J. Giraldo

Vector spherical harmonics and their application to magnetostatics

An alternative and somewhat systematic definition of the vector spherical harmonics, in analogy with the commonly used scalar spherical harmonics, is presented. The new set of vector spherical harmonics satisfies the properties of orthogonality and completeness, and is compared with other existing definitions of vector spherical harmonics. Some applications to problems in magnetostatics are illustrated.

Quantum point contact conductance in normal-metal/insulator/metal/superconductor junctions

The effect of an insulating barrier located at a distance

Electrochemical differential photoacoustic cell to study in situ the growing process of porous materials

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Optical Absorption in Ordered Arrays of Silver Nanoparticles

from a NS quantum point contact is analyzed in this work. The Bogoliubov de Gennes equations are solved for NINS junctions (S: anysotropic superconductor, I: insulator and N: normal metal), where the NIN region is a quantum wire. For

An improvement to the comparison equation method for solving the Schrödinger equation

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Quasiparticle energy spectrum and Josephson current in superconducting SNINS junctions

, bound states and resonances in the differential conductance are predicted. These resonances depend on the symmetry of the pair potential, the strength of the insulating barrier and

Local Density of States in Anisotropic N–S–N and N–I–S–N Junctions

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Effective Dielectric Response of a Composite with Aligned Ellipsoidal Inclusions

. Our results show that in a NINS quantum point contact the number of resonances vary with the symmetry of the order parameter. This is to be contrasted with the results for the NINS junction, in which only the position of the resonances changes with the symmetry.

Effective Dielectric function of a Composite with Aligned Spheroidal Inclusions

In order to study in situ the growing process of porous materials, a new electrochemical differential photoacoustic cell (DPC) was developed. This system allows to obtain the thermal signals coming from the growing process of the pores without the external noise component. The DPC is a good system to growth porous silicon and study their growing process with reproducibility. The porous silicon samples were obtained by using electrochemical etching of (100) n-type silicon wafers with different nominal resistivity values in the range of 1-25 Omega cm. The samples were formed in a solution of hydrofluoric acid and ethanol having a composition ratio of 1:1 in volume with etching voltage of 10 V and an etching time of 2 min using back illumination provided by a laser beam with a wavelength of 808 nm. The porous samples were characterized by means of Raman microscopy, x-ray diffraction, and scanning electron microscopy. The crystallite sizes of the samples were obtained through the analysis of the micro-Raman spectra using a phonon confinement model, and the analysis of the x-ray diffractograms.

Effective dielectric response of a composite with aligned spheroidal inclusions.

Silver nanoparticles (diameters between 2.0 and 6.0 nm) arranged in a 2D hexagonal lattice and embedded in a dielectric matrix are considered in this work. The array resembles somehow the one tailored by Pileni and coworkers, Phys. Rev. B 59, 13350 (1999) to study the electromagnetic coupling between metal nanoparticles and their size effects in the optical absorption coefficient. Non-local and quantum size effects in the nanometric particles are taken into account by means of a size dependent dielectric function which includes level quantization as well as diffuse surface effects.