CN113529013B - Method for cleaving two-dimensional material by using metal adhesive tape - Google Patents

Abstract

The invention discloses a method for cleaving a two-dimensional material by using a metal adhesive tape. The metal adhesive tape comprises a polymer film layer and a metal layer; the metal layer is a metal foil layer or a metal film layer, one surface of the metal layer is tightly attached to the polymer film layer, and the other surface of the metal layer is used for contacting with a crystal material to be cleaved; the method comprises the following specific steps: placing the crystal material to be cleaved between two metal adhesive tapes, pressing with force, uncovering to make the crystal material to be cleaved adhere to the metal layer respectively, and repeating the steps for multiple times to realize the stripping of the two-dimensional material; and (3) attaching the metal adhesive tape covering the crystals to a clean substrate, then lifting the adhesive tape, and leaving the thin-layer crystals on the substrate to finish the cleavage of the two-dimensional material. The invention can solve the problem of glue residue in the prior art, obtain the two-dimensional material with clean surface, and is beneficial to preparing the heterojunction sample with clean interface and high quality in the follow-up process; the two-dimensional material obtained after cleavage has no static electricity, and the dust absorption capacity of the material can be greatly reduced.

Description

A method for cleaving two-dimensional materials using metal tape

technical field

The invention relates to the technical field of nanomaterial preparation, in particular to a method for cleaving two-dimensional materials by using metal tapes.

Background technique

Mechanical cleavage technology has become one of the important methods for preparing high-quality two-dimensional materials, and has shown unique advantages in the study of intrinsic physical properties of two-dimensional materials. The mechanical cleavage method currently used generally uses traditional adhesive tape as a cleavage tool, that is, coats organic glue on the polymer film, and relies on the adhesion of the organic glue to realize the cleavage of the crystal material.

The traditional mechanical cleavage method often has glue residue on the crystal material obtained after cleavage, and the material after cleavage is charged with static electricity due to the unavoidable frictional electrification during the process of crystal replication and cleavage, and is easy to absorb dust. High-quality heterojunction samples require clean surfaces of two-dimensional materials, so glue residue and easy dust collection are not conducive to the preparation of high-quality devices, which greatly reduces device performance.

Contents of the invention

Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for mechanically cleaving two-dimensional materials. The method uses a polymer film to support "metal tape" to replace the traditional tape, and utilizes the adhesion of the metal to the crystal material to realize the cleavage of the material. The method of the invention can solve the problems of glue residue and static electricity in the prior art. Cleaner and higher-quality two-dimensional materials can be obtained more efficiently to prepare higher-performance devices.

In the present invention, the polymer film is used as a support, the metal is pasted on the polymer film to form an adhesive tape for mechanical cleavage, and the steps similar to the traditional tape cleavage are used for cleavage. The crystal material to be cleaved is pressed between two metal tapes. Since the crystal and the metal are relatively sticky, after the metal tape is lifted, the crystal is divided into two to realize the replication of the crystal. After multiple crystal replications, the crystal Gradually thinner, the crystal coverage area gradually becomes larger, and then the tape covering the thin layer of crystals is pasted on a clean substrate, and then the tape is lifted to complete the cleavage of the two-dimensional material. The technical solution of the present invention is specifically introduced as follows.

A method for cleaving a two-dimensional material by using a metal tape, the metal tape includes a polymer film layer and a metal layer; the metal layer is a metal foil layer or a metal film layer, and the upper and lower surfaces of the metal layer are respectively named A surface and B surface , the A side of the metal layer is close to the polymer film layer, and the B side is used to be in contact with the crystal material to be cleaved; the specific steps are as follows:

Step 1. Place the crystal material to be cleaved between two metal tapes, press firmly, and then uncover the metal tape, so that the crystal material to be cleaved adheres to the surface of the metal layer B, repeat this step many times, Realize the exfoliation of two-dimensional materials;

Step 2: Lay the side of the metal tape covered with a thin layer of crystal material with a clean substrate, then lift off the metal tape, the crystal is dissociated, and freshly dissociated thin layer crystals remain on the substrate, completing the second step. cleavage of dimensional materials.

Preferably, when the metal layer is a metal foil layer, the preparation method of the metal tape is as follows:

S1: Perform surface activation treatment on the polymer film to expose the dangling bonds on the surface of the polymer film;

S2: Use a sharp object to scrape off the oxide layer on the upper surface of the metal foil;

S3: After sticking the surface-activated polymer film and the upper surface of the metal foil in step S1, press the two tightly together with a tablet press;

S4: Clean and deoxidize the lower surface of the metal foil at room temperature and in an air atmosphere;

S5: The metal foil tape treated in step S4 is liquid-sealed in isopropanol, put into a glove box, and dried with an inert atmosphere, and the preparation of the metal tape is completed.

In the above step S1, the polymer film is a flexible polymer material, and the polymer film plays a supporting role, and polyimide is used for it; the surface of the polymer film is treated with oxygen plasma.

In the above step S2, the metal foil is generally a metal or alloy with good ductility, the thickness of the metal foil is between 30-200 μm, and the metal foil is made of simple metal or alloy, including but not limited to indium or gold, or indium gallium Tin alloy, the sharp object is a scraper, etc. Treating the upper surface with sharp objects can make the surface rougher and fit more closely with thermoplastic polymers. And fresh unoxidized indium can be exposed. The viscosity of indium and polyimide is stronger than that of indium oxide. Therefore, exposing fresh indium can make the polymer film and metal adhere more closely. In subsequent experiments, the metal does not will fall.

In the above step S4, first soak in acetone for 40s-80s to remove the organic matter on the lower surface of the metal foil, and then air dry it naturally on a clean bench; then soak it in dilute hydrochloric acid for 40s-80s, then immerse it in deionized water and isopropyl Alcohol; this cleaning and deoxidation step facilitates obtaining a clean and flat surface, which is beneficial to the subsequent crystal dissociation effect.

Preferably, when the metal layer is a metal film layer, the preparation method of the metal tape is as follows:

(1) Preparing metal thin films on substrates, the preparation methods include but not limited to electron beam evaporation method, thermal evaporation method, magnetron sputtering method;

(2) Spin-coat the polymer solution on the surface of the gold film, and then bake it on a hot stage to evaporate the solvent, thereby forming a polymer film on the surface of the metal film;

(3) Use scotch tape to cling to the polymer film and lift it up, and at the same time the metal film is lifted to form a metal tape whose exposed surface is a flat metal film with a roughness similar to that of a silicon wafer.

In the above step (1), the substrate is a silicon wafer, and the composition of the metal film is a variety of inert metals that can be formed into thin films, such as Au and Pt. The thickness of the metal film is 50-200 nm; in the step (2), the polymer is selected from poly Either of methyl methacrylate or polysiloxanes. Preferably, in step 1, the crystal material to be cleaved is MoS ₂ , TaS ₂ , VSe ₂ , FeSe, WSe ₂ , WS ₂ , WTe ₂ , BP or FeI ₃ crystal material.

Preferably, in step 1, the metal tape and the crystal material are pressed together with force, so that the crystal material to be cleaved and the metal tape are closely attached.

Preferably, in step 2, the substrate is a silicon wafer or sapphire.

Compared with the existing technology, compared with the previously proposed mechanical cleavage method, the metal foil replaces the organic glue on the traditional tape, and has the following advantages:

(1) It can solve the problem of glue residue and obtain two-dimensional materials with clean surfaces. The 2D material cleaved by traditional tape will leave residual glue on the surface of the 2D material and the substrate. When preparing a 2D material heterojunction sample, these residual glue may remain at the interface of the 2D material, making the interface unsmooth. clean, thereby reducing the mobility of the sample. Therefore avoiding adhesive residue is the most important advantage.

(2) The cleaved two-dimensional material is free of static electricity, which can greatly reduce the dust-absorbing ability of the material to obtain higher-quality device performance.

(3) Metal tape can be used in an ultra-high vacuum environment, while traditional tapes will deflate in an ultra-high vacuum environment, which is not conducive to maintaining ultra-high vacuum.

Description of drawings

Figure 1. Schematic representation of a polymer film.

Figure 2. Use a sharp object to scrape off the oxide layer on the surface of the metal foil, and use a sharp object to remove the oxide layer on the A side.

Figure 3. Bonding metal foil to polymer film.

Figure 4. Removing the oxide layer on the B side of the metal foil in the metal tape.

Figure 5. The crystal to be cleaved is placed between two foil tapes.

Figure 6. Peel off the foil tape.

Figure 7. Put the adhesive tape with the crystal material firmly on the substrate and lift it off.

Figure 8. Optical micrograph of the few-layer two-dimensional _MoS2 material on a silicon wafer cleaved with the example indium foil tape in Example 1.

Figure 9. Optical micrographs of FeI ₃ crystal materials with different thicknesses on the sapphire substrate cleaved with indium foil tape in Example 1.

Fig. 10. Optical micrographs of different thicknesses of black phosphorus crystal materials on silicon wafers cleaved with indium foil tape in Example 1.

Figure 11. Optical micrograph of black phosphorous sample cleaved on metal tape in Example 2.

Symbols in the figure: 1-polymer film, 2-metal foil, 3-dilute hydrochloric acid solution, 4-crystal to be cleaved, 5-substrate material.

Detailed ways

The technical solutions of the present invention will be described in detail below in conjunction with the drawings and embodiments.

Example 1

The present invention provides a method for using metal foil to cleave two-dimensional materials. The specific steps are as follows:

S1: The polymer film (Figure 1) is surface activated to expose the dangling bonds on the polymer surface; the polymer film is used as a support material, which uses a flexible polymer material, such as polyimide. The support material needs to be relatively sticky to the metal foil, so that the metal foil will not fall off the support during the subsequent crystal replication and cleavage process and affect subsequent experiments. We found that polyimide is sticky to the metal film after plasma activation treatment, and can support the crystal better in the subsequent cleavage process, so we choose polyimide as the support.

S2: The upper and lower surfaces of the metal foil are named A-side and B-side respectively. Use a sharp object to scrape off the oxide layer on the A-side of the metal foil (Figure 2); the advantage of using a scraper to treat the oxide layer is that the obtained A-side is rough It is more tightly bonded to thermoplastic polymers; the exposed unoxidized indium can make the polymer film and metal film bond closer; scraping off the oxide layer with a scraper is easier than soaking in hydrochloric acid to remove the oxide layer.

S3: After sticking the surface-activated polymer film and the metal foil A side in step S1, use a tablet press to press the two tightly together to obtain a metal tape (Figure 3);

S4: Clean and deoxidize the B side of the metal foil in the metal foil tape at room temperature and air atmosphere (Figure 4); specifically, first soak in acetone for 40s-80s to remove the organic matter on the B side of the metal foil, and then clean Naturally air-dry on the table; then soak it in dilute hydrochloric acid for 40s-80s, and then immerse it in deionized water and isopropanol successively; the surface B of the metal foil after treatment is clean and smooth

S5: Liquid seal the metal foil tape treated in step S4 in isopropanol, pass it into the glove box, and dry it with an inert atmosphere, and the preparation of the metal foil tape is completed;

S6: Place the crystal material to be cleaved between the metal tapes prepared in the two steps S5 (Figure 5), press it firmly, and then uncover it (Figure 6), so that the crystal material to be cleaved sticks to the two tapes respectively. on a metal foil tape; repeating this step several times, the crystal material to be cleaved is continuously replicated, and the two-dimensional material on the tape is continuously thinned;

S7: Closely attach the master tape to the substrate (including but not limited to silicon wafer or sapphire), and then lift the master tape (Figure 7), the few-layer two-dimensional crystal material (TaS ₂ , VSe ₂ , FeSe, WSe ₂ , WS ₂ , WTe ₂ , BP, FeI ₃ and other crystal materials) stay on the substrate.

In a specific embodiment, the metal foil adopts indium foil, and the polymer film adopts polyimide film; scrape off the oxide layer on the A side of the indium foil with a scraper; soak in acetone for 1 min to remove the organic matter on the B side of the indium foil, and then Air-dry naturally on a clean bench, soak in dilute hydrochloric acid for 1 min, then immerse it in deionized water and isopropanol successively to complete the deoxidation of the B side of the indium foil, and then dry it with argon in a glove box ;The crystal material to be cleaved is MoS ₂ , when using two adhesive tapes to replicate the crystal, after the crystal is pasted between the two adhesive tapes, press the adhesive tape and the crystal as hard as possible, and heat at 50-80°C for about 10 minutes, so that After the cleavage crystal and the metal foil are more tightly bonded, after the crystal and the metal foil are tightly bonded, the two pieces of metal tape are uncovered, the two-dimensional material is divided into two, stuck on the two tapes, and the two-dimensional material is copied . Repeat the steps of crystal replication to increase the coverage area of the crystal on the metal and make the crystal thinner. Then attach the tape covered with the crystal to the silicon chip, and press the tape and the silicon chip firmly to make the crystal and the silicon chip fully contact. The tape is torn off, the two-dimensional material is dissociated from the interlayer, and a single-layer or few-layer two-dimensional _MoS2 material is obtained on the substrate. As shown in Figure 8, it is a MoS ₂ sample dissociated onto a silicon wafer substrate with a thickness of about 5 nm.

In a specific embodiment, indium foil is used as the metal foil, _FeI3 is used as the crystal material to be cleaved, and sapphire is used as the substrate. The obtained optical micrographs of _FeI3 materials with different thicknesses are shown in Figure 9, and the thinnest sample is about 5 nm .

In a specific embodiment, the metal foil is indium foil, the crystal material to be cleaved is black phosphorus crystal, and the substrate is silicon wafer. The obtained optical micrographs of black phosphorus materials with different thicknesses are shown in Figure 10. The thinnest sample is about 10 nm.

Example 2

A method for cleaving two-dimensional materials using metal tape, the specific steps are as follows:

S1: Prepare a metal thin film on a silicon wafer with a thickness of about 100 nm. The preparation methods include but are not limited to electron beam evaporation, thermal evaporation, and magnetron sputtering;

S2: Spin-coat a polymer solution on the surface of the above-mentioned gold film, and then bake it on a hot table to evaporate the solvent, thereby forming a polymer film on the surface of the metal film. The polymer can be polymethyl methacrylate, poly Silicones;

S3: Then stick the polymer film with scotch tape, lift it up, and the metal film will be lifted at the same time, forming a "metal tape" with a flat metal film on the exposed surface, and its structure is scotch tape/polymer film / Metal film, add a layer of polymer film in the middle as a support, in order to avoid the metal film from wrinkling, which is not conducive to the subsequent cleavage process;

S4: Place the crystal material to be cleaved between the metal tapes prepared in the two steps S3, press firmly, and then uncover, so that the crystal material to be cleaved is respectively adhered to the two metal tapes; repeat multiple times In this step, the crystal material to be cleaved is continuously copied, and the two-dimensional material on the tape is continuously thinned;

S5: The tape covering the crystal is closely attached to the substrate, and then the tape is lifted off, leaving a few layers of two-dimensional crystal material on the substrate.

In a specific embodiment, the metal thin film is made of gold, and the crystal material to be cleaved is made of black phosphorus crystal, which is attached to the black phosphorus crystal with a metal tape, and then the tape is peeled off to obtain a thin layer of crystals on the metal tape. The optical micrographs of black phosphorus materials with different thicknesses obtained above are shown in Figure 11, and the thinnest sample is about 5nm.

Claims (4)

1. A method for utilizing metal tape to cleave two-dimensional materials, characterized in that the metal tape comprises a polymer film layer and a metal layer; the metal layer is a metal foil layer or a metal film layer, and the upper and lower surfaces of the metal layer are named respectively It is the A side and the B side, the A side of the metal layer is close to the polymer film layer, and the B side is used to be in contact with the crystal material to be cleaved; the specific steps are as follows: Step 1. Place the crystal material to be cleaved between two metal tapes, press it firmly, and then uncover the metal tape, so that the crystal material to be cleaved adheres to the metal layer B of the two metal tapes respectively, Repeat this step several times to achieve the peeling of the two-dimensional material; Step 2: Attach the metal layer B side of the metal tape covering the thin-layer crystal material to a clean substrate, then lift the metal tape, and leave a few layers of two-dimensional crystal material on the substrate, thus completing the second step. cleavage of dimensional materials; where: When the metal layer is a metal foil layer, the preparation method of the metal tape is as follows: S1: Perform surface activation treatment on the polymer film to expose the dangling bonds on the surface of the polymer film; S2: Use a sharp object to scrape off the oxide layer on the upper surface of the metal foil; S3: After sticking the surface-activated polymer film and the upper surface of the metal foil in step S1, press the two tightly together with a tablet press; S4: Clean and deoxidize the lower surface of the metal foil at room temperature and in an air atmosphere; S5: liquid-seal the metal foil tape treated in step S4 in isopropanol, pass it into the glove box, and dry it with an inert atmosphere, and the preparation of the metal tape is completed; wherein: In step S1, polyimide is used for the polymer film; the surface of the polymer film is treated with oxygen plasma; In step S2, the thickness of the metal foil is between 30-200 μm, and the metal foil is made of gold, indium or indium-gallium-tin alloy material; In step S4, first soak in acetone for 40s-80s to remove the organic matter on the lower surface of the metal foil, and then air dry it naturally on a clean bench; then soak it in dilute hydrochloric acid for 40s-80s, then immerse it in deionized water and isopropanol successively middle; When the metal layer is a metal film layer, the preparation method of the metal tape is as follows: (1) Prepare a metal thin film on the substrate, and its preparation method includes thermal evaporation method or magnetron sputtering method; (2) Spin-coat the polymer solution on the surface of the gold film, and then bake it on a hot stage to evaporate the solvent, thereby forming a polymer film on the surface of the metal film; (3) Use scotch tape to cling to the polymer film, lift it up, and at the same time the metal film is lifted to form a metal tape whose exposed surface is a flat metal film; where: In step (1), the substrate is a silicon wafer, and the composition of the metal film is Au or Pt; the thickness of the metal film is between 50-200 nm; In step (2), the polymer is selected from any one of polymethyl methacrylate and polysiloxanes. 2. The method according to claim 1, wherein in step 1, the crystal material to be cleaved is MoS ₂ , TaS ₂ , VSe ₂ , FeSe, WSe ₂ , WS ₂ , WTe ₂ , BP or FeI ₃ crystal Material. 3 . The method according to claim 1 , wherein in step 1, the crystal material to be cleaved and the metal tape are firmly pressed together so that the two are closely attached. 4 . 4. The method according to claim 1, characterized in that, in step 2, the substrate is a silicon wafer or sapphire.

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