A compact two-electrode field-emission X-ray source for soft X-ray spectroscopy applications

Here, a compact two-electrode field-emission X-ray source employing a blade-type tungsten cathode was designed for soft X-ray spectroscopy. The device suppressed filament-derived optical and thermal background that is intrinsic to thermionic tubes, while providing stable and tunable output. The cathode-anode spacing was optimized and an optimal gap was identified at 150 µm, enabling the source to reach 400 µA at 4 kV without short circuits at <1 × 10^-7 mbar. Spatial intensity mapping with targets tilted at 30°, 45° and 60° showed that smaller tilts yielded a more concentrated flux, with full width at half-maximum values of 28°, 54° and 76° at 2.5 kV, respectively, while the peak emission direction remained near 30° independent of the applied voltage and the tilt angle. Energy-resolved measurements with a silicon drift detector showed that the high-energy cutoff of the Bremsstrahlung continuum shifted linearly with the applied acceleration voltage, and that a reproducible Cu Lα peak appeared at 927.7 eV, confirming stable and proper operation of the source. High signal-to-noise soft X-ray emission spectroscopy of Ti Lα and O Kα lines were obtained using the source integrated at the Ultrafast X-ray Spectroscopy (UXS) endstation of the Shanghai Soft X-ray Free-Electron Laser (SXFEL) facility. The blade cathode and simplified architecture improve manufacturability and cost efficiency, providing a laboratory-scale low-background source for element-specific soft X-ray spectroscopy and pre-beamline experiments.