Fiber feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness and preparation method thereof

Abstract

The application belongs to the technical field of thermoelectric materials, and particularly relates to a fiber feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness and a preparation method thereof. The application comprises the following steps: (1) using a silicon oxide sheet and a polyimide as a substrate, fixing the substrate to a base plate, and then loading the base plate into a sputtering cavity; (2) fixing a tellurium bismuth alloy target on a direct current power source, fixing a tellurium single target on a radio frequency power source, adjusting the spacing of the tellurium bismuth alloy target, the tellurium single target and the substrate, closing the cabin door, and cleaning the substrate by using an ionization method; (3) after the cleaning is completed, a fiber feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness is grown by using an intermittent sputtering method. The application creatively grows the fiber feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness in one step under the condition of room temperature and fixed working air pressure by adjusting the total sputtering time and the sputtering bias, and can meet the demand of flexible wearable thermoelectric devices, and has potential commercial prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermoelectric materials, and particularly relates to a fiber feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness and a preparation method thereof. BACKGROUND

[0002] With the flexible development of wearable devices in daily life and biological medicine and other fields, traditional rigid semiconductors cannot meet the growing demand for wearables. Thermoelectric materials can convert heat into electricity, and flexible thermoelectric materials can be in close contact with the human body, maximizing energy conversion efficiency, and achieving wearable device power supply through human body heat, becoming a research direction with great application prospect. In the research of thermoelectric materials, bismuth telluride material has important significance for the commercialization process of thermoelectric devices due to its excellent thermoelectric performance. However, compared with the continuous development of the thermoelectric performance of bismuth telluride-based films, the mechanical performance research lags far behind, and the lack of mechanical strength and toughness limits its further commercial application. Related research on thin films has found that the grain shape, size and distribution, and the types and densities of defects contained in the grain interior, will have a significant impact on the mechanical, thermal and electrical properties of the film. Related research has found that when the grain size of the film is gradiently distributed, and the grain interior contains more dislocations, the grain boundaries and dislocations can hinder crack propagation and dislocation slip, respectively, to achieve synergistic improvement of the strength and toughness of the material.

[0003] In the prior art, document 1 (Jin Q, Jiang S, Zhao Y, et al. Flexible layer-structured Bi2Te3 thermoelectric on a carbon nanotube scaffold[J]. Nature Materials, 2018, 18(1): 62-68.) reports a (000l)-oriented bismuth telluride film deposited on a carbon nanotube by magnetron sputtering, with a working pressure of 0.5 Pa and a working temperature of 650 K. The film has no obvious loss after being cyclically bent for 100 times at a bending radius of 10 mm.

[0004] Document 2 (Zheng Z H, Shi X L, Ao D W, et al. Harvesting waste heat with flexible Bi2Te3 thermoelectric thin film[J]. Nature Sustainability, 2022, 6(2): 180-191.) reports that Ag / Bi and Te were first deposited on a polyimide substrate, respectively, with a working pressure of 1 Pa. Subsequently, the two were placed in a vacuum furnace, and a force of 5 Nmm -2External pressure was applied to make it in close contact and heat treated at 350 ℃ for 30 min. The resulting film was bent 2000 times at a bending radius of 18 mm, and the resistivity increased by 10%.

[0005] Document 3 (Karthikeyan V, Surjadi J U, Li X, et al. Three dimensional architected thermoelectric devices with high toughness and power conversion efficiency[J]. Nature Communications, 2023, 14(1): 2069.) reported that bismuth telluride thin films were deposited by thermal evaporation at room temperature, and the thin films were heat treated at 220 ℃. The resulting film has a maximum Seebeck coefficient of 187 μVK -1 at 350 K, the electrical conductivity reaches a maximum of 435 Scm -1 at 550 K, and the power factor is always stable near 6 μWcm -1 K -2 .

[0006] Document 4 (Lu Y, Zhou Y, Wang W, et al. Staggered-layer-boosted flexible Bi2Te3 films with high thermoelectric performance[J]. Nature Nanotechnology, 2023, 18(11): 1281-1288.) reported that Bi 0.5 Sb 1.5 Te3and Bi2Te 2.7 Se 0.3 single crystals were first prepared by zone melting and Bridgman method, respectively, then the obtained single crystals were cut along the (000l) cleavage plane, and p-type and n-type bismuth telluride thin films were obtained by peeling with transparent adhesive. The film was cycled 1000 times at a bending radius of 4 mm, and the electrical conductivity decreased by 9%.

[0007] Document 5 (Zheng Z H, Zhong Y M, Li Y L, et al. Ultrahigh thermoelectric properties of p‐type Bi x Sb 2−xTe3 thin films with exceptional flexibility for wearable energy harvesting[J]. Carbon Energy, 2024, 6(8): 22276-22285.) reported the first deposition of Bi / Sb and Te on different polyimide substrates by thermal evaporation, with evaporation powers of 14 W and 10 W, respectively, and an operating pressure of 2×10⁻⁶. -3 Pa, followed by heating at 350 °C for 30 min to prepare Bi. x Sb 2−x Te3 thin film. The resistivity of this film increased by 5% after 1000 cycles of bending at a bending radius of 5 mm.

[0008] Reference 6 (CN 106498354 A A method for preparing hexagonal spiral bismuth telluride thermoelectric thin films, 2017) proposes a method for preparing hexagonal spiral bismuth telluride thermoelectric thin films. First, a target is installed and a quartz glass substrate is fixed on the substrate. The distance between the target and the quartz glass substrate is adjusted, and a vacuum is drawn to a specified standard. The quartz glass substrate is heated to 300℃~400℃, and the thin film is prepared by co-sputtering under a working pressure of 0.3Pa~0.5Pa. Finally, the sputtered thin film is annealed at 250℃~350℃ to form a hexagonal spiral bismuth telluride thermoelectric thin film.

[0009] Reference 7 (CN 108447976 A A method for grain boundary regulation of the properties of n-type bismuth telluride thin films, 2018.) proposes a method for grain boundary regulation of the properties of n-type bismuth telluride thin films. The method includes the following steps: First, n-type Bi2Te3 thin films are prepared on heated substrates using magnetron sputtering technology; second, Sn is deposited on the surface of the n-type Bi2Te3 thin film using thermal evaporation technology; third, the Sn-deposited n-type Bi2Te3 is annealed at high temperature in a protective gas annealing furnace and then cooled with the furnace to obtain high-performance n-type Bi2Te3 thin films.

[0010] Reference 8 (CN 109554674 A A method for preparing a bismuth telluride thermoelectric thin film with a heterostructure, 2019) proposes a method for preparing a bismuth telluride thermoelectric thin film with a heterostructure. First, a target is installed and a magnesium oxide (MgO) single crystal is fixed on a substrate stage. The distance between the target and the quartz glass substrate is adjusted, and a vacuum is drawn to a specified standard. The magnesium oxide (MgO) substrate is heated to 320℃~400℃, and the thin film is prepared by co-sputtering under a working pressure of 1Pa~3Pa. Finally, the sputtered thin film is annealed at 350℃~450℃ to form a bismuth telluride thermoelectric thin film with a heterostructure.

[0011] Reference 9 (CN 115595542 A An ultrahard nano-heterogeneous medium-entropy alloy thin film and its preparation method, 2022.) discloses an ultrahard nano-heterogeneous medium-entropy alloy thin film and its preparation method. The ultrahard nano-heterogeneous CrCoNi alloy is a nanocrystalline composite material composed of short columnar crystals and equiaxed crystals dispersed around the columnar crystals. The heterogeneous structure here is prepared by interval sputtering. These dispersed equiaxed crystals improve the anisotropic mechanical behavior of medium / high-entropy alloy columnar nanostructures prepared by magnetron sputtering in the past.

[0012] Most existing methods for preparing thermoelectric thin films require high temperatures (at least 220°C) and involve multiple steps, limiting large-scale industrial production. The resulting films are typically single-sized columnar, hexagonal spiral, or hexagonal nanocrystals, failing to overcome the nanocrystal-flexibility constraint, resulting in limited bending cycles under large deformations and poor film flexibility. Furthermore, the low intracrystalline defect density prevents synergistic regulation of electrical and thermal conductivity to improve thermoelectric performance. Therefore, developing a one-step method at room temperature to prepare bismuth telluride thin films with novel structures and excellent mechanical and thermoelectric properties is crucial for developing high-performance flexible wearable thermoelectric devices. Summary of the Invention

[0013] The purpose of this invention is to provide a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film and its preparation method. Under room temperature and a fixed working pressure, this invention grows a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film by controlling the film thickness, grain size, and internal grain defects by changing the total sputtering time and sputtering bias.

[0014] The implementation process of this invention is as follows:

[0015] A method for preparing a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film includes the following steps:

[0016] (1) Using silicon oxide wafers and polyimide as substrates, the substrates are fixed to the base plate and then installed into the sputtering cavity;

[0017] (2) Fix the tellurium-bismuth alloy target on the DC power supply, fix the tellurium elemental target on the RF power supply, and adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target and the substrate, and clean the substrate by ionization.

[0018] (3) After cleaning, a highly tough fibrous feather-like nanocrystalline bismuth telluride thermoelectric thin film was grown by intermittent sputtering.

[0019] Furthermore, in step (1), the pretreatment process of the silicon oxide wafer and the polyimide is to select a single-sided polished silicon oxide wafer and polyimide as the substrate, immerse them in water and alcohol, and then clean them with an ultrasonic cleaner. After cleaning, the substrate surface is dried.

[0020] Furthermore, in step (2), the process of cleaning the substrate using the ionization method is to introduce argon gas under vacuum conditions, apply a sputtering bias voltage, set a pulse duty cycle, close the chamber door, and use the ionized argon ions to clean the substrate.

[0021] Furthermore, in step (3), the intermittent sputtering method involves setting the parameters of argon flow rate, working pressure, substrate rotation speed, sputtering temperature, RF power supply power, DC power supply power, sputtering bias voltage, and pulse duty cycle. The first sputtering lasts 12 to 17 minutes, and after sputtering, the RF and DC power supplies are turned off for 10 to 30 minutes. The second sputtering lasts 12 to 17 minutes, and after sputtering, the RF and DC power supplies are turned off for 10 to 30 minutes. This process is repeated 3 to 5 times.

[0022] Furthermore, in step (3), after the intermittent sputtering is completed, the radio frequency and DC power supplies are turned off, and the film is kept under vacuum for 1 to 2 hours to obtain a fibrous feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness.

[0023] Further, in step (2), the spacing between the tellurium-bismuth alloy target, the tellurium elemental target, and the substrate is 95–105 mm. Preferably, the purity of both the tellurium-bismuth alloy target and the tellurium elemental target is ≥99.9%, the atomic ratio of Bi to Te in the tellurium-bismuth alloy target is 2:3, the size of both the tellurium-bismuth alloy target and the tellurium elemental target is Φ74.2×4 mm, and the size of the backplate is Φ76.2×4 mm.

[0024] Furthermore, during the substrate cleaning process using the ionization method, the vacuum level is 1×10⁻⁶. -4 Pa ~ 5 × 10 -4 Pa; the sputtering bias voltage is 750–850V; the pulse duty cycle is set to 50%–80%.

[0025] Furthermore, in the intermittent sputtering method, the argon flow rate is set to 85–90 sccm, the working pressure is fixed at 2–3 Pa, the substrate rotation speed is set to 10–20 rpm, the sputtering temperature is set to 20–30 ℃, the RF power supply power is set to 38–42 W, the DC power supply power is set to 8–12 W, the sputtering bias voltage is set to 0–150 V, and the pulse duty cycle is set to 50%–80%.

[0026] Further, in step (1), the substrate is fixed to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then installed into the sputtering cavity. The silicon oxide wafer is in the center position, and the polyimide is around the perimeter. The silicon oxide wafer substrate and the polyimide substrate are on the same horizontal plane. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 2 to 5 mm.

[0027] A highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film, the thin film being prepared by the above-described preparation method.

[0028] The positive effects of this invention:

[0029] (1) In terms of preparation method, the present invention is the first to grow a high-toughness fibrous feather-like nanocrystalline bismuth telluride thermoelectric film in one step by adjusting the total sputtering time and sputtering bias under room temperature and fixed working pressure.

[0030] (2) In terms of mechanical properties, compared with traditional single-size columnar grains, the feather-shaped nanocrystalline bismuth telluride thermoelectric film prepared by the present invention is composed of numerous nanocrystals aggregated together, with a grain size gradient distribution from bottom to top, which enhances the strength and toughness of the bismuth telluride thermoelectric film in a synergistic way.

[0031] (3) In terms of thermoelectric performance, the feather-shaped nanocrystalline bismuth telluride thermoelectric film prepared by the present invention is composed of more grains of different sizes compared with the traditional micro columnar crystals, and has high-density fibrous stacking faults grown inside. It can avoid significant blocking of electrons while scattering phonons, and maintain high electrical conductivity while reducing thermal conductivity, thereby improving the thermoelectric performance of the material. Attached Figure Description

[0032] Figure 1 Photographs of the instruments used in the preparation method described in this invention;

[0033] Figure 2 This is a photograph of the silicon oxide wafer and polyimide substrate of the instrument used in the preparation method of the present invention after being fixed on a base plate;

[0034] Figure 3 The X-ray diffraction patterns of Examples 1-2 and Comparative Examples 1-2 are shown below.

[0035] Figure 4 The image is a scanning electron microscope image from Example 2;

[0036] Figure 5 The images shown are low-magnification transmission electron microscope images of Examples 1 and 3, where a is an image of Example 1 under dark field, b is a partial magnified view of a, c is an image of Example 3 under dark field, and d is a schematic diagram of a bismuth telluride thermoelectric thin film with high toughness fibrous feather-like nanocrystalline structure.

[0037] Figure 6 This is a high-magnification transmission electron microscope image of Example 3;

[0038] Figure 7 These are statistical images of grain size for Examples 1-2 and Comparative Example 1;

[0039] Figure 8 Statistical images of critical strain in uniaxial tensile cracks for Examples 1-2 and Comparative Examples 1-2;

[0040] Figure 9 The images shown are bending pictures of Examples 1-2 and Comparative Example 1, where a is an actual image of the bending device, b is a finite element simulation diagram of the bending process, c is a diagram of the resistance change during the bending cycle, and d is a magnified view of c.

[0041] Figure 10 The images are scanning electron microscope images of the surface before and after bending 3000 times in Example 1, where a is the image before bending in Example 1 and b is the image after bending 3000 times.

[0042] Figure 11 The conductivity of Example 1 and Comparative Example 1 ( σ ) and temperature ( T (Relationship image)

[0043] Figure 12 The power factor (PF) and temperature of Example 1 T (Relationship image)

[0044] Figure 13 A schematic diagram of electron transport and phonon scattering in a highly tough, fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film.

[0045] Figure 14 The images shown are from Example 1, where the device generates electricity using body heat after being bent 3000 times. In the image, a is a schematic diagram of the power generation device, and b is an image showing the voltage change over time. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments.

[0047] This invention utilizes magnetron sputtering technology to co-sputter a bismuth telluride alloy target and a single telluride target under conditions near room temperature and fixed gas pressure. By controlling parameters such as the total sputtering time and sputtering bias, a high-toughness fibrous feather-like nanocrystalline bismuth telluride thermoelectric thin film is grown using an intermittent sputtering method.

[0048] In this invention, "feather-like" refers to the aggregation of numerous nanocrystals with gradient sizes, forming a feather-like nanocrystal. "Fiber" refers to the strip-like stacking faults within the grains. Applying a bias voltage can repel positively charged sputtering source ions, resulting in reduced ion bombardment of the substrate and thus lowering the sputtering rate. Furthermore, when a positive bias voltage is applied, the substrate attracts negatively charged electrons. The accumulation of electrons may affect the local plasma density, reducing plasma activity and further decreasing sputtering efficiency, thereby controlling the thickness of the grown bismuth telluride thermoelectric film. Adjusting the total sputtering time can also adjust the film thickness. The film thickness is positively correlated with the grain size; that is, the greater the film thickness, the larger the grain size, and the more defects (such as dislocations and stacking faults) the grain can accommodate.

[0049] The feather-like nanocrystalline bismuth telluride thermoelectric film prepared in this invention is composed of numerous nanocrystals aggregated together, exhibiting a gradient grain size distribution from bottom to top, which synergistically enhances the strength and toughness of the bismuth telluride thermoelectric film. The smaller grains at the bottom of the feather-like nanocrystals provide strength, while the larger grains at the top provide the ability for plastic deformation, achieving a synergistic improvement in strength and plasticity. Dislocations, as the main carriers of the slip process in crystals, represent the ability of crystals to undergo plastic deformation. As the grain size increases, the number of dislocations and the slip region both increase, thereby enhancing the plastic deformation capacity of the material. Furthermore, fibrous stacking faults can be regarded as "obstacles" in the path of dislocation movement, requiring dislocations to overcome additional energy to continue slipping. When a dislocation encounters a stacking fault, it needs to overcome a greater energy barrier, thus requiring higher external stress to drive the dislocation's continued movement. This process actually increases the friction between slip layers, making the material exhibit higher strength. At the same time, stacking faults, by constraining the slip layers, further hinder the relative movement of the slip layers, allowing the material to absorb more energy during deformation and exhibiting a better toughening effect. By hindering dislocation movement, stacking faults increase energy dissipation within the grain, thereby synergistically improving the strength and toughness of the material.

[0050] ZT The thermoelectric value is an important indicator for measuring the thermoelectric properties of materials. ZT = S 2 σT / κ .in S , σ , κ and T These represent the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. Electrical conductivity... σ and thermal conductivity κThe size of the electrons and phonons is determined by electron and phonon transport, respectively; therefore, electron and phonon transport and coupling determine the final thermoelectric properties of the material. The feather-like nanocrystalline bismuth telluride thermoelectric film prepared in this invention, compared to traditional micro-columnar crystals, consists of more grains of different sizes and contains high-density fibrous stacking faults. Since phonons often have longer wavelengths than electrons, especially low-frequency phonons, the higher proportion of grain boundaries and the high-density stacking faults within the grains can effectively scatter low-frequency phonons, leading to a decrease in thermal conductivity. Simultaneously, grain boundaries and stacking faults do not significantly block shorter-wavelength electrons, i.e., they do not scatter high-frequency electrons, thus maintaining a high level of electrical conductivity. Therefore, the structure prepared in this invention can scatter phonons while avoiding significant obstruction of electrons, maintaining high electrical conductivity while reducing thermal conductivity, thereby improving the thermoelectric properties of the material.

[0051] The instrument used in the preparation method of the highly tough, fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film of this invention is a high-vacuum multi-target magnetron sputtering coating system, manufactured by Beijing Taicono Technology Co., Ltd., model JCP500. See details... Figure 1 The photograph shows the silicon oxide wafer and polyimide substrate fixed on the base plate. Figure 2 .

[0052] A method for preparing a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film includes the following steps:

[0053] (1) Select single-sided polished silicon oxide wafers and polyimide as substrates, immerse them in water and alcohol, and then clean them with an ultrasonic cleaner at least 3 times each, each time for 3 to 5 minutes. The water and alcohol must be changed before each cleaning. After cleaning, dry the substrate surface at 50 to 70 ℃. Fix the substrate to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then put it into the sputtering cavity. The silicon oxide wafer is in the center and the polyimide is around the perimeter. The silicon oxide wafer substrate and the polyimide substrate are on the same horizontal plane. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 2 to 5 mm.

[0054] (2) Fix the tellurium-bismuth alloy target to the DC power supply and the tellurium elemental target to the RF power supply. Adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target, and the substrate to 95–105 mm. Close the chamber door and wait for the mechanical pump and molecular pump to evacuate the vacuum inside the chamber to 1 × 10⁻⁶ mm. -4 Pa ~ 5 × 10 -4 After Pa, high-purity argon gas with a purity ≥99.999% is introduced, and a sputtering bias voltage of 750-850V is applied. The pulse duty cycle is set to 50%-80%, and the substrate is cleaned with ionized argon ions for 5-10 minutes.

[0055] (3) After cleaning, the argon flow rate is set to 85-90 sccm, the working pressure is fixed at 2-3 Pa, the substrate rotation speed is set to 10-20 rpm, the sputtering temperature is set to 20-30 ℃, the RF power supply power is set to 38-42 W, the DC power supply power is set to 8-12 W, the sputtering bias voltage is set to 0-150 V, and the pulse duty cycle is set to 50%-80%. The first sputtering lasts 12-17 minutes. After sputtering, the RF and DC power supplies are turned off for 10-30 minutes. The second sputtering lasts 12-17 minutes. After sputtering, the RF and DC power supplies are turned off for 10-30 minutes. This process is repeated 3-5 times. The film is grown by intermittent sputtering. After intermittent sputtering, the RF and DC power supplies are turned off. After maintaining the film under vacuum for 1-2 hours, a fibrous feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness is obtained.

[0056] In this invention, the drying temperature after cleaning of the single-sided polished silicon oxide wafer and polyimide substrate is 50–70 °C. The purity of both the tellurium-bismuth alloy target and the elemental tellurium target used in this invention is ≥99.9%. The atomic ratio of Bi to Te in the tellurium-bismuth alloy target is 2:3. The dimensions of both the tellurium-bismuth alloy target and the elemental tellurium target are Φ74.2 × 4 mm, and the backplate dimensions are Φ76.2 × 4 mm. Other tellurium-bismuth alloy targets and elemental tellurium targets with different parameters can also be selected, as long as the desired effect of this invention is achieved. The argon gas used in this invention is high-purity argon gas with a purity ≥99.999%. During the pretreatment process of the silicon oxide wafer and polyimide substrate, ultrasonic cleaning is performed at least three times, each time for 3–5 minutes. Water and alcohol must be replaced before each cleaning.

[0057] Example 1

[0058] A method for preparing a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film includes the following steps:

[0059] (1) Select single-sided polished silicon oxide wafers and polyimide as substrates, immerse them in water and alcohol, and then clean them three times with an ultrasonic cleaner for 4 minutes each time. The water and alcohol must be changed before each cleaning. After cleaning, dry the substrate surface at 70 °C. Fix the substrate to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then put it into the sputtering cavity. The silicon oxide wafer is in the center and the polyimide is around the perimeter. The silicon oxide wafer substrate and the polyimide substrate are on the same horizontal plane. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 4 mm.

[0060] (2) Fix the tellurium-bismuth alloy target to the DC power supply and the tellurium elemental target to the RF power supply. Adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target, and the substrate to 100 mm. Close the chamber door and wait for the mechanical pump and molecular pump to evacuate the vacuum in the chamber to 5 × 10⁻⁶ mm. -4After Pa is below, high-purity argon gas with a purity of ≥99.999% is introduced, and an 800V sputtering bias voltage is applied. The pulse duty cycle is set to 80%, and the substrate is cleaned for 5 minutes using ionized argon ions.

[0061] (3) After cleaning, the argon flow rate was set to 90 sccm, the working pressure was fixed at 3 Pa, the substrate rotation speed was set to 15 rpm, the sputtering temperature was set to 25 ℃, the RF power supply power was set to 40 W, the DC power supply power was set to 10 W, the sputtering bias was set to 50 V, and the pulse duty cycle was set to 80%. The first sputtering lasted 15 minutes, and after sputtering, the RF and DC power supplies were turned off for 20 minutes. The second sputtering lasted 15 minutes, and after sputtering, the RF and DC power supplies were turned off for 20 minutes. This process was repeated a total of 4 times. The intermittent sputtering method was used to grow the film to prevent the substrate temperature from rising due to continuous sputtering. At the same time, intermittent sputtering allows the atoms on the film surface to fully relax, which is more conducive to the growth of the film. After the intermittent sputtering was completed, the RF and DC power supplies were turned off, and the film was kept under vacuum for 1 hour to obtain a fibrous feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness.

[0062] Comparative Example 1

[0063] A method for preparing a bismuth telluride thermoelectric thin film includes the following steps:

[0064] (1) Select single-sided polished silicon oxide wafers and polyimide as substrates, immerse them in water and alcohol, and then clean them three times with an ultrasonic cleaner for 5 minutes each time. The water and alcohol must be changed before each cleaning. After cleaning, dry the substrate surface at 70 °C. Fix the substrate to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then put it into the sputtering cavity. The silicon oxide wafer is in the center and the polyimide is around the perimeter. The silicon oxide wafer substrate and the polyimide substrate are on the same horizontal plane. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 4 mm.

[0065] (2) Fix the tellurium-bismuth alloy target to the DC power supply and the tellurium elemental target to the RF power supply. Adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target, and the substrate to 100 mm. Close the chamber door and wait for the mechanical pump and molecular pump to evacuate the vacuum in the chamber to 5 × 10⁻⁶ mm. -4 After Pa is below, high-purity argon gas with a purity of ≥99.999% is introduced, and an 800V sputtering bias voltage is applied. The pulse duty cycle is set to 80%, and the substrate is cleaned for 5 minutes using ionized argon ions.

[0066] (3) After cleaning, the argon flow rate was set to 90 sccm, the working pressure was fixed at 3 Pa, the substrate rotation speed was set to 15 rpm, the sputtering temperature was set to 25 ℃, the RF power was set to 40 W, the DC power was set to 10 W, the sputtering bias was set to 50 V, the pulse duty cycle was set to 80%, and sputtering was carried out for 20 minutes. After continuous sputtering, the RF and DC power supplies were turned off, and the film was kept under vacuum for 1 hour to obtain a bismuth telluride thermoelectric film.

[0067] Comparative Example 2

[0068] The comparative example uses the same method and parameters as Example 1, except that the sputtering bias is set to 200 V and the pulse duty cycle is set to 80% in step (3).

[0069] Example 2

[0070] The method and parameters of this embodiment are the same as those of embodiment 1, except that the sputtering process is repeated a total of 3 times in step (3).

[0071] Example 3

[0072] A method for preparing a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film includes the following steps:

[0073] (1) Select single-sided polished silicon oxide wafers and polyimide as substrates, immerse them in water and alcohol, and then clean them 4 times each with an ultrasonic cleaner for 3 minutes each time. The water and alcohol must be changed before each cleaning. After cleaning, dry the substrate surface at 50 ℃. Fix the substrate to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then put it into the sputtering cavity. The silicon oxide wafer is in the center and the polyimide is around the perimeter. The silicon oxide wafer substrate and the polyimide substrate are on the same horizontal plane. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 5 mm.

[0074] (2) Fix the tellurium-bismuth alloy target to the DC power supply and the tellurium elemental target to the RF power supply. Adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target, and the substrate to 105 mm. Close the chamber door and wait for the mechanical pump and molecular pump to evacuate the vacuum in the chamber to 1×10⁻⁶ mm. -4 After Pa is below, high-purity argon gas with a purity of ≥99.999% is introduced, and an 850V sputtering bias voltage is applied with the pulse duty cycle set to 50%. The substrate is cleaned for 6 minutes using ionized argon ions.

[0075] (3) After cleaning, the argon flow rate was set to 85 sccm, the working pressure was fixed at 3 Pa, the substrate rotation speed was set to 10 rpm, the sputtering temperature was set to 30 ℃, the RF power supply power was set to 42 W, the DC power supply power was set to 12 W, the sputtering bias voltage was set to 130 V, and the pulse duty cycle was set to 60%. The first sputtering lasted 12 minutes, and after sputtering, the RF and DC power supplies were turned off for 10 minutes. The second sputtering lasted 12 minutes, and after sputtering, the RF and DC power supplies were turned off for 10 minutes. This process was repeated a total of 5 times. The intermittent sputtering method was used to grow the film to prevent the substrate temperature from rising due to continuous sputtering. At the same time, intermittent sputtering allows the atoms on the film surface to fully relax, which is more conducive to the growth of the film. After the intermittent sputtering was completed, the RF and DC power supplies were turned off, and the film was kept under vacuum for 1.5 hours to obtain a fibrous feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness.

[0076] Example 4

[0077] A method for preparing a highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film includes the following steps:

[0078] (1) Select single-sided polished silicon oxide wafers and polyimide as substrates, immerse them in water and alcohol, and then clean them three times with an ultrasonic cleaner for 5 minutes each time. The water and alcohol must be changed before each cleaning. After cleaning, dry the substrate surface at 60 ℃. Fix the substrate to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then put it into the sputtering cavity. The silicon oxide wafer is in the center and the polyimide is around the perimeter. The silicon oxide wafer substrate and the polyimide substrate are on the same horizontal plane. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 2 mm.

[0079] (2) Fix the tellurium-bismuth alloy target to the DC power supply and the tellurium elemental target to the RF power supply. Adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target, and the substrate to 95 mm. Close the chamber door and wait for the mechanical pump and molecular pump to evacuate the vacuum in the chamber to 3 × 10⁻⁶ mm. -4 After Pa is below, high-purity argon gas with a purity of ≥99.999% is introduced, and a sputtering bias of 750V is applied with the pulse duty cycle set to 70%. The substrate is cleaned for 10 minutes using ionized argon ions.

[0080] (3) After cleaning, the argon flow rate was set to 87 sccm, the working pressure was fixed at 2 Pa, the substrate rotation speed was set to 20 rpm, the sputtering temperature was set to 20 ℃, the RF power supply power was set to 38 W, the DC power supply power was set to 8 W, the sputtering bias was set to 0 V, and the pulse duty cycle was set to 50%. The first sputtering lasted 17 minutes, and after sputtering, the RF and DC power supplies were turned off for 30 minutes. The second sputtering lasted 17 minutes, and after sputtering, the RF and DC power supplies were turned off for 30 minutes. This process was repeated a total of 4 times. The intermittent sputtering method was used to grow the film to prevent the substrate temperature from rising due to continuous sputtering. At the same time, intermittent sputtering allows the atoms on the film surface to fully relax, which is more conducive to the growth of the film. After the intermittent sputtering was completed, the RF and DC power supplies were turned off, and the film was kept under vacuum for 2 hours to obtain a fibrous feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness.

[0081] Example 5

[0082] The method and parameters of this embodiment are the same as those of embodiment 1, except that the sputtering bias voltage is set to 5 V and the pulse duty cycle is set to 80% in step (3).

[0083] Example 6

[0084] The method and parameters of this embodiment are the same as those of embodiment 1, except that the sputtering bias voltage in step (3) is set to 150 V and the pulse duty cycle is set to 70%.

[0085] from Figure 3 As can be seen from the X-ray diffraction results of all examples and comparative examples, the maximum diffraction peak is observed at (015), indicating that the grown bismuth telluride thermoelectric films of Examples 1-2 and Comparative Examples 1-2 are bismuth telluride thermoelectric films with a preferred (015) orientation. In addition, diffraction peaks with a (110) orientation were also observed in Example 1, indicating random stacking of grains. Compared with the (015) orientation, this special film orientation is energy-disadvantageous and requires very high-density element packing during deposition; therefore, this orientation was only observed in Example 1, where the deposition time was longer.

[0086] from Figure 4 As can be seen from the image, the surface of the thin film prepared in Example 2 of this invention was observed using a scanning electron microscope. The film surface showed similar grain size, uniform distribution, and no obvious pores, exhibiting the characteristics of high-quality thin film deposition.

[0087] from Figure 5As can be seen, the feather-shaped nanocrystalline bismuth telluride thermoelectric films prepared in Examples 1 and 3 of this invention are composed of numerous nanocrystals aggregated together, exhibiting a gradient grain size distribution from bottom to top, with high-density fibrous stacking faults within the grains. Compared to traditional single-sized columnar, hexagonal spiral, and hexagonal grains, the smaller grains at the bottom of the feather-shaped nanocrystals provide strength, while the larger grains at the top provide the ability for plastic deformation, achieving a synergistic improvement in strength and plasticity.

[0088] from Figure 6 As can be seen from the high-resolution transmission electron microscope, high-density fibrous stacking faults were observed inside Example 3. These fibrous stacking faults, by constraining the slip layers, further hinder the relative movement of the slip layers, allowing the material to absorb more energy during deformation and exhibiting a better toughening effect. By hindering dislocation movement, stacking faults increase energy dissipation within the grains, thereby synergistically enhancing the strength and toughness of the bismuth telluride thermoelectric thin film.

[0089] The film was found to be (015) oriented by measuring the lattice spacing, which is consistent with the previous X-ray diffraction results.

[0090] from Figure 7 As can be seen, the average grain size of Example 1 is 32.28 nm, and the average grain size of Example 2 is 28.82 nm, both of which are larger than the average grain size of Comparative Example 1 (20.24 nm). Based on the "Holpage" effect—that material strength increases with decreasing grain size—and the theory of the mutual exclusion of strength and toughness (i.e., high-strength materials have poor toughness), Examples 1 and 2 exhibit better flexibility than Comparative Example 1.

[0091] Figure 8 Experimental Procedure and Parameter Description: A miniature integrated mechanical testing system was used to conduct uniaxial tensile tests on the prepared thin film. The film size was 60 mm × 10 mm, and the clamping distance was 20 mm. The resistance change curve of the film during the tensile process was acquired using the "IT" mode of an electrochemical workstation. The electrode clamps were fixed at both ends of the film, the voltage was constant at 10 V, and the current sensitivity was 10. -3 A. When a thin film undergoes elastic deformation, the resistance increases linearly due to the absence of damage. As strain increases further, damage will initiate, and the presence of microcracks will significantly increase the resistance, causing the resistance change curve to deviate from the linear phase. Therefore, the strain corresponding to the abrupt change in the rate of resistance change is the critical strain for crack initiation.

[0092] from Figure 8As can be seen, Example 1 has a critical strain of up to 7.3% for crack initiation, and Example 2 has a critical strain of 3.1%, both of which are higher than the critical strain values ​​of 1.8% and 0.3% for Comparative Examples 1-2, respectively, demonstrating good flexibility, which corresponds to the previous average grain size results.

[0093] Figure 9 Experimental procedure and parameter description: A bending cycle test was conducted on the prepared thin film using a self-made bending device. The film size was 60 mm × 10 mm, the clamping distance was 20 mm, and the bending radius was fixed at 8 mm. The film resistance variation curve during the bending cycle was acquired using the "IT" mode of an electrochemical workstation. The electrode clamps were fixed at both ends of the film, the voltage was constant at 10 V, and the current sensitivity was 10. -3 A. Using finite element analysis software, the strain of the upper and lower surfaces of the membrane during the bending cycle was calculated in elastic buckling analysis mode. During the calculation, one end of the membrane was kept fixed, while the other end was displaced inward until the bending radius of the membrane was 8 mm.

[0094] from Figure 9 As can be seen, the upper surface of the film is under tension and the lower surface is under compression. The maximum strain under tension is 1.93%, and the maximum strain under compression is 1.78%. Analysis of the resistance change of the film during bending cycles reveals that the resistance of Example 1 only increases by 20% after 10,000 bending cycles, and the increase in film resistance at 1,000 and 2,000 bending cycles is lower than that in other references.

[0095] Figure 10 Experimental procedure and parameter description: The surface of the thin film in Example 1 before and after 3000 bending cycles was observed under a scanning electron microscope. The scanning voltage was set to 5 kV, and the magnification was 10000x.

[0096] from Figure 10 As can be seen, compared with before bending, the film surface of Example 1 showed no obvious cracks after bending 3000 times, exhibiting good ductility.

[0097] Figure 11 Experimental procedure and parameter description: The thermoelectric material testing system was used to test the conductivity of the thin film (… σ ) and temperature ( T The relationship between the two was measured. The thin film was clamped and fixed on the sample stage. One end of the sample stage was fixed at room temperature, while the other end was heated to the set measurement temperature. The conductivity of the thin film at different temperatures could be measured using a pair of probes. The measurement temperature range was set to 300K-550K, with a total of 6 measurement temperature points. Data was collected 3 times at each temperature point and the average value was taken. The distance between the probes was fixed at 6mm.

[0098] from Figure 11As can be seen, the conductivity of both Example 1 and Comparative Example 1 increases with increasing temperature. Meanwhile, the conductivity of Example 1 is always higher than that of Comparative Example 1, exhibiting superior electrical performance.

[0099] Figure 12 Experimental procedure and parameter description: A thermoelectric material testing system was used to test the power factor (PF) of thin films in relation to temperature (…). T The relationship between the thin film and the sample stage was measured. The thin film was clamped and fixed on the sample stage. One end of the sample stage was fixed at room temperature, while the other end was heated to the set measurement temperature. The power factor of the thin film at different temperatures could be measured using a pair of probes. The measurement temperature range was set to 300 K-550 K, with a total of 6 measurement temperature points. Data was collected 3 times at each temperature point and the average value was taken. The distance between the probes was fixed at 6 mm.

[0100] from Figure 12 As can be seen, the power factor of Example 1 increases with increasing temperature, reaching a maximum of 2.76 μWm at 550 K. -1 K -2 .

[0101] from Figure 13 As can be seen, fibrous, feather-like nanocrystals can effectively scatter low-frequency phonons without affecting electron transport, thus maintaining high electrical conductivity while reducing thermal conductivity. According to... ZT Formula for calculating value ZT = S 2 σT / κ ( S , σ , κ and T (representing Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively) It can be found that low thermal conductivity and high electrical conductivity can improve the thermoelectric properties of materials.

[0102] Figure 14 The experimental procedure and parameter description: The film of Example 1 after being bent 3000 times was selected, copper glue was attached to both ends of the film, and it was connected to an electrochemical workstation through electrode clamps, where the voltage response could be detected. That is, when a finger touches the film at room temperature, due to the temperature difference between the body temperature and the ambient temperature at both ends of the film, the film can act as a power source to output voltage.

[0103] from Figure 14 As can be seen, the film of Example 1, after being bent 3000 times, can still stably output a voltage of 1mV using body temperature and ambient temperature difference, and the voltage direction can be adjusted by controlling the contact position between body temperature and electrode.

[0104] This invention compares with references 1-9 in the background art from four aspects: preparation method, preparation temperature, microstructure, and mechanical properties, as shown in Table 1:

[0105] Table 1. Comparison of preparation methods, parameters, and performance between Example 1 and prior art documents 1-9

[0106]

[0107] In summary, this invention employs a magnetron sputtering co-sputtering method to prepare bismuth telluride thermoelectric thin films in a single step at room temperature. Compared to traditional methods, no heating is required during or after the deposition process. The preparation process is streamlined, eliminating the need for multiple steps and achieving bismuth telluride thermoelectric thin film preparation in a single step at room temperature. Furthermore, compared to single-target sputtering, co-sputtering allows for better control of the film composition and sputtering rates of each target. This invention offers a simple and highly operable preparation method, facilitating large-scale industrial production.

[0108] Structurally, the bismuth telluride thermoelectric films prepared by this invention are all polycrystalline. Since the grain boundaries can effectively prevent crack propagation, they have better toughness and crack propagation resistance compared to traditionally prepared single-crystal films. In addition, compared to traditional single-sized columnar, hexagonal spiral, and hexagonal grains, the bismuth telluride thermoelectric films prepared by this invention are composed of numerous nanocrystals of different sizes aggregated together to form feather-like nanocrystals with a gradient grain size from bottom to top, and the interior of the grains is rich in high-density fibrous stacking faults.

[0109] In terms of mechanical properties, the bismuth telluride thermoelectric thin film prepared by this invention exhibits a critical strain of ~7.3% for crack formation under uniaxial tension, approaching the ~10% critical strain for crack formation in metallic copper thin films under uniaxial tension. At a bending radius of 8 mm, it can be repeatedly bent more than 10,000 times, far exceeding the 2,000 times of other thin films. Furthermore, its resistivity increase after 3,000 bends is comparable to other thin films, while the resistivity increase after 10,000 bends is only 20%. Therefore, the degree of bending and the number of bends of the bismuth telluride thermoelectric thin film prepared by this invention are higher than those prepared by conventional methods. This is because, according to the fine-grain strengthening theory, the smaller grain size at the bottom of the bismuth telluride thermoelectric thin film prepared by this invention provides strength, while the larger grain size at the top provides plastic deformation capability, achieving a synergistic improvement in strength and plasticity. Simultaneously, the high-density fibers (stacking faults) grown within the feather-like grains provide more mobile dislocations. The increase in dislocation density leads to more dislocation slip, and the high density of stacking faults enhances the resistance to dislocation slip, thus achieving the effect of strengthening and toughening.

[0110] In terms of thermoelectric properties, as the grain size increases, the reduction in the number of grain boundaries effectively reduces phonon scattering. However, the presence of numerous fibers within the grains does not reduce electron scattering. Consequently, the resulting feather-like bismuth telluride thermoelectric thin film with nanofibers exhibits high conductivity and a high power factor at high temperatures, reaching as high as 2.76 μWm at 550 K. -1 K -2 Furthermore, the fibrous, feather-like nanocrystalline bismuth telluride thermoelectric film prepared in this invention can still be connected to electrodes at both ends after being bent 3000 times, and can stably output a 1mV voltage using the temperature difference between body temperature and the environment. The voltage direction can be adjusted by controlling the contact position between body temperature and the electrode. This indicates that the fibrous, feather-like nanocrystalline bismuth telluride thermoelectric film prepared in this invention, after reasonable series encapsulation, can meet the needs of body temperature power generation in flexible wearable devices, and has potential commercial prospects.

[0111] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly tough, fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film, characterized in that, Includes the following steps: (1) Using silicon oxide wafers and polyimide as substrates, the substrates are fixed to the base plate and then installed into the sputtering cavity; (2) Fix the tellurium-bismuth alloy target on the DC power supply, fix the tellurium elemental target on the RF power supply, and adjust the distance between the tellurium-bismuth alloy target, the tellurium elemental target and the substrate, and clean the substrate by ionization. (3) After cleaning, a highly tough fibrous feather-like nanocrystalline bismuth telluride thermoelectric thin film was grown by intermittent sputtering. In step (3), the intermittent sputtering method involves setting the parameters of argon flow rate, working pressure, substrate rotation speed, sputtering temperature, RF power supply power, DC power supply power, sputtering bias, and pulse duty cycle. The first sputtering lasts 12 to 17 minutes, and after sputtering, the RF and DC power supplies are turned off for 10 to 30 minutes. The second sputtering lasts 12 to 17 minutes, and after sputtering, the RF and DC power supplies are turned off for 10 to 30 minutes. This process is repeated 3 to 5 times. In the intermittent sputtering method, the argon flow rate is set to 85–90 sccm, the working pressure is fixed at 2–3 Pa, the substrate rotation speed is set to 10–20 rpm, the sputtering temperature is set to 20–30 ℃, the RF power supply power is set to 38–42 W, the DC power supply power is set to 8–12 W, the sputtering bias voltage is set to 0–150 V, and the pulse duty cycle is set to 50%–80%.

2. The method for preparing the highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film according to claim 1, characterized in that, In step (1), the pretreatment process of the silicon oxide wafer and the polyimide is to select a single-sided polished silicon oxide wafer and polyimide as the substrate, immerse them in water and alcohol, and then clean them with an ultrasonic cleaner. After cleaning, the substrate surface is dried.

3. The method for preparing the highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film according to claim 1, characterized in that, In step (2), the process of cleaning the substrate using the ionization method is to introduce argon gas under vacuum conditions, apply a sputtering bias voltage, set a pulse duty cycle, and use the ionized argon ions to clean the substrate.

4. The method for preparing the highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film according to claim 1, characterized in that, In step (3), after intermittent sputtering, the radio frequency and DC power supplies are turned off, and the film is kept under vacuum for 1 to 2 hours to obtain a fibrous feather-like nanocrystalline bismuth telluride thermoelectric film with high toughness.

5. The method for preparing the highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film according to claim 1, characterized in that, In step (2), the distance between the tellurium-bismuth alloy target, the tellurium elemental target and the substrate is 95-105 mm.

6. The method for preparing the highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film according to claim 3, characterized in that, During the substrate cleaning process using the ionization method, the vacuum level is 1×10⁻⁶. -4 Pa ~ 5 × 10 -4 Pa; the sputtering bias voltage is 750–850V; the pulse duty cycle is set to 50%–80%.

7. The method for preparing the highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film according to claim 1, characterized in that, In step (1), the substrate is fixed to the base plate in the order of fixing the silicon oxide wafer first and then fixing the polyimide, and then it is installed into the sputtering cavity. The silicon oxide wafer is in the center position and the polyimide is around the perimeter. The distance between the outer edge of the silicon oxide wafer substrate and the inner edge of the polyimide substrate is 2 to 5 mm.

8. A highly tough fibrous, feather-like nanocrystalline bismuth telluride thermoelectric thin film, characterized in that, The thin film is prepared by the preparation method according to any one of claims 1 to 7.

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