Graphene Transfer Research Articles

Surface Morphology Analysis of Graphene Transfer on SiO2 with BPA Aptasensor Detection using Electrochemical Impedance Spectroscopy

Bisphenol A or BPA is one of the highest produced chemicals in the world. The production of polycarbonate plastic and epoxy resin are used to make variety of consumer goods and it is frequently employed BPA as a raw material. BPA is one of the endocrine disruptors which is related to a wide range of adverse health effects that can cause reproductive disorders and many kinds of cancers. In the work, the novelty of electrochemical sensor of BPA was constructed on a raphene modified electrode using graphene transfer method. In this work, High-power microscope and scanning electron microscopy were used to study the production and characterization of the graphene, with two significant mapping graphene at 20% and 80%. The existence of graphene on silicon oxide was analyzed using Raman Spectroscopy while the composition of the materials was analyze using Fourier-Transform Infrared Spectroscopy. In this analysis, both analysis data from Raman and FTIR clearly shown that 80% mapping graphene is the best option which resulting to the high surface coverage. The electrochemical performance of the mapping 80% graphene electrode was examined using Electrochemical Impedance Spectra. The increase in charge transfer resistance (Rct) both before and after the addition of BPA denotes the development of the charge at the electrode surface. The equivalent circuit shows the Rct of graphene increased from 0.4 k Ω to 1.2 k Ω and drastically increased to 300 kΩ when the device was introduced with BPA due to the existence of a negative charge carrier and the repelling contact.

Scalable and High-Quality Monolayer Graphene Transfer onto Polymer Membranes Assisted by Camphor

Scalable and High-Quality Monolayer Graphene Transfer onto Polymer Membranes Assisted by Camphor

Polymethylmethacrylate (PMMA) deposition and removal optimization in CVD-grown graphene transfer: A Taguchi technique study

The conventional method of graphene transfer involving Polymethylmethacrylate (PMMA) often results in residual PMMA, negatively impacting the optical and electrical properties of the transferred graphene layer. This study employs the Taguchi optimization technique to minimize PMMA contamination during the graphene transfer process. The quality of the transferred graphene layer was evaluated utilizing atomic force microscopy (AFM), Raman spectroscopy, and Hall Effect measurement. The optimized conditions identified were a PMMA concentration (P) of 4.5 %, a spin rotation (S) speed of 3000 rpm, an acetone bath temperature (A) at 40 °C, and a dissolution duration (T) of 60 min. These parameters achieved a promising surface coverage of 3.42 %. Interestingly, further characterization highlighted that sample #8, prepared with different parameters (P = 12 %, S = 3000 rpm, A = 24 °C, T = 60 min), exhibited a surface coverage of 5.10 % and superior properties, including high transparency, exceptional film quality, low electrical resistance (8691 Ω), and an ID/IG ratio of 0.13. These findings suggest that the optimized conditions are suitable for applications prioritizing surface coverage, while the parameters for sample #8 are recommended for achieving minimal electrical resistance, high transparency, and superior film quality. This research contributes insights into PMMA-assisted graphene transfer, offering practical guidance for tailored processes.

Amidoxime-grafted fluorinated graphene nanosheets as a trace electrochemical sensing platform of uranyl ion

Current electrode recognition materials have limited the realization of rapid real-time monitoring of trace uranyl ion (UO22+) in real-world waters. Herein, amidoxime-grafted fluorinated graphene (AO-FG) is synthesized via the addition and subsequent amidoximation reactions of FG for the electrochemical determination of trace UO22+. Spectroscopies and microscopies reveal the synthetic and morphological characteristics of AO-FG. Electrochemical measurement indicates a significant improvement in the UO22+ redox activity of FG after amidoximation, which is attributed to the introduction of more UO22+ binding sites on the electrode surface and the restoration of charge transfer of graphene. By optimizing the modifier concentration, pH, temperature, and enrichment time, the linear range of the AO-FG-based electrochemical UO22+ sensor is determined to be 0.015–0.1 ppm (R2 = 0.9945), and the detection limit reaches 9.97 × 10−10 M. Furthermore, it exhibited excellent repeatability, air stability, and reliability in the detection of UO22+ in water samples. This study constitutes a novel pathway of constructing high-efficiency, low-cost, and portable UO22+ sensors via grafting of specific groups on FG substrates.

Exploring Grid Diversity: Enhancing Graphene Transfer for Improved Cryo-EM Sample Preparation

Exploring Grid Diversity: Enhancing Graphene Transfer for Improved Cryo-EM Sample Preparation

Ice-Enabled Transfer of Graphene on Copper Substrates Enhanced by Electric Field and Cu2O.

Graphene films grown by the chemical vapor deposition (CVD) method suffer from contamination and damage during transfer. Herein, an innovative ice-enabled transfer method under an applied electric field and in the presence of Cu2O (or Cu2O-Electric-field Ice Transfer, abbreviated as CEIT) is developed. Ice serves as a pollution-free transfer medium while water molecules under the electric field fully wet the graphene surface for a bolstered adhesion force between the ice and graphene. Cu2O is used to reduce the adhesion force between graphene and copper. The combined methodology in CEIT ensures complete separation and clean transfer of graphene, resulting in successfully transferred graphene to various substrates, including polydimethylsiloxane (PDMS), Teflon, and C4F8 without pollution. The graphene obtained via CEIT is utilized to fabricate field-effect transistors with electrical performances comparable to that of intrinsic graphene characterized by small Dirac points and high carrier mobility. The carrier mobility of the transferred graphene reaches 9090 cm2V-1s-1, demonstrating a superior carrier mobility over that from other dry transfer methods. In a nutshell, the proposed clean and efficient transfer method holds great potential for future applications of graphene.

Robust, stretchable bioelectronic interfaces for cardiac pacing enabled by interfacial transfer of laser-induced graphene via water-response, nonswellable PVA gels

Implantable cardiac pacemakers are crucial therapeutic tools for managing various cardiac conditions. For effective pacing, electrodes should exhibit flexibility, deformability, biocompatibility, and high conductivity/capacitance. Laser-induced graphene (LIG) shows promise due to its exceptional electrical and electrochemical properties. However, the fragility of LIG and the non-stretchability of polyimide substrates pose challenges when interfacing with the beating heart. Here, we present a simple method for fabricating robust, flexible, and stretchable bioelectronic interfaces by transferring LIG via water-responsive, nonswellable polyvinyl alcohol (PVA) gels. PVA solution penetrates the porous structure of LIG and solidifies into PVA xerogel as the solvent evaporates. The robust PVA xerogel enables the smooth transfer of LIG and prevents stretching of the LIG network during this process, which helps maintain its conductivity. When hydrated, the xerogel becomes a stable, nonswellable hydrogel. This gives the LIG-PVA hydrogel (LIG-PVA-H) composites with excellent conductivity (119.7 ± 4.3Ω sq−1), high stretchability (up to 420%), reliability (cyclic stretch under 15% strain, with ∼ 1-time resistance increase), and good stability in phosphate buffered saline. The LIG-PVA-H composites were used as biointerfaces for electrocardiogram signal recording and electrical pacing on rat hearts ex vivo and in vivo, using commercial setups and a custom-built implantable wireless device. This work expands the application of LIG in bioelectronic interfaces and facilitates the development of electrotherapy for cardiac diseases.

Polyacrylonitrile as an Efficient Transfer Medium for Wafer-Scale Transfer of Graphene.

The disparity between growth substrates and application-specific substrates can be mediated by reliable graphene transfer, the lack of which currently strongly hinders the graphene applications. Conventionally, the removal of soft polymers, that support the graphene during the transfer, would contaminate graphene surface, produce cracks, and leave unprotected graphene surface sensitive to airborne contaminations. In this work, it is found that polyacrylonitrile (PAN) can function as polymer medium for transferring wafer-size graphene, and encapsulating layer to deliver high-performance graphene devices. Therefore, PAN, that is compatible with device fabrication, does not need to be removed for subsequent applications. The crack-free transfer of 4 in. graphene onto SiO2/Si wafers, and the wafer-scale fabrication of graphene-based field-effect transistor arrays with no observed clear doping, uniformly high carrier mobility (≈11000 cm2 V-1 s-1), and long-term stability at room temperature, are achieved. This work presents new concept for designing the transfer process of 2D materials, in which multifunctional polymer can be retained, and offers a reliable method for fabricating wafer-scale devices of 2D materials with outstanding performance.

An Improved CVD Design for Graphene Growth and Transfer Improvements

An Improved CVD Design for Graphene Growth and Transfer Improvements

Toward the Production of Super Graphene.

The quality requirements of graphene depend on the applications. Some have a high tolerance for graphene quality and even require some defects, while others require graphene as perfect as possible to achieve good performance. So far, synthesis of large-area graphene films by chemical vapor deposition of carbon precursors on metal substrates, especially on Cu, remains the main way to produce high-quality graphene, which has been significantly developed in the past 15 years. However, although many prototypes are demonstrated, their performance is still more or less far from the theoretical property limit of graphene. This review focuses on how to make super graphene, namely graphene with a perfect structure and free of contaminations. More specially, this study focuses on graphene synthesis on Cu substrates. Typical defects in graphene are first discussed together with the formation mechanisms and how they are characterized normally, followed with a brief review of graphene properties and the effects of defects. Then, the synthesis progress of super graphene from the aspects of substrate, grain size, wrinkles, contamination, adlayers, and point defects are reviewed. Graphene transfer is briefly discussed as well. Finally, the challenges to make super graphene are discussed and a strategy is proposed.

Transparent, low dark current, fast response ultraviolet and short-wavelength blue photons photodetector based on Graphene/SrTiO3 single crystal

Ultraviolet light and short-wavelength blue photons (UV-SWB) can cause damage to the human body under excessive exposure. Strontium titanate (SrTiO3), which is a crucial perovskite oxide with a direct energy band gap of ∼3.2 eV, has great potential for UV-SWB photodetection. In this work, UV-SWB photodetector with high transparency based on Graphene/SrTiO3 heterojunction was fabricated by graphene transfer method. The Graphene/SrTiO3 photodetector exhibits an ultra-low dark current of 6 pA at a 30 V bias. The response spectrum of the Graphene/SrTiO3 photodetector was 220–410 nm, covering the UV-SWB band. Under 385 nm light irradiation, the photodetector exhibits a response of 3.4 mA/W, a detectivity of 1.5 × 1010 Jones, a response time of 186 ms, and a light-to-dark current ratio of 103 magnitude at a 30 V bias. In addition, the transmittance of the photodetector in the visible light band reaches 80 %, which has excellent visualization performance. The excellent performance of Graphene/SrTiO3 photodetector is attributed to the high crystal quality of SrTiO3 wafer and the van der Waals interface constructed by Graphene/SrTiO3 reduces the bulk defect density and interfacial state density, which could be beneficial the separation and transport of photogenerated carriers in the active layer and heterojunction. This study has important reference value for the design and manufacture of UV-SWB photodetectors.

Transfer-free robust n-type graphene field-effect transistors for digital logic electronic devices

Graphene has been hailed as wonder materials for electronics due to its outstanding charge transport properties. However, its lack of an electronic bandgap has hindered its application to large-scale field-effect transistor (FET) circuits, thereby making bandgap opening a key priority. Further, the fabrication of graphene devices to date conventionally requires the transfer of graphene from its growth substrate to a target substrate, which introduces defects and deteriorates the device performance. To overcome these challenges, we demonstrate a transfer-free approach for the low-temperature growth (∼100 °C) onto TiO2–x (∼10 nm) buffer layer and in-situ nitrogen doping of monolayer graphene, which enables stretchable nitrogen-doped graphene-based FETs with cutting-edge performance and stability. Hybridizing a TiO2–x channel with the nitrogen-doped graphene, nitrogen-doped graphene-based FETs could be achieved with an on-off ratio of ∼2 × 108 and an electron mobility of ∼1,500 cm2V−1s−1 for mainstream digital logic devices. Such devices exhibit high reproducibility and wafer-scale uniformity, thermal, bias-stress, long-term stability, and robust flexibility and stretchability. The scalability and versatility of this transfer-free approach for the flexible and stretchable FETs pave the way for high-performance nitrogen-doped graphene-based digital logic circuits.

Enhancing the Consistency and Performance of Graphene-Based Devices via Al Intermediate-Layer-Assisted Transfer and Patterning.

Graphene has garnered widespread attention, and its use is being explored for various electronic devices due to its exceptional material properties. However, the use of polymers (PMMA, photoresists, etc.) during graphene transfer and patterning processes inevitably leaves residues on graphene surface, which can decrease the performance and yield of graphene-based devices. This paper proposes a new transfer and patterning process that utilizes an Al intermediate layer to separate graphene from polymers. Through DFT calculations, the binding energy of graphene-Al was found to be only -0.48 eV, much lower than that of PMMA and photoresist with graphene, making it easier to remove Al from graphene. Subsequently, this was confirmed through XPS analysis. A morphological characterization demonstrated that the graphene patterns prepared using the Al intermediate layer process exhibited higher surface quality, with significantly reduced roughness. It is noteworthy that the devices obtained with the proposed method exhibited a notable enhancement in both consistency and sensitivity during electrical testing (increase of 67.14% in temperature sensitivity). The low-cost and pollution-free graphene-processing method proposed in this study will facilitate the further commercialization of graphene-based devices.

Interlayer sp3 Bonds and Chirality at Bilayer Graphene Oxide/Calcium Silicate Hydrate Abnormally Enhance Its Interlayer Stress Transfer.

Graphene oxide (GO) is an ideal reinforcing material with super design capability, which can achieve the combination of strength and toughness. However, the actual effect of GO is far below the theoretical prediction. This is mainly due to the weak interface between the nanofiller and the matrix. In this paper, a controllable method for improving interlayer stress transfer of double-layer graphene oxide/C-S-H (D-GO-CSH)-layered nanostructures is proposed by using interlayer sp3 bond and chirality. The results show that, compared with the control group, the normalized shear stress and normalized pull-out energy of the OH-sp3 model are increased by 44.93 and 49.25%, respectively, while those of the OO-sp3 model are increased by 32.26 and 31.03%, respectively. The interlayer sp3 bonds lead to a great enhancement (more than 3 times) in normalized interlayer stress transfer of D-GO-CSH-layered nanostructures while exerting a little opposite effect (about 5%). The improvement effects induced by the interlayer sp3 bonds are also strongly dependent on their distributions and the chirality of GO. According to the fracture mechanic theory and molecular dynamics results, the strain energy percentage difference (bond length and bond angle) of the zigzag-cen model is 34.8% lower than that of the control group model, which proves that the interlayer sp3 bonds have a remarkably positive effect on the interlayer stress transfer of D-GO-CSH-layered nanostructures. This provides a new way to further improve the interlayer stress transfer, pull-out energy, and interlayer shear stress of D-GO-CSH-layered nanostructures.

Large-area, size-controlled and transferable graphene oxide-metal films for humidity sensor

The lack of low-cost methods to synthesize large-area graphene-based materials is still an important factor that limits the practical application of graphene devices. Herein, we present a facile method for producing large-area graphene oxide-metal (GO–M) films, which are size controllable and transferable. The sensor constructed using the GO–M film exhibited humidity sensitivity while being unaffected by pressure. The relationship between the sensor’s resistance and relative humidity followed an exponential trend. The GO–Mg sensor was the most sensitive among all the tested sensors. The facile synthesis of GO–M films will accelerate the widespread utilization of graphene-based materials.

Tunable Adhesion for All-Dry Transfer of 2D Materials Enabled by the Freezing of Transfer Medium.

The real applications of chemical vapor deposition (CVD)-grown graphene films require the reliable techniques for transferring graphene from growth substrates onto application-specific substrates. The transfer approaches that avoid the use of organic solvents, etchants, and strong bases are compatible with industrial batch processing, in which graphene transfer should be conducted by dry exfoliation and lamination. However, all-dry transfer of graphene remains unachievable owing to the difficulty in precisely controlling interfacial adhesion to enable the crack- and contamination-free transfer. Herein, through controllable crosslinking of transfer medium polymer, the adhesion is successfully tuned between the polymer and graphene for all-dry transfer of graphene wafers. Stronger adhesion enables crack-free peeling of the graphene from growth substrates, while reduced adhesion facilitates the exfoliation of polymer from graphene surface leaving an ultraclean surface. This work provides an industrially compatible approach for transferring 2D materials, key for their future applications, and offers a route for tuning the interfacial adhesion that would allow for the transfer-enabled fabrication of van der Waals heterostructures.

Ready-to-transfer two-dimensional materials using tunable adhesive force tapes

Graphene and other two-dimensional (2D) materials can be used to create electronic and optoelectronic devices. However, their development has been limited by the lack of effective large-area transfer processes. Here we report a transfer method that uses functional tapes with adhesive forces controlled by ultraviolet light. The adhesion of the tape is optimized for the transfer of monolayer graphene, providing a yield of over 99%. Once detached from the growth substrate, the graphene/tape stack enables easy transfer of graphene to the desired target substrate. The method can be used to transfer other 2D materials, including bilayer graphene, transition metal dichalcogenides, hexagonal boron nitride and stacked heterostructures. The solvent-free nature of the final release step facilitates transfer to various target substrates including flexible polymers, paper and three-dimensional surfaces. The tape/2D material stacks can also be cut into desired sizes and shapes, allowing site-selective device fabrication with reduced loss of 2D materials.

Parafilm Enabled Rapid and Scalable Delamination/Integration of Graphene for High‐Performance Capacitive Touch Sensor

The high electrical conductivity and bendability of graphene makes it versatile for flexible electronic sensor applications. The fabrication of such flexible sensors necessitates two important prerequisites: defect‐free transfer of graphene to a flexible substrate and creating appropriate patterns without altering graphene's inherent properties. Here, a potentially rapid and scalable method to delaminate graphene non‐destructively from a metal substrate by using flexible parafilm is reported. This method allows not only the scalable transfer of continuous graphene, but also the realization of graphene patterns on the parafilm substrate. Graphene on parafilm showed negligible doping effect with high room temperature carrier mobility exceeding 6 × 103 cm2 V−1 s−1 for a centimeter‐scale sample. Using parafilm as a substrate‐cum‐dielectric medium, a proof‐of‐concept capacitive touch sensor (CTS) arrays is demonstrated without the use of lithography, by simple cross‐assembling and mild heating. The graphene sensor thus realized in its simplistic device configuration had an enhanced sensitivity of 43% when touch and release cycles are performed on the device. The nearly non‐destructive and user‐friendly route for directly integrating graphene with a flexible substrate is expected to play a potential role in the design of graphene‐based flexible electronics.

Ion Selectivity in Multilayered Stacked Nanoporous Graphene.

Nanoporous graphene is an ideal candidate for molecular filtration as it can potentially combine high permeability with high selectivity at molecular levels. To make use of graphene in filtration setups, the defects formed during its growth and during the transfer of graphene to the carrier support pose a challenge. These uncontrolled pores can be avoided by stacking graphene layers, and then, controlled pores can be initiated with oxygen plasma. Here, we show that two-layer stacks provide the best balance of defect coverage and high selectivity compared with other stacks. Using the electrical characterization of ionic solutions in the standard diffusion cell, we compare the ionic transport and ionic selectivity of up to three-layered stacks of graphene that have been plasma-treated. We find that there is a decrease in the ionic selectivity of a two-layered stack as one more layer of graphene is added. We provide a model for this occurrence. Our results will be helpful for making practical and high-performance filtration systems from two-dimensional materials.

Ultra-thin proton conducting carrier layers for scalable integration of atomically thin 2D materials with proton exchange polymers for next-generation PEMs.

Scalable approaches for synthesis and integration of proton selective atomically thin 2D materials with proton conducting polymers can enable next-generation proton exchange membranes (PEMs) with minimal crossover of reactants or undesired species while maintaining adequately high proton conductance for practical applications. Here, we systematically investigate facile and scalable approaches to interface monolayer graphene synthesized via scalable chemical vapor deposition (CVD) on Cu foil with the most widely used proton exchange polymer Nafion 211 (N211, ∼25 μm thick film) via (i) spin-coating a ∼700 nm thin Nafion carrier layer to transfer graphene (spin + scoop), (ii) casting a Nafion film and cold pressing (cold press), and (iii) hot pressing (hot press) while minimizing micron-scale defects to <0.3% area. Interfacing CVD graphene on Cu with N211 via cold press or hot press and subsequent removal of Cu via etching results in ∼50% lower areal proton conductance compared to membranes fabricated via the spin + scoop method. Notably, the areal proton conductance can be recovered by soaking the hot and cold press membranes in 0.1 M HCl, without significant damage to graphene. We rationalize our finding by the significantly smaller reservoir for cation uptake from Cu etching for the ∼700 nm thin carrier Nafion layer used for spin + scoop transfer compared to the ∼25 μm thick N211 film for hot and cold pressing. Finally, we demonstrate performance in H2 fuel cells with power densities of ∼0.23 W cm-2 and up to ∼41-54% reduction in H2 crossover for the N211|G|N211 sandwich membranes compared to the control N211|N211 indicating potential for our approach in enabling advanced PEMs for fuel cells, redox-flow batteries, isotope separations and beyond.