Fabrication and Characteristics of Novel Graphite Field-Emitters for Application to Electron-Beam Pumped Light Sources

摘要

Light emission based on the excitation of rare gases by a low energy dc electron beam (less than 30keV) is a promising approach for realizing deep- or vacuum-ultraviolet light sources or lasers that are compact and have high efficiency [1]. Although thermal cathodes have previously been used as electron sources in these experiments, the replacement of thermal cathodes with field emitters makes it possible to construct a low energy-consumption, compact and low-cost system. Recently, carbon nano-tubes (CNT) have attracted great interest. However, CNT technologies experience problems relating to the adherence of the interface between the carbon layers and their substrate. To try to solve the problem, we fabricated novel carbon nanoneedle field-emitters by etching a graphite substrate with H{sub}2 gas using radio frequency (RF) magnetron sputtering equipment. Figure 1 shows a scanning electron microscope (SEM) image of the sputter-induced carbon nanoneedle emitter. A graphite substrate of 4mΦ was positioned on the cathode electrode and was sputtered in an H{sub}2 gas ambient at a pressure of 30Pa, a power of 600W and for a sputtering-time of 30min. The emitter is composed of a tremendous number of nanoneedles, whose apexes and height are less than 50nm and 5～10μm, respectively. The formation mechanism for these needles is still under investigation at present, but they are believed to be formed by not only the etching of the graphite substrate, but also by the growth of carbon fibers induced by Fe or Ni catalysis. This is because energy-dispersive X-ray fluorescence spectroscopy (EDXRF) measurements revealed that, whilst carbon was the principle component of the material, trace amounts of Fe and Ni (derived from the stainless steel sample holder) were also included in the needles. When a sample holder made from copper was used instead of the stainless steel holder, the nanoneedles were not formed.