A method for preparing a transmission electron microscope sample of a flexible thermoelectric material for in-situ chip observation

Abstract

This invention relates to the field of in-situ heating and electrostatic research in transmission electron microscopy (TEM), and discloses a method for preparing flexible thermoelectric material TEM samples for in-situ chip observation, comprising the following steps: (1) in-situ chip perforation; (2) ingot disc cutting; (3) block trimming; (4) pre-slicing preparation; (5) ultrathin slicing; and (6) sample transfer. By combining an optical microscope with a long-handled delineator, the probability of the thin slice falling into the target window is greatly improved. This invention reduces mechanical polishing and resin embedding, avoids thermal and electrical damage, significantly improves the transfer success rate, shortens the sample preparation time to within two hours, and reduces preparation costs. The non-destructive thin slice placed on the in-situ chip can be subjected to multiple external fields such as heat and electricity in the TEM for dynamic observation of structural evolution.

Description

Technical Field

[0001] This invention relates to the field of in-situ heating and electrification research technology for transmission electron microscopy, specifically a method for preparing flexible thermoelectric material transmission electron microscopy samples for in-situ chip observation. Background Technology

[0002] Thermoelectric technology enables the direct conversion between heat and electrical energy, and has application value in many fields. Flexible thermoelectric materials, with their deformability, can serve as an important power source for wearable devices. Plastic bulk inorganic thermoelectric materials were not reported before 2018; now, nearly ten such materials have been developed, including Ag₂S and Ag₂S ... 1-x Se x ,Ag2(S,Te),Ag2(S,Se,Te),(Ag 1-x Cu x )2S 0.7 Se 0.3 Ag2S 0.7 Se 0.295 I 0.005 、(Ag 1- x Cu x 2Se. The aforementioned flexible thermoelectric materials are mainly silver chalcogenides and their doped compounds, most of which are fast ion conductors exhibiting liquid-like behavior. The phase transition temperature from ordinary ion conductors to fast ion conductors ranges from room temperature to 200°C, depending on the type of flexible thermoelectric material. Due to the unique liquid-like behavior in the high-temperature phase, flexible thermoelectric materials readily undergo metal deposition under thermal or electric fields. The structure and phase transition of these materials are commonly characterized using macroscopic techniques such as X-ray diffraction and differential scanning calorimetry, while microscopic characterization techniques are limited by sample preparation issues. Bulk ceramic transmission electron microscopy samples are typically prepared using ion thinning and focused ion beam cutting methods. These two ion beam bombardment-based methods have the following disadvantages for flexible thermoelectric materials: (1) Both require prior mechanical polishing, which makes the surface of the flexible material uneven, resulting in a large number of scratches and high-hardness impurity particles embedded in the surface; (2) The interaction between the ion beam and the flexible thermoelectric material will cause thermal and electrical damage (amorphization and significant temperature rise), which will cause the properties of the prepared sample to deviate from the intrinsic behavior to a certain extent; (3) The deformable characteristics will lead to bending and folding of the transmission sample, that is, the quality of the transmission sample is not high and there are few usable thin areas; (4) Ion thinning and focused ion beam cutting require at least 4 hours and 2 hours respectively to prepare transmission samples, which is expensive; (5) Ion thinning does not have the corresponding fixed-point transfer tool and cannot transfer the transmission sample to the in-situ chip, while focused ion beam cutting is equipped with a transfer tool, but the transfer success rate is not high.

[0003] Unlike the two sample preparation techniques mentioned above, ultrathin sectioning only requires materials with low hardness, offering advantages such as wide applicability, large thin areas, no need for mechanical polishing, and no thermal or electrical damage, making it ideal for preparing transmission electron microscopy (TEM) samples of flexible thermoelectric materials. Patent CN105571912B describes how to harden soft materials (such as nylon and synthetic fibers) by cutting them into wedge-shaped pieces and then embedding them in epoxy resin, thus achieving ultrathin sections at room temperature. However, due to the scarcity of institutions in China possessing both ultrathin sectioning and in-situ TEM technologies, the development of ultrathin sectioning transfer technology lags significantly behind focused ion beam cutting. Patent CN110702717A addresses this by designing a limiting-positioning device to transfer ultrathin section samples onto an in-situ heated chip. However, the above transfer technology has three problems: (1) When sharp corners, needles or heavy objects (referring to the positioning device placed above the chip) act on the silicon nitride film heated in the micro-area, the film is prone to breakage, which in turn causes chip failure; (2) Although the method of using copper mesh as a scraping ring can bring the water droplet carrying the film into contact with the positioned heating area (about 2mm×2mm), the method of absorbing the water on the top of it with absorbent paper will cause the film to transfer to the absorbent paper, resulting in sample loss; (3) Since the observation area in the actual in-situ transmission electron microscope (about 0.1mm×0.1mm) is only a very small part of the center of the positioning area, the ability of the film to fall into the observation area is still highly uncertain, so the transfer success rate cannot be guaranteed.

[0004] Therefore, developing a method for preparing flexible thermoelectric material transmission electron microscopy samples for in-situ chip observation that has advantages such as safety, low cost, high success rate, and no thermal or electrical damage is of great significance for establishing the relationship between the structural evolution and performance of flexible thermoelectric materials under external field conditions such as thermal and electric fields. Summary of the Invention

[0005] This invention aims to provide a method for preparing transmission electron microscopy (TEM) samples of flexible thermoelectric materials for in-situ chip observation. This method, based on ultrathin sections, offers advantages such as safety, high success rate, convenience, short sample preparation time, low cost, recyclability, and absence of thermal and electrical damage, thus meeting the needs of phase transition studies of flexible thermoelectric materials under external field conditions.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes the following steps:

[0007] Step 1: Drill holes in the original chip;

[0008] Step 2: Cut the ingot into thin strips: Cut the ingot into thin strips with a thickness of 1mm;

[0009] Step 3, trimming: Transfer the thin strip to an ultramicrotome and trim it with a glass blade until a smooth surface is created; remove the right side of the preset reference point on the surface, and then obtain the column by rotating the sample, aligning the blade, and automatically slicing it three times.

[0010] Step 4: Preparation before sectioning: Replace the glass blade on the ultramicrotome with a diamond blade, align the column, and inject excess deionized water into the water tank;

[0011] Step 5: Slice the sample to obtain the sliced ​​sample.

[0012] Preferably, the size range of the thin strip in step two is (12-15)mm×(1-2)mm×(1-2)mm.

[0013] Preferably, in step three, the parameters of the ultrathin slicer include a total feed of 200 μm, a speed of 100 nm / s, and a slice thickness of 1 μm.

[0014] Preferably, in step four, when injecting deionized water, the water inlet and outlet of the control pipe are adjusted to make the liquid surface reflect a bright, reflective effect.

[0015] Preferably, in step five, before slicing, the countdown, speed, and slice thickness of the ultrathin slicer are 999, 10 nm / s, and 100 nm, respectively.

[0016] Preferably, in step five, the number of qualified slices obtained each time the ultrathin slice is 200-300.

[0017] Preferably, the method further includes step six, transferring the sliced ​​sample, which involves moving the sliced ​​sample to the observation area.

[0018] By adopting the above technical solution, the present invention has the following beneficial technical effects:

[0019] (1) Safety: During the transfer process, the chip heating area is in indirect contact with the thin blades of grass and the plastic dropper, except for direct contact with the tip of the long-handled drawing pen. In actual transfer, no significant external force is applied to the silicon nitride film in the heating area, so the chip heating area is very safe.

[0020] (2) High success rate: The sample transfer step only needs to be performed 1-2 times to complete the process, overcoming the shortcomings of conventional transfer methods (titration of water droplets carrying the slices and drying) such as low success rate and poor repeatability.

[0021] (3) Convenience: Compared with the three conventional preparation techniques mentioned in the background, this method reduces the mechanical polishing and resin embedding steps, thus optimizing the preparation process. The prepared sheet has excellent adsorption capacity for silicon nitride films, avoiding additional welding work to fix the sample to the target window.

[0022] (4) Short sample preparation time: Transmission samples for in-situ chip observation can be successfully prepared in just two hours.

[0023] (5) Low cost: The cost of the long-handled drawing pen and plastic dropper required for the transfer process is only a few dollars, and the other tools are all essential for the laboratory.

[0024] (6) Recyclable: The same sample can be prepared repeatedly as long as the thin film on the observation area is removed by focused ion beam cutting technology.

[0025] It should be noted that the transmission samples prepared by this method for in-situ chip observation are not limited to flexible thermoelectric materials; low-hardness metal materials are also within the scope of application of this method. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart illustrating the preparation method of the flexible thermoelectric material transmission electron microscope sample for in-situ chip observation provided in this application.

[0027] Figure 2 Optical images of the transfer results of ultrathin slice samples.

[0028] Figure 3 Ag2S 0.6 Se 0.4 Transmission electron microscopy images of the sliced ​​samples, including dark-field images (a) and corresponding energy dispersive spectroscopy (bd), as well as high-resolution images (eh) and corresponding fast Fourier transforms (il) during in-situ heating and cooling processes, at temperatures of 17°C, 84°C, 105°C and 76.5°C. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings:

[0030] A method for preparing a flexible thermoelectric material transmission electron microscopy (TEM) sample for in-situ chip observation. The flexible thermoelectric material TEM sample is used for in-situ chip observation. (See [link to relevant documentation]). Figure 1 As shown, it includes the following steps:

[0031] Step 1: In-situ chip perforation

[0032] The in-situ chip equipped with the Lightning heating and power system compatible with JEOL (Japan Electronics Corporation) transmission electron microscopes must use focused ion beam cutting technology to break through the window in the Lightning heating or power area, where the window is located on the in-situ chip.

[0033] Step 2: Cutting the cast ingot discs

[0034] Cut flexible thermoelectric material Ag2S with a thickness of 1mm using scissors. 0.6 Se 0.4 Casting ingot discs to obtain thin strips, wherein the size range of the thin strips in step two is (12-15)mm×(1-2)mm×(1-2)mm, preferably 12mm×2mm×1mm.

[0035] Step 3: Trim the block

[0036] Transfer the thin strip to an ultramicrotome for trimming. Move the glass blade equipped on the ultramicrotome to a suitable distance from the sample and slowly advance the blade until a smooth surface is shaved off the thin strip. Select a point in the center of the surface as a reference point and move the left edge of the glass blade to the reference point for alignment. Set the slicing parameters, including total feed (200 μm), speed (100 nm / s), and slice thickness (1 μm). Press the Run / Stop button to start automatic slicing. After slicing is complete, press the Reset button to manually retract the blade. Rotate the sample 180° and realign it with the previously cut boundary. Move the blade holder 100 μm to the right and start automatic slicing again. A thin, elongated protrusion can be observed on the surface. Rotate the sample 90° and select any point in the middle of the protrusion to realign the blade again and start automatic slicing. Continue rotating the sample 180° and realigning it with the boundary cut by the previous cut. Move the blade holder 100 μm to the right and start automatic slicing again. Finally, a columnar column, i.e., a cuboid column, can be observed on the sample.

[0037] Step 4: Preparation before slicing

[0038] Replace the glass cutter with a diamond cutter, and perform cutter preparation on the cuboid column and set the starting and ending positions for slicing; inject excess deionized water into the water tank, and adjust the water inlet and outlet of the control pipe to make the liquid surface reflective and shiny.

[0039] Step 5: Ultrathin Slicing

[0040] Set the initial slicing parameters (countdown, speed, and slice thickness are 999, 10 nm / s, and 100 nm, respectively) and start automatic slicing. Gradually reduce the speed and slice thickness during the slicing process, and finally control the speed and slice thickness at 1 nm / s and 30-35 nm, respectively, to obtain ultrathin sliced ​​samples. Slicing can be stopped by pressing the Run / Stop button on the ultrathin slicer.

[0041] In order to observe the sliced ​​sample, this application also includes step six: sliced ​​sample transfer, which involves moving the sliced ​​sample to the observation area.

[0042] Using a long-handled pen, move the sample section near the diamond cutting edge to the center of the water tank. Use the reverse side of a slender blade of grass to scoop up the sample section. Using a plastic dropper, place a drop of deionized water on the heating area of ​​the chip in situ. Hold the blade of grass with the sample section in a slightly tilted horizontal position to ensure full contact with the water droplet. Observe the position of the sample section in real time using an optical microscope. Rotate the filter paper placed under the chip to adjust its position. Hold the filter paper with your left hand and control the long-handled pen with your right hand. Use the soft bristles at the tip of the pen to touch the sample section. After several adjustments, the sample section will reach the observation area. If the final position of the sample section deviates from the observation area, repeat the steps. Figure 2 The image shows a successful transfer of Ag2S. 0.6 Se 0.4 An actual image of the sliced ​​sample.

[0043] In step six, the plastic dropper has a capacity of 0.2 ml and an outer diameter of 1.5 mm. The long-handled drawing pen has a nylon tip, and its tip length, tip diameter, and total length are 6.5 mm, 0.8 mm, and 165 mm, respectively.

[0044] Furthermore, the blade holder angle of the ultrathin slicer is kept constant at 6° in steps three, four, and five.

[0045] During the research process, the inventors of this application discovered that the following points need to be noted regarding this method:

[0046] (1) The observation area in step one has a silicon nitride film of a certain thickness. If the sliced ​​sample is directly transferred to an unperforated chip, the high-resolution image will be greatly affected.

[0047] (2) In step three, a Reset and blade retraction must be performed before each sample rotation and after completing the cuboid column; otherwise, it will trigger an instrument alarm or even cause damage. The automatic slicing parameters in this step remain unchanged. The blade holder should be moved to the right by at least 100 μm each time; otherwise, the cuboid column is prone to collapse during subsequent blade alignment and ultrathin slicing.

[0048] (3) In step four, the top light needs to be turned on to observe the liquid surface effect.

[0049] (4) The final slice sample usable for high-resolution imaging in step five needs to meet the following two conditions: first, its size should be consistent with the initial slice sample size (thickness around 100 nm); second, its thickness should be suitable enough to be observed as translucent under an optical microscope, rather than having a heavy metallic sheen. The number of slice samples larger than the final thickness in the initial stages should be controlled between 20-40. The number of qualified slice samples obtained from each ultrathin section should ideally be controlled between 200-300.

[0050] (5) At the beginning of step six, use a fine-tipped pen to remove any excessively thick slices. Only a few dozen slices need to be transferred at a time. Due to gravity, the slices will only remain at the edge of the convex water droplet and require external assistance to reach the observation area. Deionized water takes more than 20 minutes to disappear at room temperature; therefore, the position of the slices must be constantly observed through an optical microscope and adjusted promptly during the transfer. Figure 2 As shown.

[0051] Energy dispersive spectroscopy analysis showed that the solid solution Ag2S 0.6 Se 0.4 The sample components are evenly distributed, such as Figure 3 As shown in (ad). Figure 3 (e.g., image 1) shows the in-situ heating and cooling process of the material at a constant heating and cooling rate of 1 °C / s, involving temperatures of 17 °C, 84 °C, 105 °C, and 76.5 °C. High-resolution images and fast Fourier transforms indicate that the low-temperature phase of the solid solution (17 °C) corresponds to the low-temperature phase of Ag₂S (monoclinic structure, COD#9011414). The solid solution high-temperature phase (105℃) corresponds to the [0 1 2]c band axis of the Ag2S high-temperature phase (body-centered cubic structure, COD#1011337). The phase transition points for heating and cooling are 84℃ and 76.5℃, respectively, and the orientation at 76.5℃ is consistent with the orientation before heating (17℃), indicating that the phase transition is reversible. The above results show that the flexible thermoelectric material Ag2S can be realized by this method. 0.6 Se 0.4 In-situ high-resolution crystal structure study.

[0052] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing flexible thermoelectric material transmission electron microscopy samples for in-situ chip observation, characterized in that, Includes the following steps: (1) In-situ chip perforation: The in-situ chip must use focused ion beam cutting technology to puncture the window in the heating or energized area. (2) Ingot disc cutting: Cut a flexible thermoelectric material ingot disc with a thickness of 1mm with scissors to obtain a thin strip of 12mm×2mm×1mm. (3) Trimming: Transfer the thin strip to an ultrathin slicer for trimming, slowly feed the blade until a smooth plane is cut out; select a certain position in the center area of ​​the plane for blade alignment, set the slicing parameters and start automatic slicing. The slicing parameters involve a total feed of 200μm, a speed of 100nm / s and a slice thickness of 1μm; after three rounds of sample rotation, blade alignment and automatic slicing operations, a cuboid column can be observed on the sample. (4) Preparation before slicing: Replace the glass blade in the previous step with a diamond blade, align the cuboid column, set the starting and ending positions of the slice; inject water into the water tank. Excessive deionized water, by adjusting the water pipe inlet and outlet, the liquid surface will show a reflective bright effect. (5) Ultrathin slicing: Set the initial slicing parameters and start automatic slicing. The slicing parameters involve countdown 999, speed 10nm / s and slicing thickness 100nm. Gradually reduce the speed and slicing thickness during the slicing process. The final speed and slicing thickness should be controlled at 1nm / s and 30-35nm respectively. (6) Slicing sample transfer: Control the long-handled pen to move the thin slice near the diamond blade to the middle of the water tank. Use the reverse side of the slender grass blade to pick up the thin slice. Drop a drop of deionized water on the heating area of ​​the chip in situ. Make the grass blade with the thin slice fully contact the water drop in a slightly tilted horizontal direction. Use an optical microscope to observe the thin slice in real time. Rotate the filter paper placed under the chip to adjust the chip position. Control the pen to continuously adjust the thin slice until it reaches the observation area. In step (3), the distance the cuboid column moves to the right twice during the two tool holder movements should be no less than 100 μm. In step (6), the deionized water titration tool is a plastic dropper.

2. The preparation method according to claim 1, characterized in that, The optimal size range of the thin strip in step (2) is (12-15) mm × (1-2) mm × (1-2) mm.

3. The preparation method according to claim 1, characterized in that, In step (4), the top light needs to be turned on to observe the liquid surface effect.

4. The preparation method according to claim 1, characterized in that, The thin film that can be used for high-resolution imaging in step (5) needs to meet the following two conditions: first, the size should be consistent with the initial (thickness of about 100nm) thin film size; second, the appropriate thickness should allow for a translucent feel to be observed in an optical microscope, rather than a heavy metallic feel.

5. The preparation method according to claim 1, characterized in that, In step (5), the number of qualified slices obtained each time should be controlled between 200 and 300.

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