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Honeycomb Carbon: A Review of Graphene

Electrolytes and interphases in Li-ion batteries and beyond.

To realize graphene-based electronics, various types of graphene are required; thus, modulation of its electrical properties is of great importance. Theoretic studies show that intentional doping is a promising route for this goal, and the doped graphene might promise fascinating properties and widespread applications. However, there is no experimental example and electrical testing of the substitutionally doped graphene up to date. Here, we synthesize the N-doped graphene by a chemical vapor deposition (CVD) method. We find that most of them are few-layer graphene, although single-layer graphene can be occasionally detected. As doping accompanies with the recombination of carbon atoms into graphene in the CVD process, N atoms can be substitutionally doped into the graphene lattice, which is hard to realize by other synthetic methods. Electrical measurements show that the N-doped graphene exhibits an n-type behavior, indicating substitutional doping can effectively modulate the electrical properties of graphene. Our finding provides a new experimental instance of graphene and would promote the research and applications of graphene.

Synthesis of N-Doped Graphene by Chemical Vapor Deposition and Its Electrical Properties

Graphitic carbon nitride, g-C3N4, can be made by polymerization of cyanamide, dicyandiamide or melamine. Depending on reaction conditions, different materials with different degrees of condensation, properties and reactivities are obtained. The firstly formed polymeric C3N4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C3N4 species, based on tri-s-triazine (C6N7) units as elementary building blocks. High resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif. Due to the polymerization-type synthesis from a liquid precursor, a variety of material nanostructures such as nanoparticles or mesoporous powders can be accessed. Those nanostructures also allow fine tuning of properties, the ability for intercalation, as well as the possibility to give surface-rich materials for heterogeneous reactions. Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide. Model calculations are presented to explain this unusual case of heterogeneous, metal-free catalysis. Carbon nitride can also act as a heterogeneous reactant, and a new family of metal nitride nanostructures can be accessed from the corresponding oxides.

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Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

Polymeric graphitic carbon nitride materials (for simplicity: g-C(3)N(4)) have attracted much attention in recent years because of their similarity to graphene. They are composed of C, N, and some minor H content only. In contrast to graphenes, g-C(3)N(4) is a medium-bandgap semiconductor and in that role an effective photocatalyst and chemical catalyst for a broad variety of reactions. In this Review, we describe the "polymer chemistry" of this structure, how band positions and bandgap can be varied by doping and copolymerization, and how the organic solid can be textured to make it an effective heterogenous catalyst. g-C(3)N(4) and its modifications have a high thermal and chemical stability and can catalyze a number of "dream reactions", such as photochemical splitting of water, mild and selective oxidation reactions, and--as a coactive catalytic support--superactive hydrogenation reactions. As carbon nitride is metal-free as such, it also tolerates functional groups and is therefore suited for multipurpose applications in biomass conversion and sustainable chemistry.

Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: From Photochemistry to Multipurpose Catalysis to Sustainable Chemistry

We demonstrate the deposition of periodic arrays of uniformly sized GaN quantum dots onto a SiOx substrate. The dots are deposited using a nanolithography technique based on a combination of electron-beam-induced chemical vapor deposition and single-source molecular hydride chemistries. Under appropriate deposition conditions, we can deposit uniform dots of height 5 nm and full widths at half-maxima of 4 nm. The dot size is controlled by the spatial distribution of secondary electrons leaving the substrate surface. The smallest, most uniform void-free dots are created via nanolithography of molecules adsorbed on the substrate surface.

Synthesis of uniform GaN quantum dot arrays via electron nanolithography of D2GaN3

Extended Compositional Range for the Synthesis of SWIR and LWIR Ge1–ySny Alloys and Device Structures via CVD of SnH4 and Ge3H8

Heteroepitaxial films of Ge1-x C x (x < 7%) alloys have been grown on Si (100) substrates using ultrahigh-vacuum chemical vapour deposition reactions involving GeH4 and several different germylmethane precursors (GeH3)4-x CH x (x = 1-3), at temperatures in the range 470-540°C. The layer composition and crystallinity were assessed using Rutherford back-scattering spectroscopy, including C-resonance analysis, and the film microstructure was characterized using cross-sectional transmission electron microscopy. Irrespective of the particular germylmethane precursor used for deposition, alloys with low C concentrations had high crystallinity with low defect density, whereas those with high C content had an increased density of structural defects. Greater C incorporation generally led to films with flatter and smoother surfaces, implying that the addition of C had compensated strain due to lattice mismatch and promoted two-dimensional growth.

Structural properties of heteroepitaxial germanium-carbon alloys grown on Si (100)

Epitaxial growth of the pseudo-binary wide band gap semiconductor SiCAlN

A low temperature method for growing quaternary epitaxial films having the formula XCZN wherein X is a Group IV element and Z is a Group III element. A Gaseous flux of precursor H3XCN and a vapor flux of Z atoms are introduced into a gas-source molecular beam epitaxial (MBE) chamber to form thin film of XCZN on a substrate preferably of silicon or silicon carbide. Silicon substrates may comprise a native oxide layer, thermal oxide layer, AlN/silicon structures or an interface of Al—O—Si—N formed from interlayers of Al on the Si02 layer. Epitaxial thin film SiCAlN and AlN are provided. Bandgap engineering is disclosed. Semiconductor devices produced by the present method exhibit bandgaps and spectral ranges which make them useful for optoelectronic and microelectronic applications. SiCAlN deposited on large-diameter silicon wafers are substrates for growth of conventional Group III nitrides such as AlN. The quaternary compounds exhibit extreme hardness.

John Kouvetakis

Papers

Synthesis of uniform GaN quantum dot arrays via electron nanolithography of D2GaN3

Extended Compositional Range for the Synthesis of SWIR and LWIR Ge1–ySny Alloys and Device Structures via CVD of SnH4 and Ge3H8

Structural properties of heteroepitaxial germanium-carbon alloys grown on Si (100)

Epitaxial growth of the pseudo-binary wide band gap semiconductor SiCAlN

Low temperature epitaxial growth of quartenary wide bandgap semiconductors