Molecular embroidering of graphene

Structured covalent two-dimensional patterning of graphene with different chemical functionalities constitutes a major challenge in nanotechnology. At the same time, it opens enormous opportunities towards tailoring of physical and chemical properties with limitless combinations of spatially defined surface functionalities. However, such highly integrated carbon-based architectures (graphene embroidery) are so far elusive. Here, we report a practical realization of molecular graphene embroidery by generating regular multiply functionalized patterns consisting of concentric regions of covalent addend binding. These spatially resolved hetero-architectures are generated by repetitive electron-beam lithography/reduction/covalent-binding sequences starting with polymethyl methacrylate covered graphene deposited on a Si/SiO2 substrate. The corresponding functionalization zones carry bromobenzene-, deutero-, and chloro-addends. We employ statistical Raman spectroscopy together with scanning electron microscopy/energy dispersive X-ray spectroscopy for an unambiguous characterization. The exquisitely ordered nanoarchitectures of these covalently multi-patterned graphene sheets are clearly visualized.


S1. Materials
CVD graphene on a 1×1 cm 2 polymethyl methacrylate (PMMA) substrate was purchased from ACS Material Co. (USA). All other chemicals were purchased from Sigma Aldrich Co. (Germany). Iodine monochloride (ICl) and ethanol as solvent were dried for three days over 4 Å molecular sieves, which were preheated under vacuum for another three days. Subsequently, the dried ICl, ethanol, and the deuteroxide were degassed by pump freeze (seven iterative steps) and transferred to an argon filled glovebox (˂ 0.1 ppm O2, ˂ 0.1 ppm H2O).

S2. Patterned graphene fabrication by EBL
The graphene monolayer was deposited on a Si/SiO2 wafer by a wet transfer technique. Here, the PMMA-supported graphene, floating on top of a water surface, was fished onto the prepared Si/SiO2 wafer. Subsequently, the PMMA coating was removed by acetone vapor (60 min) and the wafer was dried in air. Afterwards, a fresh PMMA double-layer mask was applied by spin coating (3, After each individual functionalization step, the complete PMMA mask (which becomes partly damaged by the addition of the electron-trapping reagent benzonitrile, see section S3) was completely removed by acetone vapor (60 min) and a fresh PMMA double-layer mask has been applied via spin-coating to enable the next EBL patterning cycle. In this case, the previously created addend patterns become covered by the freshly deposited PMMA layer and thus the localization of the chemically functionalized areas turns out to be tricky. In order to determine the exact positions of the covalently functionalized patterned areas we initially applied a crosshair pattern (with additional letters for a better orientation, Supplementary Figure 1) on the graphene by an e-beam lithography procedure with a subsequent 5 nm titanium and 40 nm gold evaporation step (5,000 µm x 5,000 µm write field and an aperture of 120 µm with a dose of 200 μAs cm -2 ). Based on these set of distinct markers, the position for the subsequent EBL patterning spots can be located and the respective concentric shapes can be "written".
In the first EBL patterning step, periodic dots with a hole diameter of 5 µm were generated. The subsequent reductive arylation reaction has been carried out as described in section S3.
In the second EBL patterning step, periodic dots with a hole diameter of 15 µm were "written" into the PMMA mask. As it is demonstrated by the SEM-EDS analyses of the final multi-functionalized sample ( Figure 5 in the main manuscript) this lithographic removal of the PMMA protective layer does not lead to a removal of the 4-bromobenze addends introduced in the first reductive activation/functionalization step. The subsequent reductive deuteration reaction has been carried out as described in section S3.
In the third patterning step the protective PMMA layer was removed in a ring type fashion around the initially arylated and deuterated areas (outer diameter 20 µm, inner diameter 15 µm). With this setup, the covalently functionalized zones Ib and IIb (diameter of 15 µm) remain covered by the protective PMMA layer. This approach has been chosen to reduce the possibility of a reduction based addend removal of the initially bound functional groups. As outlined and discussed in detail in section S6the addition of sodium/potassium (Na/K) alloy to the aryl bound functionalization zone Ib leads to a pronounced removal of bound entities upon re-reduction on long time scales (Supplementary Figure 8 and Figure 11). The subsequent reductive chlorination reaction has been carried out as described in section S3.

S3. Step-wise covalent functionalization of graphene in the respective patterned areas
In an argon filled glovebox (˂ 0.1 ppm O2, ˂ 0.1 ppm H2O), the EBL-patterned graphene was initially activated by a reduction with a Na/K (molar ratio 1:3) alloy. Specifically, a drop of liquid Na/K alloy was dropped onto the surface of the sample and kept for 90 minutesour reduction time based This activation procedure, by reducing graphene directly with the liquid Na/K alloy, differs considerably from our previously developed method employing a Na/K-DME (DME = dimehtoxyethane) solution. [S2] The usage of DME would lead to a damaging of the protective PMMA double-layer and would render the whole area-restricted functionalization approach impossible.
After removal of the residual Na/K alloy by a constant flow of argon, several drops of 4-bromobenzenediazonium tetrafluoroborate dissolved in dried and degassed ethanol (0.5 mmol mL -1 ) were intermittently added for 15 min. Afterwards, several drops of ethanol were added to remove the unreacted diazonium salt and then one drop of benzonitrile was added to terminate the reaction. As we have shown previously, benzonitrile is capable to remove residual negative charges on graphene. [S3] Subsequently, the sample was exported from the glovebox and washed with additional 20 mL ethanol and 20 mL water. Finally, the PMMA layer was removed by acetone vapor (60 min) and the sample was characterized spectroscopically.
For the second functionalization step, the arylated graphene sample was applied with a PMMA doublelayer mask and patterned via EBL (see section S2), generating the second pattern structure. After undergoing reduction under the same condition as well as alloy removal, one drop of deuteroxide was added for 15 min for the second covalent functionalization reaction. Afterwards, the reaction was terminated by adding a drop of benzonitrile to quench the residual negative charges and washed with deuteroxide for several times. Again, the PMMA layer was removed by acetone vapor (60 min) and the sample was characterized spectroscopically.
Finally, the third pattern of the concentric ring structure was created by EBL in analogy to the other two patterns. Following the strategy of reductive activation, a few drops of iodine monochloride (ICl) diluted with dried and degassed ethanol (0.5 mmol mL -1 ) were intermittently added for 15 min. Afterwards, several drops of ethanol were added to remove the unreacted iodine monochloride and then one drop of benzonitrile was added to terminate the reaction. Subsequently, the sample was washed three times with 20 mL ethanol. Finally, acetone vapor (60 min) was used to remove the protective PMMA layer to give rise to the final sample of multiple-patterned functionalized graphene.

S4. Raman characterization of functionalized areas: Reduction time and degree of functionalization
Raman spectroscopy and in particular Scanning Raman Spectroscopy (SRS) represents a very powerful tool for the investigation of covalently functionalized graphene. This technique was therefore applied to characterize the multiply 2D-patterned sheet architectures. As shown in Supplementary Figure 2    The key advantage of a reductive activation of graphene is that it can achieve a high degree of functionalization in the bulk material. We have also clearly demonstrated that this approach can be transferred from the bulk material to a single layer of graphene and provides a method to covalently functionalize mono-layer graphene in highly homogenous fashion. [S2] Besides the actual degree of functionalization, the homogeneity of the addend coverage represents another highly important factor.
To further confirm this, we also carried out a reference experiment that a large size of graphene (0.5 × 0.5 cm) was deuterated upon reductive activation method and characterized by Raman spectroscopy (Supplementary Figure 6). It can be clearly seen that, compared to the spectral information presented for the patterned functionalization in Supplementary Figure 3  The different electronic dispersion behaviors render the Raman spectra for single layer graphene and multilayer (or bulk) graphene completely different. Generally, the G' peak of single-layer graphene is sharp and symmetrical, and has a perfect single Lorentzien peak shape. However, as the number of graphene layers increases, the electronic energy band structure of graphene is split, thus leading to many possible double resonance scattering processes. This means the G' peak can be fitted into several Lorentzien peaks and the intensity of G peak also increases because more carbon atoms will be detected in the multilayer (or bulk) graphene. In view of this, the Raman spectroscopy has the advantage to clearly, efficiently and non-destructively characterize the monolayer-graphene and gives the intrinsic information of graphene. This also enables us to use Raman spectroscopy to clearly and easily quantify the degree of functionalization of monolayer graphene. In general, the Raman ID/IG ratios correlate with a mean defect distance LD and the maximum ID/IG ratio corresponds to the LD-crit value, which was used to distinguish the low-functionalization-regime and high-functionalization-regime. [ Table 2) and here it becomes obvious that our iterative graphene functionalization protocol leads to a highly pronounced functionalization of the respective areas.
Supplementary Table 2: Comparison of quantified degree of functionalization (θ) of previously reported covalent patterning of graphene and this work.

S5. Reference experiments: Functionalization of non-activated graphene areas
In order to shed light on the initial reductive activation process, we also conducted specific reference experiments. Here, the EBL-patterned grapheneperiodic dots of 10 µm diameterwas directly reacted removed by EBL (electron-beam lithography) such that the graphene become exposed. The Raman spectra of the EBLexposed graphene zones before and after reaction (without initial reductive activation) with 4-bromobenzene diazonium-tetrafluoroborate (d), D2O (e), and ICl (f). Scale bar: 5 µm.

S6. Reference experiments: Re-reduction of covalently functionalized graphene areas
In order to shed light in the possibility of an addend removal upon the addition of the reducing reagent [S2,S11] to covalently functionalized graphene areas we have treated the multiple-patterned functionalized graphene with Na/K alloy and tracked the respective spectroscopic Raman changes over time ( Supplementary Figure 8-10).
Here it becomes apparent that the different addend zones (Ib, IIb, and IIIb) equipped with differing molecular entities, covalently bound to the graphene lattice, exhibit different de-functionalization  Table 3) and the Raman spectrum , bulk graphene [S11] and C60 derivatives [S12,S13] and a clear indication that also in monolayer graphene systems, a post functionalization reduction leads to a detachment of the previously introduced covalent functionalities.
In analogy, the chlorinated graphene within zone IIIb could also be transformed back to pristine graphene upon 3 h of reductive treatmentcorroborated by a complete disappearance of the respective Raman Dband (Supplementary Figure 10 and Figure 11). Consequently, the ID/IG ratio is reduced to around 0.1 (Supplementary Table 3).
However, a completely different behavior was observed for the deuterated graphene within zone IIb  Raman shift (cm -1 )