Spatially Resolved Covalent Functionalization Patterns on Graphene

Abstract

Spatially resolved functionalization of 2D materials is highly demanded but very challenging to achieve.T he chemical patterning is typically tackled by preventing contact between the reagent and material, which brings various accompanying challenges.P hotochemical transformation on the other hand inherently provides remote high spatiotemporal resolution using the cleanest reagent-a photon. Herein, we combine two competing reactions on ag raphene substrate to create functionalization patterns on amicrometer scale via the Mitsunobu reaction. The mild reaction conditions allow introduction of covalently dynamic linkages,w hichc an serve as reversible labels for surface-or graphene-enhanced Raman spectroscopyc haracterization of the patterns prepared. The proposed methodology thus provides ap athwayf or local introduction of arbitrary functional groups on graphene.Graphene holds ap rominent position among two-dimensional (2D) materials owing to its unique properties, [1][2][3] which can be further tuned for particular applications [4][5][6] by several methods.Among them, chemical functionalization offers the broadest variety of possibilities. [7][8][9] Although several approaches for covalent grafting have been reported, [10][11][12][13][14][15] only recently has the advancement towards specific applications revealed the need for spatially resolved methods that would provide patterned surface functionalization on the 2D material, [16][17][18] aiming at sophisticated sensor arrays or device mass production. [19] This non-trivial task has been approached from several directions,u sing for instance photolithography, [20] dip-pen lithography [21][22][23] or various writing techniques. [24][25][26] Using covalent modification for spatially resolved functionalization typically relies on preventing contact of the reagents with graphene,t hus implying the use of ar esist mask [27] or controlled deposition [28,29] at the nanoscale,w hich either adds more steps (with concomitant contamination [30] ) or severely limits the processing speed, respectively.P hotochemical reactions represent au nique alternative to the abovementioned two approaches [31] because photochemistry responds to illumination patterns without the need for aresist or spatially confined reagent deposition.Thec ritical challenge for the surface functionalization of the 2D materials is unambiguous characterization of the reaction products facing the detection and resolution limits of many methods due to the strict monolayer nature of the materials. [32] Ty pical methods such as Raman spectroscopy [33][34][35] and X-ray photoelectron spectroscopy [36] (XPS) provide only limited insight into the actual chemistry taking place at the surface,anissue which has been tackled recently by the use of surface-and graphene-enhanced Raman spectroscopy (SERS and GERS,r espectively) [14,37] and also by other methods. [38,39] Application of SERS/GERS allows direct assignment of characteristic vibrational modes to particular species and thus provides solid evidence for species...

The Covalent Functionalization of Surface‐Supported Graphene: An Update

“…An alternative to the use of plasma treatment was shown by Valenta et al., who combined oxygen plasma treatment and photo masking (Figure 10). [81] The authors achieved a spatially resolved functionalization by using the Mitsunobu reaction. In this reaction, oxygenated groups on graphene react with triphenylphosphine (PPh 3 ) and dialkyl azodicarboxylate (DIAD) to produce a good leaving group for a successive subsequent nucleophilic attack.…”