Hexagonal Single Crystal Domains of Few-Layer Graphene on Copper Foils

Hexagonal-shaped single crystal domains of few layer graphene (FLG) are synthesized on copper foils using atmospheric pressure chemical vapor deposition with a high methane flow. Scanning electron microscopy reveals that the graphene domains have a hexagonal shape and are randomly orientated on the copper foil. However, the sites of graphene nucleation exhibit some correlation by forming linear rows. Transmission electron microscopy is used to examine the folded edges of individual domains and reveals they are few-layer graphene consisting of approximately 5−10 layers in the central region and thinning out toward the edges of the domain. Selected area electron diffraction of individual isolated domains reveals they are single crystals with AB Bernal stacking and free from the intrinsic rotational stacking faults that are associated with turbostratic graphite. We study the time-dependent growth dynamics of the domains and show that the final continuous FLG film is polycrystalline, consisting of randomly connected single crystal domains

Inflating Graphene with Atomic Scale Blisters

Using 80 kV electron beam irradiation we have created graphene blister defects of additional carbon atoms incorporated into a graphene lattice. These structures are the antithesis of the vacancy defect with blister defects observed to contain up to six additional carbon atoms. We present aberration-corrected transmission electron microscopy data demonstrating the formation of a blister from an existing divacancy, together with further examples that undergo reconfiguration and annihilation under the electron beam. The relative stability of the observed variations of blister are discussed and considered in the context of previous calculations. It is shown that the blister defect is seldom found in isolation and is more commonly coupled with dislocations where it can act as an intermediate state, permitting dislocation core climb without the atom ejection from the graphene lattice required for nonconservative motion

Atomic Structure and Dynamics of Epitaxial 2D Crystalline Gold on Graphene at Elevated Temperatures

The atomic level dynamics of gold on graphene is studied at temperatures up to 800 °C using an in situ heating holder within an aberration-corrected transmission electron microscope. At this high temperature, individual gold atoms and nanoclusters are mobile across the surface of graphene and attach to defect sites and migrate along the edges of holes in graphene. Gold nanoclusters on clean graphene show crystallinity at temperatures above their predicted melting point for equivalent sized clusters due to strong epitaxial interactions with the underlying graphene lattice. Gold nanoclusters anchored to defect sites in graphene exhibit discrete rotations between fixed orientations while maintaining epitaxial correlations to the graphene. We show that gold nanoclusters can be two-dimensional with monolayer thickness and switch their crystal structure between two different phases. These results have important implications on the use of gold nanoclusters on graphene at elevated temperatures for applications, such as catalysis and plasmonics

Growth of Ultrahigh Density Single-Walled Carbon Nanotube Forests by Improved Catalyst Design

We have grown vertically aligned single-walled carbon nanotube forests with an area density of 1.5 × 10¹³ cm^–2, the highest yet achieved, by reducing the average diameter of the nanotubes. We use a nanolaminate Fe–Al₂O₃ catalyst design consisting of three layers of Al₂O₃, Fe, and Al₂O₃, in which the lower Al₂O₃ layer is densified by an oxygen plasma treatment to increase its diffusion barrier properties, to allow a thinner catalyst layer to be used. This high nanotube density is desirable for using carbon nanotubes as interconnects in integrated circuits

Formation of Klein Edge Doublets from Graphene Monolayers

With increasing possibilities for applications of graphene, it is essential to fully characterize the rich topological variations in graphene edge structures. Using aberration-corrected transmission electron microscopy, dangling carbon doublets at the edge of monolayer graphene crystals have been observed. Unlike the single-atom Klein edge often found at zigzag edges, these carbon dimers were observed in various edge structure environments, but most frequently on the more stable armchair edges. Observation of this Klein edge doublet over time reveals that its existence enhances the stability of armchair edges and is a route to atom abstraction on zigzag edges

Two-Dimensional Coalescence Dynamics of Encapsulated Metallofullerenes in Carbon Nanotubes

We report on the coalescence of a two-dimensional (2D) chain of La@C82 metallofullerene molecules encapsulated inside a single-wall carbon nanotube (SWNT). 2D packing of metallofullerenes is known to adopt a zigzag arrangement and cause elliptical distortion to the cross-section of the SWNT host. We show that after coalescence of the metallofullerenes into an inner nanotube the carbon nanotube host returns to its original circular cross-section. This is due to a relaxation of the strain caused by the packing of the encapsulated La@C82 molecules into the nanotube. We identify the formation of some novel but transient fullerene-based structures formed during the intermediate stages of coalescence of the La@C82 into an inner nanotube. These results highlight the flexible nature of SWNTs and their ability to adapt their cross-sectional profile depending upon forces induced by material encapsulated within

Design of Porous Core–Shell Manganese Oxides to Boost Electrocatalytic Dinitrogen Reduction

Harnessing the electrochemical nitrogen reduction reaction (NRR), where renewable electricity and H2O are used for NH3 production, is regarded as an effective and clean protocol for N2 fixation. The design and development of new active, selective, and durable NRR electrocatalysts are expected to achieve this. Here, we design a well-defined porous core–shell heterostructure comprising Mn2O3–MnO (as the core) and Mn3O4 (as the shell). The unique composite is shown to efficiently facilitate N2 adsorption and reduction in a neutral electrolyte, delivering an impressive NH3 FE (∼23.8%) with a reasonable NH3 formation rate (22.4 μgNH3 h–1 mgcat–1) at a cathodic voltage of −0.3 V (versus reversible hydrogen electrode). The electrocatalytic properties can be readily modulated by tuning the shell thickness. Our measured performance surpasses those of most nonmetallic, transition-metal-, and noble-metal-based catalysts reported in the prior literature. Equally importantly, the electrocatalytic activity maintains good stability up to 60 h. The outstanding electrochemical performance is attributed to the combined advantages of a large interface between the metal oxides and a unique core–shell structure with a high density of surface-exposed sites, pores, and oxygen vacancies

Aligned Rectangular Few-Layer Graphene Domains on Copper Surfaces

We show that aligned rectangular few layer graphene (FLG) domains can be produced on Cu surfaces using atmospheric pressure chemical vapor deposition. For the growth temperatures of 990 and 1000 °C the FLG domains are primarily hexagonal in shape, but at 980 °C, morphology transition of FLG domains is observed associated with different Cu grains. Rectangular FLG domains are synthesized for the first time and we show using electron backscattered diffraction that they only grow on Cu grains with (111) orientation because of the interplay between the atomic structure of the Cu lattice and the graphene domains. We show that hexagonal FLG domains can form on nearly all other non-(111) Cu surfaces. These results indicate that even at atmospheric pressure, the interplay between the Cu atomic structure and graphene formation can be strong and lead to aligned rectangular domains

Two-Dimensional Coalescence Dynamics of Encapsulated Metallofullerenes in Carbon Nanotubes

We report on the coalescence of a two-dimensional (2D) chain of La@C82 metallofullerene molecules encapsulated inside a single-wall carbon nanotube (SWNT). 2D packing of metallofullerenes is known to adopt a zigzag arrangement and cause elliptical distortion to the cross-section of the SWNT host. We show that after coalescence of the metallofullerenes into an inner nanotube the carbon nanotube host returns to its original circular cross-section. This is due to a relaxation of the strain caused by the packing of the encapsulated La@C82 molecules into the nanotube. We identify the formation of some novel but transient fullerene-based structures formed during the intermediate stages of coalescence of the La@C82 into an inner nanotube. These results highlight the flexible nature of SWNTs and their ability to adapt their cross-sectional profile depending upon forces induced by material encapsulated within

Aligned Rectangular Few-Layer Graphene Domains on Copper Surfaces

We show that aligned rectangular few layer graphene (FLG) domains can be produced on Cu surfaces using atmospheric pressure chemical vapor deposition. For the growth temperatures of 990 and 1000 °C the FLG domains are primarily hexagonal in shape, but at 980 °C, morphology transition of FLG domains is observed associated with different Cu grains. Rectangular FLG domains are synthesized for the first time and we show using electron backscattered diffraction that they only grow on Cu grains with (111) orientation because of the interplay between the atomic structure of the Cu lattice and the graphene domains. We show that hexagonal FLG domains can form on nearly all other non-(111) Cu surfaces. These results indicate that even at atmospheric pressure, the interplay between the Cu atomic structure and graphene formation can be strong and lead to aligned rectangular domains