A consideration of secondary electron emission from organic solids

The behavior of the secondary electron emission (SEE) from organic solids has been considered. It has been shown that the maximum SEE yields of many hydrocarbon compounds exponentially depend on the extinction coefficient of secondary electron defined by the π-electron fraction in molecule, which is correlated to Dionne's theoretical equation. The concept that the extinction coefficient of secondary electron is represented in terms of the fraction of the delocalized and low energy-gap electron-like π-electron will be convenient for a rough estimation of the SEE yield of other various materials. On the other hand, a novel universal equation representing the normalized SEE yield curve has also been proposed in this paper, by which an analysis of the normalized SEE yield curves of many organic solids have been tried.     

Secondary electron emission from CVD diamond films

Secondary electron emission from boron doped diamond polycrystalline membranes (hole concentration 5×10¹⁸ cm⁻³), prepared by microwave plasma assisted CVD, was investigated in both the reflection and transmission configurations. The model of secondary electrons behavior taking into account the distribution and diffusion mechanism of secondary electrons is proposed to explain the yield dependencies on primary electron energy in both configurations. The model predicts the SEE yield K=19 at the primary electron energy E₀ close to 1 keV for reflection configuration and K=3–7 at E₀=15–30 keV for transmission configuration for polycrystalline films used in the study. Experimental measurements of the SEE yield vs. primary electron energy (18 at E₀=950 eV for the reflection scheme and 3.5–4 at E₀=25 keV for the transmission one) are found to accord well with the theoretical results. Estimations, which were made using the model, show that SEE yield in transmission configuration can be increased up to 60 for the primary electron energy of about 10 keV. Since such high yields in transmission scheme may be obtained in monocrystalline membrane, another approach using porous polycrystalline diamond membranes is considered. Porous diamond membranes having SEE yield in transmission scheme of more than 10 at the primary electron energy E₀=1 keV were fabricated.     

Polymer film-type channel electron multipliers: Their characteristics and comparison with bulk-type flexible multipliers

Polymer film-type channel electron multipliers (CEMs) were developed and their characteristics investigated in comparison with bulk-type flexible CEM. As film-type CEMs, a paint-coating-type CEM and a solvent-etching-type CEM were fabricated. The paint-coating-type CEM is made by coating a “paint” which is prepared by dissolving in a solvent an electronically conductive polymeric composition having a high secondary electron emission yield. Up to the present study the mean gain of the film-type CEM, in spite of the lower resistivity of the dynode, seems to be slightly more dependent on the count rate than that of the bulk-type CEM made of the same material. However, the convenience of fabricating the dynode film by coating the dynode-forming paint on the internal surface of any shaped tube or a flexible polymer tube would overcome the slight disadvantage mentioned above.     

Electroconductive hyaluronic acid/gelatin/poly(ethylene oxide) polymeric film reinforced by reduced graphene oxide

Novel electroconductive polymeric films with enhanced mechanical performance were fabricated by encapsulating reduced graphene oxide (RGO) at different concentrations (0–50 vol %) into a hyaluronic acid/gelatin/poly(ethylene oxide) (HyA/Gel/PEO) polymeric structure. The obtained RGO-reinforced polymeric films were characterized by Fourier transform infrared and scanning electron microscopy analyses. Mechanical performances were measured with a universal mechanical testing machine. The results verified that the RGO reinforcement significantly enhanced the mechanical performances of the films. To determine the biocompatibility of the polymeric films, L929 (murine fibroblast) cell lines were used. The water uptake capacities were measured using swelling tests. A four-probe method was used to measure conductivity characteristics. The conductivity results indicated that HyA/Gel/PEO film containing 20 vol % RGO has the highest average electrical conductivity (1.832 × 10⁻⁶ S/cm). All of the results demonstrated that the obtained electroconductive films could be used in biomedical fields in the future, especially in controlled drug release systems and tissue engineering. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46905.     

Surface photo-voltage effect of hydrogenated diamond subjected to low energy electron irradiation

In this paper we report on the influence of sub-band gap photon illumination on the electron emission of hydrogenated diamond surfaces subjected to continuous low energy electron irradiation. Hydrogenated diamond surface traps charge by resonance electron attachment (REA) and formation of C–H_(ads)⁻ anionic transient surface species with a maximum cross section at an incident electron energy of ∼ 9 eV. The steady state population of these anionic surface species results in up-wards surface band bending and consequent decrease of low energy electron emission. It is demonstrated that concurrent low energy electron bombardment and illumination of the diamond surface with sub-band gap photons enhances the secondary electron emission yield of diamond. It is argued that these effects are associated to a surface photo-voltage effect, which results in unpinning of the surface band.     

Secondary electron emission in a triode carbon nanotube field emission display and its influence on the image quality

The secondary electron (SE) emission (SEE) in a triode carbon nanotube (CNT) field emission display (FED) and its influence on the image quality have been studied with a 3.5 in. vacuum-sealed FED prototype fabricated by using screen printing and frit sealing techniques. By analyzing the emission property difference of the device under two different kinds of work modes, we have found that it is the SEE from the insulator above the gate that induced the anode image distortion of FED under normal work mode. Two improved structures, by decreasing the size of insulator layer and by coating a conductive layer to stabilize the potential of the insulators, are provided to eliminate SEE influence and achieved a uniform anode image. It is expected that our results will benefit the research and design of CNT FED with high performance.     

Radiation initiated grafting of acrylic acid onto tetrafluoroethylene–ethylene copolymers

Hydrophilic carboxyl containing fluoropolymers was obtained by radiation grafting of acrylic acid onto tetrafluoroethylene—ethylene copolymers with different compositions. By using simultaneous (⁶⁰Co) and preirradiation (electron beam) techniques, the effect of the grafting conditions (monomer concentration, dose rate, dose, film thickness, etc.) on the degree of grafting was studied. A considerable effect of the polymer compositions, especially the C? F bonds content, and the batch irradiation on the degree of grafting was found. It was observed by scanning electron microscopy that the grafting took place mainly on the polymeric film surface and developed inward with increasing diffusion of the acrylic acid through the grafted layers. © 1993 John Wiley & Sons, Inc.     

Highly efficient electron emitting diode fabricated with single-crystalline diamond

Highly efficient electron emitting diodes have successfully been fabricated using single-crystalline diamond films epitaxially grown on high-pressure synthesized (100) diamond. It turns out that the crystalline quality of the diamond used is essential to the present-type electron emitter operated under extremely high electric fields of ∼10⁷ V/cm. For the electron emitting diode, the current efficiency defined as the ratio of the emission current to the driving current can reach unity in the best case. The mechanism of the highly efficient electron emission observed is discussed in relation to possible carrier excitations in the undoped diamond layer under the high fields. Using a high-power microwave-plasma chemical vapor deposition apparatus, high-quality diamond thin films were homoepitaxially grown. It is found from measuring the threshold energy of total photoelectron yields that a moderate surface oxidation process can change the surface electric dipole layer and, therefore, the electron affinity for hydrogen-terminated diamond surfaces as the Topping model shows.     

Agronomic and economic benefits of green-waste compost for peri-urban vegetable production: implications for food security

A long-term field experiment in western Sydney evaluated the effect of source-separated green-waste (garden organics) compost on peri-urban vegetable crop yields and economic returns, compared to farmer practice. Comparisons were made over 10 vegetable crops between a compost (COMP) treatment (one off application of 125 dry t ha^?1 of green waste compost at the start and then every five crops, supplemented with urea when required), a mixed (MIX) treatment (one-off compost application of 62.5 dry t ha^?1 at start and then every five crops, but with inorganic NPK fertiliser inputs for each crop) and a conventional farmer practice (FP). Both COMP and MIX treatments consistently achieved similar or higher yields than FP, but the yield gains were more pronounced for COMP. COMP and MIX treatments delivered benefit–cost ratios of 3.3 and 2.6 respectively compared to FP over the 10 crops, indicating that this system could deliver economic benefits to growers as well as improve soil quality and the environment. Follow up large applications of compost generated more substantial yield increases in responsive vegetable crops and economic benefits. The substantial capsicum crop yield response provided a classic example of closing a crops ‘yield gap’ through improvements to soil quality with organic inputs, with implications for food security. The COMP treatment lifted the capsicum yield to?~?60 t ha^?1, 50% above its perceived maximum potential crop yield for Eastern Australia. The value of larger applications of compost for soil quality, fertiliser savings, crop yield and farm income was apparent.     

Electron emission characteristics of needle type semiconductor diamond electron emitters by pulsed bias operation and X-ray generation

Electron emission characteristics of needle-type semiconductor diamond electron emitters with pulsed bias operation were evaluated. An X-ray generation experiment was performed. Fowler–Nordheim plotting confirmed that field emission completely governed the electron emission. Maximum emission current of 4.2 mA was achieved using an n-type diamond needle. The needle tip, with area smaller than 1 μm², had estimated electron emission density greater than 4.2 × 10⁵ A/cm². The effective emission area obtained from the Fowler–Nordheim plot was several 10^? 13 cm². For adopting and emission area of 1 × 10^? 12 cm², the estimated electron emission density was higher than 4.2 × 10⁹ A/cm². Furthermore, the average emission current was 0.5–0.6 mA. This large electron emission was continued for several seconds and repeatable. A threshold electric field existed for electron emission higher than 50 kV/mm; pulsed electron emissions of less than 30 ms were created by slow triangular waveform shaped bias voltage supplied at frequencies of 5–10 Hz. An improved vacuum level and pulsed bias operation prevented damage to diamond electron emitters and steady electron emission better than with thermoelectronic emission and high bias voltage supply in DC mode; continuous X-ray generation of 1 h was achieved.     

Mechanism of diamond nucleation enhancement by electron emission via hot filament chemical vapor deposition

The mechanism of diamond nucleation enhancement by electron emission in the hot filament chemical vapor deposition process has been investigated by scanning electron microscopy, Raman spectroscopy and infrared (IR) absorption spectroscopy. The maximum value of the nucleation density was found to be 10¹¹ cm⁻² with a −300 V and 250 mA bias. The electron emission from the diamond coating on the electrode excites a plasma, and greatly increases the chemical species, as we have seen by in situ IR absorption. The experimental studies showed that the diamond and chemical species were transported and scattered from the diamond coating on the electrode and through the plasma towards the substrate surface, where they caused enhanced nucleation.     

Nitrous oxide and methane emissions from cultivated seasonal wetland (dambo) soils with inorganic,organic and integrated nutrient management

In many smallholder farming areas southern Africa, the cultivation of seasonal wetlands (dambos) represent an important adaptation to climate change. Frequent droughts and poor performance of rain-fed crops in upland fields have resulted in mounting pressure to cultivate dambos where both organic and inorganic amendments are used to sustain crop yields. Dambo cultivation potentially increases greenhouse gas (GHG) emissions. The objective of the study was to quantify the effects of applying different rates of inorganic nitrogen (N) fertilisers (60, 120, 240 kg N ha^?1) as NH₄NO₃, organic manures (5,000, 10,000 and 15,000 kg ha^?1) and a combination of both sources (integrated management) on GHG emissions in cultivated dambos planted to rape (Brassica napus). Nitrous oxide (N₂O) emissions in plots with organic manures ranged from 218 to 894 µg m^?2 h^?1, while for inorganic N and integrated nutrient management, emissions ranged from 555 to 5,186 µg m^?2 h^?1 and 356–2,702 µg m^?2 h^?1 respectively. Cropped and fertilised dambos were weak sources of methane (CH₄), with emissions ranging from ?0.02 to 0.9 mg m^?2 h^?1, while manures and integrated management increased carbon dioxide (CO₂) emissions. However, crop yields were better under integrated nutrient management. The use of inorganic fertilisers resulted in higher N₂O emission per kg yield obtained (6–14 g N₂O kg^?1 yield), compared to 0.7–4.5 g N₂O kg^?1 yield and 1.6–4.6 g N₂O kg^?1 yield for organic manures and integrated nutrient management respectively. This suggests that the use of organic and integrated nutrient management has the potential to increase yield and reduce yield scaled N₂O emissions.     

High-current electron emission characteristics of cathodes based on diamond films

Using different gas source, four types of diamond thin films were prepared on silicon substrate by microwave plasma chemical vapor deposition (MPCVD) technology, and characterized in detail through scanning electron microscopy (SEM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. High-current pulsed emission characteristics, tested with a 2 MeV line-inducing injector, showed that all of CVD diamond films had high emission current density (> 70 A/cm²) and [100] textured B-doped microcrystalline diamond film possessed the largest emission current density of 115.1 A/cm². No obvious bright light and luminescent zones from side view CCD images indicated a possible pure field-emission mechanism of these diamond cathodes. Simultaneously, large decrease in the electron emission capability, above 15%, could be observed after several pulsed measurements, but this decrease could be completely recovered through the treatment of surface re-hydrogenation for emitted diamond cathodes, suggesting that emission performance of CVD diamond cathodes was closely relevant to hydrogen coverage ratio. The present data indicated that as-deposited CVD diamond films could be a potential candidate as cold cathode for the application in high-current electron emission field.     

Dispersion of non-covalently functionalized single-walled carbon nanotubes with high aspect ratios using poly(2-dimethylaminoethyl methacrylate-co-styrene)

Single-walled carbon nanotubes (SWCNTs) with high aspect ratios were well dispersed in organic solvents to form stable suspensions using poly(2-dimethylaminoethyl methacrylate-co-styrene) (poly(DMAEMA-co-St)). The polymeric dispersant poly(DMAEMA-co-St) was synthesized in various compositions by atom transfer radical polymerization. The structures and the compositions of the poly(DMAEMA-co-St) were confirmed by ¹H NMR spectroscopy. The stability and dispersion of the functionalized SWCNTs with high aspect ratios in suspension were observed by dispersion stability analysis, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The existence of unbundled SWCNTs was confirmed by Raman and ultraviolet/visible/near-infrared spectroscopy. Finally, SWCNT transparent conductive films with high transmittances and low sheet resistances were prepared on a poly(ethylene terephthalate) substrate using a spin-coating method.     

Thermionic electron emission from nitrogen-doped homoepitaxial diamond

Nitrogen-doped homoepitaxial diamond films were synthesized for application as low-temperature thermionic electron emitters. Thermionic electron emission measurements were conducted where the emission current was recorded as a function of emitter temperature. At a temperature < 600 °C an emission current was detected which increased with temperature, and the emission current density was about 1.2 mA/cm² at 740 °C. The electron emission was imaged with photoelectron emission microscopy (PEEM) and thermionic field-emission electron microscopy (T-FEEM). The image displayed uniform electron emission over the whole surface area. Thermionic emission and ultraviolet photoemission spectroscopy were employed to determine the temperature dependent electron emission energy distribution from the nitrogen-doped homoepitaxial diamond films. The photoemission spectra indicated an effective work function of 2.4 eV at 550 °C. These values indicate reduced band bending and establish the potential for efficient electron emission devices based on nitrogen-doped homoepitaxial diamond.     

Synthesis and electron field emission properties of nanodiamond films

Effects of CH₄/H₂ ratio and bias voltage of the microwave plasma-enhanced chemical vapor deposition (MPE-CVD) process on the nucleation behavior and associated characteristics of nanodiamonds were investigated. While the scanning electron microscopy (SEM) microstructure and Raman crystal structure of the films insignificantly vary with CH₄/H₂ ratio and bias voltage, electron field emission properties of the materials markedly change with these deposition parameters. The predominating factor modifying the electron field emission properties of the nanodiamond films is presumed to be the increase in the proportion of sp²-bonded grain boundaries when the grain size of the nanodiamond films decreases. Between these two major factors, the bias voltage shows more prominent effects on modifying the granular structure of the nanodiamonds than the CH₄/H₂ ratio does. The best electron field emission properties attainable are J_e=500 μA/cm² at 20 V/μm and E₀=8.5 V/μm.     

Radiation-induced crosslinking in polymer–polyfunctional monomer systems

The does dependence of crosslinking yields was determined for irradiated compositions of poly(vinyl chloride) and polyethylene with an allylic polyfunctional monomer (PFM). Therewith, the notion of the differntial crosslinking yield G^*_c was used. The dose dependence of G^*_c has a maximum for the investigated systems. The current consumption of allylic groups and PFM molecules was determined. In the investigated systems, the process of network formation proceeds through chain crosslinking of graft chains of poly-PFM. © 1996 John Wiley & Sons, Inc.     

Emission characteristics of planar field electron emitters containing carbon nanotubes operating in the high current density mode

Planar field electron emitters containing carbon nanotubes that demonstrate stable emission currents with densities about 1 A/cm² have been fabricated using the chemical vapor deposition method. The analysis of field emission characteristics based on Fowler-Nordheim theory allowed one to calculate not only the field amplification coefficient β, but also the total emission area A of all the emitting nanotubes. Using the value of A and an estimate of the emission area of an individual nanotube fulfilled in this work, the approximate number of emitting nanotubes N before and after the flow of the high density emission current, has been calculated. It has been found that the concentration of the emitting nanotubes N in such field emitters after the high density emission current flow was about 10⁵ cm⁻². Besides this, the location of light radiating nanotubes heated by high density emission currents has been investigated. This has revealed the regions of the emitter surface that gave the main contribution to the electron emission.     

Paramagnetic properties of brown coal from the Kiyaktinskoe deposit before and after mechanical treatment and electron irradiation

Results of a study of the paramagnetic characteristics of brown coal from the Kiyaktinskoe deposit (Kazakhstan) in a native state and after mechanical treatment and electron irradiation are reported. The effects of these actions on changes in the paramagnetic properties of the test coal and on the intensification of a coal hydrogenation process are discussed. It was found that the concentration of free radicals changed only slightly after mechanical treatment in a ball mill at room temperature in an atmosphere of air, whereas the concentration of Fe³⁺ ions noticeably increased. Upon the electron irradiation of coal, the dose dependence of the concentration of free radicals passed through a maximum at a dose of 100 kGy. At the same radiation dose, the yield of a kerosene-gas oil fraction upon the hydrogenation of Kiyaktinskoe coal increased, and the total yield of liquid products increased upon the irradiation of coal and a catalyst (bauxite 094) to a dose of 100 kGy. It was hypothesized that Fe³⁺ ions, which were additionally formed upon coal grinding and irradiation, can serve as an internal catalyst in the course of coal hydrogenation.     

Preparation and characterizations of Pr3+:CaF2 transparent ceramics with different doping concentrations

0.2–5.0?at% Pr³⁺-doped CaF₂ transparent ceramics were fabricated by hot-pressed processing for the first time. The phase compositions, microstructure and optical characteristics of the presented transparent ceramics were examined systematically. The average in-line transmittance of Pr:CaF₂ transparent ceramics (2.0?mm thick) with high Pr³⁺ doping concentrations (1.0–5.0?at%) exceeds 86% at the wavelength of 1200?nm. The absorption spectrum manifests that the prepared Pr:CaF₂ transparent ceramics contain some absorption peaks overlapped with emission bands of the commercial InGaN laser diodes. Further, a detailed investigation on the visible emission properties as a function of Pr³⁺ concentrations in CaF₂ transparent ceramics was reported. The emission spectra presented two main characteristic peaks at 496?nm (bluish green) and 656?nm (red) corresponded to the transitions of ³P₀→³H₄ and ³P₀→³F₂ for Pr³⁺ activator ions. With the increase of the Pr³⁺ doping concentrations, the emission intensity and decay lifetimes decreased generally attributed to the concentration quenching effect. Details on energy transfer mechanism of Pr³⁺ in CaF₂ transparent ceramics were demonstrated and discussed.