Laser-induced electron beam emission from titanium dioxide on silicon photocathodes treated with cesium and barium oxide

Abstract

Electron beam sources are essential for a wide range of applications, including microscopy, high-energy physics, quantum science, spectroscopy, interferometry or sensors technology. However, conventional electron sources face critical limitations in energy spread, beam current, and stability, underscoring the need for advancements. In this study, we present and characterize a laser-stimulated electron beam source based on a titanium dioxide (TiO₂) surface on n-type doped silicon, coated with cesium (Cs) and barium oxide (BaO) to reduce the work function. This approach harnesses the surface photovoltage (SPV) phenomenon in an n-type semiconductor, wherein laser activation drives charge drift toward the surface, reducing band bending and further lowering the work function. The electrons are then extracted through low-voltage field emission. This mechanism is in contrast to established sources that rely on direct laser excitation through multi-photon absorption. Experimental investigations were conducted using a low-energy electron microscope (LEEM) and a custom field emitter characterization setup. By illuminating the TiO₂ sample with laser wavelengths of 830 nm, 404 nm and 824 nm, and applying biased field emission between -35 and -100 eV, we achieved work functions below 1 eV, highly sensitive to surface preparation. The results demonstrate beam currents up to 30 nA, a clearly defined two-peak energy spectrum, and an energy distribution as narrow as 100 meV in the primary peak. These findings establish SPV as a promising alternative for generating electron beams with high current and narrow energy distributions, paving the way for innovative field emitter designs and applications.

Keywords: Electron beam source; Laser-induced surface photovoltage; Low-energy electron microscopy; Photocathode; Titanium dioxide.