Showing papers on "Field electron emission published in 1994"

Carrier tunneling and device characteristics in polymer light‐emitting diodes

Abstract: In this paper it is demonstrated that the characteristics of light‐emitting diodes based upon MEH‐PPV [more fully known as poly(2‐methoxy,5‐(2’‐ethyl‐hexoxy)‐1,4‐phenylene‐ vinylene)] are determined by tunneling of both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes. It is shown that manipulating these offsets can control the useful operating voltage of the device as well as its efficiency. A model is developed that clearly explains the device characteristics of a wide range of diodes based upon MEH‐PPV. The turn‐on voltage for an ideal device is shown to be equal to the band gap, i.e., 2.1 eV for MEH‐PPV, and is slightly lower at 1.8 eV for an indium‐tin oxide/MEH‐PPV/Ca device. If there is a significant difference in the barrier height, the smaller of the two barriers controls the I–V characteristics, while the larger barrier determines the device efficiency. In indium‐tin‐oxide/MEH‐PPV/Ca devices, the barrier to hole injection is ...

Characterization and Application of Materials Grown by Electron-Beam-Induced Deposition

Abstract: Electron-beam-induced deposition of materials has been known for almost 40 years from contamination writing. It has developed into "additive lithography" with nanometer resolution employed in scanning electron microscopes, in dedicated lithography systems, in reducing image projection systems, and in scanning tunneling microscopes. The technique allows deposition of nanometer- to micrometer-size structures with nanometer precision in three dimensions without supplementary process steps such as lift-off or etching procedures. Depending on the deposition conditions, novel compound materials are created from organometallic precursors which form resistors with a resistivity ranging from 103 Ω cm to 2×10-3 Ω cm and sustain current densities higher than 5×105 A/cm2 without damage. High-resolution transmission electron microscope analysis of the deposits reveals a new class of nanocrystalline compound materials. Crystals of metals or metalcarbides and oxides are immersed in a matrix of carbonaceous material. The deposition process is compatible with conventional VLSI technology. Tips for atomic force and scanning tunneling microscopy can be produced with radii of curvature as small as 5 nm. Field electron emission is obtained from deposited tips starting at an extraction voltage of 8 V and yielding 180 µ A of current at 20 V. Three-dimensional conducting structures can be produced as sensors.

Fabrication of a diamond field emitter array

Abstract: A diamond field emitter array has been fabricated. by Chemical vapor deposition. Diamond was grown on an inverted pyramidal‐shape Si substrate followed by removal of the substrate. The fabricated array was placed in a high vacuum pumping system with the pressure of ∼10−7 Torr and the emission current as a function of the anode voltage was measured. The distance between the tungsten anode and the diamond surface was held constant at 100 μm throughout the measurement. As a result, a current larger than 10−4 A was obtained for an anode voltage of 6 kV. A linear relationship in the Fowler–Nordheim plot indicated the existence of electron field emission from the fabricated diamond field emitter array.

Electron emission from ferroelectrics - a review

Abstract: The strong pulsed emission of electrons from the surface of ferroelectric (FE) materials was discovered at CERN in 1987. Since then many aspects and properties of the method of generation and propagation of electron beams from FE have been studied experimentally. The method is based on macroscopic charge separation and self-emission of electrons under the influence of their own space-charge fields. Hence, this type of emission is not limited by the Langmuir-Child law as are conventional emission methods. Charge separation and electron emission can be achieved by rapid switching of the spontaneous, ferroelectric polarization. Polarization switching may be induced by application of electrical-field or mechanical-pressure pulses, as well as by thermal heating or laser illumination of the ferroelectric emitter. At higher emission intensities plasma formation assists the FE emission and leads to a strong growth of emitted current amplitude, which is no longer limited by the FE material and the surface properties. The most attractive features of FE emission are robustness and ease of manipulation of the emitter cathodes which can be transported through atmospheric air and used without any problems in vacuum, low-pressure gas or plasma environments. Large-area arrangements of multiple emitters, switched in interleaved mode, can produce electron beams of any shape, current amplitude or time structure. The successful application of FE emission in accelerator technology has been demonstrated experimentally in several cases, e.g. for triggering high-power gas switches, for photocathodes in electron guns, and for electron-beam generators intended to generate, neutralize and enhance ion beams in ion sources and ion linacs. Other applications can be envisaged in microwave power generators and in the fields of electronics and vacuum microelectronics.

New electron excited light emitting materials

Abstract: A range of bright, multicolor phosphor systems for field emission displays is reported. These include the standard ZnO:Zn and newer, narrow band emitting systems based on green ZnGa2O4:Mn and red CaTiO3:Pr. A modified, blue emitting ZnO:(Zn/Mg) and thin films of ZnGa2O4:Mn have also been prepared.

Metal‐oxide‐semiconductor field‐effect‐transistor substrate current during Fowler–Nordheim tunneling stress and silicon dioxide reliability

Abstract: The origin of the substrate current of a metal‐oxide‐semiconductor field‐effect transistor when the gate oxide undergoes Fowler–Nordheim stress is investigated. It is also shown that anode hole injection current predicts the breakdown of silicon dioxide between 25 and 130 A and 2.4 and 12 V. While the measured substrate current is entirely due to anode hole injection for oxides thicker than 55 A, tunneling by valence‐band electrons contributes to the substrate current in thinner oxides. Valence‐band electron tunneling current is shown to increase with oxide stressing similar to low‐voltage gate oxide leakage; apparently, both are enhanced by trap‐assisted tunneling. For oxides of thickness between 25 and 130 A, the theory of anode hole injection directly verified for oxides thicker than 55 A is able to model silicon dioxide breakdown accurately.

Theoretical study of field emission from diamond

Abstract: The electron field emission from diamond surfaces is investigated theoretically using a model consisting of the projection of the energy band surfaces in the 〈111〉, 〈110〉, and 〈100〉 emission directions The effect of the negative electron affinity, the band bending, the image interaction, and surface states is examined in detail It is found that the conventional theory of electron field emission applied to crystalline diamond cannot explain the measured high‐current emission at low fields We postulate two subbands in the intrinsic band gap, which may be generated by defects or impurities With reasonable band parameters, the calculated I‐V characteristics agree with experimental data

Electron emission from diamond coated silicon field emitters

Abstract: Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias‐enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.

Method of making field emission tips using physical vapor deposition of random nuclei as etch mask

Abstract: A method of making sub-micron low work function field emission tips without using photolithography. The method includes physical vapor deposition of randomly located discrete nuclei to form a discontinuous etch mask. In one embodiment an etch is applied to low work function material covered by randomly located nuclei to form emission tips in the low work function material. In another embodiment an etch is applied to base material covered by randomly located nuclei to form tips in the base material which are then coated with low work function material to form emission tips. Diamond is the preferred low work function material.

A diagnostic study of the field emission characteristics of individual micro-emitters in CVD diamond films

Abstract: Details are given of an experimental study of the characteristics of field-induced electron emission from 15 mm diameter CVD diamond films deposited on an Mo substrate. Three dedicated techniques have been used to characterize the electron emission process: (i) the 'transparent anode imaging' technique for recording the spatial distributions of emission sites and the total current-voltage (I-V) characteristic, (ii) the 'anode probe hole' technique for measuring the I-V characteristic of individual sites, and (iii) 'field emission electron spectroscopy' for studying the energy distribution of emitted electrons. Finally, the physical implications of the findings from the electron energy spectroscopy measurement are discussed.

Optimization of thin-film tips for magnetic force microscopy

Abstract: We report results of a quantitative investigation of MFM sensitivity vs. tip coating thickness. Etched Si tips on cantilevers 225 /spl mu/m in length were sputter-coated with Co-Cr films of various thicknesses 150 /spl Aring/ >

Nanometer scale patterning and oxidation of silicon surfaces with an ultrahigh vacuum scanning tunneling microscope

Abstract: Nanoscale patterning of the Si(100)‐2×1 monohydride surface has been achieved by using an ultrahigh vacuum (UHV) scanning tunneling microscope(STM) to selectively desorb the hydrogen passivation. Hydrogen passivation on silicon represents one of the simplest possible resist systems for nanolithography experiments. After preparing high quality H‐passivated surfaces in the UHV chamber, patterning is achieved by operating the STM in field emission. The field emitted electrons stimulate the desorption of molecular hydrogen, restoring clean Si(100)‐2×1 in the patterned area. This depassivation mechanism seems to be related to the electron kinetic energy for patterning at higher voltages and the electron current for low voltage patterning. The patterned linewidth varies linearly with the applied tip bias achieving a minimum of <10 A at −4.5 V. The dependence of linewidth on electron dose is also studied. For positive tip biases up to 10 V no patterning occurs. The restoration of clean Si(100)‐2×1 is suggestive of selective area chemical modifications. This possibility has been explored by exposing the patternedsurface to oxygen and ammonia. For the oxygen case, initial oxidation of the patterned area is observed. Ammonia dosing, on the other hand, repassivates the surface in a manner different from that of atomic hydrogen. In both cases the pattern resolution is retained and the surrounding H‐passivated areas remain unaffected by the dosing.

Electron emission from chemical vapor deposited diamond and dielectric breakdown

Abstract: After coating with a smooth, nonreactive, sputtered gold layer, previously nonemitting chemical vapor deposited diamond films are observed to emit electrons in an applied field of 30–50 kV/cm in an electron emission microscope. The gold overlayer increases the effective field strength applied to the film. The consequent dielectric breakdown of the film provides conductive channels for the observed electron emission.

Transition metal carbides for use as field emission cathodes

Abstract: Field emission characteristics of clean ZrC, HfC, and TaC cathodes are reported. High current density emission, greater than 1×108 A/cm2, is discussed, and a method for determining the cathode changes leading to this high current emission condition is proposed. A close‐spaced triode designed for testing individual emitters is described, and results are reported. The effective thermionic work functions of clean and partially oxygen covered surfaces of ZrCx specimens of two different bulk compositions are reported and discussed. Clean values of 3.5 and 3.4 eV were observed for ZrC0.92 and ZrC0.86 specimens, respectively, at 1500 K. With adsorbed oxygen, values as low as 3.4 and 3.2 eV, respectively, were observed for these surfaces at 1500 K.

Energy exchange processes in electron emission at high fields and temperatures

Abstract: A new more complete theory for energy exchange processes in electron emission is formulated. It is found that the tunneling contribution to the availability of vacant states is necessary to explain the replacement process occurring in the emitter region. The introduction of the tunneling states now makes it possible to obtain both the average energies of the emitted and replacement electrons using the same formalism. At T=0 K, the average energy of replacement electrons, 〈er〉, is the same as the average energy of the emitted electrons, 〈ee〉. As T increases, 〈er〉 increases rapidly until it reaches a maximum and then decreases slowly, while 〈ee〉 increases monotonically. When T equals the inversion temperature Ti, 〈ee〉=〈er〉 and the energy exchange Δe=0. We have also calculated both Δe and Ti as a function of field F. For high temperature and fields, the value of Ti differs considerably from that obtained without the tunneling state contribution and Ti exhibits nonlinear behavior as a function of field. Tunne...

Electron Emission from Lead-Zirconate-Titanate Ferroelectric Ceramic Induced by Pulse Electric Field

Abstract: Electron emission into vacuum from a thin plate of lead-zirconate-titanate (PZT) ferroelectric ceramics has been observed under the impression of pulse electric field. Electrons are emitted not only from the ceramic surface near the electrode edge but also through the thin metal electrode. The emitted charge per one pulse little depends on pulse frequency when it is less than 2 kHz, and so the current density can be enhanced by increasing the frequency. The emission is observed even at temperatures above Curie temperature. It is considered that the emission is induced by abrupt change of dielectric flux as well as the polarization reversal.

Electron field emission from large-area cathodes: evidence for the projection model

Abstract: Field emission from two special kinds of emitters has been studied in detail: intentionally introduced particles of controlled geometry, and sites produced by intentional mechanical damage to the cathode surface. We found that the size of particles seems to play no role in their threshold field but their shapes are a determinant factor since spherical particles do not emit for fields up to 120 MV m-1. The method of creation of damage sites, and the similarity of their emission on Nb and Au substrates, suggest the possibility that emission comes from geometrical protrusions. A model of superposed geometrical protrusions is proposed to explain the enhanced field emission behaviour of this particular type of surface defect.

Field emission type flat display apparatus

Abstract: A flat display apparatus has a substrate, a plurality of pointed cathodes formed on the substrate, a planar anode facing toward the cathodes via a vacuum space, and a light emitting layer on the side of the anode which is opposite from the cathodes. The anode has a plurality of projections in positions corresponding to the cathodes. The anode projections reduce electron scatter to improve light emission from the light emitting layer. In another embodiment of the flat display apparatus, a primary electron source and a plurality of secondary electron sources connected to bias voltages are disposed on the substrate and positioned relative to one another in an alternately staggered vertical positional sequence toward a light emitting member so that electrons are successively amplified. In a further embodiment of the flat display apparatus, wherein a plurality of electron sources are disposed on the substrate, an electrode faces toward the electron sources, and a light emitting member is provided on a side of the electrode opposite and facing away from the substrate, the electron sources include a primary electron source for generating primary electrons and a secondary electron source for amplifying primary electrons from the primary electron source due to a Malta effect.

Influence of bulk states on laterally confined surface state electrons.

Abstract: Strong scattering by adatoms positioned with the tip of a scanning tunneling microscope (STM) has recently been used to confine surface state electrons to nanoscale structures. We develop a model for confinement by a circular potential on a metal surface, including substrate band structure effects. Scattering into bulk states provides an important broadening mechanism for partially confined states. Contrary to experiment the level width vanishes as the energy approaches the surface state band edge, indicating an additional dominant broadening mechanism for laterally confined surface state levels seen in the STM.

Near field emission scanning tunneling microscopy

Abstract: The close proximity between probe and sample in a scanning tunneling microscope interface may produce unwanted modifications of the interface. This is particularly severe when working with soft materials, as molecular films or biomolecules. Here, we propose the operation of the scanning tunneling microscope in the near field emission regime as an effective method to overcome those problems. A theoretical description of the probe–sample interface in the near field emission regime predicts subatomic resolution in the direction normal to the surface and lateral resolution of 3 nm for tip–sample separations of 3–5 nm. Furthermore, atomic resolution is demonstrated by imaging steps of carbon atoms.

Field emission element and process for manufacturing same

Abstract: A process for manufacturing a field emission element including a substrate, and an emitter and a gate each arranged on the substrate is provided. The emitter is formed at at least a tip portion thereof with an electron discharge section, which is formed of metal or semiconductor into a monocrystalline structure or a polycrystalline structure preferentially oriented in at least a direction perpendicular to the substrate by deposition.

Soft luminescence of field emission display

Abstract: Described are methods for making, and resultant structures of, a field emission display with soft luminescence and a comfortable image for a viewer of the display. The field emission display is formed with a baseplate and an opposing face plate. Field emission microtips are formed in openings in a conductive and insulating layer on the baseplate. An anode is formed on either the faceplate, or on the conductive layer surrounding each opening. Phosphorescent material is formed over the anode, A blocking layer is formed between the phosphor and the faceplate, such that during operation of the display direct light emission from the phosphor is blocked, resulting in indirect phosphorescence and a more comfortable display image. An optional reflective layer may be added over the conductive layer to increase phosphorescence.

Electron Tunneling through Ultrathin Gate Oxide Formed on Hydrogen-Terminated Si(100) Surfaces

Abstract: Current transport through ultrathin gate oxides grown on chemically cleaned Si(100) surfaces has been systematically investigated. It is shown that current through oxides thinner than 4.2 nm is controlled by direct tunneling (DT), while Fowler-Nordheim tunneling (FNT) predominates in transport through SiO2 thicker than 5.1 nm. In the oxide thickness range between 4.2 and 5.1 nm, DT limits the current at low electric fields and FNT at high fields. The observed tunneling current is quantitatively explained by a theory based on the Wentzel-Kramers- Brillouin method (WKB approximation). Also, the influence of the Si surface microroughness on the tunneling current is discussed.

Field emission type electron source

Abstract: A field emission type electron source capable of permitting a resistance value between a cathode wiring and each of emitter cones to be set at substantially the same level and increasing packaging density of the emitter cones. The electron source includes stripe-like cathode wirings arranged on an insulating substrate. The cathode wirings each are formed with a plurality of windows, so that a plurality of island-like cathode conductors and resistance layers different in resistance value from each other are formed separate from the cathode wiring. Then, a resistance layer, an insulating layer and a gate electrode are formed thereon. The gate electrode and insulating layer are formed with apertures in a manner to be common to both, in which the emitter cones are arranged, resulting in emission of electrons from the emitter cones of each group unit being rendered uniform.

Space‐charge effects in Spindt‐type field emission cathodes

Abstract: The field emission characteristic of a Spindt‐type cathode, cleaned extensively in a hydrogen atmosphere while emitting, is considered The maximum emission reached is about 800 μA At high current levels the I–V curve clearly deviates from a Fowler–Nordheim behavior This can be explained by the occurrence of space charge Several models are considered to simulate the experimental results The fit to the data is good except at the highest emission levels In this region the difference between the measured currents and the simulation results is due to the neglect of the variation of the field on top of the tip in the presence of space charge