Spatially Resolved Covalent Functionalization Patterns on Graphene.

Spatially resolved functionalization of 2D materials is highly demanded but very challenging to achieve. The chemical patterning is typically tackled by preventing contact between the reagent and material, which brings various accompanying challenges. Photochemical transformation on the other hand inherently provides remote high spatiotemporal resolution using the cleanest reagent-a photon. Herein, we combine two competing reactions on a graphene substrate to create functionalization patterns on a micrometer scale via the Mitsunobu reaction. The mild reaction conditions allow introduction of covalently dynamic linkages, which can serve as reversible labels for surface- or graphene-enhanced Raman spectroscopy characterization of the patterns prepared. The proposed methodology thus provides a pathway for local introduction of arbitrary functional groups on graphene.

Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds.

Manipulating nanoscopic objects by external stimuli is the cornerstone of nanoscience. Here, we report the implementation of dynamic covalent chemistry in the reversible binding and directional motion of fluorescent nanodiamond particles at a functionalized graphene surface via imine linkages. The dynamic connections allow for controlling the formation and rupture of these linkages by external stimuli. By introduction of pH gradients, the nanoparticles are driven to move along the gradient due to the different rates of the imine condensation and hydrolysis in the two environments. The multivalent nature of the particle-to-surface connection ensures that particles remain attached to the surface, whereas its dynamic character allows for exchange reaction, thus leading to displacement yet bound behavior in two-dimensional space. These results open a pathway for thermodynamically controlled manipulation of objects on the nanoscale.

Selective self-assembly and light emission tuning of layered hybrid perovskites on patterned graphene.

The emission of light in two-dimensional (2-D) layered hybrid organic lead halide perovskites, namely (R-NH3)2PbX4, can be effectively tuned using specific building blocks for the perovskite formation. Herein this behaviour is combined with a non-covalent graphene functionalization allowing excellent selectivity and spatial resolution of the perovskite film growth, promoting the formation of hybrid 2-D perovskite : graphene heterostructures with uniform coverage of up to centimeter scale graphene sheets and arbitrary shapes down to 5 µm. Using cryo-Raman microspectroscopy, highly resolved spectra of the perovskite phases were obtained and the Raman mapping served as a convenient spatially resolved technique for monitoring the distribution of the perovskite and graphene constituents on the substrate. In addition, the stability of the perovskite phase with respect to the thermal variation was inspected in situ by X-ray diffraction. Finally, time-resolved photoluminescence characterization demonstrated that the optical properties of the perovskite films grown on graphene are not hampered. Our study thus opens the door to smart fabrication routes for (opto)-electronic devices based on 2-D perovskites in contact with graphene with complex architectures.

Functionalization of Hydrogenated Chemical Vapour Deposition-Grown Graphene by On-Surface Chemical Reactions.

The reactivity of hydrogenated graphene when treated with oxidising agents, KMnO4 and KIO4 , as well as alkylated with benzyl bromide (BnBr) was studied. The probed reactions are strictly limited to the partly hydrogenated form of graphene in which most of the hydrogen atoms are located in activated benzylic/allylic positions. This, in turn, clearly demonstrates the presence of hydrogen attached to the graphene lattice. Attachment of the benzyl group was also unequivocally demonstrated by characteristic vibrations recorded in the surface-enhanced Raman spectra, and all reactions were shown to proceed solely on hydrogenated graphene as evidenced by the comparison with pristine chemical vapour deposition-grown graphene.

Decomposition of Fluorinated Graphene under Heat Treatment.

Fluorination modifies the electronic properties of graphene, and thus it can be used to provide material with on-demand properties. However, the thermal stability of fluorinated graphene is crucial for any application in electronic devices. Herein, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and Raman spectroscopy were used to address the impact of the thermal treatment on fluorinated graphene. The annealing, at up to 700 K, caused gradual loss of fluorine and carbon, as was demonstrated by XPS. This loss was associated with broad desorption of CO and HF species, as monitored by TPD. The minor single desorption peak of CF species at 670 K is suggested to rationalize defect formation in the fluorinated graphene layer during the heating. However, fluorine removal from graphene was not complete, as some fraction of strongly bonded fluorine can persist despite heating to 1000 K. The role of intercalated H2 O and OH species in the defluorination process is emphasised.