Photoelectron emission from Cs3Sb coated on a cathode tip

We developed vacuum deposition equipment for coating a photoemissive material on a cathode tip for TEM in high vacuum. For practical reasons, we firstly examined whether Cs reacts chemically with Sb at low temperature. Photoelectrons were emitted from the as-deposited layers of Sb, Cs and Sb deposited on the cathode tip at −20 °C less than 0.5 h after the second Sb deposition. Since the quantum efficiency calculated from the photocurrent was much more than 104 times as large as that of substrate materials, we concluded that Cs3Sb film was formed by the reaction of Cs and Sb at −20 °C. The quantum efficiency of the Cs3Sb 2 h after the second Sb deposition was 0.021–0.029%, but it decreased rapidly with time at temperatures of both about −20 °C and about 10.5 °C at the vacuum level of 1.2–1.4 × 10−7 Pa. Photoelectrons were successfully detected from the Cs3Sb coated on a small area of 70 μm in diameter over the cathode tip whose diameter was 0.2 mm. It was also determined that photoelectrons emitted from Cs3Sb decreased with anode voltage from 0.1 to 0.4 kV, but increased from 0.4 to 7 kV.