Two-dimensional materials

  • Article |

    Layered materials held together by weak interactions can be exfoliated into monolayers that retain the structure and composition of their bulk counterpart, but this has remained challenging to achieve for non-van der Waals materials. Now, AgCrS2 has been exfoliated into such [CrS2]Ag[CrS2] nanosheets through intercalation with tetraalkylammonium cations chosen for their suitable redox potential. The nanosheets show superionic behaviour at room temperature.

    • Jing Peng
    • , Yuhua Liu
    •  & Yi Xie
  • Article |

    Spin-crossover nanoparticles have been covalently grafted onto a semiconducting MoS2 layer to form a self-strainable heterostructure. Under light or thermal stimulus, the nanoparticles switch between their high- and low-spin states, in which they have different volumes. This generates a reversible strain over the MoS2 layer and, in turn, alters the electrical and optical properties of the heterostructure.

    • Ramón Torres-Cavanillas
    • , Marc Morant-Giner
    •  & Eugenio Coronado
  • Article |

    On-surface, ultra-high vacuum conditions enable two-dimensional polymerizations to be precisely studied—often with submolecular resolution—but these syntheses are typically thermally activated, which can lead to high defect densities and relatively small domain sizes. Now, a self-assembled monolayer of a three-bladed fantrip monomer on alkane-passivated graphite has been covalently crosslinked into a mesoscale-ordered two-dimensional polymer by [4+4] photocycloaddition.

    • Lukas Grossmann
    • , Benjamin T. King
    •  & Markus Lackinger
  • Article |

    The deposition of noble metals onto two-dimensional transition metal dichalcogenides is crucial for practical applications, including in catalysis and sensing, yet this process has remained difficult to control. Now, gold and silver have been shown to grow on colloidal transition metal dichalcogenide nanosheets into either atomically thin layers or nanoparticles whose sizes and morphologies depend on the relative strengths of the interfacial noble metal–chalcogen bonds.

    • Yifan Sun
    • , Yuanxi Wang
    •  & Raymond E. Schaak
  • Article |

    A solution-processing step has been used to prepare quantum-well structures that comprise a thin layer of perovskite sandwiched between two layers of conjugated oligothiophene derivatives. The band gap of the resulting 2D hybrid perovskites can be fine-tuned by functionalizing the organic component, which also improves the stability of the system.

    • Yao Gao
    • , Enzheng Shi
    •  & Letian Dou
  • Article |

    MoS2 single layers spontaneously undergo a slow oxygen substitution reaction under ambient conditions giving rise to solid-solution-type 2D molybdenum oxy-sulfide crystals. The oxygen substitution sites of the 2D MoS2xOx crystals act as efficient single-atom catalytic centres for the hydrogen evolution reaction.

    • János Pető
    • , Tamás Ollár
    •  & Levente Tapasztó
  • Article |

    Surface engineering is an attractive route to tune the processability, stability and functionalities of 2D materials, but typically introduces defects in the resulting structures. Now, the issue has been circumvented through pre-synthetic functionalization instead; an isoreticular family of robust layered coordination polymers has been mechanically exfoliated to give functionalized crystalline magnetic monolayers.

    • J. López-Cabrelles
    • , S. Mañas-Valero
    •  & E. Coronado
  • Article |

    The common form of salt has a 1:1 ratio of Na+ and Cl; however, species that deviate from this can be found under extreme conditions, such as high pressure. Now, as a result of cation–π interactions that promote ion–surface adsorption, Na2Cl and Na3Cl have been observed as two-dimensional crystals on graphene at ambient conditions.

    • Guosheng Shi
    • , Liang Chen
    •  & Haiping Fang
  • Article |

    The phase in which a crystal exists can have a direct influence over its properties; however, it is usually difficult to control during synthesis. Now it has been shown that micrometre-sized metallic 1T′-MoS2- and 1T′-MoSe2-layered crystals can be prepared in high phase purity on a large scale, and that they display promising electrocatalytic activity towards the hydrogen evolution reaction.

    • Yifu Yu
    • , Gwang-Hyeon Nam
    •  & Hua Zhang
  • Article |

    Complex interfacial supramolecular architectures promise unique physical and chemical properties, but are challenging to make. Now, it has been shown that a simple organic precursor can undergo a convergent multi-step on-surface transformation to give more complex building blocks that assemble into a semi-regular Archimedean tessellation with long-range order.

    • Yi-Qi Zhang
    • , Mateusz Paszkiewicz
    •  & Florian Klappenberger
  • Article |

    Converting oxygen-rich biomass into fuels requires the removal of oxygen groups through hydrodeoxygenation. MoS2 monolayer sheets decorated with isolated Co atoms bound to sulfur vacancies in the basal plane have now been synthesized that exhibit superior catalytic activity, selectivity and stability for the hydrodeoxygenation of 4-methylphenol to toluene when compared to conventionally prepared materials.

    • Guoliang Liu
    • , Alex W. Robertson
    •  & Shik Chi Edman Tsang
  • Article |

    The synthesis of well-defined planar polymers presents a significant challenge for chemists seeking to investigate their potential for use in emerging technologies. Now, a two-dimensional conjugated aromatic polymer has been synthesized via endogenous solid-state polymerization of pre-arranged monomers, and its performance as an organic anode in an ambient temperature sodium cell tested.

    • Wei Liu
    • , Xin Luo
    •  & Kian Ping Loh
  • Article |

    Isolating nanoscale species in liquids permits their scalable manipulation, enabling numerous fundamental and applied processes. Thus, achieving true dissolution of 2D materials is particularly desirable. Now, ionic salts of a range of important layered materials have been shown to spontaneously dissolve, yielding solutions of charged, monodisperse, undamaged and easy-to-manipulate 2D nanosheets.

    • Patrick L. Cullen
    • , Kathleen M. Cox
    •  & Christopher A. Howard
  • Article |

    Lateral anchoring of heteromolecules to graphene paves the way for the creation of hybrid materials with tunable properties. Now, following a surface-assisted dehydrogenative coupling reaction, the edges of graphene on silver have been functionalized with porphines. This enables the assembly of well-defined multifunctional graphene-based nanostructures.

    • Yuanqin He
    • , Manuela Garnica
    •  & Johannes V. Barth
  • Article |

    Quasicrystalline materials exhibit long-range order but no translational periodicity. Now, a random tiling quasicrystal has been fabricated on a Au(111) surface by coordination interactions between europium centres and linear dicarbonitrile linkers under stoichiometry control. The 2D metal–organic network exhibits the simultaneous presence of four-, five- and six-fold vertices and dodecagonal symmetry.

    • José I. Urgel
    • , David Écija
    •  & Johannes V. Barth
  • Article |

    Few-layer black phosphorus (BP) is a promising semiconductor, but it is highly reactive and susceptible to ambient degradation. Covalent functionalization with aryl radicals has now been shown to significantly improve the stability of exfoliated BP, as well as the performance of BP-based electronic devices through a controllable p-type doping effect.

    • Christopher R. Ryder
    • , Joshua D. Wood
    •  & Mark C. Hersam
  • Article |

    Porous-alumina filter discs typically used to prepare graphene-oxide films are found to corrode during filtration and release aluminium ions that crosslink the negatively charged sheets and make the films insoluble in water. In contrast, aluminium-free graphene-oxide films are significantly weaker and readily disintegrate in water.

    • Che-Ning Yeh
    • , Kalyan Raidongia
    •  & Jiaxing Huang
  • Article |

    Modifying or functionalizing transition metal dichalcogenides (TMDs) allows their properties to be altered and controlled. Now, non-defect-mediated covalent functionalization of single-layer semiconducting TMDs such as MoS2, WS2 and MoSe2 has been demonstrated by reacting them with organohalides, utilizing the excess charge in the 1T metallic phase.

    • Damien Voiry
    • , Anandarup Goswami
    •  & Manish Chhowalla
  • Article |

    Accessing synthetic two-dimensional polymers that are analogous to graphene is synthetically and analytically challenging. Now, single crystals of a simple-to-make monomer have been grown and then photopolymerized to form layered single crystals of covalently bonded two-dimensional polymer. Much like natural graphite, these crystals can be exfoliated to form thin sheets and single layers of the polymer.

    • Max J. Kory
    • , Michael Wörle
    •  & A. Dieter Schlüter
  • Article |

    Two-dimensional synthetic polymers can be produced through solid-state topochemical polymerization, but achieving this through a single-crystal-to-single-crystal transformation has not yet been demonstrated. Now, a fluorinated Y-shaped monomer has been preorganized in a lamellar crystal, which goes through two successive single-crystal-to-single-crystal phototransformations to give a 2D polymer; single-crystal X-ray diffraction has been used to elucidate its structure.

    • Patrick Kissel
    • , Daniel J. Murray
    •  & Benjamin T. King
  • Article |

    Carbonization of a self-assembled monolayer of a hexayne amphiphile at the air/water interface at room temperature results in the formation of functional carbon nanosheets. The nanosheets exhibit a molecularly defined thickness, are mechanically self-supporting over several micrometres, and have macroscopic lateral dimensions on the order of centimetres.

    • Stephen Schrettl
    • , Cristina Stefaniu
    •  & Holger Frauenrath