Development of Field Emission Type Ultra-High Vacuum Gauge

场致发射是电子隧穿通过由高电场- 0.5V/A降低的势垒。束缚在表面的电子的隧穿速率随气体原子和分子的吸附而敏感地变化。在这项研究中，场发射所需的高场是通过采用一个半球形的尖端的场发射显微镜（MEMS）和通过施加一个高的负电压。通过观察场发射电流随时间的降低率来测量真空度。本研究的目的是：（1）将现有真空系统改进到10^ -10 ^Torr的真空<-11>度;（2）澄清发射电流降低率与真空度之间的关系;（3）检查作为尖端材料的各种金属;（4）评价多尖端的优点<-13>;（5）研制了一种新的高效率、高可靠性的发射电流测量系统，其结果是：（1）由于真空室表面修整不够，不能获得10 μ Torr以上的真空度;（2）发现发射电流的下降率与真空度有很好的正比关系<-11>;（3）研究表明，对于真空测量，W尖端比Ir尖端更灵敏，因为W表面比Ir表面更活跃，（4）没有检查多个尖端，因为必须在项目（5）的研究之前，（5）为了有效和精确地测量发射电流，开发了二维成像法拉第笼。由于成像笼的屏幕投射从多个尖端的每个顶点发射的电流的图像，因此它允许我们一眼就直接检查所有尖端。

Field emission is the electron tunneling through the potential barrier lowered by the high electric field - 0.5V/A. The tunneling rate for the electrons confined in the surface varies sensitively with the adsorption of gas atoms and molecules. In this study the high field required for the field emission was realized by employing a hemispherical apex of a sharp tip of a field emission microscope (FIM) and by applying a high negative voltage. The vacuum was measured by observing the reduction rate of field emission current with time.The study aimed the following items : (1) Improvement of the existing vacuum system up to the vacuum of 10^<-11> - 10^<-13> Torr, (2) Clarification of the relation between the reduction rate of emission current and vacuum, (3) Examination of various metals as tip materials, (4) Evaluation of the advantageous point of multiple tips, (5) Development of a new highly efficient and reliable system to measure emission currents.The results of above items are as follows : (1) The vacuum better than 10^<-11> Torr could not be obtained possibly due to the insufficient surface refinish of the vacuum chamber, (2) It was found that the reduction rate of emission current is fairly well proportional to vacuum, (3) The study indicates that a W tip is more sensitive than an Ir tip for vacuum measurement because the W surface is more active than the Ir surface, (4) No multiple tip was examined because the study of item (5) must be preceded, (5) In order to measure the emission current efficiently and precisely, a 2-dimensional imaging Faraday cage was developed. Since the screen of the imaging cage projects the image of the currents emitted from every apex of the multiple tip, it allows us to examine all the tips directly at a single glance.