Controlling a Chemical Coupling Reaction on a Surface: Tools and Strategies for On-Surface Synthesis

Abstract

On-surface synthesis is appearing as an extremely promising research field aimed at creating new organic materials. A large number of chemical reactions have been successfully demonstrated to take place directly on surfaces through unusual reaction mechanisms. In some cases the reaction conditions can be properly tuned to steer the formation of the reaction products. It is thus possible to control the initiation step of the reaction and its degree of advancement (the kinetics, the reaction yield); the nature of the reaction products (selectivity control, particularly in the case of competing processes); as well as the structure, position, and orientation of the covalent compounds, or the quality of the as-formed networks in terms of order and extension. The aim of our review is thus to provide an extensive description of all tools and strategies reported to date and to put them into perspective. We specifically define the different approaches available and group them into a few general categories. In the last part, we demonstrate the effective maturation of the on-surface synthesis field by reporting systems that are getting closer to application-relevant levels thanks to the use of advanced control strategies.

Figure 1

Overview of the diversity of available parameters that can be tuned to gain efficient control on the reaction products during on-surface synthesis. The maturation of the field is demonstrated by the development of efficient methods aimed at creating device-ready functional materials.

Figure 2

Schematic drawings of selected reactions commonly used in on-surface synthesis, grouped as dehalogenative coupling (a–f), alkyne coupling (g–i), condensation reactions (j, k), direct C–H activation (l, m), and intramolecular dehydrogenation (n).

Figure 3

Product structure determination from STM images by comparison of (a) in situ and ex situ synthesized molecules and (b) experimental results with the calculated contrast for a given molecular structure. (c) High-resolution bond-resolving imaging with functionalized probes in STM mode. (d) High-resolution bond-resolving imaging with functionalized probes in nc-AFM mode (further compared to conventional STM imaging and to the chemical structures). (a) Reprinted with permission from ref (72). Copyright 2013 American Chemical Society. (b) Reprinted by permission from ref (73). Copyright 2012 Springer Nature. (c) Reprinted with permission from ref (25). Copyright 2018 Royal Society of Chemistry. (d) Reprinted with permission from ref (33). Copyright 2013 AAAS.

Figure 4

(a) Reaction scheme for the synthesis of graphene nanoribbons by an initial polymerization and subsequent cyclodehydrogenation together with the C 1s (b) and Br 3d (c) core level spectra as a function of the sample annealing temperature, evidencing the chemical changes. (d) NEXAFS spectra of the precursor molecule (blue, 0 °C) and GNR (red, 400 °C) under s-polarization (dashed) or p-polarization incidence of the X-rays. The inset includes spectra at intermediate temperatures (0, 120, 270, and 400 °C). (e) Time-resolved mass spectrometry at increasing temperatures monitoring the halogen desorption during the reaction scheme depicted in part a, as well as the associated integrated core level intensity of the carbon and halogen signals (f). (g) Raman breathing mode energy dependence on GNR width. (h) High-resolution electron energy loss spectroscopy of the polymers and GNRs depicted in part a. (i) Angle-resolved photoemission spectroscopy data of dibromo-terphenyl before and after polymerization into poly(paraphenylene). (a–d) Reproduced with permission from ref (50). Copyright 2014 Royal Society of Chemistry. (e, f) Reproduced with permission from ref (99). Copyright 2018 American Chemical Society. (g) Reproduced with permission from ref (107). Copyright 2018 American Chemical Society. (h) Reprinted with permission from ref (105). Copyright 2012 American Physical Society. (i) Reproduced with permission from ref (102). Copyright 2016 American Chemical Society.

Figure 5

Control of the network dimensionality and topology. (a) Schematic illustration showing the relationship among the precursor functionality, its symmetry, and the topology of the formed networks. (b–e) Mono-, di-, and tetra-bromo functionalized porphyrins (molecular models (b) and corresponding STM images (c)) were used to grow 0D (dimers), 1D (linear chains), or 2D networks, respectively (STM images (d) and corresponding molecular models (e)). (a) Reproduced with permission from ref (6). Copyright 2017 Royal Society of Chemistry. (b–e) Reprinted with permission from ref (38). Copyright 2007 Springer Nature.

Figure 6

Control of the network dimensionality and topology. Precursor design strategies to build different network dimensionalities and topologies from Schiff base reaction. (a) Zigzag chains. (b) Honeycomb network. (c) Square chessboard network. Reprinted with permission from ref (124). Copyright 2015 AIP Publishing.

Figure 7

Sequential coupling strategy. (a) Chemical structure of a porphyrin derivative (trans-Br₂I₂TPP) bearing both Br and I substituents in para positions, respectively. In a first step the I positions react to build 1D chains, and the Br positions react in a second step at a higher annealing temperature to connect the chains and build 2D networks. (b) Corresponding STM images showing the isolated precursors, supramolecular chains, covalent chains, and 2D covalent networks. (c) For a precursor bearing both bromine and boronic acid functions (DBPBA), the condensation of the boronic acid moieties leads in a first step to the formation of boroxine trimers that couple covalently at a higher annealing temperature in a second step. (d) Similar strategy with a para-bromide-boronic acid (BBBA). (a, b) Reprinted by permission from ref (145). Copyright 2012 Springer Nature. (c) Adapted with permission from ref (157). Copyright 2011 Royal Society of Chemistry. (d) Adapted with permission from ref (141). Copyright 2012 American Chemical Society.

Figure 8

Sequential coupling strategy. (a) The DN precursor can experience two distinct reaction pathways associated with different internal reorganizations of the molecule. On Au(111), a dehydrogenation reaction is followed by Ullmann coupling leading to the formation of 1D polymer chains. On Ag(111) a dehydration reaction is accompanied by dehalogenation leading to the formation of individual monomers or dimers. (b) Domino reaction with the ENA precursor. The dehydrogenative coupling of the carboxylic moieties is allowed only after the Glaser coupling of the terminal alkyne has been realized. (a) Adapted with permission from ref (159). Copyright 2017 American Chemical Society. (b) Adapted with permission from ref (161). Copyright 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 9

(a) STM images and corresponding chemical models of the various products that can be formed from terminal alkyne precursors. (b) Distribution of the occurrence of the reaction products obtained from the long version of a diethynyl precursor on Ag(111). (c) By using the shorter precursor version, the reaction selectivity is strongly enhanced toward the formation of the linear homocoupling I. (d) A 2D-like network and a large distribution of linear and 3-fold connections is obtained using DETP precursor, while with CN-DETP precursor (e) only dimer linear chains are formed. (a–c) Adapted with permission from ref (136). Copyright 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. (d, e) Adapted with permission from ref (90). Copyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 10

(a) Phenyl substituents are used to block the Ullmann coupling at the C–Br positions. Monoselective C–H bond activation and C–C dehydrogenative coupling can be obtained with DBMTP or DBOTP precursors. (b) The selectivity of the cross-coupling reaction between BB and EBB precursors can be efficiently steering by controlling the relative ratio and/or total coverage. (a) Adapted with permission from ref (166). Copyright 2018 American Chemical Society. (b) Adapted with permission from ref (174). Copyright 2017 Royal Society of Chemistry.

Figure 11

Metal adatom-directed growth. (a) Evolution of the oligomerization reaction yield of TBB precursors on h-BN/Ni(111) depending on the presence of codeposited Cu or Pd adatoms. R1 and R2 are two different sets of deposition parameters. Pd adatoms catalyze the reaction already at room temperature. (b) The codeposition of Dy adatoms can very efficiently lead to the dehalogenation of DBTP precursors and the formation of organometallic complexes at room temperature, but simultaneously act as an inhibitor for the homocoupling reaction, as compared to the bare Ag(111) surface. (c) Reaction scheme of the multistep mechanism involving the bromo-dichloro precursor BCCTP and codeposited Cu adatoms on Au(111). (d) Corresponding STM images. (a) Adapted with permission from ref (179). Copyright 2016 Royal Society of Chemistry. (b) Adapted with permission from ref (180). Copyright 2017 American Chemical Society. (c, d) Adapted with permission from ref (147). Copyright 2016 Royal Society of Chemistry.

Figure 12

(a) Sequential strategy combining metal–organic coordination and Ullmann coupling. The linear chains that are formed by coordination with Cu adatoms at room temperature get covalently coupled to form dimeric chains after annealing at 180 °C. (b) Similarly, the metal–organic networks can be used to promote a (Pd adatom-catalyzed) Sonogashira cross-coupling reaction. (a) Adapted with permission from ref (184). Copyright 2013 American Chemical Society. (b) Reproduced with permission from ref (185). Copyright 2017 Royal Society of Chemistry.

Figure 13

Supramolecular templating effect to steer the growth of covalent networks. (a) The alignment of DBTP precursors in a supramolecular phase is preserved upon annealing and stepwise formation of perfectly aligned polyphenylene chains and fused nanoribbons. (b) The formation of rylene-type graphene nanoribbons from QR precursors at low coverage produces a variety of different bonding configurations. At nearly one monolayer coverage (c), the selectivity toward straight nanoribbon (type I) formation is significantly enhanced due to steric repulsion. (a) Adapted with permission from ref (191). Copyright 2015 American Chemical Society. (b, c) Adapted with permission from ref (193). Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 14

Supramolecular templating effect to steer the growth of covalent networks. (a) Schematic representation of the formation of kinked terphenyl polymer from BBP precursors. The Br adatoms produced from the first dimerization step produces a confinement template (b) that steers the regioselectivity of polymerization reaction leading to well-aligned linear polymers (c), as opposed to the branched polymers formed from nonbrominated 4Ph precursors (d). (e) The nanoporous phase of TPP(NH₂)₂ can perfectly accommodate C₆₀ molecules that are positioned in an adequate position to covalently bind to the neighboring NH₂ moieties upon annealing (f). (a–c) Adapted with permission from ref (156). Copyright 2015 Royal Society of Chemistry. (d) Adapted with permission from ref (66). Copyright 2014 Royal Society of Chemistry. (e, f) Adapted with permission from ref (194). Copyright 2010 American Chemical Society.

Figure 15

Supramolecular templating effect to steer the growth of covalent networks. (a) Topochemical polymerization of diacetylene. The precursors are self-assembled in adequate configuration so that the polymerization takes place with minimum conformational change. (b) The Ullmann coupling of Br₄-PTCDA results in a stochastic formation of a graphene-like nanoribbon of various length and orientation. By using in situ polymerized polyphenylene chains (red arrows in part c), linear grooves are created that steer the alignment of the nanoribbons. (a) Adapted with permission from refs ( and 200). Copyright 2012 and 2008 Royal Society of Chemistry. (b, c) Adapted from ref (86). Creative Commons Attribution 4.0 International License.

Figure 16

Reversible inhibition of the Ullmann coupling. (a) DBDBT precursors directly deposited on Au(111) form zigzag chains. (b) Predosing of H₂S on Au(111) leads to the S-passivation of free Au adatoms and formation of Au–S complexes. (c) Subsequent deposition of DBDT produces intact molecules only. (d) The covalent coupling can be then activated by H₂ dosing that releases the Au adatoms by producing H₂S. Adapted with permission from ref (219). Copyright 2018 Royal Society of Chemistry.

Figure 17

Influence of the substrate nature. (a, b) Comparison of the formation of nanoporous graphene polymer from CHP precursor on Cu(111), Au(111), and Ag(111) surfaces. (a) STM images. (b) Corresponding results from Monte Carlo simulations with varying factor P corresponding to the ratio of reactivity to diffusivity. (c) The quality of the nanoporous polymer resulting from the self-condensation reaction of BDBA precursors was estimated by use of a minimal spanning tree (MST) analysis. Results from different deposition conditions are reported (Tc is the evaporation temperature, and Ts is the substrate temperature during deposition). (d–f) Comparative study of the Ullmann coupling reaction of TBB on noble metal surfaces. (d) STM images and corresponding models of the initial state (IS), the organometallic intermediate state (IntS), and the final covalently linked product (FS). Their relative occurrences in the function of the annealing temperature are reported for Cu, Au, and Cu surfaces, together with representative STM images. (e) Representation of the reaction yield for the covalent product as a function of the temperature. (f) Energy diagram representing the relative positions of the intermediate and activated states for the three different surfaces. (a) Adapted with permission from ref (43). Copyright 2012 American Chemical Society. (b) Reprinted with permission from ref (113). Copyright 2011 American Physical Society. (c–e) Adapted with permission from refs ( and 231). Copyright 2016 Springer Nature.

Figure 18

Influence of the substrate nature. (a) The Ext-TEB precursor experiences a homocoupling reaction on Au(111) but a cyclotrimerization reaction on Ag(111) (b), with an advancement controlled by the annealing temperature. (c) The low diffusivity and high reactivity of Pt(111) surfaces induces a cyclodehydrogenation reaction of the individual precursors (reaction path a) while a dehydrogenative polymerization (reaction path b) is obtained for the same two precursors on the poorly reactive and highly diffusing Au(111) surface. (a) Adapted with permission from refs ( and 140). Copyright 2016 and 2013 Springer Nature. (b) Adapted with permission from refs ( and 239). Copyright 2016 and 2014 Royal Society of Chemistry. (c) Adapted with permission from ref (221). Copyright 2013 American Chemical Society.

Figure 19

Influence of the substrate orientation. (a) The DMTP precursor undergoes two distinct reaction pathways depending on the orientation of the Cu substrate. On Cu(110), 1D oligophenylene zigzag chains are formed while on Cu(111) hyperbenzene macrocycles are formed. (b) Dual reactivity of the INDO₄ precursor on Ag substrates. On Ag(111) both coupling types are obtained for the lowest annealing temperature. On Ag(110) the oxidative coupling only is allowed leading to the formation of aligned nanoribbons. On Ag(100) the Knoevenagel coupling alone is obtained at moderate annealing temperature, and both couplings are found at higher temperature. (a) Adapted with permission from ref (246). Copyright 2016 Royal Society of Chemistry. Adapted with permission from ref (16). Copyright 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) Adapted with permission from ref (248). Copyright 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 20

Substrate templating. The regular distribution of aligned atomic steps in vicinal surfaces allows for the formation of perfectly aligned straight (a) or zigzag (b) graphene nanoribbons (GNRs). (c) The reaction of DETP on Ag(111) leads to the formation of various coupling motifs and a 2D-like polymer. Oppositely, on the Ag(877) surface (d), high selectivity toward the linear coupling scheme is obtained, together with the alignment of the linear polymer along the step edges (e). (f) The Cu(110)-(2 × 1)O surface is used as a confinement nanotemplate for the formation of organometallic oligomers from DMTP precursors. Depending on the Cu stripe width, various motifs are selectively formed. (a, b) Reprinted with permission from ref (254). Copyright 2012 American Physical Society. (c–e) Adapted with permission from ref (79). Copyright 2014 American Chemical Society. (f) Adapted with permission from ref (260). Copyright 2016 American Chemical Society.

Figure 21

Kinetics control. For OETAP precursors on Au(111), the room temperature deposition followed by annealing resulted in the formation of oligomers (a) while the direct deposition on a hot substrate produced individual phthalocyanines (b) formed from an intramolecular reaction. (c) Different coupling schemes of the DETP precursor lead to different reaction products on Au(110), in particular the cyclotrimerization (i) or the linear homocoupling (iii). The selectivity toward the linear homocoupled product could be sensitively enhanced by increasing the annealing temperature (d), and even more by direct deposition on a hot substrate (e). (f) The precursor tDBA undergoes stepwise internal transformations leading to the formation of stable intermediate species depending on the annealing temperature (the AFM images are presented above the corresponding models). (a, b) Adapted from ref (262). Creative Commons Attribution 4.0 International License. (c–e) Adapted with permission from ref (264). Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. (f) Adapted from ref (265). Creative Commons Attribution 4.0 International License.

Figure 22

Reaction of aldehyde A with diamine B2, B6, or B12 is dynamically controlled by adequate molecular stoichiometry. The shorter chains in the imine products can be replaced directly on the HOPG surface by the longer chain diamines to optimize the adsorption free energy. Adapted with permission from ref (130). Copyright 2014 Springer Nature.

Figure 23

(a) Reaction of the tetra-aldehyde 1 with the aromatic diamines 2, 3, and 4 of various lengths leads to the polymorphic imine based networks with rhombus, parallelogram, and Kagome structure. (b) Corresponding STM images and chemical models. (c) Distribution of the occurrences of the different polymorphs for different network sizes. The Kagome structure preferentially forms at low concentration while the parallelogram (and to certain amount the rhombus) structure is preferred at high concentration. (d) On Ag(111) the DMTP precursor preferentially forms hyperbenzene macrocycles in low-concentration conditions (low deposition flux), but 1D oligomers in high-concentration conditions (high deposition flux). (a–c) Adapted with permission from ref (135). Copyright 2017 American Chemical Society. (d) Adapted with permission from ref (276). Copyright 2017 American Chemical Society.

Figure 24

(a) Reversibility of the dehydration reaction of boronic acids can be achieved by heating in the presence of water pressure. Well-ordered extended networks can be obtained in this way. (b) Sequential STM images showing decomposition/repair cycles consisting of mere decomposition in ambient environment followed by the annealing procedure (each image is 100 × 100 nm²). (c) The homocoupling of DPIA leads to the formation of polymer chains in phenyloctane or to cyclic dimers in trichlorobenzene. (a, b) Adapted with permission from ref (127). Copyright 2012 Royal Society of Chemistry. (c) Reprinted with permission from ref (183). Copyright 2014 Springer Nature.

Figure 25

Tip-induced reactions. (a) Individual iodobenzene molecules are manipulated with the STM tip to form biphenyl units. From top to bottom: two iodobenzene molecules adsorbed at the step edge of Cu(111); dissociation of C–I bond in the left molecule; dissociation of C–I bond in the right molecule; removal of the right I atom; displacement of the left radical; association of the two benzene units. (b) The polymerization of BDBA precursor can be instantaneously induced inside the supramolecular phase by local mechanical removal of some molecules with the STM tip. (c) The polymerization of diacetylene can be locally initiated by electron injection with the STM tip at various locations to form poly(diacetylene) (PDA) wires that self-propagate on the surface. (d) “Chemical soldering” is performed when a PDA line reaches a pentamer of phthalocyanine (Pc) molecules that get covalently bonded to the PDA wire, eventually leading to the possibility of creating a cross-junction. (a) Reprinted with permission from ref (36). Copyright 2000 American Physical Society. (b) Reproduced with permission from ref (216) . Copyright 2011 Royal Society of Chemistry. (c) Reproduced with permission from ref (199). Copyright 2012 Royal Society of Chemistry. (d) Adapted with permission from ref (198). Copyright 2011 American Chemical Society.

Figure 26

Tip-induced reactions. (a) Nanocorrals are created at the surface of a covalently modified HOPG surface by mechanical nanoshaving. PCDA precursors preferentially adsorb inside the nanocorrals, and diacetylene polymerization can be locally initiated with the STM tip. The length of the as-formed PDA wires is limited by the nanocorral host extension. (b) Schematics of the cSPL technique: the AFM tip coated with an organometallic catalyst is brought into contact with an alkene-terminated SAM to locally epoxidize it. In a second step, selective grafting of a nucleophile is achieved. (a) Reproduced with permission from ref (291). Copyright 2017 Royal Society of Chemistry. (b) Adapted with permission from ref (294). Copyright 2016 American Chemical Society.

Figure 27

(a) Schematic representation of the reactant, intermediate polymer, and nanoribbon end product during synthesis of 7-aGNRs. Associated STM images with the overlaid models are displayed below the polymer and GNR. Below, some representative reactants and associated microscopy images of the resulting GNRs (with superimposed wireframe structures) are displayed for varying GNRs. Different edge orientations are displayed (b, armchair; c, chiral; d, zigzag). Different widths of armchair ribbons are displayed (e, 5-aGNR; f, 9-aGNR; g, 13-aGNR). Different edge structures are shown (h, cove edge; i, chevron; j, fluoranthene functionalized zigzag edge). Differently doped structures are shown (k, boron heteroatoms; l, nitrile functional groups; m, N heteroatoms. (a, i) Adapted with permission from ref (151). Copyright 2010 Springer Nature. (b) Adapted with permission from ref (371). Copyright 2013 Springer Nature. (d, j) Adapted with permission from ref (152). Copyright 2016 Springer Nature. (e) Adapted from ref (350). Creative Commons Attribution 4.0 International License. (f) Reproduced with permission from ref (107). Copyright 2018 American Chemical Society. (g) Adapted with permission from ref (348). Copyright 2013 American Chemical Society. (h) Adapted with permission from ref (352). Copyright 2015 American Chemical Society. (k) Adapted from ref (357). Creative Commons Attribution 4.0 International License. (l) Adapted with permission from ref (361). Copyright 2017 American Chemical Society. (m) Adapted with permission from ref (356). Copyright 2014 Springer Nature.

Figure 28

(a) Schematics of the hierarchic reaction process that, starting from DBBA, first forms polymers and then 7-aGNRs, which in turn serve as reactants for the next step forming GNRs of different widths (and the associated heterostructures) through the lateral fusion of the ribbons. Representative images of 7-aGNRs (b), 14-aGNRs (c), and 21-aGNRs (d), as well as of the associated 7-14-aGNR (e) and 7-14-21-aGNRs heterojunctions, are shown below. (g) STM image of a sample with hierarchically grown GNR heterojunctions through combination of the reactants displayed in part h. (i) Magnified STM image of such a GNR heterojunction. (a–f) Reproduced with permission from ref (373). Copyright 2017 American Chemical Society. (g–i) Reproduced with permission from ref (368). Copyright 2018 American Chemical Society.

Figure 29

Representative STM images and wireframe chemical structures of the different end products obtained from 10,10′-dibromo-9,9′-bianthracene on (a) Au(111), (b) Cu(111), and (c, d) Ag(111). On the latter, both 7-aGNRs (c) and layers of cyclodehydrogenated monomers (d) have been observed alike. (a) Adapted with permission from ref (151). Copyright 2010 Springer Nature. (b) Reproduced with permission from ref (384). Copyright 2015 American Chemical Society. (c, d) Adapted from ref (235). Creative Commons Attribution 4.0 International License.

Figure 30

Representation of the different end products obtained from the high-temperature lateral fusion of PPP on Au(111) (a) and on Au(322) (b). While on the former different widths of GNRs are obtained, on the latter, apart from some PPP remaining unreacted, only 6-aGNRs are obtained. Adapted with permission from ref (103). Copyright 2018 American Chemical Society.

Figure 31

Chemical structure and STM and nc-AFM images of the different polymers and GNRs obtained from the precursor displayed at the left as a function of the annealing temperature. A sulfur-doped GNR is obtained at 720 K annealing temperature. At 840 K, the S atoms are cleaved and the final product is a pure-hydrocarbon GNR. Adapted with permission from ref (364). Copyright 2018 Springer Nature.

Figure 32

(a) Artistic view of a 7-aGNR being lifted with a scanning probe. (b) Conductance as a function of tip–sample distance during a lifting experiment performed on 7-aGNRs at U = 0.1 V, displaying a steeper approach curve and a reduced slope during retraction. (c) Light emission spectrum from a 7-aGNR in a suspended geometry and U = 1.8 V. (d) dI/dV conductance spectra of chiral (3,1)-GNRs previously manipulated onto NaCl as a function of the tip–sample distance during a lifting experiment. (e) Tunneling decay constant β of 7-aGNRs obtained from lifting experiments as a function of bias. (f) Schematic view of a lifting experiment with porphyrin chains and STM images of the chain before and after various pulling events. (g) STM image of a magnetic Fe-porphyrin coupled to four low-bandgap, chiral (3,1)-GNRs. (a–c) Adapted with permission from ref (395). Copyright 2012 American Chemical Society. (d) Adapted with permission from ref (394). Copyright 2012 American Chemical Society. (e) Adapted with permission from ref (393). Copyright 2012 Springer Nature. (f) Adapted with permission from ref (391). Copyright 2016 American Chemical Society. (g) Adapted from ref (398). Creative Commons Attribution 4.0 International License.

Figure 33

(a) Schematics of the lithography process in UHV. On a Ag(100) surface, a mask is formed by depositing square-shaped NaCl islands, and the 2D-polymer from BDBA precursors is grown around. Bottom: STM images of the BDBA polymer surrounding NaCl islands (left) and of the square-shape patterned BDBA polymer after annealing and NaCl evaporation (right). (b) The template formed by the BDBA polymer network on HOPG induces structural modifications of the growth mode of C₆₀ multilayers; a quasi-close-packing structure is obtained in contrast to the standard close packing structure obtained without the polymer template. (a) Adapted with permission from ref (261). Copyright 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (b) Adapted with permission from ref (402). Copyright 2017 American Chemical Society.

Figure 34

Formation of polymerized chains on a bulk alkali-halide substrate (a) without or (b) with the help of UV light irradiation. Adapted with permission from ref (92). Copyright 2018 Springer Nature.

Figure 35

Schematic representation of a GNR transfer process sacrificing (a) or not (b) the gold substrate. (c) Raman spectra of 9-aGNRs as grown on Au and after the transfer and device fabrication. (d) Schematic view (top) and scanning electron micrograph (bottom) of a GNR based device. (e) Transport characteristics of a 9-aGNR based field-effect transistor as sketched in the inset. (a) Reprinted with permission from ref (418). Copyright 2013 AIP Publishing. (b) Reprinted with permission from ref (416). Copyright 2018 AIP Publishing. (c–e) Adapted from ref (420). Creative Commons Attribution 4.0 International License.