Production and mechanical characterization of graphene micro-ribbons

Patterning of graphene into micro- and nano-ribbons allows for the tunability in emerging fields such as flexible electronic and optoelectronic devices, and is gaining interest for the production of more efficient reinforcement for composite materials. In this work we fabricate micro-ribbons from CVD graphene by combining UV photolithography and dry etching oxygen plasma treatments. Raman spectral imaging confirms the effectiveness of the patterning procedure, which is suitable for large-area patterning of graphene on wafer-scale, and confirms that the quality of graphene remains unaltered. The produced micro-ribbons were finally transferred and embedded into a polymeric matrix and the mechanical response was investigated by in-situ mechanical investigation combining Raman spectroscopy and tensile/compressive tests

Chemical Vapour Deposition Graphene-PMMA Nanolaminates for Flexible Gas Barrier

Successful ways of fully exploiting the excellent structural and multifunctional performance of graphene and related materials are of great scientific and technological interest. New opportunities are provided by the fabrication of a novel class of nanocomposites with a nanolaminate architecture. In this work, by using the iterative lift-off/float-on process combined with wet depositions, we incorporated cm-size graphene monolayers produced via Chemical Vapour Deposition into a poly (methyl methacrylate) (PMMA) matrix with a controlled, alternate-layered structure. The produced nanolaminate shows a significant improvement in mechanical properties, with enhanced stiffness, strength and toughness, with the addition of only 0.06 vol% of graphene. Furthermore, oxygen and carbon dioxide permeability measurements performed at different relative humidity levels, reveal that the addition of graphene leads to significant reduction of permeability, compared to neat PMMA. Overall, we demonstrate that the produced graphene-PMMA nanolaminate surpasses, in terms of gas barrier properties, the traditional discontinuous graphene-particle composites with a similar filler content. Moreover, we found that the gas permeability through the nanocomposites departs from a monotonic decrease as a function of relative humidity, which is instead evident in the case of the pure PMMA nanolaminate. This work suggests the possible use of Chemical Vapour Deposition graphene-polymer nanolaminates as a flexible gas barrier, thus enlarging the spectrum of applications for this novel material

Bimetallic Au/Ag nanoparticle loading on PNIPAAm–VAA–CS8 thermoresponsive hydrogel surfaces using ss-DNA coupling, and their SERS efficiency

Thermoresponsive hydrogels can be efficiently used as templates for bimetallic noble metal surface loading for the fabrication of plasmonic surfaces with a wide range of applications. Here, we report, for the first time, an easy approach for bimetallic Au/Ag surface loading by modifying poly(N-isopropylacrylamide) (PNIPAAm) hydrogel surfaces with ss-DNA. The advantages of this approach consist of the accuracy and the simplicity by which both gold and silver nanoparticles can be adsorbed by electrostatic interactions on hydrogel templates, without requiring sophisticated chemical treatment for their conjugation or the growth of nanoparticles on a hydrogel surface. The resulting patterns possess the capability of tuning the interparticle distance upon temperature changes, and thus their plasmonic properties. The aforementioned templates have been successfully used as SERS substrates for 5 × 10-7 M adenine detection

Easy-to-fill asymmetric polymeric micro-reservoirs

In this work, we demonstrate the feasibility of micrometric asymmetric reservoirs made of thermoplastic polymers by using the gas foaming method, which has been recently introduced, and consists in forming bubbles in micro- or nano-metric bulk particles as it is done with carbonated drinks. As this simplicity anticipates, this represents a breakthrough in the area of micro and nano-particles as it responds to the needs of: i) breaking the symmetry of commonly available systems, ii) filling the particles with a multitude of host molecules and solutions, iii) having different shapes, iv) having a wide range of particle dimensions, v) having particles made of a wide range of materials. Here we report the achievement of micrometric spherical particles and of micrometric ellipsoidal particles with eccentric holes, filled with crystal violet or with quantum dots as model host molecules. Raman spectroscopy and optical and electron imaging are utilized to verify the effectiveness of the method. This study should open up the use of micro- and nano-metric reservoirs in a multitude of research areas, from the biomedicine and pharmacology, to electronics, energy and optics

Wettability of graphene by molten polymers

Graphene wetting by polymers is a critical issue to both the success of polymer-aided transfer of large size sheets onto specific substrates and to the development of well performing nanocomposites. Here we show for the first time that high temperature contact angle measurements can be performed to investigate the wettability of CVD graphene by molten polymers. In particular, poly(methyl methacrylate), a widely used polymer support for CVD graphene transfer, has been adopted herein for this proof-of-concept study and the values of contact angle and work of adhesion have been provided in the temperature range 170–200 °C

Operando characterization and molecular simulations reveal the growth kinetics of graphene on liquid copper during chemical vapor deposition

International audienceIn recent years, liquid metal catalysts have emerged as a compelling choice for the controllable, large-scale, and high-quality synthesis of two-dimensional materials. At present, there is little mechanistic understanding of the intricate catalytic process, though, of its governing factors or what renders it superior to growth at the corresponding solid catalysts. Here, we report on a combined experimental and computational study of the kinetics of graphene growth during chemical vapor deposition on a liquid copper catalyst. By monitoring the growing graphene flakes in real time using in situ radiation-mode optical microscopy, we explore the growth morphology and kinetics over a wide range of CH4-to-H2 pressure ratios and deposition temperatures. Constant growth rates of the flakes' radius indicate a growth mode limited by precursor attachment, whereas methane-flux-dependent flake shapes point to limited precursor availability. Large-scale free energy simulations enabled by an efficient machine-learning moment tensor potential trained to density-functional theory data provide quantitative barriers for key atomic-scale growth processes. The wealth of experimental and theoretical data can be consistently combined into a microkinetic model that reveals mixed growth kinetics that, in contrast to the situation at solid Cu, is partly controlled by precursor attachment alongside precursor availability. Key mechanistic aspects that directly point toward the improved graphene quality are a largely suppressed carbon dimer attachment due to the facile incorporation of this precursor species into the liquid surface and a low-barrier ring-opening process that self-heals 5-membered rings resulting from remaining dimer attachments

Correction to Real-Time Multiscale Monitoring and Tailoring of Graphene Growth on Liquid Copper

It has come to our attention that we did not correctly acknowledge the synchrotron where some of the measurements were performed. To rectify this, the acknowledgments section of our paper has been updated

Real-Time Multiscale Monitoring and Tailoring of Graphene Growth on Liquid Copper

The synthesis of large, defect-free two-dimensional materials (2DMs) such as graphene is a major challenge toward industrial applications. Chemical vapor deposition (CVD) on liquid metal catalysts (LMCats) is a recently developed process for the fast synthesis of high-quality single crystals of 2DMs. However, up to now, the lack of in situ techniques enabling direct feedback on the growth has limited our understanding of the process dynamics and primarily led to empirical growth recipes. Thus, an in situ multiscale monitoring of the 2DMs structure, coupled with a real-time control of the growth parameters, is necessary for efficient synthesis. Here we report real-time monitoring of graphene growth on liquid copper (at 1370 K under atmospheric pressure CVD conditions) via four complementary in situ methods: synchrotron X-ray diffraction and reflectivity, Raman spectroscopy, and radiation-mode optical microscopy. This has allowed us to control graphene growth parameters such as shape, dispersion, and the hexagonal supra-organization with very high accuracy. Furthermore, the switch from continuous polycrystalline film to the growth of millimeter-sized defect-free single crystals could also be accomplished. The presented results have far-reaching consequences for studying and tailoring 2D material formation processes on LMCats under CVD growth conditions. Finally, the experimental observations are supported by multiscale modeling that has thrown light into the underlying mechanisms of graphene growth