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Graphene-like (GL) layers were prepared through a two steps oxidation/reduction method starting from a high surface carbon black, and pH of the GL layers in water suspension was varied. The effect of pH of such suspension on the morphology of self-assembled GL films has been studied. Zeta potentials of the water suspensions were measured to estimate the stability of the suspension at several pH values and to select the samples for deeper investigation by atomic force microscopy (AFM). AFM measurements on four different samples are then described and discussed. The reported results show how the surface roughness and morphology are affected by the pH in the preparation process: in particular, the lowest pH sample exhibits a granular surface, while at higher pH more regular morphologies are produced, with interesting observations as concerns the thickness of some surface features. The observations are interpreted in terms of the forces acting in water suspension and of the role of hydrophobic or hydrophilic behaviors. The results demonstrate the possibility to tune the surface properties of GL films by simply acting on the pH of the suspension during the fabrication, and help to understand the microscopic physical mechanisms involved in the film assembly. (C) 2015 Elsevier B.V. All rights reserved.

Reduction of strongly oxidized carbon black by hydrazine hydrate yields water-insoluble graphene-like sheets that undergo to self-assembling in thin film on surfaces after drying. The height of a drop-casted graphene-like film was determined by atomic force microscopy (AFM) to be around 20 nm, corresponding to approximately 25 graphene-like layers. The oxidized carbon black and the corresponding reduced form were carefully characterized.

MgB 2 thin films were grown in-situ at INFM- University of Naples by a magnetron sputtering technique in a UHV system (10-7 Pa) equipped with 3 focused 2′′ magnetron sources (a stoichiometric MgB 2 and metallic Mg and B targets by Superconducting Components Inc.). The substrates (sapphire or MgO) were placed "on axis" at 7 cm from the target surface on the surface of a molybdenum heater that could be operated up to 1000°C under vacuum. Best results were obtained codepositing MgB 2 and Mg at equal sputtering power (500W) for 10 min on cold substrates, resulting in a Mg rich Mg-B precursor film. The films were then annealed inhyphen;situ at 830°C for 10 min in a In sealed Nb box in presence of saturated Mg vapor. The process is highly reproducible and can be easily scaled to produce large area films. The resulting films were about 1μm thick, with 100nm surface roughness as measured by AFM Resistive transition showed a maximum T c of 35 K and a transition width lower than 0.5 K. The residual resistivity ratio was 1.6 for the best sample. Resistivity measurements in external magnetic field up to 8 T have been performed both in parallel and perpendicular configuration. The upper critical magnetic field vs. temperature behavior has been determined from the experimental data and the superconducting anisotropy has been calculated for samples with different T c .

We report on fabrication of Y/sub 1/Nd/sub x/Ba/sub 2-x/Cu/sub 3/O/sub 7-/spl delta// and Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7-/spl delta// thin films deposited by high oxygen pressure dc sputtering. The structural properties are investigated by X-ray diffraction while Scanning Tunneling Microscopy (STM) has been used to determine the surface morphology. The critical temperature and the critical current density are obtained by transport and inductive measurements. The microwave properties have been studied at 19.8 GHz by a dielectric resonator technique. For both compounds highly epitaxial c-axis thin films are routinely obtained on SrTiO/sub 3/ and LaAlO/sub 3/ substrates. Depending on the deposition conditions, films characterized by surface resistance comparable of even better than YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// have been obtained, with a substantial improvement of the structural properties and of the surface morphology. The role played by the Nd/Ba substitution on the growth and on the superconducting properties is discussed.

A full understanding of the mechanism of the formation of a two-dimensional electron gas (2DEG) at the interface between insulating LaAlO3 (LAO) thin films and bulk SrTiO3 (STO) crystals is a prerequisite for the full exploitation of this class of materials. Here, by using a combination of advanced X-ray synchrotron-based spectroscopic and structural measurements, it is shown that a structural and electronic reconstruction of the interface occurs before the realization of the 2DEG.

The possibility of the fabrication of organic devices suitable to be applied in bio-sensing fields depends largely on the availability of organic compounds displaying robust electrical properties even in aqueous solutions and effective biocompatibility features. In this paper, we report about the good cellular biocompatibility and the electrical response stability in an ionic medium of n-type organic transistors based on the recently developed PDI-8CN(2) oligomer. The biocompatibility has been tested by analyzing the adhesion and viability of two different cell lines, human epithelial HeLa cells and murine neuronal F11 cells, on PDI-8CN(2) films grown by organic molecular beam deposition (OMBD) on SiO2 substrates. The effect of film thickness on cell attachment was also tested. Uncoated SiO2 substrates were used as control surfaces and sexithiophene (T6) as device testing control. Moreover, the possible toxicity of -CN groups of PDI-8CN(2) was tested on HeLa cell cultures, using PDI-8 and T6 molecules as controls. Results showed that, although at high concentration these organic compounds are toxic in solution, if they are presented in form of film, cell lines can attach and grow on them. The electrical response stability of PDI-8CN(2) transistors in a cellular culture medium characterized by high concentrations of ionic species has been also investigated. For this purpose, low-voltage operation devices with V-GS ranging from -5 V to 5 V, able to strongly reduce the influence of Faradaic currents coming from the electrical operation in an highly ionic environment, have been fabricated on 35 nm thick SiO2 layers and electrically characterized. These results are useful to experimentally define the main critical issues to be further addressed for the fabrication of reliable bio-sensors based on organic transistors. (C) 2012 American Institute of Physics

We have studied the effect of Nd/Ba substitution on the superconducting properties of R 1 (Nd x Ba 2− x )Cu 3 O 7 (R=Nd, Y) thin films by using microwave penetration depth and surface resistance measurements. Data on samples characterised by a Nd-excess of 4–5% have been collected by using a microstrip resonator at frequencies of 1.44 and 9.7 GHz and a symmetric dielectric resonator technique in TE 0 1 1 mode at 19.8 GHz. A quadratic bT 2 low temperature dependence of the penetration depth is observed for the Nd-rich samples, with the coefficient b decreasing with the frequency. The data can be reasonably explained in a d-wave framework supposing that Nd at Ba site behaves, both in Nd 1+ x Ba 2− x Cu 3 O 7 and Y 1 (Nd x Ba 2− x )Cu 3 O 7 , as a resonant impurity, as confirmed by scanning tunnelling spectroscopy. The changes of the temperature dependence of the penetration depth with the frequency can be explained with a two fluid approach taking into account the frequency dependence of the complex conductivity.

We report on superconducting magnesium diboride MgB(2) thin films grown on both YSZ and MgO substrates, with two different orientations, namely [110] and [211]. MgB(2) off-axis growth mode (namely, with the c-axis tilted with respect to the film surface's normal) is achievable on these substrates. Depending on the type and orientation of the substrate, tilting angle can be varied. As a consequence of tilted growth, anisotropic transport properties are observed. In very thin films, resistance measurements provide an estimate of the resistivity anisotropic ratio rho(c)/rho(ab), where rho(c) is the resistivity along the c axis and rho(ab) is the in-plane resistivity. All these findings clearly demonstrate that tilted MgB(2) films offer new exciting possibilities to both investigate intrinsic fundamental properties of MgB(2) and to explore possible applications in planar superconducting devices

Neutron irradiation was performed on MgB2 thin films grown by hybrid physical chemical vapor deposition. Samples irradiated with different neutron fluences, having different critical temperatures, were studied by scanning tunneling spectroscopy in order to investigate the effect of the introduced disorder on the superconducting and spectroscopic properties. A monotonic increase of the pi gap with increasing disorder was found. (c) 2007 Elsevier B.V. All rights reserved.

Thin films of the recently discovered magnesium diboride (MgB2) intermetalic superconducting compound have been grown using a magnetron sputtering deposition technique followed by in-situ annealing at 830 C. High quality films were obtained on both sapphire and MgO substrates. The best films showed maximum Tc = 35 K (onset), a transition width of 0.5 K, a residual resistivity ratio up to 1.6, a low temperature critical current density Jc > 1 MA/cm2 and anisotropic critical field with gamma = 2.5 close to the values obtained for single crystals. The preparation technique can be easily scaled to produce large area in-situ films., 7 pages, 4 figures

LuNi 2 B 2 C films have been prepared by a Pulsed Laser Deposition technique. The deposition parameters have been optimized to reach good superconducting, structural and morphological properties with high reliability. In order to deposit different patterned layers for in-situ junctions production, a special set-up for the in situ interchanging of shadow masks has been developed. We studied the growth of different materials to be used as barrier layers. New results on the temperature dependence of the LuNi 2 B 2 C gap using S/N contact junctions are presented and discussed.

We studied the ferroelectric and ferromagnetic properties of compressive strained and unstrained BiMnO3 thin films grown by rf-magnetron sputtering. BiMnO3 samples exhibit a two-dimensional cube-on-cube growth mode and a pseudo-cubic structure up to a thickness of 15 nm and of 25 nm when deposited on (001) SrTiO3 and (110) DyScO3, respectively. Above these thicknesses, we observe a switching to a three-dimensional island growth mode and a simultaneous structural change to a (00l) oriented monoclinic unit cell. While ferromagnetism is observed below a T-C approximate to 100K for all samples, signatures of room temperature ferroelectricity were found only in the pseudo-cubic ultra-thin films, indicating a correlation between electronic and structural orders.