Powder sample TEM characterization sample preparation method

Abstract

The invention discloses a sample preparation method for TEM (Transmission Electron Microscope) characterization of a powdery sample. The method comprises the following steps: (1) selecting a proper grid; (2) selecting a dispersing agent according to the property of the powder sample; (3) pouring the solution or the suspension into a liquid storage tank of an ultrasonic atomizer, and setting proper ultrasonic frequency, power and atomizing gas flow parameters according to the properties of the raw materials and the expected particle size requirements of the powder; and (4) collecting the sample: starting ultrasonic atomization equipment, enabling the solution or the suspension liquid to form tiny liquid drops under the ultrasonic action, spraying the tiny liquid drops along with atomized gas, and collecting the tiny liquid drops by using a proper carrying net. The invention aims to provide a sample preparation method for TEM (Transmission Electron Microscope) characterization of a powdery sample, and nano particles are uniformly deposited on a TEM carrier net by adopting an ultrasonic atomization spraying coating technology.

Description

Technical Field

[0001] The invention belongs to the technical field of sample preparation for detection technology, and in particular relates to a sample preparation method for TEM characterization of a powdered sample. Background Art

[0002] Transmission Electron Microscope (TEM) is a microscope that transmits accelerated and focused electron beams to very thin samples. The electrons collide with atoms in the sample and change direction, thus producing three-dimensional angle scattering. Since the scattering angle is related to the density and thickness of the sample, it can form images of varying brightness, which are magnified and focused and displayed on the microscope imaging device.

[0003] Generally, transmission electron microscopes are mainly used to observe fine structures smaller than 0.2 microns, i.e., submicroscopic structures or ultramicroscopic structures. In contrast, these structures cannot be seen clearly under an optical microscope. In order to clearly observe these structures, it is necessary to use a shorter wavelength light source to improve the resolution of the microscope. Therefore, in 1932, Ruska invented a transmission electron microscope using an electron beam as a light source. The wavelength of the electron beam is much shorter than that of visible light and ultraviolet light, and the wavelength of the electron beam is inversely proportional to the square root of the voltage of the emitted electron beam, that is, the higher the voltage, the shorter the wavelength. At present, the resolution of TEM can reach 0.2 nanometers.

[0004] There are many samples that can be observed with TEM, including formed metal and non-metal materials, powder particles as small as tens of nanometers, thin films only a few nanometers thick, and organic materials such as biological materials.

[0005] Transmission electron microscopy can not only be used to observe the surface structure of samples, but also to study the physical and chemical properties of materials. For powdered samples, transmission electron microscopy is mainly used for morphology observation, particle size determination, and structure and composition analysis of powdered materials. It is one of the most important research tools in the fields of materials science, biology, and medicine.

[0006] The sample preparation principles of TEM are: simple, no damage to the sample surface, and obtaining the largest possible observable thin area.

[0007] Common technical solutions for preparing powdered samples for TEM testing include ultrasonic suspension droplet sampling, embedding + ion thinning method and FIB sampling method.

[0008] For powdered samples that need to be tested by TEM, the sample requirements are as follows:

[0009] (1) The function of the sample holder is to carry the sample and enable the sample to be translated, tilted, and rotated so as to select different sample areas for observation and analysis. The TEM sample is placed between the upper and lower pole shoes of the objective lens. The space here is very small, so the TEM sample is also very small. The sample must be thin enough. The size of the powder sample is less than 0.2 microns, and the thickness of the thin film sample is less than 0.1 microns.

[0010] (2) The sample should have sufficient strength and stability to avoid damage or changes when exposed to electron beams.

[0011] (3) It should not contain moisture or other volatile substances. Samples containing moisture or other volatile substances should be dried and removed first.

[0012] (4) Avoid magnetic particles, or pre-demagnetize the magnetic sample to prevent the electron beam from being affected by the magnetic field during observation. A good TEM sample must be uniformly thinned, have good conductivity and be non-magnetic, so as to ensure that enough electrons pass through the sample and maximize the service life of the TEM instrument.

[0013] The ultrasonic suspension drop method has the following disadvantages when preparing samples for TEM testing:

[0014] 1. Sample dispersion

[0015] (1) The agglomeration problem is difficult to completely solve: Although ultrasound can make the sample initially dispersed in the suspension, for some samples such as nanoparticles with strong interactions or special surface properties, the particles may reagglomerate in a short time after the ultrasound stops. For example, due to the existence of magnetic interactions, magnetic nanoparticles are prone to reaggregate to form larger agglomerates after the ultrasonic suspension is dripped, which affects the true morphology and size distribution of the particles observed by TEM.

[0016] (2) Uneven dispersion: Improper control of ultrasonic power, time and other parameters may lead to uneven dispersion of the sample in the suspension. For example, if the ultrasonic power is too low or the time is too short, the sample is not fully dispersed; while if the power is too high or the time is too long, the sample structure may be damaged. After dripping, the unevenly dispersed sample will be unevenly distributed on the copper mesh. In some areas, the sample is too dense, making it difficult to distinguish the morphology of individual particles, and in some areas, the sample is too small, making it impossible to obtain sufficient observation information.

[0017] 2. Sample preparation process

[0018] (1) It is difficult to precisely control the size and shape of droplets: The size and shape of droplets will affect the distribution of the sample on the copper mesh and its state after drying. During the ultrasonic dripping process, the formation of droplets is affected by many factors, such as ultrasonic frequency, liquid surface tension, nozzle aperture, etc. Slight changes in these factors may lead to inconsistent droplet size and shape. Larger droplets may form a thicker sample layer on the copper mesh, which is not conducive to electron beam penetration, while smaller droplets may not provide enough sample volume for observation. Moreover, irregularly shaped droplets will cause uneven distribution of the sample on the copper mesh, affecting the accuracy of observation.

[0019] (2) Influence of the drying process: When the sample is dried on the copper mesh after dripping, the surface tension may cause the sample particles to be redistributed or aggregated. For example, for some nanoparticle suspensions, during the drying process, the evaporation of the solvent will cause the particles to be pulled to the edge of the droplet, causing the particles to aggregate at the edge of the copper mesh, with fewer particles in the center area, affecting the observation of the overall distribution of the sample. In addition, drying too fast or too slow will also affect the sample morphology. Drying too fast may cause the sample to be fixed before it has time to be evenly distributed, while drying too slowly may cause the sample to change during a long drying process. Summary of the invention

[0020] To solve the above problems, the purpose of the present invention is to provide a sample preparation method for TEM characterization of powdered samples, which uses ultrasonic atomization spray coating technology to uniformly deposit nanoparticles on the TEM grid.

[0021] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0022] The present invention provides a sample preparation method for TEM characterization of a powdered sample, comprising:

[0023] (1) Choose a suitable carrier grid;

[0024] (2) Select the dispersant according to the properties of the powder sample;

[0025] (3) Pour the solution or suspension into the liquid storage tank of the ultrasonic atomizer, and set appropriate ultrasonic frequency, power and atomizing gas flow rate parameters according to the properties of the raw materials and the expected particle size requirements of the powder;

[0026] (4) Collecting samples: Start the ultrasonic atomization equipment to form tiny droplets of solution or suspension under the action of ultrasound. The droplets are then sprayed out with the atomizing gas and collected using a suitable carrier mesh.

[0027] Furthermore, the grid is a common carbon film, an ultra-thin carbon film or a micro grid.

[0028] Furthermore, the dispersant is anhydrous ethanol, deionized water or hexane.

[0029] Furthermore, the parameters of the ultrasonic atomizer in (3) are set as follows: ultrasonic frequency 20kHz-100kHz, power 10W-100W, and atomizing gas flow rate 1L / min-10L / min.

[0030] Furthermore, the collected grid is naturally air-dried or oven-dried to ensure that the powder is evenly distributed and free of contaminants.

[0031] Furthermore, the carrier mesh is a copper mesh with a supporting film.

[0032] Compared with the prior art, the beneficial technical effects of the present invention are:

[0033] (1) It avoids the drying artifacts produced by the traditional ultrasonic suspension drop method, such as powder agglomeration and uneven distribution;

[0034] (2) The problem of material breakage caused by sample dripping when preparing TEM samples on brittle support materials has been solved.

[0035] (3) Effect achieved: Nanoparticles can be deposited evenly on the TEM grid, the deposition amount and distribution of the sample can be controlled more accurately, and the repeatability and reliability of sample preparation are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 TEM image. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with embodiments:

[0038] This embodiment provides a sample preparation method for TEM characterization of a powdered sample.

[0039] Specifically, for the sample Q345B steel, after the outdoor atmospheric exposure test, it is necessary to perform TEM characterization analysis on its rust layer.

[0040] The sample preparation process is as follows:

[0041] 1. Use a knife to gently scrape the outer rust layer into the agate mortar. Press the pestle head on the mortar body and make circular motions along the lower part of the mortar, first slowly and then quickly. During the grinding process, use a medicine spoon to scrape the sample on the mortar wall and the pestle head into the mortar.

[0042] 2. Transfer the ground sample to the prepared sample tube in time, add 15mL of anhydrous ethanol dispersant to make a sample suspension.

[0043] 3. Pour the sample suspension into the liquid storage tank of the ultrasonic nebulizer, set the ultrasonic frequency between 20kHz-100kHz, the power between 10W-100W, and the nebulizing gas flow rate between 1L / min-10L / min.

[0044] 4. Collect samples: Start the ultrasonic atomization equipment to make the solution or suspension form tiny droplets under the action of ultrasound. The droplets are sprayed out with the atomizing gas and collected using a copper mesh with a support film to become powder samples for electron microscopy observation. Figure 1 shown.

[0045] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a powdered sample for TEM characterization, characterized in that: include: (1) Choose a suitable carrier grid; (2) Select the dispersant according to the properties of the powder sample; (3) Pour the solution or suspension into the liquid storage tank of the ultrasonic atomizer, and set appropriate ultrasonic frequency, power and atomizing gas flow rate parameters according to the properties of the raw materials and the expected particle size requirements of the powder; (4) Collecting samples: Start the ultrasonic atomization equipment to form tiny droplets of solution or suspension under the action of ultrasound. The droplets are then sprayed out with the atomizing gas and collected using a suitable carrier mesh.

2. The method for preparing a powdered sample for TEM characterization according to claim 1, characterized in that: The grid is a common carbon film, an ultra-thin carbon film or a micro grid.

3. The sample preparation method for TEM characterization of a powdered sample according to claim 1, characterized in that: The dispersant is anhydrous ethanol, deionized water or hexane.

4. The method for preparing a powdered sample for TEM characterization according to claim 1, characterized in that: The parameters of the ultrasonic atomizer in (3) are set as follows: ultrasonic frequency 20kHz-100kHz, power 10W-100W, and atomizing gas flow rate 1L / min-10L / min.

5. The method for preparing a powdered sample for TEM characterization according to claim 1, characterized in that ,,The collected carrier grid is naturally dried or baked to ensure that the powder is evenly distributed and free of contaminants.

6. The method for preparing a powdered sample for TEM characterization according to claim 1, characterized in that: The carrier mesh is a copper mesh with a supporting film.

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