Alkali metal film, preparation method, application and device

Abstract

The present invention relates to an alkali metal film, a preparation method, an application and a device. The preparation method of the alkali metal film comprises the following steps: using a silicon wafer to prepare a Si-7×7 substrate; under vacuum conditions, degassing a cadmium source, and then heating to evaporate cadmium atoms onto the surface of the Si-7×7 substrate to obtain a Cd film; under vacuum conditions, degassing p-terphenyl molecules, and then heating to evaporate p-terphenyl molecules onto the surface of the Cd film to obtain a p-terphenyl molecular film; under vacuum conditions, degassing an alkali metal source, and then heating to evaporate alkali metal atoms onto the surface of the p-terphenyl molecular film to obtain an alkali metal-doped p-terphenyl molecular film; under vacuum conditions, annealing the alkali metal-doped p-terphenyl molecular film to obtain an alkali metal film. The present invention prepares an alkali metal ultra-thin film, broadens the scope of use of the alkali metal film, and improves performance.

Description

Technical Field

[0001] The present invention relates to the technical field of thin film materials, and in particular to an alkali metal thin film, a preparation method, an application and a device. Background Art

[0002] Single-atom layer thin film materials, such as graphene, possess exceptional properties, such as excellent electrical and thermal conductivity and a high specific surface area, demonstrating great potential for application in fields such as adsorption, catalysis, and optoelectronics. Electrode thin film materials, such as those used in alkali metal Li and Na batteries, also face strong demand. Therefore, the continuous development of ultra-thin film materials is crucial.

[0003] In recent years, graphene-like two-dimensional crystalline materials based on Group III and IV elements have been prepared using various methods, primarily using the "bottom-up" molecular beam epitaxy technique. However, there is currently no effective method for preparing two-dimensional alkali metal thin films. Therefore, the development of a "bottom-up" epitaxial growth method for alkali metal ultrathin films is highly desirable. Summary of the Invention

[0004] The purpose of the present invention is to provide an alkali metal film, a preparation method, an application and an apparatus to prepare an alkali metal ultra-thin film, so as to broaden the application range of the alkali metal film and improve the performance.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing an alkali metal thin film comprises the following steps:

[0007] Preparation of silicon (111)-7×7 substrate: A reconstructed surface with a single-crystal silicon crystal plane index

[111] , i.e., a silicon (111)-7×7 substrate, is obtained by using silicon wafers;

[0008] Growth of cadmium (0001) thin film: Under vacuum conditions, the cadmium source is degassed, and then heated to evaporate cadmium atoms onto the surface of the silicon (111)-7×7 substrate to obtain a cadmium metal film with a crystal plane index of (0001), i.e., a cadmium (0001) thin film;

[0009] Growth of a p-terphenyl molecule (110) film: Under vacuum conditions, the p-terphenyl molecules are degassed and then heated to evaporate the p-terphenyl molecules onto the surface of the cadmium (0001) film, thereby obtaining a molecular film having a p-terphenyl crystal plane index of (110), i.e., a p-terphenyl molecule (110) film;

[0010] Growth of an alkali metal-doped p-terphenyl molecule (110) thin film: degassing an alkali metal source under vacuum conditions, and then heating to allow alkali metal atoms to evaporate into the p-terphenyl molecule (110) thin film to obtain an alkali metal-doped p-terphenyl molecule thin film;

[0011] Growth of alkali metal thin films: Under vacuum conditions, the alkali metal-doped p-terphenyl molecular film is annealed to obtain an alkali metal thin film. Under vacuum conditions, the alkali metal atoms enter the molecular interstitial sites of the p-terphenyl molecular (110) film, forming a mixture. To obtain a high-quality alkali metal thin film, the alkali metal-doped p-terphenyl molecular film is annealed at room temperature to form a segregated and aggregated alkali metal potassium film.

[0012] The purpose of degassing the cadmium source, the p-terphenyl molecules and the alkali metal source is to obtain high-purity cadmium atoms, the p-terphenyl molecules and the alkali metal source.

[0013] Alkali metal thin films can be used in solar cells to improve film quality. Ultra-thin alkali metal films, with minimal defects and impurities, can effectively control the luminous efficiency of solar cells. They are also used in alkali metal ion batteries to increase the surface activity of negative electrode materials and enhance battery efficiency.

[0014] Preferably, the alkali metal source is selected from at least one of a lithium source, a sodium source, a potassium source, a rubidium source and a cesium source.

[0015] Preferably, the potassium source is a potassium-containing compound.

[0016] Preferably, the potassium-containing compound is a mixture of potassium chromate and zirconium-aluminum alloy.

[0017] Preferably, the lithium source, sodium source, rubidium source and cesium source are compounds containing lithium (Li), sodium (Na), rubidium (Rb) and cesium (Cs) metal ions, respectively.

[0018] The cadmium source is metallic cadmium with a purity of 99.999%.

[0019] Preferably, the preparation of the silicon (111)-7×7 substrate comprises: sequentially cleaning, degassing and annealing the silicon wafer to obtain the silicon (111)-7×7 substrate;

[0020] The cleaning is carried out by ultrasonic cleaning using alcohol and acetone in sequence;

[0021] The degassing is carried out at a vacuum degree of 6.0×10 -9 Torr and a temperature of 400-600 ° C for 8-12 hours, and then cooled to room temperature to obtain a clean silicon surface;

[0022] The annealing adopts a cyclic annealing treatment, which includes raising the temperature from room temperature to 1000-1300°C within 5-20 seconds, annealing for 13-18 seconds, cooling to 400°C, maintaining for 10-15 seconds, then raising the temperature from 400°C to 1000-1300°C within 5-20 seconds, annealing for 13-18 seconds, cooling to 400°C, maintaining for 10-15 seconds, and repeating this cycle for a total of 5-8 annealing times to obtain a silicon (111)-7×7 reconstructed surface.

[0023] Preferably, the cadmium source is degassed at a vacuum degree higher than 6.0×10 -10 Torr, the temperature of the cadmium source was raised by 20°C every 10 min, from room temperature to 60°C, and the vacuum was stabilized to 6.0×10 -10 Torr, heated for 25-35 min, and then cadmium atoms were evaporated onto the surface of the silicon (111)-7×7 substrate at a temperature of 50°C;

[0024] During the process of cadmium atoms being evaporated onto the surface of the silicon (111)-7×7 substrate, the temperature of the silicon (111)-7×7 substrate is maintained at room temperature;

[0025] The evaporation time of cadmium atoms onto the surface of the silicon (111)-7×7 substrate is 25~30min.

[0026] In the process of evaporating cadmium atoms onto the surface of the silicon (111)-7×7 substrate, the temperature of the silicon (111)-7×7 substrate is maintained at room temperature so that a cadmium (0001) film with a thickness of more than 15 atomic layers can be grown on the surface of the silicon (111)-7×7 substrate, thereby eliminating the quantum well state effect on the surface of the cadmium (0001) film.

[0027] Preferably, the degassing of the p-terphenyl molecules is carried out at a vacuum degree higher than 9.0×10 -10 Torr, the p-terphenyl molecule was heated until the vacuum degree stabilized to 9.0×10 -10 Torr;

[0028] During the process of evaporating terphenyl molecules onto the surface of the cadmium (0001) film, the temperature of the cadmium (0001) film is maintained between -180°C and -185°C.

[0029] Among them, during the process of evaporating terphenyl molecules onto the surface of the cadmium (0001) film, the temperature of the cadmium (0001) film is maintained between -180°C and 185°C in order to form a molecular film on the surface of the cadmium (0001) film for efficient adsorption of terphenyl molecules.

[0030] Preferably, the alkali metal source is degassed at a vacuum degree higher than 6.0×10-10 Torr, heat the alkali metal source until the vacuum degree stabilizes to 6.0×10 -10 Torr;

[0031] During the process of evaporating alkali metal atoms into the p-terphenyl molecule (110) film, the temperature of the p-terphenyl molecule (110) film is maintained between -150°C and 155°C. In order to obtain an effective alkali metal-doped p-terphenyl molecule film mixture, the coverage of the alkali metal atoms on the surface of the p-terphenyl molecule (110) film is 0.6 to 1.2ML.

[0032] In the process of evaporating alkali metal atoms into the p-terphenyl molecule (110) film, the temperature of the p-terphenyl molecule (110) film is maintained between -150°C and -155°C so that the alkali metal atoms and the p-terphenyl molecule (110) film form a mixture of alkali metal-doped p-terphenyl molecule film.

[0033] Preferably, the annealing treatment of the alkali metal-doped p-terphenyl molecular film is to place the alkali metal-doped p-terphenyl molecular film in a vacuum for 20 to 40 minutes to increase the temperature.

[0034] The present invention also provides an alkali metal film prepared by the preparation method of the present invention.

[0035] The present invention also provides an application of the alkali metal film prepared by the preparation method of the present invention, wherein the alkali metal film is used in solar cells and alkali metal ion batteries.

[0036] The present invention also provides a device for preparing an alkali metal film, comprising a vacuum preparation chamber, a sample holder, a crossbar, a magnetic handle, a DC power supply, a cadmium source placement component, a water circulation cooling device, a crucible, a heating furnace, and an alkali metal source placement component; the sample holder is located inside the cavity of the vacuum preparation chamber, the magnetic handle and the DC power supply are located outside the cavity of the vacuum preparation chamber, the cadmium source placement component is located at the bottom of the vacuum preparation chamber, and a portion is located inside the cavity of the vacuum preparation chamber, and the other portion is located outside the cavity of the vacuum preparation chamber, the heating furnace is located at the bottom of the vacuum preparation chamber, and a portion is located at the cavity of the vacuum preparation chamber. The crucible is located in the heating furnace, and the crucible is located outside the cavity of the vacuum preparation chamber. The alkali metal source placement component is located on the side wall of the vacuum preparation chamber, and one part is located inside the cavity of the vacuum preparation chamber, and the other part is located outside the cavity of the vacuum preparation chamber. One end of the cross bar is connected to the sample holder, and the other end is connected to the magnetic handle. The sample holder, the alkali metal source placement component, the cadmium source placement component and the water circulation cooling device are all connected to the DC power supply. The crucible is located in the heating furnace, and the crucible is located outside the cavity of the vacuum preparation chamber. The heating furnace is built into the water circulation cooling device, and the water circulation cooling device is externally connected to a room temperature water source.

[0037] When preparing an alkali metal thin film, a silicon wafer is placed on a sample holder, a crossbar is adsorbed on the inner tube wall by a magnetic handle, and the crossbar is driven to move, and the sample holder with the silicon wafer is sent into a vacuum preparation chamber, and the sample holder is placed above a heating furnace, and a direct current power supply is used to heat the silicon wafer to form a silicon (111)-7×7 substrate; a cadmium source is placed in a cadmium source placement component, and a direct current power supply is used to heat and degas the cadmium source and evaporate it onto the surface of the silicon (111)-7×7 substrate to obtain a cadmium (0001) thin film; a terphenyl molecule is placed in a crucible, and the crucible is placed in a crucible. In a heating furnace, the p-terphenyl molecules are degassed and evaporated onto the surface of a cadmium (0001) film to obtain a p-terphenyl molecule (110) film, and a water circulation cooling device is simultaneously turned on to ensure stable heating of the crucible; an alkali metal source is loaded into an alkali metal source placement component, and a direct current power supply is used to degas the alkali metal source and evaporate the alkali metal source onto the surface of the p-terphenyl molecule (110) film to obtain an alkali metal-doped p-terphenyl molecule film; and the alkali metal-doped p-terphenyl molecule film is annealed at room temperature in a vacuum preparation chamber to obtain an alkali metal film.

[0038] Beneficial effects of the present invention:

[0039] The method for preparing an alkali metal thin film of the present invention comprises the following steps: first, preparing a clean silicon (111)-7×7 substrate by using molecular beam epitaxy technology in an ultra-high vacuum environment; second, preparing an atomically resolved cadmium (0001) thin film; third, growing a p-terphenyl molecular thin film on the surface of the cadmium (0001) thin film to prepare a p-terphenyl molecular (110) thin film with a clean surface; fourth, preparing a mixture of alkali metal-doped p-terphenyl (110) molecular thin films; and fifth, annealing the alkali metal-doped p-terphenyl molecular thin film at room temperature to prepare an alkali metal thin film, thereby epitaxially growing potassium atoms on the p-terphenyl molecular thin film from bottom to top, and annealing segregation to form an alkali metal (110) surface structure. Compared with other methods, the method is more conducive to obtaining clear microstructures and properties, effectively expanding the application range of alkali metal thin films, and having promotion and application value in the field of thin film material technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the device for preparing an alkali metal thin film of the present invention;

[0041] Figure 2 This is the STM image of the p-terphenyl molecule (110) film prepared in Example 2;

[0042] Figure 3 This is the STM image of the p-terphenyl molecule (110) film prepared in Example 3;

[0043] Figure 4 This is an STM image of the alkali metal potassium-doped p-terphenyl molecular film prepared in Example 2;

[0044] Figure 5 This is an STM image of the alkali metal potassium-doped p-terphenyl molecular film prepared in Example 3;

[0045] Figure 6 This is the STM image of the alkali metal potassium film;

[0046] Among them, 1-vacuum preparation chamber, 2-sample rack, 3-cross bar, 4-magnetic handle, 5-DC power supply, 6-cadmium source placement component, 7-water circulation cooling device, 8-crucible, 9-heating furnace, 10-sample substrate, 11-alkali metal source placement component. DETAILED DESCRIPTION

[0047] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0048] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0049] Example 1

[0050] like Figure 1 As shown, a device for preparing an alkali metal thin film includes a vacuum preparation chamber 1, a sample holder 2, a crossbar 3, a magnetic handle 4, a DC power supply 5, a cadmium source placement component 6, a water circulation cooling device 7, a crucible 8, a heating furnace 9 and an alkali metal source placement component 11; the sample holder 2 is located inside the cavity of the vacuum preparation chamber 1, the magnetic handle 4 and the DC power supply 5 are located outside the cavity of the vacuum preparation chamber 1, the cadmium source placement component 6 is located at the bottom of the vacuum preparation chamber 1, and a part of it is located inside the cavity of the vacuum preparation chamber 1, and the other part is located outside the cavity of the vacuum preparation chamber 1, the heating furnace 9 is located at the bottom of the vacuum preparation chamber 1, and a part of it is located at the bottom of the vacuum preparation chamber 1. 1, and the other part is located outside the cavity of the vacuum preparation chamber 1, the alkali metal source placement component 11 is located on the side wall of the vacuum preparation chamber 1, and one part is located inside the cavity of the vacuum preparation chamber 1, and the other part is located outside the cavity of the vacuum preparation chamber 1; one end of the cross bar 3 is connected to the sample rack 2, and the other end is connected to the magnetic handle 4, the sample rack 2, the alkali metal source placement component 11, the cadmium source placement component 6 and the water circulation cooling device 7 are all connected to the DC power supply 5, the crucible 8 is located in the heating furnace 9, and the crucible 8 is located outside the cavity of the vacuum preparation chamber 1, the heating furnace 9 is built in the water circulation cooling device 7, and the water circulation cooling device 7 is externally connected to a room temperature water source;

[0051] When preparing an alkali metal thin film, a silicon wafer is placed on a sample holder 2, and a crossbar 3 is adsorbed on the inner tube wall by a magnetic handle 4 to drive the crossbar 3 to move, and the sample holder 2 containing the silicon wafer is sent into a vacuum preparation chamber 1, and the sample holder 2 is located above a heating furnace 9, and a DC power supply 5 is used to heat the silicon wafer to form a Si(111)-7×7 substrate, i.e., a sample substrate 10; a cadmium source is placed in a cadmium source placement component 6, and a DC power supply 5 is used to heat and degas the cadmium source and evaporate it onto the upper surface of the Si(111)-7×7 substrate to obtain a Cd(0001) thin film; and p-terphenyl molecules are placed in a crucible 8. , then placing the crucible 8 in a heating furnace 9, degassing the p-terphenyl molecules through the heating furnace 9 and vapor-depositing them onto the upper surface of the Cd (0001) film to obtain a p-terphenyl molecule (110) film, and at the same time starting the water circulation cooling device 7 to ensure stable heating of the crucible 8; loading the alkali metal source into the alkali metal source placement component 11, using a DC power supply 5 to degas the alkali metal source and vapor-deposit it onto the surface of the p-terphenyl molecule (110) film to obtain an alkali metal-doped p-terphenyl molecule film; and performing room temperature annealing on the alkali metal-doped p-terphenyl molecule film in a vacuum preparation chamber 1 to obtain an alkali metal film.

[0052] Example 2

[0053] A method for preparing an alkali potassium thin film using the apparatus of Example 1 comprises the following steps:

[0054] S1. Preparation of Si(111)-7×7 substrate: A Si(111)-7×7 substrate is prepared using a silicon wafer, specifically including:

[0055] S11, cutting the silicon wafer into a size of 3 mm × 15 mm, and placing it in alcohol for ultrasonic cleaning, and then placing it in acetone for ultrasonic cleaning to obtain a silicon wafer substrate;

[0056] S12, placing the cleaned silicon wafer substrate on the sample rack 2, and moving the crossbar 3 by the magnetic handle 4 to move the sample rack 2 containing the silicon wafer substrate into the vacuum preparation chamber 1, and positioning the sample rack 2 containing the silicon wafer substrate above the heating furnace 9;

[0057] S13, in the vacuum preparation chamber 1, using a DC power supply 5 to heat the silicon wafer substrate to 400° C., degas the silicon wafer substrate at 400° C. for 8 hours, and then cool it to room temperature;

[0058] S14, using a DC power supply 5 to raise the temperature of the degassed silicon wafer substrate from room temperature to 1200°C, the heating time is 10s, annealing for 15s, cooling to 400°C, holding for 12s, then raising the temperature from 400°C to 1200°C, the heating time is 10s, annealing for 15s, cooling to 400°C, holding for 12s, and so on, annealing for a total of 5 times to obtain a Si(111)-7×7 substrate;

[0059] S2. Growth of Cd(0001) thin film: Under vacuum conditions, the cadmium source is degassed, and then heated to evaporate cadmium atoms onto the surface of the Si(111)-7×7 substrate to obtain a Cd(0001) thin film, specifically including:

[0060] S21, put the metallic cadmium with purity of 99.999% into the cadmium source placement component 6, and -10 Torr, a DC power supply of 5 was used to power the heating wire, and the temperature of the cadmium source was raised by 20°C every 10 minutes, so that the cadmium source was raised from room temperature to 60°C, and the vacuum degree was stabilized to 6.0×10 -10 Torr and then heated for 30 min to fully degas the cadmium source. The cadmium source placement component 6 in this embodiment is a crucible;

[0061] S22, using a DC power supply 5 to heat the degassed cadmium source to evaporate cadmium atoms onto the upper surface of the Si(111)-7×7 substrate, the evaporation time is 28 minutes, wherein the heating temperature is 50° C., while the temperature of the Si(111)-7×7 substrate is maintained at room temperature, so as to grow a Cd(0001) film with a thickness of more than 15 atomic layers, thereby obtaining a Cd(0001) film with a thickness of more than 15 atomic layers;

[0062] S3. Growth of molecular thin film: Under vacuum conditions, the p-terphenyl molecules are degassed, and then heated to evaporate the p-terphenyl molecules onto the surface of the Cd (0001) film to obtain a p-terphenyl molecule (110) thin film, specifically comprising:

[0063] S31, put the p-terphenyl molecules into the crucible 8, and then place the crucible 8 in the heating furnace 9, and heat the crucible 8 in a vacuum furnace higher than 9.0×10 -10 Torr, the p-terphenyl molecules were heated to 40°C by the heating furnace 9 to fully degas the p-terphenyl molecules. During the degassing process, the water circulation cooling device 7 was simultaneously turned on until the vacuum degree stabilized to 9.0×10 -10 Torr;

[0064] S32, heating the degassed p-terphenyl molecules in a heating furnace 9 so that the p-terphenyl molecules are evaporated onto the surface of the Cd (0001) film, wherein the heating temperature is 32° C. while maintaining the Cd (0001) film at approximately -183° C. to form a molecular film with the p-terphenyl molecule (110) face, thereby obtaining a terphenyl molecule (110) film;

[0065] S4. Growth of an alkali metal-doped p-terphenyl molecule film: degassing the alkali metal source under vacuum conditions, and then heating to evaporate alkali metal atoms onto the surface of the p-terphenyl molecule (110) film to obtain an alkali metal-doped p-terphenyl molecule film, specifically comprising:

[0066] S41, put the potassium source into the alkali metal source placement part 11, and -10 Torr, the potassium source was heated to 420°C using a DC power supply 5. To obtain a stable power output, the DC current of the DC power supply 5 was set to 5A until the vacuum degree stabilized to 6.0×10 -10 Torr, so that the potassium source is fully degassed;

[0067] S42, using a DC power supply 5 to heat the degassed potassium source, so that potassium atoms are evaporated onto the surface of the p-terphenyl molecule (110) film, wherein the heating temperature is 400° C., the coverage is controlled to be about 0.6 ML, and the p-terphenyl molecule (110) film is maintained at about -153° C. to obtain a potassium-doped p-terphenyl molecule film;

[0068] S5. Growth of an alkali metal thin film: Annealing the alkali metal-doped p-terphenyl molecular film under vacuum conditions to obtain an alkali metal thin film, specifically comprising:

[0069] S51, when the vacuum degree is higher than 6.0×10 -10 Under the condition of 1000 Torr, the potassium-doped p-terphenyl molecular film is placed in a vacuum preparation chamber 1 at room temperature for about 20 minutes to complete the room temperature annealing process to obtain an alkali metal potassium film.

[0070] Example 3

[0071] A method for preparing an alkali potassium thin film using the apparatus of Example 1 comprises the following steps:

[0072] S1. Preparation of Si(111)-7×7 substrate: A Si(111)-7×7 substrate is prepared using a silicon wafer, specifically including:

[0073] S11, cutting the silicon wafer into a size of 3 mm × 15 mm, and placing it in alcohol for ultrasonic cleaning, and then placing it in acetone for ultrasonic cleaning to obtain a silicon wafer substrate;

[0074] S12, placing the cleaned silicon wafer substrate on the sample rack 2, and moving the crossbar 3 by the magnetic handle 4 to move the sample rack 2 containing the silicon wafer substrate into the vacuum preparation chamber 1, and positioning the sample rack 2 containing the silicon wafer substrate above the heating furnace 9;

[0075] S13, in the vacuum preparation chamber 1, using a DC power supply 5 to heat the silicon wafer substrate to 500° C., degas the silicon wafer substrate at 500° C. for 12 hours, and then cool it to room temperature;

[0076] S14, using a DC power supply 5 to raise the temperature of the degassed silicon wafer substrate from room temperature to 1300°C, the heating time is 15s, annealing for 15s, cooling to 400°C, holding for 12s, then raising the temperature from 400°C to 1300°C, the heating time is 15s, annealing for 15s, cooling to 400°C, holding for 12s, and so on, annealing for a total of 6 times to obtain a Si(111)-7×7 substrate;

[0077] S2. Growth of Cd(0001) thin film: Under vacuum conditions, the cadmium source is degassed, and then heated to evaporate cadmium atoms onto the surface of the Si(111)-7×7 substrate to obtain a Cd(0001) thin film, specifically including:

[0078] S21, put the metallic cadmium with purity of 99.999% into the cadmium source placement component 6, and -10 Torr, a DC power supply of 5 was used to power the heating wire, and the temperature of the cadmium source was raised by 20°C every 10 minutes, so that the cadmium source was raised from room temperature to 60°C, and the vacuum degree was stabilized to 6.0×10 -10 Torr and then heated for 30 min to fully degas the cadmium source. The cadmium source placement component 6 in this embodiment is a crucible;

[0079] S22, using a DC power supply 5 to heat the degassed cadmium source to evaporate cadmium atoms onto the upper surface of the Si(111)-7×7 substrate, the evaporation time is 30 minutes, wherein the heating temperature is 55° C., while the temperature of the Si(111)-7×7 substrate is maintained at room temperature, so as to grow a Cd(0001) film with a thickness of more than 20 atomic layers, thereby obtaining a Cd(0001) film with a thickness of more than 20 atomic layers;

[0080] S3. Growth of molecular thin film: Under vacuum conditions, the p-terphenyl molecules are degassed, and then heated to evaporate the p-terphenyl molecules onto the surface of the Cd (0001) film to obtain a p-terphenyl molecule (110) thin film, specifically comprising:

[0081] S31, put the p-terphenyl molecules into the crucible 8, and then place the crucible 8 in the heating furnace 9, and heat the crucible 8 in a vacuum furnace higher than 9.0×10 -10 Torr, the p-terphenyl molecules were heated to 40°C by the heating furnace 9 to fully degas the p-terphenyl molecules. During the degassing process, the water circulation cooling device 7 was simultaneously turned on until the vacuum degree stabilized to 9.0×10 -10 Torr;

[0082] S32, heating the degassed p-terphenyl molecules in a heating furnace 9 so that the p-terphenyl molecules are evaporated onto the upper surface of the Cd (0001) film, wherein the heating temperature is 35° C. while maintaining the Cd (0001) film at approximately -183° C. to form a molecular film with a p-terphenyl molecule (110) face, thereby obtaining a terphenyl molecule (110) film;

[0083] S4. Growth of an alkali metal-doped p-terphenyl molecule film: degassing the alkali metal source under vacuum conditions, and then heating to evaporate alkali metal atoms onto the surface of the p-terphenyl molecule (110) film to obtain an alkali metal-doped p-terphenyl molecule film, specifically comprising:

[0084] S41, put the potassium source into the alkali metal source placement part 11, and -10 Torr, the potassium source was heated to 420°C using a DC power supply 5. In order to obtain a stable power output, the DC current of the DC power supply 5 was set to 5.2A until the vacuum degree stabilized to 6.0×10 -10 Torr, so that the potassium source is fully degassed;

[0085] S42, using a DC power supply 5 to heat the degassed potassium source, so that potassium atoms are evaporated onto the surface of the p-terphenyl molecule (110) film, wherein the heating temperature is 410° C., the coverage is controlled to be about 0.8 ML, and the p-terphenyl molecule (110) film is maintained at about -163° C. to obtain a potassium-doped p-terphenyl molecule film;

[0086] S5. Growth of an alkali metal thin film: Annealing the alkali metal-doped p-terphenyl molecular film under vacuum conditions to obtain an alkali metal thin film, specifically comprising:

[0087] S51, when the vacuum degree is higher than 6.0×10 -10 Under the condition of 1000 Torr, the potassium-doped p-terphenyl molecular film is placed in a vacuum preparation chamber 1 at room temperature for about 25 minutes to complete the room temperature annealing process to obtain an alkali metal potassium film.

[0088] Detection and Analysis

[0089] The p-terphenyl molecule (110) thin film, alkali metal-doped p-terphenyl molecule thin film and alkali metal thin film prepared in Example 2 and Example 3 were respectively sent into a scanning tunneling microscope (STM) cavity for scanning observation of the film morphology and microstructure of the p-terphenyl molecule (110) thin film, alkali metal-doped p-terphenyl molecule thin film and alkali metal potassium thin film. The film morphology and microstructure of the p-terphenyl molecule (110) thin film prepared in Example 2 and Example 3 are as follows: Figure 2 and Figure 3As shown, the film morphology and microstructure of the alkali metal-doped p-terphenyl molecular film prepared in Example 2 and Example 3 are as follows: Figure 4 and Figure 5 As shown, the film morphology and microstructure of the alkali metal films prepared in Example 2 and Example 3 are as follows Figure 6 shown.

[0090] in, Figure 2 a and 3a represent the film morphology of the terphenyl molecule (110) film, Figure 2 b and 3b represent the microstructure of the terphenyl molecule (110) film. Figure 4 a and 5a represent the film morphology of alkali metal-doped p-terphenyl molecular films. Figure 4 b and 5b show the microstructure of alkali metal-doped p-terphenyl molecular films. Figure 6 a represents the film morphology of the alkali metal film, Figure 6 b shows the microstructure of the alkali metal film.

[0091] from Figure 2 Comparative observations in a and 3a show that the terphenyl molecule (110) films prepared in Example 2 and Example 3 exhibit different film morphologies. Figure 2 The molecular film in a can be seen as two molecular steps with no surface vacancies; Figure 3 The molecular film in a has only one high step and there are surface vacancies. However, they all show a layer island growth pattern, that is, the terphenyl molecules first completely cover the surface of the cadmium (0001) film, and then form molecular islands as the molecular coverage increases. Figure 2 From the comparative observation in b and 3b, it can be seen that the terphenyl molecule (110) films prepared in Example 2 and Example 3 exhibit different microstructures. Figure 2 In b, the p-terphenyl molecules appear in upright and flat positions, with adjacent periodic distribution structures, and the two-dimensional lattice orientation is along the direction of the substrate; Figure 3 The molecular posture in b is Figure 2 Same as in b, but with the same orientation as Figure 2 b forms an angle of 90 degrees.

[0092] from Figure 4 Comparative observations in 5a and 5a show that the alkali metal-doped terphenyl molecular films prepared in Example 2 and Example 3 exhibit different film morphologies. Figure 4 The alkali metal-doped terphenyl film in a shows two steps, and the surface is smooth and defect-free; Figure 5 The molecular film in a also has two steps, but there are defects on the surface and the edge of the step is rough. This shows that with the increase of the coverage of alkali metal atoms, the molecular arrangement of the terphenyl molecule (110) film surface changes, and some molecules migrate and desorb, thus forming defects. Figure 4 Comparative observations in 5b and 5b show that the alkali metal-doped terphenyl molecular films prepared in Example 2 and Example 3 exhibit different microstructures. Figure 4 In b, the alkali metal-doped p-terphenyl molecules exhibit an edge-sharing honeycomb-like structure; Figure 5 The alkali metal-doped terphenyl molecules in (b) exhibit a honeycomb-like structure with shared edges, which is disrupted by adjacent polymers, and the periodicity is not obvious. The results show that the alkali metal doping concentration affects the surface morphology of the mixture.

[0093] from Figure 6 a It can be seen from the observation that the alkali metal films prepared in Example 2 and Example 3 have similar morphologies, showing irregular potassium islands with a thickness of two atoms; Figure 6 b It can be seen from the observation that the microstructure of the alkali metal thin films prepared in Example 2 and Example 3 presents a surface morphology of potassium (110) surface.

[0094] In summary, the method for preparing an alkali metal thin film of the present invention utilizes molecular beam epitaxy technology in an ultra-high vacuum environment. First, a clean silicon (111)-7×7 substrate is prepared; second, an atomically resolved cadmium (0001) thin film is prepared; third, a p-terphenyl molecular thin film is grown on the surface of the cadmium (0001) thin film to prepare a p-terphenyl molecular (110) thin film with a clean surface; fourth, a mixture of alkali metal-doped p-terphenyl molecular thin films is prepared; and fifth, the alkali metal-doped p-terphenyl molecular thin film is annealed at room temperature to prepare an alkali metal thin film, thereby epitaxially growing potassium atoms on the p-terphenyl molecular thin film from bottom to top, and annealing segregates to form an alkali metal (110) surface structure. Compared with other methods, the method is more conducive to obtaining clear microstructures and properties, effectively expanding the application range of alkali metal thin films, and has promotion and application value in the field of thin film material technology.

[0095] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A method for preparing an alkali metal thin film, characterized in that: The following steps are involved: Preparation of silicon (111)-7×7 substrate: A silicon (111)-7×7 substrate is prepared by using a silicon wafer; Growth of cadmium (0001) thin films: Under vacuum conditions, the cadmium source is degassed, and then heated to evaporate cadmium atoms onto the surface of a silicon (111)-7×7 substrate to obtain a cadmium (0001) thin film. During the evaporation process, the temperature of the silicon (111)-7×7 substrate is maintained at room temperature. Growth of a p-terphenyl (110) film: The p-terphenyl molecules are degassed under vacuum conditions and then heated to evaporate the p-terphenyl molecules onto the surface of a cadmium (0001) film to obtain a p-terphenyl (110) film. During the evaporation process, the temperature of the cadmium (0001) film is maintained between -185°C and -180°C. Growth of an alkali metal-doped p-terphenyl molecule (110) thin film: degassing an alkali metal source under vacuum conditions, then heating the p-terphenyl molecule (110) thin film to allow alkali metal atoms to evaporate into the p-terphenyl molecule (110) thin film, thereby obtaining an alkali metal-doped p-terphenyl molecule thin film; during the evaporation process, the temperature of the p-terphenyl molecule (110) thin film is maintained between -155°C and -150°C; Growth of alkali metal thin film: Under vacuum conditions, the alkali metal-doped p-terphenyl molecular film is placed in a vacuum and left at room temperature for 20 to 40 minutes to increase the temperature of the alkali metal-doped p-terphenyl molecular film from -195°C to -110°C. The film is then passed into a scanning tunneling microscope (STM) and cooled to -195°C to complete the annealing process to obtain an alkali metal thin film.

2. The method for preparing an alkali metal thin film according to claim 1, wherein: The alkali metal source is selected from at least one of a lithium source, a sodium source, a potassium source, a rubidium source and a cesium source; The potassium source is a mixture of potassium chromate and zirconium aluminum alloy; The cadmium source is metallic cadmium.

3. The method for preparing an alkali metal thin film according to claim 1, wherein: The preparation of the Si(111)-7×7 substrate comprises: sequentially cleaning, degassing and annealing a silicon wafer to obtain a Si(111)-7×7 substrate; The cleaning is carried out by ultrasonic cleaning using alcohol and acetone in sequence; The degassing is carried out at a vacuum degree of 6.0×10 -9 Torr and a temperature of 400-600 ° C for 8-12 hours, and then cooled to room temperature; The annealing adopts a cyclic annealing process, which is to raise the temperature from room temperature to 1000-1300°C within 5-20 seconds, anneal for 13-18 seconds, cool down to 400°C, hold for 10-15 seconds, then raise the temperature from 400°C to 1000-1300°C within 5-20 seconds, anneal for 13-18 seconds, cool down to 400°C, hold for 10-15 seconds, and repeat this cycle for a total of 5-8 annealing times.

4. The method for preparing an alkali metal thin film according to claim 1, wherein: The cadmium source is degassed at a vacuum degree higher than 6.0×10 -10 Torr, the temperature of the cadmium source was raised by 20°C every 10 min, from room temperature to 60°C, and the vacuum was stabilized to 6.0×10 -10 After 1000 ℃, the mixture was heated for 25-35 minutes. Then, cadmium atoms were evaporated onto the surface of the silicon (111)-7×7 substrate at a temperature of 50°C. The evaporation time of cadmium atoms onto the surface of the silicon (111)-7×7 substrate is 25~30min.

5. The method for preparing an alkali metal thin film according to claim 1, wherein: The degassing of the p-terphenyl molecules is carried out at a vacuum degree higher than 9.0×10 -10 Torr, the p-terphenyl molecule was heated to 40°C until the vacuum degree stabilized to 9.0×10 -10 Torr; then, the p-terphenyl molecules were evaporated onto the surface of the cadmium (0001) film at a temperature of 35°C.

6. The method for preparing an alkali metal thin film according to claim 1, wherein: The alkali metal source is degassed at a vacuum degree higher than 6.0×10 -10 Torr, heat the alkali metal source to 420 ° C until the vacuum degree stabilizes to 6.0×10 -10 Torr; then evaporating alkali metal atoms into the p-terphenyl (110) molecular film at a temperature of 400°C; During the process of evaporating alkali metal atoms into the p-terphenyl molecule (110) film, the coverage of the alkali metal atoms on the surface of the p-terphenyl molecule (110) film is 0.6-1.2ML.

7. An alkali metal thin film obtained by the preparation method according to any one of claims 1 to 6.

8. An application of an alkali metal film prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The alkali metal thin film is used in solar cells and alkali metal ion batteries.

9. A device for implementing the method for preparing an alkali metal thin film according to any one of claims 1 to 6, characterized in that: The invention comprises a vacuum preparation chamber (1), a sample holder (2), a crossbar (3), a magnetic handle (4), a DC power supply (5), a cadmium source placement component (6), a water circulation cooling device (7), a crucible (8), a heating furnace (9) and an alkali metal source placement component (11); the sample holder (2) is located inside the cavity of the vacuum preparation chamber (1), the magnetic handle (4) and the DC power supply (5) are located outside the cavity of the vacuum preparation chamber (1), the cadmium source placement component (6) is located at the bottom of the vacuum preparation chamber (1), and a part of it is located inside the cavity of the vacuum preparation chamber (1), and the other part is located outside the cavity of the vacuum preparation chamber (1), the heating furnace (9) is located at the bottom of the vacuum preparation chamber (1), and a part of it is located at the bottom of the vacuum preparation chamber (1). The alkali metal source placement component (11) is located on the side wall of the vacuum preparation chamber (1), and a portion of the alkali metal source placement component (11) is located inside the cavity of the vacuum preparation chamber (1), and the other portion is located outside the cavity of the vacuum preparation chamber (1); one end of the cross bar (3) is connected to the sample holder (2), and the other end is connected to the magnetic handle (4); the sample holder (2), the alkali metal source placement component (11), the cadmium source placement component (6) and the water circulation cooling device (7) are all connected to the DC power supply (5); the crucible (8) is located in the heating furnace (9), and the crucible (8) is located outside the cavity of the vacuum preparation chamber (1); the heating furnace (9) is built into the water circulation cooling device (7); When preparing an alkali metal thin film, a silicon wafer is placed on a sample holder (2), and a crossbar (3) is adsorbed on the inner tube wall by a magnetic handle (4), driving the crossbar (3) to move, and the sample holder (2) containing the silicon wafer is sent into a vacuum preparation chamber (1), and the sample holder (2) is located above a heating furnace (9), and a direct current power supply (5) is used to heat the silicon wafer to form a silicon (111)-7×7 substrate; a cadmium source is placed in a cadmium source placement component (6), and a direct current power supply (5) is used to heat and degas the cadmium source and evaporate it onto the surface of the silicon (111)-7×7 substrate to obtain a cadmium (0001) thin film; and a terphenyl molecule is placed in The crucible (8) is placed in a heating furnace (9), and the terphenyl molecules are degassed by the heating furnace (9) and evaporated onto the surface of the cadmium (0001) film to obtain a terphenyl molecule (110) film, and the water circulation cooling device (7) is turned on at the same time; an alkali metal source is loaded into the alkali metal source placement component (11), and a direct current power supply (5) is used to degas the alkali metal source and evaporate it onto the surface of the terphenyl molecule (110) film to obtain an alkali metal-doped terphenyl molecule film; the alkali metal-doped terphenyl molecule film is annealed at room temperature in a vacuum preparation chamber (1) to obtain an alkali metal film.

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