Showing papers on "Field electron emission published in 1989"

Automatically focusing field emission electrode

Abstract: Several embodiments of a thin film field emission cathode array are described which automatically shape the beams of emitted particles, without the addition of shaping or other electrode structure. A potential field pattern is established to control the trajectory of the emitted particles, by controlling the electromagnetic interaction of the conductive structures responsible for the particle emission.

Transport of electrons in nonpolar fluids

Abstract: Electron transport in nonpolar fluids has been investigated for several decades. At first the emphasis was on liquified rare gases, and later on excess electrons were also studied in molecular liquids such as alkanes. Now mobility data are available for approximately 75 nonpolar liquids ( 1). Progress in this field was hampered initially by impurities like O2, CO2, and various electrophilic compounds in the liquids. The availability of adequate methods of purification has stimulated experimental studies. Some new compounds have been studied recently, and new experimental techniques are being applied. Innovative theoretical approaches are now being tried. These efforts will eventually provide a better understanding of the basic problems of electron scattering and localization in liquids. Excess electrons can be introduced in liquids either by ionization or by injection. Ionization may utilize single or multiphoton absorption or high energy radiation. Injection can be from a cathode immersed in the liquid (photoelectric effect) or by field emission. Most studies of electron trans­ port require a short excitation pulse. The electrons produced thereby can be monitored by a number of techniques (2). One is that of DC conduc­ tivity. Even though ions may be concomitantly formed, electrons move much faster than molecular ions, therefore the current at short times is due to the motion of the electrons. Another technique is that of microwave

An electron source of the field emission type

Abstract: The invention relates to an electron source (20) formed of at least one elementary electron emitter (31, 31b) comprising an emissive tip (34) having a very small radius of curvature and operating in accordance with the field emission principle. The invention applies particularly in the case of constructions employing technologies used for integrated circuits or in the area of thin-layered films, these technologies enabling a plurality of elementary emitters to be produced on one substrate. The aim of the invention is in particular to enable an electron beam (F1) to be produced, the intensity of which is independent of possible variations in electron emission by the emissive tip 34. The emissive tip (34) interacts with an extractor electrode (27), and according to a characteristic of the invention, a control electrode (29), having a negative potential relative to the extractor electrode (27), is arranged downstream of this latter in relation to the sense of propagation (41) of the beam (F1).

Conduction mechanisms in sputtered Ta2O5 on Si with an interfacial SiO2 layer

Abstract: The temperature dependence of leakage in sputtered Ta2O5 films (10–30 nm) on Si substrates with an interfacial SiO2 layer has been studied for temperatures between –50 and +100 °C and for electric fields between 0 and 2 MV/cm. The activation energy of leakage and the current‐voltage relationships have been used to identify various high field conduction mechanisms such as Poole–Frenkel transport at high temperatures and field emission at low temperatures. At low fields and intermediate temperatures, electronic hopping conduction leading to space‐charge‐limited flow at high current densities has been observed.

Solid state electron amplifier

Abstract: A microscopic voltage controlled field emission electron amplifier device consists of a dense array of field emission cathodes with individual cathode impedances employed to modulate and control the field emission currents of the device. These impedances are selected to be sensitive to an external stimulus such as light, x-rays, infrared radiation or particle bombardment; so that the field emission current varies spacially in proportion to the intensity of the controlling stimulus. When a phosphorus screen or other suitable responsive element is provided, the device functions as a solid state image convertor or intensifier.

Method for the fabrication of field emission type sources, and application thereof to the making of arrays of emitters

Abstract: Disclosed is a method for the fabrication of field emission peaks using a monocrystalline substrate with a suitable orientation coated with an insulating layer where square-shaped elementary zones with a suitable orientation with respect to the substrate have been removed. Silicon is deposited by selective epitaxy in these zones. The epitaxial growth of silicon, at high speed parallel to the substrate and at low speed along faces of the substrate at 45° to the substrate, enables the making of pyramidal peaks which, afater being coated with tungsten, form emitting peaks.

Spin‐polarized secondary electrons from a scanning tunneling microscope in field emission mode

Abstract: A new technique has been developed which opens the way to magnetic imaging with nm resolution A narrow electron beam produced with a scanning tunneling microscope operating in field emission mode impinges on the magnetic surface, and the spin polarization of the emitted secondary electrons is monitored As a first result, a hysteresis loop from an Fe‐based metallic glass shows that the low‐energy secondary electrons excited with this technique are spin polarized

Voltage shifts of Fowler-Nordheim tunneling J-V plots in thin gate oxide MOS structures due to trapped charges

Abstract: This paper describes a novel simulation of Fowler-Nordheim (F-N) tunneling of electrons from either tunneling interface, i.e. from the gate or the inversion layer of a p-type substrate into the oxide. It accounts for the effects of finite electron-hole pairs generation in the substrate and shapes of tunneling barrier created by charge trapped in the oxide for F-N tunneling.

Thermal relaxation of a laser illuminated field emitter

Abstract: The time dependence of the total emission current from a field emitter illuminated by a chopped cw laser beam has been measured in conditions where the emission of primary photoelectrons is negligibly small. When the laser beam is switched on, the emission current increases with a characteristic time that is found to be in close agreement with the thermal relaxation time of the field emitter, showing that the laser‐induced increase in emission is primarily due to tip heating. The large temperature rise and short thermal relaxation time associated with laser heating make it a widely applicable technique for controlling the temperature of a field emitter.

Electron optical performance of a scanning tunneling microscope controlled field emission microlens system

Abstract: Use of a scanning tunneling microscope (STM) controlled field emission tip in conjunction with microlenses has been explored to form an exceptionally high brightness electron source and low aberration beam forming system at the low‐keV energy range. In its basic configuration, the STM feedback principle is used for precision x, y, and z alignment of tip to microlens to form a self‐aligned field emission (SAFE) microsource. The microlenses can be made using microfabrication techniques on silicon or other suitable substrates with dimensions reduced by approximately three orders of magnitude from those of conventional lenses. As the lens aberrations generally scale with lens dimensions, such lenses can be designed to have negligible aberrations thus allowing exceptionally high brightness and resolution to be achieved. This paper discusses the electron optical performance of such a microsource and its applications with other microlenses as beam forming systems.

Studies of individual nanometer‐sized metallic clusters using scanning tunneling microscopy, field emission, and field ion microscopy

Abstract: Individual clusters of gold, grown in a gas aggregation reactor and deposited on a variety of different substrates, have been studied using a combination of scanning tunneling microscopy, field emission techniques, and field ion microscopy. The scanning tunneling microscope studies show that by proper choice of substrate, individual nanometer‐sized clusters can be reproducibly imaged and studied. The field emission and field ion microscope studies yield information about the work function and melting temperature of individual supported clusters.

Field-emission properties of surface-processed TiC tips

Abstract: Surface-processed TiC(110) tips have been developed to obtain highly stable emission as a cold field-electron emission source. The surface processing consists of heating the tip at 1000-1100 degrees C in a gas such as ethylene, oxygen or hydrogen sulphide, and the subsequent continuous emission of 10 mu A for 30 minutes. The field-emission pattern and the current stability of surface-processed TiC(110) tips have been investigated for several kinds of surface processing.

A combination electron/ion field emission source

Abstract: A combination electron/ion field emission source will be described. For ion emission the source was operated as a conventional indium or gallium liquid metal ion source (LMIS), thereby giving a beam of principally In+ or Ga+ ions with the usual range of angular intensities and total emission currents. In the case of indium it was possible to ‘‘freeze in’’ the field stabilized Taylor cone formed during LMIS operation by carefully reducing the voltage to the threshold value and then rapidly reducing both the voltage and the emitter temperature. Field electron emission was then obtained by reversing the voltage polarity. The dc electron emission angular distribution generally overlapped that observed in the LMIS mode. This process, which was determined to be reversible and reproducible, will be discussed in detail.

A novel scanning tunneling microscope controlled field emission microlens electron source

Abstract: A field emission electron source that combines scanning tunneling microscope (STM) technology with a micromachined aperture has been explored. The STM is used to position the field emission tip over a metal aperture of 0.4–2.5 μm diam. An extraction voltage ranging from 50 to 200 V applied between the tip and the aperture results in the field emission of electrons, which pass through the aperture and can be collected on the other side. The aperture is fabricated on a silicon nitride membrane using electron beam lithography and reactive ion etching. Such a source can potentially provide a very bright, high current, low voltage source of electrons. The simple aperture can be replaced by a microlens consisting of a stacked structure of two or three thin film electrodes separated by thin film insulating spacers, and a compact, high performance electron source or complete optical system can be realized. While the concept of a miniature field emission cathode is well known, incorporation of an STM into the design gives several advantages. These include fine positioning of the tip with respect to the aperture, both vertically and horizontally; active feedback stabilization of the emission current by adjusting the tip position without changing the extraction voltage; and replacability of the tip. Source characteristics as a function of aperture diameter, tip radius, and extraction voltage as well as data on noise, lifetime, maximum total current, and operating pressure are presented. An accompanying paper will present detailed calculations of the electron–optical performance.

Influence of condensed gases on field emission and the performance of superconducting RF cavities

Abstract: In a program to study the field emission (FE) and to improve the performance of one-cell 1500-MHz superconducting Nb microwave particle accelerator cavities, the authors recently achieved peak surface fields as high as 51 MV/m through the use of 1200 degrees C UHV annealing, methanol rinsing, and high-power He processing. Performance is limited by excess FE from localized points on the cavity walls. Cycling of these cavities to room temperature and admission of He processing gas frequently produce large changes in Q correlating with the appearance or disappearance of the dominant field emitter, suggesting that condensed residual and impurity gases play a significant role in enhancing FE. By intentionally condensing O/sub 2/ into a cold cavity, the authors have produced similar effects, increasing the dissipated power and reducing Q, each by an order of magnitude at the same field level. Preliminary tests have also been carried out with H/sub 2/ and water vapor. These results suggest that improvements in the outgassing and vacuum environment of these cavities may be important. >

New field emission gun with energy filtering effect

Abstract: We have developed and tested a new kind of field emission gun. This electron gun is an energy filtering field emission gun that is able to reduce the energy spread of the beam. An energy spread as small as ΔE=0.16 eV full width at half maximum has been measured, at an accelerating voltage V=10 kV, for a probe current Ip=2.1 nA and an illuminating half‐angle α=1.2 mrad.

Application of ion-beam etching techniques to the fine structure of biological specimens as examined with a field emission SEM at low voltage.

Abstract: The term “etching,” in electron microscopy, refers to the removal of specimen surface layers and includes chemical, electrolytic, and ion-beam methods. The ion-beam etching process is used to remove layers of a target material by bombarding it with ionized gas molecules. Recently, the method has been applied to the field of biological specimens; however, the practical procedures for such organic materials have not been developed. In the present study, we used an apparatus in which a beam of argon ions is collimated and focused by electrostatic lenses onto an appropriate target. We demonstrated the optimum conditions to observe biological specimens that were treated with osmium tetroxide and tannic acid. The specimens were examined uncoated at low accelerating voltage using a field emission scanning electron microscope. According to our experiments, when a biological specimen was observed under high-resolution conditions at over 50,000x magnification, the optimum condition of ion-beam etching consisted of an accelerating voltage of E = 1 keV and an ion-beam dose of It = 360 ∼ 400 μA. min, depending on parts of the specimens. In order to decrease overetching, we had to choose factors such as E = 1 ∼ 2 keV and It = 500 μA. min.

Preparation and characterization of zirconium carbide field emitters

Abstract: The authors report on experiments to determine the feasibility of using the refractory transition metal carbide ZrC as a stable field-emission cathode. Emphasis is on the preparation and analysis of methods needed to obtain stable electron emission from a cold field-emission cathode. ZrC single-crystal specimens were prepared by arc floating zone refinement from sintered stock, yielding an average bulk stoichiometry of C/Zr=0.913. Due to its brittle nature and the high temperatures required for cleaning of this carbide, new mounting methods were developed. Emitter etching procedures are reported for ZrC, as well as in situ tip sharpening techniques of neon-ion bombardment and temperatures required for thermal cleaning. A temperature of 1500 degrees C is required to remove adsorbates including oxygen. A clean ZrC field-emission pattern is shown. Ordering of work functions of various crystal planes is reported through field-emission microscopy, and comparisons are made with thermionic projection microscopy. Effective thermionic work functions are presented for clean surfaces to support further the ordering obtained. The ability of ZrC field emitters to operate at pressures far above those commonly found for field-emission cathodes is demonstrated. >

Application of a scanning tunneling microscope to field emission studies

Abstract: The authors present a scanning tunneling microscopy (STM) of a novel design, which has been integrated into their field-emission scanning microscope. It has been developed for large-area scans (50 mu m*50 mu m) with site selection under scanning electron microscopy (SEM) control and subsequent zooming to high-resolution STM scans. The authors show that significant images of relatively large areas can be obtained. Initial field-emission scans indicate that topography can be distinguished by the field-emission behavior of a surface. The lowest beta values observed on an arbitrarily chosen spot on a niobium samples were on the order of 1.6. The remaining difference from the ideal case of beta =1 is unexplained. >

Secondary electron emission in the course of the first Trichel-like pulse development in N/sub 2/+SF/sub 6/ mixtures

Abstract: Waveforms of the first negative corona current pulses in 70% N/sub 2/+30% SF/sub 6/ mixture at a pressure of 13.33 kPa were investigated as a function of applied gap voltage. Based on the observed changes of the pulse shape, the role of different emission processes in the course of the discharge development was elucidated. At corona threshold, the pulse took the form of a simple hump, consistent with secondary electron emission due to positive-ion impact. A small increase in gap voltage resulted in the formation of a double-peaked pulse form which can be explained in terms of independent photoemission and secondary emission due to positive-ion bombardment. At higher voltage values (1.5 to two times higher than the corona threshold voltage), a peculiar form of the current pulse leading edge was observed and tentatively has been attributed to a field emission. >

On electrical breakdown in superconducting accelerating cavities

Abstract: Recent results on electron loading in superconducting cavities are presented and are compared with observations in DC field emission. It is shown that electron loading is the main obstacle to achieving accelerating fields higher than 10 MV/m. Multipactor electron loading, which may limit the accelerating fields, can be processed away, but processing times might be long. There exists experimental evidence that accelerating fields of 10 MV/m can be reproducibly obtained in storage-ring accelerating multicell structures. New diagnostic tools developed for superconducting RF cavities have contributed to the knowledge of electron emission in broad areas. Experimental results in DC and RF field emission are very similar. A simple statistical model, with an exponential increase of the number of emitters toward lower beta values, may explain the frequency dependence of field-emission electron loading observed so far. >

Method of operating an electron beam measuring device

Abstract: In modern electron beam measuring devices the thermal La/B6 or field emission source is replaced by a photocathode acted upon by a pulsed laser beam. Since the width of photoelectron pulses corresponds approximately to the width of the laser pulses, theses devices are particularly suitable for stroboscopic measurements in fast gallium arsenide circuits. The expenditure on apparatus for generating the photoelectron pulses is considerable since means for doubling the frequency of the primary laser light are necessary. It is therefore proposed to irradiate the cathode of the electron beam measuring device with photons of energy EPh