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Electron Emission (electron + emission)

Distribution by Scientific Domains

Physics and Astronomy	61%
Polymers and Materials Science	15%
Chemistry	15%

Selected Abstracts

ChemInform Abstract: Electron Emission from N(BF3)3- 4 Hindered by a Sphere of Negative Charges.

CHEMINFORM, Issue 4 2002
A. Dreuw
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Fluid Model of a Sheath Formed in Front of an Electron Emitting Electrode Immersed in a Plasma with Two Electron Temperatures

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 2 2005
T. Gyergyek
Abstract The formation of a sheath in front of a negatively biased electrode (collector) that emits electrons is studied by a one-dimensional fluid model. Electron and ion emission coefficients are introduced in the model. It is assumed that the electrode is immersed in a plasma that contains energetic electrons. The electron velocity distribution function is assumed to be a sum of two Maxwellian distributions with two different temperatures, while the ions and the emitted electrons are assumed to be monoenergetic. The condition for zero electric field at the collector is derived. Using this equation the dependence of electron and ion critical emission coefficients on various parameters - like the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons - is calculated for a floating collector. A modification of the Bohm criterion due to the presence of hot and emitted electrons is also given. The transition between space charge limited and temperature limited electron emission for a current-carrying collector is also analyzed. The critical potential, where this transition occurs, is calculated as a function of several parameters like the Richardson emission current, the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cap Closing of Thin Carbon Nanotubes,

ADVANCED MATERIALS, Issue 4 2005
Jonge, N. de
Closing individual, thin, multiwalled carbon nanotubes is performed in situ in a transmission electron microscope (see Figure). The closure of the initially open end of the nanotube results from the presence of a strong electric field and the accompanied electron emission. The closed-cap nanotubes exhibit high current stability, which is of advantage for their use as electron sources. [source]

Unique Preparation of Hexaboride Nanocubes: A First Example of Boride Formation by Combustion Synthesis

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010
Raghunath Kanakala
Nanocubes of LaB6 and Sm0.8B6 have been synthesized using low-temperature combustion synthesis, a technique that had only been used previously for the preparation of oxides. The hexaboride nanocubes were prepared using lanthanum nitrate or samarium nitrate, carbohydrazide, and boron powders. The furnace temperature for synthesis was kept at 320°C, lower than the typical temperature values used in combustion processes for the preparation of oxides. After synthesis, the nanocubes were characterized using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The combustion process was analyzed using differential scanning calorimetry, which shows that the formation of the carbohydrazide and nitrate melts as well as the formation of a complex between metal ions and carbohydrazide are crucial steps for the reaction. The technique results in high-purity powders with a unique cubic morphology, in which the corners of the cubes can be used as point sources for efficient electron emission. [source]

The assessment of microscopic charging effects induced by focused electron and ion beam irradiation of dielectrics

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2007
Marion A. Stevens-Kalceff
Abstract Energetic beams of electrons and ions are widely used to probe the microscopic properties of materials. Irradiation with charged beams in scanning electron microscopes (SEM) and focused ion beam (FIB) systems may result in the trapping of charge at irradiation induced or pre-existing defects within the implanted microvolume of the dielectric material. The significant perturbing influence on dielectric materials of both electron and (Ga+) ion beam irradiation is assessed using scanning probe microscopy (SPM) techniques. Kelvin Probe Microscopy (KPM) is an advanced SPM technique in which long-range Coulomb forces between a conductive atomic force probe and the silicon dioxide specimen enable the potential at the specimen surface to be characterized with high spatial resolution. KPM reveals characteristic significant localized potentials in both electron and ion implanted dielectrics. The potentials are observed despite charge mitigation strategies including prior coating of the dielectric specimen with a layer of thin grounded conductive material. Both electron- and ion-induced charging effects are influenced by a delicate balance of a number of different dynamic processes including charge-trapping and secondary electron emission. In the case of ion beam induced charging, the additional influence of ion implantation and nonstoichiometric sputtering from compounds is also important. The presence of a localized potential will result in the electromigration of mobile charged defect species within the irradiated volume of the dielectric specimen. This electromigration may result in local modification of the chemical composition of the irradiated dielectric. The implications of charging induced effects must be considered during the microanalysis and processing of dielectric materials using electron and ion beam techniques. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source]

Light emission from different ZnO junctions and nanostructures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009
M. Willander
Abstract We will discuss our experimental results for optical spectra produced by hole-injection from different p-type organic and inorganic materials into n-type ZnO nanowires. The influence of different growth techniques and conditions on the nanowires and their emission spectral characteristics will then be analyzed and discussed. The latest findings on the mixture of the green emission band responsible for visible light emission from ZnO and the blue light emission from the organic polymer will be presented. Different high brightness light emitting diodes (HB-LEDs) from our grown ZnO nanowires are demonstrated. The p-type multi layer organic structures contain PEDOT:PSS as hole injectors combined with a hole transporting layer, and in some structures, a final top electron blocking/hole barrier stepping layer is placed. The purpose of this layer is to adjust the hole and electron emission from the corresponding junction side to optimize the LED performance. Structural scanning electron microscopy (SEM), electrical (I ,V characteristics), photoluminescence (PL) and electroluminescence (EL) characteristics of these devices are displayed. Theoretically, we study the superfluidity of a two-dimensional system of excitonic polaritons in an optical microcavity with an embedded quantum well. Using the effective low-energy action for thermodynamic phase fluctuations, we obtain an expression for the analogue of the superfluid density in the system in terms of the "current,current" correlation function. The Kosterlits,Thouless transition temperature to the superfluid state as a function of the controlling parameters is calculated. Two methods are considered for producing traps for a polariton system in an optical microcavity. The behaviour of a two-component Bose condensate of photons and excitons is analyzed theoretically for both types of the trap. The Bose condensate is described by the coupled system of equations of the Gross,Pitaevskii type. The approximate wave functions and the spatial profiles of coupled photon and exciton condensates are obtained. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Negative electron affinity on hydrogen terminated diamond

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2005
D. Takeuchi
Abstract Total photoyield spectroscopy (TPYS) is applied to characterize the surface electronic properties of p- and n-type chemical-vapour-deposited (111) homoepitaxial diamond films with hydrogen terminated (H-terminated) surfaces. All experiments on H-terminated high quality diamond show the same threshold energy of 4.4 eV and comparable spectra in the regime 4.4,5.5 eV. A H-terminated intrinsic IIa (100) sample also show the same result. The onset of electron emission at 4.4 eV on p-, intrinsic and n-type diamond indicates that Fermi levels do not affect the sub-band spectra. Obviously, direct excitation of valence-band electrons into the vacuum takes place in the close vicinity of the surface. If we assume a transition from valence band maximum the threshold energy of 4.4 eV gives a negative electron affinity (NEA) of ,1.07 eV (Eg, 5.47 eV). TPYS therefore allows a precise and direct detection of the NEA of H-terminated diamond. It is interesting that the expected rise of photoyield as NEA in the regime hv > 5.47 eV is missing in n-type diamond. We attribute this to a surface space charge region due to ionized phosphorus atoms. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Laser-assisted electron emission from CVD nano-graphite films

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006
D. A. Lyashenko
Abstract We demonstrate that irradiation with nano-second light pulses results in significant enhancement of the electron emission from nano-graphite films. The observed emission current density is as high as 10 A/cm2 at applied field of 2 V/µm. The duration of the emission pulse depends on the applied DC voltage and laser intensity. However, in our experimental conditions, the temporal profile of the electron pulse nearly reproduces that of the incident laser pulse. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Fabrication of field emitters using GaN particles

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010
Yuichiro Minakuchi
Abstract The field emission from GaN particles has been demonstrated successfully for the first time. The novel field emitting device has a simple structure consisting of an electrically conductive polymer layer and GaN particles spread randomly on it. The GaN particles used for this device, which were synthesized in advance by the two-stage vapor phase method, have vertices and ridges formed by well-developed crystal planes. The electron emission started at an electric field of about 20 V/,m, and the current reached 10 nA at 28 V/,m. The maximum current density was 0.26 mA/cm2at 43 V/,m. The Fowler-Nordheim (F-N) plot of the I - V data indicated that the observed electron emission is originated from the F-N tunneling. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The thermostimulated exoelectron emission of NaF:U,Me compounds after electron beam irradiation

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
M. M. Kidibaev
Abstract The thermostimulated exoelectron emission (TSEE) of NaF:(U,Me) compounds after electron beam irradiation in the 300,800 K temperature range has been investigated. For NaF:(U,Me) bulk, fiber and nanocrystals several regular peaks of TSEE have been found. Additional effects with the sign of thermostimulated explosive electron emission have been found too. The nature of TSEE process is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Deep electron states in indium-doped Cd0.93Mn0.07Te DLTS study

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006
A. Hajdusianek
Abstract Electron traps in indium doped Cd0.93Mn0.07Te were studied with Deep Level Transient Spectroscopy. Five electron traps were found (labeled as E1 - E5). Energy levels ET of related defects are equal to ET 1 = 0.09 eV, ET 2 = 0.12 eV, ET 3 = 0.18 eV, ET 4 = 0.56 eV and ET 5 = 0.65 eV. Three of them (E1, E2, E3 ) are related to the defects with thermally activated capture cross section. Electric field enhanced electron emission from the trap E4 was observed and described in the terms of the Poole-Frenkel - mechanism. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Isotopic metrology of carbon dioxide.

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2003

We report high-precision isotopic carbon dioxide measurements, made before and after ion source modification to gas isotope ratio mass spectrometry (IRMS) instruments. Measurement protocols were designed to explore the effects of ion source material substitution, source conductance, inlet pressure, electron emission, acceleration potential, and inlet changeover equilibration time. After modification of the IRMS instruments at the National Institute of Standards and Technology (NIST) and the Max-Planck-Institute for Chemistry (MPI-Mainz), immediate changes were observed. At NIST, measurements were no longer sensitive to inlet equilibration times greater than 15,s, and different settings of ion source conductance resulted in ,13C shifts of about 0.04, per 10, measurement difference between sample and reference, a five-fold improvement. No significant changes in machine performance were observed after a month of use. After a year, performance had degraded slightly, but was controlled by ion source cleaning and the use of low-energy ion acceleration to minimize sputtering. At MPI-Mainz, results were very similar. We report cross-contamination coefficients measured since 1996, and discuss the role of adsorption, ion implantation, and sputtering on cross contamination in mass spectrometry systems. We recommend that users of high-precision IRMS instruments test for and minimize the effects described. Published in 2003 by John Wiley & Sons, Ltd. [source]