Peter B. Lerner

Model calculations of internal field emission and J–V characteristics of a composite n-Si and N–diamond cold cathode source

A model to describe internal field emission through the interface between highly n-doped Si and nitrogen (N)-doped diamond is presented. We describe the roughness on the Si surface as a collection of sharp, spherically pointed Si asperities embedded in the diamond film. These “tips” provide enhancement of the applied electric field, which, in conjunction with the high N doping of diamond, results in the formation of a Schottky barrier which allows for tunneling or internal field emission from the Si into the conduction band of diamond. This enhanced electric field is also sufficient to induce valence band tunneling from the Si into the diamond conduction band. In our model limitations on the field mediated transport of holes from the n-doped Si/diamond interface to the cathode base leads to charging of the Si asperities. This charge accumulation results in band bending in Si and a significant reduction in the valence band current. The calculated J–V characteristics for the internal field emission lead to ...

Physics of solvation

Calculations are presented of the energetics of an impurity (atom or ion) interacting with a fluid. Two possible configurations are considered: a surface state and a solvated state. For two distinct model problems which we consider (any classical fluid and superfluid helium) we find a common behaviour: the value of a dimensionless parameter λ determines the relative stability of the surface and solvated states. For λ greater (less) than 1.9, the sovated (surface) state is favored. A more realistic estimate for a classical fluid is λ ∼ 1. Predictions are made of a universal solvation behaviour derived from the law of corresponding states. Results are presented for the solvated fraction as a function of cluster radius and temperature. Quantum corrections and the kinetics of solvation are discussed briefly.

Theoretical analysis of field emission from a metal diamond cold cathode emitter

Recently, Geis et al. [J. Vac. Sci. Technol. B 14, 2060 (1996)] proposed a cold cathode emitter based on a Spindt-type design using a diamond film doped by substitutional nitrogen. The device is characterized by high field emission currents at very low power. Two properties, the rough surface of the metallic injector and the negative electron affinity of the (111) surface of the diamond are essential for its operation. We present a first consistent quantitative theory of the operation of a Geis–Spindt diamond field emitter. Its essential features are predicated on nearly zero-field conditions in the diamond beyond the depletion layer, quasiballistic transport in the conduction band, and applicability of a modified Fowler–Nordheim equation to the transmission of electrons through the Schottky barrier at the metal-diamond interface. Calculated results are in good qualitative and quantitative agreement with the experimental results of Geis et al.

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.

The use of internal field emission to inject electronic charge carriers into the conduction band of diamond films: a review

Abstract Several thin film composite metal(semiconductor) diamond cold cathode sources have recently been fabricated exhibiting high current–low power characteristics. We have modeled the field emission in these thin film diamond electron sources as a three-step process (electron injection, transport and vacuum emission). Critical to the operation of these devices is a mechanism for populating the conduction band (CB) of diamond with charge carriers. Internal field emission has been proposed for the injection of electrons by tunneling from metal (semiconductor) substrates into the diamond CB. A thin (Schottky) tunneling barrier is created at the substrate–diamond interface by heavily doping the diamond with nitrogen and roughening the metal (semiconductor) interface to enhance the internal field. In this paper we review model calculations of the internal field emission process for both metal and semiconductor substrates. The results show good agreement with experiment, implying the usefulness of the internal field emission mechanism to provide electronic charge carriers in the CB of diamond films.

Alkali dimers on the surface of liquid helium

A recent paper by Ancilottoet al. (Zeitschrift für Physik B, in press), presented calculations of adsorption energies and the geometry of a surface dimple for alkali atoms bound to the surfaces of quantum liquids (4He,3He, H2). Here we present a study of the adsorption of two alkali dimers (Li2, Na2) on the surface of liquid helium. The calculations employ a model of an abrupt interface formulated by Ancilotto et al. as well as one using a diffuse interface. Our conclusion its that the dimers are bound to the surface more strongly than their respective monomers. In the case of dimers there is an additional degree of freedom-the orientation of the molecular axis relative to the surface. We study the influence of molecular anisotropy on adsorption by comparing the cases of “erect” and “spinning flat” orientations and conclude that the latter is energetically favored.

Classical and quantum responsivities of geometrically asymmetric metal-vacuum-metal junctions used for the rectification of infrared and optical radiations

The authors study the rectification properties of geometrically asymmetric metal-vacuum-metal junctions in which a combination of static and oscillating biases is established between a cathode that is extended by a hemispherical protrusion and a flat anode. The static current-voltage characteristics of this device are established using a transfer-matrix methodology. The rectification properties of the device are, however, analyzed in the framework of a classical model that is based on the Taylor-expansion of static current-voltage data. This enables the impedance and the classical responsivity of the device to be established. The authors then investigate how the impedance and the classical responsivity of this junction are affected by the work function of the materials, the gap spacing between the cathode and the anode, and the aspect ratio of the protrusion. They also consider the efficiency with which the energy of incident radiations can be converted using this device. The authors finally compare the responsivity obtained using this classical approach with the quantum responsivity one can define from the currents actually achieved in an oscillating barrier. This work provides additional insight for the development of a device that could be used for the energy conversion of infrared and optical radiations.The authors study the rectification properties of geometrically asymmetric metal-vacuum-metal junctions in which a combination of static and oscillating biases is established between a cathode that is extended by a hemispherical protrusion and a flat anode. The static current-voltage characteristics of this device are established using a transfer-matrix methodology. The rectification properties of the device are, however, analyzed in the framework of a classical model that is based on the Taylor-expansion of static current-voltage data. This enables the impedance and the classical responsivity of the device to be established. The authors then investigate how the impedance and the classical responsivity of this junction are affected by the work function of the materials, the gap spacing between the cathode and the anode, and the aspect ratio of the protrusion. They also consider the efficiency with which the energy of incident radiations can be converted using this device. The authors finally compare the r...

Hot electron and quasiballistic transport of nonequilibrium electrons in diamond thin films

A molecular dynamics simulation of conduction-band transport in diamond has been carried out that combines classical propagation of electrons with choice of scattering events determined by a Monte Carlo algorithm using quantum mechanical rates. The high-field regime is dominated by hot optical phonon scattering for n⩽1019 cm−3 and by electron–plasmon emission for higher electron concentrations. Electron–electron and electron–hole binary processes do not significantly influence the transport characteristics but extend the high-energy tail and asymmetry of the electron distribution, making it more “Maxwellian.” The results demonstrate the possibility of achieving quasiballistic transport in thin diamond films with a significant portion of the field energy imparted to the electrons at high fields (F≈102 V/μm) and electron concentrations up to n≈1018 cm−3.

Structure of alkali dimers at the surface of liquid helium

Calculations are presented of the equilibrium configuration (“dimple”) of a Na2 or Li2 molecule absorbed on the surface of liquid3H e or liquid4He. The computed aimer binding energies are somewhat greater than those of the monomers. The lowest energy occurs when the molecule lies flat, but the energy in the erect orientation is only ∼ 1K higher (implying relatively free rotation). The center of mass lies ∼ 4Åabove the liquid surface and the dimple has a depth ∼ 3Å. An exceptional case is Li2 on liquid3H e, for which the surface state is unstable relative to solvation in the bulk.

Analysis of the efficiency with which geometrically asymmetric metal–vacuum–metal junctions can be used for the rectification of infrared and optical radiations

The authors simulate 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 sharp tip. The authors analyze, in particular, the efficiency with which the energy of incident radiations, with frequencies in the infrared through the visible, is transferred to the electrons that cross the junction. This time-dependent electronic scattering problem is solved by using a transfer-matrix methodology. In order to validate this technique, the results achieved by using this quantum-mechanical scheme are compared with those provided by models that are based on extrapolations of static current–voltage data. The authors then discuss concepts that are relevant to the efficiency with which energy is converted in these junctions. The authors finally analyze how this efficiency is affected by the amplitude and the angular frequency of the potentials that are induced in these junctions, the work function of the metallic contact...