Phenyl Functionalization of Atomically Precise Graphene Nanoribbons

www.acsnano.org

Phenyl Functionalization of Atomically Precise Graphene Nanoribbons for Engineering Interribbon Interactions and Graphene Nanopores Mikhail Shekhirev,† Percy Zahl,‡ and Alexander Sinitskii*,†,§ †

Department of Chemistry, University of NebraskaLincoln, Lincoln, Nebraska 68588, United States Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States § Nebraska Center for Materials and Nanoscience, University of NebraskaLincoln, Lincoln, Nebraska 68588, United States

Downloaded via KAOHSIUNG MEDICAL UNIV on August 31, 2018 at 13:57:40 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: Graphene nanoribbons (GNRs) attract much attention from researchers due to their tunable physical properties and potential for becoming nanoscale building blocks of electronic devices. GNRs can be synthesized with atomic precision by on-surface approaches from specially designed molecular precursors. While a considerable number of ribbons with very diverse structures and properties have been demonstrated in recent years, there have been only limited examples of on-surface synthesized GNRs modified with functional groups. In this study, we designed a nanoribbon, in which the chevron GNR backbone is decorated with phenyl functionalities, and demonstrate the on-surface synthesis of these GNRs on Au(111). We show that the phenyl modification affects the assembly of the GNR polymer precursors through π−π interactions. Scanning tunneling spectroscopy of the modified GNRs on Au(111) revealed that they have a band gap of 2.50 ± 0.02 eV, which is comparable to that of the parent chevron GNR. The phenyl functionalization leads to a shift of the band edges to lower energies, suggesting that it could be a useful tool for the GNR band structure engineering. We also investigated lateral fusion of the phenyl-modified GNRs and demonstrate that it could be used to engineer different kinds of atomically precise graphene nanopores. A similar functionalization approach could be potentially applied to other GNRs to affect their on-surface assembly, modify their electronic properties, and realize graphene nanopores with a variety of structures. KEYWORDS: graphene nanoribbons, bottom-up synthesis, functionalization, electronic structure, self-assembly, graphene nanopore properties, including ribbons with armchair,4−14 zigzag,15 covetype,16 and chiral edges,17−20 heteroatom substitutions,21−25 and GNR heterojunctions,25−30 have been produced. With the development of synthetic approaches and a growing portfolio of atomically precise GNRs with very diverse properties, a question of how these ribbons could be assembled into ordered structures for integration into

ecause of their highly tunable electronic properties,1−3 graphene nanoribbons (GNRs) are often considered as potential building blocks of electronic devices and circuits. Following the pioneering publication by Cai et al.,4 a variety of different GNRs with atomically precise structures have been synthesized by the on-surface approach. The specially designed molecular precursors are first deposited in ultrahigh vacuum (UHV) on a metal substrate, such as Au(111), Ag(111), or Cu(111), on which they polymerize and eventually planarize upon annealing to form GNRs. Using the on-surface approach, GNRs with different structures and

B

© 2018 American Chemical Society

Received: June 13, 2018 Accepted: August 7, 2018 Published: August 7, 2018 8662

DOI: 10.1021/acsnano.8b04489 ACS Nano 2018, 12, 8662−8669

Article

Cite This: ACS Nano 2018, 12, 8662−8669

Article

ACS Nano

Figure 1. On-surface synthesis of cGNRs and mGNRs. (a) Scheme of the on-surface synthesis of cGNRs on Au(111); see text for details. (b) Molecular model of neighboring polymer 2 chains. The region where the titled phenyls engage in π−π interactions is highlighted by red. (c) Scheme of the on-surface synthesis of mGNRs on Au(111); see text for details. (d) Molecular model of neighboring polymer 5 chains. The region of the anticipated π−π interactions is highlighted by red.

highlighted by beige in Figure 1c, should extend the “tentacles” in the GNR polymer 5 that engage in π−π interactions, as shown in Figure 1d, which would result in stronger alignment of the polymer chains. The structure of the phenyl-modified chevron GNR 6, which we will refer to as mGNR, is shown in Figure 1c. While there have been a number of studies, in which GNRs were modified by incorporation of heteroatoms, such as nitrogen, boron, and sulfur, within the graphitic core structure of a ribbon,21−25,37,38 there have been only limited examples of on-surface synthesized GNRs modified with functional groups.14,28,39 Therefore, the growth and characterization of mGNRs expand the repertoire of functionalization approaches in the on-surface synthesis of atomically precise nanoribbons. The laterally extended structure of mGNRs and their propensity for alignment is also interesting for the synthesis of graphene nanopores. Graphene nanopores have recently attracted attention due to their potential for electronic, sequencing, and separation applications.39 It was demonstrated that they can be synthesized with atomic precision by lateral fusion of chevron GNRs9 or periodic GNRs comprising regions that are 7 and 13 carbon atoms wide.39 As we demonstrate in this study, the phenyl modification of cGNRs enables two scenarios of their lateral fusion, resulting in

electronic devices becomes increasingly important. A step in this direction is to study how GNRs could be grown in an ordered fashion as opposed to randomly on a substrate. The GNR growth can be affected by the choice of a substrate as the ribbons can form along terraces of a stepped surface, such as Au(788),31,32 or the ⟨112⟩ crystallographic directions of Cu(111).33 Some alignment was observed for heteroatomdoped GNRs23,25 and also in the polymer stage of the onsurface synthesis of nanoribbons due to π−π interactions,9 which is illustrated by Figure 1a,b for the chevron GNR. This is one of the most studied atomically precise GNRs, which has been synthesized from 6,11-dibromo-1,2,3,4-tetraphenyltriphenylene (molecule 1) both on metal substrates,4,23,25,31,33−35 and in solution.36 On Au(111), molecule 1 forms polymer 2 at about 250 °C, which then undergoes intramolecular cyclodehydrogenation at about 440 °C producing chevron GNRs (cGNRs, 3); see Figure 1a. As we discuss in a recent study,9 at the stage 2, the titled phenyls may engage in π−π interactions, resulting in the alignment of the adjacent polymer chains (Figure 1b). Intrigued by these results, in this study we investigated whether the π−π interactions could be purposefully engineered by modification of the cGNR structure. We propose that additional phenyls in the GNR precursor 4, which are 8663


Article

ACS Nano

GNRs,23,25,34,38,43 and functionalized chevron GNRs.28 In this work, we synthesized compound 11 using the published procedure,40 and refluxed it with 1,2-di([1,1′-biphenyl]-4yl)ethyne (compound 10) in diphenyl ether to produce the mGNR precursor (2,3-di([1,1′-biphenyl]-4-yl)-6,11-dibromo1,4-diphenyltriphenylene; compound 4). The detailed synthetic procedures for compound 10 and monomer 4 are described in the Supporting Information. Thus, this work provides another example of the versatility of this general chemical approach for producing molecular precursors for nanoribbons from the chevron GNR family. The molecules 4 were sublimed onto a cold (4.5 K) Au(111) substrate in UHV conditions, which was then heated up to 250 °C to form polymer 5. All samples were imaged using scanning tunneling microscopy (STM) at 4.5 K. We first studied polymer 5 chains on Au(111) at low surface coverage. The STM image in Figure 3a shows that the diffusing monomers primarily accumulate at the Au(111) step edges where they form polymer chains. However, the polymer structure could be better seen from an image of an isolated chain like the one shown by the top arrow; a close-up image of this polymer 5 chain is shown in the inset in Figure 3a. Previous studies demonstrated that cGNR polymers 2 on metal substrates have nonuniform heights in STM images: while triphenylene units lay flat on a surface, the phenyl groups are tilted relative to substrate due to intramolecular H−H repulsions (Figure 1b).4,9,33,35 When some phenyls in a cGNR

different kinds of atomically precise graphene nanopores. A similar approach could be potentially used to realize nanopores with other structures and properties.

RESULTS AND DISCUSSION The general approach for the synthesis of the chevron GNR precursor 1, which was demonstrated by Saleh et al.,40 proved to be very flexible and convenient for the preparation of other molecular precursors for a variety of related nanoribbons. First synthesized is compound 11 (Figure 2),40,41 which can then be

Figure 2. Synthesis of the mGNR monomer (molecule 4); see text for details.

used for Diels−Alder reactions with various 1,2-disubstitutedethynes to yield precursors for cGNRs,4,36,40 laterally extended chevron GNRs, 2 9 , 3 0 , 4 2 , 4 3 nitrogen-doped chevron

Figure 3. STM characterization of polymer 5 on Au(111). (a,b) STM images of polymer 5 chains formed on Au(111) at low surface coverage. The inset in panel a shows a fragment of the polymer chain indicated by the top arrow; some of the titled benzene rings are highlighted by green. Panel b shows two adjacent polymer chains that are indicated by the bottom arrow in panel a. Scan parameters: 0.2 V, 20 pA. (c) Height profile along the line in panel b. Blue part of the curve represents the area of a single polymer with extra phenyls lying flat on the surface. The red part of the curve represents the area in between two adjacent polymers, where the extra phenyl groups are rotated perpendicularly to the surface. (d) Molecular model of two polymer chains shown in panels b and c. (e) STM image of polymer 5 chains formed on Au(111) at high surface coverage. Scan parameters: −2 V, 7 pA. 8664


Article

ACS Nano polymer 2 are replaced with biphenyls as in mGNR polymer 5, the benzene rings of the biphenyl groups that are immediately attached to the triphenylene units should still be tilted relative to substrate due to similar intramolecular H−H repulsions. However, the “outer” phenyls that are highlighted by beige in Figure 1c are sufficiently far from each other to lay flat on a gold surface. This structure can be seen in the inset in Figure 3a, in which the titled “inner” benzene rings appear as the bright features (some of these tilted rings are highlighted by green), while the flat “outer” phenyls and triphenylene units are visibly darker and have comparable brightness. To investigate the structure of the interacting polymer chains we focused our attention on areas where two adjacent polymers form a two-dimensional assembly. A close-up STM image of one of such areas indicated by the bottom arrow in Figure 3a is shown in Figure 3b. Figure 3c demonstrates the height profile measured along the line in Figure 3b, which crosses “outer” phenyls of two adjacent polymer chains that are labeled as “1” and “2”. The blue segment of the line crosses the “outer” phenyls of chain 1 only, while the red segment crosses such phenyls of both chains. The larger apparent height observed for the red segment indicates that in the region between chains 1 and 2 the phenyls are tilted relative to the surface due to π−π interactions. This arrangement is illustrated by the molecular model in Figure 3d; the regions highlighted by red (π−π interactions between tilted phenyls) and blue (phenyls lying flat on the substrate) correspond to the colorcoded segments in Figure 3b,c. These results agree well with previous observations on cGNRs and N = 7 armchair GNRs, for which π−π interactions play an important role in the assemblies of monomers and polymer precursors.4,9 When the precursors are deposited at high coverage, the parallel assembly of the polymers becomes even more evident, as shown by the STM image in Figure 3e. The average length of the polymers was found to be 57 nm, and some of the chains were over 100 nm long. At 440 °C the polymers undergo intramolecular cyclodehydrogenation and form mGNRs as shown in Figure 1c. The STM image of mGNRs on Au(111) is shown in Figure 4a. Unlike polymer 5 chains that exhibit brighter regions in STM images due to the tilted benzene rings (Figure 3a), the mGNRs look uniform, indicating their complete planarization. The structure of mGNRs was also visualized by noncontact atomic force microscopy (nc-AFM) using a CuO terminated tip.44 The nc-AFM image in Figure 4b reveals the perfect match of mGNRs with the molecular structure in Figure 1c. Noteworthy, in polymer 5 chains the “inner” phenyls in the biphenyl groups are tilted relative to the triphenylene units, which allows the “outer” phenyls to lay flat on Au(111) avoiding H−H repulsions, as shown in the inset in Figure 3a and the scheme in Figure 3e. Similarly, planarization of the “inner” phenyls during cyclodehydrogenation should force the “outer” phenyls to slightly twist to again avoid the H−H repulsions. The appearance of the side phenyls in the nc-AFM image in Figure 4b suggests that they are slightly tilted relative to the chevron GNR backbone. The mGNR can be considered as a laterally extended cGNR, since the side phenyl groups are in conjugation with the chevron GNR backbone. From this point of view, mGNR is another member of the family of laterally extended chevron GNRs, which have been discussed in recent studies.28,30,42,43 We performed a scanning tunneling spectroscopy (STS) study of mGNRs to determine their band gap and find how the

Figure 4. Characterization of mGNRs. (a) STM image mGNRs on Au(111). Scan parameters: 0.1 V, 30 pA. (b) nc-AFM image of a fragment of mGNR. (c) STS point spectra of mGNR on an Au(111) substrate. The inset shows STM image of mGNRs with red and black circles indicating the points at which the STS spectra were measured. Scan parameters: −0.3 V, 10 pA.

phenyl functionalization/lateral extension changes the band gap of the parent cGNR. Chevron GNRs have been a subject of several STS investigations.28,45,46 When studying cGNRs on Au(111), Nguyen et al. determined the valence band (VB) edge at −0.83 eV, and the conduction band (CB) edge at 1.7 eV, producing a band gap of 2.53 eV,28 while Deniz et al. found the VB edge at −0.8 eV and the CB edge at 1.6 eV, yielding a band gap of 2.4 eV.46 Density functional theory (DFT) calculations have previously revealed that at the VB and CB energies the highest local densities of states (LDOS) are expected at the edges of the cGNRs, which was shown experimentally for pristine and fluorenone-modified cGNRs.28,29 Therefore, in order to measure band gaps of the ribbons from the cGNR family, STS spectra are typically measured at the nanoribbons’ edges.28,46 Figure 4c shows two representative spectra measured at two different edge positions on a mGNR on Au(111); the colors of the spectra match the colors of the circles in the inset in Figure 4c, which indicate the points at which the STS was performed. Both spectra show the VB edge located at −0.91 eV and the CB edge located 1.58 eV, resulting in the mGNR’s band gap of 2.49 eV. We recorded mutiple spectra at the edges of several mGNRs, all of which exhibited similar VB and CB peaks. The average value of the mGNR’s band gap that was determined from multiple measurements is 2.50 ± 0.02 eV, which is comparable to the band gap of cGNR on Au(111) found in prior STS studies.28,46 These measurements also show that the phenyl functionalization leads to a shift of the GNR band edges to lower energies, which is an effect similar to those induced by the nitrogen doping25 or fluorenone modification of cGNRs.28 These previously 8665


Article

ACS Nano reported approaches have been used to construct GNR heterojunctions,25,28 so likewise the phenyl functionalization could be employed for engineering heterojunctions comprising, for example, mGNR and cGNR units.29,30 The spectra in Figure 4c exhibit not only the band gap edges, but also several other prominent peaks. For example, the spectra recorded at all mGNR edge positions consistently showed a peak at about −1.05 V, which is likely associated with the VB-1 state. This assignment is consistent with the DFT-calculated VB-1 LDOS map of cGNR that, similarly to its VB LDOS map, predicts the highest electron density at the nanoribbon’s edges.45 On the contrary, the DFT-calculated CB and CB+1 LDOS maps of cGNR look very differentwhile in the CB map the LDOS is high along all edges, in the CB+1 map it is concentrated in the concave edge positions.45 These DFT-calculated maps are also consistent with the experimental STS data, which show that while all probed edge positions of mGNRs exhibit a prominent CB peak, the STS spectrum measured at the mGNR’s concave edge position (see the black point in the inset in Figure 4c) shows an additional peak at 1.8 V, which could be interpreted as the CB+1 state. While most of the mGNRs that we observed were well separated (Figure 4a), we also found a number of areas where ribbons were fused together. Fusion of nanoribbons is an important synthetic approach in the field of atomically precise GNRs as it allows fabrication of graphene structures that are difficult to directly produce from molecular precursors.5,10,13,47,48 The lateral fusion of nanoribbons can also be used for the synthesis of extended GNR structures and graphene nanopores.9,39 As we demonstrate in this study, phenyl-modification of cGNRs enables two scenarios of their lateral fusion, resulting in different kinds of atomically precise graphene nanopores. Because of the planarization of polymer 5 chains upon annealing, the resulting mGNRs can no longer engage in π−π interactions. Furthermore, as the structures schematically shown in Figure 5a planarize, the distance between them should increase because of the intermolecular H−H repulsions (Figure 5b). The resulting mGNRs have two options for lateral fusion, as the phenyl of one nanoribbon can engage in intermolecular cyclodehydrogenation with phenyls of another ribbon on one side (blue ovals) or the other (orange ovals). These fusion routes produce extended structures that have graphene nanopores with different sizes and shapes (Figure 5c,d). The first route results in graphene nanopores with the same size and shape (shown by the same blue color in Figure 5c), whereas the second route produces two kinds of alternating pores (shown by different colors in Figure 5d). Both of these arrangements were observed experimentally (Figure 5e,f), and the resulting nanopores differ in their sizes and shapes from those previously produced by the lateral fusion of cGNRs.9 These results demonstrate that different kinds of atomically precise graphene nanopores could be engineered through the phenyl modification of cGNRs, and a similar approach could be potentially applied to other GNRs to realize nanopores with a variety of structures and properties. The recent work by Moreno et al. provides another example of phenyl modification of a previously established GNR precursor, which produced fused graphene structures with precisely engineered nanopores.39 To get further insights into the structure of graphene nanopores produced by the mGNR fusion, we studied them by nc-AFM. The left panel in Figure 6a shows the nc-AFM image

Figure 5. Lateral fusion of mGNRs. (a) Scheme of the assembed polymer 5 chains. The region of π−π interactions is highlighted by red. (b) Scheme of the fully planarized mGNRs. Blue and orange ovals show possibilities for lateral inter-ribbon fusion. (c,d) Schemes of two variants of mGNR fusion. The resulting graphene nanopores that form between the ribbons are colored. (e) STM image of graphene nanopores formed according to the scheme c. Scan parameters: 0.3 V, 20 pA. (f) STM image of graphene nanopores formed according to the scheme d. Scan parameters: 0.1 V, 20 pA.

of the nanopore arrangement that is schematically illustrated by Figure 5c. In nc-AFM images of mGNRs and other ribbons from the chevron GNR family, including pristine cGNR,9 we occasionally observed bright dots in the concave regions of nanoribbons; one of these dots is shown by the black arrow in Figure 6a. Similar features were also observed in the N-doped GNRs synthesized from 9-methylcarbazole modified chevron GNR precursors, and were interpreted as methyl radicals.43 While methyl radicals were expected to form in that synthesis due to the homolytic cleavage of the C−N bonds in 9methylcarbazole moieties,43 they are unlikely to be present in the on-surface synthesis of mGNRs. Therefore, these bright dots observed in nc-AFM images are likely other species, such as residual bromines. These results demonstrate that the concave areas of nanoribbons from the chevron GNR family could be attractive sites for certain on-surface species, which could be potentially utilized for designing complex GNR-based heterostructures. To better illustrate the shape of graphene nanopores in Figure 6a, we highlighted one of them (the second fully visible nanopore from the left edge of the image) by blue. Then, we overlaid exactly the same blue shape over all other nanopores 8666


Article

ACS Nano

imaging can reveal subtle details of GNR and graphene nanopore structures. These results further show that it is possible to design on-surface GNR structures with out-of-plane components, as in the pristine (Figure 4b) and fused mGNRs (Figure 6), which is uncommon for most surface-synthesized GNRs demonstrated so far.

CONCLUSIONS In summary, we demonstrated the on-surface synthesis of atomically precise chevron GNRs functionalized with phenyl groups. These ribbons have been grown on Au(111) in UHV conditions from a specially designed molecular precursor. We show that the phenyl modification affects the assembly of the mGNR polymers through π−π interactions. The mGNRs on Au(111) have a band gap of 2.50 ± 0.02 eV, which is comparable to that of the parent chevron GNR. Also, the phenyl functionalization shifts the band edges to lower energies, which means that it could be a useful tool for the GNR band structure engineering. The mGNRs could be considered for combining them with other GNRs from the chevron family into GNR heterojunctions. We also investigated the lateral fusion of mGNRs and demonstrate that it could be used to engineer different kinds of atomically precise graphene nanopores. A similar functionalization approach could be potentially applied to other GNRs to affect their onsurface assembly, modify their electronic properties, and realize graphene nanopores with a variety of structures. METHODS The detailed synthetic procedures for compound 10 and monomer 4 are provided in the Supporting Information. Polymer 5 and mGNRs 6 were synthesized and investigated using an upgraded Createc based LT-STM system with custom GXSM control hardware and software.49 The substrates were prepared by three Ar+ sputtering/ annealing cycles. The precursor 4 was sublimed onto a cold (4.5 K) Au(111) substrate in UHV conditions using a home-built evaporator, and the substrate was then heated up to 200−250 °C to form polymer 5 and subsequently to 400−440 °C to form mGNRs 6. The samples were imaged using STM and nc-AFM at 4.5 K. The nc-AFM imaging was performed at a 50−150 mV STM bias using a typical tip oscillation amplitude of 50−80 pm and a Q-Plus sensor operated at about 30 kHz.

Figure 6. High-resolution nc-AFM imaging of graphene nanopores. (a) nc-AFM image of the nanopore arrangement that is schematically shown in Figure 5c. The left panel shows the original image, while in the right panel the graphene nanopores are overlaid by identical semitransparent blue shapes. (b) Molecular model of the nanopores observed in panel a showing two kinds of biphenyl bridges between the chevron GNR fragments. The benzene rings in the biphenyl bridges can be bonded either through meta (m) or para (p) positions.

in the nc-AFM image, see the right panel in Figure 6a. The resulting figure shows that the same semitransparent blue shape accurately describes the geometry of all graphene nanopores, further demonstrating that they were prepared with atomic precision. Further analysis of the nc-AFM image in Figure 6a reveals slight differences in the appearances of biphenyl bridges that connect the chevron GNR fragments. In half of these bridges the benzene rings appear to be flat (see the middle bridge in the left panel in Figure 6a as an example), whereas in the other half of them the benzene rings look tilted. These two kinds of biphenyl bridges are present between the chevron GNR fragments in an alternating fashion. The corresponding molecular model of the biphenyl bridges in Figure 6a is shown in Figure 6b. The benzene rings in these biphenyl bridges can be bonded to the cGNR units either through meta (m) or para (p) positions. When the benzene rings are bonded through the para positions, the rings can rotate around the bond axes, which minimizes the H−H repulsions, as shown in Figure 6b. However, when the benzene rings are bonded through the meta positions, the rotations are not possible and despite the H−H repulsions the rings lay flat on the surface. These results demonstrate that high-resolution nc-AFM

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.8b04489. Detailed scheme of synthesis of the mGNR precursor and synthetic procedures (PDF)

AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. ORCID

Mikhail Shekhirev: 0000-0002-8381-1276 Alexander Sinitskii: 0000-0002-8688-3451 Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS The work was supported by the Office of Naval Research (N00014-16-1-2899) and the National Science Foundation 8667


Article

ACS Nano

Graphene Nanoribbons with Zigzag Edge Topology. Nature 2016, 531, 489−492. (16) Liu, J.; Li, B.-W.; Tan, Y.-Z.; Giannakopoulos, A.; SanchezSanchez, C.; Beljonne, D.; Ruffieux, P.; Fasel, R.; Feng, X.; Müllen, K. Toward Cove-Edged Low Band Gap Graphene Nanoribbons. J. Am. Chem. Soc. 2015, 137, 6097−6103. (17) Han, P.; Akagi, K.; Federici Canova, F.; Shimizu, R.; Oguchi, H.; Shiraki, S.; Weiss, P. S.; Asao, N.; Hitosugi, T. Self-Assembly Strategy for Fabricating Connected Graphene Nanoribbons. ACS Nano 2015, 9, 12035−12044. (18) Sánchez-Sánchez, C.; Dienel, T.; Deniz, O.; Ruffieux, P.; Berger, R.; Feng, X.; Müllen, K.; Fasel, R. Purely Armchair or Partially Chiral: Noncontact Atomic Force Microscopy Characterization of Dibromo-Bianthryl-Based Graphene Nanoribbons Grown on Cu(111). ACS Nano 2016, 10, 8006−8011. (19) Schulz, F.; Jacobse, P. H.; Canova, F. F.; van der Lit, J.; Gao, D. Z.; van den Hoogenband, A.; Han, P.; Klein Gebbink, R. J. M.; Moret, M.-E.; Joensuu, P. M.; Swart, I.; Liljeroth, P. Precursor Geometry Determines the Growth Mechanism in Graphene Nanoribbons. J. Phys. Chem. C 2017, 121, 2896−2904. (20) de Oteyza, D. G.; García-Lekue, A.; Vilas-Varela, M.; MerinoDíez, N.; Carbonell-Sanromà, E.; Corso, M.; Vasseur, G.; Rogero, C.; Guitián, E.; Pascual, J. I.; Ortega, J. E.; Wakayama, Y.; Peña, D. Substrate-Independent Growth of Atomically Precise Chiral Graphene Nanoribbons. ACS Nano 2016, 10, 9000−9008. (21) Kawai, S.; Saito, S.; Osumi, S.; Yamaguchi, S.; Foster, A. S.; Spijker, P.; Meyer, E. Atomically Controlled Substitutional BoronDoping of Graphene Nanoribbons. Nat. Commun. 2015, 6, 8098. (22) Cloke, R. R.; Marangoni, T.; Nguyen, G. D.; Joshi, T.; Rizzo, D. J.; Bronner, C.; Cao, T.; Louie, S. G.; Crommie, M. F.; Fischer, F. R. Site-Specific Substitutional Boron Doping of Semiconducting Armchair Graphene Nanoribbons. J. Am. Chem. Soc. 2015, 137, 8872− 8875. (23) Vo, T. H.; Perera, U. G. E.; Shekhirev, M.; Mehdi Pour, M.; Kunkel, D. A.; Lu, H.; Gruverman, A.; Sutter, E.; Cotlet, M.; Nykypanchuk, D.; Zahl, P.; Enders, A.; Sinitskii, A.; Sutter, P. Nitrogen-Doping Induced Self-Assembly of Graphene NanoribbonBased Two-Dimensional and Three-Dimensional Metamaterials. Nano Lett. 2015, 15, 5770−5777. (24) Nguyen, G. D.; Toma, F. M.; Cao, T.; Pedramrazi, Z.; Chen, C.; Rizzo, D. J.; Joshi, T.; Bronner, C.; Chen, Y.-C.; Favaro, M.; Louie, S. G.; Fischer, F. R.; Crommie, M. F. Bottom-Up Synthesis of N = 13 Sulfur-Doped Graphene Nanoribbons. J. Phys. Chem. C 2016, 120, 2684−2687. (25) Cai, J.; Pignedoli, C. A.; Talirz, L.; Ruffieux, P.; Söde, H.; Liang, L.; Meunier, V.; Berger, R.; Li, R.; Feng, X.; Müllen, K.; Fasel, R. Graphene Nanoribbon Heterojunctions. Nat. Nanotechnol. 2014, 9, 896−900. (26) Blankenburg, S.; Cai, J. M.; Ruffieux, P.; Jaafar, R.; Passerone, D.; Feng, X. L.; Müllen, K.; Fasel, R.; Pignedoli, C. A. Intraribbon Heterojunction Formation in Ultranarrow Graphene Nanoribbons. ACS Nano 2012, 6, 2020−2025. (27) Chen, Y.-C.; Cao, T.; Chen, C.; Pedramrazi, Z.; Haberer, D.; de Oteyza, D. G.; Fischer, F. R.; Louie, S. G.; Crommie, M. F. Molecular Bandgap Engineering of Bottom-Up Synthesized Graphene Nanoribbon Heterojunctions. Nat. Nanotechnol. 2015, 10, 156−160. (28) Nguyen, G. D.; Tsai, H.-Z.; Omrani, A. A.; Marangoni, T.; Wu, M.; Rizzo, D. J.; Rodgers, G. F.; Cloke, R. R.; Durr, R. A.; Sakai, Y.; Liou, F.; Aikawa, A. S.; Chelikowsky, J. R.; Louie, S. G.; Fischer, F. R.; Crommie, M. F. Atomically Precise Graphene Nanoribbon Heterojunctions from a Single Molecular Precursor. Nat. Nanotechnol. 2017, 12, 1077. (29) Costa, P. S.; Teeter, J. D.; Enders, A.; Sinitskii, A. ChevronBased Graphene Nanoribbon Heterojunctions: Localized Effects of Lateral Extension and Structural Defects on Electronic Properties. Carbon 2018, 134, 310−315. (30) Bronner, C.; Durr, R. A.; Rizzo, D. J.; Lee, Y.-L.; Marangoni, T.; Kalayjian, A. M.; Rodriguez, H.; Zhao, W.; Louie, S. G.; Fischer, F. R.;

(CHE-1455330). This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

REFERENCES (1) Nakada, K.; Fujita, M.; Dresselhaus, G.; Dresselhaus, M. S. Edge State in Graphene Ribbons: Nanometer Size Effect and Edge Shape Dependence. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 17954−17961. (2) Son, Y.-W.; Cohen, M. L.; Louie, S. G. Half-Metallic Graphene Nanoribbons. Nature 2006, 444, 347−349. (3) Yang, L.; Park, C.-H.; Son, Y.-W.; Cohen, M. L.; Louie, S. G. Quasiparticle Energies and Band Gaps in Graphene Nanoribbons. Phys. Rev. Lett. 2007, 99, 186801. (4) Cai, J. M.; Ruffieux, P.; Jaafar, R.; Bieri, M.; Braun, T.; Blankenburg, S.; Muoth, M.; Seitsonen, A. P.; Saleh, M.; Feng, X. L.; Müllen, K.; Fasel, R. Atomically Precise Bottom-Up Fabrication of Graphene Nanoribbons. Nature 2010, 466, 470−473. (5) Huang, H.; Wei, D.; Sun, J.; Wong, S. L.; Feng, Y. P.; Castro Neto, A. H.; Wee, A. T. S. Spatially Resolved Electronic Structures of Atomically Precise Armchair Graphene Nanoribbons. Sci. Rep. 2012, 2, 983. (6) Chen, Y.-C.; de Oteyza, D. G.; Pedramrazi, Z.; Chen, C.; Fischer, F. R.; Crommie, M. F. Tuning the Band Gap of Graphene Nanoribbons Synthesized from Molecular Precursors. ACS Nano 2013, 7, 6123−6128. (7) Kimouche, A.; Ervasti, M. M.; Drost, R.; Halonen, S.; Harju, A.; Joensuu, P. M.; Sainio, J.; Liljeroth, P. Ultra-Narrow Metallic Armchair Graphene Nanoribbons. Nat. Commun. 2015, 6, 10177. (8) Talirz, L.; Söde, H.; Dumslaff, T.; Wang, S.; Sanchez-Valencia, J. R.; Liu, J.; Shinde, P.; Pignedoli, C. A.; Liang, L.; Meunier, V.; Plumb, N. C.; Shi, M.; Feng, X.; Narita, A.; Müllen, K.; Fasel, R.; Ruffieux, P. On-Surface Synthesis and Characterization of 9-Atom Wide Armchair Graphene Nanoribbons. ACS Nano 2017, 11, 1380−1388. (9) Teeter, J. D.; Costa, P. S.; Zahl, P.; Vo, T. H.; Shekhirev, M.; Xu, W.; Zeng, X. C.; Enders, A.; Sinitskii, A. Dense Monolayer Films of Atomically Precise Graphene Nanoribbons on Metallic Substrates Enabled by Direct Contact Transfer of Molecular Precursors. Nanoscale 2017, 9, 18835−18844. (10) Ma, C.; Liang, L.; Xiao, Z.; Puretzky, A. A.; Hong, K.; Lu, W.; Meunier, V.; Bernholc, J.; Li, A.-P. Seamless Staircase Electrical Contact to Semiconducting Graphene Nanoribbons. Nano Lett. 2017, 17, 6241−6247. (11) Deniz, O.; Sánchez-Sánchez, C.; Dumslaff, T.; Feng, X.; Narita, A.; Müllen, K.; Kharche, N.; Meunier, V.; Fasel, R.; Ruffieux, P. Revealing the Electronic Structure of Silicon Intercalated Armchair Graphene Nanoribbons by Scanning Tunneling Spectroscopy. Nano Lett. 2017, 17, 2197−2203. (12) Simonov, K. A.; Generalov, A. V.; Vinogradov, A. S.; Svirskiy, G. I.; Cafolla, A. A.; McGuinness, C.; Taketsugu, T.; Lyalin, A.; Mårtensson, N.; Preobrajenski, A. B. Synthesis of Armchair Graphene Nanoribbons from the 10,10′-Dibromo-9,9′-Bianthracene Molecules on Ag(111): The Role of Organometallic Intermediates. Sci. Rep. 2018, 8, 3506. (13) Basagni, A.; Sedona, F.; Pignedoli, C. A.; Cattelan, M.; Nicolas, L.; Casarin, M.; Sambi, M. Molecules−Oligomers−Nanowires− Graphene Nanoribbons: A Bottom-up Stepwise On-Surface Covalent Synthesis Preserving Long-Range Order. J. Am. Chem. Soc. 2015, 137, 1802−1808. (14) Carbonell-Sanromà, E.; Hieulle, J.; Vilas-Varela, M.; Brandimarte, P.; Iraola, M.; Barragán, A.; Li, J.; Abadia, M.; Corso, M.; Sánchez-Portal, D.; Peña, D.; Pascual, J. I. Doping of Graphene Nanoribbons via Functional Group Edge Modification. ACS Nano 2017, 11, 7355−7361. (15) Ruffieux, P.; Wang, S.; Yang, B.; Sánchez-Sánchez, C.; Liu, J.; Dienel, T.; Talirz, L.; Shinde, P.; Pignedoli, C. A.; Passerone, D.; Dumslaff, T.; Feng, X.; Müllen, K.; Fasel, R. On-Surface Synthesis of 8668


Article

ACS Nano Crommie, M. F. Hierarchical On-Surface Synthesis of Graphene Nanoribbon Heterojunctions. ACS Nano 2018, 12, 2193−2200. (31) Linden, S.; Zhong, D.; Timmer, A.; Aghdassi, N.; Franke, J. H.; Zhang, H.; Feng, X.; Müllen, K.; Fuchs, H.; Chi, L.; Zacharias, H. Electronic Structure of Spatially Aligned Graphene Nanoribbons on Au(788). Phys. Rev. Lett. 2012, 108, 216801. (32) Ruffieux, P.; Cai, J.; Plumb, N. C.; Patthey, L.; Prezzi, D.; Ferretti, A.; Molinari, E.; Feng, X.; Müllen, K.; Pignedoli, C. A.; Fasel, R. Electronic Structure of Atomically Precise Graphene Nanoribbons. ACS Nano 2012, 6, 6930−6935. (33) Teeter, J. D.; Costa, P. S.; Mehdi Pour, M.; Miller, D. P.; Zurek, E.; Enders, A.; Sinitskii, A. Epitaxial Growth of Aligned Atomically Precise Chevron Graphene Nanoribbons on Cu(111). Chem. Commun. 2017, 53, 8463−8466. (34) Bronner, C.; Stremlau, S.; Gille, M.; Brauße, F.; Haase, A.; Hecht, S.; Tegeder, P. Aligning the Band Gap of Graphene Nanoribbons by Monomer Doping. Angew. Chem., Int. Ed. 2013, 52, 4422−4425. (35) Chen, Z.; Zhang, W.; Palma, C.-A.; Lodi Rizzini, A.; Liu, B.; Abbas, A.; Richter, N.; Martini, L.; Wang, X.-Y.; Cavani, N.; Lu, H.; Mishra, N.; Coletti, C.; Berger, R.; Klappenberger, F.; Kläui, M.; Candini, A.; Affronte, M.; Zhou, C.; De Renzi, V.; del Pennino, U.; Barth, J. V.; Räder, H. J.; Narita, A.; Feng, X.; Müllen, K. Synthesis of Graphene Nanoribbons by Ambient-Pressure Chemical Vapor Deposition and Device Integration. J. Am. Chem. Soc. 2016, 138, 15488−15496. (36) Vo, T. H.; Shekhirev, M.; Kunkel, D. A.; Morton, M. D.; Berglund, E.; Kong, L. M.; Wilson, P. M.; Dowben, P. A.; Enders, A.; Sinitskii, A. Large-Scale Solution Synthesis of Narrow Graphene Nanoribbons. Nat. Commun. 2014, 5, 3189. (37) Kim, K. T.; Lee, J. W.; Jo, W. H. Charge-Transport Tuning of Solution-Processable Graphene Nanoribbons by Substitutional Nitrogen Doping. Macromol. Chem. Phys. 2013, 214, 2768−2773. (38) Vo, T. H.; Shekhirev, M.; Kunkel, D. A.; Orange, F.; Guinel, M. J. F.; Enders, A.; Sinitskii, A. Bottom-Up Solution Synthesis of Narrow Nitrogen-Doped Graphene Nanoribbons. Chem. Commun. 2014, 50, 4172−4174. (39) Moreno, C.; Vilas-Varela, M.; Kretz, B.; Garcia-Lekue, A.; Costache, M. V.; Paradinas, M.; Panighel, M.; Ceballos, G.; Valenzuela, S. O.; Peña, D.; Mugarza, A. Bottom-up Synthesis of Multifunctional Nanoporous Graphene. Science 2018, 360, 199−203. (40) Saleh, M.; Baumgarten, M.; Mavrinskiy, A.; Schafer, T.; Müllen, K. Triphenylene-Based Polymers for Blue Polymeric Light Emitting Diodes. Macromolecules 2010, 43, 137−143. (41) Saleh, M.; Park, Y.-S.; Baumgarten, M.; Kim, J.-J.; Müllen, K. Conjugated Triphenylene Polymers for Blue Oled Devices. Macromol. Rapid Commun. 2009, 30, 1279−1283. (42) Mehdi Pour, M.; Lashkov, A.; Radocea, A.; Liu, X.; Sun, T.; Lipatov, A.; Korlacki, R. A.; Shekhirev, M.; Aluru, N. R.; Lyding, J. W.; Sysoev, V.; Sinitskii, A. Laterally Extended Atomically Precise Graphene Nanoribbons with Improved Electrical Conductivity for Efficient Gas Sensing. Nat. Commun. 2017, 8, 820. (43) Marangoni, T.; Haberer, D.; Rizzo, D. J.; Cloke, R. R.; Fischer, F. R. Heterostructures through Divergent Edge Reconstruction in Nitrogen-Doped Segmented Graphene Nanoribbons. Chem. - Eur. J. 2016, 22, 13037−13040. (44) Mönig, H.; Hermoso, D. R.; Díaz Arado, O.; Todorović, M.; Timmer, A.; Schüer, S.; Langewisch, G.; Pérez, R.; Fuchs, H. Submolecular Imaging by Noncontact Atomic Force Microscopy with an Oxygen Atom Rigidly Connected to a Metallic Probe. ACS Nano 2016, 10, 1201−1209. (45) Radocea, A.; Sun, T.; Vo, T. H.; Sinitskii, A.; Aluru, N. R.; Lyding, J. W. Solution-Synthesized Chevron Graphene Nanoribbons Exfoliated onto H:Si(100). Nano Lett. 2017, 17, 170−178. (46) Deniz, O.; Sanchez-Sanchez, C.; Jaafar, R.; Kharche, N.; Liang, L.; Meunier, V.; Feng, X.; Müllen, K.; Fasel, R.; Ruffieux, P. Electronic Characterization of Silicon Intercalated Chevron Graphene Nanoribbons on Au(111). Chem. Commun. 2018, 54, 1619−1622.

(47) Chen, Z.; Wang, H. I.; Bilbao, N.; Teyssandier, J.; Prechtl, T.; Cavani, N.; Tries, A.; Biagi, R.; De Renzi, V.; Feng, X.; Kläui, M.; De Feyter, S.; Bonn, M.; Narita, A.; Müllen, K. Lateral Fusion of Chemical Vapor Deposited N = 5 Armchair Graphene Nanoribbons. J. Am. Chem. Soc. 2017, 139, 9483−9486. (48) Song, S.; Kojima, T.; Nakae, T.; Sakaguchi, H. Wide Graphene Nanoribbons Produced by Interchain Fusion of Poly(P-Phenylene) via Two-Zone Chemical Vapor Deposition. Chem. Commun. 2017, 53, 7034−7036. (49) Zahl, P.; Wagner, T. GXSM - Smart & Customizable SPM Control. Imaging and Microscopy 2015, 17, 38−41.

8669


Phenyl Functionalization of Atomically Precise Graphene Nanoribbons

Recommend Documents