Nitrated tyrosine adsorption on metal-doped graphene: A DFT study

The adsorption of nitrated tyrosine on the intrinsic and metal-doped graphene was studied by density functional theory in order to explore the possibility of using graphene-based biosensor to detect the protein tyrosine nitration (PTN). The configurations of (a) phenolic ring coordination and (b) nitro group coordination on the graphene were compared. It was found that nitrated tyrosine was physisorbed on the intrinsic graphene and favored coordinating with the intrinsic graphene by phenolic ring, while chemisorption was observed on Au, Cr and Ni-doped graphene with high binding energy. In contrast, the nitrated tyrosine favored coordinating with the metal-doped graphene through metal-nitro group configuration. The electronic density of states analysis showed strong orbital hybridization between the nitro group and metal-doped graphene. The calculation indicated that the metal-doped graphene was sensitive to the tyrosine nitration, thus suggesting the potential application of metal-doped graphene for PTN detection.     

Evaporation of water from particles in the aerodynamic lens inlet: an experimental study

The extremely high particle transmission efficiency of aerodynamic lens inlets resulted in their wide use in aerosol mass spectrometers. One of the consequences of transporting particles from high ambient pressure into the vacuum is that it is accompanied by a rapid drop in relative humidity (RH). Since many atmospheric particles exist in the form of hygroscopic water droplets, a drop in RH may result in a significant loss of water and even a change in phase. How much water is lost in these inlets is presently unknown. Since water loss can affect particle size, transmission efficiency, ionization probability, and mass spectrum, it is imperative to provide definitive experimental data that can serve to guide the field to a reasonable and uniform sampling approach. In this study, we present the results of a number of highly resolved measurements, conducted under well-defined conditions, of water evaporation from a range of particles, during their transport through an aerodynamic lens inlet. We conclude that the only sure way to avoid ambiguities during measurements of aerodynamic diameter in instruments that utilize low-pressure aerodynamic lens inlets is to dry the particles prior to sampling.     

A DFT study of halogen atoms adsorbed on graphene layers

In this work, ab initio density functional theory calculations were performed in order to study the structural and electronic properties of halogens (X = fluorine, chlorine, bromine or iodine) that were deposited on both sides of graphene single layers (X-graphene). The adsorption of these atoms on only one side of the layer with hydrogen atoms adsorbed on the other was also considered (H,X-graphene). The results indicate that the F-C bond in the F-graphene system causes an sp(2) to sp(3) transition of the carbon orbitals, and similar effects seem to occur in the H,X-graphene systems. For the other cases, two configurations are found: bonded (B) and non-bonded (NB). For the B configuration, the structural arrangement of the atoms was similar to F-graphene and H-graphene (graphane), although the electronic structures present some differences. In the NB configuration, the interaction between the adsorbed atoms and the graphene layer seems to be essentially of the van der Waals type. In these cases, the original shape of the graphene layer presents only small deviations from the pristine form and the adsorbed atoms reach equilibrium far from the sheet. The F-graphene structure has a direct bandgap of approximately 3.16?eV at the Γ point, which is a value that is close to the value of 3.50?eV that was found for graphane. The Cl-graphene (B configuration), H,F-graphene and H,Cl-graphene systems have smaller bandgap values. All of the other systems present metallic behaviours. Energy calculations indicate the possible stability of these X-graphene layers, although some considerations about the possibility of spontaneous formation have to be taken into account.     

Contact and edge effects in graphene devices

Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel.     

Clinoptilolite in study of lindane and aldrin sorption processes from water solution

The scope of this study was adsorption of lindane and aldrin from water solution onto clinoptilolite rock with the following desorption using n-hexane. Both kinetic and equilibrium tests were conducted. During kinetic experiment the most part of aldrin and a half part of lindane were sorbed during the first hours. The sorption equilibria with removal of 95% of aldrin amount and about 68% of lindane amount have been set in for 48 h. The pseudo-second-order kinetics model gives somewhat better fit to the both pesticides' sorption data that may testify to the complicated and heterogeneous nature of interaction between active zeolite surface and the pesticides polar-dipole centers. OH(-)-groups and the coordinated exchangeable cations are probably the main active positions for the pesticide sorption on the clinoptilolite surface. Equilibrium experiment results show that adsorption isotherms for the low concentrations of lindane and aldrin (10-200 and 3-100 microg/L, respectively) fit well to the Freundlich and the Liner models. Only 10% of lindane sorbed and about 60% of aldrin sorbed were desorbed from the clinoptilolite using n-hexane under static conditions.     

Optical control of edge chirality in graphene

We performed optical annealing experiments at the edges of nanopatterned graphene to study the resultant edge reconstruction. The lithographic patterning direction was orthogonal to a zigzag edge. μ-Raman spectroscopy shows an increase in the polarization contrast of the G band as a function of annealing time. Furthermore, transport measurements reveal a 50% increase of the GNR energy gap after optical exposure, consistent with an increased percentage of armchair segments. These results suggest that edge chirality of graphene devices can be optically purified post electron beam lithography, thereby enabling the realization of chiral graphene nanoribbons and heterostructures.     

Harvesting energy from water flow over graphene

Water flow over carbon nanotubes has been shown to generate an induced voltage in the flow direction due to coupling of ions present in water with free charge carriers in the nanotubes. However, the induced voltages are typically of the order of a few millivolts, too small for significant power generation. Here we perform tests involving water flow with various molarities of hydrochloric acid (HCl) over few-layered graphene and report order of magnitude higher induced voltages for graphene as compared to nanotubes. The power generated by the flow of ～0.6 M HCl solution at ～0.01 m/sec was measured to be ～85 nW for a ～30 × 16 μm size graphene film, which equates to a power per unit area of ～175 W/m(2). Molecular dynamics simulations indicate that the power generation is primarily caused by a net drift velocity of adsorbed Cl(-) ions on the continuous graphene film surface.     

Computational model of edge effects in graphene nanoribbon transistors

We present a semi-analytical model incorporating the effects of edge bond relaxation, the third nearest neighbor interactions, and edge scattering in graphene nanoribbon field-effect transistors (GNRFETs) with armchair-edge GNR (AGNR) channels. Unlike carbon nanotubes (CNTs) which do not have edges, the existence of edges in the AGNRs has a significant effect on the quantum capacitance and ballistic I-V characteristics of GNRFETs. For an AGNR with an index of m=3p, the band gap decreases and the ON current increases whereas for an AGNR with an index of m=3p+1, the quantum capacitance increases and the ON current decreases. The effect of edge scattering, which reduces the ON current, is also included in the model. This article is published with open access at Springerlink.com     

Detection of individual gas molecules adsorbed on graphene

The ultimate aim of any detection method is to achieve such a level of sensitivity that individual quanta of a measured entity can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects, which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here, we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.     

Effects of water molecules on photoluminescence from hierarchical peptide nanotubes and water probing capability

Photoluminescence (PL) spectra reveal that deficiency of water molecules in the channel cores of bioinspired hierarchical diphenylalanine ( L -Phe- L -Phe, FF) peptide nanotubes (PNTs) not only modifies the bandgap of the subnanometer crystalline structure formed by the self-assembly process, but also induces a characteristic ultraviolet PL peak the position of which is linearly proportional to the number of water molecules in the PNTs. Addition or loss of water molecules gives rise to the UV PL redshift or blueshift. Density functional theory calculation also confirms that addition of water molecules to the PNTs causes splitting of the valence-band peak, which corresponds to the shift and splitting of the observed UV PL peak. Water molecules play an important role in the biological properties of FF PNTs and the results demonstrate that the PL spectra can be used to probe the number of water molecules bonded to the FF molecules.     

Evaporation of water droplets containing carbon nanotubes

The evaporation of water droplets containing carbon nanotubes has been experimentally studied. The droplets were evaporated in a flow of dry air at temperatures in a range of T ₀ = 20−200°C and Reynolds numbers designed on the initial diameter were Re = 500−2000. The results of measurements of the droplet surface temperature and evaporation rate show that the addition of ∼0.1 wt % nanoparticles to the base liquid (water) virtually does not change the laws of heat and mass transfer.     

Synthesis of water soluble graphene

A facile and scalable preparation of aqueous solutions of isolated, sparingly sulfonated graphene is reported. (13)C NMR and FTIR spectra indicate that the bulk of the oxygen-containing functional groups was removed from graphene oxide. The electrical conductivity of thin evaporated films of graphene (1250 S/m) relative to similarly prepared graphite (6120 S/m) implies that an extended conjugated sp (2) network is restored in the water soluble graphene.     

The half-metallicity of zigzag graphene nanoribbons with asymmetric edge terminations

The spin-polarized electronic structure and half-metallicity of zigzag graphene nanoribbons (ZGNRs) with asymmetric edge terminations are investigated by using first-principles calculations. It is found that compared with symmetric hydrogen-terminated counterparts, such ZGNRs maintain a spin-polarized ground state with the anti-ferromagnetic configuration at opposite edges, but their energy bands are no longer spin degenerate. In particular, the energy gap of one spin orientation decreases remarkably. Consequently, the ground state of such ZGNRs is very close to half-metallic state, and thus a smaller critical electric field is required for the systems to achieve the half-metallic state. Moreover, two kinds of studied ZGNRs present massless Dirac-fermion band structure when they behave like half-metals.     

Intrinsic current-voltage characteristics of graphene nanoribbon transistors and effect of edge doping

We demonstrate that the electronic devices built on patterned graphene nanoribbons (GNRs) can be made with atomic-perfect-interface junctions and controlled doping via manipulation of edge terminations. Using first-principles transport calculations, we show that the GNR field effect transistors can achieve high performance levels similar to those made from single-walled carbon nanotubes, with ON/OFF ratios on the order of 10(3)-10(4), subthreshold swing of 60 meV per decade, and transconductance of 9.5 x 10(3) Sm-1.     

Processing of giant graphene molecules by soft-landing mass spectrometry

The processability of giant (macro)molecules into ultrapure and highly ordered structures at surfaces is of fundamental importance for studying chemical, physical and biological phenomena, as well as their exploitation as active units in the fabrication of hybrid devices. The possibility of handling larger and larger molecules provides access to increasingly complex functions. Unfortunately, larger molecules commonly imply lower processability due to either their low solubility in liquid media or the occurrence of thermal cracking during vacuum sublimation. The search for novel strategies to process and characterize giant building blocks is therefore a crucial goal in materials science. Here we describe a new general route to process, at surfaces, extraordinarily large molecules, that is, synthetic nanographenes, into ultrapure crystalline architectures. Our method relies on the soft-landing of ions generated by solvent-free matrix-assisted laser desorption/ionization (MALDI). The nanographenes are transferred to the gas phase, purified and adsorbed at surfaces. Scanning tunnelling microscopy reveals the formation of ordered nanoscale semiconducting supramolecular architectures. The unique flexibility of this approach allows the growth of ultrapure crystalline films of various systems, including organic, inorganic and biological molecules, and therefore it can be of interest for technological applications in the fields of electronics, (bio)catalysis and nanomedicine.     

Influence of growth parameters on the dopant configuration of nitrogen-doped graphene synthesized from phthalocyanine molecules

Synthesis of nitrogen-doped graphene (NDG) via chemical vapor deposition (CVD) using phthalocyanine, a solid precursor containing carbon and nitrogen, is reported. The effect of the growth parameters (temperature, time, and carrier gas) on the surface morphology, dopant configuration, and conductivity of the films was studied. The NDG films were synthesized at different substrate temperatures of 1050 °C, 950 °C, and 850 °C for different growth times of 5–15 min in the presence of an Ar?+?H₂ gas mixture. Significantly, pyrrolic-N type defects are observed predominantly after 5 min of growth time. At 1050 °C, pyrrolic N content is around 45.4% after 5 min of growth which decreased to 24.1% after 15 min of growth, while the graphitic-N content increased from 41.2 to 76% at the same time. It is demonstrated that the conversion of pyrrolic type of nitrogen to graphitic nitrogen defects can be arrested by changing the carrier gas from Ar?+?H₂ to Ar. The pyrrolic-N content increased to 64% by changing the gas from Ar?+?H₂ to Ar at 15 min. The electrolyte gated field-effect transistors were fabricated using the obtained films, and dopant-dependent mobility was observed. The mobility for pyrrolic-N-dominated film is 13.6 cm² V^?1 s^?1 increasing to 62.8 cm² V^?1 s^?1 for graphitic-N-dominated film.