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Papers by Pasqualantonio Pingue

$Research paper thumbnail of Little-Parks effect in single nanoscale YBa_{2}Cu_{3}O_{6+x} rings$

Physical Review B, 2010

The properties of single submicron high-temperature superconductor (HTS) rings are investigated. ... more The properties of single submicron high-temperature superconductor (HTS) rings are investigated. The Little-Parks effect is observed and is accompanied by an anomalous behavior of the magnetic dependence of the resistance, which we ascribe to non-uniform vorticity (superfluid angular momentum) within the ring arms. This effect is linked to the peculiar HTS-relationship between the values of the coherence length and the London penetration depth.

New Journal of Physics, 2015

ABSTRACT When the shear stress on a compliant surface exceeds the yield strength of the material,... more ABSTRACT When the shear stress on a compliant surface exceeds the yield strength of the material, a periodic wrinkle pattern is often observed. This phenomenon has been also recognized at the nanometer scale on polymers, metals, ionic crystals and semiconductors. In those cases, the mechanical stress can be efficiently provided by a sharp indenter elastically driven at constant velocity along the surface. Here we suggest that the formation of such surface ripples can be explained by the competition between the driving spring force and the plastic response of the substrate. In particular, we show how the ripples are expected to disappear when the indentation rate is below a critical value or, alternatively, when the sliding velocity or the lateral stiffness of the contact are too high. The model results are compared to atomic force microscopy experiments on a solvent-enriched polystyrene surface, where the rippling formation is enhanced at room temperature, compared to bulk melts. A similar approach could be employed to describe rippling phenomena on larger scales.

Physical Review B, 2000

The impact of junction transparency in driving phase-coherent charge transfer across diffusive se... more The impact of junction transparency in driving phase-coherent charge transfer across diffusive semiconductor-superconductor junctions is demonstrated.

Modern Physics Letters B, 2003

Coherent transport in Nb/GaAs superconductor-semiconductor microstructures is presented. The stru... more Coherent transport in Nb/GaAs superconductor-semiconductor microstructures is presented. The structures fabrication procedure is based on δ-doped layers grown by molecular-beam-epitaxy near the GaAs surface, followed by an As cap layer to protect the active semiconductor layers during ex situ transfer. The superconductor is then sputter deposited in situ after thermal desorption of the protective layer. Two types of structures in particular will be discussed, i.e., a reference junction and the engineered one that contains an additional insulating AlGaAs barrier inserted during the growth in the semiconductor. This latter configuration may give rise to controlled interference effects and realizes the model introduced by de Gennes and Saint-James in 1963. While both structures show reflectionless tunneling-dominated transport, only the engineered junction shows additionally a lowtemperature single marked resonance peaks superimposed to the characteristic Andreev-dominated subgap conductance. The analysis of coherent magnetotransport in both microstructures is successfully performed within the random matrix theory of Andreev transport and ballistic effects are included by directly solving the Bogoliubov-de Gennes equations. The impact of junction morphology on reflectionless tunneling and the application of the employed fabrication technique to the realization of complex semiconductor-superconductor systems are furthermore discussed.

Materials Science and Engineering: B, 2008

ABSTRACT We have fabricated and characterized Hall probes on an In0.75Al0.25As/In0.75Ga0.25As two... more ABSTRACT We have fabricated and characterized Hall probes on an In0.75Al0.25As/In0.75Ga0.25As two-dimensional electron gas with lateral sizes down to 100nm. We studied the dependence of the low temperature (4K) magnetic field sensitivity on the probe size, showing that the best flux sensitivity is achieved by devices of ≈200nm, employing highly doped systems (n∼1012cm−2). Hall bars with sizes down to the range of 200–250nm show a magnetic field sensitivity of a few Gauss, corresponding to a flux sensitivity equal to ≈10−2Φ0.

Monoatomic layers of graphite can be electrically contacted and used as building blocks for new p... more Monoatomic layers of graphite can be electrically contacted and used as building blocks for new promising devices. These experiment are today possible thanks to the fact that very thin graphite can be identified on a dielectric substrate using a simple optical microscope. We investigate the mechanism behind the strong visibility of graphite and we discuss the importance of the substrate and of the microcope objective used for the imaging.

The viscoelastic properties of thin polystyrene (PS) films depend on confinement, as it can modif... more The viscoelastic properties of thin polystyrene (PS) films depend on confinement, as it can modify the molecular dynamics affecting the glass transition. In the recent past, the authors have investigated the region next to the free interface by means of an atomic force microscope suitably modified to monitor the indentation of a tip into a film during a given lapse of time while applying a constant load. Herein, to explore the interface with the substrate, the authors report on experiments in which PS brushes grafted to native silicon oxide were used. It was found that the film wettability on brushes and H-terminated silicon can be highly improved when compared with native silicon oxide. In addition, the glass transition temperature of thin films increases up to the bulk value in the case of film/brush combinations with high molecular weight or films with high molecular weight on H-terminated silicon. Data are discussed according to hypotheses such as residual solvent presence, interface free volume, and molecular mechanical coupling. These observations can be of great interest for nanotechnological applications, especially in those instances where one needs to tailor the temperature dependence of viscoelastic properties of thin films.

Macromolecular Symposia, 2001

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

ABSTRACT In this paper we present a spatially resolved photoemission spectroscopy analysis of sil... more ABSTRACT In this paper we present a spatially resolved photoemission spectroscopy analysis of silicon-oxide nanopatterns produced by atomic force microscope (AFM) induced anodization on a n-type silicon substrate. The oxide geometry, that consists in submicrometer narrow lines of different thickness, is equivalent to the geometry used to fabricate AFM defined nanodevices such as quantum point contacts and single electron transistor. We found that the chemical properties of the oxides are spatially uniform below our spatial resolution, even in case of very thin lines, and that the oxide composition does not depend on the anodization parameters. We observed a shift of the oxide binding energies that we attributed to charging effects and that is compatible with a pure and stoichiometric silicon oxide. (C) 2002 Elsevier Science B.V. All rights reserved.

Applied …, 2009

An innovative fabrication procedure has been developed to obtain YBa2Cu3O7-x (YBCO) nanobridges f... more An innovative fabrication procedure has been developed to obtain YBa2Cu3O7-x (YBCO) nanobridges from c-axis oriented films. The novelty regards the use of a thin titanium mask used in the patterning process. The use of the Ti makes simpler the fabrication procedure guaranteeing high quality devices, as demonstrated by transport measurements. Critical temperatures and critical current densities scale with the width