Abstract
We report synthesis and characterization of a batch of three cesium potassium antimonide photocathodes that have been grown on pure copper substrates via a ternary co-deposition method whose procedure is described herein. A deposition system that was designed for synthesis of two-element photocathodes has been utilized for synthesis of the aforementioned three-element photocathodes with slope of the in situ photocurrent as the driver for the growth process. A variation of substrate temperature and deposition parameters among the three photocathodes during synthesis has yielded a maximum quantum efficiency of 6% for 140°C substrate temperature. Lifetime studies performed in a 65-kV DC electron gun on two of the photocathodes, but under oxidized states, at tens of μA average currents (ampere-level peak currents) extracted utilizing a 532-nm wavelength, 1-kHz repetition rate laser, have resulted in charge-lifetimes of 6.13 C and 13.78 C, respectively. X-ray photoelectron spectroscopy analysis of the photocathode with the highest quantum efficiency has revealed a nearly impurity-free surface with stoichiometry Cs1.3K1.8Sb1.0 when pristine. Furthermore, it has been found that oxidation of the alkali surface atoms as well as carbon adsorption from hydrocarbons and minor fluorine uptake are the causes of quantum efficiency reduction during laser illumination in the utilized experimental set-up.
Highlights
Semiconductor photocathodes are widely used for electron beam generation in particle accelerators, owing to their characteristics like high quantum efficiencies (QEs), reasonable lifetimes and subpicosecond to picosecond response times [1]
A total of three Cs-K-Sb photocathodes have been synthesized on copper substrates via a ternary co-deposition method with the slope of photocurrent as the driver, using a preparation system that was originally designed for synthesis of two-element compounds
Gearing towards maximizing the QE, the substrate temperatures and deposition parameters were varied during synthesis among three photocathodes labeled Cathode 1, Cathode 2, and Cathode 3, viz., ramped down T ≃ 124 ◦C, ramped down T ≃ 150 ◦C, and a constant T ≃ 140 ◦C, respectively
Summary
Semiconductor photocathodes are widely used for electron beam generation in particle accelerators, owing to their characteristics like high quantum efficiencies (QEs), reasonable lifetimes and subpicosecond to picosecond response times [1]. Alkali antimonide semiconductor photocathodes exhibit appreciable QEs in the green section of the laser spectrum whose generation can be achieved by a single stage frequency doubling of the aforementioned IR lasers, leading to higher wall-plug efficiencies, drive laser pulseto-pulse energy stability and simpler apparatus. With prompt response times suitable for certain fast streak camera applications and capabilities of delivering ampere-class currents [14], Cs-K-Sb photocathodes make attractive candidates for the current and generation electron accelerators like free-electron lasers [15] and energy recovery linacs [14,16] that require ultra-short, high brightness [17,18] and high current electron beams.
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