FI128645B

FI128645B - Arrangement and method for thermal desorption measurement

Info

Publication number: FI128645B
Application number: FI20185810A
Authority: FI
Inventors: Evgenii Malitckii; Yuriy Yagodzinskyy; Hannu Hänninen
Original assignee: Aalto Univ Foundation Sr
Priority date: 2018-09-28
Filing date: 2018-09-28
Publication date: 2020-09-30
Also published as: FI20185810A1; WO2020065135A1

Abstract

An arrangement (100) for detecting atoms and/or molecules desorbed from at least one sample, the arrangement comprising at least one desorption chamber (102) adapted to keep an ultra-low pressure, wherein the desorbed atoms and/or molecules may be detected by heating the sample in the desorption chamber (102). The arrangement additionally comprises a cooling system (106) for cooling the sample prior to the heating of the sample.

Description

ARRANGEMENT AND METHOD FOR THERMAL DESORPTION MEASUREMENT

TECHNICAL FIELD OF THE INVENTION The invention is related to detection of atoms or molecules in general. More specifically, the invention is related to an arrangement and method for detecting atoms and molecules desorbed from at least one sample in vacuum.

BACKGROUND OF THE INVENTION Thermal desorption measurements give information about gaseous atoms absorbed into the sample bulk. Molecules desorbed from the surface, being formed on the surface when the absorbed atoms diffuse to the surface and form the molecules, may be identified, while also the adsorption and/or absorption conditions or sites may be recognized from the obtained data. This information may be especially relevant for evaluating materials where adsorbed molecules or absorbed atoms may affect the properties of the material. For instance, in the case of metals the amount of hydrogen absorbed may affect durability or other characteristics of the metal. It is especially useful for e.g. manufacturers of materials to accurately evaluate and control the amount of absorbed atoms in order to make more durable materials. To serve the automobile industry, for instance, the use of high- strength steels is advantageous, as they enable lighter vehicle parts. The properties, especially related to durability of the steel are very important. Development of such light and durable materials is continuously evolving, o and precise and reliable measurement of the absorbed gases is vital in O 25 analysis of the material properties. S Current methods and apparatuses for thermal desorption measurements O allow some amounts of absorbed atoms and/or adsorbed molecules to E escape the sample material before measurement. The measurements can o be carried out only in certain conditions, such as in an ultra-low pressure of % 30 an ultra-high vacuum (UHV) chamber, and while these measurement 2 conditions are being prepared, some amount of absorbed atoms and/or N adsorbed molecules will escape from the sample, and are thus not detected in the measurements (when the sample is kept at e.g. room temperature during preparations). This undetected amount may still have large effects onthe material and it is beneficial to be able to make thermal desorption measurements more accurately. At the moment, related to for instance hydrogen absorbed in steel, there are no methods for the reliable control of the effects of minor hydrogen concentration on steel properties and durability. Hydrogen accumulated into high-strength steels during steel manufacturing processes often results in hydrogen-assisted cracking, e.g. in connection with the automobile industry, during stamping and punching of vehicle components. Fatigue cracks are practically impossible to detect when a component is in exploitation, reducing safety. Conventional measurements may take a significant amount of time as a vacuum chamber may have to be pumped in connection with each separate measurement, possibly taking even hours at a time.

SUMMARY OF THE INVENTION A purpose of the invention is to alleviate at least some of the problems related to the known prior art. In accordance with one aspect of the present invention, there is provided an arrangement for detecting atoms and/or molecules desorbed from at least one sample, the arrangement comprising at least one desorption chamber adapted to keep an ultra-low pressure, wherein the desorbed atoms and/or molecules may be detected by heating the sample in the desorption chamber. The arrangement additionally comprises a cooling system for cooling the sample prior to the heating of the sample. N According to one other aspect, there is provided a method according to the > 25 independent claim 13.

O S Having regard to the utility of the present invention, according to an I embodiment, the present invention may provide an arrangement and = method for enabling more accurate thermal desorption measurements. This = may be brought about by the cooling of the sample prior to it being heated in 0 30 the ultra-low pressure, as it may suppress or delay the escaping of > molecules from the sample surface during preparation for the measurement. In one embodiment of the invention, the sample is cooled in a cooling chamber from where the sample may be transferred to the desorptionchamber where the sample may then be heated and the desorbed molecules may be detected/observed. In embodiments where a cooling chamber is utilized, the cooling chamber may be adapted to host or maintain an intermediate pressure, so that the intermediate pressure may advantageously be a higher pressure than the ultra-low pressure. The pressures that are utilized in embodiments of the invention may be referred to as vacuum, wherein this term is used to describe a space keeping or maintaining a partial vacuum where the pressure in the space is lower than the surrounding atmospheric pressure.

A desorption chamber may through embodiments of the invention be protected from contamination by using a cooling chamber where the sample may be cooled. The cooling chamber may maintain a vacuum and the sample may be moved to the desorption chamber for measurements in a lower pressure vacuum than that of the cooling chamber. If the desorption chamber is kept clean, the results of measurements may be more accurate. The desorption chamber may be continuously kept at or near the ultra-low pressure e.g. through air pumping, while the cooling chamber may be brought from near atmospheric pressure to essentially the intermediate pressure preferably quickly after placing the sample therein.

In embodiments of the invention involving more than one chamber, a vacuum gate is preferably provided between the desorption chamber and the at least one other, preferably cooling chamber.

A cooling system may advantageously comprise a heat sink that is coupled N to a specimen holder carrying the sample and optionally also piping hosting > 25 a cooling agent, said piping being coupled to the heat sink. Such a cooling <Q system may be adapted to be utilized in connection with a vacuum, with & other types of cooling systems possibly not being applicable. 2 Measurements of desorbed molecules that may be enabled through = embodiments of the present invention may, in addition to information about 0 30 type and quantity of adsorbed molecules or absorbed atoms, also provide > information on what type of sites on the sample the adsorbed molecules or absorbed atoms have resided in. For instance, information related to whether they are diffusible or trapped molecules or atoms may be obtained.

Improved detection of desorbed molecules, which may be provided via the invention, may allow e.g. manufacturers of materials to more efficiently analyze and/or control the quality and/or properties of materials that they produce. Data related to desorbed molecules may provide insight on the quality of the material, which may enable quality control and/or improvement of quality through information on how properties of materials may be affected. Evaluation of how quality of the material is affected through absorbed atoms may also be enabled as the measurements may yield information on how the state of the atoms (whether they are diffusible or trapped and trap location, i.e. for instance type of lattice defect in question) may influence the quality, such as embrittlement. The trapping sites may be or give information on manufacturing defects (cracks or porosity, for instance). Improved measurement of concentration of e.g. hydrogen in materials and enhanced trapping behavior analysis may be provided, which could be significant in engineering new materials. As novel materials are being developed, it may even more prominently be seen in the future that the current measurement methods are inadequate. For example in the steel industry, especially related to high-strength steels, accurate measurements of hydrogen content may be an important issue in avoiding hydrogen-assisted cracking formation during the steel processing and exploitation. The present invention may provide improved accuracy of the total hydrogen o concentration measurement. Also distinguishing between the diffusible O 25 hydrogen (that which diffuses in the lattice of the studied e.g. steel at room © temperature) and trapped hydrogen (that of which desorption activates o approaching a certain temperature, forming peaks of hydrogen thermal 2 desorption spectra) may be provided. a > The invention may allow improvements in material quality and through this, % 30 enable manufacturing of more durable and safe products, as mechanical = behavior of for instance automobile parts may fulfill their design criteria.

N The present invention may be utilized to detect hydrogen molecules, but embodiments of the invention enable detection of also other molecules and atoms, such as helium. Helium measurement/detection may be important fore.g. nuclear applications, as helium accumulated in for instance structural materials may result in swelling and cracking of the nuclear reactor components. Embodiments of the invention may also reduce time to measurement for 5 thermal desorption analysis. If the ultra-low pressure may be maintained in the desorption chamber e.g. between subsequent measurements involving different samples, it may be possible to conduct measurements faster than with the prior art solutions. At high output, reduced time to measurement and analysis may be especially advantageous in production or other instances where fast measurements of a large number of samples are essential. Embodiments of the invention allow measurements involving molecules desorbed from e.g. steels but also for example from copper, copper and nickel alloys, titanium, or semiconductors. The application areas may for instance be in electronics or semiconductor manufacturers or users. As may be understood by the skilled person, the detection of molecules desorbed from a metal surface and the information given by such detection may be used to provide information on the absorbed atoms and also detection of adsorbed atoms and/or molecules may be enabled through the present invention. The exemplary embodiments presented in this text are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this text as an open limitation that does not exclude the N existence of unrecited features. The features recited in depending claims > 25 are mutually freely combinable unless otherwise explicitly stated.

O S The novel features which are considered as characteristic of the invention I are set forth in particular in the appended claims. The invention itseff, + however, both as to its construction and its method of operation, together = with additional objects and advantages thereof, will be best understood from 0 30 the following description of specific example embodiments when read in > connection with the accompanying drawings. The previously presented considerations concerning the various embodiments of the arrangement may be flexibly applied to theembodiments of the method mutatis mutandis, and vice versa, as being appreciated by a skilled person.

BRIEF DESCRIPTION OF THE DRAWINGS Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which: Figure 1 illustrates one embodiment of an arrangement according to the invention, and Figure 2 shows one other illustration of an arrangement, Figure 3 shows a cooling system according to one embodiment of the invention, Figure4 is an exemplary spectrum depicting the information about desorbed molecules that may be obtained through embodiments of the invention, and Figure 5 gives a flow chart of the method according to one embodiment of the invention.

DETAILED DESCRIPTION Figure 1 gives a schematic representation of an arrangement 100 according to an embodiment of the invention. The arrangement 100 comprises at least one chamber 102 adapted to keep an ultra-low pressure, which may be a vacuum/partial vacuum pressure. In the desorption chamber 102, a sample N comprising absorbed atoms may be heated in a vacuum or ultra-low S pressure to allow formed molecules to desorb from the surface, after which S the desorbed molecules may be detected as will be comprehended by a I 25 — person skilled in the art. = The desorption chamber 102 may be one that is similar to that which is LO conventionally used for thermal desorption measurements. N The ultra-low pressure may in advantageous embodiments be below 10° mbar, such as in the range of 107-109 mbar, advantageously around about 108 mbar.

The arrangement 100 additionally comprises a cooling system for cooling the sample prior to its heating in the ultra-low pressure. Cooling of the sample may delay/suppress escape or desorption of the molecules to be detected. In conventional thermal desorption measurements, at least some of the molecules leave/escape the sample during preparation for the measurement. As a thermal desorption apparatus is being prepared for the measurement, i.e., usually as the ultra-low pressure/vacuum is being prepared (in a desorption chamber, with the sample being placed in the chamber), molecules may leave the sample and remain undetected. The preparation for the measurements may reguire a significant or at least meaningful amount of time, such as 20 min or 1 h, for instance, as the measurements are typically conducted in an ultra-high vacuum (UHV) chamber and it may reguire this amount of time before the desorption chamber can be brought to this level of vacuum.

In one embodiment, the cooling system may be implemented in connection with the desorption chamber 102 so that the sample may be cooled and then heated in the same chamber 102, the heating being initiated when the desorption chamber is ready for conducting the detection of molecules, i.e. when the ultra-low pressure is reached.

In the embodiment of Figure 1, however, the arrangement 100 comprises a first chamber which is the desorption chamber 102 and additionally a second chamber, which is a cooling chamber 104, wherein the cooling chamber 104 comprises or is coupled with a cooling system 106. The sample may then be cooled in the cooling chamber 104 before being s 25 transferred to the desorption chamber 102, which may be a UHV chamber.

QA N The cooling system 106 may be adapted to cool the sample to at least a O suitable first temperature (or lower) so that the molecules that are intended S to be detected may be hindered from escaping the surface of the sample I until the measurement can be conducted. For instance, the first temperature - 30 may be at least -30 °C, which may be suitable for e.g. detecting hydrogen = molecules. A first temperature between -30°C to -150 °C may also be o suitable.

N In the embodiment of Figure 1, the desorption chamber 102 may be continuously pumped so that the ultra-low pressure, such as in an ultra-high vacuum chamber, is continuously maintained in the desorption chamber.

The ultra-low pressure that is maintained may, for instance have a pressure of about 108 mbar. By saying that the desorption/lUHV chamber is continuously pumped, it is to be understood that the ultra-low pressure may be maintained for sustained periods of time and several measurements may be conducted involving a number of samples without substantial deviation from the ultra-low pressure. Of course, the pumping of the desorption chamber to decrease the pressure from e.g. ambient pressure may still occur for instance at some time intervals to obtain the ultra-low pressure. In addition to being a cooling chamber, the chamber 104 may be an air-lock chamber which is adapted to host or keep a vacuum. A vacuum may then be created into the cooling chamber 104, so that the sample may be transferred to the desorption chamber 102 for the measurement(s). In an embodiment of the invention, the cooling chamber is adapted to host a vacuum that may be higher in pressure than that of the UHV chamber 102, — the pressure in the cooling chamber being brought to about 105 mbar. In one embodiment, the desorbed molecules that are to be detected in the measurement(s) are hydrogen molecules. In pure iron, a hydrogen atom may travel a distance of approximately 1 mm in 5 min time at room temperature. Diffusion (rate of atomic motion, or the distance that an atom may migrate in a material in a certain period of time) may in steels be slower due to large number of trapping sites. However, diffusion may be significant in measurements of desorbed molecules and adversely affect the accuracy. At a temperature of about 77 K (-196 °C), the diffusion of hydrogen in metallic materials may be nearly fully suppressed. This temperature ES 25 corresponds to the temperature of liquid nitrogen and accordingly, for N measurement/detection of hydrogen molecules, liguid nitrogen may be O advantageously applied in a cooling system 106 to cool a sample. Also S other cooling agents, such as other liguefied gases may be utilized. The I type of cooling agent may be dependent on the molecule to be detected = 30 and/or the first temperature that the sample is to be cooled to.

O 2 An arrangement 100 may also comprise a vacuum gate 108. The sample S may be transferred from the cooling chamber 104 to the desorption chamber N 102 via the vacuum gate 108. The vacuum gate may be a pneumatic vacuum gate. The vacuum gate 108 is preferably such that is only opened for transfer of the sample to the desorption chamber 102 and may allow toprevent contamination of the desorption chamber 102. An arrangement 100 may also in some embodiments comprise a sample holder 110 which may be configured to be permanently integrated with the cooling chamber 104 in a fixed manner or it may be configured to be detachable from the cooling chamber 104. The sample holder 110 may be adapted to carry at least one sample for conducting the measurement. A sample holder 110 may be configured to carry a number of samples. In one embodiment of the invention, a sample holder 110 may carry a number of samples into the cooling chamber 104 simultaneously, while carrying the samples into the desorption chamber 102 one at a time for conducting measurements of the samples separately. In one embodiment, a sample holder 110 may comprise a number of specimen trays, each holding one sample, the sample holder being adapted to have the specimen trays detached from a sample holder body for separate entry into the UHV chamber 102, possibly via the vacuum gate

108. The entry to the UHV chamber may for instance be enabled through use of a conveyor belt system. With use of such a system, a number of samples may be transferred into the cooling chamber so that the cooling chamber 104 does not have to be pumped to the intermediate pressure from an ambient pressure in connection with each sample. Cooling of a number of samples may also then be carried out simultaneously. Figure 2 gives another illustration of an arrangement or part of an arrangement 100. The figure shows the desorption chamber 102, cooling o chamber 104, vacuum gate 108, and sample holder 110. The cooling O 25 system 106 is not shown in the figure, as in this embodiment, the cooling © system is configured to reside fully within the cooling chamber 104. & The sample holder 110 is here shown in a first position, residing outside of E the cooling chamber 104. At this position, the sample holder 110 may be o loaded with one or more samples. Samples may be placed on specimen % 30 trays that are e.g. laterally displaced with respect to each other on the = sample holder, which may for instance comprise a plate or boardlike shape.

N The sample holder 110 of Figure 2 may be configured to be actuated into a second position so that the sample holder 110 may at least partly reside inside the cooling chamber 104 so that the sample or samples may bebrought into the chamber and the cooling chamber 104 may be separated from the environment in a way that allows the chamber to be brought to the intermediate pressure. The arrangement 100 may also comprise a mass spectrometer 202 operatively coupled to the desorption chamber 102 for detecting the desorbed molecules. In other embodiments of the invention, other spectrometers or measurement apparatuses may be used for detection of the molecules. For instance, a residual gas analyzer may be utilized. An arrangement 100 may also comprise a heating system for the heating of the sample. The sample may be advantageously heated to a second temperature, wherein the second temperature is higher than the aforementioned first temperature to which the sample is cooled, with the second temperature preferably being at least 600 °C. Samples may be radiatively heated in the desorption chamber 102. The heating may be conducted via an internal furnace with a resistive heating mechanism locating in the desorption chamber 102. An arrangement 100 with a heating system comprising a furnace may have a furnace comprising molybdenum and the furnace may be eguipped with heating elements comprising e.g. tungsten wire. Heating elements may be positioned to surround a sample holder. Preferably, a heat shield may allow to focus the radiative heat on the sample and prevent the overheating of the walls of the desorption chamber 102. A heating system may also comprise a thermocouple for measurement of temperature. N In some embodiments, samples may be heated to 1000 °C. In other > 25 embodiments, such as e.g. for measurements related to hydrogen, a sample <Q may be preferably heated to about 800 °C.

O = Figure 3 shows an embodiment of a cooling system 106. The cooling = system 106 may comprise a heat sink 302 that is configured to be coupled = to a specimen holder 110. The coupling may advantageously be direct o 30 physical coupling.

O N The cooling system 106 may additionally comprise piping 304, wherein the piping 304 may host a cooling agent. The piping 304 may be adapted to be coupled to the heat sink 302. The cooling agent may be a fluid, such asliquid nitrogen. Figure 3 shows also a vacuum flange 306 which may be adapted for use in cryogenic or low temperature applications. Figure 4 shows an exemplary figure that may be obtained through data from detected molecules via utilizing embodiments of the invention. Figure 4 depicts an exemplary thermal desorption spectrum of hydrogen release from a high-strength steel sample. Pressure of desorbed molecules in the desorption chamber 102 can be measured as a function of temperature increasing with a constant heating rate. The measured pressure can be recalculated to the desorption rate of the measured molecules as a function of temperature (see Figure 4). Concentration of the desorbed molecules in the specimen can be calculated from the obtained spectra of the desorption rate as area under the spectra. Also, evaluation of the trapping sites can be performed using the obtained spectra.

A method for detecting molecules desorbed from at least one sample according to the present invention comprises at least cooling the sample, heating the cooled sample at an ultra-low pressure to allow molecules to desorb from the sample, and detecting the desorbed molecules.

Further embodiments of the invention may comprise, as according to a flow chart presented in Figure 5, cooling 502 the sample, wherein the cooling may be conducted in a cooling chamber 104. An intermediate pressure may be created 504 in the cooling chamber 104, e.g. through air-pumping. The cooling of the sample and creating of the intermediate pressure may be o conducted with the sample in the cooling chamber 104 and they may be O 25 conducted essentially simultaneously or one procedure may be conducted © before the other, or they may be conducted so that they are at least partially o overlapping temporally. Preferably, the cooling 502 of the sample to at least 9 a first temperature is carried out within 1 min of the starting of the creating E 504 (pumping) of the intermediate pressure. 5 30 At 506, the sample may be transferred to the desorption chamber 102 from 2 the cooling chamber 104. The transfer may be done by passing the sample N through a vacuum gate 108. The method then may comprise heating 508 the sample in the desorption chamber 102, wherein the desorption chamber maintains the ultra-lowpressure. Finally, at 510 molecules desorbed from the sample may be detected. The ultra-low pressure may be maintained 512 in the desorption chamber throughout carrying out the other method steps.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of inventive thought and the following patent claims.

The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

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Claims

1. An arrangement (100) for detecting atoms and/or molecules desorbed from at least one sample, the arrangement comprising at least one desorption chamber (102) adapted to keep an ultra-low pressure, wherein the desorbed atoms and/or molecules may be detected by heating the sample in the desorption chamber (102), the arrangement additionally comprising at least one cooling chamber (104) operatively coupled to the desorption chamber and a cooling system (106) for cooling the sample in the cooling chamber prior to the sample being transferred to the desorption chamber, the cooling system comprising a heat sink (302) that is coupled to a sample holder carrying the sample, and wherein the cooling chamber is an airlock chamber adapted to be air-pumped to create an intermediate pressure in the cooling chamber after the sample is placed therein.

2. The arrangement of claim 1, wherein the intermediate pressure is preferably below 10° mbar.

3. The arrangement of any of the previous claims, wherein the desorption chamber is continuously air-pumped to create an ultra-low pressure that is below 10° mbar, advantageously in the range of 107-109 mbar, most advantageously in the range between 10-10? mbar.

4. The arrangement of any of the previous claims, wherein the sample is cooled to a temperature of below -30 °C, preferably to a temperature in the range from -30 °C to -150 °C. N

5. The arrangement of any of the previous claims, wherein during the > 25 heating the sample is heated to at least 600 °C.

O S

6. The arrangement of any of the previous claims, wherein the I arrangement additionally comprises a vacuum gate (108) through = which the sample may be transferred to the desorption chamber.

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7. The arrangement of any of the previous claims, wherein the cooling S 30 system additionally comprises piping (304) hosting a cooling agent, N . k . a said piping being coupled to the heat sink.

8. The arrangement of any of the previous claims, wherein the cooling system comprises a cooling agent, such as a liquefied gas, for example liquid nitrogen.

9. The arrangement of any of the previous claims, wherein the arrangement additionally comprises a mass spectrometer (202) or residual gas analyzer for detecting the desorbed molecules.

10. The arrangement of any of the previous claims, wherein the arrangement additionally comprises a heating system that is operatively coupled to the desorption chamber for heating the sample.

11. The arrangement of any of the previous claims, wherein the arrangement additionally comprises a sample holder (110) for carrying a number of samples, wherein the sample holder provides a number of samples to the cooling chamber essentially simultaneously, while providing the samples to the desorption chamber one at a time.

12. The arrangement of any of the previous claims, wherein the detected molecules are hydrogen molecules and wherein the sample comprises for example steel, copper, copper alloy, nickel alloy, titanium, or a semiconductor.

13. A method for detecting molecules desorbed from at least one sample, the method comprising - cooling the sample in a cooling chamber (104) utilizing a heat sink (302) that is coupled to a sample holder carrying the sample, - air-pumping the cooling-chamber to create an intermediate N pressure in the cooling chamber, O 25 - transferring the sample to a desorption chamber (102), S - heating the cooled sample at an ultra-low pressure in the I desorption chamber (102) to allow molecules to desorb from the + sample, and = - detecting the desorbed molecules.

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14. The method of claim 13, wherein the method additionally comprises continuous air pumping of the desorption chamber to keep the ultra- low pressure.

15. The method of claim 13 or 14, wherein the transferring of the sample comprises transfer of the sample through a vacuum gate (108) from the cooling chamber to the desorption chamber.

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