Transfer Of Graphene Films Research Articles

Recent trends in the transfer of graphene films.

Recent years have witnessed advances in chemical vapor deposition growth of graphene films on metal foils with fine scalability and thickness controllability. However, challenges for obtaining wrinkle-free, defect-free and large-area uniformity remain to be tackled. In addition, the real commercial applications of graphene films still require industrially compatible transfer techniques with reliable performance of transferred graphene, excellent production capacity, and suitable cost. Transferred graphene films, particularly with a large area, still suffer from the presence of transfer-related cracks, wrinkles and contaminants, which would strongly deteriorate the quality and uniformity of transferred graphene films. Potential applications of graphene films include moisture barrier films, transparent conductive films, electromagnetic shielding films, and optical communications; such applications call different requirements for the performance of transferred graphene, which, in turn, determine the suitable transfer techniques. Besides the reliable transfer process, automatic machines should be well developed for the future batch transfer of graphene films, ensuring the repeatability and scalability. This mini-review provides a summary of recent advances in the transfer of graphene films and offers a perspective for future directions of transfer techniques that are compatible for industrial batch transfer.

Recent Progress in the Transfer of Graphene Films and Nanostructures.

The one-atom-thick graphene has excellent electronic, optical, thermal, and mechanical properties. Currently, chemical vapor deposition (CVD) graphene has received a great deal of attention because it provides access to large-area and uniform films with high-quality. This allows the fabrication of graphene based-electronics, sensors, photonics, and optoelectronics for practical applications. Zero bandgap, however, limits the application of a graphene film as electronic transistor. The most commonly used bottom-up approaches have achieved efficient tuning of the electronic bandgap by customizing well-defined graphene nanostructures. The postgrowth transfer of graphene films/nanostructures to a certain substrate is crucial in utilizing graphene in applicable devices. In this review, the basic growth mechanism of CVD graphene is first introduced. Then, recent advances in various transfer methods of as-grown graphene to target substrates are presented. The fabrication and transfer methods of graphene nanostructures are also provided, and then the transfer-related applications are summarized. At last, the challenging issues and the potential transfer-free approaches are discussed.

Large-Area Synthesis of Superclean Graphene via Selective Etching of Amorphous Carbon with Carbon Dioxide.

Contamination commonly observed on the graphene surface is detrimental to its excellent properties and strongly hinders its application. It is still a great challenge to produce large-area clean graphene film in a low-cost manner. Herein, we demonstrate a facile and scalable chemical vapor deposition approach to synthesize meter-sized samples of superclean graphene with an average cleanness of 99 %, relying on the weak oxidizing ability of CO2 to etch away the intrinsic contamination, i.e., amorphous carbon. Remarkably, the elimination of amorphous carbon enables a significant reduction of polymer residues in the transfer of graphene films and the fabrication of graphene-based devices and promises strongly enhanced electrical and optical properties of graphene. The facile synthesis of large-area superclean graphene would open the pathway for both fundamental research and industrial applications of graphene, where a clean surface is highly needed.

Large‐Area Synthesis of Superclean Graphene via Selective Etching of Amorphous Carbon with Carbon Dioxide

AbstractContamination commonly observed on the graphene surface is detrimental to its excellent properties and strongly hinders its application. It is still a great challenge to produce large‐area clean graphene film in a low‐cost manner. Herein, we demonstrate a facile and scalable chemical vapor deposition approach to synthesize meter‐sized samples of superclean graphene with an average cleanness of 99 %, relying on the weak oxidizing ability of CO2 to etch away the intrinsic contamination, i.e., amorphous carbon. Remarkably, the elimination of amorphous carbon enables a significant reduction of polymer residues in the transfer of graphene films and the fabrication of graphene‐based devices and promises strongly enhanced electrical and optical properties of graphene. The facile synthesis of large‐area superclean graphene would open the pathway for both fundamental research and industrial applications of graphene, where a clean surface is highly needed.

All-Dry Transfer of Graphene Film by van der Waals Interactions.

We report a method that uses van der Waals interactions to transfer continuous, high-quality graphene films from Ge(110) to a different substrate held by hexagonal boron nitride carriers in a clean, dry environment. The transferred films are uniform and continuous with low defect density and few charge puddles. The transfer is effective because of the weak interfacial adhesion energy between graphene and Ge. Based on the minimum strain energy required for the isolation of film, the upper limit of the interfacial adhesion energy is estimated to be 23 meV per carbon atom, which makes graphene/Ge(110) the first as-grown graphene film that has a substrate adhesion energy lower than that of typical van der Waals interactions between layered materials. Our results suggest that graphene on Ge can serve as an ideal material platform to be integrated with other material systems by a clean assembly process.

Toward highly sensitive surface-enhanced Raman scattering: the design of a 3D hybrid system with monolayer graphene sandwiched between silver nanohole arrays and gold nanoparticles.

We report a novel graphene-metal hybrid system by introducing monolayer graphene between gold nanoparticles (Au NPs) and silver nanohole (Ag NH) arrays. The design incorporates three key advantages to promote the surface-enhanced Raman scattering (SERS) sensing capacity: (i) making full use of the single-atomic feature of graphene for generating uniform sub-nanometer spaces; (ii) maintaining the bottom layer of Ag nanoarrays with an ordered manner for facilitating the transfer of graphene films and assembly of the top layer of Au NPs; (iii) integrating the advantages of the strong plasmonic effect of Ag, the chemical stability of Au, as well as the mechanical flexibility and biological compatibility of graphene. In this configuration, the plasmonic properties can be fine-tuned by separately optimizing the horizontal or vertical gaps between the metal NPs. Exactly, sub-20 nm spaces between the horizontally patterned Ag tips constructed by adjacent Ag NHs, and sub-nanometer scale graphene gaps between the vertically distributed Au NP-Ag NH have been achieved. Finite element numerical simulations demonstrate that the multi-dimensional plasmonic couplings (including the Au NP-Au NP, Au NP-Ag NH and Ag NH-Ag NH couplings) promote for the hybrid platform an electric field enhancement up to 137 times. Impressively, the as-prepared 3D Au NP-graphene-Ag NH array hybrid structure manifests ultrahigh SERS sensitivity with a detection limit of 10-13 M for R6G molecules, as well as good reproducibility and stability. This work represents a step towards high-performance SERS substrate fabrication, and opens up a new route for graphene-plasmonic hybrids in SERS applications.

Direct transfer of graphene films for polyurethane substrate

We have proposed the direct transfer of large-area graphene films grown by chemical vapor deposition to polymeric substrate by evaporating of solvents of polyurethane/tetrahydrofurane solution. The graphene films on polyurethane substrates were characterized by Raman spectroscopy, optical and atomic force microscopies and UV–vis spectroscopy measurements. The Raman spectra revealed that it is possible to transfer in a controlled manner monolayer, bilayer and multilayer graphene films over polyurethane substrate.

Clean surface transfer of graphene films via an effective sandwich method for organic light-emitting diode applications

Graphene shows great promise as a transparent conductive electrode to replace conventional indium tin oxide (ITO) for optoelectronic applications. However, the wide applications of graphene in fields such as organic light emitting diodes (OLEDs) are restricted by the difficulty in obtaining a clean and flat graphene surface, as the large residue generated during graphene transfer can lead to a large short circuit current and consequently degradation of the device performance. Here, we report a novel sandwich method to achieve the efficient transfer of graphene with an ultra-clean and flat surface onto a flexible substrate for OLED applications. Differing from the conventional poly(methyl methacrylate) (PMMA)-supported transfer technique, an organic small molecular buffer layer, e.g., a 2-(diphenylphosphory) spirofluorene (SPPO1) layer, was inserted between PMMA and graphene, forming a PMMA/SPPO1/graphene sandwich structure. The separation of PMMA from graphene, along with the large solubility of SPPO1 in clean solvent, results in a substantial reduction of PMMA residue on the graphene. As expected, flexible OLED devices based on the PMMA/SPPO1 transferred graphene films exhibited a much enhanced performance compared to their counterparts fabricated from PMMA transferred films. Our results demonstrate the great potential of the sandwich transfer technique for the fabrication of high-performance OLED devices, as well as other optoelectronic devices.

Graphene‐Conducting Polymer Hybrid Transparent Electrodes for Efficient Organic Optoelectronic Devices

To achieve the broad utilization of the full functionality of graphene (GR) in devices, a transfer method should be developed that can simplify the process without leaving residue of the insulating supporting layer on the surface of GR. Furthermore, stable GR doping without the use of an insulating polymer is required. Here, a new GR transfer method that uses a popular conducting polymer, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), is reported as a new supporting layer for the transfer of GR films that are synthesized by chemical vapor deposition. The GR/PEDOT:PSS bilayer can be directly utilized without the removal process. Therefore, this transfer method simplifies the transfer process and solves the residue problem of conventional transfer methods. The stable doping of GR films is simultaneously achieved by using the PEDOT:PSS layer. The new GR/PEDOT:PSS hybrid electrodes are fully functional in polymer solar cells and polymer light‐emitting diodes, outperforming the conventionally transferred GR electrodes and indium tin oxide electrodes.

Simple Wafer-Scale Growth and Transfer of Graphene Film Converted from Spin-Coated Fullerene Derivative

We report a simple method for growing wafer-scale graphene films using PCBM (phenyl-C61-butyric acid methyl ester), a fullerene derivative, as a solid carbon source. PCBM films spin-coated on nickel catalyst were easily converted to graphene films having a thickness of a few layers by thermal annealing without any reactive gas. This method of converting PCBM to graphene is safe, unlike the chemical vapor deposition (CVD) method that uses explosive precursor gases. PCBM-derived graphene films were also transferred through a simple process to plastic substrates with a supporting layer for use in organic solar cells. The power conversion efficiency (PCE) of bulk heterojunction organic solar cells prepared on the PCBM-derived graphene electrode was 0.98%. This study indicates that PCBM-derived graphene films can serve as an inexpensive, flexible alternative to indium tin oxide (ITO) films, and

CVD growth and processing of graphene for electronic applications

AbstractThe remarkable properties of graphene have potential for numerous applications; however, their exploitation depends on its reliable production. The chemical vapour deposition (CVD) growth of graphene on metal surfaces has become one of the most promising strategies for the production of high quality graphene in a scaleable manner. Here, we discuss graphene growth on nickel (Ni) and copper (Cu) directly from both gaseous hydrocarbons and solid carbon precursors. Further, we discuss in detail the transfer of graphene films to insulating substrates, by direct and polymer supported transfer methods.

Reliable processing of graphene using metal etchmasks

Graphene exhibits exciting properties which make it an appealing candidate for use in electronic devices. Reliable processes for device fabrication are crucial prerequisites for this. We developed a large area of CVD synthesis and transfer of graphene films. With patterning of these graphene layers using standard photoresist masks, we are able to produce arrays of gated graphene devices with four point contacts. The etching and lift off process poses problems because of delamination and contamination due to polymer residues when using standard resists. We introduce a metal etch mask which minimises these problems. The high quality of graphene is shown by Raman and XPS spectroscopy as well as electrical measurements. The process is of high value for applications, as it improves the processability of graphene using high-throughput lithography and etching techniques.

Technique for the Dry Transfer of Epitaxial Graphene onto Arbitrary Substrates

To make graphene technologically viable, the transfer of graphene films to substrates appropriate for specific applications is required. We demonstrate the dry transfer of epitaxial graphene (EG) from the C-face of 4H-SiC onto SiO(2), GaN and Al(2)O(3) substrates using a thermal release tape. Subsequent Hall effect measurements illustrated that minimal degradation in the carrier mobility was induced following the transfer process in lithographically patterned devices. Correspondingly, a large drop in the carrier concentration was observed following the transfer process, supporting the notion that a gradient in the carrier density is present in C-face EG, with lower values being observed in layers further removed from the SiC interface. X-ray photoemission spectra collected from EG films attached to the transfer tape revealed the presence of atomic Si within the EG layers, which may indicate the identity of the unknown intrinsic dopant in EG. Finally, this transfer process is shown to enable EG films amenable for use in device fabrication on arbitrary substrates and films that are deemed most beneficial to carrier transport, as flexible electronic devices or optically transparent contacts.

Wafer-Scale Synthesis and Transfer of Graphene Films

We developed means to produce wafer scale, high-quality graphene films as large as 3 in. wafer size on Ni and Cu films under ambient pressure and transfer them onto arbitrary substrates through instantaneous etching of metal layers. We also demonstrated the applications of the large-area graphene films for the batch fabrication of field-effect transistor (FET) arrays and stretchable strain gauges showing extraordinary performances. Transistors showed the hole and electron mobilities of the device of 1100 +/- 70 and 550 +/- 50 cm(2)/(V s) at drain bias of -0.75 V, respectively. The piezo-resistance gauge factor of strain sensor was approximately 6.1. These methods represent a significant step toward the realization of graphene devices in wafer scale as well as application in optoelectronics, flexible and stretchable electronics.