A sample stage for programmed temperature desorption spectroscopy

Abstract

The present invention belongs to the technical field of sample surface chemical detection, and particularly relates to a sample stage for programmed temperature desorption spectrum. It includes an ultra-high vacuum chamber, a direct current power supply, a mass spectrometer, a heating module and a cooling module, wherein the heating module and the cooling module are both arranged in the ultra-high vacuum chamber; the heating module includes two metal supports and a heating plate connected between the two metal supports, wherein the two metal supports are arranged on the cooling module, and the two metal supports are connected to the direct current power supply through copper wires; the heating plate is used for carrying and heating and desorption of the sample, and the cooling module is used for cooling the sample; the sampling head of the mass spectrometer is arranged in the ultra-high vacuum chamber, and corresponds to the sample on the heating plate, and the mass spectrometer is used to obtain the programmed temperature desorption mass spectrum of the sample. The present invention has the advantages of simple and compact structure, high heating efficiency, fast cooling speed, small background interference, and can obtain clearer intrinsic signals.

Description

Technical Field

[0001] The invention belongs to the technical field of sample surface chemical detection, and in particular relates to a sample stage for programmed temperature desorption spectroscopy. Background Art

[0002] Temperature-programmed desorption (TPD) is a technique for detecting desorbed species during the heating process of a sample surface. In an ultra-high vacuum environment, a quantitative amount of specific molecules is adsorbed on the surface of a low-temperature sample, and then the sample is heated linearly. During the heating process, the mass spectra of species related to the adsorbed molecules are collected simultaneously, and the recorded curve of the change of mass spectrometry signal intensity with temperature is the temperature-programmed desorption spectrum. From the TPD spectrum, a lot of information about the adsorption of molecules on the surface can be obtained, including adsorption form, desorption energy, and desorption order. This information is of great value for understanding surface chemical reactions.

[0003] To obtain high-quality TPD data, the sample needs to have good heating linearity and small mass spectrometry background signal. At the same time, after the heating is completed, the sample should be cooled as much as possible to shorten the time before the next experiment. Therefore, the design of the sample stage is crucial. Sample heating methods can be roughly divided into contact and non-contact types, and resistance heating and electron beam heating belong to these two methods respectively. Contact resistance heating has good heating linearity, rapid cooling, and a relatively simple structure, but the slight deformation of the filament can easily cause the sample to break at high temperature, thereby interrupting the experiment. Non-contact heating often uses electron beam heating, which has good heating linearity and better protection for the sample. However, the structure of electron beam heating is relatively complex, so that during the heating process, the desorbed species in the area outside the sample will cause interference. At present, there is no TPD sample stage that can take into account good heating linearity, small background desorption signal, and good sample protection. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide a sample stage for programmed temperature desorption spectroscopy, aiming to solve the problem that the currently commonly used programmed temperature desorption mass spectrometry filament is difficult to achieve both good temperature rise linearity and low background interference.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a sample stage for programmed temperature desorption spectroscopy, comprising an ultra-high vacuum cavity, a direct current power supply, a mass spectrometer, a heating module and a cooling module, wherein the heating module and the cooling module are both arranged in the ultra-high vacuum cavity;

[0007] The heating module includes two metal supports and a heating plate connected between the two metal supports, wherein the two metal supports are arranged on the cooling module, and the two metal supports are connected to a DC power supply through copper wires; the heating plate is used for carrying and heating and desorbing samples, and the cooling module is used for cooling the samples; the sampling head of the mass spectrometer is arranged in an ultra-high vacuum cavity and corresponds to the sample on the heating plate, and the mass spectrometer is used to obtain a programmed temperature desorption mass spectrum of the sample.

[0008] The cooling module comprises a cold head and an insulating thermal pad, wherein the lower end of the cold head is inserted into the ultra-high vacuum cavity, and the lower end is connected to the two metal support members through the insulating thermal pad.

[0009] The insulating thermal pad is a sapphire pad; the cooling temperature of the cold head is conducted to the sample of the heating plate through the sapphire pad and the metal support.

[0010] The cold head is cooled by liquid nitrogen or liquid helium, and a refrigerant inlet and a refrigerant outlet are arranged at the upper end of the cold head.

[0011] The heating plate is a plate-like structure formed by repeatedly folding a tantalum bar or a molybdenum bar in a zigzag shape. The connecting ends at both ends of the heating plate are respectively accommodated in grooves provided on the two metal support members, and are connected to the two metal support members through elastic connecting members.

[0012] The elastic connecting member includes a pressing plate and a spring; wherein the pressing plate is connected to the outside of the groove of the metal supporting member by screws, and the spring is arranged between the pressing plate and the connecting end of the heating plate.

[0013] The spring is a tungsten spring; the screw is a molybdenum screw.

[0014] The metal support is made of oxygen-free copper.

[0015] The sample on the heating plate is connected to a thermocouple, and the thermocouple is connected to a temperature display device arranged outside the ultra-high vacuum cavity through a wire.

[0016] The temperature display instrument, direct current power supply and mass spectrometer are all connected to a computer.

[0017] Compared with the existing design, the present invention has the following advantages and beneficial effects:

[0018] 1. High heating efficiency. In the present invention, the sample is directly attached to the tantalum bar, heat can be effectively transferred, and the heating efficiency is high.

[0019] 2. Fast cooling speed. The present invention shortens the single experiment cycle and improves the experimental efficiency.

[0020] 3. Small background interference. The structure of the present invention is simple and compact. During low-temperature adsorption, most of the adsorbate is adsorbed on the sample; during linear temperature increase, most of the thermal desorption signal mainly comes from the sample, the interference signal is greatly reduced, and a clearer intrinsic signal can be obtained.

[0021] 4. Buffering the temperature shock of the sample. In the present invention, the contact degree between the tantalum bar and the copper connector can be adjusted by the tungsten spring, which has a good effect of protecting the sample.

[0022] 5. This sample stage design uses a DC power supply, which is lower in cost than electron beam heating systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of a sample stage for programmed temperature desorption spectroscopy of the present invention;

[0024] Figure 2 It is a structural schematic diagram of the heating module and the cooling module in the present invention;

[0025] Figure 3 It is a structural schematic diagram of the heating plate in the present invention;

[0026] Figure 4 It is a schematic diagram of the connection between the heating plate and the metal support member in the present invention;

[0027] Figure 5 is a temperature drop curve diagram of a sample under liquid nitrogen cooling in an embodiment of the present invention;

[0028] Figure 6 It is a multilayer H in the embodiment of the present invention. 2 Temperature programmed desorption spectrum of O on rutile titanium oxide;

[0029] In the figure: 1. Refrigerant inlet; 2. Refrigerant outlet; 3. Ultra-high vacuum chamber; 5. DC power supply; 6. Temperature display; 7. Mass spectrometer; 8. Computer; 9. Sapphire gasket; 10. Metal support; 11. Screws; 12. Tantalum bar; 13. Cold head; 14. Copper wire; 15. Copper connecting assembly; 16. Thermocouple; 17. Ceramic glue; 18. Sample; 19. Pressing piece; 20. Spring. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1-2As shown, the present invention provides a sample stage for programmed temperature desorption spectrum, including an ultra-high vacuum chamber 3, a DC power supply 5, a mass spectrometer 7, a heating module and a cooling module, wherein the heating module and the cooling module are both arranged in the ultra-high vacuum chamber 3; the heating module includes two metal supports 10 and a heating plate connected between the two metal supports 10, wherein the two metal supports 10 are arranged on the cooling module, and the two metal supports 10 are connected to the DC power supply 5 through copper wires 14; the heating plate is used for carrying and heating and desorption of the sample, and the cooling module is used for cooling the sample; the sampling head of the mass spectrometer 7 is arranged in the ultra-high vacuum chamber 3 and corresponds to the sample on the heating plate, and the mass spectrometer 7 is used to obtain the programmed temperature desorption mass spectrum of the sample.

[0032] In an embodiment of the present invention, the cooling module includes a cold head 13 and an insulating thermal pad, wherein the lower end of the cold head 13 is inserted into the ultra-high vacuum cavity 3, and the lower end is connected to the two metal support members 10 through the insulating thermal pad.

[0033] Specifically, the cold head 13 is cooled by liquid nitrogen or liquid helium, and a refrigerant inlet 1 and a refrigerant outlet 2 are provided at the upper end of the cold head 13. Preferably, the insulating thermal pad is a sapphire gasket 9, and the cooling temperature of the cold head 13 is conducted to the sample on the heating plate through the sapphire gasket 9 and the metal support 10. The sapphire gasket 9 not only plays a role in cooling, but also plays a role in electrically isolating the cooling module from the heating module. Optionally, an indium sheet or a silver sheet can be placed on the contact surface between the sapphire gasket 9 and the metal support 10 to make the cooling better.

[0034] like Figure 3 As shown, in an embodiment of the present invention, the heating plate is a plate-like structure formed by repeatedly folding a tantalum bar 12 or a molybdenum bar in a zigzag shape, and the connecting ends at both ends of the heating plate are respectively accommodated in grooves provided on two metal support members 10, and are connected to the two metal support members 10 through elastic connecting members.

[0035] like Figure 4 As shown, in an embodiment of the present invention, the elastic connecting member includes a pressing plate 19 and a spring 20, wherein the pressing plate 19 is connected to the outer side of the groove of the metal support 10 by a screw 11, and the spring 20 is arranged between the connecting end of the pressing plate 19 and the heating plate. The spring 20 can adjust the fit between the tantalum bar 12 and the metal support 10, buffer the temperature shock, and thus play a role in protecting the sample.

[0036] Preferably, the spring 20 is a tungsten spring; the screw 11 is a molybdenum screw. The tungsten spring contracts at low temperatures, and the stiffness coefficient decreases at high temperatures, both of which can reduce the tightness of the fit between the tantalum bar 12 and the metal support 10, thereby buffering the temperature shock to the sample. The metal support 10 is made of oxygen-free copper, and the upper end of the metal support 10 is connected to the copper wire 14 through a copper connecting assembly 15. Furthermore, the oxygen-free copper support is relatively slender, so that the sample is separated from other structures in space, so that during the heating process, the background desorption signal is greatly reduced. The metal support 10 plays a conductive role, and at the same time contacts with the cooling module to conduct the cooling temperature.

[0037] Furthermore, if Figure 2 As shown, the sample on the heating plate is connected to the thermocouple 16, and the thermocouple 16 is connected to the temperature display 6 arranged outside the ultra-high vacuum chamber 3 through a wire. In this embodiment, the sample 18 is fixed on the heating plate by a molybdenum screw, and the sample 18 is fitted with the heating plate. The thermocouple 16 is fixed to the upper surface of the sample 18 by a ceramic glue 17. The thermocouple 16 can accurately and sensitively feed back the sample temperature to the control program, and adjust the current passing through the tantalum strip 12 to achieve the effect of controlling the sample temperature. Optionally, the thermocouple 16 can be K-type or N-type.

[0038] Furthermore, the temperature display 6 , the DC power supply 5 and the mass spectrometer 7 are all connected to the computer 8 .

[0039] In this embodiment, a tantalum bar 12 is repeatedly folded into a heating plate. Specifically, the heated tantalum bar is cut into a zigzag shape, has a large resistance, and generates heat after passing current, which plays a role in heating the sample. At the same time, the tantalum bar 12 also plays a role in loading the sample. The metal support 10 in contact with the tantalum bar 12 is in contact with the cold head 13 through the sapphire gasket 9. The cold head 13 is cooled by liquid nitrogen or liquid helium. Under liquid nitrogen cooling, the surface temperature of the sample can be reduced to 100K, which is convenient for adsorbing various H 2 O、CO 2 After the quantitative adsorption is completed, the tantalum strip 12 is energized by the DC power supply 5. Because the tantalum strip 12 after wire cutting is in a broken line shape and has a large resistance, when the current passes through, the tantalum strip 12 generates Joule heat, which is transferred to the sample 18 attached to it, so that the sample temperature rises. The temperature of the sample 18 is read by the thermocouple 16 fixed on the surface of the sample with ceramic glue 17, and fed back to the external control program in the computer 8 in time, and the output current is adjusted by PID to control the heating rate. During the process of sample temperature rise, the pre-adsorbed small molecules will be desorbed at different temperatures and collected by the mass spectrometer 7 to obtain a programmed temperature desorption mass spectrum.

[0040] The working principle of the present invention is:

[0041] The ultra-high vacuum degree in the ultra-high vacuum chamber 3 is 10-9 When the sample temperature is below mbar, the cooling module can reduce the sample temperature to a very low level (liquid nitrogen cooling, 100K) to complete the adsorption of specific molecules. The current passing through the tantalum strip 12 on the back of the sample is adjusted by the connected DC power supply 5 to increase the sample temperature linearly. At the same time, the thermocouple 16 on the surface of the sample feeds back the sample temperature to the external PID control program, and adjusts the current size to control the heating rate (2K / S). During the heating process, the adsorbed molecules or products are desorbed and detected by the mass spectrometer 7, and a mass spectrometer signal is plotted as a function of temperature, i.e., a TPD spectrum is obtained.

[0042] The tungsten spring shortens at low temperatures and its stiffness coefficient decreases at high temperatures, which weakens the fit between the tantalum bar 12 and the metal support 10 behind the sample, buffering the temperature shock caused by misoperation, thereby playing a good role in protecting the sample.

[0043] The main feature of the present invention is that the sample is separated from other structures in space, which greatly reduces the background desorption and ensures good linear heating and fast cooling. It only takes 10 minutes for the sample to cool from room temperature to 110K. The cooling curve is as follows: Figure 5 shown.

[0044] Example 1

[0045] Measure H under the following conditions 2 Temperature-programmed desorption spectrum of O on rutile titanium oxide (110):

[0046] In this embodiment, the ultra-high vacuum degree in the ultra-high vacuum chamber 3 is 5*10 -10 mbar. Liquid nitrogen is used as the cooling medium, and the sample surface temperature can be reduced to 90K. At low temperatures, quantitative H 2 O molecules, the output current of DC power supply 5 was adjusted to increase the sample temperature at a rate of 2K / S. At the same time, the mass spectrometer was used to collect H 2 O signal (mass number 18), and obtain TPD spectrum, such as Figure 6 shown.

[0047] The present invention provides a sample stage for programmed temperature desorption spectroscopy, in which the heating function of the heating module is achieved through the resistance heating of the wire-cut tantalum strip, and the cooling of the cooling module is achieved through a cold head refrigerated by liquid nitrogen or liquid helium. The sample is fitted with the tantalum strip, which greatly improves the heating efficiency and also allows rapid cooling. The temperature is read by a thermocouple glued to the surface of the sample with ceramic glue, which improves accuracy. The tantalum strip is separated from other structures in space, so that background desorption is greatly reduced during the heating process, and the surface chemical information of the sample is reflected more truly and accurately. The tightness of the fit between the tantalum strip and the metal support is adjusted by a tungsten spring, which cushions the temperature shock to the sample. The present invention has a simple structure and low cost, and is suitable for programmed temperature desorption spectroscopy research.

[0048] The above description is only an embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, expansion, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A sample stage for programmed temperature desorption spectroscopy, characterized in that: It comprises an ultra-high vacuum chamber (3), a direct current power supply (5), a mass spectrometer (7), a heating module and a cooling module, wherein the heating module and the cooling module are both arranged in the ultra-high vacuum chamber (3); The heating module comprises two metal support members (10) and a heating plate connected between the two metal support members (10), wherein the two metal support members (10) are arranged on the cooling module, and the two metal support members (10) are connected to a direct current power source (5) via a copper wire (14); the heating plate is used for carrying and heating and desorbing the sample, and the cooling module is used for cooling the sample; a sampling head of a mass spectrometer (7) is arranged in an ultra-high vacuum cavity (3) and corresponds to the sample on the heating plate, and the mass spectrometer (7) is used for obtaining a programmed temperature desorption mass spectrum of the sample; The cooling module comprises a cold head (13) and an insulating thermal pad, wherein the lower end of the cold head (13) is inserted into the ultra-high vacuum cavity (3), and the lower end is connected to the two metal support members (10) via the insulating thermal pad; The insulating heat-conducting pad is a sapphire pad (9); the cooling temperature of the cold head (13) is conducted to the sample on the heating plate through the sapphire pad (9) and the metal support (10); The heating plate is a plate-shaped structure formed by repeatedly folding a tantalum bar (12) or a molybdenum bar in a folded line shape, and the connecting ends at both ends of the heating plate are respectively accommodated in grooves provided on the two metal support members (10), and are connected to the two metal support members (10) via an elastic connecting member; The metal support (10) is made of oxygen-free copper.

2. The sample stage for programmed temperature desorption spectroscopy according to claim 1, characterized in that: The cold head (13) is cooled by liquid nitrogen or liquid helium, and a refrigerant inlet (1) and a refrigerant outlet (2) are provided at the upper end of the cold head (13).

3. The sample stage for programmed temperature desorption spectroscopy according to claim 1, characterized in that: The elastic connecting member comprises a pressing plate (19) and a spring (20); wherein the pressing plate (19) is connected to the outside of the groove of the metal supporting member (10) by means of a screw (11), and the spring (20) is arranged between the pressing plate (19) and the connecting end of the heating plate.

4. The sample stage for programmed temperature desorption spectroscopy according to claim 3, characterized in that: The spring (20) is a tungsten spring; the screw (11) is a molybdenum screw.

5. The sample stage for programmed temperature desorption spectroscopy according to claim 1, characterized in that: The sample on the heating plate is connected to a thermocouple (16), and the thermocouple (16) is connected to a temperature display instrument (6) arranged outside the ultra-high vacuum cavity (3) through a wire.

6. The sample stage for programmed temperature desorption spectroscopy according to claim 5, characterized in that: The temperature display device (6), the DC power supply (5) and the mass spectrometer (7) are all connected to a computer (8).

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