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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

In summary, epitaxial Ge1-xSnx films with hole mobilities as high as 600 cm2V-1s-1 were deposited on Si(100) substrates by UHV-CVD and used to fabricate photoconductor devices employing standard semiconductor processing steps. Performance measurements of the produced device provided feedback for improvement of the Ge1-xSnx material quality during the growth. Photoconductor devices showed maximum 0.5% decrease of the resistance upon irradiation by 1.55 μm laser light with 5 mW power.

Photoresponse at 1.55 μm in GeSn epitaxial films grown on Si

Evolution of optical phonons in epitaxial Ge1−ySny structures

The title mol­ecule is dimeric, i.e. di-μ-tri­methyl­siloxy-bis­(di­chloro­aluminium), [Al2Cl4(C3H9Si)2], and possesses exact crystallographic inversion symmetry. The O atoms of the tri­methyl­siloxy groups bridge the two Al atoms to form a four-membered ring. The Si—O bond distance [1.711 (3) A], the Al—O mean bond distance [1.806 (4) A] and the mean Si—C bond distance [1.875 (6) A] appear to agree well with standard data. Mean values for C—Si—C, O—Si—C, and Si—O—Al angles are 112.9 (3), 105.8 (2), and 131.8 (2)° repectively. The two ring angles O—Al—O and Al—O—Al are 84.43 (16) and 95.57 (16)°, respectively.

The centrosymmetric dimer of di­chloro­(tri­methyl­siloxy)­aluminium

Highly strained metastable structures and selective area epitaxy of Ge-rich Ge1−xSix/Si(100) materials using nanoscale building blocks

The newly discovered AlPSi3 alloys 1, 2 , which are hybrids of zincblende AlP and diamond cubic Si, may represent a pathway to augmenting the optical performance of elemental silicon as a photovoltaic material, because our preliminary studies suggest that the absorption coefficient of these materials in the visible wavelength range is enhanced relative to Si. Yet, the inherent light absorption might be strongly dependent on the nanoscale structure of the alloy, namely the distribution of the Al-P bonds within the parent Si matrix 3 . Conventional TEM with the JEOL 4000EX and probe-corrected STEM/EELS analyses with Nion UltraSTEM 100 equipped with HERMES TM and Gatan Enfinium TM EELS spectrometers were used to study structure and chemistry of Al-P-Si alloys grown nearly lattice-matched on Si (001). Two samples designated 04 and 06 were analyzed in the present work.

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John Kouvetakis

Papers

Photoresponse at 1.55 μm in GeSn epitaxial films grown on Si

Evolution of optical phonons in epitaxial Ge1−ySny structures

The centrosymmetric dimer of dichloro(trimethylsiloxy)aluminium

Highly strained metastable structures and selective area epitaxy of Ge-rich Ge1−xSix/Si(100) materials using nanoscale building blocks

Atomic scale studies of structure and bonding in A1PSi3 alloys grown lattice-matched on Si(001)

John Kouvetakis

Papers

Photoresponse at 1.55 μm in GeSn epitaxial films grown on Si

Evolution of optical phonons in epitaxial Ge1−ySny structures

The centrosymmetric dimer of di­chloro­(tri­methyl­siloxy)­aluminium

Highly strained metastable structures and selective area epitaxy of Ge-rich Ge1−xSix/Si(100) materials using nanoscale building blocks

Atomic scale studies of structure and bonding in A1PSi3 alloys grown lattice-matched on Si(001)

The centrosymmetric dimer of dichloro(trimethylsiloxy)aluminium