Recent Advances in Field Electron Microscopy of Metals

Swanson, L. W.; Bell, Andy

doi:10.1016/s0065-2539(08)60236-x

Cited by 131 publications

(40 citation statements)

References 146 publications

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“…There is fluctuation in the emission current due to the nonmetallic nature of the tip, field penetration and fluctuations of the applied potential shift the position of the emitting level, the other possibility is because of the structure of the cap, whereas it is well-known that small changes in adsorbate coverage result in large variations of the work function (Minoux et al, 2005), that could lead to observed saturation at high applied voltages and strong instabilities of the emission in some voltages ranges (Binh et al, 1996;Swanson & Bell, 1973), once the adsorbates removed, the emission current will be reduced because these adsorbates enhanced the field emission current of nanotube by two or three order (Dean & Chalamala, 2000) and the deviation from FN equations will disappear. The effect of relaxation process on field emission process from SWCNT could reduce the VSW as we observed in CNT-11.…”

Section: Discussionmentioning

confidence: 99%

Switch-on Phenomena and Field Emission from Single-Walled Carbon Nanotubes Embedded in Glass

Daradkeh

Mousa

2017

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In this study, we will describe a new design of carbon nanotubes tip. Single-walled carbon nanotubes produced using high-pressure CO over Fe particles (HiPCO) at CNI, Houston, TX used in this study. These tips were manufactured by employing a drawing technique using glass puller. Field electron microscopies with tips (cathode) to screen (Anode) separation of ~10 mm was used to characterize the electron emitters. The system was evacuated down to base pressure of (~10 -8 mbar) when baked at up to (~200°C) over night. An electron field emission patterns, as well as current versus voltage characteristics and Fowler-Nordheim plots, are discussed.

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Section: Discussionmentioning

confidence: 99%

Switch-on Phenomena and Field Emission from Single-Walled Carbon Nanotubes Embedded in Glass

Daradkeh

Mousa

2017

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“…This could lead to the observed saturation at high applied voltages and strong instabilities of the emission in some voltages ranges. The difference in energy between emitted and replacement electrons provokes a tip heating or cooling (Nottingham effect), related to the position of the Fermi level (Swanson & Bell, 1973;Thien et al, 1996). On tubes with emitting states just above the Fermi level this reduces the increase of the temperature with the current.…”

Section: Discussionmentioning

confidence: 99%

“…On tubes with emitting states just above the Fermi level this reduces the increase of the temperature with the current. As for the current steps, they most likely reflect changes in the surface structure (Swanson & Bell, 1973) and/or in the adsorbate coverage (adsorption, desorption or diffusion) ( Lee et al, 1995). The former possibility is unlikely because of the structure of the cap, whereas it is well known that small changes in adsorbate coverage result in large variations of the work function (Kyritsakis & Xanthakis, 2015;Lee et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

Switch-on Phenomena and Field Emission from Multi-Walled Carbon Nanotubes Embedded in Glass

Ali

Mousa

2016

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“…This current density, J, is assumed to be due to field emitted electrons, described by the following equalion [19][20][21]:…”

Section: The Determination Of Ihe Mechanism Responsible For Initialmentioning

confidence: 99%

“…Note that for the above expressions, the local elccu-on field E must be expressed in Volt/cm, the cathode work function, <?, in eV, and temperature T in K. Also note that as T-^0, equation 5 reduces to the Fowler-Nordheim equation [19][20][21] for electron field emission from a perfectly smooth surface. The criterion for the applicability of equation 5 is [19]:…”

Section: The Determination Of Ihe Mechanism Responsible For Initialmentioning

confidence: 99%

An investigation of the breakdown voltage characteristics of a 30 kWclass ammonia arcjet

Tilley

Bromaghim

McFall

et al. 1993

29th Joint Propulsion Conference and Exhibit

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Public reporting burden for this collection of information is estimated to average 1 tiour per response, including ttie time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of infomnatlon, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of infomiation if it does not display a currently valid 0MB contr-oi number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) Sep 1993 REPORT TYPE Technical Paper PL-TP-93-3029Approved for Public Release Distribution Unlimited The primary objective of this work was to identify methods to reduce the mean dynamic breakdown voltage (MDBV) of the ammonia propellant in the ESEX 26 kW arcjet. The approach to this objective was to establish a test matrix to investigate the influence of mass flow rate, electrode gap distance, cathode tip shape, and voltage ramp rate on the MDBV. Only the mass flow rale and voltage ramp rale were observed to significantly affect the MDBV; the MDBV was observed to rise as either of ihese parameters were increased. These test results provided the basis for the start circuit redesign for the ESEX flight experiment, and also represent an initial data base of breakdown characteristics in high power ammonia arcjeis. The second objective of this work was to identify the mechanisms associated with propellant breakdown in an arcjet. Progress towards this objective includes the following. A framework for investigating breakdown mechanisms in an arcjet was established which provides explanations for the strong dependence of the MDBV on the voltage ramp rale, the mass flow rate, and other parameters. A combination of a model, the calculation of electric field contours inside of the arcjet, and SEM photographs of a cathode tip indicate that the projection model for enhance field emission cannot alone account for the mean dynamic breakdown voltages observed in ihe high power arcjet. This result suggests that dielectric surface layers on the cathode tip are responsible for the enhanced field emission required to explain the observed MDBVs. SUPPLEMENTARY NOTES I. InU"oductionA reliable ignition method is essential for ihe space qualification of an arcjet propulsion system. Arcjeis are most commonly ignited by applying a high voltage pulse across the electrodes to breakdown the propellant. Following breakdown, the arcjet rapidly (on the order of lOO's of microseconds) transitions into a steady state high power arc. This study will focus on the initial phase of arcjet ignition: propellant breakdown. In ...

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Recent Advances in Field Electron Microscopy of Metals

Cited by 131 publications

References 146 publications

Switch-on Phenomena and Field Emission from Single-Walled Carbon Nanotubes Embedded in Glass

Switch-on Phenomena and Field Emission from Single-Walled Carbon Nanotubes Embedded in Glass

Switch-on Phenomena and Field Emission from Multi-Walled Carbon Nanotubes Embedded in Glass

An investigation of the breakdown voltage characteristics of a 30 kWclass ammonia arcjet

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