Method for removing oxide layer on surface of silicon steel transmission electron microscope film sample

Abstract

The invention relates to the technical field of metal material transmission electron microscope sample preparation, in particular to a method for removing an oxide layer on the surface of a silicon steel transmission electron microscope film sample. The metal wafer is subjected to electrolysis double-spraying, and the double faces are evenly thinned; the electrolyte is formed by mixing perchloric acid and an absolute ethyl alcohol solution; liquid nitrogen is used for cooling the electrolytic cell; cleaning the metal wafer in absolute ethyl alcohol; and the cleaned metal wafer is vacuumized. The method has the advantages that the electrolytic double-spraying thinning method is combined with the ion thinning method, reasonable working parameters are selected and an oxide layer on the surface of the sample is cleaned by utilizing ion thinning on the basis that the electrolytic double-spraying sample is perforated to obtain a good thin area, so that a high-quality and high-precision metal film sample is obtained; powerful support is provided for silicon steel product mechanism research; the sample preparation speed is high, and the sample preparation cost is low; the thin area is large, the oxide layer is removed, the thin area of the cut sample is very small, the ion thinning is the second time, and the electrolytic double-spraying thin area is the largest.

Description

Technical Field

[0001] The present invention relates to the technical field of transmission electron microscope sample preparation for metal materials, and particularly relates to a method for removing an oxide layer on the surface of a transmission electron microscope thin film sample of silicon steel. Background Art

[0002] The development process of transmission electron microscope metal thin film sample preparation is a process of continuously pursuing higher precision and better results. Early preparation methods may be relatively simple and crude. For example, the metal sample is directly prepared into a thin film by mechanical cutting or grinding. These methods may have some problems, such as uneven sample surface, uneven thickness, and large mechanical damage, which will affect the observation effect of the transmission electron microscope.

[0003] With the continuous progress of technology, the preparation technology of transmission electron microscope (TEM) metal thin film samples has also been continuously improved and perfected. At present, the preparation technology of TEM metal thin film samples has been very mature. The commonly used methods include electrolytic twin-jet thinning method, ion thinning method, and FIB cutting method, etc. The principle of the electrolytic twin-jet thinning method is mainly to thin and perforate the metal specimen through electrolysis. In a low-temperature environment, by applying an appropriate electrolytic voltage to the metal specimen, the electrolyte flows from the tank to the nozzle under the action of a pump and undergoes an electrolytic reaction with the specimen. In this way, the metal specimen can be gradually thinned and perforated at specific positions, forming a thin area suitable for TEM observation. The working principle of the ion thinning method is to ionize argon gas using a high-voltage electric field to generate argon ions. These argon ions are accelerated and focused under the action of the electric field and finally bombard the sample surface. When high-energy argon ions undergo elastic collisions with the atoms on the sample surface, the energy of the atoms on the sample surface will increase. When the energy of these atoms increases to be higher than their work function, they will fly off the sample surface, thus realizing the thinning of the sample. Since the ion thinning method is not affected by the electrical properties of the material, whether the material is conductive or not, metal or non-metal or a mixture of the two, and no matter how complex the material structure is, this method can be used to prepare thin films. However, its fatal disadvantage is the slow sample preparation speed. For steel materials, due to their relatively high density, it usually takes 3 - 6 hours to prepare a sample by ion thinning. The principle of preparing TEM samples by FIB cutting is mainly based on the Focused Ion Beam (FIB) technology. First, the ion beam generated by the ion source (usually gallium Ga, but may also include other ion sources such as helium He and neon Ne) is accelerated and focused using an electron lens. Then, this focused high-energy ion beam is precisely guided to the sample surface. When the ion beam contacts the sample surface, it cuts the sample using the sputtering effect of the ion beam. By precisely controlling parameters such as the beam current size, scanning path, and cutting time of the ion beam, precise cutting and preparation of specific areas of the sample can be achieved. In this process, the cutting action of the ion beam is achieved through physical collisions with the atoms on the sample surface, thus realizing micro-nano processing of the sample. Finally, the TEM samples prepared by FIB cutting have the characteristics of high precision and high quality, and can meet the requirements of TEM observation and analysis. However, FIB cutting has problems such as too high sample preparation cost (usually more than 5000 yuan for preparing one sample), slow speed, and small thin area. For the above reasons, for electrolytic materials, especially steel materials, the electrolytic twin-jet method has been the most widely used because of its fast sample preparation speed and large thin area range.

[0004] Silicon steel samples are relatively more susceptible to rust due to their high carbon content and low alloying elements. When iron comes into contact with substances such as oxygen, water, and carbon dioxide in the air, an oxidation reaction will occur, generating oxides such as ferrous oxide and ferric oxide, forming an oxide layer, which is what we call "rusting." Since electrolytic double-spraying usually uses perchloric acid as an electrolyte, perchloric acid has extremely strong oxidizing properties. Although the samples are repeatedly cleaned with anhydrous ethanol after electrolytic double-spray thinning, residual perchloric acid is still inevitable. Moreover, when the samples are removed from anhydrous ethanol and exposed to the air, an oxide layer is easily formed on the surface of the sample, which seriously affects the transmission electron microscopy morphology observation and composition analysis.

[0005] In the prior art, application number CN202211602131.8 discloses a FIB preparation method for irregular steel samples for transmission electron microscopy testing. The length and width of the thin area of the sample prepared by this method are usually less than 10μm×10μm, which is insufficient to meet the requirements of transmission electron microscopy observation of the precipitated phase. In addition, the cost of preparing FIB cut samples is very high (usually more than 5,000 yuan).

[0006] Application No. CN201310086358.6 discloses a sample preparation method for in-situ observation of rust layers using a transmission electron microscope. This method is primarily intended to protect the rust layer from being damaged, whereas this patent provides a method for removing surface rust. Therefore, this method is not suitable for preparing the samples we need, and the sample preparation process is cumbersome.

[0007] Application number CN202210637822.5 discloses a method for preparing magnetic powder samples of steel metallurgical solid waste transmission electron microscopy. This method is mainly used to prepare powder samples, which is not suitable for the silicon steel metal film samples we need, and the sample preparation process is cumbersome. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for removing the oxide layer on the surface of a silicon steel transmission electron microscope thin film sample, which has fast sample preparation speed, low sample preparation cost, improved oxide layer removal effect, simple sample preparation process and strong practicality.

[0009] To achieve the above object, the present invention is implemented through the following technical solutions:

[0010] A method for removing an oxide layer on the surface of a silicon steel transmission electron microscope thin film sample, comprising:

[0011] S1. Sample preparation: silicon steel samples are cut and mechanically thinned on both sides to a predetermined thickness, and the samples after mechanical thinning on both sides are punched to obtain metal discs;

[0012] S2, the metal disc is electrolytically double-sprayed and thinned evenly on both sides through an electrolytic double-spray thinning instrument;

[0013] S3. The electrolyte is formed by mixing perchloric acid and absolute ethanol solution in a volume ratio of 0.6 - 1:9 - 9.4;

[0014] S4. Use liquid nitrogen to cool the electrolyte in the electrolytic cell to between -15 °C and -25 °C;

[0015] S5. The electrolytic twin-jet thinning time is 40 - 70 seconds. When the metal disc is electrolytically twin-jet perforated to a transmittance greater than the set value, the electrolytic twin-jet thinning stops;

[0016] S6. Take out the metal disc, wash it in absolute ethanol, with the number of washing times ≥ 10 times, and place it on filter paper to absorb the moisture;

[0017] S7. Vacuum the washed metal disc to above 9×10 -5 Torr to ensure the surface of the sample is dry;

[0018] In S1, the thickness range of the sample after double-sided mechanical thinning is 40 - 60 μm; the thickness range of the silicon steel sample is 200 - 500 μm, and the metal disc is a sample with a diameter of Φ3 mm for transmission electron microscopy.

[0019] In S1, the silicon steel sample is double-sided mechanically thinned successively with 150 - 300#, 400 - 700#, and 800 - 1200# sandpapers, and the sample after double-sided mechanical thinning is punched with a puncher.

[0020] In S2, the electrolytic twin-jet thinning instrument is placed in the electrolytic cell, the electrolytic cell is filled with electrolyte, and the flow rate of the injection pump of the electrolytic twin-jet thinning instrument is adjustable.

[0021] In S2, the voltage range of the electrolytic twin-jet thinning instrument is 28 - 32 V, and the transmittance range is 180 - 300.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. By adopting the electrolytic twin-jet thinning method in combination with the ion thinning method, on the basis of obtaining a good thin area by electrolytic twin-jet perforation of the sample, reasonable working parameters are selected by using ion thinning to clean the oxide layer on the surface of the sample, so as to obtain a high-quality and high-precision metal thin film sample, providing strong support for the mechanism research of silicon steel products;

[0024] 2. It usually takes 2 - 6 hours to prepare a sample by ion thinning and FIB cutting. In the present invention, the electrolytic twin-jet takes about 3 minutes and the ion thinning takes 10 minutes, totaling 13 minutes. The sample preparation speed is fast and the sample preparation cost is low; the thin area is large and the oxide layer is removed. The thin area of the FIB-cut sample is very small, the ion thinning is the second, and the electrolytic twin-jet thin area is the largest. Description of the Drawings

[0025] Figure 1It is a silicon steel sample mechanically thinned to 50μm.

[0026] Figure 2 It is the sample after electrolytic twin-jet thinning.

[0027] Figure 3 It is the morphological observation of the sample after electrolytic twin-jet under the electron microscope.

[0028] Figure 4 It is the morphological observation of the sample after electrolytic twin-jet and then ion thinning under the electron microscope. Specific implementation mode

[0029] The present invention will be described in detail below in conjunction with the accompanying drawings of the specification, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0030] The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation modes and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments. The methods used in the following embodiments are all conventional methods unless otherwise specified.

[0031] Embodiment 1

[0032] Taking non-oriented silicon steel 50AW800 as an example, the method for preparing a transmission electron microscope sample by electrolytic twin-jet and ion thinning is described as follows:

[0033] S1. Take a piece of non-oriented silicon steel of 50AW800 and cut it into small pieces of 12mm * 8mm, and cut off a metal thin sheet with a thickness of about 300μm by a wire electrical discharge machine.

[0034] S2. Use 200#, 600#, and 1000# sandpapers in sequence to mechanically thin both sides of the metal thin sheet evenly to a thin sheet with a thickness of about 50μm, see Figure 1 ; Punch the mechanically thinned sample with a puncher to obtain a metal disc with a diameter of Φ3mm.

[0035] S3. Prepare 1000ml of electrolyte by mixing perchloric acid and absolute ethanol solution at a volume ratio of 1:9, pour it into the electrolytic cell, add liquid nitrogen to the electrolytic cell for cooling, and measure the temperature of the electrolyte in the cell with a thermometer to control the temperature in the cell at -20°C.

[0036] S4. Fix the Φ3mm metal disc on the sample holder, and use the TenuPol-5 type electrolytic twin-jet instrument of struers company for twin-jet thinning. Insert the sample holder into the twin-jet electrolytic cell, adjust the twin-jet voltage to 30V, set the light transmittance to 200, and start the equipment to start thinning.

[0037] S5. The double-jet thinning time is usually about 1 minute. When the light transmittance of the sample after double-jet perforation exceeds the set value, the electrolytic double-jet instrument will automatically alarm and stop working. After removing the sample holder, wash it more than 10 times repeatedly in absolute ethanol, then take out the sample and dry it on filter paper to obtain a sample with a clean and bright surface, as shown in Figure 2 .

[0038] S6. Fix the sample on the sample holder of the GATAN 695.B ion thinning instrument, keep the perforation position in the center, send it into the sample chamber and evacuate to 6×10 -5 Torr;

[0039] Set the thinning parameters: voltage 1 KeV, rotation speed 2 RPM, time 10 minutes, ion gun double-sided ±2°, start the thinning program, and take out the sample after thinning.

[0040] S7. Fix the sample on the transmission electron microscope sample holder, put it into the transmission electron microscope sample chamber, and then the electron microscope observation can be carried out;

[0041] The electron microscope morphology of the sample after electrolytic double-jet, as shown in Figure 3 , and the electron microscope morphology of the sample after ion thinning after electrolytic double-jet, as shown in Figure 4 . By comparing the sample morphologies before and after ion thinning, it can be clearly seen that the oxide layer on the sample surface is completely eliminated after ion thinning.

[0042] Example 2

[0043] Taking the oriented silicon steel 27AG100 as an example, the method for preparing a transmission electron microscope sample by electrolytic double-jet and ion thinning is described as follows:

[0044] S1. Take a piece of 27AG100 oriented silicon steel and cut it into small pieces of 10mm×10mm, and cut off a metal thin sheet with a thickness of about 350μm by a wire electrical discharge machine.

[0045] S2. Use 240#, 600#, and 1200# sandpapers in sequence to mechanically thin both sides of the metal thin sheet evenly to a thin sheet with a thickness of about 45μm; punch the mechanically thinned sample with a puncher to obtain a metal disc with a diameter of Φ3mm.

[0046] S3. Prepare 1000 ml of electrolyte by mixing perchloric acid and absolute ethanol solution at a volume ratio of 0.9:9.1, pour it into the electrolytic cell, and add liquid nitrogen to the electrolytic cell for cooling. Measure the temperature of the electrolyte in the cell with a thermometer to control the temperature in the cell at -18°C.

[0047] S4. Fix the Φ3mm metal disc on the sample holder, and use the TenuPol-5 type electrolytic double-jet instrument of the struers company to carry out double-jet thinning. Insert the sample holder into the double-jet electrolytic cell, adjust the double-jet voltage to 28V, set the light transmittance to 200, and start the equipment to start thinning.

[0048] S5. The double-jet thinning time is usually about 1 minute. When the light transmittance of the sample after double-jet perforation exceeds the set value, the electrolytic double-jet instrument will automatically alarm and stop working. After removing the sample holder, wash it more than 10 times repeatedly in absolute ethanol, then take out the sample and blot it dry on filter paper to obtain a sample with a clean and bright surface.

[0049] S6. Fix the sample on the sample holder of the GATAN 695.B ion thinning instrument, keep the perforation position at the center, send it into the sample chamber and evacuate to 5×10 -5 Torr;

[0050] Set the thinning parameters: voltage 1 KeV, rotation speed 2 RPM, time 20 minutes, ion gun at ±1° on both sides, start the thinning program, and take out the sample after thinning.

[0051] S7. Fix the sample on the transmission electron microscope sample holder, put it into the transmission electron microscope sample chamber, and then the electron microscope observation can be carried out.

[0052] The present invention adopts the electrolytic double-jet thinning method combined with the ion thinning method. On the basis of obtaining a good thin area by electrolytic double-jet perforation of the sample, reasonable working parameters are selected by ion thinning to clean the oxide layer on the sample surface, so as to obtain a high-quality and high-precision metal thin film sample, which provides strong support for the mechanism research of silicon steel products; it usually takes 2 - 6 hours to prepare a sample by ion thinning and FIB cutting. In the present invention, the electrolytic double-jet takes about 3 minutes and the ion thinning takes 10 minutes, with a total of 13 minutes, so the sample preparation speed is fast and the sample preparation cost is low; the thin area is large and the oxide layer is removed. The thin area of the FIB-cut sample is very small, the ion thinning is the second, and the electrolytic double-jet thin area is the largest.

Claims

1. A method for removing the oxide layer on the surface of a silicon steel transmission electron microscope thin film sample, characterized in that, Including: S1. Sample preparation: Cut a silicon steel sample and perform double-sided mechanical thinning to a predetermined thickness. Punch the double-sided mechanically thinned sample to obtain a metal disc; S2. The metal disc is subjected to electrolytic double jet thinning by an electrolytic double jet thinning instrument to achieve uniform thinning on both sides; S3. The electrolyte is composed of perchloric acid and anhydrous ethanol solution mixed in a volume ratio of 0.6 - 1:9 - 9.4; S4. Use liquid nitrogen to cool the electrolyte in the electrolytic cell to a temperature between -25 °C and -15 °C; S5. The electrolytic double jet thinning time is 40 - 70 seconds. When the metal disc is electrolytically double jet perforated to a transmittance greater than the set value, the electrolytic double jet thinning stops; S6. Take out the metal disc, wash it in anhydrous ethanol, with the number of washing times ≥ 10 times, and place it on filter paper to dry; S7. Vacuum the cleaned metal wafers to above 9×10 -5 Torr to ensure the surface of the sample is dry.

2. The method for removing the oxide layer on the surface of the silicon steel transmission electron microscope thin film sample according to claim 1, characterized in that, In S1, the thickness range of the double-sided mechanically thinned sample is 40 - 60 μm; the thickness range of the silicon steel sample is 200 - 500 μm, and the metal disc is a sample with a diameter of Φ3 mm for transmission electron microscopy.

3. A method for removing the oxide layer on the surface of a silicon steel transmission electron microscope thin film sample according to claim 1, characterized in that, In S1, the silicon steel sample is double-sided mechanically thinned successively with 150 - 300#, 400 - 700#, and 800 - 1200# sandpapers, and the double-sided mechanically thinned sample is punched with a puncher.

4. A method for removing the oxide layer on the surface of a silicon steel transmission electron microscope thin film sample according to claim 1, characterized in that, In S2, the electrolytic double jet thinning instrument is placed in the electrolytic cell, the electrolytic cell is filled with electrolyte, and the flow rate of the injection pump of the electrolytic double jet thinning instrument is adjustable.

5. A method for removing the oxide layer on the surface of a silicon steel transmission electron microscope thin film sample according to claim 1, characterized in that, In S2, the voltage range of the electrolytic double jet thinning instrument is 28 - 32 V, and the transmittance range is 180 - 300.

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