Probing the selectivity of a nanostructured surface by xenon adsorption

Widmer, Roland; Passerone, Daniele; Mattle, Thomas; Sachdev, Hermann; Gröning, Oliver

doi:10.1039/b9nr00431a

Cited by 25 publications

(32 citation statements)

References 23 publications

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“…We note that on h-BN/Rh(111)-(12 × 12) the Ti atoms are located between the moiré depressions and the connected protruding areas, also referred to as wires [8]. We observe that the adsorbates are immobile at the imaging temperature of 4.7 K on both samples; for h-BN/Rh this is in accordance with former observations of individual molecules [8,12,14,15], rare gas [16,17], and transition metal adatoms [18].…”

Section: Resultssupporting

confidence: 78%

Quantifying residual hydrogen adsorption in low-temperature STMs

2013

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We report on low-temperature scanning tunneling microscopy observations demonstrating that individual Ti atoms on hexagonal boron nitride dissociate and adsorb hydrogen without measurable reaction barrier. The clean and hydrogenated states of the adatoms are clearly discerned by their apparent height and their differential conductance revealing the Kondo effect upon hydrogenation. Measurements at 50 K and 5 × 10 −11 mbar indicate a sizable hydrogenation within only 1 h originating from the residual gas pressure, whereas measurements at 4.7 K can be carried out for days without H 2 contamination problems. However, heating up a low-T STM to operate it at variable temperature results in very sudden hydrogenation at around 17 K that correlates with a sharp peak in the total chamber pressure. From a quantitative analysis we derive the desorption energies of H 2 on the cryostat walls. We find evidence for hydrogen contamination also during Ti evaporation and propose a strategy on how to dose transition metal atoms in the cleanliest fashion. The present contribution raises awareness of hydrogenation under seemingly ideal ultra-high vacuum conditions, it quantifies the H 2 uptake by isolated transition metal atoms and its thermal desorption from the gold plated cryostat walls.

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Section: Resultssupporting

confidence: 78%

Quantifying residual hydrogen adsorption in low-temperature STMs

2013

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“…On Rh(111) the h-BN forms a highly corrugated "nanomesh" consisting of regions with strong bonding, dents (sometimes referred to as pores), separated by suspended wire regions, where the h-BN-Rh(111) interaction is weaker. 18,23,26,[29][30][31] Consequently, the structure of the corrugated h-BN is a superposition of the 0.25 nm BN lattice and the network of dents with a lattice constant of 3.2 nm.As we will show in the following, deposition of I 6 -CHP on the corrugated h-BN leads to a distinct adsorption geometry imposing a non-equivalency on the six iodine sites of the molecule, which is not intrinsic to the free I 6 -CHP. The adsorption geometry, sequential dehalogenation and the subsequent coupling of I x -CHP species are analyzed by low-temperature scanning tunneling microscopy (LT-STM at 5.5 K) and density functional theory (DFT).…”

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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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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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“…However, the difference in appearance to the STM is much more striking in the present case. We note that 12 Xe atoms on h-BN=Rhð111Þ À ð12 Â 12Þ have been shown to form rings with similar appearance [12] and, therefore, wish to stress that the present ring state is attributed to a single TM adatom only.…”

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“…The inhomogeneous binding involves a splitting of the sp 2 -derived and bands by 1 eV [1,4,8] and nonuniform charge transfer from h-BN to Rh [7], leading to a spatial modulation of the work function [9][10][11] and to large lateral electric dipoles [10]. These dipoles exert electrostatic forces on polarizable adsorbates enabling the trapping of naphthalocyanine [4], of Cu-phthalocyanine [9], and of water [7,11] molecules, as well as of rare gas atoms [9,12]. Concerning metals, large Co clusters show preferred adsorption in the bound areas [13], but single metal atoms appear less well steered as they are predominately resting at the borders of the bound areas.…”

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Ring State for Single Transition Metal Atoms on Boron Nitride on Rh(111)

2012

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The low-temperature adsorption of isolated transition metal adatoms (Mn, Co, and Fe) onto hexagonal boron nitride monolayers on Rh(111) creates a bistable adsorption complex. The first state considerably weakens the hexagonal boron nitride-(h-BN-) substrate bond for 60 BN unit cells, leading to a highly symmetric ring in STM images, while the second state is imaged as a conventional adatom and leaves the BN-substrate interaction intact. We demonstrate reversible switching between the two states and, thus, controlled pinning and unpinning of the h-BN layer from the metal substrate. IðzÞ and d lnI=dz curves are used to reveal the BN deformation in the ring state. Monolayers of sp 2 -hybridized honeycomb lattices, such as graphene and hexagonal boron nitride (h-BN), grown on close-packed single crystal surfaces are fascinating substrates, in particular in their role as novel hosts for adsorbed atoms, molecules, or nanostructures, but also due to their intrinsic electronic and structural properties. A prominent example is the moiré pattern formed by h-BN=Rhð111Þ À ð12 Â 12Þ [1-6]. This system is characterized by highly inhomogeneous substrate binding of the different stacking areas of the moiré unit cell. The regions where N atoms are on top of Rh atoms are strongly bound due to the hybridization of the N lone pair orbital with the Rh d-states [6,7]. No such chemical bond is formed where N atoms are situated on the threefold Rh hollow sites. These stacking areas are, thus, only weakly bound by van der Waals interactions [7]. Since there is only one type of on-top site and two types of hollow sites, the ratio of both stacking areas is 1:2. This gives rise to strongly bound equidistant circular regions surrounded by a connected and weakly bound area, also called wires [1].The transition between the differently bound parts of the layer occurs on a lateral scale of only two atomic rows [7]. Therefore, the structure essentially consists of two levels, disconnected hexagonal bound areas close to the Rh, surrounded by a connected honeycomb area lifted off the substrate by 1.0 Å [7]. This abrupt transition is untypical for moiré patterns, however, since the layer doesn't exhibit holes [3], we refer to it as a moiré pattern and not as a nanomesh. The inhomogeneous binding involves a splitting of the sp 2 -derived and bands by 1 eV [1,4,8] and nonuniform charge transfer from h-BN to Rh [7], leading to a spatial modulation of the work function [9][10][11] and to large lateral electric dipoles [10]. These dipoles exert electrostatic forces on polarizable adsorbates enabling the trapping of naphthalocyanine [4], of Cu-phthalocyanine [9], and of water [7,11] molecules, as well as of rare gas atoms [9,12]. Concerning metals, large Co clusters show preferred adsorption in the bound areas [13], but single metal atoms appear less well steered as they are predominately resting at the borders of the bound areas. Apart from a theoretical study for Au atoms revealing large binding energy differences [14], the interaction of metal atoms w...

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Probing the selectivity of a nanostructured surface by xenon adsorption

Cited by 25 publications

References 23 publications

Quantifying residual hydrogen adsorption in low-temperature STMs

Quantifying residual hydrogen adsorption in low-temperature STMs

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

Ring State for Single Transition Metal Atoms on Boron Nitride on Rh(111)

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