Development of bi-alkali photocathode

by Hamza Nasir (MS Candidate)

Friday Nov 12, 2021, 1:30 PM → 2:00 PM Asia/Seoul

119호 (제1과학관)

Title: Development of the oxidation of kovar alloy, glass-to-metal seal, and facility for the fabrication of bi-alkali photocathode

We have been developing a novel hybrid photodetector called Silicon Photomul- tiplier Tube (SiPMT) which consists of a photocathode, a scintillator, and a silicon photomultiplier in the vacuum tube. This type of photodetector with a large light receiving area could be utilized in the photodetector array of the neutrino detec- tor at the Korean Neutrino Observatory (KNO). These types of detectors required Ultra High Vacuum (UHV), to connect these detectors with such a system need vacuum-tight sealing. For that, a Glass-Metal seal is essential for vacuum and elec- trical connections to the photocathode assembly. The glass and metal can be purely bound through chemical interaction, where the oxide present on the surface makes a strong bond with glass because a glass-oxide bond is stronger than a glass metal. Therefore, we need an oxide layer on the surface of the Kovar alloy. 

For the oxidation of Kovar alloy, we heated it at 1000 °C for 30 minutes of isothermal holding time in the presence of a wet nitrogen environment inside a furnace. After the process we observe an oxide layer on the surface of the Kovar alloy. Furthermore, the X-ray diffraction (XRD) analysis revealed the presence of a Fe$_2$O$_3$ oxide layer on the surface of the alloy which is known as a good oxide layer for the Glass to Metal seal (GTMS) in the literature. Afterward, the other end of the tube was brazed with the flange to connect them with the UHV system. The UHV system is consists of Dry scroll pump, a Turbo molecular pump, and an Ion pump, with the help of these pumps we can archive $9 \times 10^{-9}$ torrs. The oxidized Kovar tubes and pins were sealed with the glass and vacuum test has been completed by the ultrahigh vacuum and furnace system, followed by the He-leak test. Both the results illustrated that they are vacuum-tight and compatible with the UHV system. Moreover, we designed the alkali antimonide photocathode assembly with the 3D software, and eventually, we produced a prototype of the photocathode assembly which houses the internal structure inside, GTMS at the bottom for the electric and vacuum connection to the photocathode assembly, and a window part at the top for the deposition of the Bi-Alkali photocathode.

 

Supervisor: Prof. Hongjoo Kim