Search

Over the last few years it has been understood that the interface between living cells and the underlying materials can be a powerful tool to manipulate cell functions. In this study, we explore the hypothesis that the electrical cell/material interface can regulate the differentiation of cancer stem-like cells (CSCs). Electrospun polymer fibres, either polyamide 66 or poly(lactic acid), with embedded graphene nanoplatelets (GnPs), have been fabricated as CSC scaffolds, providing both the 3D microenvironment and a suitable electrical environment favorable for CSCs adhesion, growth and differentiation. We have investigated the impact of these scaffolds on the morphological, immunostaining and electrophysiological properties of CSCs extracted from human glioblastoma multiform (GBM) tumor cell line. Our data provide evidence in favor of the ability of GnP-incorporating scaffolds to promote CSC differentiation to the glial phenotype. Numerical simulations support the hypothesis that the electrical interface promotes the hyperpolarization of the cell membrane potential, thus triggering the CSC differentiation. We propose that the electrical cell/material interface can regulate endogenous bioelectrical cues, through the membrane potential manipulation, resulting in the differentiation of CSCs. Material-induced differentiation of stem cells and particularly of CSCs, can open new horizons in tissue engineering and new approaches to cancer treatment, especially GBM.

Novel electrospun fibrous biocomposites have been fabricated, based on two naturally derived materials, namely wool keratin and cinnamon essential oil, and their efficacy for the treatment of skin burns caused by UVB exposure is demonstrated. The cinnamon essential oil, successfully encapsulated in uniform, bead-free fibers, enhances the mechanical compliance of the composite, retains its antioxidant properties and is released from the keratin matrix upon its dissolution in an aqueous environment. The low-cytotoxicity material reduces the risk of infection from Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Additionally, upon contact with UV-inflammated skin, keratin–cinnamon essential oil fibers are able to down-regulate in vivo IL-6 and IL-1β cytokine production, thus limiting the inflammatory response induced by UVB radiation exposure and confirming the potential of our designed dressing as a biomedical device for burn wound care.

Ordinary textiles are very often malodorous and the origin of cross-infection. Their microclimate, consisting of moisture, contaminants, and sweat, provides favorable conditions for microbial growth. Therefore, simple approaches of surface modification using functional materials are widely adopted to introduce antibacterial properties. This study reports a simple and low cost technique that renders cotton fabrics antibacterial. Manganese (Mn)-doped photocatalytic titanium dioxide (TiO

This article belongs to the Special Issue Sustainable Development of Nanotechnologies: Risks and Opportunities for Occupational Safety and Health., A paper sensor was designed in order to detect the presence of nanomaterials, such as ZnO and silica nanoparticles, as well as graphene nanoplatelets (GnP), based on fluorescence changes of carbon nanodots. Paper strips were functionalized with carbon nanodots using polyvinyl alcohol (PVA) as binder. The carbon nanodots were highly fluorescent and, hence, rendered the (cellulosic) paper stripes emissive. In the presence of silica and ZnO nanoparticles, the fluorescence emission of the carbon nanodots was quenched and the emission decay was shortened, whereas in the presence of GnP only emission quenching occurred. These different photoluminescence (PL) quenching mechanisms, which are evident from lifetime measurements, convey selectivity to the sensor. The change in fluorescence of the carbon dot-functionalized paper is also evident to the naked eye under illumination with a UV lamp, which enables easy detection of the nanomaterials. The sensor was able to detect the nanomaterials upon direct contact, either by dipping it in their aqueous dispersions, or by sweeping it over their powders. The use of the proposed optical sensor permits the detection of nanomaterials in a straightforward manner, opening new ways for the development of optical sensors for practical applications., This research was part of the Project “Nano and Key enabling technologies within the innovation processes: risk and opportunities in occupational settings by prevention through design (NanoKey__EPTR0003))”, funded by the Italian Workers’ Compensation Authority (INAIL) and coordinated in cooperation between the INAIL Department of Occupational and Environmental Medicine Epidemiology and Hygiene, and the Italian Institute of Technology (IIT).

Poly(3-hydroxybutyrate), a green polymer originating from prokaryotic microbes, has been used to prepare composites with graphene nanoplatelets (GnP) at different concentrations. The films were fabricated by drop-casting and were hot-pressed at a temperature lower than their melting point to provide the molecular chains enough energy to reorientate while avoiding melting and degradation. It was found that hot-pressing increases crystallinity and improves mechanical properties. The Young’s modulus increased from 1.2 to 1.6 GPa for the poly(3-hydroxybutyrate) (P(3HB)) films and from 0.5 to 2.2 GPa for the 15 wt % P(3HB)/GnP composites. Electrical resistivity decreases enormously with GnP concentration and hot-pressing, reaching 6 Ω sq–1 for the hot-pressed 30 wt % P(3HB)/GnP composite. Finally, the hot-pressed P(3HB) samples exhibit remarkable oxygen barrier properties, with oxygen permeability reaching 2800 mL μm m–2 day–1, which becomes 895 mL μm m–2 day–1 when 15% GnP is added to the biopolymer matrix, one of the lowest values known for biopolymers and biocomposites. We propose that these biocomposites are used for elastic packaging and electronics.

Sustainable biocomposites have been developed by solvent mixing of poly(lactic acid) (PLA) with a fine powder of cocoa bean shells (CBS) and subsequent solution casting, using different concentrations of CBS. The inclusion of CBS recovers the crystallinity of the initially amorphous PLA films and improves the physical properties of the composites. Young's modulus increases by 80% with 75 wt % CBS inclusion; however, the composites maintain plasticity. The barrier properties of the hydrophobic composites were characterized, and the water vapor permeability is found to be ca. 3.5 × 10

We present an innovative method to fabricate hybrid polymer/inorganic nanoparticles (NPs) fibrous membranes. In particular, the proposed method is based on a solvent-free two-step process. The first step deals with the electrospinning of a polymer/NPs precursor solution, while in the second step the in situ synthesis of NPs takes place, by mean of a thermally-induced solid-state reaction. Such method (schem in Figure 1) allows to obtain fibres homogeneously decorated with NPs, overcoming the typical particles aggregation that affects nanocomposites prepared by conventional mixing methods. In addition, the in situ formation permits to have exposed NPs on the fibres surface, which combined with high surface area offered by the fibrous structure result in a multifunctional material. Herein, two examples of hybrid nanocomposite membranes obtained by this approach are reported. PMMA membranes modified with ZnO NPs have shown reversible UV-switchable wettability and permeability, improved thermal stability and antibacterial activity, which can be controlled simply varying the filler content.[1] On the other hand, PVDF/CeO2/Au fibrous nanocomposites have shown photocatalytic degradation activity induced by visible light, thanks to the modification with Au NPs, which results in a narrowing effect of the CeO2 bandgap. The Au NPs also increase the Ce+3/Ce+4 ratio that greatly enhances the radical scavenging activity of CeO2.[2] In conclusion, the versatility of the presented multifunctional membranes as well as the light-weight and flexibility offered by the polymeric fibres, make these materials valuable alternatives to the nowadays existing systems based on NPs supported on ceramic materials. Furthermore, the present findings demonstrate that the proposed fabrication method is a promising and straightforward approach to obtain polymer-based hybrid membranes for several applications such as filtration, wound management and water purification, among others. [1] Morselli D. et al., Thermally-induced in situ growth of ZnO nanoparticles in polymeric fibrous membranes, Composites Science and Technology 149 (2017) 11-19 [2] Morselli D. et al., Ceria/gold nanoparticles in situ synthesized on polymeric membranes with enhanced photocatalytic and radical scavenging activity, accepted on ACS Applied Nano Materials (2018)

Ordinary textiles are very often malodorous and the origin of cross-infection. Their microclimate, consisting of moisture, contaminants, and sweat, provides favorable conditions for microbial growth. Therefore, simple approaches of surface modification using functional materials are widely adopted to introduce antibacterial properties. This study reports a simple and low cost technique that renders cotton fabrics antibacterial. Manganese (Mn)-doped photocatalytic titanium dioxide (TiO2) nanoparticles of ∼150 nm average diameter have been prepared by sol gel and applied on textile fabrics using a silicone binder. The treated fabrics displayed 100% reduction of Staphylococcus aureus (Gram-positive) and Klebsiella pneumoniae (Gram-negative) populations within 120 min under sunlight, demonstrating first order of reduction kinetics. Moreover, the functionalized fabrics demonstrated complete degradation of a methylene blue (MB) dye adsorbed on their surface, under both UV and visible light irradiation, turning ...

The poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) conductive polymer is well known for its high conductivity and applications in conductive synthetic textiles. However, PEDOT:PSS inks/dispersions are acidic in nature (pH

In this work, we exploit the bidimensional structure and high stiffness of graphene to improve the tribological response of nylon-based composites. Graphene nanoplatelets, coupled with polytetrafluoroethylene microparticles, synergistically improve the friction coefficient and wear rate, as well as the adhesion to the substrate. The enhancement, as high as threefold for both friction and wear rate at the optimal graphene concentration (0.5% in weight), depends upon the formation of a continuous, robust transfer film with the steel rubbing counterpart, as shown by Raman measurements. The graphene-nylon coating also shows three-fold improved adhesion to the underlying substrate, attributed to the high surface energy of graphene.

Microcrystalline cellulose (MCC) and polyamide 66 (PA66) have been separately dissolved in solutions containing trifluoroacetic acid (TFA) as a common solvent, mixed after their dissolution and cast. After solvent evaporation, self-organized membranes have been formed with three dimensional (3D) porous, interconnected morphology, the porosity of which depends on the relative ratio of cellulose and PA66, and is lost when the initial MCC content exceeds 50% by weight. Thermal and chemical analysis and X-ray diffraction results indicate that the addition of cellulose induces the amorphisation of PA66, while possible chemical interaction exists between the amorphous parts of PA66 and the cellulose. The various membranes produced with different 3D porosities have been characterized in terms of dielectric constant and salt permeability and their relation to cellulose-PA66 ratio has been determined.

Alginate nanofibers with an average diameter of 75 nm have been prepared by the electrospinning process. In addition, the spinnability of the solutions in the presence of the gold precursor HAuCl4 was investigated. At low concentrations of HAuCl4 well-formed nanofibers were produced, whereas as its concentration increases the nanofibrous mats present an increased number of bead-like defects. Herein, the in situ preparation of gold nanoparticles (Au NPs) is discussed since sodium alginate (SA) acts as the reducing agent and a mechanism is proposed in order to explain the bead-effect as well as the surface morphology of the alginate fibers decorated with Au NPs.

Pyromellitic dianhydride-4,4-oxydianiline (PMDA-ODA), broadly known as Kapton, is investigated for detection and quantification of ammonia (NH3) vapors from ammonia solutions of different molarities. The PMDA-ODA films are made by solution casting on microscope glass slides and cured at 200 °C. Ammonia sensing is performed by measuring the changes in the electric current intensity under ambient conditions of temperature and humidity. The sensor exhibits fast response to ammonia vapors, for aqueous ammonia solutions with molarity as low as 3.5 mM. The adsorption processes of ammonia to the polyimide surface after exposure to ammonia vapors are investigated by FTIR and XPS, revealing that ammonia results in the disruption of imide linkages and the simultaneous creation of amides I and II. Control experiments performed on commercial Kapton adhesive tape show negligible sensitivity of the commercial product to ammonia vapors from different ammonia solution molarities. A device is also presented, demonstrating the real-time detection of ammonia vapors.

Solution processing of aliphatic polyamides (nylon) is quite challenging due to the fact that only a few solvents, such as formic acid and cresol, dissolve nylon. In general, polyamide 6,6 (nylon 6,6) is dissolved in formic acid to produce porous membranes or electrospun fibers. Herein, we propose for the first time a mixture of trifluoroacetic acid (TFA) and acetone that dissolves nylon 6,6, resulting in crystalline and non-porous films. Furthermore the same mixture of solvents was proved to be an excellent co-solvent for graphene nanoplatelets that were homogeneously dispersed in the solutions to produce reinforced nylon 6,6 polymer composites. The dispersion of the nanoplates in the polymer solution was found to be very stable over time. The mechanical and electrical properties of the developed composites were studied as a function of filler content. The Young's modulus of the nylon 6,6 films increases more than two times upon the addition of the nanoplates. Furthermore, the flexible composites exhibit semiconducting behavior, with their electrical conductivity reaching 10−2 S cm−1 for 20 wt% graphene nanoplatelet concentration.

In this work, the deposition of Y thin films by laser beams with 0.5 ps and 5 ps pulse durations at different laser fluences (1.2–6.4 J/cm2) is reported. The morphology of the deposited films and of the ablated target surface is investigated by scanning electron microscopy analyses. The present results show that the films, well adherent to the substrates, are characterized by a high abundance of sub-micrometric particulates with average size less than 0.3 μm, whose density decreases with increasing laser fluence. The formation of columnar structures observed on the target surface seems to be responsible of the poor film homogeneity. Acceptable deposition rate in the range of 0.08–0.16 A/pulse with 5 ps pulse duration is found; on the contrary with 0.5 ps pulse duration, it is not possible to get information on deposition rate as a function of the laser fluence due to the high non-uniformity of the films. A comparison with the results previously obtained in ns regime is presented and discussed. The achievements of our investigation will be useful to optimize the synthesis of photocathodes based on Y films for the production of bright electron beams in radio-frequency photoinjectors.

This paper is a review of our recent work on electrowetting properties of devices based on silicon (Si) and metal oxide (MO) electrodes. In particular, the electrowetting-on-dielectric (EWOD) properties of three- dimensional (3D) structured Si and MO electrodes are investigated and compared with those of planar ones. It is shown that the EWOD properties of these materials can be advantageously controlled by altering their geometry and/or their surface chemistry. Ultrafast laser irradiation was used in order to produce 3D superhydrophobic Si electrodes exhibiting double-scale roughness, in the micro- and nano-scales. The metal oxide electrodes were fabricated by depositing hydrophobic ZnO or TiO2 nanostructures onto the laser textured substrates using Pulsed Laser Deposition (PLD). The EWOD induced contact angle changes on the 3D structured surfaces show reversible or non-reversible behaviour depending on the geometry of the surface structures. Reversibility is observed when the double-scale rough...

We studied the effect of temporally pulse shaping upon the properties of thin layers synthesized by pulsed laser deposition with fs laser pulses generated by a Ti-sapphire laser source. We showed that the film morphology and structure can be gradually modified when applying mono-pulses of different duration or passing to a sequence of two pulses of different intensities.

Laser induced forward transfer (LIFT) of ZnO and TiO 2 thin films onto Si has been realized with femtosecond double pulses of equal intensity, as a basic form of pulse shaping. In an effort to investigate the possibility to control the spatial distribution of the transfer via pulse separation, we used separation times varying from 0 to 10 ps. We have found that the size of the transferred spots increases by as much as 50% for pulse separation up to 500 fs, while for longer pulse separations the transferred spots acquire a constant area.

The XeCl excimer laser (308 nm) was used for depositing p-type SrCu 2 O 2 (SCO) films by pulsed-laser deposition (PLD) from undoped and Ba-doped (6%) SCO targets. The SCO films were deposited at 300 °C on glass and p-type Si substrates, while the oxygen pressure was kept constant at 5 x 10 -2 Pa and their properties were investigated just after deposition and after annealing at 330 °C in forming gas. The films were amorphous just after deposition but became stoichiometric SrCu 2 O 2 polycrystalline after annealing and very resistive. The Ba-doped SCO films showed lower transmittance than the undoped ones but for both films the transmittance increased to around 70-80% in the NIR-IR spectrum. The optical energy gap was found to be around 3.24 eV after annealing. SCO films deposited on p-Si exhibited rectifying properties, behaving like p - -SCO/p-Si heterojunctions and their I-V and C-V characteristics were examined with temperature. An explanation of the diode behaviour is attempted based on materials properties and heterodiode characteristics.

Primary neurons were grown on structured silicon (Si) substrates, in the absence of chemotropic factors or synthetic extracellular matrix. The Si substrates used for the study comprise hierarchical structures in the micro- and nanolength scales. The substrates were structured via femtosecond laser irradiation of the Si wafer, in a reactive SF(6) environment. Electron microscopy revealed that the neurons formed an elaborate web of cytoplasmic processes in the absence of glial elements. The neuronal cytoplasm autografted the depth of the spikes, and the neurite sprouting took place over the spikes surface. Here we demonstrate how microfabrication of a Si surface provides an excellent platform for multifaceted studies of neuronal specimens.

Electrowetting experiments have been performed on ZnO and TiO2 nanostructured thin films grown on crystalline Si and subsequently coated by a thin dielectric layer. The contact angle is decreased upon the application of an electric field between the film and a water droplet placed on the dielectric surface until saturation is observed. The electrowetting phenomenon is reversible, with the droplet returning to its initial hydrophobic state, when the applied potential is decreased. For the actuation of the droplet, low voltage, on the order of a few volts, is required.

A comparative study of the ultrafast dynamics on ZnO thin films deposited on flat Si substrates and on Si micro-cones following ultrashort laser excitation has been carried out using time-resolved optical spectroscopy. By monitoring the transient band gap renormalization induced by nonlinearly excited carriers it is found that fast electron scattering and trapping occurs more efficiently in the micro-cones as compared to the flat films. This enhanced trapping efficiency is attributed to the defects and imperfections that are introduced by the increased surface roughness due to the conical shape.

This work reports on the photoinduced wettability changes of high quality nanostructured ZnO films grown on Si by pulsed laser deposition (PLD) under different growth parameters. The wetting behavior of the resulting films can be reversibly switched from hydrophobic to hydrophilic, through alternation of UV illumination and dark storage. The kinetics of this wetting transition are studied by monitoring the time evolution of the corresponding contact angles. Finally, the influence of the film properties over the observed wetting response is discussed.

TiO 2 has attracted a lot of attention due to its photocatalytic properties and its potential applications in environmental purification and self cleaning coatings, as well as for its high optical transmittance in the visible–IR spectral range, high chemical stability and mechanical resistance. In this paper, we report on the growth of TiO 2 nanocrystalline films on Si (1 0 0) substrates by pulsed laser deposition (PLD). Rutile sintered targets were irradiated by KrF excimer laser ( λ = 248 nm, pulse duration ∼30 ns) in a controlled oxygen environment and at constant substrate temperature of 650 °C. The structural and morphological properties of the films have been studied for different deposition parameters, such as oxygen partial pressure (0.05–5 Pa) and laser fluence (2– 4 J/cm 2 ). X-ray diffraction (XRD) shows the formation of both rutile and anatase phases; however, it is observed that the anatase phase is suppressed at the highest laser fluences. X-ray photoelectron spectroscopy (XPS) measurements were performed to determine the stoichiometry of the grown films. The surface morphology of the deposits, studied by scanning electron (SEM) and atomic force (AFM) microscopies, has revealed nanostructured films. The dimensions and density of the nanoparticles observed at the surface depend on the partial pressure of oxygen during growth. The smallest particles of about 40 nm diameter were obtained for the highest pressures of inlet gas.

Control over the wettability of solids as well as the manufacturing of functional surfaces with special wetting properties has aroused much interest because of great advantages given to various applications in daily life, industry, and agriculture. We report here the dynamic optical control of the wetting behavior of liquids on hierarchically structured ZnO surfaces produced by irradiating silicon (Si) wafers with femtosecond laser pulses and subsequently coating them with ZnO by pulsed laser deposition. The final surface exhibits roughness at two length scales, comprising micrometer-sized Si spikes decorated with ZnO nanoprotrusions. It is shown that a liquid droplet on these surfaces can be rapidly and reversibly switched between hydrophobicity and superhydrophilicity by alternating UV illumination and dark storage or thermal heating. By studying the magnitude and the rate of the photoinduced transitions, we investigated the contribution of roughness at different scales in the framework of two theoretic...

Strontium copper oxide (SCO) has been studied as p-type transparent (VIS) conductive oxide material. Also theoretical studies suggested p-type conductivity of the SrCu2O2 composition. SCO thin layers, with thicknesses of 30–2000 nm, were deposited on glass and silicon substrates both by pulsed laser deposition (PLD) and by MOCVD method. The as-grown layers showed high electrical resistance. Due to an annealing process, the resistivity significantly decreased and the layers showed p-type conductivity. Optical transparency measured on samples grown on glass substrates was found about or above 80%, including also thickness dependence. RBS measurements were applied for the determination of the chemical composition profile of the layers. A comparison revealed some specific differences between as-grown and annealed PLD samples. Due to the annealing, the ratio of oxide phases was changed and a vertical inhomogeneity in chemical composition was observed. Our measurements revealed also the influence of the deposition technique and of the substrate.

Thin films of ZnO:Al (AZO) and pure ZnO have been grown by pulsed laser deposition (PLD) at a wide temperature range (200–500 °C) and at different partial oxygen pressures (5 × 10− 5–5 × 10− 2 mbar). The films have been characterized structurally, optically and electrically. It is observed that the presence of aluminum in the ZnO films results in an enlargement of the optical band gap (~ 3.8 eV) while the transmittance is increased in comparison to pure ZnO films, to approximately 85%. Furthermore, in the AZO films occurs a lowering of the resistivity to the order of magnitude of 10− 4 Ωcm. Finally, a sharp emission excitonic peak centered at 353.5 nm was observed for the highly conductive (3.3 × 10− 4 Ωcm) ZnO:Al films.

SrCu2O2 (SCO) thin films have been fabricated by pulsed laser deposition at oxygen partial pressures between 5 × 10− 5–5 × 10− 2 mbar and substrate temperatures from 300 °C to 500 °C. All films were single-phase SrCu2O2, p-type materials. Films deposited at a substrate temperature of 300 °C and oxygen pressure 5 × 10− 4 mbar exhibited the highest transparency (∼ 80%), having conductivity 10− 3 S/cm and carrier concentration around 1013 cm− 3. Films deposited at oxygen partial pressure higher than 10− 3 mbar exhibited higher conductivity and carrier concentration but lower transmittance. Depositions at substrate temperatures higher than 300 °C gave films of high crystallinity and transmittance even for films as thick as 800 nm. The energy gap of SrCu2O2 thin films was found to be around 3.3 eV.

In this paper, we report first principles calculations and experimental studies of the optical and microstructural properties of both bulk and thin films of SrCu2O2. Polycrystalline SrCu2O2 films were grown by a conventional Pulsed Laser Deposition method in a flowing oxygen environment on corning glass 7059 and silicon substrates. Several characterization techniques, including X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman, spectroscopic ellipsometry, reflectance/transmission spectrophotometry and Atomic Force Microscopy have been used for the investigation of the microstructural and vibrational properties of both bulk and thin films of SrCu2O2. XRD shows that bulk SrCu2O2 is polycrystalline and assumes the pure tetragonal phase of SrCu2O2. The vibrational properties of the tetragonal phase of SrCu2O2 have been inferred from Raman and FTIR spectroscopies and for the first time both Raman and IR active modes have been assigned. The bulk polycrystalline SrCu2O2 optical band gap determined from spectroscopic ellipsometry was 3.34±0.01 eV. XRD results confirmed that pure non-textured polycrystalline phase SrCu2O2 thin films with a smooth surface can be grown by PLD at low temperature

Here we show that macrozwitterions of poly(ethyl 2-cyanoacrylate), commonly called Super Glue, can easily assemble into long and well defined fibers by electrospinning. The resulting fibrous networks are thermally treated on glass in order to create transparent coatings whose superficial morphology recalls the organization of the initial electrospun mats. These textured coatings are characterized by low liquid adhesion and anti-staining performance. Furthermore, the low friction coefficient and excellent scratch resistance make them attractive as solid lubricants. The inherent texture of the coatings positively affects their biocompatibility. In fact, they are able to promote the proliferation and differentiation of myoblast stem cells. Optically-transparent and biocompatible coatings that simultaneously possess characteristics of low water contact angle hysteresis, low friction and mechanical robustness can find application in a wide range of technological sectors, from the construction and automotive industries to electronic and biomedical devices.

Magnetic relaxation measurements have been performed on a bulk, melt-cast sample of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$, displaying the paramagnetic Meissner effect (PME), revealing zero external field magnetic aging in a superconducting system. The aging effect, being a cooperative phenomenon, points out that the spontaneous orbital currents existing in PME samples behave collectively. The results can be understood by modeling of the polydomain microstructure of the superconducting grains as Josephson junction networks with randomly distributed $\ensuremath{\pi}$ junctions.

The dynamic magnetic properties of a granular Bi 2 Sr 2 CaCu 2 O 8 sample that displays the paramagnetic Meissner effect have been studied by low field ac susceptibility measurements. The frequency and field dependence of the in-phase and out-of-phase components of the susceptibility show a spontaneous creation of an increasing number of microscopically giant magnetic moments in the sample with decreasing temperature below T c . The magnetic response of the sample can be explained by a superposition of shielding and flux expulsion from individual grains and a polarisation of spontaneous moments by the applied magnetic field. The polarisation mechanism is the thermal activation over energy barriers separating the up and down directions of the magnetic moments. From our experimental data, the size of the thermally active magnetic moments is estimated to be 10 7 –10 8 μ B .

We present the fabrication of a multifunctional, hybrid organic-inorganic micropatterned device, which is capable to act as a stable photosensor and, at the same time, displaying inherent superhydrophobic self-cleaning wetting characteristics. In this framework several arrays of epoxy photoresist square micropillars have been fabricated on n-doped crystalline silicon substrates and subsequently coated with a poly(3-hexylthiophene-2,5-diyl) (P3HT) layer, giving rise to an array of organic/inorganic p-n junctions. Their photoconductivity has been measured under a solar light simulator at different illumination intensities. The current-voltage (I-V) curves show high rectifying characteristics, which are found to be directly correlated with the illumination intensity. The photoresponse occurs in extremely short times (within few tens of milliseconds range). The influence of the interpillar distance on the I-V characteristics of the sensors is also discussed. Moreover, the static and dynamic wetting properties of these organic/inorganic photosensors can be easily tuned by changing the pattern geometry. Measured static water contact angles range from 125° to 164°, as the distance between the pillars is increased from 14 to 120 μm while the contact angle hysteresis decreases from 36° down to 2°.

Applied Physics A, 105 (1), ISSN:0947-8396, ISSN:1432-0630, ISSN:0340-3793

Femtosecond lasers have been used for laser induced forward transfer (LIFT) of TiO2, a wide-band semiconductor with many industrial and research applications. TiO2 polycrystalline thin films on quartz (obtained by pulsed laser deposition) were used as donors and both quartz and fluorine-doped tin dioxide coated glass substrates as acceptors. LIFT was performed at the laser wavelengths of 248 and 800 nm with pulses of 450 and 300 fs respectively. The transferred material was characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction and micro-Raman spectroscopy to determine the composition and crystalline quality, and by scanning electron microscopy and atomic force microscopy to assess the surface morphology. The relation between these properties and the laser transfer conditions, including wavelength, pulse energy and acceptor substrate, are presented. © 2010 Elsevier B.V.

Wettability control of materials has gained considerable interest over the last decade, due to the wide range of possible applications, including self cleaning surfaces, controllable drag delivery or microfluidic devices. Wetting properties of surfaces depend on the synergistic effect of the free energy of the surface in question as well as its geometry. Hence, the control of the geometry and the chemistry of a surface, results in the tailoring of its wetting behaviour [1].

Mg-based films have been prepared by pulsed laser deposition technique for photocathode applications. We have investigated the influence of pulse laser duration on morphology and photoemissive properties. Two laser sources have been used, generating pulses of 30 ns at 308 nm (XeCl excimer laser), 5 ps and 500 fs at 248 nm (KrF excimer laser) to grow Mg films onto Si and Cu substrates in high vacuum (∼10−7 Pa) and at room temperature. Morphological investigations carried out by scanning electron microscopy (SEM) have revealed that, in our experimental conditions, the number and the mean size of the droplets on the films surfaces decreases as the pulse laser duration shortens. The contamination level of Mg film surfaces have been studied by energy dispersive X-ray spectroscopy (EDX). The photoelectron performances in terms of quantum efficiency (QE) and emission stability have been tested in a UHV DC photodiode cell (10−7 Pa). Measures of the QE of the samples surfaces have revealed a decrease on the initial value for Mg-based photocathodes prepared by fs laser (from 7.8 × 10−4 to 6.6 × 10−4) PLD with respect to ps (from 6.2 × 10−4 to 7.4 × 10−4) and ns lasers (from 5.0 × 10−4 to 1.6 × 10−3). A comparison among Mg-based photocathodes prepared by ns, ps and fs PLD for the production of high brightness electron beams has been presented and discussed.

Magnetic relaxation measurements have been performed on a sample of Bi 2 Sr 2 CaCu 2 O 8 , displaying the paramagnetic Meissner effect (PME), revealing, for the first time, the collective behaviour of the spontaneous magnetic moments responsible for the PME.

Materials processing by ultrafast lasers offers several attractive possibilities for micro/nano fabrication applications. Several exciting prospects arise in the context of surface and bulk laser induced modifications. These form the basis for diverse applications, including the development and functionalization of laser engineered surfaces, the laser transfer of biomolecules and the functionalization of 3D structures constructed by multiphoton stereolithography. In particular, two examples will be discussed in the following, namely a new approach for the development of superhydrophobic, self cleaning surfaces and the fabrication of functionalized scaffolds, for tissue engineering applications.

Thin films were deposited by KrF laser ablation of CrSi2 and β-FeSi2 targets with the aim to obtain silicide thin films and layers with narrow band gap for sensor applications. The CrSi2-based films exhibit both semiconductor and metal properties, depending on the deposition conditions. Thus, the film of d ≅ 40 nm thick, deposited on Si at 740 K, presents a band gap Eg ≅ 0.18 eV, and large thermo electromotive force (e.m.f.) coefficient α ≅ 1.0–1.4 mV/K at 300 ≤ T ≤ 340 K and a coefficient of tensosensitivity (R–R0)/R0ɛ ≅ 5. The film with the same thickness, but deposited on SiO2 at 740 K, presents a metal behavior at 125 ≤ T ≤ 296 K and a semiconductor one at 77 ≤ T ≤ 125 K. Its coefficient α varies in the range 5.0–7.5 μV/K at 300 ≤ T ≤ 340 K. The 750 nm thick film deposited on SiO2 at 740 K exhibits only semiconductor behavior in the range 296–77 K with Eg ≅ 0.013 eV and α ≅ 10–15 μV/K at 293 ≤ T ≤ 340 K. The coefficient of tensosensitivity for these films is changing in the range 2–5. The β-FeSi2-based films deposited on SiO2 at 295 ≤ T ≤ 740 K show only semiconductor behavior. The thicker the film, the higher Eg: d ≅ 150 nm, Eg ≅ 0.032 eV; d ≅ 70 nm, Eg ≅ 0.027 eV; d ≅ 60 nm, Eg ≅ 0.023 eV. The higher Eg, the higher coefficient α. The coefficient of tensosensitivity for these films varies in the range 2.3–4.7. The more the semiconductor phase content in the deposited film, the higher are the values of α and (R–R0)/R0ɛ.

A novel approach to fabricating nanocomposites comprising inorganic nanoparticles embedded in an organic matrix is presented. Ultra-fast laser ablation of a titanium metal target in aqueous e-caprolactam monomer solution is used to produce ultra-small TiO2 nanoparticles and to simultaneously initiate the polymerization of the monomer without the use of chemicals. The spectroscopic analysis and TEM studies reveal the formation of an organic matrix and its conjugation to the nanoparticles' surface. The laser beam induces the formation of TiO2 nanoparticles, which subsequently act as photoinitiators of the polymerization of e-caprolactam upon absorbing the photon energy provided by the unfocused part of the beam. This work can open new pathways for cost-effective and environmentally friendly nanocomposite production, in one step.

We report on the electrical and magnetotransport properties of the contact formed between $n$-type degenerate InSb (100) substrates and polycrystalline NiMnSb thin films grown using pulsed laser deposition. Negative giant magnetoresistance is observed when the external magnetic field is oriented parallel to the in-plane current direction. We attribute the observed phenomenon to magnetic precipitates that are formed during the magnetic film deposition and are confined to a thin layer at the interface. The evidence for the formation of a thin interfacial layer is obtained through x-ray reflectivity measurements.

The nonlinear susceptibility of a melt-cast ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8}$ sample, displaying both the paramagnetic Meissner effect and magnetic aging, has been studied experimentally. The presence of magnetic aging in this sample proves that the spontaneous orbital magnetic moments exhibit correlated and frustrated dynamics at low temperatures. The possible existence of a chiral-glass phase transition was investigated by extracting a quantity corresponding to the order parameter susceptibility of the glass phase. It is shown that the expected divergent behavior of this quantity is hampered by relaxation effects and that the sample is out-of-equilibrium already at temperatures slightly below the superconducting transition temperature $({T}_{c})$. Time dependent magnetization experiments indicate that the magnetic relaxation at temperatures close to but below ${T}_{c}$ is due to isolated orbital magnetic moments, not yet being part of the collective orbital moment state that develops at slightly lower temperatures.

The flux dynamics of a bulk, melt-cast Bi 2 Sr 2 CaCu 2 O 8 (Bi2212) sample has been studied by using acsusceptibility measurements. The sample shows the paramagnetic Meissner effect (PME) and it is found that the dynamic properties of the PME are remarkably different from the dynamics of the PME of sintered Bi2212 samples. The dynamics of sintered samples implies the existence of independent spontaneous current loops, the dynamics of the melt-cast sample, in addition, suggests that the current loops in this case interact to form a low-temperature glassy phase with some similarities to a spin-glass phase.

Parametric studies have been performed on yttrium films deposited by laser ablation deposition at three different laser pulse durations. Morphological investigations of the film surface have confirmed the strong influence of pulse durations on the density, size and shape of the deposited droplets. The average ablation rate and deposition rate in ns regime resulted to be one order of magnitude higher than those obtained in ps and sub-ps regimes. Present interest in the deposition of Y thin films by laser ablation technique starts from the well known photoemission properties of this metal.