RU2757239C1 - Method for transferring graphene onto a polymer substrate - Google Patents

Abstract

FIELD: electronics.

SUBSTANCE: invention relates to the field of creating processing of materials based on 2D structures, and in particular, the invention relates to the field of producing graphene-based conductive structures on a given carrier for electronics. The method for transferring graphene onto a polymer substrate includes applying a polymer film to the surface of graphene located on the initial substrate in order to create the "polymer/graphene/initial substrate" structure; spontaneously delaminating the "polymer/graphene" system from the surface of the initial substrate while cooling the "polymer/graphene/initial substrate" structure for no longer than 10 seconds in a medium of liquid nitrogen or helium in order to achieve a large temperature jump.

EFFECT: invention provides a possibility of transferring graphene onto a polymer substrate without additional structural defects with respect to the sample on the source surface, preserving the surface of the initial carrier for further use due to the absence of introduction of any structural changes thereto, as well as reducing the amount of waste water by 30 times compared to the basic "wet" methods.

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Description

Technology area

The invention relates to the field of creating processing of materials based on 2D structures, which is transferred from the catalyst surface to a polymer substrate during technological procedures; In particular, the invention relates to the field of obtaining conductive structures based on graphene on a given carrier for electronics.

State of the art

The discovery of graphene at the beginning of the 21st century led to an explosive growth in research in the field of obtaining two-dimensional materials (MoS ₂ , h-BN, black phosphorus, etc.) and the creation of devices based on them. In particular, due to the presence of a unique set of electrophysical, optical and structural properties, graphene is considered as a promising material in various fields of science and technology. Despite the development of various production methods, it is the synthesis of single-layer graphene by chemical vapor deposition (CVD) that is considered optimal in terms of material quality, scalability and technology cost. Nevertheless, regardless of the catalyst used (copper is the most popular) or carbon source (methane is the most common), one of the key barriers determining the subsequent development of the region is the process of transfer (transfer) of graphene from the catalyst surface to the desired support (usually a dielectric in the form of polymer or silicon oxide).

The key requirements for the graphene transfer stage are versatility and reproducibility with respect to various CVD processes, the degree of preservation of the graphene structure (introduction of defects), scalability, and environmental friendliness of the approach. The processes of graphene transfer developed to date can be divided into physical and chemical. Thus, chemical methods consider carrying out such transformations at the interface between the phases (interface) of the catalyst and graphene, which lead to delamination (detachment of the layer) of the latter. In particular, a popular approach is the selective dissolution of a catalyst (eg, nickel or copper in FeCl ₃ [Kim, Keun Soo, et al. "Large-scale pattern growth of graphene films for stretchable transparent electrodes." Nature 457.7230 (2009): 706- 710], SiO ₂ in NaOH [Reina, Alfonso, et al "Transferring and identification of single-and few-layer graphene on arbitrary substrates." The Journal of Physical Chemistry C 112.46 ( 2008):. 17741-17744]) c preliminary by applying a polymer layer as a stabilizing graphene. Despite the high prevalence of this approach, it leads to the formation of folds [Liu, Nan, et al. "The origin of wrinkles on transferred graphene." Nano Research 4.10 (2011): 996] and cracks [Li, Xuesong, et al. "Transfer of large-area graphene films for high-performance transparent conductive electrodes." Nano letters 9.12 (2009): 4359-4363] in the structure of graphene, which significantly limits its potential industrial applications.

Controlling the rate of dissolution of the catalyst at the interface with graphene was achieved by the electrochemical oxidation of copper and the release of hydrogen from water at the interface [Wang, Yu, et al. "Electrochemical delamination of CVD-grown graphene film: toward the recyclable use of copper catalyst." ACS Nano 5.12 (2011): 9927-9933]. Despite the subsequent development, which made it possible to get rid of the negative influence of the Archimedean force of hydrogen bubbles [Cherian, Christie Thomas, et al. "'Bubble-Free'Electrochemical Delamination of CVD Graphene Films." Small 11.2 (2015): 189-194], this technology has a limited uniformity of delamination. Moreover, liquid methods generally lead to doping of graphene with water molecules [Wood, Joshua D., et al. "Annealing free, clean graphene transfer using alternative polymer scaffolds." Nanotechnology 26.5 (2015): 055302], and salts / substances dissolved in it [Liu, Nan, et al. "The origin of wrinkles on transferred graphene." Nano Research 4.10 (2011): 996]. It should be noted that the chemical dissolution of the catalyst leads to the formation of waste water, which increases the environmental load, and also does not allow the dissolution of such carriers as, for example, SiC.

In turn, the use of dry methods is based on overcoming the adhesion energy of the interface by using an agent with greater adhesion to graphene [Caldwell, Joshua D., et al. "Technique for the dry transfer of epitaxial graphene onto arbitrary substrates." ACS nano 4.2 (2010): 1108-1114]. The consistent development of this area has led to the use of polymers such as polyethylene [Fechine, Guilhermino JM, et al. "Direct dry transfer of chemical vapor deposition graphene to polymeric substrates." Carbon 83 (2015): 224-231], polystyrene with azide linkers [Lock, Evgeniya H., et al. "High-quality uniform dry transfer of graphene to polymers." Nano letters 12.1 (2012): 102-107] and paraffin wax [Leong, Wei Sun, et al. "Paraffin-enabled graphene transfer." Nature communications 10.1 (2019): 1-8.]. Nevertheless, overcoming the adhesion with the catalyst by peeling off graphene with the polymer significantly complicates the next technological stage in the production of devices based on graphene - the removal of the polymer, which now has high adhesion. This problem is common to all graphene transfer methods. So, at the moment, among the liquid methods, PMMA (weak adhesion) and parafilm ™ (medium adhesion) are recognized as optimal [Hsieh, Ya-Ping, Chin-Lun Kuo, and Mario Hofmann. "Ultrahigh mobility in polyolefin-supported graphene." Nanoscale 8.3 (2016): 1327-1331]. It should be noted that among other physical methods of graphene transfer, the transfer due to electrostatic forces should be noted [US 2018/0244027 A1], although the uniformity of this method and the damage to graphene are not yet clear.

An important physical unused characteristic is the variation in the adhesion energy of the catalyst / graphene interface with temperature changes, including due to the difference in the coefficients of thermal expansion (Table 1, although the exfoliation of bulk materials using low temperatures as from room temperature [Wang, Yan, et al. "Cryo-mediated exfoliation and fracturing of layered materials into 2D quantum dots." Science advances 3.12 (2017): e1701500], and with preheating to weaken the van der Waals interaction, has been shown). It should be noted that the surface tension (relative surface energy) of graphene is significantly less than that of the polymer and the catalyst surface, which is copper or copper oxide [Kinloch, Anthony J. Adhesion and adhesives: science and technology. Springer Science & Business Media, 2012].

Table 1. Material properties

material Copper Copper oxide (CuO) Graphene CTE, 1 / K

-1.1 * 10-4
(4-250K)

σ, mJ / m ² 1650 760 - 1830
(depending on crystallographic orientation) 46.7 A source http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thexp.html [Neely, Lauren A., et al. "Thermal expansion of Cu (II) O nano-and micro-particles and composites at cryogenic temperatures." physica status solidi (b) 249.9 (2012): 1698-1703].
[Mishra, Abhishek Kumar, Alberto Roldan, and Nora H. de Leeuw. "CuO surfaces and CO2 activation: a dispersion-corrected DFT + U study." The Journal of Physical Chemistry C 120.4 (2016): 2198-2214.] [Yoon, Duhee, Young-Woo Son, and Hyeonsik Cheong. "Negative thermal expansion coefficient of graphene measured by Raman spectroscopy." Nano letters 11.8 (2011): 3227-3231.]

In light of the above, there is a need to develop a new method for scalable transfer of graphene, which would preferably have the following characteristics:

• The method must be physical so as not to lead to alloying with solvents, increase in technological steps and the creation of waste water.

• The polymer must, on the one hand, have relatively high adhesion to graphene, but at the same time, it must be capable of complete dissolution and leaving the material surface.

• the surface of the catalyst should remain unchanged in order to ensure its repeated use for the production of graphene.

Disclosure of the essence of the invention

The present invention solves the above problems by soft delamination of graphene from the catalyst surface by cooling it to a low temperature.

Below will be described options for implementing the present invention, indicating the achieved technical results.

In a first aspect, the present invention relates to a method for transferring graphene from an initial surface (including but not limited to the surface of a graphene CVD growth catalyst) onto a polymer support, comprising:

• deposition of a polymer medium on the graphene surface in order to create a “polymer / graphene / initial substrate” structure;

• cooling of the object to a lowered temperature, leading to delamination of the “polymer / graphene” system from the original substrate;

• physical removal of the original substrate from the system;

• change in the temperature of the "polymer / graphene" system to the set one (including zero change) for subsequent measurements.

The material of the initial substrate (surface) is a d-element or its oxide. Cu, Ni, Au, Ag, Co, Ti, Zr, Pt, Pd, Ru, V, Cr, Mo, Mn or their combinations (i.e. alloys, intermetallic compounds (for example, γ-Ni -Co, Cu ₃ Ti ₂ , Co ₃ Mo), oxides, including complex oxides (for example, CuO, TiO ₂ , ZrO ₂ , CoCu _γ O ₄ ).

One of the technical results achieved in the present invention is graphene on a polymer substrate without additional structural defects relative to the sample on the original surface.

Another technical result, which is achieved in the present invention, is the reduction of wastewater by 30 times in comparison with the basic "wet" methods (electrochemical bubble free transfer, including etching the original copper substrate).

Another technical result, which is achieved in the present invention, is the ability to reuse the original surface in the absence of any structural changes to it.

Another technical result that is achieved in the present invention is to simplify the graphene transfer process by reducing the number of stages and simplifying the equipment used.

Another technical result, which is achieved in the present invention, is the acceleration of the process of transfer of graphene from tens of hours to tens of seconds.

In one embodiment, the application of the polymer medium is carried out with the addition of the step of pressing the "polymer / graphene / initial surface" system with a weak pressure of the order of several hundreds of Torr (from 0.1 to 3000 Torr). The use of weak pressing increases the adhesion to graphene.

In another embodiment, the polymeric coating medium is carried out with the addition of warm-phase system "polymer / graphene / initial surface" at temperatures of 70 - 300 ^C. In one embodiment, a combination of a weak pressing through release paper and preheating in order to modify the polymer surface. The use of heating increases the adhesion to graphene.

In one embodiment, cooling is performed immediately after the application of the polymer to -196 ^{° C} by placing in liquid nitrogen. Rapid cooling can reduce damage to graphene. The use of liquid nitrogen makes it possible to accelerate heat exchange and, accordingly, the rate of cooling of the medium.

In one embodiment, cooling is performed in stages to -40 ^{° C} and then to ^about -196 C. Stepwise cooling can extend the range of the polymers used by reducing their brittleness in secondary cooling. An extended range of polymers includes polyolefins (including but not limited to polyethylene and polypropylene), paraffins, polystyrene, parafilm, polymethyl methacrylate.

The resulting polymer / graphene structures can be used in many industries and in many applications as such, as an intermediate step for subsequent transfer to a dielectric substrate. Among the areas of use should be highlighted, such as, for example, in electronics as transparent electrodes, in the chemical industry as a carrier of an active catalyst component, as biological sensors.

After reading this description, the specialist will understand other technical results provided by the present invention.

The essence of the invention is illustrated by the following drawings and examples of implementation.

Brief Description of Drawings

FIG. 1 is a schematic diagram of the invention (Scheme of dry cryo-transfer of CVD graphene from a copper substrate to a polymer one. 1 - polymer; 2 - glass / polycor / quartz; 3 - copper; 4 - graphene; 5 - pressure to enhance adhesion between the polymer and graphene ; 6 - medium (liquid nitrogen).

I. The first step is mechanical treatment of the polymer to form a film;

II. The second is the application of a polymer substrate in order to exclude air gaps in the polymer by means of repeated passing through a press (rollers);

III. The polymer is then preheated to achieve uniform adhesion; the molten state reduces the tensile forces at the edges of the polymer layer;

IV. The second stage is the combination of graphene on copper with the surface of a heated polymer and a pressure of ~ 12 Torr without additional action (from 0.1 to 3000 Torr). The pressure is applied for about a minute. Then the composite continues to be heated at the same temperature for 40 minutes;

V. After the required time has elapsed, the sample is quickly immersed in liquid nitrogen, for a period not exceeding 10 seconds to achieve a large temperature jump;

Vi. During the last stage, spontaneous delamination is observed.

FIG. 2 shows photographs of a bath with liquid nitrogen, in which structures "polymer / graphene / initial surface" of arbitrary shape are placed.

FIG. 3-5 illustrate the quality of graphene transfer.

FIG. 3 shows the Raman spectra of graphene after the transfer process (PF + Graphene) and the initial substrate (PF). FIG. 3, the D vibration mode (~ 1300 cm ^-1 ) is not observed, which is responsible for the presence of defects.

FIG. 4 photographs and the results of measuring the current-voltage characteristics of graphene on a polymer substrate transferred using this technology. The proportionality of the resistance to the channel length indicates the high scalability of the approach.

FIG. 5 is a photomicrograph of optical microscopy of graphene on a polymer surface, showing surface uniformity.

The following are examples of the implementation of the present invention. The present invention is not limited to the presented examples.

Examples of

Example 1

Single-layer graphene on the copper surface is cut to predetermined sizes (for example, 0.6 * 1 cm ² ) using scissors or any other cutting devices to facilitate subsequent manipulations with the sample for successful transfer. Then the object is placed on a substrate (glass, quartz, teflon, polycor). Further, the original sample is heated at a temperature of 120 ^o C. Then a polymer of a larger (commensurate) area is brought into contact with the prepared sample. The formation of an interface between polymer and graphene is observed by changing the color of the polymer (becomes transparent). The sample in this state is heated for 30-60 minutes, depending on the thickness of the polymer film. Then the sample is cooled for 3 hours. The sample is then cooled at -20 ^° C for 2 hours and at -40 ^° C for 10 hours. The sample processed according to the above-described order of procedures is immersed in liquid nitrogen, the temperature is 190: 196 ^o C. The temperature change does not take longer than 30-60 seconds. Step cooling allows you to expand the range of polymers used by reducing their fragility during secondary cooling. An extended range of polymers includes polyolefins (including but not limited to polyethylene and polypropylene), paraffins, polystyrene, parafilm, polymethyl methacrylate.

Example 2

Single-layer graphene on the copper surface is cut to predetermined sizes (for example, 0.6 * 0.7 cm ² ) using scissors or any other cutting devices to facilitate subsequent manipulations with the sample for successful transfer. The polymer film is brought into contact with the substrate (glass, quartz, Teflon, polycor). Further, the polymer film on the substrate is heated at 175 ^° C for 40-90 minutes, depending on the initial film thickness. Next, graphene on copper is brought into contact with the treated polymer substrate at the same temperature, followed by a pressure of 12 Torr for 5 seconds. After the applied pressure, the copper / graphene / polymer / substrate stack is heated at the same temperature for 30-40 minutes. After heating, the stack is immersed in liquid nitrogen, - 196 ^o C. The time interval between the end of heating and immersion in liquid nitrogen is 1-2 seconds. Then, within 30 seconds, the graphene / polymer is separated from the copper substrate.

Example 3

Single-layer graphene on the copper surface is cut to predetermined sizes (for example, 0.6 * 1 cm ² ) using scissors or any other cutting devices to facilitate subsequent manipulations with samples for successful transfer. The graphene / copper system is transferred to a clean and flat surface and brought into contact with a parafilm film of comparable or larger size (for example, 1.5 * 3 cm ² ). The plastic film is pressed using glass substrates and release paper to level the surface. The system then "polymer / graphite / copper" on a hot plate heated ^to 200 ° C for 15 minutes followed by a rapid (within 1 minute after removal from the heating device) being placed in a liquid nitrogen bath. After 1.5 minutes, the “polymer / graphene” stack, split off from the copper, is removed from the bath for subsequent manipulations depending on the specific application.

Example 4

This example is similar to example 1 and differs in that instead of cooling, it is instantaneously placed in liquid nitrogen. Instant immersion reduces the transfer time is 15 hours and eliminate the use of the refrigerator at -40 ° ^C.

Example 5

This example is similar to example 1 and differs in that instead of one parafilm layer, two or more layers are used. As a result, the mechanical stability of the film increases with the thickness of the polymer film.

Example 6

This example is similar to example 1 and differs in that the heating of the system is performed in steps: the "graphene / initial support" system is heated to 100 ^° C for 10 minutes to 175 ^° C, the polymer is melted separately followed by connection and 5 minutes. This makes it possible to increase the adhesion of the polymer to graphene and to improve the uniformity of the transfer.

Example 7

This example is similar to example 2 and differs in that the polymer film is rolled through the rollers 10 times. As a result, the mechanical stability of the film is increased by eliminating air bubbles between the polymer layers.

Example 8

This example is similar to example 1 and differs in that the process is performed with pressing at a pressure of 3000 torr. Delamination in this case occurs unevenly over several hours.

Example 9

This example is similar to Example 1 and is characterized in that the process is performed without pressing, adhesion of the polymer to its melting graphene is provided at ¹⁵⁰ ° C for 4 hours.

Example 10

This example is similar to Example 8, and characterized in that the process is performed without pressing, adhesion of the polymer to its melting graphene is provided at ³⁰⁰ ° C for 2 hours.

Example 11

This example is similar to example 4 and differs in that the polymer / graphene / copper system is immersed in a closed cell made of a highly heat-conducting material with a low CTE. This cell is lowered into a Dewar vessel or cryostat, thereby providing a constant sample temperature, in contrast to all of the above examples, where liquid nitrogen is continuously evaporated. Because delamination occurs due to the mechanical properties of the materials; such a cell increases the uniformity of sample cleavage.

The results of experiments on obtaining the final product (graphene on a polymer substrate), various options for obtaining which are disclosed in the above examples (including with various claimed compounds for the initial support) showed the following:

1. There are no defects in the final product, as evidenced by FIG. 3, in which the D vibration mode (~ 1300 cm ^-1 ) is not observed, which is responsible for the presence of defects.

2. In the manufacture of the final product, the volume of wastewater is reduced by 30 times.

3. In the manufacture of the final product, a simplification of the graphene transfer process is achieved by reducing the number of stages and simplifying the equipment used.

4. In the manufacture of the final product, the process of graphene transfer is accelerated from tens of hours to tens of seconds.

Claims (9)

1. A method for transferring graphene onto a polymer substrate, including: a. deposition of a polymer film on the surface of graphene located on a parent substrate to create a polymer / graphene / parent substrate structure; b. spontaneous delamination of the "polymer / graphene" system from the surface of the initial substrate during cooling of the "polymer / graphene / initial substrate" structure for no more than 10 s in liquid nitrogen or helium to achieve a large temperature jump. 2. The method according to claim 1, wherein the initial substrate is made of a d-element, an intermetallic compound of d-elements, oxides and intermetallic compounds of d-elements. 3. The method according to claim 1, in which the deposition of the polymer film on the graphene surface is carried out by heating the system to temperatures of 70-300 ° C. 4. The method according to claim. 1, in which the deposition of a polymer film on the surface of graphene is carried out by heating to temperatures of 70-300 ° C and pressing the system "polymer / graphene / initial copper substrate". 5. The method according to claim 1, wherein the cooling is performed in a cryostat with liquid nitrogen or liquid helium. 6. The method according to claim 1, wherein the cooling is carried out in several stages. 7. A method according to any of the preceding claims, wherein the original substrate is reused to produce a new graphene layer.

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