Erik Sanchez

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We present a new scheme for near-field fluorescence imaging using a metal tip illuminated with femtosecond laser pulses of proper polarization. The strongly enhanced electric field at the metal tip (ഠ15 nm end diameter) results in a localized excitation source for molecular fluorescence. Excitation of the sample via two-photon absorption provides good image(More)
We present near-field Raman spectroscopy and imaging of single isolated single-walled carbon nanotubes with a spatial resolution of approximately 25 nm. The near-field origin of the image contrast is confirmed by the measured dependence of the Raman scattering signal on tip-sample distance and the unique polarization properties. The method is used to study(More)
We report fluorescence imaging of single dye molecules on a glass substrate by two-photon excitation with femtosecond pulses from a mode-locked Ti:sapphire laser. The single-molecule images exhibit a high signal to background ratio (>30:1) and a high spatial resolution (fwhm < λ / 3). A quadratic intensity dependence of single-molecule emission rate is(More)
We report the three-dimensional electromagnetic simulation of gold nanoparticles with specific geometries as a means to the rational design of apertureless near-field scanning optical microscopy ͑NSOM͒ probes. Analytical solutions for field enhancement by spheroidal particles are used to provide physical insight for probe design. These solutions indicate(More)
We report the fabrication of nanometric, conformal, smooth dielectric coatings on the ends of apertureless near-field optical probes by both ion beam and electron beam assisted deposition techniques ͑IBAD and EBAD͒. The ion beam provides a higher Si m O n growth rate than the electron beam, though the undesirable implantation of Ga ions may outweigh the(More)
We describe the theoretical treatment of fluorescence quenching in tip-enhanced nonlinear optical microscopy ͑TENOM͒. Finite difference time domain simulations demonstrate that while sharp pyramidal probes yield fluorescence signal enhancement that decays monotonically as a function of probe-fluorophore distance, more commonly used conical probes cause more(More)
A skill is a basic unit for cognitive processing that allows the use of concepts. A competence is the result of the application of a skill on a concept. Competences and their development play a central role in most educational and training programs. This paper presents a new formal model for the representation of competences in persons and machines, called(More)
A phenomenon resembling natural ball lightning can be produced via electrical arcing through silicon. We use lump silicon instead of silicon wafers to achieve higher production rates and larger, longer-lived luminous balls than previously reported. The luminous balls consist of a silicon core surrounded by a porous network of loosely bound silicon dioxide(More)
The neutral atom microscope uses a beam of thermal noncharged atoms or molecules to probe an atomic surface with very low interaction energies (<70 meV). Continued optimization of the 'pinhole' neutral atom microscope has improved resolution to 0.35 μm. Recent images are presented demonstrating resolution and the contrast mechanisms identified so far. The(More)