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

分子的牢固粘附研究了碳纳米管（CNT）的场发射特性，并证实了CNT的场发射具有很高的相干性，具体如下：1.不同针尖曲率半径的CNT的场发射具有锥角为19.2°的锥形尖端的“（denominated CNTs）"给出了两种FEM图案，即，一种是模糊的斑点状图案，另一种是清晰的五边形图案。对测得的针尖曲率半径和场致发射阈值电压进行了检验，得出了散斑图案起源于曲率半径小于ca的尖锐针尖的结论。2 nm的尖端产生的五角形图案，其曲率半径大于ca。2纳米。这一结论与以往的薄单壁碳纳米管和厚多壁碳纳米管的有限元结果是一致的。提出了碳纳米管有限元图形的类型 ...更多信息 通过测量其尖端的五角-五角间距是否大于或小于碳纳米管中的电子波长（费米波长）来确定，表明碳纳米管中的电子具有较大的相干长度（超过10 nm）。2.表面带有RuO_2的多壁碳纳米管的场发射通过滴加RuO_4溶液的方法在多壁碳纳米管上沉积RuO_2团簇。当加入适量的RuO_4溶液时，观察到稳定的亮斑（直径为1- 2nm）和阈值电压的降低。当RuO_4溶液的用量过多时，电子发射性能反而下降。3.有限元图形模拟将碳纳米管针尖上的五边形看作电子波通过的孔洞，模拟了远离孔洞形成的衍射图形。通过假设发射的电子作为一个球形传播波的源被放置在后面的孔，模拟图案再现实验图案。该模拟支持从CNT发射的电子的高相干性。少

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