Transparent, conductive, and ultrathin graphene films, as an alternative to the ubiquitously employed metal oxides window electrodes for solid-state dye-sensitized solar cells, are demonstrated. These graphene films are fabricated from exfoliated graphite oxide, followed by thermal reduction. The obtained films exhibit a high conductivity of 550 S/cm and a transparency of more than 70% over 1000−3000 nm. Furthermore, they show high chemical and thermal stabilities as well as an ultrasmooth surface with tunable wettability.

Transparent, Conductive Graphene Electrodes for Dye-Sensitized Solar Cells

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

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

A review on g-C3N4-based photocatalysts

Nitrogen-doped carbon nanotubes have been synthesized using pyrolysis and characterized by scanning tunneling spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular heterojunction devices.

/pdf/identification-of-electron-donor-states-in-n-doped-carbon-4g3h675udc.pdf

Identification of electron donor states in N-doped carbon nanotubes

Nitrogen doped carbon nanotubes have been synthesized using pyrolysis and characterized by Scanning Tunneling Spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular hetero-junction devices.

https://arxiv.org/pdf/cond-mat/0011318.pdf

Identification of Electron Donor States in N-doped Carbon Nanotubes

By utilizing the current transients in scanning tunneling spectroscopy, the local interfacial electronics between multiwalled carbon nanotubes and several supporting substrates has been investigated. Voltage offsets in the tunneling spectra are directly correlated with the formation of a dipole layer at the nanotube-substrate interface, strongly suggesting the formation of interface states. Further, a systematic variation in this local potential, as a function of tube diameter, is observed for both metallic substrates (Au) and semimetallic substrates (graphite). In both cases, for tubes with diameters between \ensuremath{\sim}5 nm and 30 nm, the interfacial potential is nearly constant as a function of tube diameter. However, for tube diameters 5 nm, a dramatic change in the local potential is observed. Using ab initio techniques, this diameter-dependent electronic interaction is shown to derive from changes in the tube-substrate hybridization that results from the curvature of the nanotubes.

/pdf/substrate-interface-interactions-between-carbon-nanotubes-15h27or71l.pdf

Substrate-interface interactions between carbon nanotubes and the supporting substrate

Changes in the local density of states (LDOS) of kinked multiwalled carbon nanotubes have been studied using scanning tunneling microscopy and spectroscopy (STM)/(STS). The measured STS spectra in the inelastically kinked region show that the LDOS is asymmetric about the Fermi level, while the spectra from regions away from the kink exhibit the usual symmetric LDOS that corresponds to perfect tubes. In the kinked region, the distribution of the unoccupied states is suppressed; this suppression of the conduction band states becomes unnoticeable ∼1.66 nm from the kink center.

Electronic structure of kinked multiwalled carbon nanotubes

We have studied the effect of strain on the electronic properties of multiwall carbon nanotubes using scanning tunneling microscopy and spectroscopy. While small elastic strain causes no change of the electronic properties of the nanotubes, tubes under large strain by lying over an inter-grain boundary of the Au substrate show drastic electronic heterogeneity. The observed variation in local electronic property is explained in terms of the mechanical relaxation of the outer most layer of the tube. This provides first evidence of the effect of mechanical modification on local electronic structure of a carbon nanotube.

/pdf/strain-induced-electronic-property-heterogeneity-of-a-carbon-o10m8bo32f.pdf

D. Tekleab

Papers

Identification of electron donor states in N-doped carbon nanotubes

Identification of Electron Donor States in N-doped Carbon Nanotubes

Substrate-interface interactions between carbon nanotubes and the supporting substrate

Electronic structure of kinked multiwalled carbon nanotubes

Strain-induced electronic property heterogeneity of a carbon nanotube