596 CHIMIA 2014, 68, Nr. 9 Computational Chemistry in switzerland

doi:10.2533/chimia.2014.596 Chimia 68 (2014) 596–601 © Schweizerische Chemische Gesellschaft Chemical Reactions on Metal-supported Hexagonal Nitride Investigated with Density Functional Theory

Pauline Bacle, Ari Paavo Seitsonen, Marcella Iannuzzi, and Jürg Hutter*

Abstract: , in order to become ultimately efficient, requires achieving the construction of elemental structures at the atomistic precision. One way toward this goal is using templated surfaces as support for directed synthesis. The nanomesh, a single-atom thick layer of hexagonal on Rh(111) [Corso et al., Science 2004, 303, 217], has appeared as one candidate that provides a periodically corrugated structure on the nanometre scale. We present density functional theory studies where we investigate various properties of the nanomesh, ranging from intrinsic defects to covalent functionalisation with hydroxyl radicals. Further we study selective dehalogenation of an organic (I6-CHP) on the nanomesh. This molecule adsorbs at particular sites of the template and has been activated for C–C coupling in recent experiments via dissociation of its halogen ligands. In all cases we find explicit templating effects, either in full agreement with experimental studies or predicting novel phenomena. The studies are evidence for the predictive power of modern electronic structure simulations and the insight that can be gained when used together with experiments on complex chemical structures. Keywords: Density functional theory calculations · Functionalisation · Nanomesh · Surfaces · Templating

1. Introduction single-layer h-BN structures have been is weak, that form the connected ‘wire’ grown on several transition metals, such network. The corrugation pattern, shown in Hexagonal boron nitride, h-BN, is as Ni(111),[6] Cu(111),[6,7] Ru(0001),[8] Fig. 1, corresponds to a modulation of the isoelectronic to graphite and the two sub- Rh(111),[5,9] Pd(111),[10] Ag(111),[11] and B–N bond length and, thereby of the elec- stances share many structural properties. Pt(111).[12] Using similar recipes, also tronic properties of the monolayer. Such a Of special interest are the single layer i.e. structures on most Pt-group variation in bond lengths contributes to the atom-thin structures that can be built from transition metal surfaces have been obtain- spatial modulation of the electrostatic po- both materials. This kind of templated ed.[8,13] The resulting long-range super- tential above the monolayer that is respon- layer is desirable in the field of nano-de- structure depends on the mismatch in the sible for trapping .[7,14–16] vices, where the precise positioning and unit cell length of the free-standing mon- The h-BN/Rh(111) nanomesh is a very the control of individual molecules are of olayer and the metal surface. In h-BN/ stable structure that withstands tempera- importance. h-BN layers that build tem- Rh(111) a lattice mismatch of −7.0% leads turesof1000Kandcanbeexposedtoliquids plating surfaces are a promising starting to a strongly corrugated structure with a without losing its properties. Reversibility point to obtain defined arrangements on a periodicity of 3.22 nm, the so-called na- of the modification of the structure using large scale. Such layers have been reported nomesh.[9] The highly regular hexagonal atomic hydrogen has also been demonstrat- to show variations in interaction strength arrangement corresponds to a coincidence ed.[17] The spatial variation of the electron- on a nanometre scale and, due to the large lattice of 13×13 h-BN on 12×12 Rh unit ic structure can be used for directed func- band gap of h-BN, are able to provide an cells. The nanomesh is characterised by tionalisation or to induce specific chemi- efficient electronic decoupling from the ‘pores’ of about 2 nm diameter that strong- cal reactions by exploiting the template supporting metal surface.[1–4] ly interact with the metal and elevated re- provided by the nanomesh. The selective Monolayers of h-BN have been grown gions, where the interaction with the metal adsorption of molecules on the nanomesh on transition metal surfaces by chemical vapour decomposition of small precursor molecules, e.g. .[5] On hot me- Fig. 1. Structure of the tallic surfaces a spontaneous formation nanomesh of h-BN/ of a single uniform epitaxial monolayer Rh(111). The colour is observed. Recently, well-characterised code of the h-BN monolayer reflects the height of the B and N atoms with respect to the substrate. The blue areas correspond to the pore, the red to *Correspondence: Prof. J. Hutter the wire regions, and Institut für Chemie the atoms coloured Universität Zürich with yellow and green Winterthurerstrasse 190, CH-8057 Zürich Tel.: +41 44 63 54 491 form the so-called E-mail [email protected] ‘rim’. Computational Chemistry in switzerland CHIMIA 2014, 68, Nr. 9 597

has been already studied for a few organ- conditions are applied in all calculations. ic molecules[9,16,18] and in great detail for In the slab models, interactions with pe- water.[19–22] riodic images in the direction perpendic- In this work, we present three signif- ular to the exposed surface are avoided by icant examples of the effects of corruga- adding about 20 Å of vacuum space above tion and of mediated interaction with the the slab. The size of the unit cell used in metal on chemical processes leading to the calculations of the full nanomesh is the functionalisation of the nanomesh. The 32.1195 Å in the lateral directions. This first example is the adsorption of a high- corresponds to a 12×12, four-layer rhodi- ly symmetric molecule (hexa-iodo-cyclo- um slab with a cell parameter of 3.785 Å hexa-phenylene), which undergoes a spe- and an adsorbed 13×13 h-BN monolayer. cific pattern in dehalogenation that can on- To simulate the dissociative reaction ly be understood in connection with the un- of water on the nanomesh, instead, a derlying template. The second example is 6×6 Rh(111) slab of seven layers is used related to the formation and aggregation of as substrate. In these models, a one to vacancy defects on the monolayer that can one commensurate structure is obtained become active centres for further site se- by stretching the h-BN overlayer to the lective processes. The third example is the Rh(111) lattice constant. The h-BN layer activation of possible reaction paths for the can be arranged with on top of a Fig. 2. The molecular structure of dissociative coupling of water molecules Rh atom and B on the next hollow site, or 5,5',5'',5''',5'''',5'''''-hexaiodo-cyclohexa- m-phenylene (l6-CHP). The geometry is non- to the nanomesh, where we demonstrate with nitrogen occupying a hollow site. The planar, with alternating buckling of the increased stabilisation of the products due registries with N atop are the most stable iodo-phenylene groups. to the presence of the metal. structures and serve as models for the pore environment, whereas when N occupies a hollow site, we have a model for the wire We find that CHP adsorbs in the pore 2. Computational Details environment. A complete assessment of with a binding energy of 88 kcal/mol. this computational setup can be found in Considering the size of the molecule and All calculations were performed us- ref. [34]. that basically all the atoms are located al- ing Kohn-Sham density functional theory most planarly above the h-BN layer, the (DFT) within the Gaussian plane wave interaction is principally of van der Waals (GPW) formalism as implemented in the 3. Templating: Formation of type. What is remarkable in the adsorption Quickstep module of the CP2K program Covalent Networks on the geometry is that three out of the six iodine package.[23,24] Dual-space pseudopoten- Nanomesh atoms lie clearly higher, by 0.33, 0.95 and tials[25–27] are used to describe the inter- 1.03 Å than the centre of the molecule, or action of valence electrons with atomic A possible path to building function- the carbon atoms, and the three other at- cores. The pseudopotentials for boron and alised graphene-containing structures in a oms are lying close to the plane formed by nitrogen assume three and five valence controlled way is the bottom-up synthesis the phenyl rings. This pattern is alternating electrons, respectively. The atomic cores from small molecules toward patterned between the raised and planar iodines. We of Rh atoms are described by a large-core assemblies. Thereby covalent carbon–car- denote the in-plane atoms as ‘A’ and the pseudopotential with nine valence elec- bon bonds are created between the molec- lifted ones as ‘B’ (Fig. 3). trons. Single- (for Rh), double- (B, N, ular units. Two recent examples of such The dissociation of an iodine atom C and I) and triple- (H and O) zeta basis Ullmann-like coupling reactions on metal from the molecule can be initiated either sets including polarised function are em- surfaces involve the dehalogenation of the with a voltage pulse from the tip of a scan- ployed to describe the valence electrons. initial molecules to form graphene nano- ning tunnelling microscope or by heating The plane wave (PW) energy cutoff for the ribbons[35] and polymeric networks on the the system. The dissociation can follow expansion of the density is set to 500 Ry. coinage metals.[36] two different kind of pathways, depending The Brillouin zone is sampled only at the Motivated by recent experi- on whether the iodine is detached from an Γ point. Exchange and correlation (XC) ments on the adsorption of CHP A or B site. We start two separate calcula- terms are evaluated with the PBE or revised (5,5',5'',5''',5'''',5'''''-hexaiodo-cyclo- tions, one for dissociation from an A site PBE[28–30] generalised gradient approxi- hexa-m-phenylene, Fig. 2) molecules on and another one from B. The former is ob- mation (GGA) XC functional. Long-range the nanomesh, we have conducted DFT tained placing the dissociated iodine atom dispersion interactions are added using the calculations in order to better understand above a boron atom on the nanomesh in the DFT-D3 formalism.[31] The XC function- the experimental observations.[37] Here we pore, and upon the relaxation the iodine at- al and its derivative are calculated on the discuss further aspects of the DFT results. om basically remained laterally at this site. same uniform density grid that is used for the Hartree energy and is defined by the choice of the PW energy cutoff. In order to a) b) c) improve the accuracy in the evaluation of the XC terms a nearest neighbour smooth- ing procedure is used. More details about these techniques are illustrated in ref. [32]. The Fermi-Dirac smearing of occupation numbers with a 300 K electronic temper- ature is used in all calculations. Broyden density mixing[33] is used to facilitate smooth convergence within a reasonable Fig. 3. a) Adsorbed CHP in the pore of the nanomesh. Dissociated structure after extraction of an number of iterations. Periodic boundary iodine at the b) A and c) B site; see text for definitions. 598 CHIMIA 2014, 68, Nr. 9 Computational Chemistry in switzerland

From this configuration, a nudged-elastic BorNsingle vacancy BN vacancy pair band (NEB) simulation is started where the c) d) a) 1BN 1BN final image is the dissociated structure in 1B Fig. 3c. On the other hand, to simulate the 1N same dissociation reaction on a B site, the 2B 3N 2N 2BN 3BN dissociated iodine atom of the final con- 3B figuration is positioned above a boron at- 4BN 4B 4N om somewhat higher on the wire region of 5N 5BN the nanomesh because there is not enough 6BN b) 6N space in the pore. The iodine then relaxes 3BN 150 laterally to a different position, returning BorNsingle vacancy 6N 4B relatively close to the rest of the molecule, 5B 100 1N 2N but without reforming a . 3N 5N 2B 4N 1B The nanomesh also responds to the disso- 50 3B ciation of iodine atoms by forming a bond [kcal/mol] with the rest of the molecule via a boron BN vacancy pair 82.63.58 2BN site. This boron atom is lifted from the rest 250 1BN

Energy 81.63.54 6N+5B 6BN of the pore, and the phenyl group, from 4N+4B 3BN

80.63.5 200 0 5 10 which the iodine comes, bends strongly 4N+4B

4BN downwards. Formation 3N+3B 150 2N+2B During imaging in scanning tunnel- 1N+1B 5BN ling microscopy (STM) the limit of tip-in- 6BN 100 1BN duced dehalogenation is reached if the 2BN 3BN 5,5'',5''''-I3-CHP is formed, i.e. a complete 0510 15 20 dissociation at B sites occurs. This is also Distance from pore center [Å] the most often observed molecule when thermal dehalogenation is performed. The Fig. 4. a) Top view of a portion of the nanomesh unit cell where the B atoms (larger spheres) and selectivity is surprising as there is no dif- N atoms (smaller spheres) are coloured according to their height above the Rh surface (same col- our code as in Fig. 1). The labelled white spheres indicate the selected sites of the vacancies. b) ference in stability calculated for single, Formation energy of vacancies as a function of the distance from the pore centre. The labels cor- isolated molecules for any order of dehal- respond to the sites indicated in panel a). In the bottom graph, in red the formation energies of the ogenation. However, a series of calcula- vacancy pairs, in black the sum of two single vacancy formation energies, computed individually. tions of CHP molecules on the nanomesh The inset shows a zoom-in on points 1, 2, and 3. c), d) Top view of three optimised structures with clearly establishes a preferred order of de- one vacancy pair. c) Global view of the nanomesh unit shell with same colour code as in Fig. 1. halogenations, leading to the final I3-CHP d) Ball-and-stick zoom-ins that show the local reconstruction around the defect (N are drawn as found in experiment. The key point is the blue, B as orange, and Rh as silver spheres). anchoring of the I5-CHP after the first dehalogenation on a boron atom. Further gen atoms, leaving vacancy defects within respectively, and E and E are the total nm dnm strong interactions of radical type carbon the h-BN layer, which are visible at the rim energies of pristine and defective nano- atoms with boron atoms after the second and at the wire of the nanomesh by STM. mesh. The reference chemical potentials and third step of multiple dehalogenations Interestingly, an annealing of the defec- of B and N are determined under the con- are then only possible in B sites. tive system leads to self-healing process- straint µ = µ + µ , where µ is the ener- BN B N BN We also investigate the energetics of es, where the defects seem to gather, first gy of a BN pair computed in free standing the isolated iodine atoms. These are ob- forming larger defects and then inducing h-BN, and µ is obtained from gas phase N tained upon the dissociation from the mol- reconstruction of the monolayer (forma- N .[40] 2 ecule and are present on the surface until tion of holes and self-healing). Formation, In panel a) of Fig. 4 the different va- two of them meet to form I and then de- stability and mobility of B and N vacancies cancy sites are labelled. We distinguish 2 sorb. The adsorption energy of one iodine on the nanomesh are of great interest in the between sites at different distances with in the pore is 31 kcal/mol, and on the wire view of employing the defective template respect to the pore centre. For each species, only 4 kcal/mol. This again demonstrates as active substrate for further functionali- we compute vacancies at different sites: at the strong difference in reactivity between sation processes. the centre of the pore (1), at the border of the pore and wire regions. The adsorption We perform DFT calculations of single the pore (2), at the rim (3 and 4), or at the site is above a boron atom, which gets lift- and vacancy pairs at different sites within wire (5 and 6). The vacancy pairs are com- ed somewhat from the local structure of the the h-BN super-honeycomb structure. The binations of two single ones, and the labels nanomesh. results are summarised in Fig. 4. After re- from 1 to 6 also refer to a growing distance moving one B or N atom, or one BN pair, from the pore centre. All calculated vacan- we fully relax the structure and compare cies on the h-BN nanomesh have a lower 4. Formation of B and N Vacancies to the pristine nanomesh. The vacancy for- formation energy than the corresponding mation energy is obtained in terms of the defect in free-standing h-BN, which are The exposure of hexagonal boron ni- chemical potentials of the atomic species, 180 kcal/mol for B vacancy, 183 kcal/mol tride single layers to low energy ions leads µ and µ , as for the N vacancy, and 197 kcal/mol for the B N to the formation of vacancy defects that are pair. This is due to the fact that the substrate mobile at elevated temperatures. Recently, can partly compensate the dangling bonds intercalation processes of Ar and Rb, form- E = E −E + n µ + n µ , (1) that are created upon the removal of boron ing the so-called ‘nanotent’ structures, have f dnm nm vN N vB B or nitrogen from h-BN. The data points in been reported after exposure of the h-BN the top graph of panel b) are the forma- nanomesh to low energy ions.[38,39] The ion where the number of removed B and N tion energies of the single vacancies. One bombardment sputters out boron and nitro- atoms per nanomesh unit cell is n or n , can observe that the stabilisation is more vB vN Computational Chemistry in switzerland CHIMIA 2014, 68, Nr. 9 599

effective when the vacancy is located in sheets, and the structural and electronic tionalisation are shifted out of plane. As the pore or at the rim. Here, the monolay- properties of OH- and H-functionalised expected, the hybridisation of N changes er is relatively close to the Rh surface and sheets. We report the results both on the from the planar sp2 to the tetrahedral sp3 with small deformation of the h-BN lattice freestanding and the metal-supported configuration when it is protonated. the broken bonds can be at least partially monolayers and discuss the differences The relative stability of the different fi- saturated by the interaction with the metal. between them. nal structures is determined by the binding Another interesting aspect is that, in most We calculate the binding energies up- energies computed from of the cases, the N vacancies are less stable on the functionalisation of a 6×6 periodic than the B vacancies. This is understood to h-BN layer with H , a hydroxyl group or 2 be due to the larger loss in binding energy a hydroxyl group together with a hydro- E = E − ( E + E ), (2) for N, since the lock-in effect responsible gen atom at the nearest-neighbour site. In bind func hBN isol for the formation of the nanomesh is main- the initial configuration, the reactants, i.e. ly due to the N-Rh interaction. h-BN layer and the molecular species, are where E is the energy of the function- func The vacancy pairs are more stable than a few Å apart. The optimal geometry is ob- alised h-BN sheet, E the energy of the hBN two single B and N vacancies because up- tained after the full relaxation of the system. bare h-BN sheet and E the sum of the on association the number of broken B–N We use H -hBN to designate the 6×6 h-BN isol 2 energies of different species that can be in- bonds is reduced. Also in this case, we sheet with one H atom on top of N and an- volved in the functionalisation. Two exam- notice that the association is particularly other one on top of the nearest-neighbour B, ples of how we compute the binding ener- stable in the pore and close to the rim, sug- OH-hBN for one hydroxyl group on top of gies are given for the case functionalisation gesting that once formed, vacancies would a B and a hydrogen atom on top of the near- by H O and by O +H remain trapped in the pore. The structure est-neighbour N, and OH-hBN• for an OH 2 2 2 of three of the vacancy pair structures, i.e. functionalising group only. The resulting 1 , 3 and 6 , are reported in panels optimised structures are displayed in Fig. 5. BN BN BN E = E − ( E + E ) (3) c) and d) of Fig. 4. In c) the entire nano- Some structural parameters in the dif- bind OH-hBN hBN H2O mesh unit cell and in d) the local structure ferent optimised geometries are reported in around the defect are shown. The 1 is in Table 1. In all cases, we observe the cleav- BN the middle of the pore and causes only a age of the in-plane B–N bond together with E = E − bind OH-hBN (4) local relaxation of the surrounding bond the local distortion of the planar lattice, as ( E + 1/2E + E ) lengths, while the dangling B atoms move the B and N atoms involved in the func- hBN O2 H2 slightly towards the substrate. The vacan- cy pair close to the rim, labelled 3 , turns BN out to be the most stable. All four dangling atoms interact strongly with one Rh atom that is displaced upward by more than 1 Å. The vacancy pair in the wire region causes a relatively large reconstruction, involving more atoms and a significant change in the shape of the rim. An eight-membered ring is formed, including one B–B and one N–N bond. Similar larger defects in the wire region have been observed in STM after ion sputtering.[41]

5. Functionalisation

The covalent chemistry of isolated h-BN nanosheets or the nanomesh has become a field of strong interest. Indeed, functionalising h-BN is highly attractive in order to make it suitable for use in an expanded range of applications. For ex- Fig. 5. Optimised geometry after the functionalisation of free-standing h-BN with H (left), OH• 2 ample, functionalisation could change (centre) and H O (right) (O atoms are drawn as red, H as white, B as orange, and N as blue 2 its solubility in common solvents or spheres). tailor its electronic and magnetic prop- erties. In many reports, non-covalent functionalisation of h-BN has been de- Table 1. Structural parameters of functionalised h-BN sheets. d(B–N) is the distance between the B and N atoms involved in the functionalisation; ∆z the vertical shifts of the atoms in the h-BN [4] B,N scribed. In other studies, edge functional- layer involved in the functionalisation; θ the tetrahedral angle formed by the B and N atom with B,N isation has been achieved, even if it usually its nearest-neighbour atoms. All distances are given in Å and angles in degrees. leadstothedestructionoftheextendedh-BN sheets with formation of nanoscale frag- Structure d(B–N) ∆z ∆z θ θ ments.[42] More recently, covalent B N B N functionalisation by peroxide-induced hy- Bare hBN 1.45 0000 droxyl groups has been achieved.[43] H-hBN 1.66 0.93 0.75 34 18 2 We performed DFT simulations to in- OH-hBN• 1.53 0.62 0.16 30 vestigate the reaction processes occurring upon chemical functionalisation of h-BN OH-hBN 1.65 0.87 0.66 32 17 600 CHIMIA 2014, 68, Nr. 9 Computational Chemistry in switzerland

h-BN, are endothermic and activated, with the corresponding activation barriers ∆E H -hBN b 2 of 34 and 25 kcal/mol. The transition state H -hBN/Rh(111) 100 2 OH-hBN (TS) configuration at the maximum of the OH-hBN/Rh(111) energy profile, together with the IS and FS OH-hBN* configurations of the supported case are OH-hBN*/Rh(111) shown in the d), c) and e) panels of Fig. 7 0 respectively. IS, TS and FS configurations on the freestanding h-BN are very similar.

(kcal/mol) At the TS the O-H bond is slightly elon- gated, but the O atom and H atoms are al- -100 ready close to the B and N binding sites, Energy respectively. The endothermicity in the reaction energy, ∆E , is much lower on react the supported h-BN, thus making the dis- -200 sociation reaction, and alongside the func- tionalisation, more accessible there. The energetics here thus follows qualitatively H2 O+H O+H2 O2+H2 OH OH+H OH+H2 O2H2 O2H2+H2 H2O (+O)* (+H)* the empirical Bronsted-Evans-Polanyi (BEP) principle about the height of the Fig. 6. Binding energies upon three kinds of functionalisation on bare h-BN and h-BN/Rh(111). activation barriers scaling (linearly) with For each kind of functionalisation several sets of isolated species (labelled on the horizontal axis) the corresponding reaction energies. The have been considered as the reference and the corresponding binding energy is calculated as probability of observing functionalisation described in the text. with water at the free-standing h-BN is fur- ther reduced due to the low barrier, ∆E ', b for back reaction of water re-association Negative values of E indicate a ther- These simulations yield the minimum and subsequent desorption. bind modynamically stable functionalisation. energy path (MEP) of the reaction and an The results are gathered in Fig. 6, where the evaluation of the activation barrier on the reference isolated species are given on the potential energy surface. The initial state 6. Summary abscissa. In most of the cases, the function- (IS) is the water molecule 2.8 Å above alisation turns out to be stable. Exceptions h-BN, with the O atom on top of a B atom, DFT-based calculations have been are the functionalisations from highly sta- one O–H bond along the B–N bond, and shown to yield a reliable description of ble species, such as H and H O. We also the other one pointing outwards. The final single layer h-BN on metal surfaces. Using 2 2 notice that the largest binding energies are state (FS) is the previously optimised OH- the same established simulation protocol, achieved starting from atomic O and atom- hBN structure. The complete band is de- we have investigated different types of ic H in both OH-hBN and OH-hBN•, and scribed by 24 replicas, initially obtained by chemical reactions involving the h-BN/ the fully saturated OH-hBN structures are linear interpolation between IS and FS, and Rh(111) system, either as a template or di- in general more stable than the correspond- then optimised with the NEB procedure. rectly as a reactant. ing radical OH-hBN• systems. The resulting MEPs are displayed in Fig. In agreement with experiment, we find The same H -hBN, OH-hBN and 7. Both reactions, on bare and supported that the highly symmetric molecule CHP 2 OH-hBN• structures have been optimised with h-BN supported on Rh(111) in the (N-top,B-fcc) registry, corresponding to the pore of the nanomesh. The resulting a) b) binding energies are reported in Fig. 6 with ΔE ’ dashed lines. The interaction with the met- 30 b 30 al stabilises the functionalisation of h-BN by about 25 kcal/mol for H -hBN, 33 kcal/ 2 20 ΔE 20 b ΔE ’ b

mol for OH-hBN and 70 kcal/mol for OH- (kcal/mol) (kcal/mol) • ΔE hBN . The stabilisation is stronger in the ΔE b 10 react 10 OH-hBN• structure, because the dangling Energy Energy ΔE N atom can interact with the metal. With react reference to H and H O, the functionalisa- 0 0 2 2 tion is still thermodynamically less stable, but on the metallic substrate the difference c) d) e) is substantially reduced. In particular, the OH-hBN structure is only 3 kcal/mol less stable. We note here that the intact, molec- ular adsorption is exothermic, by 4 kcal/ mol at the free-standing h-BN and by 3 kcal/mol in the pore of the nanomesh.[21,44] We employ the climbing-image nudged elastic band (CI-NEB) approach[45] to sim- ulate the full process of H O splitting and 2 Fig. 7. The potential energy profile along MEP upon the covalent functionalisation of a) free-stand- binding to the substrate, both at the free- ing h-BN and b) the h-BN/Rh(111) nanomesh with a water molecule. c) Initial, d) transition, and e) standing monolayer and supported h-BN. final state configuration in the latter case. Computational Chemistry in switzerland CHIMIA 2014, 68, Nr. 9 601

adsorbs preferentially in the pore of the of modern electronic structure simulations [21] Y. Ding, M. Iannuzzi, J. Hutter, J. Phys. Chem. nanomesh. Further calculations on single and the insight that can be won if such C 2011, 115, 13685. [22] Y. Ding, M. Iannuzzi, J. Hutter, J. Phys.: and multiple dehalogenation of CHP re- simulations are used together with experi- Condens. Matt. 2012, 24, 445002. veal a strong interaction of radical-type ments on complex chemical structures. [23] CP2k developers’ group under the terms of the carbon atoms of CHP with boron atoms of GNU General Public Licence; see http://www. the underlying BN sheet. The anchoring Received: May 14, 2014 CP2K.org/, 2014 provided by this interaction together with [24] J. Hutter, M. Iannuzzi, F. Schiffmann, J. [1] For reviews see for example refs [2–4]. VandeVondele, Wiley Interdisc. Rev-Comput. the hexagonal pattern of the h-BN makes [2] C. Oshima, A. Nagashima, J. Phys: Condens. Mol. 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