Laser‐Induced Direct Graphene Patterning and Simultaneous Transferring Method for Graphene Sensor Platform

General methods utilized in the fabrication of graphene devices involve graphene transferring and subsequent patterning of graphene via multiple wet‐chemical processes. In the present study, a laser‐induced pattern transfer (LIPT) method is proposed for the transferring and patterning of graphene in a single processing step. Via the direct graphene patterning and simultaneous transferring, the LIPT method greatly reduces the complexity of graphene fabrication while augmenting flexibility in graphene device design. Femtosecond laser ablation under ambient conditions is employed to transfer graphene/PMMA microscale patterns to arbitrary substrates, including a flexible film. Suspended cantilever structures are also demonstrated over a prefabricated trench structure via the single‐step method. The feasibility of this method for the fabrication of functional graphene devices is confirmed by measuring the electrical response of a graphene/PMMA device under laser illumination.     

Tailored Crumpling and Unfolding of Spray‐Dried Pristine Graphene and Graphene Oxide Sheets

For the first time, pristine graphene can be controllably crumpled and unfolded. The mechanism for graphene is radically different than that observed for graphene oxide; a multifaced crumpled, dimpled particle morphology is seen for pristine graphene in contrast to the wrinkled, compressed surface of graphene oxide particles, showing that surface chemistry dictates nanosheet interactions during the crumpling process. The process demonstrated here utilizes a spray‐drying technique to produce droplets of aqueous graphene dispersions and induce crumpling through rapid droplet evaporation. For the first time, the gradual dimensional transition of 2D graphene nanosheets to a 3D crumpled morphology in droplets is directly observed; this is imaged by a novel sample collection device inside the spray dryer itself. The degree of folding can be tailored by altering the capillary forces on the dispersed sheets during evaporation. It is also shown that the morphology of redispersed crumpled graphene powder can be controlled by solvent selection. This process is scalable, with the ability to rapidly process graphene dispersions into powders suitable for a variety of engineering applications.     

Graphene Oxide,Highly Reduced Graphene Oxide,and Graphene: Versatile Building Blocks for Carbon‐Based Materials

Isolated graphene, a nanometer‐thick two‐dimensional analog of fullerenes and carbon nanotubes, has recently sparked great excitement in the scientific community given its excellent mechanical and electronic properties. Particularly attractive is the availability of bulk quantities of graphene as both colloidal dispersions and powders, which enables the facile fabrication of many carbon‐based materials. The fact that such large amounts of graphene are most easily produced via the reduction of graphene oxide—oxygenated graphene sheets covered with epoxy, hydroxyl, and carboxyl groups—offers tremendous opportunities for access to functionalized graphene‐based materials. Both graphene oxide and graphene can be processed into a wide variety of novel materials with distinctly different morphological features, where the carbonaceous nanosheets can serve as either the sole component, as in papers and thin films, or as fillers in polymer and/or inorganic nanocomposites. This Review summarizes techniques for preparing such advanced materials via stable graphene oxide, highly reduced graphene oxide, and graphene dispersions in aqueous and organic media. The excellent mechanical and electronic properties of the resulting materials are highlighted with a forward outlook on their applications.     

High‐Concentration Solvent Exfoliation of Graphene

A method is demonstrated to prepare graphene dispersions at high concentrations, up to 1.2 mg mL^?1, with yields of up to 4 wt% monolayers. This process relies on low‐power sonication for long times, up to 460 h. Transmission electron microscopy shows the sonication to reduce the flake size, with flake dimensions scaling as t^?1/2. However, the mean flake length remains above 1 µm for all sonication times studied. Raman spectroscopy shows defects are introduced by the sonication process. However, detailed analysis suggests that predominately edge, rather than basal‐plane, defects are introduced. These dispersions are used to prepare high‐quality free‐standing graphene films. The dispersions can be heavily diluted by water without sedimentation or aggregation. This method facilitates graphene processing for a range of applications.     

Wafer‐Scale Synthesis of Graphene on Sapphire: Toward Fab‐Compatible Graphene

The adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high‐quality material on technologically relevant substrates, over wafer‐scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal‐catalysts or yielding defective graphene. In this work, a metal‐free approach implemented in commercially available reactors to obtain high‐quality monolayer graphene on c‐plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al‐rich reconstruction $\left(\sqrt{31}\times \sqrt{31}\right)R\pm 9$° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high‐quality graphene with mobilities consistently above 2000 cm² V^?1 s^?1. The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back‐end‐of‐line integration. The growth process introduced here establishes a method for the synthesis of wafer‐scale graphene films on a technologically viable basis.     

Synthesis and Superior Optical‐Limiting Properties of Fluorene‐Thiophene‐Benzothiadazole Polymer‐Functionalized Graphene Sheets

A polymer based on fluorene, thiophene, and benzothiadazole as the donor–spacer–acceptor triad is covalently coupled to reduced graphene oxide (rGO) sheets via diazonium coupling with phenyl bromide, followed by Suzuki coupling. These polymer–graphene hybrids show good solubility in organic solvents, such as chloroform, tetrahydrofuran (THF), toluene, dichlorobenzene, and N,N‐dimethylformamide (DMF), and exhibit an excellent optical‐limiting effect with a 532‐nm laser beam. The optical‐limiting threshold energy values (0.93 J cm^?2 for G–polymer 1 and 1.12 J cm^?2 for G–polymer 2) of these G–polymer hybrids are better than that of carbon nanotubes (3.6 J cm^?2).     

Cell‐Assembled Graphene Biocomposite for Enhanced Chondrogenic Differentiation

Graphene‐based nanomaterials are increasingly being explored for use as biomaterials for drug delivery and tissue engineering applications due to their exceptional physicochemical and mechanical properties. However, the two‐dimensional nature of graphene makes it difficult to extend its applications beyond planar tissue culture. Here, graphene–cell biocomposites are used to pre‐concentrate growth factors for chondrogenic differentiation. Bone marrow‐derived mesenchymal stem cells (MSCs) are assembled with graphene flakes in the solution to form graphene‐cell biocomposites. Increasing concentrations of graphene (G) and porous graphene oxide (pGO) are found to correlate positively with the extent of differentiation. However, beyond a certain concentration, especially in the case of graphene oxide, it will lead to decreased chondrogenesis due to increased diffusional barrier and cytotoxic effects. Nevertheless, these findings indicate that both G and pGO could serve as effective pre‐concentration platforms for the construction of tissue‐engineered cartilage and suspension‐based cultures in vitro.     

Nitrogen‐Superdoped 3D Graphene Networks for High‐Performance Supercapacitors

An N‐superdoped 3D graphene network structure with an N‐doping level up to 15.8 at% for high‐performance supercapacitor is designed and synthesized, in which the graphene foam with high conductivity acts as skeleton and nested with N‐superdoped reduced graphene oxide arogels. This material shows a highly conductive interconnected 3D porous structure (3.33 S cm^?1), large surface area (583 m² g^?1), low internal resistance (0.4 Ω), good wettability, and a great number of active sites. Because of the multiple synergistic effects of these features, the supercapacitors based on this material show a remarkably excellent electrochemical behavior with a high specific capacitance (of up to 380, 332, and 245 F g^?1 in alkaline, acidic, and neutral electrolytes measured in three‐electrode configuration, respectively, 297 F g^?1 in alkaline electrolytes measured in two‐electrode configuration), good rate capability, excellent cycling stability (93.5% retention after 4600 cycles), and low internal resistance (0.4 Ω), resulting in high power density with proper high energy density.