Method for preparing Bi2Te3 thermoelectric material EBSD sample through ion grinding

Abstract

The invention discloses a method for preparing a Bi2Te3 thermoelectric material EBSD sample through ion grinding. The specific method comprises the following steps: cutting a Bi2Te3 material by adopting a linear cutting technology to obtain a sample with a proper size, inlaying, grinding and polishing, and ultrasonically cleaning to remove surface impurities; the method comprises the following steps: horizontally placing a sample on an objective table, closing a cabin door, opening a mechanical pump to vacuumize to 0.01 pa, and rotating the angle of the sample table until the included angle between the ion beam jet direction and the normal direction of the surface of the sample is 85-88 degrees; the argon flow is set to be 1.5 mL / min; turning on a main circuit switch, adjusting the acceleration voltage to 2kv, setting the grinding time to be 15-20 minutes, starting an ion gun switch, opening a plate valve after the current is stabilized at 350-400uA, starting grinding, and rotating the sample table. And after grinding is finished, resetting the acceleration voltage to be 4kv, grinding again, taking out the sample, and carrying out EBSD observation.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a method for preparing Bi2Te3 thermoelectric material EBSD samples by ion milling. Background Art

[0002] Bi2Te3-based thermoelectric material is a new type of low-temperature functional material with good thermoelectric conversion performance. It is widely used in traditional fields such as engines, coolers, environmental testing, and biomedicine. It also plays an important role in high-end technology fields such as 5G communications and semiconductor devices. This material can achieve the conversion of thermal energy and electrical energy mainly through the Seebeck effect and the Peltier effect. The thermoelectric performance of the material can be evaluated by the figure of merit ZT (ZT = S 2 σT / κ, where S is the Seebeck coefficient, σ is the material conductivity, T is the temperature, and κ is the material thermal conductivity). Bi2Te3 crystal is an R3m crystal system, which belongs to a typical lamellar structure with significant anisotropy. Its thermoelectric transport performance and mechanical properties are very sensitive to the direction of the lattice. Studies have shown that the electron mobility, hole mobility and lattice thermal conductivity parallel to the basal plane are much greater than those perpendicular to the basal plane, resulting in a relatively higher thermoelectric figure of merit in Bi2Te3 single crystals parallel to the basal plane. In order to prepare higher-performance Bi2Te3 semiconductor refrigeration devices, it is crucial to accurately observe and select the grain arrangement inside the material. EBSD (backscattered electron diffraction) technology is an important means to evaluate the thermoelectric properties of bismuth telluride thermoelectric materials, which can intuitively and accurately display the grain orientation, texture and micromorphology information. Due to the poor mechanical properties of Bi2Te3 materials themselves, in the process of preparing EBSD samples, conventional grinding and polishing will cause a large number of scratches and stress concentration on the surface, resulting in unclear Kikuchi lines during EBSD observation and loss of some EBSD information of the sample. The bombardment of high-energy ion beams under vacuum can remove scratches on the sample surface and release stress. It is a new EBSD sample preparation method that is simple to operate and has low sample requirements. The factors affecting ion milling and polishing are related to the acceleration voltage, milling time, and jet angle. At present, the preparation methods of EBSD samples of bismuth telluride materials mainly include electrolytic polishing, mechanical polishing, FIB, etc. Few literatures on the grain orientation and texture of bismuth telluride report the steps and parameters related to ion milling.

[0003] Therefore, exploring an efficient, stable and simple ion milling and polishing method for Bi2Te3-based thermoelectric materials to prepare EBSD samples can provide important supplements and expansions in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing Bi2Te3 thermoelectric material EBSD samples by ion milling. The method is simple to operate, has significant effects, can prepare high-quality EBSD samples, and the obtained data resolution rate is as high as 95% or more. At the same time, the microscopic morphology is clear, the sample surface information is complete, and accurate information is provided for obtaining crystal parameters, grain orientation and texture. The method can effectively remove uneven scratches and stress layers on the sample surface, the sample surface grain boundaries are clear, the grain arrangement is obvious, and the resolution rate is high.

[0005] The technical solution of the present invention is as follows: a method for preparing Bi2Te3 thermoelectric material EBSD sample by ion milling, the method specifically comprising the following steps;

[0006] S1) using wire cutting technology to cut Bi2Te3 material to obtain samples, and then pre-treating the samples;

[0007] S2) placing the sample processed in S1) horizontally on a stage, and performing two-step ion milling on the sample in a vacuum environment to obtain an EBSD sample of a Bi2Te3-based thermoelectric material.

[0008] Further, the specific steps of S1) are:

[0009] S1.1) According to the EBSD requirements, the sample is cut in the TD, ND and RD directions by wire cutting to obtain the required sample and mark it accordingly;

[0010] S1.2) The sample obtained by the treatment in S1.1) is cold mounted at room temperature, and after cooling and solidification, it is taken out and mechanically polished;

[0011] S1.3) After grinding and polishing in S1.2), the sample is ultrasonically cleaned, then cleaned with alcohol and blown dry.

[0012] Furthermore, the sample size in S1.1) is less than 10.00 mm in length and width, and 3-5 mm in height.

[0013] Further, the room temperature cold mounting in S1.2) is room temperature epoxy resin cold mounting;

[0014] The mechanical grinding method is: first use 320#, 600#, 1000#, 1500#, and 2000# to grind the sample;

[0015] Then use a soft damping polishing cloth with polishing liquid for polishing.

[0016] Furthermore, the polishing liquid is W3 and W1.

[0017] Further, the specific steps of S2) are:

[0018] S2.1) Re-vacuum to 0.01pa, rotate the sample stage until the angle between the ion beam jet direction and the normal direction of the sample surface is 85-88°; set the argon gas flow rate to 1.5mL / min; turn on the main circuit switch of the equipment, adjust the acceleration voltage to 2kv, set the grinding time to 15-20min, start the ion gun switch, and after the current stabilizes at 350-400uA, open the plate valve, start grinding, and rotate the sample stage;

[0019] S2.2) After the grinding in S2.1) is completed, the acceleration voltage is adjusted to 4 kV and the grinding time is 13-17 min. After grinding again, the sample is taken out for EBSD observation.

[0020] Furthermore, the equipment is an IM4000Ⅱ ion milling instrument.

[0021] Furthermore, the EBSD data resolution of the Bi2Te3 sample after grinding by the method is above 95%.

[0022] Features of the present invention:

[0023] For Bi2Te3-based thermoelectric materials, an ion milling method is proposed to prepare EBSD samples. The method is simple, stable, and efficient, and provides a detailed ion milling process.

[0024] It is capable of preparing high-quality EBSD samples with a data resolution of more than 95%. At the same time, the microscopic morphology is clear and the sample surface information is complete, providing accurate information for obtaining crystal parameters, grain orientation and texture. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 EBSD image of a Bi2Te3 sample prepared by zone melting.

[0026] Figure 2 EBSD image of Bi2Te3 sample prepared by hot extrusion. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0028] The present invention discloses a method for preparing Bi2Te3 thermoelectric material EBSD sample by ion milling, the method comprising the following steps:

[0029] 1) According to the EBSD requirements, use wire cutting to cut samples of appropriate size in the three directions of TD, ND, and RD, with a length and width not exceeding 10.00mm and a height of 3-5mm, and make corresponding marks;

[0030] 2) After the sample is mounted, it is polished, and then the surface impurities are ultrasonically cleaned with deionized water, and then rinsed with alcohol and blown dry;

[0031] 3) Fine polishing by ion milling:

[0032] Glue the area of ​​the sample to be observed to the center of the sample stage, fix it horizontally on the stage, lock and close the hatch, turn on the mechanical pump to evacuate to 0.01pa; rotate the sample stage until the angle between the ion beam jet direction and the normal of the sample surface is 85-88°; set the argon flow rate to 1.5mL / min; turn on the main circuit switch, adjust the ion beam acceleration voltage to 2kv, set the grinding time to 13-17min, and start the ion gun switch; after the discharge current stabilizes at 350-400uA, connect the plate valve, the sample stage rotates, and grinding begins; after the grinding time is over, reset the acceleration voltage to 4kv, set the time to 15min, and perform grinding again; wait and take out the sample for EBSD observation.

[0033] As the preferred technical solution:

[0034] In step 2), the embedding method is room temperature epoxy resin cold embedding. The mechanical properties of Bi2Te3 samples are poor. The cold embedding method can completely preserve the observation surface without changing the internal structure of the crystal.

[0035] In step 2), since the Bi2Te3 sample is relatively soft and fragile, 320#, 600#, 1000#, 1500#, and 2000# are used to grind and polish the sample in sequence, and then W3 or W1 polishing liquid is used to polish the sample on a soft damping polishing cloth, which can effectively reduce scratches on the sample surface.

[0036] The Bi2Te3 sample after ion milling and polishing by the method of the present invention can be used for microscopic analysis such as electron scanning microscope (SEM), energy spectrum analysis and backscattered electron diffraction (EBSD), and the EBSD data resolution rate is above 95%, and the quality is extremely high.

[0037] Example 1

[0038] A method for preparing a Bi2Te3-based thermoelectric material EBSD sample by ion milling, the specific method comprising the following steps:

[0039] (1) Grinding and polishing of bismuth telluride crystal rods prepared by zone melting method.

[0040] The wire cutting method was used to cut samples of suitable size, with a length, width and height of 8mm*6mm*5mm. The three different directions of TD, ND and RD were distinguished and marked accordingly. There were obvious cutting lines and oxide layers on the surface of the cut samples. Cold mounting treatment was adopted at room temperature. After cooling and solidification, they were taken out for mechanical grinding and polishing. 320#, 600#, 1000#, 1500# and 2000# were used to polish the samples in turn to remove the surface oxide layer and large-sized scratches. In view of the soft and fragile geology of Bi2Te3 samples, soft material damping polishing cloth was used in the mechanical polishing stage with W3 and W1 polishing liquid, which can effectively reduce finer scratches on the surface of the samples. After grinding and polishing, the samples were ultrasonically cleaned to remove the grinding and polishing liquid and impurities attached to the surface, and then cleaned with alcohol and blown dry.

[0041] (2) Fine polishing by ion milling:

[0042] Glue the sample area to be observed to the center of the sample stage, fix it horizontally on the stage, lock and close the hatch, turn on the mechanical pump to evacuate to 0.01pa; rotate the sample stage until the angle between the ion beam jet direction and the normal of the sample surface is 87°; set the argon flow rate to 1.5mL / min; turn on the main circuit switch, adjust the ion beam acceleration voltage to 2kv, set the grinding time to 15min, and start the ion gun switch; after the discharge current stabilizes at 400uA, connect the plate valve, the sample stage rotates, and grinding begins; after the grinding time is over, reset the acceleration voltage to 4kv, set the time to 15min, and perform grinding again; after waiting for the grinding to end, inflate to break the vacuum and take out the sample.

[0043] (3) Observe the sample by EBSD, analyze and process the results, and obtain the inverse pole figure (IPF) of the sample, such as Figure 1 shown.

[0044] Example 2

[0045] A method for preparing a Bi2Te3-based thermoelectric material EBSD sample by ion milling, the specific method comprising the following steps:

[0046] (1) The bismuth telluride crystal rod prepared by hot extrusion method was ground and polished.

[0047] The wire cutting method was used to cut samples of suitable size, with a length, width and height of 8mm*6mm*5mm. The three different directions of TD, ND and RD were distinguished and marked accordingly. There were obvious cutting lines and oxide layers on the surface of the cut samples. Cold mounting treatment was adopted at room temperature. After cooling and solidification, they were taken out for mechanical grinding and polishing. 320#, 600#, 1000#, 1500# and 2000# were used to polish the samples in turn to remove the surface oxide layer and large-sized scratches. In view of the soft and fragile geology of Bi2Te3 samples, soft material damping polishing cloth was used in the mechanical polishing stage with W3 and W1 polishing liquid, which can effectively reduce finer scratches on the surface of the samples. After grinding and polishing, the samples were ultrasonically cleaned to remove the grinding and polishing liquid and impurities attached to the surface, and then cleaned with alcohol and blown dry.

[0048] (2) Fine polishing by ion milling:

[0049] Glue the sample area to be observed to the center of the sample stage, fix it horizontally on the stage, lock and close the hatch, turn on the mechanical pump to evacuate to 0.01pa; rotate the sample stage until the angle between the ion beam jet direction and the normal of the sample surface is 87°; set the argon flow rate to 1.5mL / min; turn on the main circuit switch, adjust the ion beam acceleration voltage to 2kv, set the grinding time to 15min, and start the ion gun switch; after the discharge current stabilizes at 400uA, connect the plate valve, the sample stage rotates, and grinding begins; after the grinding time is over, reset the acceleration voltage to 4kv, set the time to 15min, and perform grinding again; after waiting for the grinding to end, inflate to break the vacuum and take out the sample.

[0050] (3) Observe the sample by EBSD, analyze and process the results, and obtain the inverse pole figure (IPF) of the sample, such as Figure 2 shown.

[0051] The above examples are only for illustrating the technical features and concepts of the present invention, and the purpose is to enable people familiar with the technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing Bi2Te3 thermoelectric material EBSD samples by ion milling, characterized in that: The method specifically comprises the following steps: S1) using wire cutting technology to cut Bi2Te3 material to obtain samples, and then pre-treating the samples; S2) placing the sample processed in S1) horizontally on a stage, and performing two-step ion milling on the sample in a vacuum environment to obtain an EBSD sample of a Bi2Te3-based thermoelectric material.

2. The method according to claim 1, characterized in that The specific steps of S1) are: S1.1) According to the EBSD requirements, the sample is cut in the TD, ND and RD directions by wire cutting to obtain the required sample and mark it accordingly; S1.2) The sample obtained by the treatment in S1.1) is cold mounted at room temperature, and after cooling and solidification, it is taken out and mechanically polished; S1.3) After grinding and polishing in S1.2), the sample is ultrasonically cleaned, then cleaned with alcohol and blown dry.

3. The method according to claim 2, characterized in that The sample size in S1.1) is less than 10.00 mm in length and width, and 3-5 mm in height.

4. The method according to claim 2, characterized in that: The room temperature cold mounting in S1.2) is room temperature epoxy resin cold mounting; The mechanical grinding method is: first use 320#, 600#, 1000#, 1500#, and 2000# to grind the sample; Then use a soft damping polishing cloth with polishing liquid for polishing.

5. The method according to claim 4, characterized in that The polishing liquids are W3 and W1.

6. The method according to claim 1, characterized in that The specific steps of S2) are: S2.1) Re-vacuum to 0.01pa, rotate the sample stage until the angle between the ion beam jet direction and the normal direction of the sample surface is 85-88°; set the argon gas flow rate to 1.5mL / min; turn on the main circuit switch of the equipment, adjust the acceleration voltage to 2kv, set the grinding time to 15-20min, start the ion gun switch, and after the current stabilizes at 350-400uA, open the plate valve, start grinding, and rotate the sample stage; S2.2) After the grinding in S2.1) is completed, the acceleration voltage is adjusted to 4 kV and the grinding time is 13-17 min. After grinding again, the sample is taken out for EBSD observation.

7. The method according to claim 6, characterized in that The equipment is an IM4000Ⅱ ion milling instrument.

8. The method according to claim 1, characterized in that The EBSD data resolution rate of the Bi2Te3 sample ground by the method is above 95%.

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