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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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 is a fascinating material with unique properties, such as extreme mechanical strength, ultrahigh electrical and thermal conductivities and remarkable transparency. Further reduction in the ...dimensionality of graphene in the form of graphene quantum dots and graphene nanoribbons has compensated for the lack of a bandgap in the extended 2D material. These nanoscale graphenes exhibit finite bandgaps because of quantum confinement, making them attractive as next-generation semiconductors. Numerous fabrication methods for various types of graphenes have been developed, which can generally be categorized into ‘top-down’ and ‘bottom-up’ procedures. These methods afford, on different production scales, a wide range of graphene structures of different sizes, shapes and quality (defect density, edge roughness and so on). Atomically precise syntheses are indispensable for fundamental research and future technological development, but the projection of the existing methods to cost-effective bulk-scale fabrication techniques is required for upcoming industrial applications of graphenes.Numerous fabrication methods have been developed so far for the production of graphenes and nanographenes. However, how practical is the bulk production of these fascinating materials? This Perspective discusses recent advances in graphene fabrication and possibilities for translation to large-scale production.
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.
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IJS, KILJ, NUK, UL, UM, UPUK
Nanographenes with zigzag edges are predicted to manifest non-trivial π-magnetism resulting from the interplay of concurrent electronic effects, such as hybridization of localized frontier states and ...Coulomb repulsion between valence electrons. This provides a chemically tunable platform to explore quantum magnetism at the nanoscale and opens avenues towards organic spintronics. The magnetic stability in nanographenes is thus far greatly limited by the weak magnetic exchange coupling, which remains below the room-temperature thermal energy. Here, we report the synthesis of large rhombus-shaped nanographenes with zigzag peripheries on gold and copper surfaces. Single-molecule scanning probe measurements show an emergent magnetic spin singlet ground state with increasing nanographene size. The magnetic exchange coupling in the largest nanographene (C
H
, containing five benzenoid rings along each edge), determined by inelastic electron tunnelling spectroscopy, exceeds 100 meV or 1,160 K, which outclasses most inorganic nanomaterials and survives on a metal electrode.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Boundaries between distinct topological phases of matter support robust, yet exotic quantum states such as spin-momentum locked transport channels or Majorana fermions
. The idea of using such states ...in spintronic devices or as qubits in quantum information technology is a strong driver of current research in condensed matter physics
. The topological properties of quantum states have helped to explain the conductivity of doped trans-polyacetylene in terms of dispersionless soliton states
. In their seminal paper, Su, Schrieffer and Heeger (SSH) described these exotic quantum states using a one-dimensional tight-binding model
. Because the SSH model describes chiral topological insulators, charge fractionalization and spin-charge separation in one dimension, numerous efforts have been made to realize the SSH Hamiltonian in cold-atom, photonic and acoustic experimental configurations
. It is, however, desirable to rationally engineer topological electronic phases into stable and processable materials to exploit the corresponding quantum states. Here we present a flexible strategy based on atomically precise graphene nanoribbons to design robust nanomaterials exhibiting the valence electronic structures described by the SSH Hamiltonian
. We demonstrate the controlled periodic coupling of topological boundary states
at junctions of graphene nanoribbons with armchair edges to create quasi-one-dimensional trivial and non-trivial electronic quantum phases. This strategy has the potential to tune the bandwidth of the topological electronic bands close to the energy scale of proximity-induced spin-orbit coupling
or superconductivity
, and may allow the realization of Kitaev-like Hamiltonians
and Majorana-type end states
.
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KISLJ, NUK, SBMB, UL, UM, UPUK
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.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties
. Graphene ribbons with nanometre-scale widths
(nanoribbons) should exhibit half-metallicity
and ...quantum confinement. Magnetic edges in graphene nanoribbons
have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic
and quantum computing devices
. However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable
. Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.
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KISLJ, NUK, SBMB, UL, UM, UPUK
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