685 research outputs found
Tuneable molecular doping of corrugated graphene
Density functional theory (DFT) modeling of the physisorption of four
different types of molecules (toluene, bromine dimmer, water and nitrogen
dioxide) over and above graphene ripples has been performed. For all types of
molecules changes of charge transfer and binding energies in respect to flat
graphene is found. The changes in electronic structure of corrugated graphene
and turn of {\pi}-orbitals of carbon atoms in combination with chemical
structure of adsorbed molecules are proposed as the causes of difference with
the perfect graphene case and variety of adsorption properties of different
types of the molecules. Results of calculation suggest that the tops of the
ripples are more attractive for large molecules and valley between ripples for
small molecules. Stability of molecules on the ripples and energy barriers for
migration over flat and corrugated graphene is also discussed.Comment: 15 pages, 5 figures, accepted in Surface Scienc
Determination of the lateral size and thickness of solution-processed graphene flakes
We present a method to determine the lateral size distribution of solution–processed graphene via direct image analysis techniques. Initially transmission electron microscopy (TEM) and optical microscopy (OM) were correlated and used to provide a reliable benchmark. A rapid, automated OM method was then developed to obtain the distribution from thousands of flakes, avoiding statistical uncertainties and providing high accuracy. Dynamic light scattering (DLS) was further employed to develop an in-situ method to derive the number particle size distribution (PSD) for a dispersion, with a deviation lower than 22% in the sub-micron regime. Methods for determining flake thickness are also discussed
Direct exfoliation and dispersion of two-dimensional materials in pure water via temperature control
The high-volume synthesis of two-dimensional (2D) materials in the form of platelets is desirable for various applications. While water is considered an ideal dispersion medium, due to its abundance and low cost, the hydrophobicity of platelet surfaces has prohibited its widespread use. Here we exfoliate 2D materials directly in pure water without using any chemicals or surfactants. In order to exfoliate and disperse the materials in water, we elevate the temperature of the sonication bath, and introduce energy via the dissipation of sonic waves. Storage stability greater than one month is achieved through the maintenance of high temperatures, and through atomic and molecular level simulations, we further discover that good solubility in water is maintained due to the presence of platelet surface charges as a result of edge functionalization or intrinsic polarity. Finally, we demonstrate inkjet printing on hard and flexible substrates as a potential application of water-dispersed 2D materials.close1
Graphene under hydrostatic pressure
In-situ high pressure Raman spectroscopy is used to study monolayer, bilayer
and few-layer graphene samples supported on silicon in a diamond anvil cell to
3.5 GPa. The results show that monolayer graphene adheres to the silicon
substrate under compressive stress. A clear trend in this behaviour as a
function of graphene sample thickness is observed. We also study unsupported
graphene samples in a diamond anvil cell to 8 GPa, and show that the properties
of graphene under compression are intrinsically similar to graphite. Our
results demonstrate the differing effects of uniaxial and biaxial strain on the
electronic bandstructure.Comment: Accepted in Physical Review B with minor change
The role of IREB2 and transforming growth factor beta-1 genetic variants in COPD: a replication case-control study
<p>Abstract</p> <p>Background</p> <p>Genetic factors are known to contribute to COPD susceptibility and these factors are not fully understood. Conflicting results have been reported for many genetic studies of candidate genes based on their role in the disease. Genome-wide association studies in combination with expression profiling have identified a number of new candidates including <it>IREB2</it>. A meta-analysis has implicated transforming growth factor beta-1 (<it>TGFbeta1</it>) as a contributor to disease susceptibility.</p> <p>Methods</p> <p>We have examined previously reported associations in both genes in a collection of 1017 white COPD patients and 912 non-diseased smoking controls. Genotype information was obtained for seven SNPs in the <it>IREB2 </it>gene, and for four SNPs in the <it>TGFbeta1 </it>gene. Allele and genotype frequencies were compared between COPD cases and controls, and odds ratios were calculated. The analysis was adjusted for age, sex, smoking and centre, including interactions of age, sex and smoking with centre.</p> <p>Results</p> <p>Our data replicate the association of <it>IREB2 </it>SNPs in association with COPD for SNP rs2568494, rs2656069 and rs12593229 with respective adjusted p-values of 0.0018, 0.0039 and 0.0053. No significant associations were identified for <it>TGFbeta1</it>.</p> <p>Conclusions</p> <p>These studies have therefore confirmed that the <it>IREB2 </it>locus is a contributor to COPD susceptibility and suggests a new pathway in COPD pathogenesis invoking iron homeostasis.</p
Mechanically Assisted Exfoliation and Functionalization of Thermally Converted Graphene Sheets
Published versio
Surfactant-aided exfoliation of molybdenum disulfide for ultrafast pulse generation through edge-state saturable absorption
We use liquid phase exfoliation to produce dispersions of molybdenum
disulphide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical
structures of the bile salt surfactants play a crucial role in the exfoliation
and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched
in single and few (<6) layer flakes with large edge to surface area ratio. We
use the dispersions to fabricate free-standing polymer composite wide-band
saturable absorbers to develop mode-locked and Q- switched fibre lasers,
tunable from 1535-1565 and 1030-1070 nm, respectively. We attribute this
sub-bandgap optical absorption and its nonlinear saturation behaviour to
edge-mediated states introduced within the material band-gap of the exfoliated
MoS2 nanoflakes.EJRK and TH acknowledge support from the Royal Academy of Engineering (RAEng).This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/pssb.20155230
- …