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Electron Emission from Vertically Oriented Few-Layer Graphene

Electron Emission from Vertically Oriented Few-Layer Graphene. Proposed by: Kevin McMullen April 27, 2009. Overview. Applications of field emission Theory of electron emission Successes in CNTs Proposed work with graphene Objectives of proposed work. Applications.

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Electron Emission from Vertically Oriented Few-Layer Graphene

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  1. Electron Emission from Vertically Oriented Few-Layer Graphene Proposed by: Kevin McMullen April 27, 2009

  2. Overview • Applications of field emission • Theory of electron emission • Successes in CNTs • Proposed work with graphene • Objectives of proposed work K. McMullen

  3. Applications • Direct conversion from heat or solar to electrical power • Direct refrigeration • Scanning Electron Microscopy – electron guns • Flat panel displays K. McMullen

  4. Types of Electron Emission • Field Emission • Potential barrier is distorted by electric field allowing electrons to tunnel out • Thermionic Emission • Electrons thermally excited over potential barrier • Photoemission • Photon excites electron over potential barrier (Diagram from Tyler Westover Thesis) K. McMullen

  5. CNTs as Emission Sources • CNTs have been well researched as sources • Sharp tips lead to local field enhancement • Possible to emit up to 0.2 mA per MWCNT • Low electron emission field threshold K. McMullen

  6. Intercalation • SWCNT with 1.4nm diameter, in 20nm bundles • Pristine sample: φ=4.8eVIntercalated sample: φ=2.4eV • Other alkali metals (K, Na) show similar improvements Potassium intercalation from another study K. McMullen

  7. Local Field Enhancement • The field is distorted locally by a ‘sharp’ feature • Radii below 50nm show appreciable enhancement To attain 10A/cm2 need field of: 1.08V/μm for 5nm feature 614V/ μm for planar surface K. McMullen

  8. Enhancement at Open Ends • Observed current 1 million times greater after heating open tip to 1500° • Theorized that a carbon “atomic wire” was being formed at tip by E-field • Unraveling can continue and destroy the tube (Science, 1995) Geometrically sharpest possible emitter K. McMullen

  9. Proposed Work on Graphene • Few Layer Graphene (FLG) has structure similar to MWCNT • Thickness of FLG is a few nanometers→sharp in 2-D • Intercalation should be possible • ‘Unraveling’ should also be observable K. McMullen

  10. FLG Growth • 4-6 layer graphene synthesized on any substrate without catalyst • Number of layers characterized by TEM • Repeatable process K. McMullen

  11. Experimental Apparatus • Equipment available: • Test configurations for field, thermionic and photo emission • Vacuum background <10-7 Torr • Phobios Hemispherical Energy Analyzer (resolution ~0.04 eV) • PECVD for graphene growth Schematic of a PECVD (M. Meyyappan et al., Plasma Sources Sci. Tech. 2003) K. McMullen

  12. Outcomes of Proposed Work • Determine graphene emission current and its dependency on number of layers • Measure effects of intercalates on work function • Identify ‘unraveling’ of FLG • Measure work function changes caused by edge chemistry K. McMullen

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