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Sample records for electron emission characteristics

  1. Secondary electron emission characteristics of oxide electrodes in flat electron emission lamp

    NASA Astrophysics Data System (ADS)

    Chiang, Chang-Lin; Zeng, Hui-Kai; Li, Chia-Hung; Li, Jung-Yu; Chen, Shih-Pu; Lin, Yi-Ping; Hsieh, Tai-Chiung; Juang, Jenh-Yih

    2016-01-01

    The present study concerns with the secondary electron emission coefficient, γ, of the cathode materials used in the newly developed flat electron emission lamp (FEEL) devices, which essentially integrates the concept of using cathode for fluorescent lamp and anode for cathode ray tube (CRT) to obtain uniform planar lighting. Three different cathode materials, namely fluorine-doped tin oxide (FTO), aluminum oxide coated FTO (Al2O3/FTO) and magnesium oxide coated FTO (MgO/FTO) were prepared to investigate how the variations of γ and working gases influence the performance of FEEL devices, especially in lowering the breakdown voltage and pressure of the working gases. The results indicate that the MgO/FTO bilayer cathode exhibited a relatively larger effective secondary electron emission coefficient, resulting in significant reduction of breakdown voltage to about 3kV and allowing the device to be operated at the lower pressure to generate the higher lighting efficiency.

  2. Characteristics of wall sheath and secondary electron emission under different electron temperature in Hall thruster

    NASA Astrophysics Data System (ADS)

    Duan, Ping; Qin, Haijuan; Cao, Anning; Zhou, Xinwei; Chen, Long; Gao, Hong

    2013-09-01

    Characteristics of discharge channel wall plasma sheath in Hall thruster have great effects on its performance. In this paper, we establish a two-dimensional physical model in Hall thruster sheath area to investigate the influences of the different electron temperature, propellant and particle weight on sheath potential and secondary electron emission in Hall thruster, by the method of Particle In Cell (PIC) simulation. And the electric field at the particle position is obtained by solving the Poisson's equation. The numerical results show that when the electron temperature is low, the change of sheath potential drop is bigger than that with electrons at high temperature, the surface potential maintains a stable value and the stability of the sheath is good. When the electron temperature is high, the surface potential maintains persistent oscillation, and the stability of the sheath is reduced. Along with the increase of electron temperature, the coefficient of secondary electron emission in wall reduce after the first increasing. For three kinds of propellant (Ar, Kr, Xe), with the increase of ion mass, sheath potential and the secondary electron emission coefficient in turn reduce.

  3. Electron reflection and secondary emission characteristics of sputter-textured pyrolytic graphite surfaces

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.; Curren, A. N.; Sovey, J. S.

    1981-01-01

    Low secondary and reflected primary electron emission from the collector electrode surfaces is important for optimum collector efficiency and hence for high overall efficiency of microwave amplifier tubes used in communication satellites and in military systems. Ion sputter texturing of the surface effectively suppresses electron emission from pyrolytic graphite, which is a promising collector electrode material. Secondary and reflected primary electron emission characteristics of sputter textured pyrolytic graphite surfaces with microstructures of various sizes and densities are presented. The microstructure with the lowest electron emission levels, less than those of soot, consists of a dense array of tall, thin spires.

  4. Secondary electron emission characteristics of ion-textured copper and high-purity isotropic graphite surfaces

    NASA Technical Reports Server (NTRS)

    Curren, A. N.; Jensen, K. A.

    1984-01-01

    Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for untreated and ion textured oxygen free high conductivity copper and untreated and ion textured high purity isotropic graphite surfaces are presented for a range of primary electron beam energies and beam impingement angles. This investigation was conducted to provide information that would improve the efficiency of multistage depressed collectors (MDC's) for microwave amplifier traveling wave tubes in space communications and aircraft applications. For high efficiency, MDC electrode surfaces must have low secondary electron emission characteristics. Although copper is a commonly used material for MDC electrodes, it exhibits relatively high levels of secondary electron emission if its surface is not treated for emission control. Recent studies demonstrated that high purity isotropic graphite is a promising material for MDC electrodes, particularly with ion textured surfaces. The materials were tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the ion textured surfaces were compared with each other and with those of untreated surfaces of the same materials. Both the untreated and ion textured graphite surfaces and the ion treated copper surface exhibited sharply reduced secondary electron emission characteristics relative to those of untreated copper. The ion treated graphite surface yielded the lowest emission levels.

  5. Secondary electron emission characteristics of untreated and ion-textured titanium

    NASA Technical Reports Server (NTRS)

    Curren, Arthur N.; Jensen, Kenneth A.; Blackford, Gary A.

    1989-01-01

    Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield are presented for untreated (simply machined) and ion-textured, high-purity titanium over ranges of primary electron beam energies and beam impingement angles. The purpose of the investigation was to explore the feasibility of using titanium as electrode material in the multistage depressed collectors (MDC's) used in microwave amplifier traveling wave tubes (TWT's) for space communications and aircraft applications. Because of its relatively low density and thermal expansion characteristics and relatively high strength, thermal emissivity, and melting temperature, titanium presents itself as a possible candidate for the MDC electrode application. A detailed description of the method of ion texturing the titanium is included. Although the ion-treated surface considered in this study is not presented as being optimum from the standpoint of secondary electron emission suppression, it nevertheless serves to demonstrate that the surface can be modified by this procedure to significantly reduce these emission characteristics relative to those of the untreated surface. Further studies can reasonably be expected to produce surfaces with even lower secondary emission characteristics. The titanium surface were tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near-grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the surfaces were compared with each other and with textured titanium surface exhibited secondary electron emission characteristics sharply lower than those exhibited by untreated titanium or copper. Clearly, then, in consideration of the secondary electron emission suppression of ion-textured titanium along with its other favorable physical properties, it must be included as a potential candidate for use as MDC electrode

  6. Characteristics of wall sheath and secondary electron emission under different electron temperatures in a Hall thruster

    NASA Astrophysics Data System (ADS)

    Duan, Ping; Qin, Hai-Juan; Zhou, Xin-Wei; Cao, An-Ning; Chen, Long; Gao, Hong

    2014-07-01

    In this paper, a two-dimensional physical model is established in a Hall thruster sheath region to investigate the influences of the electron temperature and the propellant on the sheath potential drop and the secondary electron emission in the Hall thruster, by the particle-in-cell (PIC) method. The numerical results show that when the electron temperature is relatively low, the change of sheath potential drop is relatively large, the surface potential maintains a stable value and the stability of the sheath is good. When the electron temperature is relatively high, the surface potential maintains a persistent oscillation, and the stability of the sheath reduces. As the electron temperature increases, the secondary electron emission coefficient on the wall increases. For three kinds of propellants (Ar, Kr, and Xe), as the ion mass increases the sheath potentials and the secondary electron emission coefficients reduce in sequence.

  7. Textured carbon on copper: A novel surface with extremely low secondary electron emission characteristics

    NASA Technical Reports Server (NTRS)

    Curren, A. N.; Jensen, K. A.

    1985-01-01

    Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for a range of primary electron beam energies and beam impingement angles are presented for a series of novel textured carbon surfaces on copper substrates. (All copper surfaces used in this study were oxygen-free, high-conductivity grade). The purpose of this investigation is to provide information necessary to develop high-efficiency multistage depressed collectors (MDC's) for microwave amplifier traveling-wave tubes (TWT's) for communications and aircraft applications. To attain the highest TWT signal quality and overall efficiency, the MDC electrode surface must have low secondary electron emission characteristics. While copper is the material most commonly used for MDC electrodes, it exhibits relatively high levels of secondary electron emission unless its surface is treated for emission control. The textured carbon surface on copper substrate described in this report is a particularly promising candidate for the MDC electrode application. Samples of textured carbon surfaces on copper substrates typical of three different levels of treatment are prepared and tested for this study. The materials are tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near-grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the textured surfaces are compared with each other and with those of untreated copper. All the textured carbon surfaces on copper substrate tested exhibited sharply lower secondary electron emission characteristics than those of an untreated copper surface.

  8. The influence of oxidation properties on the electron emission characteristics of porous silicon

    NASA Astrophysics Data System (ADS)

    He, Li; Zhang, Xiaoning; Wang, Wenjiang; Wei, Haicheng

    2016-09-01

    In order to investigate the influence of oxidation properties such as oxygen content and its distribution gradient on the electron emission characteristics of porous silicon (PS) emitters, emitters with PS thickness of 8 μm, 5 μm, and 3 μm were prepared and then oxidized by electrochemical oxidation (ECO) and ECO-RTO (rapid thermal oxidation) to get different oxidation properties. The experimental results indicated that the emission current density, efficiency, and stability of the PS emitters are mainly determined by oxidation properties. The higher oxygen content and the smaller oxygen distribution gradient in the PS layer, the larger emission current density and efficiency we noted. The most favorable results occurred for the PS emitter with the smallest oxygen distribution gradient and the highest level of oxygen content, with an emission current density of 212.25 μA/cm2 and efficiency of 59.21‰. Additionally, it also demonstrates that thick PS layer benefits to the emission stability due to its longer electron acceleration tunnel. The FN fitting plots indicated that the effective emission areas of PS emitters can be enlarged and electron emission thresholds is decreased because of the higher oxygen content and smaller distribution gradient, which were approved by the optical micrographs of top electrode of PS emitters before and after electron emission.

  9. Electron reflection and secondary emission characteristics of sputter-textured pyrolytic graphite surfaces

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.; Curren, A. N.; Sovey, J. S.

    1981-01-01

    Measurements are presented of secondary electron emission and reflected primary electron characteristics of sputter-textured pyrolitic graphite surfaces with microstructures of various sizes and densities, made with an Auger cylindrical mirror analyzer in a high-vacuum chamber at pressures below 1.33 x 10 to the -7th N/sq m (10 to the -9th torr). A dense, tall, thin, spire-like microstructure, obtained at ion energies of 1000 eV and ion current densities of 5 mA/sq cm, is the most effective. The secondary electron emission from such a surface is lower than that of soot, whose secondary emission is among the lowest of any material. At a primary electron energy of 1000 eV, the secondary electron emission yield of smooth CU is about 350% greater than the lowest value obtained for sputter-textured pyrolitic graphite. The reflected primary electron index of smooth Cu is a factor of 80 greater. If the secondary electron emission yield is reduced to 0.3, which is possible with sputter-textured pyrolitic graphite, the traveling wave tube collector efficiency could be improved by as much as 4% over that for smooth copper.

  10. Beam impingement angle effects on secondary electron emission characteristics of textured pyrolytic graphite

    NASA Technical Reports Server (NTRS)

    Curren, A. N.; Jensen, K. A.

    1984-01-01

    Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for untreated and ion-textured pyrolytic graphite over a range of primary electron energy levels and electron beam impingement angles are presented. Information required to develop high efficiency multistage depressed collectors (MDC's) for microwave amplifier traveling-wave tubes for space communication and aircraft applications is provided. To attain the highest possible MDC efficiencies, the electrode surfaces must have low secondary electron emission characteristics. Pyrolytic graphite, a chemically vapor-deposited material, is a particularly promising candidate for this application. The pyrolytic graphite surfaces studied were tested over a range of primary electron beam energies and beam impingement angles from 200 to 2000 eV and direct (0 deg) to near-grazing angles (85 deg), respectively. Surfaces both parallel to and normal to the planes of material deposition were examined. The true secondary electron emission and reflected primary electron yield characteristics of the pyrolytic graphite surfaces are compared to those of sooted control surfaces.

  11. Secondary electron emission characteristics of molybdenum-masked, ion-textured OFHC copper

    NASA Technical Reports Server (NTRS)

    Curren, Arthur N.; Jensen, Kenneth A.; Roman, Robert F.

    1990-01-01

    A method for producing a uniform, highly textured surface on oxygen-free, high conductivity (OFHC) copper by ion bombardment using sputtered molybdenum as a texture-inducing masking film was developed and used to provide samples for study. The purpose was to develop a basically OFHC copper surface having very low secondary electron emission characteristics. Surfaces having low secondary electron emission are a requirement for the electrodes of very high efficiency multistage depressed collectors (MDC's). Such MDC's are used in microwave amplifier traveling wave tubes for space communications and other applications. OFHC copper is the material most commonly used for MDC electrodes because it has high thermal conductivity, it is easy to machine, and its fabrication and brazing procedures are well established. However, its untreated surface displays relatively very high levels of secondary electron emissions. Textured OFHC copper samples were tested for true secondary electron emission and relative reflected primary electron yield at primary electron beam energy levels from 200 to 2000 eV and at direct (0 deg) to oblique (60 deg) beam impingement angles. The test results for three of the samples, each of which was processed in a slightly different way, are compared with each other and with test results for a machined OFHC copper sample. Although the textured samples are not represented here as having been processed optimally, their measured secondary electron emission characteristics are significantly lower than those of the untreated OFHC copper sample over the range of conditions studied. Importantly, the relative reflected primary electron yield of one of the textured samples is conspicuously lower than that of the others. Clearly, with further development, the molybdenum-masked ion-textured OFHC copper surface will be a promising material for high-efficiency MDC electrodes.

  12. Evaluating the Field Emission Characteristics of Aluminum for DC High Voltage Photo-Electron Guns

    NASA Astrophysics Data System (ADS)

    Taus, Rhys; Poelker, Matthew; Forman, Eric; Mamun, Abdullah

    2014-03-01

    High current photoguns require high power laser light, but only a small portion of the laser light illuminating the photocathode produces electron beam. Most of the laser light (~ 65%) simply serves to heat the photocathode, which leads to evaporation of the chemicals required to create the negative electron affinity condition necessary for photoemission. Photocathode cooling techniques have been employed to address this problem, but active cooling of the photocathode is complicated because the cooling apparatus must float at high voltage. This work evaluates the field emission characteristics of cathode electrodes manufactured from materials with high thermal conductivity: aluminum and copper. These electrodes could serve as effective heat sinks, to passively cool the photocathode that resides within such a structure. However, literature suggests ``soft'' materials like aluminum and copper are ill suited for photogun applications, due to excessive field emission when biased at high voltage. This work provides an evaluation of aluminum and copper electrodes inside a high voltage field emission test stand, before and after coating with titanium nitride (TiN), a coating that enhances surface hardness. National Science Foundation Award Number: 1062320 and the Department of Defence ASSURE program.

  13. Dynamic secondary electron emission characteristics of polymers in negative charging process

    NASA Astrophysics Data System (ADS)

    Weng, Ming; Hu, Tian-Cun; Zhang, Na; Cao, Meng

    2016-04-01

    We studied the dynamic secondary electron emission (SEE) characteristics of a polyimide sample in negative charging process under electron bombardment. The time evolution of secondary electron yield (SEY) has been measured with a pulsed electron gun. The dynamic SEY, as well as the surface potential have been analyzed using a capacitance model. The shift in surface potential caused by the negative charge accumulation on the sample reduces the landing energy of the primary electrons (PEs), which in turn alters the SEY. The charging process tends to be stable when the landing energy of PEs reaches the secondary crossover energy where the corresponding SEY is 1. The surface potential has an approximately negative exponential relationship with the irradiation time. The total accumulated charge at the stable state is found to be proportional to the product of the sample capacitance and the difference between initial incident energy and the secondary crossover energy. The time constant of the exponential function is proportional to the ratio of final accumulated charge to the incident current.

  14. Field emission characteristics of a graphite nanoneedle cathode and its application to scanning electron microscopy

    SciTech Connect

    Neo, Yoichiro; Mimura, Hidenori; Matsumoto, Takahiro

    2006-02-13

    A high-brightness electron beam of more than 10{sup 11} A sr{sup -1} m{sup -2} was achieved from a graphite nanoneedle cathode, which was fabricated by simple hydrogen plasma etching of a graphite rod. A field emission was obtained at a high residual pressure of 10{sup -6} Torr. The performance of this cold cathode was demonstrated by the fabrication of a scanning electron microscope, which was operated at a high residual pressure of 10{sup -5}-10{sup -6} Torr. The brightness of this cathode offers a convenient field electron emission source that does not require a massive ultrahigh vacuum system.

  15. Effects of Al interlayer coating and thermal treatment on electron emission characteristics of carbon nanotubes deposited by electrophoretic method

    PubMed Central

    2014-01-01

    The effects of aluminum (Al) interlayer coating and thermal post-treatment on the electron emission characteristics of carbon nanotubes (CNTs) were investigated. These CNTs were deposited on conical-shaped tungsten (W) substrates using an electrophoretic method. The Al interlayers were coated on the W substrates via magnetron sputtering prior to the deposition of CNTs. Compared with the as-deposited CNTs, the thermally treated CNTs revealed significantly improved electron emission characteristics, such as the decrease of turn-on electric fields and the increase of emission currents. The observations of Raman spectra confirmed that the improved emission characteristics of the thermally treated CNTs were ascribed to their enhanced crystal qualities. The coating of Al interlayers played a role in enhancing the long-term emission stabilities of the CNTs. The thermally treated CNTs with Al interlayers sustained stable emission currents without any significant degradation even after continuous operation of 20 h. The X-ray photoelectron spectroscopy (XPS) study suggested that the cohesive forces between the CNTs and the underlying substrates were strengthened by the coating of Al interlayers. PMID:24959105

  16. Post calibration of the two-dimensional electron cyclotron emission imaging instrument with electron temperature characteristics of the magnetohydrodynamic instabilities

    NASA Astrophysics Data System (ADS)

    Choi, M. J.; Park, H. K.; Yun, G. S.; Nam, Y. B.; Choe, G. H.; Lee, W.; Jardin, S.

    2016-01-01

    The electron cyclotron emission imaging (ECEI) instrument is widely used to study the local electron temperature (Te) fluctuations by measuring the ECE intensity IECE ∝ Te in tokamak plasmas. The ECEI measurement is often processed in a normalized fluctuation quantity against the time averaged value due to complication in absolute calibration. In this paper, the ECEI channels are relatively calibrated using the flat Te assumption of the sawtooth crash or the tearing mode island and a proper extrapolation. The 2-D relatively calibrated electron temperature (Te,rel) images are reconstructed and the displacement amplitude of the magnetohydrodynamic modes can be measured for the accurate quantitative growth analysis.

  17. Post calibration of the two-dimensional electron cyclotron emission imaging instrument with electron temperature characteristics of the magnetohydrodynamic instabilities.

    PubMed

    Choi, M J; Park, H K; Yun, G S; Nam, Y B; Choe, G H; Lee, W; Jardin, S

    2016-01-01

    The electron cyclotron emission imaging (ECEI) instrument is widely used to study the local electron temperature (Te) fluctuations by measuring the ECE intensity IECE ∝ Te in tokamak plasmas. The ECEI measurement is often processed in a normalized fluctuation quantity against the time averaged value due to complication in absolute calibration. In this paper, the ECEI channels are relatively calibrated using the flat Te assumption of the sawtooth crash or the tearing mode island and a proper extrapolation. The 2-D relatively calibrated electron temperature (Te,rel) images are reconstructed and the displacement amplitude of the magnetohydrodynamic modes can be measured for the accurate quantitative growth analysis. PMID:26827320

  18. Frequency characteristics of field electron emission from long carbon nanofilaments/nanotubes in a weak AC electric field

    NASA Astrophysics Data System (ADS)

    Izrael'yants, K. R.; Orlov, A. P.; Musatov, A. L.; Blagov, E. V.

    2016-05-01

    Frequency characteristics of field electron emission from long carbon nanofilaments/nanotubes in strong dc and weak ac electric fields have been investigated. A series of narrow peaks with a quality factor of up to 1100 has been discovered in the frequency range of hundreds of kilohertz. The analysis has shown that these peaks are probably associated with mechanical oscillations of the carbon nanofilaments/nanotubes driven by the ac electric field.

  19. Continuum emission-based electron diagnostics for atmospheric pressure plasmas and characteristics of nanosecond-pulsed argon plasma jets

    NASA Astrophysics Data System (ADS)

    Park, Sanghoo; Choe, Wonho; Kim, Holak; Park, Joo Young

    2015-06-01

    Electron diagnostics based on electron-neutral atom (e-a) bremsstrahlung in the UV and visible range emitted from atmospheric pressure plasmas is presented. Since the spectral emissivity of the e-a bremsstrahlung is determined by electron density (ne) and mean electron temperature (Te) representing the Maxwellian electron energy distribution, their diagnostics is possible. As an example, emission spectra measured from capacitive discharges are presented, which show good agreement with the theoretically calculated emissivity of the e-a bremsstrahlung. For a single pin electrode nanosecond-pulsed plasma jet (n-PPJ) in argon, we investigate the electron properties and the temporal behavior of the positive streamers. Streamers with many branches are clearly observed inside the dielectric tube, while a few main streamers propagate outside the tube along the jet axis. A two-dimensional (2D) measurement of the time-averaged Te distribution was developed using a commercial digital camera and optical band pass filters based on the emissivity ratio of two wavelengths of the e-a bremsstrahlung. The viable measurement range of Te is 0.5-7 eV for the choice of two wavelengths of 300s and 900s nm and 0.5-4 eV for two wavelengths of 400s and 900s nm, which are uncontaminated by the atomic and/or molecular spectra. The 2D Te distribution obtained using 514.5 and 632.8 nm emissions helps to reveal the role of electrons in streamer characteristics in the argon n-PPJ. Time-averaged Te of 2.0 eV and 1.0 eV inside and outside the tube, respectively, were measured. The streamer dynamics of the n-PPJ is shown to be dependent on Te.

  20. Numerical study of effect of secondary electron emission on discharge characteristics in low pressure capacitive RF argon discharge

    SciTech Connect

    Liu, Qian; Liu, Yue Samir, Tagra; Ma, Zhaoshuai

    2014-08-15

    Based on the drift and diffusion approximation theory, a 1D fluid model on capacitively coupled RF argon glow discharge at low pressure is established to study the effect of secondary electron emission (SEE) on the discharge characteristics. The model is numerically solved by using a finite difference method and the numerical results are obtained. The numerical results indicate that when the SEE coefficient is larger, the plasma density is higher and the time of reaching steady state is longer. It is also found that the cycle-averaged electric field, electric potential, and electron temperature change a little as the SEE coefficient is increased. Moreover, the discharge characteristics in some nonequilibrium discharge processes with different SEE coefficients have been compared. The analysis shows that when the SEE coefficient is varied from 0.01 to 0.3, the cycle-averaged electron net power absorption, electron heating rate, thermal convective term, electron energy dissipation, and ionization all have different degrees of growth. While the electron energy dissipation and ionization are quite special, there appear two peaks near each sheath region in the discharge with a relatively larger SEE coefficient. In this case, the discharge is certainly operated in a hybrid α-γ-mode.

  1. Electron emission from ferroelectrics

    NASA Astrophysics Data System (ADS)

    Zhang, Weiming

    Ferroelectric emission (FE) was discovered at CERN in 1988. However, a diverse array of results and explanations concerning FE have appeared. This dissertation focused on understanding the influence of material properties and external parameters on this complex process. The sample preparation, pulse generator and other experimental techniques are described. Plasma emission (PE), FE and mixed PE and FE were observed and described. The field enhancement at the electrode-dielectric-vacuum triple point was suggested to be the basis for PE. An apparent delay time, instability, visible light generation and strong electrode erosion are features of PE. Comparatively, FE does not require an extraction field, exhibits no apparent delay time and a relatively stable emission, and generates either no or a very weak light signal. A direct relationship between the switching current and emission current exists for the FE. Different FE characteristics of antiferroelectric PLZT 2/95/5, "normal" ferroelectric PLZT 8/65/35 and nonferroelectric PLZT 15/65/35 were described. The strong relationship between the emission and switching current was demonstrated. Repeatable emission is exhibited by 2/95/5, which can also be pulsed at high frequency due to its fast antiferroelectric <=> ferroelectric phase transition. The strong degradation of FE from 8/65/35 was attributed to decrease in the remanent polarization. While no emission signal was detected from 15/65/35, which can be interpreted as an additional evidence that electron emission from the above two PLZT was indeed FE process. Based on the field and domain switching distribution model, sample geometry effect on FE was predicted, and verified using the results from different groups. Electron emission energy distribution of PLZT 8/65/35 showed a very narrow energy distribution (FWHM ≈ 10 eV to 20 eV), and the emission energy was on the order of the applied pulse potential. The possible application of FE for emissive flat panel

  2. Secondary Electron Emission Yields

    NASA Technical Reports Server (NTRS)

    Krainsky, I.; Lundin, W.; Gordon, W. L.; Hoffman, R. W.

    1981-01-01

    The secondary electron emission (SEE) characteristics for a variety of spacecraft materials were determined under UHV conditions using a commercial double pass CMA which permits sequential Auger electron electron spectroscopic analysis of the surface. The transparent conductive coating indium tin oxide (ITO) was examined on Kapton and borosilicate glass and indium oxide on FED Teflon. The total SEE coefficient ranges from 2.5 to 2.6 on as-received surfaces and from 1.5 to 1.6 on Ar(+) sputtered surfaces with 5 nm removed. A cylindrical sample carousel provides normal incidence of the primary beam as well as a multiple Faraday cup measurement of the approximately nA beam currents. Total and true secondary yields are obtained from target current measurements with biasing of the carousel. A primary beam pulsed mode to reduce electron beam dosage and minimize charging of insulating coatings was applied to Mg/F2 coated solar cell covers. Electron beam effects on ITO were found quite important at the current densities necessary to do Auger studies.

  3. Field emission electron source

    DOEpatents

    Zettl, Alexander Karlwalter; Cohen, Marvin Lou

    2000-01-01

    A novel field emitter material, field emission electron source, and commercially feasible fabrication method is described. The inventive field emission electron source produces reliable electron currents of up to 400 mA/cm.sup.2 at 200 volts. The emitter is robust and the current it produces is not sensitive to variability of vacuum or the distance between the emitter tip and the cathode. The novel emitter has a sharp turn-on near 100 volts.

  4. Field emission electron source

    SciTech Connect

    Zettl, A.K.; Cohen, M.L.

    2000-05-02

    A novel field emitter material, field emission electron source, and commercially feasible fabrication method is described. The inventive field emission electron source produces reliable electron currents of up to 400 mA/cm{sup 2} at 200 volts. The emitter is robust and the current it produces is not sensitive to variability of vacuum or the distance between the emitter tip and the cathode. The novel emitter has a sharp turn-on near 100 volts.

  5. Effects of RF plasma processing on the impedance and electron emission characteristics of a MV beam diode

    SciTech Connect

    Rintamaki, J.I.; Gilgenbach, R.M.; Cohen, W.E.; Jaynes, R.L.; Ang, L.K.; Lau, Y.Y.; Cuneo, M.E.; Menge, P.R.

    1999-07-01

    Experiments have proven that both the surface contaminants and microstructure topography on the cathode of an electron beam diode influence impedance collapse and electron emission current. Experiments have characterized effective RF plasma processing protocols for high voltage A-K gaps using argon and argon/oxygen gas mixtures. RF processing time, feed gas pressure, and RF power were adjusted. Time resolved optical emission spectroscopy measured contaminant (hydrogen) and bulk cathode (aluminum) plasma emission versus transported axial electron beam current. Experiments utilize the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V = {minus}0.7 to {minus}1.0 MV, I(diode) + 3--30 kA, and pulse length = 0.4 to 1.0 microseconds. Microscopic and macroscopic E-fields on the cathode were varied to characterize the scaling of breakdown conditions for contaminants versus the bulk material of the cathode after plasma processing. Electron emission was suppressed for an aluminum cathode in a high voltage A-K gap after RF plasma processing. Experiments using a two-state low power (100W) argon/oxygen RF discharge followed by a higher power (200W) pure argon RF discharge yielded an increase in turn-on voltage required for axial current emission from 662 {+-} 174 kV to 981 {+-} 97 kV. After two-stage RF plasma processing axial current emission turn-on time was increased from 100 {+-} 22 nanoseconds to 175 {+-} 42 nanoseconds. Aluminum optical emission was delayed > 150 nanoseconds after the overshoot in voltage after two-stage RF plasma processing. Removal of hydrogen contamination on the cathode surface was observed by optical spectroscopy during the MELBA pulse. Axial and diode current were reduced 40--100% after RF plasma processing. SEM analysis suggests the aluminum cathode surface is being modified by the RF plasma discharge.

  6. ELECTRON EMISSION REGULATING MEANS

    DOEpatents

    Brenholdt, I.R.

    1957-11-19

    >An electronic regulating system is described for controlling the electron emission of a cathode, for example, the cathode in a mass spectrometer. The system incorporates a transformer having a first secondary winding for the above-mentioned cathode and a second secondary winding for the above-mentioned cathode and a second secondary winding load by grid controlled vacuum tubes. A portion of the electron current emitted by the cathode is passed through a network which develops a feedback signal. The system arrangement is completed by using the feedback signal to control the vacuum tubes in the second secondary winding through a regulator tube. When a change in cathode emission occurs, the feedback signal acts to correct this change by adjusting the load on the transformer.

  7. Simulation of the generation of the characteristic X-ray emission by hot electrons in a foil

    SciTech Connect

    Kostenko, O F; Andreev, N E

    2013-03-31

    We have developed a model to calculate the yield of the characteristic X-ray radiation from a foil, taking into account the dependence of the average energy and the number of hot electrons on the intensity of the laser pulse, the self-absorption of X-rays and the effect of refluxing of hot electrons. The yield of K{sub {alpha}} radiation from a silver foil is optimised at relativistic intensities. A method is proposed for diagnosing the effect of electron refluxing, which greatly increases the yield of K{sub {alpha}} radiation. (extreme light fields and their applications)

  8. The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

    SciTech Connect

    Xie, Kan; Farnell, Casey C.; Williams, John D.

    2014-08-15

    The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10{sup −5 }Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when no electrons were emitted to the vacuum chamber wall. In addition, the anode fall growth limited the maximum propellant unitization to below ≈75% in the discharge loss curves for this ion stage. Detailed measurements on the plasma properties were carried out for the no-electron emission and 3 A emission conditions. The experimental data are compared with 1-D models, and the effectiveness of the model is discussed. The four key issues that played important roles in the process of building the near-zero different resistance I-V regime are: a significant amount of ionization by the emission electrons, a decrease in the number of reflected electrons in the plume, the electron-temperature increment, and low initial ion energy at the source outlet.

  9. The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

    NASA Astrophysics Data System (ADS)

    Xie, Kan; Farnell, Casey C.; Williams, John D.

    2014-08-01

    The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10-5 Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when no electrons were emitted to the vacuum chamber wall. In addition, the anode fall growth limited the maximum propellant unitization to below ≈75% in the discharge loss curves for this ion stage. Detailed measurements on the plasma properties were carried out for the no-electron emission and 3 A emission conditions. The experimental data are compared with 1-D models, and the effectiveness of the model is discussed. The four key issues that played important roles in the process of building the near-zero different resistance I-V regime are: a significant amount of ionization by the emission electrons, a decrease in the number of reflected electrons in the plume, the electron-temperature increment, and low initial ion energy at the source outlet.

  10. W(310) cold-field emission characteristics reflecting the vacuum states of an extreme high vacuum electron gun

    SciTech Connect

    Cho, Boklae; Shigeru, Kokubo; Oshima, Chuhei

    2013-01-15

    An extremely high vacuum cold-field electron emission (CFE) gun operating at pressures ranging from {approx}10{sup -8} Pa to {approx}10{sup -10} Pa was constructed. Only the CFE current emitting from W(310) surfaces revealed the existence of a 'stable region' with high current angular density just after tip flash heating. In the 'stable region,' the CFE current was damped very slowly. The presence of non-hydrogen gas eliminated this region from the plot. Improvement of the vacuum prolonged the 90% damping time of the CFE current from {approx}10 min to 800 min. The current angular density I{sup Prime} of CFE current was 60 and 250 {mu}A/sr in the 'stable region' for total CFE currents of 10 and 50 {mu}A, respectively. These results were about three times larger than I{sup Prime} when measured after the complete damping of the CFE current. The CFE gun generated bright scanning transmission electron microscopy images of a carbon nanotube at 30 kV.

  11. Alcohol polymerization using electron emission

    NASA Astrophysics Data System (ADS)

    Matsuura, Hiroshi; Tanikawa, Tamio; Takaba, Hiromitsu; Fujiwara, Yutaka

    2004-04-01

    We report a means of instantaneous alcohol polymerization using electron emission at room temperature. We selected 1-butanol as a source of alcohol polymer. A 1-butanol molecule has a simple molecular structure and is a good candidate for analyzing reaction mechanisms. Direct electron emission onto the surface of volatile 1-butanol prevented intense discharge and gently composed 1-butanol-polymer at room temperature in air. The strategy enabled exciting liquids and instantaneously composing new materials at room temperature.

  12. Net current measurements and secondary electron emission characteristics of the Voyager plasma science experiment and their impact on data interpretation

    NASA Technical Reports Server (NTRS)

    Mcnutt, Ralph L., Jr.

    1988-01-01

    The Voyager Plasma Science (PLS) instrument is capable of returning integral (DC) current measurements, similar in some respects to measurements made with a Langmuir probe or a retarding potential analyzer, although there are significant differences. The integral measurements were made during a calibration sequence in the solar wind, during Cruise Science Maneuvers, and within the magnetospheres of Jupiter and Saturn by Voyager 1. After the failure of the PLS experiment following the Saturn encounter, that instrument was placed in the DC return mode returning possibly usable data from early 1981 through early 1985. The DC return measurements are difficult to interpret and are above threshold values only for relatively large fluxes; the determination of the measured current level is dependent on the operating temperature of the preamplifiers which further complicates the interpretation. Nevertheless, these measurements can be used to determine the efficiency of the suppressor grid at preventing the loss of secondary electrons off the collector plate. Some DC return measurements have been invaluable in aiding in the interpretation of some electron plasma measurements not previously understood. It is found that electron spectra can be significantly modified by the presence of second generation secondary electrons produced by either first generation secondaries or photoelectrons on the support ring of the negative high voltage modulator grid within the instrument housing.

  13. Evaluation of computational models and cross sections used by MCNP6 for simulation of characteristic X-ray emission from thick targets bombarded by kiloelectronvolt electrons

    NASA Astrophysics Data System (ADS)

    Poškus, A.

    2016-09-01

    This paper evaluates the accuracy of the single-event (SE) and condensed-history (CH) models of electron transport in MCNP6.1 when simulating characteristic Kα, total K (=Kα + Kβ) and Lα X-ray emission from thick targets bombarded by electrons with energies from 5 keV to 30 keV. It is shown that the MCNP6.1 implementation of the CH model for the K-shell impact ionization leads to underestimation of the K yield by 40% or more for the elements with atomic numbers Z < 15 and overestimation of the Kα yield by more than 40% for the elements with Z > 25. The Lα yields are underestimated by more than an order of magnitude in CH mode, because MCNP6.1 neglects X-ray emission caused by electron-impact ionization of L, M and higher shells in CH mode (the Lα yields calculated in CH mode reflect only X-ray fluorescence, which is mainly caused by photoelectric absorption of bremsstrahlung photons). The X-ray yields calculated by MCNP6.1 in SE mode (using ENDF/B-VII.1 library data) are more accurate: the differences of the calculated and experimental K yields are within the experimental uncertainties for the elements C, Al and Si, and the calculated Kα yields are typically underestimated by (20-30)% for the elements with Z > 25, whereas the Lα yields are underestimated by (60-70)% for the elements with Z > 49. It is also shown that agreement of the experimental X-ray yields with those calculated in SE mode is additionally improved by replacing the ENDF/B inner-shell electron-impact ionization cross sections with the set of cross sections obtained from the distorted-wave Born approximation (DWBA), which are also used in the PENELOPE code system. The latter replacement causes a decrease of the average relative difference of the experimental X-ray yields and the simulation results obtained in SE mode to approximately 10%, which is similar to accuracy achieved with PENELOPE. This confirms that the DWBA inner-shell impact ionization cross sections are significantly more

  14. Ballistic-Electron-Emission Microscope

    NASA Technical Reports Server (NTRS)

    Kaiser, William J.; Bell, L. Douglas

    1990-01-01

    Ballistic-electron-emission microscope (BEEM) employs scanning tunneling-microscopy (STM) methods for nondestructive, direct electrical investigation of buried interfaces, such as interface between semiconductor and thin metal film. In BEEM, there are at least three electrodes: emitting tip, biasing electrode, and collecting electrode, receiving current crossing interface under investigation. Signal-processing device amplifies electrode signals and converts them into form usable by computer. Produces spatial images of surface by scanning tip; in addition, provides high-resolution images of buried interface under investigation. Spectroscopic information extracted by measuring collecting-electrode current as function of one of interelectrode voltages.

  15. Emission characteristics and electron kinetic coefficients of the plasma of a transverse volume discharge initiated in a mixture of heavy inert gases with chlorine molecules

    NASA Astrophysics Data System (ADS)

    Shuaibov, A. K.; Chygin, V. I.; Shimon, L. L.; Shevera, I. V.; Gorun, P. P.; Obukhovskii, R. O.

    2010-05-01

    The results of studying the radiation due to argon, krypton, and xenon monochloride bands, as well as to the bands of chlorine molecules, from the plasma of a transverse Ar-Kr-Xe-Cl2 volume discharge are reported. The working mixture of a pulse radiation source is optimized with regard to its pressure and elemental composition and parameters of an excitation system. By numerically solving the Boltzmann kinetic equation for the electron energy distribution function, the transport characteristics of plasma electrons and discharge power specific losses are found for different values of the reduced electric field strength. The plasma parameters are simulated for the quaternary mixture, which is most appropriate for a multiwave UV-VUV source. Qualitative analysis is conducted for the most important electron processes in the multicomponent plasma that govern the joint formation of argon, krypton, and xenon monochlorides in the transverse discharge.

  16. Plasma sheath in the presences of non-Maxwellian energetic electrons and secondary emission electrons

    NASA Astrophysics Data System (ADS)

    Ou, Jing; Lin, Binbin; Zhao, Xiaoyun; Yang, Youlei

    2016-07-01

    The formation of a sheath in front of a carbon or tungsten material plane immersed in a plasma containing non-Maxwellian energetic electrons and secondary emission electrons is studied using a 1D model. In the model, energetic electrons are described by the electron energy distribution function (EEDF) and secondary electron emission (SEE) is produced by the electrons impinging on the wall. It is found that SEE coefficient depends on not only the sheath potential but also the EEDF profile of energetic electrons when a non-Maxwellian energetic electron component is present. The energetic electrons and associated secondary emission electrons can strongly modify ion velocity at sheath edge, floating potential and I–V probe characteristic. Due to the interdependence between SEE coefficient originating from the impact of non-Maxwellian energetic electrons on the wall and the sheath potential, with the increase in the energy of energetic electrons, a sudden jump phenomenon can be found in the profiles of SEE coefficient and other quantities such as floating potential and ion velocity at the sheath edge for tungsten wall, while for carbon wall they are the continuous variation. To begin with, the energetic electron component does not dominate the sheath, and I–V probe characteristic depends on both the EEDF profile of energetic electrons and material properties. Once the energetic electron component dominates the sheath, the analysis of I–V probe characteristic will yield the energy of energetic electrons.

  17. Cyclotron side band emissions from magnetospheric electrons

    NASA Technical Reports Server (NTRS)

    Maeda, K.

    1975-01-01

    Very low frequency emissions with subharmonic cyclotron frequency from magnetospheric electrons were detected by the S(3)-A satellite (Explorer 45) whose orbit is close to the magnetic equatorial plane where the wave-particle interaction is most efficient. These emissions were observed during the main phase of a geomagnetic storm in the nightside of the magnetosphere outside of the plasmasphere. During the event of these side-band emissions, the pitch angle distributions of high energy electrons (greater than 50 keV) and of energetic protons (greater than 100 keV) showed remarkable changes with time, whereas those of low energy electrons and protons remained approximately isotropic. In this type of event, emissions consist essentially of two bands, the one below the equatorial electron gyrofrequency, and the other above. The emissions below are whistler mode, and the emissions above are electrostatic mode.

  18. Electron emission at the rail surface

    SciTech Connect

    Thornhill, L.; Battech, J. )

    1991-01-01

    In this paper the authors examine the processes by which current is transferred from the cathode rail to the plasma armature in an arc-driven railgun. Three electron emission mechanisms are considered, namely thermionic emission, field-enhanced thermionic emission (or Schottky emission), and photoemission. The author's calculations show that the dominant electron emission mechanism depends, to a great extent, on the work function of the rail surface, the rail surface temperature, the electric field at the rail surface, and the effective radiation temperature of the plasma. For conditions that are considered to be typical of a railgun armature, Schottky emission is the dominant electron emission mechanism, providing current densities on the order of 10{sup 9} A/m{sup 2}.

  19. Deterministic Cold Cathode Electron Emission from Carbon Nanofibre Arrays

    NASA Astrophysics Data System (ADS)

    Cole, Matthew T.; Teo, Kenneth B. K.; Groening, Oliver; Gangloff, Laurent; Legagneux, Pierre; Milne, William I.

    2014-05-01

    The ability to accurately design carbon nanofibre (CN) field emitters with predictable electron emission characteristics will enable their use as electron sources in various applications such as microwave amplifiers, electron microscopy, parallel beam electron lithography and advanced Xray sources. Here, highly uniform CN arrays of controlled diameter, pitch and length were fabricated using plasma enhanced chemical vapour deposition and their individual emission characteristics and field enhancement factors were probed using scanning anode field emission mapping. For a pitch of 10 µm and a CN length of 5 µm, the directly measured enhancement factors of individual CNs was 242, which was in excellent agreement with conventional geometry estimates (240). We show here direct empirical evidence that in regular arrays of vertically aligned CNs the overall enhancement factor is reduced when the pitch between emitters is less than half the emitter height, in accordance to our electrostatic simulations. Individual emitters showed narrow Gaussian-like field enhancement distributions, in excellent agreement with electric field simulations.

  20. Superthermal electron distribution measurements from polarized electron cyclotron emission

    SciTech Connect

    Luce, T.C.; Efthimion, P.C.; Fisch, N.J.

    1988-06-01

    Measurements of the superthermal electron distribution can be made by observing the polarized electron cyclotron emission. The emission is viewed along a constant magnetic field surface. This simplifies the resonance condition and gives a direct correlation between emission frequency and kinetic energy of the emitting electron. A transformation technique is formulated which determines the anisotropy of the distribution and number density of superthermals at each energy measured. The steady-state distribution during lower hybrid current drive and examples of the superthermal dynamics as the runaway conditions is varied are presented for discharges in the PLT tokamak. 15 refs., 8 figs.

  1. Field Emission Characteristics of Polyaniline/Se Nanocomposites.

    PubMed

    Shumaila; Parveen, S; Alam, Masood; Siddiqui, Azher M; Husain, M

    2015-04-01

    Polyaniline (PAni)/Se nanocomposites have been synthesized in different compositions employing chemical route and shown excellent field emission behaviour. Detailed studies on the field emission for all composites with different concentrations of dopant are performed in an indigenously fabricated set up in a vacuum chamber with a base pressure of 10(-6) Torr at room temperature and analysed with current density versus Electric field (J-E) and Fowler-Nordheim (FN) plots. Comparative field emission results showed that 10% (w/w) doped PAni/Se nanocomposite depicts highest emission characteristics, current density and field enhancement factor with turn-on field as low as 1.2 V/µm in comparison with other composites, while pure PAni shows no field emission characteristics. These composites have also been characterized by Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectrometry (FTIR). FTIR results supply the evidence for the occurrence of the polymer in its conducting state. The ease of synthesis route and interesting field emission properties recommend these composites as a promising material for field emission based applications in vacuum micro-nanoelectronic devices and also for plastic display industry. PMID:26353501

  2. Positron annihilation induced Auger electron emission

    SciTech Connect

    Weiss, A.; Jibaly, M.; Lei, Chun; Mehl, D.; Mayer, R.; Lynn, K.G.

    1988-01-01

    We report on measurements of Auger electron emission from Cu and Fe due to core hole excitations produced by the removal of core electrons by matter-antimatter annihilation. Estimates are developed of the probability of positrons annihilating with a 3p electron in these materials. Several important advantages of Positron annihilation induced Auger Electron Spectroscopy (PAES) for surface analysis are suggested. 10 refs., 2 figs.

  3. Electron pair emission from surfaces: Intensity relations

    NASA Astrophysics Data System (ADS)

    Schumann, F. O.; Aliaev, Y.; Kostanovskiy, I.; Di Filippo, G.; Wei, Z.; Kirschner, J.

    2016-06-01

    The emission of an electron pair upon single-photon absorption requires a finite electron-electron interaction. Therefore, double photoemission is a particularly sensitive tool to study the electron correlation in matter. This is supported by a recent theoretical work which predicts that the pair intensity is a direct reflection of the correlation strength. In order to explore the validity of this statement, we performed a study on a variety of materials. Among them are noble metals, transition metals, and insulators. The latter include transition metal oxides such as CoO and NiO which are also termed highly correlated. We find an increased pair emission rate of NiO and CoO compared to the metals which reach a factor of 10. We also discovered that an increase of the coincidence intensity is accompanied by an increase in the singles count rate. This demonstrates that the electron pair emission is an efficient process at surfaces contributing up to 15 % to the single-electron emission in double photoemission. We performed also electron pair emission studies upon primary electron impact and find similar intensity relations.

  4. Emissions characteristics of modern oil heating equipment

    SciTech Connect

    Krajewski, R.; Celebi, Y.; Coughlan, R.; Butcher, T.; McDonald, R.J.

    1990-07-01

    Over the last 10 years there have been some very interesting developments in oil heating. These include higher static pressure burners, air atomizing nozzles, low firing rate nozzles, low heat loss combustion chambers and condensing boilers and furnaces. The current data base on the emissions characteristics of oil-fired residential heating equipment is based primarily on data taken in the 1970's. The objective of the work described in this report is to evaluate the effects of recent developments in oil-fired equipment on emissions. Detailed emissions measurements have been made on a number of currently available residential oil burners and whole systems selected to represent recent development trends. Some additional data was taken with equipment which is in the prototype stage. These units are a prevaporizing burner and a retention head burner modified with an air atomizing nozzle. Measurements include No{sub x}, smoke numbers, CO, gas phase hydrocarbon emissions and particulate mass emission rates. Emissions of smoke, CO and hydrocarbons were found to be significantly greater under cyclic operation for all burners tested. Generally, particulate emission rates were found to be 3 to 4 times greater in cyclic operation than in steady state. Air atomized burners were found to be capable of operation at much lower excess air levels than pressure atomized burners without producing significant amounts of smoke. As burner performance is improved, either through air atomization or prevaporization of the fuel, there appears to be a general trend towards producing CO at lower smoke levels as excess air is decreased. The criteria of adjusting burners for trace smoke may need to be abandoned for advanced burners and replaced with an adjustment for specific excess air levels. 17 refs., 15 figs., 6 tabs.

  5. Chemisorptive electron emission versus sticking probability

    NASA Astrophysics Data System (ADS)

    Böttcher, Artur; Niehus, Horst

    2001-07-01

    The chemisorption of N2O on thin Cs films has been studied by monitoring the time evolution of the sticking probability as well as the kinetics of the low-energy electron emission. By combining the data sets, two time domains become distinguishable: the initial chemisorption stage is characterized by a high sticking probability (0.1electron emission. The opposite is the case within the late stage where the chemisorption saturates, a very intense electron emission is accompanied by the negligibly low sticking probability of less than 0.01. Such evident anticoincidence between the exoemission and the chemisorption excludes the model of surface harpooning as the elementary process responsible for the electron emission in the late chemisorption stage. A long-term emission decay has also been observed after turning off the flux of chemisorbing molecules. A model is proposed that attributes both, the late chemisorptive and the nonchemisorptive electron emission to the relaxation of a narrow state originated from an oxygen vacancy in the Cs oxide layer terminating the surface. The presence of such a state has been confirmed by the metastable de-excitation spectroscopy [MDS, He*(21S)].

  6. Quantum dynamics of secondary electron emission from nanographene

    NASA Astrophysics Data System (ADS)

    Ueda, Yoshihiro; Suzuki, Yasumitsu; Watanabe, Kazuyuki

    2016-07-01

    We have observed secondary electron emission (SEE) from nanographene by applying time-dependent density functional theory simulations in real-time and real-space to electron scattering on target graphene-flakes. We obtained the incident-electron energy dependence and bilayer effect on the amount of secondary electron (SE). The dynamics of SEE and collective density oscillations, which are electronic excitations induced by electron impact, were demonstrated numerically, and elucidated by the time-dependent occupation numbers of the Kohn-Sham electronic levels. The SE yields from graphene flakes are found to be ˜0.1 . The highest energy of SE is ˜20 eV, which is compatible with the characteristics observed in SEE experiments.

  7. Pore geometry of dispenser cathode surface vs. emission characteristics, and Ba recovery characteristics after ion bombardment

    NASA Astrophysics Data System (ADS)

    Higuchi, Toshiharu; Nakamura, Osamu; Matsumoto, Sadao; Uda, Eiichirou

    1999-05-01

    A study was conducted to investigate the emission characteristics and barium recovery characteristics after ion bombardment of two types of Ir-coated dispenser cathodes having a pore density on the surface layer of the cathodes of 4×10 4 and 1.3×10 4 pores/mm 2. Cathode current was measured under pulse operation in a range of 0.1-9% duty cycle. When the duty cycle dependence of emissions was examined, the current densities of both cathodes were the same in the case of 0.1% duty cycle, delivering about 12 A/cm 2. The work functions also showed the same value. However, evaluations of 4% duty cycle and 9% duty cycle found that the cathode with a higher pore density showed emission characteristics higher by 50% and 70%. Regarding the recovery time of barium and oxygen after argon ion bombardment with Auger electron spectroscopy (AES), the low-pore-density cathode required as long as 3 min for recovery, whereas the high-pore-density cathode recovered in 1.1 min. From the above experiments, it was clarified that emission characteristics under high duty and barium recovery characteristics after ion bombardment can be improved by increasing the pore density of the surface layer. The basic mechanisms leading to these results were also theoretically considered by solving surface diffusion equations.

  8. A hybrid model describing ion induced kinetic electron emission

    NASA Astrophysics Data System (ADS)

    Hanke, S.; Duvenbeck, A.; Heuser, C.; Weidtmann, B.; Wucher, A.

    2015-06-01

    We present a model to describe the kinetic internal and external electron emission from an ion bombarded metal target. The model is based upon a molecular dynamics treatment of the nuclear degree of freedom, the electronic system is assumed as a quasi-free electron gas characterized by its Fermi energy, electron temperature and a characteristic attenuation length. In a series of previous works we have employed this model, which includes the local kinetic excitation as well as the rapid spread of the generated excitation energy, in order to calculate internal and external electron emission yields within the framework of a Richardson-Dushman-like thermionic emission model. However, this kind of treatment turned out to fail in the realistic prediction of experimentally measured internal electron yields mainly due to the restriction of the treatment of electronic transport to a diffusive manner. Here, we propose a slightly modified approach additionally incorporating the contribution of hot electrons which are generated in the bulk material and undergo ballistic transport towards the emitting interface.

  9. Numerical and experimental studies of enhanced electron emission from functionalized carbon nanotube emitters

    NASA Astrophysics Data System (ADS)

    Jin, Feng; Little, Scott; Alzubi, Feras

    2007-03-01

    Vertically aligned carbon nanotubes (CNTs) were grown using plasma enhanced chemical vapor deposition (PECVD) method. The CNTs were further functionalized by coating their surface with a thin layer of low work function oxide emissive materials. The electron emission capability of the coated CNT emitters was greatly improved with the low work function emissive layer, particularly at high temperature. Thermionic emission current three orders magnitude higher was observed. The emission properties of the oxide coated CNTs were measured and characterized over a wide temperature and field ranges. It was found that neither the Fowler-Nordheim theory for field emission nor the Richardson theory for thermionic emission were adequate to describe the electron emission characteristics of these emitters in certain range of temperature and field. However, by adopting a general electron emission formulism developed by Murphy and Good, we were able to simulate the electron emission from the coated CNTs over the whole temperature and field range and fit the experimental data.

  10. Ion-induced electron emission microscopy

    DOEpatents

    Doyle, Barney L.; Vizkelethy, Gyorgy; Weller, Robert A.

    2001-01-01

    An ion beam analysis system that creates multidimensional maps of the effects of high energy ions from an unfocussed source upon a sample by correlating the exact entry point of an ion into a sample by projection imaging of the secondary electrons emitted at that point with a signal from a detector that measures the interaction of that ion within the sample. The emitted secondary electrons are collected in a strong electric field perpendicular to the sample surface and (optionally) projected and refocused by the electron lenses found in a photon emission electron microscope, amplified by microchannel plates and then their exact position is sensed by a very sensitive X Y position detector. Position signals from this secondary electron detector are then correlated in time with nuclear, atomic or electrical effects, including the malfunction of digital circuits, detected within the sample that were caused by the individual ion that created these secondary electrons in the fit place.

  11. Charge state distribution and emission characteristics in a table top reflex discharge—Effect of ion confinement and electrons accelerated across the sheath

    SciTech Connect

    Kumar, Deepak Englesbe, Alexander; Parman, Matthew; Stutman, Dan; Finkenthal, Michael

    2015-11-15

    Tabletop reflex discharges in a Penning geometry have many applications including ion sources and eXtreme Ultra-Violet (XUV) sources. The presence of primary electrons accelerated across the cathode sheaths is responsible for the distribution of ion charge states and of the unusually high XUV brightness of these plasmas. Absolutely calibrated space resolved XUV spectra from a table top reflex discharge operating with Al cathodes and Ne gas are presented. The spectra are analyzed with a new and complete model for ion charge distribution in similar reflex discharges. The plasma in the discharge was found to have a density of ∼10{sup 18 }m{sup −3} with a significant fraction >0.01 of fast primary electrons. The implications of the new model on the ion states achievable in a tabletop reflex plasma discharge are also discussed.

  12. Charge state distribution and emission characteristics in a table top reflex discharge - Effect of ion confinement and electrons accelerated across the sheath

    SciTech Connect

    Kumar, Deepak; Englesbe, Alexander; Parman, Matthew; Stutman, Dan; Finkenthal, Michael

    2015-11-05

    Tabletop reflex discharges in a Penning geometry have many applications including ion sources and eXtreme Ultra-Violet (XUV) sources. The presence of primary electrons accelerated across the cathode sheaths is responsible for the distribution of ion charge states and of the unusually high XUV brightness of these plasmas. Absolutely calibrated space resolved XUV spectra from a table top reflex discharge operating with Al cathodes and Ne gas are presented. The spectra are analyzed with a new and complete model for ion charge distribution in similar reflex discharges. The plasma in the discharge was found to have a density of ~1018m–3 with a significant fraction >0.01 of fast primary electrons. As a result, the implications of the new model on the ion states achievable in a tabletop reflex plasma discharge are also discussed.

  13. Charge state distribution and emission characteristics in a table top reflex discharge - Effect of ion confinement and electrons accelerated across the sheath

    DOE PAGESBeta

    Kumar, Deepak; Englesbe, Alexander; Parman, Matthew; Stutman, Dan; Finkenthal, Michael

    2015-11-05

    Tabletop reflex discharges in a Penning geometry have many applications including ion sources and eXtreme Ultra-Violet (XUV) sources. The presence of primary electrons accelerated across the cathode sheaths is responsible for the distribution of ion charge states and of the unusually high XUV brightness of these plasmas. Absolutely calibrated space resolved XUV spectra from a table top reflex discharge operating with Al cathodes and Ne gas are presented. The spectra are analyzed with a new and complete model for ion charge distribution in similar reflex discharges. The plasma in the discharge was found to have a density of ~1018m–3 withmore » a significant fraction >0.01 of fast primary electrons. As a result, the implications of the new model on the ion states achievable in a tabletop reflex plasma discharge are also discussed.« less

  14. Charge state distribution and emission characteristics in a table top reflex discharge—Effect of ion confinement and electrons accelerated across the sheath

    NASA Astrophysics Data System (ADS)

    Kumar, Deepak; Englesbe, Alexander; Parman, Matthew; Stutman, Dan; Finkenthal, Michael

    2015-11-01

    Tabletop reflex discharges in a Penning geometry have many applications including ion sources and eXtreme Ultra-Violet (XUV) sources. The presence of primary electrons accelerated across the cathode sheaths is responsible for the distribution of ion charge states and of the unusually high XUV brightness of these plasmas. Absolutely calibrated space resolved XUV spectra from a table top reflex discharge operating with Al cathodes and Ne gas are presented. The spectra are analyzed with a new and complete model for ion charge distribution in similar reflex discharges. The plasma in the discharge was found to have a density of ˜1018 m-3 with a significant fraction >0.01 of fast primary electrons. The implications of the new model on the ion states achievable in a tabletop reflex plasma discharge are also discussed.

  15. Effects of electron emission on sheath potential

    NASA Astrophysics Data System (ADS)

    Dow, Ansel; Khrabrov, Alexander; Kaganovich, Igor; Schamis, Hanna

    2015-11-01

    We investigate the potential profile of a sheath under the influence of surface electron emission. The plasma and sheath profiles are simulated using the Large Scale Plasma (LSP) particle-in-cell code. Using one dimensional models we corroborate the analytical relationship between sheath potential and plasma electron and emitted electron temperatures derived earlier. This work was made possible by funding from the Department of Energy for the Summer Undergraduate Laboratory Internship (SULI) program. This work is supported by the US DOE Contract No. DE-AC02-09CH11466.

  16. Secondary electron emission from Martian soil simulant

    NASA Astrophysics Data System (ADS)

    Pavlů, J.; Beránek, M.; Vaverka, J.; Å afránková, J.; Němeček, Z.; Richterová, I.

    2014-01-01

    In the recent years, growing interest in dust charging physics is connected with several lander missions running on or planned to the Moon, Mars, and Mercury for a near future. In support of these missions, laboratory simulations are a potential tool to optimize in situ exploration and measurements. In the paper, we have investigated electrical properties of a Martian soil simulant prepared at the Johnson Space Center under name JSC Mars-1 using the dust charging experiment when a single dust grain is trapped in a vacuum chamber and its secondary electron emission is studied. The exposure of the grain to the electron beam revealed that the grain surface potential is low and generally determined by a mean atomic number of the grain material at a low-energy range (<1 keV), whereas it can reach a limit of the field ion emission being irradiated by more energetic electrons. A comparison of model and experimental results reveals an influence of the grain shape and size predominantly in the range of higher (>2 keV) electron energies. We discuss possible implications of the secondary electron emission for the presence of lightnings on Mars.

  17. Integrated Detector for Ballistic Electron Emission Luminescence

    NASA Astrophysics Data System (ADS)

    Huang, Biqin; Xu, Jing; Appelbaum, Ian

    2008-03-01

    Ballistic electron emission luminescence (BEEL) uses injected hot electrons to induce interband transitions and light emission in semiconductor collectors. Local hot electron injection and rastering from a scanning tunneling probe can therefore potentially provide a means to image buried luminescent layers. However, a sensitive photon detector is required to compensate for low external efficiency. We have directly integrated a Si photodetector to a GaAs/AlGaAs BEEL structure by UHV thin-film metal wafer bonding. This room-temperature technique overcomes index mismatch and numerical aperture problems associated with far-field detection. We expect this method will make BEEL microscopy generally applicable to the study of buried luminescent layers in light emitting devices based on arbitrary material systems. THis work is funded by US DOE.

  18. Electron Field Emission from Thick Paste Carbon Materials

    NASA Astrophysics Data System (ADS)

    Reynolds, Gillian; Cheng, Lap-Tak; Bouchard, Robert; Amey, Daniel; Shah, Ismat

    2002-03-01

    Ion bombardment was used to produce electron emitting micro-scale features on surfaces printed with carbon thick film pastes. This technology can potentially enable the development of large area field emission displays (FEDs). Systematic investigations using microscopy and electron field emission experiments have demonstrated close link between paste formulation, ion processing parameters, and the development of surface microstructures. These investigations have also shed light on the fundamentals of microstructure formation and the field emission characteristics of the carbon based emitters. Several device concepts aimed towards achieving a low voltage switchable triode were also pursued with varying degree of success. In this work we summarize various material, process, and device issues related to this technology.

  19. How can secondary electron emission from dust affect Martian atmosphere?

    NASA Astrophysics Data System (ADS)

    Pavlu, Jiri; Safrankova, Jana; Nemecek, Zdenek; Beranek, Martin; Vaverka, Jakub; Richterova, Ivana

    2014-05-01

    Growing interest to Mars connected with recent and forthcoming missions led to numerous studies dealing with behavior of dust grains on the Martian surface and within its atmosphere. The present paper discusses electrical properties of a Martian soil simulant (JSC Mars-1) involving the dust charging experiment where a single dust grain is trapped and stored for a long time in a vacuum chamber and its emission characteristics, especially the secondary electron emission, are studied. The interaction of the grain with the intense electron beam showed the grain surface potential is generally low and determined by a mean atomic number of the grain material at a low-energy range (< 1 keV), whereas it can reach a limit of the field ion emission being irradiated by more energetic electrons. Experimental results are compared with numerical simulations showing a crucial influence of the grain shape and size in the range of higher (> 2 keV) electron energies. We further discuss possible implications of the secondary electron emission from dust grains for the generation of lightnings on Mars.

  20. A fully integrated isoprenoid emissions model coupling emissions to photosynthetic characteristics.

    PubMed

    Grote, Rüdiger; Morfopoulos, Catherine; Niinemets, Ülo; Sun, Zhihong; Keenan, Trevor F; Pacifico, Federica; Butler, Tim

    2014-08-01

    The lack of a mechanistic basis has hampered modelling isoprene emission responses to environmental drivers, in particular the simulation of isoprene emissions under different CO₂ concentrations. Here, we advance previous semi-mechanistic model formulations by introducing a model that explicitly links electron availability for other purpose than carbon assimilation (or available energy for secondary metabolism processes; supply-constraint) and enzyme activity (capacity-constraint) to emissions. We furthermore investigate the sensitivity of the model to variations in photosynthetic and emission-specific parameters. By comparing species-specific simulations with experimental data, we demonstrate that differences in photosynthetic characteristics can explain inter-species differences in emissions. Interestingly, the seasonal development of emissions could also be explained to some degree by the change in energy supply from photosynthesis throughout the season. In addition, we show that the principal responses are not limited to isoprene but can be formulated to describe the emission of other light-dependent volatile species. The proposed model is suitable for implementation into regional and global models, particularly those that already provide species-specific photosynthesis estimates. PMID:24661098

  1. Diamond Analyzed by Secondary Electron Emission Spectroscopy

    NASA Technical Reports Server (NTRS)

    Krainsky, Isay L.

    1998-01-01

    Diamond is a promising semiconductor material for novel electronic applications because of its chemical stability and inertness, heat conduction properties, and so-called negative electron affinity (NEA). When a surface has NEA, electrons generated inside the bulk of the material are able to come out into the vacuum without any potential barrier (work function). Such a material would have an extremely high secondary electron emission coefficient o, very high photoelectron (quantum) yield, and would probably be an efficient field emitter. Chemical-vapor-deposited (CVD) polycrystalline diamond films have even more advantages than diamond single crystals. Their fabrication is relatively easy and inexpensive, and they can be grown with high levels of doping--consequently, they can have relatively high conductivity. Because of these properties, diamond can be used for cold cathodes and photocathodes in high-power electronics and in high-frequency and high-temperature semiconductor devices.

  2. Field to thermo-field to thermionic electron emission: A practical guide to evaluation and electron emission from arc cathodes

    NASA Astrophysics Data System (ADS)

    Benilov, M. S.; Benilova, L. G.

    2013-08-01

    This work is concerned with devising a method of evaluation of electron emission in the framework of the Murphy-Good theory, which would be as simple and computationally efficient as possible while being accurate in the full range of conditions of validity of the theory. The method relies on Padé approximants. A comparative study of electron emission from cathodes of arcs in ambient gas and vacuum arcs is performed with the use of this method. Electron emission from cathodes of arcs in ambient gas is of thermionic nature even for extremely high gas pressures characteristic of projection and automotive arc lamps and is adequately described by the Richardson-Schottky formula. The electron emission from vaporizing (hot) cathodes of vacuum arcs is of thermo-field nature and is adequately described by the Hantzsche fit formula. Since no analytical formulas are uniformly valid for field to thermo-field to thermionic emission, a numerical evaluation of the Murphy-Good formalism is inevitable in cases where a unified description of the full range of conditions is needed, as is the general case of plasma-cathode interaction in vacuum arcs, and the technique proposed in this work may be the method of choice to this end.

  3. An Effective Secondary Electron Emission Suppression Treatment For Copper MDC

    NASA Technical Reports Server (NTRS)

    Curren, Arthur N.; Long, Kenwyn J.; Jensen, Kenneth A.; Roman, Robert F.

    1993-01-01

    Untreated oxygen-free, high-conductivity (OFHC) copper, commonly used for MDC electrodes, exhibits relatively high secondary electron emission characteristics. This paper describes a specialized ion-bombardment procedure for texturing copper surfaces which sharply reduces the emission properties relative to untreated copper. The resulting surface is a particle-free, robust, uniformly highly-textured all-metal structure. The use of this process requires no modifications to copper machining, brazing, or other MDC normal fabrication procedures. The flight TWT for a planned NASA deep space probe, the Cassini Mission, will incorporate copper MDC electrodes treated with the method described here.

  4. 47 CFR 2.201 - Emission, modulation, and transmission characteristics.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false Emission, modulation, and transmission characteristics. 2.201 Section 2.201 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Emissions § 2.201 Emission, modulation, and transmission characteristics....

  5. 47 CFR 2.201 - Emission, modulation, and transmission characteristics.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false Emission, modulation, and transmission characteristics. 2.201 Section 2.201 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Emissions § 2.201 Emission, modulation, and transmission characteristics....

  6. 47 CFR 2.201 - Emission, modulation, and transmission characteristics.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false Emission, modulation, and transmission characteristics. 2.201 Section 2.201 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Emissions § 2.201 Emission, modulation, and transmission characteristics....

  7. 47 CFR 2.201 - Emission, modulation, and transmission characteristics.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false Emission, modulation, and transmission characteristics. 2.201 Section 2.201 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Emissions § 2.201 Emission, modulation, and transmission characteristics....

  8. Secondary Electron Emission Spectroscopy of Diamond Surfaces

    NASA Technical Reports Server (NTRS)

    Krainsky, Isay L.; Asnin, Vladimir M.; Petukhov, Andre G.

    1999-01-01

    This report presents the results of the secondary electron emission spectroscopy study of hydrogenated diamond surfaces for single crystals and chemical vapor-deposited polycrystalline films. One-electron calculations of Auger spectra of diamond surfaces having various hydrogen coverages are presented, the major features of the experimental spectra are explained, and a theoretical model for Auger spectra of hydrogenated diamond surfaces is proposed. An energy shift and a change in the line shape of the carbon core-valence-valence (KVV) Auger spectra were observed for diamond surfaces after exposure to an electron beam or by annealing at temperatures higher than 950 C. This change is related to the redistribution of the valence-band local density of states caused by hydrogen desorption from the surface. A strong negative electron affinity (NEA) effect, which appeared as a large, narrow peak in the low-energy portion of the spectrum of the secondary electron energy distribution, was also observed on the diamond surfaces. A fine structure in this peak, which was found for the first time, reflected the energy structure of the bottom of the conduction band. Further, the breakup of the bulk excitons at the surface during secondary electron emission was attributed to one of the features of this structure. The study demonstrated that the NEA type depends on the extent of hydrogen coverage of the diamond surface, changing from the true type for the completely hydrogenated surface to the effective type for the partially hydrogenated surface.

  9. Improvements In Optically Stimulated Electron Emission

    NASA Technical Reports Server (NTRS)

    Yost, William T.; Welch, Christopher S.; Joe, Edmond J.; Hefner, Bill B., Jr.

    1994-01-01

    Optically stimulated electron emission (OSEE) used in inspection for contamination of critical bonding surfaces in solid rocket motors of Space Shuttle prior to formation of adhesive bonds on surfaces during manufacture and refurbishment. Fundamental OSEE inspection technique described in "Surface-Contamination Inspection Tool for Field Use" (MFS-25581) and "Detecting Contamination With Photoelectron Emission" (MFS-25619). OSEE measurement head easily portable, and measurement operation convenient and rapid, making it useful inspection technique in industrial environment. Reveals contamination in many situations in which other techniques do not work.

  10. Electron beam injection during active experiments. I - Electromagnetic wave emissions

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.; Kellogg, P. J.

    1990-01-01

    The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.

  11. Deterministic Cold Cathode Electron Emission from Carbon Nanofibre Arrays

    PubMed Central

    Cole, Matthew T.; Teo, Kenneth B. K.; Groening, Oliver; Gangloff, Laurent; Legagneux, Pierre; Milne, William I.

    2014-01-01

    The ability to accurately design carbon nanofibre (CN) field emitters with predictable electron emission characteristics will enable their use as electron sources in various applications such as microwave amplifiers, electron microscopy, parallel beam electron lithography and advanced Xray sources. Here, highly uniform CN arrays of controlled diameter, pitch and length were fabricated using plasma enhanced chemical vapour deposition and their individual emission characteristics and field enhancement factors were probed using scanning anode field emission mapping. For a pitch of 10 µm and a CN length of 5 µm, the directly measured enhancement factors of individual CNs was 242, which was in excellent agreement with conventional geometry estimates (240). We show here direct empirical evidence that in regular arrays of vertically aligned CNs the overall enhancement factor is reduced when the pitch between emitters is less than half the emitter height, in accordance to our electrostatic simulations. Individual emitters showed narrow Gaussian-like field enhancement distributions, in excellent agreement with electric field simulations. PMID:24787895

  12. Deterministic cold cathode electron emission from carbon nanofibre arrays.

    PubMed

    Cole, Matthew T; Teo, Kenneth B K; Groening, Oliver; Gangloff, Laurent; Legagneux, Pierre; Milne, William I

    2014-01-01

    The ability to accurately design carbon nanofibre (CN) field emitters with predictable electron emission characteristics will enable their use as electron sources in various applications such as microwave amplifiers, electron microscopy, parallel beam electron lithography and advanced Xray sources. Here, highly uniform CN arrays of controlled diameter, pitch and length were fabricated using plasma enhanced chemical vapour deposition and their individual emission characteristics and field enhancement factors were probed using scanning anode field emission mapping. For a pitch of 10 µm and a CN length of 5 µm, the directly measured enhancement factors of individual CNs was 242, which was in excellent agreement with conventional geometry estimates (240). We show here direct empirical evidence that in regular arrays of vertically aligned CNs the overall enhancement factor is reduced when the pitch between emitters is less than half the emitter height, in accordance to our electrostatic simulations. Individual emitters showed narrow Gaussian-like field enhancement distributions, in excellent agreement with electric field simulations. PMID:24787895

  13. EFFECT OF VEHICLE CHARACTERISTICS ON UNPAVED ROAD DUST EMISSIONS

    EPA Science Inventory

    This paper presents PM10 fugitive dust emission factors for a range of vehicles types and examines the influence of vehicle and wake characteristics on the strength of emissions from an unpaved road.

  14. Electron cyclotron emission diagnostics on KSTAR tokamak

    SciTech Connect

    Jeong, S. H.; Lee, K. D.; Kwon, M.; Kogi, Y.; Kawahata, K.; Nagayama, Y.; Mase, A.

    2010-10-15

    A new electron cyclotron emission (ECE) diagnostics system was installed for the Second Korea Superconducting Tokamak Advanced Research (KSTAR) campaign. The new ECE system consists of an ECE collecting optics system, an overmode circular corrugated waveguide system, and 48 channel heterodyne radiometer with the frequency range of 110-162 GHz. During the 2 T operation of the KSTAR tokamak, the electron temperatures as well as its radial profiles at the high field side were measured and sawtooth phenomena were also observed. We also discuss the effect of a window on in situ calibration.

  15. Electron cyclotron emission diagnostics on KSTAR tokamak.

    PubMed

    Jeong, S H; Lee, K D; Kogi, Y; Kawahata, K; Nagayama, Y; Mase, A; Kwon, M

    2010-10-01

    A new electron cyclotron emission (ECE) diagnostics system was installed for the Second Korea Superconducting Tokamak Advanced Research (KSTAR) campaign. The new ECE system consists of an ECE collecting optics system, an overmode circular corrugated waveguide system, and 48 channel heterodyne radiometer with the frequency range of 110-162 GHz. During the 2 T operation of the KSTAR tokamak, the electron temperatures as well as its radial profiles at the high field side were measured and sawtooth phenomena were also observed. We also discuss the effect of a window on in situ calibration. PMID:21033954

  16. A fully integrated isoprenoid emissions model coupling emissions to photosynthetic characteristics

    PubMed Central

    Grote, Rüdiger; Morfopoulos, Catherine; Niinemets, Ülo; Sun, Zhihong; Keenan, Trevor; Pacifico, Federica; Butler, Tim

    2015-01-01

    Recently, a biogenic isoprene emission model with improved CO2 dependency was developed for global change applications (Morfopoulos et al., 2013). The model is based on the mechanistic linkage between isoprene emission and the availability of reducing power. Here, we advance the model formulation by introducing an explicit link between the electron transport (supply-constraint) and enzyme activity (capacity-constraint). We furthermore investigate the sensitivity of the model to variations in photosynthetic and emission-specific parameters. By comparing species-specific simulations with experimental data, we demonstrate that differences in photosynthetic characteristics can well explain inter-species differences in emissions. Interestingly, also the seasonal development emissions could be explained to some degree by the change of energy supply from photosynthesis throughout the season. In addition, we show that the principal responses are not limited to isoprene but can be formulated to describe the emission of all light-dependent volatile species. Thus, the model is a good candidate to be implemented in regional and global models that already provide species-specific photosynthesis estimates. PMID:24661098

  17. Low emission characteristics of radiant burner

    SciTech Connect

    Bai, T.; Yeboah, Y.D.; Nie, J.X.; Wang, Z.; Shang, J.

    1998-12-31

    A commercial infrared burner is characterized in terms of its radiant efficiency and its emissions of CO, CO{sub 2}, O{sub 2}, unburned hydrocarbon, and NOx in the exhaust gases. It has been found that when methane is used as the fuel the burner reached its maximum radiation efficiency of 31.4% at the equivalence ratio {Phi} = 1. CO{sub 2} also reached its maximum value of 10.7% at {Phi} = 1. In the fuel-lean region, the concentrations of CO and unburned total hydrocarbon (UHC) were kept in a couple of hundred ppm ranges. In fuel-rich region, the CO and UHC concentrations quickly jumped to thousands of ppm or more as {Phi} increased. The NOx formation was strongly dependent on the equivalence ratio at which the burner was operated. The NOx reached its maximum of 8 ppm at {Phi} = 1, which was significantly lower than those from traditional gas burners. The NOx decreased significantly as the burner was operated at conditions away from stoichiometric. Tests were also conducted with fuel mixtures of methane and propane, which represented peak-saving gas in the industry. To simulate possible flash back, fuel mixture of methane and hydrogen was tested. Results from these tests provided insight into the effects of gas composition variations upon the IR burner performance characteristics. It has been found that the addition of propane in the fuel produced a higher combustion temperature and higher levels of NOx emission. It was also revealed by the test results that the addition of hydrogen to the methane fuel did not significantly affect the production of NOx, CO{sub 2} and CO.

  18. Electron Cyclotron Emission from Nonthermal Distributions

    NASA Astrophysics Data System (ADS)

    Harvey, R. W.; Coda, S.; Taylor, G.; Austin, M. E.; Prater, R.

    2005-10-01

    The GENRAY ray tracing code incorporates a solution of the RF energy transport equation (emission and absorption along WKB rays) including the effects of nonthermal electron distribution functions. Distributions are from self-consistent RF solutions of the bounce-averaged Fokker-Planck equation using the CQL3D 2V-1R code. We present computed spectra for two experimental situations: (1) EBW emission from electron distributions in NSTX due to future EBWCD experiments. In this case, the calculated transport of the EBW emission from overdense (omega/pe > omega/ce) NSTX plasma to the plasma edge accounts for the effects of BXO mode conversion whereby EBW waves transform to X-mode, then O-mode near the omega/pe=1 surface; and (2) EC emission in present low density DIII-D ECH experiments. A 27 keV central ECE temperature is calculated, in close agreement with the experimental value, for a plasma with 6.5 keV Thomson scattering temperature. Acknowledgment: USDOE Grants DE-AC03-99ER54463 and DE-FG03-02ER54684, and CRPP-EPFL.

  19. Electron Cyclotron Maser Emissions from Evolving Fast Electron Beams

    NASA Astrophysics Data System (ADS)

    Tang, J. F.; Wu, D. J.; Chen, L.; Zhao, G. Q.; Tan, C. M.

    2016-05-01

    Fast electron beams (FEBs) are common products of solar active phenomena. Solar radio bursts are an important diagnostic tool for understanding FEBs and the solar plasma environment in which they propagate along solar magnetic fields. In particular, the evolution of the energy spectrum and velocity distribution of FEBs due to the interaction with the ambient plasma and field during propagation can significantly influence the efficiency and properties of their emissions. In this paper, we discuss the possible evolution of the energy spectrum and velocity distribution of FEBs due to energy loss processes and the pitch-angle effect caused by magnetic field inhomogeneity, and we analyze the effects of the evolution on electron-cyclotron maser (ECM) emission, which is one of the most important mechanisms for producing solar radio bursts by FEBs. Our results show that the growth rates all decrease with the energy loss factor Q, but increase with the magnetic mirror ratio σ as well as with the steepness index δ. Moreover, the evolution of FEBs can also significantly influence the fastest growing mode and the fastest growing phase angle. This leads to the change of the polarization sense of the ECM emission. In particular, our results also reveal that an FEB that undergoes different evolution processes will generate different types of ECM emission. We believe the present results to be very helpful for a more comprehensive understanding of the dynamic spectra of solar radio bursts.

  20. Fundamental and harmonic electron cyclotron maser emission

    NASA Astrophysics Data System (ADS)

    Winglee, R. M.

    1985-10-01

    The plasma conditions and features of the energetic electron distribution in electron cyclotron maser emission for which growth in a particular mode is favored when the ratio of the plasma frequency omega(p) to the electron cyclotron frequency Omega(e) is greater than about 0.3 are determined. It is shown that growth at the fundamental is suppressed as omega(p)/Omega(e) increases and emission at harmonics of Omega(e) dominates. Growth at harmonics of Omega(e) is not restricted to the O and X modes, but can also occur for the Z mode. Whether or not growth in a particular mode dominates depends both on omega(p)/Omega(e) and on the form of the distribution. If the density of the energetic electrons is sufficiently large, the dispersion relations of the O and X modes are modified so that the group velocities of the growing O and X mode waves can be comparable to that of the growing Z mode waves.

  1. Secondary emission electron gun using external primaries

    DOEpatents

    Srinivasan-Rao, Triveni; Ben-Zvi, Ilan; Kewisch, Jorg; Chang, Xiangyun

    2007-06-05

    An electron gun for generating an electron beam is provided, which includes a secondary emitter. The secondary emitter includes a non-contaminating negative-electron-affinity (NEA) material and emitting surface. The gun includes an accelerating region which accelerates the secondaries from the emitting surface. The secondaries are emitted in response to a primary beam generated external to the accelerating region. The accelerating region may include a superconducting radio frequency (RF) cavity, and the gun may be operated in a continuous wave (CW) mode. The secondary emitter includes hydrogenated diamond. A uniform electrically conductive layer is superposed on the emitter to replenish the extracted current, preventing charging of the emitter. An encapsulated secondary emission enhanced cathode device, useful in a superconducting RF cavity, includes a housing for maintaining vacuum, a cathode, e.g., a photocathode, and the non-contaminating NEA secondary emitter with the uniform electrically conductive layer superposed thereon.

  2. Secondary emission electron gun using external primaries

    DOEpatents

    Srinivasan-Rao, Triveni; Ben-Zvi, Ilan

    2009-10-13

    An electron gun for generating an electron beam is provided, which includes a secondary emitter. The secondary emitter includes a non-contaminating negative-electron-affinity (NEA) material and emitting surface. The gun includes an accelerating region which accelerates the secondaries from the emitting surface. The secondaries are emitted in response to a primary beam generated external to the accelerating region. The accelerating region may include a superconducting radio frequency (RF) cavity, and the gun may be operated in a continuous wave (CW) mode. The secondary emitter includes hydrogenated diamond. A uniform electrically conductive layer is superposed on the emitter to replenish the extracted current, preventing charging of the emitter. An encapsulated secondary emission enhanced cathode device, useful in a superconducting RF cavity, includes a housing for maintaining vacuum, a cathode, e.g., a photocathode, and the non-contaminating NEA secondary emitter with the uniform electrically conductive layer superposed thereon.

  3. EC-5 fifth international workshop on electron cyclotron emission and electron cyclotron heating

    SciTech Connect

    Prater, R.; Lohr, J.

    1985-12-31

    This report contains papers on the following topics: electron cyclotron emission measurements; electron cyclotron emission theory; electron cyclotron heating; gyrotron development; and ECH systems and waveguide development. These paper have been indexed separately elsewhere. (LSP).

  4. Field emission characteristics from graphene on hexagonal boron nitride

    SciTech Connect

    Yamada, Takatoshi; Masuzawa, Tomoaki; Ebisudani, Taishi; Okano, Ken; Taniguchi, Takashi

    2014-06-02

    An attempt has been made to utilize uniquely high electron mobility of graphene on hexagonal boron nitride (h-BN) to electron emitter. The field emission property of graphene/h-BN/Si structure has shown enhanced threshold voltage and emission current, both of which are key to develop novel vacuum nanoelectronics devices. The field emission property was discussed along with the electronic structure of graphene investigated by Fowler-Nordheim plot and ultraviolet photoelectron spectroscopy. The result suggested that transferring graphene on h-BN modified its work function, which changed field emission mechanism. Our report opens up a possibility of graphene-based vacuum nanoelectronics devices with tuned work function.

  5. Microwave emission characteristics of sea ice

    NASA Technical Reports Server (NTRS)

    Edgerton, A. T.; Poe, G.

    1972-01-01

    A general classification is presented for sea ice brightness temperatures with categories of high and low emission, corresponding to young and weathered sea ice, respectively. A sea ice emission model was developed which allows variations of ice salinity and temperature in directions perpendicular to the ice surface.

  6. Measurements of optically thin electron cyclotron emission from relativistic electrons

    SciTech Connect

    James, R.A.; Silver, E.; Boyd, D.; Ellis, R.F.; Jantz, S.; Lasnier, C.J.; Harvey, R.W.; Lohr, J.; Prater, R.; O'Brien, M.R.

    1987-10-01

    Electron cyclotron emission (ECE) from hot, relativistic electrons has been measured simulataneously at several optically thin frequencies (f/f/sub ce/ = 4.6, 7.0, and 9.6) on the Tandem Mirror Experiment-Upgrade. A method to determine the temporal evolution of the hot electron density, n/sub h/, and temperature T/sub h/ is discussed. Calculations of T/sub h/ agree with the analysis of the high energy x-ray spectra. Heating rates vary between 3 keV/ms and 13 keV/ms and temperatures over 300 keV have been reached by the end of the 50 ms discharge. The ECE analysis provides an order of magnitude improvement in time resolution over the x-ray analysis and shows that fast reductions in the diamagnetic loop signals are predominantly a loss of perpendicular energy stored by the mirror trapped hot electrons. These techniques for determining n/sub h/(t) and T/sub t/(t) will be used on the DIII-D tokamak in order to parameterize the nonthermal electron tail produced during ECH current drive experiments. A vertical view will be utilized and a fast (70 Hz) scanning Michelson interferometer will be used to measure the ECE spectrum between the 2nd and the 15th harmonic. 11 refs., 7 figs.

  7. Graphene-oxide-semiconductor planar-type electron emission device

    NASA Astrophysics Data System (ADS)

    Murakami, Katsuhisa; Tanaka, Shunsuke; Miyashita, Akira; Nagao, Masayoshi; Nemoto, Yoshihiro; Takeguchi, Masaki; Fujita, Jun-ichi

    2016-02-01

    Graphene was used as the topmost electrode for a metal-oxide-semiconductor planar-type electron emission device. With several various layers, graphene as a gate electrode on the thin oxide layer was directly deposited by gallium vapor-assisted chemical vapor deposition. The maximum efficiency of the electron emission, defined as the ratio of anode current to cathode current, showed no dependency on electrode thickness in the range from 1.8 nm to 7.0 nm, indicating that electron scattering on the inside of the graphene electrode is practically suppressed. In addition, a high emission current density of 1-100 mA/cm2 was obtained while maintaining a relatively high electron emission efficiency of 0.1%-1.0%. The graphene-oxide-semiconductor planar-type electron emission device has great potential to achieve both high electron emission efficiency and high electron emission current density in practical applications.

  8. Influence of the Electric Field on Secondary Electron Emission Yield

    SciTech Connect

    Beranek, M.; Richterova, I.; Nemecek, Z.; Pavlu, J.; Safrankova, J.

    2008-09-07

    We have applied a technique based on levitation of a single charged grain in the quadrupole. We have used 3-6 micrometer spherical grains from amorphous carbon. These grains were charged by an electron beam with the energy tunable up to 10 keV and the grain charge was continuously monitored. If the grain is charged by an constant energy, its surface potential is set to the value when incident electrons are slow down to the energy where the secondary emission yield is equal to unity. Our investigations reveal that this energy changes proportionally to the grain surface field. Moreover, we have observed a shift of charging characteristics after a long-time electron bombardment.

  9. Electron emission from nickel-alloy surfaces in cesium vapor

    NASA Technical Reports Server (NTRS)

    Manda, M.; Jacobson, D.

    1978-01-01

    An experimental apparatus and measurement techniques are described for measuring the thermionic emission from cesium-activated materials having adequate high-temperature properties such as creep strength and corrosion resistance, which might ultimately reduce the cost of thermionic converters. The electron emission characteristics are measured for nickel, Inconel 600, and Hastelloy X probes with a 412 K cesium reservoir. It is found that the nickel alloys exhibit a peak electron emission 1.4 to 2.1 times greater than pure nickel. Both the Inconel and the Hastelloy samples have work functions of 1.64 eV at peak emission. The minimum cesiated work functions are estimated to be 1.37 eV for Inconel at a probe temperature of 750 K and 1.4 eV for Hastelloy at a probe temperature of 665 K. The bare work functions for both alloys is estimated to be about the same as for pure nickel, 4.8 eV.

  10. Emission Characteristics and Stability of Laser Ion Sources

    SciTech Connect

    Krasa, J.; Velyhan, A.; Krousky, E.; Laska, L.; Rohlena, K.; Jungwirth, K.; Ullschmied, J.; Lorusso, A.; Velardi, L.; Nassisi, V.; Czarnecka, A.; Ryc, L.; Parys, P.; Wolowksi, J.

    2010-10-13

    A new classification of laser ion sources concerning their pulse-to-pulse reproducibility in the ion emission is proposed. In particular, we distinguish between plasmas according to the electron distribution changing its characteristics at a laser intensity threshold of 10{sup 14} W/cm{sup 2}. Well reproducible continuous pulsed ion currents are typical for the intensity below the threshold. In contrast to this plasma the 'two-temperature' plasma arising for the intensity above this threshold shows not only a separation of charges in space and time but it also shows irregular and intense outbursts of ions similar to a self pulsing instability leading to a chaos. The sequence of fast ion outbursts visible on time-of-flight spectra is sensitive to details of non-linear interaction of the sub-nanosecond laser beam with the generated plasma.

  11. Characteristics of surface sterilization using electron cyclotron resonance plasma

    NASA Astrophysics Data System (ADS)

    Yonesu, Akira; Hara, Kazufumi; Nishikawa, Tatsuya; Hayashi, Nobuya

    2016-07-01

    The characteristics of surface sterilization using electron cyclotron resonance (ECR) plasma were investigated. High-energy electrons and oxygen radicals were observed in the ECR zone using electric probe and optical emission spectroscopic methods. A biological indicator (BI), Geobacillus stearothermophilus, containing 1 × 106 spores was sterilized in 120 s by exposure to oxygen discharges while maintaining a temperature of approximately 55 °C at the BI installation position. Oxygen radicals and high-energy electrons were found to be the sterilizing species in the ECR region. It was demonstrated that the ECR plasma could be produced in narrow tubes with an inner diameter of 5 mm. Moreover, sterilization tests confirmed that the spores present inside the narrow tube were successfully inactivated by ECR plasma irradiation.

  12. Self-amplified spontaneous emission free electron laser devices and nonideal electron beam transport

    NASA Astrophysics Data System (ADS)

    Lazzarino, L. L.; Di Palma, E.; Anania, M. P.; Artioli, M.; Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Cianchi, A.; Ciocci, F.; Dattoli, G.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G.; Giannessi, L.; Mostacci, A.; Musumeci, P.; Petralia, A.; Petrillo, V.; Pompili, R.; Rau, J. V.; Rossi, A. R.; Sabia, E.; Vaccarezza, C.; Villa, F.

    2014-11-01

    We have developed, at the SPARC test facility, a procedure for a real time self-amplified spontaneous emission free electron laser (FEL) device performance control. We describe an actual FEL, including electron and optical beam transport, through a set of analytical formulas, allowing a fast and reliable on-line "simulation" of the experiment. The system is designed in such a way that the characteristics of the transport elements and the laser intensity are measured and adjusted, via a real time computation, during the experimental run, to obtain an on-line feedback of the laser performances. The detail of the procedure and the relevant experimental results are discussed.

  13. Methane fueled engine performance and emissions characteristics

    SciTech Connect

    Swain, M.R.; Adt, R.R.; Bedsworth, K.; Maxwell, R.; Pappas, J.M.; Swain, M.N.

    1983-08-01

    A 1983 Ford 3.8 liter V-6 engine was fueled with methane and tested on an engine dynamometer in order to begin to generate a data base that could be used to estimate emission levels and fuel economy for a driving cycle from a 3-point mini map method. The results showed that, with the proper control of pertinent engine variables, the engine would probably meet the current State of California Emission Standards that have been formulated to account for methane as an unburned hydrocarbon, without having to resort to a catalytic converter, and with Joules fuel consumption comparable, if not better than that for a gasoline-fueled vehicle. Unburned fuel in the exhaust was found to be comprised of between 87 and 96% methane. MBTH total aldehyde emissions were found to vary between 27 and 67 molar ppm.

  14. CuO nanowires for inhibiting secondary electron emission

    NASA Astrophysics Data System (ADS)

    Aguilera, L.; Montero, I.; Dávila, M. E.; Ruiz, A.; Galán, L.; Nistor, V.; Raboso, D.; Palomares, J.; Soria, F.

    2013-04-01

    Copper oxide nanowires (NWs) grown on copper to avoid the secondary electron emission were investigated. Optimal temperatures for NW growth were found to be in the range 700-800 K. NW surface coverage of 102 µm-2 is required to strongly reduce the secondary electron yield. A total secondary electron emission coefficient below 1 was obtained for NW aspect ratio higher than 103.

  15. Electron cyclotron-electron Bernstein wave emission diagnostics for the COMPASS tokamak

    SciTech Connect

    Zajac, J.; Preinhaelter, J.; Urban, J.; Zacek, F.; Sestak, D.

    2010-10-15

    The COMPASS tokamak recently started operation at the Institute of Plasma Physics AS CR, v.v.i., Prague. A new 16-channel radiometer, operating alternatively in three frequency bands, has been designed and constructed. The system is prepared for detection of normal electron cyclotron emission (O1 or X2) or oblique electron Bernstein wave emission. The end-to-end calibration method includes all components that influence the antenna radiation pattern. A steady recalibration is possible using a noise generator connected to the radiometer input through a fast waveguide PIN-switch. Measurements of the antenna radiation characteristics (2D electric field) were performed in free space as well as in the tokamak chamber, showing the degradation effect of structures on the Gaussian beam shape. First plasma radiation temperature measurements from low-field circular plasmas are available.

  16. Characteristics of real-world vehicular emissions in Chinese cities.

    PubMed

    Yao, Zhiliang; Wang, Qidong; He, Kebin; Huo, Hong; Ma, Yongliang; Zhang, Qiang

    2007-11-01

    On-board emission measurements were performed on 49 light-duty gasoline vehicles in seven cities of China. Vehicle-specific power mode distribution and emission characteristics were analyzed based on the data collected. The results of our study show that there were significant differences in different types of roads. The emission factors and fuel consumption rates on arterial roads and residential roads were approximately 1.4-2 times those on freeways. The carbon monoxide, hydrocarbon, and nitrogen oxides emission factors of Euro II vehicles were on average 86.2, 88.2, and 64.5% lower than those of carburetor vehicles, respectively. The new vehicle emission standards implemented in China had played an important role in reducing individual vehicle emissions. More comprehensive measures need to be considered to reduce the total amount of emissions from vehicles. PMID:18069461

  17. Competition between coherent emission and broadband spontaneous emission in the quantum free electron laser

    SciTech Connect

    Robb, G. R. M.; Bonifacio, R.

    2013-03-15

    We extend previous analyses of spontaneous emission in a quantum free electron laser (QFEL) and competition between spontaneous and coherent QFEL emission to include a broad distribution of photon frequencies and momenta appropriate for spontaneous undulator radiation. We show that although the predictions of monochromatic and broadband models predict different electron momentum distributions for the quantum regime due to spontaneous emission alone after many photon emissions, the inclusion of broadband spontaneous emission has a negligible effect on the competition between spontaneous and coherent emission in the QFEL. Numerical results from both models are well described by the same condition for the threshold/critical value of spontaneous emission rate.

  18. Nanodiamond vacuum field emission device with gate modulated triode characteristics

    NASA Astrophysics Data System (ADS)

    Hsu, S. H.; Kang, W. P.; Raina, S.; Huang, J. H.

    2013-05-01

    A three-electrode nanodiamond vacuum field emission (VFE) device with gate modulated triode characteristics is developed by integrating nanodiamond emitter with self-aligned silicon gate and anode, employing a mold transfer technique in conjunction with chemical vapor deposition of nanodiamond. Triode behavior showing emission current modulation with high current density at low operating voltages is achieved. A systematic analysis based on modified Fowler-Nordheim theory is used to analyze gate modulated VFE characteristics, confirming the triode field emission mechanism and operating principle. The realization of an efficient VFE microtriode has achieved the fundamental step for further development of vacuum integrated microelectronics.

  19. Innovations in X-ray-induced electron emission spectroscopy (XIEES)

    SciTech Connect

    Pogrebitsky, K. Ju. Sharkov, M. D.

    2010-06-15

    Currently, a pressing need has arisen for controlling the local atomic and electron structure of materials irrespective of their aggregate state. Efficient approaches to the studies of short-range order are based on phenomena accompanied by interference of secondary electrons excited by primary X-ray radiation. The set of such approaches are commonly referred to as the X-ray absorption fine structure (XAFS) methods. In reality, the XAFS methods are based on the use of synchrotron radiation and applied to structural studies in two modes of measurements, transmission analysis and recording of secondary effects. Only two such effects-specifically, the X-ray fluorescence an d X-ray-induced electron emission effect-are commonly discussed. Access to synchrotron accelerators is problematic for most researchers, so a demand is created for designing laboratory systems that make direct access possible. Since the power of laboratory systems is much lower than that of synchrotrons, it is essential to use much more efficient detectors of secondary electrons. In addition, it is of interest to analyze energy characteristics with a high spatial resolution. Channel multipliers and multichannel boards are incapable of providing such a possibility. For this reason, an improved electron detector has been developed to analyze the photoemission effect in an accelerating field.

  20. Ballistic-electron-emission Microscopy of Semiconductor Heterostructures

    NASA Technical Reports Server (NTRS)

    Bell, L. Douglas; Narayanamurti, Venkatesh

    1997-01-01

    Balistic-electron-emission microscopy has developed from its beginning as a probe of Schottky barriers into a powerful nanometer-scale method for characterizing semiconductor interfaces and hot-electron transport.

  1. Field emission characteristics of nano-diamond cathode surface by graphitization pretreatment

    NASA Astrophysics Data System (ADS)

    Shi, Yan-mei; Yang, Yan-ning; Liu, Qiao-ping; Li, Wei-xia

    2016-03-01

    Cathode samples of nano-diamond by graphitization pretreatment with different temperatures were fabricated by electrophoresis, then the structures and morphologies of the cathode samples were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), and the field emission tests were conducted. The effects of graphitization pretreatment on the field emission characteristics of nano-diamond cathode surface on titanium substrate are studied. The results indicate that the surface morphologies of nano-diamond cathode samples after graphitization pretreatment change a lot, and the field emission characteristics in low-voltage area are improved obviously. However, in high-voltage area, the curve distortion happens, and it doesn't conform the mechanism of field emission characteristics.

  2. Extraction of internal emission characteristics from printed OLEDs

    NASA Astrophysics Data System (ADS)

    Hildner, Mark L.; Ziebarth, Jonathan M.

    2012-09-01

    Accurate optical modeling of OLED device performance is beneficial to OLED manufacturing because as materials and architectures are modified, experimental effort and resources are saved in the search for optimal structures. The success of such modeling depends crucially on model inputs, which include, along with layer thicknesses and optical constants, internal emission characteristics such as the internal emission spectrum (IES) of the emitter and the location and profile of emission in the emissive layer (EML). This presentation will describe two methods we have used to extract the internal emission characteristics of our printed bottom emitting OLEDs. The first method, which we devised and implemented with assumptions specific to our devices, is a simpler one for both modeling and data collection: we collected spectra at normal viewing angle for a series of devices with different architectures, and extracted a normalized IES common to all these devices. We will show how an emission location was obtained from this method with some simple model assumptions. In the more rigorous second method - one presented by van Mensfoort et al 1 - internal emission characteristics were extracted independently for each device: spectra at multiple angles were collected, which allowed the extraction of an individual IES and emission profile. We will compare the findings of the two methods and assess the validity of the assumptions used in the first method.

  3. Diffusive and inelastic scattering in ballistic-electron-emission spectroscopy and ballistic-electron-emission microscopy

    SciTech Connect

    Lee, E.Y.; Turner, B.R.; Schowalter, L.J.

    1993-07-01

    Ballistic-electron-emission microscopy (BEEM) of Au/Si(001) n type was done to study whether elastic scattering in the Au overlayer is dominant. It was found that there is no dependence of the BEEM current on the relative gradient of the Au surface with respect to the Si interface, and this demonstrates that significant elastic scattering must occur in the Au overlayer. Ballistic-electron-emission spectroscopy (BEES) was also done, and, rather than using the conventional direct-current BEES, alternating-current (ac) BEES was done on Au/Si and also on Au/PtSi/Si(001) n type. The technique of ac BEES was found to give linear threshold for the Schottky barrier, and it also clearly showed the onset of electron-hole pair creation and other inelastic scattering events. The study of device quality PtSi in Au/PtSi/Si(001) yielded an attenuation length of 4 nm for electrons of energy 1 eV above the PtSi Fermi energy. 20 refs., 5 figs.

  4. [Characteristic of Particulate Emissions from Concrete Batching in Beijing].

    PubMed

    Xue, Yi-feng; Zhou, Zhen; Zhong, Lian-hong; Yan, Jing; Qu, Song; Huang, Yu-hu; Tian, He- zhong; Pan, Tao

    2016-01-15

    With the economic development and population growth in Beijing, there is a strong need for construction and housing, which leads to the increase of the construction areas. Meanwhile, as a local provided material, the production of concrete has been raised. In the process of concrete production by concrete batching, there are numerous particulates emitted, which have large effect on the atmospheric environment, however, systematic study about the tempo-spatial characteristics of pollutant emission from concrete batching is still rare. In this study, we estimated the emission of particulates from concrete batching from 1991 to 2012 using emission factor method, analyzed the tempo-spatial characteristics of pollutant emission, established the uncertainty range by adopting Monte-Carlo method, and predicted the future emission in 2020 based on the relative environmental and economical policies. The results showed that: (1) the emissions of particulates from concrete batching showed a trend of "first increase and then decrease", reaching the maximum in 2005, and then decreased due to stricter emission standard and enhanced environmental management. (2) according to spatial distribution, the emission of particulates from concrete batch mainly concentrated in the urban area with more human activities, and the area between the fifth ring and the sixth ring contributed the most. (3) through scenarios analysis, for further reducing the emission from concrete batching in 2020, more stricter standard for green production as well as powerful supervision is needed. PMID:27078945

  5. Sheath structure transition controlled by secondary electron emission

    NASA Astrophysics Data System (ADS)

    Schweigert, I. V.; Langendorf, S. J.; Walker, M. L. R.; Keidar, M.

    2015-04-01

    In particle-in-cell Monte Carlo collision (PIC MCC) simulations and in an experiment we study sheath formation over an emissive floating Al2O3 plate in a direct current discharge plasma at argon gas pressure 10-4 Torr. The discharge glow is maintained by the beam electrons emitted from a negatively biased hot cathode. We observe three types of sheaths near the floating emissive plate and the transition between them is driven by changing the negative bias. The Debye sheath appears at lower voltages, when secondary electron emission is negligible. With increasing applied voltage, secondary electron emission switches on and a first transition to a new sheath type, beam electron emission (BEE), takes place. For the first time we find this specific regime of sheath operation near the floating emissive surface. In this regime, the potential drop over the plate sheath is about four times larger than the temperature of plasma electrons. The virtual cathode appears near the emissive plate and its modification helps to maintain the BEE regime within some voltage range. Further increase of the applied voltage U initiates the second smooth transition to the plasma electron emission sheath regime and the ratio Δφs/Te tends to unity with increasing U. The oscillatory behavior of the emissive sheath is analyzed in PIC MCC simulations. A plasmoid of slow electrons is formed near the plate and transported to the bulk plasma periodically with a frequency of about 25 kHz.

  6. Fault structure, damage and acoustic emission characteristics

    NASA Astrophysics Data System (ADS)

    Dresen, G. H.; Göbel, T.; Stanchits, S.; Kwiatek, G.; Charalampidou, E. M.

    2011-12-01

    We investigate the evolution of faulting-related damage and acoustic emission activity in experiments performed on granite, quartzite and sandstone samples with 40-50 mm diameter and 100-125 mm length. Experiments were performed in a servo-controlled MTS loading frame in triaxial compression at confining pressures ranging from 20-140 MPa. We performed a series of fracture and stick-slip sliding experiments on prefractured samples. Acoustic emissions (AE) and ultrasonic velocities were monitored using up to 14 P-wave sensors glued to the cylindrical surface of the rock. Full waveforms were stored in a 16 channel transient recording system (Daxbox, PRÖKEL, Germany). Full moment tensor analysis and polarity of AE first motions were used to discriminate source types associated with tensile, shear and pore-collapse cracking. To monitor strain, two pairs of orthogonally oriented strain-gages were glued onto the specimen surface. Fracture nucleation and growth occurred from a nucleation patch mostly located at the specimen surface or at the tip of prefabricated notches inside the specimens. Irrespective of the rock type, fracture propagation is associated with formation of a damage zone surrounding the fracture surface as revealed by distribution of cracks and AE hypocenters displaying a logarithmic decay in microcrack damage with distance normal to the fault trace. The width of the damage zone varies along the fault. After fracturing, faults were locked by increasing confining pressure. Subsequent sliding was mostly induced by driving the piston at a constant displacement rate producing large single events or multiple stick-slips. With increasing sliding distance a corrugated and rough fault surface formed displaying displacement-parallel lineations. Microstructural analysis of fault surfaces and cross-sections revealed formation of multiple secondary shears progressively merging into an anastomosing 3D-network controlling damage evolution and AE activity in the fault

  7. Electrostatic emissions between electron gyroharmonics in the outer magnetosphere

    NASA Technical Reports Server (NTRS)

    Hubbard, R. F.; Birmingham, T. J.

    1977-01-01

    A scheme was constructed and a theoretical model was developed to classify electrostatic emissions. All of the emissions appear to be generated by the same basic mechanism: an unstable electron plasma distribution consisting of cold electrons (less than 100 eV) and hot loss cone electrons (about 1 keV). Each emission class is associated with a particular range of model parameters; the wide band electric field data can thus be used to infer the density and temperature of the cold plasma component. The model predicts that gyroharmonic emissions near the plasma frequency require large cold plasma densities.

  8. Electron cyclon emission imaging of electron temperature profiles and fluctuations (invited)(abstract)

    SciTech Connect

    Cima, G.; Deng, B.; Domier, C.W.; Geck, W.R.; Hsia, R.P.; Liang, C.; Jiang, F.; Luhmann, N.C.; Brower, D.; Watts, C.

    1997-01-01

    Electron cyclotron emission (ECE) is a powerful diagnostic in a high performance/high magnetic field, magnetic confinement experiment, for a number of reasons. The most important one is probably due to the spatial localization of the ECE source, as opposed to most passive plasma diagnostics which perform line integrated measurements. The novel technique of ECE imaging, made possible by the existence of new arrays of high frequency mixers, fully exploits this property of ECE. A description of the device, an analysis of its characteristics, and a review of its preliminary results on TEXT-U will be given.

  9. Study of the microwave emissivity characteristics over Gobi Desert

    NASA Astrophysics Data System (ADS)

    Yubao, Qiu; Lijuan, Shi; Wenbo, Wu

    2014-03-01

    The microwave emissivity represents the capacity of the thermal radiation of the surface, and it is the significant parameter for understanding the geophysical processes such as surface energy budget and surface radiation. Different land covers have different emissivity properties, and the Gobi Desert in Central Asia seriously impact the sandstorms occur and develop in China, because of its special geographical environment and surface soil characteristics. In this study half-month averaged microwave emissivity from March 2003 to February 2004 over the Gobi Desert has been estimated. Emissivities in this area at different frequencies, polarization and their seasonal variations are discussed respectively. The results showed that emissivity polarization difference decrease as the frequency increases, and the polarization difference is large (0.03-0.127). The H polarization emissivity increases with increasing frequency, but the V-polarized microwave emissivity is reduced with increasing frequency because of the body scattering. In winter, emissivity decreases sharply in snow covered area, especially for higher frequencies (such as 89GHz). In addition, we compared emissivity with MODIS NDVI data at the same time in the Gobi Desert, and the results indicate that NDVI derived the good negative correlation with microwave emissivity polarization difference at 37GHz.

  10. Ion-induced electron emission from surfaces: Dynamical screening effects

    SciTech Connect

    Kouzakov, Konstantin A.; Berakdar, Jamal

    2003-08-01

    A theoretical model is developed for the description of the single-electron emission from surfaces following the impact of fast ions. The theory describes quantum mechanically the ion reflection at the surface and the excitation of the valence band electrons via an ion-electron interaction renormalized by the dielectric response of the target. Numerical calculations are presented and analyzed for the electron emission from the conduction band of an aluminum surface upon proton impact. Particular attention is devoted to the influence of the dielectric screening on the energy distributions and the angular distributions of the ejected electrons. In addition, the role of the surface electronic structure is studied.

  11. Characteristics of mesospheric optical emissions produced by lighting discharges

    NASA Astrophysics Data System (ADS)

    Veronis, Georgios; Pasko, Victor P.; Inan, Umran S.

    1999-06-01

    A new two-dimensional cylindrically symmetric electromagnetic model of the lightning-ionosphere interaction includes effects of both the lightning radiated electromagnetic pulses (EMP) and the quasi-electrostatic (QE) fields, thus allowing effective studies of lightning-ionosphere interactions on time scales ranging from several microseconds to tens of milliseconds. The temporal and spatial evolution of the electric field, lower ionospheric electron density, and optical emissions calculated with the new model are used to investigate theoretically the effects of the lightning return stroke current waveform (i.e., the current rise and fall timescales) and of the observational geometry on the optical signals observed with a photometer. For typical lightning discharges of ~100 μs duration the ionospheric response is dominated by the EMP-induced heating leading to the highly transient and laterally expanding optical flashes known as elves. The optical signal characteristics are found to be highly sensitive to both the observational geometry and the current waveform. The onset delay with respect to the lighting discharge, the duration, and the peak magnitude of optical emissions are highly dependent on the elevation and azimuth angles of field of view of individual photometric pixels. The shape of the optical signal clearly reflects the source current waveform. For a waveshape with risetime of ~50 μs or longer a double-pulse shape of the photometric signal is observed. For cloud to ground lightning discharges of ~1 ms duration removing substantial amount of charge (i.e., ~100 C from 10 km altitude), heating and ionization changes induced by the QE field lead to the mesospheric luminous glows with lateral extent <100 km, referred to as sprites.

  12. Carbon adsorption on tungsten and electronic field emission

    NASA Astrophysics Data System (ADS)

    Márquez-Mijares, Maykel; Lepetit, Bruno; Lemoine, Didier

    2016-03-01

    Electronic emission taking place at the electrodes of high voltage systems and responsible for detrimental breakdown processes is known to be strongly dependent on the cathode surface state and in particular on the presence of carbon contamination. To understand better the effect of carbon adsorption on cathode electronic emission, density functional theory calculations are reported for bulk bcc tungsten as well as for clean and carbon-covered W(100) surfaces for several coverages up to 2 ML. Adsorption geometries and energies, work functions and electronic densities of states are analyzed to assess the effect of the presence of adlayers on surface electronic field emission properties. It is shown that flat carbon adlayer deposition on clean W(100) surfaces induces an increase of the surface work function and a decrease of electronic density near the Fermi level. Both factors contribute to reducing electronic field emission levels.

  13. Effect of insulating layer on the Field Electron Emission Performance of Nano-Apex Metallic Emitters

    NASA Astrophysics Data System (ADS)

    AL-Qudah, Ala'a. A.; Mousa, Marwan S.; Fischer, A.

    2015-10-01

    This paper deals with the process of electron emission from the surface of metals (before and after coating with controlled layers of dielectric materials) into the vacuum due to an intense applied external electric field. This process is usually called cold field electron emission (CFE). The research work reported here includes the current-voltage (I-V) characteristics presented as Fowler-Nordheim (FN) plots and scanning electron micrographs in addition to the spatial emission current distributions (electron emission images). The process of coating the clean tungsten (W) emitters by layers of dielectric epoxylite resin was easy, and the measurements were performed under UHV ∼ 10-8 mbar. From comparing the results obtained in this work, significant improvement in properties of the emitters after coating are observed.

  14. Odour emission characteristics of 22 recreational rivers in Nanjing.

    PubMed

    Wan, Yu; Ruan, Xiaohong; Wang, Xinguang; Ma, Qian; Lu, Xiaoming

    2014-10-01

    The odour emission characteristics of 22 recreational rivers in Nanjing were investigated and analysed. Eight odorous compounds (ammonia (NH₃), hydrogen sulphide (H₂S), sulphur dioxide (SO₂), carbon disulphide (CS₂), nitrobenzene (C₆H₅NO₂), aniline (C₆H₅NH₂), dimethylamine (C₂H₇N), and formaldehyde (HCHO)) were measured in odour emission samples collected using a custom-made emission flux hood chamber. The results showed that all odorants were detected in all monitoring rivers. NH₃ was the main odorant, with emission rates ranging from 4.86 to 15.13 μg/min m(2). The total odour emission rate of the Nan River, at 1 427.07 OU/s, was the highest of the all investigated rivers. H₂S, NH₃ and nitrobenzene were three key odour emission contributors according to their contributions to the total odour emission. A correlation analysis of the pollutants showed there was a significant positive correlation between the emission rate of NH₃ and the concentration of ammonia nitrogen (NH₄ (+)-N) and total nitrogen (TN). The H₂S and SO₂ emission rates had a significant positive correlation with sulphides (S(2-)) and available sulphur (AS) in the water and sediment. The content of TN, NH₄(+)-N, S(2-) and AS in the water and sediment affected the concentration of H₂S, SO₂ and NH₃ in the emission gases. NH₄(+)-N, S(2-) and AS are suggested as the key odour control indexes for reducing odours emitted from these recreational rivers. The study provides useful information for effective pollution control, especially for odour emission control for the recreational rivers of the city. It also provides a demonstrate example to show how to monitor and assess a contaminated river when odour emission and its control need to be focused on. PMID:24939710

  15. Extracting Microwave Emissivity Characteristics over City using AMSR-E

    NASA Astrophysics Data System (ADS)

    Zhang, T.; Zhang, L.; Jiang, L.; Li, Y.

    2010-12-01

    The spectrums of different land types are very important in the application of remote sensing. Different spectrums of different land types can be used in surface classification, change detection, and so on. The microwave emissivity over land is the foundation of land parameters retrieval using passive microwave remote sensing. It depends on land type due to different objects’ structure, moisture and roughness on the earth. It has shown that the land surface microwave emissivity contributed to atmosphere temperature and moisture retrieval. Meanwhile, it depends on land type, vegetation cover, and moisture et al.. There are many researches on microwave emissivity of various land types, such as bare soil, vegetation, snow, but city was less mentioned [1]. However, with the development of society, the process of urbanization accelerated quickly. The area of city expanded fast and the fraction of city area increased in one microwave pixel, especially in The North China Plain (about 30%). The passive microwave pixel containing city has impact on satellite observation and surface parameters retrieval then. So it is essential to study the emissivity of city in order to improve the accuracy of land surface parameters retrieval from passive microwave remote sensing. To study the microwave emissivity of city, some ‘pure’ city pixels were selected according to IGBP classification data, which was defined the fraction cover of city is larger than 85%. The city emissivity was calculated using AMSR-E L2A brightness temperature and GLDAS land surface temperature data at different frequencies and polarizations over 2008 in China. Then the seasonal variation was analyzed along the year. Finally, the characteristic of city emissivity were compared with some meteorological data, seeking the relationship between city emissivity and climatic factors. The results have shown that the emissivity of city was different for different frequencies. It increased with the frequency becoming

  16. Gas Electron Multiplier (GEM) Chamber Characteristics Test

    SciTech Connect

    Yu, Jaehoon; White, Andy; Park, Seongtae; Hahn, Changhie; Baldeloma, Edwin; Tran, Nam; McIntire, Austin; Soha, Aria; /Fermilab

    2011-01-11

    Gas Electron Multipliers (GEMs) have been used in many HEP experiments as tracking detectors. They are sensitive to X-rays which allows use beyond that of HEP. The UTA High Energy group has been working on using GEMs as the sensitive gap detector in a DHCAL for the ILC. The physics goals at the ILC put a stringent requirement on detector performance. Especially the precision required for jet mass and positions demands an unprecedented jet energy resolution to hadronic calorimeters. A solution to meet this requirement is using the Particle Flow Algorithm (PFA). In order for PFA to work well, high calorimeter granularity is necessary. Previous studies based on GEANT simulations using GEM DHCAL gave confidence on the performance of GEM in the sensitive gap in a sampling calorimeter and its use as a DHCAL in PFA. The UTA HEP team has built several GEM prototype chambers, including the current 30cm x 30cm chamber integrated with the SLAC-developed 64 channel kPiX analog readout chip. This chamber has been tested on the bench using radioactive sources and cosmic ray muons. In order to have fuller understanding of various chamber characteristics, the experiments plan to expose 1-3 GEM chambers of dimension 35cm x 35cm x 5cm with 1cm x 1cm pad granularity with 64 channel 2-D simultaneous readout using the kPiX chip. In this experiment the experiments pan to measure MiP signal height, chamber absolute efficiencies, chamber gain versus high voltage across the GEM gap, the uniformity of the chamber across the 8cm x 8cm area, cross talk and its distance dependence to the triggered pad, chamber rate capabilities, and the maximum pad occupancy rate.

  17. Thermal and emission characteristics of a CAN combustor

    NASA Astrophysics Data System (ADS)

    Shah, Rupesh D.; Banerjee, Jyotirmay

    2016-03-01

    Experimental investigations are carried out to establish the thermal and emission characteristics of a CAN combustor. Temperature and emission levels at the combustor exit are measured for different swirler vane angles and air fuel ratios (AFR). Swirler vane angle is varied from 15° to 60° in steps of 15°. AFR is varied in the range of 41-51. Experimental analysis is carried out using methane as fuel. Measured temperature variation at combustor outlet indicates that the hot product of combustor flows near the liner wall. Gradient of temperature near the wall decreases as the swirler vane angle (and corresponding swirl number) is increased. The peak temperature reduces at higher value of AFR. Emission level of carbon monoxide decreases with increase in AFR and swirler vane orientation. A higher level of NOX emission is observed for AFR of 45. This is due to change in shape and strength of the recirculation region in the primary zone of the combustor.

  18. Flat panel ferroelectric electron emission display system

    DOEpatents

    Sampayan, S.E.; Orvis, W.J.; Caporaso, G.J.; Wieskamp, T.F.

    1996-04-16

    A device is disclosed which can produce a bright, raster scanned or non-raster scanned image from a flat panel. Unlike many flat panel technologies, this device does not require ambient light or auxiliary illumination for viewing the image. Rather, this device relies on electrons emitted from a ferroelectric emitter impinging on a phosphor. This device takes advantage of a new electron emitter technology which emits electrons with significant kinetic energy and beam current density. 6 figs.

  19. Flat panel ferroelectric electron emission display system

    DOEpatents

    Sampayan, Stephen E.; Orvis, William J.; Caporaso, George J.; Wieskamp, Ted F.

    1996-01-01

    A device which can produce a bright, raster scanned or non-raster scanned image from a flat panel. Unlike many flat panel technologies, this device does not require ambient light or auxiliary illumination for viewing the image. Rather, this device relies on electrons emitted from a ferroelectric emitter impinging on a phosphor. This device takes advantage of a new electron emitter technology which emits electrons with significant kinetic energy and beam current density.

  20. Comparative electron temperature measurements of Thomson scattering and electron cyclotron emission diagnostics in TCABR plasmas

    SciTech Connect

    Alonso, M. P.; Figueiredo, A. C. A.; Berni, L. A.; Machida, M.

    2010-10-15

    We present the first simultaneous measurements of the Thomson scattering and electron cyclotron emission radiometer diagnostics performed at TCABR tokamak with Alfven wave heating. The Thomson scattering diagnostic is an upgraded version of the one previously installed at the ISTTOK tokamak, while the electron cyclotron emission radiometer employs a heterodyne sweeping radiometer. For purely Ohmic discharges, the electron temperature measurements from both diagnostics are in good agreement. Additional Alfven wave heating does not affect the capability of the Thomson scattering diagnostic to measure the instantaneous electron temperature, whereas measurements from the electron cyclotron emission radiometer become underestimates of the actual temperature values.

  1. Secondary-electron emission from hydrogen-terminated diamond

    SciTech Connect

    Wang E.; Ben-Zvi, I.; Rao, T.; Wu, Q.; Dimitrov, D.A.; T. Xin, T.

    2012-05-20

    Diamond amplifiers demonstrably are an electron source with the potential to support high-brightness, high-average-current emission into a vacuum. We recently developed a reliable hydrogenation procedure for the diamond amplifier. The systematic study of hydrogenation resulted in the reproducible fabrication of high gain diamond amplifier. Furthermore, we measured the emission probability of diamond amplifier as a function of the external field and modelled the process with resulting changes in the vacuum level due to the Schottky effect. We demonstrated that the decrease in the secondary electrons average emission gain was a function of the pulse width and related this to the trapping of electrons by the effective NEA surface. The findings from the model agree well with our experimental measurements. As an application of the model, the energy spread of secondary electrons inside the diamond was estimated from the measured emission.

  2. Comparison of secondary electron emission simulation to experiment.

    SciTech Connect

    Insepov, Z.; Ivanov, V.; Jokela, S. J.; Veryovkin, I.; Zinovev, A.; Frisch, H.

    2011-05-01

    Monte Carlo simulation, empirical theories, and close comparison to experiment were used to parameterize the secondary electron emission (SEE) yields of several highly emissive materials for microchannel plates. In addition, a detailed experiment and analysis of gold were carried out at Argonne National Laboratory. The simulation results will be used in the selection of emissive and resistive materials for deposition and characterization experiments that will be conducted by a large-area fast detector project at Argonne.

  3. Texturing Copper To Reduce Secondary Emission Of Electrons

    NASA Technical Reports Server (NTRS)

    Jensen, Kenneth A.; Curren, Arthur N.; Roman, Robert F.

    1995-01-01

    Ion-beam process produces clean, deeply textured surfaces on copper substrates with reduced secondary electron emission. In process, molybdenum ring target positioned above and around copper substrate. Target potential repeatedly switched on and off. Switching module described in "High-Voltage MOSFET Switching Circuit" (LEW-15986). Useful for making collector electrodes for traveling-wave-tube and klystron microwave amplifiers, in which secondary emission of electrons undesirable because of reducing efficiency.

  4. Positional control of plasmonic fields and electron emission

    SciTech Connect

    Word, R. C.; Fitzgerald, J. P. S.; Könenkamp, R.

    2014-09-15

    We report the positional control of plasmonic fields and electron emission in a continuous gap antenna structure of sub-micron size. We show experimentally that a nanoscale area of plasmon-enhanced electron emission can be motioned by changing the polarization of an exciting optical beam of 800 nm wavelength. Finite-difference calculations are presented to support the experiments and to show that the plasmon-enhanced electric field distribution of the antenna can be motioned precisely and predictively.

  5. Effects of methane on giant planet’s UV emissions and implications for the auroral characteristics

    NASA Astrophysics Data System (ADS)

    Gustin, J.; Gérard, J.-C.; Grodent, D.; Gladstone, G. R.; Clarke, J. T.; Pryor, W. R.; Dols, V.; Bonfond, B.; Radioti, A.; Lamy, L.; Ajello, J. M.

    2013-09-01

    This study reviews methods used to determine important characteristics of giant planet’s UV aurora (brightness, energy of the precipitating particles, altitude of the emission peak,…), based on the absorbing properties of methane and other hydrocarbons. Ultraviolet aurorae on giant planets are mostly caused by inelastic collisions between energetic magnetospheric electrons and the ambient atmospheric H2 molecules. The auroral emission is situated close to a hydrocarbon layer and may be attenuated by methane (CH4), ethane (C2H6) and acetylene (C2H2) at selected wavelengths. As methane is the most abundant hydrocarbon, it is the main UV absorber and attenuates the auroral emission shorward of 1350 Å. The level of absorption is used to situate the altitude/pressure level of the aurora, hence the energy of the precipitated electrons, whose penetration depth is directly related to their mean energy. Several techniques are used to determine these characteristics, from the color ratio method which measures the level of absorption from the ratio between an absorbed and an unabsorbed portion of the observed auroral spectrum, to more realistic methods which combine theoretical distributions of the precipitating electrons with altitude dependent atmospheric models. The latter models are coupled with synthetic or laboratory H2 spectra and the simulated emergent spectra are compared to observations to determine the best auroral characteristics. Although auroral characteristics may be very variable with time and locations, several typical properties may be highlighted from these methods: the Jovian aurora is the most powerful, with brightness around 120 kR produced by electrons of mean energy ∼100 keV and an emission situated near the 1 μbar level (∼250 km above the 1 bar level) while Saturn’s aurora is fainter (∼10 kR), produced by electrons less than 20 keV and situated near the 0.2 μbar level (∼1100 km).

  6. Photonically excited electron emission from modified graphitic nanopetal arrays

    SciTech Connect

    McCarthy, Patrick T.; Fisher, Timothy S.; School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907 ; Vander Laan, Scott J.; Janes, David B.; School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907

    2013-05-21

    Efficient electron emission for energy conversion requires a low work function and a stable emitter material. The work function of graphene-based carbon materials can decrease significantly by intercalation with alkali metals, thus increasing their emission current. In this work, electron emission from potassium-intercalated carbon nanosheet extensions grown on electrode graphite is investigated. These petal-like structures, composed of 5-25 layers of graphene, are synthesized using microwave plasma chemical vapor deposition. Samples are intercalated with potassium, and a hemispherical energy analyzer is used to measure the emission intensity caused by both thermal and photonic excitation. The emission from the potassium-intercalated structures is found to consistently decrease the work function by 2.4 to 2.8 eV relative to non-intercalated samples. High emission intensity induced by photonic excitation from a solar simulator, with a narrow electron energy distribution relative to established theory, suggests that electron scattering decreases emitted electron energy as compared to surface photoemission. A modified photoemission theory is applied to account for electron scattering, and the sample work function and mean number of scattering events are used as parameters to fit theory to experimental data. The thermal stability of the intercalated nanopetals is investigated, and after an initial heating and cooling cycle, the samples are stable at low temperatures.

  7. Electrically induced spontaneous emission in open electronic system

    NASA Astrophysics Data System (ADS)

    Wang, Rulin; Zhang, Yu; Yam, Chiyung; Computation Algorithms Division (CSRC) Team; Theoretical; Computational Chemistry (HKU) Collaboration

    A quantum mechanical approach is formulated for simulation of electroluminescence process in open electronic system. Based on nonequilibrium Green's function quantum transport equations and combining with photon-electron interaction, this method is used to describe electrically induced spontaneous emission caused by electron-hole recombination. The accuracy and reliability of simulation depends critically on correct description of the electronic band structure and the electron occupancy in the system. In this work, instead of considering electron-hole recombination in discrete states in the previous work, we take continuous states into account to simulate the spontaneous emission in open electronic system, and discover that the polarization of emitted photon is closely related to its propagation direction. Numerical studies have been performed to silicon nanowire-based P-N junction with different bias voltage.

  8. Evidence for Chirped Auger-Electron Emission

    NASA Astrophysics Data System (ADS)

    Schütte, B.; Bauch, S.; Frühling, U.; Wieland, M.; Gensch, M.; Plönjes, E.; Gaumnitz, T.; Azima, A.; Bonitz, M.; Drescher, M.

    2012-06-01

    Auger decay carries valuable information about the electronic structure and dynamics of atoms, molecules, and solids. Here we furnish evidence that under certain conditions Auger electrons are subject to an energetic chirp. The effect is disclosed in time-resolved streaking experiments on the Xe NOO and Kr MNN Auger decay using extreme-ultraviolet pulses from the free-electron laser in Hamburg as well as from a high-order harmonic laser source. The origin of this effect is found to be an exchange of energy between the Auger electron and an earlier emitted correlated photoelectron. The observed time-dependent spectral modulations are understood within an analytical model and confirmed by extensive computer simulations.

  9. Modeling electron emission and surface effects from diamond cathodes

    SciTech Connect

    Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.

    2015-02-05

    We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. In this study, using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.

  10. Modeling electron emission and surface effects from diamond cathodes

    SciTech Connect

    Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.

    2015-02-07

    We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass, and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. Using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.

  11. Modeling electron emission and surface effects from diamond cathodes

    DOE PAGESBeta

    Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.

    2015-02-05

    We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transversemore » electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. In this study, using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.« less

  12. Analysis of electron emission from GaAs(Cs,O) by low energy electron microscopy

    NASA Astrophysics Data System (ADS)

    Jin, Xiuguang

    2015-10-01

    Low-energy electron microscopy was carried out to study the electron emission process from a GaAs photocathode with a negative electron affinity (NEA) surface. The relationship between emission current and electron affinity was investigated in detail to obtain information regarding the electron tunneling in the vacuum barrier and the electron distribution in the interior of GaAs, especially with respect to photoelectron capture in the band bending region. A comparison of the calculated quantized sub-band energies in the band bending region confirmed that the majority of photoelectrons fell within sub-bands, from where a large portion of the photoelectrons escape into the vacuum.

  13. Programmable smart electron emission controller for hot filament

    NASA Astrophysics Data System (ADS)

    Flaxer, Eli

    2011-02-01

    In electron ionization source, electrons are produced through thermionic emission by heating a wire filament, accelerating the electrons by high voltage, and ionizing the analyzed molecules. In such a system, one important parameter is the filament emission current that determines the ionization rate; therefore, one needs to regulate this current. On the one hand, fast responses control is needed to keep the emission current constant, but on the other hand, we need to protect the filament from damage that occurs by large filaments current transients and overheating. To control our filament current and emission current, we developed a digital circuit based on a digital signal processing controller that has several modes of operation. We used a smart algorithm that has a fast response to a small signal and a slow response to a large signal. In addition, we have several protective measures that prevent the current from reaching unsafe values.

  14. Measurement Of Gas Electron Multiplier (GEM) Detector Characteristics

    SciTech Connect

    Park, Seongtae; Baldelomar, Edwin; Sosebee, Mark; White, Andy; Yu, Jaehoon; Park, Kwangjune

    2011-06-01

    The High Energy Physics group of the University of Texas at Arlington has been developing gas electron multiplier detectors to use them as sensitive gap detectors in digital hadron calorimeters for the International Linear Collider, a future high energy particle accelerator. For this purpose, we constructed numerous GEM detectors that employ double GEM layers. In this study, two kinds of prototype GEM detectors were tested; one with 28x28 cm{sup 2} active area double GEM structure with a 3 mm drift gap, a 1 mm transfer gap and a 1 mm induction gap and the other with two 3x3 cm{sup 2} GEM foils in the amplifier stage with a 5 mm drift gap, a 2 mm transfer gap and a 1 mm induction gap. The detectors' characteristics from exposure to high-energy charged particles and other radiations were measured using cosmic rays and {sup 55}Fe radioactive source. From the {sup 55}Fe tests, we observed two well separated characteristic X-ray emission peaks and confirmed the detectors' functionality. We also measured chamber gains to be over 6000 at a high voltage of 395 V across each GEM electrode. The responses to cosmic rays show the spectra that fit well to Landau distributions as expected from minimum ionizing particles.

  15. Measurement Of Gas Electron Multiplier (GEM) Detector Characteristics

    NASA Astrophysics Data System (ADS)

    Park, Seongtae; Baldelomar, Edwin; Park, Kwangjune; Sosebee, Mark; White, Andy; Yu, Jaehoon

    2011-06-01

    The High Energy Physics group of the University of Texas at Arlington has been developing gas electron multiplier detectors to use them as sensitive gap detectors in digital hadron calorimeters for the International Linear Collider, a future high energy particle accelerator. For this purpose, we constructed numerous GEM detectors that employ double GEM layers. In this study, two kinds of prototype GEM detectors were tested; one with 28×28 cm2 active area double GEM structure with a 3 mm drift gap, a 1 mm transfer gap and a 1 mm induction gap and the other with two 3×3 cm2 GEM foils in the amplifier stage with a 5 mm drift gap, a 2 mm transfer gap and a 1 mm induction gap. The detectors' characteristics from exposure to high-energy charged particles and other radiations were measured using cosmic rays and 55Fe radioactive source. From the 55Fe tests, we observed two well separated characteristic X-ray emission peaks and confirmed the detectors' functionality. We also measured chamber gains to be over 6000 at a high voltage of 395 V across each GEM electrode. The responses to cosmic rays show the spectra that fit well to Landau distributions as expected from minimum ionizing particles.

  16. 100 eV electron temperatures in the Maryland centrifugal experiment observed using electron Bernstein emission

    SciTech Connect

    Reid, R. R.; Romero-Talamás, C. A.; Young, W. C.; Ellis, R. F.; Hassam, A. B.

    2014-06-15

    Thermal electron Bernstein emission has been observed at the second harmonic of the electron cyclotron frequency at the mid-plane of the Maryland Centrifugal eXperiment. The emission is received in the X-mode polarization and coupled to the Bernstein wave by the B-X mode conversion process. The average B-X coupling efficiency is approximately 20%. The observed emission indicates thermal electron temperatures an excess of 100 eV in the core of the rotating plasma. The measured electron temperature is consistent with recent ion temperature measurements and indicates that the total energy confinement time exceeds 500 μs.

  17. Electron emission and electronic stopping in the interaction of slow helium ions with aluminum

    NASA Astrophysics Data System (ADS)

    Riccardi, P.; Baragiola, R. A.; Dukes, C. A.

    2015-07-01

    We address the question of the nonlinearity of the electronic stopping power of slow helium ions in aluminum by measuring the energy distributions and yields of electron emission under the impact of 0.2 -4.5 keV 3He+ and 4He+ ions. Electron emission experiments can provide an alternative point of view to resolve controversial issues often arising in stopping power measurements. The comparison between two isotopes allows one to distinguish between the energy and velocity dependent emission mechanisms, and indicates that the reported nonlinear velocity dependence of the electronic stopping power can be attributed to residual nuclear stopping effects.

  18. Kinetic simulation of secondary electron emission effects in Hall thrusters

    SciTech Connect

    Sydorenko, D.; Smolyakov, A.; Kaganovich, I.; Raitses, Y.

    2006-01-15

    The particle-in-cell code has been developed for kinetic simulations of Hall thrusters with a focus on plasma-wall interaction. It is shown that the effect of secondary electron emission on wall losses is different from predictions of previous fluid and kinetic studies. In simulations, the electron velocity distribution function is strongly anisotropic, depleted at high energy, and nonmonotonic. Secondary electrons form two beams propagating between the walls of a thruster channel in opposite radial directions. The beams produce secondary electron emission themselves depending on their energy at the moment of impact with the wall, which is defined by the electric and magnetic fields in the thruster as well as by the electron transit time between the walls. The condition for the space-charge-limited secondary electron emission depends not only on the energy of bulk plasma electrons but also on the energy of beam electrons. The contribution of the beams to the particles and energy wall losses may be much larger than that of the plasma bulk electrons. Recent experimental studies may indirectly support the results of these simulations, in particular, with respect to the electron temperature saturation and the channel width effect on the thruster discharge.

  19. Very Stable Electron Field Emission From Strontium Titanate Coated Carbon Nanotube Matrices With Low Emission Thresholds

    SciTech Connect

    Pandey, Archana; Prasad, Abhishek; Moscatello, Jason; Engelhard, Mark H.; Wang, Chong M.; Yap, Yoke K.

    2013-01-22

    PMMA-STO-CNT matrices were created by opened-tip vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs) with conformal coating of strontium titanate and Poly(methyl methacrylate). Emission threshold of 0.8 V/μm was demonstrated, about five-fold lower than that of the as-grown VAMWCNTs. Theoretical simulation and modeling suggest that PMMA-STO-CNT matrices have suppressed screening effects and Coulombs’ repulsion forces between electrons in adjacent CNTs, leading to low emission threshold, high emission density, and prolong emission stability. These findings are important for practical application of VA-MWCNTs in field emission devices.

  20. LUNAR DUST GRAIN CHARGING BY ELECTRON IMPACT: COMPLEX ROLE OF SECONDARY ELECTRON EMISSIONS IN SPACE ENVIRONMENTS

    SciTech Connect

    Abbas, M. M.; Craven, P. D.; LeClair, A. C.; Spann, J. F.; Tankosic, D.

    2010-08-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEEs). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 {mu}m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEEs discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

  1. Lunary Dust Grain Charging by Electron Impact: Complex Role of Secondary Electron Emissions in Space Environments

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Tankosic, D.; Crave, P. D.; LeClair, A.; Spann, J. F.

    2010-01-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEES). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/ planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEES discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

  2. Lunar Dust Grain Charging by Electron Impact: Complex Role of Secondary Electron Emissions in Space Environments

    NASA Astrophysics Data System (ADS)

    Abbas, M. M.; Tankosic, D.; Craven, P. D.; LeClair, A. C.; Spann, J. F.

    2010-08-01

    Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEEs). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 μm size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEEs discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

  3. Surface Roughness Effect on Secondary Electron Emission from Beryllium under Electron Bombardment

    NASA Astrophysics Data System (ADS)

    Kawata, Jun; Ohya, Kaoru

    1994-02-01

    A direct Monte Carlo model is developed to simulate secondary electron emission from beryllium with a flat surface and Gaussian-ripple surfaces. The calculated electron yield and energy distribution of secondary electrons are in reasonable agreement with the experimental data. The emphasis is in this study put on the effect of surface roughness on secondary electron emission. The number of secondary electrons emitted largely depends on the position of bombardment of primary electrons on the ripple surface. The energy distribution of secondary electrons emitted from the ripple surface shifts towards low-energy side in comparison with the distribution for the flat surface. The over-cosine and gourd-shaped angular distributions, depending on the position of bombardment, are calculated for emission angle of electrons from the ripple surface; the distribution for the flat surface agrees quite well with the cosine distribution.

  4. Origin of electron spectra and its characteristics

    NASA Astrophysics Data System (ADS)

    Mineev, Yu. V.

    This work presents the data on differential energy spectra of cosmic electrons with energies 0.1-6.0 MeV from the Pioneer-8-11, Prognoz-4-10, IMP-6,7,8, and Intercosmos-19 (polar cap measurements) spacecraft during 1975-1998. Some different sources of energetic electron are discussed. Analysis of the spectra permits a conclusion about a preferential contribution of galactic, solar and Jupiterian sources, depending on energies and on time of measurements. The dependencies of the sign and values of north-south asymmetry on the sector structure of the interplanetary magnetic field are obtained. The asymmetry sign and the size of cosmic electron fluxes for the above energies are compared with the earlier data in the high and low electron energy ranges for solar cycles 21-22.

  5. Electron emission from conduction band of heavily phosphorus doped diamond negative electron affinity surface

    NASA Astrophysics Data System (ADS)

    Yamada, Takatoshi; Masuzawa, Tomoaki; Mimura, Hidenori; Okano, Ken

    2016-02-01

    Hydrogen (H)-terminated surfaces of diamond have attracted significant attention due to their negative electron affinity (NEA), suggesting high-efficiency electron emitters. Combined with n-type doping technique using phosphorus (P) as donors, the unique NEA surface makes diamond a promising candidate for vacuum cold-cathode applications. However, high-electric fields are needed for the electron emission from the n-type doped diamond with NEA. Here we have clarified the electron emission mechanism of field emission from P-doped diamond having NEA utilizing combined ultraviolet photoelectron spectroscopy/field emission spectroscopy (UPS/FES). An UP spectrum has confirmed the NEA of H-terminated (1 1 1) surface of P-doped diamond. Despite the NEA, electron emission occurs only when electric field at the surface exceeds 4.2  ×  106 V cm-1. Further analysis by UPS/FES has revealed that the emitted energy level is shifted, indicating that the electron emission mechanism of n-type diamond having NEA surface does not follow a standard field emission theory, but is dominated by potential barrier formed within the diamond due to upward band bending. The reduction of internal barrier is the key to achieve high-efficiency electron emitters using P-doped diamond with NEA, of which application ranges from high-resolution electron spectroscopy to novel vacuum nanoelectronics devices.

  6. Comprehensive, nonintercepting electron-beam diagnostics using spontaneous emission

    SciTech Connect

    Lumpkin, A.H.

    1989-01-01

    Characterization and optimization of electron-beam parameters are important aspects of optimizing free-electron laser (FEL) performance. The visible spontaneous emission ({lambda}{approximately}650 nm) from the 5-meter long undulator of the Boeing FEL experiment can be characterized in sufficient detail with a streak/spectrometer to deduce time-resolved electron-beam spatial position and profile, micropulse duration, and energy. 7 refs., 13 figs., 2 tabs.

  7. Modeling of high-current devices with explosive electron emission

    NASA Astrophysics Data System (ADS)

    Anishchenko, S. V.; Gurinovich, A. A.

    2014-01-01

    Based on a detailed analysis of explosive electron emission in high-current electronic devices, we formulate a system of equations that describes the expansion of cathode plasma and the generation of high-current electron beams. The system underlies the numerical algorithm for the hybrid code which enables the simulation of the charged particles’ dynamics in high-current vircators with open resonators. Using the Gabor-Morlet transform, we perform a time-frequency analysis of vircator radiation.

  8. Controlled electron emission and vacuum breakdown with nanosecond pulses

    NASA Astrophysics Data System (ADS)

    Seznec, B.; Dessante, Ph; Caillault, L.; Babigeon, J.-L.; Teste, Ph; Minea, T.

    2016-06-01

    Vacuum electron sources exploiting field emission are generally operated in direct current (DC) mode. The development of nanosecond and sub-nanosecond pulsed power supplies facilitates the emission of compact bunches of electrons of high density. The breakdown level is taken as the highest value of the voltage avoiding the thermo-emission instability. The effect of such ultra-fast pulses on the breakdown voltage and the emitted electron current is discussed as a result of the thermo-emission modelling applied to a significant protrusion. It is found that pulsing very rapidly the vacuum breakdown occurs at higher voltage values than for the DC case, because it rises faster than the heat diffusion. In addition, the electron emission current increases significantly regardless of the theoretical approach is used. A comparative study of this theoretical work is discussed for several different forms of the protrusion (elliptic and hyperbolic) and different metals (hence varying the melting point), particularly refractory (tungsten) versus conductor (titanium). Pulsed mode operation can provide an increase on breakdown voltage (up to 18%) and a significant increase (up to 330%) of the electron extracted current due to its high non-linear dependency with the voltage, for the case for the case with a hyperbolic protrusion.

  9. Surface-electronic-state effects in electron emission from the Be(0001) surface

    SciTech Connect

    Archubi, C. D.; Gravielle, M. S.; Silkin, V. M.

    2011-07-15

    We study the electron emission produced by swift protons impinging grazingly on a Be(0001) surface. The process is described within a collisional formalism using the band-structure-based (BSB) approximation to represent the electron-surface interaction. The BSB model provides an accurate description of the electronic band structure of the solid and the surface-induced potential. Within this approach we derive both bulk and surface electronic states, with these latter characterized by a strong localization at the crystal surface. We found that such surface electronic states play an important role in double-differential energy- and angle-resolved electron emission probabilities, producing noticeable structures in the electron emission spectra.

  10. Discharge and photo-luminance properties of a parallel plates electron emission lighting device.

    PubMed

    Li, Chia-Hung; Liu, Ming-Chung; Chiang, Chang-Lin; Li, Jung-Yu; Chen, Shih-Pu; Hsieh, Tai-Chiung; Chou, Yen-I; Lin, Yi-Ping; Wang, Po-Hung; Chun, Ming-Shin; Zeng, Hui-Kai; Juang, Jenh-Yih

    2011-01-01

    The gas discharge and photo-luminance properties of a planar lighting source featuring highly uniform light emission and mercury-free design were studied. The current density-voltage characteristics and the associated gas discharge of the devices operating with the values of the ratio of electric field to gas pressure (E/p) between 4.3 kV/Torr-cm and 35.7 kV/Torr-cm indicate that the width of the cathode fall extends over the entire gap between the two electrodes and the device is mostly in the obstructed discharge regime. The optical emission analysis confirmed the electron collision-induced gas emissions and strong effect of gas pressure on the phosphor emission when operated at constant current density, both are indicative of the primary roles played by the electron energy. PMID:21263712

  11. Plasma Emission by Counter-streaming Electron Beams

    NASA Astrophysics Data System (ADS)

    Ziebell, L. F.; Petruzzellis, L. T.; Yoon, P. H.; Gaelzer, R.; Pavan, J.

    2016-02-01

    The radiation emission mechanism responsible for both type-II and type-III solar radio bursts is commonly accepted as plasma emission. Recently Ganse et al. suggested that type-II radio bursts may be enhanced when the electron foreshock geometry of a coronal mass ejection contains a double hump structure. They reasoned that the counter-streaming electron beams that exist between the double shocks may enhance the nonlinear coalescence interaction, thereby giving rise to more efficient generation of radiation. Ganse et al. employed a particle-in-cell simulation to study such a scenario. The present paper revisits the same problem with EM weak turbulence theory, and show that the fundamental (F) emission is not greatly affected by the presence of counter-streaming beams, but the harmonic (H) emission becomes somewhat more effective when the two beams are present. The present finding is thus complementary to the work by Ganse et al.

  12. Molybdenum work function determined by electron emission microscopy.

    NASA Technical Reports Server (NTRS)

    Jacobson, D. L.; Campbell, A. E.

    1971-01-01

    A polycrystalline molybdenum sample was recrystallized and thermally stabilized. Quantitative measurements of the emission from each individual grain were obtained with an electron emission microscope. The effective work function for each grain was then calculated. The crystallographic orientation of each grain was determined by Laue back-reflection techniques. A polar plot of effective work function vs crystallographic orientation for the sample was constructed to provide a correlation between effective work function and crystallographic orientation.

  13. [Emission characteristics of fine particles from grate firing boilers].

    PubMed

    Wang, Shu-Xiao; Zhao, Xiu-Juan; Li, Xing-Hua; Wei, Wei; Hao, Ji-Ming

    2009-04-15

    Grate firing boilers are the main type of Chinese industrial boilers, which accounts for 85% of the industrial boilers and is one of the most important emission sources of primary air pollutants in China. In this study, five boilers in three cities were selected and tested to measure the emission characteristics of PM2.5, and gaseous pollutants were applied by a compact dilution sampling system, which was developed for this field study. Results showed that particles mass size distributions for the five industrial boilers presented single peak or double peak, former peaks near 0.14 microm and the later peaks after 1.0 microm; the cyclone dust remover and wet scrubber dust remover had effective removal efficiencies not only to PM2.5, but also to PM1.0; and under the condition of same control techniques, grate firing boiler with high capacity has less PM2.5 emission than the boiler with low capacity. In the PM2.5 collected from flue gases, SO4(2-) was the most abundant ion, accounted for 20%-40% of the PM2.5; and C was the most abundant element (7.5%-31.8%), followed by S (8.4%-18.7%). Carbon balance method was applied to calculate the emission factors of these pollutants. The emission factors of PM2.5, NO, and SO2 were in the range of 0.046-0.486 g x kg(-1), 1.63-2.47 g x kg(-1), 1.35-9.95 g x kg(-1) respectively. The results are useful for the emission inventory development of industrial boilers and the source analysis of PM2.5 in atmospheric environment. PMID:19544990

  14. Space charge and quantum effects on electron emission

    NASA Astrophysics Data System (ADS)

    Jensen, Kevin L.; Lebowitz, Joel; Lau, Y. Y.; Luginsland, John

    2012-03-01

    Space charge effects reduce electron emission by altering the surface barrier via two effects: increasing the barrier height (Schottky factor) and width to electron emission by lowering the surface field and changing the magnitude of the dipole associated with electron density variation. A one-dimensional emission model using a transit time argument to account for charge in the anode-cathode (AK) gap and an analytical model of the dipole is used to approximate the effects of each factor on the current density. The transit time model is compared to the experimental data of Longo [J. Appl. Phys. 94, 6966 (2003)] for thermal emission. Changes in the dipole contribution are primarily associated with tunneling and therefore field emission. The transit time plus dipole modification is compared to the experimental data of Barbour et al. [Phys. Rev. 92, 45 (1953)] for field emission. The model's application to thermal-field, and photoemission in general is discussed, with the former corresponding to continuous current limit and the latter to a pulsed current limit of the model.

  15. Electron impact induced light emission from zinc atoms

    NASA Astrophysics Data System (ADS)

    Cvejanovic, Danica

    2009-10-01

    Experimental studies of electron impact excitation of zinc atom are rare, primarily due to experimental difficulties. However, zinc is an interesting target because of possible applications in light sources. Also, due to its position in periodic table, zinc is an interesting case for the fundamental understanding of momentum couplings and the role of electron correlations in complex metal atoms. Recent experimental investigations have indicated the existence of highly correlated scattering mechanisms via formation of negative ion resonances and Post Collision Interaction (PCI) in the decay of autoionizing states. These can significantly modify energy dependence of the emission cross sections at low impact energies and the studies of photon emission offer a sensitive way to investigate electron correlations. Specifically, in the lowest autoionizing region of zinc, i.e. between 10 and 15 eV, both the cross sections and polarization of emitted light are affected by the formation of short lived negative ions and PCI effects. These are associated with excitation of one of the sub-valence 3d electrons and complex correlations between inner 3d and outer excited electrons in the target and also with the slow electron released into continuum, need to be included in modeling. Also the scattering of the spin polarized electrons has shown significant spin effects when excitation proceeds via negative ion resonances. Emission cross sections and comparison with theory would be discussed at the conference.

  16. Carbon-containing cathodes for enhanced electron emission

    DOEpatents

    Cao, Renyu; Pan, Lawrence; Vergara, German; Fox, Ciaran

    2000-01-01

    A cathode has electropositive atoms directly bonded to a carbon-containing substrate. Preferably, the substrate comprises diamond or diamond-like (sp.sup.3) carbon, and the electropositive atoms are Cs. The cathode displays superior efficiency and durability. In one embodiment, the cathode has a negative electron affinity (NEA). The cathode can be used for field emission, thermionic emission, or photoemission. Upon exposure to air or oxygen, the cathode performance can be restored by annealing or other methods. Applications include detectors, electron multipliers, sensors, imaging systems, and displays, particularly flat panel displays.

  17. Secondary Electron Emission from Dust and Its Effect on Charging

    SciTech Connect

    Saikia, B. K.; Kakati, B.; Kausik, S. S.; Bandyopadhyay, M.

    2011-11-29

    Hydrogen plasma is produced in a plasma chamber by striking discharge between incandescent tungsten filaments and the permanent magnetic cage [1], which is grounded. The magnetic cage has a full line cusped magnetic field geometry used to confine the plasma elements. A cylindrical Langmuir probe is used to study the plasma parameters in various discharge conditions. The charge accumulated on the dust particles is calculated using the capacitance model and the dust current is measured by the combination of a Faraday cup and an electrometer at different discharge conditions. It is found Secondary electron emission from dust having low emission yield effects the charging of dust particles in presence of high energetic electrons.

  18. Detecting and locating electronic devices using their unintended electromagnetic emissions

    NASA Astrophysics Data System (ADS)

    Stagner, Colin Blake

    Electronically-initiated explosives can have unintended electromagnetic emissions which propagate through walls and sealed containers. These emissions, if properly characterized, enable the prompt and accurate detection of explosive threats. The following dissertation develops and evaluates techniques for detecting and locating common electronic initiators. The unintended emissions of radio receivers and microcontrollers are analyzed. These emissions are low-power radio signals that result from the device's normal operation. In the first section, it is demonstrated that arbitrary signals can be injected into a radio receiver's unintended emissions using a relatively weak stimulation signal. This effect is called stimulated emissions. The performance of stimulated emissions is compared to passive detection techniques. The novel technique offers a 5 to 10 dB sensitivity improvement over passive methods for detecting radio receivers. The second section develops a radar-like technique for accurately locating radio receivers. The radar utilizes the stimulated emissions technique with wideband signals. A radar-like system is designed and implemented in hardware. Its accuracy tested in a noisy, multipath-rich, indoor environment. The proposed radar can locate superheterodyne radio receivers with a root mean square position error less than 5 meters when the SNR is 15 dB or above. In the third section, an analytic model is developed for the unintended emissions of microcontrollers. It is demonstrated that these emissions consist of a periodic train of impulses. Measurements of an 8051 microcontroller validate this model. The model is used to evaluate the noise performance of several existing algorithms. Results indicate that the pitch estimation techniques have a 4 dB sensitivity improvement over epoch folding algorithms.

  19. Field Emission Characteristics of Carbon Nanotubes and Their Applications in Sensors and Devices

    NASA Astrophysics Data System (ADS)

    Vaseashta, Ashok

    2003-03-01

    FIELD EMISSION CHARACTERISTICS OF CARBON NANOTUBES AND THEIR APPLICATIONS IN SENSORS AND DEVICES A. Vaseashta, C. Shaffer, M. Collins, A. Mwuara Dept of Physics, Marshall University, Huntington, WV V. Pokropivny Institute for Materials Sciences of NASU, Kiev, Ukraine. D. Dimova-Malinovska Bulgarian Academy of Sciences, Sofia, Bulgaria. The dimensionality of a system has profound influence on its physical behavior. With advances in technology over the past few decades, it has become possible to fabricate and study reduced-dimensional systems, such as carbon nanotubes (CNTs). Carbon nanotubes are especially promising candidate for cold cathode field emitter because of their electrical properties, high aspect ratio, and small radius of curvature at the tips. Electron emission from the carbon nanotubes was investigated. Based upon the field emission investigation of carbon nanotubes, several prototype devices have been suggested that operate with low swing voltages with sufficient high current densities. Characteristics that allow improved current stability and long lifetime operation for electrical and opto-electronics devices are presented. The aim of this brief overview is to illustrate the useful characteristics of carbon nanotubes and its possible application.

  20. Effects of enhanced cathode electron emission on Hall thruster operation

    SciTech Connect

    Raitses, Y.; Smirnov, A.; Fisch, N. J.

    2009-05-15

    Interesting discharge phenomena are observed that have to do with the interaction between the magnetized Hall thruster plasma and the neutralizing cathode. The steady-state parameters of a highly ionized thruster discharge are strongly influenced by the electron supply from the cathode. The enhancement of the cathode electron emission above its self-sustained level affects the discharge current and leads to a dramatic reduction in the plasma divergence and a suppression of large amplitude, low frequency discharge current oscillations usually related to an ionization instability. These effects correlate strongly with the reduction in the voltage drop in the region with the fringing magnetic field between the thruster channel and the cathode. The measured changes in the plasma properties suggest that the electron emission affects the electron cross-field transport in the thruster discharge. These trends are generalized for Hall thrusters of various configurations.

  1. Effects of Enhanced Eathode Electron Emission on Hall Thruster Operation

    SciTech Connect

    Y. Raitses, A. Smirnov and N. J. Fisch

    2009-04-24

    Interesting discharge phenomena are observed that have to do with the interaction between the magnetized Hall thruster plasma and the neutralizing cathode. The steadystate parameters of a highly ionized thruster discharge are strongly influenced by the electron supply from the cathode. The enhancement of the cathode electron emission above its self-sustained level affects the discharge current and leads to a dramatic reduction of the plasma divergence and a suppression of large amplitude, low frequency discharge current oscillations usually related to an ionization instability. These effects correlate strongly with the reduction of the voltage drop in the region with the fringing magnetic field between the thruster channel and the cathode. The measured changes of the plasma properties suggest that the electron emission affects the electron cross-field transport in the thruster discharge. These trends are generalized for Hall thrusters of various configurations.

  2. Secondary electron emission from surfaces with small structure

    NASA Astrophysics Data System (ADS)

    Dzhanoev, A. R.; Spahn, F.; Yaroshenko, V.; Lühr, H.; Schmidt, J.

    2015-09-01

    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.

  3. Microwave plasma CVD-grown graphene-CNT hybrids for enhanced electron field emission applications

    NASA Astrophysics Data System (ADS)

    Kaushik, Vishakha; Shukla, A. K.; Vankar, V. D.

    2014-12-01

    The growth and electron emission characteristics were investigated from a hybrid structure of multiwalled carbon nanotubes (MWCNTs) and multilayer layer graphene (MLG) deposited on silicon substrate coated with iron catalyst and an interlayer of aluminium. The hybrid structures were synthesized in a two-step process by microwave plasma-enhanced chemical vapour deposition technique. The formation of MWCNTs takes place by absorption and precipitation of carbon radicals into the catalyst particles. Thereafter, ample carbon forms MLG on tip of the MWCNTs resulting in a MLG-MWCNTs hybrid nanostructure. MLG was observed to grow branching out of the tips and sidewalls of the MWCNTs and is expected to attach by Van der Walls bonds. Transmission electron microscopy and micro-Raman spectroscopy confirmed the crystalline nature of the hybrid structures. Electron emission studies were carried out using a diode-type field emission setup. The enhancement factor was found to be ~3,500 for bare MWCNTs, ~4,070 to ~5,000 for hybrid structures and ~6,500 for N-doped MLG-MWCNTs hybrid structures. Modification in the defects structure and enhancement of emission sites are suggested to be responsible for the increase of the field emission characteristics.

  4. Peculiarities of the Field Electron Emission from Dust Grains

    SciTech Connect

    Richterova, I.; Beranek, M.; Pavlu, J.; Nemecek, Z.; Safrankova, J.

    2008-09-07

    The goal of the paper is investigation of the electron field emission that limits the attainable grain charge and can prevent electrostatic fragmentation of loosely bounded aggregates of dust grains. We have found that the effective work function of the spherical amorphous carbon grains does not depend on the relative beam energy. Preliminary results on an influence of the ion treatment/cleaning using the simultaneous electron and ion bombardments are discussed.

  5. Heterointegrated near-field photodetector for ballistic electron emission luminescence

    NASA Astrophysics Data System (ADS)

    Huang, Biqin; Appelbaum, Ian

    2009-04-01

    We use room-temperature ultrahigh-vacuum metal-film wafer bonding to integrate a Si photodetector with a AlGaAs/GaAs-based ballistic electron emission luminescence (BEEL) light emitting device. Our results, using a solid-state tunnel junction to simulate hot-electron injection with a scanning-tunneling probe, show that this design provides a means to achieve successful heterogeneous integration, potentially making BEEL applicable to arbitrary light-emitting semiconductor materials systems.

  6. Instrumentation and Measurements for Electron Emission from Charged Insulators

    NASA Technical Reports Server (NTRS)

    Sim, Alec M.

    2005-01-01

    The electron was first discovered in 1898 by Sir John Joseph Thomson and has since been the subject of detailed study by nearly every scientific discipline. At nearly the same time Heinrich Rudolf Hertz conducted a series of experiments using cathode tubes, high potentials and ultraviolet light. When applying a large potential to a cathode he found that an arching event across the metal plates would occur. In addition, when shining an ultraviolet light on the metal he found that less potential was required to induce the spark. This result, taken together with other electrical phenomena brought about by the shining of light upon metal and was eventually termed the photoelectric effect. The work of Thomson and Hertz represent the beginning of electron emission studies and a body of ideas that pervade nearly all aspects of physics. In particular these ideas tell us a great deal about the nature of physical interactions within solids. In this thesis we will focus on the emission of electrons induced by an incident electron source over a range of energies, in which one can observe changes in emitted electron flux and energy distribution. In particular, when energetic particles impinge on a solid they can impart their energy, exciting electrons within the material. If this energy is sufficient to overcome surface energy barriers such as the work function, electron affinity or surface charge potential, electrons can escape from the material. The extent of electron emission from the material can be quantified as the ratio of incident particle flux to emitted particle flux, and is termed the electron yield.

  7. Electron heating during discharges driven by thermionic emission

    SciTech Connect

    Levko, D.; Krasik, Ya. E.

    2014-11-15

    The heating of plasma electrons during discharges driven by thermionic emission is studied using one-dimensional particle-in-cell Monte Carlo collisions modeling that self-consistently takes the dependence of the thermionic current on the plasma parameters into account. It is found that at a gas pressure of 10{sup 2 }Pa the electron two-stream instability is excited. As a consequence, the electrostatic plasma wave propagates from the cathode to the anode. The trapping of electrons by this wave contributes noticeably to the heating of the plasma. At a larger gas pressure, this instability is not excited. As a consequence, plasma electrons are heated only because of the generation of energetic electrons in ionization events and the scattering of emitted electrons.

  8. Electron-bombarded ⟨110⟩-oriented tungsten tips for stable tunneling electron emission.

    PubMed

    Yamada, T K; Abe, T; Nazriq, N M K; Irisawa, T

    2016-03-01

    A clean tungsten (W) tip apex with a robust atomic plane is required for producing a stable tunneling electron emission under strong electric fields. Because a tip apex fabricated from a wire by aqueous chemical etching is covered by impurity layers, heating treatment in ultra-high vacuum is experimentally known to be necessary. However, strong heating frequently melts the tip apex and causes unstable electron emissions. We investigated quantitatively the tip apex and found a useful method to prepare a tip with stable tunneling electron emissions by controlling electron-bombardment heating power. Careful characterizations of the tip structures were performed with combinations of using field emission I-V curves, scanning electron microscopy, X-ray diffraction (transmitted Debye-Scherrer and Laue) with micro-parabola capillary, field ion microscopy, and field emission microscopy. Tips were chemically etched from (1) polycrystalline W wires (grain size ∼1000 nm) and (2) long-time heated W wires (grain size larger than 1 mm). Heating by 10-40 W (10 s) was found to be good enough to remove oxide layers and produced stable electron emission; however, around 60 W (10 s) heating was threshold power to increase the tip radius, typically +10 ± 5 nm (onset of melting). Further, the grain size of ∼1000 nm was necessary to obtain a conical shape tip apex. PMID:27036780

  9. Electron-bombarded <110>-oriented tungsten tips for stable tunneling electron emission

    NASA Astrophysics Data System (ADS)

    Yamada, T. K.; Abe, T.; Nazriq, N. M. K.; Irisawa, T.

    2016-03-01

    A clean tungsten (W) tip apex with a robust atomic plane is required for producing a stable tunneling electron emission under strong electric fields. Because a tip apex fabricated from a wire by aqueous chemical etching is covered by impurity layers, heating treatment in ultra-high vacuum is experimentally known to be necessary. However, strong heating frequently melts the tip apex and causes unstable electron emissions. We investigated quantitatively the tip apex and found a useful method to prepare a tip with stable tunneling electron emissions by controlling electron-bombardment heating power. Careful characterizations of the tip structures were performed with combinations of using field emission I-V curves, scanning electron microscopy, X-ray diffraction (transmitted Debye-Scherrer and Laue) with micro-parabola capillary, field ion microscopy, and field emission microscopy. Tips were chemically etched from (1) polycrystalline W wires (grain size ˜1000 nm) and (2) long-time heated W wires (grain size larger than 1 mm). Heating by 10-40 W (10 s) was found to be good enough to remove oxide layers and produced stable electron emission; however, around 60 W (10 s) heating was threshold power to increase the tip radius, typically +10 ± 5 nm (onset of melting). Further, the grain size of ˜1000 nm was necessary to obtain a conical shape tip apex.

  10. Source characteristics of Jovian narrow-band kilometric radio emissions

    NASA Astrophysics Data System (ADS)

    Reiner, M. J.; Fainberg, J.; Stone, R. G.; Kaiser, M. L.; Desch, M. D.; Manning, R.; Zarka, P.; Pedersen, B.-M.

    1993-07-01

    New observations of Jovian narrow-band kilometric (nKOM) radio emissions were made by the Unified Radio and Plasma Wave (URAP) experiment on the Ulysses spacecraft during the Ulysses-Jupiter encounter in early February 1992. These observations have demonstrated the unique capability of the URAP instrument for determining both the direction and polarization of nKOM radio sources. An important result is the discovery that nKOM radio emission originates from a number of distinct sources located at different Jovian longitudes and at the inner and outermost regions of the Io plasma torus. These sources have been tracked for several Jovian rotations, yielding their corotational lags, their spatial and temporal evolution, and their radiation characteristics at both low latitudes far from Jupiter and at high latitudes near the planet. Both right-hand and left-hand circularly polarized nKOM sources were observed. The polarizations observed for sources in the outermost regions of the torus seem to favor extraordinary mode emission.

  11. Flow and Emissions Characteristics of Multi-Swirler Combustor

    NASA Astrophysics Data System (ADS)

    Gutmark, Ephraim; Li, Guoqiang

    2003-11-01

    Modern industrial gas-turbine spray combustors feature multiple swirlers and distributed fuel injection for rapid mixing and stabilization. The flow field of this combustor, the related combustion characteristics and their control are discussed. The velocity flow field downstream of a Triple Annular Research Swirler (TARS) was characterized. Multiple combinations of swirlers were tested in cold flow under atmospheric conditions with and without confining combustion chamber. The experiments showed that a central recirculation zone (CTRZ), an annular jet with internal and external shear layers dominated the flow field downstream of TARS. Compared to unconfined case, flow with confined tube showed an enlarged CTRZ region and a recirculation region in the expansion corner with reduced concentration of turbulence intensity in the jet region. TARS also produced low emissions of NOx and CO. Measurements were performed to study the effects of several factors, including swirler combinations, exhaust nozzle size, air assist for fuel atomization and mixing length on NOx and CO emissions and combustion instability. The data showed that emissions and stability depend on the combination of several of these factors.

  12. Mode characteristics and directional emission for square microcavity lasers

    NASA Astrophysics Data System (ADS)

    Yang, Yue-De; Huang, Yong-Zhen

    2016-06-01

    Square microcavities with high quality factor whispering-gallery-like modes have a series of novel optical properties and can be employed as compact-size laser resonators. In this paper, the mode characteristics of square optical microcavities and the lasing properties of directional-emission square semiconductor microlasers are reviewed for the realization of potential light sources in the photonic integrated circuits and optical interconnects. A quasi-analytical model is introduced to describe the confined modes in square microcavities, and high quality factor whispering-gallery-like modes are predicted by the mode-coupling theory and confirmed by the numerical simulation. An output waveguide directly coupled to the position with weak mode field is used to achieve directional emission and control the lasing mode. Electrically-pumped InP-based directional-emission square microlasers are realized at room temperature, and the lasing spectra agree well with the mode analysis. Different kinds of square microcavity lasers, including dual-mode laser with a tunable interval, single-mode laser with a wide tunable wavelength range, and high-speed direct-modulated laser are also demonstrated experimentally.

  13. Electron beam generated whistler emissions in a laboratory plasma

    SciTech Connect

    Van Compernolle, B. Pribyl, P.; Gekelman, W.; An, X.; Bortnik, J.; Thorne, R. M.

    2015-12-10

    Naturally occurring whistler mode emissions in the magnetosphere, are important since they are responsible for the acceleration of outer radiation belt electrons to relativistic energies and also for the scattering loss of these electrons into the atmosphere. Recently, we reported on the first laboratory experiment where whistler waves exhibiting fast frequency chirping have been artificially produced [1]. A beam of energetic electrons is launched into a cold plasma and excites both chirping whistler waves and broadband waves. Here we extend our previous analysis by comparing the properties of the broadband waves with linear theory.

  14. Effect of secondary electron emission on the plasma sheath

    SciTech Connect

    Langendorf, S. Walker, M.

    2015-03-15

    In this experiment, plasma sheath potential profiles are measured over boron nitride walls in argon plasma and the effect of secondary electron emission is observed. Results are compared to a kinetic model. Plasmas are generated with a number density of 3 × 10{sup 12} m{sup −3} at a pressure of 10{sup −4} Torr-Ar, with a 1%–16% fraction of energetic primary electrons. The sheath potential profile at the surface of each sample is measured with emissive probes. The electron number densities and temperatures are measured in the bulk plasma with a planar Langmuir probe. The plasma is non-Maxwellian, with isotropic and directed energetic electron populations from 50 to 200 eV and hot and cold Maxwellian populations from 3.6 to 6.4 eV and 0.3 to 1.3 eV, respectively. Plasma Debye lengths range from 4 to 7 mm and the ion-neutral mean free path is 0.8 m. Sheath thicknesses range from 20 to 50 mm, with the smaller thickness occurring near the critical secondary electron emission yield of the wall material. Measured floating potentials are within 16% of model predictions. Measured sheath potential profiles agree with model predictions within 5 V (∼1 T{sub e}), and in four out of six cases deviate less than the measurement uncertainty of 1 V.

  15. Effect of secondary electron emission on the plasma sheath

    NASA Astrophysics Data System (ADS)

    Langendorf, S.; Walker, M.

    2015-03-01

    In this experiment, plasma sheath potential profiles are measured over boron nitride walls in argon plasma and the effect of secondary electron emission is observed. Results are compared to a kinetic model. Plasmas are generated with a number density of 3 × 1012 m-3 at a pressure of 10-4 Torr-Ar, with a 1%-16% fraction of energetic primary electrons. The sheath potential profile at the surface of each sample is measured with emissive probes. The electron number densities and temperatures are measured in the bulk plasma with a planar Langmuir probe. The plasma is non-Maxwellian, with isotropic and directed energetic electron populations from 50 to 200 eV and hot and cold Maxwellian populations from 3.6 to 6.4 eV and 0.3 to 1.3 eV, respectively. Plasma Debye lengths range from 4 to 7 mm and the ion-neutral mean free path is 0.8 m. Sheath thicknesses range from 20 to 50 mm, with the smaller thickness occurring near the critical secondary electron emission yield of the wall material. Measured floating potentials are within 16% of model predictions. Measured sheath potential profiles agree with model predictions within 5 V (˜1 Te), and in four out of six cases deviate less than the measurement uncertainty of 1 V.

  16. Sub-additivity in Electron Emission from GaAs

    NASA Astrophysics Data System (ADS)

    Brunkow, Evan; Clayburn, Nathan; Becker, Maria; Jones, Eric; Batelaan, Herman; Gay, Timothy

    2016-05-01

    When two spatially-overlapped laser pulses (775 nm center wavelength, 75 fs duration) are incident on an untreated <100> GaAs crystal surface, the electron emission rate depends on the temporal separation between the two pulses. We have shown that for delays between 0.2 and 1000ps, the emission rate is ``sub-additive'', i.e., is lower than when the beams have separation >> 1 ns. We believe the cause of this sub-additivity is an increase in reflectance and transmittance due to electrons occupying the excited state of the GaAs. We are now able to manipulate the magnitude of the sub-additivity by changing the number of electrons that are in the excited state. Sub-additivity is not observed with tungsten tip surfaces which have no excited state. Funded by NSF PHY-1505794, EPSCoR IIIA-1430519, and NSF 1306565 (HB).

  17. Chemical ionization mass spectrometry using carbon nanotube field emission electron sources.

    PubMed

    Radauscher, Erich J; Keil, Adam D; Wells, Mitch; Amsden, Jason J; Piascik, Jeffrey R; Parker, Charles B; Stoner, Brian R; Glass, Jeffrey T

    2015-11-01

    A novel chemical ionization (CI) source has been developed based on a carbon nanotube (CNT) field emission electron source. The CNT-based electron source was evaluated and compared with a standard filament thermionic electron source in a commercial explosives trace detection desktop mass spectrometer. This work demonstrates the first reported use of a CNT-based ion source capable of collecting CI mass spectra. Both positive and negative modes were investigated. Spectra were collected for a standard mass spectrometer calibration compound, perfluorotributylamine (PFTBA), as well as trace explosives including trinitrotoluene (TNT), Research Department explosive (RDX), and pentaerythritol tetranitrate (PETN). The electrical characteristics, lifetime at operating pressure, and power requirements of the CNT-based electron source are reported. The CNT field emission electron sources demonstrated an average lifetime of 320 h when operated in constant emission mode under elevated CI pressures. The ability of the CNT field emission source to cycle on and off can provide enhanced lifetime and reduced power consumption without sacrificing performance and detection capabilities. Graphical Abstract ᅟ. PMID:26133527

  18. Chemical Ionization Mass Spectrometry Using Carbon Nanotube Field Emission Electron Sources

    NASA Astrophysics Data System (ADS)

    Radauscher, Erich J.; Keil, Adam D.; Wells, Mitch; Amsden, Jason J.; Piascik, Jeffrey R.; Parker, Charles B.; Stoner, Brian R.; Glass, Jeffrey T.

    2015-11-01

    A novel chemical ionization (CI) source has been developed based on a carbon nanotube (CNT) field emission electron source. The CNT-based electron source was evaluated and compared with a standard filament thermionic electron source in a commercial explosives trace detection desktop mass spectrometer. This work demonstrates the first reported use of a CNT-based ion source capable of collecting CI mass spectra. Both positive and negative modes were investigated. Spectra were collected for a standard mass spectrometer calibration compound, perfluorotributylamine (PFTBA), as well as trace explosives including trinitrotoluene (TNT), Research Department explosive (RDX), and pentaerythritol tetranitrate (PETN). The electrical characteristics, lifetime at operating pressure, and power requirements of the CNT-based electron source are reported. The CNT field emission electron sources demonstrated an average lifetime of 320 h when operated in constant emission mode under elevated CI pressures. The ability of the CNT field emission source to cycle on and off can provide enhanced lifetime and reduced power consumption without sacrificing performance and detection capabilities.

  19. VLF-emissions from ring current electrons. An interpretation of the band of missing emissions

    NASA Technical Reports Server (NTRS)

    Maeda, K.; Smith, P. H.; Anderson, R. R.

    1976-01-01

    VLF-emissions associated with the enhancement of ring current electrons during magnetic storms and substorms which were detected by the equatorially orbiting S-A satellite (Explorer 45) are described. The emissions observed near the geomagnetic equator consist of essentially two frequency regimes, i.e., one above the electron gyrofrequency, f sub H at the equator and the other below f sub H. This is indicated as a part of the wide-band data obtained during the main phase of the December 17, 1971 magnetic storm. The upper figure is the ac-magnetic field data measured by the search-coil magnetometer with the upper cutoff of 3kHz and the lower figure is the ac-electric field data obtained by the electric field sensor with the upper cutoff of 10kHz. These figures show the time sequence of the observed emissions along the inbound orbit (No. 101) of the satellite as f sub H changes approximately from 3 kHz at 20 UT to 6 kHz at 21 UT. The emissions above f sub H are electrostatic mode, which peak near the frequencies of (n + 1/2) f sub H where n is positive integer, and sometimes emissions up to n = 10 are observed. The emissions below f sub H are whistler mode, which have a conspicuous gap along exactly half electron gyrofrequency, f sub H/2.

  20. Stimulated coherent emission from short electron bunches in free space

    SciTech Connect

    Robb, G.R.M.; Phelps, A.D.R.; Ginzburg, N.S.

    1995-12-31

    In previous papers stimulated coherent emission of short electron bunches (superradiance-SR) was considered in the frame of 1-D models. In the present work we study superradiance of an electron bunch which has a finite transverse size in the frame of a 2-D model. This model include effects of optical guiding as well as transverse electromagnetic energy escaping and diffraction. Using a nonstationary parabolic equation we described SR of a sheet shaped electron bunch in free space. It is shown that the radiation is composed of a sequence of e.m. pulses which are diffracted after escaping from the channel formed by the electron beam. This process is accompanied by a progressive increase of the electron efficiency. This enhancement is caused by the phenomenon of permanent self supporting resonance due to the variation of the radiation angle and frequency.

  1. Field emission of electrons from cathodes made of carbon fibers with a nanostructured emitting surface

    NASA Astrophysics Data System (ADS)

    Lupekhin, S. M.; Ibragimov, A. A.

    2011-06-01

    Field electron emission from cathodes made of a bunch of carbon fibers under the condition of technical vacuum is studied experimentally. A model to optimize the field emission properties of the cathode by optimizing its macrogeometry with regard to the emitting surface structure is suggested. The current-voltage characteristics of the cathode are taken in the working voltage range 1-3 kV and for anode-cathode spacings varying from 1 to 10 mm. The current density from the cathode may reach 10 A/cm2 or more.

  2. Modeling of explosive electron emission and electron beam dynamics in high-current devices

    NASA Astrophysics Data System (ADS)

    Anishchenko, S. V.; Gurinovich, A. A.

    2014-03-01

    Based on a detailed analysis of explosive electron emission in high-current electronic devices, we formulate a system of equations that describes the expansion of the cathode plasma and the generation of high-current electron beams. The system underlies the numerical algorithm for the hybrid code which enables simulating the charged particles' dynamics in high-current vircators with open resonators. Using the Gabor-Morlet transform, we perform the time-frequency analysis of vircator radiation.

  3. Secondary electron emission from lithium and lithium compounds

    DOE PAGESBeta

    Capece, A. M.; Patino, M. I.; Raitses, Y.; Koel, B. E.

    2016-07-06

    In this work, measurements of electron-induced secondary electron emission ( SEE) yields of lithium as a function of composition are presented. The results are particularly relevant for magnetic fusion devices such as tokamaks, field-reversed configurations, and stellarators that consider Li as a plasma-facing material for improved plasma confinement. SEE can reduce the sheath potential at the wall and cool electrons at the plasma edge, resulting in large power losses. These effects become significant as the SEE coefficient, γe, approaches one, making it imperative to maintain a low yield surface. This work demonstrates that the yield from Li strongly depends onmore » chemical composition and substantially increases after exposure to oxygen and water vapor. The total yield was measured using a retarding field analyzer in ultrahigh vacuum for primary electron energies of 20-600 eV. The effect of Li composition was determined by introducing controlled amounts of O2 and H2O vapor while monitoring film composition with Auger electron spectroscopy and temperature programmed desorption. The results show that the energy at which γe = 1 decreases with oxygen content and is 145 eV for a Li film that is 17% oxidized and drops to less than 25 eV for a fully oxidized film. This work has important implications for laboratory plasmas operating under realistic vacuum conditions in which oxidation significantly alters the electron emission properties of Li walls. Published by AIP Publishing.« less

  4. Secondary electron emission from lithium and lithium compounds

    NASA Astrophysics Data System (ADS)

    Capece, A. M.; Patino, M. I.; Raitses, Y.; Koel, B. E.

    2016-07-01

    In this work, measurements of electron-induced secondary electron emission (SEE) yields of lithium as a function of composition are presented. The results are particularly relevant for magnetic fusion devices such as tokamaks, field-reversed configurations, and stellarators that consider Li as a plasma-facing material for improved plasma confinement. SEE can reduce the sheath potential at the wall and cool electrons at the plasma edge, resulting in large power losses. These effects become significant as the SEE coefficient, γe, approaches one, making it imperative to maintain a low yield surface. This work demonstrates that the yield from Li strongly depends on chemical composition and substantially increases after exposure to oxygen and water vapor. The total yield was measured using a retarding field analyzer in ultrahigh vacuum for primary electron energies of 20-600 eV. The effect of Li composition was determined by introducing controlled amounts of O2 and H2O vapor while monitoring film composition with Auger electron spectroscopy and temperature programmed desorption. The results show that the energy at which γe = 1 decreases with oxygen content and is 145 eV for a Li film that is 17% oxidized and drops to less than 25 eV for a fully oxidized film. This work has important implications for laboratory plasmas operating under realistic vacuum conditions in which oxidation significantly alters the electron emission properties of Li walls.

  5. Acoustic emission characteristics of copper alloys under low-cycle fatigue conditions

    NASA Technical Reports Server (NTRS)

    Krampfner, Y.; Kawamoto, A.; Ono, K.; Green, A.

    1975-01-01

    The acoustic emission (AE) characteristics of pure copper, zirconium-copper, and several copper alloys were determined to develop nondestructive evaluation schemes of thrust chambers through AE techniques. The AE counts rms voltages, frequency spectrum, and amplitude distribution analysis evaluated AE behavior under fatigue loading conditions. The results were interpreted with the evaluation of wave forms, crack propagation characteristics, as well as scanning electron fractographs of fatigue-tested samples. AE signals at the beginning of a fatigue test were produced by a sample of annealed alloys. A sample of zirconium-containing alloys annealed repeatedly after each fatigue loading cycle showed numerous surface cracks during the subsequent fatigue cycle, emitting strong-burst AE signals. Amplitude distribution analysis exhibits responses that are characteristic of certain types of AE signals.

  6. Field electron emission from pencil-drawn cold cathodes

    NASA Astrophysics Data System (ADS)

    Chen, Jiangtao; Yang, Bingjun; Liu, Xiahui; Yang, Juan; Yan, Xingbin

    2016-05-01

    Field electron emitters with flat, curved, and linear profiles are fabricated on flexible copy papers by direct pencil-drawing method. This one-step method is free of many restricted conditions such as high-temperature, high vacuum, organic solvents, and multistep. The cold cathodes display good field emission performance and achieve high emission current density of 78 mA/cm2 at an electric field of 3.73 V/μm. The approach proposed here would bring a rapid, low-cost, and eco-friendly route to fabricate but not limited to flexible field emitter devices.

  7. Martian soil simulant: Focus on secondary electron emission

    NASA Astrophysics Data System (ADS)

    Pavlu, Jiri; Beranek, Martin; Vaverka, Jakub; Richterova, Ivana; Safrankova, Jana; Nemecek, Zdenek

    2013-04-01

    Growing interest in dust charging physics is connected with several lander missions (running or planned) to the Moon, Mars, and Mercury. In support of these missions, simulations in laboratories are expected tools to optimize in situ explorations and measurements. In this paper, we have investigated some of the electrical properties of a Martian soil simulant (JSC Mars-1) using the dust charging experiment, where a single dust grain is trapped in a vacuum chamber and its secondary electron emission is studied. The exposure of the grain to the electron beam revealed that the grain surface potential is low and generally determined by a mean atomic number of the grain material at the low-beam energies (< 1 keV). Whereas it can reach a limit of the field ion emission being irradiated by energetic electrons (> 5 keV). Observations are also compared with our advanced numerical model of the secondary electron emission which takes into account (besides chemical content and dimension) an influence of shape and surface roughness.

  8. Cyclotron side-band emissions from ring-current electrons

    NASA Technical Reports Server (NTRS)

    Maeda, K.

    1976-01-01

    The paper examines temporal variations in electron energy spectra and pitch-angle distributions during a VLF-emission event observed by Explorer 45 in the main phase of a magnetic storm. It is noted that the observed event occurred outside the plasmasphere on the night side of the magnetosphere and that the dusk-side plasmapause had a double structure during the event. It is found that the VLF emissions consisted of two frequency bands, corresponding to the whistler and electrostatic modes, and that there was a sharp band of 'missing emissions' along frequencies equal to half the equatorial electron gyrofrequency. A peculiar pitch-angle distribution for high-energy electrons (50 to 350 keV) is noted. It is concluded that the VLF-producing particles were enhanced low-energy (about 5 keV) ring-current electrons which penetrated into the night side of the magnetosphere from the magnetotail plasma sheet and which drifted eastward after encountering the steep gradient of the geomagnetic field.

  9. Instrumentation for Studies of Electron Emission and Charging From Insulators

    NASA Technical Reports Server (NTRS)

    Thomson, C. D.; Zavyalov, V.; Dennison, J. R.

    2004-01-01

    Making measurements of electron emission properties of insulators is difficult since insulators can charge either negatively or positively under charge particle bombardment. In addition, high incident energies or high fluences can result in modification of a material s conductivity, bulk and surface charge profile, structural makeup through bond breaking and defect creation, and emission properties. We discuss here some of the charging difficulties associated with making insulator-yield measurements and review the methods used in previous studies of electron emission from insulators. We present work undertaken by our group to make consistent and accurate measurements of the electron/ion yield properties for numerous thin-film and thick insulator materials using innovative instrumentation and techniques. We also summarize some of the necessary instrumentation developed for this purpose including fast response, low-noise, high-sensitivity ammeters; signal isolation and interface to standard computer data acquisition apparatus using opto-isolation, sample-and-hold, and boxcar integration techniques; computer control, automation and timing using Labview software; a multiple sample carousel; a pulsed, compact, low-energy, charge neutralization electron flood gun; and pulsed visible and UV light neutralization sources. This work is supported through funding from the NASA Space Environments and Effects Program and the NASA Graduate Research Fellowship Program.

  10. Embedding plasmonic nanostructure diodes enhances hot electron emission.

    PubMed

    Knight, Mark W; Wang, Yumin; Urban, Alexander S; Sobhani, Ali; Zheng, Bob Y; Nordlander, Peter; Halas, Naomi J

    2013-04-10

    When plasmonic nanostructures serve as the metallic counterpart of a metal-semiconductor Schottky interface, hot electrons due to plasmon decay are emitted across the Schottky barrier, generating measurable photocurrents in the semiconductor. When the plasmonic nanostructure is atop the semiconductor, only a small percentage of hot electrons are excited with a wavevector permitting transport across the Schottky barrier. Here we show that embedding plasmonic structures into the semiconductor substantially increases hot electron emission. Responsivities increase by 25× over planar diodes for embedding depths as small as 5 nm. The vertical Schottky barriers created by this geometry make the plasmon-induced hot electron process the dominant contributor to photocurrent in plasmonic nanostructure-diode-based devices. PMID:23452192

  11. Electron emission and fragmentation of molecules in intense laser fields

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Prümper, G.; Hatamoto, T.; Okunishi, M.; Mathur, D.

    2007-06-01

    We have constructed an apparatus for high-resolution electron spectroscopy and electron-ion coincidence experiments on gas-phase molecules in intense laser fields. The apparatus comprises an electron time-of-flight (TOF) spectrometer and an ion TOF spectrometer with a position detector, placed on either side of an effusive molecular beam. The ionizing radiation is either the fundamental (800 nm wavelength) of a Ti:sapphire laser or frequency doubled 400-nm light, with pulse durations of ~ 150 fs and the repetition rate of 1 kHz. We have investigated the electron emission and fragmentation of linear alcohol molecules, methanol, ethanol and 1-propanol, in laser fields with peak intensities up to ~ 1×10 14 W/cm2. Details of our apparatus are described along with an overview of some recent results.

  12. Temperature enhancement of secondary electron emission from hydrogenated diamond films

    SciTech Connect

    Stacey, A.; Prawer, S.; Rubanov, S.; Akhvlediani, R.; Michaelson, Sh.; Hoffman, A.

    2009-09-15

    The effect of temperature on the stability of the secondary electron emission (SEE) yield from approx100-nm-thick continuous diamond films is reported. At room temperature, the SEE yield was found to decay as a function of electron irradiation dose. The SEE yield is observed to increase significantly upon heating of the diamond surface. Furthermore, by employing moderate temperatures, the decay of the SEE yield observed at room temperature is inhibited, showing a nearly constant yield with electron dose at 200 deg. C. The results are explained in terms of the temperature dependence of the electron beam-induced hydrogen desorption from the diamond surface and surface band bending. These findings demonstrate that the longevity of diamond films in practical applications of SEE can be increased by moderate heating.

  13. Two dimensional electron cyclotron emission imaging study of electron temperature profiles and fluctuations in Tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Deng, Bihe

    An innovative plasma diagnostic technique, electron cyclotron emission imaging (ECEI), was successfully developed and implemented on the TEXT-U and RTP tokamaks for the study of plasma electron temperature profiles and fluctuations. Due to the high spatial and temporal resolution of this new diagnostic, plasma filamentation was observed during high power electron cyclotron resonance heating (ECRH) in TEXT-U, and was identified as multiple rotating magnetic islands. In RTP, under special plasma conditions, evidence for magnetic bubbling was first observed, which is characterized by the flattening of the electron temperature and pressure profiles over a small annular region of about 1-2 cm extent near the q = 2 surface. More important results arose from the detailed study of the broadband plasma turbulence in TEXT-U and RTP. With the first measurements of poloidal wavenumbers and dispersion relations, turbulent Te fluctuations in the confinement region of TEXT-U plasmas were identified as electron drift wave turbulence. The fluctuation amplitude is found to follow the mixing length scaling, and the fluctuation-induced conducted- heat flux can account for the observed anomalous energy transport in TEXT-U. In RTP, detailed ECEI study of broadband Te fluctuations has shown that many characteristics of the observed fluctuations are consistent with the predictions of toroidal ηi mode theory. These include the global dependence of the fluctuation frequency and amplitude on the plasma density and current. The measured isotope and impurity scalings quantitatively match the predictions of toroidal ηi mode theory. The ECEI measurements in combination with ECRH modification of T e profiles argue against the Te gradients serving as the driving force of the turbulence. With the detailed 2- D measurements of the fluctuation distribution over the plasma minor cross-section, large scale, coherent structures similar to the eigenmode structures predicted by toroidal ηi mode theory

  14. Characteristics of banded chorus-like emission measured by the TC-1 Double Star spacecraft

    NASA Astrophysics Data System (ADS)

    Macúšová, Eva; Santolík, Ondřej; Cornilleau-Wehrlin, Nicole; Yearby, Keith

    2013-04-01

    We present a study of the spatio-temporal characteristics of banded whistler-mode emissions. It covers the full operational period of the TC-1 spacecraft, between January 2004 and the end of September 2007. The analyzed data set has been visually selected from the onboard-analyzed time-frequency spectrograms of magnetic field fluctuations below 4 kHz measured by the STAFF/DWP wave instrument situated onboard the TC-1 spacecraft with a low inclination elliptical equatorial orbit. This orbit covers magnetic latitudes between -39o and 39o. The entire data set has been collected between L=2 and L=12. Our results show that almost all intense emissions (above a threshold of 10-5nT2Hz-1) occur at L-shells from 6 to 12 and in the MLT sector from 2 to 11 hours. This is in a good agreement with previous observations. We determine the bandwidth of the observed emission by an automatic procedure based on the measured spectra. This allows us to reliably calculate the integral amplitudes of the measured signals. The majority of the largest amplitudes of chorus-like emissions were found closer to the Earth. The other result is that the upper band chorus-like emissions (above one half of the electron cyclotron frequency) are much less intense than the lower band chorus-like emissions (below one half of the electron cyclotron frequency) and are usually observed closer to the Earth than the lower band. This work has received EU support through the FP7-Space grant agreement n 284520 for the MAARBLE collaborative research project.

  15. Electron emission from nickel-alloy surfaces in cesium vapor

    NASA Technical Reports Server (NTRS)

    Manda, M.; Jacobson, D.

    1978-01-01

    The cesiated electron emission was measured for three candidate electrodes for use as collectors in thermionic converters. Nickel, Inconel 600 and Hastelloy were tested with a 412 K cesium reservoir. Peak emission from the alloys was found to be comparable to that from pure nickel. Both the Inconel and the Hastelloy samples had work functions of 1.64 eV at peak emission. The minimum work functions were estimated to be 1.37 eV at a probe temperature of 750 K for Inconel and 1.40 eV for Hastelloy at 665 K. The bare work function for both alloys is estimated to be approximately the same as for pure nickel, 4.8 eV.

  16. Electron Field Emission Properties of Textured Platinum Surfaces

    NASA Technical Reports Server (NTRS)

    Sovey, James S.

    2002-01-01

    During ground tests of electric microthrusters and space tests of electrodynamic tethers the electron emitters must successfully operate at environmental pressures possibly as high as 1x10(exp -4) Pa. High partial pressures of oxygen, nitrogen, and water vapor are expected in such environments. A textured platinum surface was used in this work for field emission cathode assessments because platinum does not form oxide films at low temperatures. Although a reproducible cathode conditioning process did not evolve from this work, some short term tests for periods of 1 to 4 hours showed no degradation of emission current at an electric field of 8 V/mm and background pressures of about 1x10(exp -6) Pa. Increases of background pressure by air flow to about 3x10(exp -4) Pa yield a hostile environment for the textured platinum field emission cathode.

  17. Field Enhanced Thermionic Electron Emission from Oxide Coated Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Day, Christopher; Jin, Feng; Liu, Yan; Little, Scott

    2006-03-01

    We have created a novel nanostructure by coating carbon nanotubes with a thin functional oxide layer. The structure was fabricated by sputter deposition of a thin film of oxide materials on aligned carbon nanotubes, which were grown on a tungsten substrate with plasma enhanced chemical vapor deposition. This structure combines the low work function of the oxide coating with a high field enhancement factor introduced by carbon nanotubes and we have demonstrated that it can be used as a highly efficient electron source. A field enhancement factor as high as 2000 was observed and thermionic electron emission current at least an order of magnitude higher than the emission from a conventional oxide cathode was obtained.

  18. Vertically integrated optics for ballistic electron emission luminescence microscopy

    NASA Astrophysics Data System (ADS)

    Appelbaum, Ian; Yi, Wei; Russell, K. J.; Narayanamurti, V.; Hanson, M. P.; Gossard, A. C.

    2005-02-01

    We have integrated a photon detector directly into a ballistic electron emission luminescence (BEEL) heterostructure, just below a luminescent quantum well. Results from solid-state metal-base hot-electron transistors fabricated with this collector design indicate that more than 10% of the photons emitted by the quantum well excite photoelectrons in the detector region. The improved photonic coupling and effective collection angle in this scheme improves the BEEL signal by many orders of magnitude as compared to far-field detection with the most sensitive single-photon counters, enabling BEEL microscopy in systems with no optical components.

  19. Calibration of electron cyclotron emission radiometer for KSTAR.

    PubMed

    Kogi, Y; Jeong, S H; Lee, K D; Akaki, K; Mase, A; Kuwahara, D; Yoshinaga, T; Nagayama, Y; Kwon, M; Kawahata, K

    2010-10-01

    We developed and installed an electron cyclotron emission radiometer for taking measurements of Korea Superconducting Tokamak Advanced Research (KSTAR) plasma. In order to precisely measure the absolute value of electron temperatures, a calibration measurement of the whole radiometer system was performed, which confirmed that the radiometer has an acceptably linear output signal for changes in input temperature. It was also found that the output power level predicted by a theoretical calculation agrees with that obtained by the calibration measurement. We also showed that the system displays acceptable noise-temperature performance around 0.23 eV. PMID:21033948

  20. A planar diode operating in the regime of limited electron emission

    NASA Astrophysics Data System (ADS)

    Pushkarev, A. I.; Sazonov, R. V.

    2008-04-01

    The current-voltage characteristic of a planar diode with a graphite explosive-emission cathode has been experimentally studied at the initial stage of electron current formation. An analytical expression has been obtained for the total area of discrete emitting centers in the cellular structure approximation, assuming that the number of such emitting centers operative during the current pulse formation is constant. It is shown that the electron current buildup for a cathode surface with discrete emitting centers is satisfactorily described by a modified Child-Langmuir formula with the form factor decreasing from F = 6 to 1.

  1. Nonlinear electron magnetohydrodynamics physics. V. Triggered whistler emissions

    SciTech Connect

    Stenzel, R. L.; Strohmaier, K. D.; Urrutia, J. M.

    2008-06-15

    Laboratory experiments on whistler instabilities in the presence of small trigger waves have been performed. The instabilities arise from energizing electrons in magnetic null lines with time-varying magnetic fields. Such fields are created with loop antennas carrying large oscillating currents in the low-frequency whistler branch. X-type and O-type magnetic nulls are produced with electric fields along the toroidal separator. The magnetic field convects in the form of whistler spheromaks and whistler mirrors. Counterpropagating spheromaks merge and form field-reversed configurations (FRCs). Counterpropagating mirrors colliding with an FRC also energize electrons and produce high-frequency whistler emissions. The possibility that these emissions are triggered by incident waves from other null lines in the plasma has been investigated. A controlled experiment on triggered emissions where a test wave has been created with an independent antenna and propagated into the source region to investigate its amplification has also been performed. It is observed that the test wave does not grow but triggers a much larger instability in a spheromak. The enhanced emission has a different magnetic topology and a slightly different frequency from that of the test wave. Space-time measurements in the source region show both convective wave amplification occurs as well as an absolute instability in the current ring.

  2. Synthesis and electron emission properties of aligned carbon nanotube arrays

    NASA Astrophysics Data System (ADS)

    Neupane, Suman

    Carbon nanotubes (CNTs) have become one of the most interesting allotropes of carbon due to their intriguing mechanical, electrical, thermal and optical properties. The synthesis and electron emission properties of CNT arrays have been investigated in this work. Vertically aligned CNTs of different densities were synthesized on copper substrate with catalyst dots patterned by nanosphere lithography. The CNTs synthesized with catalyst dots patterned by spheres of 500 nm diameter exhibited the best electron emission properties with the lowest turn-on/threshold electric fields and the highest field enhancement factor. Furthermore, CNTs were treated with NH3 plasma for various durations and the optimum enhancement was obtained for a plasma treatment of 1.0 min. CNT point emitters were also synthesized on a flat-tip or a sharp-tip to understand the effect of emitter geometry on the electron emission. The experimental results show that electron emission can be enhanced by decreasing the screening effect of the electric field by neighboring CNTs. In another part of the dissertation, vertically aligned CNTs were synthesized on stainless steel (SS) substrates with and without chemical etching or catalyst deposition. The density and length of CNTs were determined by synthesis time. For a prolonged growth time, the catalyst activity terminated and the plasma started etching CNTs destructively. CNTs with uniform diameter and length were synthesized on SS substrates subjected to chemical etching for a period of 40 minutes before the growth. The direct contact of CNTs with stainless steel allowed for the better field emission performance of CNTs synthesized on pristine SS as compared to the CNTs synthesized on Ni/Cr coated SS. Finally, fabrication of large arrays of free-standing vertically aligned CNT/SnO2 core-shell structures was explored by using a simple wet-chemical route. The structure of the SnO2 nanoparticles was studied by X-ray diffraction and electron microscopy

  3. Self-emission and enhancement of laser-induced emission of electrons from ferroelectrics

    NASA Astrophysics Data System (ADS)

    Geissler, K. K.; Meineke, A.; Riege, H.; Handerek, J.

    1994-02-01

    We report on laser-induced electron emission (LIEE) from ferroelectrics (FE) at 266, 355 and 532 nm wavelength. The self-emission of charges up to 20 nC/cm 2 with kinetic energies up to several keV was observed with PLZT ceramics at laser-pulse energy densities of 13 mJ/cm 2 and a pulse width of 5 ns FWHM after high-voltage-induced polarization switching. The driving electric field is generated by the laser-induced change of the spontaneous polarization in a time scale of 1 ns. The dependence of the emission on the laser-pulse energy density is shown and the relation between the enhancement of LIEE and the laser-induced self-emission is discussed.

  4. BXO mode-converted electron Bernstein emission diagnostic (invited)

    NASA Astrophysics Data System (ADS)

    Volpe, F.; Laqua, H. P.

    2003-03-01

    Electron temperature profiles at densities above the electron cyclotron emission (ECE) cutoff are measured at the W7-AS stellarator by a novel diagnostic based on black body emission and Bernstein-extraordinary-ordinary mode conversion of electron Bernstein waves (EBWs). The radiation is collected along a special oblique line of sight by an antenna with gaussian optics. This was optimized for maximal conversion efficiency and minimal Doppler broadening by means of EBW ray tracing calculations in full stellarator geometry. The elliptical O-mode polarization detected along the oblique line of sight is changed into a linear polarization by a broadband quarter wave shifter, namely an elliptical waveguide. The signal is spectrum analyzed by an heterodyne radiometer and temperature profiles are derived from spectra by means of ray tracing. The diagnostic was applied to measurements of edge-localized modes to illustrate its advantages in terms of spatial and temporal resolution. Moreover, for the first time, the heat wave propagation method for the determination of local heat transport coefficients was extended beyond the ECE cutoff density by combining EBW emission measurements at the first harmonic (f=66-78 GHz) with modulated EBW heating at the second harmonic (140 GHz).

  5. Photoelectron emission from metal surfaces induced by radiation emitted by a 14 GHz electron cyclotron resonance ion source

    NASA Astrophysics Data System (ADS)

    Laulainen, Janne; Kalvas, Taneli; Koivisto, Hannu; Komppula, Jani; Kronholm, Risto; Tarvainen, Olli

    2016-02-01

    Photoelectron emission measurements have been performed using a room-temperature 14 GHz ECR ion source. It is shown that the photoelectron emission from Al, Cu, and stainless steel (SAE 304) surfaces, which are common plasma chamber materials, is predominantly caused by radiation emitted from plasma with energies between 8 eV and 1 keV. Characteristic X-ray emission and bremsstrahlung from plasma have a negligible contribution to the photoelectron emission. It is estimated from the measured data that the maximum conceivable photoelectron flux from plasma chamber walls is on the order of 10% of the estimated total electron losses from the plasma.

  6. Characterization of Secondary Electron Emission Properties of Plasma Facing Materials

    NASA Astrophysics Data System (ADS)

    Patino, Marlene I.; Capece, Angela M.; Raitses, Yevgeny; Koel, Bruce E.

    2015-11-01

    The behavior of wall-bounded plasmas is significantly affected by the plasma-wall interactions, including the emission of secondary electrons (SEE) from the wall materials due to bombardment by primary electrons. The importance of SEE has prompted previous investigations of SEE properties of materials especially with applications to magnetic fusion, plasma thrusters, and high power microwave devices. In this work, we present results of measurements of SEE properties of graphite and lithium materials relevant for the divertor region of magnetic fusion devices. Measurements of total SEE yield (defined as the number of emitted secondary electrons per incident primary electron) for lithium are extended up to 5 keV primary electron energy, and the energy distributions of secondary electrons are provided for graphite and lithium. Additionally, the effect of contamination on the total SEE yield of lithium was explored by exposing the material to water vapor. Auger electron spectroscopy (AES) was used to determine surface composition and temperature programmed desorption (TPD) was used to determine lithium film thickness. Results show an order of magnitude increase in total SEE yield for lithium exposed to water vapor. This work was supported by DOE contract DE-AC02-09CH11466; AFOSR grants FA9550-14-1-0053, FA9550-11-1-0282, and AF9550-09-1-0695; and DOE Office of Science Graduate Student Research Program.

  7. Anomalous conductivity and secondary electron emission in Hall effect thrusters

    SciTech Connect

    Garrigues, L.; Hagelaar, G. J. M.; Boniface, C.; Boeuf, J. P.

    2006-12-15

    This paper is devoted to the study of the effects of electron-wall interactions on cross magnetic field electron momentum and energy losses in Hall effect thrusters. By coupling a semianalytical model of the wall sheath similar to models used by several authors in this context, with a two-dimensional hybrid simulation of a Hall effect thruster, we find that the cross magnetic field conductivity enhanced by electron-wall collisions and secondary electron emission is not sufficient to explain the conductivity deduced from experiments. Calculated current-voltage curves including electron-wall collisions from a standard sheath model as the sole 'anomalous' conductivity mechanism do not reproduce the measurements, especially at high discharge voltages, and for various wall ceramics. Results also show that a one-dimensional description of electron-wall collisions with a constant radial plasma density profile as used by many authors leads to an overestimation of the contribution of electron-wall interactions to cross magnetic field conductivity.

  8. Radio Emissions from Plasma with Electron Kappa-Distributions

    NASA Astrophysics Data System (ADS)

    Fleishman, G. D.; Kuznetsov, A. A.

    2015-12-01

    Gregory Fleishman (New Jersey Institute of Technology, Newark, USA)Alexey Kuznetsov (Institute of Solar-Terrestrial Physics, Irkutsk, Russia), Currently there is a concern about the ability of the classical thermal (Maxwellian) distribution to describe quasisteady-state plasma in the solar atmosphere, including active regions. In particular, other distributions have been proposed to better fit observations, for example, kappa-distributions. If present, these distributions will generate radio emissions with different observable properties compared with the classical gyroresonance (GR) or free-free emission, which implies a way of remotely detecting these kappa distributions in the radio observations. Here we present analytically derived GR and free-free emissivities and absorption coefficients for the kappa-distribution, and discuss their properties, which are in fact remarkably different from the classical Maxwellian plasma. In particular, the radio brightness temperature from a gyrolayer increases with the optical depth τ for kappa-distribution. This property has a remarkable consequence allowing a straightforward observational test: the GR radio emission from the non-Maxwellian distributions is supposed to be noticeably polarized even in the optically thick case, where the emission would have strictly zero polarization in the case of Maxwellian plasma. This offers a way of remote probing the plasma distribution in astrophysical sources, including solar active regions as a vivid example. In this report, we present analytical formulae and computer codes to calculate the emission parameters. We simulate the gyroresonance emission under the conditions typical of the solar active regions and compare the results for different electron distributions. We discuss the implications of our findings for interpretation of radio observations. This work was supported in part by NSF grants AGS-1250374 and AGS-1262772, NASA grant NNX14AC87G to New Jersey Institute of Technology

  9. Coherent electron emission beyond Young-type interference from diatomic molecules

    NASA Astrophysics Data System (ADS)

    Agueny, H.; Makhoute, A.; Dubois, A.; Hansen, J. P.

    2016-01-01

    It has been known for more than 15 years that the differential cross section of electrons emitted from diatomic molecules during interaction with energetic charged particles oscillates as a function of electron momentum. The origin of the phenomenon is two-center interference, which naturally relates it back to the Young double-slit experiment. In addition to a characteristic frequency which can be described by lowest-order perturbation theories, the observation and origin of higher-order harmonics of the basic oscillation frequency has been much discussed. Here, we show that high harmonics of the fundamental Young-type oscillation frequency observed in electron spectra in fast ion-molecule collisions can be clearly exposed in numerical solutions of the time-dependent Schrödinger equation within a one-dimensional model. Momentum distribution of the ejected electron is analyzed and shows that the phenomenon emerges when the charged particle beam collides with diatomic molecules with substantial large internuclear distance. Frequency spectra from nonperturbative calculations for electron emission from Rb2+ and Cs2+ exhibit a pronounced high-order oscillation in contrast to similar close-coupling calculations performed on H2 targets. The electron emission from these heavy molecules contains second- and third-order harmonics which are fully reproduced in an analytic model based on the Born series. Extending to triatomic molecular targets displays an increased range of harmonics. This suggests that electron emission spectra from new experiments on heavy diatomic and linear polyatomic molecular targets may provide a unique insight into competing coherent emission mechanisms and their relative strength.

  10. An Electron Emission Effect on Dynamics of Laser Ablation

    SciTech Connect

    Nastoyashchii, A. F.

    2004-03-30

    The paper deals with the effect of electron emission on a heat transfer in the area of a plasma critical density (near plasma-solid surface boundary). As is known, experimental data show the limitation of electron thermal conductivity in the mentioned area. In the laser fusion research just the limitation of the heat transfer at target irradiation with long-wave lasers has made application of CO2-lasers unreasonable in spite of their high efficiency. On other hand, as to the applied tasks of laser ablation (e.g. in launching small-scale satellites) the aspect of the CO2-lasers application is being widely discussed. In the paper the mentioned limitation is explained on the basis of classical representations. It is marked, that the heat transfer limitations arise from the conditions of preserving plasma quasi-neutrality at the absorption area boundary where the electron density is close to critical one for the given laser wavelength. Possible mechanisms of the electron emission in the mode of the laser ablation are discussed.

  11. Electron-Impact-Induced Emission Cross Sections of Atomic Oxygen

    NASA Astrophysics Data System (ADS)

    Noren, C.; Kanik, I.; James, G. K.; Ajello, J. M.; Khakoo, M. A.

    1998-05-01

    One cannot overstate the importance of ultraviolet (UV) lines of neutral atomic oxygen. For example, the atomic oxygen resonance transition at 130.4 nm is a prominent emission feature in the vacuum ultraviolet (VUV) spectrum of the Earth's aurora and dayglow as well as the atmospheres of Venus and Mars. In this poster, we present our measurements of the electron-impact emission cross sections of the 130.4 nm atomic oxygen feature from threshold to 100 eV impact energy. A high-density atomic oxygen beam, created by a microwave discharge source, was intersected at a right angle by a magnetically focused electron beam. A 0.2m UV spectrometer system was used in the present measurements. It consists of an electron-impact collision chamber in tandem with an UV spectrometer equipped with a CsI coated channel electron multiplier detector. Emitted photons corresponding to radiative decay of collisionally excited state of the 130.4 nm atomic oxygen feature were detected.

  12. Electron Bernstein Wave Emission and Mode Conversion Physics on NSTX

    SciTech Connect

    Diem, S J; Caughman, J B; Efthimion, P; Kugel, H; LeBlanc, B P; Preinhaelter, J; Sabbagh, S A; Urban, J; Wilgen, J

    2008-05-21

    NSTX is a spherical tokamak (ST) that operates with ne up to 1020 m-3 and BT less than 0.6 T, cutting off low harmonic electron cyclotron (EC) emission widely used for Te measurements on conventional aspect ratio tokamaks. The electron Bernstein wave (EBW) can propagate in ST plasmas and is emitted at EC harmonics. These properties suggest thermal EBW emission (EBE) may be used for local Te measurements in the ST. Practically, a robust Te(R,t) EBE diagnostic requires EBW transmission efficiencies of > 90% for a wide range of plasma conditions. EBW emission and coupling physics were studied on NSTX with an obliquely viewing EBW to O-mode (B-X-O) diagnostic with two remotely steered antennas, coupled to absolutely calibrated radiometers. While Te(R,t) measurements with EBW emission on NSTX were possible, they were challenged by several issues. Rapid fluctuations in edge ne scale length resulted in > 20% changes in the low harmonic B-X-O transmission efficiency. Also, B-X-O transmission efficiency 2 during H-modes was observed to decay by a factor of 5-10 to less than a few percent. The B-X-O transmission behavior during H-modes was reproduced by EBE simulations that predict that EBW collisional damping can significantly reduce emission when Te < 30 eV inside the B-X-O mode conversion (MC) layer. Initial edge lithium conditioning experiments during H-modes have shown that evaporated lithium can increase Te inside the B-X-O MC layer, significantly increasing B-X-O transmission.

  13. Study on the frequency characteristics of nanogap electron devices

    SciTech Connect

    Xu, Ji; Wang, Qilong E-mail: bell@seu.edu.cn; Qi, Zhiyang; Zhai, Yusheng; Zhang, Xiaobing E-mail: bell@seu.edu.cn

    2015-05-28

    Ballistic electron transport in the nanogap devices will make it practical to combine the advantages of solid-state devices and vacuum electron devices including high integration and high frequency characteristics. Although a number of experiments have been exploited on frequency characteristic in nanogap, less modeling or calculations were investigated at such scale yet. In this paper, the concept of mean flight time is proposed in order to theoretically determine the frequency in nanoscale. Traditionally, we have to first determine the frequency response diagram and then deduce the cut-off frequency. This work presents a new method for exploring the frequency characteristics of electron transport in a nanogap structure by calculations and numerical simulations. A double-gate structure was applied in the simulations, and the results suggest that the nanogap structure can perform in the THz range. Additionally, an equivalent circuit model was adopted to demonstrate the validity of this method. Our results provide a model for the intrinsic ballistic transportation of electrons inside the nanogap electron devices.

  14. Surface slope characteristics from Thermal Emission Spectrometer emission phase function observations

    NASA Astrophysics Data System (ADS)

    Edwards, C. S.; Bandfield, J. L.; Christensen, P. R.

    2006-12-01

    It is possible to obtain surface roughness characteristics, by measuring a single surface from multiple emission angles and azimuths in the thermal infrared. Surfaces will have different temperatures depending on their orientation relative to the sun. A different proportion of sunlit versus shaded surfaces will be in the field of view based on the viewing orientation, resulting in apparent temperature differences. This difference in temperature can be utilized to calculate the slope characteristics for the observed area. This technique can be useful for determining surface slope characteristics not resolvable by orbital imagery. There are two main components to this model, a surface DEM, in this case a synthetic, two dimensional sine wave surface, and a thermal model (provided by H. Kieffer). Using albedo, solar longitude, slope, azimuth, along with several other parameters, the temperature for each cell of the DEM is calculated using the thermal model. A temperature is then predicted using the same observation geometries as the Thermal Emission Spectrometer (TES) observations. A temperature difference is calculated for the two complementary viewing azimuths and emission angles from the DEM. These values are then compared to the observed temperature difference to determine the surface slope. This method has been applied to TES Emission Phase Function (EPF) observations for both the spectrometer and bolometer data, with a footprint size of 10s of kilometers. These specialized types of TES observations measure nearly the same surface from several angles. Accurate surface kinetic temperatures are obtained after the application of an atmospheric correction for the TES bolometer and/or spectrometer. Initial results include an application to the northern circumpolar dunes. An average maximum slope of ~33 degrees has been obtained, which makes physical sense since this is near the angle of repose for sand sized particles. There is some scatter in the data from separate

  15. Secondary Electron Emission and the Exploration of Space

    NASA Technical Reports Server (NTRS)

    Minow, Joseph I.

    2006-01-01

    The emission of secondary electrons from surfaces exposed to the space plasma and radiation environment is a process of great importance to space system engineering design and operations. A spacecraft will collect charge until it reaches an equilibrium potential gov,erned by the balance of incoming electron and ion currents from the space environment with outgoing secondary, backscattered, and photoelectron currents. Laboratory measurements of secondary electron yields are an important parameter for use in spacecraft charging analyses because the magnitude and sign of the equilibrium potential depends on both the energy spectrum of electrons and ions in the space environment and the electrical properties of the surface materials (including the energy dependent secondary electron yields). Typical benign equilibrium potentials range &om a few tens of volts positive in interplanetary space to a few volts negative in low Earth orbit. However, spacecraft are known to charge to negative potentials exceeding one to ten kilovolts in some environments and anomalies or system failures due to electrostatic discharges originating from highly charged surfaces becomes a serious concern. This presentation will provide a review of the spacecraft charging process with special emphasis on the role of secondary electrons in controlling the current balance process. Charging examples will include spacecraft in Earth orbit and interplanetary space as well as dust charging on the lunar surface, a phenomenon of importance to future lunar surface operations.

  16. Temperature effect on the electron emission and charging of BN-SiO2 under low energy electron irradiation

    NASA Astrophysics Data System (ADS)

    Belhaj, M.; Guerch, K.; Sarrailh, P.; Arcis, N.

    2015-11-01

    The BN-SiO2 is widely used as canal material in Hall Effect Thrusters. The electron emission yield under electron impact is considered as a key material parameter that affects the thrust efficiency. The effect of the temperature on the electron emission yield of BN-SiO2 was investigated. It is found that, the electron emission drop significantly when the temperature is increased from 22 °C to 800 °C. The aim here is to report our experimental results and to discuss the representativeness of electron emission data measured on ceramics at room temperature.

  17. Atomic Number Dependence of Ion-Induced Electron Emission

    NASA Astrophysics Data System (ADS)

    Arrale, Abdikarim Mohamed

    Knowledge of the atomic number (Z_1 ) dependence of ion-induced electron emission yields (gamma) can be the basis for a general understanding of ion-atom interaction phenomena and, in particular, for the design of Z_1 -sensitive detectors that could be useful, for example, in the separation of isobars in accelerator mass spectrometry. The Z_1 dependence of ion-induced electron emission yields has been investigated using heavy ions of identical velocity (v = 2 v_0, with v_0 as the Bohr velocity) incident in a normal direction on sputter-cleaned carbon foils. Yields measured in this work plotted as a function of the ion's atomic number reveal an oscillatory behavior with pronounced maxima and minima. This nonmonotonic dependence of the yield on Z_1 will be discussed in the light of existing theories. Ion-induced electron emission yields from contaminated surfaces are well known to be enhanced relative to the yields from atomically clean surfaces. Under the bombardment of energetic ions, the surfaces become sputter-cleaned with time, and the yields from the samples are reduced accordingly. The time dependent reduction of yields observed are shown to be due to various effects such as the desorption of contaminant atoms and molecules by incident ions and the adsorption of residual gas onto previously clean sites. Experimental results obtained in the present work show the lower, saturated yield (gamma_{rm s} ) to be a function of residual gas pressure (P) and the fluence (phi_{rm i}) of the ion. We present a dynamic equilibrium model which explains the increase in yields for surface gas contamination, the decrease in yields for contaminant desorption, and the pressure/fluence dependence of the time required to reach gamma_{ rm s}. The predictions of the model agree well with the observations of gamma _{rm s} as a function of the ratio of gas flux to ion flux, and the electron yields of clean and gas covered surfaces.

  18. Spontaneous Hot-Electron Light Emission from Electron-Fed Optical Antennas.

    PubMed

    Buret, Mickael; Uskov, Alexander V; Dellinger, Jean; Cazier, Nicolas; Mennemanteuil, Marie-Maxime; Berthelot, Johann; Smetanin, Igor V; Protsenko, Igor E; Colas-des-Francs, Gérard; Bouhelier, Alexandre

    2015-09-01

    Nanoscale electronics and photonics are among the most promising research areas providing functional nanocomponents for data transfer and signal processing. By adopting metal-based optical antennas as a disruptive technological vehicle, we demonstrate that these two device-generating technologies can be interfaced to create an electronically driven self-emitting unit. This nanoscale plasmonic transmitter operates by injecting electrons in a contacted tunneling antenna feedgap. Under certain operating conditions, we show that the antenna enters a highly nonlinear regime in which the energy of the emitted photons exceeds the quantum limit imposed by the applied bias. We propose a model based upon the spontaneous emission of hot electrons that correctly reproduces the experimental findings. The electron-fed optical antennas described here are critical devices for interfacing electrons and photons, enabling thus the development of optical transceivers for on-chip wireless broadcasting of information at the nanoscale. PMID:26214575

  19. Effect of Secondary Electron Emission on Electron Cross-Field Current in E×B Discharges

    SciTech Connect

    Yevgeny Raitses, Igor D. Kaganovich, Alexander Khrabrov, Dmytro Sydorenko, Nathaniel J. Fisch and Andrei Smolyakov

    2011-02-10

    This paper reviews and discusses recent experimental, theoretical, and numerical studies of plasma-wall interaction in a weakly collisional magnetized plasma bounded with channel walls made from different materials. A lowpressure ExB plasma discharge of the Hall thruster was used to characterize the electron current across the magnetic field and its dependence on the applied voltage and electron-induced secondary electron emission (SEE) from the channel wall. The presence of a depleted, anisotropic electron energy distribution function with beams of secondary electrons was predicted to explain the enhancement of the electron cross-field current observed in experiments. Without the SEE, the electron crossfield transport can be reduced from anomalously high to nearly classical collisional level. The suppression of SEE was achieved using an engineered carbon velvet material for the channel walls. Both theoretically and experimentally, it is shown that the electron emission from the walls can limit the maximum achievable electric field in the magnetized plasma. With nonemitting walls, the maximum electric field in the thruster can approach a fundamental limit for a quasineutral plasma.

  20. Estimation of Photon Effects on Townsend Discharges for SecondaryElectronEmission Coefficient Measurements

    NASA Astrophysics Data System (ADS)

    Yoshinaga, Tomokazu; Akashi, Haruaki

    2015-09-01

    A Monte Carlo simulation (MCS) is applied to investigate the secondary electron emission in Argon Townsend discharges. The influxes of ions, photons and metastable species onto the cathode surface are estimated simply from the number of inelastic collisions. The effect of photons becomes significant especially under higher pd conditions since the photon influx increases. This suggests the possibility of the estimation of the secondary electron emission coefficient of photons by examining breakdown voltage characteristics (Paschen curves). The effect of metastable species is much smaller than those of ions and photons and is negligible. The Paschen curves evaluated with MCS agrees well with the results of one-dimensional fluid model simulation when the photon effect is neglected, showing the necessity of further improvement. Supported by JSPS KAKENHI Grant Number 26820108.

  1. Theory for two dimensional electron emission between parallel flat electrodes

    NASA Astrophysics Data System (ADS)

    Torres-Cordoba, Rafael

    2009-12-01

    The electron emission in space charge is limited for the case of a planar cathode; such emission is generated by using an approximation that models electric field formation by a dipole, which generates an oscillatory symmetrical density current j(x ), minimum value is moved around the origin and calculated throughout the Poisson equation. Such value has been previously calculated based upon the already stated conditions for the two dimensional (2D) case. In our matter under study, it is stated that a symmetric oscillatory potential, namely, μ(x ,y) is invariably generated; because of that the boundary conditions represented by both a barrier potential and a square potential will satisfy this potential as well. For the case of the square potential, it is taking into account either a potential is attractive or repulsive. In this study one of the principal problems is discussed. It is when the space charge creates a potential barrier that prohibits steady-state beam propagation. In this paper it is claimed to have found the boundary conditions that fully satisfy the potential, and the potential satisfies approximately the Poisson equation for the 2D case, and the electron emission is generated through a finite strip due to electrical dipole formation.

  2. Electron optics simulation for designing carbon nanotube based field emission x-ray source

    NASA Astrophysics Data System (ADS)

    Sultana, Shabana

    In this dissertation, electron optics simulation for designing carbon nanotube (CNT) based field emission x-ray source for medical imaging applications will be presented. However, for design optimization of x-ray tubes accurate electron beam optics simulation is essential. To facilitate design of CNT x-ray sources a commercial 3D finite element software has been chosen for extensive simulation. The results show that a simplified model of uniform electron field emission from the cathode surface is not sufficient when compared to experimental measurements. This necessitated the development of a refined model to describe a macroscopic field emission CNT cathode for electron beam optics simulations. The model emulates the random distribution of CNTs and the associated variation of local field enhancement factor. The main parameter of the model has been derived empirically from the experimentally measured I-V characteristics of the CNT cathode. Simulation results based on this model agree well with experiments which include measurements of the transmission rate and focus spot size. The model provides a consistent simulation platform for optimization of electron beam optics in CNT x-ray source design. A systematic study of electron beam optics in CNT x-ray tubes led to the development of a new generation of compact x-ray source with multiple pixels. A micro focus field emission x-ray source with a variable focal spot size has been fully characterized and evaluated. It has been built and successfully integrated into micro-CT scanners which are capable of dynamic cardiac imaging of free-breathing small animals with high spatial and temporal resolutions. In addition a spatially distributed high power multi-beam x-ray source has also been designed and integrated into a stationary digital breast tomosynthesis (s-DBT) configuration. This system has the potential to reduce the total scan time to 4 seconds and yield superior image quality in breast imaging.

  3. Instability, Collapse and Oscillation of Sheaths Caused by Secondary Electron Emission

    SciTech Connect

    M.D. Campanell, A.V. Khrabrov and I.D. Kaganovich

    2013-01-03

    The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te ) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) "coefficient" do not capture the full extent of SEE effects.

  4. Instability, collapse, and oscillation of sheaths caused by secondary electron emission

    NASA Astrophysics Data System (ADS)

    Campanell, M. D.; Khrabrov, A. V.; Kaganovich, I. D.

    2012-12-01

    The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) "coefficient" do not capture the full extent of SEE effects.

  5. Measurements on wave propagation characteristics of spiraling electron beams

    NASA Technical Reports Server (NTRS)

    Singh, A.; Getty, W. D.

    1976-01-01

    Dispersion characteristics of cyclotron-harmonic waves propagating on a neutralized spiraling electron beam immersed in a uniform axial magnetic field are studied experimentally. The experimental setup consisted of a vacuum system, an electron-gun corkscrew assembly which produces a 110-eV beam with the desired delta-function velocity distribution, a measurement region where a microwave signal is injected onto the beam to measure wavelengths, and a velocity analyzer for measuring the axial electron velocity. Results of wavelength measurements made at beam currents of 0.15, 1.0, and 2.0 mA are compared with calculated values, and undesirable effects produced by increasing the beam current are discussed. It is concluded that a suitable electron beam for studies of cyclotron-harmonic waves can be generated by the corkscrew device.

  6. Characteristics of microinstabilities in electron cyclotron and ohmic heated discharges

    NASA Astrophysics Data System (ADS)

    Pusztai, I.; Moradi, S.; Fülöp, T.; Timchenko, N.

    2011-08-01

    Characteristics of microinstabilities in electron cyclotron (EC) and ohmic heated (OH) discharges in the T10 tokamak have been analyzed by linear electrostatic gyrokinetic simulations with gyro [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] aiming to find insights into the effect of auxiliary heating on the transport. Trapped electron modes are found to be unstable in both OH and the EC heated scenarios. In the OH case the main drive is from the density gradient and in the EC case from the electron temperature gradient. The growth rates and particle fluxes exhibit qualitatively different scaling with the electron-to-ion temperature ratios in the two cases. This is mainly due to the fact that the dominant drives and the collisionalities are different. The inward flow velocity of impurities and the impurity diffusion coefficient decreases when applying EC heating, which leads to lower impurity peaking, consistently with experimental observations.

  7. Characteristics of microinstabilities in electron cyclotron and ohmic heated discharges

    SciTech Connect

    Pusztai, I.; Moradi, S.; Fueloep, T.; Timchenko, N.

    2011-08-15

    Characteristics of microinstabilities in electron cyclotron (EC) and ohmic heated (OH) discharges in the T10 tokamak have been analyzed by linear electrostatic gyrokinetic simulations with gyro[J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] aiming to find insights into the effect of auxiliary heating on the transport. Trapped electron modes are found to be unstable in both OH and the EC heated scenarios. In the OH case the main drive is from the density gradient and in the EC case from the electron temperature gradient. The growth rates and particle fluxes exhibit qualitatively different scaling with the electron-to-ion temperature ratios in the two cases. This is mainly due to the fact that the dominant drives and the collisionalities are different. The inward flow velocity of impurities and the impurity diffusion coefficient decreases when applying EC heating, which leads to lower impurity peaking, consistently with experimental observations.

  8. Diffuse synchrotron emission from galactic cosmic ray electrons

    NASA Astrophysics Data System (ADS)

    Di Bernardo, G.; Grasso, D.; Evoli, C.; Gaggero, D.

    2015-09-01

    Synchrotron diffuse radiation (SDR) emission is one of the major Galactic components, in the 100 MHz up to 100 GHz frequency range. Its spectrum and sky map provide valuable measure of the galactic cosmic ray electrons (GCRE) in the relevant energy range, as well as of the strength and structure of the Galactic magnetic fields (GMF), both regular and random ones. This emission is an astrophysical sky foreground for the study of the Cosmic Microwave Background (CMB), and the extragalactic microwave measurements, and it needs to be modelled as better as possible. In this regard, in order to get an accurate description of the SDR in the Galaxy, we use - for the first time in this context - 3-dimensional GCRE models obtained by running the DRAGON code. This allows us to account for a realistic spiral arm pattern of the source distribution, demanded to get a self-consistent treatment of all relevant energy losses influencing the final synchrotron spectrum.

  9. Ballistic Electron Emission Microscopy Studies of Ferromagnet - Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Mather, P. G.; Perrella, A. C.; Yurtsever, A.; Buhrman, R. A.

    2004-03-01

    Devices that employ spin as well as charge effects have been the subjects of extensive study recently. The magnetic tunneling transistor (1) is one important device that demonstrates an electrical means of injecting spin-polarized electrons into a semiconductor. A Schottky barrier lies at the heart of the device, and a high quality spatially homogenous and uniform barrier formed on GaAs is highly desirable. We have used ballistic electron emission microscopy (BEEM) to study CoFe, Fe and permalloy deposited on a GaAs substrate to give nanometer resolved evaluation of hot electron transport through the films and across the Schottky barrier. All films give a homogenous, uniform barrier as compared with evaporated Au/GaAs and Ag/GaAs interfaces. We will report on BEEM measurements of the hot electron transfer ratio across the Schottky barrier for the different ferromagnetic materials, and on the energy and spin-dependent hot electron attenuation lengths of the CoFe, Fe, and permalloy films. (1) Sebastiaan van Dijken, Xin Jiang, Stuart S. P. Parkin, APL, 80, 3364.

  10. ELECTRON-BEAM-INDUCED RADIO EMISSION FROM ULTRACOOL DWARFS

    SciTech Connect

    Yu, S.; Doyle, J. G.; Kuznetsov, A.; Hallinan, G.; Antonova, A.; MacKinnon, A. L.; Golden, A.

    2012-06-10

    We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short timescale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic (EM) field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of EM waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70{nu}{sub pe} ({nu}{sub pe} is the electron plasma frequency) in the non-relativistic case and from 10 to 600{nu}{sub pe} in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.

  11. Compact Electron Gun Based on Secondary Emission Through Ionic Bombardment

    PubMed Central

    Diop, Babacar; Bonnet, Jean; Schmid, Thomas; Mohamed, Ajmal

    2011-01-01

    We present a new compact electron gun based on the secondary emission through ionic bombardment principle. The driving parameters to develop such a gun are to obtain a quite small electron gun for an in-flight instrument performing Electron Beam Fluorescence measurements (EBF) on board of a reentry vehicle in the upper atmosphere. These measurements are useful to characterize the gas flow around the vehicle in terms of gas chemical composition, temperatures and velocity of the flow which usually presents thermo-chemical non-equilibrium. Such an instrument can also be employed to characterize the upper atmosphere if placed on another carrier like a balloon. In ground facilities, it appears as a more practical tool to characterize flows in wind tunnel studies or as an alternative to complex electron guns in industrial processes requiring an electron beam. We describe in this paper the gun which has been developed as well as its different features which have been characterized in the laboratory. PMID:22163896

  12. Experimental Studies on Grooved Surfaces to Suppress Secondary Electron Emission

    SciTech Connect

    Suetsugu, Y.; Fukuma, H.; Shibata, K.; Pivi, M.; Wang, L.; /SLAC

    2010-06-15

    Grooved surfaces are effective to suppress the secondary electron emission, and can be a promising technique to mitigate the electron cloud effect in positron/proton storage rings. Aiming for the application in a dipole-type magnetic field, various shapes of triangular grooved surfaces have been studied at KEK. The grooves tested here have vertex angles of 20-30{sup o}, depths of 2.5-5.0 mm, and vertex roundness of 0.05-0.2 mm. In a laboratory, the secondary electron yields (SEY) of small test pieces were measured using an electron beam in a magnetic-free condition. The grooved surfaces clearly had low SEY compared to flat surfaces of the same materials. The grooves with sharper vertexes had smaller SEY. A test chamber installed in a wiggler magnet of the KEKB positron ring was used to investigate the efficacy of the grooved surface in a strong magnetic field. In the chamber, a remarkable reduction in the electron density around the beam orbit was observed compared to the case of a flat surface with TiN coating.

  13. Temperature Coefficient of Secondary Electron Emission: A Novel Thermal Metrology

    NASA Astrophysics Data System (ADS)

    Khan, Md. Imran; Lubner, Sean Daniel; Ogletree, David Frank; Wong, Ed; Dames, Chris

    State of the art nanoscale temperature mapping techniques include Scanning Thermal Microscopy (SThM) and optical thermoreflectance, though these have the challenges of requiring sample contact and being diffraction limited, respectively. Near field scanning optical microscopy (NSOM) can beat the diffraction limit but still cannot measure temperature at 10s of nanometer resolution. SEM is well known for topographic imaging but has not been previously used for thermal mapping. Past literature suggested that secondary electron yields might have a small temperature dependence due to electron-phonon scattering and/or temperature dependence of work function. We previously measured the temperature coefficient of secondary electron emission of several group IV and III-V semiconductors and found it to range from around 100 to 1000 ppm/K. Here, we utilize this to map a spatial temperature gradient in an SEM image. We implement a double-heater structure to produce a temperature gradient along the plane of a substrate. The primary electron beam is scanned across the sample's surface while the emitted (secondary plus backscattered) electron current and net absorbed sample currents are simultaneously recorded. The results demonstrate the ability to map a spatial temperature gradient.

  14. Semi-shunt field emission in electronic devices

    NASA Astrophysics Data System (ADS)

    Karpov, V. G.; Shvydka, Diana

    2014-08-01

    We introduce a concept of semi-shunts representing needle shaped metallic protrusions shorter than the distance between a device electrodes. Due to the lightening rod type of field enhancement, they induce strong electron emission. We consider the corresponding signature effects in photovoltaic applications; they are: low open circuit voltages and exponentially strong random device leakiness. Comparing the proposed theory with our data for CdTe based solar cells, we conclude that stress can stimulate semi-shunts' growth making them shunting failure precursors. In the meantime, controllable semi-shunts can play a positive role mitigating the back field effects in photovoltaics.

  15. Emission of an intense electron beam from a ceramic honeycomb

    NASA Astrophysics Data System (ADS)

    Friedman, M.; Myers, M.; Hegeler, F.; Swanekamp, S. B.; Sethian, J. D.; Ludeking, L.

    2003-01-01

    Inserting a slab of honeycomb ceramic in front of the emitting surface of a large-area cathode improves the electron beam emission uniformity, decreases the beam current rise and fall times, and maintains a more constant diode impedance. Moreover, changing the cathode material from velvet to carbon fiber achieved a more robust cathode that starts to emit at a higher electric field without a degradation in beam uniformity. In addition, an 80% reduction in the postshot diode pressure was also observed when gamma alumina was deposited on the ceramic. A possible explanation is that reabsorption and recycling of adsorbed gases takes place.

  16. Laser excitation of clusters: observables from electron emission

    NASA Astrophysics Data System (ADS)

    Wopperer, P.; Dinh, P. M.; Reinhard, P. G.; Suraud, E.

    2012-11-01

    We give a brief review of the theoretical description of photo-electron spectra (PES) and photo-angular distributions (PAD) and discuss a few selected, typical results. The description is based on time-dependent density-functional theory at the level of the local-density approximation augmented by a self-interaction correction which is crucial for a quantitative assessment of emission processes. Coordinate-space grids are used together with absorbing boundary conditions. We discuss the basic features and trends of PES and PAD for two typical test cases, the clusters Na8 and C60.

  17. Hot Electron Transport Properties of Thin Copper Films Using Ballistic Electron Emission Microscopy

    NASA Astrophysics Data System (ADS)

    Garramone, J. J.; Abel, J. R.; Sitnitsky, I. L.; Zhao, L.; Appelbaum, I.; Labella, V. P.

    2009-03-01

    Copper is widely used material for electrical interconnects within integrated circuits and recently as a base layer for hot electron spin injection and readout into silicon. Integral to both their applications is the knowledge of the electron scattering length. To the best of our knowledge, little work exists that directly measures the scattering length of electrons in copper. In this study we used ballistic electron emission microscopy (BEEM) to measure the hot electron attenuation length of copper thin films deposited on Si(001). BEEM is a three terminal scanning tunneling microcopy (STM) based technique that can measure transport and Schottky heights of metal/semiconductor systems. We find a Schottky height of 0.67 eV and an attenuation length approaching 40 nm just above the Schottky height at 77 K. We also measure a decrease in the attenuation length with increasing tip bias to determine the relative roles of inelastic and elastic scattering.

  18. Chemical characteristics of Siberian boreal forest fire emissions

    NASA Astrophysics Data System (ADS)

    Engling, G.; Popovicheva, O.; Fan, T. S.; Eleftheriadis, K.; Diapouli, E.; Kozlov, V.

    2014-12-01

    Smoke emissions from Siberian boreal forest fires exert critical impacts on the aerosol/climate system of subarctic regions and the Arctic. It is, therefore, crucial to assess the ability of such particles to absorb/scatter incoming solar radiation as well as act as cloud condensation nuclei, which is closely linked to the physical and chemical aerosol properties. However, observations of Siberian wildfire emissions are limited, and no systematic database of smoke particle properties is available for this region to date. As part of this study, ambient aerosol samples were collected during two smoke episodes in Tomsk, Siberia, in the summers of 2012 and 2013. In addition, the chemical composition and optical properties of smoke particles derived from the combustion of typical Siberian fuels, including pine wood and debris, were determined during chamber burn experiments in a large aerosol/combustion chamber under controlled combustion conditions representative of wildfires and prescribed burns. Detailed multi-component characterization of individual particles and bulk properties was accomplished with a suite of techniques, including various types of chromatography, microscopy, spectroscopy, and thermo-optical analysis. Individual particle analysis by SEM-EDX combined with cluster analysis revealed characteristic smoke structural components and major types of particles, which allowed to discriminate between flaming and smoldering regimes, reflected in specific morphological and chemical microstructure. The physicochemical properties representing the combustion phase (smoldering versus flaming) and the degree of processing (fresh versus aged) were assessed in the ambient aerosol based on the chamber burn results. For instance, some chemical transformation (aging of smoke particles) was noticed over a period of two days in the absence of sun light in the combustion chamber for certain chemical species, while the molecular tracer levoglucosan appeared to be rather

  19. Underestimated role of the secondary electron emission in the space

    NASA Astrophysics Data System (ADS)

    Nemecek, Zdenek; Richterova, Ivana; Safrankova, Jana; Pavlu, Jiri; Vaverka, Jakub; Nouzak, Libor

    2016-07-01

    Secondary electron emission (SEE) is one of many processes that charges surfaces of bodies immersed into a plasma. Until present, a majority of considerations in theories and experiments is based on the sixty year old description of an interaction of planar metallic surfaces with electrons, thus the effects of a surface curvature, roughness, presence of clusters as well as an influence of the material conductance on different aspects of this interaction are neglected. Dust grains or their clusters can be frequently found in many space environments - interstellar clouds, atmospheres of planets, tails of comets or planetary rings are only typical examples. The grains are exposed to electrons of different energies and they can acquire positive or negative charge during this interaction. We review the progress in experimental investigations and computer simulations of the SEE from samples relevant to space that was achieved in course of the last decade. We present a systematic study of well-defined systems that starts from spherical grains of various diameters and materials, and it continues with clusters consisting of different numbers of small spherical grains that can be considered as examples of real irregularly shaped space grains. The charges acquired by investigated objects as well as their secondary emission yields are calculated using the SEE model. We show that (1) the charge and surface potential of clusters exposed to the electron beam are influenced by the number of grains and by their geometry within a particular cluster, (2) the model results are in an excellent agreement with the experiment, and (3) there is a large difference between charging of a cluster levitating in the free space and that attached to a planar surface. The calculation provides a reduction of the secondary electron emission yield of the surface covered by dust clusters by a factor up to 1.5 with respect to the yield of a smooth surface. (4) These results are applied on charging of

  20. Electron-cyclotron maser and solar microwave millisecond spike emission

    NASA Technical Reports Server (NTRS)

    Li, Hong-Wei; Li, Chun-Sheng; Fu, Qi-Jun

    1986-01-01

    An intense solar microwave millisecond spike emission (SMMSE) event was observed on May 16, 1981 by Zhao and Jin at Beijing Observatory. The peak flux density of the spikes is high to 5 x 100,000 s.f.u. and the corresponding brightness temperature (BT) reaches approx. 10 to the 15th K. In order to explain the observed properties of SMMSE, it is proposed that a beam of electrons with energy of tens KeV injected from the acceleration region downwards into an emerging magnetic arch forms so-called hollow beam distribution and causes electron-cyclotron maser (ECM) instability. The growth rate of second harmonic X-mode is calculated and its change with time is deduced. It is shown that the saturation time of ECM is t sub s approx. equals 0.42 ms and only at last short stage (delta t less than 0.2 t sub s) the growth rate decreases to zero rather rapidly. So a SMMSE with very high BT will be produced if the ratio of number density of nonthermal electrons to that of background electrons, n sub s/n sub e, is larger than 4 x .00001.

  1. Metal-Insulator Photocathode Heterojunction for Directed Electron Emission

    SciTech Connect

    Droubay, Timothy C.; Chambers, Scott A.; Joly, Alan G.; Hess, Wayne P.; Nemeth, Karoly; Harkay, Katherine C.; Spentzouris, Linda

    2014-02-14

    New photocathode materials capable of producing intense and directed electron pulses are needed for development of next generation light sources and dynamic transmission electron microscopy. Ideal photocathodes should have high photoemission quantum efficiency (QE) and be capable of delivering collimated and well-shaped pulses of consistent charge under high-field operating conditions. High-brightness and low-intrinsic emittance electron pulses have been predicted for hybrid metal-insulator photocathode designs constructed from three to four monolayer MgO films on atomically flat silver. Here we use angle-resolved photoelectron spectroscopy to confirm directional photoemission and a large increase in QE under ultraviolet laser excitation of an ultrathin MgO film on Ag(001). We observe new low-binding energy photoemission, not seen for Ag(001), and greater electron emission in the normal direction. Under 4.66 eV laser excitation, the photoemission quantum efficiency of the MgO/Ag(001) hybrid photocathode is a factor of seven greater than that for clean Ag(001).

  2. Space charge corrected electron emission from an aluminum surface under non-equilibrium conditions

    SciTech Connect

    Wendelen, W.; Bogaerts, A.; Mueller, B. Y.; Rethfeld, B.; Autrique, D.

    2012-06-01

    A theoretical study has been conducted of ultrashort pulsed laser induced electron emission from an aluminum surface. Electron emission fluxes retrieved from the commonly employed Fowler-DuBridge theory were compared to fluxes based on a laser-induced non-equilibrium electron distribution. As a result, the two- and three-photon photoelectron emission parameters for the Fowler-DuBridge theory have been approximated. We observe that at regimes where photoemission is important, laser-induced electron emission evolves in a more smooth manner than predicted by the Fowler-DuBridge theory. The importance of the actual electron distribution decreases at higher laser fluences, whereas the contribution of thermionic emission increases. Furthermore, the influence of a space charge effect on electron emission was evaluated by a one dimensional particle-in-cell model. Depending on the fluences, the space charge reduces the electron emission by several orders of magnitude. The influence of the electron emission flux profiles on the effective electron emission was found to be negligible. However, a non-equilibrium electron velocity distribution increases the effective electron emission significantly. Our results show that it is essential to consider the non-equilibrium electron distribution as well as the space charge effect for the description of laser-induced photoemission.

  3. Characteristics of an electron-beam rocket pellet accelerator

    SciTech Connect

    Tsai, C.C.; Foster, C.A.; Milora, S.L.; Schechter, D.E.

    1991-01-01

    A proof-of-principle (POP) electron-beam pellet accelerator has been developed and used for accelerating hydrogen and deuterium pellets. An intact hydrogen pellet was accelerated to a speed of 460 m/s by an electron beam of 13.5 keV. 0.3 A, and 2 ms. The maximum speed is limited by the acceleration path length (0.4 m) and pellet integrity. Experimental data have been collected for several hundred hydrogen pellets, which were accelerated by electron beams with parameters of voltage up to 16 kV, current up to 0.4 A, and pulse length up to 10 ms. Preliminary results reveal that the measured burn velocity increases roughly with the square of the beam voltage, as the theoretical model predicts. The final pellet velocity is proportional to the exhaust velocity, which increases with the beam power. To reach the high exhaust velocity needed for accelerating pellets to >1000 m/s, a new electron gun, with its cathode indirectly heated by a graphite heater and an electron beam, is being developed to increase beam current and power. A rocket casing or shell around the pellet has been designed and developed to increase pellet strength and improve the electron-rocket coupling efficiency. We present the characteristics of this pellet accelerator, including new improvements. 13 refs., 6 figs.

  4. Electron-phonon interactions in silicon: Mean free paths, related distributions and transport characteristics

    NASA Astrophysics Data System (ADS)

    Akkerman, Avraham; Murat, Michael

    2015-05-01

    The mean free path (MFP) for electron-phonon interactions in pure silicon is an important characteristic needed both for low energy electron transport calculations using Boltzmann transport equation, and for Monte Carlo simulations. Full band calculations present a basic (though complicated) approach to the solution of the problem. Simpler approaches based on analytical presentation of the scattering rates have also been used; however they are valid for a restricted range of electron energies, below 2 eV. In this paper we introduce a hybrid method that utilizes the density of energy states calculated from the full band calculations for electron energies larger than 2 eV, allowing to extend the analytical approach for energies up to 5 eV, where the impact ionization becomes the dominant mechanism of electron interactions within bulk silicon. The resulting MFPs as function of electron energy and lattice temperature, together with the integral probability distribution for given energy losses by phonon emission (or energy gain by absorption of phonons) form the database for Monte Carlo calculations. Using this method, we calculate the electron diffusivity and mobility as function of the electron and lattice temperatures. These parameters are important for solution of the two temperature model, used for calculations of the track structure created by swift ions and nanosecond laser beams.

  5. Feasibility study for a correlation electron cyclotron emission turbulence diagnostic based on nonlinear gyrokinetic simulations

    NASA Astrophysics Data System (ADS)

    White, A. E.; Howard, N. T.; Mikkelsen, D. R.; Greenwald, M.; Candy, J.; Waltz, R. E.

    2011-11-01

    This paper describes the use of nonlinear gyrokinetic simulations to assess the feasibility of a new correlation electron cyclotron emission (CECE) diagnostic that has been proposed for the Alcator C-Mod tokamak (Marmar et al 2009 Nucl. Fusion 49 104014). This work is based on a series of simulations performed with the GYRO code (Candy and Waltz 2003 J. Comput. Phys. 186 545). The simulations are used to predict ranges of fluctuation level, peak poloidal wavenumber and radial correlation length of electron temperature fluctuations in the core of the plasma. The impact of antenna pattern and poloidal viewing location on measurable turbulence characteristics is addressed using synthetic diagnostics. An upper limit on the CECE sample volume size is determined. The modeling results show that a CECE diagnostic capable of measuring transport-relevant, long-wavelength (kθρs < 0.5) electron temperature fluctuations is feasible at Alcator C-Mod.

  6. 47 CFR 2.201 - Emission, modulation, and transmission characteristics.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... frequency emissions, continuous wave and pulse radars, etc. (1) No information transmitted N (2) Telegraphy..., telemetry, telecommand D (6) Telephony (including sound broadcasting) E (7) Television (video) F...

  7. Methods for measurement of electron emission yield under low energy electron-irradiation by collector method and Kelvin probe method

    SciTech Connect

    Tondu, Thomas; Belhaj, Mohamed; Inguimbert, Virginie

    2010-09-15

    Secondary electron emission yield of gold under electron impact at normal incidence below 50 eV was investigated by the classical collector method and by the Kelvin probe method. The authors show that biasing a collector to ensure secondary electron collection while keeping the target grounded can lead to primary electron beam perturbations. Thus reliable secondary electron emission yield at low primary electron energy cannot be obtained with a biased collector. The authors present two collector-free methods based on current measurement and on electron pulse surface potential buildup (Kelvin probe method). These methods are consistent, but at very low energy, measurements become sensitive to the earth magnetic field (below 10 eV). For gold, the authors can extrapolate total emission yield at 0 eV to 0.5, while a total electron emission yield of 1 is obtained at 40{+-}1 eV.

  8. Electron field emission from freestanding Diamond nanomembranes and Application to time-of-flight mass spectrometry

    NASA Astrophysics Data System (ADS)

    Kim, Hyunseok; Park, Jonghoo; Shin, Hyuncheol; Blick, Robert H.

    2013-03-01

    We introduce a prototype of a freestanding diamond nanomembrane for large protein detection in time-of-flight mass spectrometry. Doped diamond as a material for mass spectroscopy is extremely interesting due to its mechanical and electrical properties. The freestanding diamond nanomembranes we are able to fabricate have lateral extensions of 400 μm × 400 μm with a thickness of 100nm. We employ optical lithography and a Buffered Oxide Etch (BOE) of SiO2 followed by anisotropic etching of the substrate silicon using TMAH solution and finally removing SiO2. The electron field emission from the surface of the membrane is traced in the IV characteristics at room temperature. The membrane is then applied for detection of the large ionized proteins using time-of-flight mass spectrometry. Ion detection is demonstrated in our nanomembrane MALDI-TOF analysis of Insulin (5,735 Da). That is when the ions with a large kinetic energy bombard the nanomembrane, their energy is thermalized upon impact into phonons. The phonons give a thermal energy to the electrons with the membrane, which are then excited to higher energetic states. Given an extraction voltage this leads to electron field emission from the membrane which we labeled phonon-assisted field emission (PAFE). In other words, the MALDI mass spectra are obtained by exploiting ballistic phonon propagation and quasi-diffusive phonon propagation.

  9. Optical emission characteristics of surface nanosecond pulsed dielectric barrier discharge plasma

    SciTech Connect

    Wu Yun; Li Yinghong; Jia Min; Song Huimin; Liang Hua

    2013-01-21

    This paper reports an experimental study of the optical emission characteristics of the surface dielectric barrier discharge plasma excited by nanosecond pulsed voltage. N{sub 2}(C{sup 3}{Pi}{sub u}) rotational and vibrational temperatures are almost the same with upper electrode powered with positive polarity and lower electrode grounded or upper electrode grounded and lower electrode powered with positive polarity. While the electron temperature is 12% higher with upper electrode powered with positive polarity and lower electrode grounded. When the frequency is below 2000 Hz, there is almost no influence of applied voltage amplitude and frequency on N{sub 2}(C{sup 3}{Pi}{sub u}) rotational, vibrational temperature and electron temperature. As the pressure decreases from 760 Torr to 5 Torr, N{sub 2}(C{sup 3}{Pi}{sub u}) rotational temperature remains almost unchanged, while its vibrational temperature decreases initially and then increases. The discharge mode changes from a filamentary type to a glow type around 80 Torr. In the filamentary mode, the electron temperature remains almost unchanged. In the glow mode, the electron temperature increases while the pressure decreases.

  10. Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics

    PubMed Central

    2013-01-01

    Vertically aligned single-crystal InSb nanowires were synthesized via the electrochemical method at room temperature. The characteristics of Fourier transform infrared spectrum revealed that in the syntheses of InSb nanowires, energy bandgap shifts towards the short wavelength with the occurrence of an electron accumulation layer. The current–voltage curve, based on the metal–semiconductor–metal model, showed a high electron carrier concentration of 2.0 × 1017 cm−3 and a high electron mobility of 446.42 cm2 V−1 s−1. Additionally, the high carrier concentration of the InSb semiconductor with the surface accumulation layer induced a downward band bending effect that reduces the electron tunneling barrier. Consequently, the InSb nanowires exhibit significant field emission properties with an extremely low turn-on field of 1.84 V μm−1 and an estimative threshold field of 3.36 V μm−1. PMID:23399075