We describe investigations of superconductivity in few molecular layer NbSe2 field effect transistors. While devices fabricated from NbSe2 flakes less than 8 molecular layers thick did not conduct, thicker flakes were superconducting with an onset that was only slightly depressed from the bulk value for 2H-NbSe2 (7.2K). The resistance typically showed a small, sharp high temperature transition followed by one or more broader transitions which usually ended in a wide tail to zero resistance at low temperatures. We speculate that these multiple resistive transitions are related to disorder in the layer stacking. The behavior of several flakes has been characterized as a function of temperature, applied field and back-gate voltage. We find that the conductance in the normal state and transition temperature depend weakly on the gate voltage, with both conductivity and decreasing as the electron concentration is increased. The application of a perpendicular magnetic field allows the evolution of different resistive transitions to be tracked and values of the zero temperature upper critical field, 2 (0), and coherence length, (0), to be independently estimated. Our results are analyzed in terms of available theories for these phenomena.

Lead oxide nanoparticles (PbO NPs) and carboxymethyl cellulose (CMC)/polyvinylpyrrolidone (PVP) nanocomposite films were prepared by sol‐gel and solution casting methods respectively. The structural properties of the samples were investigated by X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HR‐TEM) and Fourier transformation infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) revealed the good dispersion of PbO NPs on the surface of the blend films. CMC film exhibits a transmittance (T) of 72%, increased after mixing with PVP and then decreased to <38% after adding 4.0 wt% PbO NPs. Both the direct and indirect optical band gaps (Eg) of CMC equal to 3.97 and 3.7 eV, respectively. These values were increased after PVP addition and then decreased after loading PbO NPs. The conduction mechanism in CMC/PVP blend has changed from Schottky emission to Poole–Frenkel due to the effects of temperature and PbO NPs content. The effect of adding PVP & PbO NPs on the DC conductivity and the activation energy Ea values of the CMC are discussed. The dielectric constant (ε′) was investigated in the frequency and temperature ranges of 1 kHz–1.0 MHz and 293–393 K respectively. Its values depend on both the PbO content and temperature. The AC conductivity σac was increased with increasing PbO content. The correlated barrier hopping (CBH) was found to be the most appropriate mechanism for explaining the AC conduction behavior. POLYM. COMPOS., 39:3712–3725, 2018. © 2017 Society of Plastics Engineers

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