Development of Ultra-High Brightness Coherent Carbon Nanotube Electron Sources by Atomic Level Surface Control

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Robust adhesion of molecules (or clusters) for stable enhancement of electron field emission was pursued, and high coherency of an electron beam emitted from a carbon nanotube(CNT) was substantiated, as follows.1.Field Emission from CNTs with different radii of tip curvatureField emission microscopy(FEM) carried out for special multiwall CNTs named "d-CNTs(densest CNTs)", which have cone-shape tips with a cone angle of 19.2°, gave two kinds of FEM patterns, i.e., one is vague, speckled patterns and the other clear pentagon patterns. Inspection of the measured radii of tip curvatures and threshold voltages for field emission led to the conclusion that the speckle patterns originate from sharp tips with radius of curvature less than ca. 2 nm and the pentagon patterns originate from tips with radius curvature larger than ca. 2 nm. This conclusion is consistent with the previous FEM results for thin single-wall CNTs and thick multiwall CNTs. The types of FEM patterns from CNTs are supposed … More to be determined by whether the pentagon-pentagon distance on their tip is larger or smaller than the electron wavelength (Fermi wavelength) in CNTs, showing the large coherence length (over 10 nm) of electrons in CNTs.2.Field emission from multiwall CNTs with RuO_2 on their surfacesDeposition of RuO_2 clusters on multiwall CNTs was carried out by dropping RuO_4 solution. When an appropriate amount of RuO_4 solution was used, stable bright spots supposedly originating from RuO_2 clusters (1-2 nm in diameter) and reduction in threshold voltages were observed. When excess amount of RuO_4 solution was used, however, electron emission properties were deteriorated.3.Simulation of FEM patternsPentagons on a CNT tip being regarded as holes where electron wave pass through, diffraction patterns formed away from the holes were simulated. By assuming the emitted electrons as a spherically propagating wave whose source was placed behind the holes, simulated patterns reproduced well the experimental patterns. This simulation supports the high coherency of electrons emitted from a CNT. Less