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The unstable plume mode of hollow cathodes should be avoided in practical applications because it severely degrades the overall cathode lifetime. In this study, we investigate the spot-plume transition and plasma stability characteristics of an unused segmented lanthanum hexaboride emitter. The expansion of the unstable plume mode region is observed during a discharge experiment. Subsequently, the segmented emitter is retrieved, the inner surface of the emitter is observed, and the work function on the surface is measured at room temperature. The emitter surface exhibits color variations with oxygen and carbon detection. The downstream edge shows the original purple color and almost no degradation in the work function. The high temperature in this region promotes the desorption of carbon and oxygen. In the spot mode, this region mainly contributes to thermionic electron emission; therefore, the discharge voltage in the spot mode does not change during the discharge experiment. Carbon or carbide is detected in the middle of the axial direction on the emitter surface, where the surface temperature is not sufficiently high to desorb carbon during discharge. Based on the surface analysis results, the dominant substance in the region where carbon is detected was lanthanum carbide. An increase in the work function is indicated in the region, which appears to increase the plasma instability. According to previous studies, an increase in the work function results in a rise in the potential in the emitter, and an increase in the electron temperature in the outside plume region induces the plasma instability. Further investigation is needed to understand the mechanism connecting the rise in the work function and the rise in the electron temperature in the plume region. [ABSTRACT FROM AUTHOR]

Inverted organic light-emitting devices (OLEDs) have been aggressively developed because of their superiorities such as their high stability, low driving voltage, and low drop of brightness in display applications. The injection of electrons is a critical issue in inverted OLEDs because the ITO cathode has an overly high work function in injecting electrons into the emission layer from the cathode. We synthesized hexagonal wurtzite ZnO nanoparticles using different oxidizing agents for an efficient injection of electrons in the inverted OLEDs. Potassium hydroxide (KOH) and tetramethylammonium hydroxide pentahydrate (TMAH) were used as oxidizing agents for synthesizing ZnO nanoparticles. The band gap, surface defects, surface morphology, surface roughness, and electrical resistivity of the nanoparticles were investigated. The inverted devices with phosphorescent molecules were prepared using the synthesized nanoparticles. The inverted devices with ZnO nanoparticles using TMAH exhibited a lower driving voltage, lower leakage current, and higher maximum external quantum efficiency. The devices with TMAH-based ZnO nanoparticles exhibited the maximum external quantum efficiency of 19.1%. [ABSTRACT FROM AUTHOR]

A numerical simulation of an intense thermionic emission of electrons from the cathode into the air medium in an electrode system has been performed with regard for the possible changes in the voltage across the electrodes and in the electronic work function of the cathode. Spatial distributions of the electrons, the electron energy, the ions, the electric-field strength, and the concentration of the atomic oxygen in the air medium were constructed with the use of a simplified set of kinetic reactions. A possibility of using the thermionic emission of electrons from a cathode for the cooling of the members of flying vehicles with the aim to proof them against heat loads was demonstrated. The numerical calculations have shown that the thermionic emission of electrons from the cathode in a system of electrodes with no protective resistor at a high pressure does not provide a cooling of the system. [ABSTRACT FROM AUTHOR]

A methodology for implementing the recently developed reformulated general thermal-field equation describing simultaneous thermal and field emission contributions to electron emission is developed, with modifications directed to enhancing speed and accuracy of computation as demanded by emitter characterization and electron beam simulations. An accurate factor to correct both thermal-field (T F) and high field (Fowler-Nordheim or FN) predictions based on a rapid Lorentzian fit model is given. The analytic protrusion model is constructed from modifications to a point dipole model that allow surface elements and field enhancement factors to be rapidly evaluated. The model is applied to an analytical model of a protrusion on a bump in a diode configuration to characterize how current-voltage I (V) relations are affected by T F emission conditions. In addition, it is also shown (i) how aggressively Schottky's conjecture is undermined as the protrusion dimensions become larger; (ii) how the total current in the T F regime can be substantially larger than predicted by canonical [FN and Richardson-Laue-Dushman (RLD)] formulations; (iii) how an optimal protrusion size may exist; and (iv) how the inference of field enhancement, notional emission area, and work function are poorly predicted using conventional methods relying on the canonical FN and RLD equations even outside the thermal-field regime, even though data can be linear on FN and RLD plots. [ABSTRACT FROM AUTHOR]

Theoretical models of thermal, field, and thermal-field emission of electrons generally require the evaluation of the Gamow, or tunneling, factor. A rapid means to do so is developed using shape factor methods for general potentials, but, in particular, for the image charge (or Schottky-Nordheim) barrier from which the Fowler-Nordheim (field emission) and Richardson-Laue-Dushman (thermal emission) equations are derived. The shape factor method provides greater accuracy than the elliptical integral functions that the electron emission equations conventionally rely on and eliminates the need to use them. The mild overprediction of the field emission current by the Fowler-Nordheim equation at very high fields is corrected. Undesired behaviors associated with prior versions of the general Thermal-Field equation in the thermal-field regime are eliminated by properly identifying the maximum of the current density integrand and accounting for its shape. The methodology to rapidly identify the current density maximum in general is demonstrated for various combinations of field, temperature, and work function, and the improvements demonstrated. The utility of the reformulated methodology for the simulation of electron beams and the ability to characterize cathode configurations of technological interest are discussed. [ABSTRACT FROM AUTHOR]

Engineering a material's work function is of central importance for many technologies and in particular electron emitters used in high‐power vacuum electronics and thermionic energy converters. A low work function surface is typically achieved through unstable surface functional species, especially in high power thermionic electron emitter applications. Discovering and engineering new materials with intrinsic, stable low work functions obtainable without volatile surface species would mark a definitive advancement in the design of electron emitters. This work reports evidence for the existence of a low work function surface on a bulk, monolithic, electrically conductive perovskite oxide: SrVO3. After considering the patch field effect on the heterogeneous emitting surface of the bulk polycrystalline samples, this study suggests the presence of low work function (≈2 eV) emissive grains on SrVO3 surface. Emission current densities of 10–100 mA cm–2 at ≈1000 °C, comparable to commercial LaB6 thermionic cathodes, indicative of an overall effective thermionic work function of 2.3–2.7 eV are obtained. This study demonstrates that perovskites like SrVO3 may have intrinsically low work functions comparable to commercialized W‐based dispenser cathodes and suggests that, with further engineering, perovskites may represent a new class of low work function electron emitters. [ABSTRACT FROM AUTHOR]

Low work function materials are desirable in many applications such as electron emission and photocatalysis. We have studied low energy electron emission from low work function hydrogen terminated diamond surfaces via electron spectroscopy to gain insight into the mechanisms involved during electron excitation and emission. Electron emission was found to be dominated by electrons within the band gap energy region, allowed due to the negative electron affinity diamond surface, while sub-bandgap illumination was able to significantly increase emission current. Substantial upward surface band bending greater than 2 eV was observed for the diamond samples, which affect electron accumulation at the surfaces. Intra-bandgap states are shown to strongly influence electron emission behavior, which can have great implications for various energy conversion devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Experimental observations have long-established that there exists a smooth roll-off or knee transition between the temperature-limited (TL) and full-space-charge-limited (FSCL) emission regions of the emission current density-temperature (J – T) (Miram) curve, or the emission current density-voltage (J – V) curve for a thermionic emission cathode. In this article, we demonstrate that this experimentally observed smooth transition does not require frequently used a priori assumptions of a continuous distribution of work functions on the cathode surface. Instead, we find that the smooth transition arises as a natural consequence of the physics of nonuniform thermionic emission from a spatially heterogeneous cathode surface. We obtain this smooth transition for both J – T and J – V curves using a predictive nonuniform thermionic emission model that includes 3-D space charge, patch fields (electrostatic potential nonuniformity on the cathode surface based on local work function values), and Schottky barrier lowering physics and illustrates that a smooth knee can arise from a thermionic cathode surface with as few as two discrete work function values. Importantly, we find that the inclusion of patch field effects is crucial for obtaining accurate J – T and J – V curves, and the further inclusion of Schottky barrier lowering is needed for accurate J – V curves. This finding and the emission model provided in this article have important implications for modeling electron emission from realistic, heterogeneous surfaces. Such modeling is important for an improved understanding of the interplay of emission physics, cathode materials engineering, and the design of numerous devices employing electron emission cathodes. [ABSTRACT FROM AUTHOR]

MXenes have attracted intensive attention in chemistry and material science for their special structures and properties. In order to understand the basic physical properties of the M3C2/M3C2T2 (MSc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W; TF, O, OH) MXenes, first‐principles calculations are carried out to investigate the structural, vibrational, and mechanical properties in this work. Both the metal atoms and surface groups can significantly influence the configurations or mechanical behaviors of the MXenes. The dehydrogenation tendency is calculated to evaluate the possible forms of the M3C2(OH)2 toward M3C2O2. The work functions of MXenes functionalized by different groups are compared, and the lower work functions for the OH functionalized ones, which can be as low as 1.358 eV for the Sc3C2(OH)2, suggest potential good performance in electron emission. In addition, the stability, mechanical properties, and the Raman and infrared (IR) activity modes of the MXenes are reported. Generally, functionalized MXenes would present smaller lattice parameters, lower free energies, and stronger mechanical strength compared to their counterparts. The data obtained may provide important theoretical ground for the investigations of the applications of MXenes. [ABSTRACT FROM AUTHOR]

Observation at low voltage using scanning electron microscopes (SEMs) enables the characterization of surface details on specimens on a nanometer scale and is widely used in science and industry. However, the energy width of the electron source restricts the spatial resolution of SEMs at low voltage, but it can be narrowed by lowering the work function of the emitter material. Here, we developed a cold field emitter using a cerium hexaboride single crystal (CeB6-CFE) as a monochromatic electron source. The work function of the CeB6 (310) plane was estimated to be as low as 2.25 ± 0.17 eV, and the energy width ranged from 0.17 to 0.26 eV for angular current densities ranging from 0.10 to 80 μA/sr. This energy width was 20% to 30% narrower than that of conventional W(310)-CFEs. Using the CeB6-CFE, the spatial resolution of the SEM at an acceleration voltage of 0.5 kV was improved by 11% compared with that of an SEM using the W(310)-CFE. [ABSTRACT FROM AUTHOR]

The coexistence of two regimes of aluminum (Al) particle combustion is discussed. A slower regime occurs at a low energy accommodation coefficient (EAC) and is usually observed in Al combustion experiments. A faster regime at high EAC is also possible. The combustion enhancement observed for pre-treated Al particles can be interpreted as a switch from the slower combustion regime to the faster regime. The value of EAC is controlled by the thermionic emission of electrons. A relationship between Al particle pre-treatment and the work function, which governs the thermionic emission, and, therefore, the EAC, is a subject of further studies. [ABSTRACT FROM AUTHOR]

A technique for obtaining carbon nanotubes (CNTs) doped with nitrogen in ammonia plasma has been developed. In this technique, CNTs synthesized by a method excluding their doping with nitrogen are post-treated in ammonia plasma. This treatment leads to a more than fivefold increase in the concentration of nitrogen (from 0.7 to 3.6 at %), a sixfold decrease in the resistance, and a 10% decrease in the work function of CNTs, resulting in stabilization of the process of cold electron emission. [ABSTRACT FROM AUTHOR]

Large-size and high-quality single-crystal GdB6 conductive ceramics (length greater than 35 mm and diameter greater than 6 mm) were prepared by optical zone melting, and the single-crystal quality was characterized by single-crystal diffraction, Laue photo, crystal plane rocking curve, and single-crystal fracture scan. Electrochemical corrosion equipment of single-crystal GdB6 conductive ceramic tips was newly designed, which greatly reduced the preparation time of tips from more than 10 h to 2.75 h. The field electron emission current density of the single-crystal GdB6 conductive ceramic tip (r ≈ 500 nm) prepared by the device under applied voltage (2550 V) is 2.24 × 104 A/cm2. This paper also theoretically calculates the electronic structure and electron work function of single-crystal GdB6 under a strong electric field (0.1 V/Å). The trapping ability of the B-octahedron in the single crystal GdB6 conductive ceramics against the free electrons of Gd is greatly weakened under a strong electric field (0.1 V/Å), and the free electrons also have a certain enrichment phenomenon on the surface of GdB6. The surface barrier of single-crystal GdB6 conductive ceramic will be shortened and narrowed sharply due to the strong electric field (0.1 V/Å), which causes the work function of (100) crystal plane of single-crystal GdB6 to decrease sharply (0.38 eV). This causes the free electrons in Gd to have greater energy at the time of emission, and it is easier to get rid of the trap of surface barriers, which is conducive to field electron emission. [ABSTRACT FROM AUTHOR]

High‐temperature thermionic electron emission from different types of individual suspended carbon nanotubes (CNTs) in a homemade chip is studied. When collecting emission electrons with an external electrode, it is found that the collecting electric field influence the transport current in the CNTs, and the thermionic electron emission deviated from the traditional thermionic electron emission model and cannot reach "saturation". This effect is analyzed for single‐walled, double‐walled, multiwalled‐CNT and CNT bundles. It is found that this effect show correlation with the conductivity and diameter of the CNT. With the increase in metallicity, the influence of collecting electrode is gradually weakened. Also, the effect shows a negative correlation with the diameter of CNTs. An equation is proposed to describe the measured thermionic emission curve and determine the "effective" work function of the CNT. [ABSTRACT FROM AUTHOR]

A generalized formula for electron emission current as a function of temperature, field, and electron work function in a metal–dielectric system has been derived with regard to the quantum nature of image forces. For free electrons, the Fermi–Dirac distribution and a quantum image potential obtained in terms of the electron polaron theory have been used. The well-known Richardson–Schottky formula (for thermionic emission) and Fowler–Nordheim formula (for field emission) have been derived in the limit of the image force classical potential. It has been shown that at high temperatures and electric fields E ≥ 10 MV/cm, the polaron contribution grows with field and declines with rising temperature. The decrease in emission current is associated with the increase in effective work function of electrons, which is due to the electron polaron effect. Extrapolation formulas suitable for theoretical estimation of thermionic and cold emission currents have been obtained. [ABSTRACT FROM AUTHOR]

Using the methods of optically stimulated electron emission (OSEE) and ambient pressure photoemission spectroscopy (APS), the energy characteristics of carbyne-containing films on copper and silicon substrates have been studied. The average contact potential difference and the work function were determined, and the positions of the Fermi level for carbyne-containing films of various thicknesses were calculated. It was found that the electrons work function and the position of the Fermi level of the studied film samples do not depend on the film thickness and the type of substrate. The information content of the OSEE and APS methods for evaluating the quality of carbon coatings on substrates is shown. [ABSTRACT FROM AUTHOR]

Single-crystal CeB6 tips with different curvature radii are prepared simply and efficiently by using an independently designed electrochemical corrosion device; the average preparation time of a tip was only about 2.75 h. The field emission performance test results show that the single-crystal CeB6 tip exhibits excellent field emission performance. When the applied voltage was 2550 V, the current density of a tip with a curvature radius of about 500 nm is 2.11 × 104 A/cm2, and as the curvature radii increases, the field emission current density drops sharply. The first principle calculation of the electronic structure and work function of single-crystal CeB6 under an electric field show that the free electron energy of single-crystal CeB6 increases and is enriched at the surface under a strong electric field of 0.1 V/Å, with a reduced surface barrier. The CeB6 work function under the strong electric field was greatly reduced, which is conducive to electron emission. By calculating the difference between the vacuum level and the Fermi level, a surface work function of 0.42 eV with an applied electric field of 0.1 V/Å of CeB6 was obtained. This provides theoretical support for the single-crystal CeB6 tip exhibiting excellent field emission performance. [ABSTRACT FROM AUTHOR]

The influence of defects on the surface of the semiconductor is irreversible. The influence of intrinsic point defects on the electronic properties of n-doped GaN (0001) surface is studied based on the first principles. The results show that, the N interstitial defect (Ni) and Ga Vacancy (VGa) are the more easily formed in the case of Si doping. The defect level generated by an appropriate amount of defects contributes to the transition of electrons, thereby improving the n-type conductivity characteristics. In particular, the Ga vacancy makes the work function drop significantly, which promotes the emission of electrons. However, once the defects inside the material exceed a certain level, any defects will play a counterproductive role. This paper could provide some guidance for the preparation of n-GaN optoelectronic devices. [ABSTRACT FROM AUTHOR]

The electronic structures and work functions of the single-wall BC3 nanotubes are studied by the first-principle method. In contrast to the armchair nanotubes, the zigzag nanotubes are indirect-band semiconductors. The zigzag nanotubes can be further classified into two types, depending on the wave-vector characteristics of the conduction band minima. The bandgap energies of the armchair nanotubes are always smaller than that of the BC3 sheet, and increase with the nanotube diameter. For the two types of zigzag nanotubes, the bandgap energies are always larger than that of the BC3 sheet, and decrease with the nanotube diameters. Analysis of the bond angles between the neighboring atoms on the nanotube walls shows that the mixing of the π and σ electron orbitals exhibits opposite trends for the armchair and zigzag nanotubes. These trends are not only responsible for the above dependence of the electronic structures on the types and diameters of the nanotubes, but also give physical insight to the indirectness of the band-structures of the zigzag nanotubes. By the first-principle method, it is found that the work functions of both armchair and zigzag nanotubes scale linearly with 1/D2, D being the nanotube diameter. Moreover, it is found that the per-atom strain energies and the vacuum bandwidths of both armchair and zigzag nanotubes satisfy universal relations which also scale linearly in 1/D2. [ABSTRACT FROM AUTHOR]

Hot electrons and the associated ballistic and quasiballistic transport, heretofore neglected endemically, across the active regions of InGaN light emitting diodes (LEDs) have been incorporated into a first order simple model which explains the experimental observations of electron spillover and the efficiency degradation at high injection levels. The model is in good agreement with experiments wherein an adjustable barrier hot electron stopper, commonly called the electron blocking layer (EBL), is incorporated. The model is also in agreement with experiments wherein the electrons are cooled, eliminating hot electrons, inside a staircase electron injector (SEI) prior to their injection into the active region. Thermionic emission from the active region, even if one uses an uncharacteristically high junction temperature of 1000 K, fails to account for the carrier spillover and the experimental observations in our laboratory in samples with varying EBL barrier heights. The model has been successfully applied to both m-plane (lacking polarization induced electric field) and c-plane (with polarization induced field) InGaN double heterostructure (DH) LEDs with a 6 nm active region featuring a variable barrier hot electron stopper, and a SEI, and the various combinations thereof. The choice of DH LEDs stems from our desire to keep the sample structure simple as well as the model calculations. In this paper, the theoretical and experimental data along with their comparison followed by an insightful discussion are given. The model and the approaches to eliminate carrier spillover proposed here for InGaN LEDs are also applicable to GaN-based laser diodes. [ABSTRACT FROM AUTHOR]

Studies of mechanical force acting on electrons inside a solid are of both fundamental and practical importance. This is especially emphasized by the recent applications of the Kelvin probing technique to investigate mechanical behavior of surfaces and interfaces. However, the effect of deformation on the electron work function (EWF) and its physical mechanism have not been well understood. In this study, simultaneous responses of the EWF of copper and aluminum to deformation during bending tests were measured in situ. It was demonstrated that in the elastic range, the tensile strain decreased the EWF, whereas compressive strain increased the EWF. However, in the plastic range, the EWF always decreased with strain for both tension and compression deformations. Considering changes in electrostatic energy of a one-dimensional lattice caused by dislocation density, we proposed a simple model and quantitatively established a correlation between the EWF and strain, which is consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

An electrical model based on drift diffusion is described. We have explored systematically how the shape of the current density-voltage (J-V) curves is determined by the input parameters, information that isessential when deducing values of these parameters by fitting to experimental data for an ITO/PPV/Al organic light-emitting device (OLED), where ITO is shorthand for indium tin oxide and PPV is poly(phenylene vinylene). Our conclusion is that it is often possible to obtain a unique fit even with several parameters to fit. Our results allowing for a tunneling current show remarkable resemblance to experimental data before and after the contacts are conditioned. We have demonstrated our model on single-layer devices with ITO/PFO/Au and ITO/PEDOT/PFO/Au at room temperature and ITO/TPD/Al over temperatures from 130 to 290 K. PFO is shorthand for poly(9,9′-dialkyl-fluorene-2,7-dyl) and TPD is shorthand for N,N′-diphenyl-N,N′-bis(3-methylphenyl)1-1′-biphenyl-4,4′-diamine. Good fits to experimental data have been obtained, but in the case of the TPD device, only if a larger value for the relative permittivity εs than would be expected is used. We infer that a layer of dipoles at the ITO/TPD interface could be responsible for the observed J-V characteristics by locally causing changes in εs. The strong temperature dependence of the hole barrier height from fitting J-V characteristics to the experimental data may indicate that the temperature dependence of the thermionic emission model is incorrect. [ABSTRACT FROM AUTHOR]

Results are reported on p-GaAs homojunction interfacial work function internal photoemission far infrared (HIWIP FIR) detectors with a ∼ 10[SUB19] cm[SUB-3] carbon doped single emitter and a barrier layer for three different barrier thicknesses. A remarkably high quantum efficiency with low dark current and an increased responsivity were observed the devices with 1-, 0.1-, and 4-μm-thick barrier regions. The dark current densities for these structures are on the order of 1 - 10 μA/cm[SUB2] at 4.2 K, corresponding to a high dynamic resistance compared with previous HIWIP FIR detectors. A detector with a barrier thickness of 1 μm had a peak responsivity of 18.6 A/W, a peak detectivity D*= 9 × 10[SUB11] cm Hz√ /W, and a quantum efficiency of 40% at a wavelength of 58 μm under a reverse bias measured at 4.2 K. Cutoff wavelengths of these detectors vary with bias and are around 70 μm as expected. The main features of the absorption and responsivity spectra are well described based on a model incorporating free carrier absorption, hot hole transport, and emission over the barrier. [ABSTRACT FROM AUTHOR]

Monoatomic carbon chains and carbyne-rich composites are promising materials for many applications from protective coatings to nanoelectronic devices. Therefore, a thorough understanding of both the atomic and electronic structure of chained carbon is important. In this study, a combination of Raman scattering and electron photoemission techniques is used to study the bonding types, electron work functions and band gaps for carbyne-containing films on copper and silicon substrates. Raman mapping shows the nonuniform distribution of sp1 hybridization across the carbon-coated area on polycrystalline copper substrate due to adhesion differences. UV-excited electron emission dependence on thickness and ambient pressure confirms the difference between the silicon- and copper-based samples. Comparison with DFT calculations performed on surface slab models allows to draw conclusions about the chained composite structure. Image 106 [ABSTRACT FROM AUTHOR]

The adsorption of three gases on the wurtzite GaAs nanowires (100) surface are systematically studied via first principles. The optoelectronic properties of GaAs nanowires absorbed by CH 4 , H 2 and H 2 O are analyzed. The surface absorbed with H 2 O has the lowest adsorption energy, thus it is the easiest to adsorb on the surface. The gas adsorption makes the increase of band gaps, work functions and surface electron affinity, especially H 2 O adsorption system with the largest band gap of 1.34eV. The adsorption of these gases generates a dipole moment pointing from the GaAs nanowires to the residual gas molecules. For H 2 O molecular adsorption, which impedes the electron emission and decrease electrons emission capacity. The surface structures also reconstruct with different degrees. The residual gas adsorption can greatly affect the optical properties of the surface and undermine the performance of GaAs nanowire, particularly H 2 O adsorption. This work can help to understand the fading mechanism of the performance of optoelectronic devices based on GaAs nanowires. [ABSTRACT FROM AUTHOR]

Composite metal oxide-coated tungsten cathodes were formulated as efficient and reliable thermo-electron sources for vacuum ultraviolet ionizers. Cathode suspensions were prepared by adding metal chlorides forms of four different metals; scandium, yttrium, indium, and neodymium (Sc, Y, In and Nd) to the triple calcium, strontium, and barium (Ca, Sr, and Ba) suspension. The improvement of electron emission and reliability of the cathodes has been achieved by adding Sc, Y, In, and Nd. The metal salts were activated to the oxide cathodes by a finely programmed calcination process under ultra-high vacuum (∼10−6 torr) and the inert atmosphere. Compared to the reference suspensions, the electron emissions of neodymium and yttrium type cathodes were significantly enhanced. The optimized formulation is the cathode containing as low as 1 mole% of yttrium exhibiting the greatest performance among them. [ABSTRACT FROM AUTHOR]

Highlights • The anti-corrosion property of nano-TiO 2 /Ni composite foil becomes worse after UV light illumination, while that of the micro-TiO 2 /Ni composite foil showed little changes. • UV illumination stimulated the nano-TiO 2 semiconductor, leading to elevated conductivity in favor of passing corrosion current. • The UV illumination increased the fraction of Ni 2 O 3 component in formed oxide film on the nano-TiO 2 /Ni foil, which is porous, loose, brittle and less protective compared to the naturally formed NiO film on Ni. Abstract Effects of ultraviolet (UV) light illumination on the corrosion behavior, surface state, and activities of electrodeposited micro-TiO 2 /Ni and nano-TiO 2 /Ni composite foils in 3.5% NaCl solution were investigated by means of polarization measurement, electrochemical impedance spectra (EIS), electron work function mapping (EWF) and XPS spectra analysis using an electrochemical system, the atom force microscopy (AFM) and X-ray photoelectric spectroscopy (XPS), respectively. The UV light illumination resulted in a considerable decrease in corrosion resistance of the nano-TiO 2 /Ni composite foil but showed much less effect on the micro-TiO 2 /Ni composite foil. Surface state analysis demonstrated that the UV illumination stimulated the nano-TiO 2 semiconductor with elevated conductivity in favor of passing corrosion current. The UV illumination increased the fraction of Ni 2 O 3 component in formed oxide film on the nano-TiO 2 /Ni foil , which is porous, loose, brittle and less protective, compared to the naturally formed NiO film on Ni. The changes in surface state were responsible for variations in the corrosion behavior of micro-TiO 2 /Ni and nano-TiO 2 /Ni composite foils caused by the UV light illumination. [ABSTRACT FROM AUTHOR]

Work function (WF) and some physicochemical data for several most prominent crystal planes of three metals of typical structures are calculated within the linear approximation employing the surface dipole and 2D gas models. “Composite” crystal of a homogeneous bulk phase and a thick surface composed of eight (h k l)-oriented facets with different unsaturated bonds is treated as a nine-phase nine-component system with two degrees of freedom. It contains the two-dimensional metal-lattice plasma of free electrons and the immobile atom-core network. For twenty four (h k l) surfaces, the WF and dipole barrier term, chemical and electrostatic potential levels, electron charge densities, surface dipole fields, and other parameters are calculated and tabularized. WF values obtained from the thermodynamics based formula are compared to the ones obtained from the quantum mechanics based formula, which shows good agreement with experiment and also reveals a specific deviation in the case of field emission method for the most packed plane. A set of accurate face dependent data can be of interest to electronics and materials science workers [ABSTRACT FROM AUTHOR]

Hybrid emitters consisting of ZnO nanowires decorated with Zn nanoflakes were prepared for electron emission applications. The ZnO nuclei, having a pyramidal shape, were deposited on the ZnO:Al buffer layer, which offered surface protrusions for vertical nanowire growth. The Zn hexagonal nanoflakes, having thicknesses of 15–20 nm, were decorated to increase the conductivity and number of emission sites of the ZnO nanowires. The field enhancement factor increased from 8623 to 18108 and the work function was reduced from 5.3 to 3.35 eV after decorating the nanowires with Zn nanoflakes. A low turn-on field of 0.65 MV/m and high current density of 1.46 mA/cm 2 were obtained. The current density variation measured at 350 V was less than 23% over a measurement time of 180 min. [ABSTRACT FROM AUTHOR]

Large area, Si-nanofacets are synthesized by obliquely incident low energy Ar + -ion-beam bombardment at room temperature (RT). The field emission properties of such nanofacets are studied based on current–voltage measurements and the Fowler–Nordheim equation. Low turn-on field with relatively high current density is obtained due to the shape and an overall rough morphology. We demonstrate a tunable field emission property from the silicon nanofacets by varying the ion exposure time. Atomic force microscopy (AFM) in conjunction with Kelvin probe force microscopy (KPFM) measurements provide the information on the aspect ratio and confirms the presence of native oxide layer near the apexes of the facets, respectively. The inhomogeneous oxidation leads to an increase in the local work function at the apexes of the facets, restricting the electron emission from the same. Due to its room temperature fabrication, the present method is of great significance to the low-cost vacuum field emission devices fabrication. [ABSTRACT FROM AUTHOR]

The aim of this paper is to implement a theoretical prediction and evaluation on the quality of graphene–C 70 composite as cathode material. The pristine graphene–C 70 composite and the B-doped graphene–C 70 composites were constructed to investigate their field emission properties. The results suggest that the work function (WF) and ionization potential (IP) of the composites decrease with the increasing electric field. It implies that the electron emission becomes more and more easy. Under the field, the molecular orbital energy levels close to the vacuum level and their energy gap also has a declining trend. It means a good trend for improving the field emission properties of the composites. The above mentioned results show that the composites have the advanced capacity for electron emission and the potential for cathode material. It makes us believe that the composites will be the good field emission electron sources in the electronic device fabrication and the investigation can give a theoretical guidance for the corresponding experiments and may develop the application of fullerene for field emission. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the improvement of figures of merit for charge plasma based tunnel field-effect transistor (TFET) in terms of ON-state current, threshold voltage, sub-threshold swing, ambipolar nature, and gate to drain capacitance which provides better channel controlling of the device with improved high frequency response at ultra-low supply voltages. Regarding this, we simultaneously employ work function engineering on the drain and gate electrode of the charge plasma TFET. The use of gate work function engineering modulates the barrier on the source/channel interface leads to improvement in the ON-state current, threshold voltage, and sub-threshold swing. Apart from this, for the first time use of work function engineering on the drain electrode increases the tunneling barrier for the flow of holes on the drain/channel interface, it results into suppression of ambipolar behavior. The lowering of gate to drain capacitance therefore enhanced high frequency parameters. Whereas, the presence of dual work functionality at the gate electrode and over the drain region improves the overall performance of the charge plasma based TFET. [ABSTRACT FROM AUTHOR]

Thermionic emission performance from single crystals of CeB6 and LaB6 was investigated at different operational loads using a test machine, in order to consider CeB6 as a cathode for thermionic RF guns in the future applications. To evaluate cathode quality and uniformity for long lifetime applications, Miram curves in conjunction with their associated practical work function distribution (PWFD) were applied to the thermionic emission results. The analysis of the PWFD plot revealed that the variation of the peak in the work function and full-width at half-maximum for CeB6 is very close to that of LaB6. This suggests that emission performance, uniformity, and expected operational lifetime of a CeB6 cathode are comparable with LaB6 cathodes. In addition, previous simulation results of the back bombardment (BB) effect on CeB6 and LaB6 emphasized that CeB6 presents less sensitivity to BB electrons compared with LaB6 at a 5.5- \mu \texts pulse duration and 8-MW RF power. This gives CeB6 the potential to replace LaB6 as a thermionic cathode for an RF gun. A complete analysis of the cathode emission performance and PWFD at different operational loads for CeB6 prior to a prospective real test is presented. [ABSTRACT FROM PUBLISHER]

Field emission was achieved utilizing vertically aligned carbon nanotubes (CNTs), whose external surface was decorated with Au nanoparticles (NPs). It was found that the average length and diameter of the CNTs were \sim 4.52~\mu \textm and 45 nm, respectively. Au NPs (around 5 nm) were coated onto CNT surfaces for field emission. The turn-ON field and current density of the Au-coated CNTs clearly indicate that the Au NPs considerably enhanced field emission. Au NP decoration effectively decreased the work function and turn-ON field. [ABSTRACT FROM AUTHOR]

Low work function materials are criticalfor energy conversion and electron emission applications. Here, wedemonstrate for the first time that an ultralow work function grapheneis achieved by combining electrostatic gating with a Cs/O surfacecoating. A simple device is built from large-area monolayer graphenegrown by chemical vapor deposition, transferred onto 20 nm HfO2on Si, enabling high electric fields capacitive charge accumulationin the graphene. We first observed over 0.7 eV work function changedue to electrostatic gating as measured by scanning Kelvin probe forcemicroscopy and confirmed by conductivity measurements. The depositionof Cs/O further reduced the work function, as measured by photoemissionin an ultrahigh vacuum environment, which reaches nearly 1 eV, thelowest reported to date for a conductive, nondiamond material. [ABSTRACT FROM AUTHOR]

It is found that for objects possessing small surface structures with differing radii of curvature the secondary electron emission (SEE) yield may be significantly higher than for objects with smooth surfaces of the same material. The effect is highly pronounced for surface structures of nanometer scale, often providing a more than 100% increase of the SEE yield. The results also show that the SEE yield from surfaces with structure does not show a universal dependence on the energy of the primary, incident electrons as it is found for flat surfaces in experiments. We derive conditions for the applicability of the conventional formulation of SEE using the simplifying assumption of universal dependence. Our analysis provides a basis for studying low-energy electron emission from nanometer structured surfaces under a penetrating electron beam important in many technological applications. [ABSTRACT FROM AUTHOR]

The work functions of Cu-2.7Be and Cu-2.0Be (wt%) alloys were measured using ultraviolet photoelectron spectroscopy, and their dependence on secondary phase characteristics (composition and distribution) was investigated. The work function properties were significantly altered when the Be content was increased from 2.0 to 2.7 wt%, which was attributed to the introduction of secondary phases ( β and γ) in the alloys with higher Be content. Furthermore, the distribution of secondary phases may also have influenced the gradients of the work function curves measured by UPS. [ABSTRACT FROM AUTHOR]

This paper reviews electron emission from negative electron affinity (NEA) diamond and gives account of the recent developments in alternatives to hydrogen-termination for producing NEA diamond surfaces, particularly using lithium on oxygen-terminated diamond. We discuss the background and motivation for using alkali metals and present both experimental and computational results that cover structure, electronic properties, photoemission, and total photoyield. Secondary yield enhancement of over 200 × is demonstrated over a reference surface with positive electron affinity. [ABSTRACT FROM AUTHOR]

Abstract: A general phenomenological model is presented for obtaining the zero Kelvin work function of any crystal facet of metals and semiconductors, both clean and covered with a monolayer of electropositive atoms. It utilizes the known physical structure of the crystal and the Fermi energy of the two-dimensional electron gas assumed to form on the surface. A key parameter is the number of electrons donated to the surface electron gas per surface lattice site or adsorbed atom, which is taken to be an integer. Initially this is found by trial and later justified by examining the state of the valence electrons of the relevant atoms. In the case of adsorbed monolayers of electropositive atoms a satisfactory justification could not always be found, particularly for cesium, but a trial value always predicted work functions close to the experimental values. The model can also predict the variation of work function with temperature for clean crystal facets. The model is applied to various crystal faces of tungsten, aluminium, silver, and select metal oxides, and most demonstrate good fits compared to available experimental values. [Copyright &y& Elsevier]

The article uses the analytical equation for the work function of metals, made by one of the authors, to study the structure of aluminum alloys, which are increasingly used in the shipbuilding industry. For example, of selected alloys Al-Cu, Al-Ta and Al-Ti are presented graphically changes in work function depending on the percentage composition of the alloy. Also presented an equation that allows to evaluate the work function for multicomponent alloys. [ABSTRACT FROM AUTHOR]

The impact of the edges and the presence of dopants to the work function (WF) of graphene nanoribbons (GNR) and nanoflakes was studied by an ab initio approach. The strong dependence of the WF upon the GNR structure was found and a promising character for the field emission by the donor type impurities was observed. Basing on the predominant impact of the nanostructure edges to the emission properties, the small graphene flakes were investigated as a possible source for the electron emission. The obtained weak dependence of the low WF values of the graphene flakes on their size and shape allows to suggest that the pure carbon medium with high and uniform emission properties can be fabricated by today's technology. [ABSTRACT FROM AUTHOR]

The effects of crystallization on the electron work function and corrosion resistance of Zr65Al7.5Cu17.5Ni10amorphous alloys have been studied. The single-phase amorphous alloy exhibits a better corrosion resistance and has a higher work function than the partially and fully crystallized alloys with the same composition. The close relationship between corrosion resistance and work function indicates that the Kelvin probe technique can be a powerful tool for characterizing the corrosion behaviour of amorphous alloy on an electronic level. [ABSTRACT FROM AUTHOR]

Abstract: Plasmon-enhanced photoelectron emission in the near-field region of gold nanostructures is reported. We show that, depending on the photon energy of the excitation light, the emission from the near-field region can be markedly stronger than from the plasmonic gold itself. Photoemission micrographs also indicate that the spatial confinement of the near-field emission is stronger than in the gold and that the near-field emission exhibits a strong sensitivity on the linear and circular polarization state of the excitation light. The results are explained in terms of work-function differences between the near-field region and the plasmonic material and an interaction between propagating and localized surface plasmon modes. We suggest that the circular polarization sensitivity of the near-field surface plasmon modes may open the way to generate spin-polarized electrons in a plasmon-induced photoemission process. [Copyright &y& Elsevier]

We have used ultraviolet and inverse photoemission spectroscopy to determine the transport gaps (Et) of C60 and diindenoperylene (DIP), and the photovoltaic gap (EPVG) of five prototypical donor/acceptor interfaces used in organic photovoltaic cells (OPVCs). The transport gap of C60 (2.5 ± 0.1) eV and DIP (2.55 ± 0.1) eV at the interface is the same as in pristine films. We find nearly the same energy loss of ca 0.5 eV for all material pairs when comparing the open circuit voltage measured for corresponding OPVCs and EPVG. [ABSTRACT FROM AUTHOR]

Thermionic emission from monolayer graphene grown on representative transition metals, Ir and Ru, is characterized by low-energy electron microscopy. Work functions were determined from the temperature dependence of the emission current and from the electron energy spectrum of emitted electrons. The high-temperature work function of the strongly interacting system graphene/Ru(0001) is sufficiently low, 3.3 ± 0.1 eV, to have technological potential for large-area emitters that are spatially uniform, efficient, and chemically inert. The thermionic work functions of the less strongly interacting system graphene/Ir(111) are over 1 eV larger and vary substantially (0.4 eV) between graphene orientations rotated by 30°. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the triboelectron emission (TriboEE) occurring in sliding contact between metals and polytetrafluoroethylene (PTFE) has been investigated. The mapping of the TriboEE intensity for 16 kinds of metals onto the periodic table revealed that the order of the TriboEE intensity between two adjoining metals in the same period was well correlated with that of the work function and photoelectric threshold of metal samples and with that of the surface potential of metal samples and mated PTFE riders after the TriboEE measurement. The relationship of TriboEE intensity to the electronegativity, the ionization energy, and the electron affinity of the elements and the electrical conductivity of metals was also examined. [Copyright &y& Elsevier]

Magnetic circular dichroism (MCD) in near-threshold photoemission is measured for a perpendicularly magnetized Cs/Co/Pt(111) film with work function adjusted by Cs adsorption. For one-photon photoemission (1PPE) the MCD asymmetry is recorded at a fixed photon energy of hv = 3.06 eV and varying work function Φ. The asymmetry shows a nonmonotonous behavior in dependence of the excess energy hv-Φ with a maximum value of A1PPE = 6.2 % at Φ = 2.45 eV. The measurement explores the first excitation step of a former two-photon photoemission (2PPE) measurement with A2PPE = 8.4% demonstrating that in 2PPE from Co( 111) the first excitation step is the dominant asymmetry-generating process. An energy-dependent measurement in 2PPEat reduced work function (Φ ≈ 3eV) yields a constant asymmetry of about 17% in the photon energy range between hv = 1.53-1.66 eV. It reveals that for Co(l11) the involvement of a real intermediate state is crucial for enlarged MCD asymmetries. Both results are discussed in the framework of direct interband transitions in directions deviating from the direction of normal electron emission &Ggr;-L. The 1PPE measurement is in reasonable agreement with calculations on the basis of this model. This reveals that an ab initio calculation considering all directions of excitation with an additional restriction in energy due to the existence of the sample work function in the photoemission process adequately describes MCD asymmetries in near-threshold photoemission. [ABSTRACT FROM AUTHOR]

The effect of deformational nanostructuring on the electron work function for nickel is investigated. The current-voltage characteristic of the gas discharge with nanocrystalline nickel as the cold cathode is measured. It is found that the electron work function is considerably reduced and the ion-electron emission current in the gas discharge increases upon a decrease in the average size of nickel grains to 100 nm. The observed changes in the electron work function and in the ion-electron emission are analyzed. [ABSTRACT FROM AUTHOR]

Following an extremely interesting idea (Schieber 1984), published long ago, the work function associated with the emission of ultra-relativistic electrons from magnetically deformed metallic crystal (mainly iron) at the outer crust of a magnetar is obtained using relativistic version of Thomas-Fermi type model for electron distribution around the nuclei in this region. In the present scenario, surprisingly, the work function becomes anisotropic; the longitudinal part is an increasing function of magnetic field strength, whereas the transverse part diverges. [ABSTRACT FROM AUTHOR]