A new route towards uniformly functionalized single-layer graphene

It is shown, by DFT calculations, that the uniform functionalization of upper layer of graphite by hydrogen or fluorine does not change essentially its bonding energy with the underlying layers, whereas the functionalization by phenyl groups decreases the bonding energy by a factor of approximately ten. This means that the functionalized monolayer in the latter case can be easily separated by mild sonication. According to our computational results, such layers can be cleaned up to pure graphene, as well as functionalized further up to 25% coverage, without essential difficulties. The energy gap within the interval from 0.5 to 3 eV can be obtained by such one-side funtionalization using different chemical species.Comment: 15 pages, 3 figures, to appear in J. Phys. D: Applied Physic

Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite

We report on unusual magnetic properties observed in the nanofluid room-temperature ferromagnetic graphite (with an average particle size of l=10nm). More precisely, the measured magnetization exhibits a low-temperature anomaly (attributed to manifestation of finite size effects below the quantum temperature) as well as pronounced temperature oscillations above T=50K (attributed to manifestation of the hard-sphere type pair correlations between ferromagnetic particles in the nanofluid)

Mild sonochemical exfoliation of bromine-intercalated graphite: a new route towards graphene

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br(2) into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 mu m, corresponding to the grain size of the starting material

First-principles modeling of the polycyclic aromatic hydrocarbons reduction

Density functional theory modelling of the reduction of realistic nanographene molecules (C42H18, C48H18 and C60H24) by molecular hydrogen evidences for the presence of limits in the hydrogenation process. These limits caused the contentions between three-fold symmetry of polycyclic aromatic hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs. Increase of the binding energy between nanographenes during reduction is also discussed as possible cause of the experimentally observed limited hydrogenation of studied nanographenes.Comment: 18 pages, 7 figures, accepted to J. Phys. Chem.

Mild sonochemical exfoliation of bromine-intercalated graphite: a new route towards graphene

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br2 into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 $mu$m, corresponding to the grain size of the starting material.Comment: 10 pages 4 figure

Bromination of double-walled carbon nanotubes

Double-walled carbon nanotubes (DWCNTs) synthesized by catalytic chemical vapor deposition (CCVD) have been functionalized by bromine vapor at room temperature. At least two different bromine species were detected in the product using X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis. The primary form is negatively charged Br2 molecules exhibiting an intense resonance at ∼238 cm−1 in the Raman spectrum. The electron transfer from the nanotubes to the adsorbed molecules is detected from C 1s XPS and near-edge X-ray absorption fine structure spectra. The optical absorption spectra reveal that although the metallic nanotubes are more reactive to Br2, the outer semiconducting nanotubes also readily interact with Br2 adsorbates. The secondary bromine form is attributed to covalent C-Br bonding, and its possible sources are discussed in the light of quantum-chemical calculations. Analysis of the XPS, Raman, and optical absorption spectra of the Br-DWCNTs annealed at 100-170 ° C indicates preservation of a part of bromine molecules in samples that affects the electronic and vibration properties of nanotubes

An <I>In-Situ</I> Prepared Nano-Manipulator Tip for Electrical Characterization of Free Standing Graphene Like Sheets Inside a Focused Ion Beam/Scanning Electron Microscope

Although contacting and moving atoms has been demonstrated using probe techniques, for many nano-objects, a fast and reproducible nano-probe technique is needed to acquire a large number of electrical measurements on nano-objects that are often similar but not the identical. Nano-manipulators have become a common tool in many scanning electron microscopes (SEM) and focussed ion beam devices (FIB). They can be rapidly and reproducibly moved from one nano-object to another. In this work we present a procedure to obtain reproducible electrical measurements of nano- to micron-sized objects by using a sharp, tungsten tip with well defined surface properties. The tip is a part of a manipulator and is sharpened in-situ by using the gallium ion beam inside a focused ion beam/scanning electron microscope (FIB/SEM). The contact resistance between a Au surface and the tip is 70 kΩ before the sharpening procedure and 10 Ω after sharpening. The leakage current of the total set-up of 10pA makes it possible to measure currents through a variety of nano-objects. This measurement technique is applied to measure the resistance of as grown, water treated and two HCl treated carbon nanosheets (CNS). These CNS vary in size and morphology. Using this nano-contacting set-up, we could obtain measurements of more than 400 different CNS. The obtained histograms allow us to observe a clear decrease of the resistance between original and 3 hour acid treated CNSs. We observe that longer periods of exposure of the CNS to the HCl do not further modify the resistance.</p

Transfer of carbon nanosheet films to nongrowth, zero thermal budget substrates

Carbon-based nanostructures and materials have become a popular subject of research due to their unique thermal, mechanical, electrical, and optical properties. For example, the strong C-C bonds of graphene-based systems allow for excellent thermal conduction at room temperature and the conjugation of the sp(2) lattice enables extremely high electron mobility. However, the use of carbon nanostructures as a component in polymer composites, sensors, mirco-electro-mechanical systems, and both rigid and flexible electronics has been limited by several factors, including the incompatibility with standard photolithography techniques, the high temperatures required for the nanostructure growth, and the presence of-or complication-of removing noncarbon species. Here, the authors report on a novel method for the transfer of carbon nanosheets to a low or zero thermal budget substrate while maintaining their original morphology and electrical properties. Four-point probe measurements' post-transfer shows the retention of in-plane conductivity and scanning electron microscopy reveals the preservation of the original vertical morphology. Raman spectroscopy measurements confirm the retention of the graphitic structure of the post-transfer nanosheet film. This new transfer technique builds on the ability to conformally coat nanosheets while maintaining the original ultrahigh surface area morphology and the ability to fully incorporate nanosheets into several polymers while maintaining the original nanostructure separation. For a demonstration of the usefulness of polymer filling, carbon nanosheets were used as an ultrahigh surface area electrode for the photoactive polymer poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] in proof of principle experiments of a nanosheet-based organic photovoltaic device.</p