Search NASA⌕ Search

SEARCH · Search NASA

Results for “Electron emission”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Using Optically Stimulated Electron Emission as an Inspection Method to Monitor Surface Contamination

During redesign of the Space Shuttle reusable solid rocket motor (RSRM), NASA amended the contract with ATK Launch Systems (then Morton Thiokol Inc.) with Change Order 966 to implement a contamination control and cleanliness verification method. The change order required: (1) A quantitative inspection method (2) A written record of actual contamination levels versus a known reject level (3) A method that is more sensitive than existing methods of visual and black light inspection. Black light inspection is only useful for inspection of contaminants that fluoresce near the 365 nm spectral line and is not useful for inspection of most silicones that will not produce strong fluorescence. Black light inspection conducted by a qualified inspector under controlled light is capable of detecting Conoco HD-2 grease in gross amounts and is very subjective due to operator sensitivity. Optically stimulated electron emission (OSEE), developed at the Materials and Process Laboratory at Marshall Space Flight Center (MSFC), was selected to satisfy Change Order 966. OSEE offers several important advantages over existing laboratory methods with similar sensitivity, e.g., spectroscopy and nonvolatile residue sampling, which provide turn around time, real time capability, and full coverage inspection capability. Laboratory methods require sample gathering and in-lab analysis, which sometimes takes several days to get results. This is not practical in a production environment. In addition, these methods do not offer full coverage inspection of the large components

Lingbloom, Mike S.↗
DOE OSTI2022

Electron emission from bromouracil and uracil induced by protons and radiosensitization

Absolute double differential cross sections (DDCS) of electrons emitted from uracil and 5-bromouracil (BrU) in collisions with protons of energy 200 keV have been measured for various forward and backward emission angles over wide range of electron energies. The measured DDCS are compared with the continuum distorted wave-eikonal initial state (CDW-EIS) calculations. The optimized structure of the BrU was estimated along with the population analysis of all the occupied orbitals using a self-consistent field density. A comparison between the measured DDCS data for the two molecules show that the cross section of low energy electrons emitted from BrU is substantially larger than that for uracil. The BrU-to-uracil DDCS ratios obtained from the present measurements indicate an enhancement of the electron emission by a factor which is as large as 2.0 to 2.5. These electrons being the major agent for damaging the DNA/RNA of the malignant tissues, the present results are expected to provide an important input for the radiosensitization effect in hadron therapy. It is noteworthy to mention that the CDW-EIS calculations for Coulomb ionization cannot predict such enhancement. A large angular asymmetry is observed for uracil with a broad structure, which is absent in case of BrU.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1971

Development of reverse biased p-n junction electron emission

A cold cathode emitter of hot electrons for use as a source of electrons in vacuum gauges and mass spectrometers was developed using standard Norton electroluminescent silicon carbide p-n diodes operated under reverse bias conditions. Continued development including variations in the geometry of these emitters was carried out such that emitters with an emission efficiency (emitted current/junction current) as high as 3 x 10-0.00001 were obtained. Pulse measurements of the diode characteristics were made and showed that higher efficiency can be attained under pulse conditions probably due to the resulting lower temperatures resulting from such operation.

Fowler, P.↗
NASA NTRS1988

Observation of interface band structure by ballistic-electron-emission microscopy

The paper reports an advanced ballistic electron spectroscopy technique that was used to directly measure semiconductor band structure properties at a subsurface interface. Two interface systems having contrasting band structures were investigated by this method: Au-Si and Au-GaAs. It is concluded that the proposed method, based on scanning tunneling microscopy, enables the spatially resolved carrier-transport spectroscopy of interfaces.

Bell, L. D.↗
DOE OSTI2020

Field-Emission Electron Source Embedded in a Field-Enhanced Conduction-Cooled Superconducting RF Cavity

We present simulations and experimental progress toward the development of a high-current electron source with the potential to deliver high charge electron bunches at GHz-level repetition rates. To achieve these goals electrons are generated through field-emission and the cathode is immersed in a conduction-cooled superconducting 650-MHz RF cavity. The field-emitters consist of microscopic silicon pyramids and have a typical enhancement factor of about 500. To trigger field-emission, the peak field inside the RF cavity of about 6 MV/m is further enhanced by placing the field-emitters on the top of a superconducting Nb rod inserted in the RF cavity. So far, we cannot control the duration of the electron bunches which is of the order of RF period. Also, the present cryo-cooler power of about 2 W limits the beam current to microamp level.

43 PARTICLE ACCELERATORS↗
NASA NTRS1998

Charging of Single Micron Sized Dust Grains by Secondary Electron Emission: A Laboratory Study

We present the details of a new laboratory study whose objective is to experimentally study the interaction of micron sized particles with plasmas and electromagnetic radiation. Specifically, to investigate under what conditions and to what extent do particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and ultraviolet radiation environment The emphasis is the study of the two charging mechanisms, secondary emission of electrons and photoelectric effect. The experiment uses a technique known as electrodynamic suspension of particles. With this technique, a single charged particle is electrodynamically levitated and then exposed to a controlled environment. Its charge to mass ratio is directly measured. Viscous drag measurements and the light scattering measurements characterize its size and optical characteristics. The environment to which the particle is expose may consist of room temperature and pressure or a rarefied atmosphere where only one major gaseous constituent is present, or, as in this case, a vacuum environment under electron bombardment or UV radiation . In addition, the environment can be cycled as part of the experiment. Therefore, using this technique, a single particle can be repeatedly exposed to a controlled environment and its response measured, or a single particle can be exposed to similar environments with minor differences and its response measured as a function of only the changed environmental conditions.

Spann, James F., Jr.↗
DOE OSTI2020

Photofield electron emission from an optical fiber nanotip

In this work, we demonstrate a nanotip electron source based on a graded index multimode silica optical fiber, tapered at one end to a radius of curvature r ~50 nm and coated with a thin film of gold. We report observation of laser-induced electron photoemission at tip bias potentials below the onset of dark field emission. Single-photon photofield emission is identified as the emission mechanism that exhibits fast switching times with an upper limit on the order of 1 μ s. The explored fiber optic nanotips are flexible back-illuminated emitters, which can be operated in continuous wave and pulsed modes using lasers with photon energies in the visible range or higher. The mechanical flexibility of the source can facilitate externally controlled positioning. Multiple, individually addressable, nanotips may be assembled into a bundle for applications such as computational electron ghost imaging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2012

Development of a Robust, High Current, Low Power Field Emission Electron Gun for a Spaceflight Reflectron Time-of-Flight Mass Spectrometer

Carbon materials, including carbon nanotubes (CNTs) and nitrogen-incorporated ultrananocrystalline diamond (N-UNCD), have been of considerable interest for field emission applications for over a decade. In particular, robust field emission materials are compelling for space applications due to the low power consumption and potential for miniaturization. A reflectron time-of-flight mass spectrometer (TOF-MS) under development for in situ measurements on the Moon and other Solar System bodies uses a field emitter to generate ions from gaseous samples, using electron ionization. For these unusual environments, robustness, reliability, and long life are of paramount importance, and to this end, we have explored the field emission properties and lifetime of carbon nanotubes and nitrogen-incorporated ultrananocrystalline diamond (N-UNCD) thin films, the latter developed and patented by Argonne National Laboratory. We will present recent investigations of N-UNCD as a robust field emitter, revealing that this material offers stable performance in high vacuum for up to 1000 hours with threshold voltage for emission of about 3-4 V/lJm and current densities in the range of tens of microA. Optimizing the mass resolution and sensitivity of such a mass spectrometer has also been enabled by a parallel effort to scale up a CNT emitter to an array measuring 2 mm x 40 mm. Through simulation and experiment of the new extended format emitter, we have determined that focusing the electron beam is limited due to the angular spread of the emitted electrons. This dispersion effect can be reduced through modification of the electron gun geometry, but this reduces the current reaching the ionization region. By increasing the transmission efficiency of the electron beam to the anode, we have increased the anode current by two orders of magnitude to realize a corresponding enhancement in instrument sensitivity, at a moderate cost to mass resolution. We will report recent experimental and modeling results to describe the performance of a field emission electron gun as employed in the Volatile Analysis by Pyrolysis of Regolith (VAPoR) TOF-MS prototype.

Southard, Adrian E.↗