Production of ordered silicon nanocrystals by low-energy ion sputtering

We report on the production of ordered assemblies of silicon nanostructures by means of irradiation of a Si(100) substrate with 1.2 keV Ar ions at normal incidence. Atomic Force and High-Resolution Transmission Electron microscopies show that the silicon structures are crystalline, display homogeneous height, and spontaneously arrange into short-range hexagonal ordering. Under prolonged irradiation (up to 16 hours) all dot characteristics remain largely unchanged and a small corrugation develops at long wavelengths. We interpret the formation of the dots as a result of an instability due to the sputtering yield dependence on the local surface curvatureComment: 4 two-column pages (revtex4), 3 figures (higher quality copies in the printed jrnl. version

Reducción de los salarios de los trabajadores con educación universitaria en México: ¿son los más jóvenes o los más viejos los más perjudicados?

A reduction in the wage premium for skilled labor –and a consistent reduction of overall wage inequality-has played an important role in explaining the fall of income inequality in Latin America during the 2000-2014 period. Consistent with that pattern, wage inequality declined in Mexico since 2000. This paper investigates the possible channels on why the wages of high-skilled workers have declined. Using data from Mexican labor surveys for the period between 2000 and 2014, we investigate if the decline was driven by wages declining more sharply for younger or older workers. We find that wages of older workers declined and the decline was more pronounced the older the cohort. This would seem to support the hypothesis that older workers’ skills became obsoleteUna reducción en la prima salarial del trabajo calificado -y una reducción constante de la desigualdad salarial global- ha jugado un papel importante en la explicación de la caída de la desigualdad del ingreso en América Latina durante el período 2000-2014. En consonancia con ese patrón, la desigualdad salarial disminuyó en México desde el año 2000. Este trabajo investiga las posibles causas de por qué los salarios de los trabajadores altamente cualificados han disminuido. Utilizando datos de encuestas sobre el trabajo de México para el periodo 2000- 2014, se investiga si la reducción se debió a una disminución de salarios más acusada para los trabajadores más jóvenes o más viejos. Nos encontramos con que los salarios de los trabajadores de edad se redujeron y el descenso fue más pronunciado cuanto mayor es la cohorte. Esto parece apoyar la hipótesis de que las cualificaciones de los trabajadores de más edad se volvieron obsoleta

VLBA determination of the distance to nearby star-forming regions I. The distance to T Tauri with 0.4% accuracy

In this article, we present the results of a series of twelve 3.6-cm radio continuum observations of T Tau Sb, one of the companions of the famous young stellar object T Tauri. The data were collected roughly every two months between September 2003 and July 2005 with the Very Long Baseline Array (VLBA). Thanks to the remarkably accurate astrometry delivered by the VLBA, the absolute position of T Tau Sb could be measured with a precision typically better than about 100 micro-arcseconds at each of the twelve observed epochs. The trajectory of T Tau Sb on the plane of the sky could, therefore, be traced very precisely, and modeled as the superposition of the trigonometric parallax of the source and an accelerated proper motion. The best fit yields a distance to T Tau Sb of 147.6 +/- 0.6 pc. The observed positions of T Tau Sb are in good agreement with recent infrared measurements, but seem to favor a somewhat longer orbital period than that recently reported by Duchene et al. (2006) for the T Tau Sa/T Tau Sb system.Comment: 24 pages, 3 pages, AASTEX format, accepted for publication in Ap

Fractal characterisation of electrodispersed gold electrodes

The fractal dimension of the surface, Ds, of thin columnar gold electrodeposits (surface roughness factor 50–100) grown on gold wire cathodes by electroreducing hydrous gold oxide layers has been determined by measuring the diffusion controlled current of the Fe(CN)4−6/Fe(CN)3−6 reaction. The diffusion current (I) vs. time (t) relationships obeyed a Iαt−α dependence with Ds = 2α + 1. The initial Ds, value is 2.5 ± 0.1, and decreases to 2.3 ± 0.1 by keeping the deposit in contact with the electrolyte solution at 298 K due to the smoothing of the rough metal surface by surface diffusion.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Fractal characterisation of electrodispersed gold electrodes

The fractal dimension of the surface, Ds, of thin columnar gold electrodeposits (surface roughness factor 50–100) grown on gold wire cathodes by electroreducing hydrous gold oxide layers has been determined by measuring the diffusion controlled current of the Fe(CN)4−6/Fe(CN)3−6 reaction. The diffusion current (I) vs. time (t) relationships obeyed a Iαt−α dependence with Ds = 2α + 1. The initial Ds, value is 2.5 ± 0.1, and decreases to 2.3 ± 0.1 by keeping the deposit in contact with the electrolyte solution at 298 K due to the smoothing of the rough metal surface by surface diffusion.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

A sequential protocol combining dual neuroanatomical tract-tracing with the visualization of local circuit neurons within the striatum

We describe here an experimental approach designed to aid in the identification of complex brain circuits within the rat corpus striatum. Our aim was to characterize in a single section (i) striatal thalamic afferents, (ii) striatopallidal projection neurons and (iii) striatal local circuit interneurons. To this end, we have combined anterograde tracing using biotinylated dextran amine and retrograde neuroanatomical tracing with Fluoro-Gold. This dual tracing protocol was further implemented with the visualization of different subpopulations of striatal interneurons. The subsequent use of three different peroxidase substrates enabled us to unequivocally detect structures that were labeled within a three-color paradigm

Nonlinear porous medium flow with fractional potential pressure

We study a porous medium equation, with nonlocal diffusion effects given by an inverse fractional Laplacian operator. We pose the problem in n-dimensional space for all t>0 with bounded and compactly supported initial data, and prove existence of a weak and bounded solution that propagates with finite speed, a property that is nor shared by other fractional diffusion models.Comment: 32 pages, Late

Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application

Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching