Bismuth-oxygen selenide thin films, their preparation methods and applications

Abstract

This application discloses bismuth-oxygen selenide thin films, their preparation methods, and applications. The method for preparing bismuth-oxygen selenide thin films includes: providing a bismuth-oxygen selenide target; placing the bismuth-oxygen selenide target in a deposition chamber; and evacuating the deposition chamber to a vacuum level less than or equal to 1 × 10⁻⁶. ‑4 At a temperature of 400℃~500℃ and maintained, a pulsed laser irradiates the bismuth-oxygen-selenium target, forming an elliptical spot on the target. This generates plasma on the target, forming a bismuth-oxygen-selenium thin film on the substrate. By forming an elliptical spot on the target, a rectangular bismuth-oxygen-selenium thin film with a certain aspect ratio can be obtained. This film has a large area and uniform composition and thickness. During the preparation process, the defect content in the film can be effectively changed by controlling the energy density of the pulsed laser. Using the above method, large-area bismuth-oxygen-selenium thin films can be controllably prepared, which is beneficial for obtaining high-quality bismuth-oxygen-selenium thin films that can be used as thermoelectric materials.

Description

Technical Field

[0001] This application relates to the field of thin film material preparation technology, specifically to bismuth oxy selenium thin films, their preparation methods, and applications. Background Technology

[0002] Bismuth oxide selenium crystal is a crystal composed of [Bi₂O₂]. n 2n+ and [Se] n 2n- Layered compound semiconductors formed by two alternating layers possess a certain band gap (approximately 0.8 eV) and ultra-high mobility (exceeding 20,000 cm⁻¹ at low temperatures). 2 V -1 s -1 Bismuth oxide selenium (BOS) is considered a highly promising electronic material. Currently, BOS thin films prepared by spin coating and chemical vapor deposition have found applications in optoelectronics, transistors, energy conversion, and storage. However, achieving large-area, high-quality, continuous fabrication remains a significant challenge.

[0003] Therefore, the methods for preparing bismuth oxide selenium thin films still need improvement. Summary of the Invention

[0004] This application is based on the inventor's discoveries and understanding of the following facts and problems:

[0005] Pulsed laser deposition (PLD) is a technique that generates plasma by injecting a laser to ablate a target, depositing plasma onto a substrate surface. It can be used to prepare multi-component thin films. For the bismuth-oxygen-selenium (BOX) system, the high volatility of Bi and Se allows for precise control of their stoichiometry during film growth, tailored to specific applications. While BOX crystals with different elemental proportions may have the same phase structure, the presence of various defects, such as Bi, O, and Se vacancies, leads to significant differences in band structure, carrier concentration, surface element valence states, and electrical transport properties. Therefore, developing a controllable method for preparing large-area BOX thin films is of great importance. Meanwhile, this high-quality bismuth-oxygen selenide thin film has intrinsically high mobility and various defect structures. The defect structures (including point defects) in the bismuth-oxygen selenide thin film can effectively scatter phonons and reduce the thermal conductivity of the film. In addition, the presence of defects can cause electron doping to a certain extent, changing the band structure of the material. Electron doping increases the electron concentration, and band structure optimization improves mobility, thereby improving the electrical conductivity of the material. Therefore, this bismuth-oxygen selenide thin film is also a highly valuable low-dimensional thermoelectric material.

[0006] This application aims to at least partially alleviate or resolve at least one of the aforementioned problems.

[0007] In one aspect of this application, a method for preparing a bismuth-oxygen selenide thin film is provided. In some embodiments of this application, the method for preparing the bismuth-oxygen selenide thin film includes: providing a bismuth-oxygen selenide target; placing the bismuth-oxygen selenide target in a deposition chamber; and evacuating the deposition chamber to a vacuum level less than or equal to 1 × 10⁻⁶. -4 At a temperature of 400℃~500℃ and maintained, a pulsed laser irradiates the bismuth-oxygen-selenium target, forming an elliptical spot on the target. This generates plasma on the target, forming a bismuth-oxygen-selenium thin film on the substrate. By forming an elliptical spot on the target, a rectangular bismuth-oxygen-selenium thin film with a certain aspect ratio can be obtained. This film has a large area and uniform composition and thickness. During the preparation process, the defect content in the film can be effectively changed by controlling the energy density of the pulsed laser. Using the above method, large-area bismuth-oxygen-selenium thin films can be controllably prepared, which is beneficial for obtaining high-quality bismuth-oxygen-selenium thin films that can be used as thermoelectric materials.

[0008] In some embodiments of this application, the energy density of the pulsed laser incident on the deposition cavity is 45 mJ / cm². -2 Up to 70mJ cm -2 Therefore, pulsed laser energy densities within the aforementioned range are beneficial for forming high-quality bismuth oxide selenium thin films.

[0009] In some embodiments of this application, the frequency of the pulsed laser is 5 Hz to 10 Hz. A pulsed laser frequency within this range is beneficial for film formation and for improving the smoothness of the film layer.

[0010] In some embodiments of this application, the preparation of the bismuth-oxygen-selenium target includes: using Bi, Bi₂O₃, and Se powders as raw materials, synthesizing the bismuth-oxygen-selenium target by a solid-state method. In the bismuth-oxygen-selenium target, Bi and Se are both in excess by 5% to 10% of their mass relative to Bi₂O₂Se. Bi and Se have strong volatility, and an excess of 5% to 10% of Bi and Se in the target is beneficial for forming a thin film with an atomic ratio of Bi, O, and Se around 2:2:1.

[0011] In some embodiments of this application, the diameter of the bismuth oxy selenide target is greater than or equal to 20 mm, and the thickness of the bismuth oxy selenide target is greater than or equal to 3 mm. Target dimensions within these ranges facilitate the generation of plasma by irradiating the target with a pulsed laser and the deposition of a thin film on the substrate.

[0012] In some embodiments of this application, the ratio of the major axis to the minor axis of the elliptical light spot is between 2:1 and 4:1. A ratio of the major and minor axes of the elliptical light spot within this range is advantageous for obtaining rectangular films with aspect ratios within a certain range.

[0013] In some embodiments of this application, the substrate is SrTiO3. Choosing this material as the substrate is advantageous for epitaxially growing bismuth oxide selenium thin films on the substrate.

[0014] In another aspect of this application, a bismuth oxy selenide thin film is proposed. In some embodiments of this application, the bismuth oxy selenide thin film is prepared using the method described above. Therefore, the bismuth oxy selenide thin film is a rectangular film with high intrinsic mobility and good thermoelectric properties.

[0015] In some embodiments of this application, the bismuth-oxygen selenide film satisfies at least one of the following conditions: the length-to-width ratio of the bismuth-oxygen selenide film is 15:8 to 3:1; the length of the bismuth-oxygen selenide film is 12 mm to 15 mm; the width of the bismuth-oxygen selenide film is 4 mm to 8 mm; and the thickness of the bismuth-oxygen selenide film is 10 nm to 100 nm.

[0016] In another aspect of this application, the use of the aforementioned bismuth-oxygen selenide thin film material is proposed, and in some embodiments of this application, the aforementioned bismuth-oxygen selenide thin film is used as a thermoelectric material. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0018] Figure 1 The conductivity of the bismuth oxide selenium thin films in Examples 1-5 of this application is shown as a function of temperature.

[0019] Figure 2 The Seebeck coefficient of the bismuth-oxygen selenide thin films in Examples 1-5 of this application is shown as a function of temperature.

[0020] Figure 3 The power factor of the bismuth oxide selenium thin films in Examples 1-5 of this application is shown as a function of temperature.

[0021] Figure 4 The X-ray diffraction patterns of the bismuth-oxygen selenide thin films in Examples 1 to 5 of this application are shown. Detailed Implementation

[0022] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0023] In one aspect of this application, a method for preparing a bismuth oxide selenium thin film is provided. In some embodiments of this application, the method for preparing a bismuth oxide selenium thin film may include the following steps:

[0024] S100: Provides bismuth oxygen selenide sputtering targets.

[0025] In this step, a bismuth-oxygen-selenium (BOS) target is provided. In some embodiments of this application, the diameter of the BOS target can be greater than or equal to 20 mm. For example, the diameter of the BOS target can be 20 mm to 30 mm, specifically 20 mm, 22 mm, 25 mm, 28 mm, 30 mm, etc. In some embodiments of this application, the thickness of the BOS target can be greater than or equal to 3 mm. For example, the thickness of the BOS target can be 3 mm to 10 mm, specifically 3 mm, 5 mm, 8 mm, 10 mm, etc. Therefore, the BOS target has suitable dimensions, which facilitates the generation of plasma and deposition of a thin film structure by irradiating the target with a pulsed laser.

[0026] It should be noted that bismuth-oxygen selenide targets can be roughly cylindrical, and the surface of bismuth-oxygen selenide targets can be roughly circular.

[0027] In some embodiments of this application, the preparation of the bismuth-oxygen selenide target may include the following steps: using Bi, Bi₂O₃, and Se powders as raw materials, the bismuth-oxygen selenide target is synthesized by a solid-state method. In some embodiments of this application, relative to Bi₂O₂Se, the mass of both Bi and Se in the bismuth-oxygen selenide target can be in excess by 5% to 10%. For example, the mass of Bi can be in excess by 5%, 6%, 7%, 8%, 9%, 10%, etc., and the mass of Se can be in excess by 5%, 6%, 7%, 8%, 9%, 10%, etc. This is beneficial for preparing a thin film structure with an atomic ratio of Bi, O, and Se of approximately 2:2:1. Furthermore, the composition and valence state of the bismuth-oxygen selenide thin film can be controlled by adjusting parameters such as laser energy density, frequency, and substrate temperature, thereby obtaining a thin film material with excellent electrotransport properties.

[0028] It should be noted that "compared to Bi2O2Se, the mass of Bi and Se in the bismuth-oxygen-selenium target can be in excess by 5% to 10%" means that the masses of Bi, O, and Se atoms in Bi2O2Se are A, B, and C, respectively. In the bismuth-oxygen-selenium target, the mass of Bi can be (105% to 110%)A, the mass of O is B, and the mass of Se can be (105% to 110%)C.

[0029] S200: Place the bismuth-oxygen-selenium target in the deposition chamber and evacuate the chamber to a vacuum level less than or equal to 1×10⁻⁶. -4 Pa, the substrate temperature is raised to 400℃~500℃ and kept at that temperature, and the pulsed laser irradiates the bismuth-oxygen selenide target, forming an elliptical spot on the bismuth-oxygen selenide target, causing the bismuth-oxygen selenide target to generate plasma and form a bismuth-oxygen selenide thin film on the substrate.

[0030] The bismuth oxy selenide thin film prepared by the above method has a rectangular surface with a large rectangular surface area, and the film has excellent electrical transport properties, making it suitable for use as a thermoelectric material.

[0031] In some embodiments of this application, the vacuum level of the deposition chamber can be 1×10⁻⁶. -4 Pa, 0.8×10 -4 Pa, 0.5×10 -4 Pa, 0.2×10 -4 Pa, 1×10 -5 Pa, etc., thus the vacuum degree of the deposition cavity is relatively high, which is beneficial to change the defect ratio of Bi, O and Se by adjusting parameters such as laser energy density.

[0032] In some embodiments of this application, during the deposition of a bismuth oxide selenium thin film, the vacuum level in the deposition chamber can be maintained at less than or equal to 1 × 10⁻⁶. -4 Pa, which is beneficial for preparing bismuth oxy selenide thin films with excellent performance.

[0033] In some embodiments of this application, the temperature of the substrate can be 400°C to 500°C. For example, the temperature of the substrate can be 400°C, 420°C, 450°C, 480°C, 500°C, etc. Setting the substrate temperature within the above range is beneficial for phase formation and for the production of bismuth oxide selenide thin films.

[0034] In some embodiments of this application, the substrate may be SrTiO3. Using SrTiO3 as a substrate is beneficial for the epitaxial growth of thin film materials on it, thereby facilitating the formation of bismuth oxide selenium thin films.

[0035] In some embodiments of this application, bismuth oxide selenide thin films can be epitaxially grown on substrates with SrTiO3 (0 0 1) orientation, and the prepared epitaxial bismuth oxide selenide thin films can serve as excellent low-dimensional thermoelectric materials.

[0036] In some embodiments of this application, the energy density of the pulsed laser incident on the deposition cavity can be 45 mJ / cm². -2 Up to 70mJ cm -2 During the deposition process, the energy density of the laser pulse can reach 45 mJ / cm². -2 Up to 70mJ cm -2 Continuous adjustment within a range; for example, the energy density of a pulsed laser can be 45 mJ / cm². -2 50mJ cm -2 55mJ cm -2 60mJ cm -2 65mJcm -2 70mJ cm -2Therefore, when the energy density of the pulsed laser is within the above range, plasma can be generated by irradiating the target material and deposited on the substrate to form a bismuth-oxygen selenide thin film. The pulsed laser with the above energy density can optimize the composition of the bismuth-oxygen selenide thin film, control the valence state, defect type and defect ratio of the three elements Bi, O and Se, etc., thereby optimizing the electrical transport properties of the bismuth-oxygen selenide thin film.

[0037] The pulsed laser deposition platform comprises a series of optical components. The laser beam, through reflection and focusing, ultimately acts on the target material. The energy density of the pulsed laser can be adjusted by modifying parameters such as the laser voltage, the area and angle of the optical lens irradiated by the laser, etc., to obtain an elliptical spot with relatively uniform energy density on the target surface. This application does not specifically limit the type of laser; those skilled in the art can choose according to the actual situation.

[0038] In some embodiments of this application, the frequency of the pulsed laser can be from 5Hz to 10Hz. For example, the frequency of the pulsed laser can be 5Hz, 6Hz, 7Hz, 8Hz, 9Hz, 10Hz, etc. Setting the frequency of the pulsed laser within the above range is more conducive to film formation and also helps to improve the flatness of the bismuth oxide selenium film.

[0039] In some embodiments of this application, the thickness of the bismuth oxide selenium thin film can be adjusted by changing the number of pulses. For example, under constant conditions such as temperature, oxygen pressure, and pulse laser frequency, the thickness of the prepared bismuth oxide selenium thin film can be adjusted to be within the range of 10 nm to 100 nm by changing the number of laser pulses.

[0040] In some embodiments of this application, the ratio of the major axis to the minor axis of the elliptical light spot can be from 2:1 to 4:1. For example, the ratio of the major axis to the minor axis of the elliptical light spot can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc. Thus, a rectangular thin film with an aspect ratio within a certain range can be formed. The length-to-width ratio of the bismuth oxide selenium thin film can be adjusted by adjusting the ratio of the major axis to the minor axis of the elliptical light spot.

[0041] In one embodiment of this application, the ratio of the major axis to the minor axis of the elliptical light spot is 2:1, and the ratio of the length to the width of the prepared bismuth oxy selenide thin film is 3:1.

[0042] In some embodiments of this application, the bismuth-oxygen-selenium target can rotate and revolve. The plane of the bismuth-oxygen-selenium target is a circle; rotation refers to revolving around the center of the circle, and revolution refers to moving around a point outside the circle along a great arc with a radius. The rotational speeds are not specifically limited in this application, and those skilled in the art can set and adjust them according to actual needs.

[0043] In summary, the method proposed in this application can be used to prepare rectangular homogeneous bismuth-oxygen selenide thin films. Furthermore, the composition of the bismuth-oxygen selenide thin film and the valence states of the three elements Bi, O, and Se can be controlled by adjusting parameters such as the energy density of the pulsed laser, the frequency of the pulsed laser, and the temperature of the substrate, thereby enabling the bismuth-oxygen selenide thin film to have high intrinsic mobility and various defect structures.

[0044] In another aspect of this application, a bismuth oxy selenide (BOS) thin film is proposed. In some embodiments of this application, the BOS thin film is prepared by the method described above. Thus, the BOS thin film is a rectangular homogeneous film, and it possesses high intrinsic mobility and various defect structures, making it suitable for use as a thermoelectric material.

[0045] In some embodiments of this application, the length-to-width ratio of the bismuth-oxygen selenide film can be from 15:8 to 3:1. For example, the length-to-width ratio of the bismuth-oxygen selenide film can be 15:8, 2:1, 5:2, 3:1, etc. Thus, the bismuth-oxygen selenide film has a suitable aspect ratio and can be used as a thermoelectric material.

[0046] In some embodiments of this application, the length of the bismuth oxide selenium film can be 12mm to 15mm, for example, the length of the bismuth oxide selenium film can be 12mm, 13mm, 14mm, 15mm, etc.

[0047] In some embodiments of this application, the width of the bismuth oxide selenium film can be 4mm to 8mm, for example, the width of the bismuth oxide selenium film can be 4mm, 5mm, 6mm, 7mm, 8mm, etc.

[0048] In some embodiments of this application, the thickness of the bismuth oxide selenium thin film can be from 10 nm to 100 nm, for example, the thickness of the bismuth oxide selenium thin film can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, etc. Therefore, the bismuth oxide selenium thin film is relatively thin and can be used as a low-dimensional thermoelectric material. The bismuth oxide selenium thin film prepared using the method proposed in this application is relatively thin, and has uniform composition and thickness, indicating that the preparation method proposed in this application has high reliability.

[0049] In some embodiments of this application, the length of the bismuth oxide selenium film can be 12 mm, and the width can be 4 mm. In some embodiments of this application, the length of the bismuth oxide selenium film can be 15 mm, and the width can be 8 mm. Therefore, the bismuth oxide selenium film has suitable dimensions, a large area, and can be used as a thermoelectric material.

[0050] In another aspect of this application, uses of the aforementioned bismuth-oxygen-selenium thin film are proposed. In some embodiments of this application, the aforementioned bismuth-oxygen-selenium thin film can be used as a thermoelectric material.

[0051] The present application will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the present application in any way. Furthermore, in the following embodiments, unless otherwise specified, the materials and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0052] Example 1

[0053] Bismuth-oxygen-selenium (BOS) targets were synthesized via a solid-state method using Bi, Bi₂O₃, and Se powders as raw materials. The BOS targets were placed in a deposition chamber, which was then evacuated to a vacuum level less than or equal to 1 × 10⁻⁶. -4 Pa, the substrate temperature is raised to 400℃~500℃ and held at that temperature. A pulsed laser irradiates the bismuth-oxygen-selenium target, forming an elliptical spot on the target, generating plasma and forming a bismuth-oxygen-selenium thin film on the substrate. In Example 1, the energy density of the pulsed laser incident on the deposition cavity is 49.5 mJ / cm². -2 The frequency of the pulsed laser was 5 Hz, the duration of the pulsed laser was 5 min, and the substrate was SrTiO3.

[0054] Example 2

[0055] Unlike Example 1, the energy density of the pulsed laser incident on the deposition cavity in Example 2 is 51.5 mJ / cm². -2 The remaining steps and parameters are the same as in Example 1.

[0056] Example 3

[0057] Unlike Example 1, the energy density of the pulsed laser incident on the deposition cavity in Example 3 is 53.9 mJ / cm³. -2 The remaining steps and parameters are the same as in Example 1.

[0058] Example 4

[0059] Unlike Example 1, the energy density of the pulsed laser incident on the deposition cavity in Example 4 is 55.9 mJ / cm². -2 The remaining steps and parameters are the same as in Example 1.

[0060] Example 5

[0061] Unlike Example 1, the energy density of the pulsed laser incident on the deposition cavity in Example 5 is 60.0 mJ / cm³. -2 The remaining steps and parameters are the same as in Example 1.

[0062] The bismuth-oxygen selenide films prepared in Examples 1-5 have the same dimensions, with a length of approximately 12 mm, a width of approximately 4 mm, and a thickness of approximately 50 nm.

[0063] The conductivity, Seebeck coefficient, X-ray diffraction pattern, and power factor of the bismuth-oxygen selenide thin films prepared in Examples 1-5 were measured. The test results are shown in the appendix. Figures 1-4 .

[0064] Figure 1 The conductivity curves of the bismuth oxide selenium thin films in Examples 1-5 as a function of temperature are shown. It can be found that at room temperature (300K), the conductivity can be adjusted from 20 S cm⁻¹ to [a value missing]. -1 Increased to 180S cm -1 .at the same time, Figure 2 The Seebeck coefficient of the bismuth-oxygen-selenium thin film also confirms the variation in defect concentration within the film, with a pulsed laser energy density of 53.9 mJ / cm². -2 The bismuth-oxygen selenide thin film prepared at the highest defect content has the highest carrier concentration and therefore the absolute value of the Seebeck coefficient decreases. Similarly, although the bismuth-oxygen selenide thin film with low defect content has low conductivity, its absolute value of the Seebeck coefficient is higher.

[0065] Figure 4 X-ray diffraction results confirmed that no impurity phases were generated, and the products were all bismuth-oxygen selenide crystal structures.

[0066] In Examples 1-5, bismuth oxide selenium thin films with adjustable defects and a certain aspect ratio were obtained by changing the energy density of the pulsed laser.

[0067] Depend on Figure 3 It can be seen that the energy density of the pulsed laser is 53.9 mJ / cm². -2 The bismuth oxide selenide thin film grown under the specified conditions has the optimal power factor across the entire temperature range. By adjusting the energy density of the pulsed laser, the defect content in the bismuth oxide selenide thin film can be changed. The higher the power factor, the better the thermoelectric performance. Appropriately adjusting the energy density of the pulsed laser helps to obtain bismuth oxide selenide thin films with superior thermoelectric performance.

[0068] In the description of this specification, references to terms such as "one embodiment," "some embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0069] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing bismuth oxide selenium thin films, characterized in that, include: Provide bismuth-oxygen-selenium sputtering targets; The bismuth-oxygen-selenium target is placed in the deposition chamber, and the deposition chamber is evacuated to a vacuum level less than or equal to 1×10⁻⁶. - 4 Pa, the substrate temperature is raised to 400℃~500℃ and kept at that temperature, and the pulsed laser irradiates the bismuth-oxygen selenide target, forming an elliptical spot on the bismuth-oxygen selenide target, causing the bismuth-oxygen selenide target to generate plasma and form a bismuth-oxygen selenide thin film on the substrate. The energy density of the pulsed laser incident on the deposition cavity is 45 mJ / cm². -2 Up to 70 mJ cm -2 .

2. The method according to claim 1, characterized in that, The frequency of the pulsed laser is 5 Hz to 10 Hz.

3. The method according to claim 1, characterized in that, The preparation of the bismuth-oxygen-selenium target includes: The bismuth-oxy-selenium target material was synthesized by solid-state method using Bi, Bi2O3 and Se powders as raw materials. In the bismuth-oxy-selenium target material, the mass of Bi and Se is 5% to 10% in excess relative to Bi2O2Se.

4. The method according to claim 1, characterized in that, The diameter of the bismuth-oxygen-selenium target is greater than or equal to 20 mm, and the thickness of the bismuth-oxygen-selenium target is greater than or equal to 3 mm.

5. The method according to any one of claims 1 to 4, characterized in that, The ratio of the major axis to the minor axis of the elliptical light spot is 2:1 to 4:

1.

6. The method according to any one of claims 1 to 4, characterized in that, The substrate is SrTiO3.

7. A bismuth oxide selenium thin film, characterized in that, The bismuth oxide selenium thin film is prepared using the method described in any one of claims 1 to 6.

8. The bismuth oxide selenium thin film according to claim 7, characterized in that, The bismuth oxide selenium thin film satisfies at least one of the following conditions: The length-to-width ratio of the bismuth-oxygen selenide thin film is 15:8 to 3:1; The length of the bismuth oxide selenium thin film is 12mm~15mm; The width of the bismuth-oxygen selenium thin film is 4mm~8mm; The thickness of the bismuth-oxygen selenide thin film is 10 nm to 100 nm.

9. The bismuth oxy selenide thin film according to claim 7 or 8 is used as a thermoelectric material.

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