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Nanotwinned metals and alloys have an attractive suite of properties, but the formation of the underlying nanostructure is generally dependent on the alloy chemistry and processing conditions. This study was undertaken to investigate the effect of deposition rate on nanotwin formation in sputter deposited Ni84Mo11W5 that possess ultrahigh strength and stability. Deposition rates of 0.5–2.3 nm/s were examined and the grain size, texture, twin spacing and hardness were characterized. Minimal variations in the underlying nanostructure and attendant hardness were observed, elucidating a wide processing window and the importance of chemistry on the formation of nanotwins in this alloy.

In this work, the authors investigated MoO3 films with thickness between 30 nm and 1 μm grown at room temperature by solid phase deposition on polycrystalline Cu substrates. Atomic force microscopy, scanning electron microscopy, and scanning tunneling microscopy revealed the presence of a homogenous MoO3 film with a “grainlike” morphology, while Raman spectroscopy showed an amorphous character of the film. Nanoindentation measurements evidenced a coating hardness and stiffness comparable with the copper substrate ones, while Auger electron spectroscopy, x-ray absorption spectroscopy, and secondary electron spectroscopy displayed a pure MoO3 stoichiometry and a work function ΦMoO3 = 6.5 eV, 1.8 eV higher than that of the Cu substrate. MoO3 films of thickness between 30 and 300 nm evidenced a metallic behavior, whereas for higher thickness, the resistance–temperature curves showed a semiconducting character.In this work, the authors investigated MoO3 films with thickness between 30 nm and 1 μm grown at room temperature by solid phase deposition on polycrystalline Cu substrates. Atomic force microscopy, scanning electron microscopy, and scanning tunneling microscopy revealed the presence of a homogenous MoO3 film with a “grainlike” morphology, while Raman spectroscopy showed an amorphous character of the film. Nanoindentation measurements evidenced a coating hardness and stiffness comparable with the copper substrate ones, while Auger electron spectroscopy, x-ray absorption spectroscopy, and secondary electron spectroscopy displayed a pure MoO3 stoichiometry and a work function ΦMoO3 = 6.5 eV, 1.8 eV higher than that of the Cu substrate. MoO3 films of thickness between 30 and 300 nm evidenced a metallic behavior, whereas for higher thickness, the resistance–temperature curves showed a semiconducting character.

We present an experimental characterization of multidirectional fibre composites based on eddy current testing using HTS dc SQUID (Superconducting Quantum Interference Device) magnetometers. The correlation between the mechanical tolerance of CFRPs with different thickness and the phase gradient of the magnetic field generated by damage is shown. The eddy current based SQUID NDE is used to detect damage not visible to the naked eye and to study the effect of an impact far from the point of impact. The aim of this work is to demonstrate the capability of our technique to provide information on early stage damage due to an impact process in an unshielded environment.

We find an unambiguous relationship between disorder-driven features in the temperature dependence of the resistance and the behavior, as functions of the temperature, of the parameters necessary to describe some of the relaxation processes in the photoinduced differential time-resolved reflectivity of three samples of ${\text{Nd}}_{1.83}{\text{Ce}}_{0.17}{\text{CuO}}_{4\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$. The latter, sharing the same $\text{Ce}$ content, have been fabricated and annealed ad hoc in order to differ only for the degree of disorder, mainly related to oxygen content and location, and, consequently, for the temperature dependence of the resistance: Two of them present a minimum in the resistance and behave as a superconductor and as a metal, respectively; the third behaves as an insulator. The systematic coherence between the resistance and the relaxation parameters behaviors in temperature for all three samples is absolutely remarkable and shows that pump-probe measurements can be extremely sensitive to disorder as it drives the emergence of new excitations and of the related relaxation channels as in this paradigmatic case.

The CNTs properties have inspired interest in using CNTs as a filler in polymer composite systems to obtain ultra-light structural materials with enhanced electrical, thermal and optical characteristics. In particular, industry recognizes many potential applications such as electrostatically dissipative materials, nano-sensors and aerospace structural materials. In this paper the eddy current based SQUID and the thermographic techniques have been used to study electromagnetic properties of nano-composite materials.

Stress damage of cross-ply or quasi-isotropic carbon-fiber reinforced polymer laminates, commonly used in aerospace structures, has been monitored in real-time during quasi-static loading. The fiber displacement in the matrix due to mechanical loading have been detected using atomic force microscopy techniques. A correlation between mechanical and electrical effects in the material has been confirmed by electrical and magnetic measurement using an eddy current technique based on high critical temperature dc Superconducting Quantum Interference Device magnetometer.

An optically transparent nanographite coating has been developed on a poly-methyl methacrylate (PMMA) substrates. The adhesion to the PMMA surface combined with the shear stress allowed an uniform and continuous spreading of the graphite nanocrystals on the substrate surface with formation of a very uniform graphene multilayer coating. This coating is characterized by high piezoresitivity and it is suitable to work as sensible and reliable local strain sensor. Its piezoresistive features have been characterized by bending tests yielding a gauge factor (GF) which is of the order of 50. The structural and strain properties of the compound were studied under stress by infra-red thermography (IRT) and micro-Raman spectroscopy. The strain strength has been estimated as a function of the bending load. The electrical transport was investigated as a function of the applied stress. Features are consistent with an intergrain electrical transport mechanism among graphene platelets.

Results concerning the study of the morphology and the surface chemical properties of epitaxial YBCO and highly oriented TBCCO films before and after wet etching processes are reported. X-ray photoemission spectroscopy, Auger electron spectroscopy and scanning electron microscopy are employed to get information on the surface contamination and on the defects of the samples. The chemical modifications of surfaces and the shape of etch pits are discussed.

In this work an eddy current technique based on a HTS-SQUID (superconducting quantum interference device) is used to evaluate the relation between the magnetic field response and the damage process of one of the most promising fibre metallic laminates known as GLARE®. In particular the magnetic field response due to impact loading at energies ranging from 5 to 36 J has been detected. The magnetic field signal from GLARE® specimens in the presence of mechanical damaging is discussed according to a simple electromagnetic model.

In this work an electromagnetic non-invasive and contact-less technique using Flux-Gate first-order gradiometer is proposed to detect the magnetic field distribution during electropolishing of copper surface. The electropolishing of the copper surface employed in superconducting RF TESLA-type cavities has been monitored using magnetic field sensors. Local information regarding the dissolved copper surface during the elect ropolishing process has been obtained. An electromagnetic inversion of the magnetic field imaging have been implemented to better understand the effect of the cathode geometry on the electropolishing process. (c) 2006 Elsevier B.V. All rights reserved.

Femtosecond spectroscopy has been used to investigate the quasiparticle relaxation times in a nearly optimally doped chalcogenide superconducting FeSe0.5Te0.5 thin film. It is characterized by an enhancement of the critical temperature Tc = 19.1 K by strain. Experimental results indicate the existence of a temperature dependence of the quasiparticle recombination time τR in the superconducting state where an energy gap Δ(T) is present. A fitting procedure based on a BCS-like assumption for τR gives Δ0 = 4.1 ± 0.4 meV for the superconducting energy gap extrapolated at T = 0, which corresponds to 2Δ0/kBTc = 4.9 ± 0.5. Accordingly, an estimation of the characteristic phonon energy and the electron–phonon coupling constant λ is reported and discussed. The obtained value λ ≈ 0.6 is in good agreement with other similar determinations obtained by different techniques and numerical approaches. The small value of λ confirms that a phonon-mediated coupling cannot be the only mechanism leading to the formation of the superconducting state in FeSeTe films.

A systematic characterization of Co-doped BaFe2As2(Ba-122) thin films has been carried out. Two samples were available, one grown on CaF2substrate and the other on MgO with an Fe buffer layer. The goal was to investigate films’ magnetic and superconducting properties, their reciprocal interplay, and the role played by the Fe buffer layer in modifying them. Morphological characterization and Energy Dispersive X-ray analyses on the Fe-buffered sample demonstrate the presence of diffused Fe close to the Co-doped Ba-122 outer surface as well as irregular holes in the overlying superconducting film. These results account for hysteresis loops obtained with magneto-optic Kerr effect measurements and observed at both room and low temperatures. The magnetic pattern was visualized by magneto-optical imaging with an indicator film. Moreover, we investigated the onset of superconductivity through a measure of the superconducting energy gap. The latter is strictly related to the decay time of the excitation produced by an ultrashort laser pulse and has been determined in a pump-probe transient reflectivity experiment. A comparison of results relative to Co-doped Ba-122 thin films with and without Fe buffer layer is finally reported.

In this work we present a non-destructive technique to detect the magnetization changes due to mechanical stress produced in steel notched plates under tensile loads. The measurements have been carried out using, separately, a magnetic field probe based on HTS dc SQUID and a flux-gate gradiometer probe. The aim of this work is to demonstrate that it is possible to localize the dislocation density change in the samples and to correlate it with the change of magnetization using a contact-less and non-invasive technique.

In this work we present non-destructive evaluation measurements on fiber/metal laminate specimen by using eddy current techniques employing HTc SQUID (superconductive quantum interference device) and giant magneto-resistive (GMR) sensors. Our aim is to compare the performance and the capability of HTc SQUID and GMR sensors to detect the presence of damage inside FML composite materials. Experimental results concerning the detection of artificial defects in aeronautical structures with high magnetic sensitivity by using HTc SQUID, and with high spatial resolution using GMR, will be presented and discussed.

The main advantage of a HTS SQUID magnetometer in NDE applications is represented by its unrivalled magnetic flux sensitivity down to very low frequencies, which allows the detection of weak magnetic field variations due to defects also in materials characterized by a very low electrical conductivity. The imaging obtained by means of the magnetic flux variations can be an useful technique for an easier interpretation of SQUID magnetic responses getting along without post-processing algorithms and independent of the operator. Therefore, the SQUIDs NDE system output is compatible with the other conventional non destructive testing equipment for data fusion of aircraft inspections.

This paper deals with the electromagentic nondestructive testing performed by SQUID magnetometry on stratified aluminum alloy plates as those commonly encountered in the aircraft industry. The anomalous magnetic fields generated by flaws with know electromagnetic characteristics have been modeled by a three-dimensional specific code based on a finite element formulation. The numerical solution has correctly predicted the shape of the complicated magnetic field response due to the defect. Once accuracy and reliability of experimental data taken by superconductive probe have been tested, a benchmark-like problem has been faced. Measurements performed by conventional probes like fluxgate and inductive coil have been compared with the ones taken by innovative device based on superconductive materials.

The aerospace and aeronautical industries pay much attention to improve flight safety of the airlines. In aircraft design it is important to couple low structural weight with high damage tolerance. For this reason, a new class of advanced composite materials, named Fiber/Metal Laminates (FML), which combine the best features of organic matrix composites and metals, are used. In this work, a nondestructive evaluation of FML specimens based on an eddy-current technique that uses an HTS SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The aim is to demonstrate that this technique is capable of detecting the presence of damage hidden by plastic deformation after impact events.

Transport properties of NbN/NiCu superconductor/ferromagnet (S/F) nanostripes fabricated in both in single-wire and series-parallel, meander-type configurations are presented down to T = 4.2 K. In particular, the enhancement of the superconducting critical current has been observed at smaller widths, apparently, due to an extra pinning mechanism, arising from clustering of ferromagnetic atoms inside the thin S layer. Moreover, we observed a number of characteristic voltage steps on the nanostripe current-voltage characteristics and their nature was investigated as a function of temperature. An explanation in terms of active phase-slip phenomena has been proposed based of the time-dependent Ginzburg-Landau theory and led to an estimation of the inelastic electron-phonon relaxation time τe-ph ~ 1 ps, in agreement with the τopt = 1.2±0.3 ps value, measured by the femtosecond transient optical reflectivity spectroscopy method on the same bilayer. Transient optical properties of our superconducting S/F nano-bilayers have been also investigated and compared to those obtained for pure NbN nanostripe reference samples. Finally, electrical photoresponse signals of S/F heterostructures exposed to ultraweak pulsed (width 400 ps, repetition rate ~100 MHz) laser radiation at 850 nm wavelength exhibited the falling time of voltage responses directly dependent on the NiCu overlayer. We have also noticed that the presence of the top F layer and the resulting proximity effect reduced frequency of dark counts in our samples.

Nowadays, tailoring the material properties is essential for advanced product design in engineering systems. The need to provide key information about micro- and macro-structural behaviour of materials, without destructively sectioning the sample, has spurred the development of nondestructive evaluation methodologies. These techniques are required during material production, quality testing of components during manufacturing, and in-service inspection of structural integrity. To ensure the highest possible operational safety along with an economic efficiency, it is necessary to carry out inspections with a high sensitivity and a proven reliability. Due to its unparalleled magnetic field sensitivity over a wide frequency range and large dynamic range, SQUID-based nondestructive evaluation has unique advantages for materials and structures characterization. We will present an overview of eddy-current nondestructive analysis utilizing high T c SQUIDs with an emphasis on examples relevant to the aeronautical industry. These include the detection of deep-lying defects in multi-layer structures of Al–Ti alloys and damage of extremely lightweight graphite/epoxy composites. Both of these can be successfully treated by this approach where conventional electromagnetic probes often fail. In addition some results based on the volume integral formulation, successfully developed to simulate the response of the system to different type of flaws in Al-alloy planar structures and to solve the inverse electromagnetic problem, will be shown.

Femtosecond spectroscopy has been used to investigate the quasi-particle relaxation times in nearly optimally doped Fe-based superconductors FeSe 0.5Te0.5 and optimally doped Ba-122 thin films growth on a Fe buffer layer. Experimental results concerning the temperature dependence of the relaxation time of such pnictides both in the superconducting state are now presented and discussed. Modelling the T-dependence of relaxation times an estimation of both electron-phonon constant and superconducting energy gap in the excitation spectrum of both Fe(Se,Te) and Ba-122 compounds is obtained.

We present characterization of Ba(Fe1-x Cox) 2As2 thin film using a magneto-optical Kerr effect setup based on photoelastic modulation. The magneto optical technique has been used to analyse the thickness and the temperature dependence of the magnetic properties of epitaxial Ba(Fe1-x Cox)2As2/Fe thin films grown on MgO substrate. The first harmonics, of the reflected laser beam intensity from pnictide thin films is compared with a reference Fe thin film. The hysteretic loops of such samples at room temperature and at 5K are presented.

A YBa/sub 2/Cu/sub 3/O/sub 7-x/ artificial grain boundary Josephson junction mas fabricated on to a [110] SrTiO/sub 3/ substrate employing a MgO seed layer. YBa/sub 2/Cu/sub 3/O/sub 7-x/ grows mainly oriented (103) on SrTiO/sub 3/ and [001] on the seed layer. An artificial 45/spl deg/ a or b axis tilt or twist boundary can occur according to the orientation of the MgO edge with respect to the [001] in plane direction of the substrate. Josephson junctions of good quality and excellent reproducibility were obtained in microbridges patterned across the grain boundary. Typical features of the phenomenology of high critical temperature superconductor (HTCS) Josephson junction were observed. The maximum value of the I/sub C/R/sub N/ product is of the order of 2-3 millivolts at T=4.2 K and of the order of 50 /spl mu/V at T=77 K respectively. The modulation of the critical current with the external applied magnetic field confirms the Josephson nature of the current in the weak link.

[1] A semielliptical channel flush mounted under a metal plane and slotted along the interfocal distance of its cross section is separated from the half-space above by a diaphragm. The cavity, the diaphragm, and the half-space are all isorefractive to each other. Both the cavity and the diaphragm are filled with materials isorefractive to the medium in the half-space above. This is a two-dimensional geometry where the source is invariant with respect to the axial variable. The resulting electromagnetic boundary value problem is solved exactly using series expansions containing Mathieu functions, when the excitation source is either a plane wave or a line source. For plane wave incidence, the polarization is with either the electric or the magnetic field parallel to the axis of the structure and the direction of incidence is arbitrary in a plane perpendicular to the axis. For line source excitation, the polarization is with either the electric or the magnetic field parallel to the axis of the structure and the source is arbitrarily located. Numerical results are also provided.

(110) MgO thin films have been deposited by RF sputtering on (110) SrTiO3 and used as buffer layers for YBCO deposition. The MgO films show high morphological quality, as confirmed by X-ray specular reflectivity, and narrow (approximate to 1 degrees) X-ray diffraction peaks in the rocking curves measurements. These results are discussed in the framework of an ionic oxide growth model. XRD analyses performed on the bilayer YBCO/MgO (110) confirm the epitaxial growth of the films. with cool) YBCO//(110) MgO. XRD, AFM, SEM measurements are compared with data relative to bilayers deposited on (100) SrTiO3.

Superconducting thin-films containing randomly disordered layers of and have been synthesized through a combined approach of metal-organic chemical vapour deposition (MOCVD) and thallium vapour diffusion. The BaCaCu matrices have been deposited onto yttria stabilized zirconia (YSZ) substrates using the second generation tetraglyme and tetraglyme (hfa denotes hexafluoroacetylacetonate), and the (acac denotes acetylacetonate) as volatile metal-organic precursors. BaCaCu precursor films of composition 2:2:3 were annealed in the presence of a mixture of thallium (III), barium, calcium and copper oxides at temperatures of 840 - and oxygen partial pressure varying from 0.04 - 0.5 atm. The formation of an oriented () intergrowth structure has been observed in narrow temperature and oxygen partial pressure ranges. The electrical resistivity data show which, in accordance with the scanning electron microscopy image, appears indicative of a material with weakly linked grains.

International audience; We present here recent results on detection of surface and subsurface artificial features in Al-Ti planar structures, to show current performance of our eddy-current nondestructive evaluation system based on HTc SQUIDs. The anomalous magnetic fields generated by flaws with known electromagnetic characteristics have been modeled by three-dimensional codes based on finite element method and volume integral formulation and developed for the investigated problem. Both numerical solutions have correctly predicted the shape of the complicated magnetic field response which is mainly the result of the shape of the defect, the geometry of the inducing coil and the characteristics of the SQUID gradiometer.

The correlation between electrical conductivity and magnetic field response, due to multi-walled carbon nanotubes' (MWCNTs) distribution within the polymer matrix, has been demonstrated using a contactless and non-destructive technique. Multi-walled carbon nanotubes, both buckypaper and reinforced epoxy matrix specimens with different nanotube percentages, have been inspected using the eddy current technique based on an HTc SQUID magnetometer. The SQUID magnetic field response, due to the nanotube distribution, has been compared with the thermographic technique results. Moreover, the electrical conductivity of nanotube-reinforced composites and buckypaper has been carried out by using the Van der Pauw method.

High-quality YBCO thin films have been grown by Inverted Cylindrical Magnetron Sputtering (ICMS) on LaAlO3(100), SrTiO3(100), SrTiO3(110), and MgO(100) substrates. Transition temperatures of c-axis films exceed 90 K, and transition widths are within 1 K. Critical currents range up to 5 × 106 A/cm2 at 77 K. Structural and morphological features analyzed by x-ray diffraction and scanning electron microscopy, respectively, are found to be strongly dependent on film orientation and deposition temperature. In order to understand such dependence, a simple interpretation is proposed in terms of Gibbs energies and growth dynamics of the nucleation process.

The Inverted Cylindrical Magnetron Sputtering (ICMS) technique has been used to fabricate YBCO step-edge junction dc SQUIDs. Steps are obtained by standard ion milling procedure on LaAlO3 (100) substrates using Nb-masks patterned by reactive ion etching. Thin films are then deposited under different conditions (both step and deposition angles) and patterned by standard lithography and wet chemical etching. An analysis of junction properties in terms of step height and film thickness has been carried out. Measurements on current vs voltage, maximum dc Josephson current vs magnetic field and SQUID voltage response measurements have been performed. Their temperature dependences have been also considered. Operating temperature as high as 77 K has been achieved. At 4.2 K the SQUIDs show a maximum voltage to flux transfer function (partial derivative V/partial derivative phi)(max)=870 mu V/Phi(o) and a good periodicity of the V-phi modulation up to 20 Phi(o) without any sign of hysteresis.

Dielectric measurements were utilized to follow the advancement of cure in an epoxy/amine formulation. In contrast to earlier studies, complex impedance was measured during cure and used to calculate ionic resistivity. By using complex impedance were able to separate according to their frequency dependence the contributions to overall polarization from electrode blocking layers, migrating charges, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial-and-error frequency search and is conducive to the development of phenomenological models based on equivalent circuits. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements. © 1994 John Wiley & Sons, Inc.

Dielectric measurements were utilized to follow the advancement of cure in a bifunctional and a tetrafunctional epoxy/amine formulation. In deferance to earlier dielectric studies of cure, complex impedance was measured and used to calculate ionic resistivity. By using complex impedance we were able to separate, according to their frequency dependence, the contributions to overall polarization from electrode blocking layers, mobile charge carriers, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial-and-error frequency search, it measures dielectric response in real time, and is conducive to the development of phenomenological models based on equivalent circuits. Values of ionic resistivity measured at different cure time and temperature were used to quantify the progress of cure. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements. It was suggested that apart from the extrinsic conductivity by ionic impurities, an intrinsic mechanism which involves the reactive molecules contributes to the overall ionic conductivity. © 1995 John Wiley & Sons, Inc.