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Nanoporous materials represent a unique class of materials, given to their unforeseen magnetic, mechanical, optical and catalytic properties arising from their network of pores and ligaments. Here a polycrystalline thin film of FePd is considered as a starting system, in which the porosity is induced via dealloying. This process determines the removal of iron from the alloy and the diffusion of palladium on the surface, which in turn influences the evolution of the material’s composition, magnetic properties and optical properties. In addition, from the magnetic point of view, the material acquires a more isotropic behaviour while the magnetic moment decreases due to the removal of iron. In the same way, there is an improvement of the surface enhanced Raman scattering as the dealloying proceeds, due to the formation of clusters of palladium on the surface. This mixture of optical and magnetic properties, combined with its high corrosion resistance and biocompatibility, gives the system a strong multifunctional connotation, paving the way for new applications, ranging from magnetic trapping to detection of low concentration of molecules.

Nanoporous gold thin films have been fabricated through chemical de-alloying of Au-based nanoglass with a nanocolumnar structure, with composition Au40Cu28Ag7Pd5Si20 (at.%), that had previously been deposited by magnetron sputtering. By varying the de-alloying conditions, gold ligaments ranging from 20 to 100 nm were obtained. The microstructure and chemical composition of the as-prepared films were characterised by various techniques. Surface-enhanced Raman scattering (SERS) of thin films was investigated using rhodamine 6G. The results indicate that the main microstructural features with interconnected ligaments and defects of nanoporous gold result in significant SERS enhancement.

A Au 20 Cu 48 Ag 7 Pd 5 Si 20 metallic glass precursor has been used to synthesize nanoporous gold by chemical de-alloying in a mixture of HNO 3 and HF. Gold ligaments of size ranging from 45 to 100 nm were obtained as a function of HNO 3 concentration, electrolyte temperature and de-alloying time. The as-prepared nanoporous gold exhibited strong surface enhanced Raman scattering (SERS) effect using 4,4′-bi-pyridine as probe molecule. For application in melamine sensing, the detection limit of 10 −6 M was achieved, which indicated that this biocompatible material has great potential as SERS active substrate.

Measurement of thin film magnetostriction is a challenging task, as magnetostrictive material deformations in parts per million, in conjunction with materials at small dimensions, require high precision, often with dedicated set-ups, for reproducible results. We have developed a novel approach employing a commercial atomic force microscope (AFM) with attached electromagnets. Magnetostriction measurements are demonstrated on 50–500 nm thick Fe81Al19 films sputter deposited directly on high aspect ratio commercial AFM micro-cantilevers. A magnetostrictive deflection of the cantilever bimorph translates into a deflection force acting in a contact mode measurement, which is interpreted and recorded as a change in height. For determination of the magnetostriction coefficient λ s , we have developed a modified version of the equation for the magnetostrictive deflection of a cantilever bimorph by Guerrero and Wetherhold, taking into account long-range attractive forces acting during contact mode AFM measurements in air. The sub-atomic precision of the AFM, combined with the widespread availability of all components and the simple set-up, makes the measurement of magnetostriction on films of just a few tens of nanometers thickness easily accessible.

Nanoscale magnetic materials are the basis of emerging technologies to develop novel magnetoelectronic devices. Self-assembly of polystyrene nanospheres is here used to generate 2D hexagonal dot arrays on Fe50Pd50 thin films. This simple technique allows a wide-area patterning of a magnetic thin film. The role of disorder on functional magnetic properties with respect to conventional lithographic techniques is studied. Structural and magnetic characteristics have been investigated in arrays having different geometry (i.e. dot diameters, inter-dot distances and thickness). The interplay among microstructure and magnetization reversal is discussed. Magnetic measurements reveal a vortex domain configuration in all as-prepared films. The original domain structure changes drastically upon thermal annealing performed to promote the transformation of disordered A1 phase into the ordered, tetragonal L10 phase. First-order reversal magnetization curves have been measured to rule out the role of magnetic interaction among crystalline phases characterized by different magnetic coercivity.

The development of a new generation of ultra-sensitive sensors for analytical and bio-diagnostic devices requires a strong signal in front of very small quantity of analyte, often present in complex and interfering matrix. Taking advantage of peculiar plasmonic properties of nanoporous gold (NPG), a promising sensor for selective detection of Human Serum Albumin (HSA), a proof-of-concept bioanalyte, was prepared and tested in a conventional micro-Raman spectrometer using Surface Enhanced Raman Spectroscopy (SERS). NPG was synthesized by chemical de-alloying of an amorphous precursor, Au20Cu48Ag7Pd5Si20, starting from melt spun ribbons. A fully de-alloyed ribbon with ligaments of about 60 nm was obtained after 4 h of de-alloying at 70 °C and 10 M HNO3 + 0.5 M HF. This material is self-standing, mechanically resistant, and suitable for wide range of applications. At this stage, NPG is SERS-active toward several molecules, including pyridine, bi-pyridine, and rhodamine at very low concentration. In order to obtain the selective binding properties required to detect molecules in bio-diagnostic applications, immuno-functionalization of NPG was carried out by using an anti-HSA antibody (Ab-anti-HSA) covalently grafted on gold ligaments via the 4-aminothiophenol (4ATP) Raman probe, yielding the SERS-active nanohybrid NPG-4ATP-Ab. SERS signal recorded at increasing HSA concentrations was used for the acquisition of SERS maps and a chemometric regression model allowed to calibrate the sensor. In the best experimental conditions, we were able to get quantitative analysis of HSA at ultra-low concentrations (0.1 ng/l) with SERS. The methodology proposed in this paper has to be considered a major step toward a calibrated device for ultra-sensitive detection of biomolecules by SERS detection.

In this work, Pt nanoparticles were electrodeposited through cyclic voltammetry technique on three dimensional nanoporous gold prepared from Au-based metallic glass precursor by chemical de-alloying. The electro-catalytic properties of the as-prepared samples were tested through potential cycling towards methanol oxidation in alkaline solution. Current density plots vs scan numbers indicate that the electrodes are active for the electro-oxidation of methanol and the Pt nanoparticles electrodeposited on gold ligaments contribute to increasing catalytic properties. In particular, results indicate that nanoporous gold with 30 cycles of Pt electrodeposition exhibits competitive higher activity and longer durability towards methanol electro-oxidation.

In this study, Au-based nanoglasses in the form of thin films deposited by magnetron sputtering are comparatively dealloyed. The films have either nanograined or nanocolumnar microstructure, depending on the working pressure of Ar in the sputtering chamber. Nanocolumnar thin films exhibit much higher dealloying rate reducing effectively the dealloying time with respect to nanograined and homogenous thin films. Electrocatalysis experiments indicate that the resulting nanoporous films are active for the methanol electrooxidation, with promising results in term of stability especially for the dealloyed nanocolumnar film.

New multinary amorphous materials, based on gold, that can be produced in bulk form due to their high glass-forming tendency, were discovered recently. However little is known about their corrosion properties. In the present study, the characterization of Au 49 Cu 26 . 9 Ag 5.5 Pd 2.3 Si 16.3 amorphous ribbons produced by melt spinning is reported. Their corrosion properties were tested by incubating the samples in artificial sweat and by monitoring the changes in surface structure by SEM and XRD. Before incubation, the surface of the samples was amorphous and flat, characterized only by microfeatures due to the liquid contact with the wheel during quenching. After treatment with artificial sweat, the formation of nanosized crystallites of Au on the sample surface was observed. The surface chemical composition of both sides of the ribbon samples was investigated by XPS. Atomic concentration and chemical states of constituent elements before and after the incubation in artificial sweat were determined. The depth profiling of both sides ofthe samples was carried out by using Ar ion sputtering combined with cyclic XPS measurements. The segregation of Si on one side of the samples and the changes of chemical composition, caused by the treatment in artificial sweat, were revealed.

In this paper, two alternative integrated power systems were considered: one based on photovoltaic and hydrogen technology (electrolyzer coupled with a fuel cell), the other based on photovoltaic and batteries. The two systems, designed for off-grid applications, were sized for a photovoltaic energy production in the area of Turin, Italy, to provide 3 kW maximum power, with an average daily consumption of 10.25 kWh. The systems were compared from a technical and economical point of view and a Life Cycle Assessment analysis (LCA) was performed, to identify the main contributors to the environmental impact of the systems. From a commercial point of view, fuel cell and the electrolyzer are niche products, so the hydrogen-based power system results to be more expensive with respect to Li-ion batteries. From the environmental point of view, however, LCA results show the lower burdens of the hydrogen technology.

Experimental determinations of the glass transition and related properties in alloys are reviewed. Several recent measurements of viscosity, specific volume and heat capacity in the undercooling regime have become possible after the discovery of bulk glass forming alloys. The data allow verification of models on the kinetics and thermodynamics of such melts. The notion of melt fragility, borrowed from the description of inorganic and molecular glasses, has become popular also for metallic alloys: the kinetic fragility is described by the viscous behavior of the liquid and the thermodynamic fragility by the entropy loss on undercooling. The experimental viscosity data for metallic glass formers presently available can be reasonably framed within the strong–fragile classification. On the other hand, there are major discrepancies for the thermodynamic fragility of metallic glass formers with respect to conventional ones. The reason for such disagreement is twofold: on the experimental ground there are difficulties in obtaining fully reliable thermodynamic data in sufficiently wide temperature ranges; on the conceptual side the definition of the configurational entropy of the liquid with a suitable reference state is controversial. Among fragility indexes, the reduced width of the transition range proves most useful. The trend of the glass transition as a function of composition is also discussed in relation to the progressive ordering of the liquid on undercooling.

Mechanical properties of Al87Ni7RE6 amorphous and devitrified alloys (RE = Ce, Nd, La) are reported in this work. The microhardness of samples annealed at different devitrification stages is determined and an improvement is observed for all compositions when Al nanocrystals are present in the amorphous matrix. A further increase is found after a second transformation due to precipitation of an unknown phase in Al87Ni7Nd6. The fracture surfaces resulting from tensile tests of amorphous samples are examined both with scanning electron microscopy and transmission electron microscopy, where shear bands, vein patterns and protrusion are seen. There is no sign of crystallisation in shear bands and in vein patterns although their shape suggests a rise in temperature during deformation. Also in cold rolled samples the crystallization is avoided during deformation.

Supersaturated Au80Fe20 and Au70Fe30 solid solutions have been obtained by melt spinning. Heat treatments of as-quenched ribbons in the temperature range between 320 and 550 °C induced the precipitation of a fcc Fe-rich phase. From structural and microstructural analysis of precipitates and residual matrix, a discontinuous (cellular) transformation mechanism has been observed. Calculated driving forces for nucleation of bcc and fcc phases suggest a critical role of defect concentration on observed phase transformations.

This paper describes the crystallisation of Al 87 Ni 7 La 6 and Al 87 Ni 7 Sm 6 metallic glasses. The substitution of Sm for La in the alloy causes a variation in the transformation mode evidenced by the number of differential scanning calorimeter (DSC) peaks: two for the La containing alloy at low heating rates, than three at high heating rates, and three for the one with Sm. The glass transition becomes manifest for each alloys at a typical heating rate below which it is overlapped by the first crystallisation event due to precipitation of fine Al crystals in both materials. The Kissinger plot for Al 87 Ni 7 La 6 is not strictly linear as a possible consequence of overlapping processes. The second and third transformations of both alloys produce a metastable intermediate and the equilibrium phases, respectively. The second crystallisation steps of Al 87 Ni 7 Sm 6 and Al 87 Ni 7 La 6 involve linear Kissinger plots. The crystallisation behaviour of the two alloys is compared with that of Al 87 Ni 7 Ce 6 and Al 87 Ni 7 Nd 6 which were earlier shown to present two and three transformations, respectively.

Cu80−xNixFe20 (x=0, 5 and 20) alloys have been rapidly solidified by planar flow casting. X-ray diffraction (XRD) analysis of as-quenched ribbons shows bcc-Fe precipitates embedded in an fcc phase (x=0), two co-existing fcc solid solutions (x=5) and a complete solid solution of the parent elements (x=20). Thermal treatments in the temperature range between 400 and 600 °C give precipitation and spinodal decomposition reactions. These phase transformations have been evidenced from a variation of lattice constants, from a broadening of diffraction peaks and from TEM observations. The role of Ni content on competition between precipitation and decomposition reactions during rapid solidification and annealing is discussed in terms of thermodynamic arguments. Recent CALPHAD assessment of thermodynamic properties for Cu–Fe–Ni system has been used for an estimation of composition and volume fraction of equilibrium phases.

Immiscible alloys have been rapidly solidified for the preparation of granular materials with giant magnetoresistance properties. Au-based (Au–Co and Au–Fe) and Cu-based (Cu–Co and Cu–Fe) systems have been investigated. Single supersaturated solid solution has been obtained for Au–Fe, whereas three FCC solid solutions with different Co content have been found for Au–Co. For Cu–Co and Cu–Fe a limit of solubility in Cu has been observed. Ni additions to Cu–Fe strongly enhance solid solubility. A thermodynamic analysis has been used to describe the competition between partition-less solidification and phase separation in undercooled liquid.

Nanoporous gold (NPG) has been synthesized by electrochemical de-alloying a new precursor, amorphous Au30Cu38Ag7Pd5Si20 (at.%), starting from melt-spun ribbons. Ligaments ranging from 75 to 210 nm depending on the de-alloying time were obtained. Analytical and electrochemical evidence showed the ligaments contain residual Cu, Ag and Pd. Surface-enhanced Raman scattering from the NPG was investigated using pyridine and 4,4′-bi-pyridine as probe molecules. It was found that the activity is at maximum when the ribbon is fully de-alloyed although the ligaments then have a larger size. The enhancement is attributed to the small size of crystals in the ligaments, to their morphology and to trapped atoms.

This paper reports on studies of the effect of different rare earth (RE) elements on the devitrification behaviour of alloys of general composition Al 87 Ni 7 RE 6 (here RE = Ce, Nd). We have evidenced two crystallisation mechanisms as a function of the type of rare earth element. When RE = Ce the transformation proceeds in two steps as shown by Differential Scanning Calorimetry (DSC) traces. When RE = Nd the transformation sequence has an additional step. There is also evidence of a calorimetric continuous background for all alloys which is attributed to diffusional homogenisation of the matrix. The glass transition becomes manifest for both alloys when fast enough rates are used in DSC (higher than 10 K/min and 40K/min, respectively for Al 87 Ni 7 Ce 6 and Al 87 Ni 7 Nd 6 ). The first crystallisation step implies the precipitation of nanocrystalline Al. The kinetics of this process is influenced by the simultaneous occurrence of the glass transition. In Al 87 Ni 7 Ce 6 when it takes place above T g (i.e. at high heating rates) it also implies the formation of an intermetallic compound. Kissinger plots for the first transformation display a kink at temperatures corresponding to the glass transition range marking the change in mechanism for the transformation. In Al 87 Ni 7 Nd 6 the glass transition remain visible after partial crystallisation showing that the matrix is readily homogenised. Therefore the molten state of these alloys appears rather fragile.

Al–TM–RE (TM: transition metal, RE: rare earth metal) and Al–RE alloys were analysed with the aim of studying phase selection under various processing conditions. The metastable phases formed in binary Al-rich systems (notably Al–Sm) are revised for a unified interpretation of the literature. Two groups of alloys had different behaviour as for phase selection. In Al 88 Fe 9 Nd 3 and Al 87 Ni 10 Ce 3 stable intermetallic compounds form as primary phases during solidification. Nanocrystalline Al is formed at high undercooling. This may occur directly in rapid solidification or when fully amorphous materials are suitably annealed. In Al 90 Sm 8 Ni 2 and Al 90 Sm 8 Fe 2 metastable intermetallics form during rapid solidification together with a fraction of amorphous phase, whereas nanocrystalline Al forms on annealing the amorphous phase.

Various multicomponent alloys containing Ni-Fe-Si-B and refractory metals have been rapidly solidifed in order to check their tendency to produce glassy phases and their devitrification behaviour has been studied. Among these a Ni36Fe32Ta7Si8B17 alloy presents primary crystallization with production of fcc nanocrystals embedded in the glassy matrix. The kinetics of the transformation is determined at 530 °C showing that it consists in two steps: fast nucleation and growth of nanocrystals plus homogenization of the remaining matrix with crystal coarsening. Evidence based on TEM observations, XRD patterns and DSC experiments, are reported in favour of a homogeneous mechanism of nucleation. Faceting of nanocrystals is observed for the first time in such transformations and is attributed to a stress effect on the particles.

Metallic glasses have been obtained in the form of small ingots with the composition Zr40Ti14Cu11Ni10Be25, by means of water quenching. All glasses transform on annealing to a mixed state comprising a nanocrystalline phase embedded in an amorphous matrix. The transformation of the glasses occurs via a phase separation in the amorphous alloy, followed by the formation of the nanocrystalline phase. The process is analyzed by means of isothermal and non-isothermal differential scanning calorimetry (DSC) and X-ray diffraction. The isothermal heat of transformation has two steps as a function of temperature which are due to the transformation sequence. Similarly, non-isothermal traces have multiple signals, the intensities of which depend on the heating rate. A Ni36Fe32Ta7Si8B17 alloy has been shown to display glass forming tendency, as indicated by the reduced crystallization onset temperature of 0.6. Amorphous ribbons of this material reach a thickness of 100 μm. On annealing, an austenitic nanocrystalline phase is obtained through a nucleation and growth mechanism. In practice, the growth is limited and rarely proceeds beyond a particle size of 10 nm, as revealed by transmission electron microscopy. The present results allow a comparison of the DSC behaviour for alloys undergoing devitrification with different mechanisms.

The formation, size and morphology of crystals in Al 100-x Sm x (8

Multiferroic BFO/SRO/Si trilayers have been prepared by pulsed laser deposition in the form of thin films. As a function of the BFO layer thickness, magnetic and magneto-transport properties have been investigated at room temperature and down to 5 K. At low BFO layer thickness, a residual γ-Fe2O3 phase, which interacts interfacially with the SRO and BFO layers, is responsible for moderately hard magnetic properties of the film. On increasing BFO layer thickness, more homogeneous deposits are obtained with uniform magnetic and magneto-resistive properties.

In this study, the kinetics of nanocrystallization of amorphous Fe73.5Si13.5B9Nb3Cu1 (F1) and Fe77Si11B9Nb2.4Cu0.6 (F2) alloys is investigated. The microstructure and magnetic properties of the nanocrystalline alloys are compared. The crystallization temperature of F2 alloy is shifted towards lower temperatures with respect to F1. Thus, the crystalline volume fraction and the crystalline grain size at specific annealing temperature for the F2 alloy are higher than for the F1 alloy, accounting for the higher coercive force of F2 alloy with respect to the one of F1 alloy. According to isoconversional methods, the activation energy for crystallization is variable as a function of transformed fraction because of the continuous changes in chemical composition during the transformation. Mean values of 350 and 290 kJ/mol are obtained for F1 and F2, respectively. Microstructural observations confirm that minor changes in chemical composition affect the kinetics and final microstructure of the nanocrystalline alloy, that determine the observed magnetic properties.

FeSiB tapes have long been commercialised for their excellent soft-magnetic properties but do not manifest a glass transition temperature Tg as crystallisation intervenes. In this work, we present the crystallisation and properties of two Fe-based glasses, which show a glass transition before crystallisation. Using Ni and Co substitution, we can design glasses that form primary FCC or BCC FeNiCo solutions in their first stage of crystallisation followed by the formation of the metastable (FeNiCo)4B (C6Cr23-type cF116) intermetallic phase. Thermal and structural and magnetic properties were compared during heat treatment.

Rapid quenching techniques have been successfully applied since long time for the preparation of metallic glasses in ribbon form. Only in the recent years, the research activity addressed towards the synthesis of bulk metallic glasses (BMG), in form of ingots with a few millimetres in thickness. These materials can be obtained by casting techniques only for selected alloy compositions, characterised by a particularly high glass-forming tendency. Bulk amorphous alloys are characterised by a low modulus of elasticity and high yielding stress. The usual idea is that amorphous alloys undergo work softening and that deformation is concentrated in shear bands, which might be subjected to geometrical constraints, resulting in a substantial increase in hardness and wear resistance. The mechanical properties can be further improved by crystallisation. In fact, shear bands movement can be contrasted by incorporating a second phase in the material, which may be produced directly by controlled crystallisation. Soft magnetic properties have been obtained in Fe-based systems and they are strongly related to small variations in the microstructure, ranging from a fully amorphous phase to nanocrystalline phases with different crystal size. The high thermal stability of bulk metallic glasses makes possible the compression and shaping processes in the temperature range between glass transition and crystallisation. Aim of this paper is to present recent results on glass formation and properties of bulk metallic glasses with various compositions. Examples will be reported on Zr, Fe, Mg and Pd-based materials, focussing on mechanical and magnetic properties.

Magnetization and magnetoresistance of as quenched and joule-heated samples of the ternary alloy Cu 60 Fe 20 Ni 20 have been measured at room temperature. Magnetic measurements have been performed up to 700 K. All studied samples display magnetic frustration on the nanometer scale; the size of the magnetically correlated regions can be estimated by properly combining magnetization and resistance data. Annealing promotes the magnetoresistive effect by enhancing the agreement between size of magnetically correlated regions and electron mean free path. The magnetic behaviour of the strongly annealed samples shows the evolution from a still dominant magnetic frustration to the first appearance of hysteretic features.

A calorimetric approach has been employed to study undercooling of metals and alloys using a high temperature differential scanning instrument. The samples are kept under alumina powder, the entire cell is evacuated several times, and heated or cooled under flowing helium. Undercooling can exceed 200 K (as found for pure Ni and Fe). Ni-B, Fe-B, Pd-Si alloys around eutectic compositions, as well as several multicomponent glass-forming alloys, were also significantly undercooled and the solidification of metastable phases was detected. The heat of fusion at the eutectic temperature and the heats of solidification in the undercooling regime have been determined. The thermal data are compatible with the existence of a substantial excess specific heat of the melt for glass-forming alloys whereas the specific heat difference between liquid and crystal phases is nil for pure metals. The undercooling could be extended further when the samples were previously fluxed in molten B 2 O 3 or boro-silicates.

In the present paper, thermodynamic data of the Al-Ce and the Al-Nd systems are analysed by a new CALPHAD assessment, in which special emphasis is put on the description of the short range order in the undercooled liquid. A reliable description of the thermodynamics of the undercooled liquid and the amorphous phase can only be achieved by considering thermodynamic data of each metastable state. The results demonstrate a stabilization of the liquid phase on undercooling up to the glass transition temperature. The thermodynamic properties of intermetallic compounds are also reassessed. From the calculated Gibbs energies, the driving force for nucleation of primary fcc-Al and Al 11 RE 3 crystals from the Al-rich liquid and amorphous phase have been computed as a function of temperature.

The glass formation and crystallization of a Ni 36 Fe 32 Ta 7 Si 8 B 17 alloy is reported. In its equilibrium state it has a complex constitution made of at least four phases. It starts melting at 1227 K and displays a liquidus at 1460 K, but it shows a tendency to undercool even on cooling at 10 K/min in a HTDSC cell. Amorphous ribbons were produced by melt spinning. In DSC experiments the crystallization of the amorphous alloy occurs with a primary reaction giving a peak skewed on the high temperature side with onset at 836 K using an heating rate of 40 K/min. XRD analysis and TEM observations demonstrate that crystals with size below 10 nm and lattice parameter close to that of Ni are formed during this transformation. The mechanism of crystallization is very sensitive to changes in composition. In fact, nanocrystals are not found in alloys easily amorphized as the present one but containing a different ratio of metallic elements.