Rubus sellowii Cham. & Schlitdl. (Rosaceae) fruit nutritional potential characterization

The aim of this study was to know the physical, chemical and nutritional characteristics of Rubus sellowii (Rosaceae) fruits, known as blackberry, native plant mainly to Rio Grande do Sul State (RS), Brazil. For this, three different populations of this plant were selected and the fruits were analyzed through moisture, ash, titratable acidity, pH, lipids, fibers, carbohydrates, proteins, carotenoids, lycopene, ascorbic acid, aminogram and in vitro digestibility. Fruits showed high acidity (3.28 percent), ash and protein (1.02 and 0.93 percent) and higher ascorbic acid (38.43 mg per 100 g) if compared to Rubus cultivars. Due to Rubus sellowii nutritional properties, they provide benefits to human health.

Formation of nitrile species on Ag nanostructures supported on a-Al2O3: a new corrosion route for silver exposed to the atmosphere

The aging of supported Ag nanostructures upon storage in ambient conditions (air and room temperature) for 20 months has been studied. The samples are produced on glass substrates by pulsed laser deposition (PLD); first a 15 nm thick buffer layer of amorphous aluminum oxide (a-Al₂O₃) is deposited, followed by PLD of Ag. The amount of deposited Ag ranges from that leading to a discontinuous layer up to an almost-percolated layer with a thickness of <6 nm. Some regions of the as-grown silver layers are converted, by laser induced dewetting, into round isolated nanoparticles (NPs) with diameters of up to ∼25 nm. The plasmonic, structural and chemical properties of both as-grown and laser exposed regions upon aging have been followed using extinction spectroscopy, scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. The results show that the discontinuous as-grown regions are optically and chemically unstable and that the metal becomes oxidized faster, the smaller the amount of Ag. The corrosion leads to the formation of nitrile species due to the reaction between NO _x species from the atmosphere adsorbed at the surface of Ag, and hydrocarbons adsorbed in defects at the surface of the a-Al₂O₃ layer during the deposition of the Ag nanostructures by PLD that migrate to the surface of the metal with time. The nitrile formation thus results in the main oxidation mechanism and inhibits almost completely the formation of sulphate/sulphide. Finally, the optical changes upon aging offer an easy-to-use tool for following the aging process. They are dominated by an enhanced absorption in the UV side of the spectrum and a blue-shift of the surface plasmon resonance that are, respectively, related to the formation of a dielectric overlayer on the Ag nanostructure and changes in the dimensions/features of the nanostructures, both due to the oxidation process.

Expanding the plasmonic response of bimetallic nanoparticles by laser seeding

This work explores a cost-effective route to enhance the tuning range of the optical response of metal nanostructures on substrates beyond the ranges that are achievable through the nanostructure dimensions, composition or dewetting processes. The new route (laser seeding) uses single nanosecond laser pulses to induce dewetting in regions of a metal layer deposited on a glass substrate followed by the deposition of a second metal layer, both layers being deposited by pulsed laser deposition. In order to show the possibilities of this new route, we have chosen that the two metals were different, namely Ag and Au. The comparison of the optical response of these regions to those that were laser irradiated after deposition of the second metal layer shows that while nanoalloyed nanoparticles (NPs) are formed in the latter case, the NPs produced in the former case have a heterogeneous structure. The interface between the two metals is either sharp or a narrow region where they have mixed depending on the laser fluence used. While the nanoalloyed NPs exhibit a single, narrow surface plasmon resonance (SPR), the heterogeneous NPs show broader SPRs that peak in the near infrared and depending on conditions exhibit even two clear SPRs. The laser seeding approach in the conditions used in this work allows for the expansion of the tuning range of the color to the blue-green region, i.e. beyond the region that can be achieved through nanoalloyed NPs (yellow-red region). In addition, the results presented foresee the laser seeding route as a means to produce round and almost isolated NPs in an enhanced range of diameters.

Laser treatment of Ag@ZnO nanorods as long-life-span SERS surfaces

UV nanosecond laser pulses have been used to produce a unique surface nanostructuration of Ag@ZnO supported nanorods (NRs). The NRs were fabricated by plasma enhanced chemical vapor deposition (PECVD) at low temperature applying a silver layer as promoter. The irradiation of these structures with single nanosecond pulses of an ArF laser produces the melting and reshaping of the end of the NRs that aggregate in the form of bundles terminated by melted ZnO spherical particles. Well-defined silver nanoparticles (NPs), formed by phase separation at the surface of these melted ZnO particles, give rise to a broad plasmonic response consistent with their anisotropic shape. Surface enhanced Raman scattering (SERS) in the as-prepared Ag@ZnO NRs arrays was proved by using a Rhodamine 6G (Rh6G) chromophore as standard analyte. The surface modifications induced by laser treatment improve the stability of this system as SERS substrate while preserving its activity.

Density patterns in metal films produced by laser interference

Fringed periodic patterns have been produced by laser interference at 193 nm in an almost continuous 9.5 nm-thick Ag film that exhibits a number density of ≈189 μm(-2) holes. Patterns with four periods in the range of 1.8-10.2 μm were produced by changing the projection optics. At high fluences, the film breaks up into nanostructures around the regions exposed to intensity maxima due to laser-induced melting. At low fluences, a new process is observed that is triggered at the initial holes of the film by solid-state dewetting. Once the fluence is high enough to prevent the temperature balance across the pattern, mass transport from cold to hot regions is observed, leading to film densification in regions around intensity maxima sites. The novel patterns are thus formed by fringes of material that is more/less dense than the as-grown film, each of which is located at intensity maxima/minima sites, and have negligible topography. Comparing the present results to earlier reports in the literature shows that the thermal gradient across the pattern is influenced by the initial film microstructure, rather than by the thickness. The existence of a minimum period, which is achievable depending on the thermal continuity of the film, is also discussed.

Period dependence of laser induced patterns in metal films

Periodic fringed patterns with four periods in the range 1.8-10.2 μm have been produced in continuous Ag films that have thicknesses of 14.6 nm and 19.5 nm by exposing a phase mask to single pulses of an excimer laser operating at 193 nm. The films were patterned either as-grown or after homogeneous exposure to the same laser beam. For fluences above the threshold, the films undergo liquid-state dewetting that, from low to high fluences, leads to their break into holes, fingers or elongated features and finally to isolated nanoparticles irrespective of the period, thickness or fluence. The period determines the range of fluences to achieve the different morphologies since the temperature profile across the pattern depends on the period due to the existence of significant lateral heat flow across the pattern. The maximum temperature achieved at the intensity maxima/minima sites thus decreases/increases as the period decreases, leading to solid-state dewetting at regions around the intensity minima; the shorter the period, the higher this type of dewetting. These regions eventually overcome the melting temperature for the shortest period and intermediate fluence, leading to the complete transformation of the films. Finally, the initial film morphology (discontinuities or holes) rather than thickness plays an essential role in the level of transformation at fluences around the threshold.

Enhanced reactivity and related optical changes of Ag nanoparticles on amorphous Al₂O₃ supports

Pairs of samples containing Ag nanoparticles (NPs) of different dimensions have been produced under the same conditions but on different substrates, namely standard glass slides and a thin layer of amorphous aluminum oxide (a-Al₂O₃) on-glass. Upon storage in ambient conditions (air and room temperature) the color of samples changed and a blue-shift and damping of the surface plasmon resonance was observed. The changes are weaker for the samples on-glass and tend to saturate after 12 months. In contrast, the changes for the samples on a-Al₂O₃ appear to be still progressing after 25 months. While x-ray photoelectron spectroscopy shows a slight sulfurization and negligible oxidation of the Ag for the on-glass samples upon 25 months aging, it shows that Ag is strongly oxidized for the on a-Al₂O₃ samples and sulfurization is negligible. Both optical and chemical results are consistent with the production of a shell at the expense of a reduction of the metal core dimensions, the latter being responsible for the blue-shift and related to the small (<10 nm initial diameter) of the NPs. The enhanced reactivity of the Ag NPs on the a-Al₂O₃ supports goes along with specific morphological changes of the Ag NPs and the observation of nitrogen.

2D plasmonic and diffractive structures with sharp features by UV laser patterning

The aim of this work is to produce 2D plasmonic and diffractive structures in Ag films with sharp features for which both a deeper understanding of laser induced transformation upon modulated laser intensity and a correlation between structural and optical properties are required. We compare results obtained by exposing silver films to an excimer laser operating at 193 nm whose intensity is either modulated or homogeneous. In all cases, one laser exposure is enough to break the film into nanoparticles (NPs). The use of the modulated beam intensity leads to diffractive 2D patterns that are formed by rectangular regions of untransformed material surrounded by transformed regions covered by NPs. The former have sharp edges that are consistent with the absence of significant mass transport that is discussed in terms of the thermal gradient induced. The latter contain NPs whose diameter increases as the initial film effective thickness increases. The surface plasmons associated with the NPs in the transformed regions dominate the reflectivity spectrum and the 2D array formed by the untransformed regions is responsible for the diffractive properties. Evidence for spinodal dewetting is only observed in our case for the steep gradient conditions achieved at the border of the homogeneously irradiated regions.

The importance of the energetic species in pulsed laser deposition for nanostructuring

This work reports on the optical and structural properties of nanostructured films formed by Ag nano-objects embedded in amorphous aluminium oxide (a-Al(2)O(3)) prepared by alternate pulsed laser deposition (PLD). The aim is to understand the importance of the energetic species involved in the PLD process for nanostructuring, i.e. for organizing nanoparticles (NPs) in layers or for self-assembling them into nanocolumns (NCls), all oriented perpendicular to the substrate. In order to change the kinetic energy of the species arriving at the substrate, we use a background gas during the deposition of the embedding a-Al(2)O(3) host. It was produced either in vacuum or in a gas pressure (helium and argon) while the metal NPs were always produced in vacuum. The formation of NPs or NCls is easily identified through the features of the surface plasmon resonances (SPR) in the extinction spectra and confirmed by electron microscopy. The results show that both the layer organization and self-assembling of the metal are prevented when the host is produced in a gas pressure. This result is discussed in terms of the deceleration of species arriving at the substrate in gas that reduces the metal sputtering by host species (by ≈58%) as well as the density of the host material (by ≥19%). These reductions promote the formation of large voids along which the metal easily diffuses, thus preventing organization and self-organisation, as well as an enhancement of the amount of metal that is deposited.

Acousto-plasmonic hot spots in metallic nano-objects

We investigate the acousto-plasmonic dynamics of metallic nano-objects by means of resonant Raman scattering and time-resolved femtosecond transient absorption. We observe an unexpectedly strong acoustic vibration band in the Raman scattering of silver nanocolumns, usually not found in isolated nano-objects. The frequency and the polarization of this unexpected Raman band allow us to assign it to breathing-like acoustic vibration modes. On the basis of full electromagnetic near-field calculations coupled to the elasticity theory, we introduce a new concept of "acousto-plasmonic hot spots" which arise here because of the indented shape of the nanocolumns. These hot spots combine both highly localized surface plasmons and strong shape deformation by the acoustic vibrations at specific sites of the nano-objects. We show that the coupling between breathing-like acoustic vibrations and surface plasmons at the "acousto-plasmonic hot spots" is strongly enhanced, turning almost silent vibration modes into efficient Raman scatterers.

Interaction of self-trapped beams in high index glass

We observe attraction, repulsion and energy exchange between two self-trapped beams in a heavy-metal-oxide glass exhibiting a Kerr-like response with multiphoton absorption. The coherent interaction between spatial solitons is controlled by their relative phase and modelled by a nonlinear dissipative Schrödinger equation.

Size-dependent thermo-optical properties of embedded Bi nanostructures

The thermally induced optical transmission changes upon melting and solidification of Bi nanostructures embedded in amorphous Al(2)O(3) thin films have been studied as a function of characteristic sizes in the range 7-35 nm. The results show a repeatable optical transmission-temperature hysteresis loop with sharp changes at the melting and solidification temperatures. Both temperatures decrease linearly when the mean size of the nanostructures decreases and they are respectively higher and lower than that of the bulk melting temperature of Bi. The optical transmission shows a significant contrast that increases up to 16% as the mean size of the nanostructures increases. The results show that in addition to the usual decrease of melting temperature as the size of the nanostructures decreases, the melting temperatures for all samples are higher than that of the bulk. This unexpected result is associated to the contraction of Bi upon melting and to matrix effects related to the balance of surface energies between the solid and liquid Bi and the matrix. The solidification process shows a weaker dependence on the nanostructure size, and thus it is consistent with a mainly volume controlled process. It is shown that by controlling the characteristic dimensions of the Bi nanostructures the temperature operability of the Bi nanostructures embedded in amorphous Al(2)O(3) as a thermally driven optical switch can be tuned over 73 K.

Surface enhanced Raman scattering of silver sensitized cobalt nanoparticles in metal-dielectric nanocomposites

We report the preparation of a new type of nanocomposite containing cobalt and silver nanoparticles organized in parallel layers with a well controlled separation. This arrangement allows the observation of an enhanced low-frequency Raman signal at the vibration frequency of cobalt nanoparticles excited through the surface plasmons of silver nanoparticles. Numerical simulations of the electric field confirm the emergence of hot spots when the separation between silver and cobalt nanoparticles is small enough.

Acoustic vibration modes and electron-lattice coupling in self-assembled silver nanocolumns

Using ultrafast spectroscopy, we investigated electron-lattice coupling and acoustic vibrations in self-assembled silver nanocolumns embedded in an amorphous Al2O3 matrix. The measured electron-lattice energy exchange time is smaller in the nanocolumns than in bulk silver, with a value very close to that of isolated nanospheres with comparable surface to volume ratio. Two vibration modes were detected and ascribed to the breathing and extensional mode of the nanocolumns, in agreement with numerical simulations.

Critical separation for efficient Tm3+ -Tm3+ energy transfer evidenced in nanostructured Tm3+: Al2O3 thin films

Nanostructured amorphous Al oxide (a-Al2O3) thin films doped with Tm3+ were synthesized by alternate pulsed laser deposition. The Tm3+ ions have been deposited in layers with in-depth separation ranging from 0.75 to 6 nm. The films show two broad emission bands originated from the Tm3+ 3H4-->3F4 and 3F4-->3H6 transitions. Their intensity increases at a similar rate and the lifetimes are not modified as the layer separation decreases down to 1.5 nm, suggesting that there is no concentration quenching. At the critical value of 1.5 nm the onset of Tm3+ -Tm3+ energy transfer is evidenced by a sharp decrease of the emission intensity and lifetime. Below this critical value, the rate at which the intensity increases for the 3F4-->3H6 transition is much higher than that for the 3H4-->3F4 transition, evidencing quenching of the 3H4-->3F4 transition through a cross-relaxation mechanism. The control of the Tm3+ ions in the nanometer scale allows evidencing the onset of energy transfer processes among ions and offers a route to optimize compact photonic gain integrated devices.

Near-infrared spatial solitons in heavy metal oxide glasses

We demonstrate two-dimensional spatial solitons excited by near-infrared picosecond pulses in Kerr-like heavy metal oxide glasses with a nonlinearity one order of magnitude larger than in fused silica. Solitons were obtained at 820 nm owing to the presence of multiphoton absorption, which prevented catastrophic collapse.

Optical evidence for reactive processes when embedding Cu nanoparticles in Al(2)O(3) by pulsed laser deposition

The optical response of nanocomposite thin films formed by Cu nanoparticles (NPs) embedded in amorphous aluminium oxide (Al(2)O(3)) prepared by pulsed laser deposition (PLD) in vacuum is studied in order to investigate the possible existence of reactive processes on the Cu NPs during their covering with Al(2)O(3). The study is performed as a function of the laser fluence on the Al(2)O(3) target (0.6-4.6 J cm(-2)), while the laser fluence for Cu ablation is kept constant (1.8 J cm(-2)). The structural analysis of the films shows that they are formed by a high density of NPs with average dimensions in the 4.9-5.9 nm range. The optical response of the films has been followed in situ by real-time reflectivity measurements at 633 nm and after deposition by transmission measurements as a function of wavelength around the surface plasmon resonance (SPR). For low laser fluences on the Al(2)O(3) target, the absorption spectrum is dominated by a well-defined SPR absorption band at 1.9 eV. As the laser fluence is increased, the intensity of the absorption band associated with the SPR decreases and shifts to 2.1 eV. The films deposited at low fluences contain metallic Cu NPs and, as the laser fluence increases sputtering of Cu from the NPs and mixing of the species from the Al(2)O(3) deposition with the Cu from the NPs surface takes place. The latter process leads to the formation of an Al-Cu oxide cover on the Cu NPs. The present results provide evidence for mixing of species from the host and Cu at the surface of the NPs, and it is shown how the degree of mixing depends on the laser fluence used to ablate the Al(2)O(3) host target.

Surface plasmons and vibrations of self-assembled silver nanocolumns

Optical and vibrational properties of novel self-assembled silver nanocolumns are studied experimentally and theoretically. The split of the surface plasmon resonance into transverse and longitudinal modes verifies the one-dimensional character of the nanocolumns. In this work, we have identified the acoustic vibration modes of the nanocolumns using Raman scattering, as spheroid-like modes (l = 2, m = +/-2) involving vibrations of the nanocolumns along their minor axes and the existence of surface plasmon-vibration coupling mechanisms.

Temporally and spectrally resolved imaging of laser-induced plasmas

We report a hybrid imaging technique capable of performing measurements of the spatial, temporal, and spectral emission characteristics of laser-induced plasmas by use of a single detection system. We apply this technique to study the plasma produced by laser ablation of LiNbO3 and observe phenomena not seen in such detail with standard instruments. These include extreme line broadening up to a few nanometers accompanied by self-absorption near the target surface, and expansion dynamics that differ strongly between the different species. Overall, the wealth of quantitative information provided by this novel technique sheds new light on processes occurring during plasma expansion.

Ultrafast laser-induced phase transitions in amorphous GeSb films

Time-resolved measurements of the spectral dielectric function reveal new information about ultrafast phase transitions induced by femtosecond laser pulses in Sb-rich amorphous GeSb films. The excitation generates a nonthermal phase within 200 fs. The dielectric function of this phase differs from that of the crystalline phase, contrary to previous suggestions of a disorder-to-order transition. The observed dielectric function is close to that of the liquid phase, indicating an ultrafast transition from the amorphous phase to a different disordered state.

Optical properties of GeO(x) films obtained by laser deposition and dc sputtering in a reactive atmosphere

Optical constants of amorphous GeO(x) films as a function of wavelength are determined for the first time, to the best of our knowledge, in thin films grown by laser deposition and dc sputtering of Ge in an oxygen environment. We determined the oxygen content of the films by combining nuclear reaction analysis and Rutherford backscattering spectrometry. Spectroscopic ellipsometry is used to determine the film optical constants. Effective medium modeling is used to simulate the optical properties of the films assuming the films contain a mixture of amorphous Ge and GeO(2). The results show that substoichiometric GeO(x) films behave optically as a mixture of amorphous Ge and GeO(2). Films with low oxygen content (x < 1.0) seem to have inhomogeneous oxygen concentrations with depth. The effect of the deposition rate and oxygen pressure (and Ar pressure in sputtered films) on film stoichiometry and optical properties is also discussed.

Optical properties of laser-deposited a-Ge films: a comparison with sputtered and e-beam-deposited films

Optical properties of amorphous semiconductor films are usually strongly dependent on deposition conditions. To the best of our knowledge, this is the first publication on optical properties of amorphous Ge films that are grown by laser-assisted deposition and measured by means of spectroscopic ellipsometry over a wide spectral range (1.43-4.59 eV). Optical properties of dc magnetron-sputtered and e-beamdeposited films are also included. Effective medium modeling is used to analyze the void fraction and the film homogeneity through the thickness. The results show that laser-deposited films and dc magnetronsputtered films are similar, both being denser, more homogeneous, and more stable than e-beamdeposited films. Transmission electron microscopy analysis shows that the results of the optical study are correlated to the film structure. These results are discussed in terms of the kinetic energy of the species involved in each deposition technique and some conclusions related to the laser-assisted deposit on process are reported.