Before the experiment begins, it is necessary to check if the vacuum in each chamber of the ARPES system is normal. The vacuum in the load-lock chamber should be better than 2.0 × 10-7 Torr, the transfer chamber better than 6.0 × 10-10 Torr, the preparation chamber better than 2.0 × 10-10 Torr, and the main chamber better than 1.0 × 10-10 Torr. Additionally, it is essential to verify that the temperature readings on the temperature control panel are normal.