Advanced field emission measurement techniques for research on modern cold cathode materials and their applications for transmission-type x-ray sources.

Abstract

We report on the functional capabilities of our field emission (FE) measurement systems. The samples are prepared and inserted under clean room conditions and can be precisely xyz-positioned, heat-treated, and investigated in different vacuum environments and temperatures. The FE scanning microscope is a unique microscope being used for the localization of FE sites with high lateral resolution by means of extraction voltage U(x, y) or emission current I(x, y) maps over the cathode area of 25 × 25 mm2 and measuring the FE properties of localized emission sites or individual emitters. In contrast, the integral measurement system with the luminescent screen provides real-time integral information about the distribution of emission sites over the whole cathode during long- and short-term current stability measurements, thus allowing us to investigate the properties of various materials and their applications. Commissioning results with the upgraded systems using a silicon emitter array and a point-type graphene emitter will be given to demonstrate that both FE measurement techniques are very useful for an improved understanding and tailoring of materials for applications. The results showed that point-type graphene emitters are more preferable for practical applications. Using simulation software, a suitable triode configuration for point emitters was designed, and a current transmission ratio of ∼100% was obtained. The FE current stability of graphene emitters at pressures >10-3 Pa can be improved by heating the cathode at 100 °C-300 °C for 1 min-30 min. Finally, point-type graphene film emitters were used for transmission-type x-ray sources, and their applications in imaging and fluorescence spectroscopy are presented.