C3N—A 2D Crystalline,Hole‐Free,Tunable‐Narrow‐Bandgap Semiconductor with Ferromagnetic Properties

Graphene has initiated intensive research efforts on 2D crystalline materials due to its extraordinary set of properties and the resulting host of possible applications. Here the authors report on the controllable large‐scale synthesis of C₃N, a 2D crystalline, hole‐free extension of graphene, its structural characterization, and some of its unique properties. C₃N is fabricated by polymerization of 2,3‐diaminophenazine. It consists of a 2D honeycomb lattice with a homogeneous distribution of nitrogen atoms, where both N and C atoms show a D_6h‐symmetry. C₃N is a semiconductor with an indirect bandgap of 0.39 eV that can be tuned to cover the entire visible range by fabrication of quantum dots with different diameters. Back‐gated field‐effect transistors made of single‐layer C₃N display an on–off current ratio reaching 5.5 × 10¹⁰. Surprisingly, C₃N exhibits a ferromagnetic order at low temperatures (<96 K) when doped with hydrogen. This new member of the graphene family opens the door for both fundamental basic research and possible future applications.     

Hierarchical Fullerene Assembly: Seeded Coprecipitation and Electric Field Directed Assembly

Hierarchical C₆₀ colloidal films are assembled from nanoscale to macroscale. Fullerene molecular crystals are grown via seeded cosolvent precipitation with mixed solvent [tetrahydronaphthalene (THN)/trimethylpyridine (TMP)] and antisolvent 2‐propanol. The fullerene solutions are aged under illumination, which due to the presence of TMP reduces the free monomer concentration through fullerene aggregation into nanoparticles. The nanoparticles seed the growth of monodisperse fullerene colloids on injection into the antisolvent. Diverse colloidal morphologies are prepared as a function of injection volume and fullerene solution concentration. The high fullerene solubility of THN enables C₆₀ colloids to be prepared in quantities sufficient for assembly (5 × 10⁸). Electric fields are applied to colloidal C₆₀ platelets confined to two dimensions. The particles assemble under dipolar forces, dielectrophoretic forces, and electrohydrodynamic flows. Frequency‐dependent phase transitions occur at the critical Maxwell–Wagner crossover frequency, where the effective polarizability of the particles in the medium is substantially reduced. Structures form as a function of field strength, frequency, and confinement including hexagonal, oblique, string fluid, coexistent hexagonal‐rhombic, and tetratic.     

Synthesis of fullerene nanowhiskers using the liquid–liquid interfacial precipitation method and their mechanical,electrical and superconducting properties

Abstract

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C₆₀, C₇₀, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C₆₀ (fullerene) nanowhiskers (C₆₀NWs) exhibit superconducting behavior. Potassium-doped C₆₀NWs have realized the highest superconducting volume fraction of the alkali metal-doped C₆₀ crystals and display a high critical current density (J_c) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid–liquid interfacial precipitation method.     

Synthesis of fullerene nanowhiskers using the liquid–liquid interfacial precipitation method and their mechanical,electrical and superconducting properties

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C₆₀, C₇₀, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C₆₀ (fullerene) nanowhiskers (C₆₀NWs) exhibit superconducting behavior. Potassium-doped C₆₀NWs have realized the highest superconducting volume fraction of the alkali metal-doped C₆₀ crystals and display a high critical current density (J_c) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid–liquid interfacial precipitation method.     

Cover Picture: A Two‐Dimensional Porphyrin‐Based Porous Network Featuring Communicating Cavities for the Templated Complexation of Fullerenes (Adv. Mater. 3/2006)

A 2D porous network has been realized by self‐assembly of porphyrin modules on a silver surface, as reported by Diederich and co‐workers on p. 275. The so‐formed pores are able to host single fullerene molecules and mediate long‐range interactions between such carbon guests, resulting in the formation of large supramolecular chains and islands. The cover shows a scanning tunnelling microscopy image of several single C₆₀ molecules (large green protrusions) hosted in the 2D porous network. As indicated by the molecular model, each pore is formed by the symmetric arrangement of three porphyrin molecules and the fullerene guest is located exactly in the center of the cavity.     

New Concepts and Applications in the Macromolecular Chemistry of Fullerenes

A new classification on the different types of fullerene‐containing polymers is presented according to their different properties and applications they exhibit in a variety of fields. Because of their interest and novelty, water‐soluble and biodegradable C₆₀‐polymers are discussed first, followed by polyfullerene‐based membranes where unprecedented supramolecular structures are presented. Next are compounds that involve hybrid materials formed from fullerenes and other components such as silica, DNA, and carbon nanotubes (CNTs) where the most recent advances have been achieved. A most relevant topic is still that of C₆₀‐based donor‐acceptor (D–A) polymers. Since their application in photovoltaics D–A polymers are among the most realistic applications of fullerenes in the so‐called molecular electronics. The most relevant aspects in these covalently connected fullerene/polymer hybrids as well as new concepts to improve energy conversion efficiencies are presented. The last topics disccused relate to supramolecular aspects that are in involved in C₆₀‐polymer systems and in the self‐assembly of C₆₀‐macromolecular structures, which open a new scenario for organizing, by means of non‐covalent interactions, new supramolecular structures at the nano‐ and micrometric scale, in which the combination of the hydrofobicity of fullerenes with the versatility of the noncovalent chemistry afford new and spectacular superstructures.     

Intercalation of C<Subscript>60</Subscript> fullerene crystals with calcium and barium via self-propagating high-temperature synthesis

We report a process for rapid intercalation of C₆₀ fullerene crystals using self-propagating high-temperature synthesis. The process has been used to intercalate C₆₀ fullerene crystals with calcium and barium. The superconducting transition temperatures of the intercalated fullerites have been measured, and the calcium-intercalated C₆₀ fullerene crystals have been characterized by X-ray diffraction.     

Tunable Photonic Microspheres of Comb‐Like Supramolecules

Photonic crystals (PCs) are ideal candidates for reflective color pigments with high color purity and brightness due to tunable optical stop band. Herein, the generation of PC microspheres through 3D confined supramolecular assembly of block copolymers (polystyrene‐block‐poly(2‐vinylpyridine), PS‐b‐P2VP) and small molecules (3‐n‐pentadecylphenol, PDP) in emulsion droplets is demonstrated. The intrinsic structural colors of the PC microspheres are effectively regulated by tuning hydrogen‐bonding interaction between P2VP blocks and PDP, where reflected color can be readily tuned across the whole visible spectrum range. Also, the effects of both PDP and homopolymer (hPS) on periodic structure and optical properties of the microspheres are investigated. Moreover, the spectral results of finite element method (FEM) simulation agree well with the variation of structural colors by tuning the periodicity in PC microspheres. The supramolecular microspheres with tunable intrinsic structural color can be potentially useful in the various practical applications including display, anti‐counterfeit printing and painting.     

Tri‐s‐triazine‐Based Crystalline Carbon Nitride Nanosheets for an Improved Hydrogen Evolution

Tri‐s‐triazine‐based crystalline carbon nitride nanosheets (CCNNSs) have been successfully extracted via a conventional and cost‐effective sonication–centrifugation process. These CCNNSs possess a highly defined and unambiguous structure with minimal thickness, large aspect ratios, homogeneous tri‐s‐triazine‐based units, and high crystallinity. These tri‐s‐triazine‐based CCNNSs show significantly enhanced photocatalytic hydrogen generation activity under visible light than g‐C₃N₄, poly (triazine imide)/Li⁺ Cl^–, and bulk tri‐s‐triazine‐based crystalline carbon nitrides. A highly apparent quantum efficiency of 8.57% at 420 nm for hydrogen production from aqueous methanol feedstock can be achieved from tri‐s‐triazine‐based CCNNSs, exceeding most of the reported carbon nitride nanosheets. Benefiting from the inherent structure of 2D crystals, the ultrathin tri‐s‐triazine‐based CCNNSs provide a broad range of application prospects in the fields of bioimaging, and energy storage and conversion.     

In Situ Growth of MAPbBr3 Nanocrystals on Few‐Layer MXene Nanosheets with Efficient Energy Transfer

The performance of perovskite nanocrystals (NCs) in optoelectronics and photocatalysis is severely limited by the presence of large amounts of crystal boundaries in NCs film that greatly restricts energy transfer. Creating heterostructures based on perovskite NCs and 2D materials is a common approach to improve the energy transport at the perovskite/2D materials interface. Herein, methylamine lead bromide (MAPbBr₃, MA: CH₃NH₃⁺) perovskite NCs are homogeneously deposited on highly conductive few‐layer MXene (Ti₃C₂T_x) nanosheets to form heterostructures through an in situ solution growth method. An optimal mixed solvent ratio is essential to realize the growth of perovskite NCs on Ti₃C₂T_x nanosheets. Time‐resolved photoluminescence spectroscopy, transient absorption spectroscopy, and the photoresponse of electron‐ and hole‐only photoelectric conversion devices reveal the interfacial energy transfer behavior within MAPbBr₃/Ti₃C₂T_x heterostructures. The present investigation may provide a useful guide toward use of halide perovskite/2D material heterostructures in applications such as photocatalysis as well as optoelectronics.     

π‐Conjugated Polymer–Fullerene Covalent Hybrids via Ambient Conditions Diels–Alder Ligation

The established ability of graphitic carbon‐nanomaterials to undergo ambient condition Diels–Alder reactions with cyclopentadienyl (Cp) groups is herein employed to prepare fullerene‐polythiophene covalent hybrids with improved electron transfer and film forming characteristics. A novel precisely designed polythiophene (M _n 9.8 kD, ? 1.4) with 17 mol% of Cp‐groups bearing repeat unit is prepared via Grignard metathesis polymerization. The UV/Vis absorption and fluorescence (λ_ex 450 nm) characteristics of polythiophene with pendant Cp‐groups (λ_max 447 nm, λ_e‐max 576 nm) are comparable to the reference poly(3‐hexylthiophene) (λ_max 450 nm, λ_e‐max 576 nm). The novel polythiophene with pendant Cp‐groups is capable of producing solvent‐stable free‐standing polythiophene films, and non‐solvent assisted self‐assemblies resulting in solvent‐stable nanoporous‐microstructures. ¹H‐NMR spectroscopy reveals an efficient reaction of the pendant Cp‐groups with C₆₀. The UV/Vis spectroscopic analyses of solution and thin films of the covalent and physical hybrids disclose closer donor‐acceptor packing in the case of covalent hybrids. AFM images evidence that the covalent hybrids form smooth films with finer lamellar‐organization. The effect is particularly remarkable in the case of poorly soluble C₆₀. A significant enhancement in photo‐voltage is observed for all devices constituted of covalent hybrids, highlighting novel avenues to developing efficient electron donor‐acceptor combinations for light harvesting systems.     

Large‐Area Atomic Layers of the Charge‐Density‐Wave Conductor TiSe2

Layered transition metal (Ti, Ta, Nb, etc.) dichalcogenides are important prototypes for the study of the collective charge density wave (CDW). Reducing the system dimensionality is expected to lead to novel properties, as exemplified by the discovery of enhanced CDW order in ultrathin TiSe₂. However, the syntheses of monolayer and large‐area 2D CDW conductors can currently only be achieved by molecular beam epitaxy under ultrahigh vacuum. This study reports the growth of monolayer crystals and up to 5 × 10⁵ µm² large films of the typical 2D CDW conductor—TiSe₂—by ambient‐pressure chemical vapor deposition. Atomic resolution scanning transmission electron microscopy indicates the as‐grown samples are highly crystalline 1T‐phase TiSe₂. Variable‐temperature Raman spectroscopy shows a CDW phase transition temperature of 212.5 K in few layer TiSe₂, indicative of high crystal quality. This work not only allows the exploration of many‐body state of TiSe₂ in 2D limit but also offers the possibility of utilizing large‐area TiSe₂ in ultrathin electronic devices.     

Construction of Cuprous Oxide Electrodes Composed of 2D Single‐Crystalline Dendritic Nanosheets

An unusual anisotropic growth of Cu₂O is stabilized via the electrochemical synthesis of Cu₂O in the presence of Ag⁺ ions, which results in the formation of Cu₂O electrodes composed of 2D sheetlike crystals containing complex dendritic patterns. It is quite unusual for Cu₂O to form a 2D morphology since it has a 3D isotropic cubic crystal structure where the a, b, and c axes are equivalent. Each Cu₂O sheet is single‐crystalline in nature and is grown parallel to the {110} plane, which is rarely observed in Cu₂O crystal shapes. A various set of experiments are performed to understand the role of Ag⁺ ions on the 2D growth of Cu₂O. The results show that Ag⁺ ions are deposited as silver islands on already growing Cu₂O crystals and serve as nucleation sites for the new growth of Cu₂O crystals. As a result, the growth direction of the newly forming Cu₂O crystals is governed by the diffusion layer structure created by the pre‐existing Cu₂O crystals, which results in the formation of 2D dendritic patterns. The thin 2D crystal morphology can significantly increase the surface‐to‐volume ratio of Cu₂O crystals, which is beneficial for enhancing various electrochemical and photoelectrochemical properties of the electrodes. The photoelectrochemical properties of the Cu₂O electrodes composed of 2D dendritic crystals are investigated and compared to those of 3D dendritic crystals. This study provides a unique and effective route to maximize the {110} area per unit volume of Cu₂O, which will be beneficial for any catalytic/sensing abilities that can be anisotropically enhanced by the {110} planes of Cu₂O.     

A Fermi‐Level‐Pinning‐Free 1D Electrical Contact at the Intrinsic 2D MoS2–Metal Junction

Currently 2D crystals are being studied intensively for use in future nanoelectronics, as conventional semiconductor devices face challenges in high power consumption and short channel effects when scaled to the quantum limit. Toward this end, achieving barrier‐free contact to 2D semiconductors has emerged as a major roadblock. In conventional contacts to bulk metals, the 2D semiconductor Fermi levels become pinned inside the bandgap, deviating from the ideal Schottky–Mott rule and resulting in significant suppression of carrier transport in the device. Here, MoS₂ polarity control is realized without extrinsic doping by employing a 1D elemental metal contact scheme. The use of high‐work‐function palladium (Pd) or gold (Au) enables a high‐quality p‐type dominant contact to intrinsic MoS₂, realizing Fermi level depinning. Field‐effect transistors (FETs) with Pd edge contact and Au edge contact show high performance with the highest hole mobility reaching 330 and 432 cm² V^?1 s^?1 at 300 K, respectively. The ideal Fermi level alignment allows creation of p‐ and n‐type FETs on the same intrinsic MoS₂ flake using Pd and low‐work‐function molybdenum (Mo) contacts, respectively. This device acts as an efficient inverter, a basic building block for semiconductor integrated circuits, with gain reaching 15 at V_D = 5 V.     

Unraveling the Solution‐State Supramolecular Structures of Donor–Acceptor Polymers and their Influence on Solid‐State Morphology and Charge‐Transport Properties

Polymer self‐assembly in solution prior to film fabrication makes solution‐state structures critical for their solid‐state packing and optoelectronic properties. However, unraveling the solution‐state supramolecular structures is challenging, not to mention establishing a clear relationship between the solution‐state structure and the charge‐transport properties in field‐effect transistors. Here, for the first time, it is revealed that the thin‐film morphology of a conjugated polymer inherits the features of its solution‐state supramolecular structures. A “solution‐state supramolecular structure control” strategy is proposed to increase the electron mobility of a benzodifurandione‐based oligo(p‐ phenylene vinylene) (BDOPV)‐based polymer. It is shown that the solution‐state structures of the BDOPV‐based conjugated polymer can be tuned such that it forms a 1D rod‐like structure in good solvent and a 2D lamellar structure in poor solvent. By tuning the solution‐state structure, films with high crystallinity and good interdomain connectivity are obtained. The electron mobility significantly increases from the original value of 1.8 to 3.2 cm² V^?1 s^?1. This work demonstrates that “solution‐state supramolecular structure” control is critical for understanding and optimization of the thin‐film morphology and charge‐transport properties of conjugated polymers.     

Epitaxially Grown Ferroelectric PVDF‐TrFE Film on Shape‐Tailored Semiconducting Rubrene Single Crystal

Epitaxial crystallization of thin poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) films is important for the full utilization of their ferroelectric properties. Epitaxy can offer a route for maximizing the degree of crystallinity with the effective orientation of the crystals with respect to the electric field. Despite various approaches for the epitaxial control of the crystalline structure of PVDF‐TrFE, its epitaxy on a semiconductor is yet to be accomplished. Herein, the epitaxial growth of PVDF‐TrFE crystals on a single‐crystalline organic semiconductor rubrene grown via physical vapor deposition is presented. The epitaxy results in polymer crystals globally ordered with specific crystal orientations dictated by the epitaxial relation between the polymer and rubrene crystal. The lattice matching between the c‐axis of PVDF‐TrFE crystals and the (210) plane of orthorhombic rubrene crystals develops two degenerate crystal orientations of the PVDF‐TrFE crystalline lamellae aligned nearly perpendicular to each other. Thin PVDF‐TrFE films with epitaxially grown crystals are incorporated into metal/ferroelectric polymer/metal and metal/ferroelectric polymer/semiconductor/metal capacitors, which exhibit excellent nonvolatile polarization and capacitance behavior, respectively. Furthermore, combined with a printing technique for micropatterning rubrene single crystals, the epitaxy of a PVDF‐TrFE film is formed selectively on the patterned rubrene with characteristic epitaxial crystal orientation over a large area.     

Synthesis and Complex Study of Water‐Soluble Polymer Derivatives of C60 Fullerene

Abstract

The water‐soluble composites with fullerene content up to 5 wt% based on poly‐(N‐vinylpyrrolydone) (PVP) were obtained. The higher fullerene content is achieved by means of introducing tetraphenylporphyrine (TPP) and KBr into composites. The synthesis includes the formation of C₆₀–TPP complex and its further interaction with polymer. The formation of C₆₀–TPP complex was confirmed by ¹³C NMR, SANS, and translational diffusion. The hydrodynamic and electrooptical studies of C₆₀–TPP–PVP complexes indicate the higher symmetry of the polymer coil in the complex as compared to PVP. The C₆₀–PVP–KBr composites were also obtained by the solid state interaction under vacuum, KBr promoting the destruction of fullerene aggregates.     

Core–Shell and Layer‐by‐Layer Assembly of 3D DNA Crystals

A long‐standing goal of DNA nanotechnology has been to assemble 3D crystals to be used as molecular scaffolds. The DNA 13‐mer, BET66, self‐assembles via Crick–Watson and noncanonical base pairs to form crystals. The crystals contain solvent channels that run through them in multiple directions, allowing them to accommodate tethered guest molecules. Here, the first example of biomacromolecular core–shell crystal growth is described, by showing that these crystals can be assembled with two or more discrete layers. This approach leads to structurally identical layers on the DNA level, but with each layer differentiated based on the presence or absence of conjugated guest molecules. The crystal solvent channels also allow layer‐specific postcrystallization covalent attachment of guest molecules. Through controlling the guest‐molecule identity, concentration, and layer thickness, this study opens up a new method for using DNA to create multifunctional periodic biomaterials with tunable optical, chemical, and physical properties.     

Carbon Clusters Formation by Laser Irradiation of Carbonaceous Solids

Abstract

A laser ablation/Fourier‐transform ion cyclotron resonance mass spectrometry was used to generate fullerenes clusters from targets of carbonaceous material containing carbyne, C₆₀ photopolymer, graphite, diamond, C₆₀ fullerene crystals.     

Synthesis of Multi‐Fullerenes Encapsulated Palladium Nanocage,and Its Application in Electrochemiluminescence Immunosensors for the Detection of Streptococcus suis Serotype 2

A novel functionalized material is synthesized using surface‐decorated fullerene (C₆₀) to encapsulate hollow and porous palladium nanocages (PdNCs), and is applied to fabricate an electrochemiluminescence (ECL) immunosensor for the detection of Streptococcus suis Serotype 2 (SS2). PdNCs with hollow interiors and porous walls are prepared using a galvanic replacement reaction between silver nanocubes and metal precursor salts. Then, C₆₀ reacts with l ‐cysteine (l ‐Cys) to form l ‐Cys functionalized C₆₀ (C₆₀‐l ‐Cys), which has a better biocompatibility, conductivity, and hydrophilicity compared to C₆₀ and possesses abundant –SH groups on the surface. Because of the special interaction between –SH and PdNCs, the obtained C₆₀‐l ‐Cys is adsorbed around the PdNCs to form an interesting structure with multiple spheres encapsulating the cage. The resultant functionalized material (C₆₀‐L‐Cys‐PdNCs) has a high specific surface area, good electrocatalytic ability, and efficient photocatalytic activity, and is used to construct an ECL immunosensor for the detection of SS2. The ECL signal amplified strategy is performed by using the novel coreactant (C₆₀‐l ‐Cys) and in situ generation of O₂ thus creating the S₂O₈^2?‐O₂ ECL system. As a result, a wide linear detection range of 0.1 pg mL^?1 to 100 ng mL^?1 is acquired with a relatively low detection limit of 33.3 fg mL^?1.