Chemical Reactivity Of Graphene Research Articles

Structural Integrity Preserving and Residue-Free Transfer of Large-Area Wrinkled Graphene onto Polymeric Substrates

Wrinkled graphene offers many advantageous features resulting from modifying the structural and physical properties as well as the chemical reactivity of graphene. However, its inadequate transferability to other substrates has limited its usability. This paper reports a roll-based clean transfer approach that enables the damage-free and contamination-free transfer of large-area wrinkled graphene onto polymeric substrates without compromising the integrity of wrinkle structures. The method implements the simultaneous imidazole-assisted etching and doping of chemical vapor-deposited graphene to fabricate multilayer graphene on a thermoplastic polystyrene (PS) substrate coated with a water-soluble poly(4-styrenesulfonic acid) (PSS) sacrificial layer via a roll-based transfer process. The compliant PSS layer affords the conformal contact between the PS substrate and graphene during the wrinkle formation process, enabling the controllable fabrication of graphene wrinkle structures on a large area. The water-soluble properties of PSS simplify the typically difficult separation of wrinkled graphene from the PS substrate after its transfer onto a target substrate. This improves the transferability of wrinkled graphene, rendering the transfer process solvent-free and residue-free. This work demonstrates the feasibility of the formulated method by transferring centimeter-scale wrinkled graphene onto currently used transparent flexible substrates (i.e., polyethylene terephthalate and polydimethylsiloxane). The results indicate that the transferred wrinkled graphene possesses the desirable combination of superior stretchability, optical transmittance, sheet resistance, and electromechanical stability, rendering its suitable application to transparent flexible and stretchable electronics.

Atomically resolved TEM imaging of covalently functionalised graphene

Covalent functionalisation can be a powerful lever to tune the properties and processability of graphene. After overcoming the low chemical reactivity of graphene, covalent functionalisation led to the generation of new hybrid materials, applicable in a broad variation of fields. Although the process of functionalising graphene is nowadays firmly established, fundamental aspects of the produced hybrid materials remain to be clarified. Especially the atomically resolved imaging is only scarcely explored. Here we show aberration corrected in situ high resolution TEM imaging of dodecyl functionalised monolayer graphene at atomic resolution after an effective mechanical filtering approach. The mechanical filtering allows to separate adsorbed contamination from the covalently bound functional molecules and thus opens the possibility for the observation of this hybrid material. The obtained data is validated by DFT calculations and by a novel image simulation approach based on molecular dynamics (MD) simulations at room temperature.

Transfer-Enabled Fabrication of Graphene Wrinkle Arrays for Epitaxial Growth of AlN Films.

Formation of graphene wrinkle arrays can periodically alter the electrical properties and chemical reactivity of graphene, which is promising for numerous applications. However, large-area fabrication of graphene wrinkle arrays remains unachievable with a high density and defined orientations, especially on rigid substrates. Herein, relying on the understanding of the formation mechanism of transfer-related graphene wrinkles, the graphene wrinkle arrays are fabricated without altering the crystalline orientation of entire graphene films. The choice of the transfer medium that has poor wettability on the corrugated surface of graphene is proven to be the key for the formation of wrinkles. This work provides a deep understanding of formation process of transfer-related graphene wrinkles and opens up a new way for periodically modifying the surface properties of graphene for potential applications, including direct growth of AlN epilayers and deep ultraviolet light emitting diodes.

Sensing the quantized reactivity of graphene

We demonstrated that the variations measured in the quantum capacitance of single-layer graphene, envisioned here as a conceptual molecular model, depend on the chemical reactivity of the molecule and can be used as an analytical and sensing tool for environmental conditions. The variations are quantized as a function of the environmental changes and can be correlated with chemical reactivity indexes such as chemical hardness and softness. This not only constitutes a proof-of-principle that the chemical reactivity of graphene, as a single molecule, can be determined in situ by measuring the quantum capacitance, but also that these measurements can be used as an analytical tool.

Graphene modification based on plasma technologies

Plasma contains highly reactive species, including electrons, ions, radicals, photons, etc., which are critical for catalyzing or directly participating in chemical reactions. Plasma is a highly efficient tool in chemical synthesis and material modification, since it can make the chemical reactions that are difficult or even impossible to occur under thermal equilibrium conditions take place and accelerate through its catalysis. The chemical reactivity of graphene under conventional conditions is low, which means that the reaction of graphene requires high temperature, high pressure and/or strong acid or alkali, thereby restricting the synthesis and modification of novel graphene-derived materials. Plasma-assisted graphene reaction can trigger a series of chemical reactions, such as reduction, oxidation, defect repair, doping, grafting, epitaxial growth and cross-linking of graphene, under ambient temperature and pressure without any corrosive conditions. It provides great potentials for the functional modification of graphene and the synthesis of graphene composites, which deserve further exploration. Over the past decade, a number of studies of graphene synthesis and modification by using plasma with distinctive characteristics have been reported. However, most of reports focused on the presentation of technical routes and corresponding results, and the research on chemical reaction kinetics is still far from being fully addressed. In this review, we make a comprehensive discussion about these reports by mainly summarizing and discussing some of the representative results, in order to promote further research in the relevant fields.

Investigation of GaN with Low Threading Dislocation Density Grown on Graphene/Sputtered AlN Composite Substrate

High‐quality GaN film is grown on graphene with the underneath sputtered AlN modified layer using metal organic chemical vapor deposition. Due to the modulation effect of sputtered AlN on the surface potential and the chemical reactivity of graphene, the nucleation probability of GaN is significantly improved. The GaN epitaxial layer shows excellent crystal quality and surface morphology, and has very low threading dislocation density of 1.78 × 108 cm−2. Furthermore, the mechanism of threading dislocation suppression is revealed according to the transmission electron microscope results. The improved nucleation probability and enhanced lateral growth mode lead to the formation of short‐range stacking faults in c‐plane GaN, which block the propagation of threading dislocations along the growth direction. Moreover, the formation and evolution mechanism of the short‐range stacking faults are discussed. The results in this work not only offer a promising approach to propel the widespread application of GaN on graphene, but also provide a new idea for the regulation and suppression of defects in the growth of nitride semiconductors.

Raman Spectral Band Oscillations in Large Graphene Bubbles.

Raman spectra of large graphene bubbles showed size-dependent oscillations in spectral intensity and frequency, which originate from optical standing waves formed in the vicinity of the graphene surface. At a high laser power, local heating can lead to oscillations in the Raman frequency and also create a temperature gradient in the bubble. Based on Raman data, the temperature distribution within the graphene bubble was calculated, and it is shown that the heating effect of the laser is reduced when moving from the center of a bubble to its edge. By studying graphene bubbles, both the thermal conductivity and chemical reactivity of graphene were assessed. When exposed to hydrogen plasma, areas with bubbles are found to be more reactive than flat graphene.

Graphene for Water-Based Nanofluid Preparation: Effect of Chemical Modifications on Dispersion and Stability

Graphene, whatever its number of layers, is recognized for heat and thermal transfer ability. As it is widely known to be highly hydrophobic, its use in water-based nanofluid development requires first to improve both their dispersion and stability properties. Here, we have investigated several ways to chemically modify the surface properties of multi-layer graphene in order to increase their hydrophilic character. Chemical reactivity of graphene was deeply analyzed based on a multi-scale characterization using TEM, Raman spectroscopy and TGA-MS coupled technique. By optimizing and combining both covalent and non-covalent functionalization, stable graphene-based nanofluids under static conditions could be prepared with a straightforward approach. Moreover, we have investigated their flowing behavior. Contrary to graphene nanosheets strongly attacked by HNO3, under a gentler oxidation treatment using KMnO4, stability is well preserved under flowing conditions. Such high-stability nanofluids could help toward the practical use of graphene-based dispersions as heat transfer fluid in flowing systems.

Gate-controlled ultraviolet photo-etching of graphene edges

The chemical reactivity of graphene under ultraviolet (UV) light irradiation is investigated under positive and negative gate electric fields. Graphene edges are selectively etched when negative gate voltages are applied while the reactivity is significantly suppressed for positive gate voltages. Oxygen adsorption onto graphene is significantly affected by the Fermi level of the final state achieved during previous electrical measurements. UV irradiation after negative-to-positive gate sweeps causes predominant oxygen desorption while UV irradiation after gate sweeps in the opposite direction causes etching of graphene edges.

Phosphorus-doped graphene and (8, 0) carbon nanotube: Structural, electronic, magnetic properties, and chemical reactivity

Recently, doping non-carbon atoms into graphene or carbon nanotube (CNT) has attracted considerable attention due to its effectiveness to change or tailor their electronic and magnetic properties as well as chemical reactivity. In this work, we present a density functional theory study of the recently synthesized phosphorus (P) doped graphene and CNT. Particular attention is paid to studying the effects of P-doping on the structural, electronic, and magnetic properties as well as chemical reactivity of graphene or CNT. The results show that P dopant drastically changes the geometrical structure of graphene or CNT, rendering P and its neighboring C atoms protrude from the sidewall of CNT and graphene. Moreover, P-doping induces localized electronic states into graphene and CNTs, thus modifying the electronic properties by producing n-type behavior. Meanwhile, due to P doping, the graphene and CNT exhibit magnetic nature with spin net moment of 1.02 and 0.99μB, respectively. In order to evaluate the chemical reactivity of the two nanostructures, their interactions with several gas molecules, including NH3, H2O, O2, NO2, and NO, are further calculated. Our results may be useful not only for deeply understanding the properties of CNTs and graphenes, but also for developing various novel nanodevices.