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ABSTRACT Intensive efforts have been devoted to surface Ullmann-like coupling in recent years, due to its appealing success towards on-surface synthesis of tailor-made nanostructures. While

attentions were mostly drawn on metallic substrates, however, Ullmann dehalogenation and coupling reaction on semimetal surfaces has been seldom addressed. Herein, we demonstrate the

self-assembly of 2, 7-dibromopyrene (Br2Py) and the well controllable dehalogenation reaction of Br2Py on the Bi(111)–Ag substrate with a combination of scanning tunnelling microscopy (STM)

and density functional theory calculations (DFT). By elaborately investigating the reaction path and formed organic nanostructures, it is revealed that the pristinely inert bismuth layer

supported on the silver substrate can initiate Ullmann-like coupling in a desired manner by getting alloyed with Ag atoms underneath, while side products have not been discovered. By

clarifying the pristine nature of Bi–Ag(111) and Ullmann-like reaction mechanisms, our report proposes an ideal template for thoroughly exploring dehalogenative coupling reaction mechanisms

with atomic insights and on-surface synthesis of carbon-based architectures. SIMILAR CONTENT BEING VIEWED BY OTHERS ORDERING A RHENIUM CATALYST ON AG(001) THROUGH MOLECULE-SURFACE STEP

INTERACTION Article Open access 10 January 2022 GENERAL SYNTHESIS AND ATOMIC ARRANGEMENT IDENTIFICATION OF ORDERED BI–PD INTERMETALLICS WITH TUNABLE ELECTROCATALYTIC CO2 REDUCTION

SELECTIVITY Article Open access 21 February 2024 AL13− AND B@AL12− SUPERATOMS ON A MOLECULARLY DECORATED SUBSTRATE Article Open access 14 March 2022 INTRODUCTION Bottom-up building of

covalently bound organic architectures with well-defined arrangements is key to surface physics and surface chemistry towards molecular electronics and nanodevices1,2,3,4,5. By predesigning

chemical structures of precursors, the on-surface synthesis strategy harvests appealing successes at fabricating tailor-made nanostructures, for example, artificial graphene nanoribbons,

graphene ring, polyacenes and so on6,7,8,9,10,11,12. Particularly, Ullmann-like coupling or namely, the dehalogenative reaction of reactants on surface has been recognized as an extremely

efficient and robust approach towards constructing stable covalent molecular architectures on demand13,14,15,16,17,18,19,20,21. Despite of these encouraging progresses, on-surface

Ullmann-like coupling has been achieved mostly on metallic substrates which act as the heterogeneous catalyst for the coupling reactions, while investigations on relatively inert surfaces or

insulators are minor. On the other hand, electrically insulating substrates are crucial to sufficiently decouple the molecular structures from substrate towards future applications in

nanoelectronics. Consequently, the rational synthesis of covalent nanostructures directly on less reactive or inert surfaces is essentially meaningful. In this context, attention has thus

been paid to the surface Ullmann-like coupling supported on non-metallic substrates, for instance, on top of the graphene and boron nitride thin layer decoupled from the nickel

substrate22,23,24, on a bulk insulator25,26 and metal oxide surfaces27,28,29,30. However, due to the shortage of catalytic activity during the dehydrogenation reaction, these attempts seem

to be not so satisfactory as expected with the sacrifice of reaction selectivity after the high-temperature annealing, for instance. Thus, on-surface Ullmann-like coupling reaction based on

non-metallic surfaces requires further dedicated explorations for the fabrication of tailored nanoarchitectures, and the substrate catalytic activity also needs to be properly considered.

Bismuth, known as a typical semimetal with the reduced surface activity, was introduced recently in the form of Bi-metal complex into both the molecular self-assembly and on-surface

reaction31,32,33, whereas the catalytic performance of bismuth was still under debate, to some extent. For instance, it was demonstrated that the DBBA precursor got completely desorbed on

the bismuth decorated Au(111) surface and therefore no Ullmann-like coupling was observed31. On the other hand, the Bi(111)–Au substrate was revealed to successfully initiate the metalation

of phthalocyanine33. As demonstrated in literature, the growth mode of Bi on Au(111) differs significantly from that on Ag(111). Au(111) solely supports the atomic-layer growth of Bi atop

with the honeycomb structure, while bismuth prefers to form surface alloy by incorporating with Ag atoms after adsorption on Ag(111)34,35, which introduces rich electronic states around the

Fermi level36 and might thus effectively promote dehalogenation and homocoupling reactions. In this regard, a bismuth covered silver surface, namely, Bi/Ag(111), is chosen in this report to

investigate whether the surface Ullmann-like coupling can be initiated by thermal annealing. A symmetrically halogenated precursor, 2,7-dibromopyrene, Br2Py37 (C16H8Br2, as shown in Fig. 1)

is chosen as the precursor. By revealing the structural evolution of organic nanostructures at the atomic level via Scanning tunnelling microscopy (STM), we demonstrate herein that the thin

bismuth layer atop silver presents the promising catalytic activity towards on-surface dehalogenation, and the stepwise Ullmann-like coupling reaction is clearly revealed and comprehensively

elucidated thanks to the controllable dehalogenation reaction on the Bi/Ag(111) substrate. RESULTS AND DISCUSSION Thin bismuth layer with the (111) facet was prepared on top of a clean

Ag(111) substrate prior the deposition of Br2Py, and detailed information regarding on the preparation procedure can be found in the experimental section and Fig. S1 in the Electronic

Supplementary Material (ESM). Initial deposition of Br2Py onto the Bi–Ag(111) surface held at room temperature (RT) results in the formation of well-ordered domains on terraces of the

Bi–Ag(111) surface, as indicated by the STM topology in Fig. 1a. Apparently, the Br2Py precursors are kept intact after adsorption on Bi–Ag(111), while molecules assembled into closed packed

structures that display three azimuthal domains on surface in relation to the substrate’s three-fold symmetry (as indicated by black dashed lines in Fig. 1(a)). Further inspection reveals

that the molecular axis is in principle aligned at 30° rotation with respect to the high symmetry directions from the Bi(111) substrate (marked with white arrows), suggesting symmetry

inheriting from substrate to the assembled Br2Py array and the delicate mediating between the molecule–substrate and intermolecular interactions. The zoom-in STM image in Fig. 1b indicates

that Br2Py precursors are arranged parallel forming a rhombic unit cell with lattice parameters of a = b = 11.0 ± 0.2 Å and α = 60 ± 1°, which is in general consistent with previous reports

of Br2Py adsorbed on the metal substrate41,42, whereas the self-assembly arrangement is stabilized by both the halogen bonding (–C–Br…Br–C–) and hydrogen bonding (–C–Br…H–C–) motifs between

neighbouring molecules. Herein, the weak molecule–substrate interaction is responsible for the rotational alignment of the molecules with respect to the principal directions of

substrate38,39,40, while the intermolecular halogen bonding and hydrogen bonding motifs between Br2Py monomers are responsible for the formation of the stable self-assembly phase41,42.

Nevertheless, dark holes are also visible on surface in Fig. 1a, which are assigned to defects embedded in the Bi(111)–Ag substrate and are also visible in the following STM images.

Subsequent annealing to 380 K results in considerable changes of surface topography. First, disappearance of self-assembly phase is obvious with the significant desorption of precursors, as

seen in Fig. 2a. Undoubtedly, the desorption of Br2Py shall be assigned to the weak molecule–substrate interaction mentioned before. On the other hand, interestingly, extended oligomers (for

example, dimer, trimer and tetramer) with limited length are discovered after annealing regardless of the pristine inertness of bismuth atoms, and are revealed to be aligned at 30° with

respect to the three-fold symmetry directions of Bi(111). In addition, the oligomer can also be found along the principal symmetry direction, as seen at the bottom of Fig. 2a highlighted

with the yellow dashed line. Meanwhile, dim dots are also visible on surface which are assigned to Br atoms detached from parent molecules after the scission of the Br–C bond19,20. A close

investigation at molecular chains is shown in Fig. 2b, and it can be resolved that dimer and trimer are formed and aligned in a manner of parallel packing with one end aligned on the

Bi–Ag(111) surface. With line profiles depicted, it is discovered that the length of dimer and trimer is around 3.0 nm and 2.1 nm, respectively, which fits reasonably with the configuration

of two and three covalently linked pyrene residues. Thus, no Bi atoms are expected to be bound in between pyrene residues, and the linear trimer and dimer are in fact constructed with direct

C–C coupling. Based on these discussions, schematic molecular models for the dimer and trimer are depicted in Fig. 2c (with the adsorption energy of 1.4 eV as predicted by DFT

calculations), whereas oligomers are arranged commensurately with substrate and the Br substitutes are placed around the hollow site, while the trimer aligned along the principal three-fold

symmetric direction is also commensurately packed on the Bi(111)–Ag substrate. Besides, nonlinear oligomers (the angle between two pyrene residues is approximately 120°) are also revealed,

as seen in the left bottom in Fig. 2a and other areas on surface, and are clearly presented in Fig. 2d and e, respectively. Based on previous reports for Ullmann-like coupling on coinage

metal substrates, such nanostructures might be assigned to the formation of organometallic (OM) species with the semimetal adatom bound in between pyrene residues, while DFT simulation of

the Bi-bound dimer delineated in Fig. 2f shows reasonable agreement with the STM observation in Fig. 2d. Nevertheless, it is also possible to form OM dimer with the Ag adatom bound in the

middle which cannot be excluded unambiguously solely from STM measurements at this stage. In order to clarify this debate, comparison between Bi-bound dimer and Ag-bound dimer has also been

performed, as presented in Fig S2 in ESM, whereas STM simulation of the OM dimer with Ag atom coordinated shows apparent inconsistence with the experimental observation in Fig. 2d. In

addition, the adsorption energy of Ag-dimer is relatively higher that of Bi-dimer, making Ag-dimer the unfavourable configuration. Thus, one can conclude that these OM species are most

probably coordinated by Bi adatoms. Thus, it is interesting to reveal the Bi-C bonding motifs in OM phases herein, which has been seldom reported before. Consequently, it can be drawn that

the bismuth-silver interface indeed initiates the surface dehalogenation reaction with the inevitable desorption of Br2Py molecules after mild annealing, manifesting the unique

characteristics of Ullmann dehalogenation on Bi(111)–Ag. Further annealing to 410 K and 440 K, respectively, promotes sequential Ullmann-like coupling reactions and brings the formation of

considerably extended oligomers and polymers, as observed in Fig. 2g,h. First, 410 K annealing greatly assists the Ullmann-like coupling and results in elongated organic oligomers without

any OM species left, manifesting the relative stability of OM intermediates below 410 K annealing. More interestingly, linear chains are discovered along the step edge with significant

length at annealing to 440 K as shown in Fig. 2h, which might be initially formed at other areas, diffuse over the terrace during thermal annealing, and get stabilized at the step edge.

Again, the desorption of organics is apparent manifesting the weak molecule–substrate interaction. Meanwhile, it is revealed that the molecular chain is aligned 30° with respect to the high

symmetry direction of Bi(111), which is similar to the situation of dimer and trimer formed after annealing to 380 K in Fig. 2a. In addition, the linear chain is uniformly organized with the

peanut shape, while no metal atom can be recognized inside the chain, indicating that OM intermediates might have already been transformed into the covalently coupled nanostructures.

Nevertheless, these chains are still terminated with Br atoms with the typical bright protrusion ends as generally reported in literature43. Notably, dissociated Br atoms from parent

molecules also desorb from surface during thermal annealing, as discovered in Fig. 2g,h whereas Br atoms are only resolved in the large-scale image23,44. Further investigation of the

adsorption/desorption behaviour of Br atoms is summarized in Fig. S3 in ESM, and it is revealed that Br atoms are robustly adsorbed on Bi(111)–Ag until 630 K annealing when desorption of all

organics and Br atoms is realized and the pristine Bi–Ag surface gets recovered. Meanwhile, DFT optimized adsorption configuration for the organic chain in Fig. 2h is illustrated in Fig. 2i

with the adsorption energy of 0.7 eV, which shows reasonable agreement with the STM observation in periodicity and further confirms that OM species no longer exist at this stage. Indeed,

the STM topology of the organic chain is close related to the covalent linking of pyrene residues after debromination, in accordance to the typical π-conjugated aromatic systems. It has been

demonstrated above that the Bi(111) layer atop silver shows appealing ability in promoting the surface Ullmann-like coupling. However, due to the weak interaction between molecules and the

Bi(111) surface, the amount of polymers gets less and less after the step-by-step annealing, and even vanish after annealing to a certain temperature, which makes further exploration of

coupling reactions difficult. In order to elaborately investigate the catalytic activity of the thin Bi(111) layer atop Ag towards surface Ullmann-like coupling, an alternative measures has

also been utilized by depositing the Br2Py precursor onto the preheated Bi–Ag(111) substrate. In practice, deposition of precursors on the preheated substrate has been explored at varying

temperatures in this work, say, 440 K (high enough to initiate the aryl-aryl coupling as revealed in Fig. 2) and 530 K, respectively. While the preheated surface at 440 K indeed promotes the

homocoupling of Br2Py (presented in Fig. S4 in ESM), however, the number of reacting products is not as high at that on the 530 K preheated substrate, as preheating at a higher temperature

greatly enhances the dehalogenative reactivity towards coupling reactions. Thus, STM images obtained from the preheated surface at 530 K are focally discussed as illustrated in Fig. 3. It is

seen from Fig. 3a that, ordered array of one-dimension (1D) chains is formed immediately upon deposition, while certain amounts of clusters are randomly distributed on bare areas of

Bi(111). Apparently, these 1D chains are close packed in order by roughly following the high symmetry directions of Bi(111) at first glance. More interestingly, oligomers get incredibly

extended with the length of up to 50 nm, which is much longer than those formed before via sequential annealing. Detailed inspection in Fig. 3b shows that 1D molecular chains are constructed

in a well aligned manner that pyrene residues in neighbouring chains are directly facing to each other, while the pyrene frame is imaged as two non-identical bright protrusions. Besides,

elongated dots are clearly resolved with the regular confinement between molecular chains, which can be assigned to liberated Br atoms from parent precursors after Ullmann-like coupling, as

generally recognized in literature18,37,45. Meanwhile, the elongate shape of Br atoms might be related to the adsorption position (hollow site) with confinement in between linear chains on

Bi(111)–Ag, causing the steric effect during STM imaging. Notably, dissociated bromine atoms are not only localized in between polymer chains on Bi(111), but they can also be stably adsorbed

just on the side of linear chains, as marked by the black ellipse in Fig. 3b, which is an interesting behaviour suggesting the remarkable mediating effect on the adsorption of Br atoms from

polymer chains. In addition, further investigation of the randomly distributed clusters in Fig. 3a is elaborated in Fig. 3c. While bismuth atoms from substrate are clearly resolved, it is

discovered that the I-shape clusters are built on top of Bi(111), as marked by the dashed line in Fig. 3c. Detailed structure information is revealed by the zoom-in STM image in Fig. 3d. One

may tentatively infer that these clusters are formed by dissociated Br atoms after C–Br bond scission, which is evidently supported by further DFT calculations illustrated in Fig. 3e where

the I-shape protrusion consists of 5 Br atoms with the central one relatively dim due to the lower adsorption height. In contrast to previous reports of the accumulation of detached Br atoms

into the close packed array on other metal surfaces45,46,47, herein, different observations point out the uniqueness of adsorption of Br atoms on Bi–Ag(111) and the delicate interaction

between bromine and bismuth atoms. Not surprisingly, further annealing afterwards to higher temperature (for instance, 630 K) induces the desorption of polymer chains and the substrate is

recovered to the pristine Bi(111)–Ag surface, as discussed before in Fig. S3 in ESI. Dehalogenation of Br2Py on the Bi(111)–Ag surface has been clearly identified under different annealing

conditions, manifesting the promising catalytic ability of the bismuth-silver interface towards the on-surface aryl-aryl homocoupling reaction, which in principle clarifies the ambiguous

issue of bismuth’s activity supported on the silver substrate. Importantly, in order to get an unambiguous understanding of the catalytic mechanism of Bi(111)–Ag, deposition of Br2Py

precursors on the bismuth-covered Au(111) has also been employed and is summarized in Fig. 4. Apparently, self-assembly of Br2Py is arranged on Bi–Au(111) as expected in Fig. 4a, analogous

to that on Bi–Ag(111), with the intermolecular interaction mediated by both halogen bonding and hydrogen bonding motifs as highlighted in Fig. 4b. Interestingly, thermal annealing to 350 K

induces considerable changes of surface morphology from ordered self-assembly to disorderedly parked monomers, as observed in Fig. 4c. Meanwhile, no dehalogenation coupling of Br2Py is

discovered with the intact molecular structure well preserved, although precursors are in muddle after mild annealing at 350 K. Notably, partial desorption of organic molecules is resolved

in Fig. 4c, since parts of Bi–Au(111) surface get exposed. Surprisingly, stepwise annealing to 380 K induces the complete desorption of all Br2Py precursors, and thus brings the pristine

Bi–Au(111) surface back with the root 37 * root 37 reconstruction34, as exhibited in Fig. 4d. Based on this direct comparison, it can be concluded that the bismuth layer attached on Au(111)

is indeed unable to initiate the Ullmann-like coupling reaction, while the promotion of dehalogenation on Bi(111)–Ag should then be correlated with the unique growth behaviour of Bi on

Ag(111): by incorporating with Ag atoms on surface, bismuth atoms get alloyed with silver and thus, the Bi layer atop Ag becomes active via electron transfer from Ag48, inducing considerable

catalytic ability towards dehalogenation coupling reactions. On the other hand, in the case of Br2Py atop Bi–Au(111), since the bismuth layer prefers the atomic layer growth on Au(111)

without surface alloying, the pristine inert property of bismuth atom due to its tightly bound 6S2 electrons completely blocks the reactivity of the gold substrate underneath. Moreover, the

difference in the growth mode of Bi on Ag(111) and Au(111) can be assigned to the relativistic effect (Ag(5s14d10), Au(6s14f145d10), Bi(5d106s26p3)) and the fact that, the relative atomic

radius difference between Bi and Au is bigger than 15%, which makes it unfavourable for the substitutional solid solution according to the Hume-Rothery rule35. In addition, a comprehensive

comparison of the dehalogenative coupling of Br2Py on the bare Ag(111), Bi/Ag(111) and B/Au(111) will shed more valuable insights onto the understanding of dehalogenation reaction mechanism

on Bi(111)–Ag, which is summarized and illustrated in Fig. S5 in ESI. As observed in Fig. 2 and Fig. 3, reaction steps of Br2Py on Bi(111)–Ag involve: (1) dissymmetrical debromination of

Br2Py; (2) formation of organometallic intermediates with the adsorption of released Br atoms from parent molecules; (3) aryl–aryl coupling towards extended organic chains with C–C bonding

after further annealing; (4) desorption of bromine atoms and organic chains in the end. In contrast, dehalogenation is straightforward after adsorption of Br2Py on a bare Ag(111) surface at

room temperature, with the coexistence of intact monomers and OM dimers. Stepwise annealing first promotes the formation of extended organometallic chains, and then results in the aryl-aryl

coupling towards the ordered domain of covalent organic chains. Obviously, there are distinct differences between the Ullmann-like coupling on Bi(111)–Ag and Ag(111). First, no extensive OM

chains are discovered on Bi(111)–Ag except OM dimers and OM tetramers, while long-range ordered OM chains are clearly observed on Ag(111), indicating that the pristine inert property of

bismuth makes it hard to get many enough Bi-C bonds for the formation of long OM chains. Second, the desorption of reaction products (organic chains) is straightforward after stepwise

annealing, and the recovery of the pristine Bi(111)–Ag surface is realized at a certain temperature annealing (630 K), while on silver or other metal surfaces, covalent organic chains

usually gets destroyed before desorption and the accumulation of side produces becomes more and more visible as a function of stepwise annealing18,19,20,21. Based on these observations and

discussions, it has been demonstrated that Bi layer atop Ag(111) shows promising reactivity towards the Ullmann-like coupling of the halogenated molecule. However, the apparent desorption of

organic nanostructures during step-wise annealing procedure points out the relatively weak interaction between the covalently coupled polymer chains and the Bi(111)–Ag substrate, as well as

that between detached Br atoms and the Bi substrate. Consequently, thin bismuth layer atop Ag(111) functions as a buffer layer between organic molecules and Ag(111), and is embedded with

certain activity via surface alloying, which thus will have appealing advantages to be the catalytic platform for the investigation of the Ullmann-like coupling by initiating the

controllable coupling reactions and avoiding the accumulation of other side products49,50. With these merits, it can be inferred that bismuth layer grown on certain active metal substrates

is an appealing template to elaborately investigate the mechanism of on-surface Ullmann-like coupling reactions towards rational synthesis of tailor-made organic nanostructures. CONCLUSIONS

In summary, we have comprehensively investigate the self-assembly and Ullman-like coupling reaction of Br2Py on thin bismuth layers supported on the silver substrate, and demonstrated that

the Bi(111)–Ag surface could indeed initiate the dehalogenation reaction with mild annealing. By sequential heating of the self-assembled Br2Py molecules or depositing the Br2Py precursor on

a hot substrate, dehalogenation and aryl-aryl homocoupling reactions are unambiguously witnessed on Bi(111)–Ag. With OM intermediates formed during reactions, covalently linked organic

chains are ultimately fabricated with the considerable length. In comparison to the adsorption of Br2Py on Bi–Au(111), it is demonstrated that the reactivity of Bi(111)–Ag towards

dehalogenation reactions is correlated with surface alloying of Bi–Ag, while atomic bismuth layer atop Au(111) cannot get alloyed due to the relativistic effect, resulting in the desorption

of precursors without further dehalogenation by blocking the activity of Au(111). In addition, the weak organic-substrate interaction on Bi(111)–Ag, contributed by the pristine property of

bismuth atoms, is also notable and affords the opportunity to clearly elucidate the on-surface Ullman coupling reactions. Ultimately, our report proposes an appealing platform to deeply

understand reaction mechanisms of on-surface Ullman-like coupling with atomic insights towards rational synthesis of tailor-made organic nanostructures. METHODS STM measurements were

performed in a FERMI SPM system (ScientaOmicron) with the base pressure better than 2 × 10–10 mbar. The sample stage in STM chamber was cooled at liquid nitrogen temperature (around 78 K) as

well as the tip during scanning, while the tip was prepared by cutting Pt/Ir alloy wires. During STM scanning at the constant current mode, the bias voltage was applied to the tip and

sample was grounded. STM images were processed afterward using the WSXM software (4.0 Beta, http://www.wsxm.es/download.html)51. In order to get an atomically smooth Bi(111) layer on top of

silver and gold substrates, respectively, a clean Ag(111)/Au(111) substrate (Mateck) was obtained first by cycles of Ar + sputtering followed with thermal annealing (650 K for Ag(111), 750 K

for Au(111)), and the surface quality of Ag(111)/Au(111) was checked by STM and low energy electron diffraction (LEED). Bismuth powder (Mateck) was thoroughly degassed in an UHV evaporator

(OmniVac) prior sublimation while the deposition rate was monitored by a quartz microbalance. Upon deposition on Ag(111), the Bi(110) phase was first formed at low coverage, while the

Bi(111) layer was ultimately induced after a full coverage of one monolayer (ML). Evidence of the Bi(111) phase on silver can be found from the STM image in Fig. S1a, where close packed Bi

atoms are clearly resolved with a hexagonal pattern, and Fast Fourier transform (FFT) in Fig. S1b of STM image. Furthermore, LEED pattern recorded on the Bi/Ag(111) surface clearly indicates

the appearance of Bi(111) structure on top of Ag(111) (root 3*root 3 reconstruction)48 while the LEED pattern from the pristine Ag(111) is shown inset for comparison. It is thus can be

concluded that Bi–Ag(111) interface has been obtained. To get the Bi- Au(111) substrate, roughly 1 ML bismuth was deposited onto Au(111), with the initial structure of 5*5 reconstruction at

low coverage, and the root 37 by root 37 R25.3° periodic structures at monolayer coverage, which is usually referred as the stable phase of Bi–Au(111)34,52. DFT calculations were performed

using the Vienna ab initio simulation Package (VASP) under the framework of DFT53. The PBE functional54 was used in combination with the third-generation van der Waals dispersion correction

due to Grimme (DFT-D3)55 and the projector-augmented wave (PAW) ansatz for atomic cores. A plane-wave cut-off energy of 450 eV was employed, while the k-point sampling was chosen to be 3 × 3

 × 3 in order to obtain a realistic and accurate picture of the energetics. For simulation of the OM intermediate with the Bi-C bonding, a three-layer slab of the Ag(111) supercell (9 × 9)

was utilized with lateral dimension of 25.96 × 25.96 Å2, while the vacuum layer of 10 Å was introduced to isolate the interactions of slabs from each other. The lattice parameter of the

Ag(111) surface after optimization was found to be 2.88 Å, in good agreement with literature reports56. Afterwards, a bismuth layer was adsorbed on top of Ag(111) surface with the root

3*root 3 reconstruction, forming a Bi(111) layer with a slightly large lattice constant compared to the pristine bulk Bi(111). The bismuth layer was free together with the adsorbed OM

structures during geometry optimization, while the bottom three Ag(111) layers were kept fixed. Geometries were optimized until the forces on the active atoms dropped below 0.05 eV/Å. The

convergence criterion is 10‑4 eV in total energy difference. Simulated STM images were obtained in the framework of Tersoff-Hamann approximation with the gnuplot software (5.2,

https://sourceforge.net/projects/gnuplot/files/gnuplot/5.2.8/) by plotting partial charge densities which were acquired by a static self-consistent calculation based on the DFT optimized

configurations. REFERENCES * Yokoyama, T., Yokoyama, S., Kamikado, T., Okuno, Y. & Mashiko, S. Selective assembly on a surface of supramolecular aggregates with controlled size and

shape. _Nature_ 413, 619–621 (2001). Article  ADS  CAS  PubMed  Google Scholar  * Bartels, L. Tailoring molecular layers at metal surfaces. _Nat. Chem._ 2, 87–95 (2010). Article  CAS  PubMed

  Google Scholar  * Slater, A. G., Beton, P. H. & Champness, N. R. Two-dimensional supramolecular chemistry on surfaces. _Chem. Sci._ 2, 1440–1448 (2011). Article  CAS  Google Scholar  *

Grill, L. & Hecht, S. Covalent on-surface polymerization. _Nat. Chem._ 12, 115–130 (2020). Article  CAS  PubMed  Google Scholar  * Lindner, R. & Kühnle, A. On-surface reactions.

_ChemPhysChem_ 16, 1582–1592 (2015). Article  CAS  PubMed  Google Scholar  * Cai, J. _et al._ Atomically precise bottom-up fabrication of graphene nanoribbons. _Nature_ 466, 470–473 (2010).

Article  ADS  CAS  PubMed  Google Scholar  * Shen, Q., Gao, H. Y. & Fuchs, H. Frontiers of on-surface synthesis: From principles to applications. _Nano Today._ 13, 77–96 (2017). Article

  CAS  Google Scholar  * Sun, Q., Zhang, R. Y., Qiu, J., Liu, R. & Xu, W. On-surface synthesis of carbon nanostructures. _Adv. Mater._ 30, 1705630 (2018). Article  CAS  Google Scholar  *

de Oteyza, D. G. _et al._ Direct imaging of covalent bond structure in single-molecule chemical reactions. _Science_ 340, 1434–1437 (2013). Article  ADS  PubMed  CAS  Google Scholar  *

Sanchez-Sanchez, C. _et al._ On-surface cyclization of ortho-dihalotetracenes to four- and six-membered rings. _J. Am. Chem. Soc._ 139, 17617–17623 (2017). Article  CAS  PubMed  Google

Scholar  * Kruger, J., Eisenhut, F., M. Alonso, J., Lehmann, T., Guitian, E., Perez, D., Skidin, D., Gamaleja, F., Ryndyk, D. A., Joachim, C., _et al_. Imaging the electronic structure of

on-surface generated hexacene. _Chem. Commun_. 53, 1583−1586 (2017). * Fan, Q. _et al._ On-surface synthesis and characterization of a cycloarene: C108 graphene ring. _J. Am. Chem. Soc._

142, 894–899 (2020). Article  CAS  PubMed  Google Scholar  * Grill, L. _et al._ Nano-architectures by covalent assembly of molecular building blocks. _Nat. Nanotechnol._ 2, 687–691 (2007).

Article  ADS  CAS  PubMed  Google Scholar  * Lafferentz, L. _et al._ Controlling on-surface polymerization by hierarchical and substrate-directed growth. _Nat. Chem._ 4, 215–220 (2012).

Article  CAS  PubMed  Google Scholar  * Gourdon, A. On-surface covalent coupling in ultrahigh vacuum. _Angew. Chem. Int. Ed._ 47, 6950–6953 (2008). Article  CAS  Google Scholar  *

Lipton-Duffin, J. A., Ivasenko, O., Perepichka, D. F. & Rosei, F. Synthesis of polyphenylene molecular wires by surface-confined polymerization. _Small._ 5, 592–597 (2009). Article  CAS

  PubMed  Google Scholar  * Talirz, L., Ruffieux, P. & Fasel, R. On-surface synthesis of atomically precise graphene nanoribbons. _Adv. Mater._ 28, 6222–6231 (2016). Article  CAS  PubMed

  Google Scholar  * Lackinger, M. Surface-assisted Ullmann coupling. _Chem. Commun._ 53, 7872 (2017). Article  CAS  Google Scholar  * Clair, S. & de Oteyza, D. G. Controlling a chemical

coupling reaction on a surface: Tools and strategies for on-surface synthesis. _Chem. Rev._ 119, 4717–4776 (2019). Article  CAS  PubMed  PubMed Central  Google Scholar  * Fan, Q., Gottfried,

J. M. & Zhu, J. F. Surface-catalyzed C–C covalent coupling strategies toward the synthesis of low-dimensional carbon-based nanostructures. _Acc. Chem. Res._ 48, 2484–2494 (2015).

Article  CAS  PubMed  Google Scholar  * Simonov, K. A. _et al._ Synthesis of armchair graphene nanoribbons from the 10,10′-dibromo-9,9′-bianthracene molecules on Ag(111): The role of

organometallic intermediates. _Sci. Rep._ 8, 3506 (2018). Article  ADS  CAS  PubMed  PubMed Central  Google Scholar  * Dienel, T. _et al._ Dehalogenation and coupling of a polycyclic

hydrocarbon on an atomically thin insulator. _ACS Nano_ 8, 6571–6579 (2014). Article  CAS  PubMed  Google Scholar  * Morchutt, C., Björk, J., Krotzky, S., Gutzler, R. & Kern, K. Covalent

coupling via dehalogenation on Ni(111) supported boron nitride and graphene. _Chem. Commun._ 51, 2440–2443 (2015). Article  CAS  Google Scholar  * Zhao, W., Dong, L., Huang, C., Win, Z. M.

& Lin, N. Cu- and Pd-catalyzed Ullmann reaction on a hexagonal boron nitride layer. _Chem. Commun._ 52, 13225 (2016). Article  CAS  Google Scholar  * Kittelmann, M. _et al._ On-surface

covalent linking of organic building blocks on a bulk insulator. _ACS Nano_ 5, 8420–8425 (2011). Article  CAS  PubMed  Google Scholar  * Richter, A., Floris, A., Bechstein, R., Kantorovich,

L. & Kühnle, A. On-surface synthesis on a bulk insulator surface. _J. Phys. Condens. Matter_. 30, 133001 (2018). * Kolmer, M. _et al._ Polymerization of polyanthrylene on a titanium

dioxide (011)-(2×1) surface. _Angew. Chem. Int. Ed._ 52, 10300–10303 (2013). Article  CAS  Google Scholar  * Kolmer, M., Zuzak, R., Steiner, A.- K., Zajac, L., Engelund, M., Godlewski, S.,

Szymonski, M., Amsharov, K. Fluorine-programmed nanozipping to tailored nanographenes on rutile TiO2 surfaces. _Science_ 363, 57–60 (2019). * Kolmer, M., Steiner, A. -K., Izydorczyk, I., Ko,

W., Engelund, Szymonski M., Li, A. -P., Amsharov, K. Rational synthesis of atomically precise graphene nanoribbons directly on metal oxide surfaces. _Science_. 369, 571–575 (2020). *

Vasseur, G. _et al._ Π band dispersion along conjugated organic nanowires synthesized on a metal oxide semiconductor. _J. Am. Chem. Soc._ 138, 5685–5692 (2016). Article  CAS  PubMed  PubMed

Central  Google Scholar  * Tian, G. _et al._ Effects of monolayer Bi on the self-assembly of DBBA on Au(111). _Surf. Sci._ 665, 89–95 (2017). Article  ADS  CAS  Google Scholar  * Yan, L. H.

_et al._ Stabilizing and organizing Bi3Cu4 and Bi7Cu12 nanoclusters in two-dimensional metal-organic networks. _Angew. Chem. Int. Ed._ 57, 4617–4621 (2018). Article  CAS  Google Scholar  *

Hu, J. B. _et al._ Direct synthesis of semimetal phthalocyanines on a surface with insights into interfacial properties. _J. Phys. Chem. C._ 124, 8247–8256 (2020). Article  CAS  Google

Scholar  * Kawakami, N. _et al._ Structural evolution of Bi thin films on Au(111) revealed by scanning tunneling microscopy. _Phys. Rev. B._ 96, 205402 (2017). Article  ADS  Google Scholar 

* Zhou, D. C. _et al._ Interfacial effects on the growth of atomically thin film: Group VA elements on Au(111). _Adv. Mater. Inter._ 6, 1901050 (2019). Article  Google Scholar  * Ast, R. C.

_et al._ Giant spin splitting through surface alloying. _Phys. Rev. Lett._ 98, 186807 (2007). Article  ADS  PubMed  CAS  Google Scholar  * Hu, J. B. _et al._ Ullmann coupling of

2,7-dibromopyrene on Au(1 1 1) assisted by surface adatoms. _Appl. Surf. Sci._ 513, 145797 (2020). Article  CAS  Google Scholar  * Hooks, D. E., Fritz, T. & Ward, M. D. Epitaxy and

molecular organization on solid substrates. _Adv. Mater._ 13, 227–241 (2001). Article  CAS  Google Scholar  * Pham, T. A., Song, F. & Stöhr, M. Supramolecular self-assembly of metal-free

naphthalocyanine on Au (111). _Phys. Chem. Chem. Phys._ 16, 8881–8885 (2014). Article  CAS  PubMed  Google Scholar  * Martínez-Galera, A. J. & Gómez-Rodríguez, J. M. Structural and

electronic properties of 3,4,9,10-perylene tetracarboxylic dianhydride on h-BN/Rh(110). _J. Phys. Chem. C._ 123, 1866–1873 (2019). Article  CAS  Google Scholar  * Hu, J. B. _et al._

Structural transformation of 2,7-dibromopyrene on Au(111) mediated by halogen-bonding motifs. _ChemPhysChem_ 20, 2376–2381 (2019). Article  CAS  PubMed  Google Scholar  * Pham, T. A., Song,

F., Nguyen, M. T. & Stöhr, M. Self-assembly of pyrene derivatives on Au(111): Substituent effects on intermolecular interactions. _Chem. Commun._ 50, 14089–14092 (2014). Article  CAS 

Google Scholar  * Fritton, M. _et al._ The role of kinetics versus thermodynamics in surface-assisted Ullmann coupling on gold and silver surfaces. _J. Am. Chem. Soc._ 141, 4824–4832 (2019).

Article  CAS  PubMed  Google Scholar  * Abyazisani, M., MacLeod, J. M. & Lipton-Duffin, J. Cleaning up after the party: Removing the byproducts of on-surface Ullmann coupling. _ACS

Nano_ 13, 9270–9278 (2019). Article  CAS  PubMed  Google Scholar  * Di Giovannantonio, M. _et al._ Mechanistic picture and kinetic analysis of surface-confined Ullmann polymerization. _J.

Am. Chem. Soc._ 138, 16696–16702 (2016). Article  PubMed  CAS  Google Scholar  * Zheleva, Z. V. V., Dhanakb, R. & Held, G. Experimental structure determination of the chemisorbed

overlayers of chlorine and iodine on Au(111). _Phys. Chem. Chem. Phys._ 12, 10754–10758 (2010). Article  CAS  PubMed  Google Scholar  * Ammon, M., Tim Sander, T. & Maier, S. On-surface

synthesis of porous carbon nanoribbons from polymer chains. _J. Am. Chem. Soc._ 139, 12976–12984 (2017). Article  CAS  PubMed  Google Scholar  * Bian, G., Wang, X., Miller, T. & Chiang,

T.-C. Origin of giant Rashba spin splitting in Bi/Ag surface alloys. _Phys. Rev. B_ 88, 085427 (2013). Article  ADS  CAS  Google Scholar  * Galeotti, G. _et al._ An unexpected organometallic

intermediate in surface-confined Ullmann coupling. _Nanoscale._ 11, 7682–7689 (2019). Article  CAS  PubMed  Google Scholar  * Mairena, A. _et al._ The fate of bromine after

temperature-induced dehydrogenation of on-surface synthesized bisheptahelicene. _Chem. Sci._ 10, 2998–3004 (2019). Article  CAS  PubMed  PubMed Central  Google Scholar  * Horcas, I. _et al._

WSXM: A software for scanning probe microscopy and a tool for nanotechnology. _Rev. Sci. Instrum._ 78, 013705 (2007). Article  ADS  CAS  PubMed  Google Scholar  * He, B. C., Tian, G., Gou,

J., Liu, B. X., Shen, K. C., Tian, Q. W., Yu, Z. Q., Song, F., Xie, H. P., Gao, Y. L., Lu, Y. H., K. H., Chen, L., Huang, H. Structural and electronic properties of atomically thin Bismuth

on Au(111). _Surf. Sci_. 679, 147–153 (2019). * Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. _Phys. Rev.

B_ 54, 11169 (1996). Article  ADS  CAS  Google Scholar  * Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. _Phys. Rev. Lett._ 77, 3865–3868

(1998). Article  ADS  Google Scholar  * Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction

(DFT-D) for the 94 elements H-Pu. _J. Chem. Phys._ 132, 154104 (2010). Article  ADS  PubMed  CAS  Google Scholar  * Gao, J., Zhang, G. & Zhang, Y. Exploring Ag(111) substrate for

epitaxially growing monolayer stanene: A first-principles study. _Sci. Rep._ 6, 29107 (2016). Article  ADS  CAS  PubMed  PubMed Central  Google Scholar  Download references ACKNOWLEDGEMENTS

This work was financially supported by the National Natural Science Foundation of China (11874380, 11874427, U1732267), The National Key Research and Development Program of China

(2016YFA0401302) and the Hundred Talents Program of Chinese Academy of Sciences. AUTHOR INFORMATION Author notes * Kongchao Shen Present address: Institute of Functional Nano & Soft

Materials (FUNSOM), Soochow University, Suzhou, 215123, China AUTHORS AND AFFILIATIONS * Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese

Academy of Sciences, Shanghai, 201000, China Jinping Hu, Jinbang Hu, Hongbing Wang, Kongchao Shen, Huan Zhang, Chaoqin Huang, Zheng Jiang & Fei Song * University of Chinese Academy of

Sciences, Beijing, 100100, China Jinping Hu, Hongbing Wang, Huan Zhang, Chaoqin Huang, Zheng Jiang & Fei Song * Department of Physics, Center of Quantum Spintronics, Norwegian University

of Science and Technology, 7491, Trondheim, Norway Jinbang Hu * Shanghai Synchrotron Radiation Facility, Zhangjiang Laboratory, Shanghai Advanced Research Institute, Chinese Academy of

Sciences, Shanghai, 201000, China Lei Xie, Zheng Jiang & Fei Song * School of Physics Science and Electronics, Central South University, Changsha, 410083, China Qiwei Tian & Han

Huang Authors * Jinping Hu View author publications You can also search for this author inPubMed Google Scholar * Jinbang Hu View author publications You can also search for this author

inPubMed Google Scholar * Hongbing Wang View author publications You can also search for this author inPubMed Google Scholar * Kongchao Shen View author publications You can also search for

this author inPubMed Google Scholar * Huan Zhang View author publications You can also search for this author inPubMed Google Scholar * Chaoqin Huang View author publications You can also

search for this author inPubMed Google Scholar * Lei Xie View author publications You can also search for this author inPubMed Google Scholar * Qiwei Tian View author publications You can

also search for this author inPubMed Google Scholar * Han Huang View author publications You can also search for this author inPubMed Google Scholar * Zheng Jiang View author publications

You can also search for this author inPubMed Google Scholar * Fei Song View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS J.P.H., H.B.W. and

K.C.S. conducted STM measurements and data analysis. J.B.H. performed DFT calculations. H.Z. and C.Q.H. prepared the clean Ag surface and molecular deposition. L.X. joined STM measurements

and DFT calculations. Q.W.T. and H.H. helped preparing the Bi–Ag(111) sample. Z.J. and F.S. supervised the project. F.S. wrote the manuscript. CORRESPONDING AUTHOR Correspondence to Fei

Song. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. ADDITIONAL INFORMATION PUBLISHER'S NOTE Springer Nature remains neutral with regard to

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coupling of Br2Py by a semimetal surface. _Sci Rep_ 11, 3414 (2021). https://doi.org/10.1038/s41598-021-82973-z Download citation * Received: 23 October 2020 * Accepted: 27 January 2021 *

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