arXiv subjects

Ming Bai

Publications and source records attributed to Ming Bai.

5 recordsLinked to original sources

arXiv2012

Surface Plasmons and Field Electron Emission In Metal Nanostructures

In this paper we discuss the field enhancement due to surface plasmons resonances of metallic nanostructures, in particular nano spheres on top of a metal, and find maximum field enhancement of the order of 10^2, intensities enhancement of the order of 10^4. Naturally these fields can produce temporal fields of the order of 0.5V/Å that yield field emission of electrons. Although the fields enhancements we calculated are factor of 10 smaller than those reported in recent experiments, our results explain very well the experimental data. Very large atomic fields destabilize the system completely emitting ions, at least for static field, and produce electric breakdown. In any case, we prove that the data are striking and can solve problems in providing stabilized current of static fields for which future experiments should be done for obtaining pulsed beams of electrons.

cond-mat.mes-hall↗

arXiv2006

Theory of Transmission of Light by Sub-wavelength Cylindrical Holes in Metallic Films

This paper presents theory and finite-difference time-domain (FDTD) calculations for a single and arrays of sub-wavelength cylindrical holes in metallic films presenting large transmission. These calculations are in excellent agreement with experimental measurements. This effect has to be understood in terms of the properties exhibited by the dielectric constant of metals which cannot be treated as ideal metals for the purpose of transmission and diffraction of light. We discuss the cases of well-differentiated metals silver and tungsten. It is found that the effect of surface plasmons or other surface wave excitations due to a periodical set of holes or other roughness at the surface is marginal. The effect can enhance but also can depress the transmission of the arrays as shown by theory and experiments. The peak structure observed in experiments is a consequence of the interference of the wavefronts transmitted by each hole and is determined by the surface array period independently of the material. Without large transmission through a single hole there is no large transmission through the array. We found that in the case of Ag which at the discussed frequencies is a metal there are cylindrical plasmons at the wall of the hole, as reported by Economu et al 30 years ago, that enhanced the transmission. But it turns out, as will be explained, that for the case of W which behaves as a dielectric, there is also a large transmission when compared with that of an ideal metal waveguide. To deal with this problem one has to use the measured dielectric function of the metals. We discuss thoroughly all these cases and compare with the data.

physics.optics↗

arXiv2006

Electrostatic Force Microscopy on Oriented Graphite Surfaces: Where Insulating and Conducting Behaviors Coexist

We present measurements of the electric potential fluctuations on the surface of highly oriented pyrolytic graphite using electrostatic force and atomic force microscopy. Micrometric domain-like potential distributions are observed even when the sample is grounded. Such potential distributions are unexpected given the good metallic conductivity of graphite because the surface should be an equipotential. Our results indicate the coexistence of regions with metallic and insulating behaviors showing large potential fluctuations of the order of 0.25V. We discuss the implications of these measurements in the disorder structure of graphite.

cond-mat.mes-hall↗

arXiv2006

Is there Ballistic Conductance Quantization in Real Life Metals Nanocontacts?

Theory and a vast set of experimental work in metals, since a century, appear to show that the mean free path of conduction electrons in a real metal is about the min (bulk mean free path, smallest transversal size of the metal), a result that was already proposed by J. J. Thomson in 1901. This establishes, as discussed in this work, serious difficulties to justify conductance quantization and ballistic transport in atomic/nanocontacts or nanoconstrictions of real life metals. The ohmic resistance of the leads proves to be as important as the ballistic one of the constriction.

cond-mat.mes-hall↗

arXiv2005

Light Collimation and Focussing by a Thin Flat Metallic Slab

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a punctual source. The effect is optimised when the radiation is around the bulk, not at the surface, plasma frequency. And the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of the Aluminium whose imaginary part of the permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.

cond-mat.other↗