Experiment and computer simulations were conducted in order to study the adsorption of the phthalocyanine molecules H2Pc and CuPc on the h-BN/Rh(111) nanomesh. We combine STM investigations with the exploration of the potential energy surface as resulting from density functional theory calculations. Both approaches indicate a pronounced adsorption selectivity in the so called pore regions of the h-BN nanomesh, whereas the adsorption energy landscape in the pore turns out to be very shallow. This is seen by the inability to image the molecule stably at 77 K by scanning tunneling microscopy. Understanding the nature of the binding by rationalizing the site-selectivity and the mobility of the molecules is quite a challenge for both experiment and theory. In particular, we observe that the choice of the functional in the DFT description is crucial to be able to discriminate among adsorption sites that are very close in energy and to resolve low energy barriers. Our study reveals how the shape of the corrugated h-BN layer is the dominant factor that determines the subtle features of the potential energy surface for the adsorption of phthalocyanine.

We report on scanning tunneling microscopy (STM) studies performed with single crystalline W[001] tips on a graphite(0001) surface. Results of distance-dependent STM experiments with sub-ångström lateral resolution and density functional theory electronic structure calculations show how to controllably select one of the tip electron orbitals for highresolution STM imaging. This is confirmed by experimental images reproducing the shape of the 5dxz,yz and 5d x 2 −y 2 tungsten atomic orbitals. The presented data demonstrate that the application of oriented single crystalline probes can provide further control of spatial resolution and expand the capabilities of STM.

Catalytic activity is of pivotal relevance in enabling efficient and selective synthesis processes.Recently, covalent coupling reactions catalyzed by solid metal surfaces opened the rapidly evolving field of on-surface chemical synthesis. Tailored molecular precursors in conjunction with the catalytic activity of the metal substrate allow the synthesis of novel, technologically highly relevant materials such as atomically precise graphene nanoribbons. However, the reaction path on the metal substrate remains unclear in most cases and the intriguing question is how a specific atomic configuration between reactant and catalyst controls the reaction processes. In this study, we cover the metal substrate with a monolayer of hexagonal boron nitride (h-BN), reducing the reactivity of the metal, and gain unique access to atomistic details during the activation of a polyphenylene precursor by sequential dehalogenation and the subsequent coupling to extended oligomers. We use scanning tunneling microscopy (STM) and density functional theory (DFT) to reveal a reaction site anisotropy, induced by the registry mismatch between the precursor and the nano-structured h-BN monolayer. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 An atomically thin layer of insulating h-BN is a structurally analogous counterpart for graphene -a single layer of sp 2 -hybridised carbon atoms 1 -matching the graphene lattice almost perfectly with a small mismatch of approx. 2%. Currently, the fabrication of two-dimensional materials follows two main approaches: i) the bottom-up synthesis by substrate supported chemical vapor deposition (CVD) with suitable precursors and ii) the top-down approach by exfoliation. The assembly of graphene/h-BN heterostructures, leading to novel devices or devices with enhanced performance, usually relies on elaborate, sequential transfer processes of the produced layers. 2 The main obstacles are possible misalignment, introduction of defects and contaminations resulting from transferring layers that are just one atom thick. Only recently, the direct CVD growth of graphene on h-BN was demonstrated, offering superior properties. [3][4][5] However, the growth conditions are harsh (long exposure time, high temperatures, several cycles, etc.). Metal substrates are favored, because of their high catalytic activity, 6 but they have the disadvantage that they strongly alter the properties of the grown layers, which therefore cannot be directly used for electronic device fabrication.A common motif in on-surface chemical reactions is the activation of a precursor, the intermittent complex formed between precursor and substrate, and finally the coupling reaction. 7A long-standing question is the impact of the specific atomic configuration between substrate and reactant on the catalytic efficiency and how does the specific atomic arrangement chan...