Ruth Lahoz

Selective Dichroic Patterning by Nanosecond Laser Treatment of Ag Nanostripes

Authors thank the Projects FUNCOAT CONSOLIDER-INGENIO CDS2008 – 0023, MAT2007 – 65764, MAT2010-18447, MAT2010-21228, CEN2007 – 2014, P09-TEP-5283, Domingo Martinez Foundation, and Juan de la Cierva Grant No JCI-2009 – 05098 for J.T.

High speed inscription of uniform, large-area laser-induced periodic surface structures in Cr films using a high repetition rate fs laser

We report on the fabrication of laser-induced periodic surface structures in Cr films upon high repetition rate fs laser irradiation (up to 1 MHz, 500 fs, 1030 nm), employing beam scanning. Highly regular large-area (9  cm2) gratings with a relative diffraction efficiency of 42% can be produced within less than 6 min. The ripple period at moderate and high fluences is 0.9 μm, with a small period of 0.5 μm appearing at lower energies. The role of the irradiation parameters on the characteristics of the laser-induced periodic surface structures (LIPSS) is studied and discussed in the frame of the models presently used. We have identified the polarization vector orientation with respect to the scan direction as a key parameter for the fabrication of high-quality, large-area LIPSS, which, for perpendicular orientation, allows the coherent extension of the sub-wavelength structure over macroscopic distances. The processing strategy is robust in terms of broad parameter windows and applicable to other materials featuring LIPSS.

ZIF-8 micromembranes for gas separation prepared on laser-perforated brass supports

ZIF-8 is an imidazolate-based metal–organic framework (MOF). ZIF-8 micromembranes of 20–32 μm diameter are prepared by synthesizing the MOF on Nd:YAG laser-perforated 75 μm thick brass sheets (63/37 Cu/Zn). The laser irradiation activates the brass support, promoting ZIF-8 growth. A thick and continuous ZIF-8 membrane is crystallized on the laser irradiation outlet side of the support, while the inlet side and the inner surface of the microperforations are also coated with ZIF-8 intergrowth crystals. Laser perforated brass supports are not only cheap, flexible, strong, and easy to handle and to process as membrane materials; they are also chemically compatible with the ZIF-8 composition because of the shared Zn element. The ZIF-8 membranes obtained are characterized by XRD, SEM, EDX, TGA and N2 sorption analysis. Furthermore, the membranes are applied to the separation of equimolar H2–CH4, He–CH4, CO2–CH4 and O2–N2 mixtures confirming the expected molecular sieving effect due to the MOF microporosity.

Laser control of zeolite nucleation.

Precursor solutions for the synthesis of zeolites are irradiated by means of a Nd-YAG laser. These solutions are subsequently submitted to a hydrothermal treatment and the results analyzed by X-ray diffraction and electron microscopy. Laser irradiation promotes the formation of silica nanoparticles that nucleate into zeolite (silicalite-1), following a hydrothermal treatment. The average crystal size (in the 0.6-3.6 μm range) of the zeolite exponentially decreases as a function of laser irradiation time. In addition, a longer irradiation time results in a narrower crystal size distribution.

Changes in the Thermal Stability of 2G HTS Wires by Local Modification of the Stabilization Layer

In order to use 2G HTS wires in superconducting devices, it is important to understand the origin of thermal instabilities in these materials. Previous results showed that inhomogeneities in the critical current distribution are not the only factor that determines the heat generation distribution along the sample when the current exceeds the critical value. In this work, different types of controlled defects have been generated in the Cu-layer using laser ablation. In all cases, laser parameters have been chosen while assuring that the critical current of the superconductor does not deteriorate. It has been obtained that even if the thickness of the stabilizing layer is reduced from 20 μm to less than 10 μm in some regions, the sample response to overcurrents is not modified.

HKUST-1 coatings on laser-microperforated brass supports for water adsorption

This work describes the preparation of HKUST-1 layers on brass supports by a thermal gradient approach. Supports were perforated using laser irradiation to create 30–50 μm microholes. Perforation improved the adhesion and loading of the MOF. The microhole environment generated during the laser treatment led to well-anchored coatings. Two distinct samples were synthesized with the reaction temperature (100 and 150 °C) as the main difference. A continuous HKUST-1 coating was only achieved with the higher temperature of 150 °C. However, the microholes were totally filled with crystals in both samples reaching weight fractions of crystallized material of 2.4 and 6.6 wt%. PXRD and N2 physisorption studies confirmed the formation of HKUST-1 crystals with high quality (SBET = 1105 m2 g−1). Water adsorption was performed on both samples, showing the main sorption event below a relative pressure of 0.4 and obtaining uptakes (0.48 and 0.45 g g−1 at 293 K and p/p0 = 0.9) among the reported values for HKUST-1 powder. The HKUST-1 properties and the enhanced MOF–support interaction make these coatings candidates for use in gas storage and separation, sensing and water-based adsorption applications, such as chillers or heat pumps.

Laser Treatment of Nanoparticulated Metal Thin Films for Ceramic Tile Decoration.

This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of Cu thin films prepared by electron-beam evaporation at glancing angles. A thin film of discontinuous Cu nanoparticles was electron-beam-evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy along with UV-vis-near-IR spectroscopy and time-of-flight secondary ion mass spectrometry analysis were used to characterize the differently colored layers. On the basis of these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of the samples.

'Laser chemistry' synthesis, physicochemical properties, and chemical processing of nanostructured carbon foams

Laser ablation of selected coordination complexes can lead to the production of metal-carbon hybrid materials, whose composition and structure can be tailored by suitably choosing the chemical composition of the irradiated targets. This ‘laser chemistry’ approach, initially applied by our group to the synthesis of P-containing nanostructured carbon foams (NCFs) from triphenylphosphine-based Au and Cu compounds, is broadened in this study to the production of other metal-NCFs and P-free NCFs. Thus, our results show that P-free coordination compounds and commercial organic precursors can act as efficient carbon source for the growth of NCFs. Physicochemical characterization reveals that NCFs are low-density mesoporous materials with relatively low specific surface areas and thermally stable in air up to around 600°C. Moreover, NCFs disperse well in a variety of solvents and can be successfully chemically processed to enable their handling and provide NCF-containing biocomposite fibers by a wet-chemical spinning process. These promising results may open new and interesting avenues toward the use of NCFs for technological applications.

Laser‐Assisted Synthesis of Colloidal FeWxOy and Fe/FexOy Nanoparticles in Water and Ethanol

Homogeneous polycrystalline Fex Oy nanoparticles were generated by ablation of iron targets in water by nanosecond laser pulses at 532 nm. In ethanol, crystalline core-shell Fe/Fex Oy structures with size medians around 20 nm were produced. The ablation of FeWx Oy targets in water resulted in crystalline hollow shells and homogeneous FeWx Oy nanoparticles. In contrast, amorphous core-shell FeWx Oy nanoparticles with a median size of 17 nm were produced in ethanol. The size distribution of both the Fex Oy and the FeWx Oy particles showed a slight dependence on fluence and pulse number. This may be related to primary and secondary ablation and modification mechanisms.

Influence of the Surface Layer on YBaCuO Coated Conductors Quench Processes

The study of the thermal stability process in second-generation (2G) high-temperature superconductors is important to determine its optimal performance in applications. When a fault takes place during operation, the heat generated must be evacuated as fast as possible in order to protect the superconductor from damage. If conductors are immersed in liquid nitrogen (LN), thermal stability is strongly dependent on the tape orientation, proximity between tapes, and the characteristics of the surface, such as roughness, presence of insulating materials covering the conductor, etc., which will influence the recovery time of the conductor after a fault. In this contribution, we analyze quench and cooling processes of 2G conductors subjected to over-currents and immersed in LN. The sample surface has been modified in order to induce different roughnesses. The observed behavior has also been compared with that of samples covered with polyimide (kapton) or varnish. Information about recovery times for the different LN cooling regimes has been obtained.