Showing papers on "Field electron emission published in 1990"

Formation of silicon tips with <1 nm radius

Abstract: Electron emitters in vacuum microelectronic devices need sharp tips in order to permit electron emission at moderate voltages A method has been found for preparing uniform silicon tips with a radius of curvature less than 1 nm These tips are formed by oxidation of 5‐μm‐high silicon cones through exploitation of a known oxidation inhibition of silicon at regions of high curvature

Cold cathode field emission device with integral emitter ballasting

Abstract: A cold cathode field emission device that includes a ballast resistor (202, 303, 402) integrally formed therewith and coupled to the emitter (204, 302, 403) to allow appropriate compensation for manufacturing and performance variations in field emission from the attached emitter.

Field emission device having preformed emitters

Abstract: A field emitting device having a plurality of preformed emitter objects (201, 301). The emitter objects include sharp geometric discontinuities, and a significant number of these geometric discontinuities are oriented in a way that supports desired field emission activity. Field emission devices built with such emitters can be utilized to provide a flat display screen (Fig. 4).

Microminiaturization of electron optical systems

Abstract: The performance of miniaturized electron optical systems comprising a field emission microsource and a microlens for probe forming has been studied. A complete system measuring millimeters in length and diameter with performance exceeding that of a conventional system over a wide range of potentials (100 V–10 kV) and working distances (up to 10 mm) appears to be feasible. A scanning tunneling microscope aligned field emission microsource offers performance well suited for this application and a selective scaling approach has been developed to allow a wide range of potentials to be applied. Such miniaturized systems can be of significant importance to many areas of electron‐beam applications.

Field emission device display with vacuum seal

Abstract: A field emission display constructed from field emission devices, (which are typically fabricated on silicon substrates but which are difficult to seal to pressure levels below 1×10 -6 Torr because they are fabricated on silicon), can be enclosed in an evacuated volume, sealed using a glass frit, when an appropriate interface layer is first formed on the substrate for the field emission devices.

Simulation and design of field emitters

Abstract: Electron emission characteristics for the cone and wedge generic field emitter structures are described. Effects of variations in emitter geometry on electron current, spectral and temporal dispersion of electron emission, and emitter heating are calculated analytically and by computer simulation. Several guidelines for emitter design are suggested. >

High-resolution simulation of field emission

Abstract: High-resolution simulations of field emission electron sources have been made using the electron optics program EGN2. Electron emission distributions are made using the Fowler-Nordheim equation. Mesh resolution in the range of 1-5 {angstrom} is required to adequately model surface details that can result in emission currents in the range found experimentally. A typical problem starts with mechanical details with dimensions of about 1{mu}. To achieve high resolution a new boundary is defined by the tip, a nearby equipotential line, and a pair of field lines. The field lines (one of which is normally the axis of symmetry) define Neumann boundaries. This new boundary is then used by the boundary preprocessor POLYGON to create an enlarged version of the problem, typically by a factor of ten. This process can be repeated until adequate resolution is obtained to simulate surface details, such as microprotusion, that could sufficiently enhance the surface electric fields and cause field emission. When simulating experimental conditions under which emission of several microamperes per tip were observed, it was found that both a locally reduced work function and a surface protrusion were needed to duplicate the experimental results. If only a local region of reduced work function is used,more » the area involved and the extent of the reduction both need to be very large to reproduce the emission. If only a surface protrusion is used, it is possible to get the observed emission current with a reasonable protrusion of length a few times radius, but then the resulting beam spreads over a very large solid angle due to the strong local radial electric fields. 8 refs., 14 figs., 1 tab.« less

Imaging of dislocations using backscattered electrons in a scanning electron microscope

Abstract: A field-emission-gun scanning electron microscope (FEG SEM) has been fitted with a back-scattered electron detector in order to image dislocations by the electron channelling contrast mechanism. By using an efficient detector, optimizing its orientation with respect to the specimen and the incident beam, and applying an image-enhancement technique, it has been possible to image and characterize dislocations near the surface of bulk samples of a number of materials without the need of an electron-energy filter in front of the detector. Examples are presented of preliminary studies of dislocations in Si and Ni, Ga; the image widths are typically 20 nm, and the normal g·b = 0 invisibility criterion for screw dislocations applies. By dispensing with the electron-energy filter used by Morin et al., the design and operation of the system become very simple, and the technique should become available in commercial FEG SEMs. This non-destructive technique is likely to have wide applications to situations ...

A Simulation of Electron Scattering in Metals

Abstract: A Monte Carlo calculation model is developed to simulate trajectories of primary and ionized electrons in metals. It is constructed especially for a quantitative analysis of images in the scanning electron microscope. We perform a direct simulation considering each differential scattering cross section for elastic scattering, inner-shell electron ionization, conduction band electron ionization and bulk plasmon excitation. The spatial distribution of secondary electron emission calculated is narrower than that of backscattered electron emission at the Al surface for 1 keV primary electrons, but depending on the condition, this tendency may not always be found. The spatial distributions of both secondary and backscattered electrons show the size effect, and if the specimen to be observed is smaller, the practical resolution will be better in the scanning electron microscope.

Kinetic ion-induced electron emission from the surface of random solids

Abstract: This is a review of the published papers devoted to kinetic ion-electron emission from the surface of polycrystalline and amorphous solids. It contains the analysis of energy, angular, temperature, and other dependences of the ion-electron emission coefficient as well as of the energy and angular distributions and the statistics of electron emission events. We also give a brief account of the theoretical studies on the subject.

Composition and structure of native oxide on silicon by high resolution analytical electron microscopy

Abstract: Compositional analysis of thin nanoscale native oxide films formed on {001} silicon wafer surfaces at room temperature was done with an electron energy loss spectrometer coupled to an analytical electron microscope having a field emission source, with better than 4 nm spatial resolution. The electron energy loss spectra show a shift in the threshold onset energy of the Si–L edge of the native oxide from ∼99 eV loss corresponding to pure elemental silicon to ∼105 eV loss, and elemental analysis using the ionization regions of the core loss edges showed the composition to be SiO, within a few percent. Microdiffraction and high resolution electron microscopy (HREM) results showed that the native oxide was completely amorphous, and did not contain detectable nanocrystals. The native oxide can be removed from the Si surface by heating in UHV for a short time at 1000 °C. However, this procedure resulted in the formation of small amounts of a crystalline phase on the Si wafer surface, which was shown to be β-SiC by the same methods.

Electron field emission device

Abstract: An electron emission device is employed as an electron emission source in various applications using an electron beam. The electron emission device has a cathode layer having an edge, and a control electrode spaced and electrically insulated from the cathode layer, for drawing electrons from said edge of the cathode layer. When a voltage is applied between the cathode layer and the control electrode, a developed electric field is concentrated on the edge of the cathode layer to cause the edge to emit electrons. The electron emission device can easily be manufactured with a high yield since it does not have a needle tip for emitting electrons. A method of manufacturing the electron emission device is also disclosed.

Oxygen-induced sharpening process of W(111) tips for scanning tunneling microscope use

Abstract: Atomic resolution in scanning tunneling microscopy is usually obtained by a trial and error procedure for formation of the tunneling tip. The success of such attempts is particularly small when rough and contaminated surfaces have to be measured, where the macroscopic tip radius must be as small as possible in order to obtain a reasonable image of the sample. Here we report on a method by heating the tip in an oxygen atmosphere without an electric field, which routinely allows the generation of W(111) tips with an average tip radius of <2 nm. The sharpening of W tips by oxidation and annealing has already been reported by Muller [Z. Physik 108, 668 (1938)]. We have studied the mechanism of tip sharpening by scanning electron microscopy and in situ by field emission and field ion microscopy. The main effect is a preferential removal of (110)‐like planes, which gives rise to strong facetting of the tip apex and the formation of sharp W microtips. The arrangement of microtips is essentially determined by the...

Field emitter tips for vacuum microelectronic devices

Abstract: The design criteria for two forms of field emitters (cone and wedge) for vacuum microelectronic applications are discussed. Effects of practical variations in geometry on emission current, spatial and temporal dispersion of electron emission, and emitter heating are calculated by simulation. Several design guidelines for the geometry of the emitter–anode complex are suggested. A sharp silicon tip processing method is presented, which is based on the oxidation inhibition of silicon at regions of high curvature. Methods for forming emitters of other materials are also discussed.

Emission of electrons on switching of the Gd2(MoO4)3 ferroelectric‐ferroelastic in electric field

Abstract: We have revealed an electron emission on the switching of extrinsic gadolinium molybdate ferroelectric‐ferroelastic in electric field. Visualization of the electron flow allows directly watching of the domain structure dynamics: formation and growth of tapered domains and lateral movement of the 180° domain wall. We have found that the electron emission contributes substantially to the screening processes in the case of a crystal with free surface.

Thermal field emission observation of single-crystal LaB6

Abstract: TFE (thermal field emission) properties of LaB6 〈100〉 and 〈310〉 single crystals were investigated by emission pattern observation. It was found that field evaporation with the tip temperature held at ∼1500 °C is very useful to get a clean pattern of fourfold symmetry. Each of four bright spots in the clean pattern was presumed to correspond to 〈310〉 emission. It is proposed, as the most appropriate operating condition, to use the 〈310〉LaB6 tip at a temperature ∼1000 °C in vacuum of 10−9 Torr region, promising a new TF emitter of high brightness and stability for practical use.

Long pulse CsI impregnated field emission cathodes

Abstract: Intense pulsed electron beams are produced by applying a voltage between an anode and a cathode in a vacuum diode. The average field can be as low as 10 kV/cm, depending on the cathode material. This field is much less than predicted by the Fowler–Nordheim equation for field emission. The source for the electrons is a plasma that forms on the cathode which has a zero or very low work function. This plasma propagates into the anode–cathode gap and as a result lowers the impedance and eventually shorts the diode. The impregnation of the cathode surface with CsI was found to delay the onset of the diode impedance collapse. The time behavior of the impedance of a diode driven by 400‐kV, 1‐μs pulse was investigated. Three cathode materials with and without CsI were evaluated.

Study of field‐emitting microstructures using a scanning tunneling microscope

Abstract: Field emission from broad metal cathodes is known to be strongly enhanced at a small number of emitting sites per cm2 compared to the expected Fowler–Nordheim emission from ideal, flat surfaces. We have operated a scanning tunneling microscope (STM) in the field emission regime (typical tip voltage: +80 V) and measured the local field emission strengths and variations on niobium samples. With a modulation technique, which is an adaptation of the standard work function measurement, maps of the field enhancement factor β have been obtained. An example of an emission site is presented where STM topograph and β map are compared with a secondary electron microscope image and with field emission data obtained in a standard way using high‐voltage anodes. This demonstrates the capability of a scanning tunneling microscope to localize enhanced field emission sites (with typical β values of 50 in the present work) with high spatial resolution and to study surfaces down to the limit β=1.

Vacuum microtriode characteristics

Abstract: Pentode‐like I–V characteristics are simulated for lateral vacuum microelectronic devices with wedge‐shaped field emission cathodes. A single grid provides electrostatic isolation between the cathode and anode for a large equivalent anode series resistance. Device characteristics are presented for a structure with a field emission cathode, one control grid, an anode, and two trajectory deflection electrodes. The cathode‐to‐control grid separation for trajectory simulation is a nominal 1 μm and the emission tip radii are 0.01 and 0.05 μm. The device length including deflectors is 18 μm. Device characteristics are modelled over an anode potential range of 10–200 V. At 50 V anode potential, a transconductance of 4 μ S/mm and 0.1 S/mm is calculated based on 0.05 and 0.01 μm wedge radii, respectively.

Flat panel display using field emission devices

Abstract: A flat screen display constructed through use of cold cathode field emission devices (112), wherein the devices (112) serve to support the structural integrity of the resultant assembly, and wherein edge emission is utilized to energized luminescent material in support of the display function

Cascaded cold cathode field emission devices

Abstract: Field emission devices are cascaded in multiple stages, such that certain structures function as electrodes for field emission devices of differing stages.

Field emission from submicron emitter arrays

Abstract: The authors describe the preparation and emission characteristics of emitter tips with fourfold symmetry based on the mold techniques of H.F. Gray and R.F. Greene. By appropriate selection of film thicknesses, grid to emitter spacing of less than 0.5 mu m was achieved. The authors have prepared and studied the emission characteristics of several geometries that include emitter tips above and below the plane of the grid with grid to emitter spacings ranging from 0.4 to 1.0 mu m. Onset of emission was observed at grid potentials as low as 10 V with Fowler-Nordheim-like emission characteristics. Emission current vs voltage measurements over the temperature range 300 K to 450 K showed no detectable change in characteristics as expected in field emission. Stable current densities of 0.5 A/cm/sup 2/ (500 nA/tip) have been obtained and illumination of a phosphor anode has been demonstrated. >

Temperature dependence of the resistance in the pt/ti nonalloyed ohmic contacts to p-inas induced by rapid thermal processing

Abstract: The temperature dependence of the resistance in the Pt(60 nm)/Ti(50 nm) nonalloyed ohmic contacts to p‐InAs (Zn doped 1×1018 to 1×1019 cm−3 ) induced by rapid thermal processing in the temperature range of 300–600 °C was studied. The ohmic nature of these contacts was attributed to both the low metal‐semiconductor interfacial barriers and to the heavily doped semiconductor contacting layers. A phenomenological model was used to fit the measured temperature dependence contact resistance. The results indicated conversion from thermionic emission as the dominant carriers transport mechanism across the interfacial barrier for the as‐deposited sample to a combination of thermionic and field emission mechanism for the heat‐treated samples.