/pdf/honeycomb-carbon-a-review-of-graphene-bjl5wl6ai8.pdf

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.

/pdf/graphitic-carbon-nitride-materials-variation-of-structure-2o5pjcr9g6.pdf

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

Ga(CN)3 has been prepared for the first time with a new method for preparation of inorganic cyanides. Pure crystalline material is formed by reaction of Cl2GaN3 with SiMe3CN via elimination of SiMe3N3 and SiMe3Cl. Reaction of GaCl3 with SiMe3CN also provides Ga(CN)3. A new convenient route to GeMe3CN and SnMe3CN is described, but reactions of GaCl3 with these compounds result in Lewis acid−base adducts. The composition of Ga(CN)3 was confirmed by spectroscopic and elemental analysis. Quantitative X-ray powder diffraction was used to refine the cubic structure, which has CN groups with orientational disorder in a Prussian-blue-like network structure. The symmetry is Pm3m, a = 5.295(2) A. Ga is octahedrally surrounded by on average three C and three N atoms with a Ga−(C,N) bond length of 2.072(2) A, and the C−N bond length is 1.148(1) A. LiGa(CN)4 was prepared by reaction of Ga(CN)3 with LiCN and was characterized by quantitative X-ray diffraction. The symmetry is P43m, a = 5.874(2) A, and the structure c...

Synthetic Routes to Ga(CN)3 and MGa(CN)4 (M: Li, Cu) Framework Structures.

A hybrid substrate technology based on nearly lattice matched GaN/ZrB2-buffered Si(111) was utilized to grow AlxGa1−xN heterostructures via a new method involving displacement reactions of D2GaN3 vapors and Al atomic beams at unprecedented low temperatures of 650–700 °C, compatible with Si-processing conditions. Homogeneous films exhibited strong cathodoluminescence with narrow peak widths comparable to those observed in MOCVD samples grown at 1100 °C. The formation of the enabling GaN/ZrB2buffer is investigated theoretically using first principle simulations. As an alternative to the GaN/ZrB2buffer technology we also developed novel HfxZr1−xB2 heterostructures (x = 0–1) possessing adjustable in-plane strain, which accommodates direct growth of lattice matched AlxGa1−xN on Si(111). Spectroscopic ellipsometry indicated that the boride films possess tunable band structure evolving smoothly from ZrB2 to HfB2, in the spirit of the Virtual Crystal Approximation model. This paves the way for the fabrication of optimized hybrid substrates that enable large scale nitride device integration with Si technologies via simultaneous optical and strain engineering.

Synthesis of (Hf, Zr)B2-based heterostructures: hybrid substrate systems for low temperature Al–Ga–N integration with Si

L'invention porte sur des dispositifs de photodiode avec des couches actives de GeSn qui peuvent etre directement integres sur des plateformes Si p+ dans des conditions compatibles avec la technologie CMOS. Il a ete trouve que meme des quantites minimes d'incorporation de Sn (2 %) etendent de facon remarquable la plage de detection IR jusqu'a au moins 1 750 nm et augmentent sensiblement l'absorption. La photoreponse correspondante peut recouvrir la totalite des bandes de telecommunication en utilisant entierement des materiaux du groupe IV.

John Kouvetakis

Papers

Synthetic Routes to Ga(CN)3 and MGa(CN)4 (M: Li, Cu) Framework Structures.

Synthesis of (Hf, Zr)B2-based heterostructures: hybrid substrate systems for low temperature Al–Ga–N integration with Si

Photodétecteurs infrarouges de gesn

Consistent optical and electrical determination of carrier concentrations for the accurate modeling of the transport properties of n-type Ge

TEM characterization of SiGeC material system