Stable Electron Emission Research Articles

Field emission characteristics of an oxidized porous polysilicon field emitter using the electrochemical oxidation process

The field emission characteristics of an oxidized porous polysilicon (OPPS) were investigated with Pt/Ti multilayer electrode using the electrochemical oxidation (ECO) process. A Pt/Ti multilayer electrode, using ECO, showed highly efficient and stable electron emission characteristics; moreover, it can be applied to large area of a glass substrate with a low temperature process. Electron emission characteristics were improved with O2 annealing at 600°C after the ECO process. It was found that forming a high quality oxide layer from the ECO-formed SiO2 was crucial in improving electron emission characteristics. The Pt/Ti OPPS field emitter, which was annealed at 600°C for 5h, showed an efficiency of 3.81% at Vps=14V.

Improvement of the field emission characteristics of an oxidized porous polysilicon using annealed Pt/Ti surface emitter electrode

The field emission characteristics of an oxidized porous polysilicon were investigated with different annealing temperatures. Pt/Ti, Ir, and Au/NiCr were used as surface emitter electrodes, and Pt/Ti emitter showed highly efficient and stable electron emission characteristic compared with the conventional Au/NiCr electrode. Thin Ti layer played an important role in promotion of adhesion of Pt to SiO2 surface and uniform distribution of electric field on the OPPS surface. Additionally, the Ti layer efficiently blocked the diffusion of emitter metal, which resulted in more reliable emission characteristics. Pt/Ti emitter annealed at 350°C/1h showed the highest efficiency of 3.36% at Vps=16V, which resulted from the improvement of interfacial contact characteristics of thin emitter metal to an oxidized porous polysilicon. Annealing above 400°C showed that Pt/Ti and Ir emitter electrode were thermally more stable than Au/NiCr emitter.

Low-temperature growth and field emission of ZnO nanowire arrays

Structural, optical, and field-emission properties of ZnO nanowire arrays grown at 90°C are investigated. Single-crystalline ZnO nanowires with low level of oxygen vacancies are obtained at low temperatures. The nanowire growth is strongly dependent on the seeding method used but independent of the substrate materials, which enable large scale growth of ZnO arrays on all kinds of substrates including polymers. We have demonstrated stable electron emission at low-field strengths for nanowires grown on polystyrene and polyethylene foils, making them promising candidates for fabrication of flexible cold cathodes. Deposition of a few nanometers of gold on ZnO nanowires significantly lowers the field required for electron emission, which is explained in terms of additional field enhancement from Au islands on top of the ZnO nanowires.

Full MEMS monolithic microcolumn for wafer-level arrayal

Recently, an advanced microcolumn concept for improved throughput was proposed. However, due to the complexity of the approach, the miniaturization was limited. In addition, microcolumns must run under ultrahigh vacuum conditions in order to obtain stable electron emission at the field-emission tip. Both signal and power lines need to be connected through the ultrahigh vacuum chamber. Therefore, increases in the number of microcolumn arrays necessitate more wiring from the external control unit to the internal units, and the number of wires can become prohibitive. To solve this problem, a new concept, exploiting the possibility of an arrayed microcolumn which uses microelectromechanical systems (MEMS) technology has been developed. This paper describes a monolithic (3×3 arrayed) microcolumn, which consists of a cold field-emission tip, an input lens, an einzel lens, and novel deflectors for multiple-arrayed microcolumns. We also describe its fabrication process, which relies on improved microfabrication and MEMS technology, most notably multiwafer anodic bonding techniques and copper electroplating for the double metallization process. This paper describes an electro-optical analysis and an optimization using an equivalent circuit and a newly proposed simulation tool. We focus on the production possibilities for microcolumns constructed using MEMS technology. The emission current of the fabricated tungsten and molybdenum cold field-emission tip was several microamperes for an applied gate voltage of 100V. The probe current, which was measured in the sample grid of the wafer stage, was about 1nA. The amount of electron-beam deflection was proportional to the applied voltage at the deflector, and operated at about 1μm∕V.

Field electron emission from flat metal cathodes covered by thin polymer films

We have studied the physical properties of a new class of field electron emitters representing metal cathodes covered by thin polymer films based on a soluble imide-siloxane copolymer. Polymer coating leads to an increase in the emission current and provides for a quite stable field electron emission of flat polished molybdenum and niobium cathodes.

Field and photo-field electron emission from self-assembled Ge?Si nanostructures with quantum dots

Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was ⩽10 nm and cluster density was ∼1010 cm−2. A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm.

Field and photo-field electron emission from self-assembled Ge–Si nanostructures with quantum dots

Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was ⩽10 nm and cluster density was ∼10 10 cm −2. A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm.

Preparation and characterization of nanostructured film of graphitized diamond crystallites for field electron emission

The details are given of the preparation technique that has been developed for depositing crystalline-nanodiamond particles on large-area silicon substrates, based on an dielectrophoresis process. A patented technique was adapted to prepare the substrate surface with high density of uniformly distributed nanoprotrusions that provide local field enhancement necessary for dielectrophoresis deposition. The nanodiamond crystallites were treated at elevated temperatures to have their surfaces graphitized. High-resolution transmission microscopy and electron diffraction techniques as well as micro Raman analysis were used to study the properties of the so-prepared nanostructured film. Stable field electron emission from these films with current density of >5 mA/cm2 may be regularly obtained at fields as low as ∼3 V/μm. The current–voltage characteristics and the corresponding Fowler–Nordheim plots, emission uniformity, and current stability were studied. The findings suggest that this type of film is a potential candidate as a large-area cold cathode. A model based on emission associated nanoscale graphite network and nanotriple junction is presented.

The effect of hydrogen plasma chemical annealing on electron field emission of amorphous carbon films

Layer-by-layer deposition method, in which nanometer-thick film deposition and hydrogen plasma annealing processes were alternatively repeated, was applied to fabricate hydrogenated amorphous carbon films in our present work. It was found that the hydrogen plasma treatment changed the sp 2/sp 3 ratio due to chemical etching. Consequently, a stable vacuum electron emission with a low threshold field was achieved compared with that from conventionally deposited a-C films. The threshold electric field is as low as 2 V/μm. The influence of the hydrogen plasma chemical annealing on the field emission behavior was systematically investigated. The improvement of field emission characteristics can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp 2 clusters.

Self-recovery function of Sc–O/W( [formula omitted]) system as Schottky emitter

The damage induced by Ar + ion irradiation onto the surface of an Sc–O/W(1 0 0) system as a Schottky emitter was investigated at room and high temperatures by means of low-energy electron diffraction and Auger electron spectroscopy. The properties of the Sc–O/W(1 0 0) surface were maintained only at ∼1500 K, the operating temperature of the Sc–O/W(1 0 0) emitter, confirming that the Sc–O/W(1 0 0) surface has a self-recovery function against surface damage induced by residual gas ion sputtering. The self-recovery function is caused by the surface segregation of Sc and O atoms from the bulk. The stable electron emission of the Sc–O/W(1 0 0) Schottky emitter is attributed not only to the stability of the properties of the Sc–O/W(1 0 0) surface at the high temperature but also to the self-recovery function.

Ultra-low threshold field electron emission from conducting polymer blend

The stable electron emission of conducting polymer film with extremely low threshold of less than 0.06 V/μm has been discovered. Electron emission of more than 0.1 mA/cm 2 was observed at applied field of 15 V/μ m. The emitter consists of a layer of highly conducting polymer blend with insulating host polymer of which was removed after spinning. The conducing polymer finally forms an interpenetrating network structure. Such emitters could lead to an inexpensive flat-panel display with low driving voltage.

Electron emission from nanostructures

Stable electron emission sources have been produced in plasma-etched single crystal silicon, coated with ultra-thin amorphous diamond, using a vacuum carbon arc source, at room temperature. Diamond films have been characterised using spectroscopy, EDX and high-resolution transmission electron microscopy. Fabricated devices require significantly lower threshold fields (3 V/μm) for operation, compared to uncoated emitters and show much reduced emission current fluctuations of 3% compared to 9% for untreated arrays.

CRT lighting element with carbon field emitters

Field electron emission from carbon fibres has been investigated. Measured current–voltage characteristics followed the Fowler–Nordheim equation. A cathode ray tube lighting element of a triode vacuum tube was manufactured as an application of a carbon fibre emitter by replacing conventional thermionic cathodes with carbon field emitters. Stable and intense electron emission, luminosity and long life of the emitters were demonstrated and discussed.

Field electron emission from Ge-Si nanostructures with quantum dots

Self-assembled arrays of Ge-Si clusters with sizes of ∼ 10 nm and a density of ∼ 1010 cm−2 have been grown by molecular beam epitaxy. Stable steady-state field electron emission from such clusters has been observed and studied. The emission is characterized by resonance current peaks, which are explained by the quantization of the electron energy in nanoclusters. The estimation of the ground level energy from their emission measurements coincides with estimates obtained by other methods.

Stable field emission with low threshold field from amorphous carbon films due to layer-by-layer hydrogen plasma annealing

The layer-by-layer hydrogen plasma treatment method, alternatively repeating the process of nanometer thickness film deposition and hydrogen plasma chemical annealing, was applied to fabricate amorphous carbon (a-C) films. It was shown that hydrogen plasma treatment reduced the size of sp2 clusters and resulted in the increase of the optical band gap. Consequently, a stable vacuum electron emission with a low threshold field was achieved from layer-by-layer hydrogen plasma annealed a-C films compared with that from conventionally deposited samples. The threshold electric field was as low as 2 V/μm. The improvement of field emission characteristics could be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters.

Field emission from flexible arrays of carbon nanotubes

A property of certain samples of carbon nanotubes not to sink in the water was employed to develop an original technique of nanotubes array deposition. The arrays were characterized both by optical microscopy and by scanning electron microscopy. Field-emitting devices were produced from those arrays. They were shown to exhibit stable electron emission and high current densities. Patterned arrays were also developed and tested for applications in flat panel displays.

Surface Spectroscopy Utilizing Field Electron Emission from Thermal-field Treated Tips in STM

We have demonstrated the potentials of a field emission scanning tunneling microscope (FE-STM), in which the STM tip can be operated as a stable field electron emission gun. The tips were treated by a thermal-field (T-F) method for remolding and cleaning. A well-controlled T-F treated tip can determine the electric field between tip and sample in the STM as a geometrical boundary condition. Using the treated tip the electron standing waves excited in a vacuum gap between tip and sample were analyzed, and the electric field near sample surfaces was evaluated by assuming a simple potential model. Furthermore, by irradiating sample surfaces with a high-energy electron beam emitted from the tip, we obtained electron energy loss spectra (EELS) and Auger electron spectra from semiconductors, HOPG and metals.

Solid-state field-controlled emitters: a thin-film technology solution for industrial cathodes

Experimental measurements have shown that uniform and stable electron emission is obtained from metallic planar surfaces covered with an ultra-thin wide band-gap semiconductor (UTSC) layer, with a threshold of the applied field in the range of 50 V μm −1 and at 300 K. Numerical simulation analysis of a serial two-step mechanism model has been developed. The theoretical results confirm the main experimental characteristics and showed that a band bending of ≈5 eV is obtained for an UTSC layer thickness in the range of 3–7 nm.

Stable and uniform electron emission from nanostructured carbon films

We have systematically studied the electron-emission characteristics of nanostructured carbon films with various amounts of nanoclusters and degrees of nanotube alignment. According to our observation, the dense packing and/or alignment of nanotubes is detrimental to the low-field emission, which we attributed to the electrostatic screening effect. The best emission was observed from the carbon films dominated by nanoclusters; the turn-on field was 1.6 V/μm and the emission-site density was considerably higher than 5×104 site/cm2. The emission from the nanocluster-dominated film was uniform and stable. Raman spectroscopy identified the nanoclusters as crystalline graphite with some structural defects. It is conceivable that the modification of the boning hybridization at the cluster surface resulted in a diamond-like density of states, and that the corresponding small electron affinity was responsible for the excellent emission the from nanoclusters.

Spatial variation of field emission current on nitrogen-doped diamond-like carbon surfaces by scanning probe method

Field emission characteristics of nitrogen-doped diamond-like carbon (DLC) films deposited by the radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) method were investigated by the scanning probe system specially designed for the micro-scale field emission current measurements. The structural changes in the films were examined by using Raman spectroscopy. Random and inhomogeneous distribution of electron emission sites was observed. The emission current and conductivity of the films were significantly increased with self-bias voltage. Activated electron emission characteristics were observed in all samples and showed stable electron emission. The activation of the films was directly related to emission site size. It indicated that electron emission activation possibly originated from the changes in sp 2 and sp 3 bonding ratio and/or formation of conductive channels.