STABLE ELECTRON EMISSION FROM GRAPHITE-NANONEEDLES AND THEIR APPLICATION TO SCANNING ELECTRON MICROSCOPES

摘要

Nanometer sized carbon cathodes have attracted special interest from the point of view of high brightness electron sources. Recently achieved high brightness point electron emission from carbon nanotubes (CNTs) [1] and graphite-nanocrater (GRANC) [2] show promising aspects to downsize old-fashioned thermal emission devices such as micro-focus X-ray generators and electron microscopes. However, the drawbacks of these field emission (FE) sources for practical use are requirement of massive vacuum systems to obtain extremely low residual pressure less than 10{sup}(-9) torr. When these cathodes are operated at high residual pressure (10{sup}(-6) torr), these emission sources have problems related to current stability and longevity. Here we demonstrate both the stable and high brightness field emission from graphite nanoneedle (GRANN) cathode fabricated by simple plasma etching of a graphite rod [3]. Bright electron emission of the order of 10{sup}12 Asr{sup}(-1)m{sup}(-2) is obtained from GRANN cathode [4]. As well as the bright emission, a stable emission under high residual pressure (10{sup}(-5) torr) is obtained by lightly heating the GRANN cathode (Thermal-FE operation). The performance of the GRANN cathode is demonstrated by the construction of an FE scanning electron microscope (SEM) with the GRANN cathode and clear FE-SEM images are obtained at high residual pressure of the order of 10{sup}(-5) torr.