A multi-period Bi2Te3 / ZnSb thermoelectric thin film material and a preparation method thereof

Abstract

The application discloses a kind of multi-period Bi2Te3 / ZnSb thermoelectric thin film materials and preparation method thereof, characterized in that the thin film material is deposited alternately by Bi2Te3 thin film layer and ZnSb thin film layer Composite, the thickness ratio of Bi2Te3 single layer and ZnSb single layer is (3-7):(7-3) and the thickness sum is 10nm, its preparation method steps are as follows: in the magnetron sputtering coating system, the sputtering power of fixed Bi2Te3 target and ZnSb target is 50W, the sputtering time of Bi2Te3 target is controlled to be 7-16s, the sputtering time of ZnSb target is 14-33s, double-target is sputtered alternately at room temperature, after 10 cycles, the deposited state multi-period Bi2Te3 / ZnSb thermoelectric thin film material is obtained, the advantages are that the composition is controllable and uniform, the performance is high, the intrinsic contradiction of decoupling conductivity and Seebeck coefficient can be solved, which is conducive to promoting higher thermoelectric performance.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, and in particular relates to a multi-period Bi2Te3 / ZnSb thermoelectric thin film material and its preparation method. Background Technology

[0002] Thermoelectric conversion technology is a novel clean energy technology that directly converts heat energy into electrical energy based on the Seebeck effect. Thermoelectric power generation devices made from thermoelectric materials have many outstanding advantages, such as requiring no transmission components, quiet operation, small size, and zero pollution, making them of great application value in fields such as thermoelectric power generation. Using thermoelectric materials to recover waste heat for power generation will generate enormous economic and social benefits.

[0003] The performance of thermoelectric semiconductor devices can be expressed by the dimensionless thermoelectric figure of merit ZT = S 2 The power factor (PF) of thermoelectric materials is expressed as σT / κ, where S, σ, κ, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. ZT is limited by the thermal conductivity of the material, which is an inherent property of the material. 2 σ directly represents the output capability of a thermoelectric device, and thermoelectric materials with high ZT and PF are extremely rare. The power factor depends on the Seebeck coefficient and conductivity, which are tunable. However, the Seebeck coefficient and conductivity of thermoelectric materials are strongly coupled, exhibiting an inverse relationship, meaning the power factor cannot be increased indefinitely but rather has a maximum point. This significantly limits the improvement of the material's thermoelectric performance. Therefore, it is necessary to develop novel thermoelectric materials with promising applications, breaking the coupling relationship between the Seebeck coefficient and conductivity to formulate strategies for improving their power factor. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a multi-periodic Bi2Te3 / ZnSb thermoelectric thin film material with a simple preparation process and a high power factor, and the preparation method thereof.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a multi-cycle Bi2Te3 / ZnSb thermoelectric thin film material, which is composed of alternating deposition of Bi2Te3 thin film layer and ZnSb thin film layer, wherein the thickness ratio of Bi2Te3 thin film layer to ZnSb thin film layer is (3~7):(7~3), the alternation cycle is 8-12 times, and the thickness of one cycle is 10nm.

[0006] Preferably, the thickness ratio of the Bi2Te3 thin film layer to the ZnSb thin film layer is 3:7.

[0007] Preferably, the thickness ratio of the Bi2Te3 thin film layer to the ZnSb thin film layer is 5:5.

[0008] Preferably, the thickness ratio of the Bi2Te3 thin film layer to the ZnSb thin film layer is 7:3.

[0009] Preferably, the alternation cycle of the Bi2Te3 thin film layer and the ZnSb thin film layer is 10 times. One layer of Bi2Te3 and one layer of ZnSb constitutes one cycle, and each sample has an alternation cycle of ten times, resulting in ten layers of Bi2Te3 and ten layers of ZnSb.

[0010] Preferably, the thin film material is obtained by alternating sputtering of a Bi2Te3 alloy target and a ZnSb alloy target in a magnetron sputtering coating system.

[0011] The specific steps of the above-mentioned multi-period Bi2Te3 / ZnSb thin film material preparation method are as follows: In the magnetron sputtering deposition system, a quartz wafer or a silicon oxide wafer is used as the substrate. Bi2Te3 alloy targets and ZnSb alloy targets are respectively installed in two magnetron RF sputtering targets. The sputtering chamber of the magnetron sputtering deposition system is evacuated until the vacuum level reaches 6.0 × 10⁻⁶. -6 Pa, then high-purity argon gas with a volume flow rate of 50 mL / min is introduced into the sputtering chamber until the gas pressure in the sputtering chamber reaches the starting gas pressure required for sputtering. Then, the sputtering power of the Bi2Te3 target is fixed at 50 W, the sputtering power of the ZnSb target is fixed at 50 W, the sputtering time of the Bi2Te3 target is adjusted to 7-16 s, and the sputtering time of the ZnSb target is adjusted to 14-33 s. The film is deposited by alternating sputtering of the two targets at room temperature. After 10 cycles, the multi-period Bi2Te3 / ZnSb thermoelectric thin film material in the deposited state is obtained. The thickness ratio of the Bi2Te3 monolayer to the ZnSb monolayer is (3-7):(7-3) and the sum of the thicknesses is 10 nm.

[0012] Compared with existing technologies, the advantages of this invention are as follows: This invention provides a multi-period Bi₂Te₃ / ZnSb thermoelectric thin film material and its preparation method, wherein the thickness ratio of Bi₂Te₃ to ZnSb in the thin film is Bi₂Te₃ / ZnSb(3:7), Bi₂Te₃ / ZnSb(5:5), and Bi₂Te₃ / ZnSb(7:3). Compared with traditional thermoelectric materials, multi-period thin films generally have better thermoelectric properties because there is interface optimization and band engineering inside the thin film, which refines the carrier transport. Preferably, the multi-period Bi₂Te₃ / ZnSb(3:7) thermoelectric material has the highest Seebeck coefficient of 265.1 μW / mK. 2 The pure ZnSb thin film exhibits the highest power factor at 584 K, which is 186 μW / mK. 2 [Chem.Eng.J.,2022,444:136599], the highest power factor of pure Bi2Te3 thin film is 85.2 μW / mK. 2This invention optimizes the thermoelectric performance of multi-period nanocomposite thermoelectric thin films from a structural perspective. By combining materials with different carrier concentrations, a carrier distribution corresponding to the asymmetric Fermi level is introduced, decoupling the contradictory relationship between the Seebeck coefficient and conductivity, and obtaining a higher power factor, which is more than three times higher than that of pure Bi2Te3. Attached Figure Description

[0013] Figure 1 The X-ray diffraction patterns of the monolayer Bi2Te3 thin film of the present invention at different annealing temperatures are shown below.

[0014] Figure 2 X-ray diffraction patterns of the multi-period Bi2Te3 / ZnSb(3:7) thin film of the present invention at different annealing temperatures;

[0015] Figure 3 The X-ray diffraction patterns of the multi-period Bi2Te3 / ZnSb(5:5) thin film of the present invention at different annealing temperatures are shown below.

[0016] Figure 4 The X-ray diffraction patterns of the multi-period Bi2Te3 / ZnSb(7:3) thin film of the present invention at different annealing temperatures are shown below.

[0017] Figure 5 The graph shows the relationship between the conductivity of the monolayer Bi2Te3, 10-cycle Bi2Te3 / ZnSb (3:7), Bi2Te3 / ZnSb (5:5) and Bi2Te3 / ZnSb (7:3) films of the present invention and temperature.

[0018] Figure 6 The graph shows the Seebeck coefficient of the monolayer Bi2Te3, 10-cycle Bi2Te3 / ZnSb (3:7), Bi2Te3 / ZnSb (5:5) and Bi2Te3 / ZnSb (7:3) films of the present invention as a function of temperature.

[0019] Figure 7 The graph shows the power factor of the monolayer Bi2Te3, 10-cycle Bi2Te3 / ZnSb (3:7), Bi2Te3 / ZnSb (5:5) and Bi2Te3 / ZnSb (7:3) films of the present invention as a function of temperature.

[0020] Figure 8 This is a transmission electron microscopy (TEM) image of the multi-period Bi2Te3 / ZnSb(3:7) thin film of the present invention after annealing at 550K.

[0021] Figure 9The power factor of the single-layer Bi2Te3, 5-cycle Bi2Te3 / ZnSb(3:7), Bi2Te3 / ZnSb(5:5) and Bi2Te3 / ZnSb(7:3) thermoelectric thin films of the present invention is related to temperature. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. I. Specific Implementation Methods

[0024] Example 1

[0025] A multi-period Bi₂Te₃ / ZnSb thin film material is disclosed, which is composed of alternating Bi₂Te₃ and ZnSb thin film layers with a thickness ratio of 3:7. The specific steps are as follows: In a magnetron sputtering deposition system, a quartz wafer or silicon oxide wafer is used as the substrate. Bi₂Te₃ alloy targets and ZnSb alloy targets are respectively installed in two magnetron RF sputtering targets. The sputtering chamber of the magnetron sputtering deposition system is evacuated until the vacuum level reaches 6.0 × 10⁻⁶. -6 Pa, and then high-purity argon gas with a volume flow rate of 50 mL / min is introduced into the sputtering chamber until the gas pressure in the sputtering chamber reaches the starting gas pressure required for sputtering. Then, the sputtering power of Bi2Te3 target is fixed at 50 W, the sputtering power of ZnSb target is fixed at 50 W, the sputtering time of Bi2Te3 target is adjusted to 7 s (thickness of 3 nm), and the sputtering time of ZnSb target is adjusted to 33 s (thickness of 7 nm). At room temperature, the two targets are alternately sputtered to deposit a film. After 10 cycles, the multi-period Bi2Te3 / ZnSb thermoelectric thin film material in the deposited state is obtained.

[0026] The prepared thin film material was subjected to in-situ thermoelectric parameter testing. Figures 5-7 It can be seen that the thermoelectric properties of the thin film prepared in this example are as follows: in the range of 350-650K, its conductivity increases from 659.6 S / m to 36308.4 S / m (e.g., ...). Figure 5 (As shown); the Seebeck coefficient increased from 62.2 μV / K to 129.7 μV / K, and then decreased to 7.9 μV / K (as shown). Figure 6 (As shown); power factor from 5.5 μW / mK 2 Increased to 265.1 μW / mK 2 It then dropped to 2.2 μW / mK. 2 (like Figure 7 (As shown); in the range of 350-550K, the contradictory relationship between its Seebeck coefficient and conductivity is decoupled, and both increase with increasing temperature, which contributes to the rapid increase of the power factor.

[0027] Example 2

[0028] Similar to Example 1 above, the difference is that during the sputtering process, the sputtering time of the Bi2Te3 target is controlled to be 12s (thickness of 5nm) and the sputtering time of the ZnSb target is controlled to be 23s (thickness of 5nm). The film is deposited by alternating sputtering of the two targets at room temperature. After 10 cycles, a multi-cycle Bi2Te3 / ZnSb thermoelectric thin film material in the deposited state is obtained, with a Bi2Te3 to ZnSb thickness ratio of 5:5.

[0029] The prepared thin film material was subjected to in-situ thermoelectric parameter testing. Figures 5-7 The thermoelectric properties of the thin film prepared in this example can be seen as follows: In the range of 350-650 K, its conductivity increased from 548.9 S / m to 49775.6 S / m, and then decreased to 41719.7 S / m; the Seebeck coefficient increased from 6.9 μV / K to 46.3 μV / K, and then decreased to 10.5 μV / K; the power factor increased from 0.02 μW / mK. 2 Increased to 107.0 μW / mK 2 It then dropped to 4.6 μW / mK. 2 Within the range of 350-550K, the contradictory relationship between its Seebeck coefficient and conductivity is decoupled, and both increase with increasing temperature, leading to a rapid increase in the power factor.

[0030] Example 3

[0031] Similar to Example 1 above, the difference is that during the sputtering process, the sputtering time of the Bi2Te3 target is controlled to be 16s (thickness of 7nm) and the sputtering time of the ZnSb target is controlled to be 14s (thickness of 3nm). The film is deposited by alternating sputtering of the two targets at room temperature. After 10 cycles, a multi-cycle Bi2Te3 / ZnSb thermoelectric thin film material in the deposited state is obtained, with a Bi2Te3 to ZnSb thickness ratio of 7:3.

[0032] The prepared thin film material was subjected to in-situ thermoelectric parameter testing. Figures 5-7 The thermoelectric properties of the thin film prepared in this example can be seen as follows: In the range of 350-650 K, its conductivity increased from 2113.8 S / m to 51930.2 S / m; the Seebeck coefficient increased from -4.7 μV / K to 72.3 μV / K, and then decreased to 0.04 μV / K; the power factor increased from 0.05 μW / mK. 2 Increased to 221.4 μW / mK 2 It then decreased to 0.01 μW / mK. 2 Within the range of 350-550K, the contradictory relationship between its Seebeck coefficient and conductivity is decoupled, and both increase with increasing temperature, leading to a rapid increase in the power factor.

[0033] Controlled Trial

[0034] The process is basically the same as in Example 1, except that the alloy Bi2Te3 target is installed in a magnetron sputtering target, the sputtering power is set to 50W, and the single-target sputtering coating is carried out for 5 minutes at room temperature to obtain a pure Bi2Te3 thermoelectric thin film material.

[0035] The prepared thin film material was subjected to in-situ thermoelectric parameter testing. Figures 5-7 The thermoelectric properties of the thin film prepared in this example can be seen as follows: In the range of 300-650 K, its conductivity increased from 2721.8 S / m to 8598.0 S / m; the Seebeck coefficient increased from -85.4 μV / K to -108.3 μV / K, and then decreased to -99.6 μV / K; the power factor increased from 19.9 μW / mK. 2 Increased to 85.2 μW / mK 2 .

[0036] The sputtering times of the target materials, the thicknesses of Bi2Te3 and ZnSb in the different embodiments described above are shown in Table 1.

[0037] Table 1 Thickness ratio of multi-periodic Bi2Te3 / ZnSb thermoelectric thin film materials prepared under different conditions

[0038] II. Analysis of Experimental Results

[0039] The results of the different embodiments described above are analyzed as follows:

[0040] Figure 1 X-ray diffraction patterns of the deposited monolayer Bi₂Te₃ thermoelectric thin film are presented, obtained in the deposited state and after annealing at 400K, 500K, and 600K. The figures show that the pure Bi₂Te₃ thin film exhibits single-phase crystallization (Bi₂Te₃) behavior.

[0041] Figure 2 X-ray diffraction patterns of the deposited multi-period Bi₂Te₃ / ZnSb(3:7) thermoelectric thin film are presented in the deposited state, after annealing at 400 K, 500 K, 550 K, and 600 K, and in the deposited state. The figures show that the multi-period Bi₂Te₃ / ZnSb(3:7) thin film exhibits behavior ranging from single-phase precipitation (ZnSb) to multi-phase coexistence (ZnSb, Sb₂Te, and (Bi,Sb)).

[0042] Figure 3X-ray diffraction patterns of the deposited multi-period Bi₂Te₃ / ZnSb(5:5) thermoelectric thin film are presented in the deposited state, after annealing at 400 K, 500 K, 550 K, and 600 K, and in the deposited state. The figures show that the multi-period Bi₂Te₃ / ZnSb(5:5) thin film exhibits behavior ranging from single-phase precipitation (ZnSb) to multi-phase coexistence (ZnSb, Sb₂Te, and (Bi,Sb)).

[0043] Figure 4 X-ray diffraction patterns of the deposited multi-periodic Bi₂Te₃ / ZnSb(7:3) thermoelectric thin film are presented in the deposited state, after annealing at 400 K, 500 K, 550 K, and 600 K, and in the deposited state. The figures show that the multi-periodic Bi₂Te₃ / ZnSb(7:3) thin film exhibits behavior ranging from single-phase precipitation (ZnSb) to multi-phase coexistence (ZnSb, Sb₂Te, and (Bi,Sb)).

[0044] Figure 5 The conductivity of Bi₂Te₃, Bi₂Te₃ / ZnSb(3:7), Bi₂Te₃ / ZnSb(5:5), and Bi₂Te₃ / ZnSb(7:3) thermoelectric films as a function of temperature is shown. We can see that the conductivity of the Bi₂Te₃, Bi₂Te₃ / ZnSb(3:7), and Bi₂Te₃ / ZnSb(7:3) samples all increase with increasing temperature, while the conductivity of the Bi₂Te₃ / ZnSb(5:5) sample shows a trend of first increasing and then decreasing. Furthermore, the conductivity of the multi-phase Bi₂Te₃ / ZnSb sample is much higher than that of the Bi₂Te₃ sample, indicating that the coexistence of ZnSb, Sb₂Te, and (Bi,Sb) phases contributes to the improvement of conductivity. The Bi₂Te₃ / ZnSb(7:3) sample has the highest conductivity at 650 K, reaching 51930.2 S / m.

[0045] Figure 6The Seebeck coefficients of Bi₂Te₃, Bi₂Te₃ / ZnSb(3:7), Bi₂Te₃ / ZnSb(5:5), and Bi₂Te₃ / ZnSb(7:3) thermoelectric thin films are shown as a function of temperature. We can see that the Seebeck coefficients of the Bi₂Te₃ samples are all negative, indicating their N-type conductivity, while the Seebeck coefficients of the Bi₂Te₃ / ZnSb(3:7), Bi₂Te₃ / ZnSb(5:5), and Bi₂Te₃ / ZnSb(7:3) samples are mostly positive, indicating their P-type semiconductors. With a gradual increase in the ZnSb content, the overall Seebeck coefficient of the thin film increases. Below 550 K, the absolute value of the Seebeck coefficient continues to increase with increasing temperature; above 550 K, the absolute value of the Seebeck coefficient decreases. This is consistent with the trend of conductivity, decoupling the contradictory relationship between the parameters. At 550 K, the Bi2Te3 / ZnSb(3:7) sample had the highest Seebeck coefficient, which was 129.7 μV / K.

[0046] Figure 7 The power factor of Bi₂Te₃, Bi₂Te₃ / ZnSb(3:7), Bi₂Te₃ / ZnSb(5:5), and Bi₂Te₃ / ZnSb(7:3) thermoelectric films versus temperature is shown. We can see that the power factor of the Bi₂Te₃ sample increases with temperature, while the power factors of the Bi₂Te₃ / ZnSb(3:7), Bi₂Te₃ / ZnSb(5:5), and Bi₂Te₃ / ZnSb(7:3) samples increase below 550 K and decrease above 550 K. At 550 K, the power factor of the Bi₂Te₃ / ZnSb(3:7) sample reaches its peak value of 265.1 μW / mK. 2 .

[0047] Figure 8 Transmission electron microscopy (TEM) images of the deposited Bi₂Te₃ / ZnSb(7:3) thermoelectric thin film after annealing at 550 K are presented. It can be seen that the layered structure disappears after annealing, the film becomes dense internally without voids, and the ZnSb, Sb₂Te, and (Bi,Sb) grains are randomly packed with distinct lattice fringes.

[0048] Figure 9 The power factor versus temperature variation graphs for five cycle-cycle thermoelectric thin films—Bi2Te3, Bi2Te3 / ZnSb(3:7), Bi2Te3 / ZnSb(5:5), and Bi2Te3 / ZnSb(7:3)—are presented. Their thermoelectric performance is lower than that of the sample with a cycle of 10. Therefore, this invention preferably describes the sample with a cycle of 10.

[0049] In summary, the multi-period Bi₂Te₃ / ZnSb thin-film thermoelectric material prepared in this invention addresses the issue from a structural perspective. It utilizes Zn-Sb phase change material and traditional Bi₂Te₃ thermoelectric material to fabricate multi-period Zn-Sb / Bi₂Te₃ thin films at the nanoscale as the functional medium for thermoelectric devices, improving the thermoelectric performance of traditional Bi₂Te₃ thin films. These films exhibit the highest electrical conductivity, approximately six times that of pure Bi₂Te₃. The coexistence of ZnSb, Sb₂Te, and (Bi,Sb) phases, along with refined grains, helps to decouple the contradictory relationship between the Seebeck coefficient and electrical conductivity, resulting in a higher power factor—nearly three times higher than that of pure Bi₂Te₃. Multi-period Bi₂Te₃ / ZnSb thin-film thermoelectric materials hold promise as a novel approach to improving the thermoelectric performance of thin-film materials.

[0050] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A multi-period Bi2Te3 / ZnSb thermoelectric thin film material, characterized in that: The thin film material is composed of alternating deposition of Bi2Te3 thin film layer and ZnSb thin film layer, with the thickness ratio of Bi2Te3 thin film layer to ZnSb thin film layer being 3:7 or 7:3, the alternation cycle being 8-12 times, and the thickness of one cycle being 10nm.

2. The multi-period Bi₂Te₃ / ZnSb thin film material according to claim 1, characterized in that: The Bi2Te3 thin film layer and the ZnSb thin film layer are alternated in a cycle of 10 times.

3. The multi-period Bi₂Te₃ / ZnSb thin film material according to claim 1, characterized in that: The thin film material is obtained by alternating sputtering of a Bi2Te3 alloy target and a ZnSb alloy target in a magnetron sputtering coating system.

4. A method for preparing the multi-period Bi2Te3 / ZnSb thin film material according to claim 1, characterized in that... The specific steps are as follows: In the magnetron sputtering coating system, a quartz wafer or a silicon oxide wafer is used as the substrate. Bi2Te3 alloy targets and ZnSb alloy targets are respectively installed in two magnetron RF sputtering targets. The sputtering chamber of the magnetron sputtering coating system is evacuated until the vacuum level reaches 6.0 × 10⁻⁶. -6 Pa, then high-purity argon gas with a volume flow rate of 50 mL / min is introduced into the sputtering chamber until the gas pressure in the sputtering chamber reaches the starting gas pressure required for sputtering. Then, the sputtering power of the Bi2Te3 target is fixed at 50 W, the sputtering power of the ZnSb target is fixed at 50 W, the sputtering time of the Bi2Te3 target is adjusted to 7-16 s, and the sputtering time of the ZnSb target is adjusted to 14-33 s. At room temperature, the two targets are alternately sputtered to deposit a film. After 10 cycles, a multi-period Bi2Te3 / ZnSb thermoelectric thin film material in the deposited state is obtained. The thickness ratio of the Bi2Te3 monolayer to the ZnSb monolayer is 3:7 or 7:3 and the sum of the thicknesses is 10 nm.

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