MicroSQUID Force microscopy in a dilution refrigerator

We present a new generation of a scanning MicroSQUID microscope operating in an inverted dilution refrigerator. The MicroSQUIDs have a size of 1.21$ \ \mum\textsuperscript{2} and a magnetic flux sensitivity of 120 \mu\Phi_{0} / \sqrt{\textrm{Hz}}$and thus a field sensitivity of$550^{-6} \ \Phi_{0} / \sqrt{\textrm{Hz}}$550$ \ \mu \textrm{G}/ \sqrt{\textrm{Hz}}$. The scan range at low temperatures is about 80$\mu$m and a coarse displacement of 5 mm in x and y direction has been implemented. The MicroSQUID-to-sample distance is regulated using a tuning fork based force detection. A MicroSQUID-to-sample distance of 420 nm has been obtained. The reliable knowledge of this distance is necessary to obtain a trustworthy estimate of the absolute value of the superconducting penetration depth. An outlook will be given on the ongoing direction of development

A thermostable trilayer resist for niobium lift-off

We have developped a novel lift-off process for fabrication of high quality superconducting submicron niobium structures. The process makes use of a thermostable polymer with a high transition temperature T_{g}= 235 C and an excellent chemical stability. The superconducting critical temperature of 100 nm wide niobium lines is above 7 K. An example of shadow evaporation of a Nb-Cu submicron hybrid structure is given. A potential application of this process is the fabrication of very small single electron devices using refratory metals.Comment: 6 pages, 6 eps figures, submitted to Journal of Vacuum Science and Technology

Spin-Valve Effect of the Spin Accumulation Resistance in a Double Ferromagnet - Superconductor Junction

We have measured the transport properties of Ferromagnet - Superconductor nanostructures, where two superconducting aluminum (Al) electrodes are connected through two ferromagnetic iron (Fe) ellipsoids in parallel. We find that, below the superconducting critical temperature of Al, the resistance depends on the relative alignment of the ferromagnets' magnetization. This spin-valve effect is analyzed in terms of spin accumulation in the superconducting electrode submitted to inverse proximity effect

Slippage and boundary layer probed in an almost ideal gas by a nanomechanical oscillator

We have measured the interaction between $^4$He gas at 4.2$~$K and a high-quality nano-electro-mechanical string device for its first 3 symmetric modes (resonating at 2.2$~$MHz, 6.7$~$MHz and 11$~$MHz with quality factor $Q > 0.1$ million) over almost 6 orders of magnitude in pressure. This fluid can be viewed as the best experimental implementation of an almost-ideal monoatomic and inert gas which properties are tabulated. The experiment ranges from high pressure where the flow is of laminar Stokes-type presenting slippage, down to very low pressures where the flow is molecular. In the molecular regime, when the mean-free-path is of the order of the distance between the suspended nano-mechanical probe and the bottom of the trench we resolve for the first time the signature of the boundary (Knudsen) layer onto the measured dissipation. Our results are discussed in the framework of the most recent theories investigating boundary effects in fluids (both analytic approaches and Monte-Carlo DSMC simulations)

Transverse conductivity in the sliding CDW state of NbSe_3

The dynamical properties of longitudinal and transverse conduction of NbSe$_3$ single-crystals have been simultaneously studied when the current is applied along the b axis (chain direction). In the vicinity of the threshold electric field for CDW sliding, the transverse conduction sharply decreases. When a rf field is applied, voltage Shapiro steps for longitudinal transport are observed as usual, but also current Shapiro steps in the transverse direction. The possible mechanisms of this effect are discussed.Comment: 4 pages, 5 figures, accepted in PR

Fabrication of stable and reproducible sub-micron tunnel junctions

We have performed a detailed study of the time stability and reproducibility of sub-micron $Al/AlO_{x}/Al$ tunnel junctions, fabricated using standard double angle shadow evaporations. We have found that by aggressively cleaning the substrate before the evaporations, thus preventing any contamination of the junction, we obtained perfectly stable oxide barriers. We also present measurements on large ensembles of junctions which prove the reproducibility of the fabrication process. The measured tunnel resistance variance in large ensembles of identically fabricated junctions is in the range of only a few percents. Finally, we have studied the effect of different thermal treatments on the junction barrier. This is especially important for multiple step fabrication processes which imply annealing the junction.Comment: 4 pages, 3 figure

Sedimental Coal Ashes: Its pozzolanic effects in Portland cement clinker

Las centrales termoeléctricas generan una gran cantidad de residuos sólidos como producto de la combustión del carbón, conocidos como cenizas. Existen dos tipos de cenizas: volantes - de tamaño muy fino-, que son arrastradas por la corriente de humos de los sistemas de eliminación de partículas y, -las sedimentadas - más gruesas, que se funden y se aglomeran acumulándose en el fondo del homo o en los tubos de las calderas. Intentando resolver factores técnico-económicos y ecológicos al mismo tiempo, en este trabajo presentamos los resultados obtenidos de la incorporación de un 20% en peso de cenizas sedimentadas (Cs) como adición activa al cemento Portland. Se estudia la potencial puzolanidad de la adición y se muestran resultados de seguimiento de la hidratación a temprana edad, variación de color y resistencia mecánica del material compuesto obtenido por molienda conjunta del clinker portland y el material residual.The power plants generate a large amount of solid waste, known as ash, as a product of combustion of coal. There are two types of ash: fly - very fine in size- which are carried by the flow of smoke removal systems, and sedimentary particles -coarse particles - which are melted and agglomerated accumulated in the bottom of the furnace or in the boiler tubes. Trying to resolve technical-economic and ecologic factors at the same time, this work presents the results of adding a 20% weight of sediment ash (Cs) as an active addition to the Portland cement. The potential pozzolanity of the addition is studied and it is shown proceeding of the hydration at early age, color variation and mechanical strength of the composite material obtained by grinding together Portland clinker with the residual material.Centro de Tecnología de Recursos Minerales y CerámicaFacultad de Ingenierí

Sedimental Coal Ashes: Its pozzolanic effects in Portland cement clinker

Las centrales termoeléctricas generan una gran cantidad de residuos sólidos como producto de la combustión del carbón, conocidos como cenizas. Existen dos tipos de cenizas: volantes - de tamaño muy fino-, que son arrastradas por la corriente de humos de los sistemas de eliminación de partículas y, -las sedimentadas - más gruesas, que se funden y se aglomeran acumulándose en el fondo del homo o en los tubos de las calderas. Intentando resolver factores técnico-económicos y ecológicos al mismo tiempo, en este trabajo presentamos los resultados obtenidos de la incorporación de un 20% en peso de cenizas sedimentadas (Cs) como adición activa al cemento Portland. Se estudia la potencial puzolanidad de la adición y se muestran resultados de seguimiento de la hidratación a temprana edad, variación de color y resistencia mecánica del material compuesto obtenido por molienda conjunta del clinker portland y el material residual.The power plants generate a large amount of solid waste, known as ash, as a product of combustion of coal. There are two types of ash: fly - very fine in size- which are carried by the flow of smoke removal systems, and sedimentary particles -coarse particles - which are melted and agglomerated accumulated in the bottom of the furnace or in the boiler tubes. Trying to resolve technical-economic and ecologic factors at the same time, this work presents the results of adding a 20% weight of sediment ash (Cs) as an active addition to the Portland cement. The potential pozzolanity of the addition is studied and it is shown proceeding of the hydration at early age, color variation and mechanical strength of the composite material obtained by grinding together Portland clinker with the residual material.Centro de Tecnología de Recursos Minerales y CerámicaFacultad de Ingenierí

Sedimental Coal Ashes: Its pozzolanic effects in Portland cement clinker

Las centrales termoeléctricas generan una gran cantidad de residuos sólidos como producto de la combustión del carbón, conocidos como cenizas. Existen dos tipos de cenizas: volantes - de tamaño muy fino-, que son arrastradas por la corriente de humos de los sistemas de eliminación de partículas y, -las sedimentadas - más gruesas, que se funden y se aglomeran acumulándose en el fondo del homo o en los tubos de las calderas. Intentando resolver factores técnico-económicos y ecológicos al mismo tiempo, en este trabajo presentamos los resultados obtenidos de la incorporación de un 20% en peso de cenizas sedimentadas (Cs) como adición activa al cemento Portland. Se estudia la potencial puzolanidad de la adición y se muestran resultados de seguimiento de la hidratación a temprana edad, variación de color y resistencia mecánica del material compuesto obtenido por molienda conjunta del clinker portland y el material residual.The power plants generate a large amount of solid waste, known as ash, as a product of combustion of coal. There are two types of ash: fly - very fine in size- which are carried by the flow of smoke removal systems, and sedimentary particles -coarse particles - which are melted and agglomerated accumulated in the bottom of the furnace or in the boiler tubes. Trying to resolve technical-economic and ecologic factors at the same time, this work presents the results of adding a 20% weight of sediment ash (Cs) as an active addition to the Portland cement. The potential pozzolanity of the addition is studied and it is shown proceeding of the hydration at early age, color variation and mechanical strength of the composite material obtained by grinding together Portland clinker with the residual material.Centro de Tecnología de Recursos Minerales y CerámicaFacultad de Ingenierí