Topological insulators for the generation of electron beams

Abstract

Measurements of photo-yields from various topological insulators (TIs) in ultra-high vacuum were made. Marked differences in the photoelectric yield were found between the freshly in-vacuum cleaved and the atmosphere cleaved TI samples. The spectral dependence of their quantum efficiency (QE) was obtained in as-cleaved and cesiated TI samples. Inferred work functions ranging from 5 to 5.5 eV were found in all TI samples before cesiation, and they were lowered by ∼0.5 eV after cesiation. At the ultraviolet wavelength of 268 nm, the QE of all samples is ∼2 × 10−7 before cesiation but improved to 10−4–10−3 after cesiation. Knowledge of the QE has practical implication and can serve as a useful guide for the development of a spin-polarized electron source. However, the spin polarized nature of the photo-emitted electron remains yet to be explored.

Present and future trends in spin ARPES

“…The quantum efficiencies reported so far (ref. [122]) are more than one order of magnitude lower than for GaAs superlattices [123,124], but the research is only at its inception compared to that on semiconductor superlattices. Even more critical for the purpose of realizing pure spin-polarized beams, there is no measurement to this point of the spin polarization obtained by photoemission close to the visible range, a regime typical for photocathode emission but problematic instead for ARPES [125], and upon alkali treatment on the TI surface, necessary to lower the work function.…”