Microscopic Observation and Analysis of Field Electron Emission Sites by using an Electron Emission Microscope and Auger Electron Spectrometer

Field electron emission is recognized as one of important phenomena related to the occurrence of electrical breakdown in vacuum. In this paper, we investigated the distribution of field electron emission sites on a plane electrode before and after current conditioning procedure. The investigation was carried out by scanning the electrode to measure the emission current flowing through the pin-hole of the objective lens of Electron Emission Microscope. As a result, before current conditioning localized emission sites were found. Those emission sites and the current from the sites were unstable in the early stage of high voltage application. During current conditioning and electrode scanning, some of emission sites disappeared, while the others continued to flow current. Sometimes new emission sites appeared at the other points on the electrode surface. After the investigation of emission sites distribution, microscopic observation on some of emission sites were carried out by using the Electron Emission Microscope. Electron emission microscope enables simultaneous observations of field electron emission image and photo electron emission image. The observation revealed that field electron emission occurred at the foreign particles on the electrode surface, and only some of them became electron emission sites. To characterize the emission sites, we observed the absorption current image and analyzed the chemical composition of the emission sites by using an Auger Electron Spectrometer. Observation and analysis suggest that the foreign particle was a semiconducting or insulating material composed of carbon.