RESUMO
The dielectric effect was theoretically investigated in order to describe the electric field in the vicinity of a junction of a metal, dielectric, and vacuum. The assumption of two-dimensional symmetry of the junction leads to a simple analytic form and to a systematic numerical calculation for the field. The electric field obtained for the triple junction was found to be enhanced or reduced according to a certain criterion determined by the contact angles and dielectric constant. Further numerical calculations of the dielectric effect show that an electric field can experience a larger enhancement or reduction for a quadruple junction than that achieved for the triple junction. It was also found that even though it changes slowly in comparison with the shape effect, the dielectric effect was noticeably large over the entire range of the shape change.
RESUMO
We use a transfer-matrix methodology to simulate the rectification of infrared and optical radiation by geometrically asymmetric metal-vacuum-metal junctions in which one of the metals is flat while the other is extended by a tip. We determine in particular the power this junction could provide to an external load and the efficiency with which the energy of incident radiations is converted. We consider first situations in which the external radiation is monochromatic, with typical frequencies in the infrared and optical domains. We then consider situations in which the external radiation consists of a full range of frequencies, with amplitudes that are representative of a focused beam of solar radiation. We investigate in particular how the efficiency of the rectification is affected by the aspect ratio of the tip, the work function of the metallic elements and the occurrence of polarization resonances. Our results demonstrate that the rectification of infrared and optical radiation is possible using devices of the type considered in this work. They finally provide a quantitative analysis of the efficiency of this rectification.
RESUMO
We simulate with a transfer-matrix methodology the rectification properties of geometrically asymmetric metal-vacuum-metal junctions in which one of the metals is flat while the other is extended by a tip. We consider both tungsten and silver as the material for the tip and we study the influence of the dielectric function of these materials on the rectification properties of the junction. We determine in particular the power that these junctions could provide to an external load when subject to a bias whose typical frequency is in the infrared or optical domain. We also study the rectification ratio of these junctions, which characterizes their ability to rectify the external bias by providing currents with a strong dc component. The results show that these quantities exhibit a significant enhancement for frequencies Ω that correspond to a resonant polarization of the tip. With silver and the geometry considered in this paper, this arises for [Formula: see text] values of the order of 3.1 eV in the visible range. Our results hence indicate that the frequency at which the device is the most efficient for the rectification of external signals could be controlled by the geometry or the material used for the tip.
RESUMO
We present three-dimensional simulations of field emission from an open (5,5) carbon nanotube without adsorption, by using a transfer-matrix methodology. By introducing pseudopotentials for the representation of carbon atoms and by repeating periodically a basic unit of the nanotube, band-structure effects are manifested in the distributions of energies. A representation of the band structure of the (5,5) nanotube is presented. The total-energy distributions of both the incident and field-emitted electrons contain peaks, which are related to discontinuities in the band structure or to standing waves in the carbon nanotube (a total length of 5.657 nm is considered). These peaks move to lower energies when the extraction field is increased. Such peaks should be observable in field-emission experiments.
