The atomically precise control over the size, shape and structure of nanographenes (NGs) or the introduction of heteroatom dopants into their sp2‐carbon lattice confer them valuable electronic, ...optical and magnetic properties. Herein, we report on the design and synthesis of a hexabenzocoronene derivative embedded with graphitic nitrogen in its honeycomb lattice, achieved via on‐surface assisted cyclodehydrogenation on the Au(111) surface. Combined scanning tunnelling microscopy/spectroscopy and non‐contact atomic force microscopy investigations unveil the chemical and electronic structures of the obtained dicationic NG. Kelvin probe force microscopy measurements reveal a considerable variation of the local contact potential difference toward lower values with respect to the gold surface, indicative of its positive net charge. Altogether, we introduce the concept of cationic nitrogen doping of NGs on surfaces, opening new avenues for the design of novel carbon nanostructures.
A hexabenzocoronene derivative embedded with graphitic nitrogen in its honeycomb lattice is prepared by on‐surface assisted cyclodehydrogenation on the Au(111) surface. Combined scanning tunnelling microscopy/spectroscopy and non‐contact atomic force microscopy investigations unveil the chemical and electronic structures of the obtained dicationic nanographene.
The chemical processing of low‐dimensional carbon nanostructures is crucial for their integration in future devices. Here we apply a new methodology in atomically precise engineering by combining ...multistep solution synthesis of N‐doped molecular graphene nanoribbons (GNRs) with mass‐selected ultra‐high vacuum electrospray controlled ion beam deposition on surfaces and real‐space visualisation by scanning tunnelling microscopy. We demonstrate how this method yields solely a controllable amount of single, otherwise unsublimable, GNRs of 2.9 nm length on a planar Ag(111) surface. This methodology allows for further processing by employing on‐surface synthesis protocols and exploiting the reactivity of the substrate. Following multiple chemical transformations, the GNRs provide reactive building blocks to form extended, metal–organic coordination polymers.
N‐doped molecular graphene nanoribbons, deposited by electrospray controlled ion beam deposition, form extended, metal–organic coordination polymers after multiple chemical transformations employing on‐surface synthesis protocols. These transformations and the nature of the metal–organic coordination motifs are investigated by high‐resolution scanning tunnelling microscopy.
Replacement of sp2‐hybridized carbon in polycyclic aromatic hydrocarbons (PAHs) by boron affords electron‐deficient π‐scaffolds due to the vacant pz‐orbital of three‐coordinate boron with the ...potential for pronounced electronic interactions with electron‐rich metal surfaces. Using a diboraperylene diborinic acid derivative as precursor and a controlled on‐surface non‐covalent synthesis approach, we report on a self‐assembled chiral supramolecular kagome network on an Ag(111) surface stabilized by intermolecular hydrogen‐bonding interactions at low temperature. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal a flat band at ca. 0.33 eV above the Fermi level which is localized at the molecule center, in good agreement with tight‐binding model calculations of flat bands characteristic for kagome lattices.
A planar diboraperylene diborinic acid B2−Per self‐assembles into a chiral kagome supramolecular network on an Ag(111) substrate and is stabilized by hydrogen bonding between BOH subunits of adjacent molecules. The kagome supramolecular network exhibits a dispersionless flat band at ca. 0.33 eV above the Fermi level, which is observed by scanning tunneling microscopy/spectroscopy and further proved by tight‐binding model calculations.
Tuning the bandgap of nanoporous graphene is desirable for applications such as the charge transport layer in organic‐hybrid devices. The holy grail in the field is the ability to synthesize 2D ...nanoporous graphene with variable pore sizes, and hence tunable band gaps. Herein, the on‐surface synthesis of nanoporous graphene with variable bandgaps is demonstrated. Two types of nanoporous graphene are synthesized via hierarchical CC coupling, and are verified by low‐temperature scanning tunneling microscopy and non‐contact atomic force microscopy. Nanoporous graphene‐1 is non‐planar, and nanoporous graphene‐2 is a single‐atom thick planar sheet. Scanning tunneling spectroscopy measurements reveal that nanoporous graphene‐2 has a bandgap of 3.8 eV, while nanoporous graphene‐1 has a larger bandgap of 5.0 eV. Corroborated by first‐principles calculations, it is proposed that the large bandgap opening is governed by the confinement of π‐electrons induced by pore generation and the non‐planar structure. The finding shows that by introducing nanopores or a twisted structure, semi metallic graphene is converted into semiconducting nanoporous graphene‐2 or insulating wide‐bandgap nanoporous graphene‐1.
Nanopores turn semi metallic graphene into semiconducting nanoporous graphene‐2 or insulating nanoporous graphene‐1. These two nanoporous graphenes with variable structures and band gaps are synthesized via surface‐assisted reactions. Nanoporous graphene‐1 with a twisted structure shows an insulating bandgap of 5.0 eV, and nanoporous graphene‐2 has a semiconducting bandgap of 3.8 eV, opening new applications for nanoporous graphene.
1,4,5,8,9,12‐Hexaazatriphenylene (HAT) is one of the smallest polyheterocyclic aromatic building blocks for forming conjugated metal–organic frameworks (cMOFs). However, the strong inter‐molecular ...steric hindrance impedes the growth of HAT‐based cMOFs. Here we employ on‐surface synthesis to grow single‐layer two‐dimensional cMOFs of M3(HAT)2 (M=Ni, Fe, Co). Using scanning tunnelling microscopy and density‐functional theory (DFT) analysis, we resolve that the frameworks comprise a hexagonal lattice of HAT molecules and a Kagome lattice of metal atoms. The DFT analysis indicates that Ni, Co and Fe carry a magnetic moment of 1.1, 2.5, and 3.7 μB, respectively. We anticipate that the small π‐conjugated core of HAT and strong bidentate chelating coordination give rise to appealing electronic and magnetic properties.
1,4,5,8,9,12‐Hexaazatriphenylene (HAT)‐based two‐dimensional conjugated metal–organic frameworks of M3(HAT)2 (M=Fe, Ni, Co) were synthesized by means of an on‐surface self‐assembly protocol which effectively overcomes the strong inter‐molecular steric hindrance.
The incorporation of Si atoms into organic compounds significantly increases a variety of functionality, facilitating further applications. Recently, on‐surface synthesis was introduced into ...organosilicon chemistry as 1,4‐disilabenzene bridged nanostructures were obtained via coupling between silicon atoms and brominated phenyl groups at the ortho position on Au(111). Here, we demonstrate a high generality of this strategy via syntheses of silole derivatives and nanoribbon structures with eight‐membered sila‐cyclic rings from dibrominated molecules at the bay and peri positions on Au(111), respectively. Their structures and electronic properties were investigated by a combination of scanning tunneling microscopy/spectroscopy and density functional theory calculations. This work demonstrates a great potential to deal with heavy group 14 elements in on‐surface silicon chemistry.
Silole derivatives and nanoribbon structures with eight‐membered sila‐cyclic rings were successfully synthesized on Au(111) through reactions between bromo‐substituted molecules and silicon atoms. Their chemical structures were investigated by bond‐resolved STM and DFT calculations. The band gaps of the silole derivatives and the nanoribbon measured with STS measurements were 3.1 eV and 2.5 eV, respectively.
(Bi)carbonate adsorption on Cu(100) in 0.1 M KHCO3 has been studied by in situ scanning tunneling microscopy. Coexistence of different ordered adlayer phases with (
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...)R45° and (4×4) unit cells was observed in the double layer potential regime. The adlayer is rather dynamic and undergoes a reversible order‐disorder phase transition at 0 V vs. the reversible hydrogen electrode. Density functional calculations indicate that the adlayer consists of coadsorbed carbonate and water molecules and is strongly stabilized by liquid water in the adjacent electrolyte.
The molecular‐scale structure of the interface between copper electrodes and bicarbonate electrolyte, a key system for electrochemical CO2 reduction, is clarified by in situ scanning tunneling microscopy, revealing two highly complex coexisting adlayer structures above a critical potential. Ab initio calculations identify these as carbonate/water coadsorbate layers and indicate a strongly stabilizing effect of the adjacent liquid solution.
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