Imaging Bond Formation Between a Gold Atom and Pentacene on an Insulating Surface

Repp, Jascha; Meyer, Gerhard; Paavilainen, Sami; Olsson, Fredrik; Persson, Mats

doi:10.1126/science.1126073

Cited by 310 publications

(315 citation statements)

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“…The reason is that the locally varying surface potential can lead to an asymmetric shape of the frontier orbitals whose influence on the STM becomes important when scanning at high biases on insulating substrates. [32][33][34] Page 18 of 29 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…”

Section: Oligomer Formation By Covalent Couplingmentioning

confidence: 99%

“…The rather homogenous structure of these dielectric spacers is of manifold advantage to studying individual molecules. [32][33][34] However, the adsorption energy landscape for molecular species usually shows only subtle corrugation and already at low coverage (well below a closed monolayer) immediate 2-dimensional domain formation is observed, with molecular close-packing or even aggregation into 3-dimensional structures similar to single crystal insulators. 35,36 Page 5 of 29 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 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...…”

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confidence: 99%

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Dehalogenation and Coupling of a Polycyclic Hydrocarbon on an Atomically Thin Insulator

et al. 2014

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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...

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Section: Oligomer Formation By Covalent Couplingmentioning

confidence: 99%

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confidence: 99%

Dehalogenation and Coupling of a Polycyclic Hydrocarbon on an Atomically Thin Insulator

et al. 2014

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“…T he atomic-scale details of the contacts in molecular electronics are of crucial importance for the electrical characteristics of the device [1][2][3] . The contacts are typically realized through specific chemistries by using terminal functional groups, for example, thiols for bonding to gold 4,5 .…”

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Suppression of electron–vibron coupling in graphene nanoribbons contacted via a single atom

et al. 2013

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Graphene nanostructures, where quantum confinement opens an energy gap in the band structure, hold promise for future electronic devices. To realize the full potential of these materials, atomic-scale control over the contacts to graphene and the graphene nanostructure forming the active part of the device is required. The contacts should have a high transmission and yet not modify the electronic properties of the active region significantly to maintain the potentially exciting physics offered by the nanoscale honeycomb lattice. Here we show how contacting an atomically well-defined graphene nanoribbon to a metallic lead by a chemical bond via only one atom significantly influences the charge transport through the graphene nanoribbon but does not affect its electronic structure. Specifically, we find that creating well-defined contacts can suppress inelastic transport channels.

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“…Using elastic electron scattering, total charge densities could be measured on the nanometer scale [1,2]. On the surface, molecular orbitals could be resolved using STM [3]. But the direct mapping of individual electronic states in real space in the bulk phase -the key to materials design -has been elusive so far.…”

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confidence: 99%

Mapping Electronic Orbitals in Real Space

Löffler

2015

Microsc Microanal

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Electronic states are the key to most material properties including mechanical stability, chemical bonding, electrical conductivity, magnetism and optical properties. Because of their paramount importance across many fields, their direct mapping has attracted much attention in recent years. Using elastic electron scattering, total charge densities could be measured on the nanometer scale [1,2]. On the surface, molecular orbitals could be resolved using STM [3]. But the direct mapping of individual electronic states in real space in the bulk phase -the key to materials design -has been elusive so far.In this work, an overview is given over recent developments of mapping individual, specific electronic orbitals using transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). In TEM, it is possible to focus the probe beam to sub-Ångström spatial resolution using a state-of-the-art aberration corrected instrument. By sending a focused electron probe through the sample, energy and momentum can be exchanged between the probe electrons and the sample electrons, giving rise to a unique energy and momentum distribution of the probe beam after the sample which can be measured. By selecting an appropriate energy range using a slit aperture, specific transitions to individual states in the sample can be selected [4], and by scanning the probe beam over the sample, information about the probability distribution of those states in real space can be deduced. Fig. 1 shows an example of an orbital map of the e g contributions to Rutile.To interpret the experimental data, a thorough understanding of the image formation mechanism and extensive computer simulations are indispensable. In the particular case of combining TEM and EELS, both elastic and inelastic scattering effects of the probe beam inside the specimen need to be considered [5]. The elastic scattering effects are usually taken into account using either the multislice approach or the Bloch wave approach. For modelling the inelastic scattering, a very versatile tool is the mixed dynamic form factor (MDFF) in the density matrix framework. Only recently, a novel approach to diagonalize the MDFF was developed [6]. It not only allows to combine realistic predictions of the electronic orbitals in the material (e.g., from density functional theory calculations) with the inelastic scattering calculation with reasonable computational effort, but also provides physical insight into the underlying scattering processes. One crucial result of this theoretical and numerical treatment is that the point-group symmetry of the atom under investigation plays a decisive role in the shape of the resulting maps. Only if the symmetry is low enough (as is the case in Rutile, but also near defects, interfaces, etc.), a bonding direction can be imaged.By combining simulations and experiments, it is thus possible to map orbital information in the bulk in real space using state-of-the-art TEMs. This will pave the way for completely new possibilities and materials design, ...

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Imaging Bond Formation Between a Gold Atom and Pentacene on an Insulating Surface

Cited by 310 publications

References 16 publications

Dehalogenation and Coupling of a Polycyclic Hydrocarbon on an Atomically Thin Insulator

Dehalogenation and Coupling of a Polycyclic Hydrocarbon on an Atomically Thin Insulator

Suppression of electron–vibron coupling in graphene nanoribbons contacted via a single atom

Mapping Electronic Orbitals in Real Space

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