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Because of novel features in their structural, electronic, magnetic and optical properties, especially potential applications in nanoelectronics, the few-layer graphene intercalation compounds (FLGICs) have been intensively studied recently. In this work, the dielectric constant of the doped graphene of stage-1 FeCl3-GIC is obtained by fitting the optical contrast spectra. And fully intercalated stage-1 FeCl3-FLGICs were prepared by micromechanical cleavage method from graphite intercalation compounds (GICs) for the first time. Finally, we demonstrated that the thickness of stage-1 FeCl3-GICs by micromechanical cleavage can be determined by optical contrast spectra. This method also can be used to other FLGICs, such as SbCl5-FLGICs and AuCl5-FLGICs, etc. [ABSTRACT FROM AUTHOR]

Uniaxially aligned and cross-aligned arrays of ultra fine polymer fibers have been fabricated by a novel and effective centrifugal electrospinning setup with rotating polymer solution jets . Comparing with conventional electrospinning (10-30 kV) and centrifugal spinning (4,000-12,000 rpm), this technique only requires a lower working voltage (2.8-6.0 kV), a slower rotational speed (360- 540 rpm), and a shorter spinning distance (2.0-4.0 cm). In addition, the influences of experimental parameters such as working voltage, rotational speed, collecting distance, and solution concentration on the alignment of the as-spun fibers are investigated using image analysis techniques. It is found that the working voltage and rotational speed mainly influence the perpendicular and linear velocities of the fibers, respectively. The polymer fibers tend to show higher alignment degree when these two velocities are very close. Optimum conditions (working voltage 3.0 kV, rotational speed 420 rpm, collecting distance 2.5 cm, and solution concentration 18 wt%) to maximize alignment degree (~97%) of polystyrene fibers are also obtained. [ABSTRACT FROM AUTHOR]

Electrospun nanofibers with designed or controlled structures have drawn much attention. In this study, we report an interesting new closed-loop structure in individual cerium nitrate/polyvinyl alcohol (Ce(NO3)3/PVA) and NaCl/PVA fibers, which are fabricated by electrospinning with a nail collector. The electrospinning parameters such as voltage and Ce(NO3)3 (or NaCl) concentration are examined for the formation of the closed-loop structure. The results suggest that the increase of the spinning voltage or addition of Ce(NO3)3 (or NaCl) is favorable for the formation of the closed-loop structure, and the increase of loop numbers and the decrease of loop size. Further analyses indicate that the formation mechanism of the closed-loop fibers can be predominantly attributed to the Coulomb repulsion in the charged jets. [ABSTRACT FROM AUTHOR]

Transition-metal dichalcogenide (TMD) semiconductors have been widely studied due to their distinctive electronic and optical properties. The property of TMD flakes is a function of their thickness, or layer number (N). How to determine the N of ultrathin TMD materials is of primary importance for fundamental study and practical applications. Raman mode intensity from substrates has been used to identify the N of intrinsic and defective multilayer graphenes up to N = 100. However, such analysis is not applicable to ultrathin TMD flakes due to the lack of a unified complex refractive index () from monolayer to bulk TMDs. Here, we discuss the N identification of TMD flakes on the SiO2/Si substrate by the intensity ratio between the Si peak from 100 nm (or 89 nm) SiO2/Si substrates underneath TMD flakes and that from bare SiO2/Si substrates. We assume the real part of of TMD flakes as that of monolayer TMD and treat the imaginary part of as a fitting parameter to fit the experimental intensity ratio. An empirical namely, of ultrathin MoS2, WS2 and WSe2 flakes from monolayer to multilayer is obtained for typical laser excitations (2.54 eV, 2.34 eV or 2.09 eV). The fitted of MoS2 has been used to identify the N of MoS2 flakes deposited on 302 nm SiO2/Si substrate, which agrees well with that determined from their shear and layer-breathing modes. This technique of measuring Raman intensity from the substrate can be extended to identify the N of ultrathin 2D flakes with N-dependent For application purposes, the intensity ratio excited by specific laser excitations has been provided for MoS2, WS2 and WSe2 flakes and multilayer graphene flakes deposited on Si substrates covered by a 80–110 nm or 280–310 nm SiO2 layer. [ABSTRACT FROM AUTHOR]

Conducting polypyrrole (PPY) nanowires doped with p-toluene sulfonamide (PTSA) were synthesized by a template-free self-assembly method. Electrical transport characteristics, i.e. current–voltage (I–V) behavior, of an individual PPY/PTSA nanowire have been explored in a wide temperature range from 300 down to 40 K. The fitting results of I–V curves indicated that the electrical conduction mechanism can be explained by the space-charge-limited current (SCLC) theory from 300 down to 100 K. In this temperature range, traps play an important role for this non-crystalline system. The corresponding trap energy and trap concentration have also been calculated based on the SCLC theory. Interestingly, there is no trap at 160 K, different from other temperatures. The obtained carrier mobility for the polymer nanowires is 0.964 cm2 V−1 s−1 on the basis of trap free SCLC theory. In the temperature range of 80–40 K, little current can flow through the nanowire especially at lower voltages, however, the current follows the equation I ∞ (V/Vt−1)ζ at higher bias, which could be attributed to Coulomb blockade effect. Additionally, the differential conductance dI/dV curves also show some clear Coulomb oscillations. [ABSTRACT FROM AUTHOR]

We synthesize the homogenous graphene films on cheap industrial Cu foils using low pressure chemical vapor deposition. The quality and the number of layers of graphene are characterized by Raman spectra. Through carefully tuning the growth parameters, we find that the growth temperature, hydrocarbon concentration and the growth time can substantially affect the growth of high-quality graphene. Both single and bilayer large size homogenous graphenes have been synthesized in optimized growth conditions. The growth of graphene on Cu surface is found to be self ceasing in the bilayer graphene process with the low solubility of carbon in Cu. Furthermore, we have optimized the transfer process, and clear graphene films almost free from impurity are successfully transferred onto Si/SiO2 substrates. The field effect transistors of bilayer graphene are fabricated, which demonstrates a maximum hole (electron) mobility of 4300 cm2 V−1s−1 (1920 cm2V−1s−1) at room temperature. [ABSTRACT FROM AUTHOR]

The in-plane shear (C) modes between neighbor layers of 2-4 layer graphenes (2-4LGs) and the corresponding 2-4 layer graphene scrolls (2-4LGSs) rolled up by 2-4LGs at edges are investigated by Raman scattering. In contrast to the result that only one C mode is observed in 3-4LGs, all the C modes of 3-4LGs are observed in 3-4LGSs, whose frequencies agree with the theoretical prediction by the force-constant and linear chain models. The results indicate that the C mode intensity of 2-4LGSs is resonantly enhanced by the electronic transition gaps of band structures of 2-4LGS structures at edges, which makes it possible to observe all the C modes. Indeed, for a simple assumption, the calculated band structures of twisted (n+n)LGs (n=2,3,4) show parallel conduction and valence bands and the corresponding Van Hove singularities in the joint density of states along Γ-M, Γ-K and/or K-M directions. The intensity resonance of the C modes provides direct evidence to explain how the band structure of few layer graphenes can be sensitive to local stacking configurations. This result can be extended to n layer graphene (n>4) for understanding the basic phonon and electronic properties of multilayer graphenes. This observation of all the C modes in graphene scrolls can be foreseen in other two-dimensional materials with similar scroll structures. [ABSTRACT FROM AUTHOR]