Transfer method of uniform graphene film
Technical Field
The invention belongs to the technical field of conductive materials, and particularly relates to a transfer method of a uniform graphene film.
Background
Transparent electrodes with high optical transparency, electrical conductivity and uniformity are an important component of devices including touch screens, displays, solar cells and light emitting diodes. Graphene is a new carbonaceous material with a two-dimensional cellular structure formed by tightly packing single-layer or multiple-layer carbon atoms, wherein the carbon atoms are mutually subjected to SP (SP) passage2The carbon atoms are hybridized into bonds, each carbon atom and three adjacent carbon atoms form a strong sigma bond, the connection is very firm, a stable hexagonal shape is formed, and the light transmittance and the electrical conductivity are excellent. These characteristics make graphene an ideal substitute material for Indium Tin Oxide (ITO) which is a traditional transparent electrode material, and particularly, a high-quality single-layer or multi-layer graphene film is successfully grown on some metals by a Chemical Vapor Deposition (CVD) method, which greatly promotes the development of a graphene thin film transparent electrode. It has some inherent disadvantages including the increased cost of indium thin and brittleness due to its ceramic nature.
It is known that transparent electrodes having high conductivity and uniformity are essential for application devices. Typically, after PMMA/graphene is transferred to a target substrate with a polymer as a carrier (usually PMMA), the PMMA needs to be removed to expose the graphene surface to act as an electrode. However, in the process of removing PMMA, gaps are inevitably generated in graphene, and the generated gaps reduce charge transfer channels, thereby making the graphene sheet resistance uneven. Meanwhile, according to the experimental result, the size of the surface resistance is proportional to the size of the graphene gap, that is, the larger the gap area is, the larger the graphene surface resistance is, the smaller the conductivity is, and thus the requirement of the transparent electrode on high conductivity cannot be met. Similarly, the graphene film grown on some metals by the chemical vapor deposition method replicates the morphology of the metal substrate, and the PMMA is used to transfer the graphene from the metal substrate, so the unevenness of the microstructure of the metal substrate also causes poor flatness of the graphene, which also has a great influence on the uniformity and conductivity of the graphene transparent electrode. Therefore, it is very important to develop a method capable of improving the flatness of graphene, reducing the sheet resistance of graphene and improving the uniformity of the sheet resistance of graphene.
Disclosure of Invention
The invention aims to make up for the defects of the prior art and provides a uniform graphene film transfer method.
The invention is realized by the following technical scheme:
a uniform graphene film transfer method comprises the following steps:
(1) growing on the surface of copper foil with the thickness of 24-25um by a chemical vapor deposition method to obtain continuous graphene, spin-coating PMMA with the concentration of 100mg/ml on the surface of the graphene by a spin coater, and baking for 5-6min on a constant temperature table at the temperature of 168-172 ℃;
(2) after baking, putting the surface which is not coated with PMMA into a plasma cleaning machine for treatment for 1-2min, removing graphene on the copper foil on the back surface, and then putting PMMA/graphene/copper foil into FeCl with the concentration of 5mol/L3Etching copper foil in the solution for 25-35min, transferring to deionized water, soaking for 8-12min, and transferring to new 5mol/L FeCl3Etching the residual copper foil in the solution for 2-2.5 h to remove floccules on the copper foil, transferring the completely etched copper foil to deionized water to clean the residual FeCl3Etching solution, transferring to dilute hydrochloric acid to further clean the surface residueRemaining FeCl3Etching liquid and other impurities, finally transferring the graphene film into deionized water to clean residual hydrochloric acid on the surface of the graphene film, and after cleaning is finished, beating the graphene film for 14-16min by using a plasma cleaning machine to obtain SiO2Obtaining a sample PMMA/graphene/SiO by taking PMMA/graphene with Si2/Si;
(3) Mixing PMMA/graphene/SiO2Drying the Si sample for 2.5-3h, completely baking the sample on a constant temperature table, and then putting the sample into a tubular furnace for low-pressure annealing to remove PMMA glue;
(4) annealing and then carrying out graphene/SiO2Taking out the Si sample, spin-coating PMMA glue again, placing the sample on a constant temperature table at 165-175 ℃, baking for 5-6min, and scraping the sample to enable the SiO to be in a side-scraping mode2Exposing the/Si substrate, then putting the exposed/Si substrate into 1 mol/L HF acid for etching, transferring the substrate into deionized water after etching, and cleaning up residual HF to obtain PMMA/graphene;
(5) and (3) putting the two pieces of cleaned PET into a plasma cleaning machine for treatment for 15-16min, making the surfaces of the PET hydrophilic, and then reversely buckling PMMA/graphene to obtain graphene/PMMA, and finally transferring the graphene/PMMA/PET onto a target substrate PET to obtain the graphene/PMMA/PET with good flatness.
The PMMA model is Sigma Aldrich, #182265, and the molecular weight is 996K.
In the step 3, the temperature is controlled to be 55-65 ℃ firstly, the temperature is kept for 25-30min, then the temperature is raised to be 95-105 ℃, the temperature is kept for 25-30min, then the temperature is raised to be 165-175 ℃, and the temperature is kept for 25-30 min.
The low-pressure annealing condition in the step 3 is controlled to be 580-620 ℃ and 20 sccm Ar for 2-2.5 hours.
The invention has the advantages that:
(1) the novel graphene film transfer method does not remove PMMA carriers, does not affect the application of the graphene film as a transparent electrode, avoids the generation of graphene gaps in the PMMA removing process, and is good in continuity and uniform in conductivity.
(2) In the process of transferring graphene, the silicon wafer with the oxide layer is used as an intermediary transfer substrate, and the transferred graphene film has better flatnessThe conductivity is higher, the surface resistance value is smaller, and the conductivity is mainly distributed at 210 omega sq-1About, the minimum energy is 109 Ω sq-11/5 for graphene sheet resistance transferred directly from copper foil to remove PMMA carrier.
(3) The change coefficient of the resistance of the graphene transparent electrode film prepared by the novel graphene film transfer method can reach 3.37%, and the graphene transparent electrode film has good uniformity.
(4) The novel graphene film uniform transparent electrode transfer method is simple in process and low in cost.
Detailed Description
The technical scheme of the invention is further explained by combining the specific examples as follows:
a uniform graphene film transfer method comprises the following steps:
(1) growing on the surface of copper foil with the thickness of 25um by a chemical vapor deposition method to obtain continuous graphene, spin-coating PMMA with the concentration of 100mg/ml on the surface of the graphene by a spin coater, and baking for 5min at 170 ℃ on a constant temperature table after the spin coating;
(2) after baking, the side which is not coated with PMMA is placed into a plasma cleaning machine for treatment for 1min, graphene on the copper foil on the back side is removed, and then PMMA/graphene/copper foil is placed into FeCl with the concentration of 5mol/L3Etching copper foil in the solution for 30min, transferring to deionized water, soaking for 10min, and transferring to new 5mol/L FeCl3Etching the residual copper foil in the solution for 2 h to remove floccules on the copper foil, transferring the completely etched copper foil to deionized water to clean the residual FeCl3Etching solution, transferring to dilute hydrochloric acid to further clean FeCl remained on the surface of the etching solution3Etching liquid and other impurities, finally transferring the graphene film into deionized water to clean residual hydrochloric acid on the surface of the graphene film, and after cleaning is finished, beating the graphene film for 15min by using a plasma cleaning machine to obtain SiO2Obtaining a sample PMMA/graphene/SiO by taking PMMA/graphene with Si2/Si;
(3) Mixing PMMA/graphene/SiO2Drying the Si sample for 2.5h, completely baking the sample on a constant temperature table, wherein the baking process is carried outFirstly controlling the temperature to be 60 ℃, keeping the temperature for 30min, then heating to 100 ℃, keeping the temperature for 30min, then heating to 170 ℃, keeping the temperature for 30min, then placing the material into a tubular furnace for low-pressure annealing, controlling the condition to be 20 sccm Ar at 600 ℃, keeping the annealing for 2 hours, and removing PMMA glue;
(4) annealing and then carrying out graphene/SiO2Taking out the Si sample, spin-coating PMMA glue again, placing the sample on a constant temperature table at 170 ℃, baking for 5min, and scraping the sample to enable the SiO to be in a side-scraping mode2Exposing the/Si substrate, then putting the exposed/Si substrate into 1 mol/L HF acid for etching, transferring the substrate into deionized water after etching, and cleaning up residual HF to obtain PMMA/graphene;
(5) and (3) putting the two pieces of cleaned PET into a plasma cleaning machine for treatment for 15min, making the surfaces of the PET hydrophilic, and then reversely buckling PMMA/graphene to obtain graphene/PMMA, and finally transferring the graphene/PMMA/PET onto a target substrate PET to obtain the graphene/PMMA/PET with good flatness.