The growth of large-area bilayer graphene has been of technological importance for graphene electronics. The successful application of graphene bilayers critically relies on the precise control of the stacking orientation, which determines both electronic and vibrational properties of the bilayer system. Toward this goal, an effective characterization method is critically needed to allow researchers to easily distinguish the bilayer stacking orientation (i.e., AB stacked or turbostratic). In this work, we developed such a method to provide facile identification of the stacking orientation by isotope labeling. Raman spectroscopy of these isotopically labeled bilayer samples shows a clear signature associated with AB stacking between layers, enabling rapid differentiation between turbostratic and AB-stacked bilayer regions. Using this method, we were able to characterize the stacking orientation in bilayer graphene grown through Low Pressure Chemical Vapor Deposition (LPCVD) with enclosed Cu foils, achieving almost 70% AB-stacked bilayer graphene. Furthermore, by combining surface sensitive fluorination with such hybrid (12)C/(13)C bilayer samples, we are able to identify that the second layer grows underneath the first-grown layer, which is similar to a recently reported observation.

Trace level identification of explosive molecules are very important not only for security screening but also for the environment and human health. Driven by the need, the current article reports for the first time gold nanocage–graphene oxide hybrid platform for the spectral fingerprint and the trace level identification of RDX and TNT. Reported experimental data using RDX show that the surface-enhanced Raman spectroscopy (SERS) enhancement factor for graphene oxide (GO) attached gold nanocage assembly is 4 orders of magnitude higher than only nanocage, and it is due to the enormous field enhancement for the nanocage assembly. The current article demonstrates that label-free nitro-explosive identification limits using hybrid platform can be as low as 10 fM for TNT and 500 fM for RDX, which indicate that gold nanocage–graphene oxide assembly can be very attractive for a variety of practical applications.

This paper reports for the first time the development of a large-scale SERS substrate from a popcorn-shaped gold nanoparticle-functionalized single walled carbon nanotubes hybrid thin film for the selective and highly sensitive detection of explosive TNT material at a 100 femtomolar (fM) level.

The interaction of gold nanoclusters (Au n , n ) 2, 4, 6, 8, 10, 12) with nucleic acid purine base guanine (G) and the Watson-Crick guanine-cytosine (GC) base pair through the major groove site (N7 site of guanine) of DNA was investigated theoretically. Geometries of complexes were optimized at the density functional theory (DFT) level employing the hybrid B3LYP functional. The 6-31G(d) basis set was used for all atoms except gold, for which the LANL2DZ effective core potential (ECP) was used. Natural population analysis was performed to determine NBO charges. The vertical first ionization potential and electron affinity of guanine and the guanine-cytosine base pair and their complexes with gold nanoclusters were also analyzed. It was revealed that gold clusters interact more strongly with the GC base pair than with isolated guanine. It was found that consequent to the binding of gold nanoclusters a substantial amount of electronic charge was transferred from guanine (or the guanine-cytosine base pair) to the gold clusters. Furthermore, the amount of the electronic charge transferred to the gold cluster was found to be larger for GC-Au n complexes than that in the G-Au n complexes. The vertical ionization potential, electron affinity, and biological significance of the interaction of gold nanoclusters with nucleic acid building blocks have also been discussed.

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This study investigated the effectiveness of a graphene- and aptamer-based field-effect-transistor-like (FET-like) sensor in detecting lead and potassium ions. The sensor consists of a graphene-covered Si/SiO2 wafer with thrombin binding aptamer (TBA) attached to the graphene layer and terminated by a methylene blue (MB) molecule. K(+) and Pb(2+) both bind to TBA and cause a conformational change, which results in MB moving closer to the graphene surface and donating an electron. Thus, the abundance of K(+) and Pb(2+) can be determined by monitoring the current across the source and drain channel. Device transfer curves were obtained with ambipolar field effect observed. Current readings were taken for K(+) concentrations of 100 μM to 50 mM and Pb(2+) concentrations of 10 μM to 10 mM. As expected, I d decreased as ion concentration increased. In addition, there was a negative shift in V Dirac in response to increased ion concentration.

Theoretical study at the B3LYP/6-31G(d)∪LANL2DZ level was carried out to explore the structures and properties of nanocontacts in Pd n −C60−Pd n systems. Predicted interaction energies between the palladium clusters and the C60 were corrected for the basis set superposition error. It is revealed that palladium clusters interact more strongly with C60 than the analogous gold clusters. Further, generally in the case of C60−Pd complexes, electronic charges are transferred from metal clusters to C60 which is contrary to the direction of a charge transfer in C60−Au complexes. HOMO−LUMO energy gaps in Pd n −C60−Pd n system are found to be lower than C60 as well as the corresponding Au n −C60−Au n complexes. Charge transport properties in the Pd n −C60−Pd n system are discussed in terms of molecular orbitals and the Fermi energy level. Molecular electrostatic potential (MEP) mappings were performed for the qualitative visualization of the Schottky barrier at the C60−Pd interface. Similarity and differences between the Pd n −C60−Pd n and Au n −C60−Au n systems are also explored.