Chemically derived graphene oxide (GO) possesses a unique set of properties arising from oxygen functional groups that are introduced during chemical exfoliation of graphite. Large‐area thin‐film ...deposition of GO, enabled by its solubility in a variety of solvents, offers a route towards GO‐based thin‐film electronics and optoelectronics. The electrical and optical properties of GO are strongly dependent on its chemical and atomic structure and are tunable over a wide range via chemical engineering. In this Review, the fundamental structure and properties of GO‐based thin films are discussed in relation to their potential applications in electronics and optoelectronics.
For over 150 years, oxidation of graphite has been known to result in water‐soluble graphite oxide. However, it has been only recently recognized that graphite oxide splits into atomically thin graphene oxide (GO) upon dissolution. GO can be produced on a large scale, handled in solution, assembled into thin films, and deposited on arbitrary substrates. This Review introduces fundamental properties of GO and summarizes recent achievements in device applications.
Efficient intercalation of ions in layered materials forms the basis of electrochemical energy storage devices such as batteries and capacitors. Recent research has focused on the exfoliation of ...layered materials and then restacking the two-dimensional exfoliated nanosheets to form electrodes with enhanced electrochemical response. Here, we show that chemically exfoliated nanosheets of MoS2 containing a high concentration of the metallic 1T phase can electrochemically intercalate ions such as H(+), Li(+), Na(+) and K(+) with extraordinary efficiency and achieve capacitance values ranging from ∼400 to ∼700 F cm(-3) in a variety of aqueous electrolytes. We also demonstrate that this material is suitable for high-voltage (3.5 V) operation in non-aqueous organic electrolytes, showing prime volumetric energy and power density values, coulombic efficiencies in excess of 95%, and stability over 5,000 cycles. As we show by X-ray diffraction analysis, these favourable electrochemical properties of 1T MoS2 layers are mainly a result of their hydrophilicity and high electrical conductivity, as well as the ability of the exfoliated layers to dynamically expand and intercalate the various ions.
Two‐dimensional (2D) transition‐metal dichalcogenide (TMD) nanosheets have emerged as a fascinating new class of materials for catalysis. These nanosheets are active for several important catalysis ...reactions including hydrogen evolution from water. The rich chemistry of TMDs combined with numerous strategies that allow tuning of their electronic properties make these materials very attractive for understanding the fundamental principles of electro‐ and photocatalysis, as well as for developing highly efficient, renewable, and affordable catalysts for large‐scale production of hydrogen. Recent developments are highlighted and important challenges in using TMDs as catalysts are also discussed.
Transition metal dichalcogenide (TMD) nanosheets are promising catalysts for evolution of hydrogen. TMDs possess a wide range of electronic and catalytic properties so that important fundamental parameters related to catalysis can be investigated. Recent progress on the study of 2D TMD nanosheets for enhancing their electro‐ and photocatalytic activity is discussed.
The electrical properties of solution-processed composite thin films consisting of functionalized graphene sheets (FGS) as the filler and polystyrene (PS) as the host material are described. We ...demonstrate that transistors from graphene-based composite thin films exhibit ambipolar field effect characteristics, suggesting transport via percolation among FGS in the insulating PS matrix. Device characteristics as a function of the FGS size are also reported. The results indicate that devices fabricated using the largest size FGS yield the highest mobility values. This simple and scaleable fabrication scheme based on a commodity plastic could be useful for low-cost, macro-scale electronics.
Owing to their large absorption cross-sections and high photoluminescence quantum yields, lead halide perovskite quantum dots (PQDs) are regarded as a promising candidate for various optoelectronics ...applications. However, easy degradation of PQDs in water and in a humid environment is a critical hindrance for applications. Here we develop a Pb-S bonding approach to synthesize water-resistant perovskite@silica nanodots keeping their emission in water for over six weeks. A two-photon whispering-gallery mode laser device made of these ultra-stable nanodots retain 80% of its initial emission quantum yield when immersed in water for 13 h, and a two-photon random laser based on the perovskite@silica nanodots powder could still operate after the nanodots were dispersed in water for up to 15 days. Our synthetic approach opens up an entirely new avenue for utilizing PQDs in aqueous environment, which will significantly broaden their applications not only in optoelectronics but also in bioimaging and biosensing.
The oxygen reduction reaction (ORR)one of the two half-reactions in fuel cellsis one of the bottlenecks that has prevented fuel cells from finding a wide range of applications today. This is ...because ORR is inherently a sluggish reaction; it is also because inexpensive and sustainable ORR electrocatalysts that are not only efficient but also are based on earth-abundant elements are hard to come by. Herein we report the synthesis of novel carbon-based materials that can contribute to solving these challenges associated with ORR. Mesoporous oxygen- and nitrogen-doped carbons were synthesized from in situ polymerized mesoporous silica-supported polyaniline (PANI) by carbonization of the latter, followed by etching away the mesoporous silica template from it. The synthetic method also allowed the immobilization of different metals such as Fe and Co easily into the system. While all the resulting materials showed outstanding electrocatalytic activity toward ORR, the metal-free, PANI-derived mesoporous carbon (dubbed PDMC), in particular, exhibited the highest activity, challenging conventional paradigms. This unprecedented activity by the metal-free PDMC toward ORR was attributed to the synergetic activities of nitrogen and oxygen (or hydroxyl) species that were implanted in it by PANI/mesoporous silica during pyrolysis.
The integration of novel materials such as single-walled carbon nanotubes and nanowires into devices has been challenging, but developments in transfer printing and solution-based methods now allow ...these materials to be incorporated into large-area electronics. Similar efforts are now being devoted to making the integration of graphene into devices technologically feasible. Here, we report a solution-based method that allows uniform and controllable deposition of reduced graphene oxide thin films with thicknesses ranging from a single monolayer to several layers over large areas. The opto-electronic properties can thus be tuned over several orders of magnitude, making them potentially useful for flexible and transparent semiconductors or semi-metals. The thinnest films exhibit graphene-like ambipolar transistor characteristics, whereas thicker films behave as graphite-like semi-metals. Collectively, our deposition method could represent a route for translating the interesting fundamental properties of graphene into technologically viable devices.
Chemically derived graphene oxide (GO) is an atomically thin sheet of graphite that has traditionally served as a precursor for graphene, but is increasingly attracting chemists for its own ...characteristics. It is covalently decorated with oxygen-containing functional groups - either on the basal plane or at the edges - so that it contains a mixture of sp(2)- and sp(3)-hybridized carbon atoms. In particular, manipulation of the size, shape and relative fraction of the sp(2)-hybridized domains of GO by reduction chemistry provides opportunities for tailoring its optoelectronic properties. For example, as-synthesized GO is insulating but controlled deoxidation leads to an electrically and optically active material that is transparent and conducting. Furthermore, in contrast to pure graphene, GO is fluorescent over a broad range of wavelengths, owing to its heterogeneous electronic structure. In this Review, we highlight the recent advances in optical properties of chemically derived GO, as well as new physical and biological applications.
Graphene-nanoparticle hybrid material research in regard to bioapplications is examined and reviewed. This differs from graphene use in cancer therapy.
Nanoscale heterostructures with quantum dots, nanowires, and nanosheets have opened up new routes toward advanced functionalities and implementation of novel electronic and photonic devices in ...reduced dimensions. Coherent and passivated heterointerfaces between electronically dissimilar materials can be typically achieved through composition or doping modulation as in GaAs/AlGaAs and Si/NiSi or heteroepitaxy of lattice matched but chemically distinct compounds. Here we report that single layers of chemically exfoliated MoS2 consist of electronically dissimilar polymorphs that are lattice matched such that they form chemically homogeneous atomic and electronic heterostructures. High resolution scanning transmission electron microscope (STEM) imaging reveals the coexistence of metallic and semiconducting phases within the chemically homogeneous two-dimensional (2D) MoS2 nanosheets. These results suggest potential for exploiting molecular scale electronic device designs in atomically thin 2D layers.
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