Showing papers on "Field electron emission published in 1993"

Similarities in the 'cold' electron emission characteristics of diamond coated molybdenum electrodes and polished bulk graphite surfaces

Abstract: Details are given of an experimental study of field emission characteristics of diamond-coated Mo electrodes: in particular, a transparent anode imaging technique was used to monitor the spatial distribution of the individual emission centres. This study has revealed the important fact that substantial emission can be obtained at fields as low as 5 MV m-1. In order to investigate the physical nature of the emission process, a comparative study has been made of emission obtained from a diamond-coated electrode and a bulk carbon graphite electrode. Significantly, it was found that both the graphite-rich diamond film and the diamond-rich graphite electrode shared a similar high-emissivity characteristic, with a high surface density of emission sites. It has also been noted that CVD diamond films have two important properties that are favourable to low-field cold electron emission, namely their negative electron affinity and the presence of graphite inclusions.

Field-dependence of the area-density of 'cold' electron emission sites on broad-area CVD diamond films

Abstract: A high area density of field-induced electron emission sites has been observed on broad-area (12 mm in diameter) CVD diamond films deposited on molybdenum substrates. Furthermore, it was found that the density increased with the electric field applied to the surface of the films. These findings indicate that the CVD diamond film has to be seen as a potentially favoured candidate among electronic materials for the development of new types of cold cathode electron source.

Formation of Nanometer-Scale Grooves in Silicon with a Scanning Tunneling Microscope

Abstract: Grooves a few nanometers wide can be formed on a Si(111) surface with a scanning tunneling microscope when the tip is above a critical voltage. This may provide a promising approach to nanodevice fabrication. The dependence of the critical voltage on tunneling current, tip polarity, and tip material was studied with silver, gold, platinum, and tungsten tips. The results are consistent with field emission of positive and negative silicon ions. The variation of critical voltage with current is explained quantitatively by a simple tunneling equation that includes the effect of the contact potential between tip and sample.

Femtosecond thermionic emission from metals in the space-charge-limited regime

Abstract: We study femtosecond-laser-pulse-induced electron emission from W(100), Al(110), and Ag(111) in the subdamage regime (1–44 mJ/cm2 fluence) by simultaneously measuring the incident-light reflectivity, total electron yield, and electron-energy distribution curves of the emitted electrons. The total-yield results are compared with a space-charge-limited extension of the Richardson–Dushman equation for short-time-scale thermionic emission and with particle-in-a-cell computer simulations of femtosecond-pulsed-induced thermionic emission. Quantitative agreement between the experimental results and two calculated temperature-dependent yields is obtained and shows that the yield varies linearly with temperature beginning at a threshold electron temperature of ~0.25 eV The particle-in-a-cell simulations also reproduce the experimental electron-energy distribution curves. Taken together, the experimental results, the theoretical calculations, and the results of the simulations indicate that thermionic emission from nonequilibrium electron heating provides the dominant source of the emitted electrons. Furthermore, the results demonstrate that a quantitative theory of space-charge-limited femtosecond-pulse-induced electron emission is possible.

Principles and mechanisms of ion induced electron emission

Abstract: The mechanisms responsible for emission of electron from solids are described, separating them, when possible, into electron excitation, electron transport and cascade multiplication, and transmission through the surface barrier. Discussions include important energy quantities and quantum mechanical effects in the transport of slow electrons in the solid and through the surface barrier. Some new aspects not previously described are explored, such as how much information can be obtained by treating insulators as dense gases, electron loss from the projectile, differences between prompt and delayed excitation processes and final state effects in multiple electron emission.

Theory of electron emission in high fields from atomically sharp emitters: Validity of the Fowler–Nordheim equation

Abstract: Field emission from metallic emitters is generally described by the Fowler–Nordheim (FN) theory, which is based on a planar model of the tip with a classical image correction. Within the free‐electron model and the Wentzel–Kramers–Brillouin approximation, the planar tip model leads to the well‐known FN equation. The form of this equation predicts that a plot of log J/F2 versus 1/F, where J is the current density and F is the field, should be a straight line within the rather narrow region of field strengths of typical field emission experiments, 3–5 V/nm. This has been experimentally confirmed for conventional emitters, (i.e., electrolytically etched tips with radii ≳50 nm). However, field emitters fabricated with today’s new techniques are much sharper with radii of curvature of the order of nanometers or even the size of a single atom. Hence, the local geometry of the tip may become an important factor in the electron emission process. To investigate the effects of the shape and/or size on emission, the authors, in a recent series of papers, studied the dependence of the current–voltage characteristics on the local geometry of pointed emitters. It was found that the calculated results, plotted as log J/V2 versus 1/V, do not exhibit the straight line behavior predicted by the FN theory. In addition, there is a dramatic increase in the tunneling current for a fixed external bias, V, relative to the FN result for a planar model of the tip with the same bias voltage. Using the exact current integral additional results have been obtained exhibiting the effects of emitter curvature on electron emission in high fields and temperatures. These results continue to differ with the predictions of the β‐modified FN equation. Therefore, the adequacy of a β factor in the conventional planar model FN equation to account for emitter curvature is examined. It is demonstrated that even the use of β‐modified FN equation is not valid when applied to sharp emitters (rt≤10 nm) and will lead to spurious results when extracting information such as field values or emitting area from experimental FN curves. The explanation for this is discussed.

Ultrasharp tips for field emission applications prepared by the vapor–liquid–solid growth technique

Abstract: A technique for preparation of ultrasharp tips, preferentially of silicon, useful for field‐emission research and applications is described. Regular arrays of tips, as well as triodelike microstructures (‘‘Spindt cathodes’’), can be prepared in such a way. In addition, high‐aspect‐ratio tips suitable for field‐ion microscopy and field‐electron microscopy can be prepared by this technique. Finally, a version of the technique allowing to prepare special‐shape probes for scanning tunneling microscopes and related instruments is given.

Thermo-field emission and the Nottingham effect

Abstract: The thermo-field emission current and Nottingham effect are calculated for a wide range of temperatures (

Triode structure flat panel display employing flat field emission cathodes.

Abstract: A flat panel display for displaying visual information includes a plurality of corresponding light-emitting anodes (130), and field-emission cathodes (170), each of the anodes emitting light in response to emission from each of the corresponding cathodes, each of the cathodes (170) including a layer of low work function material having a relatively flat emission surface of a plurality of distributed localized electron emission sites and a grid assembly (102) interposed between the corresponding anodes (130) and cathodes (170) to thereby control emission levels to the anodes from the corresponding cathodes.

Atomic and nanometer-scale modification of materials : fundamentals and applications

Abstract: Atom manipulation with the scanning tunneling microscope STM-induced modification and electrical properties of surfaces on the atomic and nanometer scales alkali metals on III - V (110) semiconductor surfaces - overlayer properties and manipulation via STM field ion evaporation from tip and sample in the STM for atomic-scale surface modification writing of local, electrically active structures in amorphous silicon films by STM atomic-scale imaging and modification of spins using a magnetic-sensitive STM physics and chemistry in high electric fields field-induced transfer of an atom between two closely spaced electrodes vibrational heating and atom transfer with the STM tip-induced modifications of electronic and atomic structure field emission from single-atom protrusion tips - electron spectroscopy and local heating four-point resistance measurements of wires written with a scanning tunneling microscope high resolution patterning with the STM AFM data storage using thermomechanical writing BEEM - a probe of nanoscale modification nanoscale fashioning of materials growth and in-situ processing of low dimensional quantum structures quantum dot fabrication by optical lithography and selective etching high frequency (MHz) nanoactuators for tips and tip-arrays light pressure lithography semiconductor quantum dot resonant tunneling spectroscopy single electron effects in small metallic tunnel junctions fabrication and electric conductance of a finite atomic gold wire - a theoretical study structure, dynamics and electronic properties of molecular nanostructures observed by STM the modification of semi-conductor surfaces by molecular self-assembly molecular self-assembly and micromachining characterization of the interaction of C60 with Au (111) molecular and cellular organizates on the electrode surface for electronic control of their functions characterization and application of nanoscale artifacts in scanning tunneling microscopy.

Electron emission from ferroelectric materials

Abstract: Ferroelectric materials are a new class of electron emitters. Electron emission occurs due to the appearance of an unscreened charge and an electrostatic field at the polar surfaces of these crystals under pyroelectric, piezoelectric, and anomalous photovoltaic effects as well as during spontaneous polarization reversal. Small external perturbation (for example, a temperature variation of a few degrees or less) is enough for this emission effect to occur. Emission current density up to 103 A cm−2 and electron energy up to about 105 eV have been reported. It is shown that this phenomenon drastically differs from other kinds of electron emissions. The physical nature of this effect is discussed.

Method of making superhard tips for micro-probe microscopy and field emission

Abstract: Forming micro-probe tips for an atomic force microscope, a scanning tunneling microscope, a beam electron emission microscope, or for field emission, by first thinning a tip of a first material, such as silicon. The tips are then reacted with a second material, such as atoms from an organic or ammonia vapor, at a temperature of about 1000° C.±200° C. and vacuum conditions for several minutes. Vapors such as methane, propane or acetylene will be converted to SiC or WC while ammonia will be converted to Si 3 N 4 . The converted material will have different physical, chemical and electrical properties. For example, a SiC tip will be superhard, approaching diamond in hardness. Electrically conductive tips are suitable for field emission.

Ultrasharp tips for field emission applications prepared by the vapor-liquid-solid growth technique

Abstract: A technique for preparation of ultrasharp tips, preferentially of silicon, useful for field‐emission research and applications is described. Regular arrays of tips, as well as triodelike microstructures (‘‘Spindt cathodes’’), can be prepared in such a way. In addition, high‐aspect‐ratio tips suitable for field‐ion microscopy and field‐electron microscopy can be prepared by this technique. Finally, a version of the technique allowing to prepare special‐shape probes for scanning tunneling microscopes and related instruments is given.

Influences of gases on the field emission

Abstract: Influences of gases on the field emission were measured using the specimens of Spindt‐type Mo field emitter array. Gases were introduced into a vacuum chamber where the specimens were driven with pulse and dc voltages to emit electrons. In case of pulse drive, effects of N2 , H2 , Ar, or CO2 on emitter arrays could hardly be observed until the vacuum level reduced to 5×10−6 Torr. When the vacuum level was recovered to the background level, emission showed the recovery to be almost the same value as that before gas introduction. When pulse driven, a small amount of H2 gas reduced the work function of the emitter surface and increase the emission characteristics of emission array. In case of dc drive, on the other hand, emission began decreasing at 10−7 Torr. The introduction of SO2 led to the decrease of emission to ∼70% of the initial value at 5×10−6 Torr because of the contamination of emitter tips caused by SO2 when pulse driven. It was also clarified that CH4 , H2 , and CO adsorbed to emitters to reduc...

Method for making a silicon field emission device

Abstract: There is disclosed a silicon field emission emitter and a method for making a silicon field emission emitter which has a good electronic characteristic and a simplified making process. The silicon field emission emitter in accordance with the embodiment of the present invention includes a silicon substrate of high density, an insulating layer on the silicon substrate of high density, a cavity formed in the insulating layer, an emitter formed with the silicon substrate of high density in a body in the cavity, and a gate electrode formed on the insulating layer. The insulating layer is made of the thermal oxide film having the thickness of 4000 angstroms and the gate electrode coats the emitter tip.

Nanosources and manipulation of atoms under high fields and temperatures : applications

Abstract: Part 1 Introduction: Local Probe Methods and Miniaturization. Part 2 Nano-sources and Applications: Low Energy Electron Microscopy. Nanotips and Transmission Low Energy Electron Diffraction. Lensless Low Energy Electron Point Source Microscopy. Electron Focusing - Computer Simulation. Nanotip Fashioning and Nanosource Characteristics. Electron Emission from Nanometer-Size Metallic Clusters - Electronic States and Structural Stability of Supported Au Clusters. On the Energy Dissipation in Field Emission and Tunneling Microscopy. Miniaturized Electron Microscope. Direct Observation of the Motion of Individual Surface Atoms on a Picosecond Timescale. Single-Electron Manipulation under High-Field at Room Temperature. Focused Ion Beams and their Applications in Microfabrication. Miniaturized Liquid Metal Ion Sources (MIL-MIS). Integrated Microtips - Application to Flat Displays. Part 3 Tip-Surface Interactions and Applications - Field-Induced Transfer of an Electropositive Atom between Two Closely Spaced Electrodes. Molecular Dynamics Simulations of Metal Surfaces - Surface Melting and Non-Melting, and Tip-Surface Interactions. Atomic Manipulation using Field Evaporation. What is Underneath? Moving Atoms and Molecules to Find Out. Local Experiments using Nanofabricated Structures in STM. Quantum Atom Switch - Tunneling of Xe Atoms. The Eigler Xe Switch - its Atomic Structure from Xe Energy Minimization and STM Image Calculations. Friction and Forces on an Atomic Scale. Atomic-Scale Adhesion. Local Modification of Langmuir-Blodgett Films by AFM. Layered Semiconductors as Materials for (sub)Nanometer Scale Surface Modification with the STM. Micromachined Silicon Tools for Nanometer-Scale Science.

Analysis of a diode with a ferroelectric cathode

Abstract: It has been shown experimentally that electron current densities of more than 30 A/cm2 can be achieved from a cathode made of ferroelectric ceramic, when applying a field of order 0.1 MV/m. This current exceeds the Child–Langmuir current by two orders of magnitude. The current in the diode varies linearly with the applied voltage, provided that the latter is positive. In this theoretical study we show that the ferroelectric material plays a crucial role in the emission process. When a voltage is applied to the ferroelectric, the internal polarization field varies and the amount of screening charge required decreases. As a result, the electrons distribution near the cathode changes, forming a cloud which fills part of the diode gap. If now a positive voltage is applied to the anode, electrons are readily transferred through the diode gap. The qualitative and quantitative results of the theory are in good accordance with the experiment.

Emission characteristics of metal-oxide-semiconductor electron tunneling cathode

Abstract: We have fabricated a metal–oxide–semiconductor (MOS) electron tunneling cathode with ultrathin SiO2 and examined the emission characteristics. We found that the emission occurred from an entire gate area by electron tunneling through the potential barrier in the MOS diode and the emission current was 0.7% of the total current flowing through the diode. The emission was also found to be nearly independent of pressure.

A proposal of a vacuum micro quantum interference transistor

Abstract: A quantum interference transistor that can be fabricated by available technology and can operate at room temperature is proposed. This device uses the phase interference effect of a vacuum electron that is not influenced by thermal fluctuations, in contrast to an electron in solid‐state materials. The device consists of a field emitter, a collector, and segmented capacitors between the emitter and the collector. The capacitors control electron trajectories and the phase interference of the electron in vacuum by their electrical potential. This quantum interference effect is found not to be the same as the Aharonov–Bohm effect contrary to our expectations. We are convinced that the new transistor is capable of room‐temperature operation because the large kinetic energy of the electron in vacuum suppresses energy fluctuations caused by the field emission itself and by thermal fluctuations in the emitter material to about 50 meV. The switching time of the transistor is limited in order to average the number ...

Brightness measurements of nanometer-sized field-emission-electron sources

Abstract: The brightness of nanometer‐sized field‐emission‐electron sources have been measured experimentally. Ultrasharp tungsten (111) single‐crystal tips were fabricated in situ using Ne sputtering and field evaporation, and monitored using field ion microscopy. The average brightness of single‐atom‐terminated nanotips was found to be 3.3×108 A cm−2 sr−1 at 470 V, or 7.7×1010 A cm−2 sr−1 when extrapolated to 100 kV. These results show an improvement of about two orders of magnitude in source brightness over existing cold field‐emission‐electron sources, and produce a beam with greater particle flux per unit energy than those obtainable using current synchrotron/wiggler/undulator devices.

Rates of Electron Emission from Negatively Charged, Impact-Heated Fullerenes

Abstract: Thermal emission of electrons is ordinarily considered to be exclusively a property of macroscopic condensed matter. Slow electron emission occurs for certain small metal clusters as well as for silicon and carbon clusters, but the nature of this process has not been established. Electron emission rates have been obtained and analyzed from extensive real-time measurements on negatively charged fullerenes for several sizes and over a wide, continuous range of energies. These results confirm that delayed electron emission is a simple activated process that depends strongly on the internal energy and size of the cluster and that it has a common underlying mechanism, independent of size. However, the Arrhenius form deduced is inconsistent with the emission rate theory used for bulk surfaces. These results allow the question of the correct microscopic description of this newly observed electron emission process to be assessed.

Field‐emitter array performance enhancement using hydrogen glow discharges

Abstract: The changes in the current‐voltage characteristics and electron emission spatial distribution of microfabricated field emitters following exposure to hydrogen low‐pressure glow discharges have been investigated. The hydrogen discharge was found to result in a work function decrease typically between 0.5 and 1.5 eV following a dose of 1018–1019 ions/cm2. The net result is a reduction in the operating voltage and an improvement in the spatial uniformity of the electron emission.

Trace elemental analysis at nanometer spatial resolution by parallel-detection electron energy loss spectroscopy.

Abstract: Parallel-detection electron energy loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM) and a field emission source provides an unprecedented sensitivity for elemental microanalysis. By deflecting the energy loss spectrum across a parallel detector and computing the difference spectrum from sequentially collected energy-shifted spectra, the effects due to detector pattern noise are nearly eliminated so that signals less than 0.1% of the background can be readily detected. Measurements on a series of glass standard reference materials show that EELS provides both high spatial resolution and trace sensitivity at the 10 atomic ppm level for a wide range of elements including the alkaline earths, 3-d transition metals, and the lanthanides. For analytical volumes with dimensions of the order of 10 nm, this translates into near-single atom detectability.

Influence of cathode material on emission characteristics of field emitters for microelectronics devices

Abstract: In order to find out the cathode material suitable to vacuum microelectronics devices, dependence of cathode material of field emitters was investigated with respect to the emission characteristics. Since the field emitters for vacuum microelectronics devices are fabricated by thin film processes, the characteristics of the electron emission from deposited materials should be examined. In the present study, a dozen materials were deposited onto the tungsten needle fabricated by well‐controlled electrochemical etching. Measurement of the emission was performed at the pressure of 10−9 Torr range. The current–voltage characteristics and the stability measurements revealed that the gold emitters indicated excellent properties: stable and high current at low extraction voltage. The effective surface work function and the effective emission area were evaluated from the Fowler–Nordheim theory, assuming that the emission area rapidly decreases with reducing the apex radius. From this analysis, it is clarified that the gold emitter had the lowest effective work function among the examined emitters. The results can be interpreted as that in order to obtain stable emission characteristics, materials with inert surface should be selected.

Aberrations of emission cathodes: Nanometer diameter field-emission electron sources

Abstract: The electron optical properties of nanometer sized field‐emission cathodes are examined for suitability as electron sources for low‐voltage scanning electron microscopy, low‐voltage transmission point projection microscopy, and low‐voltage transmission and reflection electron holography. First‐order electron optical properties, aperture and chromatic aberrations, and source coherence are computed using an all‐orders numerical method, and compared with analytically computed properties where possible. The electron optical properties of planar emitters, conventional field‐emission tips, and new nanotip structures are compared in the absence of space‐charge effects. It is found that the spherical and chromatic aberrations of nanotips are dominated by their base structures and that beams produced by nanotips can be considered as totally coherent.

Role of space charge in field emission cathodes

Abstract: Space charge plays an extremely important role in thermionic vacuum tubes. Normally it can be neglected in the operation of field emitter cathodes because the very high electric fields at the cathode negates the formation of space charge. However at very high current densities, it may be evident in field emission cathodes. This article explores the region where space charge affects the potential distribution in field emission cathodes of the type proposed for use in vacuum microelectronics applications. Rectangular, cylindrical, and spherical geometries are considered.

Influence of cathode material on emission characteristics of field emitters for microelectronics devices

Abstract: In order to find out the cathode material suitable to vacuum microelectronics devices, dependence of cathode material of field emitters was investigated with respect to the emission characteristics. Since the field emitters for vacuum microelectronics devices are fabricated by thin film processes, the characteristics of the electron emission from deposited materials should be examined. In the present study, a dozen materials were deposited onto the tungsten needle fabricated by well‐controlled electrochemical etching. Measurement of the emission was performed at the pressure of 10−9 Torr range. The current–voltage characteristics and the stability measurements revealed that the gold emitters indicated excellent properties: stable and high current at low extraction voltage. The effective surface work function and the effective emission area were evaluated from the Fowler–Nordheim theory, assuming that the emission area rapidly decreases with reducing the apex radius. From this analysis, it is clarified that the gold emitter had the lowest effective work function among the examined emitters. The results can be interpreted as that in order to obtain stable emission characteristics, materials with inert surface should be selected.

Emission characteristics of silicon vacuum triodes with four different gate geometries

Abstract: Arrays of 10*10, 30*30, and 50*50 phosphorus-doped 0.005-0.025 Omega -cm, monocrystalline silicon field emitters have been fabricated with an emitter height of approximately 4.5 mu m, a cone angle of 110 degrees , and four gate openings ranging from 1.8 to 5.3 mu m. The placement of the rims of the gates range from coplanar with the apexes of the emitters for the 1.8- mu m devices to fully recessed for the 5.3- mu m devices. The devices have been characterized in terms of geometry-dependent beta factors, scaling of emission currents with array size, temperature dependency from room temperature to 48 K, pressure dependency from 2.5*10/sup -9/ to 0.8*10/sup -5/ torr, current fluctuations at room temperature and at 48 K, and image formation. All of the measurements have been performed by operating the devices in the gate-induced field emission mode. >