A method for preparing granular samples for scanning electron microscope analysis

Abstract

The invention relates to a method for preparing a granular sample for scanning electron microscope analysis, comprising the steps of screening, ultrasonically vibrating a culture dish, pasting with conductive adhesive, ultrasonically vibrating a sample holder, and purging with an ear bulb. The method screens the granular sample to prepare scanning electron microscope samples of different specifications, and then uniformly disperses the sample through ultrasonic vibration and then inlays the sample with conductive adhesive tape. Separately observing samples of different specifications facilitates statistics and prevents granular samples of different sizes from piling up and failing to adhere firmly to the conductive adhesive tape. Conductive adhesive tapes of different thicknesses are used to adhere the dispersed granular samples, and two methods are used to remove granular samples that are not firmly adhered, thereby minimizing the possibility of granular samples falling off during scanning electron microscope analysis and preventing damage to the scanning electron microscope equipment.

Description

Technical Field

[0001] The present invention relates to the field of scanning electron microscope analysis technology, and in particular to a method for preparing a granular sample for scanning electron microscope analysis. Background Art

[0002] The electron optical system of a scanning electron microscope (SEM) consists of an electron gun, magnetic lens, scanning coil, and sample chamber. High-resolution SEMs also feature a vacuum system composed of mechanical and molecular pumps. Particles and dust must be kept away from the electron gun, magnetic lens, and scanning coil of the SEM, as this will affect the image quality and even damage the high-voltage generator of the SEM due to discharge. Furthermore, the molecular pump in the vacuum system is very fragile. If particles enter the high-speed rotating molecular pump, it will be damaged and cause it to stop immediately.

[0003] Based on the structural characteristics of the scanning electron microscope, there are very clear basic requirements for samples used for scanning electron microscope analysis, namely: the samples must be as dry as possible, and samples containing volatile substances need to be heated and dried first; samples with poor conductivity will have a charging effect, resulting in snowflake-like images, etc., so samples with surface contamination need to be cleaned before use.

[0004] In scientific research and failure analysis, it is often necessary to analyze small, granular samples, such as the powdered raw materials used in powder metallurgy and the powder particles remaining in cracked boiler high-pressure pipes. These granular samples generally have poor conductivity, are lightweight, and have uneven sizes. When analyzed in a scanning electron microscope (SEM), these particles can easily escape from the sample holder or conductive adhesive during the microscope's vacuum pumping process and enter the electron gun or molecular pump, affecting analysis and even damaging the microscope.

[0005] "Preparation of Powder Samples for Scanning Electron Microscopy" (Ma Yuanhui et al., Laboratory Science, February 28, 2011) states that preparing SEM samples generally requires three steps: dispersion, laying, and coating with a conductive film. A common method involves sprinkling a small amount of powder directly onto the sample stage, adding a few drops of dispersant, and rubbing with a glass rod to disperse the particles. After the dispersant has completely evaporated, the sample is placed under the microscope for observation. This conventional sample preparation method has several drawbacks: 1) Improper rubbing can lead to failure to disperse the particles and agglomeration, with larger particles migrating to the edges, distorting observations. 2) If the dispersant is a viscous liquid, while effective in dispersing, it will form a thin film on the sample surface after evaporation, absorbing electrons and degrading image quality. 3) For brittle particles, rubbing can shatter them, distorting observations. For these situations, the paper recommends several methods for obtaining clear images and accurate observations. 1. Conductive adhesive bonding method: Use a thin layer of conductive tape to stick the powder to the sample stage. The basic method is: first evenly stick a small strip of conductive tape (Ag tape, C tape, etc.) on the sample stage, then sprinkle a little powder on the stuck tape, turn the sample stage downward to let the particles that are not in contact with the tape fall off, and then use an ear bulb to blow away the loosely bonded powder, so that a uniform layer of powder is left on the tape surface. The key to preparing powder using this method is not to sprinkle too much powder, and do not use a glass plate to flatten the powder surface, otherwise the particles will sink into the tape, resulting in image distortion. 2. Direct powdering method: Sprinkle the powder directly on the sample stage, add a few drops of dispersant (ethanol or other dispersion medium), shake the sample stage lightly to make the powder evenly distributed, and after the dispersant evaporates, use an ear bulb to blow away the loosely adsorbed powder, and then it can be directly placed in the electron microscope for observation. This method is simple to prepare samples, but the dispersibility is poor. The particles are easy to agglomerate during the volatilization of the dispersant. It is suitable for coarser powders. This method is quick and convenient, suitable for naturally dispersible solid powders, but it can be difficult to obtain a single-layer distribution of particles. 3. Ultrasonic method: Place a small amount of powder in a small beaker, add an appropriate amount of ethanol or distilled water, and sonicate for a few minutes. Then, quickly use a dropper to drop the evenly dispersed powder solution onto a sample stage or tin foil. Gently blow dry with heated air before placing the sample under an electron microscope. If using tin foil, tape it to the conductive tape on the sample stage before placing it under the electron microscope. This method provides excellent dispersion and is particularly suitable for ultrafine and nanopowders that are prone to agglomeration.

[0006] The Chinese invention patent with the authorization announcement number CN 108169266 B discloses “a method for preparing a scanning electron microscope sample of micron-sized ionic crystal powder”. It believes that “at present, the most commonly used method for such powder samples is the conductive adhesive adhesion method. The shortcomings of this method are mainly reflected in two points: first, because fine powder samples usually have higher surface energy than bulk samples, the particles are easy to aggregate into agglomerates and overlap each other, so the dispersion degree of the prepared sample is not high; second, the adhesion between the powder particles and the conductive adhesive cannot be guaranteed, resulting in a high risk of contaminating the electronic optical system of the scanning electron microscope.” Therefore, the preparation method adopted includes the following steps: (1) dispersion; (2) sampling; (3) preparation of resin glue; (4) cold mounting sample preparation; (5) gold spraying. The powder scanning electron microscope sample prepared by this method has uniform powder dispersion, which can avoid the problems of particle agglomeration and agglomeration. The powder sample is tightly bonded to the resin glue, has high adhesion, and the powder can be firmly embedded. Compared with traditional methods, it can effectively solve the problem of weak bonding between the powder and the conductive glue, which causes the sample to fly off the sample stage during vacuuming or testing and contaminate the microscope cavity; after gold plating, the conductivity of the powder sample is increased, ensuring the clarity of the image, and clear and high-resolution electron microscope observation can be achieved.

[0007] However, the method employed in the aforementioned invention patent is complex, inefficient, and costly. The powder sample is added to a dispersion solution, stirred, and dispersed, and then the dispersion solution is evaporated at a certain temperature. However, this evaporation process can easily affect the powder sample and, therefore, is not suitable for all powder samples. Furthermore, the sample is cured with resin and the surface is sputtered with gold, both of which can easily affect the final observation results. If the shortcomings of the existing conductive adhesive adhesion method could be addressed, it would become the most effective and feasible method. Summary of the Invention

[0008] The present invention provides a method for preparing granular samples for scanning electron microscope analysis. The granular samples are sieved to prepare scanning electron microscope samples of different specifications, and then uniformly dispersed by ultrasonic vibration and mounted with conductive tape. Separate observation of samples of different specifications facilitates statistics and prevents granular samples of different sizes from piling up on each other and failing to adhere firmly to the conductive tape. Conductive tapes of different thicknesses are used to adhere the dispersed granular samples, and two methods are used to remove granular samples that are not firmly adhered. This can minimize the possibility of granular samples falling off during scanning electron microscope analysis and prevent damage to the scanning electron microscope equipment.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for preparing a granular sample for scanning electron microscopy analysis comprises the following steps:

[0011] 1) Screening the granular samples, and placing the granular samples of the same specifications in the same culture dish after screening;

[0012] 2) Ultrasonic vibration is applied to multiple culture dishes containing granular samples of different specifications to uniformly disperse the granular samples in the culture dishes;

[0013] 3) According to the specifications of the granular samples, use conductive tape of corresponding thickness to stick the granular samples in the culture dish, so that the granular samples in the same culture dish are evenly adhered to the same conductive tape;

[0014] 4) The conductive tape with the granular sample attached is attached to the sample holder, and then the sample holder is subjected to ultrasonic vibration to remove the granular sample that is not firmly attached;

[0015] 5) Use an ear suction bulb to blow away the conductive tape with the granular sample adhered to it, and remove the granular sample that is not firmly attached again to obtain a scanning electron microscope sample.

[0016] In the step 1), the granular sample is first subjected to a heating and drying treatment before being screened.

[0017] In the step 3), the conductive tape is folded to form a multi-layer conductive tape, and then the granular sample is pasted.

[0018] In step 4), both ends of the guide tape extend to the outside of the sample holder in corresponding directions.

[0019] In the step 5), when the conductive tape with the granular sample attached thereto is purged with the ear suction bulb, the included angle between the air outlet direction of the ear suction bulb and the guide tape is 35° to 55°.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The granular samples are sieved to prepare SEM samples of different sizes, which are then evenly dispersed by ultrasonic vibration and mounted with conductive tape. Observing samples of different sizes separately facilitates statistics and prevents granular samples of different sizes from piling up and being unable to be firmly attached to the conductive tape.

[0022] 2) Using conductive tapes of different thicknesses to adhere the dispersed granular samples and using two methods to remove loosely adhered granular samples can minimize the possibility of granular samples falling off during SEM analysis and prevent damage to the SEM equipment;

[0023] 3) The prepared SEM samples have good conductivity and image quality, making sample analysis more convenient;

[0024] 4) It perfectly solves the shortcomings of the existing conductive adhesive adhesion method. Compared with other methods, it has the advantages of simple operation, low cost and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope analysis image of the granular sample described in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The method for preparing a granular sample for scanning electron microscopy analysis according to the present invention comprises the following steps:

[0027] 1) Screening the granular samples, and placing the granular samples of the same specifications in the same culture dish after screening;

[0028] 2) Ultrasonic vibration is applied to multiple culture dishes containing granular samples of different specifications to uniformly disperse the granular samples in the culture dishes;

[0029] 3) According to the specifications of the granular samples, use conductive tape of corresponding thickness to stick the granular samples in the culture dish, so that the granular samples in the same culture dish are evenly adhered to the same conductive tape;

[0030] 4) The conductive tape with the granular sample attached is attached to the sample holder, and then the sample holder is subjected to ultrasonic vibration to remove the granular sample that is not firmly attached;

[0031] 5) Use an ear suction bulb to blow away the conductive tape with the granular sample adhered to it, and remove the granular sample that is not firmly attached again to obtain a scanning electron microscope sample.

[0032] In the step 1), the granular sample is first subjected to a heating and drying treatment before being screened.

[0033] In the step 3), the conductive tape is folded to form a multi-layer conductive tape, and then the granular sample is pasted.

[0034] In step 4), both ends of the guide tape extend to the outside of the sample holder in corresponding directions.

[0035] In the step 5), when the conductive tape with the granular sample attached thereto is purged with the ear suction bulb, the included angle between the air outlet direction of the ear suction bulb and the guide tape is 35° to 55°.

[0036] The process and principle of the method for preparing a granular sample for SEM analysis described in the present invention are as follows:

[0037] 1. If the granular sample is moist or contains volatile substances, it needs to be heated and dried first;

[0038] 2. When screening granular samples, first clean the sieve to remove any residual material from the last use, then sieve the granular samples through sieves with different sieve sizes, and place the granular samples of the same specifications after screening in the same culture dish.

[0039] 3. Place the culture dishes containing granular samples of different specifications in ultrasonic vibration, and try to evenly disperse the granular samples in the culture dishes.

[0040] 4. Use conductive tape of varying thicknesses to tape the granular sample in the Petri dish, depending on the size of the granular sample. For larger granular samples, fold the conductive tape in half to create a double layer, then tape the granular sample to the tape. Due to the increased thickness of the conductive tape, larger granular samples will fit seamlessly onto the tape. In this manner, choose between a single layer or multiple layers of conductive tape, depending on the size of the granular sample. The use of conductive tape also increases the conductivity of the granular sample.

[0041] 5. Stick the conductive tape with the granular sample on it to the rectangular sample holder. The length of the conductive tape should be greater than the length of the rectangular sample holder in the corresponding direction to ensure that the remaining conductive tape can be used to stick to the sample holder when the sample holder is separated from the culture dish. Then place the sample holder with the granular sample in ultrasonic vibration to remove the granular sample that is not firmly attached.

[0042] 6. Use an ear suction bulb to blow air at a certain angle (preferably 45 degrees) towards the conductive tape that adheres to the granular sample to remove the granular sample that is not firmly adhered. The obtained SEM sample can be sent to the SEM for analysis.

[0043] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0044] [Example]

[0045] In this embodiment, a granular sample for SEM analysis was prepared. The granular sample was powder from the rust layer on the inner wall of a high-pressure water pipe. The preparation process of the granular sample was as follows:

[0046] 1) The granular samples are first subjected to heat drying treatment, and then sieved. After sieving, the granular samples of the same specifications are placed in the same culture dish;

[0047] 2) Ultrasonic vibration is applied to multiple culture dishes containing granular samples of different specifications to uniformly disperse the granular samples in the culture dishes;

[0048] 3) According to the specifications of the granular samples, use conductive tape of corresponding thickness to stick the granular samples in the culture dish, so that the granular samples in the same culture dish are evenly adhered to the same conductive tape;

[0049] 4) The conductive tape with the granular sample attached is attached to the sample holder, and then the sample holder is subjected to ultrasonic vibration to remove the granular sample that is not firmly attached;

[0050] 5) Use an ear suction ball to blow away the conductive tape with the granular sample attached. The angle between the air outlet direction of the ear suction ball and the guide tape is 45 degrees. Remove the granular sample that is not firmly attached again to obtain the scanning electron microscope analysis sample. The analysis image is as follows Figure 1 shown.

[0051] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a granular sample for scanning electron microscopy analysis, characterized in that: The steps include: 1) Screen the granular samples and place the granular samples of the same specifications in the same culture dish after screening; 2) Perform ultrasonic vibration on multiple culture dishes containing granular samples of different specifications to evenly disperse the granular samples in the culture dishes; 3) Based on the specifications of the granular samples, use conductive tape of corresponding thickness to stick the granular samples in the culture dish, so that the granular samples in the same culture dish are evenly adhered to the same conductive tape; specifically, the conductive tape is folded to form multiple layers of conductive tape, and then the granular samples are stuck; 4) Attach the conductive tape with the granular sample to the sample holder, then ultrasonically vibrate the sample holder to remove any granular sample that is not firmly attached. 5) Use an ear suction bulb to blow away the conductive tape with the granular sample attached, and remove the granular sample that is not firmly attached again to obtain the scanning electron microscope sample.

2. The method for preparing a granular sample for scanning electron microscopy analysis according to claim 1, characterized in that: In the step 1), the granular sample is first subjected to a heating and drying treatment before being screened.

3. The method for preparing a granular sample for scanning electron microscopy analysis according to claim 1, characterized in that: In step 4), both ends of the guide tape extend to the outside of the sample holder in corresponding directions.

4. The method for preparing a granular sample for scanning electron microscopy analysis according to claim 1, wherein: In step 5), when the conductive tape with the granular sample attached thereto is purged with the ear suction bulb, the included angle between the air outlet direction of the ear suction bulb and the guide tape is 35° to 55°.

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