Large-size single crystal gold sheet based on polycrystalline gold film recrystallization and preparation method of large-size single crystal gold sheet

Abstract

The invention discloses a large-size single crystal gold sheet based on polycrystalline gold film recrystallization and a preparation method of the large-size single crystal gold sheet, the thickness of the gold sheet is 10-100nm, the transverse size of the single crystal gold sheet is greater than 20 microns, and the transverse size of the large-size single crystal gold sheet is greater than 50 microns. According to the method, the single crystal gold piece is synthesized based on polycrystalline gold film recrystallization, the coverage rate of the single crystal gold piece can reach more than 1000 pieces per square centimeter, only two substances of tetra-n-octyl ammonium bromide and gold are involved, compared with a solution growth method, impurities are more difficult to introduce, the synthesized gold piece has fewer surface pollutants, and the quality of the gold piece is improved. The covering of another substrate plays an indispensable role in the initial nucleation link of the gold platelets, and no gold platelets are synthesized if nucleation cannot be carried out. And meanwhile, large-size growth is also facilitated in the subsequent growth link, so that compared with the prior art, a gold sheet with a larger size can be obtained within the same time, the root mean square roughness of the surface of the single crystal gold sheet is smaller than 0.5 nm, the ultra-flat surface quality is achieved, and the optical loss of the single crystal gold sheet is greatly reduced.

Description

Technical Field

[0001] The invention relates to the field of metal nanomaterials, and in particular to a large-size single-crystal gold sheet based on polycrystalline gold film recrystallization and a preparation method thereof. Background Art

[0002] Low-dimensional single-crystalline gold nanomaterials (such as gold nanoparticles, gold nanowires, gold flakes, etc.) have important application prospects in surface enhanced Raman scattering, (bio)chemical sensing, nonlinear optics and nanophotonic devices due to their unique physicochemical properties and the ability to localize the nanoscale light field given by the surface plasmon response, and have attracted extensive attention from researchers. Generally, people use a combination of metal deposition and electron beam lithography (EBL) or focused ion beam (FIB) technology to prepare gold nanoplasmonic structures. However, the surface of the gold nanoplasmonic structure prepared by this method is rough and polycrystalline. The scattering of electrons on the rough surface and grain boundaries will introduce optical losses, thereby significantly reducing the quality factor of the plasmon resonance and the maximum near-field enhancement that can be achieved, ultimately limiting the application performance of the plasmonic nanostructure. In addition, for polycrystalline gold films, grains with different crystal orientations have different hardnesses when facing ion beam etching. Therefore, gold nanostructures prepared by FIB processing usually have poor sidewall smoothness and poor morphology consistency, which will further introduce scattering losses and inconsistent optical responses of the samples. Therefore, improving the structural quality (including crystal quality and surface roughness) of gold nanomaterials used to prepare plasmonic devices is crucial to fully exert the application performance of plasmonic nanostructures.

[0003] In the current study, researchers have developed a variety of wet chemical methods (achieved by reducing chloroaurate ions in solution) to prepare single-crystalline gold flakes, including polyol reduction, biomolecule reduction, electrochemical synthesis, and photochemical synthesis. However, when using these methods to prepare single-crystalline gold flakes, most of the gold flakes are freely formed in the reaction solution, and the yield of high-quality single-crystalline gold flakes obtained on the substrate is relatively low. At the same time, the gold flakes synthesized on the substrate are usually contaminated by the gold nanoparticle byproducts in the reaction solution.

[0004] Therefore, although single crystal gold flakes have important application prospects in basic research and the construction of a new generation of optoelectronics, electronics and quantum devices, there is still a lack of simple and efficient methods to prepare large-sized single crystal gold flakes. The present invention adopts a method for preparing large-sized single crystal gold flakes based on recrystallization of polycrystalline gold film, which has a simple preparation process, high single crystal gold flake yield and low pollution.

[0005] The prior art has the following technical problems:

[0006] 1) It takes a long time to prepare large-sized gold flakes with a size > 50 μm.

[0007] 2) The synthesis yield of single crystal gold sheets synthesized on-chip is low.

[0008] 3) The surface of single crystal gold sheets synthesized by solution method often has pollutants such as particles, which affects the actual effect of subsequent gold sheets in device applications. Summary of the invention

[0009] The purpose of the present invention is to provide a large-sized single-crystal gold sheet based on polycrystalline gold film recrystallization and a preparation method thereof. The method can be used to obtain a large-sized single-crystal gold sheet conveniently and efficiently.

[0010] The invention discloses a method for preparing a large-size single-crystal gold sheet based on polycrystalline gold film recrystallization. The preparation method comprises the following steps: firstly decomposing the polycrystalline gold film prepared by sputtering and then recrystallizing the polycrystalline gold film by tetra-n-octylammonium bromide (TOABr), thereby synthesizing the large-size single-crystal gold sheet.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0012] The invention discloses a large-size single-crystal gold sheet based on polycrystalline gold film recrystallization. The thickness of the gold sheet is 10-100nm, and the lateral size of the large-size single-crystal gold sheet is greater than 20μm.

[0013] As a further improvement, the large-sized single crystal gold sheet described in the present invention has a lateral dimension greater than 50 μm.

[0014] As a further improvement, the surface root mean square roughness of the large-sized single-crystal gold sheet described in the present invention is less than 1 nm.

[0015] The present invention also discloses a method for preparing a large-size single crystal gold sheet based on recrystallization of a polycrystalline gold film, comprising the following steps:

[0016] 1) Preparation of initial polycrystalline gold film: preparing a polycrystalline gold film on a substrate by magnetron sputtering or thermal evaporation method;

[0017] 2) Preparation of large-sized single-crystalline gold flakes: Tetra-n-octylammonium bromide solid is placed on the surface of the polycrystalline gold film prepared in step 1), and heated to the reaction temperature on a hot plate. The reaction is carried out for a period of time to allow the gold film to react completely. Then, another substrate is covered on the surface of the molten liquid, and the substrates are heated and decomposed at the decomposition temperature for a certain period of time. The two substrates are removed, and the tetra-n-octylammonium bromide remaining on the surface is rinsed with an organic solvent, and dried with nitrogen. Large-sized single-crystalline gold flakes can be obtained on the surfaces of the two substrates.

[0018] As a further improvement, in steps 1) and 2) of the present invention, the substrate is a silicon wafer, a glass wafer, mica, quartz, calcium fluoride or sapphire.

[0019] As a further improvement, the organic solvent in step 2) of the present invention is acetone, ethanol or isopropanol.

[0020] As a further improvement, the reaction temperature in step 2) of the present invention is 130°C-150°C.

[0021] As a further improvement, in step 2) of the present invention, the decomposition temperature is ≥160° C. and the decomposition time is 1-3 hours.

[0022] As a further improvement, the coverage rate of the large-sized single crystal gold flakes synthesized by the present invention is greater than 1000 flakes / square centimeter.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) In the present invention, a polycrystalline gold film recrystallization method is used, and setting the decomposition temperature to ≥160°C is a necessary condition. At the same time, the synthesis of single crystal gold flakes at a higher decomposition temperature has a high efficiency, and the decomposition time is 1-3 hours, which is used to achieve the preparation of large-sized single crystal gold flakes with a lateral size of >20μm. A single crystal gold flake with a maximum size of 130μm can be obtained within 3 hours, and the number of gold flakes with a lateral size of >50μm is >50%;

[0025] (2) In the present invention, the synthesis of single crystal gold flakes based on recrystallization of polycrystalline gold film, especially the synthesis method of first completely reacting the gold in the gold film into a molten liquid and then decomposing and recrystallizing at high temperature, has a very high yield, and the coverage rate of single crystal gold flakes can reach >1000 pieces / square centimeter;

[0026] (3) In the present invention, since only two substances, tetra-n-octylammonium bromide and gold, are involved, it is less likely to introduce impurities compared to the solution growth method, and the surface pollutants of the synthesized gold flakes are less;

[0027] (4) In the present invention, covering another substrate plays an indispensable role in the initial nucleation stage of the gold flakes. Failure to nucleate will result in the synthesis of no gold flakes. At the same time, it is also conducive to the growth of large sizes in the subsequent growth stage, so that larger gold flakes can be obtained in the same time compared with the prior art;

[0028] (4) In the present invention, the surface root mean square roughness of the single crystal gold sheet is less than 0.5 nm, with ultra-flat surface quality, greatly reducing its optical loss;

[0029] (5) In the present invention, a wide range of substrates can be selected, such as silicon wafer substrates, glass substrates, quartz substrates, sapphire substrates, mica substrates, calcium fluoride substrates, etc., which are all suitable for this method, thus expanding the application occasions of large-area single crystal gold wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process of the present invention;

[0031] Figure 2 This is an optical microscope picture of a single crystal gold sheet synthesized on a silicon wafer substrate;

[0032] Figure 3 This is an atomic force microscope image of the gold sheet surface;

[0033] Figure 4 This is the selected area electron diffraction pattern of a single crystal gold sheet obtained using a high-resolution transmission electron microscope. DETAILED DESCRIPTION

[0034] The preparation process of the present invention is further described below in conjunction with the accompanying drawings. The present invention discloses a large-sized single-crystal gold sheet based on the recrystallization of a polycrystalline gold film and a preparation method thereof. The specific process of synthesizing a large-area single-crystal gold sheet is as follows:

[0035] Embodiment 1:

[0036] Figure 1 The schematic diagram of the process of the present invention is as follows: Step 1: Prepare a 1.5 cm*2 cm silicon wafer substrate, and sputter at a rate of 0.17 nm / s at 5×10 -6 A 30 nm thick polycrystalline gold film was sputtered under 200-1000 Torr conditions.

[0037] Step 2: Place the initial polycrystalline gold film prepared in step 1 on a hot plate, raise the temperature of the hot plate to 140°C, add 0.3g of tetra-n-octylammonium bromide solid to the surface, and the tetra-n-octylammonium bromide solid will melt and evenly cover the surface of the gold film. Keep heating at 140°C for 1 hour to completely melt the polycrystalline gold film. Then take another silicon wafer substrate, cover it on the liquid, raise the temperature to 160°C and heat for 2 hours to decompose the gold flakes again. After the reaction is completed, rinse both silicon wafer substrates repeatedly with acetone and ethanol to remove the residual tetra-n-octylammonium bromide on the surface. The single crystal gold flake is prepared and can be stored in ethanol for a long time.

[0038] Embodiment 2:

[0039] Step 1: Prepare a 1.5 cm*2 cm glass substrate and sputter at a rate of 0.17 nm / s at 5×10 -6 A 30 nm thick polycrystalline gold film was sputtered under 200-10000 Torr conditions.

[0040] Step 2: Place the initial polycrystalline gold film prepared in step 1 on a hot plate, raise the temperature of the hot plate to 140°C, add 0.3g of tetra-n-octylammonium bromide solid to the surface, and the tetra-n-octylammonium bromide solid will melt and evenly cover the surface of the gold film. Keep heating at 140°C for 1 hour to completely melt the polycrystalline gold film. Then take another silicon wafer substrate, cover it on the liquid, raise the temperature to 160°C and heat for 2 hours to decompose the gold flakes again. After the reaction is completed, rinse both substrates repeatedly with acetone and ethanol to remove the residual tetra-n-octylammonium bromide on the surface. The single crystal gold flake is prepared and can be stored in ethanol for a long time.

[0041] Embodiment three:

[0042] Step 1: Prepare a 1.5 cm*2 cm glass substrate and sputter at a rate of 0.17 nm / s at 5×10 -6 A 30 nm thick polycrystalline gold film was sputtered under 200-10000 Torr conditions.

[0043] Step 2: Place the initial polycrystalline gold film prepared in step 1 on a hot plate, raise the temperature of the hot plate to 140°C, add 0.3g of tetra-n-octylammonium bromide solid to the surface, and the tetra-n-octylammonium bromide solid will melt and evenly cover the surface of the gold film. Keep heating at 140°C for 1 hour to completely melt the polycrystalline gold film. Then take another sapphire substrate, cover it on the liquid, raise the temperature to 160°C and heat for 2 hours to decompose the gold flakes again. After the reaction is completed, rinse both substrates repeatedly with acetone and ethanol to remove the residual tetra-n-octylammonium bromide on the surface. The single crystal gold flakes are prepared and can be stored in ethanol for a long time.

[0044] Embodiment 4:

[0045] Step 1: Prepare a 1.5cm*2cm silicon wafer substrate and sputter it at a rate of 0.17nm / s at 5×10 - 6 A 30 nm thick polycrystalline gold film was sputtered under 200-10000 Torr conditions.

[0046] Step 2: Place the initial polycrystalline gold film prepared in step 1 on a hot plate, raise the temperature of the hot plate to 140°C, add 0.3g of tetra-n-octylammonium bromide solid to the surface, and the tetra-n-octylammonium bromide solid will melt and evenly cover the surface of the gold film. Keep heating at 140°C for 1 hour to completely melt the polycrystalline gold film. Then take another mica substrate, cover it on the liquid, raise the temperature to 160°C and heat for 2 hours to decompose the gold flakes again. After the reaction is completed, rinse both substrates repeatedly with acetone and ethanol to remove the residual tetra-n-octylammonium bromide on the surface. The single crystal gold flakes are prepared and can be stored in ethanol for a long time.

[0047] Embodiment five:

[0048] Step 1: Prepare a 1.5cm*2cm silicon wafer substrate and sputter it at a rate of 0.17nm / s at 5×10 -6 A 40 nm thick polycrystalline gold film was sputtered under 200-10 ... Torr

[0049] Step 2: Place the initial polycrystalline gold film prepared in step 1 on a hot plate, raise the temperature of the hot plate to 140°C, add 0.3g of tetra-n-octylammonium bromide solid to the surface, and the tetra-n-octylammonium bromide solid will melt and evenly cover the surface of the gold film. Keep heating at 140°C for 1.2 hours to completely melt the polycrystalline gold film. Then take another silicon wafer substrate, cover it on the liquid, raise the temperature to 160°C and heat for 2 hours to decompose the gold flakes again. After the reaction is completed, rinse both substrates repeatedly with acetone and ethanol to remove the residual tetra-n-octylammonium bromide on the surface. The single crystal gold flake is prepared and can be stored in ethanol for a long time.

[0050] The prepared single crystal gold sheet was characterized, such as Figure 2 , 3 , as shown in 4: Figure 2 The optical microscope image shows that it has large yield and lateral size >20μm; Figure 3 Atomic force microscope images show that the surface roughness of the synthesized gold sheet is about 0.3nm, with atomic-level surface flatness; Figure 4 The electron diffraction pattern shows that the synthesized gold flakes have a single crystal structure.

[0051] Comparative Example 1:

[0052] In Example 1, the temperature was raised to 160°C for heating for 2 hours, which was replaced by maintaining the temperature at 140°C for heating for 2 hours. The remaining technical features were the same as those in Example 1. If the temperature was not raised to 160°C but maintained at 140°C during the decomposition stage, no gold flakes were synthesized. Therefore, in the present invention, the temperature increase is necessary for decomposition.

[0053] Comparative Example 2:

[0054] In Example 1, the step of taking another silicon wafer substrate and covering the liquid is eliminated, and the other technical characteristics are the same as those in Example 1. It can be seen that if another substrate is not covered on the surface during the decomposition stage, no gold sheet is synthesized. Therefore, covering another substrate is necessary in the present invention.

[0055] The tetra-n-octylammonium bromide used in this example was purchased from Aladdin Company, USA, and acetone and ethanol were purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd.

[0056] The above implementation method is only a description of the preferred implementation mode of the present invention, and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solution of the present invention by ordinary engineering and technical personnel in the field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A large-size single-crystal gold sheet based on recrystallization of polycrystalline gold film, characterized in that: The thickness of the gold sheet is 10-100 nm, and the lateral size of the single crystal gold sheet is greater than 20 μm.

2. The large-size single-crystal gold sheet based on polycrystalline gold film recrystallization according to claim 1, characterized in that: The large-size single crystal gold sheet has a lateral size of more than 50 μm.

3. The large-size single crystal gold sheet based on polycrystalline gold film recrystallization according to claim 1, characterized in that: The root mean square roughness of the surface of the large-sized single-crystal gold sheet is less than 1 nm.

4. A method for preparing a large-size single-crystal gold sheet based on recrystallization of a polycrystalline gold film, characterized in that: The steps include: 1) Preparation of initial polycrystalline gold film: preparing a polycrystalline gold film on a substrate by magnetron sputtering or thermal evaporation method; 2) Preparation of large-sized single-crystalline gold flakes: Tetra-n-octylammonium bromide solid is placed on the surface of the polycrystalline gold film prepared in step 1), and heated to the reaction temperature on a hot plate. The reaction is carried out for a period of time to allow the gold film to react completely. Then, another substrate is covered on the surface of the molten liquid, and the substrates are heated and decomposed at the decomposition temperature for a certain period of time. The two substrates are removed, and the tetra-n-octylammonium bromide remaining on the surface is rinsed with an organic solvent, and dried with nitrogen. Large-sized single-crystalline gold flakes can be obtained on the surfaces of the two substrates.

5. The method for preparing large-size single-crystal gold based on recrystallization of polycrystalline gold film according to claim 4, characterized in that: In the steps 1) and 2), the substrate is a silicon wafer, a glass wafer, mica, quartz, calcium fluoride or sapphire.

6. The method for preparing large-size single-crystal gold based on recrystallization of polycrystalline gold film according to claim 4 or 5, characterized in that: In the step 2), the organic solvent is acetone, ethanol or isopropanol.

7. The method for preparing large-size single-crystal gold based on recrystallization of polycrystalline gold film according to claim 6, characterized in that: The reaction temperature in step 2) is 130°C-150°C.

8. The method for preparing large-size single-crystal gold based on recrystallization of polycrystalline gold film according to claim 7, characterized in that: In the step 2), the decomposition temperature is ≥160° C. and the decomposition time is 1-3 hours.

9. The method for preparing a large-size single crystal gold sheet based on recrystallization of a polycrystalline gold film according to claim 4, 5, 7 or 8, characterized in that: The coverage rate of the synthesized large-size single crystal gold sheets is greater than 1000 sheets / square centimeter.

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