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1. Atomistic-Scale Simulations on Graphene Bending Near a Copper Surface

   https://doi.org/10.3390/catal11020208  

   Kowalik, Malgorzata; Hossain, Md Jamil; Lele, Aditya; Zhu, Wenbo; Banerjee, Riju; Granzier-Nakajima, Tomotaroh; Terrones, Mauricio; Hudson, Eric W.; van Duin, Adri C. (February 2021, Catalysts)

   null (Ed.)

   Molecular insights into graphene-catalyst surface interactions can provide useful information for the efficient design of copper current collectors with graphitic anode interfaces. As graphene bending can affect the local electron density, it should reflect its local reactivity as well. Using ReaxFF reactive molecular simulations, we have investigated the possible bending of graphene in vacuum and near copper surfaces. We describe the energy cost for graphene bending and the binding energy with hydrogen and copper with two different ReaxFF parameter sets, demonstrating the relevance of using the more recently developed ReaxFF parameter sets for graphene properties. Moreover, the draping angle at copper step edges obtained from our atomistic simulations is in good agreement with the draping angle determined from experimental measurements, thus validating the ReaxFF results. 

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2. Enhancing the Chemical Reactivity of Graphene through Substrate Engineering

   https://doi.org/10.1002/smll.202408116  

   Tu, Jia; Yan, Mingdi (December 2024, Small)

   Abstract Covalent functionalization of pristine graphene can modify its properties, enabling applications in optoelectronics, biomedical fields, environmental science, and energy. However, the chemical reactivity of pristine graphene is relatively low, and as such, methods have been developed to increase the reactivity of graphene. This review focuses on substrate engineering as an effective strategy to enhance the reactivity of graphene through strain and charge doping. Nanoparticles, metals with different crystal orientations, and stretchable polymers are employed to introduce strains in graphene, leading to enhanced chemical reactivity and increased degree of functionalization. Charge doping through orbital hybridization with metals and charge puddles induced by oxide substrates generally enhance the reactivity of graphene, while alkyl‐modified surfaces and 2D materials often reduce graphene reactivity via charge screening and van der Waals interactions that increase the stability of the graphene layer, respectively. This review summarizes methods for creating and characterizing strains and charge doping in graphene and discusses their effects on the chemical functionalization of graphene in various reactions. 

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3. Measuring nanoscale friction at graphene step edges

   https://doi.org/10.1007/s40544-019-0334-y  

   Chen, Zhe Kim (January 2020, Friction)

   Although graphene is well known for super-lubricity on its basal plane, friction at its step edge is not well understood and contradictory friction behaviors have been reported. In this study, friction of mono-layer thick graphene step edges was studied using atomic force microscopy (AFM) with a Si tip in dry nitrogen atmosphere. It is found that, when the tip slides over a ‘buried’ graphene step edge, there is a resistive force during the step-up motion and an assistive force during the step-down motion due to the topographic height change. The magnitude of these two forces is small and the same in both step-up and step-down motions. As for the ‘exposed’ graphene step edge, friction increases in magnitude and exhibits more complicated behaviors. During the step-down motion of the tip over the exposed step edge, both resistive and assistive components can be detected in the lateral force signal of AFM if the scan resolution is sufficiently high. The resistive component is attributed to chemical interactions between the functional groups at the tip and step-edge surfaces, and the assistive component is due to the topographic effect, same as the case of buried step edge. If a blunt tip is used, the distinct effects of these two components become more prominent. In the step-up scan direction, the blunt tip appears to have two separate topographic effects elastic deformation of the contact region at the bottom of the tip due to the substrate height change at the step edge and tilting of the tip while the vertical position of the cantilever (the end of the tip) ascends from the lower terrace to the upper terrace. The high-resolution measurement of friction behaviors at graphene step edges will further enrich understanding of interfacial friction behaviors on graphene-covered surfaces. 

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4. Using metal substrates to enhance the reactivity of graphene towards Diels–Alder reactions

   https://doi.org/10.1039/D2CP01842J  

   Yang, Xiaojian; Chen, Feiran; Kim, Min A.; Liu, Haitao; Wolf, Lawrence M.; Yan, Mingdi (August 2022, Physical Chemistry Chemical Physics)

   The Diels–Alder (DA) reaction, a classic cycloaddition reaction involving a diene and a dienophile to form a cyclohexene, is among the most versatile organic reactions. Theories have predicted thermodynamically unfavorable DA reactions on pristine graphene owing to its low chemical reactivity. We hypothesized that metals like Ni could enhance the reactivity of graphene towards DA reactions through charge transfer. The results indeed showed that metal substrates enhanced the reactivity of graphene in the DA reactions with a diene, 2,3-dimethoxy butadiene (DMBD), and a dienophile, maleic anhydride (MAH), with the activity enhancement in the order of Ni > Cu, and both are more reactive than graphene supported on silicon wafer. The rate constants were estimated to be two times higher for graphene supported on Ni than on silicon wafer. The computational results support the experimentally obtained rate trend of Ni > Cu, both predicted to be greater than unsupported graphene, which is explained by the enhanced graphene–substrate interaction reflected in charge transfer effects with the strongly interacting Ni. This study opens up a new avenue for enhancing the chemical reactivity of pristine graphene through substrate selection. 

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5. On the Reactivity Enhancement of Graphene by Metallic Substrates towards Aryl Nitrene Cycloadditions

   https://doi.org/10.1002/chem.202100227  

   Yang, Xiaojian; Chen, Feiran; Kim, Min A; Liu, Haitao; Wolf, Lawrence M; Yan, Mingdi (March 2021, Chemistry – A European Journal)

   null (Ed.)

   Pristine graphene is fairly inert chemically, and as such, most application‐driven studies use graphene oxide, or reduced graphene oxide. Using substrates to modulate the reactivity of graphene represents a unique strategy in the covalent functionalization of this otherwise fairly inert material. We found that the reactivity of pristine graphene towards perfluorophenyl azide (PFPA) can be enhanced by a metal substrate on which graphene is supported. Results on the extent of functionalization, defect density, and reaction kinetics all show that graphene supported on Ni (G/Ni) has the highest reactivity toward PFPA, followed by G/Cu and then G/silicon wafer. DFT calculations suggest that the metal substrate stabilizes the physisorbed nitrene through enhanced electron transfer to the singlet nitrene from the graphene surface assisted by the electron rich metal substrate. The G/Ni substantially stabilizes the singlet nitrene relative to G/Cu and the free‐standing graphene. The product structure is also predicted to be substrate dependent. These findings open the opportunities to enhance the reactivity of pristine graphene simply through the selection of the substrate. This also represents a new and powerful approach to increasing the reactivity of singlet nitrene through direct electron communication with graphene. 

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