be a control sample, comprising a
material that is known to absorb no hydrogen. Such control samples
may be used to assist in the calibration of sorption tests by
quantifying how much hydrogen is present in a low-volume conduit
106 at a specific pressure and temperature and at any time during
the sorption test.
[0056] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *