A high-speed quantitative measurement method for microgram-level material gas adsorption and desorption process

Abstract

The application discloses a high-speed quantitative measurement method for microgram-level material gas adsorption and desorption process, and realizes in-situ measurement of gas layer thickness change in a sealed microcavity in a transmission electron microscope on the basis of a sample position measurement method based on micro-area electron diffraction Thon ring, realizes in-situ high-speed measurement of gas capacity released or absorbed by a sample by establishing a relationship curve between the gas layer thickness and the microcavity gas pressure, and achieves high-speed and quantitative measurement of the microgram-level or nanogram-level material gas adsorption and desorption process in a millisecond or even faster scale. The difficulty of directly measuring the gas pressure in-situ in the gas microcavity is solved for the first time, and the method has important significance for studying the gas charging and discharging process of trace materials by means of the electron microscope sealed microcavity in-situ technology. In addition, the method has very high sensitivity and can realize high-precision measurement of sub-nanometer-level gas layer thickness change (<10 ‑9 m) and millibar-level gas pressure change (<10 ‑1 Pa) in the electron microscope microcavity.

Description

Technical Field

[0001] This invention relates to the field of methods for testing the adsorption and desorption performance of gas storage materials, and particularly to a high-speed quantitative measurement method for the adsorption and desorption process of gases in microgram-level materials. Background Technology

[0002] Hydrogen energy, due to its abundant resources and environmental friendliness, is an ideal alternative to traditional fossil fuels. However, hydrogen storage has become a bottleneck restricting its development and application, making the development and research of hydrogen storage materials a current research hotspot. A crucial indicator in evaluating the performance of hydrogen storage materials is their hydrogen release kinetics. Currently, the field primarily utilizes temperature-programmed heating combined with thermogravimetric analysis to quantitatively evaluate gas adsorption and desorption performance. These evaluation methods require large-scale samples (hundreds of milligrams). Because the storage and release of gas by different particles at the microscopic level are difficult to synchronize precisely, the kinetic data obtained by these methods are essentially averages of a large number of powder particles. To gain a deeper understanding of the intrinsic structural kinetics of phase change gas storage / release in materials, it is necessary to simultaneously monitor the gas release process and material structural evolution with higher spatial and temporal resolution for trace samples. Therefore, how to quantitatively analyze the phase change gas storage process of trace materials has become an urgent problem to be solved.

[0003] In-situ electron microscopy (ESM) technology, building upon the high spatial resolution of existing electron microscopy techniques, has developed environmental field loading and dynamic observation techniques to achieve high spatial and temporal resolution in-situ analysis of materials under controlled environments. This technology plays an increasingly important role in key scientific discoveries in energy chemistry, semiconductor physics, and other fields. The "gas chip" technology involves designing a window unit at the front end of the sample holder, constructing a sealed microcavity within the electron microscope, connecting the sample holder to a gas system, and controlling the inlet and outlet pressures using two pressure gauges in the gas holder. This allows for a stable supply of flowing gas with consistent pressure and flow rate to the gas chip without affecting the high vacuum environment of the electron microscope chamber. In-situ ESM has unique advantages in studying the structural changes during the hydrogen charging and discharging processes of hydrogen storage materials, enabling millisecond-level real-time tracking of the phase structure evolution of individual particles. However, because electron microscopes can only load microgram-level samples, and currently it is not possible to simultaneously monitor phase transitions and measure trace amounts of gas in situ in real time, it is difficult to quantitatively analyze the amount of hydrogen released or absorbed during the hydrogen charging and discharging processes of hydrogen storage materials. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention discloses a high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials, specifically including the following steps:

[0005] S1: Disperse the sample to be tested evenly onto the surface of the lower chip in the gas chip, load the chip onto the in-situ sample holder of the transmission electron microscope, complete the leak detection, and insert it into the transmission electron microscope;

[0006] S2: Select an appropriate magnification and enter recording mode to photograph the SiN area of ​​the chip that can be observed. x High-resolution images of the thin film were obtained, and Fourier transforms were performed on the images to simultaneously obtain the upper and lower SiN chips. x Amorphous rings of thin films are passed through a gas chip, and the gas pressure is gradually increased to obtain upper and lower SiN chips. x The relationship between the amorphous rings of the thin film and the gas pressure;

[0007] S3: Select a suitable air pressure and photograph the SiN area of ​​the chip again. x High-resolution images of the thin film were obtained by closing the valves at both ends of the sample holder, heating the sample to the temperature at which the gas would be released, and recording the SiN in the observable area of ​​the chip using a high-speed camera. x Changes in the high-resolution image of the thin film;

[0008] S4: Combine the upper and lower SiN chips obtained in S2 x Radial integration was performed on the amorphous ring of the thin film, and the resulting curve was fitted with a contrast transfer function to obtain the upper and lower SiN wafers, respectively. x The height of the thin film is calculated by subtracting the two height values ​​to obtain the relationship between the thickness of the gas layer in the chip and the gas pressure.

[0009] S5: Place the sample from S3 onto the SiN chip before and after gas release. x Radial integration is performed on the amorphous ring of the thin film to obtain the rapid change process of the gas layer thickness in the chip before and after gas release. This process is compared with the relationship between the gas layer thickness and gas pressure in S4, thereby completing the quantitative measurement of the amount of gas adsorbed and desorbed by the microgram-level material loaded in the transmission electron microscope.

[0010] Furthermore, in S1, a gas microcavity is constructed in a transmission electron microscope, and high-speed quantitative measurement of the gas adsorption and desorption process of microgram-level materials is achieved based on the high precision of electron diffraction.

[0011] Furthermore, in S2, the magnification is above 200K, and high-resolution images of amorphous thin films in gas microcavities are captured. The Fourier transform diagram shows that two sets of rings can be observed simultaneously.

[0012] Furthermore, in S3, the valves at both ends of the sample rod are closed when the sample releases the gas it stores.

[0013] Furthermore, S3 uses a high-speed camera to record high-resolution images of changes in the gas microcavity thin film, enabling high-speed measurement of the adsorption and desorption gas process at the sub-millisecond scale.

[0014] Furthermore, S3 performed radial integration and contrast transfer function fitting on the amorphous rings of the upper and lower chips obtained simultaneously, and subtracted the underfocus amount of the upper and lower chips obtained by fitting to obtain the thickness of the gas layer in the gas chip.

[0015] Furthermore, in S5, the change in the thickness of the gas layer in the chip before and after gas release is compared with the relationship curve between the gas layer thickness and the microcavity gas pressure established in S2.

[0016] Furthermore, the method is not limited to O2 and H2 gases, but is applicable to various scenarios where changes in the amount of gaseous substances in a sealed microcavity are caused by physical or chemical processes such as solid storage / release, adsorption / desorption.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention, based on a sample position measurement method using micro-area electron diffraction Thon rings, enables in-situ measurement of gas layer thickness changes within a sealed microcavity using a transmission electron microscope (TEM). This allows for in-situ, high-speed measurement of the gas volume released or absorbed by the sample, achieving high-speed, quantitative measurement of gas adsorption and desorption processes in micrograms and even nanograms of materials at millisecond or faster scales. It solves the problem of in-situ measurement of gas pressure within a gas chip microcavity, and is of great significance for studying the gas filling and releasing processes of trace materials using in-situ TEM techniques for sealed microcavities. Furthermore, this method exhibits very high sensitivity, capable of achieving sub-nanometer-level gas layer thickness changes (<10 nm) within the TEM microcavity. -9 (meters) and gas millibar pressure changes (<10) -1 High-precision measurement of (Pa).

[0019] This invention, based on a sample position measurement method using micro-area electron diffraction Thon rings, enables in-situ measurement of gas layer thickness changes within a sealed microcavity using a transmission electron microscope (TEM). This allows for in-situ, high-speed measurement of the gas volume released or absorbed by the sample, achieving high-speed, quantitative measurement of gas adsorption and desorption processes in micrograms and even nanograms of materials at millisecond or faster scales. It solves the problem of in-situ measurement of gas pressure within a gas chip microcavity, and is of great significance for studying the gas filling and releasing processes of trace materials using in-situ TEM techniques for sealed microcavities. Furthermore, this method exhibits very high sensitivity, capable of achieving sub-nanometer-level gas layer thickness changes (<10 nm) within the TEM microcavity. -9 (meters) and gas millibar pressure changes (<10) -1 High-precision measurement of (Pa). Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The SiN gas chip used in the embodiments of the present invention x High-resolution photographs of thin films;

[0022] Figure 2 for Figure 1 The Fourier transform diagram shows the amorphous rings of the upper and lower chips.

[0023] Figure 3 for Figure 2 The contrast transfer function and fitting curve of the amorphous ring of the middle and lower chips after radial integration, and the fitting result of the underfocus amount;

[0024] Figure 4 This is a schematic diagram showing the shape of the upper and lower chips after the in-situ gas chip is ventilated.

[0025] Figure 5 This illustrates the relationship between the gas layer thickness and chip pressure measured in this embodiment of the invention. Detailed Implementation

[0026] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention:

[0027] A high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials, specifically including the following steps:

[0028] S1: Disperse the sample to be tested evenly onto the surface of the lower chip in the gas chip, load the chip onto the in-situ sample holder of the transmission electron microscope, complete the leak detection, and insert it into the transmission electron microscope.

[0029] S2: Select an appropriate magnification and enter recording mode to photograph the SiN area of ​​the chip that can be observed. x High-resolution images of the thin film were obtained, and Fourier transforms were performed on the images to simultaneously obtain the upper and lower SiN chips. x Amorphous rings of thin films are formed, and then gas is introduced into a gas chip while gradually increasing the gas pressure to obtain upper and lower SiN chips. x The relationship between the amorphous rings of the thin film and the gas pressure.

[0030] S3: Select a suitable air pressure and photograph the SiN area of ​​the chip again. xHigh-resolution images of the thin film were obtained, then the valves at both ends of the sample holder were closed, the sample was heated to the temperature at which the gas was released, and the SiN in the observable area of ​​the chip was recorded using a high-speed camera. x Changes in the high-resolution image of the thin film.

[0031] S4: Combine the upper and lower SiN chips obtained in step 2 x Radial integration was performed on the amorphous ring of the thin film, and then the resulting curve was fitted with a contrast transfer function to obtain the upper and lower SiN chips, respectively. x The height of the thin film is calculated, and the difference between the two height values ​​is used to obtain the relationship between the thickness of the gas layer in the chip and the gas pressure.

[0032] S5: Place the sample from step 3 onto the SiN chip before and after gas release. x Radial integration is performed on the amorphous ring of the thin film to obtain the rapid change process of the gas layer thickness in the chip before and after gas release. This process is then compared with the relationship between the gas layer thickness and gas pressure in step 4, thus completing the quantitative measurement of the amount of gas adsorbed and desorbed by the microgram-level material loaded in the transmission electron microscope.

[0033] The principle of the method of this invention is:

[0034] According to Abbe's imaging principle, the relationship between focal length f, object distance u, and image distance v in a transmission electron microscope can be written as:

[0035] 1 / f = 1 / u + 1 / v

[0036] When the SiN in the chip x When the film height changes, both the focal length and image distance change simultaneously. The formula can be rewritten as:

[0037] 1 / (f-Δf)=1 / (u+ΔZ)+1 / v_2

[0038] However, since the magnification of the electron microscope remains unchanged, it can be written as:

[0039] M = v / u = v_2 / (u + Δz)

[0040] Therefore, according to formulas 1, 2, and 3, SiN x The relationship between the change in film height and the change in electron microscopy underfocus can be expressed as:

[0041] Δf=-MΔZ / (1+M)

[0042] Since the magnification M in a transmission electron microscope is much greater than 1, the change in underfocus can be considered as the value of the SiN chip. x The height variation of the thin film. Based on this, we further examine SiN... xBy performing a Fourier transform on the high-resolution image of the thin film and then radially integrating the resulting amorphous ring, the intensity distribution curve of the amorphous ring in the frequency domain can be obtained. The corresponding function is the contrast transfer function, which can be written as:

[0043] sin χ (μ)=sin(πΔfλμ^2+1 / 2πC_sλ^3μ^4)

[0044] Considering the envelope function, the intensity distribution function can be written as:

[0045] T(μ)=E(μ)*sin χ (μ)=E_c(μ)*E_s(μ)*sin χ (μ)

[0046] =exp[-1 / 2(πλδ)^2μ^4]*exp[-(πα / λ)^2(Csλ^3μ^3+λμ)^2]*sin(πΔfλμ^2+1 / 2πC_sλ^3μ^4)

[0047] Therefore, by fitting the curve using the contrast transfer function, the SiN value can be calculated. x The change in the amount of underfocus in the film results in a change in its height.

[0048] Furthermore, for gas-emitting chips, SiN x Fourier transform of the high-resolution image of the thin film allows for the simultaneous acquisition of the amorphous rings of both the upper and lower chips. By fitting contrast transfer functions to each ring and subtracting the resulting underfocus amounts, the thickness of the gas layer between the chips can be obtained, along with the relationship between the gas layer thickness and gas pressure. The change in the chip gas layer thickness before and after gas release from the sample is then calculated, thus completing the in-situ measurement of the minute gas pressure change in the chip caused by the trace amount of gas released from the sample using a transmission electron microscope.

[0049] Furthermore, step 2 requires a higher magnification to image the SiN. x High resolution thin films.

[0050] Furthermore, in steps 2 and 3, the adjustment of the sample stage height and the amount of underfocus should simultaneously distinguish the amorphous rings of the upper and lower chips.

[0051] Furthermore, in step 3, the high-speed imaging function of cameras such as Oneview can be used to perform high-time-resolution analysis on the thickness of the gas layer caused by the gas released or absorbed by the sample.

[0052] Example 1

[0053] This embodiment illustrates the measurement process of the amount of hydrogen released by the microgram-level hydrogen storage material MgH2.

[0054] Specifically, since MgH2 readily reacts with O2 and H2O, the sample was ground in a glove box and then brushed onto the surface of the lower chip of the gas chip. The upper and lower chips were then mounted onto the in-situ gas rod of the transmission electron microscope (TEM), and after leak testing, the microscope was inserted. The TEM magnification was set to 200K to image the SiN in the observable area of ​​the chip. x High-resolution images of thin films (e.g.) Figure 1 As shown, by performing a Fast Fourier Transform on the obtained high-resolution image, the upper and lower SiN chips can be obtained simultaneously. x Amorphous rings of thin films (e.g.) Figure 2 As shown), the amorphous ring image was imported into ImageJ software. The Radial Profile function was used to perform radial integration on the amorphous rings of the upper and lower chips respectively. Then, the obtained curve data was imported into Origin for contrast transfer function fitting, and the fitting equation was established in Origin:

[0055] T(μ)=exp[-1 / 2(πλδ)^2μ^4]*exp[-(πα / λ)^2(C_sλ^3μ^3+λμ)^2]*sin(πΔfλμ^2+1 / 2πC_sλ^3μ^4)

[0056] In this electron microscope, the accelerating voltage of 300 kV corresponds to an electron wavelength of λ of 0.00196 nm. δ represents the underfocus distribution caused by aberrations, and α is the half-angle representing the Gaussian distribution. Depending on the transmission electron microscope, the values ​​of δ and α range from 0.1 to 1. s The spherical aberration coefficient is the spherical aberration coefficient for transmission electron microscopy. In this case, the spherical aberration coefficient is -1 μm.

[0057] After fitting the amorphous ring of the lower chip, the resulting underfocus amount is as follows: Figure 3 As shown. Similarly, the underfocus amount of the upper chip can be obtained. By subtracting the two height values, the thickness of the gas layer in the chip can be obtained. After the gas chip is vented, the shapes of the upper and lower chips are as follows. Figure 4 As shown. Therefore, as the gas pressure inside the gas chip increases (0 mbar, 50 mbar, 100 mbar, 200 mbar, 500 mbar…), the relationship curve between the thickness of the gas layer in the chip and the gas pressure inside the gas chip can be obtained, as shown. Figure 5 As shown.

[0058] Next, 300 mbar H2 was introduced into the gas chip, and the SiN in the observable area of ​​the chip was photographed again. x High-resolution images of the thin film were obtained, and then the valves at both ends of the sample holder were closed to keep the gas inside the chip stagnant. The sample was heated to 300°C to release H2. While keeping the sample stage height and underfocus constant, the SiN in the observable area of ​​the chip was recorded using a Oneview camera. xThe change process of the thin film in high-resolution images. The thickness of the gas layer before and after H2 release from the sample was calculated, and compared with the gas pressure in the relationship curve, thus revealing the gas pressure change caused by the release of gas from a microgram-level sample loaded on the chip. This was achieved by recording SiN images with a Oneview camera. x The high-resolution variation process of the thin film is calculated separately to determine the change in gas layer thickness, enabling rapid quantitative analysis of gas adsorption and desorption processes on a sub-millisecond scale. Because this method achieves nanometer-level resolution when fitting chip underfocus, it can realize SiN… x This method measures pressure changes at the nanometer scale in thin films and at the millibar level in gas chips. Therefore, it has high sensitivity for measuring chip pressure.

[0059] The transmission electron microscope used in this invention is a Thermo Scientific Themis G3 ETEM, and the in-situ sample holder is a DENSsolutions Climate in-situ gas holder. Unless otherwise specified, all other raw materials or processing techniques are commercially available and conventional in the art.

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials, characterized in that, include: S1: Disperse the sample to be tested evenly onto the surface of the lower chip in the gas chip, load the chip onto the in-situ sample holder of the transmission electron microscope, complete the leak detection, and insert it into the transmission electron microscope; S2: Select an appropriate magnification and enter recording mode to photograph the SiN area of ​​the chip that can be observed. x High-resolution images of the thin film were obtained, and Fourier transforms were performed on the images to simultaneously obtain the upper and lower SiN chips. x Amorphous rings of thin films are passed through a gas chip, and the gas pressure is gradually increased to obtain upper and lower SiN chips. x The relationship between the amorphous rings of the thin film and the gas pressure; S3: Select a suitable air pressure and photograph the SiN area of ​​the chip again. x High-resolution images of the thin film were obtained by closing the valves at both ends of the sample holder, heating the sample to the temperature at which the gas would be released, and recording the SiN in the observable area of ​​the chip using a high-speed camera. x Changes in the high-resolution image of the thin film; S4: Combine the upper and lower SiN chips obtained in S2 x Radial integration was performed on the amorphous ring of the thin film, and the resulting curve was fitted with a contrast transfer function to obtain the upper and lower SiN wafers, respectively. x The height of the thin film is calculated by subtracting the two height values ​​to obtain the relationship between the thickness of the gas layer in the chip and the gas pressure. S5: Place the sample from S3 onto the SiN chip before and after gas release. x Radial integration is performed on the amorphous ring of the thin film to obtain the rapid change process of the gas layer thickness in the chip before and after gas release. This process is compared with the relationship between the gas layer thickness and gas pressure in S4, thereby completing the quantitative measurement of the amount of gas adsorbed and desorbed by the microgram-level material loaded in the transmission electron microscope.

2. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that: In S1, a gas microcavity is constructed in a transmission electron microscope, and high-speed quantitative measurement of the gas adsorption and desorption process of microgram-level materials is achieved based on the high precision of electron diffraction.

3. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that: In S2, with a magnification of over 200K, high-resolution images of amorphous thin films in a gas microcavity are captured, and two sets of rings can be observed simultaneously in the Fourier transform diagram.

4. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that: In S3, the valves at both ends of the sample rod are closed when the sample releases the gas it stores.

5. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that: The S3 uses a high-speed camera to record high-resolution images of changes in a gas microcavity thin film, enabling high-speed measurement of gas adsorption and desorption processes on a sub-millisecond scale.

6. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that: S3 performed radial integration and contrast transfer function fitting on the amorphous rings of the upper and lower chips obtained simultaneously, and subtracted the underfocus amount of the upper and lower chips obtained by fitting to obtain the thickness of the gas layer in the gas chip.

7. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that: In S5, the change in the thickness of the gas layer in the chip before and after gas release is compared with the relationship curve between the gas layer thickness and the microcavity gas pressure established in S2.

8. The high-speed quantitative measurement method for the adsorption and desorption of gas by microgram-level materials according to claim 1, characterized in that, The method is not limited to O2 or H2 gases, but is applicable to various scenarios where changes in the amount of gaseous substances in a sealed microcavity are caused by physical or chemical processes such as solid storage / release, adsorption / desorption.

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