Effect of ion-beam surface treatment on photocathode emission

To meet the needs of high-frequency, miniaturized vacuum microwave devices, a new photocathode for microwave vacuum electronic device has been studied. Untreated oxygen-free copper, commonly used for photocathode substrate, exhibits relatively high photoemission characteristics. In this paper, we describe a specialized ion-beam bombardment procedure for textured copper surfaces, thereby improving the photoemission properties relative to untreated copper. The emission characteristics of antimony cesium photocathode on oxygen-free copper substrate before and after surface treatment are studied The photoemission and texture of post-treated oxygen-free copper surface are examined by scanning electron microscope. The results show that the treated surface has a particle-free, robust, uniformly highly-textured all-metal structure. This processing technology does not require to modify the copper machining and brazing, nor normal fabrication procedures of other photocathodes. In the experiment, the maximum photoemission current density of photocathode for the untreated substrate is 60.5 and that for the treated substrate is 146.0 mA/cm(2), and their corresponding quantum efficiencies are calculated to be 2.67 x 10(-3) and 1.71 x 10(-2), respectively. So, the quantum efficiency is enhanced by 6.41 times. The analysis indicates that the improvement of the quantum efficiency of the treated photocathode is mainly due to the enhancement of the light absorption rate. The results show that the photoemission is enhanced significantly after the substrate has been treated, and there is still much room for improvement.