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Deposition of Au nanoparticles (NPs) through UV ultra-short-pulse laser ablation in vacuum is a methodology suitable for obtaining high purity supported plasmonic NPs with a superb adherence to both planar and patterned substrates. Furthermore, the peculiarity that upon sub-picosecond laser irradiation NPs form directly within the target leads to narrow and controlled size-distribution. While extensive literature theoretically models phase changes and pressure relaxation of metal targets under sub-picosecond irradiation, the evolution of the nanostructured deposit through different ablation regimes is poorly documented experimentally. In this paper, besides modeling the temporal evolution of electron and lattice temperature following sub-picosecond laser pulse irradiation of Au bulk at the threshold ablation fluence (0.1 J/cm2), we report an accurate statistical, morphological and structural characterization of the AuNP distributions as a function of the laser fluence tuned from 0.1 to 3 J/cm2 to drive the target through two ablation regimes. The occurrence of photomechanical spallation and phase explosion at low and high fluence, respectively, is correlated with the evolution of the NP deposits, which are discussed by providing a physical insight in the interplay between fluence-driven ablation regimes of the target, arrangement kinetics of the deposited species (NPs and vapour species) and (crystalline or amorphous) phase of the NPs. This knowledge is key for controlling the surface plasmon resonance response of AuNPs depending on the designed application.

The ablation of a metal target at laser energy densities in the range of 1–10 TW/cm2 leads to the generation of nanoparticles (NP) of the ablated material. This aspect is of particular interest if the immobilization of NPs on three-dimensional (3D) substrates is necessary as for example in sensing applications. In this work the deposition of Au NP by irradiation of a Au bulk target with a sub-picosecond laser beam (500 fs; 248 nm; 10 Hz) on 2D (silica and Si(100)) and 3D substrates (silica nanowire forests) is reported for different number of laser pulses (500, 1000, 1500, 2000, 2500). A uniform coverage of small Au NPs (with a diameter of few nm) on both kinds of substrates has been obtained using a suitable number of laser pulses. The presence of spherical droplets, with a diameter ranging from tens of nm up to few μm was also detected on the substrate surface and their presence can be explained by the weak electron-phonon coupling of Au. The optical characterization of the samples on 2D and 3D substrates evidenced the surface plasmon resonance peak characteristic of the Au NPs although further improvements of the size-distribution are necessary for future applications in sensing devices.

Precious corals are some of the most valuable living marine resources, growing and commercially exploited only in limited areas of the world, namely the Mediterranean Sea and the Northern Pacific Ocean. Their skeleton is formed by calcium carbonate crystallized in the form of calcite whereas their color is because of the presence of partially demethylated polyene pigments. Recently, Pacific corals have been included in the appendix II of CITES list, while Mediterranean corals are still excluded. Different Corallium species of Corallidae family (e.g. Corallium rubrum, Corallium elatius and Corallium secundum) collected from different locations of the Mediterranean Sea and the Pacific Ocean were analyzed by Raman spectroscopy for the characterization of the reddish pigment and by X-ray fluorescence (XRF) for the determination of the chemical composition of their skeletons, in order to obtain molecular and elemental data with two relatively easy and non-destructive techniques, which can be used quite steadily for authentication purposes. Raman analysis demonstrated the presence of specific vibrational bands useful to identify the colored pigments as a mixture involving methylated and demethylated polyenes such as carotenoids and parrodienes, characterized by the presence of ―CH3 groups along the polyene chain. The ratio between the Raman signal and fluorescence background was found to vary as a function of the macroscopic color of the coral, but Raman analyses resulted inadequate for distinguishing between corals having similar color but different origins. On the other side, XRF data provided reliable information for an appropriate separation between Pacific and Mediterranean corals at the elemental level. The results of this study will be of great relevance for the authentication and identification of the origin of corals in trade market by means of completely non-destructive techniques. Copyright © 2016 John Wiley & Sons, Ltd.

The formation of Pd nanoparticles (NPs) by matrix-assisted pulsed laser evaporation (MAPLE) of a palladium acetate solution has been studied as a function of the carrier solvent, laser-pulse number, metal precursor concentration and post-deposition thermal heating. Structural and compositional analyses demonstrate that: (i) the conventional MAPLE process can induce self-reduction of the metal salt precursor, thereby leading to the formation of metallic Pd(0) NPs; (ii) the solvent critically determines the size, morphology, and size distribution of the resulting NPs; and (iii) the cumulative effects of laser-pulse number and solute concentration are less influential than the type of solvent used. For diethyl ether-derived samples, a bimodal distribution of NP sizes spanning from ∼1 nm up to 20 nm was obtained. Conversely, by using acetone, a mono-modal distribution of sizes in the ∼1 nm–6 nm range (mean diameter of 1.5±0.7 nm) and a more uniform and densepacked surface coverage (NP coverage was twice as dense as the one obtained with diethyl ether) resulted in. These observations point out that solvents with low dynamical viscosity coefficients and high volatility favor the formation of larger and more broadly dispersed NPs. A general theoretical picture has been proposed to describe the NP formation pathways on account of the solvent properties and the mechanisms underlying the MAPLE process enabled by the technique.

Random lasers are based on disordered materials with optical gain. These devices can exhibit either intensity or resonant feedback, relying on diffusive or interference behaviour of light, respectively, which leads to either coupling or independent operation of lasing modes. We study for the first time these regimes in complex, solid-state nanostructured materials. The number of lasing modes and their intensity correlation features are found to be tailorable in random lasers made of light-emitting, electrospun polymer fibers upon nanoparticle doping. By material engineering, directional waveguiding along the length of fibers is found to be relevant to enhance mode correlation in both intensity feedback and resonant feedback random lasing. The here reported findings can be used to establish new design rules for tuning the emission of nano-lasers and correlation properties by means of the compositional and morphological properties of complex nanostructured materials., 30 pages, 10 figures

Pulsed laser–based techniques for depositing and processing materials are an important area of modern experimental and theoretical scientific research and development, with promising, challenging opportunities in the fields of nanofabrication and nanostructuring. Understanding the interplay between deposition/processing conditions, laser parameters, as well as material properties and dimensionality is demanding for improved fundamental knowledge and novel applications. This book introduces and discusses the basic principles of pulsed laser–matter interaction, with a focus on its peculiarities and perspectives compared to other conventional techniques and state-of-the-art applications. The book starts with an overview of the growth topics, followed by a discussion of laser–matter interaction depending on laser pulse duration, background conditions, materials, and combination of materials and structures. The information outlines the foundation to introduce examples of laser nanostructuring/processing of materials, pointing out the importance of pulsed laser–based technologies in modern (nano)science. With respect to similar texts and monographs, the book offers a comprehensive review including bottom-up and top-down laser-induced processes for nanoparticles and nanomicrostructure generation. Theoretical models are discussed by correlation with advanced experimental protocols in order to account for the fundamentals and underline physical mechanisms of laser–matter interaction. Reputed, internationally recognized experts in the field have contributed to this book. In particular, this book is suitable for a reader (graduate students as well as postgraduates and more generally researchers) new to the subject of pulsed laser ablation in order to gain physical insight into and advanced knowledge of mechanisms and processes involved in any deposition/processing experiment based on pulsed laser–matter interaction. Since knowledge in the field is given step by step comprehensively, this book serves as a valid introduction to the field as well as a foundation for further specific readings.

SIBA Get it!(opens in a new window)|View at Publisher| Export | Download | Add to List | More... Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms Volume 331, 15 July 2014, Pages 168-171 Comparative study of metal and non-metal ion implantation in polymers: Optical and electrical properties (Article) Resta, V.a , Quarta, G.a, Farella, I.b, Maruccio, L.a, Cola, A.b, Calcagnile, L.a a Department of Engineering for Innovation, University of Salento, Via Monteroni, Lecce I-73100, Italy b Institute for Microelectronics and Microsystems, Unit of Lecce, National Council of Research (IMM/CNR), Lecce I-73100, Italy View references (28) Abstract The implantation of 1 MeV metal (63Cu+, 107Ag+, 197Au+) and non-metal ( 4He+, 12C+) ions in a polycarbonate (PC) matrix has been studied in order to evaluate the role of ion species in the modification of optical and electrical properties of the polymer. When the ion fluence is above ∼1 × 1013 ions cm-2, the threshold for latent tracks overlapping is overcome and π-bonded carbon clusters grow and aggregate forming a network of conjugated CC bonds. For fluences around 1 × 1017 ions cm-2, the aggregation phenomena induce the formation of amorphous carbon and/or graphite like structures. At the same time, nucleation of metal nanoparticles (NPs) from implanted species can take place when the supersaturation threshold is overcome. The optical absorption of the samples increases in the visible range and the optical band gap redshifts from 3.40 eV up to 0.70 eV mostly due to the carbonization process and the formation of C0x clusters and cluster aggregates. Specific structures in the extinction spectra are observed when metal ions are selected in contrast to the non-metal ion implanted PC, thus revealing the possible presence of noble metal based NPs interstitial to the C0x cluster network. The corresponding electrical resistance decreases much more when metal ions are implanted with at least a factor of 2 orders of magnitude difference than the non-metal ions based samples. An absolute value of ∼107 Ω/sq has been measured for implantation with metals at doses higher than 5 × 1016 ions cm-2, being 1017 Ω/sq the corresponding sheet resistance for pristine PC.

Silica two-dimensional substrates and nanowires (NWs) forests have been successfully decorated with Au nanoparticles (NPs) through laser ablation by using a pulsed ArF excimer laser, for sensor applications. A uniform coverage of both substrate surfaces with NPs has been achieved controlling the number of laser pulses. The annealing of the as-deposited particles resulted in a uniform well-defined distribution of spherical NPs with an increased average diameter up to 25 nm. The deposited samples on silica NWs forest present a very good plasmonic resonance which resulted to be very sensitive to the changes of the environment (ethanol/water solutions with increasing concentration of ethanol) allowing the detection of changes on the second decimal digit of the refractive index, demonstrating its potentiality for further biosensing functionalities.

Electrospinning technologies for the realization of active polymeric nanomaterials can be easily up-scaled, opening perspectives to industrial exploitation, and due to their versatility they can be employed to finely tailor the size, morphology and macroscopic assembly of fibers as well as their functional properties. Light-emitting or other active polymer nanofibers, made of conjugated polymers or of blends embedding chromophores or other functional dopants, are suitable for various applications in advanced photonics and sensing technologies. In particular, their almost one-dimensional geometry and finely tunable composition make them interesting materials for developing novel lasing devices. However, electrospinning techniques rely on a large variety of parameters and possible experimental geometries, and they need to be carefully optimized in order to obtain suitable topographical and photonic properties in the resulting nanostructures. Targeted features include smooth and uniform fiber surface, dimensional control, as well as filament alignment, enhanced light emission, and stimulated emission. We here present various optimization strategies for electrospinning methods which have been implemented and developed by us for the realization of lasing architectures based on polymer nanofibers. The geometry of the resulting nanowires leads to peculiar light-scattering from spun filaments, and to controllable lasing characteristics., Comment: Comments: 7 pages, 4 figures, 20 references. Invited contribution. Copyright (2016) Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited

Efficient solar energy conversion is strongly related to the development of new materials with enhanced functional properties. In this context, a wide variety of inorganic, organic, or hybrid nanostructured materials have been investigated. In particular, in hybrid organic–inorganic nanocomposites are combined the convenient properties of organic polymers, such as easy manipulation and mechanical flexibility, and the unique size-dependent properties of nanocrystals (NCs). However, applications of hybrid nanocomposites in photovoltaic devices require a homogeneous and highly dense dispersion of NCs in polymer in order to guarantee not only an efficient charge separation, but also an efficient transport of the carriers to the electrodes without recombination. In previous works, we demonstrated that cadmium thiolate complexes are suitable precursors for the in situ synthesis of nanocrystalline CdS. Here, we show that the soluble [Cd(SBz)2]2·(1-methyl imidazole) complex can be efficiently annealed in a conjugated polymer obtaining a nanocomposite with a regular and compact network of NCs. The proposed synthetic strategies require annealing temperatures well below 200 °C and short time for the thermal treatment, i.e., less than 30 min. We also show that the same complex can be used to synthesize CdS NCs in mesoporous TiO2. The adsorption of cadmium thiolate molecule in TiO2 matrix can be obtained by using chemical bath deposition technique and subsequent thermal annealing. The use of NCs, quantum dots, as sensitizers of TiO2 matrices represents a very promising alternative to common dye-sensitized solar cells and an interesting solution for heterogeneous photocatalysis.

Highly porous nanocrystalline films of TiO 2 sensitized with semiconductor nanocrystals (NCs) are very promising for photovoltaic applications, NCs being more versatile and efficient than organic dyes as sensitizer. In this framework, the visible light absorption of TiO 2 can be improved by the superposition of CdS NC absorption band, that is tunable between 2.5 and 5.2 eV. Here, we report on a novel in situ approach for the synthesis of CdS NCs in mesoporous sol-gel TiO 2 anatase films by using as starting reagent for CdS, [Cd(SBz) 2 ]MI, where MI represents 1-methylimidazole. The precursor has been adsorbed into the TiO 2 pores and then decomposed at 480 °C, the procedure being studied for TiO 2 films with different porosity. The matrices have been investigated by atomic force microscopy. X-ray diffraction measurements on TiO 2 matrix and on the corresponding CdS/TiO 2 nanocomposite material revealed a variation of the NCs size of both TiO 2 and CdS as a function of the matrix porosity. The optical properties of the TiO 2 and CdS/TiO 2 have been studied by UV-Vis transmission spectroscopy. CdS/TiO 2 nanocomposites, having higher absorption efficiency with respect to TiO 2 , are suitable as building blocks for 3rd generation solar cell design.

We present a method of spatial and dimensional controlled formation of CdS quantum dots into polymer matrices by light irradiation. The initial samples consist of Cd thiolate precursors doped in TOPAS polymer matrix. Under pulsed UV laser irradiation the precursors are photolysed driving to the nucleation of CdS nanocrystals, with increasing size and concentration, related to the number of UV pulses. The formed quantum dots are localized in the irradiated area, while the host polymer remains macroscopically unaffected by the UV irradiation. In this study we investigate how the formation of the nanocrystals (size, dimensions, and concentration) is affected by the use of different irradiation conditions (wavelength, number of pulses), revealing information about the different pathways followed during the formation. The change of the size of the dots results in the change of the peak of their emission due to the quantum size effect, which is studied by fluorescence measurements. The results are reinforced by TEM microscopy and by XRD measurements. The main advantages of the presented method are the size tuning of the produced dots and their spatial confinement inside the host matrix, not possible by the other methods used until now (thermal annealing, mixing etc.).

The irradiation of a polycarbonate (PC) matrix with 28Si+ ions has been performed by selecting three different energies: 0.5 MeV, 1.0 MeV and 2.0 MeV. The comparative study of the modifications induced in the polymer as a function of the incident ion beam energy has been carried out in the range of fluences between 5 × 1013 ions cm−2 and 1 × 1015 ions cm−2. The changes induced in the structure of the matrix towards the production of conducting plastics for optoelectronics devices have been evaluated by Raman and Photoluminescence spectroscopy. The carbonization process of the polymer generates a network made of sp2-bonded graphitic clusters embedded in a sp3-bonded matrix. The amount of nanocrystalline-graphite with respect to amorphous-carbon increases as ion energy and fluence increase, in accordance with the increase of the sp2-order arrangement. With 0.5 MeV the modification process is at an initial stage so that the changes, in terms of structure and PL emission, are observed only for the highest fluence, while for 1.0 MeV it has been achieved a higher density of small cluster with an order and homogeneity even better than for 2.0 MeV. The irradiation process with a suitable set of experimental parameters allows tuning the PC emission from ∼510 nm (pristine matrix) up to ∼550–600 nm.

The Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique is emerging as an alternative route to the conventional methods for depositing organic materials, although the MAPLE-deposited films very often present high surface roughness and characteristic morphological features. Films of the blue-emitting polymer, poly(9,9-dioctylfluorene)—PFO, have been deposited by MAPLE to investigate the influence of the laser fluence and repetition rate on both their topography and emission properties. The laser fluence has been changed from 150 up to 450 mJ/cm2 , while laser repetition rates of 2 and 10 Hz have been considered. The interplay/relationship between the topography and the emission properties of the MAPLE-deposited films has been studied by confocal microscopy, photoluminescence spectrometry and atomic force microscopy. It has been found that under high irradiation (fluence of 450 mJ/cm2) conditions, the sample surface is characterized by bubbles presenting the intrinsic PFO blue emission. Instead, while improvements in the film morphology can be observed for lowered fluence and laser repetition rate, green emission becomes predominant in such conditions. Such result is very interesting to better understand the MAPLE ablation mechanism, which is discussed in this study.

The implantation of 1 MeV 63Cu+ ions in polycarbonate (PC) matrices has been carried out in order to evaluate the morphological and structural modifications induced in the polymer as a function of the ion fluence in the range 5 × 1013 ions cm−2 to 1 × 1017 ions cm−2. Atomic Force Microscopy analysis reveals a significant roughness increase of the polymer surface only for fluences higher than 5 × 1016 ions cm−2 with the presence of hillock structures which surface density increases with increasing the ion fluence. X-ray Diffraction measurements of PC implanted with fluences in the range between 5 × 1015 at cm−2 and 5 × 1016 at cm−2 reveal an increase of the disorder inside the PC matrix, as a consequence of the damaging process induced by the ion irradiation. Evidences about the presence of exotic phase structures ascribed to both cubic Cu2O and cubic Cu have been found.

A straight synthetic route to fabricate hybrid nanocomposite films of well-dispersed CdS nanocrystals (NCs) in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) is reported. A soluble cadmium complex [Cd(SBz)2]2·MI, obtained by incorporating a Lewis base (1-methylimidazole, MI) on the cadmium bis(benzyl)thiol, is used as starting reagent in an in situ thermolytic process. CdS NCs with spherical shape nucleate and grow well below 200°C in a relatively short time (30 min). Photoluminescence spectroscopy measurements performed on CdS/MEH-PPV nanocomposites show that CdS photoluminescence peaks are totally quenched inside MEH-PPV, if compared to CdS/PMMA nanocomposites, as expected due to overlapping of the polymer absorption and CdS emission spectra. The CdS NCs are well-dispersed in size and homogeneously distributed within MEH-PPV matrix as proved by transmission electron microscopy. Nanocomposites with different precursor/polymer weight ratios were prepared in the range from 1:4 to 4:1. Highly dense materials, without NCs clustering, were obtained for a weight/weight ratio of 2:3 between precursor and polymer, making these nanocomposites particularly suitable for optoelectronic and solar energy conversion applications.

1 MeV copper ions were implanted in polycarbonate (PC) matrices with fluences ranging from 5 x 10(13) ions cm(-2) to 1 x 10(17) ions cm(-2) in order to modify the optical and electrical properties of the polymer host. Increasing the ion fluence, an increase of the overall absorption and a redshift of the optical band gap were observed, from the initial value of 3.40 eV for the pristine PC to 0.80 eV measured for 1 x 10(17) ions cm(-2). For fluences above 5 x 10(14) ions cm(-2) a broad optical absorption bands at 450-475 nm and 520 nm were observed and, from 1 x 10(16) ions cm(-2), an additional band appeared at 570 nm. Both bands redshift when the fluence is increased. On the contrary, the optical response of the highest fluence sample is characterized by an overall band at 580 nm. The chemical modifications observed in the polymer range from induced -OH stretching, C=O and -C=C- double bonds and -C C and CH triple bonds formation, as the ion fluence increases. The implantation process affects the electrical properties of the polymer leading to a strong reduction in sheet resistance when ion fluence exceeds 5 x 10(16) ions cm(-2). A value of similar to 7.1 x 10(7) Omega/sq has been obtained for the highest fluence, i.e. about 10 order of magnitude lower than the pristine PC.

A highly dense and uniform layer of Au nanoparticles (NPs) on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film has been produced by the pulsed laser deposition (PLD) technique toward the production of an improved efficiency photovoltaic device. The advantage of PLD over other techniques is the easy and precise control of the Au NPs size and spatial distribution, without needing of further NP surface functionalization. The efficiency enhancement factor related to Au NPs doping has been evaluated in a solar cell based on poly-(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) diffused bilayer. The short-circuit current density, J SC, increases by 18 % and the power conversion efficiency by 22 %, respectively, in comparison with an equivalent device without Au NPs. The optical and morphological properties of the Au NPs layer have been selected in order to evaluate the contribution of the surface plasmon resonance as enhancement factor of the solar cell efficiency, in a range size where light scattering is negligible.

A poly-(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C-61-butyric-acid-methyl-ester (PCBM) bilayer structure has been realized by single step matrix-assisted pulsed laser evaporation (ss-MAPLE) technique using the same solvent for both the polymers under vacuum conditions. Our ss-MAPLE procedure allows the fabrication of polymeric multilayer device stacks, which are very difficult to realize with the conventional solvent assisted deposition methods. A proof of concept bilayer P3HT/PCBM solar cell based on ss-MAPLE deposition has been realized and characterized. This demonstration qualifies ss-MAPLE as a general and alternative technique for the implementation of polymeric materials in hetero-structure device technology.

The in situ synthesis and patterning of pis nanocrystals (NCs): is obtained: by laser processing. of a transparent polymer matrix doped with a. Cadmium thiolate Methylimidazole (MI): modified complex, [Cd(SBz)(2)](2)center dot MI. The precursor molecule structure ensures a uniform distribution inside the polymer and gives,rise to a regular and homogeneous net-Work of CdS NCs in the quantum size regime with finely tunable bandgap by varying the laser fluence in the range 25-75 mJ cm(-2) and Shot number from 10. to 100. The simultaneous in situ synthesis of CdS NCs and patterning,has been performed in confined regions with a 10 mu m resolution by scanning the focused laser beam in the polymer/precursor composite: The emission signal of the irradiated regions presents contributions from both the band gap. and the defect emission band; around 3.4 and 2.2 eV, respectively, the relative intensity of them depending on the laser fluence and number of shots. Complex geometries of mu-patterned CdS NCs inside the polymer matrix are achievable, thus enlarging the perspectives in the development of nanodevices and organic light emitting diode(OLED) systems.

The in situ synthesis and patterning of CdS nanocrystals in a polymer matrix is performed via multi-photon absorption. Quantum-sized CdS nanocrystals are obtained by irradiating a cadmium thiolate precursor dispersed in a transparent polymer matrix with a focused near infrared femtosecond laser beam. High resolution transmission electron microscopy evidences the formation of nanocrystals with wurtzite crystalline phase. Fluorescent, nanocomposite patterns with sub-micron spatial resolution are fabricated by scanning the laser beam on the polymer-precursor composite. Moreover, the emission energy of the CdS nanocrystals can be tuned in the range 2.5-2.7 eV, by changing the laser fluences in the range 0.10-0.45 J cm -2. This method enables therefore the synthesis of luminescent, CdS-based composites to be used within patterned nanophotonic and light-emitting devices.

The effects induced during the covering/embedding of metal nanoparticles (NPs) produced by pulsed laser deposition (PLD) and their impact on the structural and optical properties have been studied by producing pairs of samples containing Au NPs that are either uncovered (i.e., at the surface) or covered (i.e., embedded in an amorphous a-Al2O3 host). The main result is that covering species can sputter up to 100% of the Au atoms, the smaller the NPs the higher the sputtered fraction. This fraction has been simulated using standard models for ion bombardment and taking into account the kinetic energy distribution of arriving species and the cohesive energy dependence on NPs dimensions. Although all models well predict the order of magnitude of the sputtering yield, the calculated values are generally smaller than the experimental ones and do not account for the experimental dependence on NPs dimensions. This disagreement is discussed in terms of the limitations of standard models that do not take into account the lower adhesion of small NPs to the substrate, the high flux of species involved in PLD and, possibly to lesser extent, the use of some bulk material parameters. The metal sputtering during the coverage regulates the NPs morphology, through a reduction of dimensions and dimension dispersion. Most changes of structural features and optical spectra when covering the NPs are directly related to the variation in the amount of metal with the exception of a strong blueshift of the surface plasmon resonance when NPs are covered. This shift could be consistent with mixing of covering layer species and metal at the surface of the NPs. © 2011 American Institute of Physics., This work was partially supported by MAT2009-14282- C02-01 (Spain).

Inorganic-organic nanocomposites, with II-VI or III-V semiconductor nanocrystals (NCs) embedded in semiconducting polymer matrix, are very promising materials for photovoltaic applications.Here, we present an effective and easy synthesis procedure to obtain a hybrid nanocomposite with CdS NCs dispersed in poly[2-methoxy-5-(2-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) conjugated polymer. CdS NCs are synthesized directly within the matrix through the decomposition of a suitable unimolecular precursor dispersed homogeneously in the polymer.We show that CdS NCs are formed at low annealing temperature avoiding structural damages and without affecting the functional properties of the MEH-PPV polymer. The NCs diameter ranges between 1.5nm and 4nm depending on the annealing temperature. In addition, no coalescence phenomena of CdS NCs were noticed in TEM observations even at very high particle density (40 wt %).

Polymer films embedding cadmium thiolate precursors have been irradiated with ultraviolet laser pulses resulting in the formation of cadmium sulfide crystalline nanoparticles through a macroscopically non-destructive procedure for the host matrix. Controlling the number of the incident laser pulses, the gradual increase of the size of the nanoparticles is accomplished, and consequently the progressive change of the emission characteristics of the formed nanocomposites. The X-ray diffraction and transmission electron microscopy measurements were used for the full characterization of the nanoparticles. This study compares two polymer matrices, poly(methyl methacrylate) and a cyclic olefin copolymer, and reveals the importance of each one for the emission characteristics of the formed cadmium sulfide nanocrystals. It is found that the poly(methyl methacrylate) matrix contributes to the increase of the trap states on the surface of the formed nanocrystals, causing the broadening of their emission. On the other hand the cadmium sulfide nanoparticles, grown into the cyclic olefin copolymer matrix, exhibit narrower emission spectra.

This work compares the morphology of gold nanoparticles (NPs) produced at room temperature on single-crystalline (MgO nanocubes and plates) and amorphous (carbon/glass plates) substrates by pulsed laser deposition (PLD). The results show that similar deposition and nucleation rates (>5× 1013 cm-2 s-1) are achieved irrespective of the nature of the substrate. Instead, the shape of NPs is substrate dependent, i.e., quasispheres and faceted NPs in amorphous and single-crystalline substrates, respectively. The shape of the latter is octahedral for small NPs and truncated octahedral for large ones, with the degree of truncation being well explained using the Wulff-Kaichew theorem. Furthermore, epitaxial growth at room temperature is demonstrated for single-crystalline substrate. The large fraction of ions having energies higher than 200 eV and the large flux of species arriving to the substrate (1016 at. cm-2 s-1) involved in the PLD process are, respectively, found to be responsible for the high nucleation rates and epitaxial growth at room temperature. © 2009 The American Physical Society., This work has partially been supported by EU Grant No. HPRN-CT-2002-00328 and MEC Spain Grant No. MAT2005-06508-C02-01 .

In this work we report on the synthesis and the characterization of CdS nanocrystals (NCs) in mesoporous TiO2 anatase films as a first step towards the production of quantum dot sensitized TiO2 based solar cells. A novel in-situ approach has been devised using a unimolecular precursor, containing both the metal and the non-metal part. A [Cd(SR)2]Ln cadmium thiolate complex, where L represents 1-methylimidazole, has been prepared in order to maximize the adsorption into the TiO2 pores. The thiolate complex absorbed in TiO2 can be decomposed at 500°C in argon atmosphere in order to obtain the final CdS/TiO2 composite material. The optical properties of the final product have been monitored by UV-Vis transmission spectroscopy carried out with non polarized light and at normal incidence with respect to the sample surface. The morphology and porosity of the TiO2 matrix have been investigated by scanning electron microscopy. X-ray diffraction and transmission electron microscopy have been performed in order to study the crystalline structure of the samples and to estimate the TiO2 and CdS NCs size. The proposed synthesis strategy allows us to fabricate tailored band gap CdS/TiO2 composite material, with 10 nm to 100 nm diameter for TiO2 anatase crystallite pores and 3.2 nm average diameter for CdS NCs.

A method of in situ formation of patterns of size controlled CdS nanocrystals in a polymer matrix by pulsed UV irradiation is presented. The films consist of Cd thiolate precursors with different carbon chain lengths embedded in TOPAS polymer matrices. Under UV irradiation the precursors are photolyzed, driving to the formation of CdS nanocrystals in the quantum size regime, with size and concentration defined by the number of incident UV pulses, while the host polymer remains macroscopically/microscopically unaffected. The emission of the formed nanocomposite materials strongly depends on the dimensions of the CdS nanocrystals, thus, their growth at the different phases of the irradiation is monitored using spatially resolved photoluminescence by means of a confocal microscope. X-ray diffraction measurements verified the existence of the CdS nanocrystals, and defined their crystal structure for all the studied cases. The results are reinforced by transmission electron microscopy. It is proved that the selection of the precursor determines the efficiency of the procedure, and the quality of the formed nanocrystals. Moreover it is demonstrated that there is the possibility of laser induced formation of well-defined patterns of CdS nanocrystals, opening up new perspectives in the development of nanodevices.

4 pags. ; 4 figs., Gold nanoparticles with enhanced efficiency as substrates for surface-enhanced Raman and infrared spectroscopies have been grown by pulsed laser deposition on glass and CaF2 substrates. Transmission electron microscopy analysis has evidenced the presence of nanoparticles with characteristic sizes of several nanometers in diameter. The capabilities of the produced nanoparticles as enhancer substrates have been investigated using the dithiocarbamate fungicide thiram as a test molecule. The enhancement factors and features of SERS and SEIRA spectra are compared to those observed from large Au nanoparticles produced by evaporation at high temperatures. Slight changes in favor of the new substrates are discussed., The Ministerio de Educacio´n y Ciencia of Spain (Projects FIS2004-00108 and MAT2005-06508-C02-01), the Comunidad de Madrid (MICROSERES Program, S-0505/TIC-0191), and the European Community’s Human Potential NanoCluster (HPRN-CT-2002-00328) are gratefully acknowledged for financial support.

The expansion dynamics of the plasma generated during pulsed laser deposition of gold in vacuum has been investigated at the laser fluences of 2.5, 6.0, and 9.0 J cm-2. A severe distortion of the expansion is observed in the presence of a substrate that is accompanied at 9.0 J cm-2 by the appearance of a secondary plasma front expanding from the substrate surface. Langmuir probe analysis at 9.0 J cm-2 shows that the substrate surface is bombarded by a high transient flux of energetic Au+ ions (3.0× 1019 ions cm-2 s-1) having very large kinetic energies (>400 eV). Analysis of the plasma dynamics shows that these observations are consistent with self-sputtering of Au neutrals from the substrate induced by incident Au ions while a fraction of them are backscattered. Self-sputtering is found to be 2 orders of magnitude larger than backscattering. The comparison with experimental data allows concluding that the apparent recoil of the plasma front is caused by collision with self-sputtered neutrals, while the secondary emission is originated by backscattered ions. © 2007 The American Physical Society., This work was partially supported by MAT2005-06508- C02-01, MEC Spain . M.G.-S. acknowledges support from the CSIC and the European Social Fund through an I3P technical contract.

6 págs. 5 figs., This work reports on the optical response and morphological changes of gold nanoparticles (NPs) induced by laser irradiation with single nanosecond laser pulses of different fluences and wavelengths. The as-grown specimens consist of irregularly shaped NPs (10–13 nm in average dimensions) produced by pulsed laser deposition on a substrate. They exhibit a broad optical absorption band related to the surface plasmon resonance (SPR) peaking in the range of 634–685 nm. After irradiation with fluences above a threshold value, a blueshift, a decrease of the overall absorption, and a narrowing of the SPR band are observed. The SPR peak wavelength and amplitude after irradiation at increasing fluences reach an approximately constant value, irrespective of the irradiation wavelength. This value is consistent with a homogeneous distribution of spherical gold NPs with a mean diameter close to the average initial dimensions as determined by transmission electron microscopy. The results demonstrate that the conversion of irregularly shaped NPs into spherical NPs with reduced dimension dispersion is a thermally driven process and occurs within a fluence interval defined by the melting threshold of all NPs and the ablation threshold. Whereas the useful fluence interval is controlled by the effective fluence absorbed, that is dependent on the laser wavelength and thermal properties of the substrate, the final shape and dimensions of the NPs are independent of the irradiation wavelength provided the fluence is within this useful interval., This work has partially been supported by HPRN-CT-2002-00328, EU and MAT2005-06508-C02-01, MEC (Spain). One of the authors (J.B.) acknowledges the funding of the CSIC through a contract in the frame of the I3P program (Ref. No. I3P-Pc2002), cofunded by the European Social Fund.

Thin films of Praseodymium-doped chalcogenide glasses [GeS 2 -Ga 2 S 3 -CsI] were prepared by pulsed laser deposition (PLD) technique. The targets were ablated using XeCl (308 nm) and KrF (248 nm) excimer lasers. The films were deposited on microscope glass slides, SiO 2 plates and lithium niobate (LiNbO 3 ) substrates at room temperature and at 300 °C. Morphological, compositional and structural characteristics of deposited films were investigated by different techniques. (Rutherford backscattering spectrometry, scanning electron microscopy and x-ray diffraction). Optical transmission of films and target, at normal incidence, were recorded in the 200-3500 nm spectral region. The optical constants (refractive index n and extinction coefficient k) vs wavelength, as well as the film thickness, were calculated from these spectra with the aid of a computer code. The presence of praseodymium in the doped chalcogenide thin film was analysed by exciting the electrons to the 1 G 4 level and collecting the photoluminescence spectrum in the 1.335 µm region. The waveguiding properties of the deposited films were investigated by the prism coupling technique (m-lines spectroscopy).

This work studies the changes in the optical response and morphological features of 6±1nm diameter Au nanoparticles (NPs) when covered by a layer of a-Al2O3 by pulsed laser deposition (PLD). The laser fluence used for ablating the Al2O3 target is varied in order to modify the kinetic energy (KE) of the species bombarding the NPs during their coverage. When the ion KE200eV. © 2014 AIP Publishing LLC., This work has been partially supported by MAT2011- 28345-C02-02 (Spain) project. R.P. acknowledges the grant JCI-2012_13034 from the Juan de la Cierva program.