Graphene nanoribbons (GNRs) are quasi‐1D graphene strips, which have attracted attention as a novel class of semiconducting materials for various applications in electronics and optoelectronics. GNRs ...exhibit unique electronic and optical properties, which sensitively depend on their chemical structures, especially the width and edge configuration. Therefore, precision synthesis of GNRs with chemically defined structures is crucial for their fundamental studies as well as device applications. In contrast to top‐down methods, bottom‐up chemical synthesis using tailor‐made molecular precursors can achieve atomically precise GNRs. Here, the synthesis of GNRs on metal surfaces under ultrahigh vacuum (UHV) and chemical vapor deposition (CVD) conditions is the main focus, and the recent progress in the field is summarized. The UHV method leads to successful unambiguous visualization of atomically precise structures of various GNRs with different edge configurations. The CVD protocol, in contrast, achieves simpler and industry‐viable fabrication of GNRs, allowing for the scale up and efficient integration of the as‐grown GNRs into devices. The recent updates in device studies are also addressed using GNRs synthesized by both the UHV method and CVD, mainly for transistor applications. Furthermore, views on the next steps and challenges in the field of on‐surface synthesized GNRs are provided.
Precision synthesis of graphene nanoribbons (GNRs) with chemically defined structures is crucial for their fundamental studies as well as device applications. The recent progress in the surface‐assisted synthesis of GNRs under ultrahigh vacuum and chemical vapor deposition conditions is summarized, and the updates in the applications of on‐surface synthesized GNRs, especially directing toward transistor devices, are subsequently addressed.
Abstract
Metal single-atom catalysts (M-SACs) have emerged as an attractive concept for promoting heterogeneous reactions, but the synthesis of high-loading M-SACs remains a challenge. Here, we ...report a multilayer stabilization strategy for constructing M-SACs in nitrogen-, sulfur- and fluorine-co-doped graphitized carbons (M = Fe, Co, Ru, Ir and Pt). Metal precursors are embedded into perfluorotetradecanoic acid multilayers and are further coated with polypyrrole prior to pyrolysis. Aggregation of the metals is thus efficiently inhibited to achieve M-SACs with a high metal loading (~16 wt%). Fe-SAC serves as an efficient oxygen reduction catalyst with half-wave potentials of 0.91 and 0.82 V (versus reversible hydrogen electrode) in alkaline and acid solutions, respectively. Moreover, as an air electrode in zinc–air batteries, Fe-SAC demonstrates a large peak power density of 247.7 mW cm
−2
and superior long-term stability
.
Our versatile method paves an effective way to develop high-loading M-SACs for various applications.
Graphene nanoribbons (GNRs) are quasi-one-dimensional subunits of graphene and have open bandgaps in contrast to the zero-bandgap graphene. The high potential of GNRs as a new family of carbon-based ...semiconductors,
e.g.
for nanoelectronic and optoelectronic applications, has boosted the research attempts towards fabrication of GNRs. The predominant top-down methods such as lithographical patterning of graphene and unzipping of carbon nanotubes cannot prevent defect formation. In contrast, bottom-up chemical synthesis, starting from tailor-made molecular precursors, can achieve atomically precise GNRs. In this account, we summarize our recent research progress in the bottom-up synthesis of GNRs through three different methods, namely (1) in solution, (2) on-surface under ultrahigh vacuum (UHV) conditions, and (3) on-surface through chemical vapour deposition (CVD). The solution synthesis allows fabrication of long (>600 nm) and liquid-phase-processable GNRs that can also be functionalized at the edges. On the other hand, the on-surface synthesis under UHV enables formation of zigzag GNRs and
in situ
visualization of their chemical structures by atomic-resolution scanning probe microscopy. While the on-surface synthesis under UHV is typically costly and has limited scalability, the industrially viable CVD method can allow lower-cost production of large GNR films. We compare the three methods in terms of the affordable GNR structures and the resulting control of their electronic and optical properties together with post-processing for device integration. Further, we provide our views on future perspectives in the field of bottom-up GNRs.
Graphene nanoribbons (GNRs) with various structures and properties can be synthesized in solution or on surface.
In this article, we describe our chemical approach, developed over the course of a decade, towards the bottom‐up synthesis of structurally well‐defined graphene nanoribbons (GNRs). GNR synthesis can ...be achieved through two different methods, one being a solution‐phase process based on conventional organic chemistry and the other invoking surface‐assisted fabrication, employing modern physics methodologies. In both methods, rationally designed monomers are polymerized to form non‐planar polyphenylene precursors, which are “graphitized” and “planarized” by solution‐mediated or surface‐assisted cyclodehydrogenation. Through these methods, a variety of GNRs have been synthesized with different widths, lengths, edge structures, and degrees of heteroatom doping, featuring varying (opto)electronic properties. The ability to chemically tailor GNRs with tuned properties in a well‐defined manner will contribute to the elucidation of the fundamental physics of GNRs, as well as pave the way for the development of GNR‐based nanoelectronics and optoelectronics.
Fabrication of chemically precise graphene nanoribbons (GNRs) has been achieved based on bottom‐up syntheses from small oligophenylene precursors. The GNR synthesis can be carried out through two different methods: a conventional solution synthesis and an on‐surface fabrication under ultrahigh vacuum conditions. In both methods, carefully designed monomers are polymerized to non‐planar polyphenylene precursors, which are “graphitized” and “planarized” by solution‐mediated or surface‐assisted cyclodehydrogenation. Through these protocols we have successfully prepared a number of GNRs with different widths and lengths, edge structures, and heteroatom doping, demonstrating tailor‐made (opto)electronic properties.
Dehydrogenation reactions are key steps in many metal‐catalyzed chemical processes and in the on‐surface synthesis of atomically precise nanomaterials. The principal role of the metal substrate in ...these reactions is undisputed, but the role of metal adatoms remains, to a large extent, unanswered, particularly on gold substrates. Here, we discuss their importance by studying the surface‐assisted cyclodehydrogenation on Au(111) as an ideal model case. We choose a polymer theoretically predicted to give one of two cyclization products depending on the presence or absence of gold adatoms. Scanning probe microscopy experiments observe only the product associated with adatoms. We challenge the prevalent understanding of surface‐assisted cyclodehydrogenation, unveiling the catalytic role of adatoms and their effect on regioselectivity. The study adds new perspectives to the understanding of metal catalysis and the design of on‐surface synthesis protocols for novel carbon nanomaterials.
Using scanning tunneling microscopy and electronic structure theory, we show that, contrary to previous consensus, surface adatoms can play a central role in the highly chemoselective cyclodehydrogenation of organic polymers.
The vast potential of organic materials for electronic, optoelectronic and spintronic devices entails substantial interest in the fabrication of π-conjugated systems with tailored functionality ...directly at insulating interfaces. On-surface fabrication of such materials on non-metal surfaces remains to be demonstrated with high yield and selectivity. Here we present the synthesis of polyaromatic chains on metallic substrates, insulating layers, and in the solid state. Scanning probe microscopy shows the formation of azaullazine repeating units on Au(111), Ag(111), and h-BN/Cu(111), stemming from intermolecular homo-coupling via cycloaddition reactions of CN-substituted polycyclic aromatic azomethine ylide (PAMY) intermediates followed by subsequent dehydrogenation. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry demonstrates that the reaction also takes place in the solid state in the absence of any catalyst. Such intermolecular cycloaddition reactions are promising methods for direct synthesis of regioregular polyaromatic polymers on arbitrary insulating surfaces.
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