Procedimiento y dispositivo optico microfabricado para la detección de bandas de absorción/emisión en el infrarrojo

Fecha de publicación de la solicitud: 01/10/98.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento y dispositivo óptico microfabricado para la detección de bandas de absorcion/emision en el infrarrojo. Facilita la deteccion de sustancias químicas y emisores de radiación con unos costes muy inferiores a los de los sistemas conocidos y con una precision suficiente para muchas aplicaciones tales como la detección de gases en mezclas. El procedimiento consiste en generar una radiación que sea plana en una banda característica de la sustancia o fuente a detectar y que atraviesa un ambiente en el que se encuentra dicha sustancia, efectuandose despues una modulación de la radiación y una detección de la radiación modulada que aportar a una señal directamente relacionada con la concentración de dicha sustancia en el referido ambiente. El dispositivo correspondiente incluye una lámpara (1) a la que se ajusta una guía óptica (2), de manera que se ilumine o radie el ambiente bajo estudio; disponiendose enfrentadamente a dicha guía (2) un detector (4), e intercalandose entre ambos un modulador (3).Peer reviewe

Seleniuro de Plata: un candidato a la alta eficiencia termoeléctrica

Ponencia presentada en las IV Jornadas de Jóvenes Investigadores, celebradas en Madrid el 9 de julio de 2015.El actual interés en los materiales termoeléctricos se centra en su capacidad de transformar una diferencia de temperatura en una diferencia de Voltaje (efecto Seebeck). Igualmente a la creación de una diferencia de temperatura debida a un voltaje eléctrico (efecto Peltier), siendo posible utilizarlos como fuentes y sumideros de calor en aplicaciones industriales como un medio alternativo de refrigeración y enfriamiento. Entre las principales ventajas de los dispositivos termoeléctricos sobre los demás sistemas de refrigeración ¿ sistemas de compresión ¿ se encuentra una mayor fiabilidad en el tiempo de uso al no contar con partes móviles, la no utilización de gases de efecto invernadero y la ausencia de vibración debido a que son dispositivos de estado sólido con un tamaño reducido llegando a ser muy eficientes en aplicaciones locales.Peer Reviewe

A New Hydrogen Sensor Based on a Pt/GaAs Schottky Diode

4 páginas, 7 figuras, 1 tabla.-- PACS: 82.45.Jn; 07.07.Df; 85.30.Hi.A new hydrogen-sensitive detector based on a Pt/GaAs Schottky diode has been fabricated. The devices have beencharacterized by dark current-voltage and capacitance-voltage measurements, as a function of temperature and gas phasecomposition. At 150°C, the detection limit for hydrogen is 6 ppm in a nitrogen environment and 200 ppm in air.Peer reviewe

Mossbauer and magnetization studies of amorphous NdFeB compositionally modulated thin films

Several NdFeB compositionally modulated thin films are studied by using both conversion electron Mossbauer spectra and SQUID (superconducting quantum-interference-device) magnetometry. Both the hyperfine fields and the easy magnetization magnitude are not correlated with the modulation characteristic length (lambda) while the magnetization perpendicular to the thin-film plane decreases as lambda increases. The spectra were recorded at room temperature being the gamma rays perpendicular to the substrate plane. The magnetization measurements were recorded by using a SHE SQUID magnetometer in applied magnetic fields up to 5.5 T and in the temperature range between 1.8 and 30 K

Decrease of the adhesion force with vapor pressure

Trabajo presentado a NanoSpain 2010 celebrado en Málaga del 23-26 Marzo, 2010. -- Incluye comunicación oral y póster.Experimental evidence of a monotonous decrease of the capillary forces between hydrophilic surfaces with increasing relative humidity from 0 to 100% is presented. In concordance with the results of a theoretical simulation, we identified the objects’ shape as the origin of different adhesion force vs. RH behaviours when treating with nanoscale objects. If the water neck is formed between a flat surface and a nanometric object presenting a truncated cone shape the adhesion force decreases with increasing vapour pressure. The variety of meniscus force behaviours found for different shapes emphasizes the importance of geometry in capillary phenomena at the nanometric scale.Peer reviewe

Coercive and anisotropy fields in patterned amorphous FeSi submicrometric structures

Amorphous FexSi12x films have been prepared on Si substrates in order to fabricate submicrometric magnetic structures with soft magnetic behavior. The magnetic properties compositional dependence of the unpatterned samples has been analyzed to select the Fe content (x50.7) with the lowest coercive and anisotropy fields values. Arrays of Fe0.7Si0.3 lines have been fabricated by electron beam lithography combined with a liftoff technique, with typical dimensions of 200 nm linewidth and 1 mm line spacing. These arrays present coercive fields parallel to the line direction as small as 9 Oe.Peer reviewe

Correlation between magnetic and transport properties in nanocrystalline Fe thin films: A grain-boundary magnetic disorder effect

We report on transport and magnetic measurements of islanded Fe(110) thin films. The electrical resistivity exhibits an anomalous increase at low temperatures, which disappears under the action of a magnetic field. Since such an anomaly completely disappears under the action of a magnetic field, it is inferred that it originates from spin-dependent scattering. We interpret the strong changes in the spin-dependent scattering in our films to be due to a low-temperature spin freezing of the island boundary magnetic regions that impedes ferromagnetic exchange between islands. A consequence of this magnetic behavior is the random arrangement of the individual magnetization, determined by the magnetocrystalline anisotropy of each island, resulting in an increase of the resistivity below the freezing temperature.Z.S. and J.L.M. acknowledge the Comunidad de Madrid for financial support. Work was performed under the financial support of the Comunidad de Madrid and the Spanish Commission of Science and Technology.Peer reviewe

Optical phonons in isotope superlattices of GaAs, GaP, and GaSb studied by Raman scattering

We have investigated the LO-phonon Raman spectra of [100] oriented gallium isotope superlattices (69GaX)n(71GaX)n [X=P,As; both elements have a single stable isotope] at low temperature. When the number of monolayers 2n within one superlattice (SL) unit cell is varied, anticrossings between phonons confined in the 69GaX and 71GaX layers are observed. We have used a planar bond-charge model to calculate the frequencies and intensities of the modes as a function of layer thickness. For the GaP isotope SL’s, we find that a simulation of isotopically mixed interface layers is in good agreement with the experiment, while the assumption of ideal interfaces does not reproduce the data well. Spectra from the GaAs isotope SL’s are substantially broadened compared to the LO phonon width in bulk samples, thus allowing only a qualitative discussion of phonon-confinement effects. Predictions for GaSb isotope SL’s, in which both Ga and Sb isotopes can be substituted, are given. Raman spectra of bulk GaAs with varying gallium-isotope ratio are also discussed.Peer reviewe

Self‐assembled quantum dots of InSb grown on InP by atomic layer molecular beam epitaxy: Morphology and strain relaxation

Self-organized InSb dots grown by atomic layer molecular beam epitaxy on InP substrates have been characterized by atomic force and transmission electron microscopy. Measurement of high-energy electron diffraction during the growth indicates a Stransky–Krastanov growth mode beyond the onset of 1.4 InSb monolayer ~ML! deposition. The dots obtained after a total deposition of 5 and 7 ML of InSb present a truncated pyramidal morphology with rectangular base oriented along the ^110& directions, elongated towards the @110# direction with $111$113%/$114$111%A lateral facets in @11 ¯ 0# views, and ~001! flat top surfaces. The mismatch between the dot and the substrate has been accommodated by a network of 90° misfit dislocation at the interface. A corrugation of the InP substrate surrounding the dot has been also observedThis work has been funded by the Spanish CICYT Project MAT95-0966.Peer reviewe

Structure and magnetism of single-phase epitaxial γ′-Fe4N

Single phase epitaxial pure γ′-Fe4N films are grown on MgO (001) by molecular beam epitaxy of iron in the presence of nitrogen obtained from a radio frequency atomic source. The epitaxial, single phase nature of the films is revealed by x-ray diffraction and by the local magnetic environment investigated by Mössbauer spectroscopy. The macroscopic magnetic properties of the γ′-Fe4N films are studied in detail by means of transverse Kerr effect measurements. The hysteresis loops are consistent with the cubic atomic structure, displaying easy [100] magnetization directions. The films are single domain at remanence, and the reversal is dominated by 180° or 90° domain wall nucleation and propagation, depending on the applied field direction. When 90° domain walls are responsible for the magnetization reversal, this proceeds in two stages, and the measured coercive fields vary accordingly. Magnetic domain observations reveal the two distinct reversal —driven by 180° or 90° domain walls— modes displaying large domains, of the order of mm. From magnetometer techniques, the saturation magnetization, μ0Ms, is measured to be 1.8 T. A magneto-optical torque technique is used to obtain a value of the anisotropy constant of 2.9×104J/m3.The authors acknowledge partial financing from EC project HIDEMAR G5RD-CT-2002-00731 and PHANTOMS network. The authors are indebted to A. Gupta and K. V. Rao from the department of Materials Science and Engineering, KTH, Sweden for help with the low T SQUID measurements, and to L. Ballcels and M. A. García from Materials Science ICMM CSIC, Spain for high-T VSM measurements. This work was part of the research program of the Foundation for Fundamental Research on Matter-FOM, The Netherlands. J.M.G.M. acknowledges financing through the Ramón y Cajal program from the Spanish MCyT.Peer reviewe