Growth Kinetics of Graphene on Cu(111) Foils from Methane, Ethyne, Ethylene, and Ethane.

Chemical vapor deposition of carbon precursors on Cu-based substrates at temperatures exceeding 1000 °C is currently a typical route for the scalable synthesis of large-area high-quality single-layer graphene (SLG) films. Using molecules with higher activities than CH may afford lower growth temperatures that might yield fold- and wrinkle-free graphene. The kinetics of growth of graphene using hydrocarbons other than CH are of interest to the scientific and industrial communities.

Effect of Sample Geometry on Graphitization of Polyacrylonitrile.

In this study, it is analyzed how sample geometry (spheres, nanofibers, or films) influences the graphitization behavior of polyacrylonitrile (PAN) molecules. The chemical bonding and changes in the composition of these three geometries are studied at the oxidation, carbonization, and graphitization stages via scanning electron microscopy (SEM), in situ thermogravimetric-infrared (TGA-IR) analysis, elemental analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The influence of molecular alignment on the graphitization of the three sample geometries is investigated using synchrotron wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM).

Growth of diamond in liquid metal at 1 atm pressure.

Natural diamonds were (and are) formed (thousands of million years ago) in the upper mantle of Earth in metallic melts at temperatures of 900-1,400 °C and at pressures of 5-6 GPa (refs. ). Diamond is thermodynamically stable under high-pressure and high-temperature conditions as per the phase diagram of carbon.

3D microprinting of inorganic porous materials by chemical linking-induced solidification of nanocrystals.

Three-dimensional (3D) microprinting is considered a next-generation manufacturing process for the production of microscale components; however, the narrow range of suitable materials, which include mainly polymers, is a critical issue that limits the application of this process to functional inorganic materials. Herein, we develop a generalised microscale 3D printing method for the production of purely inorganic nanocrystal-based porous materials. Our process is designed to solidify all-inorganic nanocrystals via immediate dispersibility control and surface linking-induced interconnection in the nonsolvent linker bath and thereby creates multibranched gel networks.

Protocol for the electrochemical polymerization of polyhydrocarbons from chlorinated methanes and an analysis of its polymerization reaction pathway.

The mass production of polyhydrocarbons (PHCs) is achieved through electrochemical polymerization and its synthetic pathway is investigated using a combination of electrochemical techniques, NMR, and Fourier transform infrared (FTIR) spectroscopy. Here, we present a protocol for the electrochemical polymerization of PHCs from chlorinated methanes and an analysis of its polymerization reaction pathway. We describe steps for large-scale synthesis and characterization of PHCs and studying electrochemical polymerization reactions using cyclic voltammetry and chronoamperometry techniques along with NMR and FTIR spectroscopy using isotope-labeled reactants.

Direct Electrochemical Functionalization of Graphene Grown on Cu Including the Reaction Rate Dependence on the Cu Facet Type.

We present an electrochemical method to functionalize single-crystal graphene grown on copper foils with a (111) surface orientation by chemical vapor deposition (CVD). Graphene on Cu(111) is functionalized with 4-iodoaniline by applying a constant negative potential, and the degree of functionalization depends on the applied potential and reaction time. Our approach stands out from previous methods due to its transfer-free method, which enables more precise and efficient functionalization of single-crystal graphene.

Growth Mechanism and Kinetics of Diamond in Liquid Gallium from Quantum Mechanics Molecular Dynamics Simulations.

Ruoff and co-workers recently demonstrated low-temperature (1193 K) homoepitaxial diamond growth from liquid gallium solvent. To develop an atomistic mechanism for diamond growth underlying this remarkable demonstration, we carried out density functional theory-based molecular dynamics (DFT-MD) simulations to examine the mechanism of single-crystal diamond growth on various low-index crystallographic diamond surfaces (100), (110), and (111) in liquid Ga with CH. We find that carbon linear chains form in liquid Ga and then react with the growing diamond surface, leading first to the formation of carbon rings on the surface and then initiation of diamond growth.

Long-range ordered porous carbons produced from C.

Carbon structures with covalent bonds connecting C molecules have been reported, but their production methods typically result in very small amounts of sample, which restrict the detailed characterization and exploration necessary for potential applications. We report the gram-scale preparation of a new type of carbon, long-range ordered porous carbon (LOPC), from C powder catalysed by α-LiN at ambient pressure. LOPC consists of connected broken C cages that maintain long-range periodicity, and has been characterized by X-ray diffraction, Raman spectroscopy, magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, aberration-corrected transmission electron microscopy and neutron scattering.

Decoupling of CVD-grown epitaxial graphene using NaCl intercalation.

The structural and electronic properties of graphene grown on catalytic metal surfaces are significantly modified graphene-substrate interaction. To minimize the influence of the metal substrate, a dielectric buffer layer can be introduced between the graphene and metal substrate. However, the catalytic synthesis of graphene limits the potential alternatives for buffer layers.

Using Single-Crystal Graphene to Form Arrays of Nanocapsules Enabling the Observation of Light Elements in Liquid Cell Transmission Electron Microscopy.

We have designed and fabricated a TEM (transmission electron microscopy) liquid cell with hundreds of graphene nanocapsules arranged in a stack of two SiN membranes. These graphene nanocapsules are formed on arrays of nanoholes patterned on the SiN membrane by focused ion beam milling, allowing for better resolution than for the conventional graphene liquid cells, which enables the observation of light elements, such as atomic structures of silicon. We suggest that multiple nanocapsules provide opportunities for consecutive imaging under the same conditions in a single liquid cell.

Epitaxial single-crystal hexagonal boron nitride multilayers on Ni (111).

Large-area single-crystal monolayers of two-dimensional (2D) materials such as graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides have been grown. hBN is considered to be the 'ideal' dielectric for 2D-materials-based field-effect transistors (FETs), offering the potential for extending Moore's law. Although hBN thicker than a monolayer is more desirable as substrate for 2D semiconductors, highly uniform and single-crystal multilayer hBN growth has yet to be demonstrated.

Silica Particle-Mediated Growth of Single Crystal Graphene Ribbons on Cu(111) Foil.

The authors report the growth of micrometer-long single-crystal graphene ribbons (GRs) (tapered when grown above 900 °C, but uniform width when grown in the range 850 °C to 900 °C) using silica particle seeds on single crystal Cu(111) foil. Tapered graphene ribbons grow strictly along the Cu<101> direction on Cu(111) and polycrystalline copper (Cu) foils. Silica particles on both Cu foils form (semi-)molten Cu-Si-O droplets at growth temperatures, then catalyze nucleation and drive the longitudinal growth of graphene ribbons.

Single-crystal two-dimensional material epitaxy on tailored non-single-crystal substrates.

The use of single-crystal substrates as templates for the epitaxial growth of single-crystal overlayers has been a primary principle of materials epitaxy for more than 70 years. Here we report our finding that, though counterintuitive, single-crystal 2D materials can be epitaxially grown on twinned crystals. By establishing a geometric principle to describe 2D materials alignment on high-index surfaces, we show that 2D material islands grown on the two sides of a twin boundary can be well aligned.

Folding and Fracture of Single-Crystal Graphene Grown on a Cu(111) Foil.

A single-crystal graphene film grown on a Cu(111) foil by chemical vapor deposition (CVD) has ribbon-like fold structures. These graphene folds are highly oriented and essentially parallel to each other. Cu surface steps underneath the graphene are along the <110> and <211> directions, leading to the formation of the arrays of folds.

Encoding Enantiomeric Molecular Chiralities on Graphene Basal Planes.

Graphene has demonstrated broad applications due to its prominent properties. Its molecular structure makes graphene achiral. Here, we propose a direct way to prepare chiral graphene by transferring chiral structural conformation from chiral conjugated amino acids onto graphene basal plane through π-π interaction followed by thermal fusion.

Large-Area Uniform 1-nm-Level Amorphous Carbon Layers from 3D Conformal Polymer Brushes. A "Next-Generation" Cu Diffusion Barrier?

A reliable method for preparing a conformal amorphous carbon (a-C) layer with a thickness of 1-nm-level, is tested as a possible Cu diffusion barrier layer for next-generation ultrahigh-density semiconductor device miniaturization. A polystyrene brush of uniform thickness is grafted onto 4-inch SiO /Si wafer substrates with "self-limiting" chemistry favoring such a uniform layer. UV crosslinking and subsequent carbonization transforms this polymer film into an ultrathin a-C layer without pinholes or hillocks.

Proton affinity and gas phase basicity of diamandoid molecules: diamantane to CH.

Calculated proton affinities (PAs) and gas phase basicities (GPBs) are reported for diamantane (CH), triamantane (CH), 'globular and planar' isomers of tetramantane (CH) and pentamantane (CH), and for one 'globular' isomer of each of the larger diamondoid molecules: CH, CH, CH, and CH. Assuming CH as the parent diamondoid molecule, we calculated PA and GPB values for a variety of CH isomers, as well as for the reaction CH + H yielding CH + H(g); the latter is slightly favored based on GPB values for diamantane through pentamantane, but less favored compared to certain CH isomers of CH, CH, and CH. Indeed, the GPB values of CH, CH, and CH classifiy them as 'superbases'.

Wafer-scale single-crystal monolayer graphene grown on sapphire substrate.

The growth of inch-scale high-quality graphene on insulating substrates is desirable for electronic and optoelectronic applications, but remains challenging due to the lack of metal catalysis. Here we demonstrate the wafer-scale synthesis of adlayer-free ultra-flat single-crystal monolayer graphene on sapphire substrates. We converted polycrystalline Cu foil placed on AlO(0001) into single-crystal Cu(111) film via annealing, and then achieved epitaxial growth of graphene at the interface between Cu(111) and AlO(0001) by multi-cycle plasma etching-assisted-chemical vapour deposition.

Multifunctional Macroassembled Graphene Nanofilms with High Crystallinity.

A "cooling-contraction" method to separate large-area (up to 4.2 cm in lateral size) graphene oxide (GO)-assembled films (of nanoscale thickness) from substrates is reported. Heat treatment at 3000 °C of such free-standing macroscale films yields highly crystalline "macroassembled graphene nanofilms" (nMAGs) with 16-48 nm thickness.

Single-crystal, large-area, fold-free monolayer graphene.

Chemical vapour deposition of carbon-containing precursors on metal substrates is currently the most promising route for the scalable synthesis of large-area, high-quality graphene films. However, there are usually some imperfections present in the resulting films: grain boundaries, regions with additional layers (adlayers), and wrinkles or folds, all of which can degrade the performance of graphene in various applications. There have been numerous studies on ways to eliminate grain boundaries and adlayers, but graphene folds have been less investigated.

The Wet-Oxidation of a Cu(111) Foil Coated by Single Crystal Graphene.

The wet-oxidation of a single crystal Cu(111) foil is studied by growing single crystal graphene islands on it followed by soaking it in water. O-labeled water is also used; the oxygen atoms in the formed copper oxides in both the bare and graphene-coated Cu regions come from water. The oxidation of the graphene-coated Cu regions is enabled by water diffusing from the edges of graphene along the bunched Cu steps, and along some graphene ripples where such are present.

Sub-4 nm Nanodiamonds from Graphene-Oxide and Nitrated Polycyclic Aromatic Hydrocarbons at 423 K.

Nanodiamonds are interesting materials from the point of view of their biocompatibility and their chemical, spectroscopic, and mechanical properties. Current synthetic methods for nanodiamonds involve harsh environments, which are potentially hazardous in addition to being expensive. We report a low-temperature (423 K) hydrothermal approach to form nanodiamonds by using graphene-oxide or nitrated polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, or pyrene) as a starting material.

A general approach to composites containing nonmetallic fillers and liquid gallium.

We report a versatile method to make liquid metal composites by vigorously mixing gallium (Ga) with non-metallic particles of graphene oxide (G-O), graphite, diamond, and silicon carbide that display either paste or putty-like behavior depending on the volume fraction. Unlike Ga, the putty-like mixtures can be kneaded and rolled on any surface without leaving residue. By changing temperature, these materials can be stiffened, softened, and, for the G-O-containing composite, even made porous.

Reference-free THz-TDS conductivity analysis of thin conducting films.

We present a reference-free method to determine electrical parameters of thin conducting films by steady state transmission-mode terahertz time-domain spectroscopy (THz-TDS). We demonstrate that the frequency-dependent AC conductivity of graphene can be acquired by comparing the directly transmitted THz pulse with a transient internal reflection within the substrate which avoids the need for a standard reference scan. The DC sheet conductivity, scattering time, carrier density, mobility, and Fermi velocity of graphene are retrieved subsequently by fitting the AC conductivity with the Drude model.