Graphene is the name given to a two-dimensional sheet of sp2-hybridized carbon. Its extended honeycomb network is the basic building block of other important allotropes; it can be stacked to form 3D graphite, rolled to form 1D nanotubes, and wrapped to form 0D fullerenes. Long-range π-conjugation in graphene yields extraordinary thermal, mechanical, and electrical properties, which have long been the interest of many theoretical studies and more recently became an exciting area for experimentalists. While studies of graphite have included those utilizing fewer and fewer layers for some time,1 the field was delivered a jolt in 2004, when Geim and co-workers at Manchester University first isolated single-layer samples from graphite (see Figure 1).2 This led to an explosion of interest, in part because two-dimensional crystals were thought to be thermodynamically unstable at finite temperatures.3,4 Quasi-twodimensional films grown by molecular beam epitaxy (MBE) are stabilized by a supporting substrate, which often plays a significant role in growth and has an appreciable influence on electrical properties.5 In contrast, the mechanical exfoliation technique used by the Manchester group isolated the two-dimensional crystals from three-dimensional graphite. Resulting singleand few-layer flakes were pinned to the substrate by only van der Waals forces and could be made free-standing by etching away the substrate.6-9 This minimized any induced effects and allowed scientists to probe graphene’s intrinsic properties. The experimental isolation of single-layer graphene first and foremost yielded access to a large amount of interesting physics.10,11 Initial studies included observations of graphene’s ambipolar field effect,2 the quantum Hall effect at room temperature,12-17 measurements of extremely high carrier mobility,7,18-20 and even the first ever detection of single molecule adsorption events.21,22 These properties generated huge interest in the possible implementation of graphene in a myriad of devices. These include future generations of high-speed and radio frequency logic devices, thermally and electrically conductive reinforced composites, sensors, and transparent electrodes for displays and solar cells. Despite intense interest and continuing experimental success by device physicists, widespread implementation of graphene has yet to occur. This is primarily due to the difficulty of reliably producing high quality samples, especially in any scalable fashion.23 The challenge is really 2-fold because performance depends on both the number of layers present and the overall quality of the crystal lattice.19,24-26 So far, the original top-down approach of mechanical exfoliation has produced the highest quality samples, but the method is neither high throughput nor high-yield. In order to exfoliate a single sheet, van der Waals attraction between exactly the first and second layers must be overcome without disturbing any subsequent sheets. Therefore, a number of alternative approaches to obtaining single layers have been explored, a few of which have led to promising proof-ofconcept devices. Alternatives to mechanical exfoliation include primarily three general approaches: chemical efforts to exfoliate and stabilize individual sheets in solution,27-32 bottom-up methods to grow graphene directly from organic precursors,33-36 and attempts to catalyze growth in situ on a substrate.37-43 Each of these approaches has its drawbacks. For chemically derived graphene, complete exfoliation in solution so far requires extensive modification of the 2D crystal lattice, which degrades device performance.31,44 Alternatively, bottom-up techniques have yet to produce large and uniform † Department of Chemistry and Biochemistry and California NanoSystems Institute. ‡ Department of Materials Science and Engineering and California NanoSystems Institute. Chem. Rev. 2010, 110, 132–145 132

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

Honeycomb Carbon: A Review of Graphene

Electrolytes and interphases in Li-ion batteries and beyond.

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

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

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

Direct-gap photoluminescence and electroluminescence has been observed in Ge 1−y Sn y alloys. The emission in both cases is dominated by direct transitions exhibiting the expected compositional dependence. The data are consistent with the expected reduction of the Γ-L separation.

Direct gap photoluminescence and electroluminescence in Ge 1−y Sn y alloys

Synthesis of Ethynyl-Substituted Precursors to Carbon-Nitrogen-Sulfur Extended Structures: Reactions of C3N3F3 and C2N2SCl2 with Alkali- Metal (Trimethylsilyl)acetylides.

Ge1-ySny alloys represent a promising new class of IR semiconductors with tunable direct band gaps beyond that of Ge, allowing the optoelectronic capabilities of the material to be significantly extended into the mid IR. These alloys become direct gap semiconductors for y = 0.09 [1], making them an attractive alternative to Ge for application in purely group-IV interband lasers that are integrated onto Si-platforms. Significant progress has been made in recent years with the demonstration of high efficiency photodetectors and light emitting diodes containing up to 8% Sn [2,3]. However systematic optical studies of devices with concentrations near the indirect-to-direct transition are still lacking. A major problem with the synthesis of highly saturated materials with y > 0.08 is the strong dependence of the lattice parameter on the Sn content. This produces a significant lattice mismatch with Si and Ge platforms, making it difficult to integrate materials with sufficiently low defect densities as required for viable device performance. Furthermore, the associated compressive strains become an issue, rendering the material more indirect and adversely affecting light emission. For the fabrication of practical devices, relaxed films with large thickness are desirable but such films contain deleterious misfit dislocations that increase the non-radiative recombination rate. In this paper, we report the development of optimized growth protocols that enable fabrication of a new class of photodiodes featuring thick, bulk-like components with purposely designed microstructures. The device configurations comprise nGe/Ge1-ySny/p-Ge1-ySny stacks grown directly upon Si(100). The constituent layers feature defectengineered interfaces, allowing the fabrication of devices exhibiting strong direct-gap electroluminescence over a wide concentration range 0 ≤ y ≤ 0.11 for the first time. The intrinsic active regions are grown largely relaxed on Ge-buffered Si following low-temperature routes based on specialty Ge3H8 and SnD4 chemical sources. The devices contain only one defected interface between the intrinsic layer and the Ge buffer, while all other junctions are selected to be lattice-matched and thus devoid of dislocations.

/pdf/influence-of-device-microstructure-on-the-optical-properties-1x8r259h6x.pdf

Influence of Device Microstructure on The Optical Properties of Ge1-ySny (y=00.11) LEDs Produced by Next Generation Deposition Methods

The synthesis of butane-like (GeH3)2(SiH2)2 (1), (GeH3)2SiH(SiH3) (2), and (GeH3)2(SiH2GeH2) (3) Si−Ge hydrides with applications in low-temperature synthesis of Ge-rich Si1-xGex optoelectronic alloys has been demonstrated. The compositional, vibrational, structural, and thermochemical properties of these compounds were studied by FTIR, multinuclear NMR, mass spectrometry, Rutherford backscattering, and density functional theory (DFT) simulations. The analyses indicate that the linear (GeH3)2(SiH2)2 (1) and (GeH3)2(SiH2GeH2) (3) compounds exist as a mixture of the classic normal (n) and gauche (g) conformational isomers which do not seem to interconvert at 22 °C. The conformational proportions in the samples were determined using a new fitting procedure, which combines calculated molecular spectra to reproduce those observed by varying the global intensity, frequency scale, and admixture coefficients of the individual conformers. The (GeH3)2(SiH2)2 (1) species was then utilized to fabricate Si0.50Ge0.50 s...

/pdf/synthesis-of-butane-like-sige-hydrides-enabling-precursors-36348hbb5l.pdf

Synthesis of Butane-Like SiGe Hydrides: Enabling Precursors for CVD of Ge-Rich Semiconductors.

Synthesis and Structure of a Novel Lewis Acid‐Base Adduct, (H3C)3SiN3. times.GaCl3, en Route to Cl2GaN3 and Its Derivatives: Inorganic Precursors to Heteroepitaxial GaN.

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