CN108447976B - Method for regulating performance of n-type bismuth telluride film by crystal boundary - Google Patents
Method for regulating performance of n-type bismuth telluride film by crystal boundary Download PDFInfo
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- CN108447976B CN108447976B CN201810109017.9A CN201810109017A CN108447976B CN 108447976 B CN108447976 B CN 108447976B CN 201810109017 A CN201810109017 A CN 201810109017A CN 108447976 B CN108447976 B CN 108447976B
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- H—ELECTRICITY
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- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
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- H10N10/851—Thermoelectric active materials comprising inorganic compositions
- H10N10/852—Thermoelectric active materials comprising inorganic compositions comprising tellurium, selenium or sulfur
Abstract
The invention discloses a method for regulating and controlling the performance of an n-type bismuth telluride film by crystal boundaries, relates to a thermoelectric material regulating and controlling method, belongs to the field of new energy materials, and solves the problems that the crystal boundary structure and chemical properties are discontinuously changed along with the change of thermodynamic parameters such as temperature, pressure, chemical potential and the like in the prior art. The method comprises the following steps: first step with commercial Bi2Te3The target and the Te target are used as target materials, and the magnetron sputtering technology is adopted to prepare n-type Bi on a heating substrate2Te3A film. The second step is to evaporate commercial Sn as raw material in n-type Bi2Te3The surface of the film is plated with Sn. Thirdly, the n-type Bi plated with Sn is annealed by a protective gas annealing furnace2Te3After annealing at high temperature, furnace cooling is carried out to obtain high-performance n-type Bi2Te3A film. The method provides an optimized process scheme with high performance, low cost, simple equipment, simple process, easy operation control, uniform performance and stability for the performance optimization of the low-temperature power generation micro device.
Description
Technical Field
The invention relates to a thermoelectric material regulation method, in particular to a method for regulating the performance of an n-type bismuth telluride film by crystal boundaries.
Background
The thermoelectric material has unique advantages in the fields of thermoelectric refrigeration and thermoelectric power generation, and becomes one of the development directions of the future energy industry as an environment-friendly novel energy material. However, the performance of the thermoelectric material still needs to be improved, the conversion efficiency of waste heat recovery is low, and the utilization efficiency of energy needs to be improved on the basis of technical theory and experimental data. Conversion efficiency of thermoelectric devices is determined by thermoelectric figure of merit of thermoelectric materialsZT(a dimensionless value) is determined,ZTthe values are determined by the parameters of electrical conductivity (σ), Seebeck coefficient (α) and thermal conductivity (κ), and the coupling between these parameters prevents the performance improvement. The conventional doping method seeks the maximum power factor (alpha) by regulating and controlling the optimal carrier concentration through the doping content2σ), this method does not effectively reduce the coupling between conductivity and Seebeck coefficient.
The grain boundary engineering is a method capable of comprehensively improving the performance of the thermoelectric material. For example, small-angle or highly coherent grain boundaries can suppress scattering on the carrier, but effectively scatter phonon transport, so that the thermal conductivity is limited while the electrical conductivity is improved, and the dense dislocation array embedded in the grain boundaries obviously reduces the thermal conductivity, thereby greatly improving the performance of the thermoelectric material. Grain boundaries with appropriate energy barriers can filter low energy carrier traversal, significantly enhancing the seebeck coefficient without significantly affecting the conductivity. However, the conventional method is accompanied by changes in the intragranular characteristics, including a complicated metallurgical process, to maximize the thermoelectric performance by elaborating the inter-and intragranular characteristics step by step. The grain boundary also shows phase behavior change in the process, and the structure and chemical properties of the grain boundary are discontinuously changed along with the change of thermodynamic parameters such as temperature, pressure and chemical potential. Annealing is another key process to improve the microstructure and electrical transport behavior, which is the process necessary to eliminate unwanted crystal defects, especially for improving grain boundary relaxation phenomena of nanostructures.
Disclosure of Invention
The invention aims to provide a method for regulating and controlling the performance of an n-type bismuth telluride film by crystal boundary, and the method is simple and easy to control in process and uniform in performance2Te3) The film performance optimizing and regulating method solves the problem that the crystal boundary structure and chemical property are discontinuously changed along with the change of temperature, pressure, chemical potential and other thermodynamic parameters.
The purpose of the invention is realized by the following technical scheme:
a method for regulating and controlling the performance of a n-type bismuth telluride film by crystal boundaries comprises the following steps:
firstly, preparing an n-type Bi2Te3 thin film on a heating substrate by using a commercial Bi2Te3 target and a commercial Te target as target materials and adopting a magnetron sputtering technology;
secondly, plating an Sn film on the surface of the n-type Bi2Te3 by using commercial Sn as a raw material and adopting an evaporation technology;
thirdly, annealing the n-type Bi2Te3 film plated with the Sn film by using a protective gas annealing furnace at high temperature, and cooling along with the furnace;
in the first step of the film preparation process: the temperature of the heating substrate is 573K to 623K; the purities of the commercial Bi2Te3 target and the Te target are both 99.99 wt%; the Bi2Te3 target and the Te target are circular targets or rectangular targets; the Bi2Te3 target and the Te target respectively use independent sputtering power supplies, the Bi2Te3 target adopts a direct current or radio frequency power supply, the Te target adopts a radio frequency or direct current power supply, and the Bi2Te3 target and the Te target work simultaneously in a co-sputtering mode; the heating substrate is a glass sheet or a silicon sheet; the thickness of the n-type Bi2Te3 film is 760 nm;
in the second film preparation process: the evaporation is electron beam evaporation or thermal evaporation or laser evaporation; purity of commercial Sn is 99.99 wt%; the thickness of the evaporated Sn film is 1 nm-15 nm;
in the third annealing step: the protective gas is 95% argon gas and 5% hydrogen gas or pure argon gas; the annealing temperature is 473K-573K; the pressure of the protective gas is greater than the atmospheric pressure; the annealing time is 0.5-2 h.
The invention has the advantages and effects that:
n-type Bi prepared on a heated substrate by the method of the invention2Te3The film has higher crystallization degree and controllable pore diameter on the surface. After annealing, the conductivity of the film is increased, the Seebeck coefficient is not changed greatly, the barrier height is reduced, the coupling effect between the conductivity and the Seebeck is effectively reduced, and the power factor is improved. Therefore, the method provides an optimized process scheme with high performance, low cost, simple equipment, simple process, easy operation control, uniform performance and stability for the performance optimization of the low-temperature power generation micro device.
Drawings
FIG. 1(a) is a process flow diagram;
FIG. 1(b) is a schematic view showing rapid diffusion of Sn atoms along grain boundaries;
FIG. 2 is a schematic view of a shielding gas annealing furnace;
FIG. 3 shows n-type Bi sputter deposited at a substrate temperature of 623K2Te3A surface topography photograph of the film;
FIG. 4 shows n-type Bi2Te3A surface appearance photo of the film after annealing for 2 hours at 473K;
FIG. 5 shows n-type Bi2Te3A surface appearance photo of the film after annealing for 2 hours under 573K;
FIG. 6 shows n-type Bi after Sn plating2Te3Surface shape of film after annealing at 473K for 2hA physiognomic photograph;
FIG. 7 shows n-type Bi after Sn plating2Te3A surface appearance photo of the film after annealing for 2 hours under 573K;
in the figure: a cylinder of 195% argon +5% hydrogen; 2, annealing furnace; 3 a molecular pump unit; 4, a gas flow meter; 5, a barometer; 6, a suck-back prevention valve; 7, an air extraction opening; 8, an air inlet; 9 exhaust port.
Detailed Description
The present invention will be described in detail with reference to examples.
As shown in fig. 1(a), in the specific implementation process, the invention selects tin (Sn), which is a cheap and easily available metal material with a low melting point and a wide research range, as a diffusion element, and the process flow is as follows: first step with commercial Bi2Te3The target and the Te target are used as target materials, and the magnetron sputtering technology is adopted to prepare n-type Bi on a heating substrate2Te3A film. The second step is to evaporate commercial Sn as raw material in n-type Bi2Te3And the surface of the film is plated with Sn by adopting an electron beam. Thirdly, the n-type Bi plated with Sn is annealed by a protective gas annealing furnace2Te3Respectively annealing at high temperature and annealing diffusion, and furnace cooling to obtain high-performance n-type Bi2Te3A film.
As shown in FIG. 1(b), Bi is shown from the schematic view of the rapid diffusion of Sn atoms along grain boundaries in the present invention2Te3Sn film deposited on the surface of the film diffuses to Bi along grain boundary under the action of annealing2Te3Inside the film and act on Bi2Te3The grain boundary reduces the barrier height of the crystal boundary, promotes more low-energy carriers to participate in transmission, and improves the carrier concentration and the mobility.
As shown in FIG. 2, the structure of the protective gas annealing furnace of the present invention is as follows, a gas cylinder of 195% argon +5% hydrogen; 2, annealing furnace; 3 a molecular pump unit; 4, a gas flow meter; 5, a barometer; 6, a suck-back prevention valve; 7, an air extraction opening; 8, an air inlet; 9 exhaust port.
The present invention will be described in detail with reference to examples.
The first embodiment is as follows:
first step with commercial Bi 4 inches in diameter2Te3The target (99.99 wt%) and Te target (99.99 wt%) are used as target materials, and magnetron sputtering technology is adopted to prepare n-type Bi for 50 minutes on a glass sheet with the substrate temperature of 623K2Te3Film of Bi2Te3The thickness of the film was 760 nm. Wherein, Bi2Te3The surface topography of the film obtained by deposition under the conditions that the target is operated in a direct current mode and the power is 40W and the Te target is operated in a radio frequency mode and the power is 50W is shown in figure 3, and Bi can be seen from the figure2Te3Coarse grains, an average grain size of about 350nm, a rough surface morphology that facilitates metallic Sn diffusion along grain boundaries, and a distribution of voids with a diameter of about 200 nm.
Secondly, measuring the room-temperature conductivity, the Seebeck coefficient and the power factor of the film to be 398S/cm, 124 mu V/K and 6.12 mu W/cm-K respectively2。
Example two:
first step with commercial Bi 4 inches in diameter2Te3The target (99.99 wt%) and Te target (99.99 wt%) are used as target materials, and magnetron sputtering technology is adopted to prepare n-type Bi for 50 minutes on a glass sheet with the substrate temperature of 623K2Te3Film of Bi2Te3The thickness of the film was 760 nm. Wherein, Bi2Te3The target was operated in dc mode with a power of 40W, and the Te target was operated in rf mode with a power of 50W.
In the second step, 95% argon and 5% hydrogen (volume ratio) are used as shielding gas, and a self-built shielding gas annealing furnace (figure 2) is used for annealing n-type Bi2Te3After the film is annealed at 473K for 2h and cooled along with the furnace, the surface appearance of the film is shown in figure 4, and because the annealing temperature (473K) is lower than the preparation temperature (623K) of the film, the surface appearance after annealing is not obviously different from that before annealing.
Thirdly, measuring the room-temperature conductivity, the Seebeck coefficient, the power factor and the barrier change value of the film to be 305S/cm, 128 muV/K and 4.99 muW/cm.K respectively2And-2.40 meV.
Example three:
the first step isCommercial Bi of 4 inches diameter2Te3The target (99.99 wt%) and Te target (99.99 wt%) are used as target materials, and magnetron sputtering technology is adopted to prepare n-type Bi for 50 minutes on a glass sheet with the substrate temperature of 623K2Te3Film of Bi2Te3The thickness of the film was 760 nm. Wherein, Bi2Te3The target was operated in dc mode with a power of 40W, and the Te target was operated in rf mode with a power of 50W.
In the second step, 95% argon and 5% hydrogen (volume ratio) are used as shielding gas, and a self-built shielding gas annealing furnace (figure 2) is used for annealing n-type Bi2Te3After the film is annealed for 2h at 573K and cooled along with the furnace, the surface topography of the film is shown in FIG. 5, although the annealing temperature is increased by 100 ℃ compared with that in the second example, the annealing temperature (573K) is still lower than the preparation temperature (623K) of the film, so that the film topography obtained at the annealing temperature is not obviously different from that in the second example.
Thirdly, measuring the room-temperature conductivity, the Seebeck coefficient, the power factor and the barrier change value of the film to be 224S/cm, 142 muV/K and 4.51 muW/cm.K respectively2And-2.20 meV.
Example four:
first step with commercial Bi 4 inches in diameter2Te3The target (99.99 wt%) and Te target (99.99 wt%) are used as target materials, and magnetron sputtering technology is adopted to prepare n-type Bi for 50 minutes on a glass sheet with the substrate temperature of 623K2Te3Film of Bi2Te3The thickness of the film was 760 nm. Wherein, Bi2Te3The target was operated in dc mode with a power of 40W, and the Te target was operated in rf mode with a power of 50W.
The second step adopts electron beam evaporation technology to form Bi in n type2Te3The surface of the evaporation system is plated with a Sn film with the thickness of about 10 nm, and the vacuum degree of the evaporation system<10-5Pa, electron gun current of 1.00 +/-0.02 mA, gun voltage of 73 +/-5 mV, and deposition rate of 0.3 +/-0.2 angstroms/s.
Thirdly, adopting 95 percent argon and 5 percent hydrogen (volume ratio) as protective gas, and using a self-built protective gas annealing furnace (figure 2) to carry out annealing on the n plated with the Sn filmType Bi2Te3The film is annealed at 473K for 2h and then cooled with the furnace, the surface appearance of the film is shown in figure 6, and the figure shows that Sn is uniformly distributed in Bi in small crystal grains2Te3The large grain surface is not continuous and does not form a film, indicating that the surface Sn is opposite to Bi2Te3The film performance is not greatly influenced.
The fourth step of measuring the room temperature conductivity, the Seebeck coefficient, the power factor and the barrier change value of the film are 622S/cm, 111 MuV/K and 7.664 MuW/cm.K respectively2And-13.40 meV.
Example five:
first step with commercial Bi 4 inches in diameter2Te3The target (99.99 wt%) and Te target (99.99 wt%) are used as target materials, and magnetron sputtering technology is adopted to prepare n-type Bi for 50 minutes on a glass sheet with the substrate temperature of 623K2Te3Film of Bi2Te3The thickness of the film was 760 nm. Wherein, Bi2Te3The target was operated in dc mode with a power of 40W, and the Te target was operated in rf mode with a power of 50W.
The second step adopts electron beam evaporation technology to form Bi in n type2Te3The surface of the evaporation system is plated with a Sn film with the thickness of about 10 nm, and the vacuum degree of the evaporation system<10-5Pa, electron gun current of 1.00 +/-0.02 mA, gun voltage of 73 +/-5 mV, and deposition rate of 0.3 +/-0.2 angstroms/s.
The third step is to adopt 95 percent argon and 5 percent hydrogen (volume ratio) as the protective gas and use a self-built protective gas annealing furnace (figure 2) to carry out annealing on the n-type Bi after the Sn film is plated2Te3After the film is annealed for 2h under 573K and cooled along with the furnace, the surface appearance of the film is shown in figure 7, and the Sn is still distributed in Bi in small grains2Te3The large grain surface is not continuous and is not formed into a film, but because the annealing temperature (573K) is higher than the melting point (505K) of metal Sn, the melting phenomenon of Sn occurs, which is favorable for the Sn to diffuse to Bi along the grain boundary2Te3Inside the film, the film properties are affected.
The fourth step of measuring the room temperature conductivity, the Seebeck coefficient, the power factor and the potential barrier change value of the film are 619S/cm and 117µV/K、8.473µW/cm· K2And-17.80 meV.
Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.
Claims (1)
1. A method for regulating and controlling the performance of an n-type bismuth telluride film by crystal boundaries is characterized by comprising the following steps:
firstly, preparing an n-type Bi2Te3 thin film on a heating substrate by using a commercial Bi2Te3 target and a commercial Te target as target materials and adopting a magnetron sputtering technology;
secondly, plating an Sn film on the surface of the n-type Bi2Te3 by using commercial Sn as a raw material and adopting an evaporation technology;
thirdly, annealing the n-type Bi2Te3 film plated with the Sn film by using a protective gas annealing furnace at high temperature, and cooling along with the furnace;
in the first step of the film preparation process: the temperature of the heating substrate is 573K to 623K; the purities of the commercial Bi2Te3 target and the Te target are both 99.99 wt%; the Bi2Te3 target and the Te target are circular targets or rectangular targets; the Bi2Te3 target and the Te target respectively use independent sputtering power supplies, the Bi2Te3 target adopts a direct current or radio frequency power supply, the Te target adopts a radio frequency or direct current power supply, and the Bi2Te3 target and the Te target work simultaneously in a co-sputtering mode; the heating substrate is a glass sheet or a silicon sheet; the thickness of the n-type Bi2Te3 film is 760 nm;
in the second step of the film preparation process: the evaporation is electron beam evaporation or thermal evaporation or laser evaporation; purity of commercial Sn is 99.99 wt%; the thickness of the evaporated Sn film is 1 nm-15 nm;
in the third annealing step: the protective gas is 95% argon gas and 5% hydrogen gas or pure argon gas; the annealing temperature is 573K; the pressure of the protective gas is greater than the atmospheric pressure; the annealing time is 0.5-2 h.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102257648A (en) * | 2008-12-19 | 2011-11-23 | 开利公司 | Bulk-processed, enhanced figure-of-merit thermoelectric materials |
| CN104078557A (en) * | 2014-07-07 | 2014-10-01 | 天津大学 | Preparation method for p-type Bi0.5Sb1.5Te3-based nano-porous thermoelectric composite material |
| CN205473952U (en) * | 2016-03-25 | 2016-08-17 | 沈阳大学 | Device of controllable function film of preparation structure |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102257648A (en) * | 2008-12-19 | 2011-11-23 | 开利公司 | Bulk-processed, enhanced figure-of-merit thermoelectric materials |
| CN104078557A (en) * | 2014-07-07 | 2014-10-01 | 天津大学 | Preparation method for p-type Bi0.5Sb1.5Te3-based nano-porous thermoelectric composite material |
| CN205473952U (en) * | 2016-03-25 | 2016-08-17 | 沈阳大学 | Device of controllable function film of preparation structure |
Non-Patent Citations (1)
| Title |
|---|
| 《Interfacial reactions in Sn/Bi2Te3, Sn/Bi2Se3 and Sn/Bi2(Te1-xSex)3 couples》;Sinn-wen Chen, et al.;《Journal of Alloys and Compounds》;20140528;第611卷;313-318 * |
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