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Sample records for field emitters based

  1. Field emitter based extractor gauges and residual gas analyzers

    SciTech Connect

    Changkun Dong; G. Rao Myneni

    1999-04-01

    Attempts at using the Spindt-type molybdenum field emitter arrays in the extractor gauges and a residual gas analyzer are presented in this article. The sensitivity of the fuel emitter gauge is as high as 11 Torr{sup -1}. The departure from linearity of the pressure versus ion current measurements did not exceed 10% over the pressure range of 10{sup -10} - 10{sup -6} Torr. Stable sensitivities for nitrogen, helium, and hydrogen were achieved below 10{sup -7} Torr with the field emitter residual gas analyzer. The slightly reduced emission current and sensitivity, after long-term operation, are of concern and need to be addressed. Residual gas spectra indicate that when using field emitters, the electron stimulated desorption ions (O{sup +}, F{sup +}, and Cl{sup +}) are reduced as compared to those made using a hot filament source.

  2. Asymmetrical field emitter

    DOEpatents

    Fleming, J.G.; Smith, B.K.

    1995-10-10

    A method is disclosed for providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure. 17 figs.

  3. Diamond fiber field emitters

    DOEpatents

    Blanchet-Fincher, Graciela B.; Coates, Don M.; Devlin, David J.; Eaton, David F.; Silzars, Aris K.; Valone, Steven M.

    1996-01-01

    A field emission electron emitter comprising an electrode formed of at least one diamond, diamond-like carbon or glassy carbon composite fiber, said composite fiber having a non-diamond core and a diamond, diamond-like carbon or glassy carbon coating on said non-diamond core, and electronic devices employing such a field emission electron emitter.

  4. Pulsed hybrid field emitter

    DOEpatents

    Sampayan, Stephen E.

    1998-01-01

    A hybrid emitter exploits the electric field created by a rapidly depoled ferroelectric material. Combining the emission properties of a planar thin film diamond emitter with a ferroelectric alleviates the present technological problems associated with both types of emitters and provides a robust, extremely long life, high current density cathode of the type required by emerging microwave power generation, accelerator technology and display applications. This new hybrid emitter is easy to fabricate and not susceptible to the same failures which plague microstructure field emitter technology. Local electrode geometries and electric field are determined independently from those for optimum transport and brightness preservation. Due to the large amount of surface charge created on the ferroelectric, the emitted electrons have significant energy, thus eliminating the requirement for specialized phosphors in emissive flat-panel displays.

  5. Pulsed hybrid field emitter

    DOEpatents

    Sampayan, S.E.

    1998-03-03

    A hybrid emitter exploits the electric field created by a rapidly depoled ferroelectric material. Combining the emission properties of a planar thin film diamond emitter with a ferroelectric alleviates the present technological problems associated with both types of emitters and provides a robust, extremely long life, high current density cathode of the type required by emerging microwave power generation, accelerator technology and display applications. This new hybrid emitter is easy to fabricate and not susceptible to the same failures which plague microstructure field emitter technology. Local electrode geometries and electric field are determined independently from those for optimum transport and brightness preservation. Due to the large amount of surface charge created on the ferroelectric, the emitted electrons have significant energy, thus eliminating the requirement for specialized phosphors in emissive flat-panel displays. 11 figs.

  6. Systems and Methods for Implementing Robust Carbon Nanotube-Based Field Emitters

    NASA Technical Reports Server (NTRS)

    Manohara, Harish (Inventor); Kristof, Valerie (Inventor); Toda, Risaku (Inventor)

    2015-01-01

    Systems and methods in accordance with embodiments of the invention implement carbon nanotube-based field emitters. In one embodiment, a method of fabricating a carbon nanotube field emitter includes: patterning a substrate with a catalyst, where the substrate has thereon disposed a diffusion barrier layer; growing a plurality of carbon nanotubes on at least a portion of the patterned catalyst; and heating the substrate to an extent where it begins to soften such that at least a portion of at least one carbon nanotube becomes enveloped by the softened substrate.

  7. Stationary scanning x-ray source based on carbon nanotube field emitters

    NASA Astrophysics Data System (ADS)

    Yang, Guang; Zhang, Jian; Cheng, Yuan; Gao, Bo; Qiu, Qi; Lee, Yueh; Lu, Jianping; Zhou, Otto

    2006-03-01

    Carbon nanotube is an ideal field emitter thanks to its large aspect ratio and small diameter. Based on its field emission property, we have developed a stationary scanning x-ray source, which can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal-oxide-semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis.

  8. Field emitters with nanoscale tips based on Mo oxide fabricated by electrochemical methods

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Takeo; Sato, Takahiro; Kitamura, Shin; Kitao, Akiko; Kubota, Oichi; Ozaki, Eiji; Motoi, Taiko

    2016-04-01

    Field emitters with nanoscale tips and a fabrication technique using a nanoscale gap are described. Each fabrication technique makes it possible to form emitters on a meter-scale glass substrate. The emitter has a configuration with one side gate to reduce the electron scattering losses at the counter electrode to improve the emission efficiency. All thin film layers constituting the emitter are fabricated by plasma-enhanced chemical vapor deposition and sputtering deposition. Nanoscale tips are formed between a shallow gap less than 7 nm deep by the joule heating of a Mo complex oxide, which is produced by the electro chemical etching of a deposited Mo layer. To our knowledge, this is the first work that shows a uniform efficiency of 5% or more achieved at an anode voltage of 10 kV and an operation voltage of 23 V.

  9. Planar Field Emitters and High Efficiency Photocathodes Based on Ultrananocrystalline Diamond

    NASA Technical Reports Server (NTRS)

    Sumant, Anirudha V. (Inventor); Baryshev, Sergey V. (Inventor); Antipov, Sergey P. (Inventor)

    2016-01-01

    A method of forming a field emitter comprises disposing a first layer on a substrate. The first layer is seeded with nanodiamond particles. The substrate with the first layer disposed thereon is maintained at a first temperature and a first pressure in a mixture of gases which includes nitrogen. The first layer is exposed to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, which has a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %. The field emitter has about 10.sup.12 to about 10.sup.14 emitting sites per cm.sup.2. A photocathode can also be formed similarly by forming a nitrogen doped ultrananocrystalline diamond film on a substrate similar to the field emitter, and then hydrogen terminating the film. The photocathode is responsive to near ultraviolet light as well as to visible light.

  10. Planar field emitters and high efficiency photocathodes based on ultrananocrystalline diamond

    DOEpatents

    Sumant, Anirudha V.; Baryshev, Sergey V.; Antipov, Sergey P.

    2016-08-16

    A method of forming a field emitter comprises disposing a first layer on a substrate. The first layer is seeded with nanodiamond particles. The substrate with the first layer disposed thereon is maintained at a first temperature and a first pressure in a mixture of gases which includes nitrogen. The first layer is exposed to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, which has a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %. The field emitter has about 10.sup.12 to about 10.sup.14 emitting sites per cm.sup.2. A photocathode can also be formed similarly by forming a nitrogen doped ultrananocrystalline diamond film on a substrate similar to the field emitter, and then hydrogen terminating the film. The photocathode is responsive to near ultraviolet light as well as to visible light.

  11. Limit of validity of the thermionic-field-emission treatment of electron injection across emitter-base junctions in abrupt heterojunction bipolar transistors

    NASA Astrophysics Data System (ADS)

    Kumar, T.; Cahay, M.; Shi, S.; Roenker, K.; Stanchina, W. E.

    1995-06-01

    A hybrid model is developed to simulate electron transport through the emitter-base heterojunction and the base region of abrupt heterojunction bipolar transistors. The energy distribution of the injected electron flux through the emitter-base junction is calculated using a rigorous quantum-mechanical treatment of electron tunneling and thermionic emission across the spike at the emitter-base junction. The results are compared with those predicted by the conventional thermionic-field-emission model. For both models, the electron fluxes injected across the emitter-base junction are used as initial energy distributions in a regional Monte Carlo calculation to model electron transport through the base. The average base transit times are calculated using the impulse response technique as a function of the emitter-base voltage. The differences between the thermionic-field-emission model and the rigorous quantum-mechanical approaches to model electron transport through abrupt heterojunction bipolar transistors are pointed out.

  12. Shielding in ungated field emitter arrays

    NASA Astrophysics Data System (ADS)

    Harris, J. R.; Jensen, K. L.; Shiffler, D. A.; Petillo, J. J.

    2015-05-01

    Cathodes consisting of arrays of high aspect ratio field emitters are of great interest as sources of electron beams for vacuum electronic devices. The desire for high currents and current densities drives the cathode designer towards a denser array, but for ungated emitters, denser arrays also lead to increased shielding, in which the field enhancement factor β of each emitter is reduced due to the presence of the other emitters in the array. To facilitate the study of these arrays, we have developed a method for modeling high aspect ratio emitters using tapered dipole line charges. This method can be used to investigate proximity effects from similar emitters an arbitrary distance away and is much less computationally demanding than competing simulation approaches. Here, we introduce this method and use it to study shielding as a function of array geometry. Emitters with aspect ratios of 102-104 are modeled, and the shielding-induced reduction in β is considered as a function of tip-to-tip spacing for emitter pairs and for large arrays with triangular and square unit cells. Shielding is found to be negligible when the emitter spacing is greater than the emitter height for the two-emitter array, or about 2.5 times the emitter height in the large arrays, in agreement with previously published results. Because the onset of shielding occurs at virtually the same emitter spacing in the square and triangular arrays, the triangular array is preferred for its higher emitter density at a given emitter spacing. The primary contribution to shielding in large arrays is found to come from emitters within a distance of three times the unit cell spacing for both square and triangular arrays.

  13. Shielding in ungated field emitter arrays

    SciTech Connect

    Harris, J. R.; Jensen, K. L.; Shiffler, D. A.; Petillo, J. J.

    2015-05-18

    Cathodes consisting of arrays of high aspect ratio field emitters are of great interest as sources of electron beams for vacuum electronic devices. The desire for high currents and current densities drives the cathode designer towards a denser array, but for ungated emitters, denser arrays also lead to increased shielding, in which the field enhancement factor β of each emitter is reduced due to the presence of the other emitters in the array. To facilitate the study of these arrays, we have developed a method for modeling high aspect ratio emitters using tapered dipole line charges. This method can be used to investigate proximity effects from similar emitters an arbitrary distance away and is much less computationally demanding than competing simulation approaches. Here, we introduce this method and use it to study shielding as a function of array geometry. Emitters with aspect ratios of 10{sup 2}–10{sup 4} are modeled, and the shielding-induced reduction in β is considered as a function of tip-to-tip spacing for emitter pairs and for large arrays with triangular and square unit cells. Shielding is found to be negligible when the emitter spacing is greater than the emitter height for the two-emitter array, or about 2.5 times the emitter height in the large arrays, in agreement with previously published results. Because the onset of shielding occurs at virtually the same emitter spacing in the square and triangular arrays, the triangular array is preferred for its higher emitter density at a given emitter spacing. The primary contribution to shielding in large arrays is found to come from emitters within a distance of three times the unit cell spacing for both square and triangular arrays.

  14. Nitrogen incorporated ultrananocrystalline diamond based field emitter array for a flat-panel x-ray source

    NASA Astrophysics Data System (ADS)

    Posada, Chrystian M.; Grant, Edwin J.; Divan, Ralu; Sumant, Anirudha V.; Rosenmann, Daniel; Stan, Liliana; Lee, Hyoung K.; Castaño, Carlos H.

    2014-04-01

    A field emission based flat-panel transmission x-ray source is being developed as an alternative for medical and industrial imaging. A field emitter array (FEA) prototype based on nitrogen incorporated ultrananocrystalline diamond film has been fabricated to be used as the electron source of this flat panel x-ray source. The FEA prototype was developed using conventional microfabrication techniques. The field emission characteristics of the FEA prototype were evaluated. Results indicated that emission current densities of the order of 6 mA/cm2 could be obtained at electric fields as low as 10 V/μm to 20 V/μm. During the prototype microfabrication process, issues such as delamination of the extraction gate and poor etching of the SiO2 insulating layer located between the emitters and the extraction layer were encountered. Consequently, alternative FEA designs were investigated. Experimental and simulation data from the first FEA prototype were compared and the results were used to evaluate the performance of alternative single and double gate designs that would yield better field emission characteristics compared to the first FEA prototype. The best simulation results are obtained for the double gate FEA design, when the diameter of the collimator gate is around 2.6 times the diameter of the extraction gate.

  15. Flat Panel Light Source with Lateral Gate Structure Based on SiC Nanowire Field Emitters

    NASA Astrophysics Data System (ADS)

    Youh, Meng-Jey; Tseng, Chun-Lung; Jhuang, Meng-Han; Chiu, Sheng-Cheng; Huang, Li-Hu; Gong, Jyun-An; Li, Yuan-Yao

    2015-06-01

    A field-emission light source with high luminance, excellent luminance uniformity, and tunable luminance characteristics with a novel lateral-gate structure is demonstrated. The lateral-gate triode structure comprises SiC nanowire emitters on a Ag cathode electrode and a pair of Ag gate electrodes placed laterally on both sides of the cathode. The simple and cost-effective screen printing technique is employed to pattern the lateral-gates and cathode structure on soda lime glass. The area coverage of the screen-printed cathode and gates on the glass substrate (area: 6 × 8 cm2) is in the range of 2.04% - 4.74% depending on the set of cathode-gate electrodes on the substrate. The lateral-gate structure with its small area coverage exhibits a two-dimensional luminance pattern with high brightness and good luminance uniformity. A maximum luminance of 10952 cd/cm2 and a luminance uniformity of >90% can be achieved with a gate voltage of 500 V and an anode voltage of 4000 V, with an anode current of 1.44 mA and current leakage to the gate from the cathode of about 10%.

  16. Flat Panel Light Source with Lateral Gate Structure Based on SiC Nanowire Field Emitters.

    PubMed

    Youh, Meng-Jey; Tseng, Chun-Lung; Jhuang, Meng-Han; Chiu, Sheng-Cheng; Huang, Li-Hu; Gong, Jyun-An; Li, Yuan-Yao

    2015-01-01

    A field-emission light source with high luminance, excellent luminance uniformity, and tunable luminance characteristics with a novel lateral-gate structure is demonstrated. The lateral-gate triode structure comprises SiC nanowire emitters on a Ag cathode electrode and a pair of Ag gate electrodes placed laterally on both sides of the cathode. The simple and cost-effective screen printing technique is employed to pattern the lateral-gates and cathode structure on soda lime glass. The area coverage of the screen-printed cathode and gates on the glass substrate (area: 6 × 8 cm(2)) is in the range of 2.04% - 4.74% depending on the set of cathode-gate electrodes on the substrate. The lateral-gate structure with its small area coverage exhibits a two-dimensional luminance pattern with high brightness and good luminance uniformity. A maximum luminance of 10,952 cd/cm(2) and a luminance uniformity of >90% can be achieved with a gate voltage of 500 V and an anode voltage of 4000 V, with an anode current of 1.44 mA and current leakage to the gate from the cathode of about 10%. PMID:26042359

  17. Flat Panel Light Source with Lateral Gate Structure Based on SiC Nanowire Field Emitters

    PubMed Central

    Youh, Meng-Jey; Tseng, Chun-Lung; Jhuang, Meng-Han; Chiu, Sheng-Cheng; Huang, Li-Hu; Gong, Jyun-An; Li, Yuan-Yao

    2015-01-01

    A field-emission light source with high luminance, excellent luminance uniformity, and tunable luminance characteristics with a novel lateral-gate structure is demonstrated. The lateral-gate triode structure comprises SiC nanowire emitters on a Ag cathode electrode and a pair of Ag gate electrodes placed laterally on both sides of the cathode. The simple and cost-effective screen printing technique is employed to pattern the lateral-gates and cathode structure on soda lime glass. The area coverage of the screen-printed cathode and gates on the glass substrate (area: 6 × 8 cm2) is in the range of 2.04% – 4.74% depending on the set of cathode-gate electrodes on the substrate. The lateral-gate structure with its small area coverage exhibits a two-dimensional luminance pattern with high brightness and good luminance uniformity. A maximum luminance of 10952 cd/cm2 and a luminance uniformity of >90% can be achieved with a gate voltage of 500 V and an anode voltage of 4000 V, with an anode current of 1.44 mA and current leakage to the gate from the cathode of about 10%. PMID:26042359

  18. Stationary scanning x-ray source based on carbon nanotube field emitters

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Yang, G.; Cheng, Y.; Gao, B.; Qiu, Q.; Lee, Y. Z.; Lu, J. P.; Zhou, O.

    2005-05-01

    We report a field emission x-ray source that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal-oxide-semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis with a simplified experimental setup.

  19. Stationary scanning x-ray source based on carbon nanotube field emitters

    SciTech Connect

    Zhang, J.; Yang, G.; Cheng, Y.; Gao, B.; Qiu, Q.; Lee, Y.Z.; Lu, J.P.; Zhou, O.

    2005-05-02

    We report a field emission x-ray source that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal-oxide-semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis with a simplified experimental setup.

  20. Group-III Nitride Field Emitters

    NASA Technical Reports Server (NTRS)

    Bensaoula, Abdelhak; Berishev, Igor

    2008-01-01

    Field-emission devices (cold cathodes) having low electron affinities can be fabricated through lattice-mismatched epitaxial growth of nitrides of elements from group III of the periodic table. Field emission of electrons from solid surfaces is typically utilized in vacuum microelectronic devices, including some display devices. The present field-emission devices and the method of fabricating them were developed to satisfy needs to reduce the cost of fabricating field emitters, make them compatible with established techniques for deposition of and on silicon, and enable monolithic integration of field emitters with silicon-based driving circuitry. In fabricating a device of this type, one deposits a nitride of one or more group-III elements on a substrate of (111) silicon or other suitable material. One example of a suitable deposition process is chemical vapor deposition in a reactor that contains plasma generated by use of electron cyclotron resonance. Under properly chosen growth conditions, the large mismatch between the crystal lattices of the substrate and the nitride causes strains to accumulate in the growing nitride film, such that the associated stresses cause the film to crack. The cracks lie in planes parallel to the direction of growth, so that the growing nitride film becomes divided into microscopic growing single-crystal columns. The outer ends of the fully-grown columns can serve as field-emission tips. By virtue of their chemical compositions and crystalline structures, the columns have low work functions and high electrical conductivities, both of which are desirable for field emission of electrons. From examination of transmission electron micrographs of a prototype device, the average column width was determined to be about 100 nm and the sharpness of the tips was determined to be characterized by a dimension somewhat less than 100 nm. The areal density of the columns was found to about 5 x 10(exp 9)/sq cm . about 4 to 5 orders of magnitude

  1. Silicon based light emitters utilizing radiation from dislocations; electric field induced shift of the dislocation-related luminescence

    NASA Astrophysics Data System (ADS)

    Arguirov, T.; Mchedlidze, T.; Kittler, M.; Reiche, M.; Wilhelm, T.; Hoang, T.; Holleman, J.; Schmitz, J.

    2009-05-01

    Dislocation rich regions can be controllably formed at a certain location inside a silicon wafer. We studied the light emission properties of such regions located in an electric field of a p-n junction under different excitation conditions. It was found that the luminescence spectra of the dislocations are significantly influenced by the presence of the junction. The dislocation-related luminescence peak position appears red-shifted due to the built-in electric field. A suppression of that field by photo-generation of carriers or by applying a forward bias voltage at the junction leads to a gradual decrease in the energy position of the peaks. The dependence of the peak position on the electric field was found to be a quadratic function, similar to that observed for semiconductor nanostructures. We show that the shift of the peak position is due to the Stark effect on dislocation-related excitonic states. The characteristic constant of the shift, obtained by fitting the data with the quadratic Stark effect equation, was 0.0186 meV/(kV/cm) 2. The observed effect opens new possibilities for integration of a silicon based light emitter, combining the radiation from dislocations with a Stark effect based modulator.

  2. A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

    NASA Astrophysics Data System (ADS)

    Heo, Sung Hwan; Kim, Hyun Jin; Ha, Jun Mok; Cho, Sung Oh

    2012-05-01

    A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy·cm2 min-1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution.

  3. A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

    PubMed Central

    2012-01-01

    A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy·cm2 min−1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution. PMID:22594627

  4. Physical electrostatics of small field emitter arrays/clusters

    NASA Astrophysics Data System (ADS)

    Forbes, Richard G.

    2016-08-01

    This paper aims to improve qualitative understanding of electrostatic influences on apex field enhancement factors (AFEFs) for small field emitter arrays/clusters. Using the "floating sphere at emitter-plate potential" (FSEPP) model, it re-examines the electrostatics and mathematics of three simple systems of identical post-like emitters. For the isolated emitter, various approaches are noted. An adequate approximation is to consider only the effects of sphere charges and (for significantly separated emitters) image charges. For the 2-emitter system, formulas are found for charge-transfer ("charge-blunting") effects and neighbor-field effects, for widely spaced and for "sufficiently closely spaced" emitters. Mutual charge-blunting is always the dominant effect, with a related (negative) fractional AFEF-change δtwo. For sufficiently small emitter spacing c, |δtwo| varies approximately as 1/c; for large spacing, |δtwo| decreases as 1/c3. In a 3-emitter equispaced linear array, differential charge-blunting and differential neighbor-field effects occur, but differential charge-blunting effects are dominant, and cause the "exposed" outer emitters to have higher AFEF (γ0) than the central emitter (γ1). Formulas are found for the exposure ratio Ξ = γ0/γ1, for large and for sufficiently small separations. The FSEPP model for an isolated emitter has accuracy around 30%. Line-charge models (LCMs) are an alternative, but an apparent difficulty with recent LCM implementations is identified. Better descriptions of array electrostatics may involve developing good fitting equations for AFEFs derived from accurate numerical solution of Laplace's equation, perhaps with equation form(s) guided qualitatively by FSEPP-model results. In existing fitting formulas, the AFEF-reduction decreases exponentially as c increases, which is different from the FSEPP-model formulas. This discrepancy needs to be investigated, using systematic Laplace-based simulations and appropriate results

  5. Technology for producing carbon field emitters

    SciTech Connect

    Khatapova, R.M.; Demskaya, L.L.; Romanova, V.K.

    1985-12-01

    This paper describes methods for producing field emitters from carbon filaments. Coating of Ni and two-layer coatings of Ni-Mo with a thickness of 10-40 um are applied to the carbon filaments by electrochemical deposition so that they can be spot welded to a metal holder. A technology for attaching carbon filaments with a refractory adhesive composition is also described. Field emitters with point radius of curvature of 0.2-0.4 um are made from three types of carbon filament.

  6. The effects of emitter-tied field plates on lateral PNP ionizing radiation response

    SciTech Connect

    Barnaby, H.J.; Schrimpf, R.D.; Cirba, C.R.; Pease, R.L.; Fleetwood, D.M.; Kosier, S.L.

    1998-03-01

    Radiation response comparisons of lateral PNP bipolar technologies reveal that device hardening may be achieved by extending the emitter contact over the active base. The emitter-tied field plate suppresses recombination of carriers with interface traps.

  7. Improved Photoresist Coating for Making CNT Field Emitters

    NASA Technical Reports Server (NTRS)

    Toda, Risaku; Manohara, Harish

    2009-01-01

    An improved photoresist-coating technique has been developed for use in the fabrication of carbon-nanotube- (CNT) based field emitters is described. The improved photoresist coating technique overcomes what, heretofore, has been a major difficulty in the fabrication process.

  8. Innovative Field Emitters for High-Voltage Electronic Devices

    NASA Astrophysics Data System (ADS)

    Sominski, G. G.; Sezonov, V. E.; Taradaev, E. P.; Tumareva, T. A.; Zadiranov, Yu. M.; Kornishin, S. Yu.; Stepanova, A. N.

    2015-12-01

    We describe multitip field emitters with protective coatings, which were developed in Peter the Great St. Petersburg Polytechnic University. The coatings ensure long-term operation of the emitters under high currents and technical vacuum. Innovative multi-layer emitters composed of contacting nanolayers of materials with different work functions are presented as well. The possibility by using the developed emitters in high-voltage electronic devices is demonstrated.

  9. Emission stability enhancement of a tip-type carbon-nanotube-based field emitter via hafnium interlayer deposition and thermal treatment

    NASA Astrophysics Data System (ADS)

    Kim, Jong-Pil; Chang, Han-Beet; Kim, Bu-Jong; Park, Jin-Seok

    2012-03-01

    Carbon nanotubes (CNTs) were deposited on a tip-type tungsten substrate via electrophoretic deposition, in which a hafnium thin film was used as an interlayer. The long-term (up to 24 h) emission stability of the CNT-based field emitter was remarkably enhanced when the hafnium interlayer was coated and thermally treated. This is attributed to the enhanced adhesion between the substrate and the CNTs. An x-ray photoelectron spectroscopy study and nano-scratch measurement provided a convincing evidence of the increase in the adhesive force.

  10. Gas ionization sensors with carbon nanotube/nickel field emitters.

    PubMed

    Huang, Bohr-Ran; Lin, Tzu-Ching; Yang, Ying-Kan; Tzeng, Shien-Der

    2011-12-01

    Gas ionization sensors based on the field emission properties of the carbon nanotube/nickel (CNT/Ni) field emitters were first developed in this work. It is found that the breakdown electric field (E(b)) slightly decreases from 2.2 V/microm to 1.9 V/microm as the pressure of H2 gas increases from 0.5 Torr to 100 Torr. On the contrary, E(b) obviously increases from 2.9 V/microm to 6.5 V/microm as O2 gas pressure increases from 0.5 Torr to 100 Torr. This may be explained by the depression of the electron emission that caused by the adsorption of the O2 gas on the CNT emitters. The Raman spectra of the CNT/Ni emitters also show that more defects were generated on the CNTs after O2 gas sensing. The Joule heating effect under high current density as performing H2 sensing was also observed. These effects may contribute the pressure dependence on the breakdown electric field of the CNT/Ni gas ionization sensors. PMID:22409010

  11. Sharpening of field emitter tips using high-energy ions

    DOEpatents

    Musket, Ronald G.

    1999-11-30

    A process for sharpening arrays of field emitter tips of field emission cathodes, such as found in field-emission, flat-panel video displays. The process uses sputtering by high-energy (more than 30 keV) ions incident along or near the longitudinal axis of the field emitter to sharpen the emitter with a taper from the tip or top of the emitter down to the shank of the emitter. The process is particularly applicable to sharpening tips of emitters having cylindrical or similar (e.g., pyramidal) symmetry. The process will sharpen tips down to radii of less than 12 nm with an included angle of about 20 degrees. Because the ions are incident along or near the longitudinal axis of each emitter, the tips of gated arrays can be sharpened by high-energy ion beams rastered over the arrays using standard ion implantation equipment. While the process is particularly applicable for sharpening of arrays of field emitters in field-emission flat-panel displays, it can be effectively utilized in the fabrication of other vacuum microelectronic devices that rely on field emission of electrons.

  12. Neutralization of space charge on high-current low-energy ion beam by low-energy electrons supplied from silicon based field emitter arrays

    SciTech Connect

    Gotoh, Yasuhito; Tsuji, Hiroshi; Taguchi, Shuhei; Ikeda, Keita; Kitagawa, Takayuki; Ishikawa, Junzo; Sakai, Shigeki

    2012-11-06

    Neutralization of space charge on a high-current and low-energy ion beam was attempted to reduce the divergence with an aid of low-energy electrons supplied from silicon based field emitter arrays (Si-FEAs). An argon ion beam with the energy of 500 eV and the current of 0.25 mA was produced by a microwave ion source. The initial beam divergence and the emittance were measured at the entrance of the analysis chamber in order to estimate the intrinsic factors for beam divergence. The current density distribution of the beam after transport of 730 mm was measured by a movable Faraday cup, with and without electron supply from Si-FEAs. A similar experiment was performed with tungsten filaments as an electron source. The results indicated that the electron supply from FEA had almost the same effect as the thermionic filament, and it was confirmed that both electron sources can neutralize the ion beam.

  13. A glass-sealed field emission x-ray tube based on carbon nanotube emitter for medical imaging

    NASA Astrophysics Data System (ADS)

    Yeo, Seung Jun; Jeong, Jaeik; Ahn, Jeung Sun; Park, Hunkuk; Kwak, Junghwan; Noh, Eunkyong; Paik, Sanghyun; Kim, Seung Hoon; Ryu, Jehwang

    2016-04-01

    We report the design and fabrication of a carbon nanotube based a glass-sealed field emission x-ray tube without vacuum pump. The x-ray tube consists of four electrodes with anode, focuser, gate, and cathode electrode. The shape of cathode is rectangular for isotropic focal spot size at anode target. The obtained x-ray images show clearly micrometer scale.

  14. Arrays of Bundles of Carbon Nanotubes as Field Emitters

    NASA Technical Reports Server (NTRS)

    Manohara, Harish; Bronkowski, Michael

    2007-01-01

    Experiments have shown that with suitable choices of critical dimensions, planar arrays of bundles of carbon nanotubes (see figure) can serve as high-current-density field emitter (cold-cathode) electron sources. Whereas some hot-cathode electron sources must be operated at supply potentials of thousands of volts, these cold-cathode sources generate comparable current densities when operated at tens of volts. Consequently, arrays of bundles of carbon nanotubes might prove useful as cold-cathode sources in miniature, lightweight electron-beam devices (e.g., nanoklystrons) soon to be developed. Prior to the experiments, all reported efforts to develop carbon-nanotube-based field-emission sources had yielded low current densities from a few hundred microamperes to a few hundred milliamperes per square centimeter. An electrostatic screening effect, in which taller nanotubes screen the shorter ones from participating in field emission, was conjectured to be what restricts the emission of electrons to such low levels. It was further conjectured that the screening effect could be reduced and thus emission levels increased by increasing the spacing between nanotubes to at least by a factor of one to two times the height of the nanotubes. While this change might increase the emission from individual nanotubes, it would decrease the number of nanotubes per unit area and thereby reduce the total possible emission current. Therefore, to maximize the area-averaged current density, it would be necessary to find an optimum combination of nanotube spacing and nanotube height. The present concept of using an array of bundles of nanotubes arises partly from the concept of optimizing the spacing and height of field emitters. It also arises partly from the idea that single nanotubes may have short lifetimes as field emitters, whereas bundles of nanotubes could afford redundancy so that the loss of a single nanotube would not significantly reduce the overall field emission.

  15. Nanostructure TEM analysis of diamond cold cathode field emitters

    SciTech Connect

    Wade, Travis S.; Ghosh, Nikkon; Wittig, James Edward; Kang, Weng; Allard Jr, Lawrence Frederick; Unocic, Kinga A; Davidson, James; Tolk, Norman H.

    2012-01-01

    Diamond cold cathode devices have demonstrated significant potential as electron field emitters. Ultra-sharp diamond pyramidal tips (~5nm tip radius) have been fabricated and show improvement in emission when compared to conventional field emitters. However, the emission mechanisms in these complex diamond nanostructures are not well understood. Transmission electron microscopy performed in this study provides new insight into tip structure and composition with implications for field emission and diamond growth.

  16. Field energy and RMS emittance in intense particle beams

    SciTech Connect

    Wangler, T.P.; Crandall, K.R.; Mills, R.S.; Reiser, M.

    1986-04-25

    An equation is presented for continuous beam with azimuthal symmetry and continuous linear focusing; the equation expresses a relationship between the rate of change for squared rms emittance and the rate of change for a quantity we call the nonlinear field energy. The nonlinear field energy depends on the shape of the charge distribution and corresponds to the residual field energy possessed by beams with nonuniform charge distributions. The equation can be integrated for the case of an rms matched beam to yield a formula for space-charge-induced emittance growth that we have tested numerically for a variety of initial distributions. The results provide a framework for discussing the scaling of rms emittance growth and an explanation for the well-established lower limit on output emittance.

  17. Process for making a cesiated diamond film field emitter and field emitter formed therefrom

    DOEpatents

    Anderson, David F.; Kwan, Simon W.

    1999-01-01

    A process for making a cesiated diamond film comprises (a) depositing a quantity of cesium iodide on the diamond film in a vacuum of between about 10.sup.-4 Torr and about 10.sup.-7 Torr, (b) increasing the vacuum to at least about 10.sup.-8 Torr, and (c) imposing an electron beam upon the diamond film, said electron beam having an energy sufficient to dissociate said cesium iodide and to incorporate cesium into interstices of the diamond film. The cesiated diamond film prepared according to the process has an operating voltage that is reduced by a factor of at least approximately 2.5 relative to conventional, non-cesiated diamond film field emitters.

  18. Process for making a cesiated diamond film field emitter and field emitter formed therefrom

    DOEpatents

    Anderson, D.F.; Kwan, S.W.

    1999-03-30

    A process for making a cesiated diamond film comprises (a) depositing a quantity of cesium iodide on the diamond film in a vacuum of between about 10{sup {minus}4} Torr and about 10{sup {minus}7} Torr, (b) increasing the vacuum to at least about 10{sup {minus}8} Torr, and (c) imposing an electron beam upon the diamond film, said electron beam having an energy sufficient to dissociate said cesium iodide and to incorporate cesium into interstices of the diamond film. The cesiated diamond film prepared according to the process has an operating voltage that is reduced by a factor of at least approximately 2.5 relative to conventional, non-cesiated diamond film field emitters. 2 figs.

  19. Field Emitter Magnetic Sensor with Steered Focused Electron Beam

    NASA Astrophysics Data System (ADS)

    Nicolaescu, Dan; Filip, Valeriu; Itoh, Junji

    2001-04-01

    A novel field emission magnetic sensor is proposed and its operation is theoretically analyzed. The sensor comprises a dual-gate wedge field emitter with a split gate having the double role of focusing and steering the electron beam. The electron beam deflection due to the Lorentz force is compensated by appropriate potentials applied to this electrode. The modeling results have been obtained using the Simion 3D 7.0 software package. The device has high sensitivity and its operation is not influenced by fluctuations in the emission current. Arrangements of mutually normal wedge emitters can be used for two-dimensional magnetic field sensing.

  20. Excellent oxidation endurance of boron nitride nanotube field electron emitters

    SciTech Connect

    Song, Yenan; Song, Yoon-Ho; Milne, William I.; Jin Lee, Cheol

    2014-04-21

    Boron nitride nanotubes (BNNTs) are considered as a promising cold electron emission material owing to their negative electron affinity. BNNT field emitters show excellent oxidation endurance after high temperature thermal annealing of 600 °C in air ambient. There is no damage to the BNNTs after thermal annealing at a temperature of 600 °C and also no degradation of field emission properties. The thermally annealed BNNTs exhibit a high maximum emission current density of 8.39 mA/cm{sup 2} and show very robust emission stability. The BNNTs can be a promising emitter material for field emission devices under harsh oxygen environments.

  1. Chemically doped three-dimensional porous graphene monoliths for high-performance flexible field emitters

    NASA Astrophysics Data System (ADS)

    Kim, Ho Young; Jeong, Sooyeon; Jeong, Seung Yol; Baeg, Kang-Jun; Han, Joong Tark; Jeong, Mun Seok; Lee, Geon-Woong; Jeong, Hee Jin

    2015-03-01

    Despite the recent progress in the fabrication of field emitters based on graphene nanosheets, their morphological and electrical properties, which affect their degree of field enhancement as well as the electron tunnelling barrier height, should be controlled to allow for better field-emission properties. Here we report a method that allows the synthesis of graphene-based emitters with a high field-enhancement factor and a low work function. The method involves forming monolithic three-dimensional (3D) graphene structures by freeze-drying of a highly concentrated graphene paste and subsequent work-function engineering by chemical doping. Graphene structures with vertically aligned edges were successfully fabricated by the freeze-drying process. Furthermore, their number density could be controlled by varying the composition of the graphene paste. Al- and Au-doped 3D graphene emitters were fabricated by introducing the corresponding dopant solutions into the graphene sheets. The resulting field-emission characteristics of the resulting emitters are discussed. The synthesized 3D graphene emitters were highly flexible, maintaining their field-emission properties even when bent at large angles. This is attributed to the high crystallinity and emitter density and good chemical stability of the 3D graphene emitters, as well as to the strong interactions between the 3D graphene emitters and the substrate.Despite the recent progress in the fabrication of field emitters based on graphene nanosheets, their morphological and electrical properties, which affect their degree of field enhancement as well as the electron tunnelling barrier height, should be controlled to allow for better field-emission properties. Here we report a method that allows the synthesis of graphene-based emitters with a high field-enhancement factor and a low work function. The method involves forming monolithic three-dimensional (3D) graphene structures by freeze-drying of a highly concentrated

  2. Surface treatment and surface coating of silicon field emitter array

    NASA Astrophysics Data System (ADS)

    Hajra, Mahua Sudhakrishna

    The objectives of this research were to fabricate ungated Si field emitter arrays (FEA's), and then to identify ways to improve the performance of the emitters. In the first and second chapters, the basis of the research, including background, theory, and the goals of the research is presented. The third chapter discusses the fabrication methods used to form the ungated Si FEA's. The fourth chapter gives the details about surface treatment procedures used to improve initial operation. The fifth and the sixth chapter discuss the different surface coating materials used to study the emission properties of the Si field emitters. The seventh chapter summarizes the work and suggests possible follow up research. The four surface treatments discussed in chapter four employ, respectively, residual gas ions, low-energy electron-stimulated desorption, a hydrogen-enhanced residual gas atmosphere, and a plasma of a Ar (96%) and H2 (4%) gas mixture. The method, using the hydrogen-enriched residual gas atmosphere is very unique in that it uses getters to produce the hydrogen rich atmosphere. The method, using a plasma of Ar (96%) and H2 (4%) gas mixture, is an effective in-situ cleaning procedure, which can be performed prior to packaging the devices. In chapters five and six is a comparison of the field-emission properties of the Si FEA coated with various materials, including (1) nanoparticle clusters of diamond and gallium nitride (GaN), (2) a thin film of ultrananocrystalline diamond (UNCD), (3) a lead zirconate titanate (PZT) coating, and (4) carbon nanotubes. Among the above coatings, the conformal coating of UNCD produced electron emission at an extremely low threshold field of between 2 to 5 V/mum. A further study of the behavior of electron emission from UNCD-coated Si FEA during in-situ exposure to H2, N2, and Ar respectively showed that when the emitting surface is exposed to H 2, at 10-5 Torr and 10-4 Torr, the initial emission current (2 muA) increases by a factor

  3. Spectrum of classes of point emitters of electromagnetic wave fields.

    PubMed

    Castañeda, Román

    2016-09-01

    The spectrum of classes of point emitters has been introduced as a numerical tool suitable for the design, analysis, and synthesis of non-paraxial optical fields in arbitrary states of spatial coherence. In this paper, the polarization state of planar electromagnetic wave fields is included in the spectrum of classes, thus increasing its modeling capabilities. In this context, optical processing is realized as a filtering on the spectrum of classes of point emitters, performed by the complex degree of spatial coherence and the two-point correlation of polarization, which could be implemented dynamically by using programmable optical devices. PMID:27607498

  4. Diamond coated silicon field emitter array

    SciTech Connect

    S. Albin; W. Fu; A. Varghese; A. C. Lavarias; G. R. Myneni

    1999-07-01

    Diamond coated silicon tip arrays, with and without a self-aligned gate, were fabricated, and current-voltage characteristics of 400 tips were measured. Diamond films were grown uniformly on Si tips using microwave plasma after nucleation with 10 nm diamond suspension and substrate bias. An emission current of 57 ?A was obtained at 5 V from the ungated array tips separated from an anode at 2 ?m. In the case of the gated arrays with 1.5 ?m aperture, an emission current of 3.4 ?A was measured at a gate voltage of 80 V for an anode separation of 200 ?m. The turn-on voltages for these two types of devices were 0.2 and 40 V, respectively. Diamond coated Si tip arrays have potential applications in field emission based low voltage vacuum electronic devices and microsensors.

  5. Photosensitivity of p-type black Si field emitter arrays

    NASA Astrophysics Data System (ADS)

    Mingels, S.; Porshyn, V.; Prommesberger, C.; Langer, C.; Schreiner, R.; Lützenkirchen-Hecht, D.; Müller, G.

    2016-04-01

    We have investigated the properties of black Si field emitter arrays under strong electric fields and laser illumination. A low onset field of 1.8 MV/m for an emission current of 1 nA was obtained. A pronounced saturation region of the dark and photo-enhanced current was observed, which provided a short-term stability of 0.1% at 0.4 μA and 0.7% at 1.0 μA, respectively. As maximum value for the photosensitivity, an on-off current switching ratio of 43 reaching about 13 μA was achieved at a laser power of 15 mW. Electron spectra in the dark and under laser illumination are presented, showing a current and light-sensitive voltage drop across the emitters as well as hints for hot electron emission.

  6. Field emission properties from flexible field emitters using carbon nanotube film

    NASA Astrophysics Data System (ADS)

    Shin, Dong Hoon; Jung, Seung Il; Yun, Ki Nam; Chen, Guohai; Song, Yoon-Ho; Saito, Yahachi; Milne, William I.; Lee, Cheol Jin

    2014-07-01

    Flexible carbon nanotube (CNT) field emitters are fabricated using CNT films on polyethylene terephthalate films. The flexible CNT emitters, which are made using double-walled CNTs, show high emission performance and also indicate stable field emission properties under several bending conditions. The flexible CNT emitters have a low turn-on field of about 0.82 V/μm and a high emission current density of about 2.0 mA/cm2 at an electric field of 1.6 V/μm. During stability tests, the flexible CNT emitters initially degrade over the first 4 h but exhibit no further significant degradation over the next 16 h testing while being continually bent. A flexible lamp made using the flexible CNT emitter displays uniform and bright emission patterns in a convex mode.

  7. Compliance with High-Intensity Radiated Fields Regulations - Emitter's Perspective

    NASA Technical Reports Server (NTRS)

    Statman, Joseph; Jamnejad, Vahraz; Nguyen, Lee

    2012-01-01

    NASA's Deep Space Network (DSN) uses high-power transmitters on its large antennas to communicate with spacecraft of NASA and its partner agencies. The prime reflectors of the DSN antennas are parabolic, at 34m and 70m in diameter. The DSN transmitters radiate Continuous Wave (CW) signals at 20 kW - 500 kW at X-band and S-band frequencies. The combination of antenna reflector size and high frequency results in a very narrow beam with extensive oscillating near-field pattern. Another unique feature of the DSN antennas is that they (and the radiated beam) move mostly at very slow sidereal rate, essentially identical in magnitude and at the opposite direction of Earth rotation.The DSN is in the process of revamping its documentation to provide analysis of the High Intensity Radiation Fields (HIRF) environment resulting from radio frequency radiation from DSN antennas for comparison to FAA regulations regarding certification of HIRF protection as outlined in the FAA regulations on HIRF protection for aircraft electrical and electronic systems (Title 14, Code of Federal Regulations (14 CFR) [section sign][section sign] 23.1308, 25.1317, 27.1317, and 29.1317).This paper presents work done at JPL, in consultation with the FAA. The work includes analysis of the radiated field structure created by the unique DSN emitters (combination of transmitters and antennas) and comparing it to the fields defined in the environments in the FAA regulations. The paper identifies areas that required special attention, including the implications of the very narrow beam of the DSN emitters and the sidereal rate motion. The paper derives the maximum emitter power allowed without mitigation and the mitigation zones, where required.Finally, the paper presents summary of the results of the analyses of the DSN emitters and the resulting DSN process documentation.

  8. Field emission behavior of carbon nanotube field emitters after high temperature thermal annealing

    SciTech Connect

    Sun, Yuning; Shin, Dong Hoon; Yun, Ki Nam; Leti, Guillaume; Hwang, Yeon Mo; Song, Yenan; Saito, Yahachi; Lee, Cheol Jin

    2014-07-15

    The carbon nanotube (CNT) field emitters have been fabricated by attaching a CNT film on a graphite rod using graphite adhesive material. The CNT field emitters showed much improved field emission properties due to increasing crystallinity and decreasing defects in CNTs after the high temperature thermal annealing at 900 °C in vacuum ambient. The CNT field emitters showed the low turn-on electric field of 1.15 V/μm, the low threshold electric field of 1.62 V/μm, and the high emission current of 5.9 mA which corresponds to a current density of 8.5 A/cm{sup 2}. In addition, the CNT field emitters indicated the enhanced field emission properties due to the multi-stage effect when the length of the graphite rod increases. The CNT field emitter showed good field emission stability after the high temperature thermal annealing. The CNT field emitter revealed a focused electron beam spot without any focusing electrodes and also showed good field emission repeatability.

  9. Spacecraft charging control by thermal, field emission with lanthanum-hexaboride emitters

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1978-01-01

    Thermal, field emitters of lanthanum (or perhaps cerium) hexaboride (LaB6) with temperature variability up to about 1500K are suggested for spacecraft charging control. Such emitters operate at much lower voltages with considerably more control and add plasma-diagnostic versatility. These gains should outweigh the additional complexity of providing heat for the LaB6 thermal, field emitter.

  10. A novel inexpensive device for the electrochemical generation of metallic emitters for field desorption.

    PubMed

    Rechsteiner, C E; Mathis, D E; Bursey, M M; Buck, R P

    1977-02-01

    Details for the construction of a novel, inexpensive device for the electrochemical generation of metallic emitters for field desorption mass spectrometry are described. Use of the device for the generation of cobalt and nickel emitters is demonstrated. PMID:836944

  11. Membrane-Based Emitter for Coupling Microfluidics with Ultrasensitive Nanoelectrospray Ionization-Mass Spectrometry

    SciTech Connect

    Sun, Xuefei; Kelly, Ryan T.; Tang, Keqi; Smith, Richard D.

    2011-06-09

    An integrated poly(dimethylsiloxane) (PDMS) membrane-based microfluidic emitter for high performance nanoelectrospray ionization-mass spectrometry (nanoESI-MS) has been fabricated and evaluated. The ~100-μm-thick emitter was created by cutting a PDMS membrane that protrudes beyond the bulk substrate. The reduced surface area at the emitter enhances the electric field and reduces wetting of the surface by the electrospray solvent. As such, the emitter provides highly stable electrospray at flow rates as low as 10 nL/min, and is compatible with electrospray solvents containing a large organic component (e.g., 90% methanol). This approach enables facile emitter construction, and provides excellent stability, reproducibility and sensitivity, as well as compatibility with multilayer soft lithography.

  12. Flexible Field Emitter for X-ray Generation by Implanting CNTs into Nickel Foil

    NASA Astrophysics Data System (ADS)

    Sun, Bin; Wang, Yan; Ding, Guifu

    2016-07-01

    This paper reports a novel implanting micromachining technology. By using this method, for the first time, we could implant nano-scale materials into milli-scale metal substrates at room temperature. Ni-based flexible carbon nanotube (CNT) field emitters were fabricated by the novel micromachining method. By embedding CNT roots into Ni foil using polymer matrix as transfer media, effective direct contact between Ni and CNTs was achieved. As a result, our novel emitter shows relatively good field emission properties such as low turn-on field and good stability. Moreover, the emitter was highly flexible with preservation of the field emission properties. The excellent field emission characteristics attributed to the direct contact and the strong interactions between CNTs and the substrate. To check the practical application of the novel emitter, a simple X-ray imaging system was set up by modifying a traditional tube. The gray shadow that appears on the sensitive film after being exposed to the radiation confirms the successful generation of X-ray.

  13. Flexible Field Emitter for X-ray Generation by Implanting CNTs into Nickel Foil.

    PubMed

    Sun, Bin; Wang, Yan; Ding, Guifu

    2016-12-01

    This paper reports a novel implanting micromachining technology. By using this method, for the first time, we could implant nano-scale materials into milli-scale metal substrates at room temperature. Ni-based flexible carbon nanotube (CNT) field emitters were fabricated by the novel micromachining method. By embedding CNT roots into Ni foil using polymer matrix as transfer media, effective direct contact between Ni and CNTs was achieved. As a result, our novel emitter shows relatively good field emission properties such as low turn-on field and good stability. Moreover, the emitter was highly flexible with preservation of the field emission properties. The excellent field emission characteristics attributed to the direct contact and the strong interactions between CNTs and the substrate. To check the practical application of the novel emitter, a simple X-ray imaging system was set up by modifying a traditional tube. The gray shadow that appears on the sensitive film after being exposed to the radiation confirms the successful generation of X-ray. PMID:27401089

  14. Discrete space charge affected field emission: Flat and hemisphere emitters

    SciTech Connect

    Jensen, Kevin L.; Shiffler, Donald A.; Tang, Wilkin; Rittersdorf, Ian M.; Lebowitz, Joel L.; Harris, John R.; Lau, Y. Y.; Petillo, John J.; Luginsland, John W.

    2015-05-21

    Models of space-charge affected thermal-field emission from protrusions, able to incorporate the effects of both surface roughness and elongated field emitter structures in beam optics codes, are desirable but difficult. The models proposed here treat the meso-scale diode region separate from the micro-scale regions characteristic of the emission sites. The consequences of discrete emission events are given for both one-dimensional (sheets of charge) and three dimensional (rings of charge) models: in the former, results converge to steady state conditions found by theory (e.g., Rokhlenko et al. [J. Appl. Phys. 107, 014904 (2010)]) but show oscillatory structure as they do. Surface roughness or geometric features are handled using a ring of charge model, from which the image charges are found and used to modify the apex field and emitted current. The roughness model is shown to have additional constraints related to the discrete nature of electron charge. The ability of a unit cell model to treat field emitter structures and incorporate surface roughness effects inside a beam optics code is assessed.

  15. What future for quantum dot-based light emitters?

    NASA Astrophysics Data System (ADS)

    Nurmikko, Arto

    2015-12-01

    Synthesis of semiconductor colloidal quantum dots by low-cost, solution-based methods has produced an abundance of basic science. Can these materials be transformed to high-performance light emitters to disrupt established photonics technologies, particularly semiconductor lasers?

  16. Silicon solar cells with polysilicon emitters and back surface fields

    NASA Astrophysics Data System (ADS)

    Du, Jiang; Berndt, Lyall P.; Tarr, N. Garry

    2010-06-01

    The first solar cells using in-situ doped polysilicon contacts to form both emitter and back surface field (BSF) regions are reported. The use of polysilicon contacts permits extremely low thermal budget processing (maximum 850°C 5 sec for dopant activation), preserving substrate properties. The effectiveness of the BSF is best seen with backside illumination, where the photocurrent under natural sunlight is found to be over 30% of that obtained with frontside illumination, even though the substrate thickness is comparable to the minority carrier diffusion length. The applicability of the structure to bifacial operation is considered.

  17. Field emission from optimized structure of carbon nanotube field emitter array

    NASA Astrophysics Data System (ADS)

    Chouhan, V.; Noguchi, T.; Kato, S.

    2016-04-01

    The authors report a detail study on the emission properties of field emitter array (FEA) of micro-circular emitters of multiwall carbon nanotubes (CNTs). The FEAs were fabricated on patterned substrates prepared with an array of circular titanium (Ti) islands on titanium nitride coated tantalum substrates. CNTs were rooted into these Ti islands to prepare an array of circular emitters. The circular emitters were prepared in different diameters and pitches in order to optimize their structure for acquiring a high emission current. The pitch was varied from 0 to 600 μm, while a diameter of circular emitters was kept constant to be 50 μm in order to optimize a pitch. For diameter optimization, a diameter was changed from 50 to 200 μm while keeping a constant edge-to-edge distance of 150 μm between the circular emitters. The FEA with a diameter of 50 μm and a pitch of 120 μm was found to be the best to achieve an emission current of 47 mA corresponding to an effective current density of 30.5 A/cm2 at 7 V/μm. The excellent emission current was attributed to good quality of CNT rooting into the substrate and optimized FEA structure, which provided a high electric field on a whole circular emitter of 50 μm and the best combination of the strong edge effect and CNT coverage. The experimental results were confirmed with computer simulation.

  18. Fowler-Nordheim plot characteristics for ZnO virtual field emitter array

    NASA Astrophysics Data System (ADS)

    Al-Tabbakh, Ahmed A.

    2015-09-01

    Linear and nonlinear Fowler-Nordheim (FN) plots from semiconductors emitters arrays were equally reported by researchers with occasionally inexplicit justification of either behaviour. Interpretation of experimental field emission data depends on explaining the FN plot behaviour from these arrays. The FN plot behaviour was investigated for virtual arrays of ZnO emitters with defined geometries based on fundamental electron tunnelling from semiconductors. The effects of emitters' size distribution, saturation of conduction band (CB) current and contribution of valence band (VB) current on FN plot behaviour were investigated and discussed in detail. Comparison with some experimental results was introduced in support of the discussion. Results showed that saturation of CB current and contribution of VB electrons may not always be manifested as a well-observed deviation from linear characteristic of the FN plot. In addition, the dependence of the CB current on the emitters' geometries was found to affect the FN plot behaviour. The present investigation is thought to be of great importance to field emission community and help for better interpretation of experimental field emission data.

  19. Argon inclusion in sputtered films and the effect of the gas on molybdenum field emitter arrays

    NASA Astrophysics Data System (ADS)

    Chalamala, Babu R.; Reuss, Robert H.

    2001-04-01

    Residual gas analysis of a number of field emission displays showed that argon desorbed from molybdenum metal lines was the dominant gas in sealed vacuum packages. We present experimental results on the emission characteristics of molybdenum field emitter arrays in argon ambient. In argon, the emission current dropped rapidly similar to that in oxygenic gas ambients. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest a model based on shallow implantation of argon into the field emitter tips that increases the effective width of the tunneling barrier. Experimental support for this model comes from the following observations: emission current degraded only when the device was turned on; after gas exposure, significant current recovery which followed diffusion type behavior was noted; degradation and recovery rates were functions of partial pressure; and no detectable effects associated with sputtering were observed. This mechanism is also consistent with ion pumping known to occur in field emission displays.

  20. Quantum emitters dynamically coupled to a quantum field

    SciTech Connect

    Acevedo, O. L.; Quiroga, L.; Rodríguez, F. J.; Johnson, N. F.

    2013-12-04

    We study theoretically the dynamical response of a set of solid-state quantum emitters arbitrarily coupled to a single-mode microcavity system. Ramping the matter-field coupling strength in round trips, we quantify the hysteresis or irreversible quantum dynamics. The matter-field system is modeled as a finite-size Dicke model which has previously been used to describe equilibrium (including quantum phase transition) properties of systems such as quantum dots in a microcavity. Here we extend this model to address non-equilibrium situations. Analyzing the system’s quantum fidelity, we find that the near-adiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is chosen as the starting point. We also explore signatures of the crossing of the critical points on the radiation subsystem by monitoring its Wigner function; then, the subsystem can exhibit the emergence of non-classicality and complexity.

  1. High-density Au nanorod optical field-emitter arrays.

    PubMed

    Hobbs, R G; Yang, Y; Keathley, P D; Swanwick, M E; Velásquez-Garcíia, L F; Kärtner, F X; Graves, W S; Berggren, K K

    2014-11-21

    We demonstrate the design, fabrication, characterization, and operation of high-density arrays of Au nanorod electron emitters, fabricated by high-resolution electron beam lithography, and excited by ultrafast femtosecond near-infrared radiation. Electron emission characteristic of multiphoton absorption has been observed at low laser fluence, as indicated by the power-law scaling of emission current with applied optical power. The onset of space-charge-limited current and strong optical field emission has been investigated so as to determine the mechanism of electron emission at high incident laser fluence. Laser-induced structural damage has been observed at applied optical fields above 5 GV m(-1), and energy spectra of emitted electrons have been measured using an electron time-of-flight spectrometer. PMID:25354583

  2. High-density Au nanorod optical field-emitter arrays

    NASA Astrophysics Data System (ADS)

    Hobbs, R. G.; Yang, Y.; Keathley, P. D.; Swanwick, M. E.; Velásquez-García, L. F.; Kärtner, F. X.; Graves, W. S.; Berggren, K. K.

    2014-11-01

    We demonstrate the design, fabrication, characterization, and operation of high-density arrays of Au nanorod electron emitters, fabricated by high-resolution electron beam lithography, and excited by ultrafast femtosecond near-infrared radiation. Electron emission characteristic of multiphoton absorption has been observed at low laser fluence, as indicated by the power-law scaling of emission current with applied optical power. The onset of space-charge-limited current and strong optical field emission has been investigated so as to determine the mechanism of electron emission at high incident laser fluence. Laser-induced structural damage has been observed at applied optical fields above 5 GV m-1, and energy spectra of emitted electrons have been measured using an electron time-of-flight spectrometer.

  3. Study of the Electric Field Screening Effect on Low Number of Carbon Fiber Field Emitters

    NASA Astrophysics Data System (ADS)

    Tang, Wilkin; Shiffler, Don; Lacour, Matthew; Golby, Ken; Knowles, Tim

    2015-11-01

    Field emitter arrays have the potential to provide high current density, low voltage operation, and high pulse repetition for radar and communication. It is well known that packing density of the field emitter arrays significantly affects the emission current.1 Previously we conducted experiments using two- and four-cathode configurations. Here we extend our previous work and present experimental results for nine cathodes in a square and cylindrical configuration. The experiments used nine cathodes with variable spacing to investigate the effect of electric field screening on current emission. Emission characteristic is compared for the case of two, four and nine field emitters with different spacing. Particle-in-cell simulations are performed to compare with the experiments. Work supported by an LRIR from the Air Force Office of Scientific Research.

  4. X-ray tube with a graphite field emitter inflamed at high temperature

    PubMed Central

    Iwai, Yusuke; Koike, Takayoshi; Hayama, Youhei; Jouzuka, Atsuo; Nakamura, Tomonori; Onizuka, Yoshihiro; Miyoshi, Motosuke; Mimura, Hidenori

    2013-01-01

    The authors developed a class of novel graphite-based field emitters, known as graphite field emitters inflamed at high temperature (GFEIHTs), which includes numerous edges and juts. The GFEIHT field emission characteristics are investigated in a vacuum tube (10−7 Pa), and an anode current exceeding 2 mA is obtained. The authors also fabricated tipped-off x-ray tubes using GFEIHTs. No degradation in the anode current is observed under the operating conditions of 16.6 kV anode voltage and 160 μA anode current. The current dispersion, defined as the standard deviation (σ)/mean over 24 h, is 2.8%. The authors successfully demonstrated radiography and x-ray fluorescence spectrometry using an x-ray tube with GFEIHT. PMID:23847750

  5. Effective hybrid graphene/carbon nanotubes field emitters by electrophoretic deposition

    NASA Astrophysics Data System (ADS)

    Koh, Angel T. T.; Chen, Ting; Pan, Likun; Sun, Zhuo; Chua, Daniel H. C.

    2013-05-01

    Hybrid graphene and carbon nanotube (CNT) field emitters were fabricated with electrophoretic deposition (EPD). The combination of both materials was used to improve the turn-on field for pure carbon nanotubes emitters and the reliability of pure graphene emitters deposited by the same method. The CNT was envisioned to hold down the graphene flakes, like a safety belt or Velcro, at high voltages to prevent an early short circuit at relatively low voltages. These hybrid emitters were studied for their field emission performance in relation to the EPD deposition duration. It was observed that the emitters performed better when the EPD duration was increased due to the increase in the amount and density of graphene flakes. Possible reasons for the improvement of field emission performance were suggested. The roles of graphene and CNT in these hybrid emitters were also discussed.

  6. Field Emitter Arrays and Displays Produced by Ion Tracking Lithography

    SciTech Connect

    Felter, T E; Musket, R G; Bernhardt, A F

    2004-12-28

    When ions of sufficient electronic energy loss traverse a dielectric film or foil, they alter the chemical bonding along their nominally straight path within the material. A suitable etchant can quickly dissolve these so-called latent tracks leaving holes of small diameter ({approx}10nm) but long length - several microns. Continuing the etching process gradually increases the diameter reproducibly and uniformly. The trackable medium can be applied as a uniform film onto large substrates. The small, monodisperse holes produced by this track etching can be used in conjunction with additional thin film processing to create functional structures attached to the substrate. For example, Lawrence Livermore National Laboratory and Candescent Technologies Corporation (CTC) co-developed a process to make arrays of gated field emitters ({approx}100nm diameter electron guns) for CTC's ThinCRT{trademark} displays, which have been fabricated to diagonal dimensions > 13. Additional technological applications of ion tracking lithography will be briefly covered.

  7. In-plane carbon nanotube field emitters for high temperature integrated electronics

    NASA Astrophysics Data System (ADS)

    Monica, Andrew Hayes

    Lateral carbon nanotube (CNT)-based field emission devices have been developed for the purpose of fabricating diodes, triodes, and ultimately integrated circuits. The goal of this research is to create CNT-based field emission devices that offer high performance operation in harsh environments, particularly high temperature. Silicon based technologies suffer from an inherent inability to operate at temperatures above ˜300°C; however, a need still exists for such electronics. The devices developed by this research seek to address the need for robust microelectronics capable of wide temperature range operation without the need for elaborate cooling systems. The field emitter structures consist of carbon nanotubes that are created using one of two distinct techniques: dielectrophoretic assembly or thermal chemical vapor deposition synthesis. I will discuss how such techniques can be used to create lateral CNT structures suitable for planar field emission while also enabling complete compatibility with modern semiconductor processing techniques. The electrical and thermal performance results of planar CNT field emitters operating in diode and triode configurations are also reported. Carbon nanotube based field emission devices, such as those I have developed, have characteristics that could result in benefits to an exceedingly wide range of applications beyond operation in harsh environments. High-frequency analog applications are particularly of interest because of the very low capacitances and the high current/unit area capability of typical CNT field emitters, which is in the Amps/cm2 range. Also, since field emitted current is a very strong function of the applied electric field, these devices will undoubtedly find potential use in applications requiring large gain.

  8. Electric Field Screening by the Proximity of Two Knife-Edge Field Emitters of Finite Width

    NASA Astrophysics Data System (ADS)

    Wong, P.; Tang, W.; Lau, Y. Y.; Hoff, B.

    2015-11-01

    Field emitter arrays have the potential to provide high current density, low voltage operation, and high pulse repetition for radar and communication. It is well known that packing density of the field emitter arrays significantly affect the emission current. Previously we calculated analytically the electric field profile of two-dimensional knife-edge cathodes with arbitrary separation by using a Schwarz-Christoffel transformation. Here we extend this previous work to include the finite width of two identical emitters. From the electric field profile, the field enhancement factor, thereby the severity of the electric field screening, are determined. It is found that for two identical emitters with finite width, the magnitude of the electric field on the knife-edge cathodes depends strongly on the ratio h / a and h / r , where h is the height of the knife-edge cathode, 2a is the distance between the cathodes, and 2 r represents their width. Particle-in-cell simulations are performed to compare with the analytical results on the emission current distribution. P. Y. Wong was supported by a Directed Energy Summer Scholar internship at Air Force Research Laboratory, Kirtland AFB, and by AFRL Award No. FA9451-14-1-0374.

  9. Nanostructured ultrafast silicon-tip optical field-emitter arrays.

    PubMed

    Swanwick, Michael E; Keathley, Phillip D; Fallahi, Arya; Krogen, Peter R; Laurent, Guillaume; Moses, Jeffrey; Kärtner, Franz X; Velásquez-García, Luis F

    2014-09-10

    Femtosecond ultrabright electron sources with spatially structured emission are an enabling technology for free-electron lasers, compact coherent X-ray sources, electron diffractive imaging, and attosecond science. In this work, we report the design, modeling, fabrication, and experimental characterization of a novel ultrafast optical field emission cathode comprised of a large (>100,000 tips), dense (4.6 million tips·cm(-2)), and highly uniform (<1 nm tip radius deviation) array of nanosharp high-aspect-ratio silicon columns. Such field emitters offer an attractive alternative to UV photocathodes while providing a direct means of structuring the emitted electron beam. Detailed measurements and simulations show pC electron bunches can be generated in the multiphoton and tunneling regime within a single optical cycle, enabling significant advances in electron diffractive imaging and coherent X-ray sources on a subfemtosecond time scale, not possible before. At high charge emission yields, a slow rollover in charge is explained as a combination of the onset of tunneling emission and the formation of a virtual cathode. PMID:25075552

  10. Elementary framework for cold field emission from quantum-confined, non-planar emitters

    NASA Astrophysics Data System (ADS)

    Patterson, A. A.; Akinwande, A. I.

    2015-05-01

    For suitably small field emitters, the effects of quantum confinement at the emitter tip may have a significant impact on the emitter performance and total emitted current density (ECD). Since the geometry of a quantum system uniquely determines the magnitude and distribution of its energy levels, a framework for deriving ECD equations from cold field electron emitters of arbitrary geometry and dimensionality is developed. In the interest of obtaining semi-analytical ECD equations, the framework is recast in terms of plane wave solutions to the Schrödinger equation via the use of the Jeffreys-Wentzel-Kramers-Brillouin approximation. To demonstrate the framework's consistency with our previous work and its capabilities in treating emitters with non-planar geometries, ECD equations were derived for the normally unconfined cylindrical nanowire (CNW) and normally confined (NC) CNW emitter geometries. As a function of the emitter radius, the NC CNW emitter ECD profile displayed a strong dependence on the Fermi energy and had an average ECD that exceeded the Fowler-Nordheim equation for typical values of the Fermi energy due to closely spaced, singly degenerate energy levels (excluding electron spin), comparatively large electron supply values, and the lack of a transverse, zero-point energy. Such characteristics suggest that emitters with non-planar geometries may be ideal for emission from both an electron supply and electrostatics perspective.

  11. Elementary framework for cold field emission from quantum-confined, non-planar emitters

    SciTech Connect

    Patterson, A. A. Akinwande, A. I.

    2015-05-07

    For suitably small field emitters, the effects of quantum confinement at the emitter tip may have a significant impact on the emitter performance and total emitted current density (ECD). Since the geometry of a quantum system uniquely determines the magnitude and distribution of its energy levels, a framework for deriving ECD equations from cold field electron emitters of arbitrary geometry and dimensionality is developed. In the interest of obtaining semi-analytical ECD equations, the framework is recast in terms of plane wave solutions to the Schrödinger equation via the use of the Jeffreys-Wentzel-Kramers-Brillouin approximation. To demonstrate the framework's consistency with our previous work and its capabilities in treating emitters with non-planar geometries, ECD equations were derived for the normally unconfined cylindrical nanowire (CNW) and normally confined (NC) CNW emitter geometries. As a function of the emitter radius, the NC CNW emitter ECD profile displayed a strong dependence on the Fermi energy and had an average ECD that exceeded the Fowler-Nordheim equation for typical values of the Fermi energy due to closely spaced, singly degenerate energy levels (excluding electron spin), comparatively large electron supply values, and the lack of a transverse, zero-point energy. Such characteristics suggest that emitters with non-planar geometries may be ideal for emission from both an electron supply and electrostatics perspective.

  12. Space charge effects on the current-voltage characteristics of gated field emitter arrays

    NASA Astrophysics Data System (ADS)

    Jensen, K. L.; Kodis, M. A.; Murphy, R. A.; Zaidman, E. G.

    1997-07-01

    Microfabricated field emitter arrays (FEAs) can provide the very high electron current densities required for rf amplifier applications, typically on the order of 100 A/cm2. Determining the dependence of emission current on gate voltage is important for the prediction of emitter performance for device applications. Field emitters use high applied fields to extract current, and therefore, unlike thermionic emitters, the current densities can exceed 103A/cm2 when averaged over an array. At such high current densities, space charge effects (i.e., the influence of charge between cathode and collector on emission) affect the emission process or initiate conditions which can lead to failure mechanisms for field emitters. A simple model of a field emitter will be used to calculate the one-dimensional space charge effects on the emission characteristics by examining two components: charge between the gate and anode, which leads to Child's law, and charge within the FEA unit cell, which gives rise to a field suppression effect which can exist for a single field emitter. The predictions of the analytical model are compared with recent experimental measurements designed to assess space charge effects and predict the onset of gate current. It is shown that negative convexity on a Fowler-Nordheim plot of Ianode(Vgate) data can be explained in terms of field depression at the emitter tip in addition to reflection of electrons by a virtual cathode created when the anode field is insufficient to extract all of the current; in particular, the effects present within the unit cell constitute a newly described effect.

  13. Fabrication of Gate-Electrode Integrated Carbon-Nanotube Bundle Field Emitters

    NASA Technical Reports Server (NTRS)

    Toda, Risaku; Bronikowski, Michael; Luong, Edward; Manohara, Harish

    2008-01-01

    A continuing effort to develop carbon-nanotube-based field emitters (cold cathodes) as high-current-density electron sources has yielded an optimized device design and a fabrication scheme to implement the design. One major element of the device design is to use a planar array of bundles of carbon nanotubes as the field-emission tips and to optimize the critical dimensions of the array (principally, heights of bundles and distances between them) to obtain high area-averaged current density and high reliability over a long operational lifetime a concept that was discussed in more detail in Arrays of Bundles of Carbon Nanotubes as Field Emitters (NPO-40817), NASA Tech Briefs, Vol. 31, No. 2 (February 2007), page 58. Another major element of the design is to configure the gate electrodes (anodes used to extract, accelerate, and/or focus electrons) as a ring that overhangs a recess wherein the bundles of nanotubes are located, such that by virtue of the proximity between the ring and the bundles, a relatively low applied potential suffices to generate the large electric field needed for emission of electrons.

  14. Relation between field energy and RMS emittance in intense particle beams

    SciTech Connect

    Wangler, T.P.; Crandall, K.R.; Mills, R.S.; Reiser, M.

    1985-10-01

    An equation is presented for continuous beams with azimuthal symmetry and continuous linear focusing, which expresses a relationship between the rate of change for squared rms emittance and the rate of change for a quantity we call the nonlinear field energy. The nonlinear field energy depends on the shape of the charge distribution and corresponds to the residual field energy possessed by beams with nonuniform charge distributions. The equation can be integrated for the case of an rms matched beam to yield a formula for space-charge-induced emittance growth that we have tested numerically for a variety of initial distributions. The results provide a framework for discussing the scaling of rms emittance growth and an explanation for the well-established lower limit on output emittance.

  15. Relation between field energy and RMS emittance in intense particle beams

    SciTech Connect

    Wangler, T.P.; Crandall, K.R.; Mills, R.S.; Reiser, M.

    1985-01-01

    An equation is presented for continuous beams with azimuthal symmetry and continuous linear focusing, which expresses a relationship between the rate of change for squared rms emittance and the rate of change for a quantity we call the nonlinear field energy. The nonlinear field energy depends on the shape of the charge distribution and corresponds to the residual field energy possessed by beams with nonuniform charge distributions. The equation can be integrated for the case of an rms matched beam to yield a formula for space-charge-induced emittance growth that we have tested numerically for a variety of initial distributions. The results provide a framework for discussing the scaling of rms emittance growth and an explanation for the well-established lower limit on output emittance. 15 refs., 4 figs.

  16. On the Importance of Symmetrizing RF Coupler Fields for Low Emittance Beams

    SciTech Connect

    Li, Zenghai; Zhou, Feng; Vlieks, Arnold; Adolphsen, Chris; /SLAC

    2011-06-23

    The input power of accelerator structure is normally fed through a coupling slot(s) on the outer wall of the accelerator structure via magnetic coupling. While providing perfect matching, the coupling slots may produce non-axial-symmetric fields in the coupler cell that can induce emittance growth as the beam is accelerated in such a field. This effect is especially important for low emittance beams at low energies such as in the injector accelerators for light sources. In this paper, we present studies of multipole fields of different rf coupler designs and their effect on beam emittance for an X-band photocathode gun being jointly designed with LLNL, and X-band accelerator structures. We will present symmetrized rf coupler designs for these components to preserve the beam emittance.

  17. Fabrication and field emission properties of triode-type carbon nanotube emitter arrays.

    PubMed

    Wu, Jianfeng; Wyse, Madeline; McClain, Devon; Thomas, Nicole; Jiao, Jun

    2009-02-01

    We report here an effective method for the fabrication of a large number of triode-type microgated carbon nanotube field emitter arrays. Our technique combines dual-beam focused ion beam technology and plasma-enhanced chemical vapor deposition, avoiding the tedious lithography and wet chemistry procedures conventionally used to fabricate such structures. Field emission testing revealed that increasing gate voltage by as little as 0.3 V had significant impact on the local electric fields, lowering the turn on and threshold fields by 3.6 and 3.0 V/microm, respectively. The field enhancement factor of the emitter arrays was also increased from 149 to 222. A quantum mechanical model for such triode-type field emission indicates that the local electric field generated by a negatively or positively biased gate directly impacts the tunneling barrier thickness and thus the achievable emitter current. PMID:19161333

  18. Possible emittance growth induced by nonlinear space charge fields for arbitrary particle distributions

    NASA Astrophysics Data System (ADS)

    Kikuchi, Takashi; Horioka, Kazuhiko

    2016-06-01

    A procedure to obtain a ratio of beam radii at final and initial states in arbitrary particle distributions is proposed, and is applied to the estimation of possible emittance growth for Gaussian and thermal equilibrium distributions. The ratios are estimated for Gaussian and thermal equilibrium distributions as a function of tune depression. The possible emittance growth as a function of tune depression and nonlinear field energy factor is also estimated with and without a constant radius ratio approximation. It is confirmed that the possible emittance growths are almost the same in comparison to the cases with and without the constant radius ratio approximation at each distribution.

  19. Experimental investigation of relationship between nonlinear field energy and emittance growth

    NASA Astrophysics Data System (ADS)

    Young, D.; McCready, S. S.; McHarg, M. G.; Brasure, L. D.

    1989-11-01

    Understanding the phenomena of emittance growth in space-charge-dominated particle beams is important to any application that requires a small final emittance. Many researchers have looked at the process of emittance growth under these conditions. Wangler, et al., uses the idea of nonlinear field energy to describe emittance growth. In brief, a beam with a nonuniform radial intensity distribution has a potential energy associated with this distribution. As the beam propagates through a solenoidal magnetic field, this potential energy is turned into transverse kinetic energy and manifests itself as emittance growth. The experimental results shows that there is a relationship between the initial intensity profile and the tune ratio to the emittance of charged particle beams in solenoidal focusing fields. The results also agree with the predicted beam intensity profile changes under focusing for peaked and flat beams. This experiment shows that an experiment to verify this theory by using two different beam intensity profiles is feasible. More experimentation in this area is recommended.

  20. High brightness fiber laser pump sources based on single emitters and multiple single emitters

    NASA Astrophysics Data System (ADS)

    Scheller, Torsten; Wagner, Lars; Wolf, Jürgen; Bonati, Guido; Dörfel, Falk; Gabler, Thomas

    2008-02-01

    Driven by the potential of the fiber laser market, the development of high brightness pump sources has been pushed during the last years. The main approaches to reach the targets of this market had been the direct coupling of single emitters (SE) on the one hand and the beam shaping of bars and stacks on the other hand, which often causes higher cost per watt. Meanwhile the power of single emitters with 100μm emitter size for direct coupling increased dramatically, which also pushed a new generation of wide stripe emitters or multi emitters (ME) of up to 1000μm emitter size respectively "minibars" with apertures of 3 to 5mm. The advantage of this emitter type compared to traditional bars is it's scalability to power levels of 40W to 60W combined with a small aperture which gives advantages when coupling into a fiber. We show concepts using this multiple single emitters for fiber coupled systems of 25W up to 40W out of a 100μm fiber NA 0.22 with a reasonable optical efficiency. Taking into account a further efficiency optimization and an increase in power of these devices in the near future, the EUR/W ratio pushed by the fiber laser manufacturer will further decrease. Results will be shown as well for higher power pump sources. Additional state of the art tapered fiber bundles for photonic crystal fibers are used to combine 7 (19) pump sources to output powers of 100W (370W) out of a 130μm (250μm) fiber NA 0.6 with nominal 20W per port. Improving those TFB's in the near future and utilizing 40W per pump leg, an output power of even 750W out of 250μm fiber NA 0.6 will be possible. Combined Counter- and Co-Propagated pumping of the fiber will then lead to the first 1kW fiber laser oscillator.

  1. Portable Infrared Reflectometer Designed and Manufactured for Evaluating Emittance in the Laboratory or in the Field

    NASA Technical Reports Server (NTRS)

    Jaworske, Donald A.

    2000-01-01

    The optical properties of materials play a key role in spacecraft thermal control. In space, radiant heat transfer is the only mode of heat transfer that can reject heat from a spacecraft. One of the key properties for defining radiant heat transfer is emittance, a measure of how efficiently a surface can reject heat in comparison to a perfect black body emitter. Heat rejection occurs in the infrared region of the spectrum, nominally in the range of 2 to 25 mm. To calculate emittance, one obtains the reflectance over this spectral range, calculates spectral absorptance by difference, and then uses Kirchhoff s Law and the Stefan-Boltzmann equation to calculate emittance. A new portable infrared reflectometer, the SOC 400t, was designed and manufactured to evaluate the emittance of surfaces and coatings in the laboratory or in the field. It was developed by Surface Optics Corporation under a contract with the NASA Glenn Research Center at Lewis Field to replace the Center s aging Gier-Dunkle DB-100 infrared reflectometer. The specifications for the new instrument include a wavelength range of 2 to 25 mm; reflectance repeatability of +/-1 percent; self-calibrating, near-normal spectral reflectance measurements; a full scan measurement time of 3.5 min, a sample size of 1.27 cm (0.5 in.); a spectral resolution selectable from 4, 8, 16, or 32/cm; and optical property characterization utilizing an automatic integration to calculate total emittance in a selectable temperature range.

  2. Microelectrode for energy and current control of nanotip field electron emitters

    SciTech Connect

    Lüneburg, S.; Müller, M. Paarmann, A. Ernstorfer, R.

    2013-11-18

    Emerging experiments and applications in electron microscopy, holography, and diffraction benefit from miniaturized electron guns for compact experimental setups. We present a highly compact microelectrode integrated field emitter that consists of a tungsten nanotip coated with a few micrometers thick polyimide film followed by a several nanometers thick gold film, both positioned behind the exposed emitter apex by approximately 10–30 μm. The control of the electric field strength at the nanometer scale tip apex allows suppression, extraction, and energy tuning of field-emitted electrons. The performance of the microelectrode is demonstrated experimentally and supported by numerical simulations.

  3. Electron gun using carbon-nanofiber field emitter

    NASA Astrophysics Data System (ADS)

    Sakai, Y.; Haga, A.; Sugita, S.; Kita, S.; Tanaka, S.-I.; Okuyama, F.; Kobayashi, N.

    2007-01-01

    An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10

  4. Electron gun using carbon-nanofiber field emitter

    SciTech Connect

    Sakai, Y.; Haga, A.; Sugita, S.; Kita, S.; Tanaka, S.-I.; Okuyama, F.; Kobayashi, N.

    2007-01-15

    An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10

  5. Tunneling-enabled spectrally selective thermal emitter based on flat metallic films

    SciTech Connect

    Wang, Zhu; Tan, Yixuan; Zhou, Ming; Yu, Zongfu; Luk, Ting Shan; Ji, Dengxin; Gan, Qiaoqiang

    2015-03-09

    Infrared thermal emission from metals has important energy applications in thermophotovoltaics, radiative cooling, and lighting. Unfortunately, the emissivity of flat metal films is close to zero because the screening effect prevents metals' fluctuating currents from emitting to the far field. As a result, metal films are often used as reflecting mirrors instead of thermal emitters. Recently, nanostructured metals, such as metamaterials, have emerged as an interesting way to enhance and to spectrally control thermal emission based on plasmonic resonant effects. However, they require sophisticated lithography. Here, we proposed and experimentally demonstrated a completely different mechanism to achieve spectrally selective metallic emitters based on a tunneling effect. This effect allows a simple flat metal film to achieve a near-unity emissivity with controlled spectral selectivity for efficient heat-to-light energy conversion.

  6. Tunneling-enabled spectrally selective thermal emitter based on flat metallic films

    SciTech Connect

    Wang, Zhu; Luk, Ting S.; Tan, Yixuan; Ji, Dengxin; Zhou, Ming; Gan, Qiaoqiang; Yu, Zongfu

    2015-03-11

    Infrared thermal emission from metals has important energy applications in thermophotovoltaics, radiative cooling, and lighting. The emissivity of flat metal films is close to zero because the screening effect prevents metals' fluctuating currents from emitting to the far field. As a result, metal films are often used as reflecting mirrors instead of thermal emitters. Recently, nanostructured metals, such as metamaterials, have emerged as an interesting way to enhance and to spectrally control thermal emission based on plasmonic resonant effects. However, they require sophisticated lithography. Here, we proposed and experimentally demonstrated a completely different mechanism to achieve spectrally selective metallic emitters based on atunneling effect. Furthermore, this effect allows a simple flat metal film to achieve a near-unity emissivity with controlled spectral selectivity for efficient heat-to-light energy conversion.

  7. A fine-focusing x-ray source using carbon-nanofiber field emitter

    SciTech Connect

    Sugimoto, W.; Sugita, S.; Sakai, Y.; Goto, H.; Watanabe, Y.; Ohga, Y.; Kita, S.; Ohara, T.

    2010-08-15

    A fine-focusing x-ray source has been constructed employing a field electron emitter prepared by growing carbon-nanofibers (CNFs) on a metal tip. The x-ray source is composed of a CNF field electron emitter, an electrostatic lens, two magnetic lenses, and a W-target for generating x-rays by electron impact. The CNFs provided field electrons with a current density of J{approx}5x10{sup 9} A/m{sup 2}, which was evaluated with the aid of Fowler-Nordheim theory. The electron beam extracted from the CNF emitter was accelerated to the energies of E=10-25 keV, and then focused by the lenses. By recording the x-ray images of test charts, the optimum resolution of the x-ray source was estimated to be approximately D{sub x}=0.5 {mu}m.

  8. A multi-wavelength study of z = 3.15 Lyman-α emitters in the GOODS South Field

    NASA Astrophysics Data System (ADS)

    Nilsson, K. K.; Møller, P.; Möller, O.; Fynbo, J. P. U.; Michałowski, M. J.; Watson, D.; Ledoux, C.; Rosati, P.; Pedersen, K.; Grove, L. F.

    2007-08-01

    Context: Lyα-emitters have proven to be excellent probes of faint, star-forming galaxies in the high redshift universe. However, although the sample of known emitters is increasingly growing, their nature (e.g. stellar masses, ages, metallicities, star-formation rates) is still poorly constrained. Aims: We aim to study the nature of Lyα-emitters, to find the properties of a typical Lyα-emitting galaxy and to compare these properties with the properties of other galaxies at similar redshift, in particular Lyman-break galaxies. Methods: We have performed narrow-band imaging at the VLT, focused on Lyα at redshift z ≈ 3.15, in the GOODS-S field. We have identified a sample of Lyα-emitting candidates, and we have studied their Spectral Energy Distributions (SEDs). Results: We find that the emitters are best fit by an SED with low metallicity (Z/Z⊙ = 0.005), low dust extinction (AV ≈ 0.26) and medium stellar masses of approximately 109 M⊙. The age is not very well constrained. One object out of 24 appears to be a high redshift Lyα-emitting dusty starburst galaxy. We find filamentary structure as traced by the Lyα-emitters at the 4σ level. The rest-frame UV SED of these galaxies is very similar to that of Lyman Break Galaxies (LBGs) and comply with the selection criteria for U-band drop-outs, except they are intrinsically fainter than the current limit for LBGs. Conclusions: Lyα-emitters are excellent probes of galaxies in the distant universe, and represent a class of star-forming, dust and AGN free, medium mass objects. Based on observations carried out at the European Southern Observatory (ESO) under prog. ID No. 70.A-0447, 274.A-5029 and LP168.A-0485.

  9. Estimation of Metal-Deposited Field Emitters for the Micro Vacuum Tube

    NASA Astrophysics Data System (ADS)

    Ishikawa, Junzo; Tsuji, Hiroshi; Inoue, Kazunori; Nagao, Masayoshi; Sasaki, Takahiro; Kaneko, Takashi; Gotoh, Yasuhito

    1993-03-01

    The material dependence on the emission characterisitics of metal-deposited field emitters has been investigated in order to determine the cathode material suitable for vacuum microelectronics devices. It is shown that the relationships between the intercepts and the slopes of the experimental F-N plots give the apparent differences of the materials even though the radii of the apices are not equal among the emitters. We derive the modified F-N equation from the experimental values and the semi-empirical assumption as a linear variation of the work function with electrical field due to an adsorption effect. From this equation we calculate the emitting area, the radius of the emitter apex and the work function.

  10. Highly reliable field electron emitters produced from reproducible damage-free carbon nanotube composite pastes with optimal inorganic fillers.

    PubMed

    Kim, Jae-Woo; Jeong, Jin-Woo; Kang, Jun-Tae; Choi, Sungyoul; Ahn, Seungjoon; Song, Yoon-Ho

    2014-02-14

    Highly reliable field electron emitters were developed using a formulation for reproducible damage-free carbon nanotube (CNT) composite pastes with optimal inorganic fillers and a ball-milling method. We carefully controlled the ball-milling sequence and time to avoid any damage to the CNTs, which incorporated fillers that were fully dispersed as paste constituents. The field electron emitters fabricated by printing the CNT pastes were found to exhibit almost perfect adhesion of the CNT emitters to the cathode, along with good uniformity and reproducibility. A high field enhancement factor of around 10,000 was achieved from the CNT field emitters developed. By selecting nano-sized metal alloys and oxides and using the same formulation sequence, we also developed reliable field emitters that could survive high-temperature post processing. These field emitters had high durability to post vacuum annealing at 950 °C, guaranteeing survival of the brazing process used in the sealing of field emission x-ray tubes. We evaluated the field emitters in a triode configuration in the harsh environment of a tiny vacuum-sealed vessel and observed very reliable operation for 30 h at a high current density of 350 mA cm(-2). The CNT pastes and related field emitters that were developed could be usefully applied in reliable field emission devices. PMID:24434798

  11. Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters

    NASA Astrophysics Data System (ADS)

    Heo, Kwang; Lee, Byung Yang; Lee, Hyungwoo; Cho, Dong-guk; Arif, Muhammad; Kim, Kyu Young; Choi, Young Jin; Hong, Seunghun

    2016-07-01

    We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

  12. Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters.

    PubMed

    Heo, Kwang; Lee, Byung Yang; Lee, Hyungwoo; Cho, Dong-Guk; Arif, Muhammad; Kim, Kyu Young; Choi, Young Jin; Hong, Seunghun

    2016-07-01

    We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices. PMID:27233004

  13. Flexible electron field emitters fabricated using conducting ultrananocrystalline diamond pyramidal microtips on polynorbornene films

    SciTech Connect

    Sankaran, K. J.; Tai, N. H.; Lin, I. N.

    2014-01-20

    High performance flexible field emitters made of aligned pyramidal shaped conducting ultrananocrystalline diamond (C-UNCD) microtips on polynorbornene substrates is demonstrated. Flexible C-UNCD pyramidal microtips show a low turn-on field of 1.80 V/μm with a field enhancement factor of 4580 and a high emission current density of 5.8 mA/cm{sup 2} (at an applied field of 4.20 V/μm) with life-time stability of 210 min. Such an enhancement in the field emission is due to the presence of sp{sup 2}-graphitic sheath with a nanowire-like diamond core. This high performance flexible C-UNCD field emitter is potentially useful for the fabrication of diverse, flexible electronic devices.

  14. Characterization of NiSi nanowires as field emitters and limitations of Fowler-Nordheim model at the nanoscale

    NASA Astrophysics Data System (ADS)

    Belkadi, Amina B.; Gale, E.; Isakovic, A. F.

    2015-03-01

    Nanoscale field emitters are of technological interest because of the anticipated faster turn-on time, better sustainability and compactness. This report focuses on NiSi nanowires as field emitters for two reasons: (a) possible enhancement of field emission in nanoscale field emitters over bulk, and (b) achieving the same field emission properties as in bulk, but at a lower energy cost. To this end, we have grown, fabricated and characterized NiSi nanowires as field emitters. Depending on the geometry of the NiSi nanowires (aspect ratio, shape etc.), the relevant major field emission parameters, such as (1) the turn-on field, (2) the work function, and (3) the field enhancement factor, can be comparable or even superior to other recently explored nanoscale field emitters, such as CdS and ZnO. We also report on a comparative performance of various nanoscale field emitters and on the difficulties in the performance comparison in the light of relatively poor applicability of the standard Folwer-Nordheim model for field emission analysis for the case of the nanoscale field emitters. Proposed modifications are discussed. This work is supported through SRC-ATIC Grant 2011-KJ-2190. We also acknoweldge BNL-CFN and Cornell CNF facilities and staff.

  15. Doped carbon nanostructure field emitter arrays for infrared imaging

    DOEpatents

    Korsah, Kofi [Knoxville, TN; Baylor, Larry R [Farragut, TN; Caughman, John B [Oak Ridge, TN; Kisner, Roger A [Knoxville, TN; Rack, Philip D [Knoxville, TN; Ivanov, Ilia N [Knoxville, TN

    2009-10-27

    An infrared imaging device and method for making infrared detector(s) having at least one anode, at least one cathode with a substrate electrically connected to a plurality of doped carbon nanostructures; and bias circuitry for applying an electric field between the anode and the cathode such that when infrared photons are adsorbed by the nanostructures the emitted field current is modulated. The detectors can be doped with cesium to lower the work function.

  16. Stable electron field emission from carbon nanotubes emitter transferred on graphene films

    NASA Astrophysics Data System (ADS)

    Zhao, Ning; Chen, Jing; Qu, Ke; Khan, Qasim; Lei, Wei; Zhang, Xiaobing

    2015-08-01

    Carbon nanotubes (CNTs) arrays grown by microwave plasma enhanced chemical vapor deposition (MPCVD) method was transferred onto the substrate covered with graphene layer obtained by thermal chemical vapor deposition (CVD) technology. The graphene buffer layer provides good electrical and thermal contact to the CNTs. The field emission characteristics of this hybrid structure were investigated in this study. Compared with the CNTs arrays directly grown on the silicon substrate, the hybrid emitter shows better field emission performance, such as high emission current and long-term emission stability. The presence of this graphene layer was shown to improve the field emission behavior of CNTs. This work provides an effective way to realize stable field emission from CNTs emitter and similar hybrid structures.

  17. Field electron emission enhancement of graphenated MWCNTs emitters following their decoration with Au nanoparticles by a pulsed laser ablation process.

    PubMed

    Gautier, L-A; Le Borgne, V; Delegan, N; Pandiyan, R; El Khakani, M A

    2015-01-30

    A plasma-enhanced chemical vapor deposition (PECVD) process was adapted to alter the growth of multiwall carbon nanotubes (MWCNTs) so that graphene sheets grow out of their tips. Gold nanoparticle (Au-NP) decoration of graphenated MWCNTs (g-MWCNTs) was obtained by subsequent decoration by a pulsed laser deposition (PLD) process. By varying the number of laser ablation pulses (N(Lp)) in the PLD process, we were able to control the size of the gold nanoparticles and the surface coverage of the decorated g-MWCNTs. The presence of Au-NPs, preferentially located at the tip of the g-MWCNTs emitters, is shown to significantly improve the field electron emission (FEE) properties of the global g-MWCNT/Au-NP nanohybrid films. Indeed, the electric field needed to extract a current density of 0.1 μA cm(-)(2) from the g-MWCNT/Au-NP films was decreased from 2.68 V μm(-1) to a value as low as 0.96 V μm(-1). On the other hand, UV photoelectron spectroscopy (UPS) characterization revealed a decrease in the global work function of the Au-decorated g-MWCNT nanohybrids compared to that of bare g-MWCNT emitters. Surprisingly, the work function of g-MWCNT was found to decrease from 4.9 to 4.7 eV with the addition of Au-NPs-a value lower than the work function of both materials worth 5.2 and 4.9 eV for gold and g-MWCNT, respectively. Our results show that the N(Lp) dependence of the FEE characteristics of the g-MWCNT/Au-NP emitters correlates well with their work function changes. Fowler-Nordheim-theory-based calculations suggest that the significant FEE enhancement of the emitters is also caused by the Au-NPs acting as nanoscale electric field enhancers. PMID:25567743

  18. Field electron emission enhancement of graphenated MWCNTs emitters following their decoration with Au nanoparticles by a pulsed laser ablation process

    NASA Astrophysics Data System (ADS)

    Gautier, L.-A.; Le Borgne, V.; Delegan, N.; Pandiyan, R.; El Khakani, M. A.

    2015-01-01

    A plasma-enhanced chemical vapor deposition (PECVD) process was adapted to alter the growth of multiwall carbon nanotubes (MWCNTs) so that graphene sheets grow out of their tips. Gold nanoparticle (Au-NP) decoration of graphenated MWCNTs (g-MWCNTs) was obtained by subsequent decoration by a pulsed laser deposition (PLD) process. By varying the number of laser ablation pulses (NLp) in the PLD process, we were able to control the size of the gold nanoparticles and the surface coverage of the decorated g-MWCNTs. The presence of Au-NPs, preferentially located at the tip of the g-MWCNTs emitters, is shown to significantly improve the field electron emission (FEE) properties of the global g-MWCNT/Au-NP nanohybrid films. Indeed, the electric field needed to extract a current density of 0.1 μA cm-2 from the g-MWCNT/Au-NP films was decreased from 2.68 V μm-1 to a value as low as 0.96 V μm-1. On the other hand, UV photoelectron spectroscopy (UPS) characterization revealed a decrease in the global work function of the Au-decorated g-MWCNT nanohybrids compared to that of bare g-MWCNT emitters. Surprisingly, the work function of g-MWCNT was found to decrease from 4.9 to 4.7 eV with the addition of Au-NPs—a value lower than the work function of both materials worth 5.2 and 4.9 eV for gold and g-MWCNT, respectively. Our results show that the NLp dependence of the FEE characteristics of the g-MWCNT/Au-NP emitters correlates well with their work function changes. Fowler-Nordheim-theory-based calculations suggest that the significant FEE enhancement of the emitters is also caused by the Au-NPs acting as nanoscale electric field enhancers.

  19. Fabrication of carbon nanotube emitters on the graphite rod and their high field emission performance

    SciTech Connect

    Sun, Yuning; Hoon Shin, Dong; Nam Yun, Ki; Song, Yenan; Saito, Yahachi; Jin Lee, Cheol

    2014-01-27

    Carbon nanotube (CNT) emitters with small emission area were fabricated on graphite rods using CNT films. By introducing the edge polishing process, the field emission performance of the CNT emitter was much improved, which showed a very high emission current of 6.34 mA (1.6 A/cm{sup 2}) under an applied electric field of 5.3 V/μm. It also indicates good long-term emission stability, which reveals no degradation in the emission current for 20 h. The emission patterns demonstrate uniform and well-focused electron beam spots. The enhanced field emission performance is mainly attributed to the suppressed edge emission after the edge polishing process.

  20. Spectrum of classes of point emitters: new tool for nonparaxial optical field modeling.

    PubMed

    Castañeda, Román; Muñoz, Hernán

    2016-08-01

    Numerical modeling of optical fields provides valuable support to both theoretical research and technological development in many optics fields. Fourier methods have been the most widely used tools of numerical modeling. However, important limitations have restricted their application in contemporary research that involve high numerical apertures, short propagation distances, and spatially partially coherent states of light, for instance. The spectrum of classes of point emitters is introduced as a numerical tool that overcomes such limitations for the design, analysis, and synthesis of nonparaxial optical fields in arbitrary states of spatial coherence. In this context, optical processing is realized as the filtering on the spectrum of classes of point emitters performed by the complex degree of spatial coherence that could be implemented dynamically by using programmable devices. PMID:27505639

  1. Silicon based solar cells using a multilayer oxide as emitter

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Wu, Weiliang; Liu, Zongtao; Shen, Hui

    2016-08-01

    In this work, n-type silicon based solar cells with WO3/Ag/WO3 multilayer films as emitter (WAW/n-Si solar cells) were presented via simple physical vapor deposition (PVD). Microstructure and composition of WAW/n-Si solar cells were studied by TEM and XPS, respectively. Furthermore, the dependence of the solar cells performances on each WO3 layer thickness was investigated. The results indicated that the bottom WO3 layer mainly induced band bending and facilitated charge-carriers separation, while the top WO3 layer degraded open-circuit voltage but actually improved optical absorption of the solar cells. The WAW/n-Si solar cells, with optimized bottom and top WO3 layer thicknesses, exhibited 5.21% efficiency on polished wafer with area of 4 cm2 under AM 1.5 condition (25 °C and 100 mW/cm2). Compared with WO3 single-layer film, WAW multilayer films demonstrated better surface passivation quality but more optical loss, while the optical loss could be effectively reduced by implementing light-trapping structures. These results pave a new way for dopant-free solar cells in terms of low-cost and facile process flow.

  2. Study on beam emittance evolution in a nonlinear plasma wake field accelerator with mobile plasma ions

    NASA Astrophysics Data System (ADS)

    An, Weiming; Joshi, Chan; Mori, Warren; Lu, Wei

    2014-10-01

    We study the electron beam evolution in a nonlinear blowout PWFA when the accelerated beam has a very small matched spot size that can cause the plasma ions collapsing towards the beam. Contrary to the common belief, very small emittance growth of the accelerated electron beam is found when the plasma ion collapsing destroys the perfect linear focusing force in the plasma wake field. The improved quasi-static PIC code QuickPIC also allows us to use very high resolution and to model asymmetric spot sizes. Simulation results show that the accelerated beam will reach a steady state after several cm propagation in the plasma (which is why we can do simulations and not let the drive beam evolve). We find that for round beams the ion density (which is Li+) enhancement is indeed by factors of 100, but that the emittance only grows by around 20 percent. For asymmetric spot sizes, the ion collapse is less and emittance growth is zero in the plane with the largest emittance and about 20 percent in the other plane.

  3. Behavior of molecules and molecular ions near a field emitter

    NASA Astrophysics Data System (ADS)

    Gault, Baptiste; Saxey, David W.; Ashton, Michael W.; Sinnott, Susan B.; Chiaramonti, Ann N.; Moody, Michael P.; Schreiber, Daniel K.

    2016-03-01

    The cold emission of particles from surfaces under intense electric fields is a process which underpins a variety of applications including atom probe tomography (APT), an analytical microscopy technique with near-atomic spatial resolution. Increasingly relying on fast laser pulsing to trigger the emission, APT experiments often incorporate the detection of molecular ions emitted from the specimen, in particular from covalently or ionically bonded materials. Notably, it has been proposed that neutral molecules can also be emitted during this process. However, this remains a contentious issue. To investigate the validity of this hypothesis, a careful review of the literature is combined with the development of new methods to treat experimental APT data, the modeling of ion trajectories, and the application of density-functional theory simulations to derive molecular ion energetics. It is shown that the direct thermal emission of neutral molecules is extremely unlikely. However, neutrals can still be formed in the course of an APT experiment by dissociation of metastable molecular ions. This work is a partial contribution of the US Government and therefore is not subject to copyright in the United States.

  4. 128x96 pixel field emitter-array image sensor with HARP target

    NASA Astrophysics Data System (ADS)

    Yamagishi, Toshio; Nanba, Masakazu; Osada, Katsunori; Takiguchi, Yoshiro; Okazaki, Saburo; Egami, Norifumi; Tanioka, Kenkichi; Tanaka, Mitsuru; Itoh, Shigeo

    2002-04-01

    In pursuit of developing a next-generation pick-up device having high definition and ultrahigh sensitivity features, research continues on a new type of image sensor that combines a HARP target and a field emitter array. A new field emitter array on a small-sized substrate is designed and a unique packaging technique is proposed. The prototype device is sealed in a vacuum package with a thickness of only about 10 mm and has 128 horizontal and 96 vertical pixels. Experimental results show that images could be successfully reproduced for the first time ever in a device of this type. Highly sensitive characteristics and propr resolution were also obtained with the device. The prototype image sensor can operate stably for more than 250 hours, demonstrating its feasibility and potential as a next- generation image pickup device.

  5. 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.

  6. Robust Radar Emitter Recognition Based on the Three-Dimensional Distribution Feature and Transfer Learning

    PubMed Central

    Yang, Zhutian; Qiu, Wei; Sun, Hongjian; Nallanathan, Arumugam

    2016-01-01

    Due to the increasing complexity of electromagnetic signals, there exists a significant challenge for radar emitter signal recognition. To address this challenge, multi-component radar emitter recognition under a complicated noise environment is studied in this paper. A novel radar emitter recognition approach based on the three-dimensional distribution feature and transfer learning is proposed. The cubic feature for the time-frequency-energy distribution is proposed to describe the intra-pulse modulation information of radar emitters. Furthermore, the feature is reconstructed by using transfer learning in order to obtain the robust feature against signal noise rate (SNR) variation. Last, but not the least, the relevance vector machine is used to classify radar emitter signals. Simulations demonstrate that the approach proposed in this paper has better performances in accuracy and robustness than existing approaches. PMID:26927111

  7. Highly tunable-emittance radiator based on semiconductor-metal transition of VO2 thin films

    NASA Astrophysics Data System (ADS)

    Hendaoui, Ali; Émond, Nicolas; Chaker, Mohamed; Haddad, Émile

    2013-02-01

    This paper describes a VO2-based smart structure with an emittance that increases with the temperature. A large tunability of the spectral emittance, which can be as high as 0.90, was achieved. The transition of the total emittance with the temperature was fully reversible according to a hysteresis cycle, with a transition temperature of 66.5 °C. The total emittance of the device was found to be 0.22 and 0.71 at 25 °C and 100 °C, respectively. This emittance performance and the structure simplicity are promising for the next generation of energy-efficient cost-effective passive thermal control systems of spacecrafts.

  8. Robust Radar Emitter Recognition Based on the Three-Dimensional Distribution Feature and Transfer Learning.

    PubMed

    Yang, Zhutian; Qiu, Wei; Sun, Hongjian; Nallanathan, Arumugam

    2016-01-01

    Due to the increasing complexity of electromagnetic signals, there exists a significant challenge for radar emitter signal recognition. To address this challenge, multi-component radar emitter recognition under a complicated noise environment is studied in this paper. A novel radar emitter recognition approach based on the three-dimensional distribution feature and transfer learning is proposed. The cubic feature for the time-frequency-energy distribution is proposed to describe the intra-pulse modulation information of radar emitters. Furthermore, the feature is reconstructed by using transfer learning in order to obtain the robust feature against signal noise rate (SNR) variation. Last, but not the least, the relevance vector machine is used to classify radar emitter signals. Simulations demonstrate that the approach proposed in this paper has better performances in accuracy and robustness than existing approaches. PMID:26927111

  9. Thermal emittance enhancement of graphite-copper composites for high temperature space based radiators

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Forkapa, Mark J.; Cooper, Jill M.

    1991-01-01

    Graphite-copper composites are candidate materials for space based radiators. The thermal emittance of this material, however, is a factor of two lower than the desired emittance for these systems of greater than or equal to 0.85. Arc texturing was investigated as a surface modification technique for enhancing the emittance of the composite. Since the outer surface of the composite is copper, and samples of the composite could not be readily obtained for testing, copper was used for optimization testing. Samples were exposed to various frequencies and currents of arcs during texturing. Emittances near the desired goal were achieved at frequencies less than 500 Hz. Arc current did not appear to play a major role under 15 amps. Particulate carbon was observed on the surface, and was easily removed by vibration and handling. In order to determine morphology adherence, ultrasonic cleaning was used to remove the loosely adherent material. This reduced the emittance significantly. Emittance was found to increase with increasing frequency for the cleaned samples up to 500 Hz. The highest emittance achieved on these samples over the temperature range of interest was 0.5 to 0.6, which is approximately a factor of 25 increase over the untextured copper emittance.

  10. Characterization of X-ray charge neutralizer using carbon-nanotube field emitter

    NASA Astrophysics Data System (ADS)

    Okawaki, Shuhei; Abo, Satoshi; Wakaya, Fujio; Yamashita, Hayato; Abe, Masayuki; Takai, Mikio

    2016-06-01

    An X-ray charge neutralizer using a screen-printed carbon-nanotube field emitter is demonstrated to show the possibility of a large-area flat-panel charge neutralizer, although the device dimensions in the present work are not very large. The X-ray yields and spectra are characterized to estimate the ion generation rate as one of the figures of merit of neutralizers. Charge neutralization characteristics are measured and show good performance.

  11. Ultralow biased field emitter using single-wall carbon nanotube directly grown onto silicon tip by thermal chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kazuhiko; Kinosita, Seizo; Gotoh, Yoshitaka; Uchiyama, Tetsuo; Manalis, Scott; Quate, Calvin

    2001-01-01

    A carbon-nanotube field emitter which has single-wall carbon nanotubes with a diameter of 1-2 nm grown directly onto the Si tips by thermal chemical vapor deposition was developed. Owing to the 10-20 times smaller diameter of the nanotube than the conventional silicon (Si) tip, the fabricated carbon-nanotube field emitter showed an ultralow threshold voltage of 10 V for the field emission of electrons, which is more than ten times smaller value than the conventional Si emitter.

  12. Enhanced Field-Emission Performance from Carbon Nanotube Emitters on Nickel Foam Cathodes

    NASA Astrophysics Data System (ADS)

    Song, Meng; Xu, Peng; Han, Lijing; Yi, Lan; Wang, Xu; Li, Zhenhua; Shang, Xuefu; Wang, Xiumin; Wu, Huizhen; Zhao, Pei; Song, Yenan; Wang, Miao

    2016-04-01

    We present a three-dimensionally configured cathode with enhanced field-emission performance formed by combining carbon nanotube (CNT) emitters with a nickel foam (NiF) substrate via a conventional screen-printing technique. The CNT/NiF cathode has low turn-on electric field of 0.53 V μm-1 (with current density of 10 μA cm-2) and threshold electric field of 0.87 V μm-1 (with current density of 0.1 mA cm-2), and a very high field enhancement factor of 1.4 × 104. The porous structure of the NiF substrate can greatly improve the field-emission properties due to its large specific surface area that can accommodate more CNTs and increase the emitter density, as well as its high electrical and thermal conductivities that facilitate current transition and heat dissipation in the cathode. Most importantly, the local electric field was also enhanced by the multistage effect resulting from the rough metal surface, which furthermore leads to a high field enhancement factor. We believe that this improved field-emission performance makes such cathodes promising candidates for use in various field-emission applications.

  13. Field and laboratory evaluation of a diffusive emitter for semipassive release of PCE to an aquifer

    SciTech Connect

    Arildskov, N.P.; Devlin, J.F.

    2000-02-01

    In controlled field experiments or model aquifers, it is sometimes desirable to introduce solutes below the water table without perturbing the flow system. Diffusive emitters offer a means of achieving that goal. In this study, two laboratory experiments were conducted to evaluate nylon tubing as a diffusive emitter for tetrachloroethene (PCE). The initial approach was to pump a saturated aqueous PCE solution through a piece of nylon tubing immersed in a flow-through contractor vessel. Millipore water was pumped through the contractor vessel at a constant rate. Due to PCE diffusion through the nylon, a steady-state concentration in the contractor vessel eventually developed. The process was well described by a computer model that accounted for retarded diffusion through the nylon. In a second experiment, pieces of nylon tubing were exposed to a relatively low concentration of PCE in water for 10 days in gently rotated hypovials. With the aid of a second diffusion model, the bulk diffusion coefficient was obtained from the concentration history of the solution. With the different experimental conditions taken into account, there was reasonably good agreement between the bulk diffusion coefficients in the two experiments. The results were used in the field design of a semipassive release system. Evaluation of this system showed a lower than expected steady-state concentration of PCE inside the releasing wells. The difference is likely due to lower temperature, variable PCE concentrations in the nylon tubing, and nonideal mixing in the wells. The work has shown that laboratory derived diffusion coefficients for polymeric materials are likely to be larger than, but within an order of magnitude of, the effective diffusion coefficients exhibited by emitters in the field. Nevertheless, with temperature corrections taken into account and proper well development, these values could be used to design emitters that would suit most practical applications.

  14. Planar ultrananocrystalline diamond field emitter in accelerator radio frequency electron injector: Performance metrics

    SciTech Connect

    Baryshev, Sergey V. Antipov, Sergey; Jing, Chunguang; Qiu, Jiaqi; Shao, Jiahang; Liu, Wanming; Gai, Wei; Pérez Quintero, Kenneth J.; Sumant, Anirudha V.; Kanareykin, Alexei D.

    2014-11-17

    A case performance study of a planar field emission cathode (FEC) based on nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, was carried out in an RF 1.3 GHz electron gun. The FEC was a 100 nm (N)UNCD film grown on a 20 mm diameter stainless steel disk with a Mo buffer layer. At surface gradients 45–65 MV/m, peak currents of 1–80 mA (equivalent to 0.3–25 mA/cm{sup 2}) were achieved. Imaging with two YAG screens confirmed emission from the (N)UNCD surface with (1) the beam emittance of 1.5 mm × mrad/mm-rms and (2) longitudinal FWHM and rms widths of non-Gaussian energy spread of 0.7% and 11% at an electron energy of 2 MeV. Current stability was tested over the course of 36 × 10{sup 3} RF pulses (equivalent to 288 × 10{sup 6 }GHz oscillations)

  15. Application of Anisotropic Conductive Film to Fabrication of Molybdenum Field Emitter Arrays Using Transfer Mold Technique

    NASA Astrophysics Data System (ADS)

    Cho, Eou Sik; Ahn, Min Hyung; Kwon, Sang Jik

    2008-08-01

    In the fabrication of molybdenum field emitter arrays (Mo FEA) by the transfer mold technique, anisotropic conductive film (ACF) was applied to the bond between the inverted mold structure and the transferred glass substrate. Without any electrical treatment of electrostatic bonding, the inverted mold was successfully bonded to an indium tin oxide (ITO) glass substrate under optimized thermal and pressure conditions. No additional conductive layers were used in the bonding process, and the bonded ACF was not chemically affected in the wet-etch process of the silicon inverted mold structure. The fabricated Mo FEA was structurally and electrically investigated and an anode current of 10 nA per emitter was obtained at a gate bias of 94 V. The results demonstrate the possibility of selective conduction in the fabrication of transfer mold FEA using ACF bonding.

  16. Ultrafast electron microscopy and diffraction with laser-driven field emitters

    NASA Astrophysics Data System (ADS)

    Ropers, Claus

    2015-03-01

    Ultrafast structural dynamics in solids and nanostructures can be investigated by an increasing number of sophisticated electron and x-ray diffraction techniques. Electrons are particularly suited for this purpose, exhibiting high scattering cross-sections and allowing for beam control by versatile electrostatic or magnetic lens systems. The capabilities of time-resolved electron imaging techniques critically depend on the employed source of laser-driven ultrashort electron pulses. Nanoscopic sources offer exceptional possibilities for the generation of electron probe pulses with very short durations and high spatial beam coherence. In this talk, I will discuss recent progress in the development of ultrafast electron microscopy and diffraction based on nanoscopic photocathodes. In particular, we implemented ultrafast low-energy electron diffraction (ULEED) and ultrafast transmission electron microscopy (UTEM) driven by nonlinear photoemission from field emission tips. ULEED enables the study of structural changes with high temporal resolution and ultimate surface sensitivity, at sub-keV electron energies. As a first application of this technique, we studied the structural phase transition in a stripe-like polymer superstructure on freestanding monolayer graphene. An advanced UTEM instrument was realized by custom modifications of a standard transmission electron microscope, leading to electron focal spot sizes in the microscope's sample plane of about 10 nm and electron pulse durations of less than 700 fs. Utilizing these features, we investigate the quantum-coherent interaction between the ultrashort electron pulse and the optical near-field of an illuminated nanostructure. Finally, further applications and prospects of ultrafast electron imaging, diffraction and spectroscopy using nanoscale field emitters will be discussed.

  17. Thermodynamic characterization of a diamond-based electron emitter

    NASA Astrophysics Data System (ADS)

    Fisher, T. S.; Strauss, A. M.; Davidson, J. L.; Kang, W. P.

    2000-01-01

    This paper contains a thermodynamic analysis of electron emission from a micro-fabricated diamond tip array. The analysis is based on experimental measurements of the current-voltage characteristics of an actual device. Field enhancement, applied field, and electrical current density are shown to influence thermodynamic performance. The idealized thermodynamic analysis predicts cooling rates above 10 W/cm2 for an existing device under room temperature operation and that 100 W/cm2 may be possible for future devices. .

  18. Demonstration of cathode emittance dominated high bunch charge beams in a DC gun-based photoinjector

    NASA Astrophysics Data System (ADS)

    Gulliford, Colwyn; Bartnik, Adam; Bazarov, Ivan; Dunham, Bruce; Cultrera, Luca

    2015-03-01

    We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (≥100 pC) beams produced in the DC gun-based Cornell energy recovery linac photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittances measured at 9-9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These results, previously thought achievable only with RF guns, demonstrate that DC gun based photoinjectors are capable of delivering beams with sufficient single bunch charge and beam quality suitable for many current and next generation accelerator projects such as Energy Recovery Linacs and Free Electron Lasers.

  19. Demonstration of cathode emittance dominated high bunch charge beams in a DC gun-based photoinjector

    SciTech Connect

    Gulliford, Colwyn Bartnik, Adam Bazarov, Ivan; Dunham, Bruce; Cultrera, Luca

    2015-03-02

    We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (≥100 pC) beams produced in the DC gun-based Cornell energy recovery linac photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittances measured at 9–9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These results, previously thought achievable only with RF guns, demonstrate that DC gun based photoinjectors are capable of delivering beams with sufficient single bunch charge and beam quality suitable for many current and next generation accelerator projects such as Energy Recovery Linacs and Free Electron Lasers.

  20. A digital miniature x-ray tube with a high-density triode carbon nanotube field emitter

    SciTech Connect

    Jeong, Jin-Woo; Kang, Jun-Tae; Choi, Sungyoul; Kim, Jae-Woo; Song, Yoon-Ho; Ahn, Seungjoon

    2013-01-14

    We have fabricated a digital miniature x-ray tube (6 mm in diameter and 32 mm in length) with a high-density triode carbon nanotube (CNT) field emitter for special x-ray applications. The triode CNT emitter was densely formed within a diameter of below 4 mm with the focusing-functional gate. The brazing process enables us to obtain and maintain a desired vacuum level for the reliable electron emission from the CNT emitters after the vacuum packaging. The miniature x-ray tube exhibited a stable and reliable operation over 250 h in a pulse mode at an anode voltage of above 25 kV.

  1. PHOTOMETRIC PROPERTIES OF Ly{alpha} EMITTERS AT z {approx} 4.86 IN THE COSMOS 2 SQUARE DEGREE FIELD

    SciTech Connect

    Shioya, Y.; Taniguchi, Y.; Nagao, T.; Saito, T.; Trump, J.; Sasaki, S. S.; Ideue, Y.; Nakajima, A.; Matsuoka, K.; Murayama, T.; Scoville, N. Z.; Capak, P.; Ellis, R. S.; Sanders, D. B.; Kartaltepe, J.; Mobasher, B.; Aussel, H.; Koekemoer, A.; Carilli, C.; Garilli, B.

    2009-05-01

    We present results of a survey for Ly{alpha} emitters at z {approx} 4.86 based on optical narrowband ({lambda} {sub c} = 7126 A, {delta}{lambda} = 73 A) and broadband (B, V, r', i', and z') observations of the Cosmic Evolution Survey field using Suprime-Cam on the Subaru Telescope. We find 79 Ly{alpha} emitter (LAE) candidates at z {approx} 4.86 over a contiguous survey area of 1.83 deg{sup 2}, down to the Ly{alpha} line flux of 1.47 x 10{sup -17} erg s{sup -1} cm{sup -2}. We obtain the Ly{alpha} luminosity function with a best-fit Schechter parameters of log L* = 42.9{sup +0.5} {sub -0.3} erg s{sup -1} and {phi}* = 1.2{sup +8.0} {sub -1.1} x 10{sup -4} Mpc{sup -3} for {alpha} = -1.5 (fixed). The two-point correlation function for our LAE sample is {xi}(r) = (r/4.4{sup +5.7} {sub -2.9} Mpc){sup -1.90{+-}}{sup 0.22}. In order to investigate the field-to-field variations of the properties of Ly{alpha} emitters, we divide the survey area into nine tiles of 0.{sup 0}5 x 0.{sup 0}5 each. We find that the number density varies with a factor of {approx_equal}2 from field to field with high statistical significance. However, we find no significant field-to-field variance when we divide the field into four tiles with 0.{sup 0}7 x 0.{sup 0}7 each. We conclude that at least 0.5 deg{sup 2} survey area is required to derive averaged properties of LAEs at z {approx} 5, and our survey field is wide enough to overcome the cosmic variance.

  2. Pepper-pot based emittance measurements of the AWA photoinjector.

    SciTech Connect

    Power, J. G.; Conde, M. E.; Gai, W.; Gao, F.; Konecny, D.; Liu, W.; Yusof, Z.; Rihaoui, M.; Piot, Ph.; High Energy Physics; Northern Illinois Univ.

    2008-01-01

    The Argonne Wakefield Accelerator (AWA) RF photocathode gun is a 1.5 cell, L-band, RF photocathode gun operating at 77 MV/m, with emittance compensating solenoids, a magnesium photocathode, and generates an 8 MeV, 1 nC - 100 nC beam. In this paper, we report on a parametric set of measurements to characterize the transverse trace space of the 1 nC electron beam directly out of the gun. We emphasize details of the experimental setup, image analysis, and end with a comparison of the measurements to PARMELA simulations.

  3. Wide-range Vacuum Measurements from MWNT Field Emitters Grown Directly on Stainless Steel Substrates.

    PubMed

    Zhang, Jian; Li, Detian; Zhao, Yangyang; Cheng, Yongjun; Dong, Changkun

    2016-12-01

    The field emission properties and the vacuum measurement application are investigated from the multi-walled carbon nanotubes (MWNTs) grown directly on catalytic stainless steel substrates. The MWNT emitters present excellent emission properties after the acid treatment of the substrate. The MWNT gauge is able to work down to the extreme-high vacuum (XHV) range with linear measurement performance in wide range from 10(-11) to 10(-6) Torr. A modulating grid is attempted with improved gauge sensitivity. The extension of the lower pressure limit is attributed largely to low outgassing effect due to direct growth of MWNTs and justified design of the electron source. PMID:26738501

  4. Wide-range Vacuum Measurements from MWNT Field Emitters Grown Directly on Stainless Steel Substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Li, Detian; Zhao, Yangyang; Cheng, Yongjun; Dong, Changkun

    2016-01-01

    The field emission properties and the vacuum measurement application are investigated from the multi-walled carbon nanotubes (MWNTs) grown directly on catalytic stainless steel substrates. The MWNT emitters present excellent emission properties after the acid treatment of the substrate. The MWNT gauge is able to work down to the extreme-high vacuum (XHV) range with linear measurement performance in wide range from 10-11 to 10-6 Torr. A modulating grid is attempted with improved gauge sensitivity. The extension of the lower pressure limit is attributed largely to low outgassing effect due to direct growth of MWNTs and justified design of the electron source.

  5. Reliability tests of gated silicon field emitters for use in space

    NASA Astrophysics Data System (ADS)

    Aplin, K. L.; Collingwood, C. M.; Kent, B. J.

    2004-07-01

    Neutralizers are required to prevent spacecraft charging from satellite ion propulsion. This paper discusses the development of a gated silicon tip field emitter (FE) neutralizer, specified to deliver 6 mA, with each tip emitting a mean current of 7 nA. It is important to investigate factors affecting the lifetime of field emitter arrays for a space application, as longevity and reliability are both critical requirements. Semi-automated procedures to prepare 400 arrays, each consisting of 765 FEs, for life tests are described with failure conditions strictly defined by mission constraints. Results of 25 life tests on 72 arrays driven to failure at constant emission current are summarized, and a case study of one test is presented. Two of the three failure mechanisms identified are consistent with thermal failure and damage by ion bombardment. Reduced field enhancement from tip erosion caused by ion bombardment is a common explanation for FE failure. However, scanning electron microscope examination of tip apex diameters showed no significant relationship between array failure and apex geometry. The third failure mechanism was associated with short-lived arrays and may be caused by manufacturing defects. Substantial intrinsic variability was observed in the arrays tested, even with the rigorous production standards required for space applications. Arrays without manufacturing defects had lifetimes of thousands of hours.

  6. Magnetic field control of near-field radiative heat transfer and the realization of highly tunable hyperbolic thermal emitters

    NASA Astrophysics Data System (ADS)

    Moncada-Villa, E.; Fernández-Hurtado, V.; García-Vidal, F. J.; García-Martín, A.; Cuevas, J. C.

    2015-09-01

    We present a comprehensive theoretical study of the magnetic field dependence of the near-field radiative heat transfer (NFRHT) between two parallel plates. We show that when the plates are made of doped semiconductors, the near-field thermal radiation can be severely affected by the application of a static magnetic field. We find that irrespective of its direction, the presence of a magnetic field reduces the radiative heat conductance, and dramatic reductions up to 700% can be found with fields of about 6 T at room temperature. We show that this striking behavior is due to the fact that the magnetic field radically changes the nature of the NFRHT. The field not only affects the electromagnetic surface waves (both plasmons and phonon polaritons) that normally dominate the near-field radiation in doped semiconductors, but it also induces hyperbolic modes that progressively dominate the heat transfer as the field increases. In particular, we show that when the field is perpendicular to the plates, the semiconductors become ideal hyperbolic near-field emitters. More importantly, by changing the magnetic field, the system can be continuously tuned from a situation where the surface waves dominate the heat transfer to a situation where hyperbolic modes completely govern the near-field thermal radiation. We show that this high tunability can be achieved with accessible magnetic fields and very common materials like n -doped InSb or Si. Our study paves the way for an active control of NFRHT and it opens the possibility to study unique hyperbolic thermal emitters without the need to resort to complicated metamaterials.

  7. Advances In Vertical Solid-State Current Limiters For Individual Field Emitter Regulation In High-Density Arrays

    NASA Astrophysics Data System (ADS)

    Hill, Frances A.; Velásquez-García, Luis F.

    2015-12-01

    We report the design, fabrication, and characterization of improved solid-state elements intended for individual regulation of field emitters part of high-density arrays. We demonstrate a high-yield, CMOS compatible fabrication process of single-crystal, vertical, ungated, n-type silicon field-effect transistors (FETs); each device behaves as a current source when is biased at a voltage larger than its drain-source saturation voltage. An ungated FET in saturation connected in series to a field emitter can compensate for the wide variation in current-voltage characteristics of the field emitters due to the tip radii spread present in any field emitter array, which should result in emitter burn-out protection, larger array utilization, and smaller array emission non-uniformity. Using 1-2 Ωcm single-crystal n-Si wafers, we fabricated arrays of 25 μm tall vertical ungated FETs with 0.5 μm diameter that span two orders of magnitude of array size. Experimental characterization of the arrays demonstrates that the current is limited with > 3.5 V bias voltage to the same ∼6 μA (6 A.cm-2) per-FET value. Finite element simulations of the device predict a saturation voltage close to the experimental value and a saturation current within a factor of two of the experimental value.

  8. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2012-04-10

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  9. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2013-10-29

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  10. Investigation of Field Emitter Array Vacuum Microtriodes for Space Electronics Applications

    NASA Technical Reports Server (NTRS)

    Smith, Mark A.; Kapoor, Vik J.

    1997-01-01

    Research into processing techniques for fabrication of vacuum microelectronic devices has been carried out, with special emphasis being given to the growth of silicon dioxide thin films. Oxide films ranging from 30 nm to approximately 2 micrometers have been grown on single crystal silicon wafers. Metal-oxide-semiconductor capacitor test structures have been made from some of these oxide films, and current-versus-voltage plots for these structures have been measured. It has been observed that the rate of applied voltage across the oxide films produces marked differences in measured leakage current. Breakdown fields across two of the thinnest oxide films have been measured and are comparable with highest values reported in literature. Several silicon wafers were processed to make field- emitter array diodes, and were delivered to collaborators at NASA-Lewis Research Center for final fabrication steps and testing.

  11. Transmission type flat-panel X-ray source using ZnO nanowire field emitters

    SciTech Connect

    Chen, Daokun; Song, Xiaomeng; Zhang, Zhipeng; Chen, Jun; Li, Ziping; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

    2015-12-14

    A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18–20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

  12. Transmission type flat-panel X-ray source using ZnO nanowire field emitters

    NASA Astrophysics Data System (ADS)

    Chen, Daokun; Song, Xiaomeng; Zhang, Zhipeng; Li, Ziping; She, Juncong; Deng, Shaozhi; Xu, Ningsheng; Chen, Jun

    2015-12-01

    A transmission type flat-panel X-ray source in diode structure was fabricated. Large-scale patterned ZnO nanowires grown on a glass substrate by thermal oxidation were utilized as field emitters, and tungsten thin film coated on silica glass was used as the transmission anode. Uniform distribution of X-ray generation was achieved, which benefited from the uniform electron emission from ZnO nanowires. Self-ballasting effect induced by the intrinsic resistance of ZnO nanowire and decreasing of screening effect caused by patterned emitters account for the uniform emission. Characteristic X-ray peaks of W-L lines and bremsstrahlung X-rays have been observed under anode voltages at a range of 18-20 kV, the latter of which were the dominant X-ray signals. High-resolution X-ray images with spatial resolution less than 25 μm were obtained by the flat-panel X-ray source. The high resolution was attributed to the small divergence angle of the emitted X-rays from the transmission X-ray source.

  13. Conditioning with α-emitter based radioimmunotherapy in canine allogeneic hematopoietic cell transplantation

    PubMed Central

    Kornblit, Brian; Chen, Yun; Sandmaier, Brenda M.

    2012-01-01

    With the introduction of nonmyeloablative conditioning, hematopoietic cell transplantation (HCT) has become a viable treatment option for patients who due to age or comorbidities are ineligible for high dose conditioning. However, relapse and toxicities are still major problems in HCT. Radioimmunotherapy (RIT)-based conditioning is a promising approach that has the ability to specifically target radiation to hematopoietic cells. The most widely investigated isotopes are the β-emitters, but because of long path lengths and low linear energy transfer, α-emitters which have more favorable physical characteristics, might prove to be a better alternative. In the current study we have investigated the efficacy and safety of α-emitter based RIT as the only form of conditioning in a preclinical model of canine allogeneic HCT. PMID:22772070

  14. Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao-Guo; Wang, Yuan; Zhang, Kai-Zhi; Yang, Guo-Jun; Shi, Jin-Shui; Deng, Jian-Jun; Li, Jin

    2014-01-01

    One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns (FWHM) electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm (FWHM) in diameter and the corresponding beam divergence is about 10.5 mrad.

  15. Thermophotovoltaic energy converters based on thin film selective emitters and InGaAs photovoltaic cells

    SciTech Connect

    Fatemi, N.S.; Hoffman, R.H.; Wilt, D.M.; Lowe, R.A.; Garverick, L.M.; Scheiman, D.

    1996-02-01

    This paper presents the results of an investigation to demonstrate thermophotovoltaic energy conversion using InGaAs photovoltaic cells, yttrium-aluminum-garnet- (YAG-) based selective emitters, and bandpass/reflector filters, with the heat source operating at 1100{degree}C. InGaAs cells were grown on InP by organometallic vapor phase epitaxy with bandgaps of 0.60 and 0.75 eV and coupled to Ho-, Er-, and Er-Tm-doped YAG selective emitters. Infrared reflector and/or shortpass filters were also used to increase the ratio of in-band to out-of-band radiation from the selective emitters. Efficiencies as high as 13.2{percent} were recorded for filtered converters. {copyright} {ital 1996 American Institute of Physics.}

  16. Generation of Radiation Pressure in Thermally Induced Ultrasonic Emitter Based on Nanocrystalline Silicon

    NASA Astrophysics Data System (ADS)

    Hirota, Jun; Shinoda, Hiroyuki; Koshida, Nobuyoshi

    2004-04-01

    To confirm the applicability of thermally induced ultrasonic emission from nanocrystalline silicon (nc-Si) devices as radiation pressure generators, the dynamic response has been investigated under a pulse operation mode. The nc-Si emitter is fabricated on a p-type Si wafer by conventional electrochemical anodization with subsequent formation of the surface electrode. Due to the flat nature of the frequency response of this emitter, the device emits an acoustic wave with little distortion under the pulse-drive condition. It is shown that a significant radiation pressure of 34.5 Pa is generated by a concentrated burst-like electrical input, and that a beam located at a distance can be levitated as a result of the mechanical loading effect. This silicon-based emitter is attractive for applications to integrated nano- or micro-electromechanical systems.

  17. Large area InN terahertz emitters based on the lateral photo-Dember effect

    SciTech Connect

    Wallauer, Jan Grumber, Christian; Walther, Markus; Polyakov, Vladimir; Iannucci, Robert; Cimalla, Volker; Ambacher, Oliver

    2015-09-14

    Large area terahertz emitters based on the lateral photo-Dember effect in InN (indium nitride) are presented. The formation of lateral photo-Dember currents is induced by laser-illumination through a microstructured metal cover processed onto the InN substrate, causing an asymmetry in the lateral photogenerated charge carrier distribution. Our design uses simple metal structures, which are produced by conventional two-dimensional micro-structuring techniques. Having favoring properties as a photo-Dember material InN is particularly well-suited as a substrate for our emitters. We demonstrate that the emission intensity of the emitters can be significantly influenced by the structure of the metal cover leaving room for improvement by optimizing the masking structures.

  18. Neutralization of Space Charge Effects for Low Energy Ion Beams Using Field Emitters

    SciTech Connect

    Nicolaescu, D.; Sakai, S.; Matsuda, K.; Gotoh, Y.; Ishikawa, J.

    2008-11-03

    The paper presents models and computations for neutralization of space charge effects using electrons provided by field emitter arrays. Different ion species ({sup 11}B{sup +},{sup 31}P{sup +},{sup 75}As{sup +}) with energy in the range E{sub ion} = 200 eV-1 keV have been considered. The ion beam divergence is studied as a function of electron beam geometry and physical parameters (electron and ion energy, electron/ion current ratio I{sub el}/I{sub ion}). The electron beam geometry takes into account electron source positions and initial launching angles. It is shown that optimal ion beam neutralization occurs for low energy electrons emitted parallel to the ion beam.

  19. An ordered Si nanowire with NiSi2 tip arrays as excellent field emitters.

    PubMed

    Liu, Chun-Yi; Li, Wun-Shan; Chu, Li-Wei; Lu, Ming-Yen; Tsai, Cho-Jen; Chen, Lih-Juann

    2011-02-01

    A method was developed to grow ordered silicon nanowire with NiSi(2) tip arrays by reacting nickel thin films on silica-coated ordered Si nanowire (NW) arrays. The coating of thin silica shell on Si NW arrays has the effect of limiting the diffusion of nickel during the silicidation process to achieve the single crystalline NiSi(2) NWs. In the meantime, it relieves the distortion of the NWs caused by the strain associated with formation of NiSi(2) to maintain the straightness of the nanowire and the ordering of the arrays. Other nickel silicide phases such as Ni(2)Si and NiSi were obtained if the silicidation processes were conducted on the ordered Si NWs without a thin silica shell. Excellent field emission properties were found for NiSi(2)/Si NW arrays with a turn on field of 0.82 V µm(-1) and a threshold field of 1.39 V µm(-1). The field enhancement factor was calculated to be about 2440. The stability test showed a fluctuation of about 7% with an applied field of 2.6 V µm(-1) for a period of 24 h. The excellent field emission characteristics are attributed to the well-aligned and highly ordered arrangement of the single crystalline NiSi(2)/Si heterostructure field emitters. In contrast to other growth methods, the present growth of ordered nickel silicide/Si NWs on silicon is compatible with silicon nanoelectronics device processes, and also provides a facile route to grow other well-aligned metal silicide NW arrays. The advantages will facilitate its applications as field emission devices. PMID:21178255

  20. Modeling of carbon nanotube-based devices: from nanoFETs to THz emitters

    NASA Astrophysics Data System (ADS)

    Di Carlo, Aldo; Pecchia, Alessandro; Petrolati, Eleonora; Paoloni, Claudio

    2006-08-01

    In the first part of the present contribution, we will report on transport calculations of nanoscaled devices based on Carbon Nanotubes obtained via self-consistent density-functional method coupled with non-equilibrium Green's function approaches. In particular, density functional tight-binding techniques are very promising due to their intrinsic efficiency. This scheme allows treatment of systems comprising a large number of atoms and enables the computation of the current flowing between two or more contacts in a fully self-consistent manner with the open boundary conditions that naturally arise in transport problems. We will give a description of this methodology and application to field effect transistor based on Carbon nanotubes. The advances in manufacturing technology are allowing new opportunities even for vacuum electron devices producing radio-frequency radiation. Modern micro and nano-technologies can overcome the typical severe limitations of vacuum tube devices. As an example, Carbon Nanotubes used as cold emitters in micron-scaled triodes allow for frequency generation up to THz region. The purpose of the second part of this contribution will be a description of the modelling of Carbon Nanotube based vacuum devices such as triodes. We will present the calculation of important figures of merit and possible realizations.

  1. Plannar light source using a phosphor screen with single-walled carbon nanotubes as field emitters

    NASA Astrophysics Data System (ADS)

    Bahena-Garrido, Sharon; Shimoi, Norihiro; Abe, Daisuke; Hojo, Toshimasa; Tanaka, Yasumitsu; Tohji, Kazuyuki

    2014-10-01

    We developed and successfully fabricated a plannar light source device using a phosphor screen with single-walled carbon nanotubes (SWCNTs) as field emitters in a simple diode structure composed of the cathode containing the highly purified and crystalline SWCNTs dispersed into an organic In2O3-SnO2 precursor solution and a non-ionic surfactant. The cathode was activated by scratching process with sandpaper to obtain a large field emission current with low power consumption. The nicks by scratching were treated with Fourier analysis to determine the periodicity of the surface morphology and designed with controlling the count number of sandpapers. The anode, on the other hand, was made with phosphor deliberately optimized by coverage of ITO nanoparticles and assembled together with the cathode by the new stable assembling process resulting to stand-alone flat plane-emission panel. The device in a diode structure has a low driving voltage and good brightness homogeneity in that plane. Furthermore, field emission current fluctuation, which is an important factor in comparing luminance devices too, has a good stability in a simple diode panel. The flat plane-emission device employing the highly purified and crystalline SWCNTs has the potential to provide a new approach to lighting in our life style.

  2. An electrically driven, ultrahigh-speed, on-chip light emitter based on carbon nanotubes.

    PubMed

    Mori, Tatsuya; Yamauchi, Yohei; Honda, Satoshi; Maki, Hideyuki

    2014-06-11

    The integration of high-speed light emitters on silicon chips is an important issue that must be resolved in order to realize on-chip or interchip optical interconnects. Here, we demonstrate the first electrically driven ultrafast carbon nanotube (CNT) light emitter based on blackbody radiation with a response speed (1-10 Gbps) that is more than 10(6) times higher than that of conventional incandescent emitters and is either higher than or comparable to that of light-emitting diodes or laser diodes. This high-speed response is explained by the extremely fast temperature response of the CNT film, which is dominated by the small heat capacity of the CNT film and its high heat dissipation to the substrate. Moreover, we experimentally demonstrate 140 ps width pulsed light generation and real-time optical communication. This CNT-based emitter with the advantages of ultrafast response speeds, a small footprint, and integration on silicon can enable novel architectures for optical interconnects, photonic, and optoelectronic integrated circuits. PMID:24796644

  3. Simulation of the enhancement factor from an individual 3D hemisphere-on-post field emitter by using finite elements method.

    PubMed

    Roveri, D S; Sant'Anna, G M; Bertan, H H; Mologni, J F; Alves, M A R; Braga, E S

    2016-01-01

    This paper presents a 3D computational framework for evaluating electrostatic properties of a single field emitter characterized by the hemisphere-on-post geometry. Numerical simulations employed the finite elements method by using Ansys-Maxwell software. Extensive parametric simulations were focused on the threshold distance from which the emitter field enhancement factor (γ) becomes independent from the anode-substrate gap (G). This investigation allowed demonstrating that the ratio between G and the emitter height (h) is a reliable reference for a broad range of emitter dimensions; furthermore, results permitted establishing G/h ≥ 2.2 as the threshold condition for setting the anode without affecting γ. PMID:26555324

  4. Statistical model for field emitter activation on metallic surfaces used in high-gradient accelerating structures

    NASA Astrophysics Data System (ADS)

    Lagotzky, S.; Müller, G.

    2016-01-01

    Both super- and normal-conducting high-gradient linear accelerators are limited by enhanced field emission (EFE) in the accelerating structures, e.g. due to power loss or ignition of discharges. We discuss the dependence of the number density of typical emitters, i.e. particulates and surface defects, on the electric field level at which they are activated for naturally oxidized metallic surfaces. This activation is explained by the transition of a metal-insulator interface into geometric features that enhance the EFE process. A statistical model is successfully compared to systematic studies of niobium and copper relevant for recent and future linear accelerators. Our results show that the achievable surface quality of Nb might be sufficient for the suppression of EFE in the superconducting accelerating structures for the actual European XFEL but not for the planned International Linear Collider. Moreover, some effort will be required to reduce EFE and thus the breakdown rate of the normal conducting Cu structures for the Compact Linear Collider.

  5. Breakdown voltage reliability improvement in gas-discharge tube surge protectors employing graphite field emitters

    NASA Astrophysics Data System (ADS)

    Žumer, Marko; Zajec, Bojan; Rozman, Robert; Nemanič, Vincenc

    2012-04-01

    Gas-discharge tube (GDT) surge protectors are known for many decades as passive units used in low-voltage telecom networks for protection of electrical components from transient over-voltages (discharging) such as lightning. Unreliability of the mean turn-on DC breakdown voltage and the run-to-run variability has been overcome successfully in the past by adding, for example, a radioactive source inside the tube. Radioisotopes provide a constant low level of free electrons, which trigger the breakdown. In the last decades, any concept using environmentally harmful compounds is not acceptable anymore and new solutions were searched. In our application, a cold field electron emitter source is used as the trigger for the gas discharge but with no activating compound on the two main electrodes. The patent literature describes in details the implementation of the so-called trigger wires (auxiliary electrodes) made of graphite, placed in between the two main electrodes, but no physical explanation has been given yet. We present experimental results, which show that stable cold field electron emission current in the high vacuum range originating from the nano-structured edge of the graphite layer is well correlated to the stable breakdown voltage of the GDT surge protector filled with a mixture of clean gases.

  6. Emittance Theory for Thin Film Selective Emitter

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.; Lowe, Roland A.; Good, Brian S.

    1994-01-01

    Thin films of high temperature garnet materials such as yttrium aluminum garnet (YAG) doped with rare earths are currently being investigated as selective emitters. This paper presents a radiative transfer analysis of the thin film emitter. From this analysis the emitter efficiency and power density are calculated. Results based on measured extinction coefficients for erbium-YAG and holmium-YAG are presented. These results indicated that emitter efficiencies of 50 percent and power densities of several watts/sq cm are attainable at moderate temperatures (less than 1750 K).

  7. Application of the general thermal field model to simulate the behaviour of nanoscale Cu field emitters

    SciTech Connect

    Eimre, Kristjan; Aabloo, Alvo; Parviainen, Stefan Djurabekova, Flyura; Zadin, Vahur

    2015-07-21

    Strong field electron emission from a nanoscale tip can cause a temperature rise at the tip apex due to Joule heating. This becomes particularly important when the current value grows rapidly, as in the pre-breakdown (the electrostatic discharge) condition, which may occur near metal surfaces operating under high electric fields. The high temperatures introduce uncertainties in calculations of the current values when using the Fowler–Nordheim equation, since the thermionic component in such conditions cannot be neglected. In this paper, we analyze the field electron emission currents as the function of the applied electric field, given by both the conventional Fowler–Nordheim field emission and the recently developed generalized thermal field emission formalisms. We also compare the results in two limits: discrete (atomistic simulations) and continuum (finite element calculations). The discrepancies of both implementations and their effect on final results are discussed. In both approaches, the electric field, electron emission currents, and Joule heating processes are simulated concurrently and self-consistently. We show that the conventional Fowler–Nordheim equation results in significant underestimation of electron emission currents. We also show that Fowler–Nordheim plots used to estimate the field enhancement factor may lead to significant overestimation of this parameter especially in the range of relatively low electric fields.

  8. Floating emitter solar cell

    NASA Technical Reports Server (NTRS)

    Chih, Sah (Inventor); Cheng, Li-Jen (Inventor)

    1987-01-01

    A front surface contact floating emitter solar cell transistor is provided in a semiconductor body (n-type), in which floating emitter sections (p-type) are diffused or implanted in the front surface. Between the emitter sections, a further section is diffused or implanted in the front surface, but isolated from the floating emitter sections, for use either as a base contact to the n-type semiconductor body, in which case the section is doped n+, or as a collector for the adjacent emitter sections.

  9. Strong-Field Emission From High Aspect Ratio Si Emitter Arrays

    NASA Astrophysics Data System (ADS)

    Keathley, Phillip; Swanwick, Michael; Sell, Alexander; Putnam, William; Guerrera, Stephen; Velásquez-García, Luis; Kärtner, Franz

    2013-03-01

    We discuss photoelectron emission from an arrays of high aspect ratio, sharp Si emitters both experimentally and theoretically. The structures are prepared from highly doped single-crystal silicon having a pencil-like shape with end radii of curvature of around 10 nm. The tips were illuminated at a grazing incidence of roughly 84deg.with a laser pulse having a center wavelength of 800 nm, and a pulse duration of 35 fs from a regenerative amplifier system. Native oxide coated Si tips were characterized using a time of flight (TOF) electron energy spectrometer. An annealing process was observed, resulting in a red shift of the energy spectra along with an increased electron yield. Total current yield from samples having the oxide stripped were also studied. Apeak total emission of 0.68 pC/bunch, corresponding to around 1.5x103 electrons/tip/pulse was observed at a DC bias of 70 V. Both spectral and current characterization results are consistent with a stong-field photoemission process at the surface of the tip apex. This work was funded by Defense Advanced Research Projects Agency (DARPA)/Microsystems Technology Office and the Space and Naval Warfare Systems Center (SPAWAR) under contract N66001-11-1-4192.

  10. Protein deposition on field-emitter tips and its removal by UV radiation

    NASA Astrophysics Data System (ADS)

    Panitz, J. A.; Giaever, I.

    1980-07-01

    Protein deposition on field-emitter tips has been examined using Transmission Electron Microscopy to view the protein coated tip profile. A single layer of adsorbed protein is barely if at all detectable, but double and triple layers produced by the immunologic reaction can be directly observed. As a result, the thickness and morphology of antigen-antibody layers has been directly observed for the first time. Tips exposed first to Bovine Serum Albumin (BSA) and then to anti-BSA rabbit serum are covered with a reasonably uniform, double protein layer ≈130 Å thick. This layer can be built-up to a triple layer ≈275 Å thick by additional exposure to anti-rabbit IgG goat serum. Surface tension forces during the drying process which follows protein deposition appear to affect the thickness and morphology of the protein layers. The oxidation and subsequent change in the morphology of a protein layer exposed to ultraviolet radiation has also been observed using TEM. The destruction of a triple protein layer at a rate of ≈0.5 Å/s is observed for tungsten tips exposed to ≈6 W of UV radiation from a high-pressure mercury arc in laboratory ambient. These results are compared to those obtained from a simple, visual test for protein layer adsorption in which submonolayer coverages of protein can be detected with the unaided eye.

  11. Nanofabrication of arrays of silicon field emitters with vertical silicon nanowire current limiters and self-aligned gates

    NASA Astrophysics Data System (ADS)

    Guerrera, S. A.; Akinwande, A. I.

    2016-07-01

    We developed a fabrication process for embedding a dense array (108 cm‑2) of high-aspect-ratio silicon nanowires (200 nm diameter and 10 μm tall) in a dielectric matrix and then structured/exposed the tips of the nanowires to form self-aligned gate field emitter arrays using chemical mechanical polishing (CMP). Using this structure, we demonstrated a high current density (100 A cm‑2), uniform, and long lifetime (>100 h) silicon field emitter array architecture in which the current emitted by each tip is regulated by the silicon nanowire current limiter connected in series with the tip. Using the current voltage characteristics and with the aid of numerical device models, we estimated the tip radius of our field emission arrays to be ≈4.8 nm, as consistent with the tip radius measured using a scanning electron microscope (SEM).

  12. Nanofabrication of arrays of silicon field emitters with vertical silicon nanowire current limiters and self-aligned gates.

    PubMed

    Guerrera, S A; Akinwande, A I

    2016-07-22

    We developed a fabrication process for embedding a dense array (10(8) cm(-2)) of high-aspect-ratio silicon nanowires (200 nm diameter and 10 μm tall) in a dielectric matrix and then structured/exposed the tips of the nanowires to form self-aligned gate field emitter arrays using chemical mechanical polishing (CMP). Using this structure, we demonstrated a high current density (100 A cm(-2)), uniform, and long lifetime (>100 h) silicon field emitter array architecture in which the current emitted by each tip is regulated by the silicon nanowire current limiter connected in series with the tip. Using the current voltage characteristics and with the aid of numerical device models, we estimated the tip radius of our field emission arrays to be ≈4.8 nm, as consistent with the tip radius measured using a scanning electron microscope (SEM). PMID:27292120

  13. High-efficiency white organic light-emitting diodes based on a blue thermally activated delayed fluorescent emitter combined with green and red fluorescent emitters.

    PubMed

    Higuchi, Takahiro; Nakanotani, Hajime; Adachi, Chihaya

    2015-03-25

    A new device architecture for highly efficient white organic light-emitting diodes is proposed, using a molecule exhibiting blue thermally activated delayed fluorescence as a common source of singlet excitons for molecules emitting red and green light based on conventional fluorescence. The device, with an optimum combination of materials, shows a maximum external quantum efficiency of over 12% without using phosphorescent emitters. PMID:25664428

  14. Preservation of Ultra Low Emittances Using Adiabatic Matching in Future Plasma Wakefield-based Colliders

    SciTech Connect

    Gholizadeh, Reza; Muggli, Patric; Katsouleas, Tom; Mori, Warren

    2009-01-22

    The Plasma Wakefield Accelerator is a promising technique to lower the cost of the future high energy colliders by offering orders of magnitude higher gradients than the conventional accelerators. It has been shown that ion motion is an important issue to account for in the extreme regime of ultra high energies and ultra low emittances, characteristics of future high energy collider beams. In this regime, the transverse electric field of the beam is so high that in simulations, the plasma ions cannot be considered immobile at the time scale of electron plasma oscillation, thereby leading to a nonlinear focusing force. Therefore, the transverse emittance of a beam will not be preserved under these circumstances. However, we show that matched profile in case of a nonlinear focusing force still exists and can be derived from Vlasov equation. Furthermore, we introduce a plasma section that can reduce the emittance growth by adiabatically reducing the ion mass and hence increasing the nonlinear term in the focusing force. Simulation results are presented.

  15. Flexible three-dimensional SnO2 nanowire arrays: atomic layer deposition-assisted synthesis, excellent photodetectors, and field emitters.

    PubMed

    Deng, Kaimo; Lu, Hao; Shi, Zhiwei; Liu, Qiong; Li, Liang

    2013-08-28

    Flexible three-dimensional SnO2 nanowire arrays were synthesized on a carbon cloth template in combination with atomic layer deposition and vapor transport. The as-grown nanostructures were assembled by high density quasi-aligned nanowires with a large aspect ratio. Nanoscale photodetectors based on the flexible nanostructure demonstrate excellent ultraviolet light selectivity, a high speed response time less than 0.3 s, and dark current as low as 2.3 pA. Besides, field emission measurements of the hierarchical structure show a rather low turn-on field (3.3 Vμm(-1)) and threshold field (4.5 Vμm(-1)), as well as an excellent field enhancment factor (2375) with a long-term stability up to 20 h. These results indicate that the flexible three-dimensional SnO2 nanowire arrays can be used as functional building blocks for efficient photodetectors and field emitters. PMID:23879602

  16. Metal Optics Based nanoLEDs: In Search of a Fast, Efficient, Nanoscale Light Emitter

    NASA Astrophysics Data System (ADS)

    Eggleston, Michael Scott

    Since the invention of the laser, stimulated emission has been the de facto king of optical communication. Lasers can be directly modulated at rates as high as 50GHz, much faster than a typical solid state light-emitting diode (LED) that is limited by spontaneous emission to <1GHz. Unfortunately, lasers have a severe scaling problem; they require large cavities operated at high power to achieve efficient lasing. A properly designed LED can be made arbitrarily small and still operate with high-efficiency. On-chip interconnects is an area that is in desperate need of a high-speed, low-power optical emitter that can enable on-chip links to replace current high-loss metal wires. In this work, I will show that by utilizing proper antenna design, a nanoLED can be created that is faster than a laser while still operating at >50% efficiency. I start by formulating an optical antenna circuit model whose elements are based completely off of antenna geometry. This allows for intuitive antenna design and suggests that rate enhancements up to ~3,000x are possible while keeping antenna efficiency >50%. Such a massive speed-up in spontaneous emission would enable an LED that can be directly modulated at 100's of GHz, much faster than any laser. I then use the circuit model to design an arch-dipole antenna, a dipole antenna with an inductive arch across the feedgap. I experimentally demonstrate a free-standing arch-dipole based nanoLED with rate enhancement of 115x and 66% antenna efficiency. Because the emitter is InGaAsP, a common III-V material, I experimentally show that this device can be easily and efficiently coupled into an InP waveguide. Experimental coupling efficiencies up to 70% are demonstrated and directional antennas are employed that offer front to back emission ratios of 3:1. Finally, I show that a nanoLED can still have high quantum yield by using a transition metal dichalcogenide, WSe2, as the emitter material. By coupling a monolayer of WSe2 to a cavity

  17. Tungsten band edge absorber/emitter based on a monolayer of ceramic microspheres.

    PubMed

    Dyachenko, P N; do Rosário, J J; Leib, E W; Petrov, A Yu; Störmer, M; Weller, H; Vossmeyer, T; Schneider, G A; Eich, M

    2015-09-21

    We report on a band edge absorber/emitter design for high-temperature applications based on an unstructured tungsten substrate and a monolayer of ceramic microspheres. The absorber was fabricated as a monolayer of ZrO(2) microparticles on a tungsten layer with a HfO(2) nanocoating. The band edge of the absorption is based on critically coupled microsphere resonances. It can be tuned from visible to near-infrared range by varying the diameter of the microparticles. The absorption properties were found to be stable up to 1000°C. PMID:26406752

  18. Trends in the emitter-base bias dependence of the average base transit time through abrupt heterojunction bipolar transistors

    NASA Astrophysics Data System (ADS)

    Kumar, T.; Cahay, M.; Roenker, K.

    1996-11-01

    The average base transit time is computed using a current impulse response technique for three typical abrupt Npn heterojunction bipolar transistors as a function of the emitter-base bias, VBE. This technique is based on a hybrid model of carrier transport incorporating a quantum-mechanical analysis of carrier injection at the emitter-base junction and a Monte Carlo analysis of base transport. For typical AlGaAs/GaAs and InP/InGaAs structures, the base transit time first increases with VBE, reaches a maximum, and then decreases towards a value close to the one predicted using a semi-Maxwellian injection of carriers into the base at an energy equal to the emitter-base conduction band spike. For a typical InAlAs/InGaAs structure, the average base transit time is found to decrease with an increase in VBE. For all structures, we show that there is a correlation between the bias dependence of the average base transit time and the bias dependence of the average number of collisions per carrier (calculated for carriers transmitted across the base).

  19. SEARCHING FOR z {approx} 7.7 Ly{alpha} EMITTERS IN THE COSMOS FIELD WITH NEWFIRM

    SciTech Connect

    Krug, Hannah B.; Veilleux, Sylvain; Tilvi, Vithal; Malhotra, Sangeeta; Rhoads, James; Hibon, Pascale; Swaters, Rob

    2012-02-01

    The study of Ly{alpha} emission in the high-redshift universe is a useful probe of the epoch of reionization, as the Ly{alpha} line should be attenuated by the intergalactic medium (IGM) at low to moderate neutral hydrogen fractions. Here we present the results of a deep and wide imaging search for Ly{alpha} emitters in the Cosmological Evolution Survey field. We have used two ultra-narrowband filters (filter width of {approx}8-9 A) on the NOAO Extremely Wide-Field Infrared Mosaic camera, installed on the Mayall 4 m telescope at Kitt Peak National Observatory, in order to isolate Ly{alpha} emitters at z = 7.7; such ultra-narrowband imaging searches have proved to be excellent at detecting Ly{alpha} emitters. We found 5{sigma} detections of four candidate Ly{alpha} emitters in a survey volume of 2.8 Multiplication-Sign 10{sup 4} Mpc{sup 3} (total survey area {approx}760 arcmin{sup 2}). Each candidate has a line flux greater than 8 Multiplication-Sign 10{sup -18} erg s{sup -1} cm{sup -2}. Using these results to construct a luminosity function and comparing to previously established Ly{alpha} luminosity functions at z = 5.7 and z = 6.5, we find no conclusive evidence for evolution of the luminosity function between z = 5.7 and z = 7.7. Statistical Monte Carlo simulations suggest that half of these candidates are real z = 7.7 targets, and spectroscopic follow-up will be required to verify the redshift of these candidates. However, our results are consistent with no strong evolution in the neutral hydrogen fraction of the IGM between z = 5.7 and z = 7.7, even if only one or two of the z = 7.7 candidates are spectroscopically confirmed.

  20. Active spacecraft potential control: An ion emitter experiment. [Cluster mission

    NASA Technical Reports Server (NTRS)

    Riedler, W.; Goldstein, R.; Hamelin, M.; Maehlum, B. N.; Troim, J.; Olsen, R. C.; Pedersen, A.; Grard, R. J. L.; Schmidt, R.; Rudenauer, F.

    1988-01-01

    The cluster spacecraft are instrumented with ion emitters for charge neutralization. The emitters produce indium ions at 6 keV. The ion current is adjusted in a feedback loop with instruments measuring the spacecraft potential. The system is based on the evaporation of indium in the apex field of a needle. The design of the active spacecraft potential control instruments, and the ion emitters is presented.

  1. Vertically aligned self-assembled gold nanorods as low turn-on, stable field emitters

    NASA Astrophysics Data System (ADS)

    Apte, Amey; Joshi, Padmashree; Bhaskar, Prashant; Joag, Dilip; Kulkarni, Sulabha

    2015-11-01

    In this work we have investigated field emission from self-assembled, vertically aligned, gold nanorod arrays, which were synthesized via a colloidal growth method. A field emission current density of ∼1 mA/cm2 was measured for these gold nanorod arrays using an anode-cathode separation of ∼3.5 mm. The field emission investigation of these gold nanorod arrays was carried out at a base pressure of ∼10-8 mbar. The turn on field, defined as the electric field required to obtain a current density of 1 μA/cm2, is observed to be 1.9 V/μm. Assuming a work function value of 5.3 eV, the field enhancement factor β is estimated to be ∼2931, which is higher than the reported values for other gold nanostructures/arrays.

  2. Ultra High p-doping Material Research for GaN Based Light Emitters

    SciTech Connect

    Vladimir Dmitriev

    2007-06-30

    The main goal of the Project is to investigate doping mechanisms in p-type GaN and AlGaN and controllably fabricate ultra high doped p-GaN materials and epitaxial structures. Highly doped p-type GaN-based materials with low electrical resistivity and abrupt doping profiles are of great importance for efficient light emitters for solid state lighting (SSL) applications. Cost-effective hydride vapor phase epitaxial (HVPE) technology was proposed to investigate and develop p-GaN materials for SSL. High p-type doping is required to improve (i) carrier injection efficiency in light emitting p-n junctions that will result in increasing of light emitting efficiency, (ii) current spreading in light emitting structures that will improve external quantum efficiency, and (iii) parameters of Ohmic contacts to reduce operating voltage and tolerate higher forward currents needed for the high output power operation of light emitters. Highly doped p-type GaN layers and AlGaN/GaN heterostructures with low electrical resistivity will lead to novel device and contact metallization designs for high-power high efficiency GaN-based light emitters. Overall, highly doped p-GaN is a key element to develop light emitting devices for the DOE SSL program. The project was focused on material research for highly doped p-type GaN materials and device structures for applications in high performance light emitters for general illumination P-GaN and p-AlGaN layers and multi-layer structures were grown by HVPE and investigated in terms of surface morphology and structure, doping concentrations and profiles, optical, electrical, and structural properties. Tasks of the project were successfully accomplished. Highly doped GaN materials with p-type conductivity were fabricated. As-grown GaN layers had concentration N{sub a}-N{sub d} as high as 3 x 10{sup 19} cm{sup -3}. Mechanisms of doping were investigated and results of material studies were reported at several International conferences providing

  3. A realistic fabrication and design concept for quantum gates based on single emitters integrated in plasmonic-dielectric waveguide structures

    PubMed Central

    Kewes, Günter; Schoengen, Max; Neitzke, Oliver; Lombardi, Pietro; Schönfeld, Rolf-Simon; Mazzamuto, Giacomo; Schell, Andreas W.; Probst, Jürgen; Wolters, Janik; Löchel, Bernd; Toninelli, Costanza; Benson, Oliver

    2016-01-01

    Tremendous enhancement of light-matter interaction in plasmonic-dielectric hybrid devices allows for non-linearities at the level of single emitters and few photons, such as single photon transistors. However, constructing integrated components for such devices is technologically extremely challenging. We tackle this task by lithographically fabricating an on-chip plasmonic waveguide-structure connected to far-field in- and out-coupling ports via low-loss dielectric waveguides. We precisely describe our lithographic approach and characterize the fabricated integrated chip. We find excellent agreement with rigorous numerical simulations. Based on these findings we perform a numerical optimization and calculate concrete numbers for a plasmonic single-photon transistor. PMID:27364604

  4. A realistic fabrication and design concept for quantum gates based on single emitters integrated in plasmonic-dielectric waveguide structures

    NASA Astrophysics Data System (ADS)

    Kewes, Günter; Schoengen, Max; Neitzke, Oliver; Lombardi, Pietro; Schönfeld, Rolf-Simon; Mazzamuto, Giacomo; Schell, Andreas W.; Probst, Jürgen; Wolters, Janik; Löchel, Bernd; Toninelli, Costanza; Benson, Oliver

    2016-07-01

    Tremendous enhancement of light-matter interaction in plasmonic-dielectric hybrid devices allows for non-linearities at the level of single emitters and few photons, such as single photon transistors. However, constructing integrated components for such devices is technologically extremely challenging. We tackle this task by lithographically fabricating an on-chip plasmonic waveguide-structure connected to far-field in- and out-coupling ports via low-loss dielectric waveguides. We precisely describe our lithographic approach and characterize the fabricated integrated chip. We find excellent agreement with rigorous numerical simulations. Based on these findings we perform a numerical optimization and calculate concrete numbers for a plasmonic single-photon transistor.

  5. 2-μm Ho emitter-based coherent DIAL for CO(2) profiling in the atmosphere.

    PubMed

    Gibert, F; Edouart, D; Cénac, C; Le Mounier, F; Dumas, A

    2015-07-01

    We report on the use of a thulium-fiber-pumped holmium-based emitter in a coherent differential absorption lidar (CDIAL) experiment for high time and space resolution of CO(2) absorption field in the atmosphere. The 2-μm high-power dual-wavelength single-mode Q-switched Ho:YLF oscillator delivers 10-mJ pulses with a duration of 40 ns at 2 kHz. Both short pulse duration and high repetition rate were chosen to increase the DIAL precision and time and space resolution in coherent detection. The CDIAL provides 150-m range and 15-min time-resolved CO(2) absorption coefficient with a calculated instrumental error of 0.5% at 500 m and less than 2% at 1 km. Dry-air CO(2) mixing ratio estimates from the DIAL system are compared with simultaneous in situ gas analyzer measurements during a 20-h-long experiment. PMID:26125375

  6. A realistic fabrication and design concept for quantum gates based on single emitters integrated in plasmonic-dielectric waveguide structures.

    PubMed

    Kewes, Günter; Schoengen, Max; Neitzke, Oliver; Lombardi, Pietro; Schönfeld, Rolf-Simon; Mazzamuto, Giacomo; Schell, Andreas W; Probst, Jürgen; Wolters, Janik; Löchel, Bernd; Toninelli, Costanza; Benson, Oliver

    2016-01-01

    Tremendous enhancement of light-matter interaction in plasmonic-dielectric hybrid devices allows for non-linearities at the level of single emitters and few photons, such as single photon transistors. However, constructing integrated components for such devices is technologically extremely challenging. We tackle this task by lithographically fabricating an on-chip plasmonic waveguide-structure connected to far-field in- and out-coupling ports via low-loss dielectric waveguides. We precisely describe our lithographic approach and characterize the fabricated integrated chip. We find excellent agreement with rigorous numerical simulations. Based on these findings we perform a numerical optimization and calculate concrete numbers for a plasmonic single-photon transistor. PMID:27364604

  7. Hybrid permeable metal-base transistor with large common-emitter current gain and low operational voltage.

    PubMed

    Feng, Chengang; Yi, Mingdong; Yu, Shunyang; Hümmelgen, Ivo A; Zhang, Tong; Ma, Dongge

    2008-04-01

    We demonstrate the suitability of N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB), an organic semiconductor widely used in organic light-emitting diodes (OLEDs), for high-gain, low operational voltage nanostructured vertical-architecture transistors, which operate as permeable-base transistors. By introducing vanadium oxide (V2O5) between the injecting metal and NPB layer at the transistor emitter, we reduced the emitter operational voltage. The addition of two Ca layers, leading to a Ca/Ag/Ca base, allowed to obtain a large value of common-emitter current gain, but still retaining the permeable-base transistor character. This kind of vertical devices produced by simple technologies offer attractive new possibilities due to the large variety of available molecular semiconductors, opening the possibility of incorporating new functionalities in silicon-based devices. PMID:18572611

  8. Effect of increased crystallinity of single-walled carbon nanotubes used as field emitters on their electrical properties

    SciTech Connect

    Shimoi, Norihiro

    2015-12-07

    Single-walled carbon nanotubes (SWCNTs) synthesized by arc discharge are expected to exhibit good field emission (FE) properties at a low driving voltage. We used a coating containing homogeneously dispersed highly crystalline SWCNTs produced by a high-temperature annealing process to fabricate an FE device by a wet-coating process at a low cost. Using the coating, we succeeded in reducing the power consumption of field emitters for planar lighting devices. SWCNTs synthesized by arc discharge have crystal defects in the carbon network, which are considered to induce inelastic electron tunneling that deteriorates the electrical conductivity of the SWCNTs. In this study, the blocking of the transport of electrons in SWCNTs with crystal defects is simulated using an inelastic electron tunneling model. We succeeded in clarifying the mechanism underlying the electrical conductivity of SWCNTs by controlling their crystallinity. In addition, it was confirmed that field emitters using highly crystalline SWCNTs can lead to new applications operating with low power consumption and new devices that may change our daily lives in the future.

  9. Highly Transparent Conducting Polymer Top Contacts for Future III-Nitride Based Single Photon Emitters

    NASA Astrophysics Data System (ADS)

    Riess, Sally; Mikulics, Martin; Winden, Andreas; Adam, Roman; Marso, Michel; Grützmacher, Detlev; Hardtdegen, Hilde

    2013-08-01

    In this paper we report on a simple conductive polymer based contacting technology for III-nitride based nanostructures with respect to the electrical operation within the telecommunication wavelength range. Singularly addressable InN/GaN pyramidal nanostructures were selectively grown by metalorganic vapour phase epitaxy (MOVPE) and subsequently integrated into a high-frequency device layout for future ultrafast electro-optical operation. The employment of the p-conducting polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) is found to increase the light transmittance up to 89% at a wavelength of 1550 nm compared to 72% in the case of a conventional Ni/Au thin layer top contact. DC measurements using a quasi operation mode for 1000 h reveal no degradation and only a moderate increase of the dark currents. Thus, conducting polymer technology shows tremendous potential for future highly efficient and reliable room temperature operation of nitride based single photon emitters (SPEs).

  10. Multinozzle Emitter Arrays for Nanoelectrospray Mass Spectrometry

    SciTech Connect

    Mao, Pan; Wang, Hung-Ta; Yang, Peidong; Wang, Daojing

    2011-06-16

    Mass spectrometry (MS) is the enabling technology for proteomics and metabolomics. However, dramatic improvements in both sensitivity and throughput are still required to achieve routine MS-based single cell proteomics and metabolomics. Here, we report the silicon-based monolithic multinozzle emitter array (MEA), and demonstrate its proof-of-principle applications in high-sensitivity and high-throughput nanoelectrospray mass spectrometry. Our MEA consists of 96 identical 10-nozzle emitters in a circular array on a 3-inch silicon chip. The geometry and configuration of the emitters, the dimension and number of the nozzles, and the micropillar arrays embedded in the main channel, can be systematically and precisely controlled during the microfabrication process. Combining electrostatic simulation and experimental testing, we demonstrated that sharpened-end geometry at the stem of the individual multinozzle emitter significantly enhanced the electric fields at its protruding nozzle tips, enabling sequential nanoelectrospray for the high-density emitter array. We showed that electrospray current of the multinozzle emitter at a given total flow rate was approximately proportional to the square root of the number of its spraying-nozzles, suggesting the capability of high MS sensitivity for multinozzle emitters. Using a conventional Z-spray mass spectrometer, we demonstrated reproducible MS detection of peptides and proteins for serial MEA emitters, achieving sensitivity and stability comparable to the commercial capillary emitters. Our robust silicon-based MEA chip opens up the possibility of a fully-integrated microfluidic system for ultrahigh-sensitivity and ultrahigh-throughput proteomics and metabolomics.

  11. Role of the resistivity of insulating field emitters on the energy of field-ionised and field-evaporated atoms.

    PubMed

    Arnoldi, L; Silaeva, E P; Vurpillot, F; Deconihout, B; Cadel, E; Blum, I; Vella, A

    2015-12-01

    In order to improve the accuracy of laser atom probe analyses, it is important to understand all the physical processes induced by the combination of the high electrical field and the femtosecond laser beam during field evaporation. New information can be accessed from the energy of evaporated surface atoms or field-ionised atoms of an imaging gas. In order to study the ions energy, we combine La-APT and FIM analyses in a new experimental setup equipped with electrostatic lenses. We report measurements for semiconductors and oxides and we study the influence of the illumination conditions (laser power and wavelength), the evaporation rate, the sample geometry and the tip preparation processes. The results are discussed taking into account the resistive properties of non-metallic samples and the photo-stimulated conductivity. This work clarifies the role of the laser and DC field in the energy deficit of field evaporated ions. PMID:25484362

  12. Bright white organic light-emitting diodes based on two blue emitters with similar molecular structures

    NASA Astrophysics Data System (ADS)

    Wang, Liduo; Lei, Gangtie; Qiu, Yong

    2005-06-01

    We show that highly efficient and chromatically stable white organic electroluminescent devices can be obtained, based on two blue emitters with similar structures: 9,10-di-(2-naphthyl)-anthracene (ADN) and 9,10-di-(2-naphthyl)-2-terbutyl-anthracene doped with yellow-orange emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) at ultralow doping concentrations (0.01%-0.05%). The relative intensity of the blue and orange-yellow emissions could be fine-tuned by varying the doping concentrations of rubrene in the host to achieve pure white emission. The energy-transfer mechanism of ADN and rubrene with ultralow doping concentrations is discussed in terms of the long exciton diffusion distance of ADN.

  13. Plume-based analysis of vehicle fleet air pollutant emissions and the contribution from high emitters

    NASA Astrophysics Data System (ADS)

    Wang, J. M.; Jeong, C.-H.; Zimmerman, N.; Healy, R. M.; Wang, D. K.; Ke, F.; Evans, G. J.

    2015-03-01

    An automated identification and integration method has been developed to investigate in-use vehicle emissions under real-world conditions. This technique was applied to high time resolution air pollutant measurements of in-use vehicle emissions performed under real-world conditions at a near-road monitoring station in Toronto, Canada during four seasons, through month-long campaigns in 2013-2014. Based on carbon dioxide measurements, over 100 000 vehicle-related plumes were automatically identified and fuel-based emission factors for nitrogen oxides; carbon monoxide; particle number, black carbon; benzene, toluene, ethylbenzene, and xylenes (BTEX); and methanol were determined for each plume. Thus the automated identification enabled the measurement of an unprecedented number of plumes and pollutants over an extended duration. Emission factors for volatile organic compounds were also measured roadside for the first time using a proton transfer reaction time-of-flight mass spectrometer; this instrument provided the time resolution required for the plume capture technique. Mean emission factors were characteristic of the light-duty gasoline dominated vehicle fleet present at the measurement site, with mean black carbon and particle number emission factors of 35 mg kg-1 and 7.7 × 1014 kg-1, respectively. The use of the plume-by-plume analysis enabled isolation of vehicle emissions, and the elucidation of co-emitted pollutants from similar vehicle types, variability of emissions across the fleet, and the relative contribution from heavy emitters. It was found that a small proportion of the fleet (< 25%) contributed significantly to total fleet emissions; 95, 93, 76, and 75% for black carbon, carbon monoxide, BTEX, and particle number, respectively. Emission factors of a single pollutant may help classify a vehicle as a high emitter. However, regulatory strategies to more efficiently target multi-pollutants mixtures may be better developed by considering the co

  14. Plume-based analysis of vehicle fleet air pollutant emissions and the contribution from high emitters

    NASA Astrophysics Data System (ADS)

    Wang, J. M.; Jeong, C.-H.; Zimmerman, N.; Healy, R. M.; Wang, D. K.; Ke, F.; Evans, G. J.

    2015-08-01

    An automated identification and integration method has been developed for in-use vehicle emissions under real-world conditions. This technique was applied to high-time-resolution air pollutant measurements of in-use vehicle emissions performed under real-world conditions at a near-road monitoring station in Toronto, Canada, during four seasons, through month-long campaigns in 2013-2014. Based on carbon dioxide measurements, over 100 000 vehicle-related plumes were automatically identified and fuel-based emission factors for nitrogen oxides; carbon monoxide; particle number; black carbon; benzene, toluene, ethylbenzene, and xylenes (BTEX); and methanol were determined for each plume. Thus the automated identification enabled the measurement of an unprecedented number of plumes and pollutants over an extended duration. Emission factors for volatile organic compounds were also measured roadside for the first time using a proton transfer reaction time-of-flight mass spectrometer; this instrument provided the time resolution required for the plume capture technique. Mean emission factors were characteristic of the light-duty gasoline-dominated vehicle fleet present at the measurement site, with mean black carbon and particle number emission factors of 35 mg kg fuel-1 and 7.5 × 1014 # kg fuel-1, respectively. The use of the plume-by-plume analysis enabled isolation of vehicle emissions, and the elucidation of co-emitted pollutants from similar vehicle types, variability of emissions across the fleet, and the relative contribution from heavy emitters. It was found that a small proportion of the fleet (< 25 %) contributed significantly to total fleet emissions: 100, 100, 81, and 77 % for black carbon, carbon monoxide, BTEX, and particle number, respectively. Emission factors of a single pollutant may help classify a vehicle as a high emitter; however, regulatory strategies to more efficiently target multi-pollutant mixtures may be better developed by considering the co

  15. High Stability Electron Field Emitters Synthesized via the Combination of Carbon Nanotubes and N₂-Plasma Grown Ultrananocrystalline Diamond Films.

    PubMed

    Chang, Ting-Hsun; Hsieh, Ping-Yen; Kunuku, Srinivasu; Lou, Shiu-Cheng; Manoharan, Divinah; Leou, Keh-Chyang; Lin, I-Nan; Tai, Nyan-Hwa

    2015-12-16

    An electron field emitter with superior electron field emission (EFE) properties and improved lifetime stability is being demonstrated via the combination of carbon nanotubes and the CH4/N2 plasma grown ultrananocrystalline diamond (N-UNCD) films. The resistance of the carbon nanotubes to plasma ion bombardment is improved by the formation of carbon nanocones on the side walls of the carbon nanotubes, thus forming strengthened carbon nanotubes (s-CNTs). The N-UNCD films can thus be grown on s-CNTs, forming N-UNCD/s-CNTs carbon nanocomposite materials. The N-UNCD/s-CNTs films possess good conductivity of σ = 237 S/cm and marvelous EFE properties, such as low turn-on field of (E0) = 3.58 V/μm with large EFE current density of (J(e)) = 1.86 mA/cm(2) at an applied field of 6.0 V/μm. Moreover, the EFE emitters can be operated under 0.19 mA/cm(2) for more than 350 min without showing any sign of degradation. Such a superior EFE property along with high robustness characteristic of these combination of materials are not attainable with neither N-UNCD films nor s-CNTs films alone. Transmission electron microscopic investigations indicated that the N-UNCD films contain needle-like diamond grains encased in a few layers of nanographitic phase, which enhanced markedly the transport of electrons in the N-UNCD films. Moreover, the needle-like diamond grains were nucleated from the s-CNTs without the necessity of forming the interlayer that facilitate the transport of electrons crossing the diamond-to-Si interface. Both these factors contributed to the enhanced EFE behavior of the N-UNCD/s-CNTs films. PMID:26600097

  16. Longitudinal emittance in high-current ion accelerators

    SciTech Connect

    Wangler, T.P.; Bhatia, T.S.; Neuschaefer, G.H.; Pabst, M.

    1989-01-01

    The control of longitudinal emittance in an ion linear accelerator is important for minimizing both chromatic aberrations and beam halo. The root-mean-square (rms) longitudinal emittance grouth can result from either the nonlinear rf focusing fields or the nonlinear space-charge fields. We will present conclusions based on numerical beam-dynamics studies for both the radio-frequency quadrupole (RFQ), and the drift-tube linac (DTL). We will discuss the scaling of longitudinal emittance produced during the adiabatic bunching in an RFQ and will show the benefits of ramped DTL accelerating field designs to maintain high longitudinal focusing strength with increasing particle energy. 15 refs., 8 figs.

  17. Amorphous-diamond electron emitter

    DOEpatents

    Falabella, Steven

    2001-01-01

    An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.

  18. Resonant tunneling device with two-dimensional quantum well emitter and base layers

    DOEpatents

    Simmons, J.A.; Sherwin, M.E.; Drummond, T.J.; Weckwerth, M.V.

    1998-10-20

    A double electron layer tunneling device is presented. Electrons tunnel from a two dimensional emitter layer to a two dimensional tunneling layer and continue traveling to a collector at a lower voltage. The emitter layer is interrupted by an isolation etch, a depletion gate, or an ion implant to prevent electrons from traveling from the source along the emitter to the drain. The collector is similarly interrupted by a backgate, an isolation etch, or an ion implant. When the device is used as a transistor, a control gate is added to control the allowed energy states of the emitter layer. The tunnel gate may be recessed to change the operating range of the device and allow for integrated complementary devices. Methods of forming the device are also set forth, utilizing epoxy-bond and stop etch (EBASE), pre-growth implantation of the backgate or post-growth implantation. 43 figs.

  19. Undulator-Based Laser Wakefield Accelerator Electron Beam Energy Spread and Emittance Diagnostic

    SciTech Connect

    Bakeman, M.S.; Van Tilborg, J.; Nakamura, K.; Gonsalves, A.; Osterhoff, J.; Sokollik, T.; Lin, C.; Robinson, K.E.; Schroeder, C.B.; Toth, Cs.; Weingartner, R.; Gruner, F.; Esarey, E.; Leemans, W.P.

    2010-06-01

    The design and current status of experiments to couple the Tapered Hybrid Undulator (THUNDER) to the Lawrence Berkeley National Laboratory (LBNL) laser plasma accelerator (LPA) to measure electron beam energy spread and emittance are presented.

  20. Undulator-Based Laser Wakefield Accelerator Electron Beam Energy Spread and Emittance Diagnostic

    SciTech Connect

    Bakeman, M. S.; Van Tilborg, J.; Nakamura, K.; Gonsalves, A.; Osterhoff, J.; Robinson, K. E.; Schroeder, C. B.; Toth, Cs.; Esarey, E.; Leemans, W. P.; Sokollik, T.; Lin, C.; Weingartner, R.; Gruener, F.

    2010-11-04

    The design and current status of experiments to couple the Tapered Hybrid Undulator (THUNDER) to the Lawrence Berkeley National Laboratory (LBNL) laser plasma accelerator (LPA) to measure electron beam energy spread and emittance are presented.

  1. Resonant tunneling device with two-dimensional quantum well emitter and base layers

    DOEpatents

    Simmons, Jerry A.; Sherwin, Marc E.; Drummond, Timothy J.; Weckwerth, Mark V.

    1998-01-01

    A double electron layer tunneling device is presented. Electrons tunnel from a two dimensional emitter layer to a two dimensional tunneling layer and continue traveling to a collector at a lower voltage. The emitter layer is interrupted by an isolation etch, a depletion gate, or an ion implant to prevent electrons from traveling from the source along the emitter to the drain. The collector is similarly interrupted by a backgate, an isolation etch, or an ion implant. When the device is used as a transistor, a control gate is added to control the allowed energy states of the emitter layer. The tunnel gate may be recessed to change the operating range of the device and allow for integrated complementary devices. Methods of forming the device are also set forth, utilizing epoxy-bond and stop etch (EBASE), pre-growth implantation of the backgate or post-growth implantation.

  2. Effect of purity, edge length, and growth area on field emission of multi-walled carbon nanotube emitter arrays

    NASA Astrophysics Data System (ADS)

    Shahi, Monika; Gautam, S.; Shah, P. V.; Jha, P.; Kumar, P.; Rawat, J. S.; Chaudhury, P. K.; HASH0x9890f80, Harsh; Tandon, R. P.

    2013-05-01

    Present report aims to study the effect of purity, edge length, and growth area on field emission of patterned carbon nanotube (CNT) emitter arrays. For development of four CNT emitter arrays (CEAs), low resistively silicon substrates were coated with thin film of iron catalyst using photolithography, sputtering, and lift off process. Four CEAs were synthesized on these substrates using thermal chemical vapor deposition with minor changes in pretreatment duration. Out of these, two CEAs have 10 μm × 10 μm and 40 μm × 40 μm solid square dots of CNTs with constant 20 μm inter-dot separation. Other two CEAs have ring square bundles of CNTs and these CEAs are envisioned as 10 μm × 10 μm square dots with 4 μm × 4 μm scooped out area and 15 μm × 15 μm square dots with 5 μm × 5 μm lift out area with constant 20 μm inter-dot spacing. Solid square dot structures have exactly constant edge length per unit area with more than four-fold difference in CNT growth area however ring square dot patterns have minor difference in edge length per unit area with approximately two times difference in CNT growth area. Quality and morphology of synthesized CEAs were assessed by scanning electron microscope and Raman characterization which confirm major differences. Field emission of all CEAs was carried out under same vacuum condition and constant inter-electrode separation. Field emission of solid square dot CEAs show approximately identical current density-electric field curves and Fowler-Nordheim plots with little difference in emission current density at same electric field. Similar results were observed for ring square structure CEAs when compared separately. Maximum emission current density observed from these four CEAs reduces from 14.53, 12.23, 11.01, to 8.66 mA/cm2 at a constant electric field of 5 V/μm, according to edge length of 1361.7, 1221.08, 872.20, to 872.16 mm rather than growth area and purity. Although, the 40 μm × 40 μm CEAs possessed highest

  3. Effect of purity, edge length, and growth area on field emission of multi-walled carbon nanotube emitter arrays

    SciTech Connect

    Shahi, Monika; Gautam, S.; Shah, P. V.; Jha, P.; Kumar, P.; Rawat, J. S.; Chaudhury, P. K.; Harsh; Tandon, R. P.

    2013-05-28

    Present report aims to study the effect of purity, edge length, and growth area on field emission of patterned carbon nanotube (CNT) emitter arrays. For development of four CNT emitter arrays (CEAs), low resistively silicon substrates were coated with thin film of iron catalyst using photolithography, sputtering, and lift off process. Four CEAs were synthesized on these substrates using thermal chemical vapor deposition with minor changes in pretreatment duration. Out of these, two CEAs have 10 {mu}m Multiplication-Sign 10 {mu}m and 40 {mu}m Multiplication-Sign 40 {mu}m solid square dots of CNTs with constant 20 {mu}m inter-dot separation. Other two CEAs have ring square bundles of CNTs and these CEAs are envisioned as 10 {mu}m Multiplication-Sign 10 {mu}m square dots with 4 {mu}m Multiplication-Sign 4 {mu}m scooped out area and 15 {mu}m Multiplication-Sign 15 {mu}m square dots with 5 {mu}m Multiplication-Sign 5 {mu}m lift out area with constant 20 {mu}m inter-dot spacing. Solid square dot structures have exactly constant edge length per unit area with more than four-fold difference in CNT growth area however ring square dot patterns have minor difference in edge length per unit area with approximately two times difference in CNT growth area. Quality and morphology of synthesized CEAs were assessed by scanning electron microscope and Raman characterization which confirm major differences. Field emission of all CEAs was carried out under same vacuum condition and constant inter-electrode separation. Field emission of solid square dot CEAs show approximately identical current density-electric field curves and Fowler-Nordheim plots with little difference in emission current density at same electric field. Similar results were observed for ring square structure CEAs when compared separately. Maximum emission current density observed from these four CEAs reduces from 14.53, 12.23, 11.01, to 8.66 mA/cm{sup 2} at a constant electric field of 5 V/{mu}m, according to edge

  4. Tunable, Room Temperature CMOS-Compatible THz Emitters Based on Nonlinear Mixing in Microdisk Resonators

    NASA Astrophysics Data System (ADS)

    Sinha, Raju; Karabiyik, Mustafa; Ahmadivand, Arash; Al-Amin, Chowdhury; Vabbina, Phani Kiran; Shur, Michael; Pala, Nezih

    2016-03-01

    We propose and investigate in detail a novel tunable, compact, room temperature terahertz (THz) emitter using individual microdisk resonators for both optical and THz waves with the capability of radiating THz field in 0.5-10 THz range with tuning frequency resolution of 0.05 THz. Enhanced THz generation is achieved by employing a nonlinear optical disk resonator with a high value of second-order nonlinearity ( χ (2)) in order to facilitate the difference-frequency generation (DFG) via nonlinear mixing with the choice of two appropriate input infrared optical waves. Efficient coupling of infrared waves from bus to the nonlinear disk is ensured by satisfying critical coupling condition. Phase matching condition for efficient DFG process is also met by employing modal phase matching technique. Our simulations show that THz output power can be reached up to milliwatt (mW) level with high optical to THz conversion efficiency. The proposed source is Silicon on Insulator (SoI) technology compatible enabling the monolithic integration with Si complementary metal-oxide-semiconductor (CMOS) electronics including plasmonic THz detectors.

  5. Controlled synthesis of large-scale, uniform, vertically standing graphene for high-performance field emitters.

    PubMed

    Jiang, Lili; Yang, Tianzhong; Liu, Fei; Dong, Jing; Yao, Zhaohui; Shen, Chengmin; Deng, Shaozhi; Xu, Ningsheng; Liu, Yunqi; Gao, Hong-Jun

    2013-01-11

    Large-scale, uniform, vertically standing graphene with atomically thin edges are controllably synthesized on copper foil using a microwave-plasma chemical vapor deposition system. A growth mechanism for this system is proposed. This film shows excellent field-emission properties, with low turn-on field of 1.3 V μm(-1) , low threshold field of 3.0 V μm(-1) and a large field-enhancement factor more than 10 000. PMID:23135968

  6. Selective Emitters

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L. (Inventor)

    1992-01-01

    This invention relates to a small particle selective emitter for converting thermal energy into narrow band radiation with high efficiency. The small particle selective emitter is used in combination with a photovoltaic array to provide a thermal to electrical energy conversion device. An energy conversion apparatus of this type is called a thermo-photovoltaic device. In the first embodiment, small diameter particles of a rare earth oxide are suspended in an inert gas enclosed between concentric cylinders. The rare earth oxides are used because they have the desired property of large emittance in a narrow wavelength band and small emittance outside the band. However, it should be emphasized that it is the smallness of the particles that enhances the radiation property. The small particle selective emitter is surrounded by a photovoltaic array. In an alternate embodiment, the small particle gas mixture is circulated through a thermal energy source. This thermal energy source can be a nuclear reactor, solar receiver, or combustor of a fossil fuel.

  7. Reconstruction of exciton wave functions of coupled quantum emitters including spin with ultrafast spectroscopy using localized nanooptical fields

    NASA Astrophysics Data System (ADS)

    Specht, Judith F.; Richter, Marten

    2016-04-01

    Coulomb-induced resonance energy transfer mechanisms between coupled nanostructures lead to the formation of new, delocalized exciton states. Their hybrid wave functions can be decomposed into the basis of local states of the uncoupled system by the use of coherent, spatially resolved spectroscopy. The suggested quantum state tomography protocol combines nanooptical fields with a four-wave mixing technique: At least one pulse of the pulse sequence is spatially localized at a specific quantum emitter. It was suggested to use nanoplasmonic structures together with pulse-shaped fields for the localization. In this paper, the method is applied to a system of two coupled semiconductor quantum dots. The basic reconstruction concept first proposed in Richter et al. (Phys Rev B 86:085308, 2012) and Schlosser et al. (New J Phys 15:025004, 2013) is extended to the case of including different spin states of the excitons in the quantum dots. For this purpose, the theoretical scheme has to be modified and the localized fields need the ability to change their polarization. We show that the application of the developed reconstruction scheme to two-dimensional spectra gives full access to the internal structure of the interacting quantum states.

  8. A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources

    SciTech Connect

    Vecchione, T.; Ben-Zvi, I.; Dowell, D.H.; Feng, J.; Rao, T.; Smedley, J.; Wan, W.; Padmore, H.A.

    2011-07-21

    Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.

  9. A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources

    SciTech Connect

    Vecchione, T.; Feng, J.; Wan, W.; Padmore, H. A.; Ben-Zvi, I.; Dowell, D. H.; Rao, T.; Smedley, J.

    2011-07-18

    Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.

  10. The influence of emitter conditioning on the performance of a tungsten <111> cold field emission gun operating at 300 kV

    NASA Astrophysics Data System (ADS)

    Ross, I. M.; Li, W.; Walther, T.

    2014-06-01

    In this contribution, we examine the influence of emitter conditioning for a <111> tungsten cold field emission gun on the emission and beam characteristics of a double aberration corrected electron microscope. By varying the post flash build-up parameters we can control the effective emitter tip radius. A sharp emitter yields an energy resolution of 0.31eV but relatively low beam current whereas an increased tip radius results in a reduction in energy resolution to 0.4eV but much higher potential beam current. Consequently, careful control of the build-up parameters can be used as a means of tailoring the emission to suit specific instrumental requirements.

  11. The growth of graphite phase on an iridium field electron emitter

    NASA Astrophysics Data System (ADS)

    Bernatskii, D. P.; Pavlov, V. G.

    2016-06-01

    The growth of graphite on the surface of an iridium tip in pyrolysis of benzene to give a ribbed crystal has been found by the methods of field electron and desorption microscopy. The formation of a graphite crystal results in the electric field factor increasing. The adsorption of alkali metals on the surface of graphite is accompanied by the intercalation effect.

  12. On-chip polarized light emitters based on (6,5) chirality-sorted carbon nanotube aligned arrays

    NASA Astrophysics Data System (ADS)

    Ma, Ze; Liang, Shuang; Liu, Yang; Wang, Fanglin; Wang, Sheng; Peng, Lian-Mao

    2016-02-01

    Electrically driven light-emitters based on carbon nanotubes are highly promising candidates for on-chip optical interconnection and nanophotonics. Here, we fabricated on-chip polarized light-emitters based on (6,5) chirality-sorted carbon nanotube aligned arrays obtained via an evaporation-induced self-assembly method. Electroluminescence results shows an impact excitation dominant mechanism originated from (6,5) defect-brightened dark exciton emission and trion emission. The degree of polarization of the carbon nanotube aligned arrays is characterized quantitatively and the average value is ˜76.8%. The importance of parallelism and orientation of nanotubes when integrated with on-chip waveguides is also discussed.

  13. Effect of thin emitter set-back layer on GaAs delta-doped emitter bipolar junction transistor

    NASA Astrophysics Data System (ADS)

    Lew, K. L.; Yoon, S. F.

    2005-05-01

    GaAs delta-doped emitter bipolar junction transistors (δ-BJT) with different emitter set-back layer thicknesses of 10to50nm were fabricated to study the emitter set-back layer thickness effect on device dc performance. We found that the current gain decreases following decrease in the emitter set-back layer thickness. A detailed analysis was performed to explain this phenomenon, which is believed to be caused by reduction of the effective barrier height in the δ-BJT. This is due to change in the electric-field distribution in the delta-doped structure caused by the built-in potential of the base-emitter (B-E ) junction. Considering the recombination and barrier height reduction effects, the thickness of the emitter set-back layer should be designed according to the B-E junction depletion width with a tolerance of ±5nm. The dc performance of a δ-BJT designed based on this criteria is compared to that of a Al0.25Ga0.75As /GaAs heterojunction bipolar transistor (HBT). Both devices employed base doping of 2×1019cm-3 and base-to-emitter doping ratio of 40. Large emitter area (AE≈1.6×10-5cm-2) and small emitter area (AE≈1.35×10-6cm-2) device current gains of 40 and 20, respectively, were obtained in both types of transistors passivated by (NH4)2S treatment. The measured current gain of the GaAs δ-BJT is the highest reported for a homojunction device with such high base-to-emitter doping ratio normally used in HBT devices.

  14. A metal-insulator-metal electron emitter based on a porous Al{sub 2}O{sub 3} film

    SciTech Connect

    Xue, Tao; Liang, Zhi-Hu Zhang, Xiao-Ning; Liu, Chun-Liang

    2015-04-20

    A metal-insulator-metal electron emitter containing a sandwiched insulator layer composed of porous aluminum oxide Al{sub 2}O{sub 3} was fabricated. The electron emission characteristics of the electron emitter were investigated under vacuum and xenon. Treatment with H{sub 3}PO{sub 4} and rapid thermal oxidation increased the electric field inside the insulator and improved the quality of porous Al{sub 2}O{sub 3}, resulting in higher efficiency and less fluctuation of electron emission. The maximum current and efficiency of electron emission reached 1.05 mA/cm{sup 2} and 51.2%, respectively, under a pressure of 1.0×10{sup −4} Pa. In addition, electrons were injected into xenon and 147 nm vacuum ultraviolet emission was detected in xenon at a pressure of 5.0 × 10{sup 2 }Pa. This electron emitter has a great potential for use as an ultraviolet radiation source.

  15. Self-oscillations in an electromechanical system with a field emitter

    NASA Astrophysics Data System (ADS)

    Kleshch, V. I.; Obraztsov, A. N.; Obraztsova, E. D.

    2009-11-01

    Electromechanical oscillations have been detected in a system consisting of a vacuum diode with a field cathode made of single-walled carbon nanotubes. As a dc voltage between such a cathode and an anode is applied, stable mechanical oscillations are observed along with oscillations of the self-sustained emission current. An empirical model of this phenomenon is proposed. It is described with a system of one-dimensional equations of mechanical motion and electrical processes in the system. An analysis of these equations is performed and a qualitative consistency of theoretical and experimental results is demonstrated. It is proved that the observed phenomenon is common for all systems with field nanoemitters. The suggested mechanism of the excitation of the self-sustained oscillations can be used to explain the experimentally observed features of such nanoemitters.

  16. Simultaneous improvement of emission color, singlet-triplet energy gap, and quantum efficiency of blue thermally activated delayed fluorescent emitters using a 1-carbazolylcarbazole based donor.

    PubMed

    Kim, Mounggon; Choi, Jeong Min; Lee, Jun Yeob

    2016-08-21

    Blue thermally activated delayed fluorescent (TADF) emitters having 1-carbazolylcarbazole based donor moieties were developed to resolve the low quantum efficiency and large singlet-triplet energy splitting issues of the linker free TADF emitters. Investigation of the 1-carbazolylcarbazole derived donors as the donor units of two blue TADF emitters in comparison with 3-carbazolylcarbazole demonstrated that the 1-carbazolylcarbazole based donors increased the triplet energy, decreased the singlet-triplet energy gap, blue-shifted the emission color, and enhanced the quantum efficiency of the blue TADF devices. PMID:27443818

  17. White Electroluminescent Lighting Device Based on a Single Quantum Dot Emitter.

    PubMed

    Kim, Jong-Hoon; Jo, Dae-Yeon; Lee, Ki-Heon; Jang, Eun-Pyo; Han, Chang-Yeol; Jo, Jung-Ho; Yang, Heesun

    2016-07-01

    Using a single emitter of Cu-Ga-S/ZnS quantum dots, all-solution-processed white electroluminescent lighting device that not only exhibits the record quantities of 1007 cd m(-2) in luminance and 1.9% in external quantum efficiency but also possesses satisfactorily high color rendering indices of 83-88 is demonstrated. PMID:27135303

  18. GEANT4 simulations for beam emittance in a linear collider based on plasma wakefield acceleration

    SciTech Connect

    Mete, O. Xia, G.; Hanahoe, K.; Labiche, M.

    2015-08-15

    Alternative acceleration technologies are currently under development for cost-effective, robust, compact, and efficient solutions. One such technology is plasma wakefield acceleration, driven by either a charged particle or laser beam. However, the potential issues must be studied in detail. In this paper, the emittance evolution of a witness beam through elastic scattering from gaseous media and under transverse focusing wakefields is studied.

  19. Design of emitter structures based on resonant perfect absorption for thermophotovoltaic applications.

    PubMed

    Foley, Jonathan J; Ungaro, Craig; Sun, Keye; Gupta, Mool C; Gray, Stephen K

    2015-11-30

    We report a class of thermophotovoltaic emitter structures built upon planar films that support resonant modes, known as perfectly-absorbing modes, that facilitate an exceptional optical response for selective emission. These planar structures have several key advantages over previously-proposed designs for TPV applications: they are simple to fabricate, are stable across a range of temperatures and conditions, and are capable of achieving some of the highest spectral efficiencies reported of any class of emitter structure. Utilization of these emitters leads to exceptionally high device efficiencies under low operating temperature conditions, which should open new opportunities for waste heat management. We present a theoretical framework for understanding this performance, and show that this framework can be leveraged as a search algorithm for promising candidate structures. In addition to providing an efficient theoretical methodology for identifying high-performance emitter structures, our methodology provides new insight into underlying design principles and should pave way for future design of structures that are simple to fabricate, temperature stable, and possess exceptional optical properties. PMID:26698788

  20. Heralded quantum repeater based on the scattering of photons off single emitters using parametric down-conversion source

    PubMed Central

    Song, Guo-Zhu; Wu, Fang-Zhou; Zhang, Mei; Yang, Guo-Jian

    2016-01-01

    Quantum repeater is the key element in quantum communication and quantum information processing. Here, we investigate the possibility of achieving a heralded quantum repeater based on the scattering of photons off single emitters in one-dimensional waveguides. We design the compact quantum circuits for nonlocal entanglement generation, entanglement swapping, and entanglement purification, and discuss the feasibility of our protocols with current experimental technology. In our scheme, we use a parametric down-conversion source instead of ideal single-photon sources to realize the heralded quantum repeater. Moreover, our protocols can turn faulty events into the detection of photon polarization, and the fidelity can reach 100% in principle. Our scheme is attractive and scalable, since it can be realized with artificial solid-state quantum systems. With developed experimental technique on controlling emitter-waveguide systems, the repeater may be very useful in long-distance quantum communication. PMID:27350159

  1. Heralded quantum repeater based on the scattering of photons off single emitters using parametric down-conversion source

    NASA Astrophysics Data System (ADS)

    Song, Guo-Zhu; Wu, Fang-Zhou; Zhang, Mei; Yang, Guo-Jian

    2016-06-01

    Quantum repeater is the key element in quantum communication and quantum information processing. Here, we investigate the possibility of achieving a heralded quantum repeater based on the scattering of photons off single emitters in one-dimensional waveguides. We design the compact quantum circuits for nonlocal entanglement generation, entanglement swapping, and entanglement purification, and discuss the feasibility of our protocols with current experimental technology. In our scheme, we use a parametric down-conversion source instead of ideal single-photon sources to realize the heralded quantum repeater. Moreover, our protocols can turn faulty events into the detection of photon polarization, and the fidelity can reach 100% in principle. Our scheme is attractive and scalable, since it can be realized with artificial solid-state quantum systems. With developed experimental technique on controlling emitter-waveguide systems, the repeater may be very useful in long-distance quantum communication.

  2. Heralded quantum repeater based on the scattering of photons off single emitters using parametric down-conversion source.

    PubMed

    Song, Guo-Zhu; Wu, Fang-Zhou; Zhang, Mei; Yang, Guo-Jian

    2016-01-01

    Quantum repeater is the key element in quantum communication and quantum information processing. Here, we investigate the possibility of achieving a heralded quantum repeater based on the scattering of photons off single emitters in one-dimensional waveguides. We design the compact quantum circuits for nonlocal entanglement generation, entanglement swapping, and entanglement purification, and discuss the feasibility of our protocols with current experimental technology. In our scheme, we use a parametric down-conversion source instead of ideal single-photon sources to realize the heralded quantum repeater. Moreover, our protocols can turn faulty events into the detection of photon polarization, and the fidelity can reach 100% in principle. Our scheme is attractive and scalable, since it can be realized with artificial solid-state quantum systems. With developed experimental technique on controlling emitter-waveguide systems, the repeater may be very useful in long-distance quantum communication. PMID:27350159

  3. Electromagnetic near-field interactions of a dipolar emitter with metal and metamaterial nanoslabs

    SciTech Connect

    Hakkarainen, Timo; Setaelae, Tero; Friberg, Ari T.

    2011-09-15

    We investigate the emission properties of a polarizable point dipole placed within a subwavelength distance from a silver or a slightly absorbing, negative-index metamaterial nanoslab. Using electromagnetic theory we show that in the immediate vicinity of the slab the dipole-slab interaction prevents the dipole from radiating. For the metamaterial slab close to the perfect-lens arrangement, the interaction is relatively weak and of short range. In particular, a region exists in the near zone of the metamaterial slab where the dipole emission is not disturbed by the interaction, and a bright intensity distribution of subwavelength width is created on the opposite side of the slab. This suggests that a low-loss metamaterial slab can act as a near-field imaging device which does not disturb the object. For the silver slab the interaction is stronger and it reaches over the near-field zone, adversely influencing the imaging capabilities in terms of brightness and resolution. The results are important for the development of metal and metamaterial superlenses.

  4. Flexible Field Emitter for X-ray Generation by Implanting CNTs into Nickel Foil.

    PubMed

    Sun, Bin; Wang, Yan; Ding, Guifu

    2016-12-01

    This paper reports on a flexible Ni micro wire with CNTs embedded into its surface. By using micromachining technology, for the first time, we could implant nanoscale materials into micro-scale metal substrate at room temperature. Thanks to the effective direct contact and the strong interactions between CNTs and the substrate, field emission current of 1.11 mA (current density of 22.2 mA/cm(2)) could be achieved from the micro wire. Moreover, the wire shows excellent mechanical properties for large amplitude bending, which is beneficial for geometric designing. To check the practical application of the wire, a simplified X-ray imaging system was set up by modifying a conventional tube. The gray shade that appears on the sensitive film after being exposed to the radiation confirms the X-ray generation. PMID:27613070

  5. Hyperbolic metamaterial-based near-field thermophotovoltaic system for hundreds of nanometer vacuum gap.

    PubMed

    Jin, Seokmin; Lim, Mikyung; Lee, Seung S; Lee, Bong Jae

    2016-03-21

    Artificially designed hyperbolic metamaterial (HMM) possesses extraordinary electromagnetic features different from those of naturally existing materials. In particular, the dispersion relation of waves existing inside the HMM is hyperbolic rather than elliptical; thus, waves that are evanescent in isotropic media become propagating in the HMM. This characteristic of HMMs opens a novel way to spectrally control the near-field thermal radiation in which evanescent waves in the vacuum gap play a critical role. In this paper, we theoretically investigate the performance of a near-field thermophotovoltaic (TPV) energy conversion system in which a W/SiO2-multilayer-based HMM serves as the emitter at 1000 K and InAs works as the TPV cell at 300 K. By carefully designing the thickness of constituent materials of the HMM emitter, the electric power of the near-field TPV devices can be increased by about 6 times at 100-nm vacuum gap as compared to the case of the plain W emitter. Alternatively, in regards to the electric power generation, HMM emitter at experimentally achievable 100-nm vacuum gap performs equivalently to the plain W emitter at 18-nm vacuum gap. We show that the enhancement mechanism of the HMM emitter is due to the coupled surface plasmon modes at multiple metal-dielectric interfaces inside the HMM emitter. With the minority carrier transport model, the optimal p-n junction depth of the TPV cell has also been determined at various vacuum gaps. PMID:27136882

  6. Carbon nanotube electron field emitters for x-ray imaging of human breast cancer.

    PubMed

    Gidcumb, Emily; Gao, Bo; Shan, Jing; Inscoe, Christy; Lu, Jianping; Zhou, Otto

    2014-06-20

    For imaging human breast cancer, digital breast tomosynthesis (DBT) has been shown to improve image quality and breast cancer detection in comparison to two-dimensional (2D) mammography. Current DBT systems have limited spatial resolution and lengthy scan times. Stationary DBT (s-DBT), utilizing an array of carbon nanotube (CNT) field emission x-ray sources, provides increased spatial resolution and potentially faster imaging than current DBT systems. This study presents the results of detailed evaluations of CNT cathodes for x-ray breast imaging tasks. The following were investigated: high current, long-term stability of CNT cathodes for DBT; feasibility of using CNT cathodes to perform a 2D radiograph function; and cathode performance through several years of imaging. Results show that a breast tomosynthesis system using CNT cathodes could run far beyond the experimentally tested lifetime of one to two years. CNT cathodes were found capable of producing higher currents than typical DBT would require, indicating that the s-DBT imaging time can be further reduced. The feasibility of using a single cathode of the s-DBT tube to perform 2D mammography in 4 s was demonstrated. Over the lifetime of the prototype s-DBT system, it was found that both cathode performance and transmission rate were stable and consistent. PMID:24869902

  7. Chemical Vapor Deposited Few-Layer Graphene as an Electron Field Emitter.

    PubMed

    Behural, Sanjay K; Nayak, Sasmita; Yang, Qiaoqin; Hirose, Akira; Janil, Omkar

    2016-01-01

    Chemical vapor deposition (CVD) growth of graphene on polycrystalline copper (Cu) foil in a low pressure conditions has been presented, aiming to achieve the highest quality with large-scale fabrications, which requires comprehensive understanding and effective controlling of the growth process. Herein, few-layer graphene (FLG) films with large-domain sizes were grown on Cu metal catalyst substrates using a vertical mass-flow hot-filament CVD reactor, with the intention of large scale production, by optimizing the CVD system and three of the process parameters: (i) gas flow compositions, (ii) substrate annealing time and (iii) graphene deposition time. The detailed scanning electron microscope and Raman spectroscopy analysis indicate that all the above mentioned process parameters affect growth of FLG film on Cu substrate. The presence of two intense peaks, G and 2D-band at 1583.6 and 2702.6 cm⁻¹ for synthesized sample at optimized conditions (H₂/CH₄ ratio of 50:1 at graphene deposition time of 10 minutes and substrate annealed time for 20 minutes) revealed the formation of FLG films with large domain size. These graphene films on Cu have shown the room temperature field electron emission characteristics, hence appears to be prospective candidate for vacuum nanoelectronics. PMID:27398456

  8. Carbon nanotube electron field emitters for x-ray imaging of human breast cancer

    NASA Astrophysics Data System (ADS)

    Gidcumb, Emily; Gao, Bo; Shan, Jing; Inscoe, Christy; Lu, Jianping; Zhou, Otto

    2014-06-01

    For imaging human breast cancer, digital breast tomosynthesis (DBT) has been shown to improve image quality and breast cancer detection in comparison to two-dimensional (2D) mammography. Current DBT systems have limited spatial resolution and lengthy scan times. Stationary DBT (s-DBT), utilizing an array of carbon nanotube (CNT) field emission x-ray sources, provides increased spatial resolution and potentially faster imaging than current DBT systems. This study presents the results of detailed evaluations of CNT cathodes for x-ray breast imaging tasks. The following were investigated: high current, long-term stability of CNT cathodes for DBT; feasibility of using CNT cathodes to perform a 2D radiograph function; and cathode performance through several years of imaging. Results show that a breast tomosynthesis system using CNT cathodes could run far beyond the experimentally tested lifetime of one to two years. CNT cathodes were found capable of producing higher currents than typical DBT would require, indicating that the s-DBT imaging time can be further reduced. The feasibility of using a single cathode of the s-DBT tube to perform 2D mammography in 4 s was demonstrated. Over the lifetime of the prototype s-DBT system, it was found that both cathode performance and transmission rate were stable and consistent.

  9. Carbon nanotube electron field emitters for X-ray imaging of human breast cancer

    PubMed Central

    Gidcumb, Emily; Gao, Bo; Shan, Jing; Inscoe, Christy; Lu, Jianping; Zhou, Otto

    2014-01-01

    For imaging human breast cancer, digital breast tomosynthesis (DBT) has been shown to improve image quality and breast cancer detection in comparison to 2D mammography. Current DBT systems have limited spatial resolution and lengthy scan times. Stationary digital breast tomosynthesis (s-DBT), utilizing an array of carbon nanotube (CNT) field emission X-ray sources, provides increased spatial resolution and potentially faster imaging than current DBT systems. This study presents the results of detailed evaluations of CNT cathodes for X-ray breast imaging tasks. The following were investigated: high current, long-term stability of CNT cathodes for DBT; feasibility of using CNT cathodes to perform a 2D radiograph function; and cathode performance through several years of imaging. Results show that a breast tomosynthesis system using CNT cathodes could run far beyond the experimentally tested lifetime of one to two years. CNT cathodes were found capable of producing higher currents than typical DBT would require, indicating that the s-DBT imaging time can be further reduced. The feasibility of using a single cathode of the s-DBT tube to perform 2D mammography in 4 seconds, was demonstrated. Over the lifetime of the prototype s-DBT system, it was found that both cathode performance and transmission rate were stable and consistent. PMID:24869902

  10. Extraction of emission parameters for large-area field emitters, using a technically complete Fowler-Nordheim-type equation

    NASA Astrophysics Data System (ADS)

    Forbes, Richard G.

    2012-03-01

    In papers on cold field electron emission from large-area field emitters (LAFEs), it has become widespread practice to publish a misleading Fowler-Nordheim-type (FN-type) equation. This equation over-predicts the LAFE-average current density by a large highly variable factor thought to usually lie between 103 and 109. This equation, although often referenced to FN’s 1928 paper, is a simplified equation used in undergraduate teaching, does not apply unmodified to LAFEs and does not appear in the 1928 paper. Technological LAFE papers often do not cite any theoretical work more recent than 1928, and often do not comment on the discrepancy between theory and experiment. This usage has occurred widely, in several high-profile American and UK applied-science journals (including Nanotechnology), and in various other places. It does not inhibit practical LAFE development, but can give a misleading impression of potential LAFE performance to non-experts. This paper shows how the misleading equation can be replaced by a conceptually complete FN-type equation that uses three high-level correction factors. One of these, or a combination of two of them, may be useful as an additional measure of LAFE quality; this paper describes a method for estimating factor values using experimental data and discusses when it can be used. Suggestions are made for improved engineering practice in reporting LAFE results. Some of these should help to prevent situations arising whereby an equation appearing in high-profile applied-science journals is used to support statements that an engineering regulatory body might deem to involve professional negligence.

  11. Control of focusing forces and emittances in plasma-based accelerators using near-hollow plasma channels

    SciTech Connect

    Schroeder, C. B.; Esarey, E.; Benedetti, C.; Leemans, W. P.

    2013-08-15

    A near-hollow plasma channel, where the plasma density in the channel is much less than the plasma density in the walls, is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator. In this geometry the low density in the channel contributes to the focusing forces, while the accelerating fields are determined by the high density in the channel walls. The channel also provides guiding for intense laser pulses used for wakefield excitation. Both electron and positron beams can be accelerated in a nearly symmetric fashion. Near-hollow plasma channels can effectively mitigate emittance growth due to Coulomb scattering for high-energy physics applications.

  12. Control of focusing forces and emittances in plasma-based accelerators using near-hollow plasma channels

    SciTech Connect

    Schroeder, Carl; Esarey, Eric; Benedetti, Carlo; Leemans, Wim

    2013-08-06

    A near-hollow plasma channel, where the plasma density in the channel is much less than the plasma density in the walls, is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator. In this geometry the low density in the channel contributes to the focusing forces, while the accelerating fields are determined by the high density in the channel walls. The channel also provides guiding for intense laser pulses used for wakefield excitation. Both electron and positron beams can be accelerated in a nearly symmetric fashion. Near-hollow plasma channels can effectively mitigate emittance growth due to Coulomb scattering for high energy physics applications.

  13. Direct bonding between spacer and field emitter array using an electron-beam-evaporated interlayer

    NASA Astrophysics Data System (ADS)

    Park, Heung-Woo; Ju, Byeong-Kwon; Lee, Yun-Hi; Kang, In-Byeong; Samaan, Noel D.; Haskard, Malcolm R.; Park, Jung-Ho; Oh, Myung-Hwan

    1997-06-01

    This work reports a direct bonding method between silicon wafers using an interlayer. Thermal oxide, sputtered silicon nitride, molybdenum film and electron-beam evaporated silicon oxide were used as an interlayer. Silicon wafers were hydrophilized by one of the host nitric acid, the sulfuric acid based solution and the ammonium hydroxide based solution, mated at class 100 hemisphere and heat treated. After hydrophilization of silicon wafers, the changes of the surface roughness' were studied by the atomic force microscopy and the voids and the non-bonded areas were inspected by the infra-red transmission microscope. The bonding interfaces of the bonded pairs were inspected by a high resolution scanning electron microscope. Surface energies and tensile strengths of the bonded pairs were also tested by the crack propagation method and the push-pull meter, respectively. Surface energy of the Si-Si wafer pair annealed at 150 degree(s)C for 48 hours was about 7200 [erg/cm2] and its tensile strength was more than 18 MPa. This tensile strength is comparable with the bulk strength of the used silicon wafer.

  14. Constraints on drivers for visible light communications emitters based on energy efficiency.

    PubMed

    Del Campo-Jimenez, Guillermo; Perez-Jimenez, Rafael; Lopez-Hernandez, Francisco Jose

    2016-05-01

    In this work we analyze the energy efficiency constraints on drivers for Visible light communication (VLC) emitters. This is the main reason why LED is becoming the main source of illumination. We study the effect of the waveform shape and the modulation techniques on the overall energy efficiency of an LED lamp. For a similar level of illumination, we calculate the emitter energy efficiency ratio η (PLED/PTOTAL) for different signals. We compare switched and sinusoidal signals and analyze the effect of both OOK and OFDM modulation techniques depending on the power supply adjustment, level of illumination and signal amplitude distortion. Switched and OOK signals present higher energy efficiency behaviors (0.86≤η≤0.95) than sinusoidal and OFDM signals (0.53≤η≤0.79). PMID:27137609

  15. Role of the optical pulse repetition rate in the efficiency of terahertz emitters

    NASA Astrophysics Data System (ADS)

    Reklaitis, Antanas

    2016-07-01

    Excitation of n-GaAs and p-InAs terahertz emitters by the series of optical pulses is studied by ensemble Monte Carlo simulations. It is found that the spatial separation of photoexcited electrons and holes dramatically reduces the recombination intensity in n-GaAs emitter, the operation of which is based on the surface field effect. The spatial separation of carriers does not affect the recombination intensity in p-InAs emitter, the operation of which is based on the photo-Dember effect. Therefore, the recovery time of equilibrium state after optical pulse in n-GaAs emitter significantly exceeds the corresponding recovery time in p-InAs emitter. This fact leads to a substantial reduction of photocurrent amplitude in n-GaAs emitter excited by the optical pulse series at high repetition rate.

  16. Highly efficient white organic light-emitting diodes based on fluorescent blue emitters

    NASA Astrophysics Data System (ADS)

    Rosenow, Thomas C.; Furno, Mauro; Reineke, Sebastian; Olthof, Selina; Lüssem, Björn; Leo, Karl

    2010-12-01

    Beside inorganic LEDs and fluorescent lamps, organic light-emitting diodes (OLEDs) are evolving into a serious alternative to incandescent lamps. Up to now, it was assumed that all-phosphorescent OLEDs are required for reaching sufficiently high efficiencies. However, the stability of phosphorescent blue emitters is a major challenge. We present a novel approach to achieve highly efficient (up to 90 lm/W at 1000 cd/m2 using a macroextractor) white light emission from OLEDs. The here presented combination of a fluorescent blue and a phosphorescent red emitter simultaneously allows for a strong blue emission and efficient triplet transfer to the phosphor. The spectrum is extended in the green and yellow region by a full phosphorescent unit stacked on top of the triplet harvesting device. This superposition of four different emitters results in color coordinates close to illuminant A and a color rendering index of 80. Furthermore, color stability is given with respect to varying driving conditions and estimations of the electrical and optical efficiencies are provided.

  17. RFI emitter location techniques

    NASA Technical Reports Server (NTRS)

    Rao, B. L. J.

    1973-01-01

    The possibility is discussed of using Doppler techniques for determining the location of ground based emitters causing radio frequency interference with low orbiting satellites. An error analysis indicates that it is possible to find the emitter location within an error range of 2 n.mi. The parameters which determine the required satellite receiver characteristic are discussed briefly along with the non-real time signal processing which may by used in obtaining the Doppler curve. Finally, the required characteristics of the satellite antenna are analyzed.

  18. Current gain above 10 in sub-10 nm base III-Nitride tunneling hot electron transistors with GaN/AlN emitter

    NASA Astrophysics Data System (ADS)

    Yang, Zhichao; Zhang, Yuewei; Krishnamoorthy, Sriram; Nath, Digbijoy N.; Khurgin, Jacob B.; Rajan, Siddharth

    2016-05-01

    We report on a tunneling hot electron transistor amplifier with common-emitter current gain greater than 10 at a collector current density in excess of 40 kA/cm2. The use of a wide-bandgap GaN/AlN (111 nm/2.5 nm) emitter was found to greatly improve injection efficiency of the emitter and reduce cold electron leakage. With an ultra-thin (8 nm) base, 93% of the injected hot electrons were collected, enabling a common-emitter current gain up to 14.5. This work improves understanding of the quasi-ballistic hot electron transport and may impact the development of high speed devices based on unipolar hot electron transport.

  19. Monitoring the irradiation field of 12C and 16O SOBP beams using positron emitters produced through projectile fragmentation reactions

    NASA Astrophysics Data System (ADS)

    Inaniwa, Taku; Kohno, Toshiyuki; Tomitani, Takehiro; Sato, Shinji

    2008-02-01

    In order to effectively utilize the prominent properties of heavy ions in radiotherapy, it is important to evaluate both the position of the field irradiated with incident ions and the absorbed dose distribution in a patient's body. One of the methods for this purpose is the utilization of the positron emitters produced through the projectile fragmentation reactions of stable heavy ions with target nuclei. In heavy-ion therapy, spread-out Bragg peak (SOBP) beams are used to achieve uniform biological dose distributions in the whole tumor volume. Therefore, in this study, we designed SOBP beams of 30 and 50 mm water-equivalent length (mmWEL) in width for 12C and 16O, and carried out irradiation experiments using them. Water, polyethylene and polymethyl methacrylate were selected as targets to simulate a human body. Pairs of annihilation gamma rays were detected by means of a limited-angle positron camera for 500 s, and annihilation gamma-ray distributions were obtained. The maximum likelihood estimation (MLE) method was applied to the detected distributions for evaluating the positions of the distal and proximal edges of the SOBP in a target. The differences between the positions evaluated with the MLE method and those derived from the measured dose distributions were less than 1.7 mm and 2.5 mm for the distal and the proximal edge, respectively, in all irradiation conditions. When the positions of both edges are determined with the MLE method, the most probable shape of the dose distribution in a target can be estimated simultaneously. The close agreement between the estimated and the measured distributions implied that the shape of the dose distribution in an irradiated target could be evaluated from the detected annihilation gamma-ray distribution.

  20. EMITTANCE COMPENSATION FOR MAGNETIZED BEAMS

    SciTech Connect

    KEWISCH,J.; CHANG, X.

    2007-06-25

    Emittance compensation is a well established technique for minimizing the emittance of an electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincide the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating game. We describe a method and tools for a compensation that includes the beam magnetization.

  1. 100 W/100 μm passively cooled fiber coupled diode laser at 976 nm based on multiple 100 μm single emitters

    NASA Astrophysics Data System (ADS)

    Werner, Marcel; Wessling, Christian; Hengesbach, Stefan; Traub, Martin; Hoffmann, Hans-Dieter

    2009-02-01

    We developed a high brightness fiber coupled diode laser module based on single diode lasers providing more than 60 Watts output power from a 100 micron fiber at the optimum fiber laser pump wavelength of 976 nm. The advantage of using multiple single emitters on a submount compared to using bars or mini bars is the direct fiber coupling by use of optical stacking and the fact that no beam transformation is needed. We achieved best brightness with a high fill factor, optical efficiency of more then 80% and wall-plug efficiency of more then 40%. The use of single emitters on a submount also extends the life span due to reduced failure (xn vs. x) per device (n individual emitters vs. n emitters on a bar (mini array)). Low drive current enables modulation.

  2. Continuous and reversible operation of Bi2212 based THz emitters just below Tc

    NASA Astrophysics Data System (ADS)

    Minami, Hidetoshi; Orita, Naoki; Koike, Takashi; Yamamoto, Takashi; Kadowaki, Kazuo

    2010-12-01

    Continuous and reversible operation of the THz-light emitters comprised of the intrinsic Josephson junction (iJJ) system of high-Tc superconductor BiSrCaCuO (Bi2212) is reported. This reversible emission is observed in samples made of lightly underdoped crystals when a part of the mesa device is so overheated by Joule heating that the temperature reaches Tm near but still below Tc, while the irreversible type of emission occurs at less overheated condition. The large temperature gradient in the mesa due to overheating under high bias currents seems to be responsible for the new observed reversible emission.

  3. Clinical CT-based calculations of dose and positron emitter distributions in proton therapy using the FLUKA Monte Carlo code

    PubMed Central

    Parodi, K; Ferrari, A; Sommerer, F; Paganetti, H

    2008-01-01

    Clinical investigations on post-irradiation PET/CT (positron emission tomography / computed tomography) imaging for in-vivo verification of treatment delivery and, in particular, beam range in proton therapy are underway at Massachusetts General Hospital (MGH). Within this project we have developed a Monte Carlo framework for CT-based calculation of dose and irradiation induced positron emitter distributions. Initial proton beam information is provided by a separate Geant4 Monte Carlo simulation modeling the treatment head. Particle transport in the patient is performed in the CT voxel geometry using the FLUKA Monte Carlo code. The implementation uses a discrete number of different tissue types with composition and mean density deduced from the CT scan. Scaling factors are introduced to account for the continuous Hounsfield Unit dependence of the mass density and of the relative stopping power ratio to water used by the treatment planning system (XiO (Computerized Medical Systems Inc.)). Resulting Monte Carlo dose distributions are generally found in good correspondence with calculations of the treatment planning program, except few cases (e.g. in the presence of air/tissue interfaces). Whereas dose is computed using standard FLUKA utilities, positron emitter distributions are calculated by internally combining proton fluence with experimental and evaluated cross-sections yielding 11C, 15O, 14O, 13N, 38K and 30P. Simulated positron emitter distributions yield PET images in good agreement with measurements. In this paper we describe in detail the specific implementation of the FLUKA calculation framework, which may be easily adapted to handle arbitrary phase spaces of proton beams delivered by other facilities or include more reaction channels based on additional cross-section data. Further, we demonstrate the effects of different acquisition time regimes (e.g., PET imaging during or after irradiation) on the intensity and spatial distribution of the irradiation

  4. Clinical CT-based calculations of dose and positron emitter distributions in proton therapy using the FLUKA Monte Carlo code

    NASA Astrophysics Data System (ADS)

    Parodi, K.; Ferrari, A.; Sommerer, F.; Paganetti, H.

    2007-07-01

    Clinical investigations on post-irradiation PET/CT (positron emission tomography/computed tomography) imaging for in vivo verification of treatment delivery and, in particular, beam range in proton therapy are underway at Massachusetts General Hospital (MGH). Within this project, we have developed a Monte Carlo framework for CT-based calculation of dose and irradiation-induced positron emitter distributions. Initial proton beam information is provided by a separate Geant4 Monte Carlo simulation modelling the treatment head. Particle transport in the patient is performed in the CT voxel geometry using the FLUKA Monte Carlo code. The implementation uses a discrete number of different tissue types with composition and mean density deduced from the CT scan. Scaling factors are introduced to account for the continuous Hounsfield unit dependence of the mass density and of the relative stopping power ratio to water used by the treatment planning system (XiO (Computerized Medical Systems Inc.)). Resulting Monte Carlo dose distributions are generally found in good correspondence with calculations of the treatment planning program, except a few cases (e.g. in the presence of air/tissue interfaces). Whereas dose is computed using standard FLUKA utilities, positron emitter distributions are calculated by internally combining proton fluence with experimental and evaluated cross-sections yielding 11C, 15O, 14O, 13N, 38K and 30P. Simulated positron emitter distributions yield PET images in good agreement with measurements. In this paper, we describe in detail the specific implementation of the FLUKA calculation framework, which may be easily adapted to handle arbitrary phase spaces of proton beams delivered by other facilities or include more reaction channels based on additional cross-section data. Further, we demonstrate the effects of different acquisition time regimes (e.g., PET imaging during or after irradiation) on the intensity and spatial distribution of the irradiation

  5. The End of the Reionization Epoch Probed by Lyα Emitters at z = 6.5 in the Subaru Deep Field

    NASA Astrophysics Data System (ADS)

    Kashikawa, Nobunari; Shimasaku, Kazuhiro; Malkan, Matthew A.; Doi, Mamoru; Matsuda, Yuichi; Ouchi, Masami; Taniguchi, Yoshiaki; Ly, Chun; Nagao, Tohru; Iye, Masanori; Motohara, Kentaro; Murayama, Takashi; Murozono, Kouji; Nariai, Kyoji; Ohta, Kouji; Okamura, Sadanori; Sasaki, Toshiyuki; Shioya, Yasuhiro; Umemura, Masayuki

    2006-09-01

    We report an extensive search for Lyα emitters (LAEs) at z=6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru and Keck identified eight more LAEs, giving a total of 17 spectroscopically confirmed LAEs at z=6.5. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyα luminosity function of LAEs at z=6.5, which reveals an apparent deficit at the bright end of ~0.75 mag fainter L*, compared with that observed at z=5.7. The difference in the LAE luminosity functions between z=5.7 and 6.5 is significant at the 3 σ level, which is reduced to 2 σ when cosmic variance is taken into account. This result may imply that the reionization of the universe has not been completed at z=6.5. We found that the spatial distribution of LAEs at z=6.5 was homogeneous over the field. We discuss the implications of these results for the reionization of the universe. The data presented herein were partly obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  6. Midwave Infrared (2-6{micro}m) Emitter-Based Chemical Sensor Systems

    SciTech Connect

    Allerman, A.A.; Biefeld, R.M.; Kurtz, S.R.

    1999-02-01

    Long wavelength (2-6 {micro}m) diode emitters are desirable for many applications including monitoring of chemical species in the environment and manufacturing, long wavelength fiber-optic communications, lidar, and JR detector counter-measures. No practical diode lasers are available for any of these applications because the band structure of bulk III-V, II-VI, and IV-VI semiconductor alloys results in large Auger recombination rates at these wavelengths. Experimental and theoretical work at Sandia has resulted in new understanding of the electronic properties of narrow bandgap III-V heterostructures, and we have found methods of reducing the Auger rates in certain InAsSb superlattices and quantum wells. These devices enable us to begin chemical sensing demonstrations of important species such as CO-CO{sub 2} and numerous other compounds. This project will involve developing chemical sensing systems and determining the sensitivity and limitations of these systems. Concurrently, we will improve upon infrared emitters used in these systems.

  7. Control of focusing forces and emittances in plasma-based accelerators using near-hollow plasma channels

    NASA Astrophysics Data System (ADS)

    Schroeder, Carl; Benedetti, Carlo; Esarey, Eric; Leemans, Wim

    2013-10-01

    A near-hollow plasma channel, where the plasma density in the channel is much less than the plasma density in the walls, is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator. In this geometry the low density in the channel determines the focusing forces, while the accelerating field is determined by the high density in the channel walls. The channel also provides guiding for intense laser pulses used for wakefield excitation. Beam loading using a near-hollow plasma channel is examined. Properly shaping and phasing the witness particle beam, high-gradient acceleration can be achieved with high-efficiency, and without induced energy spread or emittance growth. Both electron and positron beams can be accelerated in a nearly symmetric fashion. Near-hollow plasma channels can effectively mitigate emittance growth due to Coulomb scattering for high-energy physics applications. Supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

  8. Two-stage plasma gun based on a gas discharge with a self-heating hollow emitter.

    PubMed

    Vizir, A V; Tyunkov, A V; Shandrikov, M V; Oks, E M

    2010-02-01

    The paper presents the results of tests of a new compact two-stage bulk gas plasma gun. The plasma gun is based on a nonself-sustained gas discharge with an electron emitter based on a discharge with a self-heating hollow cathode. The operating characteristics of the plasma gun are investigated. The discharge system makes it possible to produce uniform and stable gas plasma in the dc mode with a plasma density up to 3x10(9) cm(-3) at an operating gas pressure in the vacuum chamber of less than 2x10(-2) Pa. The device features high power efficiency, design simplicity, and compactness. PMID:20192469

  9. Electron beam collimation with a 40 000 tip metallic double-gate field emitter array and in-situ control of nanotip sharpness distribution

    NASA Astrophysics Data System (ADS)

    Helfenstein, P.; Guzenko, V. A.; Fink, H.-W.; Tsujino, S.

    2013-01-01

    The generation of highly collimated electron beams from a double-gate field emitter array with 40000 metallic tips and large collimation gate apertures is reported. Field emission beam measurements demonstrated the reduction of the beam envelope down to the array size by applying a negative potential to the on-chip gate electrode for the collimation of individual field emission beamlets. Owing to the optimized gate structure, the concomitant decrease of the emission current was minimal, leading to a net enhancement of the current density. Furthermore, a noble gas conditioning process was successfully applied to the double-gate device to improve the beam uniformity in-situ with orders of magnitude increase of the active emission area. The results show that the proposed double-gate field emission cathodes are promising for high current and high brightness electron beam applications such as free-electron lasers and THz power devices.

  10. An empirical study of the performance of APMOVPE AM0 InP homojunction solar cells as a function of emitter thickness and doping, and base doping

    NASA Technical Reports Server (NTRS)

    Wanlass, M. W.; Gessert, T. A.; Emery, K. A.; Coutts, T. J.

    1989-01-01

    Their excellent radiation resistance and conversion efficiencies greater than 20 percent, measured under global conditions, make InP shallow-homojunction solar cells very attractive for space or terrestrial application. In addition, modeling studies show that, for optimized design, efficiencies of these devices should exceed 20 percent even under AM0 conditions. However, a systematic experimental investigation of the influence of the various cell design parameters on cell performance has not as yet been made. For the n+/p/p+ structures investigated in the previous modeling study, the design parameters include the impurity concentrations and thicknesses of the emitter and base layers. In the work reported here, researchers discuss an experimental investigation of the effects on cell performance of varying the impurity concentrations of the emitter and base and thickness of the emitter.

  11. Current gain in sub-10 nm base GaN tunneling hot electron transistors with AlN emitter barrier

    SciTech Connect

    Yang, Zhichao Zhang, Yuewei; Nath, Digbijoy N.; Rajan, Siddharth; Khurgin, Jacob B.

    2015-01-19

    We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3 were attained in common-emitter configuration with collector current density in excess of 50 kA/cm{sup 2}. The use of a combination of 1 nm GaN/3 nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices.

  12. Combining Transmission Geometry Laser Ablation and a Non Contact Continuous Flow Surface Sampling Probe/Electrospray Emitter for Mass Spectrometry-Based Chemical Imaging

    SciTech Connect

    Ovchinnikova, Olga S; Kertesz, Vilmos; Van Berkel, Gary J

    2011-01-01

    This paper describes the coupling of ambient pressure transmission geometry laser ablation with a liquid phase sample collection into a continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging. The flow probe/emitter device was placed in close proximity to the surface to collect the sample plume produced by laser ablation. The sample collected was immediately aspirated into the probe and on to the electrospray emitter, ionized and detected with the mass spectrometer. Freehand drawn ink lines and letters and an inked fingerprint on microscope slides were analyzed. The circular laser ablation area was about 210 m in diameter and under the conditions used in these experiments the spatial resolution, as determined by the size of the surface features distinguished in the chemical images, was about 100 m.

  13. Emittance Growth in the NLCTA First Chicane

    SciTech Connect

    Sun, Yipeng; Adolphsen, Chris; /SLAC

    2011-08-19

    In this paper, the emittance growth in the NLCTA (Next Linear Collider Test Accelerator) first chicane region is evaluated by simulation studies. It is demonstrated that the higher order fields of the chicane dipole magnet and the dipole corrector magnet (which is attached on the quadrupoles) are the main contributions for the emittance growth, especially for the case with a large initial emittance ({gamma}{epsilon}{sub 0} = 5 {micro}m for instance). These simulation results agree with the experimental observations.

  14. Morphological Properties of Lyα Emitters at Redshift 4.86 in the Cosmos Field: Clumpy Star Formation or Merger?

    NASA Astrophysics Data System (ADS)

    Kobayashi, Masakazu A. R.; Murata, Katsuhiro L.; Koekemoer, Anton M.; Murayama, Takashi; Taniguchi, Yoshiaki; Kajisawa, Masaru; Shioya, Yasuhiro; Scoville, Nick Z.; Nagao, Tohru; Capak, Peter L.

    2016-03-01

    We investigate morphological properties of 61 Lyα emitters (LAEs) at z = 4.86 identified in the COSMOS field, based on Hubble Space Telescope Advanced Camera for Surveys (ACS) imaging data in the F814W band. Out of the 61 LAEs, we find the ACS counterparts for 54 LAEs. Eight LAEs show double-component structures with a mean projected separation of 0.″63 (˜4.0 kpc at z = 4.86). Considering the faintness of these ACS sources, we carefully evaluate their morphological properties, that is, size and ellipticity. While some of them are compact and indistinguishable from the point-spread function (PSF) half-light radius of 0.″07 (˜0.45 kpc), the others are clearly larger than the PSF size and spatially extended up to 0.″3 (˜1.9 kpc). We find that the ACS sources show a positive correlation between ellipticity and size and that the ACS sources with large size and round shape are absent. Our Monte Carlo simulation suggests that the correlation can be explained by (1) the deformation effects via PSF broadening and shot noise or (2) the source blending in which two or more sources with small separation are blended in our ACS image and detected as a single elongated source. Therefore, the 46 single-component LAEs could contain the sources that consist of double (or multiple) components with small spatial separation (i.e., ≲0.″3 or 1.9 kpc). Further observation with high angular resolution at longer wavelengths (e.g., rest-frame wavelengths of ≳4000 Å) is inevitable to decipher which interpretation is adequate for our LAE sample. Based on observations with NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555, and also based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  15. SEARCH FOR z {approx} 6.96 Ly{alpha} EMITTERS WITH MAGELLAN/IMACS IN THE COSMOS FIELD

    SciTech Connect

    Hibon, P.; Malhotra, S.; Rhoads, J.; Willott, C.

    2011-11-10

    We report a search for z {approx} 6.96 Ly{alpha} emitters (LAEs) using a narrowband filter, centered at 9680 A with the Inamori-Magellan Area Camera and Spectrograph instrument on the Magellan telescope at Las Campanas Observatory. We obtain a sample of six LAE candidates of luminosity {approx}10{sup 42} erg s{sup -1} in a total area of 465 arcmin{sup 2} corresponding to a comoving volume of {approx}72,000 Mpc{sup 3}. From this result, we derive a Ly{alpha} luminosity function (LF) at z {approx} 6.96 and compare our sample with the only z {approx} 6.96 LAE spectroscopically confirmed to date. We find no evolution between the z = 5.7 and z {approx} 7 Ly{alpha} LFs if a majority of our candidates are confirmed. Spectroscopic confirmation for this sample will enable more robust conclusions.

  16. Micro-emitter heating by rf current

    NASA Astrophysics Data System (ADS)

    Volkov, V.; Petrov, V. M.

    2016-05-01

    One factor limiting the accelerating gradients in radiofrequency (rf) cavities are field emission currents emitted by micro-emitters. The value of emitter heating power plays a key role in theories of an rf cavity processing allowing to enhance the accelerating gradient. In this paper, the emitter heating by rf current is studied. This heating mechanism associates with a large heating power (by several orders of magnitude higher than the power of field emission current) and demonstrates explicit dependence on the frequency of the electromagnetic rf field (scales with the square of the rf field frequency).

  17. Emittance Theory for Cylindrical Fiber Selective Emitter

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.

    1998-01-01

    A fibrous rare earth selective emitter is approximated as an infinitely long, cylinder. The spectral emittance, e(sub x), is obtained L- by solving the radiative transfer equations with appropriate boundary conditions and uniform temperature. For optical depth, K(sub R), where alpha(sub lambda), is the extinction coefficient and R is the cylinder radius, greater than 1 the spectral emittance depths, K(sub R) alpha(sub lambda)R, is nearly at its maximum value. There is an optimum cylinder radius, R(sub opt) for maximum emitter efficiency, n(sub E). Values for R(sub opt) are strongly dependent on the number of emission bands of the material. The optimum radius decreases slowly with increasing emitter temperature, while the maximum efficiency and useful radiated power increase rapidly with increasing, temperature.

  18. Emittance Theory for Cylindrical Fiber Selective Emitter

    NASA Technical Reports Server (NTRS)

    Chubb, Donald L.

    1998-01-01

    A fibrous rare earth selective emitter is approximated as an infinitely long cylinder. The spectral emittance, epsilon(lambda), is obtained by solving the radiative transfer equations with appropriate boundary conditions and uniform temperature. For optical depths, Kappa(R) = alpha(lambda)R, where alpha(lambda) is the extinction coefficient and R is the cylinder radius, greater than 1 the spectral emittance is nearly at its maximum value. There is an optimum cylinder radius, R(opt), for maximum emitter efficiency, eta(E). Values for R(opt) are strongly dependent on the number of emission bands of the material. The optimum radius decreases slowly with increasing emitter temperature, while the maximum efficiency and useful radiated power increase rapidly with increasing temperature.

  19. Construction of LRET-based nanoprobe using upconversion nanoparticles with confined emitters and bared surface as luminophore.

    PubMed

    Li, Zhen; Lv, Songwei; Wang, Yali; Chen, Shiyu; Liu, Zhihong

    2015-03-11

    Upconversion nanoparticles (UCNPs) are promising energy donors for luminescence resonance energy transfer (LRET) and have widely been used to construct nanoprobes. To improve the LRET efficiency, which is currently a limiting factor for UCNPs-based bioassay, we herein propose a strategy to construct LRET-based nanoprobe using UCNPs with confined emitters and bared surface as the luminophore, with Ca(2+) as the proof-of-concept target. The sandwich-structure upconversion nanoparticles (SWUCNPs) are designed with a core-inner shell-outer shell architecture, in which the emitting ions (Ln(3+)) are precisely located in the inner shell near the particle surface, which is close enough to external energy acceptors. The target receptor (Fluo-4) is directly tagged on bared surface of SWUCNPs, which further reduces the donor-to-acceptor distance. Our strategy contributes to significantly improved LRET efficiency and hence affords an ultrahigh sensitivity for Ca(2+) detection. The as-constructed nanoprobe is structurally stable and exhibits good biocompatibility, which ensures uptake and reliable observation in living cells. The nanoprobe can be used for monitoring the different levels of cytosol [Ca(2+)] in living cells. Furthermore, it is applicable in Ca(2+) imaging in mice liver tissues. PMID:25707940

  20. Effect of external static magnetic field on the emittance and total charge of electron beams generated by laser-Wakefield acceleration.

    PubMed

    Hosokai, Tomonao; Kinoshita, Kenichi; Zhidkov, Alexei; Maekawa, Akira; Yamazaki, Atsushi; Uesaka, Mitsuru

    2006-08-18

    Significant enhancement of emittance and an increase of the total charge of femtosecond electron beams produced by a 12 TW, 40 fs laser pulse, tightly focused in a He gas jet, are observed after applying a static magnetic field, B> or =0.2 T, directed along the axis of laser pulse propagation. The effect appears when plasma produced by a laser prepulse becomes magnetized in the vicinity of the focus point: the electron Larmor frequency exceeds the collisional frequency, while periphery of the plasma remains unmagnetized. The entailed change in the shape of the plasma suppresses the diffraction of the main laser pulse that results in a much higher charge of electrons self-injected during the longitudinal wave breaking of the laser wake as well as the excellent stability of the beams. PMID:17026240

  1. Delayed fluorescence in a solution-processable pure red molecular organic emitter based on dithienylbenzothiadiazole: a joint optical, electroluminescence, and magnetoelectroluminescence study.

    PubMed

    Chen, Ping; Wang, Li-Ping; Tan, Wan-Yi; Peng, Qi-Ming; Zhang, Shi-Tong; Zhu, Xu-Hui; Li, Feng

    2015-02-01

    The discovery of triplet excitons participating in the photoluminescent processes in a growing number of pure organic emitters represents an exciting impetus for a diversity of promising opto, bio, and optoelectronic applications. In this contribution, we have studied a small-molecule dithienylbenzothiadiazole-based red-emitting dye red-1b, which shows clearly delayed fluorescence under optical and electrical excitation. The OLED device that contained red-1b as a nondoped solution-processable emitter exhibited a moderately high utilization of exciton amounting to ≈31% and slow efficiency roll-off. Magnetoelectroluminescence measurements revealed the coexistence of reverse intersystem crossing from the lowest triplet state to singlet state (RISC, E-type triplet to singlet up-conversion) and triplet-triplet annihilation (TTA, P-type triplet to singlet up-conversion). Specifically, in low current-density regime, the moderately high exciton utilization is attributed to RISC (i.e., thermally activated delayed fluorescence, TADF), whereas in high current-density regime, TTA may contribute to suppressing efficiency roll-off. Furthermore, the results showed that red-1b may represent a new kind of organic red emitters that display delayed fluorescence in a way differing from the few red emitters investigated so far. PMID:25585040

  2. Emittance concept and growth mechanisms

    SciTech Connect

    Wangler, T.P.

    1996-05-01

    The authors present an introduction to the subjects of emittance and space-charge effects in charged-particle beams. This is followed by a discussion of three important topics that are at the frontier of this field. The first is a simple model, describing space-charge-induced emittance growth, which yields scaling formulas and some physical explanations for some of the surprising results. The second is a discussion of beam halo, an introduction to the particle-core model, and a brief summary of its results. The third topic is an introduction to the hypothesis of equipartitioning for collisionless particle beams.

  3. Emittance concept and growth mechanisms

    SciTech Connect

    Wangler, T.P.

    1996-06-01

    We present an introduction to the subjects of emittance and space-charge effects in charged-particle beams. This is followed by a discussion of three important topics that are at the frontier of this field. The first is a simple model, describing space-charge-induced emittance growth, which yields scaling formulas and some physical explanations for some of the surprising results. The second is a discussion of beam halo, an introduction to the particle-core model, and a brief summary of its results. The third topic is an introduction to the hypothesis of equipartitioning for collisionless particle beams. {copyright} {ital 1996 American Institute of Physics.}

  4. Highly efficient and electrically robust carbon irradiated semi-insulating GaAs based photoconductive terahertz emitters

    SciTech Connect

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S. S. Nanal, Vandana; Pillay, R. G.

    2014-02-10

    We demonstrate here an efficient photoconductive THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters (PCEs) by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 μm deep, we have created lot of defects and decreased the lifetime of photo-excited carriers inside the substrate. Depending on the irradiation dose, we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the device. This has resulted in increasing maximum cut-off of the applied voltage across PCE electrodes to operate the device without thermal breakdown from ∼35 V to >150 V for the 25 μm electrode gaps. At optimum operating conditions, carbon irradiated (10{sup 14} ions/cm{sup 2}) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ∼800.

  5. Auger effect in yellow light emitters based on InGaN–AlGaN–GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Huong Ngo, Thi; Gil, Bernard; Valvin, Pierre; Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe

    2016-05-01

    The Auger effect and its impact on the internal quantum efficiency (IQE) of yellow light emitters based on silicon-doped InGaN–AlGaN–GaN quantum wells are investigated by power dependence measurement and using an ABC model. Photoluminescence intensity recorded as a function of excitation power density follows a linear dependence up to a threshold P T that depends on the design of the sample. Above this threshold, the variation of the intensity becomes sublinear, which is characteristic of the onset of Auger recombination processes. After extracting the evolution of IQE with pump power from the experimental data, we use a modified ABC modeling that includes the residual n-type doping to estimate the contribution of different recombination channels. We find that the Auger effect dominates in the high-excitation regime. In addition, we find that intercalating an AlGaN-strain-compensating layer reduces not only the coefficient of nonradiative recombination rates but also reduces the onset of Auger recombination.

  6. Si-based light emitter in an integrated photonic circuit for smart biosensor applications

    NASA Astrophysics Data System (ADS)

    Germer, S.; Cherkouk, C.; Rebohle, L.; Helm, M.; Skorupa, W.

    2013-05-01

    The motivation for integrated Silicon-based optoelectronics is the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive biochemical sensors in the environmental control or medicine leads to the development of integrated high resolution sensors. Here we present initial results in the integration and butt-coupling of a Si-based light emitting device (LED) [1-3] to a waveguide into a photonic circuit. Our first approach deals with the design, fabrication and characterization of the dielectric high contrast waveguide as an important component, beside the LED, for the development of a Si-based biodetection system. In this work we demonstrate design examples of Si3N4/SiO2-waveguides, which were calculated using MATLAB, the effective index method (EIM) and the finite element method (FEM), with a 0.45μm thick and 0.7μm wide core which shows a high confinement factor of ~74% and coupling efficiency of ~66% at 1.55μm, respectively. The fabrication was done by plasma enhanced chemical vapour deposition (PECVD), optical lithography and reactive ion etching (RIE). Additionally, we characterized the deposited layers via ellipsometry and the etched structures by scanning electron microscopy (SEM). The obtained results establish principles for Si-based LED butt-coupling to a powerful optical waveguide-based interconnect with effective light absorption and an adequate coupling efficiency.

  7. Nanowire-based structures for infrared to ultraviolet emitters studied by cathodoluminescence.

    PubMed

    Gustafsson, Anders

    2016-05-01

    Nanowires are structures with features on the nanoscale, and it is therefore essential to study their properties on that scale. We present optical data from a variety of nanowire-based structures using cathodoluminescence imaging and spectroscopy. One important feature of nanowires is the stacking sequence of the crystal, either zincblede, wurtzite or a mix of the two. We show that this has an impact on the optical properties. In radial quantum wells, the thickness can be controlled on a monolayer level, in the case of flat side facets of the nanowires. With rough side facets, the quantum well collapses into quantum dots, as revealed by cathodoluminescence imaging. In order to extend the emission wavelength of light-emitting diodes into the ultraviolet or to cover the whole visible range, we use nanowire-seeded truncated pyramids as bases for these devices, based on either GaInN (visible) and AlGaN (ultraviolet). PMID:26372921

  8. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    NASA Astrophysics Data System (ADS)

    Muzha, A.; Fuchs, F.; Tarakina, N. V.; Simin, D.; Trupke, M.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.; Dyakonov, V.; Krueger, A.; Astakhov, G. V.

    2014-12-01

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

  9. Room-temperature near-infrared silicon carbide nanocrystalline emitters based on optically aligned spin defects

    SciTech Connect

    Muzha, A.; Fuchs, F.; Simin, D.; Astakhov, G. V.; Tarakina, N. V.; Trupke, M.; Soltamov, V. A.; Mokhov, E. N.; Baranov, P. G.; Dyakonov, V.; and others

    2014-12-15

    Bulk silicon carbide (SiC) is a very promising material system for bio-applications and quantum sensing. However, its optical activity lies beyond the near infrared spectral window for in-vivo imaging and fiber communications due to a large forbidden energy gap. Here, we report the fabrication of SiC nanocrystals and isolation of different nanocrystal fractions ranged from 600 nm down to 60 nm in size. The structural analysis reveals further fragmentation of the smallest nanocrystals into ca. 10-nm-size clusters of high crystalline quality, separated by amorphization areas. We use neutron irradiation to create silicon vacancies, demonstrating near infrared photoluminescence. Finally, we detect room-temperature spin resonances of these silicon vacancies hosted in SiC nanocrystals. This opens intriguing perspectives to use them not only as in-vivo luminescent markers but also as magnetic field and temperature sensors, allowing for monitoring various physical, chemical, and biological processes.

  10. Highly Efficient Sky-Blue Fluorescent Organic Light Emitting Diode Based on Mixed Cohost System for Thermally Activated Delayed Fluorescence Emitter (2CzPN).

    PubMed

    Sun, Jin Won; Kim, Kwon-Hyeon; Moon, Chang-Ki; Lee, Jeong-Hwan; Kim, Jang-Joo

    2016-04-20

    The mixed cohosts of 1,3-bis(N-carbazolyl)benzene and 2,8-bis(diphenylphosphoryl)dibenzothiophene have been developed for a highly efficient blue fluorescent oragnic light emitting diode (OLED) doped with a thermally activated delayed fluorescence (TADF) emitter [4,5-di (9H-carbazol-9-yl) phthalonitrile (2CzPN)]. We have demonstrated one of the highest external quantum efficiency of 21.8% in blue fluorescent OLEDs, which is identical to the theoretically achievable maximum electroluminescence efficiency using the emitter. Interestingly, the efficiency roll-off is large even under the excellent charge balance in the device and almost the same as the single host based devices, indicating that the efficiency roll-off in 2CzPN based TADF host is related to the material characteristics, such as low reverse intesystem crossing rate rather than charge imbalance. PMID:27019330