Thomas E. Sullivan

An analytical solution for microtip field emission current and effective emission area

Classical field emission theory relates the material work function and applied electric field at the emitter surface to tunneling current density, based upon the one-dimensional, planar Fowler–Nordheim equation. The extension of this theory to nonplanar, tip-anode geometries is complicated by the spatial variation of the electric field and resultant current density along the microtip surface. To relate this spatially dependent electric field to the applied voltage in this tip-to-plane geometry, experimenters have adopted empirically determined field enhancement factors (i.e., F=βV) and emission area terms to explain quantitative measurements of microtip current. In this work, the nature of the field enhancement and area terms are defined analytically by employing an exact three-dimensional electric field solution in prolate spheroidal coordinates and examining the relationship between total tip current and current density. The analytical and numerical results based on this model provide a physical context...

Nanoscale Devices for Rectification of High Frequency Radiation from the Infrared through the Visible: A New Approach

We present a new and viable method for optical rectification. This approach has been demonstrated both theoretically and experimentally and is the basis fot the development of devices to rectify radiation through the visible. This technique for rectification is based not on conventional material or temperature asymmetry as used in MIM (metal/insulator/metal) or Schottky diodes, but on a purely sharp geometric property of the antenna. This sharp “tip” or edge with a collector anode constitutes a tunnel junction. In these devices the rectenna (consisting of the antenna and the tunnel junction) acts as the absorber of the incident radiation and the rectifier. Using current nanofabrication techniques and the selective atomic layer deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum. To assess the viability of our approach, we review the development of nanoantenna structures and tunnel junctions capable of operating in the visible region. In addition, we review the detailed process of rectification and present methodologies for analysis of diode data. Finally, we present operational designs for an optical rectenna and its fabrication and discuss outstanding problems and future work.

Three‐dimensional electrostatic potential, and potential‐energy barrier, near a tip‐base junction

The geometry of an atomically sharp or nearly atomically sharp tip in proximity to a planar anode may be closely approximated in the prolate‐spheroidal coordinate system. An exact three‐dimensional electrostatic‐potential solution for a free charge in such a tip/base junction is given in this letter, including calculations for both the symmetrical on‐axis case and the asymmetric off‐axis case. An exact solution for the potential‐energy barrier is also given; this solution has immediate applications in three‐dimensional tunneling studies and in calculations of electron trajectories in micron‐ and submicron‐sized field‐emitter arrays.

Methods for calculating electrostatic quantities due to a free charge in a nanoscale three‐dimensional tip/base junction

The exact solutions for fully three‐dimensional electrostatic quantities due to a free charge in a nanoscale tip/base junction, such as the scanning‐tunneling microscope, are given for the problem as modeled in the prolate‐spheroidal coordinate system. These exact solutions consist of summation series of integrals of conical functions, and methods for calculating these exact solutions with high accuracy are described in detail in this paper. Calculated results for the surface‐charge distribution on the tip and the base due to a free electron in a nanoscale tip/base junction are also presented. This analysis has important implications for the ultimate objective of quantifying electron tunneling, from first principles, in nonplanar geometries such as sharp vacuum field emitters.

Monte Carlo simulation of hot electron charge transport in diamond under an internal electric field

Charge transport in diamond is studied using the Monte Carlo method, in which the scattering of electrons by phonons is considered stochastically. It is assumed that electrons are injected into the diamond conduction band with an initial equilibrium energy distribution and they are then accelerated by the internal field subject to phonon scattering. It is found that the electron energy distribution is independent of the field up to ≂0.1 V/μm. For larger fields, ‘‘hot’’ electron transport is predicted, i.e., the distribution shows a tail which depends on the internal field and the thickness of the diamond film. It implies that if electron field emission is from the conduction band in a diamond film, the transport and the energy spectrum of the emitted electrons should exhibit hot electron features.

The Role of Geometry in Nanoscale Rectennas for Rectification and Energy Conversion

We have previously presented a method for optical rectification that has been demonstrated both theoretically and experimentally and can be used for the development of a practical rectification and energy conversion device for the electromagnetic spectrum including the visible portion. This technique for optical frequency rectification is based, not on conventional material or temperature asymmetry as used in MIM or Schottky diodes, but on a purely geometric property of the antenna tip or other sharp edges that may be incorporated on patch antennas. This “tip” or edge in conjunction with a collector anode providing connection to the external circuit constitutes a tunnel junction. Because such devices act as both the absorber of the incident radiation and the rectifier, they are referred to as “rectennas.” Using current nanofabrication techniques and the selective Atomic Layer Deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum (see Section 2).

Nanoscale Rectennas with Sharp Tips for Absorption and Rectification of Optical Radiation

We present a method for optical rectification that has been demonstrated both theoretically and experimentally and can be used for the development of a practical rectification device for the electromagnetic spectrum including the visible portion. This technique for optical frequency rectification is based, not on conventional material or temperature asymmetry as used in MIM or Schottky diodes, but on a purely geometric property of the antenna tip or other sharp edges that may be incorporated on patch antennas. This “tip” or edge in conjunction with a collector anode providing connection to the external circuit constitutes a tunnel junction. Because such devices act as both the absorber of the incident radiation and the rectifier, they are referred to as “rectennas.” Using current nanofabrication techniques and the selective Atomic Layer Deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum.

Infrared and Optical Laser Rectification in STM Junctions

Scanning tunneling microscope (STM) has been used to characterize the rectifying properties of metal nanojunctions. Advances in nanofabrication have made it possible to fabricate solid state nanotunnel junctions similar to point contact and STM junctions. (AIP)

Expert system diagnosis of CMOS VLSI fabrication problems

Abstract not available.