Electron Emission Characteristics Research Articles

Enhanced Field Electron Emission from Photocurrent Treated Nanostructured Indium Oxide Films

Field electron emission currents from nanostructured films always have unsatisfied stability. This paper introduces a photocurrent treatment technique to enhance the filed emission properties, and gives a kind of nanostructured indium oxide film suitable for the technique. The products were prepared on patterned ITO glass substrate by using chemical vapor deposition method. With the increase of reaction time, the morphologies of the films changed from cocoonlike particles to hybrid thin films, and finally flowerlike nanostructures were formed. Photocurrent and field electron emission characteristics of the products have been studied. After photocurrent treatment, the flowerlike indium oxide films show stable field emission current (fluctuation is less than 5%), low field emission threshold (at 7.5 V/m, the current density is 1 mA/cm2) and high enhancement factor of electrical field of 778. The field emission test results validated that the photocurrent treated flowerlike indium oxide films may act as electron emitters and applied in display applications.

Secondary electron emission characteristics of nanostructured silver surfaces

Multipactor induced by secondary electron emission (SEE) is a potential risk for many high-power systems. It is of great importance to suppress the total electron emission yield (TEEY) to mitigate the detrimental effect. Metal black has been reported as effective TEEY suppressor, but the theoretical model for describing its SEE characteristics is still scarce. In this work, we propose a periodic nanostructure model, with each unit composed of a combination of a top hemispherical nanograin and a fractal rectangular groove-like gap, to describe the silver black nanostructure. Using this model, we investigate the SEE characteristics of the silver black nanostructure theoretically. Simulation results indicate that the groove-like gaps in the nanostructure suppress the TEEY, while the top hemispherical nanograins enhance it; and the suppression on the true secondary electron yield is much stronger than that on the back-scattered electron yield (BSEY). In addition, we observe two interesting phenomena: first, the nanostructure enhances the BSEY even if it suppresses the TEEY when the proportion of top nanograins reaches 30%; second, the suppression on TEEY of the nanostructure becomes weak at relatively high primary electron energy. To verify the simulation results, we fabricate several silver nanostructures by thermal evaporation with gas pressure varied from 40 to 70 Pa. Measurement results indicate that all the fabricated nanostructures can suppress TEEY to some degree; and the more top hemispherical nanograins the nanostructure possesses, the higher TEEY revealed. For the measured SEE characteristics of the nanostructures fabricated at 40 and 45 Pa, we observe a higher BSEY than that of the flat surface. These experimental results qualitatively verify the simulated estimations. This work is of significance to comprehend SEE characteristics in related applications such as multipactor suppression.

Formulae for maximum yield and mean escape depth of secondary electrons emitted from metals

Based on the characteristics of secondary electron emission, the former formulae for the maximum yield of metals [Formula: see text] and primary range in the energy range of [Formula: see text] eV, relation [Formula: see text] among secondary electron escape probability [Formula: see text], average energy required to produce an internal secondary electron [Formula: see text], [Formula: see text], primary energy of [Formula: see text] ([Formula: see text] and parameter [Formula: see text] was deduced. On the basis of [Formula: see text] and the former formula for [Formula: see text], relation [Formula: see text] among mean escape depth of secondary electrons emitted from metals [Formula: see text], atomic number [Formula: see text], back-scattering coefficient [Formula: see text], material density [Formula: see text], [Formula: see text], atomic weight [Formula: see text] and [Formula: see text] was deduced. According to the deduced [Formula: see text], the formula for the ratio of [Formula: see text] to [Formula: see text] and experimental ratio of [Formula: see text] to [Formula: see text], relation [Formula: see text] among [Formula: see text], original work function [Formula: see text] and [Formula: see text] were empirically obtained. According to the characteristics of metal surface, [Formula: see text], [Formula: see text] and [Formula: see text], the formula for [Formula: see text] as a function of [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] and that for [Formula: see text] as a function of [Formula: see text], [Formula: see text] and [Formula: see text] were deduced, respectively. The influences of surface change on [Formula: see text] and [Formula: see text] were analyzed. Calculated [Formula: see text] and [Formula: see text] were compared with the corresponding experimental ones. It was concluded that the deduced formulae for [Formula: see text] and [Formula: see text] can be used to estimate [Formula: see text] and [Formula: see text], respectively.

Locally Resolved Electron Emission Area and Unified View of Field Emission from Ultrananocrystalline Diamond Films.

In this paper, we study the effect of the actual, locally resolved, field emission area on electron emission characteristics of uniform planar conductive nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) field emitters. High resolution imaging experiments were carried out in a field emission microscope with a specialty imaging anode screen such that electron emission micrographs were taken concurrently with measurements of I-V characteristics. An automated image processing algorithm was applied to process the extensive imaging data sets and calculate the emission area per image. It was routinely found that field emission from as-grown planar (N)UNCD films was always confined to a counted number of discrete emitting centers across the surface, which varied in size and electron emissivity. It was established that the actual field emission area critically depends on the applied electric field and that the field emission area and overall electron emissivity improve with the sp2-fraction present in the film, irrespective of the original substrate roughness or morphology. Most importantly, when as-measured I-E characteristics were normalized by the electric field-dependent emission area, the resulting j-E curves demonstrated a strong kink and departed from the Fowler-Nordheim law, finally saturating at a value on the order of 100 mA/cm2. This value was nearly identical for all studied films regardless of substrate. It was concluded that the saturation value is specific to the intrinsic fundamental properties of (N)UNCD.

Formulae for secondary electron yield from insulators and semiconductors

The processes and characteristics of secondary electron emission in insulators and semiconductors were studied, and the formulae for the maximum yield (δ m) at W p0m ≤ 800 eV and the secondary electron yield from insulators and semiconductors δ at the primary incident energy of 2 keV ≤ W p0 < 10 keV (δ 2–10) and 10 keV ≤ W p0 ≤ 100 keV (δ 10–100) were deduced. The calculation results were compared with their corresponding experimental data. It is concluded that the deduced formulae can be used to calculate δ 2–100 at W p0m ≤ 800 eV.

Improved electron emission properties of the porous silicon emitter by chemical surface modification

A new chemical dipping method using nickel chloride (NiCl2) solution is proposed to improve the characteristics of an electron emitter based on porous silicon (PS). Two groups of PS samples were prepared, one group was then left untreated, while the other group was treated by the chemical dipping method. Energy dispersive x-ray (EDX) and x-ray photoemission spectroscopy (XPS) studies confirm the uniform filling of the reduced Ni and the formation of the SiO2 in the chemically dipped sample. The gold electrode was sputtered on the modified PS surface and the study of J-V characteristics show that the modified samples have more favorable rectifying behavior and longer-term durability than the unmodified one. The measured results showed that the voltage threshold ∼8 V, PVCR value ∼1.08, emission current density ∼48 μA cm−2, emission efficiency ∼0.72%, and stable emission were achieved for the modified sample; most of these electron emission characteristics were better than those from the unmodified emitter. Such improvements are mainly due to the decrease of the contact barrier height between the PS and the gold electrode, as is evident from analyzing the logarithmic J-V characteristics. The chemical dipping method is therefore expected to be a valuable technique to enhance the electron emission characteristics of the PS emitter.

Work Function Characterization of Potassium-Intercalated, Boron Nitride Doped Graphitic Petals

This paper reports on characterization techniques for electron emission from potassium-intercalated boron nitride modified graphitic petals. Carbon-based materials offer potentially good performance in electron emission applications owing to high thermal stability and a wide range of nanostructures that increase emission current via field enhancement. Furthermore, potassium adsorption and intercalation of carbon-based nanoscale emitters decreases work functions from approximately 4.6 eV to as low as 2.0 eV. In this study, boron nitride modifications of graphitic petals were performed. Hexagonal boron nitride is a planar structure akin to graphene and has demonstrated useful chemical and electrical properties when embedded in graphitic layers. Photoemission induced by simulated solar excitation was employed to characterize the emitter electron energy distributions, and changes in the electron emission characteristics with respect to temperature identified annealing temperature limits. After several heating cycles, a single stable emission peak with work function of 2.8 eV was present for the intercalated graphitic petal sample up to 1000 K. Up to 600 K, the potassium-intercalated boron nitride modified sample exhibited improved retention of potassium in the form of multiple emission peaks (1.8 eV, 2.5 eV, and 3.3 eV) resulting in a large net electron emission relative to the unmodified graphitic sample. However, upon further heating to 1000 K, the unmodified graphitic petal sample demonstrated better stability and higher emission current than the boron nitride modified sample. Both samples deintercalated above 1000 K.

Study of thermal-field emission properties and investigation of temperature dependent noise in the field emission current from vertical carbon nanotube emitters

We have investigated temperature dependent field electron emission characteristics of vertical carbon nanotubes (CNTs). The generalized expression for electron emission from well-defined cathode surface is given by Millikan and Lauritsen [1] for the combination of temperature and electric field effect. The same expression has been used to explain the electron emission characteristics from vertical CNT emitters. Furthermore, this has been applied to explain the electron emission for different temperatures ranging from room temperature to 1500K. The real-time field electron emission images at room temperature and 1500K are recorded by using Charge Coupled Device (CCD) in order to understand the effect of temperature on distribution of electron emission spots and ring like structures in Field Emission Microscope (FEM) image. The FEM images could be used to calculate the total number of emitters per cm2 for electron emission. The calculated number of emitters per cm2 from FEM image is typically, 4.5 × 107 and the actual number emitters per cm2 present as per Atomic Force Microscopy (AFM) data is 1.2 × 1012. The measured Current-Voltage (I-V) characteristics exhibit non linear Folwer-Nordheim (F-N) type behavior. The fluctuations in the emission current were recorded at different temperatures and Fast Fourier transformed into temperature dependent power spectral density. The latter was found to obey power law relation S(f) = A(Iδ/fξ), where δ and ξ are temperature dependent current and frequency exponents respectively.

Light-Emitting Illumination and Field Emission Device of Potassium Hydroxide-Doped Electrochemically Reduced Graphene Oxide

This paper presents a parallel plate-type field emission device of potassium hydroxide-doped electrochemically reduced graphene oxide (GO) manufactured using highly oriented pyrolytic graphite through electrochemical exfoliation. The material properties of the GO were tested through Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The optimal electron emission characteristics of the device were as follows: turn-on field = 2.03 V/ $\mu \text{m}$ , field emission current $= \,\, 16.4~\mu \text{A}$ , and field emission enhancement factor = 8377. At an emission peak wavelength of 563.7 nm, the optimal device had a light flux of 4.21 lumens and an illumination of 140.3 lux. These properties can be utilized in various optoelectronic devices, such as nanoelectronics devices, sensors, electrochemical systems, and energy storage devices.

Formulae for low-energy secondary electron yield from different kinds of emitters as a function of measurable variables

Based on the characteristics of secondary electron emission and the relationships among parameters of secondary electron yield [Formula: see text] in the low-energy range of [Formula: see text] eV (low-energy [Formula: see text]), the universal formula for low-energy [Formula: see text] as a function of [Formula: see text], [Formula: see text] and maximum [Formula: see text] was deduced, where [Formula: see text] and [Formula: see text] are the incident energies of primary electron and of [Formula: see text], respectively. From the deduced universal formula and experimental low-energy [Formula: see text] from metals, semiconductors and insulators, special formula for low-energy [Formula: see text] from metals as a function of [Formula: see text], [Formula: see text] and [Formula: see text] and that for low-energy [Formula: see text] from semiconductors and insulators as a function of [Formula: see text], [Formula: see text] and [Formula: see text] were deduced, respectively. The results were analyzed, it can be concluded that the two deduced special formulae can be used to calculate low-energy [Formula: see text] from metals, semiconductors and insulators, respectively.

Effect of the cesium and potassium doping of multiwalled carbon nanotubes grown in an electrical arc on their emission characteristics

The effect of cesium and potassium atoms deposited onto multiwalled carbon nanotubes grown in an electrical arc on their emission characteristics was studied. The current–voltage characteristics of the field electron emission of specimens with cesium or potassium doped multiwalled carbon nanotubes of this type were revealed to retain their linear character in the Fowler–Nordheim coordinates within several orders of magnitude of change in the emission current. The deposition of cesium and potassium atoms was shown to lead to a considerable increase in the emission current and a decrease in the work function φ of studied emitters with multiwalled nanotubes. The work function was established to decrease to φ ~ 3.1 eV at an optimal thickness of coating with cesium atoms and to φ ~ 2.9 eV in the case of doping with potassium atoms. Cesium and potassium deposition conditions optimal for the attainment of a maximum emission current were found.

Analysis on electron emission characteristics of MgO layer with MgO crystal powder under various panel temperatures in ac-plasma display panels

ABSTRACTThis paper examines the electron emission characteristics of the MgO layer in the case of spraying the MgO crystal powders based on the two monitoring parameters such as the electric field strength and the panel temperature. In particular, in order to analyze the effects of the electric field strength on the electron emission characteristics of the MgO layer with MgO crystal powders, the variations in the wall voltage induced by the electron emission are measured relative to the electric field strength between the address-sustain electrodes during an address period under various panel temperature conditions ranging from −5 to 65°C. As a result, it is observed that the electron emission characteristics of the MgO layer with MgO crystal powder strongly depend on the electric field strength rather than the thermal effect of exo-electron emission, which is confirmed by the measurement result of the wall voltage variation relative to the electric field strength under the low panel temperature of −5°C.

Discharge and structural characteristics of MgO thin films under various O2 and H2 gas flow rates during MgO deposition when using ion plating method in microdischarge cells

ABSTRACTThis paper has investigated the characteristics of structure and discharge for the MgO thin films grown by the ion plating process by varying the oxygen (O2) and hydrogen (H2) flow rates. The structural characteristics of the MgO film are measured by scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). The discharge characteristics are examined based on the firing voltage, secondary electron emission, sustain delay, and address delay. By increasing the O2 flow rates during ion plating process, the grain sizes of the MgO thin films are decreased and the firing voltages are decreased, which would be due to the improvement of secondary electron emission characteristics. In addition, as the O2 gas flow rates are increased in the range from 200 to 260 sccm, the sustain delay times are reduced, on the contrary, the address delay times are increased. Whereas, by increasing the H2 flow rates, the grain sizes of the MgO thin films are increased. In particular, the lower firing voltages are measured at a H2 flow rate of 40 sccm, which also would be due to an enhancement of secondary electron emission characteristics. When H2 flow rates are increased from 0 to 40 sccm, the address delay times are greatly reduced. Whereas, when H2 flow rates are beyond 40 sccm, the address delay times are slightly increased. However, the sustain delay times are slightly increased as the H2 flow rates are increased from 0 to 60 sccm. Accordingly, the optimal control of both O2 and H2 flow rates during the MgO film deposition using ion plating method can contribute to enhancing the discharge characteristics in ac plasma display panels (ac-PDPs).

In situ study of graphene crystallinity effect on field electron emission characteristics

Crystallinity and field electron emission characteristics of few-layer graphene (FLG) have been investigated synchronously by using in situ transmission electron microscope (TEM) to reveal their relationship. The crystallinity of a single FLG sheet is modified from polycrystalline to amorphous by TEM electron beam irradiation. In the meantime, the field electron emission measurement shows that the degradation of crystallinity has a negative effect on the field electron emission characteristics. This can be attributed to the violently decline of electrical conductivity of FLG. The results indicate that crystallinity is a key factor to the field electron emission of FLG, and thus, conditions leading to the degradation of crystallinity of FLG should be avoided.

Microplasma device architectures with various diamond nanostructures

Diamond nanostructures (DNSs) were fabricated from three different morphological diamonds, microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films, using a reactive ion etching method. The plasma illumination (PI) behavior of microplasma devices using the DNSs and the diamond films as cathode were investigated. The Paschen curve approach revealed that the secondary electron emission coefficient (γ value) of diamond materials is similar irrespective of the microstructure (MCD, NCD, and UNCD) and geometry of the materials (DNSs and diamond films). The diamond materials show markedly larger γ-coefficient than conventional metallic cathode materials such as Mo that resulted in markedly better PI behavior for the corresponding microplasma devices. Moreover, the PI behavior, i.e. the voltage dependence of plasma current density (Jpl−V), plasma density (ne−V), and the robustness of the devices, varied markedly with the microstructure and geometry of the cathode materials that was closely correlated to the electron field emission (EFE) properties of the cathode materials. The UNCD nanopillars, possessing good EFE properties, resulted in superior PI behavior, whereas the MCD diamond films with insufficient EFE properties led to inferior PI behavior. Consequently, enhancement of plasma characteristics is the collective effects of EFE behavior and secondary electron emission characteristics of diamond-based cathode materials.

Comparison of Electron Emission Characteristics of W and CNT Field Emitter for Microcolumn

Comparison of Electron Emission Characteristics of W and CNT Field Emitter for Microcolumn

Improvement of electron emission characteristics of porous silicon emitter by using cathode reduction and electrochemical oxidation

A new simple and convenient post-treat technique combined the cathode reduction (CR) and electrochemical oxidation (ECO) was proposed to improve the electron emission properties of the surface-emitting cold cathodes based on the porous silicon (PS). It is demonstrated here that by introducing this new technique combined CR and ECO, the emission properties of the diode have been significantly improved than those as-prepared samples. The experimental results showed that the emission current densities and efficiencies of sample treated by CR were 62μA/cm2 and 12.10‰, respectively, nearly 2 orders of magnitude higher than those of as-prepared sample. Furthermore, the CR-treated PS emitter shows higher repeatability and stability compared with the as-prepared PS emitter. The scanning electron microscope (SEM), atomic force microscope (AFM), energy dispersive spectrometer (EDS), furier transformed infrared (FTIR) spectroscopy results indicated that the improved mechanism is mainly due to the passivation of the PS, which not only improve the PS morphology by the passivation of the H+ but also improve the uniformity of the oxygen content distribution in the whole PS layer. Therefore, the method combined the CR treatment and ECO is expected to be a valuable technique to enhance the electron emission characteristics of the PS emitter.

A study of the electrical properties of the porous GaP (111) surface

Local electrical properties of the surface of porous GaP have been measured by the method of tunneling spectroscopy in ultrahigh vacuum. Two surface areas with different electrical properties were found. The effect of anomalous field-induced photoemission was observed. The most probable reason for this effect is the presence of Ga2O3 and GaP nanoclusters and the high density of acceptor-type surface states associated with these clusters. Integral characteristics of the field electron emission from the sample surface were obtained by using a computerized recording system with online processing of current–voltage characteristics.

Secondary electron emission characteristics of graphene films with copper substrate**Supported by the National Natural Science Foundation of China (11475166) National Natural Science Foundation of China (11205155) and National Natural Science Foundation of China (11575214).

For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield (SEY) material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25 °C and vacuum pressure of (2 − 6) × 10−9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6–8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators.

Electrical Characteristics of Flat Cesium Antimonide Photocathode Emitters in Panel Devices

The Cs₃Sb photocathode was formed by non-vacuum process technology. An in-situ vacuum device was fabricated successively with flat cesium antimonide photocathode emitters fabricated in a process chamber. The electrical properties of the device were characterized. Electron emission from the devices was induced by photoemitted electrons, which were accelerated by an anode electric field that was shielded from the photoemitter surface. The electrical characteristics of the devices were investigated by measuring the anode current as a function of device operation times with respect to applied anode voltages. Planar blue LED light with a 450 nm wavelength was used as an excitation source. The results showed that the cesium antimonide photocathode emitter has the potential of long lifetime with stable electron emission characteristics in panel devices. These features demonstrate that the cesium antimony photocathodes produced by non-vacuum processing technology is suitable for flat cathodes in panel device applications.