Characterization of metallic field emitter array devices fabricated by molding for x-ray free electron laser applications

Abstract

A low-emittance and high-brightness electron source is a prerequisite for the successful development of sub-nm wavelength x-ray free electron lasers (XFEL). For that application, a field emitter array (FEA) device equipped with a focusing gate is potentially advantageous over the state-of-the-art photocathode. In the low-emittance gun design of the PSI-XFEL project at the Paul Scherrer Institut, the cathode is assumed to emit above 0.2 nC within 10-40 ps, or -10 A, from an array of total area below 1 mm in diameter. So far, the current of the commercially available FEA device is limited to -0.1 A/mm2. To reach higher currents, we explore the field-emission properties of pyramidal-shaped molybdenum FEAs based on the molding-technique. For high-current applications, the pyramidal tip with low-aspect ratio is advantageous over a conical/cylindrical one because of the higher thermal conductance and thermal spread. Here we present fabrication and characterization of pyramidal-shaped molybdenum FEAs with relatively small numbers of tips (1) to measure the maximum current Imax per tip for single-gate devices, and (2) to explore the spatially- and energy-resolved photoemission in FEAs without gate electrodes.