Dehalogenation and coupling of a polycyclic hydrocarbon on an atomically thin insulator.

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 and density functional theory to reveal a reaction site anisotropy, induced by the registry mismatch between the precursor and the nanostructured h-BN monolayer.

Site-selective adsorption of phthalocyanine on h-BN/Rh(111) nanomesh.

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.

Magnetization states of all-oxide spin valves controlled by charge-orbital ordering of coupled ferromagnets.

Charge-orbital ordering is commonly present in complex transition metal oxides and offers interesting opportunities for novel electronic devices. In this work, we demonstrate for the first time that the magnetization states of the spin valve can be directly manipulated by charge-orbital ordering. We investigate the interlayer exchange coupling (IEC) between two epitaxial magnetite layers separated by a nonmagnetic epitaxial MgO dielectric. We find that the state of the charge-orbital ordering in magnetite defines the strength, and even the sign of the IEC. First-principles calculations further show that the charge-orbital ordering modifies the spin polarized electronic states at the Fe(3)O(4)/MgO interfaces and results in a sufficiently large phase shift of wave function which are responsible for the observed IEC sign change across Verwey temperature. Our findings may open new interesting avenues for the electric field control of the magnetization states of spin valves via charge-orbital ordering driven IEC sign change.

Correlation between charge-transfer and rotation of C60 on WO2/W(110).

Understanding molecular switching between different charge states is crucial to further progress in molecule-based nano-electronic devices. Herein we have employed scanning tunnelling microscopy to visualize different charge states of a single C60 molecule within a molecular layer grown on the WO2/W(110) surface. The results obtained demonstrate that individual C60 molecules within the layer switch between neutral and negatively charged states in the temperature range of 220-260 K over the time scale of the experiment. The charging of the C60 causes changes in the local density of electron states and consequently a variation in tunnelling current. Using density functional theory calculations, it was found that the charged state corresponds to the negatively charged C60(-), which has accepted an electron. The switching of the molecule into the charged state is triggered continuously by tunnelling electrons when the STM tip is static above an individual C60 molecule with a bias applied. Molecular movement accompanies the molecule's switching between these states.