Disentangling epitaxial growth mechanisms of solution derived functional oxide thin films

This study investigates the mechanisms of epitaxial development and functional properties of oxide thin films (Ce0.9Zr0.1O2−y, LaNiO3, and Ba0.8Sr0.2TiO3) grown on single crystal substrates (Y2O3:ZrO2, LaAlO3, and SrTiO3) by the chemical solution deposition approach. Rapid thermal annealing furnaces are very powerful tools in this study providing valuable information of the early stages of nucleation, the kinetics of epitaxial film growth, and the coarsening of nanocrystalline phases. Advanced transmission electron microscopies, X-ray diffraction, and atomic force microscopy are employed to investigate the film microstructure and morphology, microstrain relaxation, and epitaxial crystallization. This study demonstrates that the isothermal evolution toward epitaxial film growth follows a self-limited process driven by atomic diffusion, and surface and interface energy minimization. All investigated oxides experience a transformation from the polycrystalline to the epitaxial phase. This study unequivocally evidences that the film thickness highly influences the epitaxial crystallization rate due to the competition between heterogeneous and homogeneous nucleation barriers and the fast coarsening of polycrystalline grains as compared to epitaxial growth. The investigated films possess good functional properties, and this study successfully confirms an improvement at long annealing times that can be correlated with grain boundary healing processes. Thick epitaxial films can be crystallized by growing sequential individual epitaxial layers.We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-56063-C2-1-R, co-financed by the European Regional Development Fund), and the projects MAT2011-28874-C02-01, ENE2014-56109-C3-3-R and Consolider Nanoselect (CSD2007-00041), and from the Catalan Government (2014-SGR-753 and Xarmae). AQ and MdlM are also grateful for JAE-Predoc fellowship from CSIC (E-08-2012-1321248 and E-08-2013-1028356, co-financed by the European Social Fund).Peer Reviewe

Ultrafast epitaxial growth kinetics in functional oxide thin films grown by pulsed laser annealing of chemical solutions

The crystallization process and physical properties of different functional oxide thin films (CeZrO, LaNiO, BaSrTiO, and LaSrMnO) on single crystal substrates (YO:ZrO, LaAlO, and SrTiO) are studied by pulsed laser annealing (PLA). A Nd:YAG laser source (λ = 266 nm, 10 Hz and τ ∼3 ns) is employed to crystallize chemical solution deposited (CSD) amorphous/nanocrystalline films under atmospheric conditions. We provide new insight on the influence of photochemical and photothermal interactions on the epitaxial crystallization kinetics of oxide thin films during the transformation from amorphous/polycrystalline material (i.e., atomic diffusion, epitaxial growth rates, and activation energies of nucleation and crystallization). The epitaxial growth is investigated by varying the laser fluence and the applied number of pulses. The morphology, structure, and epitaxial evolution of films are evaluated by means of atomic force and transmission electron microscopies and X-ray diffraction. Highly epitaxial oriented films of 20-40 nm in thickness are obtained by PLA. The crystallization kinetics of laser treatments is determined to be orders of magnitude faster than thermal treatments with similar activation energies (1.5-4.1 eV), mainly due to the large temperature gradients inducing modified atomic diffusion mechanisms derived mainly from photothermal interactions, as well as a minor contribution of photochemical effects. The fast heating rates achieved by PLA also contribute to the fast epitaxial growth due to reduced coarsening of polycrystalline material. The measurement of the physical properties (electrical resistivity and magnetism) of laser processed CSD films has revealed significantly good functionalities, close to those of thermally grown films, but with much shorter processing times.We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2013-0295 and SEV-2015- 0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-51778-C2-1-R, co-financed by the European Regional Development Fund), and the projects MAT2011-28874-C02-01, ENE2014-56109-C3-3-R and Consolider Nanoselect CSD2007-00041, and from the Catalan Government with 2014-SGR-753, 2014-SGR-1638 and Xarmae. AQ and MdlM are also grateful to CSIC and European Social Fund program for JAE-Predoc fellowships (E-08-2012-1321248 and E-08-2013-1028356).Peer Reviewe

Tocopherol composition and antioxidant activity of Spanish wild vegetables

Traditional use of noncultivated vegetables has decreased with the development of agriculture and global supply chains. However, some species are still consumed as part of our traditional Mediterranean diet. Plants are among the most important sources of natural antioxidants for retarding lipid oxidative rancidity in foods or for pharmaceutical applications against chronic diseases related to free radicals production. The present study reports tocopherols composition and antioxidant activity of eight wild greens traditionally used in Spain. According to the edible part consumed, two groups were differentiated. Leafy vegetables whose young stems with leaves are consumed (Apium nodiflorum (L.) Lag., Foeniculum vulgare Mill., Montia fontana L. and Silene vulgaris (Moench) Garcke), and wild asparagus whose young shoots with leaf buds scarcely developed are eaten (Asparagus acutifolius L., Bryonia dioica Jacq., Humulus lupulus L. and Tamus communis L.). Among the leafy vegetables, Silene vulgaris and Apium nodiflorum presented the highest antioxidant capacity and antioxidants contents. Among the wild asparagus, the highest antioxidant capacity was obtained in Humulus lupulus

Distributed Amplifiers in MMIC Technology based on Composite Right/Left-Handed Transmision Lines

Abstract – Three MMIC distributed amplifiers based on Composite Right/Left-Handed Transmission Lines are presented in order to illustrate the actual performance of these devices, and the features that can be obtained with this distributed amplifier topology. Measurement results and/or qualified simulations have been included for two amplifiers with dual-band performance and for a high-power one. Also different frequency bands are illustrated, with examples at X-, C- and S-band operation.Universidad de Málaga.Campus de Excelencia Internacional Andalucía Tech. Ministerio de Ciencia e Innovación (Programa Consolider-Ingenio 2010) under Grant CSD2008-00066 (‘EMET’), and Junta de Andalucía (Spain) under Grant P10-TIC-6883

Growth of ferroelectric Ba0.8Sr0.2TiO3 epitaxial films by UV pulsed laser irradiation of chemical solution derived precursor layers

© 2015 AIP Publishing LLC. Highly crystalline epitaxial Ba0.8Sr0.2TiO3 (BST) thin-films are grown on (001)-oriented LaNiO3-buffered LaAlO3 substrates by pulsed laser irradiation of solution derived barium-zirconium-titanium precursor layers using a UV Nd:YAG laser source at atmospheric conditions. The structural analyses of the obtained films, studied by X-ray diffractometry and transmission electron microscopy, demonstrate that laser processing allows the growth of tens of nm-thick BST epitaxial films with crystalline structure similar to that of films obtained through conventional thermal annealing methods. However, the fast pulsed nature of the laser employed leads to crystallization kinetic evolution orders of magnitude faster than in thermal treatments. The combination of specific photothermal and photochemical mechanisms is the main responsible for the ultrafast epitaxial laser-induced crystallization. Piezoresponse microscopy measurements demonstrate equivalent ferroelectric behavior in laser and thermally annealed films, being the piezoelectric constant ∼25 pm V-1.This work was financed by the Ministry of Economy and Competitiveness under the Project Nos. MAT2011-28874-C02-01, ENE2014-56109-C3-3-R, and MAT2014-51778-C2-1-R and Consolider Nanoselect CSD2007-00041 by Generalitat de Catalunya (2009 SGR 770, 2014 SGR 753 and Xarmae) and by the Spanish National Research Council under the Contract No. 200960I015. A.Q. and M.d.l.M. are also grateful for JAE-Predoc fellowship and European Social Fund program. Fruitful discussions with Dr. Susagna Ricart for solution synthesis are also acknowledged.Peer Reviewe

Assessment of nutritional and biological activity of wild bulbs of Allium ampeloprasum L.

Allium ampeloprasum L. posee un gran potencial nutricional con presencia de compuestos antioxidantes de interés para la salud. Diversos estudios epidemiológicos han demostrado los efectos beneficiosos del consumo de diversas especies pertenecientes al género Allium, destacando sus efectos anticancerígenos. En el presente trabajo se estudia el contenido de nutrientes (hidratos de carbono, proteínas, grasa y minerales), compuestos bioactivos (ácidos orgánicos, vitamina C, tocoferoles, perfil de ácidos grasos) y actividad antioxidante (DPPH, poder reductor, inhibición de la decoloración del β-caroteno y TBARS) la parte comestible del ajo porro (A. ampeloprasum). Para ello, se recolectaron muestras de los puerros (bulbos y parte basal de las hojas) de dicha especie silvestre en dos localidades diferentes del centro peninsular durante dos años consecutivos (2007-2008), sobre los cuales se llevaron a cabo los análisis mencionados. Los resultados del análisis de los compuestos anteriormente mencionado indican que, a pesar de la amplia variabilidad natural detectada, esta planta destacó por ser una buena fuente de fibra (3,5 – 4,7 g/100 g), hierro (0,20 – 0,92 mg/100 g) y cinc (0,03 – 1,67 mg/100 g) en comparación con otras especies del mismo género, así como por su bajo valor calórico (59-97 Kcal/100 g). Asimismo, presentó un alto porcentaje de ácidos grasos poliinsaturados, siendo el ácido linoleico el principal ácido graso (53% del total de ácidos grasos). Se obtuvieron valores equilibrados en cuanto a la presencia de compuestos bioactivos hidrófilos y lipófilos en esta planta. La bioactividad de este bulbo se caracterizó por su actividad antioxidante medida como poder reductor (correlacionado con los tocoferoles) y TBARS (correlacionado con los compuestos fenólicos totales).Allium ampeloprasum L. has a great nutritional value as it presents antioxidant compounds with potentially beneficial effects on human. Different epidemiological studies have shown the healthy effects of the consumption of various species of the genus Allium, highlighting its anticancer effects. In the present work, the nutritional composition (carbohydrates, proteins, fat and minerals), bioactive compounds (organic acids, vitamin C, tocopherols and fatty acids) and antioxidant activity (DPPH, reducing power, inhibition of β-carotene bleaching and TBARS methods) of the edible part of the wild leek (A. Ampeloprasum) were studied. Samples of wild leek were collected from two different wild populations located in the center of the Iberian Peninsula for three consecutive years (2007-2008), on which the aforementioned analysis were conducted. Despite the large natural variability detected, this plant stood out as a good source of fiber (3.5 to 4.7 g/100 g), iron (0.20 to 0.92 mg/100 g) and zinc (0.03 to 1.67 mg/100 g), compared to other species of the same genus. Wild leeks also showed a high proportion of polyunsaturated fatty acids, being linoleic acid the major one (53% of total fatty acids). Values were balanced in terms of the presence of hydrophilic and lipophilic bioactive compounds in this plant. The bioactivity of this species was better characterized by antioxidant activity measured as reducing power assay (correlated with tocopherols) and TBARS (correlated with total phenolic compounds).ERDF and the Spanish Ministry of Education and Science (CGL2006-09546/BOS). The authors are also grateful to Fundação para a Ciência e a Tecnologia (FCT, Portugal) and COMPETE/QREN/EU for financial support to CIMO (strategic project PEst- OE/AGR/UI0690/2011). P. García-Herrera thanks to the Spanish Ministry of Education and Science (CGL2006-09546/BOS) for her UCM predoctoral fellowship

Nutrients, phytochemicals and antioxidant activity in wild populations of Allium ampeloprasum, a valuable underutilized vegetable

Wild Allium species with a long tradition of use, such as Allium ampeloprasum L. could provide interesting bioactive compounds to current diet. The nutrient and bioactive compound content of this wild vegetable has been scarcely known. Therefore, the aim of this work is to provide a detailed chemical quantification of nutrients, hydrophilic and lipophilic bioactive compounds and the antioxidant capacity of the edible parts of wild leek, as well as data about plant production and availability of the species in their natural habitats. Wild leek can be considered as a low energy food, being a good source of fiber and zinc, compared to its cultivated relatives, and has revealed a predominance of polyunsaturated fatty acids, linoleic acid being the main fatty acid. Additionally, the natural yield of this species, although lower than other cultivated Allium species, was found to be stable and well-adapted to human-disturbed environments. For these reasons, this non-conventional wild bulb should be revalorized as a good alternative to increase the diversity of vegetables consumed and enhance the quality of current occidental diets.ERDF and the Spanish Ministry of Education and Science (CGL2006-09546/BOS). The authors are also grateful to Fundação para a Ciência e a Tecnologa (FCT, Portugal) and COMPETE/QREN/EU for financial support to CIMO (strategic project PEst-OE/AGR/UI0690/2011). P. García-Herrera thanks to the Spanish Ministry of Education and Science for her UCM predoctoral fellowship. We also thank to Ramón Morales, Laura Aceituno, and Susana González for their collaboration in the gathering and preparation of the samples, and also to Carmen Díez for her support in mineral analysis

Disentangling Epitaxial Growth Mechanisms of Solution Derived Functional Oxide Thin Films

Altres ajuts: CSIC E-08-2012-1321248 i E-08-2013-1028356This study investigates the mechanisms of epitaxial development and functional properties of oxide thin films (CeZrO , LaNiO, and BaSrTiO) grown on single crystal substrates (YO:ZrO, LaAlO, and SrTiO) by the chemical solution deposition approach. Rapid thermal annealing furnaces are very powerful tools in this study providing valuable information of the early stages of nucleation, the kinetics of epitaxial film growth, and the coarsening of nanocrystalline phases. Advanced transmission electron microscopies, X-ray diffraction, and atomic force microscopy are employed to investigate the film microstructure and morphology, microstrain relaxation, and epitaxial crystallization. This study demonstrates that the isothermal evolution toward epitaxial film growth follows a self-limited process driven by atomic diffusion, and surface and interface energy minimization. All investigated oxides experience a transformation from the polycrystalline to the epitaxial phase. This study unequivocally evidences that the film thickness highly influences the epitaxial crystallization rate due to the competition between heterogeneous and homogeneous nucleation barriers and the fast coarsening of polycrystalline grains as compared to epitaxial growth. The investigated films possess good functional properties, and this study successfully confirms an improvement at long annealing times that can be correlated with grain boundary healing processes. Thick epitaxial films can be crystallized by growing sequential individual epitaxial layers

Effect of the cap layer growth temperature on the Sb distribution in InAs/InSb/InAs sub-monolayer heterostructures for mid-infrared devices

Sub-monolayer (SML) deposition of InSb within InAs matrix by migration enhanced epitaxy (MEE) tends to form type II SML nanostructures offering efficient light emission within the mid-infrared (MIR) range between 3-5 µm. In this work, we report on the Sb distribution in InSb/InAs SML nanostructures with InAs cap layers grown at temperatures lower than that associated with the under-grown InSb active layer. Analysis by transmission electron microscopy (TEM) in 002 dark field (DF) conditions shows that the reduction in the growth temperature of the InAs cap layer increases the amount of Sb deposited in the layers, in good agreement with the X-ray diffraction (XRD) results. TEM micrographs also show that the layers are formed by random InSbAs agglomerates, where the lower cap temperature leads to a more continuous InSb layer. Quantitative atomic column resolved high angle annular dark field (HAADF)-scanning (S)TEM analyses also reveal atomic columns with larger composition of Sb for the structure with the lowest InAs cap layer temperature. The dependence of the Sb distribution on InAs cap growth temperature allows tuning the corresponding emission wavelength in the MIR range, as shown by the photoluminescence (PL) emission spectra