Reduced Graphene: Synthesis, Properties, and Applications
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REVIEW Laser Direct-Writing www.advmattechnol.de Laser-Reduced Graphene: Synthesis, Properties, and Applications Zhengfen Wan, Erik W. Streed, Mirko Lobino, Shujun Wang, Robert T. Sang, Ivan S. Cole, David V. Thiel, and Qin Li* produce graphene with relatively high Laser reduction of graphene oxide has attracted significant interest in recent crystalline quality, including mechanical years, because it offers a highly flexible, rapid, and chemical-free graphene exfoliation of graphite,[6,7] epitaxial [8–10] fabrication route that can directly write on almost any solid substrate growth, and chemical vapor deposi- tion (CVD).[11–14] Another class of methods with down to sub-micrometer feature size. Laser-reduced graphene (LRG) adopts graphene oxide (GO) as the pre- is explored for various important applications such as supercapacitors, cursor for the synthesis of graphene with sensors, field effect transistors, holograms, solar cells, flat lenses, varied qualities. GO can be reduced to gra- bolometers, thermal sound sources, cancer treatment, water purification, phene by various reduction routes such as [15,16] [17–19] [20] lithium-ion batteries, and electrothermal heaters. This contribution reviews thermal, chemical, electrical, [21] [22,23] [24] most recent research progress on the aspects of fabrication, properties, microwave, photo, laser, or a combination of these methods.[25] Table 1 and applications of LRG. Particular attention is paid to the mechanism of summarizes several typical reduction LRG formation, which is still debatable. The three main theories, including methods for graphene oxide and the the photochemical process, the photothermal process, and a combination respective conductivity (or sheet resistance) of both processes, are discussed. Strategies for tuning the properties of reduced graphene, which is related to [26] and performance of LRG, such as the laser parameters, chemical doping, the reduction quality and defect density. Among these techniques, laser reduction structure modulation, and environment control, are highlighted. LRGs is considered very promising for graphene with better performance including smaller feature size, higher conductivity, devices[27] including supercapacitors,[28–31] and more flexible morphology design in both 2D and 3D formats will offer sensors,[32–35] field effect transistors tremendous opportunities for advancement in electronics, photonic, and (FETs),[36–38] thin film transistors,[39] holo- optoelectronic applications. grams,[40] solar cells,[41–46] and flat lenses.[47] During laser reduction, the precursors, typi- cally a GO film, are irradiated with the laser 1. Introduction and converted in situ into reduced graphene oxide (rGO). Besides the reduction of pure GO, doped GO can also be produced with Graphene is a flat monolayer of carbon atoms tightly packed laser irradiation. This method eliminates the use of highly corro- into a 2D honeycomb lattice.[1] Graphene has attracted tremen- sive and toxic chemicals, and avoids the requirement for high tem- dous attention because of its unique properties including high peratures.[48] This process is also compatible with substrates that electrical and thermal conductivities, optical transparency, and cannot tolerate high temperatures including polymers. Moreover, mechanical strength, which are highly desirable in a broad the laser writing process can achieve localized reduction of GO range of applications.[2–4] Therefore, it is of great importance and is highly flexible in micropattern creation, which makes laser to develop effective fabrication methods for high-quality gra- reduction very suitable for microdevice fabrication. The record phene.[5] A variety of methods have been employed to directly feature size of laser direct-writing technology to date is down to Z. Wan, Prof. M. Lobino, Dr. S. Wang, Prof. Q. Li Dr. E. W. Streed, Prof. M. Lobino, Prof. R. T. Sang Queensland Micro- and Nanotechnology Centre Centre for Quantum Dynamics Griffith University Griffith University Nathan, QLD 4111, Australia Nathan, QLD 4111, Australia E-mail: [email protected] Dr. E. W. Streed Z. Wan, Dr. S. Wang, Prof. D. V. Thiel, Prof. Q. Li Institute for Glycomics School of Engineering and the Built Environment Griffith University Griffith University Southport, QLD 4222, Australia QLD 4111, Australia Prof. I. S. Cole The ORCID identification number(s) for the author(s) of this article Advanced Manufacturing and Fabrication can be found under https://doi.org/10.1002/admt.201700315. RMIT University Melbourne, VIC 3000, Australia DOI: 10.1002/admt.201700315 Adv. Mater. Technol. 2018, 1700315 1700315 (1 of 19) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advancedsciencenews.com www.advmattechnol.de 0.55 µm.[40] The whole process of laser reduction can be com- pleted in several minutes,[49] which greatly improves the effi- Zhengfen Wan received ciency of production. his M.S. degree in Physics Recently, there have been many new developments on the in 2010 from Zhejiang subject of laser reduction for synthesis of graphene. This report University, China. He joined aims to summarize the recent developments in this active field. Prof. Qin Li’s research group Particular attention is paid to the precursor material for laser at Griffith University in 2016 reduction, the mechanisms of laser reduction, and the diverse to pursue his Ph.D. His range of applications of this technology. research interests include In the published literature, different precursors, mainly GO laser fabrication and gra- and polymers, were used for laser reduction. After laser irradia- phene materials for advanced tion, the resulting graphene materials are referred variously in manufacturing of functional different papers as laser-induced graphene,[29] laser-scribed gra- materials. phene,[49] or simply reduced graphene oxide.[28] The term laser- reduced graphene (LRG) is adopted throughout this paper. Qin Li is an Associate Professor at the Queensland Micro- and Nanotechnology 2. Laser Reduction with Various Precursors Centre and Environmental Engineering, Griffith 2.1. Graphene Oxide University. Dr. Li received her Bachelor and Master degrees As a typical precursor of LRG, GO contains only one or a few from Zhejiang University, layers of carbon atoms with a similar structure to graphene, and obtained her Ph.D. in but the plane of carbon atoms in GO is decorated with oxygen- 2002 from The University of containing groups.[50] Due to its oxygen-containing groups, it is Queensland. She was a Marie highly hydrophilic and can form stable aqueous colloids,[51,52] Curie International Incoming which enables convenient, solution-based processes for indus- Fellow hosted by Max Planck Institute for Polymer Research trial production. On the other hand, the presence of oxygenated from 2006 to 2008. Her research expertise includes carbon groups on the basal plane also disrupts the π–π conjugation, nanodots, graphene quantum dots, graphene materials, making GO an electrical insulator.[53] colloids and photonic materials, nanosensors, and environ- GO can be produced from graphite on a large scale with cost- mental nanotechnologies. effective chemical methods.[54] Several different methods are employed for GO synthesis, including the Brodie method,[55] the Staudenmaier method,[56] and the Hummers method,[57] or their modifications. Among these methods, the modified Hummers which consists of closely stacked individual graphene layers. method (MHM) is the most commonly used approach for GO After the graphite is mixed with concentrated sulfuric acid [50] fabrication. The raw material for MHM synthesis is graphite, (H2SO4), sodium nitrate (NaNO3), and potassium permanganate Table 1. Typical techniques for reduced graphene and their properties. Technique Key procedure Conductivity/Resistivity Ref. Thermal reduction GO annealing at 1100 °C 5.5 × 104 S m−1 [122] GO annealing at various temperatures 1.78 × 103 S m−1 [131] Chemical Reaction Hydrazine reduction of GO 2 × 102 S m−1 [17,132] Hydroiodic acid reduction of GO 2.98 × 104 S m−1 [133] Electrical reduction Reducing GO using electrical stimulus – [20] Microwave reduction GO annealing at 300 °C for 1 h under argon, then microwaved for – [21] 1–2 s under argon Electron beam lithography Reducing GO with focused electron beam – [134] 6 −1 a) Photoreduction UV irradiation on the TiO2 and GO mixture 4.6 × 10 Ω sq [135] Camera flash on GO and polymer mixture – [23] Combined method Hydrazine reduction and thermal annealing at 1100 °C 5.5 × 104 S m−1 [136] Hydrazine reduction and thermal annealing at 1100 °C 104 S m−1 [25] Laser reduction Laser direct irradiation on GO 2.56 × 104 S m−1 [24] a)Film thickness data unavailable for unit conversion. Adv. Mater. Technol. 2018, 1700315 1700315 (2 of 19) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advancedsciencenews.com www.advmattechnol.de (KMnO4), its graphene layers are mainly oxidized by the active and spin-coating. With laser irradiation, the GO film can be [62] oxidizing agent, typically dimanganese heptoxide (Mn2O7), reduced in air at room temperature. Furthermore, the LRG [58,59] which results from the reaction of KMnO4 with H2SO4. microcircuits can also be fabricated via direct laser patterning [24] The addition of NaNO3 further increases the interlayer distance on GO films, shown in Figure 2a–c. Figure 2d illustrates between graphene sheets and enhances the oxidation.[60] the atomic force microscopy (AFM) characterization of laser- Dimiev and Tour carried out a comprehensive study on